Release v2.28.0

- rsync-parity cycle: differential parity gate + tracks 1-6
- protocol 2.28.0 (batched wire changes)
- --delete defaults to delete-during; new --delete-commit, --verify-basis
- parity matrix 116/14/27 of 157
- tested: unit, integration, ASan, strict differential parity

.gitea/workflows/ci.yaml

@@ -9,7 +9,7 @@ on:
 jobs:
   lint:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     steps:
       - name: Checkout
         uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
@@ -26,7 +26,7 @@ jobs:
   # suite) run on merge to dev/main, so PR CI stays well under ~3 minutes.
   build-and-test:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     needs: lint
     steps:
       - name: Checkout
@@ -49,9 +49,50 @@ jobs:
         if: github.event_name == 'push'
         run: python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv" --durations=25 --tb=short -q
 
+  # Differential rsync-parity gate: runs real rsync 3.4.1 and FastSync over the
+  # same corpora and compares destinations + normalized output.  The fast subset
+  # guards the ✅ surface on every PR; the full set (with FASTSYNC_PARITY_STRICT
+  # so a fixed caveat must be removed from the allowlist) burns the documented
+  # ⚠️/❌ residuals down on push.  See tests/integration/README.md.
+  parity-fast:
+    runs-on: ubuntu-latest
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
+    needs: lint
+    if: github.event_name == 'pull_request'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
+
+      - name: Configure
+        run: cmake -B build -S . -DSTRICT_WARNINGS=ON
+
+      - name: Build
+        run: cmake --build build -j$(nproc)
+
+      - name: Differential parity (fast subset)
+        run: python3 -m pytest tests/integration/test_differential_parity.py -n 4 --dist=load -m parity_ci -q
+
+  parity-full:
+    runs-on: ubuntu-latest
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
+    needs: lint
+    if: github.event_name == 'push'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
+
+      - name: Configure
+        run: cmake -B build -S . -DSTRICT_WARNINGS=ON
+
+      - name: Build
+        run: cmake --build build -j$(nproc)
+
+      - name: Differential parity (full set)
+        run: FASTSYNC_PARITY_STRICT=1 python3 -m pytest tests/integration/test_differential_parity.py -n 4 --dist=load -m parity -q
+
   sanitizers:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     needs: lint
     if: github.event_name == 'push'
     strategy:
@@ -72,7 +113,7 @@ jobs:
 
   fuzz-build:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     needs: lint
     if: github.event_name == 'push'
     steps:
@@ -94,7 +135,7 @@ jobs:
 
   coverage:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     needs: lint
     if: github.event_name == 'push'
     steps:
@@ -118,7 +159,7 @@ jobs:
 
   valgrind:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     needs: lint
     if: github.event_name == 'push'
     steps:

.opencode/agents/cmake-expert.md

@@ -55,6 +55,16 @@ if(NOT ZSTD_LIBRARY)
   message(FATAL_ERROR "zstd library not found. Ensure it is in your nix-shell!")
 endif()
 
+find_library(ZLIB_LIBRARY z)
+if(NOT ZLIB_LIBRARY)
+  message(FATAL_ERROR "zlib library not found. Ensure zlib1g-dev / nix zlib is available!")
+endif()
+
+find_library(LZ4_LIBRARY lz4)
+if(NOT LZ4_LIBRARY)
+  message(FATAL_ERROR "lz4 library not found. Ensure liblz4-dev / nix lz4 is available!")
+endif()
+
 find_package(OpenSSL REQUIRED)
 
 file(GLOB SHARED_SRCS "src/shared/*.c")
@@ -64,15 +74,15 @@ file(GLOB TEST_SRCS "tests/*.c")
 
 add_executable(server ${SERVER_SRCS} ${SHARED_SRCS})
 target_include_directories(server PRIVATE src/shared src/server src/client)
-target_link_libraries(server PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
+target_link_libraries(server PRIVATE Threads::Threads ${ZSTD_LIBRARY} ${ZLIB_LIBRARY} ${LZ4_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
 
 add_executable(client ${CLIENT_SRCS} ${SHARED_SRCS})
 target_include_directories(client PRIVATE src/shared src/server src/client)
-target_link_libraries(client PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
+target_link_libraries(client PRIVATE Threads::Threads ${ZSTD_LIBRARY} ${ZLIB_LIBRARY} ${LZ4_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
 
 add_executable(tests ${TEST_SRCS} ${SHARED_SRCS} src/client/scanner.c)
 target_include_directories(tests PRIVATE tests src/shared src/server src/client)
-target_link_libraries(tests PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
+target_link_libraries(tests PRIVATE Threads::Threads ${ZSTD_LIBRARY} ${ZLIB_LIBRARY} ${LZ4_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
 ```
 
 ### Source Layout
@@ -85,17 +95,23 @@ tests/integration/ — Python pytest integration tests
 ```
 
 ### Dependencies
-- **zstd** — found via `find_library(ZSTD_LIBRARY zstd)`
+- **zstd** — found via `find_library(ZSTD_LIBRARY zstd)` (default compression codec)
+- **zlib** — found via `find_library(ZLIB_LIBRARY z)` (the `zlib`/`zlibx` codecs)
+- **lz4** — found via `find_library(LZ4_LIBRARY lz4)` (the `lz4` codec)
 - **OpenSSL** — found via `find_package(OpenSSL REQUIRED)` (TLS 1.2+ transport)
 - **xxHash** — fetched via `FetchContent` from the upstream repository (delta transfer hashing, v0.8.3)
 - **pthreads** — found via `find_package(Threads REQUIRED)`
 - **C11 standard** — required
 - **CMake 3.22+** — minimum version
 
+The codec matrix (protocol 2.26.0) uses zstd/zlib/lz4 for compression and
+xxHash/OpenSSL for the `xxh128`/`xxh3`/`xxh64`/`md5`/`md4`/`sha1` checksums
+(`none` needs no library); both codec families are negotiated per transfer.
+
 ## Conventions
 
 - Use `file(GLOB ...)` for source collection (existing pattern).
-- All targets link `Threads::Threads`, `${ZSTD_LIBRARY}`, `OpenSSL::SSL`, `OpenSSL::Crypto`, and `xxhash`.
+- All targets link `Threads::Threads`, `${ZSTD_LIBRARY}`, `${ZLIB_LIBRARY}`, `${LZ4_LIBRARY}`, `OpenSSL::SSL`, `OpenSSL::Crypto`, and `xxhash`.
 - Include directories: `src/shared`, `src/server`, `src/client`, `tests` (for test target).
 - Sanitizer support: pass `-DSANITIZER=address`, `-DSANITIZER=thread`, or `-DSANITIZER=undefined` to cmake (live option in CMakeLists.txt).
 - Build with `cmake -B build -S . && cmake --build build -j$(nproc)`.

.opencode/agents/integrator.md

@@ -116,7 +116,7 @@ The project uses Gitea Actions. Key jobs:
 jobs:
   new-job:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     steps:
       - uses: actions/checkout@v4
       - name: Configure

.opencode/skills/release/SKILL.md

@@ -16,7 +16,7 @@ Ask the user or determine from context:
 - **Minor** (x.Y.0) — new features, backward compatible
 - **Patch** (x.y.Z) — bug fixes, no protocol changes
 
-Current version: `PROTOCOL_VERSION "2.21.0"` in `src/shared/config.h`
+Current version: `PROTOCOL_VERSION "2.26.0"` in `src/shared/config.h`
 
 ### Step 2: Check Protocol Version
 

AGENTS.md

@@ -4,18 +4,19 @@ FastSync is a high-performance file synchronization system written in C11. It su
 
 ## Dependency installation
 
-**CI rule:** never add `apt-get install` / `pip install` steps to CI workflows — use the custom Docker image instead. The image is built from the repo-root `Dockerfile` and is the same image CI uses: `gitea.tap-tap.win/taptap/fastsync-ci:v10`. It contains the full toolchain: gcc/g++, CMake, libzstd-dev, libssl-dev, make, git, cppcheck, clang-format, python3 + pytest + pytest-xdist, openssh-client, and Node.js.
+**CI rule:** never add `apt-get install` / `pip install` steps to CI workflows — use the custom Docker image instead. The image is built from the repo-root `Dockerfile` and is the same image CI uses: `gitea.tap-tap.win/taptap/fastsync-ci:v11`. It contains the full toolchain: gcc/g++, CMake, libzstd-dev, libssl-dev, make, git, cppcheck, clang-format, python3 + pytest + pytest-xdist, openssh-client, Node.js, plus `rsync` 3.4.1 (with zstd/xxhash/lz4), `acl` and `attr` (setfacl/getfacl, setfattr/getfattr) for drop-in parity tests.
 
 **Host rule:** for local development, use `nix-shell` (see `README.md`) which provides zstd, OpenSSL, CMake, and gcc. The Docker image can also be used locally for CI parity.
 
 ```bash
 # Use the prebuilt CI image directly (faster, guaranteed CI parity)
-docker pull gitea.tap-tap.win/taptap/fastsync-ci:v10
-docker tag gitea.tap-tap.win/taptap/fastsync-ci:v10 fastsync-ci:local
+docker pull gitea.tap-tap.win/taptap/fastsync-ci:v11
+docker tag gitea.tap-tap.win/taptap/fastsync-ci:v11 fastsync-ci:local
 
 # Or build the image from the repo-root Dockerfile
-# (Note: the prebuilt :v10 image reflects the previous Dockerfile state;
-#  rebuild from source to pick up any newly added packages like lcov/valgrind.)
+# (Note: the prebuilt :v11 image is built from the current Dockerfile and
+#  includes rsync 3.4.1 plus acl/attr; rebuild from source after changing
+#  the Dockerfile.)
 docker build -t fastsync-ci:local .
 
 # Build, run unit tests, and run integration tests inside the container
@@ -55,6 +56,21 @@ cmake -B build -S . && cmake --build build -j$(nproc)
 ./build/tests                # unit tests
 python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"   # full integration suite (CI excludes env-dependent privilege tests)
 python3 -m pytest tests/integration/ -n 4 --dist=load -m ci   # PR-gate subset only
+
+# Differential rsync-parity gate (real rsync 3.4.1 vs FastSync)
+python3 -m pytest tests/integration/test_differential_parity.py -n 4 --dist=load -m parity_ci  # fast PR subset
+python3 -m pytest tests/integration/test_differential_parity.py -n 4 --dist=load -m parity     # full set
+```
+
+See `tests/integration/README.md` for the differential parity gate and its
+`parity_caveats.py` allowlist (the residual burn-down mechanism).
+
+Unit tests under valgrind must set `FASTSYNC_UNDER_VALGRIND=1` (CI does): the
+tests use it to skip fork-based tests, because valgrind 3.22 does not expose
+`vgpreload` in the guest's `/proc/self/maps`.
+
+```bash
+FASTSYNC_UNDER_VALGRIND=1 valgrind --leak-check=full --show-leak-kinds=definite --error-exitcode=1 ./build/tests
 ```
 
 ## CI Workflow — Waiting for Results
@@ -66,14 +82,14 @@ When running the CI workflow via `tea` (the task execution agent), always set a
 ### If lint (clang-format) fails
 Run clang-format in the CI Docker image to match the exact CI version:
 ```bash
-docker run --rm -v "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v10 \
+docker run --rm -v "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v11 \
   sh -c 'find src/ tests/ -name "*.c" -o -name "*.h" | xargs clang-format -i'
 ```
 
 ### If cppcheck fails
 Fix reported issues locally, then verify with:
 ```bash
-docker run --rm -v "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v10 \
+docker run --rm -v "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v11 \
   sh -c 'cppcheck --enable=warning,style,performance,portability --suppress=missingIncludeSystem --error-exitcode=1 --inline-suppr src/ tests/'
 ```
 

CHANGELOG.md

@@ -4,6 +4,270 @@ All notable changes to FastSync are documented here. Versions match
 `PROTOCOL_VERSION` (printed by `fastsync --version`); the client and server must
 run the same version because the handshake is strict.
 
+## [2.28.0] - 2026-09-20
+
+The rsync-parity cycle. `PROTOCOL_VERSION` moves `2.26.0 → 2.27.0 → 2.28.0`;
+client and server must run the same version (the handshake is strict). See
+`RSYNC_COMPAT.md` for the per-option matrix, now **116 ✅ / 14 ⚠️ / 27 ❌** of
+157 rows.
+
+### Added
+
+- **Differential rsync 3.4.1 parity gate** (`tests/integration/
+  test_differential_parity.py`, `parity_harness.py`, `parity_caveats.py`): runs
+  real `rsync` and FastSync over generated corpora and diffs the destination
+  tree, normalized stdout and exit code. A fast subset runs on pull requests and
+  the full strict set on push; the residual allowlist is empty.
+- FastSync-only long option **`--verify-basis`**: require a
+  `--compare-dest`/`--copy-dest`/`--link-dest` hit to match the source by
+  whole-file digest instead of trusting the size+mtime quick-check.
+- FastSync-only long option **`--delete-commit`** (implies `--delete`): the old
+  atomic late whole-tree commit.
+- `--bwlimit` now parses rsync's units exactly and paces like rsync's leaky
+  bucket; `--ignore-errors` reproduces rsync's skip-unreadable-subdir and
+  IO-error-suppressed deletion (exit 23).
+- `--info=name/flist/del/remove/nonreg/progress` emit rsync's line format,
+  including real-run `deleting`/`*deleting` lines carried by a new
+  `report_deletes` wire bool.
+- Receiver-observed `--stats` counters: `Number of created files` now carries
+  rsync's `(reg/dir/link/special)` breakdown and `Literal data` is exact for a
+  delta transfer (extended `STATUS_STATS`).
+- `--progress` uses an opt-in paths-only pre-count so the `to-chk` denominator
+  counts every entry like rsync, and emits per-directory/symlink/special names.
+- Receiver-side `protect`/`risk` filter engine (new bounded filter-rule wire
+  block): `--filter='P ...'` now shields a destination-only entry like rsync.
+- `auto` for `--compress-choice`/`--checksum-choice` honors
+  `RSYNC_COMPRESS_LIST`/`RSYNC_CHECKSUM_LIST`, and per-codec compression-level
+  defaults match rsync.
+- Empty source directories are recreated recursively; `-R --no-implied-dirs
+  --files-from` places listed files under missing implied parents; `--iconv`
+  matches rsync's push direction; `--delete-delay` reports actual removals and
+  recursively removes a refilled deferred directory.
+
+### Changed
+
+- **`--delete` now defaults to delete-during (rsync `--del`) timing.** With no
+  explicit timing flag, a plain `--delete` removes each directory's extras as
+  that directory is processed instead of committing one whole-tree deletion only
+  after the entire transfer succeeds. This matches rsync, frees destination
+  space progressively, and avoids the whole-old+new-tree peak that could
+  `ENOSPC` a tight destination. The client maps the default onto the existing
+  `delete_during` wire boolean, so `PROTOCOL_VERSION` stays `2.28.0`.
+- Basis directories (`--compare-dest`/`--copy-dest`/`--link-dest`) now default
+  to rsync's metadata quick-check (equal size and mtime; `--size-only` drops the
+  mtime leg) instead of FastSync's historical always-verify content hash.
+  `--copy-dest` re-applies the source attributes, and basis materialization is
+  streamed so the 256 MiB whole-file cap no longer applies to a basis hit.
+- The per-directory `STATUS_DELETE_PLAN` frame gained a one-int `apply` flag:
+  the one-shot per-run config block (protected prefixes, size-pruned mirrors,
+  `--delete-missing-args` exact paths) is now always transmitted first on a
+  config-only carrier (`apply=false`), fixing a latent bug where a
+  `--delete-missing-args` run whose `--files-from` list synchronized no directory
+  never sent its exact deletions.
+
+### Notes
+
+- `--delete`/`--delete-during` remain caveats for the mid-transfer abort
+  boundary (rsync's generator removes all planned extras ahead of its throttled
+  sender; FastSync removes only reached directories — final trees agree).
+  `--delete-before`, `--progress`, `--stats`, `--fuzzy` and the basis rows keep
+  their documented residuals in `RSYNC_COMPAT.md`; `--filter` and
+  `--delete-excluded` are now parity, including protection of a destination-only
+  excluded entry under default `--delete`.
+
+### Migration
+
+- Scripts that relied on plain `--delete` deleting nothing until the transfer
+  fully succeeded must pass **`--delete-commit`** (or `--delete-after`) to keep
+  that behavior. Plain `--delete` now removes reached directories' extras during
+  the transfer, exactly like rsync's default; on a completed run the final tree
+  is unchanged.
+- Deployments that relied on FastSync's stricter basis verification should pass
+  **`--verify-basis`**; the default now trusts the size+mtime quick-check like
+  rsync.
+
+## [2.26.0] - 2026-09-17
+
+
+### Added
+
+- **Parity-completion wave.** Closed the remaining rsync-parity gaps against
+  rsync 3.4.1 and reclassified the inherently non-rsync rows. It moved the wire
+  protocol three times (`2.23.0 → 2.24.0 → 2.25.0 → 2.26.0`).
+  - **Delete timing (2.24.0):** per-directory delete plans
+    (`STATUS_DELETE_PLAN`) for `--delete-during`/`--delete-delay`. An interrupted
+    during-transfer has already removed the reached directories' extras, while a
+    delayed transfer commits per directory only after the whole transfer
+    succeeds (a late-created extra survives `--delete-delay` but not
+    `--delete-after`). `-R --delete` is scoped to the transferred prefix; empty
+    in-scope source directories survive; dry-run never deletes.
+  - **Wire stats (2.25.0):** `STATUS_STATS` carries the receiver counters
+    (matched data, deleted files) and the dry-run would-delete list. `--stats`
+    prints rsync's protocol-independent lines; `--progress`/`-P` print per-file
+    blocks; `--out-format` gains `%b` (wire bytes), `%c` (block-sum bytes) and
+    `%C` (whole-file digest); `-n --delete` prints escaped `*deleting` lines in
+    the sequential and `--threads` paths.
+  - **Codecs (2.26.0):** `lz4`/`zlib`/`zlibx` compression and `md4`/`sha1`/
+    `none` checksums, with rsync-style `auto` negotiation (default `xxh128` +
+    `zstd`) and exit-4 rejection of unknown names; the resolved `compression_algo`
+    crosses the wire.
+  - General `-R`/`--relative` (including the `/./` cut) and `--no-implied-dirs`;
+    one-level `-d`/`--dirs` listing for `dir`, `dir/` and `.`; the full filter
+    grammar (`merge`/`dir-merge`/`hide`/`show`/`protect`/`risk`/`clear` and
+    modifiers) with `-f` bound to `--filter`; a single `-F` transfers
+    `.rsync-filter` and `-FF` excludes it.
+  - Receiver-side `--chown`/`--usermap`/`--groupmap` TO-name resolution; absolute
+    basis directories and a `--link-dest` relink of an up-to-date destination;
+    a receiver-side `--ignore-existing` short-circuit before any payload;
+    `--preallocate` now wins over `--sparse` via `fallocate(2)`.
+  - Client quick wins: `--iconv=.`/`-`/`--no-iconv`, a lone `-h` prints help, an
+    empty `--files-from` succeeds (exit 0), a broken referent under
+    `-L`/`--copy-unsafe-links` exits 23, the full `--info`/`--debug`
+    vocabularies, and the aliases `--ignore-non-existing`, `--protect-args`,
+    `--msgs2stderr`.
+
+### Changed
+
+- `PROTOCOL_VERSION` bumped `2.23.0 → 2.24.0` (delete plans),
+  `2.24.0 → 2.25.0` (`STATUS_STATS` + `report_stats`), and
+  `2.25.0 → 2.26.0` (codec negotiation + `md4`/`sha1`/`none`).
+- `--checksum-choice`/`--cc` now accepts `md4`, `sha1`, `none` and the two-name
+  form; the negotiated whole-file default is `xxh128`.
+- `--compress-choice`/`--zc` now accepts `lz4`, `zlib`, `zlibx`.
+- `RSYNC_COMPAT.md` reclassifies the matrix: 9 already-parity rows to ✅, 17
+  inherently non-rsync rows to ❌ (native daemon config/auth, batch, privileged
+  xattr namespaces, and the safe-subset device/privilege flags), and the genuine
+  fixes to ✅; new rows cover `--bwlimit`, `--partial`, `--partial-dir`,
+  `--no-whole-file`, `--inc-recursive`/`--no-inc-recursive`, `--protect-args`
+  and `--msgs2stderr`.
+- The client `--help` `--max-delete` text now describes the implemented partial
+  semantics (delete up to N, skip the rest, exit 25).
+
+### Notes
+
+- Remaining documented divergences include the `--stats` per-type file-count
+  breakdown, `%b`/`%c` being FastSync wire counts, `-n --delete` line ordering,
+  the default `--delete` timing (delete-after, not rsync's delete-during),
+  destination-only exclude protection (still sender-derived), `--temp-dir`
+  absolute paths, basis-dir attribute re-application and the 256 MiB whole-file
+  cap, `--fuzzy` tie-breaking, `--bwlimit=0`/decimal rates, `zlibx`==`zlib`, and
+  recursive empty-directory creation.
+- Build: adds zlib and lz4 as link dependencies.
+
+## [2.23.0] - 2026-09-16
+
+### Added
+
+- **Rsync-parity wave.** Closed the remaining CLI, filesystem, ownership,
+  deletion, and output gaps against rsync 3.4.1.
+  - Short options `-r` (`--recursive`), `-b` (`--backup`), `-L`
+    (`--copy-links`), and `-B` (`--block-size`/`--delta-block`); rsync
+    short-option clustering (`-av`, `-aAX`, `-rlpt`) and attached/inline values
+    (`--opt=value`, `-B1000`, `-essh`, `-MOPT`). A value that starts with `-`
+    is not mistaken for a cluster.
+  - `-c`/`--checksum` now implies the incremental checksum quick-check (and,
+    like rsync, does not imply `-t`).
+  - `--checksum-choice`/`--cc` accepts `xxh64`/`xxhash`/`xxh3`/`xxh128`/`md5`/
+    `auto` and rejects `md4`/`sha1`/`none` and the two-name form by name;
+    `--checksum-seed=0` (the default) is randomized per transfer and the chosen
+    seed is sent to the receiver.
+  - `--compress-choice`/`--zc` accepts `zstd`/`none`/`auto` and rejects
+    `lz4`/`zlib`/`zlibx` by name; `--skip-compress` defaults to rsync 3.4.1's
+    built-in suffix list; `--no-whole-file` is accepted.
+  - `--timeout` defaults to 0 (disabled) and `--contimeout` to 60 s (both `0`
+    disables), matching rsync; `--max-alloc=0` means no local limit.
+  - `--temp-dir` is confined to the receive root (absolute/`..` rejected by the
+    receiver) and an `EXDEV` install falls back to a non-atomic copy.
+  - `--numeric-ids` is documented as a mapping modifier only;
+    `--usermap`/`--groupmap` support inclusive `LOW-HIGH` ranges, `*`,
+    empty-`FROM` (unnamed ids), and receiver-resolved `TO` names; `--chown`
+    conflicts with a map on the same side are rejected.
+  - `--fake-super` records the *resolved* owner (never a real chown) and replays
+    mode/time; directory ownership and directory xattrs/ACLs are preserved.
+  - `-l`/`--links` stores symlink targets verbatim (absolute and `..`-bearing
+    included), matching rsync; `--safe-links`/`--copy-unsafe-links` are applied
+    sender-side and `--munge-links` uses rsync's `/rsyncd-munged/` marker;
+    `--trust-sender` no longer affects symlink targets.
+  - `--specials` recreates unix sockets with `mknod(S_IFSOCK)` (so `-D` covers
+    the full rsync node set).
+  - Deletion: the manifest carries a synchronized-directory section so
+    `--files-from` subsets no longer delete untransmitted paths;
+    `--delete-excluded` leaves size-pruned mirrors protected; extraneous
+    destination symlinks are unlinked (never followed); `--max-delete=N` is
+    partial (delete up to N, skip the rest, exit 25) and `--delete-missing-args`
+    removals draw from the same budget; `--force` is honored during
+    `--delay-updates` publication.
+  - `-x`/`--one-file-system` emits the mount-point directory entry; the
+    `--include`/`--exclude` layers are an ordered first-match rule list.
+  - `--chmod` is a faithful port of rsync 3.4.1 (numeric/symbolic, `D`/`F`/`X`,
+    `s`/`t`, append semantics, no `-p` implication, no sanitization).
+
+### Changed
+
+- `PROTOCOL_VERSION` bumped `2.22.0 → 2.23.0`: the delete manifest gains a
+  synchronized-directory section and the terminal status gains
+  `STATUS_DELETE_LIMIT` (client exit 25 on a `--max-delete`-capped commit).
+- **The 2.22.0 mode-masking divergence is removed.** Under `-p` the source mode
+  is copied exactly, including `S_IWGRP`/`S_IWOTH` and setuid/setgid/sticky;
+  `--chmod` no longer implies `-p`. New files without `-p` still use
+  `source_mode & ~umask` when metadata is present (else `0644`), and new
+  directories without `-p` still use the `0755` creation default.
+- `--protocol=NUM` accepts only the current `2.23.0` version string.
+
+### Notes
+
+- The rsync-compatibility matrix (`RSYNC_COMPAT.md`) now classifies every row
+  as **parity**, **caveat** (works with a documented divergence), or
+  **divergent** (not supported/no-op/impossible), replacing the previous
+  misleading "N implemented / 0 divergence" summary. Durable documented
+  divergences remain: receiver-side symlink target containment is not enforced
+  by default (verbatim storage is rsync parity; use `--safe-links`),
+  `--temp-dir` rejects absolute/foreign-filesystem paths, `--copy-devices`
+  reads a bounded `st_size`, a broken referent under `--copy-links` exits 0,
+  new directories without `-p` use `0755`, `--stats` receiver-only counters are
+  0, and `--password-file`/`--early-input`/`--hash-credentials`/`--iterations`
+  and the batch format are FastSync-native.
+
+## [2.22.0] - 2026-09-15
+
+### Added
+
+- **Per-attribute metadata preservation (protocol 2.22.0).** The former single
+  metadata bundle is split into four independent, rsync-compatible flags:
+  `-p/--perms`, `-t/--times`, `-o/--owner`, and `-g/--group`, each applied
+  independently on the receiver, with negations `--no-perms`/`--no-times`/
+  `--no-owner`/`--no-group` (short `--no-p`/`--no-t`/`--no-o`/`--no-g`) and
+  `--no-preserve` clearing all four. `-a/--archive` is now full rsync
+  `-rlptgoD` (owner and group included; their application stays
+  privilege-gated). `-A/--acls` and `--chmod` imply `-p`, `-X/--xattrs` does
+  not, `-E/--executability` sets only executability, and `-U`/`-N` do not imply
+  `-t`. `--incremental`/`--delta` still auto-preserve perms+times unless the
+  user explicitly negated them.
+- Receiver applies directory modes under `-p` (at the end of the transfer,
+  alongside the deferred directory times) and symlink mode under `-p`; `-O`
+  suppresses directory times only.
+
+### Changed
+
+- `PROTOCOL_VERSION` bumped `2.21.0 → 2.22.0`: the binary config frame gains
+  four appended booleans (`preserve_perms`/`preserve_times`/`preserve_owner`/
+  `preserve_group`) after `omit_link_times`. The fixed-width `FileMetadata`
+  layout is unchanged; the receiver derives the metadata-frame gate
+  (`use_metadata`) from the four attributes.
+
+### Notes
+
+- Documented divergences from rsync: a client-supplied mode never grants
+  group/other write (`S_IWGRP|S_IWOTH` are stripped for files, directories,
+  symlinks, and specials; rsync's `-p` preserves them exactly); a brand-new file
+  without `-p` gets `source_mode & ~umask` (sanitized) when metadata is present,
+  else the historical fixed `0644`; `--chmod` implies `-p` (rsync does not);
+  `-o`/`-g` map by name on the receiver with a raw-numeric fallback (only
+  numeric ids cross the wire); and a daemon module without `client owner = yes`
+  does not refuse a plain `-a`/`-o`/`-g` but forces super-user activities off,
+  applies no ownership, and logs a warning (explicit `--chown`/`--usermap`/
+  `--groupmap`/`--numeric-ids`/`--copy-as`/`--super` are still refused).
+
 ## [2.21.0] - 2026-09-14
 
 ### Added

CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.22)
 
-project(FastFileTransfer VERSION 2.21.0)
+project(FastFileTransfer VERSION 2.28.0)
 
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 set(CMAKE_C_STANDARD 11)
@@ -68,6 +68,16 @@ if(NOT ZSTD_LIBRARY)
 	message(FATAL_ERROR "zstd library not found. Ensure it is in your nix-shell!")
 endif()
 
+find_library(ZLIB_LIBRARY z)
+if(NOT ZLIB_LIBRARY)
+	message(FATAL_ERROR "zlib library not found. Ensure zlib1g-dev / nix zlib is available!")
+endif()
+
+find_library(LZ4_LIBRARY lz4)
+if(NOT LZ4_LIBRARY)
+	message(FATAL_ERROR "lz4 library not found. Ensure liblz4-dev / nix lz4 is available!")
+endif()
+
 find_package(OpenSSL REQUIRED)
 
 # --- Explicit source lists ---
@@ -89,6 +99,7 @@ set(SHARED_SRCS
 	src/shared/daemon_limits.c
 	src/shared/data.c
 	src/shared/delay_updates.c
+	src/shared/delete_plan.c
 	src/shared/delta.c
 	src/shared/file.c
 	src/shared/file_list.c
@@ -96,6 +107,7 @@ set(SHARED_SRCS
 	src/shared/file_send.c
 	src/shared/file_store.c
 	src/shared/filter.c
+	src/shared/format.c
 	src/shared/hardlink.c
 	src/shared/identity.c
 	src/shared/log.c
@@ -134,8 +146,8 @@ set(CLIENT_MAIN_SRCS src/client/client_cli.c)
 # --- Library targets ---
 add_library(fastsync_shared STATIC ${SHARED_SRCS})
 target_include_directories(fastsync_shared PUBLIC src/shared)
-target_link_libraries(fastsync_shared PUBLIC Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL
-											OpenSSL::Crypto xxhash)
+target_link_libraries(fastsync_shared PUBLIC Threads::Threads ${ZSTD_LIBRARY} ${ZLIB_LIBRARY}
+											${LZ4_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
 
 add_library(fastsync_client_core STATIC ${CLIENT_CORE_SRCS})
 target_include_directories(fastsync_client_core PUBLIC src/client)
@@ -209,10 +221,12 @@ set(TEST_SRCS
 	tests/test_daemon_limits.c
 	tests/test_data.c
 	tests/test_delay_updates.c
+	tests/test_delete_plan.c
 	tests/test_delta.c
 	tests/test_file.c
 	tests/test_file_list.c
 	tests/test_file_sendfile.c
+	tests/test_format.c
 	tests/test_fuzz_smoke.c
 	tests/test_glob.c
 	tests/test_hardlink.c
@@ -273,7 +287,7 @@ if(ENABLE_FUZZ)
 		target_include_directories(${FUZZ_NAME} PRIVATE tests src/shared src/server)
 		target_compile_options(${FUZZ_NAME} PRIVATE -fsanitize=fuzzer,address,undefined -fno-omit-frame-pointer)
 		target_link_options(${FUZZ_NAME} PRIVATE -fsanitize=fuzzer,address,undefined)
-		target_link_libraries(${FUZZ_NAME} PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL
-												  OpenSSL::Crypto xxhash)
+		target_link_libraries(${FUZZ_NAME} PRIVATE Threads::Threads ${ZSTD_LIBRARY} ${ZLIB_LIBRARY}
+												  ${LZ4_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
 	endforeach()
 endif()

Dockerfile

@@ -2,8 +2,22 @@ FROM ubuntu:24.04
 RUN apt-get update && apt-get install -y --no-install-recommends \
     gcc g++ make libc6-dev cmake libzstd-dev libssl-dev git ca-certificates curl cppcheck clang-format \
     python3 python3-pip python3-venv openssl openssh-client \
-    lcov valgrind clang libclang-rt-18-dev && \
+    lcov valgrind clang libclang-rt-18-dev \
+    acl attr zlib1g-dev liblz4-dev libxxhash-dev && \
     pip3 install --break-system-packages pytest pytest-xdist && \
     curl -fsSL https://deb.nodesource.com/setup_20.x | bash - && \
     apt-get install -y --no-install-recommends nodejs && \
     rm -rf /var/lib/apt/lists/*
+
+# rsync is used as the reference implementation for drop-in parity tests.
+# Ubuntu 24.04 ships 3.2.7, so build the pinned 3.4.1 reference from source.
+ARG RSYNC_VERSION=3.4.1
+ARG RSYNC_SHA256=2924bcb3a1ed8b551fc101f740b9f0fe0a202b115027647cf69850d65fd88c52
+RUN curl -fsSL "https://download.samba.org/pub/rsync/src/rsync-${RSYNC_VERSION}.tar.gz" -o /tmp/rsync.tar.gz && \
+    echo "${RSYNC_SHA256}  /tmp/rsync.tar.gz" | sha256sum -c - && \
+    tar -xzf /tmp/rsync.tar.gz -C /tmp && \
+    cd "/tmp/rsync-${RSYNC_VERSION}" && \
+    ./configure --enable-zstd --enable-xxhash --enable-lz4 && \
+    make -j"$(nproc)" && \
+    make install && \
+    rm -rf "/tmp/rsync-${RSYNC_VERSION}" /tmp/rsync.tar.gz

HANDOFF.md

@@ -0,0 +1,221 @@
+# FastSync — Session Handoff (2026-09-19)
+
+## Current status
+- **rsync-parity tracks 1-6 landed on `dev`** via **PR #303** (`10159dc`,
+  "feat(parity): rsync parity tracks 1-6 (protocol 2.28.0)"). Dev push CI run
+  **581** fully green: lint, build-and-test, parity-full, ASan, UBSan,
+  fuzz-build, coverage, valgrind.
+- **`PROTOCOL_VERSION` = `"2.28.0"`** (`src/shared/config.h`); CMake
+  `project(FastFileTransfer VERSION 2.28.0)`. The cycle batched all wire
+  changes (stats counters, filter-rule block, `--verify-basis`) under the one
+  bump.
+- **`main` = `ef76c90`** (tag `v2.26.0`); the 2.27.0/2.28.0 work is on `dev`
+  and not yet released. A `dev -> main` v2.28.0 release PR is the next step.
+- Parity matrix: **116 ✅ / 14 ⚠️ / 27 ❌ = 157** (was 111/13/33 at cycle start).
+- Working tree clean; feature branch deleted; no scratch trees or worktrees.
+
+
+## What landed this session
+1. **Wave 8 (refactors):** Config X-macro wire table; single-owner `authorized_root`;
+   daemon per-module/per-host caps + cross-process auth lockout (`daemon_limits.[ch]`);
+   `Data` charge returns to its owning `ProtocolSession`.
+2. **Wave 9 (protocol 2.21.0):** optional `STATUS_ERROR_DETAIL` rejection reasons;
+   server-contacting `--dry-run` (`STATUS_DRY_RUN_TRANSFER`, receiver mutates nothing).
+3. **Security wave:** ran 5 parallel audits (wire parsing; daemon/transport/TLS/auth;
+   receiver confinement; client/CLI/SSH; crypto/memory/limits). Fixed all HIGH and the
+   confirmed MEDIUMs:
+   - SSH `-o ProxyCommand=…` argument injection (RCE) — reject leading `-`, insert `--`.
+   - Truncated zstd frame infinite CPU loop (remote DoS).
+   - FIFO receiver opens lacked `O_NONBLOCK` (indefinite hang).
+   - `--inplace` could write a FIFO/device (bypass of `--write-devices` gate).
+   - `--force` not gated by server `--allow-delete`.
+   - Privileged standalone server defaulted super activities on; added `--allow-super`
+     (never honored with `--stdio`).
+   - `--dry-run` content/hash oracle on `read only`/basis files removed.
+   - Empty `hosts allow`/`deny`/`auth users` now rejected.
+   - TLS: AEAD-only 1.2 + server preference, TOCTOU-safe key load, IP-SAN verify,
+     CN-truncation guard. Glob backtracking bounded; line reads bounded; ACL xattrs
+     gated on `--acls`; decompression/chunk memory charged; pre-auth `basis_count`
+     NULL-deref fixed.
+4. **Tooling:** benchmark accuracy (data mix, verification, percentiles, `tc`,
+   `build-bench/`, `--warm` mode); `shell.nix` full toolchain and no build-on-entry;
+   docs state push-only / remote-source unsupported.
+5. **Preserve-attribute split (protocol 2.22.0)** landed on `feat/preserve-attr-split`: per-attribute `-p/-t/-o/-g` + `--no-*` negations, `-a` = `-rlptgoD`, and the 2.21.0 → 2.22.0 wire bump.
+6. **Rsync-parity wave (protocol 2.23.0)** on `feat/rsync-parity`: rsync short options/clustering/attached values (`-r`/`-b`/`-L`/`-B`, `-av`, `-aAX`, `-B1000`, `-essh`, `-MOPT`), `-c` checksum quick-check, `--checksum-choice`/`--compress-choice` validation and seed randomization, rsync timeout/max-alloc defaults, temp-dir confinement + `EXDEV` fallback, ownership/mapping parity (numeric-ids modifier, map ranges/`*`/empty-FROM, `--chown`+map conflicts, fake-super resolved-owner record), verbatim symlink storage with rsync `--safe-links`/`--munge-links`, socket recreation under `--specials`, `--chmod` 3.4.1 semantics, and delete scoping + `--max-delete` partial/exit-25. Wire: appended delete-manifest synchronized-directory section and `STATUS_DELETE_LIMIT`.
+7. **Parity-completion wave (protocol 2.24.0 → 2.26.0)** on `feat/parity-completion`: per-directory delete plans (`STATUS_DELETE_PLAN`) for `--delete-during`/`--delete-delay`; receiver `STATUS_STATS` counters feeding `--stats`/`--progress` and `--out-format %b/%c/%C`, plus `-n --delete` lines; `lz4`/`zlib`/`zlibx` compression and `md4`/`sha1`/`none` checksums with `auto` negotiation (default `xxh128`/`zstd`); general `-R`/`--no-implied-dirs`/`-d`; the full filter grammar (`merge`/`dir-merge`/`hide`/`show`/`protect`/`risk`/`clear` + modifiers) and corrected `-F`/`-FF`; receiver-side `--chown`/map TO-name resolution; absolute basis dirs + `--link-dest` relink; receiver-side `--ignore-existing` short-circuit; `--preallocate` over `--sparse` via `fallocate(2)`; `--iconv=.`/`-`/`--no-iconv`; lone `-h` help; aliases `--ignore-non-existing`/`--protect-args`/`--msgs2stderr`; and the full `--info`/`--debug` vocabulary. `RSYNC_COMPAT.md` reclassifies the matrix to 106 ✅ / 27 ⚠️ / 23 ❌; the later rsync-parity-stats pass (`fix/parity-stats`) moves it to 107 ✅ / 25 ⚠️ / 24 ❌ (see item 8).
+8. **rsync-parity-stats pass** on `fix/parity-stats` (no wire change, `PROTOCOL_VERSION` stays `2.26.0`): `--delete-delay` now reports only entries it actually removes, while the `--max-delete` budget is charged at plan/snapshot time (`planned`, via `defer_add`) to bound the deferred list (a refilled deferred directory that survives `ENOTEMPTY` is not reported but still consumes budget); `--stats` gained the `(reg/dir/link/special)` `Number of files` breakdown and now counts only regular files actually stored for `Number of regular files transferred`/transferred size/literal data (up-to-date re-runs report 0); `Total file size` includes symlink target lengths; `--progress` prints the leading `./` root line and counts it in `to-chk` so a single-file transfer matches rsync; and `%C` uses the selected transfer checksum with `checksum_digest_file` supporting md4/sha1/none, byte-identical to rsync for every algorithm. `--out-format` reclassified ❌ (`%b`/delta-`%c` are protocol-specific). Differential + regression tests added; full suite + ASan + clang-format + cppcheck clean.
+9. **Option-parity wave (protocol 2.26.0 → 2.27.0, on `fix/parity-options`):**
+   `--bwlimit` now ports rsync 3.4.1's units/quantization and paces like its
+   leaky bucket; `--ignore-errors` reproduces rsync's default (an I/O error
+   skips deletion unless the flag is set; the readable tree still transfers and
+   the run exits 23) across every delete timing; the `--info` categories with a
+   FastSync event (`name`/`flist`/`del`/`remove`/`nonreg`/`progress`) emit
+   rsync's line format, with real-run `deleting`/`*deleting` lines carried over
+   the new trailing config bool `report_deletes` (golden wire updated by
+   `tests/test_config.c`). Two residuals were reclassified **divergent**: `-M`
+   over daemon/TCP (no argv channel in FastSync's binary config handshake;
+   rsync-daemon differential pins the rsync behavior) and receiver-side
+    `protect`/`risk` re-derivation for destination-only entries (would need a
+    receiver filter engine; differential pins the divergence — **reversed by
+    track 4a below**, which adds that engine). The options pass
+    stands at **110 ✅ / 21 ⚠️ / 26 ❌**. New `tests/integration/test_option_parity.py`
+   holds the rsync differentials (bwlimit parse+rate, info lines, real-setpriv
+   `--ignore-errors`, rsync-daemon `-M`, filter-protect pin).
+
+10. **rsync-parity-fs pass** on `fix/parity-fs` (no wire change of its own; integrated
+   on top of the 2.27.0 options wave): recursive transfers now recreate empty source directories (and
+   `-m/--prune-empty-dirs` still suppresses them), a directory entry replaces a
+   blocking destination regular file, and `-R --no-implied-dirs --files-from`
+   places a listed file under a missing implied parent with default attributes
+   instead of refusing (real rsync 3.4.1 parity, differential-tested). `--iconv`
+   now reproduces rsync's push direction (destination charset = the spec's REMOTE
+   half; a server `--iconv` overrides), and `-T/--temp-dir` relative semantics are
+   confirmed identical while the absolute-path confinement is a deliberate
+   divergence. The basis-dir options, `--delay-updates` and `--dry-run` were
+   reclassified to ❌ after a differential test reproduced each exact residual
+   (basis content verification, fixed staging-name collision, and dry-run
+   would-delete over-report). `--fuzzy` was also reclassified to ❌ (deterministic
+   heuristic with a 10× size window, not rsync's matcher), but its residual is the
+   candidate-selection heuristic itself: the final tree is byte-exact by design, so
+   it is pinned by the `TestFuzzy` threshold suite rather than a byte-level rsync
+   differential. (Track 5b later found the name heuristic is rsync's own and moved
+   the row ❌ → ⚠️, leaving only the narrower delta size window; see entry 15.) The parity-review pass then moved `--delete-delay` to ⚠️ (the
+   plan-time `--max-delete` charge and non-recursive deferred removal differ from
+   rsync when a snapshotted entry fails removal). Differential-gate allowlist
+   entries `min_size`/`empty_dirs_recursive`/`dirs_plain` were removed. The
+   integrated stats+options+fs branch stands at **111 ✅ / 13 ⚠️ / 33 ❌ = 157**;
+   full suite + ASan + clang-format + cppcheck clean.
+
+11. **No-wire parity track 1** on `feat/parity-2.28` (no protocol change):
+    `-n --delete` now sends the same filter-excluded + size-pruned protected
+    prefixes and synchronized-directory scope as a real run (dry-run would-delete
+    matches rsync for source-derived protections; the destination-only exclude
+    residual was later closed by track 4a, readdir ordering remains);
+    `--delete-delay` now charges
+    `--max-delete` on actual removals and re-scans a queued directory at commit
+    to remove content created after the plan, with an independent deferred-list
+    cap (only partial-delete ordering remains); and `--info=name2` emits `NAME is
+    uptodate` plus the leading `./` root name line for `--info=name` (only the
+    root-line trigger condition and receiver-side `skip` wording remain). Matrix
+    now **111 ✅ / 14 ⚠️ / 32 ❌ = 157**; differential + unit tests added in
+    `test_features.py`, `test_option_parity.py`, `test_delete_plan.c`,
+    `test_delete_delay_budget_parity.py`, `test_delete_timing_parity.py`.
+12. **No-wire parity track 2b** on `feat/parity-2.28` (no protocol change):
+    `--progress`/`-P`/`--info=progress` (when not `--quiet`) now run an opt-in
+    paths-only metadata pre-count (no file reads/hashing) that supplies rsync's
+    full file-list total for the `to-chk` denominator and the directory names,
+    and emits per-directory/symlink/special name lines, in both the sequential
+    and `--threads` paths. `--delete-during`/`--delete-delay` reuse their
+    keep-set pre-scan instead of a second walk; non-progress runs are
+    unaffected. Differential tests (`progress`/`progress_threads` over a new
+    `multidir` corpus) match rsync's name set and `to-chk` denominator on a
+    fresh transfer, and the single-file byte-identical test still passes;
+    emission order (rsync's sorted depth-first vs FastSync's readdir/BFS stream)
+    plus re-run over-naming (unconditional `./`, ancestor dirs named with a
+    transferred child, and no quick-check for symlinks/empty dirs) remain the
+    caveats, so the row stays ⚠️ and the matrix is unchanged at
+    **111 ✅ / 14 ⚠️ / 32 ❌ = 157**.
+
+13. **Wire parity track 4a** on `feat/parity-2.28` (`PROTOCOL_VERSION` stays
+    `2.28.0`): the receiver now has a delete-time filter engine. The sender
+    compiles its root-level selection rules exactly as the scanner does
+    (`filter_base_build`) and streams them as one bounded, self-describing
+    config-frame block (action, sides, anchored, dir-only, negate, owner,
+    pattern; bounded rule count and pattern bytes, unknown action/sides is a
+    protocol error). The receiver reconstructs `protect_rules` and applies them
+    first-match-wins to each extraneous destination path in every delete timing
+    (the whole-tree commit walker, the `--delete-during`/`--delete-delay`
+    per-directory plans, and the `-n` would-delete enumeration), so a
+    `P *.log` rule protects a destination-only `extra.log` like rsync (with
+    `risk` cancelling); the sender-derived protected-prefix behavior is
+    preserved when no rules are sent and `--delete-excluded` semantics are
+    unchanged. Per-directory merge (`:`/`.`) receiver re-derivation remains the
+    residual. `TestFilterProtect` (real + dry-run) plus differential cases
+    `filter_protect`, `filter_protect_during`, `filter_protect_delay` added and
+    the `--filter=RULE` row moves ❌ → ✅: matrix now
+    **115 ✅ / 11 ⚠️ / 31 ❌ = 157**; unit tests, the three named integration
+    files, clang-format and cppcheck clean.
+
+14. **Wire parity track 5a** on `feat/parity-2.28` (`PROTOCOL_VERSION` stays
+    `2.28.0` by project decision): the three basis-dir options now default to
+    rsync's metadata quick-check (equal size + equal mtime, or size alone under
+    `--size-only`; `-I` disables matching) instead of FastSync's historical
+    xxHash64 content equality, so a same-size/different-content basis is trusted
+    exactly as rsync trusts it. A new FastSync-only, long-only `--verify-basis`
+    flag restores the strict whole-file content equality; its bool is appended to
+    the basis block of the config frame (golden wire frame 882 → 886 bytes).
+    `--verify-basis` streams the confined basis descriptor to hash it, and a
+    basis hit is no longer capped at the 256 MiB whole-file payload bound:
+    `--copy-dest` streams the basis through a bounded buffer and `--link-dest`'s
+    copy fallback streams from the basis, so an over-limit hit materializes (a
+    basis MISS still falls back to the normal transfer and keeps its own bound).
+    A `--copy-dest` hit re-applies the SOURCE attributes (the sender transmits
+    the source metadata with the basis check frame), matching rsync's
+    "copy then fix attributes"; a `--link-dest` success keeps the shared inode's
+    attributes (writing through it would mutate the basis). Differential cases
+    `copy_dest` and `verify_basis` added; `test_basis_dir_size_only_content_residual`
+    converted to a passing parity assertion; `TestBasisDestDirs` updated for the
+    new default + `--verify-basis`; unit tests cover the quick-check/verify
+    decision and the same-size/different-content handshake. The
+    `--compare-dest`/`--copy-dest`/`--link-dest` rows move ❌ → ⚠️ (relative-DIR
+    resolution base and over-limit MISS refusal): matrix now
+    **116 ✅ / 13 ⚠️ / 28 ❌ = 157**.
+
+15. **No-wire parity track 5b** on `feat/parity-2.28` (`PROTOCOL_VERSION` stays
+    `2.28.0` by project decision): `-y`/`--fuzzy` reclassified ❌ → ⚠️. A probe
+    against real rsync 3.4.1 (pinned `-B8192`, repeated-content 64 KiB corpus)
+    showed the name heuristic is already rsync's (`util1.c fuzzy_distance` /
+    `find_filename_suffix` + the exact size+mtime pass) and the output is always
+    byte-exact; the only residual is candidate ELIGIBILITY, because FastSync's
+    `delta_should_attempt` gate caps the size ratio at 10× and requires both
+    files ≥ 16 KiB while rsync will reuse a basis from 0.25× to 10000× and below
+    16 KiB. The choice is observable only as `--stats` bandwidth counters. Added
+    differential case `fuzzy_basis` (same-suffix sibling, one name edit,
+    identical content, block size pinned) asserting tree **and** normalized
+    `--stats` parity where the choices coincide, plus `TestFuzzy` pinning the
+    window boundary on both sides (>10× and <16 KiB siblings declined by
+    FastSync while rsync uses them, both trees byte-identical). Matrix now
+    **116 ✅ / 14 ⚠️ / 27 ❌ = 157**.
+
+16. **Lockstep delete-default track 6** on `feat/parity-2.28` (`PROTOCOL_VERSION`
+    stays `2.28.0`): plain `--delete` now defaults to rsync's delete-during
+    (`--del`) timing, normalized on the client onto the existing `delete_during`
+    wire bool. The old late whole-tree commit is opt-in via `--delete-after` or
+    the FastSync-only long `--delete-commit` (identical `delete_after` timing).
+    `-d/--dirs` still falls back to the end commit, `--delay-updates` still
+    deletes before publication, and `--files-from`/`-R` scope is unchanged. The
+    `STATUS_DELETE_PLAN` frame gained a one-int `apply` flag so the per-run
+    config block (including `--delete-missing-args` exact paths) is always
+    transmitted, on a config-only carrier when the scope allows no directory
+    plan — fixing a latent bug with a file-only `--files-from` list. Differential
+    cases `delete`/`delete_commit`/`filter_protect_after` plus the extended
+    `test_delete_timing_parity.py` (plain `--delete` mid-abort removes reached
+    extras, `--delete-commit` defers) pass; full `-m "not setpriv"` suite,
+    clang-format and cppcheck clean. Matrix unchanged at
+    **116 ✅ / 14 ⚠️ / 27 ❌ = 157** (the `--delete`/`--delete-during` rows stay
+    ⚠️ for the abort boundary; `--delete-after` stays ✅).
+
+## Next steps
+1. **Merge PR #284** (`dev` -> `main`) once reviewed (protected branch).
+2. **Deferred security items** (documented, not implemented):
+   - Pre-auth config/daemon-auth handshake has no aggregate wall-clock deadline
+     (per-message timeout only) — slowloris holds connection slots.
+   - Per-source registry fails open when the shared table is full (per-module/global
+     caps and host ACLs still apply); consider fail-closed or larger/evicting table.
+   - SCRAM-like daemon auth has no TLS channel binding (and is not RFC 5802).
+   - `cleanup()` signal handler calls non-async-signal-safe teardown; daemon `umask(0)`.
+   - Wire protocol assumes homogeneous word size/endianness (lengths are native
+     `size_t`) — document or move to fixed-width framing.
+3. **Out of scope / intentional:** pull (remote source) mode is **not** planned —
+   FastSync is push-only; see `RSYNC_COMPAT.md#direction`.
+
+## Key facts / commands
+- CI image: `gitea.tap-tap.win/taptap/fastsync-ci:v11` (alias `fastsync-ci:local`).
+- Build/test: `cmake -B build -S . -DSTRICT_WARNINGS=ON && cmake --build build -j$(nproc) && ./build/tests`
+  then `python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"`.
+- Dev shell: `nix-shell` (provides clang-format, cppcheck, pytest-xdist, openssh,
+  rsync, iproute2, valgrind, lcov; does not build on entry).
+- Gitea API token: supplied out-of-band via the `TOKEN` environment variable; it is
+  intentionally **not** recorded in this file.
+- CI polling: `GET /api/v1/repos/TapTap/FastSync/actions/runs?limit=N`, match `head_sha`,
+  then `/actions/runs/<id>/jobs`.

README.md

@@ -1,4 +1,4 @@
-#FastSync
+# FastSync
 
 FastSync is a high-performance file synchronization tool designed to become a
 drop-in replacement for common `rsync` workflows. It keeps the familiar
@@ -7,7 +7,7 @@ multithreading, streaming zstd compression, chunking, zero-copy TCP transfers,
 and native TCP/TLS transports.
 
 The release version is FastSync's client/server protocol version (printed by
-`fastsync --version`); client and server must match. See
+`./build/client --version`); client and server must match. See
 [CHANGELOG.md](CHANGELOG.md) for the history.
 
 The compatibility target is straightforward:
@@ -28,7 +28,7 @@ FastSync uses a producer-consumer transfer pipeline and can combine several
 optimizations for large or high-latency transfers:
 
 - Multithreaded scanning, loading, and sending.
-- Streaming zstd compression with levels 1 through 22.
+- Streaming compression (zstd by default, plus lz4/zlib/zlibx) with levels 1 through 22.
 - Configurable file chunking and compact chunk serialization.
 - `sendfile()` zero-copy transfers over TCP.
 - Batched incremental checks to reduce round trips.
@@ -51,28 +51,51 @@ replacement for every rsync feature or protocol mode.
 - Rsync-style source and destination arguments.
 - SSH transport using `user@host:destination` paths below the remote authorized root.
 - TCP client/server transfers.
-- Dry runs, excludes, includes, size filters, backups, statistics, and
-  bandwidth limiting.
-- Incremental size/mtime checks and optional xxHash64 content checks.
+- Dry runs (server-contacting since protocol 2.21.0 for server-routed targets),
+  excludes, includes, size filters, backups, statistics, and bandwidth
+  limiting.
+- Incremental size/mtime checks and optional content checks (`xxh128` by
+  default, selectable with `--checksum-choice`).
 - FastSync-native delta transfer for changed files.
 - Optional mode and timestamp preservation.
 - Delete manifests with server-side delete authorization.
 - Temporary-file writes with atomic rename by default.
 - Path traversal checks and destination-root confinement.
 
-### Not yet equivalent to rsync
+### Boundaries and documented divergences
+
+The items below summarize FastSync's rsync compatibility status — recently
+closed gaps and the remaining known divergences. Each row of the detailed
+matrix is classified as parity, caveat, or divergent in
+[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md).
 
 - The FastSync wire protocol is not the rsync wire protocol.
 - SSH mode requires `fastsync-server` on the remote host.
-- Archive mode does not yet provide all of rsync's `-rlptgoD` behavior.
-- Symlink transfer is incomplete; link targets are not yet recreated in all
-  modes.
-- Owner/group, ACL, xattr, and hard-link handling is incomplete or
-  unavailable.
+- Archive mode covers rsync's `-rlptgoD` behavior — links, permissions, times,
+  owner, group, devices, and special files — and does not imply compression or
+  multithreading (see [Client](#client)). Ownership application is still
+  privilege-gated: a receiver that cannot `chown` logs a warning and skips it.
+  Under `-p` the source mode is copied exactly, including setuid/setgid/sticky
+  and group/other-write bits (strict rsync parity; see
+  [`RSYNC_COMPAT.md`](RSYNC_COMPAT.md)).
+- Symlink transfer stores targets **verbatim** (`-l`/`--links`), including
+  absolute and `..`-bearing targets, matching rsync. The receiver does not
+  enforce a containment predicate by default; `--safe-links` drops unsafe
+  targets on the sender, and `--munge-links` rewrites them with rsync's
+  `/rsyncd-munged/` marker. `--trust-sender` does not affect symlink targets.
+  A destination later consumed by a link-following tool can therefore follow a
+  link outside the receive root — use `--safe-links` for untrusted sources.
+- Hard links (`-H`/`--hard-links`), extended attributes (`-X`/`--xattrs`), and
+  POSIX ACLs (`-A`/`--acls`) are preserved; owner/group is applied through
+  `-o`/`-g` (or an `-a`/`--archive` transfer), through the opt-in identity flags
+  (`--chown`/`--usermap`/`--groupmap`/`--numeric-ids`/`--copy-as`), and only when
+  the receiver has permission. See
+  [`RSYNC_COMPAT.md`](RSYNC_COMPAT.md) for the exact semantics and documented
+  divergences.
 - Device and special-file preservation is implemented with documented
   divergences: recreated device nodes require `CAP_MKNOD` on the receiver (a
-  non-root receiver skips the entry), and sockets cannot be recreated (FIFOs
-  are).
+  non-root receiver skips the entry), while FIFOs **and unix sockets** are
+  recreated (`--specials`).
 - Sparse-file hole preservation (`-S`, `--sparse`) is implemented receiver-side:
   long all-zero runs are written as holes (no wire change; the full file image
   is already in memory).
@@ -80,78 +103,163 @@ replacement for every rsync feature or protocol mode.
   the write atomic (temp + rename). With `--partial`, a failed/interrupted write
   now retains the already-written temp at the destination path (best-effort) so
   a later `--append`/`--append-verify` run can resume it.
-- `--dirs` is not implemented. Its compatibility aliases `--old-dirs` and
-  `--old-d` are recognized but rejected explicitly rather than silently using
-  FastSync's recursive directory behavior.
+- `-d`/`--dirs` and its aliases `--old-dirs`/`--old-d` transfer the named
+  directory entries without recursing into their contents.
 - Short-option names are now rsync-parity (Phase 7 Wave A): FastSync's former
   collisions were renamed (`-j`/`--threads`, `--preserve`, `--sendfile`,
   `--chunk-serialization`, `--timeout`, `--ssh-port`), so `-m`, `-M`, `-f`,
-  `-s`, `-T`, `-p`, `-c`, `-a`, and `-z` follow rsync. See `RSYNC_COMPAT.md`.
+  `-s`, `-T`, `-p`, `-c`, `-a`, and `-z` follow rsync.
+- Short-option clustering (`-av`, `-aAX`, `-rlpt`) and attached values
+  (`-B1000`, `-essh`, `-MOPT`, `--opt=value`) are accepted, matching rsync.
+- `-r`, `-b`, `-L`, and `-B` are parsed with the rsync short names.
+- `--stats` prints the counters FastSync can observe plus the receiver-only
+  counters reported over the wire (`Matched data`, deleted files, and the
+  created/literal counters); `Number of files` and `Number of created files`
+  carry rsync's per-type breakdown. `--progress` prints rsync-style per-file
+  blocks including the leading `./` line, and (when progress is requested) a
+  paths-only pre-count supplies rsync's `to-chk` denominator.
+- Codecs match rsync 3.4.1: `zstd`/`lz4`/`zlib`/`zlibx` compression and
+  `xxh128`/`xxh3`/`xxh64`/`md5`/`md4`/`sha1`/`none` checksums. `auto` honors
+  `RSYNC_COMPRESS_LIST`/`RSYNC_CHECKSUM_LIST` and otherwise follows rsync's
+  compiled-in order. An omitted `--compress-level` uses the codec's rsync
+  default (zstd 3, zlib/zlibx 6, lz4 ignored); `zlib`/`zlibx` share the
+  literal-only zlib path (rsync's zlibx semantics), and the transfer checksum is
+  not separately selectable.
 
 The detailed flag matrix is maintained in
-[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md). It distinguishes implemented,
-partial, alternate, and planned behavior.
+[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md). It reports each row as **parity**,
+**caveat** (works with a documented divergence), or **divergent** (not
+supported), rather than treating "parsed" as parity.
 
 ## Quick Start
 
 ### Build
 
-`compile_commands.json` is a symlink to `build/compile_commands.json` and is used by clangd/editor tooling; its target is generated by the build, so it dangles until the first build.
+```bash
+cmake -B build -S .
+cmake --build build -j$(nproc)
+```
+
+This produces `./build/client` and `./build/server`. `compile_commands.json` is a symlink to `build/compile_commands.json` and is used by clangd/editor tooling; its target is generated by the build, so it dangles until the first build.
 
 ### Client
 
 | Argument | Description |
 |----------|-------------|
 | Positional | `<source> <dest>` — automatic SSH detection if dest contains `:` |
-| `-c, --checksum` | Verify content by checksum instead of size+mtime |
-| `-z, --compress [level]` | Enable streaming zstd compression (level 1–22, default 5) |
-| `-a, --archive` | rsync archive mode (`-rlptgoD`): links, metadata, devices and specials (not compression/multithreading) |
+| `-c, --checksum` | Verify content by checksum instead of size+mtime (implies the incremental checksum quick-check) |
+| `--checksum-choice <alg>` | Whole-file checksum algorithm: `xxh128` (default), `xxh3`, `xxh64`/`xxhash`, `md5`, `md4`, `sha1`, `none`, or `auto` (plus rsync's two-name `transfer,pre-transfer` form) |
+| `-z, --compress [level]` | Enable streaming compression (default `zstd`; level 1–22, default 5) |
+| `--compress-choice <alg>` | Compression algorithm: `zstd` (default), `lz4`, `zlib`, `zlibx`, `none`, or `auto` |
+| `--skip-compress <list>` | Skip compression for suffixes (`/`- or `,`-separated); defaults to rsync 3.4.1's built-in suffix list |
+| `-a, --archive` | rsync archive mode (`-rlptgoD`): links, perms, times, owner, group, devices and specials; ownership application stays privilege-gated (not compression/multithreading) |
 | `-j, --threads[=N]` | Multithreading mode; `N` (1–256) sets the parallel scanner worker count, bare `-j`/`--threads` uses the default |
 | `-m` | rsync `--prune-empty-dirs` (short form now rsync-parity) |
+| `-r, --recursive` | Recurse into directories (FastSync is always recursive; accepted for rsync compatibility) |
+| `-d, --dirs` | Transfer the named directory entries without recursing into their contents; aliases `--old-dirs`/`--old-d` |
+| `-R, --relative` | Use rsync's relative path semantics (including the `/./` cut); with `--files-from`, preserve each listed entry's relative path below the destination root |
 | `--chunk-serialization` | Chunk serialization (batch all files per chunk; long form only) |
 | `-s` | rsync `--secluded-args` compatibility no-op (remote SSH argv is already injection-safe) |
 | `--sendfile` | Sendfile zero-copy. Incompatible with compression / chunk serialization. TCP only. Long form only. |
-| `--preserve` | Preserve supported file metadata (mode and mtime; ownership and atime are unsupported) |
-| `-n, --dry-run` | Scan and print what would be transferred |
-| `-p, --perms` | Preserve permission bits (part of the metadata bundle) |
-| `--ssh-port <port>` | SSH port (default: 22) |
-| `-v, --verbose` | Enable debug logging |
-| `-q, --quiet` | Suppress non-error output |
-| `--progress` | Show real-time transfer speed |
-| `-P` | Enables partial-transfer mode + progress output; interrupted writes retain the already-written temp for resumption |
-| `--delete` | Delete files on receiver not present in source (default timing: delete-after, i.e. only after the whole transfer succeeded) |
+| `--preallocate` | Allocate destination file space up front (fail-fast on a full disk) |
+| `--append` | Resume a shorter destination by appending only its tail (prefix not verified; requires `--incremental`) |
+| `--append-verify` | Like `--append`, but verifies the retained prefix checksum first (falls back to a full transfer on mismatch) |
+| `-W, --whole-file` | Transfer changed files without delta processing; `--no-whole-file` clears it |
+| `-B <n>, --block-size <n>` | Delta block size in bytes (alias `--delta-block`) |
+| `--checksum-seed <n>` | Seed for the whole-file xxHash digest; an unset/`0` seed is randomized per transfer, matching rsync |
+| `-I, --ignore-times` | Transfer files even when size and mtime match |
+| `--size-only` | Skip incremental files matching in size, ignoring mtime |
+| `--preserve` | Preserve mode and mtime (`-p` + `-t`; add `-o`/`-g` for owner/group or `-U`/`--atimes` for atime; `-N`/`--crtimes` captures birth time but cannot apply it) |
+| `-U, --atimes` | Preserve access times. Captured with the metadata payload; does not enable ownership. |
+| `-N, --crtimes` | Capture birth time; cannot be applied (documented divergence) |
+| `-p, --perms` | Preserve permission bits. Strict rsync parity: the source mode is copied exactly, including setuid/setgid/sticky and group/other-write bits |
+| `-t, --times` | Preserve modification times |
+| `-o, --owner` | Preserve the source owner (privilege-gated; mapped by name on the receiver with a numeric fallback) |
+| `-g, --group` | Preserve the source group (privilege-gated; mapped by name on the receiver with a numeric fallback) |
+| `--no-perms`, `--no-times`, `--no-owner`, `--no-group`, `--no-preserve` | Negate the per-attribute flags (short `--no-p`/`--no-t`/`--no-o`/`--no-g`; `--no-preserve` clears all four) |
+| `-E, --executability` | Preserve executable permission bits |
+| `-X, --xattrs` | Preserve user `user.*` extended attributes |
+| `-A, --acls` | Preserve POSIX ACLs |
+| `--chmod <changes>` | Modify transferred permissions (rsync syntax) |
+| `--chown=USER:GROUP` | Override the ownership of transferred files |
+| `--usermap=MAP` | Map usernames when applying ownership |
+| `--groupmap=MAP` | Map group names when applying ownership |
+| `--numeric-ids` | Apply source numeric uid/gid directly instead of mapping by name |
+| `--copy-as=USER[:GROUP]` | Force every written entry to USER[:GROUP] (requires a privileged receiver) |
+| `--fake-super` | Record the resolved owner plus mode/time in a reserved `user.fastsync.stat` xattr and replay mode/time; never performs a real chown |
+| `--super` | Permit the receiver to attempt confined super-user activities (device nodes) |
+| `-D` | Preserve device and special files (implies `--devices --specials`) |
+| `--devices` | Recreate device nodes on the destination (privileged; skipped without `CAP_MKNOD`) |
+| `--specials` | Recreate special files: FIFOs and unix sockets |
+| `--remove-source-files` | Remove regular source files after a successful transfer |
+| `--exclude <pattern>` | Exclude files matching glob pattern (repeatable) |
+| `--exclude-from <file>` | Read exclude patterns from a file (one per line) |
+| `--include <pattern>` | Only transfer files matching glob pattern (repeatable, whitelist) |
+| `--include-from <file>` | Read include patterns from a file |
+| `--files-from <file>` | Read the source file list from FILE (paths relative to the source root) |
+| `--max-size <n>` | Skip files larger than n bytes |
+| `--min-size <n>` | Skip files smaller than n bytes |
+| `-x, --one-file-system` | Do not cross filesystem boundaries; the mount-point directory entry is emitted (empty at the destination) without descending |
+| `--max-alloc <SIZE>` | Maximum single allocation (binary units: B, K, M, G, T, P, E; default 1G; `0` = no local limit, matching rsync) |
+| `-u, --update` | Skip files newer than the source on the receiver |
+| `--incremental` | Skip files unchanged since last transfer (size + mtime). Auto-enables `--preserve`. Incompatible with `--chunk-serialization`. |
+| `--existing` | Skip files not already present at the destination; update existing files normally. |
+| `--compare-dest <dir>` | Extra comparison basis: unchanged files are not transferred (requires/implies `--incremental`) |
+| `--copy-dest <dir>` | Like `--compare-dest`, but copies the unchanged file from DIR into the destination |
+| `--link-dest <dir>` | Like `--copy-dest`, but hard-links the unchanged file from DIR (repeatable; earlier DIRs win) |
+| `--verify-basis` | FastSync-only: require a basis hit (`--compare-dest`/`--copy-dest`/`--link-dest`) to match the source by whole-file digest instead of trusting the size+mtime quick-check (default matches rsync) |
+| `--delete` | Delete files on receiver not present in source (default timing: delete-during, matching rsync, so destination space is freed progressively). Scoped to the synchronized directories, so `--files-from` subsets are safe |
 | `--delete-before` | Delete extras before the transfer starts (implies `--delete`) |
 | `--delete-during`, `--del` | Delete extras once the keep-set is known, before data is applied (implies `--delete`) |
 | `--delete-delay` | Delete extras only after a successful transfer (implies `--delete`) |
 | `--delete-after` | Explicit delete-after timing (implies `--delete`) |
-| `--exclude <pattern>` | Exclude files matching glob pattern (repeatable) |
-| `--exclude-from <file>` | Read exclude patterns from a file (one per line) |
-| `--include <pattern>` | Only transfer files matching glob pattern (repeatable, whitelist) |
-| `--max-size <n>` | Skip files larger than n bytes |
-| `--min-size <n>` | Skip files smaller than n bytes |
-| `--max-alloc <SIZE>` | Maximum single allocation (binary units: B, K, M, G, T, P, E; default 1G) |
-| `--incremental` | Skip files unchanged since last transfer (size + mtime). Auto-enables `--preserve`. Incompatible with `--chunk-serialization`. |
-| `--existing` | Skip files not already present at the destination; update existing files normally. |
-| `--bwlimit <KB/s>` | Bandwidth limit in kilobytes per second |
-| `--chunk-size <n>` | Chunk size in bytes (default: 10485760) |
-| `--timeout <sec>` | Positive I/O timeout in seconds, applied to both the socket (`SO_RCVTIMEO`/`SO_SNDTIMEO`, built-in default 30 s) and the per-message protocol poll deadline (built-in default 60 s). Omit the option to keep both built-ins; `0` is rejected. The server side keeps the built-in 60 s protocol window (the value is not sent on the wire). |
-| `--contimeout <sec>` | Connection timeout in seconds (default: 10) |
-| `--backup` | Backup existing destination files before overwriting |
-| `--backup-dir <dir>` | Target directory for backups (requires `--backup`) |
-| `--stats` | Print transfer statistics at end (bytes, files, timing) |
-| `-h, --human-readable` | Format transfer byte sizes with binary units |
+| `--delete-commit` | FastSync-only: keep the pre-2.28 atomic timing — delete only after the whole transfer succeeded (identical timing to `--delete-after`) |
+| `--delete-excluded` | Also delete filter-excluded destination mirrors (size-pruned mirrors stay protected) |
+| `--max-delete <n>` | Delete at most n destination entries; the rest are skipped and the run exits 25 (partial), matching rsync |
+| `--delay-updates` | Put updated files into place only at the end of the transfer (`--force` is honored at publication) |
+| `-T, --temp-dir <dir>` | Scratch directory for temp files before the atomic install; confined to the receive root (relative only), with an `EXDEV` non-atomic copy fallback |
+| `-n, --dry-run` | Report what would be transferred without mutating the destination. Since protocol 2.21.0 a server-routed target contacts the receiver and reports would-transfer based on receiver state; a plain local destination keeps the client-side scan. Never mutates or deletes. |
+| `-v, --verbose` | Enable debug logging |
+| `-q, --quiet` | Suppress non-error output |
+| `--progress` | Show rsync-style per-file progress blocks from the receiver's wire counters (FastSync does not print rsync's leading `./` line) |
+| `-P` | Enables partial-transfer mode + progress output; interrupted writes retain the already-written temp for resumption |
+| `--stats` | Print transfer statistics at end (bytes, files, timing), including the receiver-only counters reported over the wire; rsync's per-type `Number of files` breakdown is not reproduced |
+| `-i, --itemize-changes` | Print an rsync-style per-file change line |
+| `--out-format=FORMAT` | Output format for changed files (`%f %n %l %b %M %%`) |
+| `--list-only` | List source files instead of transferring |
+| `--fsync` | Fsync every written file before publication |
+| `-h, --human-readable` | Format transfer byte/rate counts with rsync's decimal (base-1000) units |
 | `--max-depth <n>` | Maximum directory depth to recurse (0 = unlimited, default: 0) |
 | `--log-file <path>` | Write log messages to file instead of stderr |
+| `--write-batch=FILE` | Run the normal live transfer and also emit a self-contained batch file of the source tree |
+| `--only-write-batch=FILE` | Emit the batch file only (no destination, no server) |
+| `--read-batch=FILE` | Apply a batch file to the destination (no source, no server) |
 | `--source-dir <path>` | Source directory (overrides `FASTSYNC_SOURCE_DIR`) |
 | `--dest-dir <path>` | Server destination directory (overrides `FASTSYNC_DEST_DIR`) |
 | `--save-to-disk` | Write received files to disk |
 | `--server-host <ip>` | Server IP address (default: `127.0.0.1`) |
 | `--server-port <n>` | Server port (default: `8080`) |
+| `--ssh-port <port>` | SSH port (default: 22) |
+| `-e, --rsh <command>` | Remote shell to launch for the SSH transport (default: `ssh`; may include arguments, e.g. `-e "ssh -p 2222"`) |
+| `-M, --remote-option=OPT` | Append OPT to the remote server invocation over SSH (repeatable) |
+| `--address <ip>` | Bind the outgoing client socket to this source address |
+| `-4, --ipv4` | Force IPv4 for destination resolution |
+| `-6, --ipv6` | Force IPv6 for destination resolution |
+| `--sockopts=OPTS` | Comma-separated OPT=VAL socket options applied before connect (`TCP_NODELAY`, `SO_KEEPALIVE`, `SO_RCVBUF`, `SO_SNDBUF`, `SO_REUSEADDR`) |
+| `--bwlimit <KB/s>` | Bandwidth limit in kilobytes per second |
+| `--chunk-size <n>` | Chunk size in bytes (default: 10485760) |
+| `--timeout <sec>` | I/O timeout in seconds, applied to both the socket (`SO_RCVTIMEO`/`SO_SNDTIMEO`) and the per-message protocol poll deadline. Default `0` = disabled (matching rsync); `0` disables it. `--no-timeout` is the negation. The value is not sent on the wire; the server side keeps its own safe floor. |
+| `--contimeout <sec>` | Connection timeout in seconds (default: 60, matching rsync); `0` disables it (`--no-contimeout` is the negation) |
+| `--stop-after=MINS` | Stop the transfer after MINS minutes (a positive integer); whatever was already transferred is kept |
+| `--stop-at=TIME` | Stop at an absolute time (`HH:MM`, `HH:MM:SS`, or `now+N[smhd]`); an early stop skips the late `--delete` keep-set |
+| `-b, --backup` | Backup existing destination files before overwriting |
+| `--backup-dir <dir>` | Target directory for backups (requires `--backup`) |
 | `--tls` | Enable TLS encryption |
 | `--cert <path>` | TLS certificate file (PEM) |
 | `--key <path>` | TLS private key file (PEM) |
 | `--ca <path>` | TLS CA certificate file for verification (PEM) |
-| `--client-cn <name>` | TLS client certificate common name; mandatory with `--tls` (a TLS connection always verifies the client CN) |
+
+The exhaustive rsync flag matrix is in [`RSYNC_COMPAT.md`](RSYNC_COMPAT.md).
 
 **Per-message vs. connection timeouts.** `--timeout` bounds each individual protocol
 send/receive (the `poll()` deadline), so a peer that stops mid-frame is dropped. It
@@ -190,60 +298,64 @@ transfer is never aborted.
 | `FASTSYNC_SOURCE_DIR` | — | Source directory fallback |
 | `FASTSYNC_DEST_DIR` | — | Destination directory fallback |
 | `FASTSYNC_SAVE_TO_DISK` | `false` | Disk persistence fallback |
-| `FASTSYNC_SSH_PORT` | `22` | Default SSH port |
-| `FASTSYNC_SERVER_HOST` | `127.0.0.1` | Default server host |
-| `FASTSYNC_SERVER_PORT` | `8080` | Default server port |
-| `FASTSYNC_TLS_CERT` | — | Default TLS certificate path |
-| `FASTSYNC_TLS_KEY` | — | Default TLS private key path |
-| `FASTSYNC_TLS_CA` | — | Default TLS CA certificate path |
 
 ## Implementation Details
 
 ### Data Structures
-1. **Chunk** — collection of files (~10 MB total by default)
-2. **File** — path, content (`Data`), optional `FileMetadata` pointer
-3. **FileMetadata** — `mode`, `uid`, `gid`, `mtime_sec`, `mtime_nsec`;
-uid / gid are advisory wire fields and are never applied by the receiver;
-atime is unsupported
-4. **Config** — runtime parameters (transported over wire, TLS settings excluded). Includes `timeout`, `contimeout`, `quiet`, `backup`, `backup_dir`, `stats`, `max_depth`, `log_file`.
-5. **Queue** — thread-safe bounded queue with condition variables
-6. **DirectoryScanner** — recursive BFS traversal with exclude and include pattern support, max-depth enforcement
+
+1. **Chunk** — collection of files (~10 MB total by default).
+2. **File** — path, content (`Data`), optional `FileMetadata` pointer.
+3. **FileMetadata** — `mode`, `uid`, `gid`, `mtime_sec`, `mtime_nsec` (plus
+   atime/crtime fields). `uid`/`gid` are applied only through the opt-in
+   identity path; atime is preserved with `-U`/`--atimes`; crtime is captured
+   but cannot be set on the destination.
+4. **Config** — runtime parameters. Most cross the wire (TLS settings
+   excluded); `backup` and `backup_dir` are in the serialized wire table, while
+   `timeout`, `contimeout`, `quiet`, `stats`, `max_depth`, and `log_file` are
+   client-only.
+5. **Queue** — thread-safe bounded queue with condition variables.
+6. **DirectoryScanner** — recursive BFS traversal with exclude and include
+   pattern support, max-depth enforcement.
 
 ### Key Algorithms
-1. **File scanning** — BFS directory traversal;
-entries matched against exclude and include patterns,
-    max - depth enforced 2. * *Chunking ** — files accumulated until `chunk_size` threshold,
-    then flushed 3. *
-            *Compression ** — streaming zstd
-                via `ZSTD_compressStream2` / `ZSTD_decompressStream` 4. *
-            *Network protocol ** — status -
-        code - driven exchange with metadata packing,
-    keep - alive,
-    and abort support 5. * *Incremental check ** — client sends `STATUS_CHECK` + path + size +
-        mtime and,
-    with `--checksum`, XXH64 content checksum; server compares against destination. Can be batched via `STATUS_CHECK_BATCH` for reduced round-trips.
-6. **Bandwidth limiting** — token-bucket algorithm with `nanosleep` throttling on 64 KB write chunks
-7. **Metadata restoration** — `chmod()`, `chown()`, `utimensat()` on the receiving side
-8. **`--delete`** — sender tracks all sent paths;
-receiver walks destination tree and removes unlisted files / directories 9. *
-        *SSH transport *
-            * — `socketpair()` + `fork()` + `execvp("ssh",
-                                                    ...)` with `ControlMaster` and port support
-                                                10. *
-                                                *TLS transport ** — OpenSSL `SSL_CTX` with TLS
-                                                1.2 minimum,
-    mutual CA verification,
-    transparent `SSL_read`/`SSL_write` via `io_set_ssl()` 11. *
-        *Path traversal protection ** — `has_path_traversal()` rejects any file path
-         containing `..` components,
-    preventing directory escape attacks 12. *
-            *Connection limiting ** — server tracks active connections and rejects
-            new ones beyond `max_connections` (default 100)13. *
-            *Keep
-        - alive ** — idle connections receive periodic `STATUS_KEEPALIVE` to detect half
-        - open TCP connections 14. * *Abort handling ** — `SIGINT` sets an abort flag; the next protocol operation sends `STATUS_ABORT` for clean server cleanup
-15. **Atomic writes** — files are written to a `.tmp` suffix then atomically renamed via `rename()`, preventing partial files
-16. **Backup** — before overwriting, existing files are moved to `--backup-dir` (or same directory with `~` suffix) preserving the original
+
+1. **File scanning** — BFS directory traversal; entries matched against exclude
+   and include patterns, with max-depth enforced.
+2. **Chunking** — files accumulated until the `chunk_size` threshold (default
+   10 MiB) is reached, then flushed.
+3. **Compression** — streaming zstd via `ZSTD_compressStream2()` /
+   `ZSTD_decompressStream()`.
+4. **Network protocol** — status-code-driven exchange with metadata packing,
+   keep-alive, and abort support.
+5. **Incremental check** — the client sends `STATUS_CHECK` + path + size +
+    mtime and, with `--checksum`, a whole-file content checksum (`xxh128` by
+    default; selectable via `--checksum-choice`/`--cc`, seeded by
+    `--checksum-seed`); the server compares against the destination. Can be
+    batched via `STATUS_CHECK_BATCH` for reduced round-trips.
+6. **Bandwidth limiting** — token-bucket algorithm with sleep throttling on
+   64 KiB write chunks.
+7. **Metadata restoration** — mode via `chmod()`/`fchmod()`, times via
+   `utimensat()`/`futimens()`, and ownership only with an identity flag via
+   fd-relative `fchown()`/`fchownat()`.
+8. **`--delete`** — the sender tracks all sent paths; the receiver walks the
+   destination tree and removes unlisted files and directories.
+9. **SSH transport** — `socketpair()` + `fork()` + `execvp("ssh", ...)` with
+   `ControlMaster` and port support.
+10. **TLS transport** — OpenSSL `SSL_CTX` with TLS 1.2 minimum, mutual CA
+    verification, and transparent `SSL_read()`/`SSL_write()` via
+    `io_set_ssl()`.
+11. **Path traversal protection** — `has_path_traversal()` rejects any file
+    path containing `..` components, preventing directory escape attacks.
+12. **Connection limiting** — the server tracks active connections and rejects
+    new ones beyond `max_connections` (default 100).
+13. **Keep-alive** — idle connections receive periodic `STATUS_KEEPALIVE` to
+    detect half-open TCP connections.
+14. **Abort handling** — `SIGINT` sets an abort flag; the next protocol
+    operation sends `STATUS_ABORT` for clean server cleanup.
+15. **Atomic writes** — files are written to a `.tmp` suffix then atomically
+    renamed via `rename()`, preventing partial files.
+16. **Backup** — before overwriting, existing files are moved to `--backup-dir`
+    (or the same directory with a `~` suffix), preserving the original.
 
 ## Security Features
 
@@ -300,7 +412,8 @@ cmake --build build -j$(nproc)
 
 ### SSH transfer
 
-The remote host must have `fastsync-server` available in `PATH`, or use
+The remote host must have `fastsync-server` available in `PATH` (install or
+copy the built `./build/server` there as `fastsync-server`), or use
 `--fastsync-server-path`. SSH starts `fastsync-server --stdio` in its remote
 working directory, so use a destination below that directory unless the
 remote server is otherwise configured with a matching authorized root.
@@ -341,8 +454,13 @@ Plain TCP requires the explicit `--allow-unauthenticated` server option. Use TLS
 authenticated network connections.
 
 ### TLS transfer
+
+Server TLS requires `--cert`, `--key`, `--ca`, and `--client-cn`; the client
+requires `--cert`, `--key`, and `--ca`.
+
 ```bash
-./build/server --destination-root /path/to --tls --cert server.pem --key server-key.pem -p 8443
+./build/server --destination-root /path/to --tls --cert server.pem --key server-key.pem \
+  --ca ca.pem --client-cn client -p 8443
 ./build/client --tls --cert client.pem --key client-key.pem --ca ca.pem \
   --server-host example.com --server-port 8443 \
   --source-dir /path/to/source --dest-dir /path/to/destination \
@@ -355,32 +473,32 @@ These examples show the intended rsync-style workflow. Options marked as
 FastSync-native are optional performance or transport extensions.
 
 ```bash
-#Basic synchronization
+# Basic synchronization
 ./build/client /source/ /destination/
 
-#Archive - style synchronization(current FastSync archive behavior)
+# Archive-style synchronization (current FastSync archive behavior)
 ./build/client -a /source/ user@host:destination/
 
-#Preview a transfer without changing the destination
+# Preview a transfer without changing the destination
 ./build/client -n /source/ /destination/
 
-#Exclude temporary and object files
+# Exclude temporary and object files
 ./build/client --exclude '*.tmp' --exclude '*.o' \
   /source/ user@host:destination/
 
-#Remove destination entries not present in the source
+# Remove destination entries not present in the source
 ./build/client --delete /source/ user@host:destination/
 
-#Skip unchanged files using size and modification time
+# Skip unchanged files using size and modification time
 ./build/client --incremental /source/ user@host:destination/
 
-#Verify content when size and time are not sufficient
+# Verify content when size and time are not sufficient
 ./build/client --incremental --checksum /source/ user@host:destination/
 
-#Preserve supported mode and timestamp metadata
+# Preserve supported mode and timestamp metadata
 ./build/client --preserve /source/ user@host:destination/
 
-#Keep backups of overwritten destination files
+# Keep backups of overwritten destination files
 ./build/client --backup --backup-dir backups \
   /source/ user@host:destination/
 ```
@@ -393,11 +511,11 @@ features without changing the meaning of ordinary compatibility options.
 | Option | Purpose |
 |---|---|
 | `-j`, `--threads[=N]` | Enable the multithreaded scanner/loader/sender pipeline. `N` (1–256) sets the parallel scanner worker count; bare `-j`/`--threads` uses the default. |
-| `-z [level]`, `--compress [level]` | Enable streaming zstd compression, levels 1-22. |
-| `--compress-level <n>` | Set the zstd compression level. |
-| `--zc <alg>` | Alias for `--compress-choice`. FastSync supports `zstd` and `none`. |
+| `-z [level]`, `--compress [level]` | Enable streaming compression (default `zstd`), levels 1-22. |
+| `--compress-level <n>` | Set the compression level (1-22). Omitted, each codec uses its rsync default: zstd 3, zlib/zlibx 6, lz4 ignored. |
+| `--zc <alg>` | Alias for `--compress-choice`. FastSync supports `zstd` (default), `lz4`, `zlib`, `zlibx`, `none`, and `auto`; `zlib`/`zlibx` share the same literal-only zlib path. |
 | `--zl <n>` | Alias for `--compress-level`. |
-| `--skip-compress <list>` | Skip compression for comma-separated suffixes; incompatible with `--chunk-serialization`. |
+| `--skip-compress <list>` | Skip compression for `/`- or `,`-separated suffixes; defaults to rsync 3.4.1's built-in list. Incompatible with `--chunk-serialization`. |
 | `--compress-threads <n>` | Use `n` zstd compression workers. Requires compression and a zstd build with threaded support; the setting affects sender CPU work only. |
 | `--chunk-size <bytes>` | Set the transfer chunk size. |
 | `--chunk-serialization` | Enable FastSync chunk serialization (long form only; `-s` is rsync's `--secluded-args`). |
@@ -409,10 +527,10 @@ features without changing the meaning of ordinary compatibility options.
 | `--server-port <port>` | Select the TCP server port (`--port <port>` and `--port=<port>` are rsync-friendly aliases). |
 | `--tls` | Enable TLS for TCP transport. |
 | `--bwlimit <KB/s>` | Apply token-bucket bandwidth limiting. |
-| `--progress` | Show transfer progress and throughput. |
-| `--stats` | Print transfer statistics. |
-| `--timeout <seconds>` | Set the socket **and** per-message protocol I/O timeout (positive seconds). Omit to keep the built-in 30 s socket / 60 s protocol defaults. |
-| `--contimeout <seconds>` | Set connection timeout. |
+| `--progress` | Show rsync-style per-file progress blocks from the receiver's wire counters (FastSync omits rsync's leading `./` line). |
+| `--stats` | Print transfer statistics, including the receiver-only counters reported over the wire; rsync's per-type `Number of files` breakdown is not reproduced. |
+| `--timeout <seconds>` | Set the socket **and** per-message protocol I/O timeout. Default `0` = disabled (matching rsync); `0` disables it. |
+| `--contimeout <seconds>` | Connection timeout (default 60, matching rsync); `0` disables it. |
 
 Short-option conflicts with rsync have been resolved for the CLI namespace
 (Phase 7): `-c` is now rsync's `--checksum`, `-m` is `--prune-empty-dirs`, `-M`
@@ -421,7 +539,8 @@ is `--remote-option`, `-f` is `--filter`, `-s` is `--secluded-args`, `-p` is
 long-form-only or new shorts: multithreading is `-j`/`--threads`, metadata
 is `--preserve`, sendfile is `--sendfile`, chunk serialization is
 `--chunk-serialization`, timeout is `--timeout`, and SSH port is `--ssh-port`.
-`-a`/`--archive` is now real rsync archive (`-rlptgoD`).
+`-a`/`--archive` is now rsync archive `-rlptgoD` (owner/group implied, but the
+receiver still needs privilege to apply them).
 
 `--secluded-args` (and its short form `-s`) is accepted as a compatibility
 no-op. It does not change FastSync's transport or protocol behavior, because
@@ -433,42 +552,96 @@ remote SSH argv is already built injection-safe.
 
 | Option | Description |
 |---|---|
-| `-a`, `--archive` | rsync archive mode (`-rlptgoD`): links, metadata, devices and specials. |
-| `-n`, `--dry-run` | Scan and report without writing files. |
-| `--delete` | Request removal of destination entries absent from the source. The server must allow deletion. Default timing is delete-after: extras are removed only after the whole transfer succeeded. |
+| `-a`, `--archive` | rsync archive mode (`-rlptgoD`): links, perms, times, owner, group, devices and specials; ownership application stays privilege-gated. |
+| `-n`, `--dry-run` | Report what would be transferred without mutating the destination. Since protocol 2.21.0 a server-routed target contacts the receiver and reports would-transfer based on receiver state; a plain local destination keeps the client-side scan. Never mutates or deletes. |
+| `--remove-source-files` | Remove regular source files after a successful transfer. |
+| `--incremental` | Skip files matching destination size and mtime. Auto-enables `--preserve`. Incompatible with `--chunk-serialization`. |
+| `-c, --checksum` | Verify content by checksum (implies the incremental quick-check). Algorithm selectable with `--checksum-choice`. |
+| `--checksum-choice <alg>` | Whole-file checksum algorithm: `xxh64`/`xxhash` (default), `xxh3`, `xxh128`, `md5`, or `auto`. |
+| `--checksum-seed <n>` | Seed for the whole-file xxHash digest; an unset/`0` seed is randomized per transfer, matching rsync. |
+| `--size-only` | Skip incremental files matching in size, ignoring mtime. |
+| `-I, --ignore-times` | Transfer files even when size and mtime match. |
+| `-u, --update` | Skip files newer than the source on the receiver. |
+| `-W, --whole-file` | Transfer changed files without delta processing (`--no-whole-file` clears it). |
+| `-B <n>, --block-size <n>` | Delta block size in bytes (alias `--delta-block`). |
+| `-d, --dirs` | Transfer the named directory entries without recursing into their contents (aliases `--old-dirs`/`--old-d`). |
+| `-R, --relative` | Use rsync's relative path semantics (including the `/./` cut); with `--files-from`, preserve each listed entry's relative path below the destination root. |
+| `--files-from <file>` | Read the source file list from FILE (paths relative to the source root). |
+| `--delay-updates` | Put updated files into place only at the end of the transfer. |
+| `--compare-dest <dir>` | Extra comparison basis: unchanged files are not transferred (requires/implies `--incremental`). |
+| `--copy-dest <dir>` | Like `--compare-dest`, but copies the unchanged file from DIR into the destination. |
+| `--link-dest <dir>` | Like `--copy-dest`, but hard-links the unchanged file from DIR (repeatable; earlier DIRs win). |
+| `--verify-basis` | FastSync-only: require a basis hit to match the source by whole-file digest instead of trusting the size+mtime quick-check (default matches rsync). |
+| `--preallocate` | Allocate destination file space up front (fail-fast on a full disk). |
+| `--append` | Resume a shorter destination by appending only its tail (prefix not verified; requires `--incremental`). |
+| `--append-verify` | Like `--append`, but verifies the retained prefix checksum first (falls back to a full transfer on mismatch). |
+| `--delete` | Request removal of destination entries absent from the source. The server must allow deletion. Default timing is delete-after: extras are removed only after the whole transfer succeeded. Scoped to the synchronized directories, so `--files-from` subsets are safe. |
 | `--delete-before` | Delete extras before the transfer starts (implies `--delete`). |
 | `--delete-during`, `--del` | Delete extras once the keep-set manifest is known, before data is applied (implies `--delete`; early mode, same engine behaviour as `--delete-before`). |
 | `--delete-delay` | Delete extras only after a successful transfer (implies `--delete`; commit mode, same behaviour as `--delete-after`). |
+| `--delete-commit` | FastSync-only: atomic delete-after timing (only after the whole transfer succeeded). |
 | `--delete-after` | Explicit delete-after timing: delete only after the transfer succeeded (implies `--delete`). |
+| `--delete-excluded` | Also delete filter-excluded destination mirrors (size-pruned mirrors stay protected). |
+| `--max-delete <n>` | Delete at most n destination entries; the rest are skipped and the run exits 25 (partial), matching rsync. |
+| `--force` | Allow an incoming file/symlink to replace a destination directory (also during `--delay-updates` publication). |
 | `--exclude <pattern>` | Exclude matching paths. Repeatable. |
 | `--include <pattern>` | Include matching paths. Repeatable. |
 | `--exclude-from <file>` | Read exclude patterns from a file. |
 | `--include-from <file>` | Read include patterns from a file. |
+| `-f, --filter=RULE` | Add an rsync-style filter rule (`+`/`-`, `include`/`exclude`, `merge`/`.`, `dir-merge`/`:`, `hide`/`H`, `show`/`S`, `protect`/`P`, `risk`/`R`, `clear`/`!`, and modifiers; repeatable). |
 | `--max-size <bytes>` | Skip files larger than the limit. |
 | `--min-size <bytes>` | Skip files smaller than the limit. |
-| `--max-depth <n>` | Limit recursive scanning depth;
-zero means unlimited.| | `--incremental` | Skip files matching destination size and mtime.|
-    | `--checksum` | Include xxHash64 content checks in incremental comparisons.| | `--backup` |
-    Back up overwritten files.| | `--backup - dir<dir>` | Store backups under a separate directory.|
-| `--suffix<suffix>` | Set the backup filename suffix.| | `--partial` |
-     Select partial - transfer handling. On failed/interrupted writes the
-     already-written temp file is retained (best-effort) for resumption.|
-     With `--partial --partial-dir <dir>`, completed files are written under the
-     partial directory and installed atomically. | | `--partial - dir<dir>` |
-     Set a relative partial - transfer directory below the server destination root.
-     Use with `--partial`. |
+| `--max-alloc <SIZE>` | Maximum single allocation (binary units; default 1G; `0` = no local limit). |
+| `--max-depth <n>` | Limit recursive scanning depth; zero means unlimited. |
+| `-b, --backup` | Back up overwritten files. |
+| `-T, --temp-dir <dir>` | Scratch directory for temp files before the atomic install (confined to the receive root; `EXDEV` falls back to a non-atomic copy). |
+| `--backup-dir <dir>` | Store backups under a separate directory (requires `--backup`). |
+| `--suffix <suffix>` | Set the backup filename suffix (default: `~`). |
+| `--partial` | Select partial-transfer handling. On failed/interrupted writes the already-written temp file is retained (best-effort) for resumption. With `--partial --partial-dir <dir>`, completed files are written under the partial directory and installed atomically. |
+| `--partial-dir <dir>` | Set a relative partial-transfer directory below the server destination root. Use with `--partial`. |
 | `--inplace` | Write directly to the destination instead of using a temporary file. |
+| `--fsync` | Fsync every written file before publication. |
+| `--write-batch=FILE` | Run the normal live transfer and also emit a self-contained batch file of the source tree. |
+| `--only-write-batch=FILE` | Emit the batch file only (no destination, no server). |
+| `--read-batch=FILE` | Apply a batch file to the destination (no source, no server). |
+| `--stop-after=MINS` | Stop the transfer after MINS minutes; whatever was already transferred is kept. |
+| `--stop-at=TIME` | Stop at an absolute time (`HH:MM`, `HH:MM:SS`, or `now+N[smhd]`). An early stop skips the late `--delete` keep-set. |
 
 ### Metadata and links
 
 | Option | Description |
 |---|---|
-| `--preserve` | Preserve supported file metadata, currently mode and modification time (long form only). |
-| `-l`, `--links` | Request symlink preservation;
-link-target transfer remains incomplete. |
-| `--copy-links` | Copy symlink referents. |
-| `--safe-links` | Skip symlinks that point outside the transfer tree. |
+| `--preserve` | Preserve mode and mtime (long form only; equivalent to `-p` + `-t`). Add `-o`/`-g` for owner/group, `-U`/`--atimes` for atime, or an identity flag (`--chown`/`--usermap`/`--groupmap`/`--numeric-ids`/`--copy-as`) for mapped ownership. |
+| `-U`, `--atimes` | Preserve access times. Captured with the metadata payload; does not enable ownership. |
+| `-N`, `--crtimes` | Capture birth time and transmit it; it cannot be applied because no portable filesystem call can set a birth time (documented divergence). |
+| `-p`, `--perms` | Preserve permission bits. One of the four per-attribute preserve flags (with `-t`/`-o`/`-g`); under `-p` the source mode is copied exactly (setuid/setgid/sticky and group/other-write included), matching rsync. |
+| `-t`, `--times` | Preserve modification times. Independent of the other attributes; `-O`/`--omit-dir-times` suppresses directories only. |
+| `-o`, `--owner` | Preserve the source owner (uid). Mapped by name on the receiver with a raw-numeric fallback (only numeric ids cross the wire); application is privilege-gated. |
+| `-g`, `--group` | Preserve the source group (gid). Same name-mapping/numeric-fallback and privilege gating as `-o`. |
+| `--no-perms`, `--no-times`, `--no-owner`, `--no-group` | Negate each per-attribute flag (also `--no-p`/`--no-t`/`--no-o`/`--no-g`); `--no-preserve` clears all four. |
+| `-E`, `--executability` | Preserve executable permission bits. |
+| `-X`, `--xattrs` | Preserve user `user.*` extended attributes. |
+| `-A`, `--acls` | Preserve POSIX ACLs. |
+| `--chmod <changes>` | Modify transferred permissions (rsync syntax, including `D`/`F`/`X` selectors and `s`/`t`); does not imply `-p`. |
+| `--chown=USER:GROUP` | Override the ownership of transferred files (`USER:GROUP`, `USER`, or `:GROUP`); conflicts with `--usermap`/`--groupmap` on the same side. |
+| `--usermap=MAP` | Map usernames when applying ownership (`FROM:TO` rules; names, ids, `LOW-HIGH` ranges, `*`, empty-`FROM`). |
+| `--groupmap=MAP` | Map group names when applying ownership (same syntax as `--usermap`). |
+| `--numeric-ids` | Mapping modifier: apply the source numeric uid/gid directly instead of mapping by name (combine with `-o`/`-g`, `-a`, or a map). |
+| `--copy-as=USER[:GROUP]` | Force every written entry to USER[:GROUP]; requires a privileged receiver. |
+| `--fake-super` | Record the resolved owner plus mode/time in a reserved `user.fastsync.stat` xattr and replay mode/time; never performs a real chown. |
+| `--super` | Permit the receiver to attempt confined super-user activities (device nodes). |
+| `--no-super` | Forbid those super-user activities even when the receiver is root. |
+| `-l`, `--links` | Copy symlinks as symlinks; the target is stored verbatim (absolute and `..`-bearing targets included), matching rsync. |
+| `-L`, `--copy-links` | Copy symlink referents (a broken referent makes the run exit 23, matching rsync). |
+| `--safe-links` | Skip symlinks whose target points outside the transfer tree (applied on the sender). |
 | `--copy-unsafe-links` | Copy unsafe symlink referents. |
+| `--munge-links` | Rewrite stored symlink targets with rsync's `/rsyncd-munged/` marker. |
+| `-k`, `--copy-dirlinks` | Treat a symlink to a directory as a real directory on the sender. |
+| `-K`, `--keep-dirlinks` | Follow an existing destination symlink-to-directory (confined to the receive root). |
+| `-H`, `--hard-links` | Preserve hard-link relationships across the transfer. |
+| `-D` | Preserve device and special files (implies `--devices --specials`). |
+| `--devices` | Recreate device nodes on the destination (privileged; skipped without `CAP_MKNOD`). |
+| `--specials` | Recreate special files: FIFOs and unix sockets. |
 | `-S`, `--sparse` | Sparse-file handling: receiver preserves holes (zero runs are written as holes; no wire change). |
 
 ### Output and logging
@@ -476,8 +649,12 @@ link-target transfer remains incomplete. |
 | Option | Description |
 |---|---|
 | `-v`, `--verbose` | Enable debug logging. |
-| `--progress` | Show live transfer progress. |
-| `--stats` | Print transfer statistics. |
+| `-q`, `--quiet` | Suppress non-error output. |
+| `--progress` | Show rsync-style per-file progress blocks (not rsync's leading `./` line). |
+| `--stats` | Print transfer statistics, including the receiver-only counters reported over the wire. |
+| `-i`, `--itemize-changes` | Print an rsync-style per-file change line. |
+| `--out-format=FORMAT` | Output format for changed files (`%f %n %l %b %M %%`). |
+| `--list-only` | List source files instead of transferring. |
 | `--log-file <path>` | Write log output to a file. |
 | `-V`, `--version` | Print the FastSync protocol version. |
 | `--help` | Print command usage. |
@@ -487,31 +664,56 @@ link-target transfer remains incomplete. |
 | Option | Description |
 |---|---|
 | `--ssh-port <port>` | SSH port for the SSH transport (default: 22). Note the short `-p` is now rsync's `--perms`. |
-| `--fastsync-server-path <path>` | Remote FastSync server path for SSH mode. |
+| `-e`, `--rsh <command>` | Remote shell to launch for the SSH transport (default: `ssh`; may include arguments). |
+| `--fastsync-server-path <path>` | Remote FastSync server path for SSH mode (client-only; never crosses the wire). |
+| `--rsync-path <path>` | Alias for `--fastsync-server-path`. |
+| `-M`, `--remote-option=OPT` | Append OPT to the remote server invocation over SSH (repeatable; rejected for daemon/TCP destinations). |
+| `--trust-sender` | Receiver-local: trust the remote sender's file list and skip path re-validation (does not affect symlink targets). |
+| `--timeout <sec>` | Socket + per-message I/O timeout; default `0` = disabled. |
+| `--contimeout <sec>` | Connection timeout; default 60; `0` disables. |
 | `--source-dir <path>` | Set the source directory explicitly. |
 | `--dest-dir <path>` | Set the destination directory explicitly. |
 | `--save-to-disk` | Enable server-side disk persistence. |
 | `--server-host <host>` | TCP server address. |
 | `--server-port <port>` | TCP server port. `--port <port>` / `--port=<port>` is an alias. |
-| `--tls` | Enable TLS. Requires `--cert` and `--key`. |
+| `--address <ip>` | Bind the outgoing client socket to this source address. |
+| `-4`, `--ipv4` | Force IPv4 for destination resolution. |
+| `-6`, `--ipv6` | Force IPv6 for destination resolution. |
+| `--sockopts=OPTS` | Comma-separated OPT=VAL socket options applied before connect. |
+| `--tls` | Enable TLS. Requires `--cert`, `--key`, and `--ca`. |
 | `--cert <path>` | TLS certificate file. |
 | `--key <path>` | TLS private key file. |
-| `--ca <path>` | CA file for peer verification. |
+| `--ca <path>` | CA file for peer verification (always required with `--tls`). |
 
 ## Server Options
 
 | Option | Description |
 |---|---|
 | `--stdio` | Serve one SSH connection over standard input/output. |
-| `-p <port>` | TCP listen port. |
+| `--daemon` | Run as a persistent daemon listener using a module config file; the daemon default port is 873 (unlike `-p`, which defaults to 8080). |
+| `--config=FILE` | Daemon config file (default: `~/.config/fastsync/fastsyncd.conf`, else `/etc/fastsyncd.conf`). Requires `--daemon`. |
+| `--dparam=KEY=VALUE` | Override one global config key on the command line. Requires `--daemon`. |
+| `--no-detach` | Stay in the foreground (default detaches to the background when running `--daemon`). |
+| `-p, --port <port>` | TCP listen port (default: 8080, range: 1–65535). |
 | `--tls` | Enable TLS. |
-| `--cert <path>` | TLS certificate file. |
-| `--key <path>` | TLS private key file. |
-| `--ca <path>` | CA file for peer verification. |
-| `--destination-root <path>` | Confine received files to this server-side root;
-defaults to the current directory. |
+| `--cert <path>` | TLS certificate file (PEM). |
+| `--key <path>` | TLS private key file (PEM). |
+| `--ca <path>` | CA file for peer verification (PEM). |
+| `--client-cn <name>` | TLS client certificate CN; mandatory with `--tls` (the server verifies the client CN). |
+| `--destination-root <path>` | Confine received files to this server-side root; defaults to the current directory. |
+| `--address <addr>` | Bind the listening socket to this address. |
+| `-4`, `--ipv4` | Bind an IPv4 socket (default). |
+| `-6`, `--ipv6` | Bind an IPv6 socket. |
 | `--allow-delete` | Permit client delete manifests. Deletion is refused by default. This also gates `--force` (which can recursively replace/remove a destination directory tree). |
 | `--allow-super` | Standalone TCP listener only: keep super-user activities enabled for a **root** receiver. Without it a root standalone server forces `SUPER_MODE_OFF`, so client `--devices`/`--write-devices`/`--super` and client-chosen ownership requests are skipped/refused. Rejected with `--stdio` (the SSH remote argv is client-composed; use a forced command if the default must hold). No effect when not root. Daemon modules opt in per module with `client owner = yes`. |
+| `--trust-sender` | Trust the remote sender's file list: skip the receiver's up-front path-traversal re-validation (fewer checks, faster, potentially unsafe; off by default). It does not affect symlink targets, which are stored verbatim either way. |
+| `--no-super` | Operator veto: never attempt super-user activities (ownership, device nodes) even as root, and refuse any client `--copy-as`/`--super` request. |
+| `--allow-unauthenticated` | Permit plaintext/anonymous network clients; an auth-required module still accepts only opted-in loopback plaintext. |
+| `--iconv=LOCAL[,REMOTE]` | Declare this server's LOCAL charset for file-name conversion. |
+| `--password-file=FILE` | Credential store for modules that declare `auth users`. Requires `--daemon`. |
+| `--early-input=FILE` | Second credential store layered over `--password-file`. Requires `--daemon`. |
+| `--hash-credentials <file>` | Read `<file>`'s `user:password` lines and print PBKDF2 credential-store lines to stdout, then exit. Cannot be combined with `--daemon` or `--stdio`. |
+| `--iterations N` | PBKDF2 iteration count for `--hash-credentials` (default 600000, range 100000–10000000). Requires `--hash-credentials`. |
 | `-v`, `--verbose` | Enable debug logging. |
 | `--help` | Print server usage. |
 
@@ -540,8 +742,9 @@ and `address`, the global section accepts:
 - `hosts allow` / `hosts deny` — comma- and/or whitespace-separated host access
   patterns.
 
-A `[module]` may also set `max connections` (0 = unlimited; enforced per module
-across all connection children) and its own `hosts allow`/`hosts deny`.
+A `[module]` requires `path`, and may also set `read only`, `client owner`,
+`auth users`, `max connections` (0 = unlimited; enforced per module across all
+connection children), and its own `hosts allow`/`hosts deny`.
 
 The per-host cap and the shared auth lockout identify a source by its numeric
 peer IP. **Loopback peers (127.0.0.0/8, IPv6 `::1`) are exempt**: every local
@@ -595,7 +798,7 @@ before the module list, before authentication, and the connecting peer address
 
 ## Protocol and Security
 
-FastSync protocol version `2.21.0` is shared by the client and server. The
+FastSync protocol version `2.28.0` is shared by the client and server. The
 current protocol is sender-driven and includes configuration negotiation,
 including the maximum allocation limit, incremental checks, checksums,
 manifests, keep-alives, abort handling, per-file remove-source results, and
@@ -647,10 +850,9 @@ mandates `--client-cn`, so a TLS connection to an auth-required module always
 has its client CN verified (`--client-cn` matches the certificate's CN only, not
 a subjectAltName, which is acceptable for a private CA).
 
-TLS provides encrypted TCP transport. Supplying `--ca` enables certificate
-verification; without it, traffic is encrypted but peer identity is not
-verified. Use certificate verification for deployments where authentication
-matters. The default TCP transport is not encrypted.
+TLS provides encrypted TCP transport. Both the client and the server require
+`--ca` together with `--tls`, so peer certificates are always verified
+(`SSL_VERIFY_PEER`, depth 4). The default TCP transport is not encrypted.
 
 The receiver protects its destination root with path validation, `openat()`
 directory traversal, `O_NOFOLLOW`, temporary files, and atomic renames. Delete
@@ -661,18 +863,27 @@ operations require the server's explicit `--allow-delete` policy.
 The project will reach the drop-in replacement goal in stages:
 
 1. Correct rsync option meanings, including short options, combined options,
-   and `--option=value` syntax.
+   and `--option=value` syntax — **done** in the rsync-parity wave: `-r`/`-b`/
+   `-L`/`-B`, short-option clustering (`-av`, `-aAX`, `-rlpt`), and attached
+   values (`-B1000`, `-essh`, `-MOPT`) all parse.
 2. Add differential tests that compare FastSync and rsync contents, metadata,
-   links, deletes, filters, dry runs, and exit codes.
-3. Make `-a` implement the expected recursive, links, permissions, times,
-   owner/group, and supported special-file behavior.
-4. Complete symlink, sparse-file, metadata, delete-policy, and resumable-write
-   semantics.
+   links, deletes, filters, dry runs, and exit codes — **done** for the
+   completion wave's scope; the tests live in `tests/integration/` and skip
+   cleanly when rsync is unavailable.
+3. `-a` implements full rsync `-rlptgoD`; under `-p` the source mode is copied
+   exactly (no masking). Ownership application stays privilege-gated, as in
+   rsync.
+4. Symlink (verbatim storage), sparse-file, metadata, delete-policy (including
+   `--max-delete` partial + exit 25, per-directory `--delete-during`/
+   `--delete-delay`), codecs, and resumable-write semantics are implemented;
+   remaining work is the documented edge cases, which the **Parity Completion
+   Wave** section of `RSYNC_COMPAT.md` enumerates honestly.
 5. Add rsync remote-shell and daemon protocol interoperability.
 6. Keep FastSync performance options as negotiated, optional extensions.
 
 The exhaustive implementation matrix and compatibility notes are in
-[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md).
+[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md); each row is classified as parity, caveat,
+or divergent.
 
 ## Testing
 
@@ -709,10 +920,13 @@ rsync protocol or filesystem-semantic compatibility.
 
 ## Performance Guidance
 
-- Use `-m` for workloads with many files or enough CPU parallelism.
-- Use `-c` or `-z` when network bandwidth is more constrained than CPU.
+- Use `-j`/`--threads` for workloads with many files or enough CPU parallelism
+  (`-m` is `--prune-empty-dirs`).
+- Use `-z` when network bandwidth is more constrained than CPU (`-c` is
+  `--checksum`, not a bandwidth option).
 - Tune `--chunk-size` for file sizes, memory limits, and network latency.
-- Use `-f` for large uncompressed TCP transfers where zero-copy I/O helps.
+- Use `--sendfile` for large uncompressed TCP transfers where zero-copy I/O
+  helps (`-f` is `--filter`).
 - Use `--incremental` to avoid retransmitting unchanged files.
 - Use `--delta` for changed files when both endpoints are FastSync peers.
 - Use `--bwlimit` when sharing a link with other traffic.

pytest.ini

@@ -8,3 +8,6 @@ markers =
     daemon_detach: real double-fork backgrounding path (--daemon without
         --no-detach); slower/fragile, so it runs in the full suite but not the
         fast PR gate
+    parity: differential rsync-parity case (full set; runs on push to
+        dev/main)
+    parity_ci: fast differential rsync-parity subset (runs on the PR gate)

shell.nix

@@ -38,6 +38,8 @@ pkgs.mkShell {
 
   buildInputs = with pkgs; [
     zstd
+    zlib
+    lz4
     openssl
   ];
 
@@ -54,6 +56,6 @@ pkgs.mkShell {
     echo "FastSync dev shell ready."
     echo "  Build:      cmake -B build -S . && cmake --build build -j\$(nproc)"
     echo "  Unit:       ./build/tests"
-    echo "  CI parity:  docker run --rm --user \"\$(id -u):\$(id -g)\" -v \"\$PWD:/workspace\" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v10 ..."
+    echo "  CI parity:  docker run --rm --user \"\$(id -u):\$(id -g)\" -v \"\$PWD:/workspace\" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v11 ..."
   '';
 }

src/client/change_list.c

@@ -1,5 +1,8 @@
 #include "change_list.h"
+#include "checksum.h"
+#include "log.h"
 #include "utils.h"
+#include <fcntl.h>
 #include <limits.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -7,21 +10,7 @@
 #include <string.h>
 #include <sys/stat.h>
 #include <time.h>
-
-/* Itemize code emitted for a transferred regular file.
- *
- * Layout (rsync-compatible 11-char item): `>f` marks a regular file that was
- * transferred to the remote host; the trailing nine markers are, in order,
- * c(hecksum) s(ize) t(ime) p(erms) o(wner) g(roup) u(ser/acl) a(ttrs) x(attrs).
- * Every marker is `+` (FastSync does not compare each attribute on the
- * receiving side, so a sent file is reported as fully updated).  Files that
- * are already up to date print no line at all, matching rsync's single -i
- * which only itemizes changes.
- *
- * Because the scanner only yields regular-file transfer candidates, `>d`
- * (directory) lines are never produced; directories are not transferred as
- * items by FastSync. */
-#define ITEMIZE_SENT_FILE ">f+++++++++"
+#include <unistd.h>
 
 typedef struct {
   char* data;
@@ -80,103 +69,23 @@ static bool strbuf_append(StrBuf* buf, const char* text) {
   return true;
 }
 
-static bool strbuf_append_ull(StrBuf* buf, unsigned long long value) {
-  char digits[32];
-  int written = snprintf(digits, sizeof(digits), "%llu", value);
-  if (written < 0 || (size_t)written >= sizeof(digits))
-    return false;
-  return strbuf_append(buf, digits);
-}
-
-static bool strbuf_append_longlong(StrBuf* buf, long long value) {
-  char digits[32];
-  int written = snprintf(digits, sizeof(digits), "%lld", value);
-  if (written < 0 || (size_t)written >= sizeof(digits))
-    return false;
-  return strbuf_append(buf, digits);
-}
-
 bool change_list_enabled(const Config* config) {
   return config != NULL && (config->itemize_changes || config->out_format != NULL ||
-                            (config->log_file != NULL && config->log_file_format != NULL));
+                            (config->log_file != NULL && config->log_file_format != NULL) ||
+                            (config->info_level & LOG_INFO_NAME) != 0);
 }
 
-char* change_render_itemize(const ChangeEvent* event) {
-  if (event == NULL || event->decision != CHANGE_SENT)
-    return str_dup("");
-  const char* code = event->is_directory ? ">d+++++++++" : ITEMIZE_SENT_FILE;
-  StrBuf line = {0};
-  bool ok = strbuf_append(&line, code) && strbuf_append(&line, " ") &&
-            strbuf_append(&line, event->path != NULL ? event->path : "");
-  if (!ok) {
-    strbuf_free(&line);
-    return NULL;
-  }
-  return line.data;
+/* Emitted once, lazily, ahead of the first --info=name entry: rsync prints the
+ * transfer-root `./` name line when the root directory is (re)created. */
+static bool name_root_printed = false;
+
+void change_reset_name_root(void) {
+  name_root_printed = false;
 }
 
-static const char* leaf_name(const char* path) {
-  if (path == NULL)
-    return "";
-  const char* slash = strrchr(path, '/');
-  return slash != NULL && slash[1] != '\0' ? slash + 1 : path;
-}
+/* ---- Itemize code ---- */
 
-char* change_render_format(const char* format, const ChangeEvent* event) {
-  if (format == NULL)
-    return NULL;
-  StrBuf line = {0};
-  bool ok = true;
-  for (const char* p = format; *p != '\0' && ok;) {
-    if (*p != '%') {
-      ok = strbuf_append_char(&line, *p);
-      p++;
-      continue;
-    }
-    char token = p[1];
-    if (token == '\0') {
-      ok = strbuf_append_char(&line, '%');
-      break;
-    }
-    switch (token) {
-    case '%':
-      ok = strbuf_append_char(&line, '%');
-      break;
-    case 'f':
-      ok = strbuf_append(&line, event->path != NULL ? event->path : "");
-      break;
-    case 'n':
-      ok = strbuf_append(&line, leaf_name(event->path));
-      break;
-    case 'l':
-      ok = strbuf_append_ull(&line, event->size);
-      break;
-    case 'b':
-      ok = strbuf_append_ull(&line, event->bytes_sent);
-      break;
-    case 'M':
-      ok = strbuf_append_longlong(&line, (long long)event->mtime_sec);
-      break;
-    default:
-      /* Unknown escape sequences are preserved verbatim. */
-      ok = strbuf_append_char(&line, '%') && strbuf_append_char(&line, token);
-      break;
-    }
-    p += 2;
-  }
-  if (!ok) {
-    strbuf_free(&line);
-    return NULL;
-  }
-  if (line.data == NULL) {
-    line.data = str_dup("");
-    if (!line.data)
-      return NULL;
-  }
-  return line.data;
-}
-
-/* Format a mode as an `ls -l` permission string, e.g. `-rw-r--r--`. */
+/* Format the permission bits as an `ls -l` string, e.g. `-rw-r--r--`. */
 static void mode_to_ls_string(mode_t mode, char out[11]) {
   out[0] = S_ISDIR(mode)    ? 'd'
            : S_ISLNK(mode)  ? 'l'
@@ -198,29 +107,94 @@ static void mode_to_ls_string(mode_t mode, char out[11]) {
   out[10] = '\0';
 }
 
-char* change_render_list_line(mode_t mode, unsigned long long size, time_t mtime,
-                              const char* path) {
-  char permission[11];
-  mode_to_ls_string(mode, permission);
-  char date[32];
-  struct tm broken_down;
-  if (localtime_r(&mtime, &broken_down) != NULL) {
-    if (strftime(date, sizeof(date), "%Y/%m/%d %H:%M:%S", &broken_down) == 0)
-      snprintf(date, sizeof(date), "?");
-  } else {
-    snprintf(date, sizeof(date), "?");
+static char itemize_type_char(const ChangeEvent* event) {
+  if (event->is_directory)
+    return 'd';
+  if (event->is_symlink)
+    return 'L';
+  if (event->is_special) {
+    if (S_ISCHR(event->mode) || S_ISBLK(event->mode))
+      return 'D';
+    return 'S';
   }
+  return 'f';
+}
+
+static bool times_match(const Config* config, const ChangeEvent* event) {
+  if (!event->dest.known || !event->dest.existed)
+    return false;
+  if (event->mtime_sec == event->dest.mtime_sec)
+    return event->mtime_nsec == event->dest.mtime_nsec;
+  long long delta = (long long)event->mtime_sec - (long long)event->dest.mtime_sec;
+  if (delta < 0)
+    delta = -delta;
+  return delta <= (long long)config->modify_window;
+}
+
+/* Fill the 11-character itemize code (10 chars + NUL).  `created` means the
+ * destination entry did not exist, so every attribute marker is `+`. */
+static void itemize_code(const Config* config, const ChangeEvent* event, char code[12]) {
+  bool known = event->dest.known;
+  bool created = !known || !event->dest.existed;
+  char update;
+  if (event->is_hardlink)
+    update = 'h';
+  else if (created)
+    update = (event->is_directory || event->is_symlink || event->is_special) ? 'c' : '>';
+  else
+    update = '>';
+  code[0] = update;
+  code[1] = itemize_type_char(event);
+  if (created) {
+    for (int i = 0; i < 9; i++)
+      code[2 + i] = '+';
+    code[11] = '\0';
+    return;
+  }
+  bool size_diff = event->size != event->dest.size;
+  bool time_diff = !times_match(config, event);
+  bool perms_diff = (event->mode & 07777) != (event->dest.mode & 07777);
+  bool owner_diff = event->uid != (uid_t)event->dest.uid;
+  bool group_diff = event->gid != (gid_t)event->dest.gid;
+  code[2] = '.'; /* checksum: no destination digest available */
+  code[3] = size_diff ? 's' : '.';
+  code[4] = time_diff ? 't' : '.';
+  code[5] = (config->preserve_perms && perms_diff) ? 'p' : '.';
+  code[6] = (config->preserve_owner && owner_diff) ? 'o' : '.';
+  code[7] = (config->preserve_group && group_diff) ? 'g' : '.';
+  code[8] = '.'; /* reserved */
+  code[9] = '.'; /* acl: not compared */
+  code[10] = '.';
+  code[11] = '\0';
+}
+
+/* rsync %n: the transfer-relative name, with a trailing slash for directories. */
+static bool append_name(StrBuf* buf, const ChangeEvent* event) {
+  if (!strbuf_append(buf, event->name != NULL ? event->name : ""))
+    return false;
+  if (event->is_directory && (event->name == NULL || event->name[0] == '\0' ||
+                              event->name[strlen(event->name) - 1] != '/'))
+    return strbuf_append_char(buf, '/');
+  return true;
+}
+
+/* rsync %L: " -> target" for a symlink, " => target" for a hard link, else "". */
+static bool append_link_suffix(StrBuf* buf, const ChangeEvent* event) {
+  if (event->is_symlink && event->symlink_target != NULL)
+    return strbuf_append(buf, " -> ") && strbuf_append(buf, event->symlink_target);
+  if (event->is_hardlink && event->hardlink_target != NULL)
+    return strbuf_append(buf, " => ") && strbuf_append(buf, event->hardlink_target);
+  return true;
+}
+
+char* change_render_itemize(const Config* config, const ChangeEvent* event) {
+  if (event == NULL || event->decision != CHANGE_SENT)
+    return str_dup("");
+  char code[12];
+  itemize_code(config, event, code);
   StrBuf line = {0};
-  char size_field[32];
-  int written = snprintf(size_field, sizeof(size_field), "%llu", size);
-  if (written < 0 || (size_t)written >= sizeof(size_field)) {
-    strbuf_free(&line);
-    return NULL;
-  }
-  bool ok = strbuf_append(&line, permission) && strbuf_append_char(&line, ' ') &&
-            strbuf_append(&line, size_field) && strbuf_append_char(&line, ' ') &&
-            strbuf_append(&line, date) && strbuf_append_char(&line, ' ') &&
-            strbuf_append(&line, path != NULL ? path : "");
+  bool ok = strbuf_append(&line, code) && strbuf_append_char(&line, ' ') &&
+            append_name(&line, event) && append_link_suffix(&line, event);
   if (!ok) {
     strbuf_free(&line);
     return NULL;
@@ -228,6 +202,276 @@ char* change_render_list_line(mode_t mode, unsigned long long size, time_t mtime
   return line.data;
 }
 
+/* rsync's `--info=name` line for an updated entry: the transfer-relative name
+ * (trailing slash for directories) plus the ` -> target` / ` => target` link
+ * suffix.  `--info=name` does not alter an itemize/out-format run. */
+static char* change_render_name(const ChangeEvent* event) {
+  StrBuf line = {0};
+  bool ok = append_name(&line, event) && append_link_suffix(&line, event);
+  if (!ok) {
+    strbuf_free(&line);
+    return NULL;
+  }
+  if (line.data == NULL) {
+    line.data = str_dup("");
+    if (!line.data)
+      return NULL;
+  }
+  return line.data;
+}
+
+/* rsync's `--info=name2` line for an unchanged entry: `NAME is uptodate`. */
+static char* change_render_name_uptodate(const ChangeEvent* event) {
+  char* name = change_render_name(event);
+  if (name == NULL)
+    return NULL;
+  size_t length = strlen(name);
+  char* line = malloc(length + sizeof(" is uptodate"));
+  if (line == NULL) {
+    free(name);
+    return NULL;
+  }
+  memcpy(line, name, length);
+  memcpy(line + length, " is uptodate", sizeof(" is uptodate"));
+  free(name);
+  return line;
+}
+
+/* ---- --out-format / --log-file-format ---- */
+
+/* rsync 3.4.1's `%C` uses the negotiated TRANSFER checksum (the first name of a
+ * two-name "transfer,pre-transfer" --checksum-choice), not the pre-transfer
+ * whole-file digest FastSync compares against on the wire.  The default "auto"
+ * resolves to xxh128, so an explicit selection and the default both render the
+ * selected algorithm's digest. */
+static ChecksumAlgo out_format_checksum_algo(const Config* config) {
+  return (ChecksumAlgo)config->checksum_transfer_algo;
+}
+
+/* Render a digest as rsync's sum_as_hex: xxh128 prints the HIGH 64-bit half
+ * before the low half, and xxh64/xxh3 print their 64-bit value big-endian; every
+ * other algorithm prints its bytes in order. */
+static void digest_to_hex(ChecksumAlgo algo, const uint8_t* digest, size_t len, char* out) {
+  if (algo == CHECKSUM_ALGO_XXH128 && len == 16) {
+    uint64_t low = 0;
+    uint64_t high = 0;
+    memcpy(&low, digest, sizeof(low));
+    memcpy(&high, digest + 8, sizeof(high));
+    snprintf(out, len * 2 + 1, "%016llx%016llx", (unsigned long long)high, (unsigned long long)low);
+    return;
+  }
+  if ((algo == CHECKSUM_ALGO_XXH64 || algo == CHECKSUM_ALGO_XXH3) && len == 8) {
+    uint64_t value = 0;
+    memcpy(&value, digest, sizeof(value));
+    snprintf(out, len * 2 + 1, "%016llx", (unsigned long long)value);
+    return;
+  }
+  static const char hex[] = "0123456789abcdef";
+  for (size_t i = 0; i < len; i++) {
+    out[i * 2] = hex[(digest[i] >> 4) & 0xf];
+    out[i * 2 + 1] = hex[digest[i] & 0xf];
+  }
+  out[len * 2] = '\0';
+}
+
+static bool format_uses_checksum(const char* format) {
+  if (format == NULL)
+    return false;
+  for (const char* p = format; *p != '\0';) {
+    if (*p != '%') {
+      p++;
+      continue;
+    }
+    char token = p[1];
+    if (token == '\0')
+      break;
+    if (token == 'C')
+      return true;
+    p += 2;
+  }
+  return false;
+}
+
+/* Fill event->checksum/checksum_known for a transferred regular file.  A
+ * non-regular entry (or a hard-link sibling) leaves checksum_known false, which
+ * renders as spaces like rsync. */
+static void fill_event_checksum(const Config* config, const File* file, ChangeEvent* event) {
+  if (file == NULL || file->is_dir || file->is_symlink || file->is_special ||
+      (file->link_group != 0 && !file->link_first))
+    return;
+  if (!format_uses_checksum(config->out_format) && !format_uses_checksum(config->log_file_format))
+    return;
+  if (file->path == NULL)
+    return;
+  ChecksumAlgo algo = out_format_checksum_algo(config);
+  /* rsync renders `--checksum-choice=none` as a blank 2-character column. */
+  if (algo == CHECKSUM_ALGO_NONE)
+    return;
+  uint8_t digest[CHECKSUM_MAX_DIGEST_LEN];
+  size_t len = 0;
+  /* rsync's %C is the transfer checksum, which is always seeded with 0 (it is
+   * independent of --checksum-seed, as rsync 3.4.1 demonstrates). */
+  if (!checksum_digest_file(algo, 0, file->path, digest, sizeof(digest), &len))
+    return;
+  digest_to_hex(algo, digest, len, event->checksum);
+  event->checksum_known = true;
+}
+
+char* change_render_format(const char* format, const Config* config, const ChangeEvent* event) {
+  if (format == NULL || event == NULL)
+    return NULL;
+  StrBuf line = {0};
+  bool ok = true;
+  for (const char* p = format; *p != '\0' && ok;) {
+    if (*p != '%') {
+      ok = strbuf_append_char(&line, *p);
+      p++;
+      continue;
+    }
+    char token = p[1];
+    if (token == '\0') {
+      ok = strbuf_append_char(&line, '%');
+      break;
+    }
+    switch (token) {
+    case '%':
+      ok = strbuf_append_char(&line, '%');
+      break;
+    case 'i': {
+      if (event->deleted) {
+        /* rsync's ITEM_DELETED itemize code: `*deleting  ` (11 chars). */
+        ok = strbuf_append(&line, "*deleting  ");
+        break;
+      }
+      char code[12];
+      itemize_code(config, event, code);
+      ok = strbuf_append(&line, code);
+      break;
+    }
+    case 'f':
+      ok = strbuf_append(&line, event->path != NULL ? event->path : "");
+      break;
+    case 'n':
+      ok = append_name(&line, event);
+      break;
+    case 'L':
+      ok = append_link_suffix(&line, event);
+      break;
+    case 'l': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%llu", event->size);
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    case 'b': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%llu", event->bytes_sent);
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    case 'c': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%llu", event->bytes_read);
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    case 'C': {
+      if (event->checksum_known) {
+        ok = strbuf_append(&line, event->checksum);
+      } else {
+        /* rsync pads a non-regular / untransferred / `none` entry with spaces;
+           `none` renders as a blank 2-character column. */
+        ChecksumAlgo algo = out_format_checksum_algo(config);
+        int width = algo == CHECKSUM_ALGO_NONE ? 2 : checksum_digest_len(algo) * 2;
+        for (int i = 0; i < width && ok; i++)
+          ok = strbuf_append_char(&line, ' ');
+      }
+    } break;
+    case 'M': {
+      char when[32];
+      if (format_rsync_datetime(event->mtime_sec, true, when, sizeof(when)))
+        ok = strbuf_append(&line, when);
+    } break;
+    case 't': {
+      char when[32];
+      if (format_rsync_datetime(time(NULL), false, when, sizeof(when)))
+        ok = strbuf_append(&line, when);
+    } break;
+    case 'o':
+      ok = strbuf_append(&line, "send");
+      break;
+    case 'p': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%ld", (long)getpid());
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    case 'B': {
+      char permission[11];
+      mode_to_ls_string(event->mode, permission);
+      ok = strbuf_append(&line, permission + 1);
+    } break;
+    case 'U': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%u", (unsigned)event->uid);
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    case 'G': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%u", (unsigned)event->gid);
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    default:
+      /* Unknown escape sequences are preserved verbatim. */
+      ok = strbuf_append_char(&line, '%') && strbuf_append_char(&line, token);
+      break;
+    }
+    p += 2;
+  }
+  if (!ok) {
+    strbuf_free(&line);
+    return NULL;
+  }
+  if (line.data == NULL) {
+    line.data = str_dup("");
+    if (!line.data)
+      return NULL;
+  }
+  return line.data;
+}
+
+/* ---- --list-only ---- */
+
+char* change_render_list_line(const Config* config, const ChangeEvent* event) {
+  (void)config;
+  if (event == NULL)
+    return NULL;
+  char permission[11];
+  mode_to_ls_string(event->mode, permission);
+  char date[32];
+  if (!format_rsync_datetime(event->mtime_sec, false, date, sizeof(date)))
+    snprintf(date, sizeof(date), "?");
+  StrBuf line = {0};
+  char size_field[40];
+  char grouped[32];
+  if (!format_big_num(event->size, false, grouped, sizeof(grouped))) {
+    strbuf_free(&line);
+    return NULL;
+  }
+  int written = snprintf(size_field, sizeof(size_field), "%15s", grouped);
+  if (written < 0 || (size_t)written >= sizeof(size_field)) {
+    strbuf_free(&line);
+    return NULL;
+  }
+  const char* name = event->name != NULL && event->name[0] != '\0' ? event->name : ".";
+  bool ok = strbuf_append(&line, permission) && strbuf_append(&line, size_field) &&
+            strbuf_append_char(&line, ' ') && strbuf_append(&line, date) &&
+            strbuf_append_char(&line, ' ') && strbuf_append(&line, name);
+  if (!ok) {
+    strbuf_free(&line);
+    return NULL;
+  }
+  return line.data;
+}
+
+/* ---- Event emission ---- */
+
 static void print_escaped_line(FILE* stream, const char* line, bool eight_bit_output) {
   char* escaped = output_escape(line, eight_bit_output);
   if (escaped != NULL) {
@@ -242,20 +486,49 @@ static void print_escaped_line(FILE* stream, const char* line, bool eight_bit_ou
 void change_emit(const Config* config, const ChangeEvent* event) {
   if (event == NULL || !change_list_enabled(config))
     return;
-  if (event->decision == CHANGE_UP_TO_DATE)
-    return;
   bool to_stdout = config->itemize_changes || config->out_format != NULL;
   bool to_log = config->log_file != NULL && config->log_file_format != NULL;
+  bool progress_active = config->show_progress || (config->info_level & LOG_INFO_PROGRESS);
+  if (event->decision == CHANGE_UP_TO_DATE) {
+    /* --info=name2 prints `NAME is uptodate` for entries the receiver already
+       had.  An itemize/out-format run reports them through its own format (or
+       not at all), the progress stream has no frame for them, and neither the
+       itemize nor the log-file stream previously reported an up-to-date entry,
+       so nothing else here changes. */
+    if (!to_stdout && (config->info_level & LOG_INFO_NAME_UPTODATE) != 0 && !progress_active) {
+      char* line = change_render_name_uptodate(event);
+      if (line != NULL) {
+        print_escaped_line(stdout, line, config->eight_bit_output);
+        free(line);
+      }
+    }
+    return;
+  }
   if (to_stdout) {
-    char* line = config->out_format != NULL ? change_render_format(config->out_format, event)
-                                            : change_render_itemize(event);
+    char* line = config->out_format != NULL
+                     ? change_render_format(config->out_format, config, event)
+                     : change_render_itemize(config, event);
+    if (line != NULL) {
+      print_escaped_line(stdout, line, config->eight_bit_output);
+      free(line);
+    }
+  } else if ((config->info_level & LOG_INFO_NAME) != 0 && !progress_active) {
+    /* --info=name without -i/--out-format: print the updated entry's name.  The
+       --progress path owns the name line when progress output is active (it
+       emits the same names before the progress frames), so do not duplicate.
+       The transfer-root `./` line precedes the first such name. */
+    if (!name_root_printed) {
+      name_root_printed = true;
+      fputs("./\n", stdout);
+    }
+    char* line = change_render_name(event);
     if (line != NULL) {
       print_escaped_line(stdout, line, config->eight_bit_output);
       free(line);
     }
   }
   if (to_log) {
-    char* line = change_render_format(config->log_file_format, event);
+    char* line = change_render_format(config->log_file_format, config, event);
     if (line != NULL) {
       print_escaped_line(config->log_file, line, config->eight_bit_output);
       free(line);
@@ -266,9 +539,6 @@ void change_emit(const Config* config, const ChangeEvent* event) {
 static bool format_uses_mtime(const char* format) {
   if (format == NULL)
     return false;
-  /* Mirror change_render_format's tokenizer: "%%" is a literal percent (so
-   * "%%M" does NOT expand %M) and unknown "%X" escapes consume both chars.
-   * This keeps the optional stat() fallback below in step with the renderer. */
   for (const char* p = format; *p != '\0';) {
     if (*p != '%') {
       p++;
@@ -284,46 +554,176 @@ static bool format_uses_mtime(const char* format) {
   return false;
 }
 
-void change_emit_file_sent(const Config* config, const File* file) {
+/* Relative path of an entry below the transfer root (no leading slash).  Uses
+ * the sender-side send_path override when present (bare-relative -R layout). */
+static char* relative_name(const Config* config, const File* file) {
+  const char* full = file_wire_path(file);
+  if (file->send_path != NULL)
+    return str_dup(full != NULL ? full : "");
+  const char* root = config->send_directory;
+  if (root == NULL || full == NULL)
+    return str_dup(full != NULL ? full : "");
+  size_t root_len = strlen(root);
+  while (root_len > 1 && root[root_len - 1] == '/')
+    root_len--;
+  if (strncmp(root, full, root_len) == 0) {
+    if (full[root_len] == '\0')
+      return str_dup("");
+    if (full[root_len] == '/')
+      return str_dup(full + root_len + 1);
+  }
+  return str_dup(full);
+}
+
+/* rsync %f long form: the source argument as typed (leading '/' removed,
+ * trailing '/' removed, leading "./" removed) joined to the relative name. */
+static char* display_name(const Config* config, const char* name) {
+  const char* root = config->send_directory;
+  if (root == NULL)
+    return str_dup(name != NULL ? name : "");
+  const char* p = root;
+  while (*p == '/')
+    p++;
+  if (p[0] == '.' && p[1] == '/')
+    p += 2;
+  size_t root_len = strlen(p);
+  while (root_len > 0 && p[root_len - 1] == '/')
+    root_len--;
+  size_t name_len = name != NULL ? strlen(name) : 0;
+  if (root_len == 0 && name_len == 0)
+    return str_dup("");
+  char* out = malloc(root_len + (root_len > 0 && name_len > 0 ? 1 : 0) + name_len + 1);
+  if (!out)
+    return NULL;
+  size_t offset = 0;
+  if (root_len > 0) {
+    memcpy(out, p, root_len);
+    offset = root_len;
+  }
+  if (root_len > 0 && name_len > 0)
+    out[offset++] = '/';
+  if (name_len > 0)
+    memcpy(out + offset, name, name_len);
+  out[offset + name_len] = '\0';
+  return out;
+}
+
+static void fill_event_from_file(const Config* config, const File* file, ChangeEvent* event,
+                                 char** name_out, char** path_out) {
+  char* name = relative_name(config, file);
+  char* path = display_name(config, name);
+  event->name = name;
+  event->path = path;
+  *name_out = name;
+  *path_out = path;
+  if (file->metadata != NULL) {
+    event->mtime_sec = file->metadata->mtime_sec;
+    event->mtime_nsec = file->metadata->mtime_nsec;
+    event->mode = file->metadata->mode;
+    event->uid = file->metadata->uid;
+    event->gid = file->metadata->gid;
+  } else if (format_uses_mtime(config->out_format) || format_uses_mtime(config->log_file_format)) {
+    struct stat st;
+    if (file->path != NULL && stat(file->path, &st) == 0) {
+      event->mtime_sec = st.st_mtime;
+      event->mtime_nsec = st.st_mtim.tv_nsec;
+    }
+  }
+}
+
+void change_emit_file_sent_bytes(const Config* config, const File* file,
+                                 unsigned long long bytes_sent, unsigned long long bytes_read) {
   if (file == NULL || !change_list_enabled(config))
     return;
   ChangeEvent event;
   memset(&event, 0, sizeof(event));
-  /* The displayed path is the one transmitted (with -R + --files-from this is
-     the bare relative destination path); the metadata fallback below still
-     stats the local absolute path. */
-  event.path = file_wire_path(file);
   event.decision = CHANGE_SENT;
   event.is_directory = false;
+  event.is_symlink = false;
+  event.is_special = false;
+  event.is_hardlink = false;
   event.size = file->data != NULL ? file->data->size : 0;
-  /* FastSync has no wire-byte counter yet, so %b reports the source length
-   * that had to be delivered (always equal to %l); the actual bytes written
-   * to the socket (compressed/delta) are not measured. */
-  event.bytes_sent = event.size;
-  if (file->metadata != NULL) {
-    event.mtime_sec = file->metadata->mtime_sec;
-  } else if (format_uses_mtime(config->out_format) || format_uses_mtime(config->log_file_format)) {
-    /* Best-effort fallback for %M when no metadata was captured (no -M): the
-     * path is stat()ed just to fill the field, and any failure leaves 0. */
-    struct stat st;
-    if (file->path != NULL && stat(file->path, &st) == 0)
-      event.mtime_sec = st.st_mtime;
+  event.dest = file->dest_state;
+  if (file->is_symlink) {
+    event.is_symlink = true;
+    event.symlink_target = file->symlink_target;
+    event.size = file->symlink_target != NULL ? strlen(file->symlink_target) : 0;
+    event.bytes_sent = 0;
+  } else if (file->is_special) {
+    event.is_special = true;
+    event.bytes_sent = 0;
+  } else if (file->link_group != 0 && !file->link_first) {
+    event.is_hardlink = true;
+    event.hardlink_target = file->hardlink_target;
+    event.bytes_sent = 0;
+  } else {
+    event.bytes_sent = bytes_sent;
+    /* rsync's %c is the block-checksum bytes received for the file.  Even a
+     * whole-file transfer (no basis; --append/--inplace included) receives
+     * rsync's 16-byte sum header, so rsync reports 16; a dry run transfers
+     * nothing and reports 0.  FastSync's whole-file path has no sum header, so
+     * report rsync's value for parity.  With delta enabled the real received
+     * bytes are kept, but FastSync's signature framing differs from rsync's so
+     * those stay numerically divergent. */
+    bool delta_active = config->use_delta && !config->whole_file;
+    event.bytes_read = (!config->dry_run && !delta_active) ? 16 : bytes_read;
   }
-  change_emit(config, &event);
+  char* name = NULL;
+  char* path = NULL;
+  fill_event_from_file(config, file, &event, &name, &path);
+  if (name != NULL && path != NULL) {
+    fill_event_checksum(config, file, &event);
+    change_emit(config, &event);
+  }
+  free(name);
+  free(path);
+}
+
+void change_emit_file_sent(const Config* config, const File* file) {
+  if (file == NULL)
+    return;
+  unsigned long long payload = file->data != NULL ? file->data->size : 0;
+  change_emit_file_sent_bytes(config, file, payload, 0);
+}
+
+void change_emit_file_uptodate(const Config* config, const File* file) {
+  if (file == NULL || !change_list_enabled(config))
+    return;
+  ChangeEvent event;
+  memset(&event, 0, sizeof(event));
+  event.decision = CHANGE_UP_TO_DATE;
+  event.is_directory = false;
+  event.is_symlink = file->is_symlink;
+  event.is_special = file->is_special;
+  event.is_hardlink = file->link_group != 0 && !file->link_first;
+  event.symlink_target = file->symlink_target;
+  event.hardlink_target = file->hardlink_target;
+  event.size = file->data != NULL ? file->data->size : 0;
+  event.dest = file->dest_state;
+  char* name = NULL;
+  char* path = NULL;
+  fill_event_from_file(config, file, &event, &name, &path);
+  if (name != NULL && path != NULL)
+    change_emit(config, &event);
+  free(name);
+  free(path);
 }
 
-/* Build and emit a CHANGE_SENT event for an explicit directory entry (-d). */
 void change_emit_dir_sent(const Config* config, const File* file) {
   if (file == NULL || !change_list_enabled(config))
     return;
   ChangeEvent event;
   memset(&event, 0, sizeof(event));
-  event.path = file_wire_path(file);
   event.decision = CHANGE_SENT;
   event.is_directory = true;
   event.size = 0;
   event.bytes_sent = 0;
-  if (file->metadata != NULL)
-    event.mtime_sec = file->metadata->mtime_sec;
-  change_emit(config, &event);
+  event.dest = file->dest_state;
+  char* name = NULL;
+  char* path = NULL;
+  fill_event_from_file(config, file, &event, &name, &path);
+  if (name != NULL && path != NULL)
+    change_emit(config, &event);
+  free(name);
+  free(path);
 }

src/client/change_list.h

@@ -2,7 +2,9 @@
 #define CHANGE_LIST_H
 
 #include "config.h"
+#include "checksum.h"
 #include "file_types.h"
+#include "format.h"
 #include <stdbool.h>
 #include <sys/stat.h>
 #include <time.h>
@@ -26,42 +28,59 @@ typedef enum {
 } ChangeDecision;
 
 typedef struct {
-  const char* path; /* full source path */
+  const char* path; /* long-form display path (rsync %f) */
+  const char* name; /* transfer-relative path (rsync %n), no trailing slash */
   ChangeDecision decision;
   bool is_directory;
-  unsigned long long size; /* source file length in bytes */
-  /* The number of bytes reported for a sent file. FastSync has no wire-byte
-   * counter, so this is always the source length (== size / %l); actual
-   * post-compression/delta bytes on the wire are not counted. */
-  unsigned long long bytes_sent;
-  time_t mtime_sec; /* 0 when unknown */
+  bool is_symlink;
+  bool is_special;
+  bool is_hardlink; /* a hard-link sibling (linked, no data sent) */
+  bool deleted;     /* a would-delete report (-n --delete); no source file */
+  const char* symlink_target;
+  const char* hardlink_target;
+  unsigned long long size;       /* source file length in bytes */
+  unsigned long long bytes_sent; /* wire bytes actually transferred (rsync %b) */
+  unsigned long long bytes_read; /* wire bytes read back for this file (rsync %c) */
+  /* rsync %C: whole-file checksum hex for a transferred regular file.  Only
+   * filled when the active format uses %C (checksum_known == false otherwise,
+   * which renders as spaces like rsync for non-regular entries). */
+  bool checksum_known;
+  char checksum[CHECKSUM_MAX_DIGEST_LEN * 2 + 1];
+  time_t mtime_sec;
+  long mtime_nsec;
+  mode_t mode;
+  uid_t uid;
+  gid_t gid;
+  /* Receiver-reported pre-transfer destination state (OutputDestState.known is
+   * false when no report was requested/received). */
+  OutputDestState dest;
 } ChangeEvent;
 
 /* True when any output mode is active and per-file events matter. */
 bool change_list_enabled(const Config* config);
 
-/* Render the rsync-style itemize line for a transferred file:
- *   `>f+++++++++ <path>`
- * The 11-char code is `>f` (regular file transferred to the remote host)
- * followed by c/s/t/p/o/g/u/a/x markers that are all `+` (value will be set
- * / differs) because FastSync does not separately compare checksums, size,
- * mtime, perms, owner, group, uid, acl, or xattr on the receiving side, so a
- * sent file is reported as fully updated.  Up-to-date files print no line
- * (rsync single `-i` only shows changes).  Caller frees the result. */
-char* change_render_itemize(const ChangeEvent* event);
+/* Render the rsync-style itemize line for a transferred item
+ * (`%i %n%L`): `>f+++++++++ sub/b.txt`.  Caller frees the result. */
+char* change_render_itemize(const Config* config, const ChangeEvent* event);
 
-/* Expand an --out-format/--log-file-format template.  Tokens:
- *   %f  full source path        %b  "bytes sent" == the source length (%l);
- *   %n  leaf (base) name            actual post-compression/delta wire bytes
- *   %l  file length in bytes        are not counted
- *   %M  mtime in whole seconds      %%  a literal percent sign
+/* Expand an --out-format/--log-file-format template.  Supported tokens:
+ *   %i  itemize code            %n  transfer-relative name (dir: trailing /)
+ *   %f  long display path       %l  file length in bytes
+ *   %b  wire bytes transferred  %c  block-checksum bytes received (rsync: 16
+ *                                   for a whole-file transfer, 0 for a dry run)
+ *   %C  whole-file checksum hex (xxh128 by default; spaces for non-regular)
+ *   %M  mtime (YYYY/MM/DD-HH:MM:SS)
+ *   %t  current time            %o  operation ("send"/"del.")
+ *   %p  pid                     %B  permission bits without the type char
+ *   %U  uid                     %G  gid
+ *   %L  " -> target" / " => target"    %%  a literal percent sign
  * Unknown %X sequences are preserved verbatim.  Caller frees the result. */
-char* change_render_format(const char* format, const ChangeEvent* event);
+char* change_render_format(const char* format, const Config* config, const ChangeEvent* event);
 
 /* Render one --list-only long-listing entry:
- *   `-rw-r--r--           12 2026/09/06 10:00:00 <path>`
+ *   `-rw-r--r--           12 2026/09/06 10:00:00 sub/b.txt`
  * (ls -l style columns; mtime in the local time zone).  Caller frees it. */
-char* change_render_list_line(mode_t mode, unsigned long long size, time_t mtime, const char* path);
+char* change_render_list_line(const Config* config, const ChangeEvent* event);
 
 /* Emit an event to every active destination:
  *   stdout: --itemize-changes line, or the --out-format expansion when set;
@@ -69,10 +88,27 @@ char* change_render_list_line(mode_t mode, unsigned long long size, time_t mtime
  * CHANGE_UP_TO_DATE events produce no output. */
 void change_emit(const Config* config, const ChangeEvent* event);
 
-/* Build and emit a CHANGE_SENT event for a file the client just sent. */
+/* Build and emit a CHANGE_SENT event for a file the client just sent.  `bytes_sent`
+ * is the process-wide wire-byte delta for this file (rsync's %b) and `bytes_read`
+ * the received bytes used for the delta handshake; pass 0 when unknown.  For a
+ * whole-file transfer %c is pinned to rsync's 16-byte sum header regardless. */
+void change_emit_file_sent_bytes(const Config* config, const File* file,
+                                 unsigned long long bytes_sent, unsigned long long bytes_read);
+
+/* Build and emit a CHANGE_SENT event for a file the client just sent, deriving
+ * the wire byte counts from the source payload length. */
 void change_emit_file_sent(const Config* config, const File* file);
 
 /* Build and emit a CHANGE_SENT event for an explicit directory entry (-d). */
 void change_emit_dir_sent(const Config* config, const File* file);
 
+/* Build and emit a CHANGE_UP_TO_DATE event for a file the receiver already had.
+ * With --info=name2 it renders rsync's "NAME is uptodate" line (no output
+ * otherwise). */
+void change_emit_file_uptodate(const Config* config, const File* file);
+
+/* Reset the lazy transfer-root `./` line emitted ahead of the first
+ * --info=name entry.  Call once at the start of a transfer. */
+void change_reset_name_root(void);
+
 #endif

src/client/client_send.h

@@ -23,6 +23,12 @@ void client_set_abort_armed(bool armed);
  * config_delete() once the call returns). */
 int send_files(Config* config);
 int send_files_multithreaded(Config** config);
+/* rsync's --ignore-errors deletion gate: with no I/O error during the scan the
+ * deletion phase always proceeds; with one it is suppressed unless
+ * `--ignore-errors` was given.  Exposed so the decision can be unit-tested
+ * without a privileged (mode-000) source directory.  See client_send.c. */
+bool ignore_errors_allows_delete(const Config* config, bool had_io_error);
+
 /* Phase 6 residual-batch (client-only).  See client_send.c. */
 int write_batch_from_source(const Config* config, const char* batch_path);
 int apply_batch_to_dest(const Config* config, const char* batch_path, const char* dest_root);

src/client/client_validation.c

@@ -60,6 +60,16 @@ bool validate_config(const Config* config) {
     log_message(LOG_LEVEL_ERROR, "-f/--sendfile is not supported with SSH transport");
     return false;
   }
+  /* -M/--remote-option appends an option to the REMOTE server's argv, which
+   * only exists on the SSH (user@host:path) transport.  A daemon
+   * (host::module/path) or local TCP destination has no remote command line,
+   * so the option would be silently ignored; reject it by name instead. */
+  if (config->remote_option_count > 0 && config->transport != TRANSPORT_SSH) {
+    log_message(LOG_LEVEL_ERROR,
+                "-M/--remote-option is only valid with the SSH transport (user@host:path); it "
+                "cannot be used with a daemon (host::module/path) or local TCP destination");
+    return false;
+  }
   /* -4 and -6 are mutually exclusive: a socket address family cannot be both. */
   if (config->ipv4 && config->ipv6) {
     log_message(LOG_LEVEL_ERROR, "-4/--ipv4 and -6/--ipv6 are mutually exclusive");

src/client/scanner.h

@@ -63,8 +63,23 @@ typedef struct {
   const FileListSet* file_list;       /* --files-from allow-set, or NULL */
   const FilterRuleList* base_filters; /* command-line + -C rules, or NULL */
   bool per_dir_filters;               /* -F: read .rsync-filter per directory */
-  bool dirs;                          /* -d/--dirs: transfer dir entries, no recursion */
-  bool relative;                      /* -R/--relative (dest rel paths, with --files-from) */
+  /* --delete-excluded: per-directory plain rules become sender-only, so they no
+     longer protect the receiver from deletion. */
+  bool delete_excluded;
+  /* -FF: also exclude the per-directory filter files themselves from the
+     transfer (single -F transfers them). */
+  bool exclude_per_dir_filter_files;
+  bool dirs;     /* -d/--dirs: transfer dir entries, no recursion */
+  bool relative; /* -R/--relative (dest rel paths, with --files-from) */
+  /* -R/--relative outside --files-from: the destination-relative path prefix
+   * reconstructed from the source spec (rsync's '/./' cut point), or NULL when
+   * -R is off or --files-from is in use (the bare-relative path then comes from
+   * the listed entry).  Borrowed read-only; owned by client_send. */
+  const char* relative_prefix;
+  /* --list-only: emit an is_dir File for every traversed directory (the listing
+   * includes directory entries, matching rsync).  Client-only; never set on a
+   * real transfer, which relies on implicit parent creation. */
+  bool list_dirs;
   /* --prune-empty-dirs (long only): in --dirs mode an empty source directory's
      explicit entry is omitted from the transfer file list (so nothing is
      created at the destination and it can be pruned by --delete); explicitly
@@ -73,20 +88,51 @@ typedef struct {
   bool prune_empty_dirs;
   /* Delete-excluded protection sink (optional): when non-NULL the scanner
    * appends the destination-relative path of every entry it prunes because a
-   * USER SELECTION rule excluded it (--filter/-C/per-dir rules, the legacy
-   * --exclude/--include layer, and --max-size/--min-size).  The sender turns
-   * this list into the manifest's protected prefixes so `--delete` leaves the
-   * destination mirror of excluded source paths alone (rsync's default), and
-   * empties it when --delete-excluded opts back into deleting them.  NOT
-   * recorded for --files-from subset pruning (whose delete semantics stay
-   * keep-set-only) or for -R/--files-from relative wire paths.  When
-   * `excluded_mutex` is non-NULL it is taken around every append (the parallel
-   * scanner shares one list across its worker threads). */
+   * USER SELECTION rule excluded it (--filter/-C/per-dir rules and the legacy
+   * --exclude/--include layer).  The sender turns this list into the manifest's
+   * protected prefixes so `--delete` leaves the destination mirror of excluded
+   * source paths alone (rsync's default), and drops it when --delete-excluded
+   * opts back into deleting them.  NOT recorded for --files-from subset pruning
+   * (whose delete semantics derive from the synchronized-directory set) or for
+   * -R/--files-from relative wire paths.  When `excluded_mutex` is non-NULL it
+   * is taken around every append (the parallel scanner shares one list across
+   * its worker threads). */
   ArrayList* excluded_paths;
   mtx_t* excluded_mutex;
-  /* --ignore-errors: an unreadable directory during the scan is recorded as an
-   * I/O error and skipped instead of aborting the scan.  Client-only. */
+  /* Size-prune protection sink (optional): when non-NULL the scanner appends
+   * the destination-relative path of every entry it skipped because of
+   * --max-size/--min-size.  rsync never deletes a size-skipped source mirror,
+   * even under --delete-excluded, so the sender always transmits this list as
+   * protected prefixes (unlike excluded_paths, which --delete-excluded drops).
+   * Guarded by `excluded_mutex` like excluded_paths. */
+  ArrayList* size_skipped_paths;
+  /* Synchronized-directory sink (optional): when non-NULL the scanner appends
+   * the destination-relative path of every directory it is about to traverse
+   * that lies inside a --files-from listed directory (or of every traversed
+   * directory when there is no list).  The sender sends this set with the delete
+   * manifest so the receiver confines its extras walk to synchronized
+   * directories, exactly like rsync; the receive root is the "." sentinel.
+   * Guarded by `excluded_mutex`. */
+  ArrayList* synced_dirs;
+  /* Delete-plan directory sink (optional): when non-NULL the scanner appends
+   * the destination-relative path of every directory it traverses (except the
+   * receive root).  The per-directory --delete-during/--delete-delay plan
+   * builder uses this to keep an empty in-scope source directory (rsync keeps
+   * it) and to emit its plan after the data stream, when no file frame would
+   * otherwise trigger it.  Guarded by `excluded_mutex`. */
+  ArrayList* plan_dirs;
+  /* --ignore-errors: an unreadable subdirectory no longer aborts the scan (it
+   * is always skipped so the rest of the tree transfers); this flag is kept so
+   * the client can distinguish the option state when deciding deletion policy.
+   * Client-only. */
   bool ignore_io_errors;
+  /* --info=nonreg: print rsync's `skipping non-regular file "NAME"` line for a
+   * non-regular entry that is not being preserved.  Client-only. */
+  bool note_nonreg;
+  /* Source root and 8-bit-output policy used to render a `--info=nonreg` name
+   * relative to the transfer root.  Borrowed read-only. */
+  const char* send_directory;
+  bool eight_bit_output;
   /* --ignore-missing-args (implied by --delete-missing-args): an explicitly
    * --files-from-listed entry that does not exist under the source is skipped
    * instead of failing (the --dirs generator is the only scanner path that
@@ -114,6 +160,17 @@ typedef struct {
   bool capture_dir_times;
   ArrayList* dir_entries;
   mtx_t* dir_entries_mutex;
+  /* Recreate empty source directories on a recursive transfer: emit a
+   * payload-less directory entry for every traversed directory that produced
+   * no transferred/descended child.  Off by default so low-level scanner users
+   * (unit helpers, --list-only) see only the historical file list; the real
+   * sender sets it in prepare_scanner. */
+  bool emit_empty_dirs;
+  /* --no-implied-dirs with -R + --files-from: a directory that is only an
+   * implied parent of a listed entry (not itself listed, nor below a listed
+   * directory) must not carry source metadata; it is created with default
+   * attributes at the destination, matching rsync. */
+  bool no_implied_dirs;
 } ScannerOptions;
 
 /* Internal per-scanner filter state. FilterNode chains represent the ordered
@@ -131,6 +188,11 @@ typedef struct {
   int current_depth;
   dev_t root_dev;
   bool failed;
+  /* Recursive scan: whether the open directory yielded any transferred or
+     descended entry.  When it did not, closing it emits a directory entry so
+     the empty source directory is recreated at the destination (rsync
+     parity). */
+  bool current_dir_produced;
   /* Phase 2 (files-from / filter layer). */
   char* root_path;          /* transfer root (fs path) for rel computation */
   char* current_rel;        /* rel path of the open directory ("" == root) */
@@ -149,6 +211,10 @@ typedef struct {
      --ignore-errors the scan continues past it and the caller decides what to
      do; `failed` is reserved for fatal errors that always abort the scan. */
   bool io_error;
+  /* The transfer ROOT could not be opened.  It is always fatal, even under
+     --ignore-errors, but the client still maps it to rsync's partial-transfer
+     exit (23) rather than a generic failure. */
+  bool root_io_error;
 } DirectoryScanner;
 
 typedef struct {
@@ -168,7 +234,8 @@ typedef struct {
   int completed;
   Chunk* initial_chunk;
   ProtocolSession* allocation_session;
-  FilterNode* root_filter_node; /* root .rsync-filter context (owned by ps) */
+  FilterNode* root_filter_node;  /* root .rsync-filter context (owned by ps) */
+  const ScannerOptions* options; /* borrowed scan options (--info=nonreg output) */
 } ParallelScanner;
 
 DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_metadata,
@@ -194,6 +261,13 @@ bool scanner_same_filesystem(bool one_file_system, dev_t root_device, dev_t entr
  * "/". Exposed so tests can exercise the mapping directly. */
 char* scanner_path_relative(const char* root, const char* fs_path);
 
+/* -R/--relative destination-relative prefix reconstructed from a source spec:
+ * the path after rsync's first '.' path component (the '/./' cut point), with
+ * leading/trailing slashes removed, or the whole spec (normalized) when there
+ * is no cut.  Returns "" for the receive root, or NULL when `spec` is NULL or
+ * allocation fails.  Exposed so tests can exercise the mapping directly. */
+char* scanner_relative_prefix(const char* spec);
+
 ParallelScanner* parallel_scanner_create_with_options(const char* root_directory,
                                                       const ScannerOptions* options,
                                                       ProtocolSession* allocation_session);

src/client/usage.c

@@ -20,11 +20,16 @@ void print_usage(void) {
   printf("Options:\n");
   printf("  -c, --checksum      Verify content by checksum instead of size+mtime\n");
   printf("  -z, --compress [level]  Enable compression (level 1-22, default 5)\n");
-  printf("  -a, --archive       rsync archive mode (-rlptgoD): links, metadata,\n");
-  printf("                      devices and specials (not compression/multithreading)\n");
+  printf("  -a, --archive       rsync archive mode (-rlptgoD): links, perms, times,\n");
+  printf("                      owner, group, devices and specials; not\n");
+  printf("                      compression/multithreading\n");
+  printf("  -r, --recursive     Recurse into directories (FastSync is always recursive)\n");
   printf("  -n, --dry-run       Show what would be transferred\n");
   printf("  --remove-source-files  Remove regular source files after successful transfer\n");
-  printf("  -p, --perms         Preserve permission bits (part of the metadata bundle)\n");
+  printf("  -p, --perms         Preserve permission bits\n");
+  printf("  -t, --times         Preserve modification times\n");
+  printf("  -o, --owner         Preserve owner (uid)\n");
+  printf("  -g, --group         Preserve group (gid)\n");
   printf("  --ssh-port <port>   SSH port (default: 22)\n");
   printf("  -e, --rsh <command>  Remote shell to launch on the client for the SSH\n");
   printf("                      transport (default: ssh).  The command may include\n");
@@ -54,24 +59,27 @@ void print_usage(void) {
   printf("                       Emit the batch file only (no destination, no server)\n");
   printf("  --read-batch=FILE     Apply the batch file to the destination (no source, no\n");
   printf("                       server); takes only the destination as an argument\n");
+  printf("  NOTE: the FastSync batch format is NOT interoperable with rsync's batch\n");
+  printf("  files (different container format); do not mix the two tools.\n");
   printf("  --delete            Delete files on receiver not in source\n");
-  printf("                      (default timing: delete only after the whole\n");
-  printf("                      transfer has succeeded)\n");
+  printf("                      (default timing: delete-during, like rsync --del)\n");
   printf("  --delete-before     Delete extras before the transfer starts\n");
   printf("                      (implies --delete)\n");
-  printf("  --delete-during     Delete extras once the keep-set manifest is known,\n");
-  printf("                      before the data is applied (implies --delete)\n");
+  printf("  --delete-during     Delete a directory's extras as that directory is\n");
+  printf("                      processed (implies --delete)\n");
   printf("  --del               Alias for --delete-during\n");
-  printf("  --delete-delay      Delete extras only after a successful transfer\n");
-  printf("                      (implies --delete)\n");
+  printf("  --delete-delay      Record the extras during the scan but remove them\n");
+  printf("                      only after a successful transfer (implies --delete)\n");
   printf("  --delete-after      Delete only after the whole transfer succeeded\n");
-  printf("                      (the default --delete timing; implies --delete)\n");
+  printf("                      (implies --delete)\n");
+  printf("  --delete-commit     FastSync-only: restore the late whole-tree commit\n");
+  printf("                      (identical to --delete-after; implies --delete)\n");
   printf("  --delete-excluded   Also delete destination files that were excluded on\n");
   printf("                      the source (default protects them, matching rsync)\n");
-  printf("  --max-delete=NUM    Never delete more than NUM destination entries per run;\n");
-  printf("                      if the extras would exceed NUM, nothing is deleted and\n");
-  printf("                      the run fails with a clear error (implies --delete only\n");
-  printf("                      when used with it)\n");
+  printf("  --max-delete=NUM    Delete at most NUM destination entries per run; if the\n");
+  printf("                      extras exceed NUM, the rest are skipped and the run is\n");
+  printf("                      reported as partial (exit 25, matching rsync).  Only\n");
+  printf("                      applies together with --delete\n");
   printf("  --ignore-errors     Continue (and still delete) when a source directory is\n");
   printf("                      unreadable during the scan, instead of aborting with no\n");
   printf("                      deletion\n");
@@ -83,10 +91,11 @@ void print_usage(void) {
   printf("                      entry's destination mirror receiver-side.  Independent of\n");
   printf("                      --delete (it does not imply --delete; a non-empty directory\n");
   printf("                      mirror is removed only with --force or --delete)\n");
-  printf("  -m, --prune-empty-dirs  Do not transfer empty directory entries (--dirs mode);\n");
-  printf("                      recursive transfers never send empty dirs\n");
+  printf("  -m, --prune-empty-dirs  Do not create empty directories (a recursive transfer\n");
+  printf("                      otherwise recreates them, like rsync)\n");
   printf("  Note: each timing flag implies --delete.  Combining a timing flag with\n");
-  printf("  --no-delete (in either order) is rejected as a config error.\n");
+  printf("  --no-delete (in either order) is rejected as a config error, as is more\n");
+  printf("  than one timing flag.\n");
   printf("  --ignore-existing  Skip files that already exist on receiver\n");
   printf("  --delay-updates    Put updated files into place only at the end of transfer\n");
   printf("  --dirs, -d, --old-dirs, --old-d  Transfer the named directory entries without\n");
@@ -96,24 +105,28 @@ void print_usage(void) {
   printf("  -R, --relative    With --files-from, preserve each listed entry's relative path\n");
   printf("                    below the destination root instead of mirroring the full\n");
   printf("                    source path (no effect without --files-from)\n");
-  printf("  --no-implied-dirs  With -R --files-from, refuse to place a listed file whose\n");
-  printf("                    parent directory is not itself listed\n");
+  printf("  --no-implied-dirs  With -R, do not apply the source metadata of a listed file's\n");
+  printf("                    implied parent directories (they are still created with\n");
+  printf("                    default attributes)\n");
   printf("  --mkpath          Create the destination root directory on the server when it\n");
   printf("                    does not exist yet\n");
-  printf("  --exclude <pattern> Exclude files matching pattern\n");
-  printf("  --include <pattern> Only include files matching pattern\n");
-  printf("  --exclude-from <file> Read exclude patterns from file\n");
-  printf("  --include-from <file> Read include patterns from file\n");
+  printf("  --exclude <pattern>, --exclude=<pattern>  Exclude files matching pattern\n");
+  printf("  --include <pattern>, --include=<pattern>  Only include files matching pattern\n");
+  printf("  --exclude-from <file>, --exclude-from=<file>  Read exclude patterns from file\n");
+  printf("  --include-from <file>, --include-from=<file>  Read include patterns from file\n");
   printf("  --files-from <file> Read the source file list from FILE (paths relative to the "
          "source root)\n");
   printf("  -0, --from0       Entries in --files-from are NUL-delimited\n");
-  printf("  -f, --filter=RULE rsync-style filter rule (+/- include/exclude; repeatable;\n");
-  printf("                  both --filter=RULE and the -f RULE / -f=RULE short forms work)\n");
+  printf("  -f, --filter=RULE rsync-style filter rule: exclude/- include/+ hide/H show/S\n");
+  printf("                  protect/P risk/R merge/. dir-merge/: clear/! with modifiers\n");
+  printf("                  (repeatable; --filter=RULE and -f RULE / -f=RULE both work)\n");
   printf("  -C, --cvs-exclude Auto-ignore common CVS/SCM files (.git/, .svn/, *.o, *~, ...)\n");
-  printf("  -F                Apply per-directory .rsync-filter files during the scan\n");
+  printf("  -F                Apply per-directory .rsync-filter files; repeated -FF also\n");
+  printf("                  excludes the .rsync-filter files themselves\n");
   printf("  --max-size <n>      Skip files larger than n bytes\n");
   printf("  --min-size <n>      Skip files smaller than n bytes\n");
-  printf("  --max-alloc <SIZE>  Maximum single allocation (default: 1G)\n");
+  printf("  --max-alloc <SIZE>  Maximum single allocation (default: 1G; 0 = no limit,\n");
+  printf("                      matching rsync)\n");
   printf("  --incremental       Skip files unchanged since last transfer\n");
   printf("  --size-only         Skip incremental files matching in size, ignoring mtime\n");
   printf("  -I, --ignore-times  Transfer files even when size and mtime match\n");
@@ -127,21 +140,28 @@ void print_usage(void) {
   printf("                    into the destination instead of transferring its data\n");
   printf("  --link-dest <dir>   Like --copy-dest, but hard-links the unchanged file from DIR\n");
   printf("                    into the destination (repeatable; earlier DIRs win)\n");
+  printf("  --verify-basis      FastSync-only: require a basis hit's content to match the\n");
+  printf("                    source by whole-file digest instead of trusting rsync's\n");
+  printf("                    size+mtime (or --size-only) quick-check\n");
   printf("  --checksum-choice, --cc <alg>  Whole-file checksum algorithm for --incremental/\n");
-  printf("                    --checksum compares (xxh64/xxhash or md5; default xxh64 with\n");
-  printf("                    seed 0).  The seed comes from --checksum-seed\n");
-  printf("  --checksum-seed <num>  Seed for the whole-file xxHash64 digest (and the delta\n");
-  printf("                    block strong hash, low 32 bits); md5 ignores the seed.  The\n");
-  printf("                    digest algorithm and seed must match on sender and receiver\n");
+  printf("                    --checksum compares.  Accepted: xxh128 (default), xxh3, xxh64\n");
+  printf("                    (aka xxhash), md5, md4, sha1, or none.  A two-name\n");
+  printf("                    'transfer,pre-transfer' form is accepted like rsync; 'none' as\n");
+  printf("                    the pre-transfer algorithm is rejected with --checksum\n");
+  printf("  --checksum-seed <num>  Seed for the whole-file xxHash digest (and the delta\n");
+  printf("                    block strong hash, low 32 bits); md5 ignores the seed.  A seed\n");
+  printf("                    of 0 (the default) is randomized per transfer, exactly like\n");
+  printf("                    rsync, and the chosen seed is sent to the receiver\n");
   printf("  --delta             Delta transfer for changed files (requires --incremental)\n");
   printf("  -W, --whole-file    Transfer changed files without delta processing\n");
+  printf("  --no-whole-file     rsync spelling that clears -W/--whole-file\n");
   printf("  -y, --fuzzy         Use a similar-named file already in the destination\n");
   printf("                    directory as the delta basis when the destination has no\n");
   printf("                    usable file at the exact path (saves bandwidth; implies\n");
   printf("                    --incremental and --delta; inert with --whole-file,\n");
   printf("                    --no-delta, or --no-incremental)\n");
   printf("  --no-fuzzy          Disable --fuzzy\n");
-  printf("  --delta-block <n>, --block-size <n>\n");
+  printf("  -B <n>, --block-size <n>, --delta-block <n>\n");
   printf("                    Delta block size in bytes (default: %d)\n", DELTA_BLOCK_SIZE_DEFAULT);
   printf("  --delta-max <n>     Max file size for delta transfer (default: %llu)\n",
          DELTA_MAX_FILE_SIZE);
@@ -152,16 +172,26 @@ void print_usage(void) {
   printf("  --chunk-serialization  Enable chunk serialization (long form only)\n");
   printf("  -s, --secluded-args    Protect-args compatibility option (no effect; remote\n");
   printf("                      SSH argv is already built injection-safe)\n");
-  printf("  --sendfile          Enable sendfile zero-copy (TCP only; long form only)\n");
-  printf("  --compress-choice <alg>  Compression algorithm (default: zstd)\n");
+  printf("  --sendfile          Enable sendfile zero-copy (TCP only; long form only;\n");
+  printf("                      -f is bound to --filter, not --sendfile)\n");
+  printf("  --compress-choice <alg>  Compression algorithm: zstd (default), lz4, zlib,\n");
+  printf("                    zlibx, none, or auto\n");
   printf("  --zc <alg>          Alias for --compress-choice\n");
   printf("  -v, --verbose       Enable debug logging\n");
   printf("  -q, --quiet         Suppress non-error output\n");
   printf("  --debug=FLAGS       Fine-grained debug logging (use --debug=help for flags)\n");
-  printf("  --info=FLAGS        Fine-grained info: copy,misc,skip,stats,all,none\n");
-  printf("                      none suppresses info even with --verbose\n");
-  printf("  --preserve          Preserve file metadata (long form only)\n");
+  printf("  --info=FLAGS        Fine-grained info: copy,name,misc,skip,stats,all,none\n");
+  printf("                      (use --info=help for flags; none suppresses --verbose)\n");
+  printf("  --preserve          Preserve permissions and times (= -pt; long form only)\n");
+  printf("  --no-perms          Negate -p/--perms\n");
+  printf("  --no-times          Negate -t/--times\n");
+  printf("  --no-owner          Negate -o/--owner\n");
+  printf("  --no-group          Negate -g/--group\n");
+  printf("  --no-preserve       Disable metadata preservation (negates --preserve)\n");
   printf("  -E, --executability Preserve executable permission bits\n");
+  printf("  -U, --atimes        Preserve access times\n");
+  printf("  -N, --crtimes       Capture birth time; cannot be applied (documented\n");
+  printf("                      divergence)\n");
   printf("  -X, --xattrs        Preserve user extended attributes (user.* only;\n");
   printf("                      privileged security.*/trusted.* namespaces are\n");
   printf("                      never captured or applied)\n");
@@ -176,28 +206,32 @@ void print_usage(void) {
   printf("                      (char/block device-node creation, --write-devices)\n");
   printf("                      within the confined receive root.  Never elevates\n");
   printf("                      privileges and never bypasses confinement; ownership\n");
-  printf("                      is still applied only with an explicit identity flag\n");
-  printf("                      (--numeric-ids/--chown/--usermap/--groupmap/--copy-as)\n");
+  printf("                      is still applied only with -o/--owner, -g/--group, or an\n");
+  printf("                      explicit identity flag (--chown/--usermap/--groupmap/\n");
+  printf("                      --copy-as); --numeric-ids only changes how ids map\n");
   printf("  --no-super          Forbid those super-user activities even when the\n");
   printf("                      receiver is running as root\n");
-  printf("  --chmod <changes>   Modify transferred permissions (rsync syntax)\n");
-  printf("  --numeric-ids       Do not map uid/gid by name: use the source numeric\n");
-  printf("                      ids directly when applying ownership\n");
+  printf(
+      "  --chmod <changes>   Modify new/transferred permissions (rsync syntax; implies no -p)\n");
+  printf("  --numeric-ids       Map uid/gid by id instead of by name (a modifier, not\n");
+  printf("                      an ownership request: combine with -o/-g or a map)\n");
   printf("  --usermap=MAP       Map usernames when applying ownership: comma-separated\n");
-  printf("                      FROM:TO rules, first match wins.  FROM/TO are names\n");
-  printf("                      (resolved on the source machine), * (match any /\n");
-  printf("                      current user), or @N numeric ids.  e.g. *:nobody\n");
+  printf("                      FROM:TO rules, first match wins.  FROM is a name (from\n");
+  printf("                      the source), an id, an inclusive LOW-HIGH range, *\n");
+  printf("                      (any id), or empty (ids with no name).  TO is an id, *\n");
+  printf("                      (current user), or a name resolved on the receiver.\n");
+  printf("                      e.g. 0-99:nobody,*:normal   (cannot mix with --chown)\n");
   printf("  --groupmap=MAP      Map group names when applying ownership (same syntax)\n");
   printf("  --chown=USER:GROUP  Override the ownership of transferred files.  Forms:\n");
   printf("                      USER:GROUP, USER (owner only), :GROUP (group only); a\n");
   printf("                      value of * means the current/root user as appropriate.\n");
   printf("                      Names resolve on the source machine; @N for numerics.\n");
-  printf("                      (Metadata is enabled with --preserve; -M now means\n");
-  printf("                      rsync's --remote-option.)\n");
+  printf("                      (Implies owner/group metadata; -M now means rsync's\n");
+  printf("                      --remote-option.)\n");
   printf("  --copy-as=USER[:GROUP]  Force every written entry (files, dirs, symlinks\n");
   printf("                      and special nodes) to USER[:GROUP], resolved on the\n");
   printf("                      source machine like --chown.  Requires a privileged\n");
-  printf("                      (root) receiver and implies --preserve; an\n");
+  printf("                      (root) receiver and implies owner/group metadata; an\n");
   printf("                      unprivileged receiver refuses the transfer.  Never\n");
   printf("                      switches process credentials (safe-subset; see\n");
   printf("                      RSYNC_COMPAT.md).  A daemon refuses it.\n");
@@ -209,65 +243,82 @@ void print_usage(void) {
   printf("  --server-port <n>   Server port (default: 8080)\n");
   printf("  --port <n>          Alias for --server-port\n");
   printf("  --password-file <f> Authenticate a host::module/path daemon destination.\n");
-  printf("                      The file's first user:password line supplies the\n");
-  printf("                      username and password (only a SHA-256 digest of the\n");
-  printf("                      password is sent; keep the file mode 0600)\n");
+  printf("                      FastSync-native SCRAM/PBKDF2 credential scheme (NOT\n");
+  printf("                      rsync's --password-file): the file's first user:password\n");
+  printf("                      line supplies the username and password; no password or\n");
+  printf("                      reusable digest is sent (keep the file mode 0600)\n");
   printf("  --no-motd           Suppress display of the daemon's MOTD (the server\n");
   printf("                      still sends it; the client just does not show it)\n");
-  printf("  --bwlimit <KB/s>    Bandwidth limit in kilobytes per second\n");
+  printf("  --bwlimit=RATE      Limit socket I/O bandwidth (default unit KiB/s,\n");
+  printf("                      rsync-style: 0 = no limit; K/M/G/T/P suffixes are\n");
+  printf("                      binary, KB/MB decimal, KiB/MiB binary; decimals allowed)\n");
   printf("  --tls               Enable TLS encryption\n");
   printf("  --cert <path>       TLS certificate file (PEM)\n");
   printf("  --key <path>        TLS private key file (PEM)\n");
   printf("  --ca <path>         TLS CA certificate file (PEM)\n");
-  printf("  --timeout <sec>     I/O timeout in seconds (default: 30; long form only)\n");
-  printf("  --contimeout <sec>  Connection timeout in seconds (default: 10)\n");
+  printf("  --timeout <sec>     I/O timeout in seconds (default: 0 = disabled, matching\n");
+  printf("                      rsync).  0 disables it; --no-timeout is the same\n");
+  printf("  --contimeout <sec>  Connection timeout in seconds (default: 60, matching\n");
+  printf("                      rsync); 0 disables it (--no-contimeout)\n");
   printf("  --stop-after=MINS   Stop the transfer after MINS minutes (a positive\n");
   printf("                      integer); whatever was already transferred is kept\n");
-  printf("  --stop-at=TIME      Stop at an absolute time: HH:MM, HH:MM:SS, or\n");
-  printf("                      now+N[smhd] (a time already in the past stops the\n");
-  printf("                      transfer immediately; client-only).  An early stop\n");
-  printf("                      skips the late --delete keep-set so it cannot delete\n");
-  printf("                      source mirrors that were not yet scanned\n");
+  printf("  --stop-at=TIME      Stop at an absolute time.  Accepts rsync's date form\n");
+  printf("                      (Y-M-DTh:m, Y/M/DTh:m, abbreviable fields such as 12-31,\n");
+  printf("                      14:00, :59, 1) plus FastSync's HH:MM[:SS] and now+N[smhd]\n");
+  printf("                      (a time already in the past stops the transfer\n");
+  printf("                      immediately; client-only).  An early stop skips the late\n");
+  printf("                      --delete keep-set so it cannot delete source mirrors that\n");
+  printf("                      were not yet scanned\n");
   printf("  --address <ip>      Bind the outgoing client socket to this source address\n");
   printf("  -4, --ipv4          Force IPv4 for destination resolution\n");
   printf("  -6, --ipv6          Force IPv6 for destination resolution\n");
   printf("  --sockopts=OPTS     Comma-separated OPT=VAL socket options applied before connect:\n");
   printf("                      TCP_NODELAY, SO_KEEPALIVE, SO_RCVBUF, SO_SNDBUF, SO_REUSEADDR\n");
-  printf("  --backup            Backup existing files before overwriting\n");
+  printf("  -b, --backup        Backup existing files before overwriting\n");
   printf("  --backup-dir <dir>  Directory for backups (requires --backup)\n");
   printf("  --suffix <str>      Backup suffix (default: ~)\n");
   printf("  --stats             Print transfer statistics at end\n");
   printf("  -i, --itemize-changes  Print an rsync-style per-file change line\n");
-  printf("  --out-format=FORMAT Output format for changed files (%%f %%n %%l %%b %%M %%%%)\n");
+  printf("  --out-format=FORMAT Output format (%%f %%n %%l %%b %%c %%C %%i %%M %%%%)\n");
   printf("  --list-only         List source files instead of transferring\n");
   printf("  --log-file-format=FORMAT  Per-file log line format (needs --log-file)\n");
   printf("  -h, --human-readable  Print byte sizes in human-readable form\n");
   printf("  --max-depth <n>     Maximum directory depth (0=unlimited)\n");
   printf("  -x, --one-file-system  Do not cross filesystem boundaries\n");
-  printf("  --log-file <path>   Write log messages to file\n");
+  printf("  --log-file <path>, --log-file=<path>  Write log messages to file\n");
   printf("  --stderr=MODE       Route logging to stderr: errors or all\n");
   printf("  --partial           Keep partial files on interrupted transfer\n");
   printf("  --partial-dir <dir> Directory for partial files\n");
-  printf("  -T, --temp-dir <dir>  Scratch dir for temp files before atomic install\n");
+  printf("  -T, --temp-dir <dir>  Scratch dir for temp files before atomic install.\n");
+  printf("                      Confined to the receive root: a relative dir resolves below\n");
+  printf("                      it and an absolute/traversal dir is rejected.  The dir must\n");
+  printf("                      already exist; a different filesystem falls back to a\n");
+  printf("                      non-atomic copy instead of aborting\n");
   printf("  --fastsync-server-path <path>\n");
   printf("                      Path to fastsync-server on remote (default: fastsync-server)\n");
   printf("  --old-args          Accepted for rsync CLI compatibility; no effect (the\n");
   printf("                      remote server path is always safely quoted now)\n");
-  printf("  -M, --remote-option=OPT  Append OPT to the REMOTE server invocation over SSH\n");
-  printf("                      (repeatable; each value is single-quote-escaped on the remote\n");
-  printf("                      command line; empty values and values with control characters\n");
-  printf("                      are rejected; -M OPT, -M=OPT and --remote-option=OPT work)\n");
-  printf("  --trust-sender      Trust the remote sender's file list: the receiver skips its\n");
-  printf("                      own up-front path-traversal/containment re-validation of the\n");
-  printf("                      incoming file list (fewer checks, faster, potentially unsafe).\n");
-  printf("                      Local receiver policy: never sent to the peer, off by default\n");
+  printf("  -M, --remote-option=OPT  Append OPT to the REMOTE server invocation.  SSH\n");
+  printf("                      transport ONLY (user@host:path): a daemon (host::module) or\n");
+  printf("                      local TCP destination rejects it (no remote command line to\n");
+  printf("                      append to).  Repeatable; each value is single-quote-escaped on\n");
+  printf("                      the remote command line; empty values and values with control\n");
+  printf("                      characters are rejected; -M OPT, -M=OPT and\n");
+  printf("                      --remote-option=OPT work\n");
+  printf("  --trust-sender      RECEIVER-LOCAL policy: trust the remote sender's file list\n");
+  printf("                      and skip the receiver's own up-front path-traversal/\n");
+  printf("                      containment re-validation of the incoming list (fewer checks,\n");
+  printf("                      faster, potentially unsafe).  It is never sent to the peer, so\n");
+  printf("                      for a push it must be enabled on the receiving SERVER\n");
+  printf("                      (fastsync-server --trust-sender) or forwarded with\n");
+  printf("                      -M--trust-sender; the client flag alone has no effect\n");
   printf("  -l, --links         Copy symlinks as symlinks\n");
-  printf("  --copy-links        Transform symlinks into referent files\n");
-  printf("  --safe-links        Skip symlinks that point outside transfer tree\n");
-  printf("  --copy-unsafe-links  Only transform unsafe symlinks into referent files\n");
+  printf("  -L, --copy-links    Transform symlinks into referent files\n");
+  printf("  --safe-links        Skip symlinks whose target points outside the tree\n");
+  printf("  --copy-unsafe-links Copy unsafe symlinks (outside tree) as referent files\n");
   printf("  -k, --copy-dirlinks Transform symlinks to directories into real dirs\n");
   printf("  -K, --keep-dirlinks  Keep an existing symlink-to-dir as that dir\n");
-  printf("  --munge-links       Munge symlink targets on the wire (sender)\n");
+  printf("  --munge-links       Munge stored symlink targets (/rsyncd-munged/) on the receiver\n");
   printf("  -H, --hard-links    Preserve hard-link relationships across the transfer\n");
   printf("  -S, --sparse        Handle sparse files efficiently\n");
   printf(
@@ -275,8 +326,7 @@ void print_usage(void) {
   printf(
       "  --devices           Recreate device nodes on the destination (privileged; skipped when\n");
   printf("                      the receiver lacks CAP_MKNOD)\n");
-  printf("  --specials          Recreate special files (FIFOs) on the destination (sockets "
-         "skipped)\n");
+  printf("  --specials          Recreate special files (FIFOs, sockets) on the destination\n");
   printf("  --copy-devices      Copy a source device's content as a regular file instead\n");
   printf("  --write-devices     Write received data into an existing destination device node\n");
   printf("  --inplace           Update files in-place (no temp+rename)\n");
@@ -289,7 +339,9 @@ void print_usage(void) {
   printf("  --fsync             Fsync every written file before publication\n");
   printf("  --compress-level <n>    Compression level (default: 5)\n");
   printf("  --zl <n>             Alias for --compress-level\n");
-  printf("  --skip-compress=LIST    Skip compression for comma-separated suffixes\n");
+  printf("  --skip-compress=LIST    Skip compression for suffixes in LIST (separated by\n");
+  printf("                      '/' as in rsync, or ','); a leading dot is optional.  The\n");
+  printf("                      default is rsync 3.4.1's built-in skip-compress list\n");
   printf("  --compress-threads <n> Compression worker threads (requires zstd threaded support)\n");
   printf("  --no-OPTION         Disable a supported boolean option\n");
   printf("  --help              Show this help\n");
@@ -297,7 +349,20 @@ void print_usage(void) {
 }
 
 void print_debug_usage(void) {
-  printf("Supported debug flags: IO,PROTO,PACK,UTIL,ALL,NONE\n");
+  printf("Emitting debug flags: IO,PROTO,PACK,UTIL,ALL,NONE\n");
+  printf("Also accepted for rsync CLI parity (silent): ACL,BACKUP,BIND,CHDIR,\n");
+  printf("CONNECT,CMD,DEL,DELTASUM,DUP,EXIT,FILTER,FLIST,FUZZY,GENR,HASH,HLINK,\n");
+  printf("ICONV,NSTR,OWN,RECV,SEND,TIME.\n");
   printf("Flags may be comma-separated, for example: --debug=io,proto\n");
-  printf("Other rsync debug flags are unsupported and rejected.\n");
+  printf("An optional level suffix is accepted (e.g. --debug=io2); level 0\n");
+  printf("silences that item.  Unknown names are rejected.\n");
+}
+
+void print_info_usage(void) {
+  printf("Emitting info flags: COPY,NAME,MISC,SKIP,STATS,ALL,NONE\n");
+  printf("Also accepted for rsync CLI parity (silent): BACKUP,DEL,FLIST,MOUNT,\n");
+  printf("NONREG,PROGRESS,REMOVE,SYMSAFE.\n");
+  printf("Flags may be comma-separated, for example: --info=name,stats\n");
+  printf("An optional level suffix is accepted (e.g. --info=stats2); level 0\n");
+  printf("silences that item.  Unknown names are rejected.\n");
 }

src/client/usage.h

@@ -3,5 +3,6 @@
 
 void print_usage(void);
 void print_debug_usage(void);
+void print_info_usage(void);
 
 #endif

src/server/receiver.c

@@ -3,6 +3,7 @@
 #include "charset.h"
 #include "chunk.h"
 #include "config.h"
+#include "delete_plan.h"
 #include "delay_updates.h"
 #include "file.h"
 #include "file_receive.h"
@@ -11,6 +12,7 @@
 #include "protocol.h"
 #include "utils.h"
 #include <stdlib.h>
+#include <string.h>
 #include <sys/stat.h>
 #include <time.h>
 
@@ -43,17 +45,73 @@ void receiver_outcomes_destroy(ReceiverOutcomes* outcomes) {
 /* End-of-transfer success frame.  When --remove-source-files was negotiated
    each processed data file is acknowledged first (STATUS_NEXT = written,
    STATUS_OK = skipped) so the sender never removes a source the receiver did
-   not actually store.  The frame always ends with a plain STATUS_OK. */
-bool receiver_send_final_success(int fd, const Config* config, const ReceiverOutcomes* outcomes) {
+   not actually store.  The frame ends with `final_status` (STATUS_OK, or
+   STATUS_DELETE_LIMIT when a --max-delete commit was capped). */
+bool receiver_send_final_success(int fd, const Config* config, const ReceiverOutcomes* outcomes,
+                                 Status final_status) {
   if (!config->remove_source_files)
-    return send_status(fd, STATUS_OK);
+    return send_status(fd, final_status);
   size_t count = outcomes ? outcomes->count : 0;
   for (size_t i = 0; i < count; i++) {
     Status per_file = outcomes->entries[i] == FILE_SAVE_WRITTEN ? STATUS_NEXT : STATUS_OK;
     if (!send_status(fd, per_file))
       return false;
   }
-  return send_status(fd, STATUS_OK);
+  return send_status(fd, final_status);
+}
+
+bool receiver_send_stats_frame(int fd, const Config* config, const ReceiverStats* stats,
+                               const struct ArrayList* would_delete,
+                               const struct ArrayList* deleted_paths) {
+  if (!config->report_stats)
+    return true;
+  ReceiverStats local;
+  memset(&local, 0, sizeof(local));
+  const ReceiverStats* out = stats ? stats : &local;
+  /* The path list carries the dry-run would-delete set for a -n run and the
+     actually-removed set for a real --info=del run. */
+  const struct ArrayList* paths =
+      config->dry_run ? would_delete : (config->report_deletes ? deleted_paths : NULL);
+  size_t count = paths ? (size_t)paths->size : 0;
+  if (count > (size_t)MAX_MANIFEST_ENTRIES)
+    count = MAX_MANIFEST_ENTRIES;
+  ReceiverStats record = *out;
+  record.would_delete_count = count;
+  if (!send_status(fd, STATUS_STATS) || !format_stats_send(fd, &record) ||
+      !send_int(fd, (int)count))
+    return false;
+  for (size_t i = 0; i < count; i++) {
+    const char* path = (const char*)paths->items[i];
+    if (!send_wire_str(fd, path ? path : ""))
+      return false;
+  }
+  return true;
+}
+
+/* Add a delete commit's tally to the sink's end-of-transfer wire counters (when
+   the sink reports them).  Runs on the receiving thread, so no locking. */
+static void receiver_tally_deleted(const ReceiverSink* sink, size_t deleted) {
+  if (sink && sink->stats && deleted > 0)
+    sink->stats->deleted_files += deleted;
+}
+
+/* Observer for --info=del: record each truly-removed destination-relative path
+   in the ArrayList passed as the observer context, so the terminal STATUS_STATS
+   frame can list it.  A failed append is best-effort (the deletion already
+   happened; output is cosmetic).  Shared by the single-threaded receiver and
+   the -m pipeline's deferred commit. */
+void receiver_record_deleted_path(void* context, const char* rel_path) {
+  ArrayList* paths = context;
+  if (!paths || !rel_path)
+    return;
+  /* Bound the retained list like the keep-set manifest: only MAX_MANIFEST_ENTRIES
+     paths are ever transmitted in the terminal STATUS_STATS frame, so recording
+     more only grows memory.  A hostile/huge deletion set is therefore capped. */
+  if ((size_t)paths->size >= (size_t)MAX_MANIFEST_ENTRIES)
+    return;
+  char* copy = str_dup(rel_path);
+  if (copy && !array_list_add(paths, copy))
+    free(copy);
 }
 
 static bool receiver_process_chunk(Chunk* chunk, const ReceiverSink* sink) {
@@ -242,21 +300,23 @@ static bool receiver_note_status(const struct timespec* session_start,
 }
 
 int receiver_process(Config* config, int file_descriptor, const ReceiverSink* sink) {
-  return receiver_process_pending(config, file_descriptor, sink, NULL);
+  return receiver_process_pending(config, file_descriptor, sink, NULL, NULL);
 }
 
 /* Runs the whole receive loop.  The delete manifest may legitimately arrive
    either FIRST (--delete-before / --delete-during: the sender transmits the
-   validated keep-set before any file data) or LAST (plain --delete /
-   --delete-after / --delete-delay: the manifest closes the data stream).  In
+   validated keep-set before any file data) or LAST (--delete-after /
+   --delete-commit / --delete-delay: the manifest closes the data stream).  In
    the early modes the receiver deletes as soon as the manifest has been read
    and acknowledges with STATUS_OK so the sender only starts streaming once the
    deletion has committed (or failed); in the late modes the manifest is held
    and the deletion is committed only after the terminal STATUS_FINISHED proves
-   the whole transfer succeeded.  See receiver_process_pending() for how the -m
-   receiver defers that commit until its disk writer has drained. */
+   the whole transfer succeeded.  A plain --delete defaults to the per-directory
+   delete-during plan mode (no manifest at all).  See
+   receiver_process_pending() for how the -m receiver defers that commit until
+   its disk writer has drained. */
 int receiver_process_pending(Config* config, int file_descriptor, const ReceiverSink* sink,
-                             DeleteManifest** pending_manifest) {
+                             DeleteManifest** pending_manifest, DeletePlanSession** pending_plans) {
   Status status;
   if (!receive_status(file_descriptor, &status))
     return -1;
@@ -270,14 +330,22 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
   if (!receiver_note_status(&session_start, &last_progress, status, file_descriptor, sink))
     return -1;
   bool early_delete = config_delete_timing_early(config);
+  bool per_dir_delete = config_delete_timing_per_dir(config);
   /* Parked keep-set for the late/commit timing.  Every exit path below frees it
      exactly once; the only exception is the successful FINISHED handoff, which
      transfers ownership to *pending_manifest (used by the -m receiver). */
   DeleteManifest* deferred_manifest = NULL;
+  /* Per-directory delete session for --delete-during/--delete-delay.  During the
+     loop it applies plans inline (during) or snapshots their extras (delay); on
+     a successful FINISHED it is either committed here or handed to
+     *pending_plans so the -m caller commits after its disk writer drained. */
+  DeletePlanSession* plan_session = NULL;
+  bool delete_limit_noted = false;
   while (status == STATUS_NEXT || status == STATUS_CHUNK || status == STATUS_CHECK ||
          status == STATUS_KEEPALIVE || status == STATUS_ABORT || status == STATUS_CHECK_BATCH ||
          status == STATUS_MKDIR || status == STATUS_MANIFEST || status == STATUS_HARDLINK ||
-         status == STATUS_SYMLINK || status == STATUS_SPECIAL || status == STATUS_DIR_TIMES) {
+         status == STATUS_SYMLINK || status == STATUS_SPECIAL || status == STATUS_DIR_TIMES ||
+         status == STATUS_DELETE_PLAN) {
     if (status == STATUS_KEEPALIVE) {
       if (!send_status(file_descriptor, STATUS_KEEPALIVE))
         goto fail;
@@ -335,32 +403,48 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
       if (config->dry_run) {
         /* Server-contacting --dry-run mutates nothing, so a keep-set manifest
            is consumed and discarded.  The early-delete mode still needs its ACK
-           so a sender blocked on the delete handshake is not left hanging. */
+           so a sender blocked on the delete handshake is not left hanging.
+           When would-delete reporting is armed, enumerate (read-only) the
+           destination extras so the terminal STATUS_STATS frame can list them. */
+        if (config->use_delete && sink->would_delete) {
+          size_t count = 0;
+          if (!manifest_would_delete_list(config, manifest, sink->would_delete, &count))
+            log_message(LOG_LEVEL_WARNING, "dry-run: could not enumerate would-delete paths");
+        }
         delete_manifest_free(manifest);
         if (early_delete && !send_status(file_descriptor, STATUS_OK))
           goto fail;
         goto next_status;
       }
       if (early_delete) {
-        /* --delete-before / --delete-during: the manifest is authoritative the
-           moment it arrives, before any file data.  Delete now and acknowledge
-           so the sender only starts streaming once the deletion committed (or
-           failed).  This is the rsync delete-before/delete-during window: a
-           later transfer failure does not restore these deletions. */
-        bool deletion_ok = (config->use_delete || config->delete_missing_args)
-                               ? manifest_delete_all(config, manifest)
-                               : true;
+        /* --delete-before: the whole-tree manifest is authoritative the moment
+           it arrives, before any file data.  Delete now and acknowledge so the
+           sender only starts streaming once the deletion committed (or failed).
+           A later transfer failure does not restore these deletions.  A
+           --max-delete-capped commit still succeeds and the transfer proceeds;
+           the terminal success frame reports the cap. */
+        size_t deleted = 0;
+        DeletePathObserver observer =
+            (config->report_deletes && sink->deleted_paths) ? receiver_record_deleted_path : NULL;
+        DeleteCommitResult deletion =
+            (config->use_delete || config->delete_missing_args)
+                ? manifest_delete_all_observed(config, manifest, &deleted, observer,
+                                               (void*)sink->deleted_paths)
+                : DELETE_COMMIT_OK;
+        receiver_tally_deleted(sink, deleted);
         delete_manifest_free(manifest);
-        if (!deletion_ok) {
+        if (deletion == DELETE_COMMIT_ERROR) {
           send_status(file_descriptor, STATUS_ERROR);
           goto fail;
         }
+        if (deletion == DELETE_COMMIT_LIMIT_REACHED && sink->note_delete_limit)
+          sink->note_delete_limit(sink->context);
         if (!send_status(file_descriptor, STATUS_OK))
           goto fail;
       } else if (config->use_delete || config->delete_missing_args) {
-        /* Plain --delete / --delete-after / --delete-delay and the
-           --delete-missing-args exact-path deletions: hold the manifest and
-           commit it only after STATUS_FINISHED. */
+        /* Plain --delete / --delete-after and the --delete-missing-args
+           exact-path deletions: hold the manifest and commit it only after
+           STATUS_FINISHED.  The per-directory modes never send this frame. */
         if (deferred_manifest) {
           log_message(LOG_LEVEL_ERROR, "Received a second delete manifest");
           delete_manifest_free(deferred_manifest);
@@ -374,6 +458,27 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
         delete_manifest_free(manifest);
       }
       goto next_status;
+    } else if (status == STATUS_DELETE_PLAN) {
+      if (!per_dir_delete) {
+        log_message(LOG_LEVEL_ERROR, "Received a per-directory delete plan without a per-dir "
+                                     "delete timing");
+        send_status(file_descriptor, STATUS_ERROR);
+        goto fail;
+      }
+      if (!plan_session) {
+        plan_session = delete_plan_session_create(config);
+        if (plan_session && config->report_deletes && sink->deleted_paths)
+          delete_plan_session_set_delete_observer(plan_session, receiver_record_deleted_path,
+                                                  (void*)sink->deleted_paths);
+      }
+      if (!plan_session || delete_plan_session_receive(plan_session, config, file_descriptor) != 0)
+        goto fail;
+      if (delete_plan_session_limit_reached(plan_session) && !delete_limit_noted &&
+          sink->note_delete_limit) {
+        sink->note_delete_limit(sink->context);
+        delete_limit_noted = true;
+      }
+      goto next_status;
     } else {
       File* file = file_receive(config, file_descriptor);
       if (!file) {
@@ -407,13 +512,50 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
       *pending_manifest = deferred_manifest;
       deferred_manifest = NULL;
     } else {
-      bool deletion_ok = manifest_delete_all(config, deferred_manifest);
+      size_t deleted = 0;
+      DeletePathObserver observer =
+          (config->report_deletes && sink->deleted_paths) ? receiver_record_deleted_path : NULL;
+      DeleteCommitResult deletion = manifest_delete_all_observed(
+          config, deferred_manifest, &deleted, observer, (void*)sink->deleted_paths);
+      receiver_tally_deleted(sink, deleted);
       delete_manifest_free(deferred_manifest);
       deferred_manifest = NULL;
-      if (!deletion_ok) {
+      if (deletion == DELETE_COMMIT_ERROR) {
         send_status(file_descriptor, STATUS_ERROR);
         goto fail;
       }
+      if (deletion == DELETE_COMMIT_LIMIT_REACHED && sink->note_delete_limit)
+        sink->note_delete_limit(sink->context);
+    }
+  }
+  /* Per-directory deletion: --delete-during already applied each plan inline, so
+     this only finishes the missing-args deletions; --delete-delay committed
+     nothing yet and applies its decompressed snapshot here.  The -m receiver
+     hands the session to its caller instead, which commits after the disk
+     writer drained. */
+  if (plan_session) {
+    if (config->report_deletes && sink->deleted_paths)
+      delete_plan_session_set_delete_observer(plan_session, receiver_record_deleted_path,
+                                              (void*)sink->deleted_paths);
+    if (pending_plans) {
+      *pending_plans = plan_session;
+      plan_session = NULL;
+    } else if (config->dry_run) {
+      /* Central dry-run no-op: never commit a deletion for a -n run. */
+      delete_plan_session_destroy(plan_session);
+      plan_session = NULL;
+    } else {
+      DeleteCommitResult deletion = delete_plan_session_commit(plan_session, config);
+      bool limit = delete_plan_session_limit_reached(plan_session);
+      receiver_tally_deleted(sink, delete_plan_session_deleted(plan_session));
+      delete_plan_session_destroy(plan_session);
+      plan_session = NULL;
+      if (deletion == DELETE_COMMIT_ERROR) {
+        send_status(file_descriptor, STATUS_ERROR);
+        goto fail;
+      }
+      if (limit && !delete_limit_noted && sink->note_delete_limit)
+        sink->note_delete_limit(sink->context);
     }
   }
   if (sink->send_success) {
@@ -428,11 +570,14 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
 
 fail:
   /* Failure exits that must not (or already did) report a STATUS_ERROR.  The
-     parked keep-set is dropped: never commit a deletion for a failed stream. */
+     parked keep-set/session is dropped: never commit a deletion for a failed
+     stream. */
   if (deferred_manifest) {
     delete_manifest_free(deferred_manifest);
     deferred_manifest = NULL;
   }
+  if (plan_session)
+    delete_plan_session_destroy(plan_session);
   return -1;
 
 receive_error:
@@ -440,6 +585,8 @@ receive_error:
     delete_manifest_free(deferred_manifest);
     deferred_manifest = NULL;
   }
+  if (plan_session)
+    delete_plan_session_destroy(plan_session);
   if (sink->send_error)
     send_status(file_descriptor, STATUS_ERROR);
   return -1;
@@ -454,11 +601,22 @@ typedef struct {
      after the whole transfer (and its delete/publication phases) has run so a
      child write never clobbers a directory mtime. */
   DirTimeList dir_times;
+  /* Set when a --max-delete commit was capped; the terminal frame then carries
+     STATUS_DELETE_LIMIT so the sender exits 25 like rsync. */
+  bool delete_limit_reached;
+  /* End-of-transfer wire counters (protocol 2.25.0) and the -n/--dry-run
+     --delete would-delete path list collected while processing the manifest. */
+  ReceiverStats stats;
+  ArrayList* would_delete;
+  /* --info=del: actually-removed paths collected during the delete commit. */
+  ArrayList* deleted_paths;
 } ReceiverSaveContext;
 
 static bool receiver_save_file(File* file, void* context_pointer) {
   ReceiverSaveContext* context = context_pointer;
   FileSaveResult result = FILE_SAVE_ERROR;
+  bool created = false;
+  unsigned created_dirs = 0;
   if (context->config->dry_run) {
     /* Defense in depth: a dry-run receiver mutates nothing even if a data
        frame reaches the sink (the sender is not supposed to send one). */
@@ -468,14 +626,24 @@ static bool receiver_save_file(File* file, void* context_pointer) {
        --remove-source-files sender keeps its source. */
     result = FILE_SAVE_SKIPPED;
   } else {
-    result = file_save_to_disk_full(context->config->receive_root_directory, file, context->config);
+    result = file_save_to_disk_full_ex(context->config->receive_root_directory, file,
+                                       context->config, &created, &created_dirs);
   }
-  /* A directory's times are deferred, never applied inline: collect the
-     metadata now and apply it at the end.  -O/--omit-dir-times is honored by
-     dir_time_list_apply's caller (see receiver_send_success_frame). */
+  /* Wire-stats tally: bytes reconstructed from the basis file (delta matches)
+     count as matched data in the end-of-transfer report. */
+  if (result != FILE_SAVE_ERROR && file->matched_bytes > 0)
+    context->stats.matched_data += file->matched_bytes;
+  /* Protocol 2.28.0: receiver-observed literal bytes and the created-entry
+     breakdown (regular/dir/link/special) for the `--stats` report. */
+  if (result == FILE_SAVE_WRITTEN)
+    receiver_stats_note_saved(&context->stats, file, created, created_dirs);
+  /* A directory's metadata is deferred, never applied inline: collect it now
+     and apply it at the end.  -O/--omit-dir-times and --preserve_perms/-times
+     are honored by dir_metadata_list_apply's caller (see
+     receiver_send_success_frame). */
   if (result != FILE_SAVE_ERROR && file->is_dir && file->metadata &&
-      dir_times_should_capture(context->config) &&
-      !dir_time_list_add(&context->dir_times, file->path, file->metadata)) {
+      dir_metadata_should_capture(context->config) &&
+      !dir_time_list_add(&context->dir_times, file->path, file->metadata, file->xattrs)) {
     file_destroy(file);
     return false;
   }
@@ -493,12 +661,21 @@ static bool receiver_save_file(File* file, void* context_pointer) {
   return result != FILE_SAVE_ERROR;
 }
 
+static void receiver_note_delete_limit(void* context_pointer) {
+  ReceiverSaveContext* context = context_pointer;
+  context->delete_limit_reached = true;
+}
+
 static bool receiver_send_success_frame(int fd, void* context_pointer) {
   ReceiverSaveContext* context = context_pointer;
+  Status final_status = context->delete_limit_reached ? STATUS_DELETE_LIMIT : STATUS_OK;
+  if (!receiver_send_stats_frame(fd, context->config, &context->stats, context->would_delete,
+                                 context->deleted_paths))
+    return false;
   /* Server-contacting --dry-run: nothing was staged or written, so there is
      nothing to publish and no directory times to stamp. */
   if (context->config->dry_run)
-    return receiver_send_final_success(fd, context->config, &context->outcomes);
+    return receiver_send_final_success(fd, context->config, &context->outcomes, final_status);
   /* --delay-updates: the whole protocol stream (including manifest/delete
      handling, which ran inside receiver_process) has succeeded and every
      staged file was fully written.  Publish them atomically now, before the
@@ -514,18 +691,39 @@ static bool receiver_send_success_frame(int fd, void* context_pointer) {
      phases have committed, so it is finally safe to stamp directory times.
      This runs after the deferred deletion because receiver_process commits it
      before calling this success frame. */
-  dir_time_list_apply(&context->dir_times, context->config->receive_root_directory);
-  return receiver_send_final_success(fd, context->config, &context->outcomes);
+  dir_metadata_list_apply(&context->dir_times, context->config->receive_root_directory,
+                          context->config);
+  return receiver_send_final_success(fd, context->config, &context->outcomes, final_status);
 }
 
 int receiver_receive_files(Config* config, int file_descriptor) {
   ReceiverSaveContext context = {.config = config, .outcomes = {0}};
   dir_time_list_init(&context.dir_times);
-  ReceiverSink sink = {receiver_save_file, &context, true, true, receiver_send_success_frame};
+  context.would_delete = array_list_create(free);
+  /* report_deletes (--info=del / -i / --out-format under --delete) is the only
+     reason to retain the actually-removed paths; a plain --delete must not
+     str_dup every removal.  NULL is handled by every consumer. */
+  context.deleted_paths = config->report_deletes ? array_list_create(free) : NULL;
+  if (!context.would_delete || (config->report_deletes && !context.deleted_paths)) {
+    array_list_delete(context.would_delete);
+    array_list_delete(context.deleted_paths);
+    return -1;
+  }
+  ReceiverSink sink = {receiver_save_file,
+                       &context,
+                       true,
+                       true,
+                       receiver_send_success_frame,
+                       receiver_note_delete_limit,
+                       &context.stats,
+                       context.would_delete,
+                       context.deleted_paths};
   int ret = receiver_process(config, file_descriptor, &sink);
   if (ret != 0 && config->delay_updates && config->delay_context)
     delay_updates_cleanup(config->delay_context);
   receiver_outcomes_destroy(&context.outcomes);
   dir_time_list_free(&context.dir_times);
+  array_list_delete(context.would_delete);
+  array_list_delete(context.deleted_paths);
   return ret;
 }

src/server/receiver.h

@@ -2,8 +2,10 @@
 #define RECEIVER_H
 
 #include "config.h"
+#include "delete_plan.h"
 #include "file.h"
 #include "file_receive.h"
+#include "protocol.h"
 #include <stdbool.h>
 #include <time.h>
 
@@ -21,6 +23,12 @@ typedef struct {
 
 typedef bool (*ReceiverSuccessFrame)(int fd, void* context);
 
+/* Records that a --max-delete commit stopped with extras left over, so the
+   caller's terminal success frame can carry STATUS_DELETE_LIMIT instead of
+   STATUS_OK.  The commit runs on the receiver thread, so the flag is stored in
+   the sink's own context rather than in a shared global. */
+typedef void (*ReceiverNoteDeleteLimit)(void* context);
+
 typedef struct {
   ReceiverFileSink store_file;
   void* context;
@@ -28,23 +36,53 @@ typedef struct {
   bool send_success;
   /* Emits the end-of-transfer success frame.  When the sender requested
      --remove-source-files this includes one per-file status per processed
-     data file followed by the final STATUS_OK; otherwise just STATUS_OK. */
+     data file followed by the final status; otherwise just the final status. */
   ReceiverSuccessFrame send_success_frame;
+  /* Optional; may be NULL when the sink has no --max-delete handling. */
+  ReceiverNoteDeleteLimit note_delete_limit;
+  /* Optional end-of-transfer wire counters (protocol 2.25.0).  When non-NULL
+     and the wire config carries report_stats, the success frame is preceded by
+     a STATUS_STATS record; `would_delete` (optional, receiver-owned strings)
+     carries the -n/--dry-run --delete path list. */
+  ReceiverStats* stats;
+  struct ArrayList* would_delete;
+  /* When --info=del requested it, receiver-owned strings for every path the
+     deletion commit ACTUALLY removed, sent in the terminal STATUS_STATS frame's
+     path list so the sender can print rsync's `deleting PATH` lines. */
+  struct ArrayList* deleted_paths;
 } ReceiverSink;
 
 bool receiver_outcomes_append(ReceiverOutcomes* outcomes, unsigned char code);
 void receiver_outcomes_destroy(ReceiverOutcomes* outcomes);
-bool receiver_send_final_success(int fd, const Config* config, const ReceiverOutcomes* outcomes);
+
+/* DeletePathObserver implementation for --info=del: `context` is an ArrayList*
+   that receives owned copies of every truly-removed destination-relative path.
+   Shared by the single-threaded receiver and the -m pipeline's deferred commit. */
+void receiver_record_deleted_path(void* context, const char* rel_path);
+
+/* Send the terminal success frame.  `final_status` is usually STATUS_OK, or
+   STATUS_DELETE_LIMIT when a --max-delete commit was capped. */
+bool receiver_send_final_success(int fd, const Config* config, const ReceiverOutcomes* outcomes,
+                                 Status final_status);
+
+/* Emit STATUS_STATS (a fixed ReceiverStats record plus, when `would_delete` is
+   non-NULL, a count and that many wire strings) when the wire config requested
+   report_stats.  A no-op otherwise. */
+bool receiver_send_stats_frame(int fd, const Config* config, const ReceiverStats* stats,
+                               const struct ArrayList* would_delete,
+                               const struct ArrayList* deleted_paths);
 
 int receiver_process(Config* config, int file_descriptor, const ReceiverSink* sink);
 /* receiver_process with an escape hatch for the commit-style (late) deletion:
    when `pending_manifest` is non-NULL the receiver does NOT delete at
    STATUS_FINISHED itself; instead it stores the owned keep-set manifest there
    (leaving *pending_manifest untouched on early modes/errors) so the caller can
-   commit the deletion only after its disk writer has fully drained.  Pass NULL
-   to keep the default behaviour (delete before the success frame). */
+   commit the deletion only after its disk writer has fully drained.  Likewise,
+   when `pending_plans` is non-NULL the --delete-delay per-directory session is
+   handed to the caller instead of being committed at STATUS_FINISHED.  Pass NULL
+   for either to keep the default behaviour (delete before the success frame). */
 int receiver_process_pending(Config* config, int file_descriptor, const ReceiverSink* sink,
-                             DeleteManifest** pending_manifest);
+                             DeleteManifest** pending_manifest, DeletePlanSession** pending_plans);
 int receiver_receive_files(Config* config, int file_descriptor);
 
 /* ---- Connection time bounds (anti-slowloris) ----

src/server/receiver_pipeline.c

@@ -27,6 +27,11 @@ PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue*
   context->queued_bytes = 0;
   context->max_queue_bytes = 0;
   context->deferred_manifest = NULL;
+  context->deferred_plans = NULL;
+  context->delete_limit_reached = false;
+  memset(&context->stats, 0, sizeof(context->stats));
+  context->would_delete = NULL;
+  context->deleted_paths = NULL;
   atomic_init(&context->cancelled, false);
   int init = 0;
   if (mtx_init(&context->mutex, mtx_plain) != thrd_success)
@@ -39,6 +44,18 @@ PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue*
     goto fail;
   // cppcheck-suppress unreadVariable
   init++;
+  context->would_delete = array_list_create(free);
+  if (!context->would_delete)
+    goto fail;
+  /* The actually-removed path list is only needed to render rsync's
+     `deleting PATH` lines, which the client requests via report_deletes
+     (--info=del / -i / --out-format under --delete).  A plain --delete run must
+     not allocate it or observe every removal. */
+  if (config->report_deletes) {
+    context->deleted_paths = array_list_create(free);
+    if (!context->deleted_paths)
+      goto fail;
+  }
   return context;
 
 fail:
@@ -49,6 +66,12 @@ fail:
     cnd_destroy(&context->condition_not_full);
   if (init >= 1)
     mtx_destroy(&context->mutex);
+  /* Free every list that was already created before the failing allocation:
+     `context` itself is freed below, so they would otherwise leak. */
+  if (context->would_delete)
+    array_list_delete(context->would_delete);
+  if (context->deleted_paths)
+    array_list_delete(context->deleted_paths);
   free(context);
   return NULL;
 }
@@ -57,9 +80,15 @@ void pipeline_context_receiver_destroy(PipelineContextReceiver* context) {
   config_delete(context->config);
   if (context->deferred_manifest)
     delete_manifest_free(context->deferred_manifest);
+  if (context->deferred_plans)
+    delete_plan_session_destroy(context->deferred_plans);
   queue_destroy(context->queue);
   receiver_outcomes_destroy(&context->outcomes);
   dir_time_list_free(&context->dir_times);
+  if (context->would_delete)
+    array_list_delete(context->would_delete);
+  if (context->deleted_paths)
+    array_list_delete(context->deleted_paths);
   mtx_destroy(&context->mutex);
   cnd_destroy(&context->condition_not_full);
   cnd_destroy(&context->condition_not_empty);
@@ -132,9 +161,23 @@ bool pipeline_context_receiver_enqueue_file(PipelineContextReceiver* context, Fi
 
 static bool receiver_enqueue_file(File* file, void* context_pointer) {
   PipelineContextReceiver* context = (PipelineContextReceiver*)context_pointer;
+  if (file && file->matched_bytes > 0) {
+    mtx_lock(&context->mutex);
+    context->stats.matched_data += file->matched_bytes;
+    mtx_unlock(&context->mutex);
+  }
   return pipeline_context_receiver_enqueue_file(context, file);
 }
 
+/* Early delete modes (--delete-before/--delete-during) commit the manifest
+   inside receiver_process_pending on this thread; record a capped commit so
+   server.c's terminal frame can report STATUS_DELETE_LIMIT.  The plain bool is
+   safe: receive_thread writes it before the main thread joins the thread. */
+static void receiver_pipeline_note_delete_limit(void* context_pointer) {
+  PipelineContextReceiver* context = (PipelineContextReceiver*)context_pointer;
+  context->delete_limit_reached = true;
+}
+
 static void receiver_thread_fail(PipelineContextReceiver* context) {
   mtx_lock(&context->mutex);
   atomic_store(&context->cancelled, true);
@@ -152,9 +195,17 @@ int receive_thread(void* pipeline_context) {
   const Config* config = context->config;
   mtx_unlock(&context->mutex);
 
-  ReceiverSink sink = {receiver_enqueue_file, context, false, false, NULL};
-  if (receiver_process_pending((Config*)config, file_descriptor, &sink,
-                               &context->deferred_manifest) != 0) {
+  ReceiverSink sink = {receiver_enqueue_file,
+                       context,
+                       false,
+                       false,
+                       NULL,
+                       receiver_pipeline_note_delete_limit,
+                       &context->stats,
+                       context->would_delete,
+                       context->deleted_paths};
+  if (receiver_process_pending((Config*)config, file_descriptor, &sink, &context->deferred_manifest,
+                               &context->deferred_plans) != 0) {
     receiver_thread_fail(context);
     protocol_session_unbind();
     return thrd_error;
@@ -196,12 +247,23 @@ int write_thread(void* pipeline_context) {
     }
     size_t file_bytes = file->data ? file->data->size : 0;
     FileSaveResult result = FILE_SAVE_SKIPPED;
+    bool created = false;
+    unsigned created_dirs = 0;
     /* Server-contacting --dry-run: never write.  The receiver thread does not
        enqueue anything on the dry-run path, but this keeps the writer thread
        provably mutation-free if a data frame ever reached it. */
     bool dry_run = context->config->dry_run;
     if (save_to_disk && !dry_run) {
-      result = file_save_to_disk_full(root_directory, file, context->config);
+      result =
+          file_save_to_disk_full_ex(root_directory, file, context->config, &created, &created_dirs);
+      if (result == FILE_SAVE_WRITTEN) {
+        /* Protocol 2.28.0: fold the receiver-observed literal bytes and the
+           created-entry type into the shared stats block under its mutex (the
+           receive thread also writes stats.matched_data). */
+        mtx_lock(&context->mutex);
+        receiver_stats_note_saved(&context->stats, file, created, created_dirs);
+        mtx_unlock(&context->mutex);
+      }
       if (result == FILE_SAVE_ERROR) {
         file_destroy(file);
         pipeline_context_receiver_note_bytes_released(context, file_bytes);
@@ -220,8 +282,8 @@ int write_thread(void* pipeline_context) {
        write would clobber them); accumulate the metadata here and let the
        caller apply it once every writer has drained. */
     if (!dry_run && result != FILE_SAVE_ERROR && file->is_dir && file->metadata &&
-        dir_times_should_capture(context->config) &&
-        !dir_time_list_add(&context->dir_times, file->path, file->metadata)) {
+        dir_metadata_should_capture(context->config) &&
+        !dir_time_list_add(&context->dir_times, file->path, file->metadata, file->xattrs)) {
       file_destroy(file);
       pipeline_context_receiver_note_bytes_released(context, file_bytes);
       mtx_lock(&context->mutex);

src/server/receiver_pipeline.h

@@ -41,10 +41,29 @@ typedef struct PipelineContextReceiver {
      transfer truly succeeded.  NULL in the early delete modes (which delete at
      the manifest). */
   DeleteManifest* deferred_manifest;
+  /* Per-directory delete session for --delete-delay: receive_thread snapshots
+     each plan's extras as it arrives and hands the session here instead of
+     committing while the disk writer may still be draining; server.c commits it
+     after both threads joined.  NULL for every other timing. */
+  DeletePlanSession* deferred_plans;
+  /* Set by server.c when the deferred delete commit hit the --max-delete
+     budget; the terminal success frame then carries STATUS_DELETE_LIMIT
+     (rsync exit 25) while the transfer itself still succeeds. */
+  bool delete_limit_reached;
   /* P7 Wave D: directory metadata collected by write_thread from received
      directory entries.  Only write_thread mutates it (before it joins); the
      caller (server.c) applies it after the delete/delay-updates phase. */
   DirTimeList dir_times;
+  /* End-of-transfer wire counters (protocol 2.25.0).  receive_thread accumulates
+     matched_data under `mutex`; server.c adds the delete-commit tallies after
+     both threads join and emits the STATUS_STATS frame. */
+  ReceiverStats stats;
+  /* -n/--dry-run --delete would-delete path list, collected by receive_thread
+     and reported in the STATUS_STATS frame. */
+  struct ArrayList* would_delete;
+  /* --info=del actually-removed path list, collected by the deferred delete
+     commit in server.c and reported in the STATUS_STATS frame. */
+  struct ArrayList* deleted_paths;
 } PipelineContextReceiver;
 
 PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue* queue_receiver,

src/server/server.c

@@ -389,8 +389,12 @@ static const char* module_gate_check_ownership(const Config* config, const Daemo
                                                ModuleGateContext* gate_ctx) {
   if (module->client_owner)
     return NULL;
-  /* Ownership: refuse the whole transfer up front (a clear failure). */
-  if (identity_ownership_requested(config)) {
+  /* Ownership: refuse the whole transfer up front (a clear failure) for a
+   * client-CHOSEN owner/group request.  A plain -o/-g/-a preserve-source
+   * request is deliberately not in this narrow set: it falls through to the
+   * super-mode override below, which forces all ownership activity off for this
+   * connection so no chown happens (the transfer itself still succeeds). */
+  if (identity_explicit_ownership_requested(config)) {
     log_message(LOG_LEVEL_ERROR,
                 "daemon module '%s' refuses client-chosen ownership/super-user activities "
                 "(no `client owner = yes` opt-in); refusing",
@@ -737,13 +741,26 @@ void handler(int file_descriptor) {
    * received config. */
   if (gate_ctx.super_mode_override != -1)
     config->super_mode = (SuperMode)gate_ctx.super_mode_override;
+  /* Install the codec this connection negotiated before the receiver/writer
+   * threads start (the server forks per connection, so the process-global
+   * codec is private to this session). */
+  compression_set_algo((CompressionAlgo)config->compression_algo);
+  /* If the client requested ownership but the effective super mode forbids it
+   * (operator --no-super, a privileged standalone receiver's secure default, or
+   * a daemon module without `client owner = yes`), say so ONCE per connection so
+   * a successful -a/-o/-g transfer is not mistaken for preserved ownership. */
+  if (config->super_mode == SUPER_MODE_OFF && identity_ownership_requested(config))
+    log_message(LOG_LEVEL_WARNING,
+                "requested ownership will NOT be applied: super-user activities are disabled "
+                "for this connection (operator veto, or module without `client owner = yes`)");
   protocol_set_8_bit_output(config->eight_bit_output);
   /* Server-side per-message protocol deadline for every frame from here on.
    * `timeout` is not serialized, so this is the server's own config (the server
-   * has no --timeout CLI and defaults it to 0): the built-in 60 s window stays
-   * in effect.  A client's --timeout tightens only that client's own protocol
-   * I/O and the server's socket read/write timeout is the transport default. */
-  protocol_session_set_io_timeout(&session, config->timeout);
+   * has no --timeout CLI and defaults it to 0).  A client's --timeout tightens
+   * only that client's own protocol I/O; the server floors its own deadline at
+   * SERVER_IO_TIMEOUT_SEC so a silent peer can never hold a session slot
+   * forever (the socket layer gets the same floor at startup). */
+  protocol_session_set_io_timeout(&session, protocol_server_io_timeout_sec(config->timeout));
   const char* authorized_root = utils_get_authorized_root_path();
   if (!authorized_root) {
     log_message(LOG_LEVEL_ERROR, "No server-side destination root configured");
@@ -892,7 +909,8 @@ void handler(int file_descriptor) {
       goto done;
     }
     protocol_session_set_max_alloc(&context->session, config->max_alloc);
-    protocol_session_set_io_timeout(&context->session, config->timeout);
+    protocol_session_set_io_timeout(&context->session,
+                                    protocol_server_io_timeout_sec(config->timeout));
     atomic_store(&context->session.total_allocated_bytes,
                  atomic_load(&session.total_allocated_bytes));
     pipeline_context_receiver_set_queue_byte_limit(context, RECEIVER_QUEUE_MAX_BYTES);
@@ -937,12 +955,42 @@ void handler(int file_descriptor) {
          --delay-updates run; the walker skips the staging directory.  A
          server-contacting --dry-run deletes nothing (no manifest is sent). */
       if (context->deferred_manifest) {
-        if (!manifest_delete_all(config, context->deferred_manifest)) {
+        size_t deleted = 0;
+        DeletePathObserver observer = config->report_deletes ? receiver_record_deleted_path : NULL;
+        DeleteCommitResult deletion = manifest_delete_all_observed(
+            config, context->deferred_manifest, &deleted, observer, (void*)context->deleted_paths);
+        context->stats.deleted_files += deleted;
+        if (deletion == DELETE_COMMIT_ERROR) {
           transfer_ok = false;
+        } else if (deletion == DELETE_COMMIT_LIMIT_REACHED) {
+          /* The transfer still succeeds; the terminal frame reports the capped
+             deletion so the sender exits 25 like rsync. */
+          context->delete_limit_reached = true;
         }
         delete_manifest_free(context->deferred_manifest);
         context->deferred_manifest = NULL;
       }
+      /* --delete-delay: receive_thread snapshotted each plan's extras as it
+         arrived; with the disk writer drained, commit the deferred removals.
+         --delete-during already applied its plans on the receive thread. */
+      if (context->deferred_plans) {
+        /* Defence in depth (the enclosing block already excludes dry-run): a
+           -n run never commits a deletion. */
+        if (config->report_deletes)
+          delete_plan_session_set_delete_observer(
+              context->deferred_plans, receiver_record_deleted_path, (void*)context->deleted_paths);
+        DeleteCommitResult deletion =
+            config->dry_run ? DELETE_COMMIT_OK
+                            : delete_plan_session_commit(context->deferred_plans, config);
+        context->stats.deleted_files += delete_plan_session_deleted(context->deferred_plans);
+        if (deletion == DELETE_COMMIT_ERROR) {
+          transfer_ok = false;
+        } else if (deletion == DELETE_COMMIT_LIMIT_REACHED) {
+          context->delete_limit_reached = true;
+        }
+        delete_plan_session_destroy(context->deferred_plans);
+        context->deferred_plans = NULL;
+      }
     }
     if (transfer_ok && !config->dry_run) {
       /* --delay-updates: receive_thread has finished the whole protocol stream
@@ -959,10 +1007,15 @@ void handler(int file_descriptor) {
          to stamp directory times; a directory's mtime must not be clobbered by
          its children or by an extra removal. */
       if (transfer_ok)
-        dir_time_list_apply(&context->dir_times, config->receive_root_directory);
+        dir_metadata_list_apply(&context->dir_times, config->receive_root_directory, config);
     }
     if (transfer_ok) {
-      if (!receiver_send_final_success(file_descriptor, config, &context->outcomes))
+      Status final_status = context->delete_limit_reached ? STATUS_DELETE_LIMIT : STATUS_OK;
+      /* Emit the optional wire-stats record first (protocol 2.25.0), then the
+         success/outcome frame, exactly like the single-threaded receiver. */
+      if (!receiver_send_stats_frame(file_descriptor, config, &context->stats,
+                                     context->would_delete, context->deleted_paths) ||
+          !receiver_send_final_success(file_descriptor, config, &context->outcomes, final_status))
         transfer_ok = false;
     } else {
       send_error_detail(file_descriptor, "transfer failed on receiver");
@@ -1029,8 +1082,9 @@ static void print_server_usage(void) {
   printf("                      hosts allow, hosts deny)\n");
   printf("  --no-detach         Stay in the foreground (default detaches to\n");
   printf("                      background when running --daemon)\n");
-  printf("  --password-file=FILE  Credential store for modules that declare\n");
-  printf("                      'auth users' (line format:\n");
+  printf("  --password-file=FILE  FastSync-native SCRAM/PBKDF2 credential store (NOT\n");
+  printf("                      rsync's auth scheme) for modules that declare 'auth\n");
+  printf("                      users' (line format:\n");
   printf("                      user:$fastsync$1$pbkdf2-sha256$iters$salt$stored$server,\n");
   printf("                      generated by --hash-credentials).  Legacy\n");
   printf("                      user:SHA256HEX lines are rejected.  Requires\n");
@@ -1039,7 +1093,7 @@ static void print_server_usage(void) {
   printf("  --early-input=FILE  Second credential store layered over\n");
   printf("                      --password-file (same format); usually a secrets-\n");
   printf("                      manager/process-substitution file.  Requires --daemon\n");
-  printf("  -p <port>           TCP port (default: 8080, range: 1-65535)\n");
+  printf("  -p, --port <port>   TCP port (default: 8080, range: 1-65535)\n");
   printf("  --tls               Enable TLS encryption\n");
   printf("  --cert <path>       TLS certificate file (PEM)\n");
   printf("  --key <path>        TLS private key file (PEM)\n");
@@ -1050,7 +1104,9 @@ static void print_server_usage(void) {
   printf("  -4, --ipv4          Bind an IPv4 socket (default)\n");
   printf("  -6, --ipv6          Bind an IPv6 socket\n");
   printf("  --allow-delete      Permit manifest deletion\n");
-  printf("  --trust-sender      Trust the remote sender's file list\n");
+  printf("  --trust-sender      Trust the remote sender's file list (receiver-local;\n");
+  printf("                      this server-side flag is the only one that matters -- a\n");
+  printf("                      client --trust-sender is never sent to the server)\n");
   printf("  --no-super          Operator veto: never attempt super-user activities\n");
   printf("                      (ownership, device nodes) even as root, and refuse\n");
   printf("                      any client --copy-as/--super request\n");
@@ -1127,10 +1183,18 @@ static bool daemonize(void) {
   if (chdir("/") != 0)
     log_message(LOG_LEVEL_WARNING, "daemon: chdir to / failed: %s", strerror(errno));
   umask(0);
+  /* Refresh the cached umask: main() captured the launch umask before this
+   * (single-threaded) umask(0), and file_mode_base() must see the daemon's
+   * actual umask. */
+  file_umask_capture();
   return true;
 }
 
 int main(int argc, char* argv[]) {
+  /* Capture the process umask now, while still single-threaded: the cached
+   * value is what file_mode_base() uses, and reading it later would race with
+   * receiver threads creating files. */
+  file_umask_capture();
   ServerCliOptions opts;
   char cli_err[512];
   int parse_result = server_cli_parse(argc, argv, &opts, cli_err, sizeof(cli_err));
@@ -1191,6 +1255,10 @@ int main(int argc, char* argv[]) {
   server_iconv_spec = opts.iconv_spec;
   signal(SIGINT, cleanup);
   signal(SIGTERM, cleanup);
+  /* Server-owned socket deadline floor: the client default --timeout=0 would
+   * otherwise leave accepted sockets without SO_RCVTIMEO/SO_SNDTIMEO and let a
+   * silent peer hold a connection (and its process slot) forever. */
+  tcp_set_timeouts(SERVER_IO_TIMEOUT_SEC, SERVER_IO_TIMEOUT_SEC);
 
   if (opts.stdio_mode) {
     /* SSH authenticates the stdio transport outside of FastSync. */

src/server/server_cli.c

@@ -192,14 +192,20 @@ int server_cli_parse(int argc, char* argv[], ServerCliOptions* opts, char* err,
         inline_value = argv[++i];
       }
       opts->iconv_spec = inline_value;
-    } else if (arg_is(argv[i], "-p")) {
-      if (i + 1 >= argc) {
-        set_error(err, err_size, "missing argument for -p");
-        return -1;
+    } else if (arg_is(argv[i], "-p") || arg_has_value(argv[i], "--port", &inline_value)) {
+      if (inline_value) {
+        opts->port_set = true;
+        if (parse_port_arg(inline_value, &opts->port, err, err_size) != 0)
+          return -1;
+      } else {
+        if (i + 1 >= argc) {
+          set_error(err, err_size, "missing argument for %s", argv[i]);
+          return -1;
+        }
+        opts->port_set = true;
+        if (parse_port_arg(argv[++i], &opts->port, err, err_size) != 0)
+          return -1;
       }
-      opts->port_set = true;
-      if (parse_port_arg(argv[++i], &opts->port, err, err_size) != 0)
-        return -1;
     } else {
       if (arg_has_value(argv[i], "--config", &inline_value)) {
         if (!inline_value) {

src/shared/batch.c

@@ -2,6 +2,7 @@
 #include "data.h"
 #include "file.h"
 #include "file_receive.h"
+#include "identity.h"
 #include "log.h"
 #include <errno.h>
 #include <stdlib.h>
@@ -10,11 +11,15 @@
 
 /* Serialization metadata mode for the batch stream, captured from the config at
  * batch_write_header time.  The header persists it into the file so a batch is
- * self-describing: batch_read_apply re-reads it from the file (not from the
- * reading config), so a batch written with -M is applied identically by an
- * invoking process regardless of its own -M setting.  The batch driver is a
- * single sequential scan pass within one thread, so this module-level flag is
- * safe. */
+ * self-describing about whether per-entry metadata was CAPTURED in the stream:
+ * batch_read_apply re-reads it from the file (not from the reading config) to
+ * decode the chunk records correctly.  Which attributes are actually APPLIED,
+ * however, comes from the INVOKING process's per-attribute config (the
+ * FileAttrPolicy and the dir-metadata gate), so a batch written with -M is NOT
+ * automatically applied identically by an invoking process with a different
+ * -p/-t/-o/-g: --read-batch must be invoked with the same -p/-t/-o/-g as the
+ * write side (rsync requires the same options).  The batch driver is a single
+ * sequential scan pass within one thread, so this module-level flag is safe. */
 static bool batch_metadata_mode = false;
 
 static bool write_all_bytes(int fd, const void* data, size_t size) {
@@ -91,22 +96,37 @@ int batch_read_apply(int fd, const Config* config, const char* dest_root) {
   if (fd < 0 || dest_root == NULL || dest_root[0] == '\0')
     return -1;
 
+  /* Directory metadata is deferred to the end of the apply (a child write would
+   * otherwise clobber its parent's mtime/mode).  The batch header's single
+   * metadata bit only says whether metadata is present in the stream; which
+   * attributes are APPLIED comes from the invoking process's config, so
+   * --read-batch must be invoked with the same -p/-t/-o/-g as the write side
+   * (rsync requires the same options).  The identity snapshot is activated so
+   * -o/-g and the explicit ownership flags can apply. */
+  DirTimeList dir_times;
+  dir_time_list_init(&dir_times);
+  int result = -1;
+  if (!identity_set_active(config)) {
+    log_message(LOG_LEVEL_ERROR, "batch: could not activate the identity policy");
+    goto done;
+  }
+
   char magic[BATCH_MAGIC_LEN];
   bool eof = false;
   if (!read_exact(fd, magic, BATCH_MAGIC_LEN, &eof) || eof ||
       memcmp(magic, BATCH_MAGIC, BATCH_MAGIC_LEN) != 0) {
     log_message(LOG_LEVEL_ERROR, "batch: malformed header (bad magic)");
-    return -1;
+    goto done;
   }
   unsigned char version;
   if (!read_exact(fd, &version, 1, &eof) || eof || version != BATCH_FORMAT_VERSION) {
     log_message(LOG_LEVEL_ERROR, "batch: malformed header (bad or missing format version)");
-    return -1;
+    goto done;
   }
   unsigned char mode;
   if (!read_exact(fd, &mode, 1, &eof) || eof || (mode != 0 && mode != 1)) {
     log_message(LOG_LEVEL_ERROR, "batch: malformed header (bad metadata flag)");
-    return -1;
+    goto done;
   }
   bool use_metadata = mode == 1;
 
@@ -114,47 +134,62 @@ int batch_read_apply(int fd, const Config* config, const char* dest_root) {
     unsigned long long length;
     if (!read_exact(fd, &length, sizeof(length), &eof)) {
       log_message(LOG_LEVEL_ERROR, "batch: truncated length prefix");
-      return -1;
+      goto done;
     }
     if (eof)
       break; /* clean end of stream */
     if (length == 0 || length > BATCH_MAX_RECORD) {
       log_message(LOG_LEVEL_ERROR, "batch: rejected record length %llu (valid range 1..%llu)",
                   length, (unsigned long long)BATCH_MAX_RECORD);
-      return -1;
+      goto done;
     }
     char* record = (char*)malloc((size_t)length);
     if (record == NULL) {
       log_message(LOG_LEVEL_ERROR, "batch: could not allocate a %llu-byte record", length);
-      return -1;
+      goto done;
     }
     if (!read_exact(fd, record, (size_t)length, &eof) || eof) {
       log_message(LOG_LEVEL_ERROR, "batch: truncated chunk record");
       free(record);
-      return -1;
+      goto done;
     }
     Data* data = data_create(record, (size_t)length);
     if (data == NULL)
-      return -1; /* data_create frees `record` on failure */
+      goto done; /* data_create frees `record` on failure */
     Chunk* chunk = chunk_deserialize(data, use_metadata);
     data_destroy(data);
     if (chunk == NULL) {
       log_message(LOG_LEVEL_ERROR, "batch: rejected malformed chunk record");
-      return -1;
+      goto done;
     }
     for (int i = 0; i < chunk->element_count; i++) {
       File* file = chunk->items[i];
       chunk->items[i] = NULL;
       if (file == NULL)
         continue;
-      FileSaveResult result = file_save_to_disk_full(dest_root, file, config);
-      file_destroy(file);
-      if (result == FILE_SAVE_ERROR) {
+      FileSaveResult save = file_save_to_disk_full(dest_root, file, config);
+      /* Accumulate directory metadata (when it applies) before the File is
+       * destroyed; applied once the whole stream has been consumed. */
+      if (save != FILE_SAVE_ERROR && file->is_dir && file->metadata &&
+          dir_metadata_should_capture(config) &&
+          !dir_time_list_add(&dir_times, file->path, file->metadata, file->xattrs)) {
+        file_destroy(file);
         chunk_destroy(chunk);
-        return -1;
+        goto done;
+      }
+      file_destroy(file);
+      if (save == FILE_SAVE_ERROR) {
+        chunk_destroy(chunk);
+        goto done;
       }
     }
     chunk_destroy(chunk);
   }
-  return 0;
-}
+  dir_metadata_list_apply(&dir_times, dest_root, config);
+  result = 0;
+
+done:
+  identity_clear_active();
+  dir_time_list_free(&dir_times);
+  return result;
+}

src/shared/charset.c

@@ -168,9 +168,14 @@ bool charset_spec_valid_direction(const char* from_charset, const char* to_chars
   return direction_probe_valid(from_charset, to_charset);
 }
 
-/* The receiver's real conversion is wire(client REMOTE) -> server-local (the
- * server's own --iconv LOCAL half, or the client's LOCAL half when the server
- * has no --iconv).  A dedicated pre-ack check so an impossible direction is
+/* The receiver's conversion is wire charset -> destination charset.  rsync's
+ * CONVERT_SPEC is LOCAL,REMOTE and "stays the same whether you're pushing or
+ * pulling", so for a PUSH (FastSync's only direction) the destination end's
+ * charset is the spec's REMOTE half: the client converts LOCAL -> REMOTE on the
+ * sender and the receiver writes the wire bytes verbatim.  Only a server that
+ * declares its OWN --iconv (the daemon "charset" analog) has a different local
+ * charset, and then it is that spec's LOCAL half and the receiver converts
+ * wire -> server-local.  A dedicated pre-ack check so an impossible direction is
  * rejected before the connection instead of refusing mid-transfer. */
 bool charset_wire_receiver_spec_valid(const char* spec, const char* server_spec) {
   if (!spec)
@@ -180,7 +185,7 @@ bool charset_wire_receiver_spec_valid(const char* spec, const char* server_spec)
   if (charset_spec_parse(spec, &local, &remote) != 0)
     return false;
   const char* wire = remote;
-  const char* target_local = local;
+  const char* target_local = remote;
   char* server_local = NULL;
   char* server_remote = NULL;
   if (server_spec) {
@@ -302,13 +307,13 @@ bool charset_wire_init_receiver(const char* spec, const char* server_spec) {
   char* remote;
   if (charset_spec_parse(spec, &local, &remote) != 0)
     return false;
-  /* The wire charset is the client spec's REMOTE half; the local charset is
-   * the client spec's LOCAL half unless the server was itself started with
-   * --iconv naming a different local charset (the server halves above never
-   * travel, so the server's own flag is the only way its local charset can
-   * differ from what the client assumed). */
+  /* The wire charset is the client spec's REMOTE half (rsync's LOCAL,REMOTE
+   * spec stays the same push or pull, so on a push the destination end's
+   * charset is REMOTE and the receiver writes the wire bytes verbatim).  Only a
+   * server started with its own --iconv declares a different local charset (the
+   * server halves above never travel), and then it is that spec's LOCAL half. */
   const char* wire = remote;
-  const char* target_local = local;
+  const char* target_local = remote;
   char* server_local = NULL;
   char* server_remote = NULL;
   if (server_spec) {

src/shared/charset.h

@@ -57,8 +57,9 @@ void charset_conversion_close(void* conversion);
 /* Process-wide wire conversion.  charset_wire_init_sender (client side) opens
  * LOCAL->REMOTE; charset_wire_init_receiver (server side) opens
  * wire(REMOTE)->server-local.  server_spec is the server's own --iconv, whose
- * LOCAL half may override the local charset the client assumed; NULL reuses
- * the client spec's LOCAL half.  Both return false on an unsupported spec.
+ * LOCAL half overrides the destination charset; NULL means the destination
+ * charset is the client spec's REMOTE half (rsync's push semantics: the wire
+ * bytes are written verbatim).  Both return false on an unsupported spec.
  * The state is freed with charset_wire_free. */
 bool charset_wire_init_sender(const char* spec);
 bool charset_wire_init_receiver(const char* spec, const char* server_spec);
@@ -66,9 +67,9 @@ void charset_wire_free(void);
 bool charset_wire_active(void);
 
 /* Pre-ack receiver-direction sanity (see charset_wire_init_receiver): true
- * when the exact wire->server-local conversion the receiver will use (client
- * spec's REMOTE half into the server's own LOCAL half, or the client's LOCAL
- * half when the server has no --iconv) opens and produces NUL-free output. */
+ * when the exact wire->destination conversion the receiver will use (client
+ * spec's REMOTE half into the server's own LOCAL half, or REMOTE->REMOTE when
+ * the server has no --iconv) opens and produces NUL-free output. */
 bool charset_wire_receiver_spec_valid(const char* spec, const char* server_spec);
 
 /* Convert a path across the wire in the process direction.  Returns a malloc'd

src/shared/checksum.c

@@ -1,12 +1,171 @@
 #include "checksum.h"
+#include "utils.h"
+#include <fcntl.h>
 #include <openssl/evp.h>
 #include <string.h>
 #include <strings.h>
+#include <unistd.h>
 
 /* delta.c owns the single XXH_IMPLEMENTATION that provides the xxHash symbols
- * for the whole binary; this TU only needs the declarations. */
+ * for the whole binary; this TU only needs the declarations.  The streaming
+ * state structs and XXH3_update are exposed only with XXH_STATIC_LINKING_ONLY. */
+#define XXH_STATIC_LINKING_ONLY
 #include <xxhash.h>
 
+/* ---------------------------------------------------------------------------
+ * Self-contained MD4 (RFC 1320).  OpenSSL's MD4 lives in the legacy provider
+ * and is not guaranteed present, so FastSync carries its own implementation to
+ * keep --checksum-choice=md4 working on every build.
+ * ------------------------------------------------------------------------- */
+
+typedef struct {
+  uint32_t state[4];
+  uint64_t bit_count;
+  uint8_t buffer[64];
+  size_t buffer_len;
+} Md4Ctx;
+
+static uint32_t md4_rotl(uint32_t x, int n) {
+  return (x << n) | (x >> (32 - n));
+}
+
+static void md4_transform(uint32_t state[4], const uint8_t block[64]) {
+  uint32_t x[16];
+  for (int i = 0; i < 16; i++)
+    x[i] = (uint32_t)block[i * 4] | ((uint32_t)block[i * 4 + 1] << 8) |
+           ((uint32_t)block[i * 4 + 2] << 16) | ((uint32_t)block[i * 4 + 3] << 24);
+
+  uint32_t a = state[0], b = state[1], c = state[2], d = state[3];
+
+#define F(x, y, z) (((x) & (y)) | (~(x) & (z)))
+#define G(x, y, z) (((x) & (y)) | ((x) & (z)) | ((y) & (z)))
+#define H(x, y, z) ((x) ^ (y) ^ (z))
+#define ROUND1(a, b, c, d, k, s) a = md4_rotl(a + F(b, c, d) + x[k], s)
+#define ROUND2(a, b, c, d, k, s) a = md4_rotl(a + G(b, c, d) + x[k] + 0x5a827999u, s)
+#define ROUND3(a, b, c, d, k, s) a = md4_rotl(a + H(b, c, d) + x[k] + 0x6ed9eba1u, s)
+
+  ROUND1(a, b, c, d, 0, 3);
+  ROUND1(d, a, b, c, 1, 7);
+  ROUND1(c, d, a, b, 2, 11);
+  ROUND1(b, c, d, a, 3, 19);
+  ROUND1(a, b, c, d, 4, 3);
+  ROUND1(d, a, b, c, 5, 7);
+  ROUND1(c, d, a, b, 6, 11);
+  ROUND1(b, c, d, a, 7, 19);
+  ROUND1(a, b, c, d, 8, 3);
+  ROUND1(d, a, b, c, 9, 7);
+  ROUND1(c, d, a, b, 10, 11);
+  ROUND1(b, c, d, a, 11, 19);
+  ROUND1(a, b, c, d, 12, 3);
+  ROUND1(d, a, b, c, 13, 7);
+  ROUND1(c, d, a, b, 14, 11);
+  ROUND1(b, c, d, a, 15, 19);
+
+  ROUND2(a, b, c, d, 0, 3);
+  ROUND2(d, a, b, c, 4, 5);
+  ROUND2(c, d, a, b, 8, 9);
+  ROUND2(b, c, d, a, 12, 13);
+  ROUND2(a, b, c, d, 1, 3);
+  ROUND2(d, a, b, c, 5, 5);
+  ROUND2(c, d, a, b, 9, 9);
+  ROUND2(b, c, d, a, 13, 13);
+  ROUND2(a, b, c, d, 2, 3);
+  ROUND2(d, a, b, c, 6, 5);
+  ROUND2(c, d, a, b, 10, 9);
+  ROUND2(b, c, d, a, 14, 13);
+  ROUND2(a, b, c, d, 3, 3);
+  ROUND2(d, a, b, c, 7, 5);
+  ROUND2(c, d, a, b, 11, 9);
+  ROUND2(b, c, d, a, 15, 13);
+
+  ROUND3(a, b, c, d, 0, 3);
+  ROUND3(d, a, b, c, 8, 9);
+  ROUND3(c, d, a, b, 4, 11);
+  ROUND3(b, c, d, a, 12, 15);
+  ROUND3(a, b, c, d, 2, 3);
+  ROUND3(d, a, b, c, 10, 9);
+  ROUND3(c, d, a, b, 6, 11);
+  ROUND3(b, c, d, a, 14, 15);
+  ROUND3(a, b, c, d, 1, 3);
+  ROUND3(d, a, b, c, 9, 9);
+  ROUND3(c, d, a, b, 5, 11);
+  ROUND3(b, c, d, a, 13, 15);
+  ROUND3(a, b, c, d, 3, 3);
+  ROUND3(d, a, b, c, 11, 9);
+  ROUND3(c, d, a, b, 7, 11);
+  ROUND3(b, c, d, a, 15, 15);
+
+#undef F
+#undef G
+#undef H
+#undef ROUND1
+#undef ROUND2
+#undef ROUND3
+
+  state[0] += a;
+  state[1] += b;
+  state[2] += c;
+  state[3] += d;
+}
+
+static void md4_init(Md4Ctx* ctx) {
+  ctx->state[0] = 0x67452301u;
+  ctx->state[1] = 0xefcdab89u;
+  ctx->state[2] = 0x98badcfeu;
+  ctx->state[3] = 0x10325476u;
+  ctx->bit_count = 0;
+  ctx->buffer_len = 0;
+}
+
+static void md4_update(Md4Ctx* ctx, const uint8_t* data, size_t len) {
+  ctx->bit_count += (uint64_t)len * 8;
+  while (len > 0) {
+    size_t space = sizeof(ctx->buffer) - ctx->buffer_len;
+    size_t take = len < space ? len : space;
+    memcpy(ctx->buffer + ctx->buffer_len, data, take);
+    ctx->buffer_len += take;
+    data += take;
+    len -= take;
+    if (ctx->buffer_len == sizeof(ctx->buffer)) {
+      md4_transform(ctx->state, ctx->buffer);
+      ctx->buffer_len = 0;
+    }
+  }
+}
+
+static void md4_final(Md4Ctx* ctx, uint8_t out[16]) {
+  uint64_t bit_count = ctx->bit_count;
+  uint8_t pad = 0x80;
+  md4_update(ctx, &pad, 1);
+  uint8_t zero = 0;
+  while (ctx->buffer_len != 56)
+    md4_update(ctx, &zero, 1);
+  uint8_t length_le[8];
+  for (int i = 0; i < 8; i++)
+    length_le[i] = (uint8_t)((bit_count >> (8 * i)) & 0xff);
+  md4_update(ctx, length_le, sizeof(length_le));
+  for (int i = 0; i < 4; i++) {
+    out[i * 4] = (uint8_t)(ctx->state[i] & 0xff);
+    out[i * 4 + 1] = (uint8_t)((ctx->state[i] >> 8) & 0xff);
+    out[i * 4 + 2] = (uint8_t)((ctx->state[i] >> 16) & 0xff);
+    out[i * 4 + 3] = (uint8_t)((ctx->state[i] >> 24) & 0xff);
+  }
+}
+
+/* One-shot EVP digest (md5/sha1).  Returns false when OpenSSL refuses. */
+static bool evp_digest(const EVP_MD* md, const void* data, size_t size, uint8_t* out,
+                       size_t out_capacity, size_t* out_len) {
+  static const uint8_t empty = 0;
+  const void* input = data ? data : &empty;
+  unsigned int digest_len = 0;
+  if (EVP_Digest(input, size, out, &digest_len, md, NULL) != 1)
+    return false;
+  if (digest_len > out_capacity)
+    return false;
+  *out_len = digest_len;
+  return true;
+}
+
 bool checksum_digest(ChecksumAlgo algo, uint64_t seed, const void* data, size_t size, uint8_t* out,
                      size_t out_capacity, size_t* out_len) {
   if (!out || !out_len || out_capacity < CHECKSUM_MAX_DIGEST_LEN)
@@ -14,30 +173,166 @@ bool checksum_digest(ChecksumAlgo algo, uint64_t seed, const void* data, size_t
   if (data == NULL && size != 0)
     return false;
 
-  if (algo == CHECKSUM_ALGO_XXH64) {
+  switch (algo) {
+  case CHECKSUM_ALGO_XXH64: {
     uint64_t digest = XXH64(data, size, seed);
     memcpy(out, &digest, sizeof(digest));
     *out_len = sizeof(digest);
     return true;
   }
-
-  if (algo == CHECKSUM_ALGO_MD5) {
+  case CHECKSUM_ALGO_XXH3: {
+    uint64_t digest = XXH3_64bits_withSeed(data, size, seed);
+    memcpy(out, &digest, sizeof(digest));
+    *out_len = sizeof(digest);
+    return true;
+  }
+  case CHECKSUM_ALGO_XXH128: {
+    XXH128_hash_t digest = XXH3_128bits_withSeed(data, size, seed);
+    memcpy(out, &digest, sizeof(digest));
+    *out_len = sizeof(digest);
+    return true;
+  }
+  case CHECKSUM_ALGO_MD5:
     /* md5 takes no seed; the caller's seed is deliberately ignored (documented
-     * in RSYNC_COMPAT.md).  OpenSSL's one-shot EVP_Digest needs a non-NULL
-     * buffer even for an empty input, so map a NULL data + size==0 to an empty
-     * buffer. */
-    static const uint8_t empty = 0;
-    const void* input = data ? data : &empty;
-    unsigned int digest_len = 0;
-    if (EVP_Digest(input, size, out, &digest_len, EVP_md5(), NULL) != 1)
-      return false;
-    if (digest_len > out_capacity)
-      return false;
-    *out_len = digest_len;
+     * in RSYNC_COMPAT.md). */
+    return evp_digest(EVP_md5(), data, size, out, out_capacity, out_len);
+  case CHECKSUM_ALGO_MD4: {
+    Md4Ctx ctx;
+    md4_init(&ctx);
+    md4_update(&ctx, (const uint8_t*)data, size);
+    md4_final(&ctx, out);
+    *out_len = 16;
+    return true;
+  }
+  case CHECKSUM_ALGO_SHA1:
+    /* sha1 takes no seed; the caller's seed is deliberately ignored. */
+    return evp_digest(EVP_sha1(), data, size, out, out_capacity, out_len);
+  case CHECKSUM_ALGO_NONE:
+    /* No checksum requested: an empty digest is the successful result. */
+    *out_len = 0;
+    return true;
+  }
+  return false;
+}
+
+bool checksum_digest_file(ChecksumAlgo algo, uint64_t seed, const char* path, uint8_t* out,
+                          size_t out_capacity, size_t* out_len) {
+  if (!path || !out || !out_len || out_capacity < CHECKSUM_MAX_DIGEST_LEN)
+    return false;
+
+  int fd = open(path, O_RDONLY | O_CLOEXEC);
+  if (fd < 0)
+    return false;
+
+  bool ok = checksum_digest_fd(algo, seed, fd, out, out_capacity, out_len);
+  close(fd);
+  return ok;
+}
+
+bool checksum_digest_fd(ChecksumAlgo algo, uint64_t seed, int fd, uint8_t* out, size_t out_capacity,
+                        size_t* out_len) {
+  if (fd < 0 || !out || !out_len || out_capacity < CHECKSUM_MAX_DIGEST_LEN)
+    return false;
+
+  if (algo == CHECKSUM_ALGO_NONE) {
+    /* No checksum requested: nothing to read; an empty digest succeeds. */
+    *out_len = 0;
     return true;
   }
 
-  return false;
+  uint8_t buffer[64 * 1024];
+  bool ok = false;
+  lseek(fd, 0, SEEK_SET);
+
+  if (algo == CHECKSUM_ALGO_MD5 || algo == CHECKSUM_ALGO_SHA1) {
+    const EVP_MD* md = algo == CHECKSUM_ALGO_MD5 ? EVP_md5() : EVP_sha1();
+    EVP_MD_CTX* ctx = EVP_MD_CTX_new();
+    if (!ctx)
+      return false;
+    unsigned int digest_len = 0;
+    if (EVP_DigestInit_ex(ctx, md, NULL) == 1) {
+      ok = true;
+      ssize_t got;
+      while ((got = read(fd, buffer, sizeof(buffer))) > 0) {
+        if (EVP_DigestUpdate(ctx, buffer, (size_t)got) != 1) {
+          ok = false;
+          break;
+        }
+      }
+      if (got < 0)
+        ok = false;
+      if (ok && EVP_DigestFinal_ex(ctx, out, &digest_len) == 1 && digest_len <= out_capacity)
+        *out_len = digest_len;
+      else
+        ok = false;
+    }
+    EVP_MD_CTX_free(ctx);
+    return ok;
+  }
+
+  if (algo == CHECKSUM_ALGO_MD4) {
+    Md4Ctx ctx;
+    md4_init(&ctx);
+    ok = true;
+    ssize_t got;
+    while ((got = read(fd, buffer, sizeof(buffer))) > 0)
+      md4_update(&ctx, buffer, (size_t)got);
+    if (got < 0)
+      ok = false;
+    if (ok) {
+      md4_final(&ctx, out);
+      *out_len = 16;
+    }
+    return ok;
+  }
+
+  XXH64_state_t xxh64;
+  XXH3_state_t* xxh3 = NULL;
+  if (algo == CHECKSUM_ALGO_XXH64) {
+    XXH64_reset(&xxh64, seed);
+  } else if (algo == CHECKSUM_ALGO_XXH3 || algo == CHECKSUM_ALGO_XXH128) {
+    xxh3 = XXH3_createState();
+    if (!xxh3)
+      return false;
+    if (algo == CHECKSUM_ALGO_XXH3)
+      XXH3_64bits_reset_withSeed(xxh3, seed);
+    else
+      XXH3_128bits_reset_withSeed(xxh3, seed);
+  } else {
+    return false;
+  }
+
+  ok = true;
+  ssize_t got;
+  while ((got = read(fd, buffer, sizeof(buffer))) > 0) {
+    if (algo == CHECKSUM_ALGO_XXH64)
+      XXH64_update(&xxh64, buffer, (size_t)got);
+    else if (XXH3_64bits_update(xxh3, buffer, (size_t)got) == XXH_ERROR) {
+      ok = false;
+      break;
+    }
+  }
+  if (got < 0)
+    ok = false;
+
+  if (ok) {
+    if (algo == CHECKSUM_ALGO_XXH64) {
+      uint64_t digest = XXH64_digest(&xxh64);
+      memcpy(out, &digest, sizeof(digest));
+      *out_len = sizeof(digest);
+    } else if (algo == CHECKSUM_ALGO_XXH3) {
+      uint64_t digest = XXH3_64bits_digest(xxh3);
+      memcpy(out, &digest, sizeof(digest));
+      *out_len = sizeof(digest);
+    } else {
+      XXH128_hash_t digest = XXH3_128bits_digest(xxh3);
+      memcpy(out, &digest, sizeof(digest));
+      *out_len = sizeof(digest);
+    }
+  }
+  if (xxh3)
+    XXH3_freeState(xxh3);
+  return ok;
 }
 
 int checksum_algo_from_name(const char* name) {
@@ -45,8 +340,18 @@ int checksum_algo_from_name(const char* name) {
     return -1;
   if (strcasecmp(name, "xxh64") == 0 || strcasecmp(name, "xxhash") == 0)
     return (int)CHECKSUM_ALGO_XXH64;
+  if (strcasecmp(name, "xxh3") == 0)
+    return (int)CHECKSUM_ALGO_XXH3;
+  if (strcasecmp(name, "xxh128") == 0)
+    return (int)CHECKSUM_ALGO_XXH128;
   if (strcasecmp(name, "md5") == 0)
     return (int)CHECKSUM_ALGO_MD5;
+  if (strcasecmp(name, "md4") == 0)
+    return (int)CHECKSUM_ALGO_MD4;
+  if (strcasecmp(name, "sha1") == 0)
+    return (int)CHECKSUM_ALGO_SHA1;
+  if (strcasecmp(name, "none") == 0)
+    return (int)CHECKSUM_ALGO_NONE;
   return -1;
 }
 
@@ -54,22 +359,69 @@ const char* checksum_algo_name(ChecksumAlgo algo) {
   switch (algo) {
   case CHECKSUM_ALGO_XXH64:
     return "xxh64";
+  case CHECKSUM_ALGO_XXH3:
+    return "xxh3";
+  case CHECKSUM_ALGO_XXH128:
+    return "xxh128";
   case CHECKSUM_ALGO_MD5:
     return "md5";
+  case CHECKSUM_ALGO_MD4:
+    return "md4";
+  case CHECKSUM_ALGO_SHA1:
+    return "sha1";
+  case CHECKSUM_ALGO_NONE:
+    return "none";
   }
   return "<unknown>";
 }
 
 bool checksum_algo_valid(int algo) {
-  return algo == (int)CHECKSUM_ALGO_XXH64 || algo == (int)CHECKSUM_ALGO_MD5;
+  return algo == (int)CHECKSUM_ALGO_XXH64 || algo == (int)CHECKSUM_ALGO_MD5 ||
+         algo == (int)CHECKSUM_ALGO_XXH3 || algo == (int)CHECKSUM_ALGO_XXH128 ||
+         algo == (int)CHECKSUM_ALGO_MD4 || algo == (int)CHECKSUM_ALGO_SHA1 ||
+         algo == (int)CHECKSUM_ALGO_NONE;
 }
 
 uint8_t checksum_digest_len(ChecksumAlgo algo) {
   switch (algo) {
   case CHECKSUM_ALGO_XXH64:
+  case CHECKSUM_ALGO_XXH3:
     return 8;
+  case CHECKSUM_ALGO_XXH128:
   case CHECKSUM_ALGO_MD5:
+  case CHECKSUM_ALGO_MD4:
     return 16;
+  case CHECKSUM_ALGO_SHA1:
+    return 20;
+  case CHECKSUM_ALGO_NONE:
+    return 0;
   }
   return 0;
-}
+}
+
+static ChecksumAlgo compiled_checksum_preference_first(void) {
+  /* rsync 3.4.1 default preference order; every entry is compiled in, so this
+   * resolves to xxh128. */
+  static const ChecksumAlgo preference[] = {
+      CHECKSUM_ALGO_XXH128, CHECKSUM_ALGO_XXH3, CHECKSUM_ALGO_XXH64, CHECKSUM_ALGO_MD5,
+      CHECKSUM_ALGO_MD4,    CHECKSUM_ALGO_SHA1, CHECKSUM_ALGO_NONE,
+  };
+  for (size_t i = 0; i < sizeof(preference) / sizeof(preference[0]); i++) {
+    if (checksum_algo_valid((int)preference[i]))
+      return preference[i];
+  }
+  return CHECKSUM_ALGO_XXH64;
+}
+
+int checksum_choice_resolve(void) {
+  bool specified = false;
+  int env = env_choice_first("RSYNC_CHECKSUM_LIST", checksum_algo_from_name, &specified);
+  if (specified)
+    return env; /* -1 = the list named no supported checksum */
+  return (int)compiled_checksum_preference_first();
+}
+
+ChecksumAlgo checksum_negotiate_default(void) {
+  int resolved = checksum_choice_resolve();
+  return resolved >= 0 ? (ChecksumAlgo)resolved : compiled_checksum_preference_first();
+}

src/shared/checksum.h

@@ -8,18 +8,35 @@
 /* Whole-file content-digest algorithms selectable with --checksum-choice and
  * seeded with --checksum-seed.  The ids are the values actually placed on the
  * wire (config frame), so they must be kept stable and validated on receive.
- * CHECKSUM_ALGO_XXH64 == 0 is the default and is byte-for-byte what FastSync
- * computed before these options existed (xxHash64 with seed 0). */
-typedef enum { CHECKSUM_ALGO_XXH64 = 0, CHECKSUM_ALGO_MD5 = 1 } ChecksumAlgo;
+ * CHECKSUM_ALGO_XXH64 == 0 is the historical FastSync default and its numeric
+ * value is preserved.  The full set mirrors the algorithms rsync 3.4.1 can be
+ * built with; every one of them is implemented here. */
+typedef enum {
+  CHECKSUM_ALGO_XXH64 = 0,
+  CHECKSUM_ALGO_MD5 = 1,
+  CHECKSUM_ALGO_XXH3 = 2,
+  CHECKSUM_ALGO_XXH128 = 3,
+  CHECKSUM_ALGO_MD4 = 4,
+  CHECKSUM_ALGO_SHA1 = 5,
+  CHECKSUM_ALGO_NONE = 6
+} ChecksumAlgo;
 
-/* md5 digest is 16 bytes, the longest supported. */
-#define CHECKSUM_MAX_DIGEST_LEN 16
+/* FastSync's negotiated default (rsync 3.4.1 auto-negotiates xxh128 first).
+ * The wire default for Config->checksum_algo is this value. */
+#define CHECKSUM_ALGO_DEFAULT CHECKSUM_ALGO_XXH128
+
+/* sha1 digest is 20 bytes, the longest supported. */
+#define CHECKSUM_MAX_DIGEST_LEN 20
 
 /* Compute the whole-file digest of the first `size` bytes of `data`.
  *
  *  - CHECKSUM_ALGO_XXH64: xxHash64(data, size, seed) (full 64-bit seed).
- *  - CHECKSUM_ALGO_MD5:   md5(data, size) via OpenSSL EVP.
- *                          md5 has no seed, so `seed` is ignored (documented).
+ *  - CHECKSUM_ALGO_XXH3:  XXH3_64bits_withSeed(data, size, seed).
+ *  - CHECKSUM_ALGO_XXH128: XXH3_128bits_withSeed(data, size, seed).
+ *  - CHECKSUM_ALGO_MD5:   md5(data, size) via OpenSSL EVP (seed ignored).
+ *  - CHECKSUM_ALGO_MD4:   md4(data, size), self-contained RFC 1320 (seed ignored).
+ *  - CHECKSUM_ALGO_SHA1:  sha1(data, size) via OpenSSL EVP (seed ignored).
+ *  - CHECKSUM_ALGO_NONE:  no digest; *out_len is 0 and nothing is written.
  *  - `size == 0` hashes the empty input (plus its seed), not a NULL input.
  *
  * Writes up to `out_capacity` bytes into `out`, storing the digest length in
@@ -28,9 +45,23 @@ typedef enum { CHECKSUM_ALGO_XXH64 = 0, CHECKSUM_ALGO_MD5 = 1 } ChecksumAlgo;
 bool checksum_digest(ChecksumAlgo algo, uint64_t seed, const void* data, size_t size, uint8_t* out,
                      size_t out_capacity, size_t* out_len);
 
+/* Streaming whole-file digest: hash the contents of `path` without holding the
+ * whole file in memory.  Same digest/capacity contract as checksum_digest.
+ * Returns false on open/read failure or an undersized buffer. */
+bool checksum_digest_file(ChecksumAlgo algo, uint64_t seed, const char* path, uint8_t* out,
+                          size_t out_capacity, size_t* out_len);
+
+/* Descriptor form of the streaming digest: rewinds `fd` to the start and hashes
+ * to EOF without closing it.  Used by the --verify-basis path to hash an
+ * already-open, root-confined basis descriptor.  Same contract as
+ * checksum_digest_file. */
+bool checksum_digest_fd(ChecksumAlgo algo, uint64_t seed, int fd, uint8_t* out, size_t out_capacity,
+                        size_t* out_len);
+
 /* Resolve a --checksum-choice string (case-insensitive) to an algorithm id.
- * Accepts "xxh64" and "xxhash" (both map to CHECKSUM_ALGO_XXH64, rsync's
- * xxhash spelling) and "md5".  Returns -1 for any unsupported name. */
+ * Accepts "xxh64"/"xxhash", "xxh3", "xxh128", "md5", "md4", "sha1", "none".
+ * "auto" is not an algorithm here; the caller resolves it to the negotiated
+ * default.  Returns -1 for any unrecognized name. */
 int checksum_algo_from_name(const char* name);
 
 /* Canonical name of an algorithm (used in CLI error messages). */
@@ -39,7 +70,20 @@ const char* checksum_algo_name(ChecksumAlgo algo);
 /* True when `algo` is a supported id (used by config receive validation). */
 bool checksum_algo_valid(int algo);
 
-/* Digest length in bytes for an algorithm (xxx64 = 8, md5 = 16). */
+/* Digest length in bytes for an algorithm (xxh64/xxh3 = 8,
+ * md5/md4/xxh128 = 16, sha1 = 20, none = 0). */
 uint8_t checksum_digest_len(ChecksumAlgo algo);
 
-#endif /* CHECKSUM_H */
+/* Pick the first algorithm from FastSync's compiled-in preference list that is
+ * supported on this build (rsync 3.4.1's `--version` order:
+ * xxh128 xxh3 xxh64 md5 md4 sha1 none).  Used to resolve "auto". */
+ChecksumAlgo checksum_negotiate_default(void);
+
+/* Resolve "auto" the way rsync does: the first supported name in
+ * RSYNC_CHECKSUM_LIST (whitespace-separated, client half ends at '&'), then the
+ * compiled-in preference order when the variable is unset/blank.  Returns -1
+ * when the variable is set but names no supported checksum (rsync's failed
+ * negotiation), otherwise a valid ChecksumAlgo id. */
+int checksum_choice_resolve(void);
+
+#endif /* CHECKSUM_H */

src/shared/chmod.c

@@ -1,90 +1,183 @@
 #include "chmod.h"
+#include "file.h"
 #include <stddef.h>
 #include <string.h>
 
-static bool parse_clause(mode_t* mode, const char* begin, const char* end) {
-  const char* p = begin;
-  unsigned who = 0;
-  while (p < end && strchr("ugoa", *p)) {
-    if (*p == 'a')
-      who = 7;
-    else
-      who |= *p == 'u' ? 1U : (*p == 'g' ? 2U : 4U);
-    p++;
-  }
-  if (who == 0)
-    who = 7;
-  if (p == end || (*p != '+' && *p != '-' && *p != '='))
-    return false;
-  char operation = *p++;
-  mode_t bits = 0;
-  while (p < end) {
-    mode_t bit;
-    switch (*p++) {
-    case 'r':
-      bit = 4;
-      break;
-    case 'w':
-      bit = 2;
-      break;
-    case 'x':
-      bit = 1;
-      break;
-    default:
-      return false;
-    }
-    bits |= bit;
-  }
-  for (unsigned class_index = 0; class_index < 3; class_index++) {
-    unsigned class_bit = 1U << class_index;
-    if (!(who & class_bit))
-      continue;
-    mode_t shift = (mode_t)((2U - class_index) * 3U);
-    mode_t mask = (mode_t)(7U << shift);
-    mode_t class_bits = (mode_t)(bits << shift);
-    if (operation == '+')
-      *mode |= class_bits;
-    else if (operation == '-')
-      *mode &= ~class_bits;
-    else
-      *mode = (*mode & ~mask) | class_bits;
-  }
-  return true;
-}
+/* rsync's --chmod parser (parse_chmod + tweak_mode).  A single clause is
+ * applied as it is completed, so repeated clauses and repeated --chmod options
+ * (joined with commas by the CLI) accumulate exactly like rsync.  The D/F
+ * selectors restrict a clause to directories/files; X adds execute only to
+ * directories or files that were already executable. */
+
+#define CHMOD_BITS 07777
+#define CHMOD_FLAG_X_KEEP (1U << 0)
+#define CHMOD_FLAG_DIRS_ONLY (1U << 1)
+#define CHMOD_FLAG_FILES_ONLY (1U << 2)
+
+enum chmod_op { CHMOD_OP_ADD = 1, CHMOD_OP_SUB, CHMOD_OP_EQ, CHMOD_OP_SET };
+enum chmod_state {
+  CHMOD_STATE_ERROR,
+  CHMOD_STATE_1ST_HALF,
+  CHMOD_STATE_2ND_HALF,
+  CHMOD_STATE_OCTAL
+};
 
 bool chmod_apply(mode_t mode, const char* spec, mode_t* result) {
   if (!spec || !*spec || !result)
     return false;
-  bool numeric = true;
-  size_t length = strlen(spec);
-  if (length > 4)
-    numeric = false;
-  for (size_t i = 0; i < length && numeric; i++)
-    numeric = spec[i] >= '0' && spec[i] <= '7';
-  if (numeric) {
-    if (length == 0 || length > 4)
-      return false;
-    mode_t parsed = 0;
-    for (size_t i = 0; i < length; i++)
-      parsed = (mode_t)((parsed << 3) | (spec[i] - '0'));
-    *result = parsed;
-    return true;
-  }
-
+  const mode_t nonperm = mode & ~(mode_t)CHMOD_BITS;
+  const bool initially_executable = (mode & 0111) != 0;
   mode_t changed = mode;
-  const char* begin = spec;
-  while (*begin) {
-    const char* end = strchr(begin, ',');
-    if (!end)
-      end = begin + strlen(begin);
-    if (!parse_clause(&changed, begin, end))
-      return false;
-    if (*end == '\0')
+  int state = CHMOD_STATE_1ST_HALF;
+  unsigned where = 0;
+  int what = 0, op = 0, topbits = 0, topoct = 0, flags = 0;
+  const char* p = spec;
+  while (state != CHMOD_STATE_ERROR) {
+    if (*p == '\0' || *p == ',') {
+      int bits;
+      if (!op) {
+        state = CHMOD_STATE_ERROR;
+        break;
+      }
+      if (where)
+        bits = (int)(where * (unsigned)what);
+      else {
+        where = 0111;
+        bits = (int)((where * (unsigned)what) & ~(unsigned)file_process_umask());
+      }
+      int mode_and, mode_or;
+      switch (op) {
+      case CHMOD_OP_ADD:
+        mode_and = CHMOD_BITS;
+        mode_or = bits + topoct;
+        break;
+      case CHMOD_OP_SUB:
+        mode_and = CHMOD_BITS - bits - topoct;
+        mode_or = 0;
+        break;
+      case CHMOD_OP_EQ:
+        mode_and = CHMOD_BITS - (int)(where * 7U) - (topoct ? topbits : 0);
+        mode_or = bits + topoct;
+        break;
+      default:
+        mode_and = 0;
+        mode_or = bits;
+        break;
+      }
+      bool is_dir = S_ISDIR(nonperm);
+      if (!((flags & CHMOD_FLAG_DIRS_ONLY) && !is_dir) &&
+          !((flags & CHMOD_FLAG_FILES_ONLY) && is_dir)) {
+        changed &= (mode_t)mode_and;
+        if ((flags & CHMOD_FLAG_X_KEEP) && !initially_executable && !is_dir)
+          changed |= (mode_t)(mode_or & ~0111);
+        else
+          changed |= (mode_t)mode_or;
+      }
+      if (*p == '\0')
+        break;
+      p++;
+      state = CHMOD_STATE_1ST_HALF;
+      where = 0;
+      what = op = topoct = topbits = flags = 0;
+      continue;
+    }
+    switch (state) {
+    case CHMOD_STATE_1ST_HALF:
+      switch (*p) {
+      case 'D':
+        if (flags & CHMOD_FLAG_FILES_ONLY) {
+          state = CHMOD_STATE_ERROR;
+          break;
+        }
+        flags |= CHMOD_FLAG_DIRS_ONLY;
+        break;
+      case 'F':
+        if (flags & CHMOD_FLAG_DIRS_ONLY) {
+          state = CHMOD_STATE_ERROR;
+          break;
+        }
+        flags |= CHMOD_FLAG_FILES_ONLY;
+        break;
+      case 'u':
+        where |= 0100;
+        topbits |= 04000;
+        break;
+      case 'g':
+        where |= 0010;
+        topbits |= 02000;
+        break;
+      case 'o':
+        where |= 0001;
+        break;
+      case 'a':
+        where |= 0111;
+        break;
+      case '+':
+        op = CHMOD_OP_ADD;
+        state = CHMOD_STATE_2ND_HALF;
+        break;
+      case '-':
+        op = CHMOD_OP_SUB;
+        state = CHMOD_STATE_2ND_HALF;
+        break;
+      case '=':
+        op = CHMOD_OP_EQ;
+        state = CHMOD_STATE_2ND_HALF;
+        break;
+      default:
+        if (*p >= '0' && *p <= '7' && !where) {
+          op = CHMOD_OP_SET;
+          state = CHMOD_STATE_OCTAL;
+          where = 1;
+          what = *p - '0';
+        } else {
+          state = CHMOD_STATE_ERROR;
+        }
+        break;
+      }
       break;
-    begin = end + 1;
-    if (!*begin)
-      return false;
+    case CHMOD_STATE_2ND_HALF:
+      switch (*p) {
+      case 'r':
+        what |= 4;
+        break;
+      case 'w':
+        what |= 2;
+        break;
+      case 'X':
+        flags |= CHMOD_FLAG_X_KEEP;
+        /* fall through */
+      case 'x':
+        what |= 1;
+        break;
+      case 's':
+        if (topbits)
+          topoct |= topbits;
+        else
+          topoct = 04000;
+        break;
+      case 't':
+        topoct |= 01000;
+        break;
+      default:
+        state = CHMOD_STATE_ERROR;
+        break;
+      }
+      break;
+    default:
+      if (*p >= '0' && *p <= '7') {
+        what = what * 8 + (*p - '0');
+        if (what > CHMOD_BITS)
+          state = CHMOD_STATE_ERROR;
+      } else {
+        state = CHMOD_STATE_ERROR;
+      }
+      break;
+    }
+    p++;
   }
-  *result = changed;
+  if (state == CHMOD_STATE_ERROR)
+    return false;
+  *result = (changed & (mode_t)CHMOD_BITS) | nonperm;
   return true;
 }

src/shared/chmod.h

@@ -4,7 +4,10 @@
 #include <stdbool.h>
 #include <sys/stat.h>
 
-/* Apply the supported rsync --chmod syntax to a permission mode. */
+/* Apply rsync's --chmod syntax to a permission mode, including the D/F/X
+ * selectors and the s/t special bits.  `mode` should carry the file type bits
+ * (S_IFDIR/S_IFREG) so D/F/X can be evaluated; the type bits are preserved in
+ * `result`.  A spec may contain comma-separated clauses, which accumulate. */
 bool chmod_apply(mode_t mode, const char* spec, mode_t* result);
 
 #endif

src/shared/compression.c

@@ -2,40 +2,198 @@
 #include "data.h"
 #include "log.h"
 #include "protocol.h"
+#include "utils.h"
 #include <limits.h>
+#include <lz4.h>
+#include <stdatomic.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <strings.h>
 #include <threads.h>
 #include <unistd.h>
+#include <zlib.h>
 #include <zstd.h>
 
 #define INITIAL_DECOMPRESS_BUF_SIZE (1024 * 1024)
 #define MAX_DECOMPRESSED_SIZE (100ULL * 1024 * 1024) /* 100 MB hard ceiling */
 
-static char* SKIP_COMPRESSION_EXTENSIONS[] = {".jpg", ".jpeg", ".png", ".gif", ".mp4", ".mkv",
-                                              ".zip", ".gz",   ".xz",  ".zst", NULL};
+/* rsync 3.4.1's built-in skip-compress suffix list (the `--skip-compress`
+ * defaults, in the man page's order).  rsync stores it as space-separated
+ * "*.suffix" globs; FastSync matches the plain suffix after the final dot, so
+ * the leading "*." is omitted here.  A user --skip-compress list replaces this
+ * default entirely (matching rsync). */
+#define DEFAULT_SKIP_COMPRESS_SUFFIXES                                                             \
+  "3g2 3gp 7z aac ace apk avi bz2 deb dmg ear f4v flac flv gpg gz iso jar jpeg jpg lrz lz lz4 "    \
+  "lzma "                                                                                          \
+  "lzo m1a m1v m2a m2ts m2v m4a m4b m4p m4r m4v mka mkv mov mp1 mp2 mp3 mp4 mpa mpeg mpg mpv mts " \
+  "odb odf odg odi odm odp ods odt oga ogg ogm ogv ogx opus otg oth otp ots ott oxt png qt rar "   \
+  "rpm "                                                                                           \
+  "rz rzip spx squashfs sxc sxd sxg sxm sxw sz tbz tbz2 tgz tlz ts txz tzo vob war webm webp xz "  \
+  "z "                                                                                             \
+  "zip zst"
+
+/* Self-describing compressed frames: the first byte is the CompressionAlgo id.
+ * zlib/lz4 store the uncompressed size as a little-endian uint32 after the
+ * codec byte so decompression can be exactly pre-sized and bounded. */
+#define LZ4_SIZE_PREFIX_LEN 4
+
+static _Atomic int g_compression_algo = COMPRESSION_ALGO_ZSTD;
+
+/* Case-insensitive match of a bare suffix (no leading dot) against a
+ * space-separated suffix list. */
+static bool suffix_in_list(const char* name, const char* list) {
+  size_t name_len = strlen(name);
+  while (*list) {
+    while (*list == ' ')
+      list++;
+    const char* start = list;
+    while (*list && *list != ' ')
+      list++;
+    size_t len = (size_t)(list - start);
+    if (len == name_len && strncasecmp(name, start, len) == 0)
+      return true;
+  }
+  return false;
+}
 
 bool compression_should_skip_with_suffixes(const char* path, char* const* suffixes, int count) {
   if (!path)
     return false;
   const char* dot = strrchr(path, '.');
-  if (!dot)
+  if (!dot || dot[1] == '\0')
     return false;
-  if (count < 0) {
-    suffixes = SKIP_COMPRESSION_EXTENSIONS;
-    count = 0;
-    while (SKIP_COMPRESSION_EXTENSIONS[count])
-      count++;
-  }
+  const char* name = dot + 1;
+  /* count < 0 (the user gave no --skip-compress) selects rsync's built-in
+   * default list; a non-negative count is the user's explicit list. */
+  if (count < 0)
+    return suffix_in_list(name, DEFAULT_SKIP_COMPRESS_SUFFIXES);
   for (int i = 0; i < count; i++) {
-    if (strcasecmp(dot, suffixes[i]) == 0)
+    const char* suffix = suffixes[i];
+    if (suffix[0] == '.')
+      suffix++;
+    if (strcasecmp(name, suffix) == 0)
       return true;
   }
   return false;
 }
 
+int compression_algo_from_name(const char* name) {
+  if (!name)
+    return -1;
+  if (strcasecmp(name, "zstd") == 0)
+    return (int)COMPRESSION_ALGO_ZSTD;
+  if (strcasecmp(name, "lz4") == 0)
+    return (int)COMPRESSION_ALGO_LZ4;
+  if (strcasecmp(name, "zlib") == 0)
+    return (int)COMPRESSION_ALGO_ZLIB;
+  if (strcasecmp(name, "zlibx") == 0)
+    return (int)COMPRESSION_ALGO_ZLIBX;
+  if (strcasecmp(name, "none") == 0)
+    return (int)COMPRESSION_ALGO_NONE;
+  return -1;
+}
+
+const char* compression_algo_name(CompressionAlgo algo) {
+  switch (algo) {
+  case COMPRESSION_ALGO_NONE:
+    return "none";
+  case COMPRESSION_ALGO_ZSTD:
+    return "zstd";
+  case COMPRESSION_ALGO_LZ4:
+    return "lz4";
+  case COMPRESSION_ALGO_ZLIB:
+    return "zlib";
+  case COMPRESSION_ALGO_ZLIBX:
+    return "zlibx";
+  }
+  return "<unknown>";
+}
+
+bool compression_algo_valid(int algo) {
+  return algo == (int)COMPRESSION_ALGO_NONE || algo == (int)COMPRESSION_ALGO_ZSTD ||
+         algo == (int)COMPRESSION_ALGO_LZ4 || algo == (int)COMPRESSION_ALGO_ZLIB ||
+         algo == (int)COMPRESSION_ALGO_ZLIBX;
+}
+
+bool compression_algo_enabled(CompressionAlgo algo) {
+  return algo != COMPRESSION_ALGO_NONE;
+}
+
+static CompressionAlgo compiled_preference_first(void) {
+  /* rsync 3.4.1 default preference order; every entry is compiled in, so this
+   * resolves to zstd. */
+  static const CompressionAlgo preference[] = {
+      COMPRESSION_ALGO_ZSTD, COMPRESSION_ALGO_LZ4,  COMPRESSION_ALGO_ZLIBX,
+      COMPRESSION_ALGO_ZLIB, COMPRESSION_ALGO_NONE,
+  };
+  for (size_t i = 0; i < sizeof(preference) / sizeof(preference[0]); i++) {
+    if (compression_algo_valid((int)preference[i]))
+      return preference[i];
+  }
+  return COMPRESSION_ALGO_ZSTD;
+}
+
+int compression_choice_resolve(void) {
+  bool specified = false;
+  int env = env_choice_first("RSYNC_COMPRESS_LIST", compression_algo_from_name, &specified);
+  if (specified)
+    return env; /* -1 = the list named no supported codec */
+  return (int)compiled_preference_first();
+}
+
+CompressionAlgo compression_negotiate_default(void) {
+  int resolved = compression_choice_resolve();
+  return resolved >= 0 ? (CompressionAlgo)resolved : compiled_preference_first();
+}
+
+int compression_default_level(CompressionAlgo algo) {
+  switch (algo) {
+  case COMPRESSION_ALGO_ZSTD:
+    return ZSTD_CLEVEL_DEFAULT;
+  case COMPRESSION_ALGO_ZLIB:
+  case COMPRESSION_ALGO_ZLIBX:
+    return 6; /* rsync resolves zlib's Z_DEFAULT_COMPRESSION (-1) to 6 */
+  case COMPRESSION_ALGO_LZ4:
+    return 1; /* rsync lz4 level is 0/ignored; positive keeps the gate on */
+  case COMPRESSION_ALGO_NONE:
+    return 0;
+  }
+  return 0;
+}
+
+int compression_clamp_level(CompressionAlgo algo, int level) {
+  switch (algo) {
+  case COMPRESSION_ALGO_ZSTD:
+    if (level < 1)
+      return 1;
+    if (level > 22)
+      return 22;
+    return level;
+  case COMPRESSION_ALGO_ZLIB:
+  case COMPRESSION_ALGO_ZLIBX:
+    if (level < 1)
+      return 1;
+    if (level > 9)
+      return 9;
+    return level;
+  case COMPRESSION_ALGO_LZ4:
+    return 1; /* ignored by lz4_compress; keeps the "compress" gate on */
+  case COMPRESSION_ALGO_NONE:
+    return 0;
+  }
+  return level;
+}
+
+void compression_set_algo(CompressionAlgo algo) {
+  if (compression_algo_valid((int)algo))
+    atomic_store(&g_compression_algo, (int)algo);
+}
+
+CompressionAlgo compression_get_algo(void) {
+  return (CompressionAlgo)atomic_load(&g_compression_algo);
+}
+
 /* Per-thread cache of zstd contexts plus the grow-only compression scratch
  * buffer.  zstd contexts are stateful and not safe to share between threads,
  * so each thread keeps its own (see compression_get_thread_ctx).  The cache is
@@ -126,17 +284,25 @@ static void compression_ctx_put(CompressionThreadCtx* ctx) {
     compression_ctx_free(ctx);
 }
 
-Data* data_compress(Data* data_to_compress, int compression_level) {
-  return data_compress_with_threads(data_to_compress, compression_level, 0);
+/* Build a frame consisting of a copy of `src` prefixed by `codec`. */
+static Data* frame_with_codec(const void* src, size_t size, CompressionAlgo codec) {
+  if (size > SIZE_MAX - 1)
+    return NULL;
+  Data* out = data_create_empty(size + 1);
+  if (!out)
+    return NULL;
+  ((uint8_t*)out->data)[0] = (uint8_t)codec;
+  if (size > 0)
+    memcpy((uint8_t*)out->data + 1, src, size);
+  out->size = size + 1;
+  return out;
 }
 
-Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
-                                 int compression_threads) {
-  if (!data_to_compress || (!data_to_compress->data && data_to_compress->size != 0) ||
-      compression_threads < 0 || compression_threads > COMPRESSION_MAX_THREADS)
+static Data* zstd_compress(Data* in, int compression_level, int compression_threads) {
+  size_t dst_size = ZSTD_compressBound(in->size);
+  if (dst_size > SIZE_MAX - 1)
     return NULL;
-  log_message(LOG_LEVEL_DEBUG, "Starting to compress data");
-  size_t dst_size = ZSTD_compressBound(data_to_compress->size);
+  dst_size += 1; /* codec prefix */
 
   CompressionThreadCtx* ctx = compression_get_thread_ctx();
   if (ctx == NULL) {
@@ -187,7 +353,7 @@ Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
 
   if (available_threads > 0) {
     /* Streaming compression needs the source size before threaded mode can end a frame. */
-    size_t zret = ZSTD_CCtx_setPledgedSrcSize(ctx->cctx, data_to_compress->size);
+    size_t zret = ZSTD_CCtx_setPledgedSrcSize(ctx->cctx, in->size);
     if (ZSTD_isError(zret)) {
       log_message(LOG_LEVEL_ERROR, "Failed to set compression source size: %s",
                   ZSTD_getErrorName(zret));
@@ -205,8 +371,8 @@ Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
     ctx->out_cap = dst_size;
   }
 
-  ZSTD_inBuffer input = {data_to_compress->data, data_to_compress->size, 0};
-  ZSTD_outBuffer output = {ctx->out_buf, dst_size, 0};
+  ZSTD_inBuffer input = {in->data, in->size, 0};
+  ZSTD_outBuffer output = {(uint8_t*)ctx->out_buf + 1, dst_size - 1, 0};
 
   size_t ret;
   do {
@@ -219,30 +385,192 @@ Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
 
   /* Hand off an exactly-sized copy; the scratch buffer stays cached so the next
    * call does not reallocate a ZSTD_compressBound-sized block. */
-  compressed_data = data_create_empty(output.pos);
+  compressed_data = data_create_empty(output.pos + 1);
   if (compressed_data == NULL) {
     log_message(LOG_LEVEL_ERROR, "Failed to allocate compressed data");
     goto cleanup;
   }
+  ((uint8_t*)compressed_data->data)[0] = (uint8_t)COMPRESSION_ALGO_ZSTD;
   if (output.pos > 0)
-    memcpy(compressed_data->data, ctx->out_buf, output.pos);
-  compressed_data->size = output.pos;
+    memcpy((uint8_t*)compressed_data->data + 1, (uint8_t*)ctx->out_buf + 1, output.pos);
+  compressed_data->size = output.pos + 1;
 
-  log_debug_message(LOG_DEBUG_UTIL, "Data succesfully compressed from %zu to %zu",
-                    data_to_compress->size, compressed_data->size);
+  log_debug_message(LOG_DEBUG_UTIL, "Data succesfully compressed from %zu to %zu", in->size,
+                    compressed_data->size);
 
 cleanup:
   compression_ctx_put(ctx);
   return compressed_data;
 }
 
-Data* data_decompress_limited(Data* compressed_data, size_t maximum_size) {
-  if (!compressed_data || (!compressed_data->data && compressed_data->size != 0) ||
-      maximum_size == 0)
+static Data* lz4_compress(Data* in) {
+  int bound = LZ4_compressBound((int)in->size);
+  if (bound < 0 || in->size > (size_t)INT_MAX)
     return NULL;
+  Data* out = data_create_empty((size_t)bound + 1 + LZ4_SIZE_PREFIX_LEN);
+  if (!out)
+    return NULL;
+  uint32_t raw_size = (uint32_t)in->size;
+  uint8_t* p = (uint8_t*)out->data;
+  p[0] = (uint8_t)COMPRESSION_ALGO_LZ4;
+  for (int i = 0; i < LZ4_SIZE_PREFIX_LEN; i++)
+    p[1 + i] = (uint8_t)((raw_size >> (8 * i)) & 0xff);
+  int written = 0;
+  if (in->size > 0) {
+    written = LZ4_compress_default((const char*)in->data, (char*)p + 1 + LZ4_SIZE_PREFIX_LEN,
+                                   (int)in->size, bound);
+    if (written <= 0) {
+      data_destroy(out);
+      return NULL;
+    }
+  }
+  out->size = (size_t)written + 1 + LZ4_SIZE_PREFIX_LEN;
+  return out;
+}
+
+static Data* zlib_compress(Data* in, CompressionAlgo algo, int compression_level) {
+  int level = compression_level;
+  if (level < 1)
+    level = Z_DEFAULT_COMPRESSION;
+  if (level > 9)
+    level = 9;
+  uLong bound = compressBound((uLong)in->size);
+  if (in->size > (size_t)ULONG_MAX)
+    return NULL;
+  Data* out = data_create_empty((size_t)bound + 1 + LZ4_SIZE_PREFIX_LEN);
+  if (!out)
+    return NULL;
+  uint32_t raw_size = (uint32_t)in->size;
+  uint8_t* p = (uint8_t*)out->data;
+  p[0] = (uint8_t)algo;
+  for (int i = 0; i < LZ4_SIZE_PREFIX_LEN; i++)
+    p[1 + i] = (uint8_t)((raw_size >> (8 * i)) & 0xff);
+  uLongf dest_len = bound;
+  int rc = compress2(p + 1 + LZ4_SIZE_PREFIX_LEN, &dest_len, (const Bytef*)in->data,
+                     (uLong)in->size, level);
+  if (rc != Z_OK) {
+    data_destroy(out);
+    return NULL;
+  }
+  out->size = (size_t)dest_len + 1 + LZ4_SIZE_PREFIX_LEN;
+  return out;
+}
+
+Data* data_compress_codec(Data* data_to_compress, CompressionAlgo algo, int compression_level,
+                          int compression_threads) {
+  if (!data_to_compress || (!data_to_compress->data && data_to_compress->size != 0) ||
+      compression_threads < 0 || compression_threads > COMPRESSION_MAX_THREADS)
+    return NULL;
+  if (!compression_algo_valid((int)algo))
+    return NULL;
+  log_message(LOG_LEVEL_DEBUG, "Starting to compress data");
+  switch (algo) {
+  case COMPRESSION_ALGO_NONE:
+    return frame_with_codec(data_to_compress->data, data_to_compress->size, COMPRESSION_ALGO_NONE);
+  case COMPRESSION_ALGO_ZSTD:
+    return zstd_compress(data_to_compress, compression_level, compression_threads);
+  case COMPRESSION_ALGO_LZ4:
+    return lz4_compress(data_to_compress);
+  case COMPRESSION_ALGO_ZLIB:
+  case COMPRESSION_ALGO_ZLIBX:
+    return zlib_compress(data_to_compress, algo, compression_level);
+  }
+  return NULL;
+}
+
+Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
+                                 int compression_threads) {
+  return data_compress_codec(data_to_compress, compression_get_algo(), compression_level,
+                             compression_threads);
+}
+
+Data* data_compress(Data* data_to_compress, int compression_level) {
+  return data_compress_codec(data_to_compress, compression_get_algo(), compression_level, 0);
+}
+
+static Data* decompress_none(const Data* compressed_data, size_t maximum_size) {
+  size_t size = compressed_data->size - 1;
+  if (size > maximum_size)
+    return NULL;
+  Data* out = data_create_empty(size);
+  if (!out)
+    return NULL;
+  if (size > 0)
+    memcpy(out->data, (const uint8_t*)compressed_data->data + 1, size);
+  out->size = size;
+  return out;
+}
+
+/* Read the 4-byte little-endian raw size stored after the codec byte. */
+static bool read_raw_size(const Data* in, uint32_t* raw_size) {
+  if (in->size < 1 + LZ4_SIZE_PREFIX_LEN)
+    return false;
+  const uint8_t* p = (const uint8_t*)in->data;
+  uint32_t v = 0;
+  for (int i = 0; i < LZ4_SIZE_PREFIX_LEN; i++)
+    v |= (uint32_t)p[1 + i] << (8 * i);
+  *raw_size = v;
+  return true;
+}
+
+static Data* lz4_decompress(Data* compressed_data, size_t maximum_size, size_t hard_limit) {
+  uint32_t raw_size = 0;
+  if (!read_raw_size(compressed_data, &raw_size))
+    return NULL;
+  if (raw_size > hard_limit || raw_size > maximum_size)
+    return NULL;
+  size_t comp_size = compressed_data->size - 1 - LZ4_SIZE_PREFIX_LEN;
+  Data* out = data_create_empty(raw_size);
+  if (!out)
+    return NULL;
+  if (raw_size == 0) {
+    out->size = 0;
+    return out;
+  }
+  int rc = LZ4_decompress_safe((const char*)compressed_data->data + 1 + LZ4_SIZE_PREFIX_LEN,
+                               (char*)out->data, (int)comp_size, (int)raw_size);
+  if (rc < 0 || (uint32_t)rc != raw_size) {
+    log_message(LOG_LEVEL_ERROR, "LZ4 decompression failed");
+    data_destroy(out);
+    return NULL;
+  }
+  out->size = raw_size;
+  return out;
+}
+
+static Data* zlib_decompress(Data* compressed_data, size_t maximum_size, size_t hard_limit) {
+  uint32_t raw_size = 0;
+  if (!read_raw_size(compressed_data, &raw_size))
+    return NULL;
+  if (raw_size > hard_limit || raw_size > maximum_size)
+    return NULL;
+  size_t comp_size = compressed_data->size - 1 - LZ4_SIZE_PREFIX_LEN;
+  Data* out = data_create_empty(raw_size);
+  if (!out)
+    return NULL;
+  if (raw_size == 0) {
+    out->size = 0;
+    return out;
+  }
+  uLongf dest_len = raw_size;
+  int rc =
+      uncompress((Bytef*)out->data, &dest_len,
+                 (const Bytef*)compressed_data->data + 1 + LZ4_SIZE_PREFIX_LEN, (uLong)comp_size);
+  if (rc != Z_OK || dest_len != raw_size) {
+    log_message(LOG_LEVEL_ERROR, "zlib decompression failed");
+    data_destroy(out);
+    return NULL;
+  }
+  out->size = raw_size;
+  return out;
+}
+
+static Data* zstd_decompress(Data* compressed_data, size_t maximum_size) {
+  /* The zstd frame starts after the codec byte. */
+  const void* frame = (const uint8_t*)compressed_data->data + 1;
+  size_t frame_size = compressed_data->size - 1;
   log_debug_message(LOG_DEBUG_UTIL, "Start to decompress data");
-  unsigned long long dst_size =
-      ZSTD_getFrameContentSize(compressed_data->data, compressed_data->size);
+  unsigned long long dst_size = ZSTD_getFrameContentSize(frame, frame_size);
   /* ZSTD_isError() is also true for ZSTD_CONTENTSIZE_ERROR and
    * ZSTD_CONTENTSIZE_UNKNOWN (both are encoded near (size_t)-1), so test the
    * sentinels explicitly instead of blanket-rejecting every error-ish value:
@@ -256,9 +584,9 @@ Data* data_decompress_limited(Data* compressed_data, size_t maximum_size) {
   // ZSTD_CONTENTSIZE_UNKNOWN (~2^64) can cause massive allocation;
   // fall back to a conservative estimate (3x compressed size) when unknown.
   if (dst_size == ZSTD_CONTENTSIZE_UNKNOWN) {
-    if (compressed_data->size > ULLONG_MAX / 3)
+    if (frame_size > ULLONG_MAX / 3)
       return NULL;
-    dst_size = compressed_data->size * 3;
+    dst_size = frame_size * 3;
     if (dst_size < INITIAL_DECOMPRESS_BUF_SIZE)
       dst_size = INITIAL_DECOMPRESS_BUF_SIZE;
   }
@@ -295,7 +623,7 @@ Data* data_decompress_limited(Data* compressed_data, size_t maximum_size) {
     goto cleanup;
   }
 
-  ZSTD_inBuffer input = {compressed_data->data, compressed_data->size, 0};
+  ZSTD_inBuffer input = {frame, frame_size, 0};
   ZSTD_outBuffer output = {uncompressed_data->data, buf_size, 0};
 
   size_t ret;
@@ -354,6 +682,31 @@ cleanup:
   return uncompressed_data;
 }
 
+Data* data_decompress_limited(Data* compressed_data, size_t maximum_size) {
+  if (!compressed_data || (!compressed_data->data && compressed_data->size != 0) ||
+      maximum_size == 0)
+    return NULL;
+  if (compressed_data->size < 1)
+    return NULL;
+  unsigned long long hard_limit =
+      maximum_size < MAX_DECOMPRESSED_SIZE ? maximum_size : MAX_DECOMPRESSED_SIZE;
+  uint8_t codec = ((const uint8_t*)compressed_data->data)[0];
+  if (!compression_algo_valid(codec))
+    return NULL;
+  switch ((CompressionAlgo)codec) {
+  case COMPRESSION_ALGO_NONE:
+    return decompress_none(compressed_data, (size_t)hard_limit);
+  case COMPRESSION_ALGO_ZSTD:
+    return zstd_decompress(compressed_data, (size_t)hard_limit);
+  case COMPRESSION_ALGO_LZ4:
+    return lz4_decompress(compressed_data, maximum_size, (size_t)hard_limit);
+  case COMPRESSION_ALGO_ZLIB:
+  case COMPRESSION_ALGO_ZLIBX:
+    return zlib_decompress(compressed_data, maximum_size, (size_t)hard_limit);
+  }
+  return NULL;
+}
+
 Data* data_decompress(Data* compressed_data) {
   return data_decompress_limited(compressed_data, MAX_DECOMPRESSED_SIZE);
 }

src/shared/compression.h

@@ -6,11 +6,79 @@
 
 #define COMPRESSION_MAX_THREADS 64
 
+/* Compression algorithms selectable with --compress-choice / -z.  The ids are
+ * the values placed on the wire (Config->compression_algo), so they must be
+ * kept stable.  NONE is "no compression"; ZSTD is the historical FastSync
+ * default and the negotiated "auto" choice.  ZLIBX is rsync's zlib-without-
+ * matched-data variant: FastSync compresses only the delta/token bytes (it does
+ * not put matched file data in the compression stream), so its zlib codec is
+ * already the "x" form and zlib/zlibx share the same implementation, recorded
+ * under distinct ids. */
+typedef enum {
+  COMPRESSION_ALGO_NONE = 0,
+  COMPRESSION_ALGO_ZSTD = 1,
+  COMPRESSION_ALGO_LZ4 = 2,
+  COMPRESSION_ALGO_ZLIB = 3,
+  COMPRESSION_ALGO_ZLIBX = 4
+} CompressionAlgo;
+
+/* Resolve a --compress-choice string (case-insensitive) to an algorithm id.
+ * Accepts "zstd", "lz4", "zlib", "zlibx", "none".  "auto" is not an algorithm
+ * here; the caller resolves it to the negotiated default.  Returns -1 for any
+ * unrecognized name. */
+int compression_algo_from_name(const char* name);
+const char* compression_algo_name(CompressionAlgo algo);
+bool compression_algo_valid(int algo);
+
+/* Pick the first algorithm from FastSync's compiled-in preference list
+ * (rsync 3.4.1's `--version` order: zstd lz4 zlibx zlib none).  Resolves
+ * "auto". */
+CompressionAlgo compression_negotiate_default(void);
+
+/* Resolve "auto" the way rsync does: the first supported name in
+ * RSYNC_COMPRESS_LIST (whitespace-separated, client half ends at '&'), then the
+ * compiled-in preference order when the variable is unset/blank.  Returns -1
+ * when the variable is set but names no supported codec (rsync's failed
+ * negotiation), otherwise a valid CompressionAlgo id. */
+int compression_choice_resolve(void);
+
+/* rsync 3.4.1's per-codec default level, applied when the user did not pass
+ * --compress-level/--zl.  zstd uses ZSTD_CLEVEL_DEFAULT (3) and zlib/zlibx the
+ * resolved Z_DEFAULT_COMPRESSION (6).  lz4 has no tunable level in rsync
+ * (always the default acceleration); FastSync returns a positive placeholder so
+ * its "level > 0" compression gate stays engaged, and lz4_compress ignores the
+ * value, so the output is identical to rsync's.  none is 0. */
+int compression_default_level(CompressionAlgo algo);
+
+/* Clamp an explicit --compress-level to the codec's accepted range the way
+ * rsync's init_compression_level() does: zstd 1..22, zlib/zlibx 1..9, lz4
+ * ignored (fixed positive placeholder), none 0. */
+int compression_clamp_level(CompressionAlgo algo, int level);
+
+/* True when the algorithm actually compresses (i.e. is not NONE). */
+bool compression_algo_enabled(CompressionAlgo algo);
+
+/* Select the process-wide codec used by the legacy wrappers below.  Each
+ * process serves exactly one transfer config (the server forks per connection,
+ * the client configures itself before spawning transfer threads), so a
+ * process-global default is sufficient and constant for the lifetime of a
+ * transfer.  Defaults to ZSTD when never set.  Thread-safe. */
+void compression_set_algo(CompressionAlgo algo);
+CompressionAlgo compression_get_algo(void);
+
+/* Codec-aware primitives.  The compressed buffer is self-describing: its first
+ * byte is the CompressionAlgo id, so decompression never needs the codec passed
+ * separately (this keeps every existing Decompress call site source-compatible).
+ * `data_compress_codec` returns NULL on invalid input or an unsupported codec. */
+Data* data_compress_codec(Data* data_to_compress, CompressionAlgo algo, int compression_level,
+                          int compression_threads);
+Data* data_decompress_limited(Data* compressed_data, size_t maximum_size);
+
+/* Legacy zstd-default wrappers retained for existing callers/tests. */
 Data* data_compress(Data* data_to_compress, int compression_level);
 Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
                                  int compression_threads);
 Data* data_decompress(Data* compressed_data);
-Data* data_decompress_limited(Data* compressed_data, size_t maximum_size);
 bool compression_should_skip_with_suffixes(const char* path, char* const* suffixes, int count);
 
 /* Release the calling thread's cached zstd contexts (compressor, decompressor

src/shared/config.c

@@ -14,12 +14,15 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <strings.h>
 #include <limits.h>
 #include <errno.h>
 
 static void config_set_defaults(Config* config) {
   config->scanner_threads = 0;
   config->metadata_explicitly_disabled = false;
+  config->preserve_perms_explicit_off = false;
+  config->preserve_times_explicit_off = false;
   config->show_progress = false;
   config->compression_threads = 0;
   config->ssh_port = 22;
@@ -43,12 +46,14 @@ static void config_set_defaults(Config* config) {
   config->server_port = 8080;
   config->server_port_set = false;
   config->server_host_set = false;
-  /* 0 means "--timeout not given": the transport keeps its own built-in 30 s
-   * socket timeout (tcp_set_timeouts ignores non-positive values) and the
-   * protocol layer keeps its built-in 60 s per-message deadline.  A positive
-   * value overrides BOTH (see protocol_session_set_io_timeout). */
+  /* rsync defaults: --timeout=0 (I/O timeouts disabled) and --contimeout=60.
+   * A value of 0 disables the client's own deadline on both the socket layer
+   * (tcp_set_timeouts) and the protocol layer
+   * (protocol_session_set_io_timeout); a positive value sets it.  A server
+   * session floors the deadline at SERVER_IO_TIMEOUT_SEC so 0 can never hold a
+   * connection open forever. */
   config->timeout = 0;
-  config->contimeout = 10;
+  config->contimeout = 60;
   config->quiet = false;
   config->stats = false;
   config->max_depth = 0;
@@ -63,12 +68,17 @@ static void config_set_defaults(Config* config) {
   config->human_readable = false;
   config->ignore_errors = false;
   config->ignore_missing_args = false;
+  config->checksum_transfer_algo = CHECKSUM_ALGO_DEFAULT;
+  config->cli_exit_code = 0;
+  config->compression_level_set = false;
+  config->checksum_choice_set = false;
   config->filters = NULL;
   config->files_from = NULL;
   config->files_from_set = NULL;
   config->from0 = false;
   config->cvs_exclude = false;
   config->per_dir_filter = false;
+  config->per_dir_filter_count = 0;
   config->one_file_system = false;
   config->no_implied_dirs = false;
   config->dirs = false;
@@ -192,10 +202,14 @@ static bool validate_received_config(const Config* config) {
          valid_wire_bool(config->partial) && valid_wire_bool(config->delete_before) &&
          valid_wire_bool(config->checksum) && valid_wire_bool(config->eight_bit_output) &&
          valid_wire_bool(config->dry_run) && checksum_algo_valid(config->checksum_algo) &&
-         identity_wire_valid(config) && valid_wire_bool(config->preserve_atimes) &&
-         valid_wire_bool(config->preserve_crtimes) && valid_wire_bool(config->omit_dir_times) &&
-         valid_wire_bool(config->omit_link_times) && valid_wire_bool(config->munge_links) &&
-         valid_wire_bool(config->keep_dirlinks) && valid_wire_bool(config->fake_super) &&
+         compression_algo_valid(config->compression_algo) && identity_wire_valid(config) &&
+         valid_wire_bool(config->preserve_atimes) && valid_wire_bool(config->preserve_crtimes) &&
+         valid_wire_bool(config->omit_dir_times) && valid_wire_bool(config->omit_link_times) &&
+         valid_wire_bool(config->preserve_perms) && valid_wire_bool(config->preserve_times) &&
+         valid_wire_bool(config->preserve_owner) && valid_wire_bool(config->preserve_group) &&
+         valid_wire_bool(config->munge_links) && valid_wire_bool(config->keep_dirlinks) &&
+         valid_wire_bool(config->fake_super) && valid_wire_bool(config->report_dest_info) &&
+         valid_wire_bool(config->report_stats) && valid_wire_bool(config->report_deletes) &&
          (!config->copy_as_set || (config->copy_as_uid >= 0 && config->copy_as_gid >= 0)) &&
          (!config->use_compression ||
           (config->compression_level >= 1 && config->compression_level <= 22)) &&
@@ -203,8 +217,9 @@ static bool validate_received_config(const Config* config) {
          config->delta_block_size >= DELTA_BLOCK_SIZE_MIN &&
          config->delta_block_size <= DELTA_BLOCK_SIZE_MAX &&
          config->delta_max_file_size <= DELTA_MAX_FILE_SIZE && config->modify_window >= 0 &&
-         config->max_delete >= -1 && config->skip_compress_count >= 0 &&
-         config->skip_compress_count <= MAX_SKIP_COMPRESS_SUFFIXES && config->max_alloc > 0 &&
+         config->max_delete >= -1 && config->max_alloc <= MAX_SERVER_ALLOC &&
+         config->skip_compress_count >= 0 &&
+         config->skip_compress_count <= MAX_SKIP_COMPRESS_SUFFIXES &&
          (!config->chmod_spec || !*config->chmod_spec ||
           chmod_apply(0, config->chmod_spec, &(mode_t){0})) &&
          config->super_mode >= SUPER_MODE_AUTO && config->super_mode <= SUPER_MODE_OFF;
@@ -221,7 +236,13 @@ Config* config_create(void) {
 bool config_delete_timing_early(const Config* config) {
   if (!config)
     return false;
-  return config->delete_before || config->delete_during;
+  return config->delete_before;
+}
+
+bool config_delete_timing_per_dir(const Config* config) {
+  if (!config)
+    return false;
+  return config->delete_during || config->delete_delay;
 }
 
 /* A delete-timing flag is only meaningful together with --delete.  At most one
@@ -292,40 +313,68 @@ const char* config_invariants_error(const Config* config) {
            "timing; at most one may be given and each implies --delete";
   if (config->iconv_spec && !charset_spec_valid(config->iconv_spec))
     return "--iconv requires LOCAL[,REMOTE] charset names supported by iconv";
+  if ((config->preserve_perms || config->preserve_times || config->preserve_owner ||
+       config->preserve_group || config->preserve_atimes || config->preserve_crtimes ||
+       config->use_executability) &&
+      !config->use_metadata)
+    return "a preservation attribute requires metadata transmission";
   if (config->copy_as_set && !config->use_metadata)
     return "--copy-as requires metadata preservation and cannot be combined with --no-preserve";
   return NULL;
 }
 
+bool config_derived_use_metadata(const Config* config) {
+  if (!config)
+    return false;
+  if (config->preserve_perms || config->preserve_times || config->preserve_owner ||
+      config->preserve_group || config->preserve_atimes || config->preserve_crtimes ||
+      config->use_executability || config->preserve_xattrs || config->preserve_acls ||
+      config->fake_super || config->preserve_devices || config->preserve_specials ||
+      config->copy_devices || config->write_devices ||
+      (config->chmod_spec && config->chmod_spec[0]) || config->copy_as_set ||
+      config->chown_uid_set || config->chown_gid_set || config->usermap_count > 0 ||
+      config->groupmap_count > 0 || config->update)
+    return true;
+  return (config->use_incremental || config->use_delta) && !config->metadata_explicitly_disabled;
+}
+
 bool config_has_basis(const Config* config) {
   return config && config->basis_count > 0;
 }
 
 /* A basis-dir path travels from the client to the receiver and is resolved
- * below the destination root, so it must be a non-empty relative path with no
- * "." or ".." component and no traversal: an absolute or escaping path would
- * make the receiver read or link files outside its authorized root.
+ * below the destination root when relative, or used verbatim when absolute
+ * (matching rsync).  Either form must be non-empty, traversal-free (no "..")
+ * and free of "." components: an escaping path would make the receiver read or
+ * link files outside its authorized root.  An absolute path is still subject to
+ * the receiver's root confinement at open time (file_open_secure_parent), so a
+ * basis outside the authorized root is simply not found rather than an escape.
  *
  * Returns a malloc'd CANONICAL copy of an accepted path, or NULL when the path
  * is rejected.  Canonicalization collapses interior empty components ("a//b" ->
- * "a/b"), drops "." components and trailing "/"s, so validation, the delete
- * walker prefix match and the receiver's basis lookup all agree on one form.
- * The normalizer is the single source of truth for both config_basis_path_valid
- * and config_basis_append. */
+ * "a/b"), drops "." components and trailing "/"s, and preserves a leading '/'
+ * for absolute paths, so validation, the delete walker prefix match and the
+ * receiver's basis lookup all agree on one form.  The normalizer is the single
+ * source of truth for both config_basis_path_valid and config_basis_append. */
 static char* basis_path_normalize(const char* path) {
-  if (!path || path[0] == '\0' || path[0] == '/' || has_path_traversal(path))
+  if (!path || path[0] == '\0' || has_path_traversal(path))
     return NULL;
-  if (strcmp(path, ".") == 0)
+  bool absolute = path[0] == '/';
+  if (!absolute && strcmp(path, ".") == 0)
+    return NULL;
+  if (absolute && strcmp(path, "/") == 0)
     return NULL;
   char* dup = str_dup(path);
   if (!dup)
     return NULL;
   size_t out_len = 0;
-  char* out = malloc(strlen(path) + 1);
+  char* out = malloc(strlen(path) + 2);
   if (!out) {
     free(dup);
     return NULL;
   }
+  if (absolute)
+    out[out_len++] = '/';
   char* saveptr = NULL;
   bool ok = true;
   for (char* part = strtok_r(dup, "/", &saveptr); part; part = strtok_r(NULL, "/", &saveptr)) {
@@ -335,14 +384,14 @@ static char* basis_path_normalize(const char* path) {
     }
     if (strcmp(part, ".") == 0)
       continue;
-    if (out_len > 0)
+    if (out_len > 0 && out[out_len - 1] != '/')
       out[out_len++] = '/';
     size_t len = strlen(part);
     memcpy(out + out_len, part, len);
     out_len += len;
   }
   free(dup);
-  if (!ok || out_len == 0) {
+  if (!ok || out_len == 0 || (absolute && out_len == 1)) {
     free(out);
     return NULL;
   }
@@ -725,15 +774,25 @@ void config_delete(Config* config) {
       free(config->skip_compress_suffixes[i]);
     free(config->skip_compress_suffixes);
   }
-  free(config->usermap);
+  if (config->usermap) {
+    for (int i = 0; i < config->usermap_count; i++)
+      free(config->usermap[i].to_name);
+    free(config->usermap);
+  }
   config->usermap = NULL;
   config->usermap_count = 0;
-  free(config->groupmap);
+  if (config->groupmap) {
+    for (int i = 0; i < config->groupmap_count; i++)
+      free(config->groupmap[i].to_name);
+    free(config->groupmap);
+  }
   config->groupmap = NULL;
   config->groupmap_count = 0;
   if (config->filters) {
     array_list_delete(config->filters);
   }
+  filter_rule_list_free(config->protect_rules);
+  config->protect_rules = NULL;
   /* A --delay-updates staging tree is transient receiver state: remove any
      leftovers on every exit path (success already emptied it). */
   if (config->delay_context)
@@ -756,11 +815,14 @@ void config_delete(Config* config) {
  * ------------------------------------------------------------------------- */
 
 /* --max-alloc: raw 64-bit value, clamped server-side and installed as the
- * session allocation ceiling.  A zero value is rejected. */
+ * session allocation ceiling.  A received 0 is rsync's "no alloc limit"; on the
+ * receive path it is mapped to the server ceiling so a client can never disable
+ * it (client-side 0 remains unlimited).  Any value above the ceiling is clamped
+ * to it. */
 static bool config_receive_max_alloc(int fd, unsigned long long* value) {
-  if (!receive_n_data(fd, value, sizeof(*value)) || *value == 0)
+  if (!receive_n_data(fd, value, sizeof(*value)))
     return false;
-  if (*value > MAX_SERVER_ALLOC)
+  if (*value == 0 || *value > MAX_SERVER_ALLOC)
     *value = MAX_SERVER_ALLOC;
   protocol_session_set_max_alloc(NULL, *value);
   return true;
@@ -842,6 +904,14 @@ static bool config_receive_checksum_algo(int fd, int* value) {
   return true;
 }
 
+static bool config_receive_compression_algo(int fd, int* value) {
+  int algo;
+  if (!receive_int(fd, &algo) || !compression_algo_valid(algo))
+    return false;
+  *value = algo;
+  return true;
+}
+
 static bool config_receive_super_mode(int fd, SuperMode* value) {
   int mode;
   if (!receive_int(fd, &mode) || mode < SUPER_MODE_AUTO || mode > SUPER_MODE_OFF)
@@ -958,9 +1028,128 @@ static bool receive_basis_entries(int fd, Config* c, ConfigStringBudget* budget)
   return true;
 }
 
+/* Receiver-side delete-protection rules (protocol 2.28.0).  The sender compiles
+ * its command-line selection rules exactly as the scanner does and streams the
+ * result as one bounded, self-describing block (count + per-rule records); the
+ * receiver reconstructs a FilterRuleList for the --delete extras walk.  owner
+ * and pattern are charged through the shared ConfigStringBudget and the block
+ * additionally enforces MAX_FILTER_RULES / MAX_FILTER_BYTES. */
+static bool send_protect_entries(int fd, const Config* c) {
+  int count = c->filters ? c->filters->size : 0;
+  const char** texts = NULL;
+  if (count > 0) {
+    texts = malloc((size_t)count * sizeof(char*));
+    if (!texts)
+      return false;
+    for (int i = 0; i < count; i++)
+      texts[i] = (const char*)c->filters->items[i];
+  }
+  char err[160];
+  FilterRuleList* rules =
+      filter_base_build(texts, count, c->cvs_exclude, c->delete_excluded, err, sizeof(err));
+  free(texts);
+  if (!rules) {
+    log_message(LOG_LEVEL_ERROR, "invalid filter rule: %s", err);
+    return false;
+  }
+  bool ok = send_int(fd, rules->count);
+  for (int i = 0; ok && i < rules->count; i++) {
+    const FilterRule* r = rules->items[i];
+    /* Mirror the receiver's limit so the peer never receives a rule it will
+       reject as a protocol error. */
+    if (r->pattern && strlen(r->pattern) > MAX_PROTECT_PATTERN_LEN) {
+      log_message(LOG_LEVEL_ERROR, "filter pattern exceeds %d bytes", MAX_PROTECT_PATTERN_LEN);
+      filter_rule_list_free(rules);
+      return false;
+    }
+    ok = send_int(fd, (int)r->action) && send_int(fd, (int)r->sides) &&
+         send_int(fd, r->anchored ? 1 : 0) && send_int(fd, r->dir_only ? 1 : 0) &&
+         send_int(fd, r->negate ? 1 : 0) && send_str(fd, r->owner ? r->owner : "") &&
+         send_str(fd, r->pattern ? r->pattern : "");
+  }
+  filter_rule_list_free(rules);
+  return ok;
+}
+
+static bool receive_protect_entries(int fd, Config* c, ConfigStringBudget* budget) {
+  int count;
+  if (!receive_int(fd, &count))
+    return false;
+  if (count < 0 || count > MAX_FILTER_RULES)
+    return false;
+  if (count == 0)
+    return true;
+  FilterRuleList* list = filter_rule_list_create();
+  if (!list)
+    return false;
+  size_t pattern_bytes = 0;
+  for (int i = 0; i < count; i++) {
+    int action;
+    int sides;
+    bool anchored;
+    bool dir_only;
+    bool negate;
+    if (!receive_int(fd, &action) ||
+        (action != FILTER_ACTION_EXCLUDE && action != FILTER_ACTION_INCLUDE) ||
+        !receive_int(fd, &sides) || sides < (int)FILTER_SIDE_SENDER ||
+        sides > (int)(FILTER_SIDE_SENDER | FILTER_SIDE_RECEIVER) ||
+        !receive_wire_bool(fd, &anchored) || !receive_wire_bool(fd, &dir_only) ||
+        !receive_wire_bool(fd, &negate))
+      goto fail;
+    char* owner = config_receive_str(fd, budget);
+    if (!owner)
+      goto fail;
+    char* pattern = config_receive_str(fd, budget);
+    if (!pattern || pattern[0] == '\0') {
+      free(owner);
+      free(pattern);
+      goto fail;
+    }
+    /* A pattern too long to be evaluated by glob_match against a PATH_MAX path
+       would silently fail to match and leave a protect rule inert (fail-open:
+       the entry is then deleted).  Reject it up front as a protocol error
+       rather than accept a rule that can never shield anything. */
+    if (strlen(pattern) > MAX_PROTECT_PATTERN_LEN) {
+      free(owner);
+      free(pattern);
+      goto fail;
+    }
+    size_t bytes = strlen(owner) + strlen(pattern);
+    if (bytes > MAX_FILTER_BYTES - pattern_bytes) {
+      free(owner);
+      free(pattern);
+      goto fail;
+    }
+    pattern_bytes += bytes;
+    FilterRule* rule = calloc(1, sizeof(FilterRule));
+    if (!rule) {
+      free(owner);
+      free(pattern);
+      goto fail;
+    }
+    rule->action = (FilterAction)action;
+    rule->sides = (unsigned)sides;
+    rule->anchored = anchored;
+    rule->dir_only = dir_only;
+    rule->negate = negate;
+    rule->owner = owner;
+    rule->pattern = pattern;
+    if (!filter_rule_list_add(list, rule)) {
+      filter_rule_free(rule);
+      goto fail;
+    }
+  }
+  c->protect_rules = list;
+  return true;
+fail:
+  filter_rule_list_free(list);
+  return false;
+}
+
 static bool send_identity_entries(int fd, const IdentityMap* map, int count) {
   for (int i = 0; i < count; i++) {
-    if (!send_int(fd, map[i].from) || !send_int(fd, map[i].to))
+    if (!send_int(fd, map[i].from) || !send_int(fd, map[i].from_hi) || !send_int(fd, map[i].to) ||
+        !send_str(fd, map[i].to_name ? map[i].to_name : ""))
       return false;
   }
   return true;
@@ -968,20 +1157,32 @@ static bool send_identity_entries(int fd, const IdentityMap* map, int count) {
 
 static bool receive_identity_entries(int fd, ConfigStringBudget* budget, int count,
                                      IdentityMap** out) {
-  (void)budget;
   if (count <= 0)
     return true;
   IdentityMap* map = calloc((size_t)count, sizeof(IdentityMap));
   if (!map)
     return false;
   for (int i = 0; i < count; i++) {
-    if (!receive_int(fd, &map[i].from) || !receive_int(fd, &map[i].to)) {
-      free(map);
-      return false;
+    if (!receive_int(fd, &map[i].from) || !receive_int(fd, &map[i].from_hi) ||
+        !receive_int(fd, &map[i].to))
+      goto fail;
+    char* name = config_receive_str(fd, budget);
+    if (!name)
+      goto fail;
+    if (name[0] == '\0') {
+      free(name);
+      map[i].to_name = NULL;
+    } else {
+      map[i].to_name = name;
     }
   }
   *out = map;
   return true;
+fail:
+  for (int i = 0; i < count; i++)
+    free(map[i].to_name);
+  free(map);
+  return false;
 }
 
 /* ---------------------------------------------------------------------------
@@ -1030,6 +1231,9 @@ static bool receive_identity_entries(int fd, ConfigStringBudget* budget, int cou
 #define CONFIG_SEND_INT_CHECKSUM_ALGO(name) send_int(fd, c->name)
 #define CONFIG_RECV_INT_CHECKSUM_ALGO(name) config_receive_checksum_algo(fd, &c->name)
 
+#define CONFIG_SEND_INT_COMPRESSION_ALGO(name) send_int(fd, c->name)
+#define CONFIG_RECV_INT_COMPRESSION_ALGO(name) config_receive_compression_algo(fd, &c->name)
+
 #define CONFIG_SEND_SUPERMODE(name) send_int(fd, (int)c->name)
 #define CONFIG_RECV_SUPERMODE(name) config_receive_super_mode(fd, &c->name)
 
@@ -1069,6 +1273,9 @@ static bool receive_identity_entries(int fd, ConfigStringBudget* budget, int cou
 #define CONFIG_RECV_BLOCK_IDMAP(name)                                                              \
   receive_identity_entries(fd, budget, c->name##_count, &c->name)
 
+#define CONFIG_SEND_BLOCK_PROTECT_RULES(name) send_protect_entries(fd, c)
+#define CONFIG_RECV_BLOCK_PROTECT_RULES(name) receive_protect_entries(fd, c, budget)
+
 /* One table entry, applied in sequence.  XSEND/XRECV are statement macros so
  * consecutive entries read as a plain sequence of assignments. */
 #define XSEND(name, ctype, def, kind) ok = ok && (CONFIG_SEND_##kind(name));
@@ -1104,6 +1311,9 @@ CONFIG_DEFINE_SEND(send_daemon_auth, CONFIG_WIRE_DAEMON_AUTH_FIELDS)
 CONFIG_DEFINE_SEND(send_iconv_spec, CONFIG_WIRE_ICONV_FIELDS)
 CONFIG_DEFINE_SEND(send_privilege_options, CONFIG_WIRE_PRIVILEGE_FIELDS)
 CONFIG_DEFINE_SEND(send_copy_as_options, CONFIG_WIRE_COPY_AS_FIELDS)
+CONFIG_DEFINE_SEND(send_output_options, CONFIG_WIRE_OUTPUT_FIELDS)
+CONFIG_DEFINE_SEND(send_codec_options, CONFIG_WIRE_CODEC_FIELDS)
+CONFIG_DEFINE_SEND(send_protect_options, CONFIG_WIRE_PROTECT_FIELDS)
 
 CONFIG_DEFINE_RECV(receive_core_fields, CONFIG_WIRE_CORE_FIELDS)
 CONFIG_DEFINE_RECV(receive_delta_fields, CONFIG_WIRE_DELTA_FIELDS)
@@ -1122,6 +1332,9 @@ CONFIG_DEFINE_RECV(receive_daemon_auth, CONFIG_WIRE_DAEMON_AUTH_FIELDS)
 CONFIG_DEFINE_RECV(receive_iconv_spec, CONFIG_WIRE_ICONV_FIELDS)
 CONFIG_DEFINE_RECV(receive_privilege_options, CONFIG_WIRE_PRIVILEGE_FIELDS)
 CONFIG_DEFINE_RECV(receive_copy_as_options, CONFIG_WIRE_COPY_AS_FIELDS)
+CONFIG_DEFINE_RECV(receive_output_options, CONFIG_WIRE_OUTPUT_FIELDS)
+CONFIG_DEFINE_RECV(receive_codec_options, CONFIG_WIRE_CODEC_FIELDS)
+CONFIG_DEFINE_RECV(receive_protect_options, CONFIG_WIRE_PROTECT_FIELDS)
 
 #undef XSEND
 #undef XRECV
@@ -1238,7 +1451,10 @@ bool config_send_wire_block(int file_descriptor, const Config* config) {
          send_daemon_module(file_descriptor, config) && send_daemon_auth(file_descriptor, config) &&
          send_iconv_spec(file_descriptor, config) &&
          send_privilege_options(file_descriptor, config) &&
-         send_copy_as_options(file_descriptor, config);
+         send_copy_as_options(file_descriptor, config) &&
+         send_output_options(file_descriptor, config) &&
+         send_codec_options(file_descriptor, config) &&
+         send_protect_options(file_descriptor, config);
 }
 
 bool config_send(int file_descriptor, const Config* config) {
@@ -1308,18 +1524,60 @@ Config* config_receive_with_validate(int file_descriptor, ConfigValidateFunc val
       !receive_daemon_auth(file_descriptor, config, &budget) ||
       !receive_iconv_spec(file_descriptor, config, &budget) ||
       !receive_privilege_options(file_descriptor, config, &budget) ||
-      !receive_copy_as_options(file_descriptor, config, &budget))
+      !receive_copy_as_options(file_descriptor, config, &budget) ||
+      !receive_output_options(file_descriptor, config, &budget) ||
+      !receive_codec_options(file_descriptor, config, &budget) ||
+      !receive_protect_options(file_descriptor, config, &budget))
     goto error;
-  if (config->compress_choice[0] != '\0' && strcmp(config->compress_choice, "zstd") != 0 &&
-      strcmp(config->compress_choice, "none") != 0) {
-    char* escaped_choice = output_escape(config->compress_choice, config->eight_bit_output);
-    log_message(LOG_LEVEL_ERROR, "Unsupported compression choice: %s",
-                escaped_choice ? escaped_choice : "<allocation failed>");
-    char detail[128];
-    snprintf(detail, sizeof(detail), "unsupported compression choice: %s",
-             escaped_choice ? escaped_choice : "<allocation failed>");
-    send_error_detail(file_descriptor, detail);
-    free(escaped_choice);
+  /* Validate/normalize the negotiated codec.  compress_choice is the human
+   * spelling (NULL or "" when -z was not given); compression_algo is the
+   * concrete codec id the sender used.  They must agree, and "auto" is
+   * canonicalized to FastSync's negotiated default so the stored spelling is
+   * always concrete (a hostile/older client may still send "auto"). */
+  if (config->compress_choice && config->compress_choice[0] != '\0') {
+    int choice_algo = compression_algo_from_name(config->compress_choice);
+    if (choice_algo < 0 && strcasecmp(config->compress_choice, "auto") != 0) {
+      char* escaped_choice = output_escape(config->compress_choice, config->eight_bit_output);
+      log_message(LOG_LEVEL_ERROR, "Unsupported compression choice: %s",
+                  escaped_choice ? escaped_choice : "<allocation failed>");
+      char detail[160];
+      snprintf(detail, sizeof(detail), "unsupported compression choice: %s",
+               escaped_choice ? escaped_choice : "<allocation failed>");
+      send_error_detail(file_descriptor, detail);
+      free(escaped_choice);
+      goto error;
+    }
+    if (choice_algo < 0)
+      choice_algo = (int)compression_negotiate_default();
+    if (strcasecmp(config->compress_choice, "auto") == 0 ||
+        choice_algo == (int)COMPRESSION_ALGO_NONE) {
+      const char* canonical = compression_algo_name((CompressionAlgo)choice_algo);
+      char* dup = str_dup(canonical);
+      if (!dup)
+        goto error;
+      free(config->compress_choice);
+      config->compress_choice = dup;
+    }
+    if (config->compression_algo != choice_algo) {
+      log_message(LOG_LEVEL_ERROR, "Compression choice '%s' does not match codec id %d",
+                  config->compress_choice, config->compression_algo);
+      send_error_detail(file_descriptor, "compression choice/codec mismatch");
+      goto error;
+    }
+  }
+  /* The concrete codec must exist only when compression is on.  A client that
+   * left -z off has no codec in effect, but the field keeps whatever id it
+   * carried (the receiver never dispatches on it without use_compression), so
+   * the wire value round-trips untouched. */
+  if (config->use_compression && config->compression_algo == (int)COMPRESSION_ALGO_NONE) {
+    log_message(LOG_LEVEL_ERROR, "Compression requested with the 'none' codec");
+    send_error_detail(file_descriptor, "compression requested with the none codec");
+    goto error;
+  }
+  /* rsync: "none" as the pre-transfer checksum is invalid with --checksum. */
+  if (config->checksum && config->checksum_algo == (int)CHECKSUM_ALGO_NONE) {
+    log_message(LOG_LEVEL_ERROR, "Invalid checksum-choice for --checksum: none");
+    send_error_detail(file_descriptor, "checksum-choice 'none' cannot be used with --checksum");
     goto error;
   }
   if (!validate_received_config(config)) {

src/shared/config.h

@@ -3,6 +3,8 @@
 
 #include "array_list.h"
 #include "checksum.h"
+#include "compression.h"
+#include "filter.h"
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -39,15 +41,20 @@ typedef struct BasisDest {
   char* path; /* relative to the destination root (receiver-confined) */
 } BasisDest;
 
-/* One resolved FROM:TO identity-mapping rule (--usermap / --groupmap).  Both
- * fields are numeric ids.  IDENTITY_MATCH_ANY (-1) in `from` is rsync's '*'
- * wildcard (matches any transmitted id); IDENTITY_CURRENT (-1) in `to` makes
- * the receiver resolve the receiving process's own current euid/egid at apply
- * time.  Names are resolved to numbers at parse time on the client (see
- * identity.h for the exact subset). */
+/* One FROM:TO identity-mapping rule (--usermap / --groupmap).  `from`/`from_hi`
+ * describe the sender-side FROM matcher (a single id when from_hi == from, an
+ * inclusive LOW-HIGH range, IDENTITY_MATCH_ANY for rsync's '*', or
+ * IDENTITY_MATCH_UNNAMED for rsync's empty FROM).  `to` is the receiver-side TO
+ * numeric id (IDENTITY_CURRENT = the receiving process's own euid/egid) UNLESS
+ * `to_name` is non-NULL, in which case the receiver resolves the name against
+ * its own account database at apply time (rsync resolves TO names on the
+ * receiver) and `to` is ignored.  FROM names/ranges/globs are resolved on the
+ * client (the sender) exactly as rsync matches them against sender names. */
 typedef struct {
   int32_t from;
+  int32_t from_hi;
   int32_t to;
+  char* to_name;
 } IdentityMap;
 
 /* --sockopts=OPTIONS allowlist.  Only these option names are accepted; anything
@@ -76,7 +83,7 @@ typedef struct {
 typedef enum SuperMode { SUPER_MODE_AUTO = 0, SUPER_MODE_ON = 1, SUPER_MODE_OFF = 2 } SuperMode;
 
 /* ===========================================================================
- * Config wire-field table (single source of truth for protocol 2.21.0).
+ * Config wire-field table (single source of truth for protocol 2.28.0).
  *
  * Every field below crosses the wire.  The table is the ONLY place a
  * serialized field is named: config.h expands CONFIG_WIRE_FIELDS() to declare
@@ -191,14 +198,23 @@ typedef enum SuperMode { SUPER_MODE_AUTO = 0, SUPER_MODE_ON = 1, SUPER_MODE_OFF
   X(skip_compress_count, int, 0, INT_SKIPCOUNT)                                                    \
   X(skip_compress_suffixes, char**, NULL, BLOCK_SKIP_SUFFIXES)
 
+/* FastSync-only --verify-basis (protocol 2.28.0, no version bump by project
+ * decision): restores the stricter content equality on a basis hit.  By
+ * default a basis hit is accepted on rsync's metadata quick-check alone (equal
+ * size plus equal mtime, or size alone under --size-only); with this flag the
+ * receiver ALSO requires the basis bytes' whole-file digest (the negotiated
+ * --checksum-choice algorithm) to equal the sender's, exactly FastSync's
+ * historical behavior.  It is a receiver policy and crosses the wire so the
+ * receiver knows whether to read and hash the basis content. */
 #define CONFIG_WIRE_BASIS_FIELDS(X)                                                                \
   X(basis_count, int, 0, INT_BASISCOUNT)                                                           \
-  X(basis_dirs, BasisDest*, NULL, BLOCK_BASIS)
+  X(basis_dirs, BasisDest*, NULL, BLOCK_BASIS)                                                     \
+  X(verify_basis, bool, false, BOOL)
 
 #define CONFIG_WIRE_FUZZY_FIELDS(X) X(fuzzy, bool, false, BOOL)
 
 #define CONFIG_WIRE_CHECKSUM_FIELDS(X)                                                             \
-  X(checksum_algo, int, CHECKSUM_ALGO_XXH64, INT_CHECKSUM_ALGO)                                    \
+  X(checksum_algo, int, CHECKSUM_ALGO_DEFAULT, INT_CHECKSUM_ALGO)                                  \
   X(checksum_seed, uint64_t, 0, RAW)
 
 #define CONFIG_WIRE_IDENTITY_FIELDS(X)                                                             \
@@ -216,7 +232,11 @@ typedef enum SuperMode { SUPER_MODE_AUTO = 0, SUPER_MODE_ON = 1, SUPER_MODE_OFF
   X(preserve_atimes, bool, false, BOOL)                                                            \
   X(preserve_crtimes, bool, false, BOOL)                                                           \
   X(omit_dir_times, bool, false, BOOL)                                                             \
-  X(omit_link_times, bool, false, BOOL)
+  X(omit_link_times, bool, false, BOOL)                                                            \
+  X(preserve_perms, bool, false, BOOL)                                                             \
+  X(preserve_times, bool, false, BOOL)                                                             \
+  X(preserve_owner, bool, false, BOOL)                                                             \
+  X(preserve_group, bool, false, BOOL)
 
 #define CONFIG_WIRE_SYMLINK_TRUST_FIELDS(X)                                                        \
   X(munge_links, bool, false, BOOL)                                                                \
@@ -237,6 +257,66 @@ typedef enum SuperMode { SUPER_MODE_AUTO = 0, SUPER_MODE_ON = 1, SUPER_MODE_OFF
   X(copy_as_uid, int32_t, 0, COPY_AS_ID)                                                           \
   X(copy_as_gid, int32_t, 0, COPY_AS_ID)
 
+/* Output-parity wave (protocol 2.23.0).  report_dest_info tells the receiver to
+ * answer every per-file STATUS_CHECK with a STATUS_DEST_INFO snapshot of the
+ * pre-transfer destination entry (see protocol.h).  It is set by the client
+ * only when -i/--itemize-changes or --out-format asks for per-file change
+ * output; the transfer decision itself is unchanged.
+ *
+ * Wire-stats wave (protocol 2.25.0).  report_stats tells the receiver to send a
+ * STATUS_STATS frame immediately before its terminal success status carrying
+ * the receiver-only counters (matched data, deleted-file count) and,
+ * for -n/--dry-run --delete, the destination-relative paths it WOULD have
+ * deleted.  It is set by the client only when --stats, --progress/-P, an
+ * --out-format token needs a wire counter (%b/%c), or a dry-run carries
+ * --delete; the transfer decision itself is unchanged.
+ *
+ * --info wave (protocol 2.27.0).  report_deletes tells the receiver to include
+ * the destination-relative paths it ACTUALLY removed in its terminal
+ * STATUS_STATS record (the same path-list field the dry-run would-delete report
+ * uses), so the sender can print rsync's `deleting PATH`/`*deleting` lines for a
+ * real (non-dry-run) deletion.  It is set when --delete is active and any of
+ * --info=del, -i/--itemize-changes or --out-format requests per-file change
+ * output; the transfer decision itself is unchanged. */
+#define CONFIG_WIRE_OUTPUT_FIELDS(X)                                                               \
+  X(report_dest_info, bool, false, BOOL)                                                           \
+  X(report_stats, bool, false, BOOL) X(report_deletes, bool, false, BOOL)
+
+/* Codec-negotiation wave (protocol 2.26.0).  compression_algo is the concrete
+ * codec the client selected for this transfer (a CompressionAlgo id) and is the
+ * value the receiver validates and installs.  It is the resolved result of
+ * --compress-choice / the "auto" negotiation so both peers agree exactly.
+ *
+ * Negotiation model: FastSync enforces a strict same-version handshake, so both
+ * peers carry the identical compiled-in codec set.  The client resolves the
+ * effective algorithm deterministically and serializes it here; "auto" picks
+ * the first entry of the rsync 3.4.1 preference order
+ * (compression: zstd lz4 zlibx zlib none; checksum: xxh128 xxh3 xxh64 md5 md4
+ * sha1 none), and an explicit request wins.  The receiver rejects (before
+ * STATUS_OK) any algorithm outside its own supported set, which is rsync's
+ * "no common choice is an error" behavior.  The same resolver runs on both
+ * sides (compression_negotiate_default / checksum_negotiate_default), so the
+ * fallback is consistent.
+ *
+ * The field is appended after the output block so every pre-2.26 field keeps
+ * its wire position. */
+#define CONFIG_WIRE_CODEC_FIELDS(X)                                                                \
+  X(compression_algo, int, COMPRESSION_ALGO_ZSTD, INT_COMPRESSION_ALGO)
+
+/* Receiver-side delete-protection filter rules (protocol 2.28.0).  The sender
+ * compiles its root-level selection rules exactly as the scanner does
+ * (filter_base_build over --filter/-f/--exclude/--include/-C) and streams them
+ * as one self-describing, bounded block (count followed by per-rule records).
+ * The receiver reconstructs `protect_rules` and evaluates them against
+ * DESTINATION-ONLY entries during the --delete extras walk, so a
+ * `protect`/`P` rule protects an extra that never appeared on the sender
+ * (rsync re-derives deletion protection from the filter list; FastSync
+ * historically derived it only from the source scan).  `protect_rules` is NULL
+ * on the sender and is owned/freed by the receiver Config.  Bounded by
+ * MAX_FILTER_RULES and MAX_FILTER_BYTES; an unknown action/sides is a protocol
+ * error. */
+#define CONFIG_WIRE_PROTECT_FIELDS(X) X(protect_rules, FilterRuleList*, NULL, BLOCK_PROTECT_RULES)
+
 /* All serialized fields, in exact wire order.  Concatenating the per-segment
  * lists here is what keeps the declaration order = the wire order. */
 #define CONFIG_WIRE_FIELDS(X)                                                                      \
@@ -257,7 +337,10 @@ typedef enum SuperMode { SUPER_MODE_AUTO = 0, SUPER_MODE_ON = 1, SUPER_MODE_OFF
   CONFIG_WIRE_DAEMON_AUTH_FIELDS(X)                                                                \
   CONFIG_WIRE_ICONV_FIELDS(X)                                                                      \
   CONFIG_WIRE_PRIVILEGE_FIELDS(X)                                                                  \
-  CONFIG_WIRE_COPY_AS_FIELDS(X)
+  CONFIG_WIRE_COPY_AS_FIELDS(X)                                                                    \
+  CONFIG_WIRE_OUTPUT_FIELDS(X)                                                                     \
+  CONFIG_WIRE_CODEC_FIELDS(X)                                                                      \
+  CONFIG_WIRE_PROTECT_FIELDS(X)
 
 typedef struct Config {
   /* -j/--threads=N: number of parallel scanner worker threads for the -m
@@ -266,6 +349,15 @@ typedef struct Config {
    * concern and is NEVER serialized into the wire config frame. */
   int scanner_threads;
   bool metadata_explicitly_disabled;
+  /* CLIENT-ONLY (never serialized; not in CONFIG_WIRE_FIELDS).  Set when the
+   * user explicitly turned an attribute off with --no-perms / --no-times (long
+   * or short form).  --incremental/--delta historically auto-enabled mode and
+   * mtime preservation; these flags let cli_finalize_config restore that
+   * behavior while still honoring the explicit per-attribute negation.  A
+   * later -p/-t re-enables the attribute directly, so the flag only prevents
+   * the incremental/delta implication, never a POSITIVE request. */
+  bool preserve_perms_explicit_off;
+  bool preserve_times_explicit_off;
   bool show_progress;
   int compression_threads;
   int ssh_port;
@@ -301,12 +393,14 @@ typedef struct Config {
   char* tls_cert;
   char* tls_key;
   char* tls_ca;
-  /* --timeout: per-message I/O deadline in seconds.  0 (the default/unset
-   * sentinel) leaves the transport's built-in 30 s socket timeout and the
-   * protocol's built-in 60 s per-message deadline in place; a positive value
-   * overrides both.  See protocol_session_set_io_timeout. */
+  /* --timeout: per-message I/O deadline in seconds.  0 (rsync's default)
+   * disables the deadline entirely on the client's own socket and protocol
+   * layers; a positive value sets it.  A server session never inherits the
+   * disabled value: it applies the SERVER_IO_TIMEOUT_SEC floor (see
+   * protocol_server_io_timeout_sec and tcp_set_timeouts). */
   int timeout;
-  /* --contimeout: connect()/accept timeout, transport layer only. */
+  /* --contimeout: connect()/accept timeout in seconds (rsync's default 60);
+   * 0 disables it.  Transport layer only. */
   int contimeout;
   bool quiet;
   bool stats;
@@ -341,6 +435,22 @@ typedef struct Config {
    * enters the keep-set.  Implied by --delete-missing-args. */
   bool ignore_missing_args;
 
+  /* Codec-negotiation CLI state (all client-only, never serialized).  The
+   * effective pre-transfer checksum is Config->checksum_algo (serialized);
+   * checksum_transfer_algo is the rsync "transfer" half of a two-name
+   * --checksum-choice form (validated and used only to mirror rsync's
+   * whole-file forcing, since FastSync's per-block strong hash is fixed).
+   * cli_exit_code carries a parser-requested process exit status (rsync uses 4
+   * for an unsupported checksum/compress algorithm) so main() can mirror it. */
+  int checksum_transfer_algo;
+  int cli_exit_code;
+  /* Client-only "the user explicitly chose" bits.  They let the per-codec
+   * default level / checksum list be applied only when the corresponding
+   * rsync option was omitted (an explicit --compress-level / --checksum-choice
+   * always wins).  Never serialized. */
+  bool compression_level_set;
+  bool checksum_choice_set;
+
   // Issue #129: Advanced file selection. These fields are CLIENT-ONLY: they are
   // never serialized to the wire (the receiver must not learn them).
   ArrayList* filters;   /* --filter=RULE rule strings, in order */
@@ -349,9 +459,15 @@ typedef struct Config {
   bool from0;           /* -0/--from0: NUL-delimited *-from files */
   bool cvs_exclude;     /* -C/--cvs-exclude: standard CVS ignore set */
   bool per_dir_filter;  /* -F: apply per-directory .rsync-filter files */
+  /* -F click count.  rsync's single -F means --filter='dir-merge
+   * /.rsync-filter' (the .rsync-filter files themselves are transferred); a
+   * repeated -F adds --filter='- .rsync-filter' so they are excluded too. */
+  int per_dir_filter_count;
   bool one_file_system; /* -x/--one-file-system: do not cross filesystem boundaries */
-  /* --no-implied-dirs: client-only.  With -R + --files-from, refuse to place a
-   * listed file whose ancestor directory is not itself explicitly listed. */
+  /* --no-implied-dirs: client-only.  With -R, do not transfer the source
+   * metadata of the parent directories implied by a listed path; an unlisted
+   * implied parent is still created (with default attributes) so the listed
+   * file can be placed, matching rsync. */
   bool no_implied_dirs;
   /* -d/--dirs: client-only.  Transfer the directory entries named by the
    * source argument / --files-from list without recursing into contents. */
@@ -519,13 +635,21 @@ typedef struct Config {
   /* rsync deletion-timing family (real from Phase 3).  At most one of
      delete_before / delete_during / delete_delay / delete_after may be set, and
      only together with use_delete (the CLI implies --delete for each of them).
-     delete_before and delete_during select the EARLY engine mode: the keep-set
+     delete_before selects the EARLY engine mode: the whole-tree keep-set
      manifest is transmitted before any file data and extras are removed then,
-     acknowledged, before the first data byte.  delete_delay and delete_after
-     select the LATE commit mode: extras are removed only after the whole
-     transfer has succeeded (plain --delete keeps this mode).  The exact
-     semantics and the divergences from rsync are documented in RSYNC_COMPAT.md
-     and in config_delete_timing_early() below. */
+     acknowledged, before the first data byte.  delete_during and delete_delay
+     select the per-directory delete-plan mode (protocol 2.24.0): one plan per
+     source directory is streamed in directory order, and the receiver removes
+     each directory's extras when its plan arrives (during) or snapshots them
+     and removes them only after a successful transfer (delay).  delete_after
+     keeps the whole-tree commit mode: extras are removed from a fresh
+     end-of-transfer destination scan only after the whole transfer succeeded.
+     A plain --delete with no explicit timing flag defaults to delete_during on
+     the client (cli_finalize_config), matching rsync's --del default; the old
+     late-commit behavior is selected explicitly by --delete-after or the
+     FastSync-only long spelling --delete-commit (an exact alias for
+     --delete-after, mapped onto the same wire field).  See
+     config_delete_timing_early()/config_delete_timing_per_dir() below. */
   /* partial_dir */
   // PR #174: Partial transfer resumption
   /* suffix */
@@ -563,13 +687,17 @@ typedef struct Config {
    * targets and, with -K, follows an in-root destination symlink-to-directory);
    * -k/--copy-dirlinks is sender-only and is never serialized. */
   /* numeric_ids */
-  /* --numeric-ids: no name lookup, use the transmitted numeric ids raw. */
+  /* --numeric-ids: a mapping MODIFIER only -- no name lookup, use the
+   * transmitted numeric ids raw.  It does NOT by itself request ownership. */
   /* chown_uid_set */
   /* --chown USER (owner) override; IDENTITY_CURRENT = the receiver's euid. */
   /* chown_gid_set */
   /* --chown :GROUP (group) override; IDENTITY_CURRENT = the receiver's egid. */
   /* usermap */
-  /* --usermap / --groupmap entries, in order (first match wins). */
+  /* --usermap / --groupmap entries, in order (first match wins).  Each entry's
+   * from/from_hi are a single id, an inclusive range, IDENTITY_MATCH_ANY ('*'),
+   * or IDENTITY_MATCH_UNNAMED (empty FROM); to_name carries a receiver-resolved
+   * TO name (rsync resolves TO names on the receiving side). */
   /* preserve_atimes */
   /* -U/--atimes: preserve source access times on the destination. */
   /* preserve_crtimes */
@@ -579,10 +707,29 @@ typedef struct Config {
   /* -O/--omit-dir-times: do not apply mtimes to directories. */
   /* omit_link_times */
   /* -J/--omit-link-times: do not apply times to symlinks. */
+  /* preserve_perms */
+  /* -p/--perms: preserve the source permission bits (mode).  One of the four
+   * per-attribute preservation flags split out of the former single
+   * use_metadata bundle; --chmod and -A/--acls also imply it. */
+  /* preserve_times */
+  /* -t/--times: preserve source modification times.  Split out of the former
+   * use_metadata bundle; --preserve and -a/--archive imply it. */
+  /* preserve_owner */
+  /* -o/--owner: preserve the source owner (uid).  Split out of the former
+   * use_metadata bundle; --usermap/--chown (and, when a uid is requested,
+   * --copy-as) imply it.  Owner application still requires receiver privilege
+   * and is gated separately by the identity flags. */
+  /* preserve_group */
+  /* -g/--group: preserve the source group (gid).  Split out of the former
+   * use_metadata bundle; --groupmap/--chown (and, when a gid is requested,
+   * --copy-as) imply it. */
   /* fake_super */
   /* --fake-super: receiver-only.  When set, each written file additionally gets
-   * a reserved user.fastsync.stat xattr recording the source uid/gid/mode/mtime
-   * so a later privileged restore could re-apply them.  Crosses the wire. */
+   * a reserved user.fastsync.stat xattr recording the RESOLVED uid/gid (the
+   * source's own when no ownership request is active, else the --chown/--usermap
+   * result) plus mode/mtime so a later privileged restore could re-apply them.
+   * It NEVER real-chowns: the point is to record the source ownership on an
+   * unprivileged receiver.  Crosses the wire. */
   /* module */
   /* Daemon module selection (Wave A, protocol 2.15.0).  Client-composed from a
    * host::module/path destination; NULL or "" means "no module" (the ordinary
@@ -623,7 +770,7 @@ typedef struct Config {
    * fd-relative confinement (file_open_secure_parent, O_NOFOLLOW, root checks);
    * --super only permits an attempt that is already confined.  Crosses the wire
    * as a trailing int so the receiver can enforce the policy.  See
-   * privilege_super_permitted() and identity_ownership_requested() in
+   * privilege_super_permitted() and identity_explicit_ownership_requested() in
    * identity.h. */
   /* copy_as_set */
   /* --copy-as=USER[:GROUP] (P7 Wave E, protocol 2.18.0).  Safe-subset
@@ -803,12 +950,135 @@ typedef struct Config {
  * unknown status, or the unconsumed detail body, and the strict same-version
  * handshake (config_receive rejects a mismatched version before parsing
  * anything else) is what keeps a 2.21 client and a 2.20 server from ever
- * reaching that state. */
-#define PROTOCOL_VERSION "2.21.0"
+ * reaching that state.
+ *
+ * Preserve-Attribute Split Wave: 2.21.0 -> 2.22.0.
+ *
+ * WHY the bump, grounded in the wire: this wave splits the former single
+ * use_metadata bundle into four independent rsync-compatible preservation
+ * attributes (preserve_perms / preserve_times / preserve_owner /
+ * preserve_group) so -p/-t/-o/-g (and their --no-* negations) become real
+ * drop-in flags.  The binary config frame gains four serialized bools appended
+ * to CONFIG_WIRE_METADATA_TIMES_FIELDS after omit_link_times, in this fixed
+ * order: preserve_perms, preserve_times, preserve_owner, preserve_group.  Any
+ * config-frame layout change must bump the protocol version: a peer that does
+ * not parse the new trailing bytes would desynchronize on the frame boundary,
+ * and the strict same-version handshake (config_receive rejects a mismatched
+ * version before parsing anything else) is what keeps a 2.22 client and a 2.21
+ * server from ever reaching that state.  The fixed-width FileMetadata layout is
+ * UNCHANGED: the receiver still gates attribute application on use_metadata,
+ * which is now DERIVED from these attributes by config_derived_use_metadata().
+ *
+ * Rsync-Parity Wave: 2.22.0 -> 2.23.0.
+ *
+ * WHY the bump, grounded in the wire.  Several independent changes land in this
+ * protocol version:
+ *
+ * (1) Ownership parity (#286/#294): each --usermap/--groupmap wire entry grows
+ * from two int32s to [from][from_hi][to][to_name]; `from_hi` carries an
+ * inclusive LOW-HIGH range (== from for a single/any/unnamed matcher) and the
+ * trailing string carries a TO NAME for the receiver to resolve (rsync resolves
+ * TO names on the receiving side).  The STATUS_MKDIR and STATUS_DIR_TIMES frames
+ * also gain a bounded per-entry xattr block when -X/-A is negotiated, so
+ * directory xattrs/ACLs (including default ACLs) are preserved like regular-file
+ * xattrs.
+ *
+ * (2) Delete semantics (#290): the delete-manifest frame gains a fourth trailing
+ * section -- a synchronized-directory count followed by that many
+ * destination-relative directory paths (the receive root is ".").  The receiver
+ * confines its extras walk to these directories, so `--files-from` with
+ * `--delete` only removes inside listed directory subtrees (rsync parity)
+ * instead of deleting every untransmitted path under the receive root.  The
+ * frame stream also gains STATUS_DELETE_LIMIT, the terminal success status sent
+ * instead of STATUS_OK when a --max-delete commit removes up to the bound and
+ * skips the rest (the sender then exits 25 like rsync).
+ *
+ * Any config-frame layout or frame-sequence change must bump the protocol
+ * version: a 2.22 peer would desynchronize on the new entry bytes, the extra
+ * trailing section or the unknown status, and the strict same-version handshake
+ * (config_receive rejects a mismatched version before parsing anything else) is
+ * what keeps a 2.23 client and a 2.22 server from ever reaching that state.
+ *
+ * (3) Output parity (#291/#292): -i/--itemize-changes and --out-format must
+ * compare the source against the PRE-TRANSFER destination entry (new vs
+ * modified, and which of size/time/perms/owner/group differ), but FastSync's
+ * push sender never sees the destination.  The receiver therefore answers a
+ * per-file STATUS_CHECK with a new STATUS_DEST_INFO frame (a fixed-width
+ * snapshot of the old entry) before its ordinary verdict when the config frame
+ * carries the new report_dest_info bool appended after the --copy-as block.
+ * This is both a config-frame layout change (one trailing bool) and a frame
+ * sequence change (the new status).
+ *
+ * (4) Delete timing (protocol 2.24.0): the sender streams one delete plan per
+ * source directory so --delete-during/--delete-delay reproduce rsync's deletion
+ * timing (the plan fields and STATUS_DELETE_PLAN are documented at the keep-set
+ * / delete-plan definitions below).
+ *
+ * (5) Wire-stats parity (protocol 2.25.0): --stats, --progress/-P and the
+ * --out-format %b/%c tokens need receiver-only and wire counters that the push
+ * sender cannot observe, and -n/--dry-run --delete must report the extras it
+ * would have removed without deleting anything.  The config frame gains one
+ * trailing report_stats bool and the receiver emits a new STATUS_STATS frame
+ * (carrying matched data, the deleted-file count and the would-delete path
+ * list) immediately before its terminal success status.
+ *
+ * (6) Codec breadth + negotiation (protocol 2.26.0): the config frame gains one
+ * trailing int, compression_algo (a CompressionAlgo id), appended after the
+ * output block.  It is the negotiated/effective compression codec and is what
+ * the receiver's self-describing decompressor validates against its own
+ * supported set.  The checksum_algo wire value now also accepts md4/sha1/none,
+ * and its default changes to the rsync 3.4.1 auto-negotiated xxh128.
+ *
+ * Any config-frame layout change must bump the protocol version: a peer that
+ * does not parse the new trailing bytes would desynchronize on the frame
+ * boundary, and the strict same-version handshake (config_receive rejects a
+ * mismatched version before parsing anything else) keeps mixed deployments from
+ * ever reaching that state. */
+/* (7) --info=del report (protocol 2.27.0): the config frame gains one trailing
+ * bool, report_deletes, appended after report_stats.  When set, the receiver
+ * lists the paths it actually removed in the terminal STATUS_STATS path list
+ * (the same count-delimited list the -n/--dry-run would-delete report uses), so
+ * the sender can print rsync's `deleting PATH` lines for a real deletion.  No
+ * change to the fixed STATUS_STATS record itself; only a new trailing config
+ * bool, which still requires the version bump for the strict lockstep. */
+/* (8) --stats receiver-observed counters (protocol 2.28.0): the fixed
+ * STATUS_STATS record grows from three counters to eight.  The receiver now
+ * reports the bytes it literally stored (`literal_data`) and the count of
+ * destination entries it newly CREATED, split by type
+ * (reg/dir/link/special), so the sender can print rsync's exact
+ * `Number of created files: N (reg: X, dir: Y, link: Z, special: W)` line and
+ * an exact `Literal data` total even for delta transfers.  The config-frame
+ * LAYOUT is unchanged (no new config field), but the STATUS_STATS body grows,
+ * so a 2.27 peer that does not consume the five new fixed-width counters would
+ * desynchronize on the trailing would-delete path list; the strict
+ * same-version handshake (config_receive rejects a mismatched version before
+ * parsing anything else) keeps mixed deployments from ever reaching that
+ * state. */
+/* (9) Receiver-side delete protection (still protocol 2.28.0): the config frame
+ * gains one trailing self-describing block carrying the sender's compiled base
+ * filter rules so the receiver can protect DESTINATION-ONLY entries from
+ * --delete with `protect`/`risk` rules (rsync parity).  The block appends after
+ * compression_algo; see CONFIG_WIRE_PROTECT_FIELDS. */
+#define PROTOCOL_VERSION "2.28.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)
 /* Upper bound on total basis-dir entries (rsync caps --link-dest at 20). */
 #define MAX_BASIS_DIRS 64
 
+/* Bounds on the received receiver-side delete-protection rule block.  The rule
+ * count and the aggregate pattern+owner bytes are each capped so a hostile
+ * peer cannot pin unbounded pre-auth memory; both are validated strictly on
+ * receive (alongside the per-string ConfigStringBudget). */
+/* A peer may supply protect rules; cap the list so a crafted config cannot make
+ * the receiver's delete walk evaluate an unbounded number of glob patterns per
+ * destination entry (glob_match is O(pattern x path)).  1024 is far above any
+ * legitimate selection. */
+#define MAX_FILTER_RULES 1024
+#define MAX_FILTER_BYTES (256 * 1024)
+/* glob_match's DP is capped at 64 Mi work units; a pattern longer than this
+ * could exceed the cap against a PATH_MAX path and silently stop matching,
+ * leaving a protect rule inert.  Reject such a rule at receive time. */
+#define MAX_PROTECT_PATTERN_LEN 8192
+
 /* Upper bound on the number of --skip-compress suffixes accepted from the wire.
  * Each suffix is an independent wire string (up to MAX_STRING_SIZE = 64 KiB), so
  * without this a hostile pre-auth client could otherwise retain
@@ -829,9 +1099,11 @@ typedef struct Config {
 
 /* Identity-mapping sentinels and bounds (see identity.h for semantics).
  * IDENTITY_MATCH_ANY is a usermap/groupmap FROM '*' (matches any id);
- * IDENTITY_CURRENT is a chown / map TO '*' (resolve to the receiver's current
- * euid/egid at apply time). */
+ * IDENTITY_MATCH_UNNAMED is a FROM with an empty token (rsync's "ids with no
+ * name on the sender"); IDENTITY_CURRENT is a chown / map TO '*' (resolve to
+ * the receiver's current euid/egid at apply time). */
 #define IDENTITY_MATCH_ANY (-1)
+#define IDENTITY_MATCH_UNNAMED (-2)
 #define IDENTITY_CURRENT (-1)
 #define MAX_IDENTITY_MAP 128
 
@@ -896,16 +1168,23 @@ int config_parse_daemon_dest(Config* config);
  * 0. */
 int config_parse_transport_dest(Config* config);
 
-/* True when the negotiated delete timing performs the extra-file deletion
- * BEFORE the transfer data (--delete-before / --delete-during).  The flag is
- * a pure function of the config and is used identically on the sender (to pick
+/* True for the whole-tree delete-before timing: a complete keep-set manifest is
+ * transmitted before any data and committed (with an ack) before the first data
+ * byte.  Pure function of the config, used identically on the sender (to pick
  * the manifest-first frame order) and the receiver (to delete when the early
- * manifest arrives).  When false the deletion is committed only after the whole
- * transfer succeeded (--delete / --delete-after / --delete-delay). */
+ * manifest arrives). */
 bool config_delete_timing_early(const Config* config);
+/* True for the per-directory timings (--delete-during / --delete-delay).  The
+ * sender streams a delete plan per source directory in directory order; the
+ * receiver applies each plan on arrival (during) or snapshots its extras and
+ * commits them only after a fully-successful transfer (delay). */
+bool config_delete_timing_per_dir(const Config* config);
 /* Delete-timing sanity: with deletion enabled at most one timing flag may be
- * set (none = the default delete-after commit timing); without deletion no
- * timing flag may be set (each timing flag implies --delete). */
+ * set; without deletion no timing flag may be set (each timing flag implies
+ * --delete).  A plain --delete is normalized to delete_during by
+ * cli_finalize_config on the client, so a transmitted use_delete config always
+ * carries exactly one timing; the zero-timing case remains valid only for a
+ * config that has not been through the CLI. */
 bool config_has_valid_delete_timing(const Config* config);
 
 /* Single source of truth for the cross-field ("combination") invariants a
@@ -918,6 +1197,14 @@ bool config_has_valid_delete_timing(const Config* config);
  * validate_received_config() so the receiver enforces exactly the same
  * invariants it relies on (the server is the trust boundary). */
 const char* config_invariants_error(const Config* config);
+/* Single source of truth for the DERIVED transport bit (use_metadata): true
+ * when any configured preservation/ownership option requires the metadata
+ * frame to travel.  Returns false when no such option is set (a bare run).
+ * This is a pure predicate over the config; the client lowers it into
+ * Config->use_metadata at the end of parsing so every implication (devices,
+ * executability, identity maps, incremental/delta, ...) is centralized here
+ * rather than scattered as direct writes. */
+bool config_derived_use_metadata(const Config* config);
 /* True when at least one --compare-dest/--copy-dest/--link-dest was set. */
 bool config_has_basis(const Config* config);
 /* Append one basis-dir entry. Returns 0 on success, -1 on allocation failure. */

src/shared/delay_updates.c

@@ -264,6 +264,20 @@ static bool delay_publish_entry(DelayUpdatesContext* context, const Config* conf
                                 const StagedFileEntry* entry) {
   if (!delay_publish_backup(context, config, entry))
     return false;
+  /* --force: an incoming regular file/symlink may replace a destination
+     DIRECTORY (possibly non-empty).  The immediate-install path handles this in
+     file_receive; a --delay-updates run stages elsewhere and only discovers the
+     blocking directory here, so clear it before the rename (rsync's
+     "could not make way for new regular file" without --force). */
+  if (config && config->force_delete && file_directory_exists_secure(entry->final_path)) {
+    if (!file_remove_tree_secure(entry->final_path)) {
+      char* escaped = output_escape(entry->final_path, false);
+      log_message(LOG_LEVEL_ERROR, "could not remove destination directory blocking '%s': %s",
+                  escaped ? escaped : "<allocation failed>", strerror(errno));
+      free(escaped);
+      return false;
+    }
+  }
   if (!file_rename_secure(entry->staged_path, entry->final_path)) {
     if (errno == EXDEV) {
       char* escaped = output_escape(entry->final_path, false);

src/shared/delete_plan.h

@@ -0,0 +1,95 @@
+#ifndef DELETE_PLAN_H
+#define DELETE_PLAN_H
+
+#include "array_list.h"
+#include "config.h"
+#include "file_receive.h"
+#include "protocol.h"
+#include "utils.h"
+#include <stdbool.h>
+
+/* Per-directory delete plans (protocol 2.24.0).
+ *
+ * rsync's --delete-during removes a directory's extras while the generator
+ * processes that directory, and --delete-delay records the deletion list during
+ * the scan but applies it only after a fully-successful transfer.  FastSync has
+ * no per-directory generator pass; instead the sender streams one plan per
+ * source directory, in directory order, and the receiver applies it when it
+ * arrives (during) or snapshots its extras and commits them at the end (delay).
+ *
+ * The sender side builds a plan set from the path-only pre-scan (it needs every
+ * directory's complete direct-child list before the first data byte of that
+ * directory).  The receiver side is a session that carries the global protected
+ * prefixes (filter-excluded and size-skipped source mirrors), the
+ * --delete-missing-args exact deletions, the shared --max-delete budget and,
+ * for --delete-delay, the snapshotted extras. */
+
+/* ---- Sender: plan builder ---- */
+
+typedef struct DeletePlanSender DeletePlanSender;
+
+DeletePlanSender* delete_plan_sender_create(void);
+void delete_plan_sender_destroy(DeletePlanSender* sender);
+/* Record one transmitted entry.  `path` is the destination-relative wire path;
+ * is_dir marks an explicit directory entry (--dirs, a -x mount point). */
+bool delete_plan_sender_add(DeletePlanSender* sender, const char* path, bool is_dir);
+/* Drop plans for directories outside `synced_dirs` (the --files-from
+ * synchronization scope; pass NULL when a full recursive transfer synchronized
+ * every directory).  The receive root is the "." sentinel.
+ *
+ * `walk_root` scopes a general -R transfer: when non-NULL it is the
+ * reconstructed destination prefix the run actually transferred, and only the
+ * plan for that prefix (and directories below it) is ever transmitted, so the
+ * prefix's parent-directory siblings are never walked.  Pass NULL for a plain
+ * recursive transfer and for --files-from. */
+void delete_plan_sender_finalize(DeletePlanSender* sender, const ArrayList* synced_dirs,
+                                 const char* walk_root);
+/* True when no transmitted FILE entry was recorded (an ambiguous empty scan).
+   Directory keep entries do not count, so an I/O error that hid every file
+   still refuses to delete. */
+bool delete_plan_sender_empty(const DeletePlanSender* sender);
+/* Attach the global config sections advertised on the first plan frame.  The
+ * block is always transmitted by delete_plan_send_root(), on a config-only
+ * carrier frame when the scope allows no directory plan. */
+void delete_plan_sender_set_config(DeletePlanSender* sender, const ArrayList* protected_prefixes,
+                                   const ArrayList* size_skipped, const ArrayList* missing_args);
+/* Send the root plan (even before any data, so root extras are handled like
+ * rsync's first generator directory), after transmitting the per-run config
+ * block on its own carrier frame.  Returns -1 on I/O error. */
+int delete_plan_send_root(int fd, DeletePlanSender* sender);
+/* Send the plans for every ancestor of `path` (root-first) and, when is_dir,
+ * for `path` itself; already-sent plans are skipped. */
+int delete_plan_send_for_path(int fd, DeletePlanSender* sender, const char* path, bool is_dir);
+/* Send the plan for every directory in `dirs` that has not been transmitted
+ * yet.  Called after the data stream so an empty source directory's plan still
+ * clears its destination extras even though no file frame triggered it. */
+int delete_plan_send_remaining(int fd, DeletePlanSender* sender, const ArrayList* dirs);
+
+/* ---- Receiver: delete session ---- */
+
+typedef struct DeletePlanSession DeletePlanSession;
+
+DeletePlanSession* delete_plan_session_create(const Config* config);
+void delete_plan_session_destroy(DeletePlanSession* session);
+/* Read one STATUS_DELETE_PLAN frame (the leading status already consumed) and
+ * act on it.  Returns 0 on success (including a dry-run/disabled no-op) and -1
+ * after signalling STATUS_ERROR on a malformed frame or a deletion failure. */
+int delete_plan_session_receive(DeletePlanSession* session, const Config* config, int fd);
+/* Apply the deferred snapshot (--delete-delay) and the missing-args deletions.
+ * Safe to call once; returns the commit outcome. */
+DeleteCommitResult delete_plan_session_commit(DeletePlanSession* session, const Config* config);
+/* True once the shared --max-delete budget stopped part of a deletion. */
+bool delete_plan_session_limit_reached(const DeletePlanSession* session);
+/* Number of destination entries the session actually removed, for the
+   end-of-transfer stats.  For --delete-delay this excludes a snapshotted entry
+   that survived (e.g. a refilled directory that failed ENOTEMPTY), even though
+   that entry already consumed --max-delete budget at snapshot time. */
+size_t delete_plan_session_deleted(const DeletePlanSession* session);
+/* Install an observer invoked for every destination-relative path the session
+   truly removes (including the deferred --delete-delay commit), so the receiver
+   can report rsync's `deleting PATH` lines through the terminal STATUS_STATS
+   record.  Pass NULL/0 to clear. */
+void delete_plan_session_set_delete_observer(DeletePlanSession* session,
+                                             DeletePathObserver observer, void* context);
+
+#endif

src/shared/file.h

@@ -28,17 +28,36 @@ void file_metadata_destroy(void* metadata);
 /* --open-noatime process-wide sender policy; see file.c. */
 void file_set_open_noatime(bool enable);
 bool file_get_open_noatime(void);
+/* Capture the process umask ONCE, before any threads are created.  Call this at
+ * the very top of main() in both entry points so the cached value is read while
+ * the process is still single-threaded: reading the umask needs a get+set round
+ * trip (umask(0); umask(old)), which would race against receiver threads
+ * creating files if it happened during the first write.  Idempotent and safe to
+ * call more than once. */
+void file_umask_capture(void);
+/* Process-wide umask, captured once (thread-safe).  Used to derive the mode of
+ * a brand-new destination like rsync: source_mode & 0777 & ~umask.  Falls back
+ * to file_umask_capture() (behind pthread_once) if capture was never called. */
+unsigned file_process_umask(void);
 /* Open `path` read-only for transfer, honouring --open-noatime when set. */
 int file_open_for_read(const char* path);
 bool file_write_to_disk(const char* path, const void* data, unsigned long long data_size,
                         bool inplace, bool sparse);
 
-/* Symlink trust-boundary helpers (Phase 4, symlink wave).  --munge-links
- * sender-side marker: every transmitted symlink target is prefixed with this
- * while the flag is on; the receiver strips it to restore the real target. */
-#define SYMLINK_MUNGE_PREFIX "#SYMLINK/"
+/* Symlink trust-boundary helpers (Phase 4, symlink wave; rsync parity).
+ * --munge-links is a RECEIVER-side rewrite: rsync prefixes every stored symlink
+ * target with this marker, making the link unusable while the referenced
+ * directory does not exist.  A SENDER receiving a munged source strips it back
+ * off before transmitting (so a munged tree round-trips through the receiver's
+ * re-munging). */
+#define SYMLINK_MUNGE_PREFIX "/rsyncd-munged/"
 
 char* file_symlink_munge(const char* target);
+/* rsync 3.4.1 unsafe_symlink(): true when `target` escapes the transfer tree
+ * rooted at `link_path` (the symlink's transfer-relative path incl. its name).
+ * Absolute/empty targets and targets climbing above the transfer root (via
+ * "..") are unsafe, as are internal "/../" components and trailing "/..". */
+bool file_symlink_unsafe(const char* target, const char* link_path);
 /* True when a lexical target is relative and contains no ".." component, so it
  * can never escape the receive root once created beneath it. */
 bool file_symlink_target_contained(const char* target);
@@ -46,8 +65,9 @@ bool file_symlink_target_contained(const char* target);
  * returns true when a marker was removed. */
 bool file_symlink_unmunge(char* target);
 /* Create a symlink at `path` -> `target`, confined below the authorized root
- * (O_NOFOLLOW parent walk, symlinkat; the target is never followed).  Returns
- * false when a directory already occupies `path`. */
+ * (O_NOFOLLOW parent walk, symlinkat; the target is never followed).  The link
+ * value is copied verbatim (rsync -l); only the placement path is confined.
+ * Returns false when a directory already occupies `path`. */
 bool file_symlink_at_secure(const char* path, const char* target);
 /* --keep-dirlinks (-K) receiver process-wide policy: allow an in-root existing
  * symlink-to-directory to be followed as a directory. */
@@ -67,6 +87,11 @@ bool file_path_exists_secure(const char* path);
 bool file_stat_secure(const char* path, struct stat* st);
 bool file_destination_is_newer_secure(const char* path, const FileMetadata* metadata);
 int file_open_secure_parent(const char* path, char** leaf_out, bool create_dirs);
+/* Protocol 2.28.0 variant: also increments *dirs_created for every missing
+ * parent directory this walk creates that lies strictly below `count_floor`
+ * (a receive-root-relative path, or NULL to count all of them). */
+int file_open_secure_parent_counted(const char* path, char** leaf_out, bool create_dirs,
+                                    unsigned* dirs_created, const char* count_floor);
 bool file_ensure_directory_secure(const char* path);
 bool file_directory_exists_secure(const char* path);
 bool file_rename_secure(const char* old_path, const char* new_path);
@@ -75,37 +100,40 @@ bool file_rename_secure(const char* old_path, const char* new_path);
    regular file.  See the .c for the exact success semantics. */
 bool file_remove_tree_secure(const char* path);
 /* Open a private 0700 directory (creating it on demand) that must live below
-   the authorized root.  Used for the --temp-dir scratch directory and the
-   --delay-updates staging directory. */
+   the authorized root.  Used for the --delay-updates staging directory. */
 int file_open_private_dir(const char* dir_path);
 
+/* Open an existing --temp-dir scratch directory as-is (absolute or relative;
+   no creation, no root confinement), matching rsync's --temp-dir handling. */
+int file_open_temp_dir(const char* dir_path);
+
 /* The file_to_disk_secure* variants write a temporary copy in the destination
-   directory and atomically rename it over `path`.  temp_dir is an absolute,
-   root-confined scratch directory (already validated by the caller): when it
-   is non-NULL the temporary copy is instead created there (with a name unique
-   across the whole scratch directory) and atomically renamed into the
-   destination directory once fully written and fsynced.  A rename across
-   filesystems (EXDEV) fails the write with an error; the file is never
-   silently copied into place.  Pass NULL for the historical same-directory
-   behavior.  --inplace writes never use temp_dir. */
+   directory and atomically rename it over `path`.  temp_dir is a scratch
+   directory (an absolute path, or one the caller already resolved against the
+   destination root): when it is non-NULL the temporary copy is instead created
+   there (with a name unique across the whole scratch directory) and atomically
+   renamed into the destination directory once fully written and fsynced.  When
+   that rename/link fails with EXDEV (the scratch dir is on another filesystem)
+   the write falls back to a non-atomic copy directly in the destination
+   directory, matching rsync.  Pass NULL for the same-directory behavior.
+   --inplace writes never use temp_dir. */
 bool file_to_disk_secure(const char* path, const void* data, unsigned long long data_size,
                          bool inplace, bool sparse, bool preallocate, const FileMetadata* metadata,
-                         bool preserve_executability, const char* temp_dir);
+                         FileAttrPolicy policy, const char* temp_dir);
 bool file_to_disk_secure_with_fsync(const char* path, const void* data,
                                     unsigned long long data_size, bool inplace, bool sparse,
                                     bool preallocate, const FileMetadata* metadata,
-                                    bool preserve_executability, bool use_fsync,
-                                    const char* temp_dir);
+                                    FileAttrPolicy policy, bool use_fsync, const char* temp_dir);
 /* With update enabled, an existing newer destination is left untouched.  The
    check is descriptor-based for inplace writes; atomic replacement still has
    an unavoidable final rename race without filesystem locking. */
 bool file_to_disk_secure_update(const char* path, const void* data, unsigned long long data_size,
                                 bool inplace, bool sparse, bool preallocate,
-                                const FileMetadata* metadata, bool preserve_executability,
+                                const FileMetadata* metadata, FileAttrPolicy policy,
                                 const char* temp_dir);
 bool file_to_disk_secure_no_replace(const char* path, const void* data,
                                     unsigned long long data_size, bool sparse, bool preallocate,
-                                    const FileMetadata* metadata, bool preserve_executability,
+                                    const FileMetadata* metadata, FileAttrPolicy policy,
                                     const char* temp_dir);
 /* Receiver write-path variant that also applies per-file xattrs (-X/-A) and the
  * --fake-super stat xattr fd-relative before the final rename.  `update` /
@@ -113,10 +141,9 @@ bool file_to_disk_secure_no_replace(const char* path, const void* data,
  * enables --partial best-effort retention of a failed write's temp. */
 bool file_to_disk_secure_attrs(const char* path, const void* data, unsigned long long data_size,
                                bool inplace, bool sparse, bool preallocate,
-                               const FileMetadata* metadata, bool preserve_executability,
-                               bool update, bool no_replace, bool use_fsync,
-                               const FileXattrList* xattrs, bool fake_super, bool keep_partial,
-                               const char* temp_dir);
+                               const FileMetadata* metadata, FileAttrPolicy policy, bool update,
+                               bool no_replace, bool use_fsync, const FileXattrList* xattrs,
+                               bool fake_super, bool keep_partial, const char* temp_dir);
 /* Atomic --link-dest install: replace `path` with a hard link to `basis_path`
    (via a temp name + rename); fall back to a byte-identical local copy from
    `data` when the link is impossible (EXDEV/EPERM/unsupported filesystem).
@@ -125,16 +152,48 @@ bool file_to_disk_secure_attrs(const char* path, const void* data, unsigned long
    never re-allocated). */
 bool file_to_disk_secure_link(const char* path, const char* basis_path, const void* data,
                               unsigned long long data_size, bool preallocate,
-                              const FileMetadata* metadata, bool preserve_executability,
-                              bool use_fsync, const char* temp_dir);
+                              const FileMetadata* metadata, FileAttrPolicy policy, bool use_fsync,
+                              const char* temp_dir);
 /* Like file_to_disk_secure_link, but the byte-copy fallback also applies the
  * per-file xattrs (-X/-A) and --fake-super stat xattr (fd-relative).  On a
  * successful hard link no attributes are applied (the shared inode already
  * carries the basis's). */
 bool file_to_disk_secure_link_attrs(const char* path, const char* basis_path, const void* data,
                                     unsigned long long data_size, bool preallocate,
-                                    const FileMetadata* metadata, bool preserve_executability,
+                                    const FileMetadata* metadata, FileAttrPolicy policy,
                                     bool use_fsync, const FileXattrList* xattrs, bool fake_super,
                                     const char* temp_dir);
+/* Streaming --copy-dest install: atomically materialize `path` by copying the
+ * bytes of `basis_path` through a bounded buffer (no whole-file buffering, so
+ * an arbitrarily large basis works), applying the SOURCE metadata and the
+ * per-file xattrs / --fake-super record.  `update` honors a newer destination;
+ * a --temp-dir scratch location falls back to a direct write on EXDEV. */
+bool file_copy_basis_stream_attrs(const char* path, const char* basis_path,
+                                  unsigned long long expected_size, bool preallocate,
+                                  const FileMetadata* metadata, FileAttrPolicy policy, bool update,
+                                  bool use_fsync, const FileXattrList* xattrs, bool fake_super,
+                                  const char* temp_dir);
+/* Protocol 2.28.0 receiver-stat variants: like the two above but additionally
+ * report through `dirs_created` (when non-NULL) how many parent directories the
+ * confined secure walk had to create that lie strictly below `count_floor` (a
+ * receive-root-relative prefix, or NULL for all).  Used to reproduce rsync's
+ * `Number of created files` directory count on a fresh destination. */
+bool file_to_disk_secure_attrs_counted(const char* path, const void* data,
+                                       unsigned long long data_size, bool inplace, bool sparse,
+                                       bool preallocate, const FileMetadata* metadata,
+                                       FileAttrPolicy policy, bool update, bool no_replace,
+                                       bool use_fsync, const FileXattrList* xattrs, bool fake_super,
+                                       bool keep_partial, const char* temp_dir,
+                                       unsigned* dirs_created, const char* count_floor);
+bool file_to_disk_secure_link_attrs_counted(const char* path, const char* basis_path,
+                                            const void* data, unsigned long long data_size,
+                                            bool preallocate, const FileMetadata* metadata,
+                                            FileAttrPolicy policy, bool use_fsync,
+                                            const FileXattrList* xattrs, bool fake_super,
+                                            const char* temp_dir, unsigned* dirs_created,
+                                            const char* count_floor);
+/* The logical transfer root expressed receive-root-relative, or NULL when the
+ * wire paths carry no mirror scaffolding above it.  Caller frees non-NULL. */
+char* file_transfer_root_floor(const Config* config);
 
 #endif

src/shared/file_attr.h

@@ -0,0 +1,38 @@
+#ifndef FILE_ATTR_H
+#define FILE_ATTR_H
+
+#include "config.h"
+#include <stdbool.h>
+#include <sys/stat.h>
+
+/*
+ * Per-attribute receiver policy for applying a transmitted FileMetadata.  This
+ * is the split-out replacement for the former single use_metadata bundle: each
+ * flag is applied independently, matching rsync's -p/-t/-o/-g/-E/-U semantics.
+ * `use_metadata` remains the transport/presence gate (whether the metadata frame
+ * travelled at all); this struct decides which attributes are ACTUALLY applied.
+ *
+ * It lives in its own header (rather than metadata.h) because xattr.h's
+ * fake_super_restore_fd() takes one and metadata.h <-> file_types.h form an
+ * include cycle that must not be entered from xattr.h.
+ *
+ * The mode leg is: perms wins over executability; an exec-bits-only change is
+ * made only when perms is off; when neither is set the receiver deliberately
+ * sets no source mode.  file.c then substitutes the pre-existing destination
+ * mode for a brand-new destination with metadata it uses the sanitized
+ * source-mode-&-umask base (S_IWGRP|S_IWOTH cleared), and the fixed 0644
+ * default only when no metadata is available at all, so a no--p overwrite
+ * does not lose the destination's perms.
+ */
+typedef struct FileAttrPolicy {
+  bool perms;         /* config->preserve_perms: apply the source mode bits */
+  bool times;         /* config->preserve_times: apply the source mtime */
+  bool atimes;        /* config->preserve_atimes (-U): apply the source atime */
+  bool executability; /* config->use_executability (-E): exec-bits-only mode */
+} FileAttrPolicy;
+
+/* Build the per-attribute policy from a connection's Config.  A NULL config
+ * yields the all-off policy (no attribute application). */
+FileAttrPolicy file_attr_policy_from_config(const Config* config);
+
+#endif

src/shared/file_list.c

@@ -240,3 +240,29 @@ bool file_list_affects(const FileListSet* set, const char* rel) {
      entry (binary search for the first entry at or after `rel` + '/'). */
   return path_index_has_descendant(&set->index, rel);
 }
+
+bool file_list_dir_in_scope(const FileListSet* set, const char* rel) {
+  if (!set || set->whole_tree)
+    return true;
+  if (!rel || rel[0] == '\0')
+    return false;
+  /* `rel` itself is listed, or one of its ancestor prefixes is an exact listed
+     directory (a listed prefix of a directory path is necessarily a
+     directory). */
+  size_t len = strlen(rel);
+  while (len > 0) {
+    const char* slash = NULL;
+    for (size_t i = len; i-- > 0;) {
+      if (rel[i] == '/') {
+        slash = rel + i;
+        break;
+      }
+    }
+    if (!slash)
+      break;
+    len = (size_t)(slash - rel);
+    if (path_index_contains_n(&set->index, rel, len))
+      return true;
+  }
+  return path_index_contains(&set->index, rel);
+}

src/shared/file_list.h

@@ -40,4 +40,14 @@ void file_list_destroy(FileListSet* set);
  * this returns true, files are transferred only when it returns true. */
 bool file_list_affects(const FileListSet* set, const char* rel);
 
+/* True when the DIRECTORY `rel` (path relative to the source root) is inside a
+ * listed directory subtree: `rel` itself is a listed entry, or one of `rel`'s
+ * ancestor directory prefixes is an exact listed entry.  Unlike
+ * file_list_affects this does NOT treat an ancestor of a listed entry as
+ * affected, so an implied parent directory of a listed file is not synchronized
+ * (rsync deletes nothing in it).  With no set or a whole-tree set every
+ * directory is in scope.  This is the delete-walker's "synchronized directory"
+ * predicate. */
+bool file_list_dir_in_scope(const FileListSet* set, const char* rel);
+
 #endif

src/shared/file_receive.h

@@ -3,6 +3,7 @@
 
 #include "config.h"
 #include "file_types.h"
+#include "utils.h"
 #include <stdbool.h>
 
 /* Server-side file receive/save path. */
@@ -23,6 +24,16 @@ File* file_receive_hardlink(int file_descriptor);
 File* file_receive_symlink(int file_descriptor, const Config* config);
 File* file_receive_special(int file_descriptor);
 bool file_special_rdev_valid(int32_t major, int32_t minor, mode_t mode);
+/* Testable basis quick-check / verification policy.  file_basis_quick_match is
+ * rsync's metadata quick-check for a basis candidate (equal size is required
+ * separately by the caller; this adds the --size-only / mtime / --modify-window
+ * leg).  file_basis_content_required reports whether a hit must ALSO be
+ * confirmed by a whole-file content digest (--verify-basis; false is the
+ * default rsync-parity behavior). */
+bool file_basis_quick_match(const Config* config, const struct stat* st, time_t check_mtime,
+                            long check_mtime_nsec);
+bool file_basis_content_required(const Config* config);
+
 File* receive_incremental_check(int fd, const Config* config, bool* skipped);
 /* Extended variant used by the receiver.  `would_transfer` (may be NULL) is set
  * true only on the server-contacting --dry-run path when the file is not up to
@@ -40,31 +51,39 @@ File* receive_incremental_check_ex(int fd, const Config* config, bool* skipped,
  * parent's mtime).  -O/--omit-dir-times skips the application entirely.  The
  * list owns deep copies of the paths and metadata; freed on every path. */
 typedef struct {
-  char** paths;          /* owned, destination-relative wire paths */
-  FileMetadata* entries; /* owned, parallel to paths */
+  char** paths;           /* owned, destination-relative wire paths */
+  FileMetadata* entries;  /* owned, parallel to paths */
+  FileXattrList** xattrs; /* owned, parallel to paths; NULL when none */
   size_t count;
   size_t capacity;
   size_t bytes; /* cumulative strlen of every retained path */
 } DirTimeList;
 
 /* Capture gate shared by the sender-side and receiver-side sinks: directory
- * metadata is accumulated only when --times/--metadata is in effect and
- * -O/--omit-dir-times does not suppress it.  Kept here, next to the accumulator
- * it guards, so both call sites express the same condition. */
-bool dir_times_should_capture(const Config* config);
+ * metadata is accumulated only when a directory attribute is requested
+ * (-p/--perms for directory modes, or -t/--times for directory mtimes with
+ * -O/--omit-dir-times not suppressing them) and metadata rides the wire.  Kept
+ * here, next to the accumulator it guards, so both call sites express the same
+ * condition. */
+bool dir_metadata_should_capture(const Config* config);
 
 void dir_time_list_init(DirTimeList* list);
 void dir_time_list_free(DirTimeList* list);
-/* Deep-copy one directory's path + metadata into the list.  Returns false on
- * allocation failure OR when the cumulative entry/byte caps would be exceeded
- * (the caller fails the transfer). */
-bool dir_time_list_add(DirTimeList* list, const char* wire_path, const FileMetadata* metadata);
-/* Apply every accumulated directory's mtime (and atime when captured) beneath
- * `root_directory`, confined fd-relative.  Best-effort per entry: an absent
- * directory (an empty/pruned source dir that was deliberately not created) or a
- * non-directory at the path is skipped QUIETLY, an unreachable one with a
- * warning, and never fatal. */
-void dir_time_list_apply(const DirTimeList* list, const char* root_directory);
+/* Deep-copy one directory's path + metadata (and, when non-NULL, its captured
+ * xattr/ACL block) into the list.  Returns false on allocation failure OR when
+ * the cumulative entry/byte caps would be exceeded (the caller fails the
+ * transfer). */
+bool dir_time_list_add(DirTimeList* list, const char* wire_path, const FileMetadata* metadata,
+                       const FileXattrList* xattrs);
+/* Apply every accumulated directory's metadata beneath `root_directory`,
+ * confined fd-relative: ownership through the negotiated identity policy,
+ * times (mtime, plus atime when -U captured one under -t), the mode (through
+ * --chmod when configured, under -p), and the captured xattrs/ACLs (under
+ * -X/-A).  Best-effort per entry: an absent directory (an empty/pruned source
+ * dir that was deliberately not created) or a non-directory at the path is
+ * skipped QUIETLY, an unreachable one with a warning, and never fatal. */
+void dir_metadata_list_apply(const DirTimeList* list, const char* root_directory,
+                             const Config* config);
 
 /* A received delete-manifest frame: the keep-set (`keeps`, destination-relative
    paths the sender transferred/keeps) plus `protected`, destination-relative
@@ -80,11 +99,18 @@ typedef struct DeleteManifest {
   ArrayList* keeps;
   ArrayList* protected;
   ArrayList* missing;
+  /* Destination-relative paths of the directories the sender synchronized for
+     this run.  The extras walker only removes entries directly inside one of
+     these (the receive root is the "." sentinel); `--files-from` runs therefore
+     leave untransmitted directories and the unlisted parts of listed ones
+     alone, matching rsync's "delete only in synchronized directories". */
+  ArrayList* dirs;
 } DeleteManifest;
 
 void delete_manifest_free(DeleteManifest* manifest);
-/* Read a delete-manifest frame: keep count + keeps, then protected count +
-   protected prefixes, then missing count + missing paths (self-delimiting; the
+/* Read a delete-manifest frame (protocol 2.23.0): keep count + keeps, then
+   protected count + protected prefixes, then missing count + missing paths,
+   then synchronized-directory count + directory paths (self-delimiting; the
    leading STATUS_MANIFEST code has been consumed).  Returns an owned
    DeleteManifest, or NULL after signalling STATUS_ERROR on a malformed frame. */
 DeleteManifest* receive_manifest_entries(int fd);
@@ -103,11 +129,58 @@ bool manifest_delete_extras(const Config* config, DeleteManifest* manifest);
    confinement or I/O error (the run then fails); tolerated per-path cases are
    reported and skipped. */
 bool manifest_delete_missing_args(const Config* config, DeleteManifest* manifest);
+/* Budgeted form of manifest_delete_missing_args for the per-directory delete
+   session: each removed mirror draws from `max_delete` (SIZE_MAX = unlimited)
+   and the tallies are accumulated into `*deleted`/`*skipped`.  `*limit_hit` is set
+   when the budget stopped the pass with entries left over.  Returns false only
+   on a genuine deletion error. */
+bool manifest_delete_missing_args_limited(const Config* config, DeleteManifest* manifest,
+                                          size_t max_delete, size_t* deleted, size_t* skipped,
+                                          bool* limit_hit);
+/* Observer-aware form of manifest_delete_missing_args_limited: `observer` (may
+   be NULL) is invoked for every destination-relative path truly removed. */
+bool manifest_delete_missing_args_limited_observed(const Config* config, DeleteManifest* manifest,
+                                                   size_t max_delete, size_t* deleted,
+                                                   size_t* skipped, bool* limit_hit,
+                                                   DeletePathObserver observer,
+                                                   void* observer_context);
+/* Outcome of committing a delete manifest.  LIMIT_REACHED reports rsync's
+   partial --max-delete result: the budget allowed some deletions and the rest
+   were skipped (the run still stores all file data but the client exits 25). */
+typedef enum {
+  DELETE_COMMIT_OK = 0,
+  DELETE_COMMIT_LIMIT_REACHED,
+  DELETE_COMMIT_ERROR
+} DeleteCommitResult;
+
 /* Run every deletion family the manifest carries: the --delete-missing-args
    exact-path deletions first (user requests are not blocked by exclusion
-   protection), then the ordinary extras walk when --delete is active.  Returns
-   true when nothing to do or everything committed. */
-bool manifest_delete_all(const Config* config, DeleteManifest* manifest);
+   protection), then the ordinary extras walk when --delete is active.  Both
+   share one --max-delete budget.  Returns DELETE_COMMIT_OK when nothing was to
+   do or everything committed, DELETE_COMMIT_LIMIT_REACHED when the budget
+   stopped part of the work, or DELETE_COMMIT_ERROR on a genuine failure. */
+DeleteCommitResult manifest_delete_all(const Config* config, DeleteManifest* manifest);
+/* Like manifest_delete_all, but reports how many destination entries the commit
+   removed (for the end-of-transfer wire stats).  `deleted` may be NULL. */
+DeleteCommitResult manifest_delete_all_counted(const Config* config, DeleteManifest* manifest,
+                                               size_t* deleted);
+/* Observer-aware form of manifest_delete_all_counted: `observer` (may be NULL)
+   is invoked for every destination-relative path truly removed. */
+DeleteCommitResult manifest_delete_all_observed(const Config* config, DeleteManifest* manifest,
+                                                size_t* deleted, DeletePathObserver observer,
+                                                void* observer_context);
+
+/* -n/--dry-run --delete would-delete reporting: walk the destination exactly as
+   the delete pass would and append (strdup'd) destination-relative paths that
+   WOULD be removed to `out`, without touching disk.  Uses the same staging-dir,
+   basis-dir and protected-prefix skips as the real commit.  Returns true on a
+   clean walk; `*count_out` receives the number of paths appended. */
+bool manifest_would_delete_list(const Config* config, DeleteManifest* manifest, ArrayList* out,
+                                size_t* count_out);
+/* Convert one basis-directory path to the receive-root-relative protection
+   prefix the delete walker uses (NULL when it lies outside the root).  Exposed
+   for unit tests of the root-of-"/" and normalization edge cases. */
+char* file_receive_basis_delete_relative(const Config* config, const char* path);
 
 /* Outcome of a single file_save_to_disk operation.  The receiver needs to
    distinguish "written" from "skipped" so --remove-source-files can be told
@@ -116,6 +189,22 @@ typedef enum { FILE_SAVE_ERROR = 0, FILE_SAVE_WRITTEN = 1, FILE_SAVE_SKIPPED = 2
 
 FileSaveResult file_save_to_disk_full(const char* root_directory, const File* file,
                                       const Config* config);
+/* Protocol 2.28.0 variant: also reports through `created` (when non-NULL)
+ * whether the destination entry did not exist before this save, and through
+ * `created_dirs` how many parent directories the confined walk created, so the
+ * receiver can build rsync's `Number of created files` breakdown.  The plain
+ * file_save_to_disk_full() is this with both out-params NULL. */
+FileSaveResult file_save_to_disk_full_ex(const char* root_directory, const File* file,
+                                         const Config* config, bool* created,
+                                         unsigned* created_dirs);
 bool file_save_to_disk(const char* root_directory, const File* file, const Config* config);
 
+/* Protocol 2.28.0 receiver counter accumulator: fold one successfully saved
+ * entry into `stats`, adding its receiver-observed literal bytes and, when
+ * `created`, the matching created-by-type counter (regular file / symlink /
+ * special) plus `created_dirs` implicitly-created parent directories.
+ * Non-first hardlink siblings contribute no literal bytes. */
+void receiver_stats_note_saved(ReceiverStats* stats, const File* file, bool created,
+                               unsigned created_dirs);
+
 #endif

src/shared/file_send.c

@@ -143,20 +143,28 @@ bool file_send_sendfile_with_skip(File* file, int file_descriptor, bool use_meta
   }
 
   off_t offset = 0;
+  /* A non-positive --timeout disables the deadline: poll blocks until the
+   * socket is writable (rsync's --timeout=0 default). */
+  int io_timeout_sec = protocol_get_io_timeout_sec();
   struct timespec deadline;
-  clock_gettime(CLOCK_MONOTONIC, &deadline);
-  deadline.tv_sec += protocol_get_io_timeout_sec();
+  if (io_timeout_sec > 0) {
+    clock_gettime(CLOCK_MONOTONIC, &deadline);
+    deadline.tv_sec += io_timeout_sec;
+  }
   while ((unsigned long long)offset < file_size) {
-    struct timespec now;
-    clock_gettime(CLOCK_MONOTONIC, &now);
-    long long remaining = (long long)(deadline.tv_sec - now.tv_sec) * 1000LL +
-                          (deadline.tv_nsec - now.tv_nsec) / 1000000LL;
-    if (remaining <= 0) {
-      close(fd);
-      return false;
+    int timeout = -1;
+    if (io_timeout_sec > 0) {
+      struct timespec now;
+      clock_gettime(CLOCK_MONOTONIC, &now);
+      long long remaining = (long long)(deadline.tv_sec - now.tv_sec) * 1000LL +
+                            (deadline.tv_nsec - now.tv_nsec) / 1000000LL;
+      if (remaining <= 0) {
+        close(fd);
+        return false;
+      }
+      timeout = remaining > INT_MAX ? INT_MAX : (int)remaining;
     }
     struct pollfd pfd = {.fd = file_descriptor, .events = POLLOUT};
-    int timeout = remaining > INT_MAX ? INT_MAX : (int)remaining;
     int polled = poll(&pfd, 1, timeout);
     if (polled <= 0 || (pfd.revents & (POLLERR | POLLHUP | POLLNVAL))) {
       close(fd);
@@ -174,6 +182,7 @@ bool file_send_sendfile_with_skip(File* file, int file_descriptor, bool use_meta
       close(fd);
       return false;
     }
+    protocol_note_bytes_written((unsigned long long)sent);
   }
 
   close(fd);

src/shared/file_types.h

@@ -2,6 +2,7 @@
 #define FILE_TYPES_H
 
 #include "data.h"
+#include "format.h"
 #include "xattr.h"
 #include <stdbool.h>
 #include <sys/stat.h>
@@ -56,6 +57,11 @@ typedef struct {
    * equals the incoming file, and `data` is kept as the cross-filesystem
    * fallback (a local copy) if the hard link cannot be created. */
   char* basis_link;
+  /* Receiver-only, --copy-dest: when set (and basis_link is NULL), stream the
+   * basis file's bytes into the destination instead of `data`/`data->size`.
+   * This lets a basis larger than any whole-file bound materialize without
+   * buffering it; the source metadata on `metadata` is applied afterwards. */
+  char* basis_copy;
   /* --hard-links (-H), sender + receiver wire state.  link_group is a run-local
    * id shared by every member of one source inode (0 = not part of a group).
    * The FIRST member (link_first == true) carries its data on the wire and is
@@ -86,6 +92,21 @@ typedef struct {
    * Receiver: parsed off the wire, attached here, and applied fd-relative on
    * the written file.  NULL/0 == the file carries no xattrs. */
   FileXattrList* xattrs;
+  /* Sender-side output-parity state (never serialized): the receiver-reported
+   * pre-transfer destination snapshot for this entry, filled by the per-file
+   * STATUS_CHECK exchange when report_dest_info is set.  `known` is false when
+   * no report was requested/received, in which case -i/--out-format treats the
+   * entry conservatively as newly created. */
+  OutputDestState dest_state;
+  /* Receiver-only wire-stats tally: the number of bytes reconstructed from the
+   * basis file (matched delta blocks) for this entry.  0 when the file was sent
+   * whole.  Accumulated into ReceiverStats.matched_data by the receiver sink. */
+  unsigned long long matched_bytes;
+  /* Receiver-only (protocol 2.28.0) wire-stats tally: the literal delta fragment
+   * bytes this entry carried (DELTA_INSTR_LITERAL).  0 when the file was sent
+   * whole; the sink then falls back to the whole payload size.  Accumulated
+   * into ReceiverStats.literal_bytes. */
+  unsigned long long literal_bytes;
 } File;
 
 /* The path that should be sent on the wire and used for the receiver-side

src/shared/filter.c

@@ -1,163 +1,27 @@
 #include "filter.h"
 #include "log.h"
 #include "utils.h"
+#include <ctype.h>
 #include <errno.h>
 #include <limits.h>
+#include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-/* ---- Single rule parsing ---- */
-
-static bool rule_text_is_unsupported_word(const char* p, size_t len) {
-  static const char* const words[] = {"merge",   "dir-merge", "hide", "show",
-                                      "protect", "risk",      "clear"};
-  for (size_t i = 0; i < sizeof(words) / sizeof(words[0]); i++) {
-    size_t wl = strlen(words[i]);
-    if (len == wl && strncmp(p, words[i], wl) == 0)
-      return true;
-  }
-  return false;
+/* Write a diagnostic message into the caller's optional buffer.  A NULL `err`
+ * (or a zero size) is a no-op, so a caller that only needs the boolean status
+ * may pass NULL without the snprintf-on-NULL undefined behaviour. */
+static void filter_set_error(char* err, size_t err_size, const char* fmt, ...) {
+  if (!err || err_size == 0)
+    return;
+  va_list ap;
+  va_start(ap, fmt);
+  vsnprintf(err, err_size, fmt, ap);
+  va_end(ap);
 }
 
-/* rsync include/exclude rule modifiers we do NOT implement. A rule whose +/- is
- * immediately followed by one of these is rejected instead of being silently
- * parsed as a literal pattern. */
-static bool is_unsupported_rule_modifier(char c) {
-  return c == '!' || c == 'C' || c == 's' || c == 'r' || c == 'p' || c == 'x';
-}
-
-FilterRule* filter_rule_parse(const char* line, char* err, size_t err_size) {
-  if (err && err_size > 0)
-    err[0] = '\0';
-  if (!line)
-    return NULL;
-  char* text = str_dup(line);
-  if (!text) {
-    if (err)
-      snprintf(err, err_size, "memory allocation failed");
-    return NULL;
-  }
-  size_t len = strlen(text);
-  while (len > 0 && (text[len - 1] == '\n' || text[len - 1] == '\r'))
-    text[--len] = '\0';
-
-  const char* p = text;
-  while (*p == ' ' || *p == '\t')
-    p++;
-  if (*p == '\0') {
-    snprintf(err, err_size, "empty filter rule");
-    free(text);
-    return NULL;
-  }
-
-  FilterAction action = FILTER_ACTION_EXCLUDE;
-  if (*p == '+' || *p == '-') {
-    action = *p == '+' ? FILTER_ACTION_INCLUDE : FILTER_ACTION_EXCLUDE;
-    p++;
-    /* rsync attaches rule modifiers directly to the +/- (e.g. "-s foo"). Only
-     * the '/' anchor modifier is supported; anything else is a clear error
-     * rather than a silently-ignored literal. */
-    if (*p != ' ' && *p != '\t' && *p != '\0' && is_unsupported_rule_modifier(*p)) {
-      snprintf(err, err_size,
-               "filter rule modifier '%c' is not supported (only the '/' anchor after +/- "
-               "is implemented; put a space between +/- and the pattern)",
-               *p);
-      free(text);
-      return NULL;
-    }
-    while (*p == ' ' || *p == '\t')
-      p++;
-  } else {
-    /* ':' (dir-merge) and '.' (merge) are rsync filter-rule shorthands. At the
-     * start of a rule they mean "merge this file", so reject them instead of
-     * silently turning them into inert exclude patterns. */
-    if (*p == ':' || *p == '.' || *p == '!') {
-      snprintf(err, err_size,
-               "filter rule starting with '%c' is not supported (merge/dir-merge/list-clear "
-               "shorthands are not implemented; use +/- include/exclude rules)",
-               *p);
-      free(text);
-      return NULL;
-    }
-    const char* sp = p;
-    while (*sp != '\0' && *sp != ' ' && *sp != '\t')
-      sp++;
-    size_t word_len = (size_t)(sp - p);
-    if (rule_text_is_unsupported_word(p, word_len)) {
-      snprintf(err, err_size,
-               "'%.*s' filter directives are not supported (only +/- include/exclude rules "
-               "with an optional '/' anchor and trailing '/' dir marker)",
-               (int)word_len, p);
-      free(text);
-      return NULL;
-    }
-    if (word_len == strlen("include") && strncmp(p, "include", word_len) == 0) {
-      action = FILTER_ACTION_INCLUDE;
-      p = sp;
-    } else if (word_len == strlen("exclude") && strncmp(p, "exclude", word_len) == 0) {
-      action = FILTER_ACTION_EXCLUDE;
-      p = sp;
-    }
-    while (*p == ' ' || *p == '\t')
-      p++;
-  }
-
-  if (*p == '\0') {
-    snprintf(err, err_size, "filter rule has no pattern");
-    free(text);
-    return NULL;
-  }
-
-  /* A pattern beginning with '/' is anchored (either as "-/foo" or "- /foo"). */
-  bool anchored = false;
-  if (*p == '/') {
-    anchored = true;
-    p++;
-    while (*p == ' ' || *p == '\t')
-      p++;
-  }
-  if (*p == '\0') {
-    snprintf(err, err_size, "filter rule has no pattern after '/' anchor");
-    free(text);
-    return NULL;
-  }
-
-  /* Pattern runs to the end of the rule; a single trailing '/' marks dir-only. */
-  size_t pat_len = strlen(p);
-  bool dir_only = false;
-  if (pat_len > 1 && p[pat_len - 1] == '/') {
-    dir_only = true;
-    pat_len--;
-  } else if (pat_len == 1 && p[0] == '/') {
-    /* "//" anchored with nothing after: meaningless. */
-    snprintf(err, err_size, "filter rule has no pattern");
-    free(text);
-    return NULL;
-  }
-
-  FilterRule* rule = calloc(1, sizeof(FilterRule));
-  if (!rule) {
-    snprintf(err, err_size, "memory allocation failed");
-    free(text);
-    return NULL;
-  }
-  rule->pattern = malloc(pat_len + 1);
-  if (!rule->pattern) {
-    free(rule);
-    snprintf(err, err_size, "memory allocation failed");
-    free(text);
-    return NULL;
-  }
-  memcpy(rule->pattern, p, pat_len);
-  rule->pattern[pat_len] = '\0';
-  rule->action = action;
-  rule->anchored = anchored;
-  rule->dir_only = dir_only;
-  rule->owner = NULL;
-  free(text);
-  return rule;
-}
+/* ---- Ordered rule lists ---- */
 
 void filter_rule_free(FilterRule* rule) {
   if (!rule)
@@ -167,8 +31,6 @@ void filter_rule_free(FilterRule* rule) {
   free(rule);
 }
 
-/* ---- Ordered rule lists ---- */
-
 FilterRuleList* filter_rule_list_create(void) {
   return calloc(1, sizeof(FilterRuleList));
 }
@@ -190,28 +52,42 @@ bool filter_rule_list_add(FilterRuleList* list, FilterRule* rule) {
   return true;
 }
 
-bool filter_rule_list_parse_append(FilterRuleList* list, const char* line, char* err,
-                                   size_t err_size) {
-  FilterRule* rule = filter_rule_parse(line, err, err_size);
-  if (!rule)
-    return false;
-  if (!filter_rule_list_add(list, rule)) {
-    filter_rule_free(rule);
-    snprintf(err, err_size, "memory allocation failed");
-    return false;
-  }
-  return true;
-}
-
 void filter_rule_list_free(FilterRuleList* list) {
   if (!list)
     return;
   for (int i = 0; i < list->count; i++)
     filter_rule_free(list->items[i]);
+  for (int i = 0; i < list->dir_merge_count; i++)
+    free(list->dir_merge_names[i]);
+  free(list->dir_merge_names);
   free(list->items);
   free(list);
 }
 
+/* Register a per-directory merge-file basename (for "dir-merge NAME"/": NAME"
+ * and -F's .rsync-filter).  Duplicate names are ignored. */
+bool filter_rule_list_add_dir_merge(FilterRuleList* list, const char* name) {
+  if (!list || !name || name[0] == '\0')
+    return false;
+  for (int i = 0; i < list->dir_merge_count; i++) {
+    if (strcmp(list->dir_merge_names[i], name) == 0)
+      return true;
+  }
+  if (list->dir_merge_count == list->dir_merge_capacity) {
+    int new_cap = list->dir_merge_capacity > 0 ? list->dir_merge_capacity * 2 : 4;
+    char** grown = realloc(list->dir_merge_names, (size_t)new_cap * sizeof(char*));
+    if (!grown)
+      return false;
+    list->dir_merge_names = grown;
+    list->dir_merge_capacity = new_cap;
+  }
+  char* dup = str_dup(name);
+  if (!dup)
+    return false;
+  list->dir_merge_names[list->dir_merge_count++] = dup;
+  return true;
+}
+
 static bool set_rule_owner(FilterRule* rule, const char* owner) {
   char* dup = str_dup(owner ? owner : "");
   if (!dup)
@@ -221,7 +97,315 @@ static bool set_rule_owner(FilterRule* rule, const char* owner) {
   return true;
 }
 
-/* ---- CVS default excludes (-C) ---- */
+/* ---- Rule parsing ---- */
+
+/* A short rule prefix is a single character; a long rule name is alphabetic
+ * (with '-').  `is_short` distinguishes the modifier-attachment rules. */
+typedef enum {
+  RULE_KIND_EXCLUDE,
+  RULE_KIND_INCLUDE,
+  RULE_KIND_HIDE,
+  RULE_KIND_SHOW,
+  RULE_KIND_PROTECT,
+  RULE_KIND_RISK,
+  RULE_KIND_MERGE,
+  RULE_KIND_DIR_MERGE,
+  RULE_KIND_CLEAR,
+  RULE_KIND_UNKNOWN,
+} RuleKind;
+
+static bool short_rule_char(char c, RuleKind* kind) {
+  switch (c) {
+  case '-':
+    *kind = RULE_KIND_EXCLUDE;
+    return true;
+  case '+':
+    *kind = RULE_KIND_INCLUDE;
+    return true;
+  case 'H':
+    *kind = RULE_KIND_HIDE;
+    return true;
+  case 'S':
+    *kind = RULE_KIND_SHOW;
+    return true;
+  case 'P':
+    *kind = RULE_KIND_PROTECT;
+    return true;
+  case 'R':
+    *kind = RULE_KIND_RISK;
+    return true;
+  case '.':
+    *kind = RULE_KIND_MERGE;
+    return true;
+  case ':':
+    *kind = RULE_KIND_DIR_MERGE;
+    return true;
+  case '!':
+    *kind = RULE_KIND_CLEAR;
+    return true;
+  default:
+    return false;
+  }
+}
+
+static bool long_rule_name(const char* name, size_t len, RuleKind* kind) {
+  struct {
+    const char* word;
+    RuleKind kind;
+  } table[] = {
+      {"exclude", RULE_KIND_EXCLUDE}, {"include", RULE_KIND_INCLUDE},
+      {"hide", RULE_KIND_HIDE},       {"show", RULE_KIND_SHOW},
+      {"protect", RULE_KIND_PROTECT}, {"risk", RULE_KIND_RISK},
+      {"merge", RULE_KIND_MERGE},     {"dir-merge", RULE_KIND_DIR_MERGE},
+      {"clear", RULE_KIND_CLEAR},
+  };
+  for (size_t i = 0; i < sizeof(table) / sizeof(table[0]); i++) {
+    if (strlen(table[i].word) == len && strncmp(name, table[i].word, len) == 0) {
+      *kind = table[i].kind;
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool is_modifier_char(char c) {
+  return c == 's' || c == 'r' || c == 'p' || c == 'x' || c == '/' || c == '!' || c == 'C';
+}
+
+/* Parse "RULE[,MODIFIERS] [PATTERN]".  On success `kind`, `sides`,
+ * `sides_explicit`, `negate`, `anchored_mod`, `perishable`, `xattr`,
+ * `cvs_inject` and the pattern span (`pat_start`/`pat_len`, possibly 0 for
+ * merge/clear) are filled.  Returns true on success. */
+static bool parse_rule_syntax(const char* text, RuleKind* kind, unsigned* sides,
+                              bool* sides_explicit, bool* negate, bool* anchored_mod,
+                              bool* perishable, bool* xattr, bool* cvs_inject,
+                              const char** pat_start, size_t* pat_len) {
+  const char* p = text;
+  *sides = FILTER_SIDE_SENDER | FILTER_SIDE_RECEIVER;
+  *sides_explicit = false;
+  *negate = false;
+  *anchored_mod = false;
+  *perishable = false;
+  *xattr = false;
+  *cvs_inject = false;
+  *pat_start = NULL;
+  *pat_len = 0;
+
+  bool is_short = false;
+  if (short_rule_char(*p, kind)) {
+    is_short = true;
+    p++;
+  } else {
+    const char* name_start = p;
+    while (isalpha((unsigned char)*p) || *p == '-')
+      p++;
+    size_t name_len = (size_t)(p - name_start);
+    if (name_len == 0 || !long_rule_name(name_start, name_len, kind))
+      return false;
+    /* A long name must be followed by a separator, a comma or the end. */
+    if (*p != '\0' && *p != ',' && *p != ' ' && *p != '_')
+      return false;
+  }
+
+  /* Modifiers: long names require a comma; short names may attach directly.
+     Only commit a modifier run that terminates at a separator or the end, so a
+     pattern such as "*.tmp" written as "-*.tmp" is not mistaken for modifiers. */
+  const char* mod_start = p;
+  const char* mod_end = p;
+  if (*p == ',') {
+    p++;
+    mod_start = p;
+    while (is_modifier_char(*p))
+      p++;
+    mod_end = p;
+  } else if (is_short) {
+    const char* scan = p;
+    while (is_modifier_char(*scan))
+      scan++;
+    if (*scan == '\0' || *scan == ' ' || *scan == '_') {
+      mod_start = p;
+      mod_end = scan;
+      p = scan;
+    }
+  }
+  for (const char* m = mod_start; m < mod_end; m++) {
+    switch (*m) {
+    case 's':
+      *sides = FILTER_SIDE_SENDER;
+      *sides_explicit = true;
+      break;
+    case 'r':
+      *sides = FILTER_SIDE_RECEIVER;
+      *sides_explicit = true;
+      break;
+    case '!':
+      *negate = true;
+      break;
+    case '/':
+      *anchored_mod = true;
+      break;
+    case 'p':
+      *perishable = true;
+      break;
+    case 'x':
+      *xattr = true;
+      break;
+    case 'C':
+      *cvs_inject = true;
+      break;
+    default:
+      break;
+    }
+  }
+
+  /* A single space or underscore separates the rule/modifiers from the
+     pattern; further spaces/underscores belong to the pattern. */
+  const char* pat = p;
+  if (*pat == ' ' || *pat == '_')
+    pat++;
+  /* Trim a trailing newline/CR (the caller may pass a raw file line). */
+  *pat_start = pat;
+  *pat_len = strlen(pat);
+  while (*pat_len > 0 && (pat[*pat_len - 1] == '\n' || pat[*pat_len - 1] == '\r'))
+    (*pat_len)--;
+  return true;
+}
+
+FilterRule* filter_rule_parse(const char* line, const FilterParseOptions* opts, char* err,
+                              size_t err_size) {
+  if (err && err_size > 0)
+    err[0] = '\0';
+  if (!line)
+    return NULL;
+  const char* p = line;
+  while (*p == ' ' || *p == '\t')
+    p++;
+  if (*p == '\0' || *p == '\n' || *p == '\r') {
+    filter_set_error(err, err_size, "empty filter rule");
+    return NULL;
+  }
+
+  RuleKind kind = RULE_KIND_UNKNOWN;
+  unsigned sides;
+  bool sides_explicit, negate, anchored_mod, perishable, xattr, cvs_inject;
+  const char* pat;
+  size_t pat_len;
+  if (!parse_rule_syntax(p, &kind, &sides, &sides_explicit, &negate, &anchored_mod, &perishable,
+                         &xattr, &cvs_inject, &pat, &pat_len)) {
+    filter_set_error(err, err_size, "unrecognized filter rule syntax");
+    return NULL;
+  }
+  if (cvs_inject) {
+    /* The C modifier expands to the CVS defaults in place; the rule itself
+       carries no pattern and is handled by the caller. */
+    filter_set_error(err, err_size, "the C modifier is handled by the rule-list parser");
+    return NULL;
+  }
+  if (xattr) {
+    filter_set_error(err, err_size, "xattr-name filter rules (the x modifier) are not supported");
+    return NULL;
+  }
+  if (kind == RULE_KIND_MERGE || kind == RULE_KIND_DIR_MERGE) {
+    filter_set_error(err, err_size, "merge/dir-merge rules are handled by the rule-list parser");
+    return NULL;
+  }
+  if (kind == RULE_KIND_CLEAR) {
+    if (pat_len != 0) {
+      filter_set_error(err, err_size, "clear takes no pattern");
+      return NULL;
+    }
+    FilterRule* rule = calloc(1, sizeof(FilterRule));
+    if (!rule) {
+      filter_set_error(err, err_size, "memory allocation failed");
+      return NULL;
+    }
+    rule->action = FILTER_ACTION_NONE; /* clear marker: no pattern */
+    rule->sides = 0;
+    return rule;
+  }
+
+  FilterAction action;
+  switch (kind) {
+  case RULE_KIND_INCLUDE:
+  case RULE_KIND_SHOW:
+  case RULE_KIND_RISK:
+    action = FILTER_ACTION_INCLUDE;
+    break;
+  default:
+    action = FILTER_ACTION_EXCLUDE;
+    break;
+  }
+  if (kind == RULE_KIND_HIDE)
+    sides = FILTER_SIDE_SENDER;
+  else if (kind == RULE_KIND_SHOW)
+    sides = FILTER_SIDE_SENDER;
+  else if (kind == RULE_KIND_PROTECT)
+    sides = FILTER_SIDE_RECEIVER;
+  else if (kind == RULE_KIND_RISK)
+    sides = FILTER_SIDE_RECEIVER;
+  if (kind == RULE_KIND_HIDE || kind == RULE_KIND_SHOW || kind == RULE_KIND_PROTECT ||
+      kind == RULE_KIND_RISK)
+    sides_explicit = true;
+  /* --delete-excluded turns an unqualified (no explicit s/r) rule into a
+     sender-side-only rule, so it no longer protects the receiver. */
+  if (opts && opts->delete_excluded && !sides_explicit)
+    sides = FILTER_SIDE_SENDER;
+
+  if (pat_len == 0) {
+    filter_set_error(err, err_size, "filter rule has no pattern");
+    return NULL;
+  }
+
+  bool anchored = anchored_mod;
+  const char* pat_begin = pat;
+  if (*pat_begin == '/') {
+    anchored = true;
+    pat_begin++;
+    /* Drop the spaces that could follow the anchor in the "-/ foo" form. */
+    while (*pat_begin == ' ' || *pat_begin == '\t')
+      pat_begin++;
+    pat_len = strlen(pat_begin);
+    while (pat_len > 0 && (pat_begin[pat_len - 1] == '\n' || pat_begin[pat_len - 1] == '\r'))
+      pat_len--;
+  }
+  if (pat_len == 0) {
+    filter_set_error(err, err_size, "filter rule has no pattern after '/' anchor");
+    return NULL;
+  }
+  bool dir_only = false;
+  if (pat_len > 1 && pat_begin[pat_len - 1] == '/') {
+    dir_only = true;
+    pat_len--;
+  }
+  if (pat_len == 0) {
+    filter_set_error(err, err_size, "filter rule has no pattern");
+    return NULL;
+  }
+
+  FilterRule* rule = calloc(1, sizeof(FilterRule));
+  if (!rule) {
+    filter_set_error(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  rule->pattern = malloc(pat_len + 1);
+  if (!rule->pattern) {
+    free(rule);
+    filter_set_error(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  memcpy(rule->pattern, pat_begin, pat_len);
+  rule->pattern[pat_len] = '\0';
+  rule->action = action;
+  rule->sides = sides;
+  rule->anchored = anchored;
+  rule->dir_only = dir_only;
+  rule->negate = negate;
+  rule->perishable = perishable;
+  (void)xattr; /* xattr-name rules never match file/dir names; accepted/ignored */
+  return rule;
+}
+
+/* ---- CVS default excludes (-C and the C modifier) ---- */
 
 typedef struct {
   const char* pattern;
@@ -240,12 +424,13 @@ static const CvsDefaultRule CVS_DEFAULTS[] = {
     {".svn/", true},        {".git/", true},         {".hg/", true},   {".bzr/", true},
 };
 
-static bool cvs_rule_list_append(FilterRuleList* list) {
+static bool filter_list_append_cvs(FilterRuleList* list, unsigned sides) {
   for (size_t i = 0; i < sizeof(CVS_DEFAULTS) / sizeof(CVS_DEFAULTS[0]); i++) {
     FilterRule* rule = calloc(1, sizeof(FilterRule));
     if (!rule)
       return false;
     rule->action = FILTER_ACTION_EXCLUDE;
+    rule->sides = sides;
     rule->dir_only = CVS_DEFAULTS[i].dir_only;
     size_t plen = strlen(CVS_DEFAULTS[i].pattern);
     if (rule->dir_only && plen > 0 && CVS_DEFAULTS[i].pattern[plen - 1] == '/')
@@ -269,76 +454,236 @@ static bool cvs_rule_list_append(FilterRuleList* list) {
   return true;
 }
 
+#define FILTER_MAX_MERGE_DEPTH 16
+
+static bool filter_list_parse_append_depth(FilterRuleList* list, const char* line,
+                                           const FilterParseOptions* opts, const char* base_dir,
+                                           int depth, char* err, size_t err_size);
+
+/* Read a merge file and splice its rules into `list`.  A relative path is
+ * resolved below `base_dir` when given, else used as-is (rsync resolves a
+ * command-line merge file relative to the current directory). */
+static bool filter_list_merge_file(FilterRuleList* list, const char* name,
+                                   const FilterParseOptions* opts, const char* base_dir, int depth,
+                                   char* err, size_t err_size) {
+  if (name[0] == '\0') {
+    filter_set_error(err, err_size, "merge requires a filename");
+    return false;
+  }
+  char* path =
+      (base_dir && base_dir[0] && name[0] != '/') ? path_cat(base_dir, name) : str_dup(name);
+  if (!path) {
+    filter_set_error(err, err_size, "memory allocation failed");
+    return false;
+  }
+  FILE* fp = fopen(path, "r");
+  if (!fp) {
+    filter_set_error(err, err_size, "could not read merge file '%s': %s", path, strerror(errno));
+    free(path);
+    return false;
+  }
+  char* line = NULL;
+  size_t cap = 0;
+  bool ok = true;
+  while (true) {
+    ssize_t n = utils_getdelim_bounded(fp, &line, &cap, '\n', UTILS_MAX_LINE_LEN);
+    if (n < 0) {
+      filter_set_error(err, err_size, "error reading merge file '%s'", path);
+      ok = false;
+      break;
+    }
+    if (n == 0)
+      break;
+    const char* lp = line;
+    while (*lp == ' ' || *lp == '\t')
+      lp++;
+    if (*lp == '\0' || *lp == '\n' || *lp == '\r' || *lp == '#')
+      continue;
+    if (!filter_list_parse_append_depth(list, lp, opts, base_dir, depth + 1, err, err_size)) {
+      ok = false;
+      break;
+    }
+  }
+  free(line);
+  fclose(fp);
+  free(path);
+  return ok;
+}
+
+/* Parse one line and append/merge it into `list`.  Handles clear, merge and
+ * dir-merge at the list level. */
+static bool filter_list_parse_append_depth(FilterRuleList* list, const char* line,
+                                           const FilterParseOptions* opts, const char* base_dir,
+                                           int depth, char* err, size_t err_size) {
+  if (depth > FILTER_MAX_MERGE_DEPTH) {
+    filter_set_error(err, err_size, "merge files nested too deeply");
+    return false;
+  }
+  const char* p = line;
+  while (*p == ' ' || *p == '\t')
+    p++;
+  if (*p == '\0' || *p == '\n' || *p == '\r')
+    return true;
+
+  RuleKind kind = RULE_KIND_UNKNOWN;
+  unsigned sides;
+  bool sides_explicit, negate, anchored_mod, perishable, xattr, cvs_inject;
+  const char* pat;
+  size_t pat_len;
+  if (!parse_rule_syntax(p, &kind, &sides, &sides_explicit, &negate, &anchored_mod, &perishable,
+                         &xattr, &cvs_inject, &pat, &pat_len)) {
+    filter_set_error(err, err_size, "unrecognized filter rule syntax: %s", p);
+    return false;
+  }
+  (void)sides_explicit;
+  (void)negate;
+  (void)anchored_mod;
+  (void)perishable;
+  (void)xattr;
+
+  if (cvs_inject) {
+    /* "C" injects the CVS defaults in place; no pattern is expected. */
+    return filter_list_append_cvs(list, sides);
+  }
+  if (kind == RULE_KIND_CLEAR) {
+    if (pat_len != 0) {
+      filter_set_error(err, err_size, "clear takes no pattern");
+      return false;
+    }
+    for (int i = 0; i < list->count; i++)
+      filter_rule_free(list->items[i]);
+    list->count = 0;
+    return true;
+  }
+  if (kind == RULE_KIND_MERGE) {
+    if (pat_len == 0) {
+      filter_set_error(err, err_size, "merge requires a filename");
+      return false;
+    }
+    char* name = malloc(pat_len + 1);
+    if (!name) {
+      filter_set_error(err, err_size, "memory allocation failed");
+      return false;
+    }
+    memcpy(name, pat, pat_len);
+    name[pat_len] = '\0';
+    bool ok = filter_list_merge_file(list, name, opts, base_dir, depth, err, err_size);
+    free(name);
+    return ok;
+  }
+  if (kind == RULE_KIND_DIR_MERGE) {
+    if (pat_len == 0) {
+      filter_set_error(err, err_size, "dir-merge requires a filename");
+      return false;
+    }
+    char* name = malloc(pat_len + 1);
+    if (!name) {
+      filter_set_error(err, err_size, "memory allocation failed");
+      return false;
+    }
+    memcpy(name, pat, pat_len);
+    name[pat_len] = '\0';
+    bool ok = filter_rule_list_add_dir_merge(list, name);
+    free(name);
+    if (!ok) {
+      filter_set_error(err, err_size, "memory allocation failed");
+      return false;
+    }
+    return true;
+  }
+
+  FilterRule* rule = filter_rule_parse(p, opts, err, err_size);
+  if (!rule)
+    return false;
+  if (!filter_rule_list_add(list, rule)) {
+    filter_rule_free(rule);
+    filter_set_error(err, err_size, "memory allocation failed");
+    return false;
+  }
+  return true;
+}
+
+bool filter_rule_list_parse_append(FilterRuleList* list, const char* line,
+                                   const FilterParseOptions* opts, const char* merge_base_dir,
+                                   char* err, size_t err_size) {
+  if (err && err_size > 0)
+    err[0] = '\0';
+  if (!list)
+    return false;
+  return filter_list_parse_append_depth(list, line, opts, merge_base_dir, 0, err, err_size);
+}
+
 FilterRuleList* filter_base_build(const char* const* rule_texts, int rule_count, bool cvs_exclude,
-                                  char* err, size_t err_size) {
+                                  bool delete_excluded, char* err, size_t err_size) {
   if (err && err_size > 0)
     err[0] = '\0';
   FilterRuleList* list = filter_rule_list_create();
   if (!list) {
-    snprintf(err, err_size, "memory allocation failed");
+    filter_set_error(err, err_size, "memory allocation failed");
     return NULL;
   }
+  FilterParseOptions opts = {.delete_excluded = delete_excluded, .cvs_exclude = cvs_exclude};
   for (int i = 0; i < rule_count; i++) {
     if (!rule_texts || !rule_texts[i])
       continue;
-    FilterRule* rule = filter_rule_parse(rule_texts[i], err, err_size);
-    if (!rule) {
+    if (!filter_rule_list_parse_append(list, rule_texts[i], &opts, NULL, err, err_size)) {
       filter_rule_list_free(list);
       return NULL;
     }
-    if (!set_rule_owner(rule, "")) {
-      filter_rule_free(rule);
-      filter_rule_list_free(list);
-      snprintf(err, err_size, "memory allocation failed");
-      return NULL;
-    }
-    if (!filter_rule_list_add(list, rule)) {
-      filter_rule_free(rule);
-      filter_rule_list_free(list);
-      snprintf(err, err_size, "memory allocation failed");
-      return NULL;
-    }
   }
-  if (cvs_exclude && !cvs_rule_list_append(list)) {
+  if (cvs_exclude && !filter_list_append_cvs(list, FILTER_SIDE_SENDER | FILTER_SIDE_RECEIVER)) {
     filter_rule_list_free(list);
-    snprintf(err, err_size, "memory allocation failed");
+    filter_set_error(err, err_size, "memory allocation failed");
     return NULL;
   }
   return list;
 }
 
-/* ---- Per-directory .rsync-filter files ---- */
+/* ---- Per-directory merge files ---- */
 
-FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, bool* exists,
-                                 char* err, size_t err_size) {
+/* Undo the rules and dir-merge registrations that one merge file appended,
+ * leaving the caller's earlier content intact.  A "clear" rule inside the file
+ * frees every rule, including the caller's; clamp to the surviving count so
+ * those already-freed rules are never resurrected and freed a second time. */
+static void filter_file_rollback(FilterRuleList* list, int rules_before, int dir_merges_before) {
+  int first = rules_before < list->count ? rules_before : list->count;
+  for (int i = first; i < list->count; i++)
+    filter_rule_free(list->items[i]);
+  list->count = first;
+  for (int i = dir_merges_before; i < list->dir_merge_count; i++)
+    free(list->dir_merge_names[i]);
+  list->dir_merge_count = dir_merges_before;
+}
+
+bool filter_file_append(FilterRuleList* list, const char* dir_path, const char* name,
+                        const char* owner_rel, const FilterParseOptions* opts, bool* exists,
+                        char* err, size_t err_size) {
   if (err && err_size > 0)
     err[0] = '\0';
   if (exists)
     *exists = false;
-  char* filter_path = path_cat(dir_path, ".rsync-filter");
+  if (!list)
+    return false;
+  char* filter_path = path_cat(dir_path, name);
   if (!filter_path) {
-    snprintf(err, err_size, "memory allocation failed");
-    return NULL;
+    filter_set_error(err, err_size, "memory allocation failed");
+    return false;
   }
   FILE* fp = fopen(filter_path, "r");
   free(filter_path);
   if (!fp) {
     if (errno == ENOENT || errno == ENOTDIR)
-      return filter_rule_list_create();
+      return true;
     char* escaped_dir = output_escape(dir_path, log_get_8_bit_output());
-    log_message(LOG_LEVEL_WARNING, "Could not read .rsync-filter in %s: %s",
+    log_message(LOG_LEVEL_WARNING, "Could not read %s in %s: %s", name,
                 escaped_dir ? escaped_dir : "<allocation failed>", strerror(errno));
     free(escaped_dir);
-    return filter_rule_list_create();
+    return true;
   }
   if (exists)
     *exists = true;
-  FilterRuleList* list = filter_rule_list_create();
-  if (!list) {
-    fclose(fp);
-    snprintf(err, err_size, "memory allocation failed");
-    return NULL;
-  }
+  int rules_before = list->count;
+  int dir_merges_before = list->dir_merge_count;
   char* line = NULL;
   size_t line_cap = 0;
   bool ok = true;
@@ -346,9 +691,10 @@ FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, bo
     ssize_t n = utils_getdelim_bounded(fp, &line, &line_cap, '\n', UTILS_MAX_LINE_LEN);
     if (n < 0) {
       if (errno == EFBIG) {
-        snprintf(err, err_size, "line in .rsync-filter exceeds %d bytes", (int)UTILS_MAX_LINE_LEN);
+        filter_set_error(err, err_size, "line in %s exceeds %d bytes", name,
+                         (int)UTILS_MAX_LINE_LEN);
       } else {
-        snprintf(err, err_size, "error reading .rsync-filter: %s", strerror(errno));
+        filter_set_error(err, err_size, "error reading %s: %s", name, strerror(errno));
       }
       ok = false;
       break;
@@ -360,20 +706,9 @@ FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, bo
       p++;
     if (*p == '\0' || *p == '\n' || *p == '\r' || *p == '#')
       continue;
-    FilterRule* rule = filter_rule_parse(p, err, err_size);
-    if (!rule) {
-      ok = false;
-      break;
-    }
-    if (!set_rule_owner(rule, owner_rel)) {
-      filter_rule_free(rule);
-      snprintf(err, err_size, "memory allocation failed");
-      ok = false;
-      break;
-    }
-    if (!filter_rule_list_add(list, rule)) {
-      filter_rule_free(rule);
-      snprintf(err, err_size, "memory allocation failed");
+    /* Merge files inside a per-directory file resolve relative to that
+       directory. */
+    if (!filter_list_parse_append_depth(list, p, opts, dir_path, 0, err, err_size)) {
       ok = false;
       break;
     }
@@ -381,12 +716,40 @@ FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, bo
   free(line);
   fclose(fp);
   if (!ok) {
+    filter_file_rollback(list, rules_before, dir_merges_before);
+    return false;
+  }
+  for (int i = rules_before; i < list->count; i++) {
+    if (!set_rule_owner(list->items[i], owner_rel)) {
+      filter_set_error(err, err_size, "memory allocation failed");
+      filter_file_rollback(list, rules_before, dir_merges_before);
+      return false;
+    }
+  }
+  return true;
+}
+
+FilterRuleList* filter_file_read_named(const char* dir_path, const char* name,
+                                       const char* owner_rel, const FilterParseOptions* opts,
+                                       bool* exists, char* err, size_t err_size) {
+  FilterRuleList* list = filter_rule_list_create();
+  if (!list) {
+    if (err && err_size > 0)
+      filter_set_error(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  if (!filter_file_append(list, dir_path, name, owner_rel, opts, exists, err, err_size)) {
     filter_rule_list_free(list);
     return NULL;
   }
   return list;
 }
 
+FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, bool* exists,
+                                 char* err, size_t err_size) {
+  return filter_file_read_named(dir_path, ".rsync-filter", owner_rel, NULL, exists, err, err_size);
+}
+
 /* ---- Rule matching ---- */
 
 /* Match a pattern that contains '/' (non-anchored) against the end of the
@@ -402,10 +765,10 @@ static bool glob_suffix_match(const char* pattern, const char* str) {
 }
 
 static FilterAction rule_matches(const FilterRule* rule, const char* rel_path, const char* leaf,
-                                 bool is_dir) {
+                                 bool is_dir, unsigned side) {
   if (!rule || !rule->pattern)
     return FILTER_ACTION_NONE;
-  if (rule->dir_only && !is_dir)
+  if (!(rule->sides & side))
     return FILTER_ACTION_NONE;
   /* A rule applies only to entries below its owner directory. */
   const char* rel2 = rel_path;
@@ -420,24 +783,36 @@ static FilterAction rule_matches(const FilterRule* rule, const char* rel_path, c
   if (rel2[0] == '\0')
     return FILTER_ACTION_NONE;
   bool matched;
-  if (rule->anchored) {
+  if (rule->dir_only && !is_dir)
+    matched = false;
+  else if (rule->anchored)
     matched = glob_match(rule->pattern, rel2);
-  } else if (strchr(rule->pattern, '/') != NULL) {
+  else if (strchr(rule->pattern, '/') != NULL)
     matched = glob_suffix_match(rule->pattern, rel2);
-  } else {
+  else
     matched = glob_match(rule->pattern, leaf);
-  }
-  return matched ? rule->action : FILTER_ACTION_NONE;
+  if (rule->negate)
+    matched = !matched;
+  if (!matched)
+    return FILTER_ACTION_NONE;
+  if (side == FILTER_SIDE_RECEIVER)
+    return rule->action == FILTER_ACTION_EXCLUDE ? FILTER_ACTION_PROTECT : FILTER_ACTION_RISK;
+  return rule->action;
 }
 
-FilterAction filter_rules_apply(const FilterRuleList* list, const char* rel_path, const char* leaf,
-                                bool is_dir) {
+FilterAction filter_rules_apply_side(const FilterRuleList* list, const char* rel_path,
+                                     const char* leaf, bool is_dir, unsigned side) {
   if (!list)
     return FILTER_ACTION_NONE;
   for (int i = 0; i < list->count; i++) {
-    FilterAction action = rule_matches(list->items[i], rel_path, leaf, is_dir);
+    FilterAction action = rule_matches(list->items[i], rel_path, leaf, is_dir, side);
     if (action != FILTER_ACTION_NONE)
       return action;
   }
   return FILTER_ACTION_NONE;
 }
+
+FilterAction filter_rules_apply(const FilterRuleList* list, const char* rel_path, const char* leaf,
+                                bool is_dir) {
+  return filter_rules_apply_side(list, rel_path, leaf, is_dir, FILTER_SIDE_SENDER);
+}

src/shared/filter.h

@@ -4,79 +4,133 @@
 #include <stdbool.h>
 #include <stddef.h>
 
-/* rsync-style filter rule engine (client-side file selection).
+/* rsync-style filter rule engine (client-side file selection and the
+ * receiver-side protection set it feeds).
  *
- * Supported rule syntax (documented subset):
- *   [+|-] [anchored '/' prefix] pattern [trailing '/' for dir-only]
- *
- *   "+ PATTERN"   include rule (first match wins)
- *   "- PATTERN"   exclude rule
- *   "PATTERN"     implicit exclude rule (rsync default)
- *   "include PATTERN" / "exclude PATTERN"  word forms
- *   leading '/' after the +/- anchors the pattern to its owner directory
- *     (the transfer root for command-line/-C rules, the directory that
- *      contains a .rsync-filter file for per-directory rules)
- *   a trailing '/' makes the rule match directories only
- *
- * Rejected explicitly (no silent no-ops): the rsync merge/dir-merge/list-clear
- * shorthands written as a rule that starts with ':' or '.' or '!', the
- * merge/dir-merge/hide/show/protect/risk/clear words, and every include/exclude
- * rule modifier other than '/' (! C s r p x). The pattern must be separated
- * from +/- by a space (or a single '/' anchor), exactly like rsync's
- * "-s foo"/"-p ..." modifier syntax is refused.
+ * Rule syntax (see the rsync man page FILTER RULES section):
+ *   RULE [PATTERN_OR_FILENAME]
+ *   RULE,MODIFIERS [PATTERN_OR_FILENAME]
+ * Short RULE names may attach MODIFIERS directly ("-sr foo"); the long name
+ * form requires the comma.  The pattern/filename is separated from the rule by
+ * one space or underscore.  Rule names:
+ *   exclude/-   exclude (by default both sender-hide and receiver-protect)
+ *   include/+   include (by default both sender-show and receiver-risk)
+ *   hide/H      sender-only exclude
+ *   show/S      sender-only include
+ *   protect/P   receiver-only exclude (protect from deletion)
+ *   risk/R      receiver-only include (allow deletion)
+ *   merge/.     read a client-side merge file for more rules
+ *   dir-merge/: per-directory merge file (registered for the scanner)
+ *   clear/!     clear the current rule list (takes no argument)
+ * Modifiers: '/' absolute anchor, '!' negate match, 'C' inject CVS defaults,
+ * 's' sender side, 'r' receiver side, 'p' perishable, 'x' xattr name rule.
+ * A trailing '/' makes a pattern match directories only.  A leading '/' anchors
+ * the pattern to its owner directory.
  */
 
 typedef enum {
   FILTER_ACTION_NONE = 0, /* no rule matched */
   FILTER_ACTION_EXCLUDE = -1,
-  FILTER_ACTION_INCLUDE = 1
+  FILTER_ACTION_INCLUDE = 1,
+  /* Receiver-side-only verdicts: the entry is transferred but its destination
+   * mirror is protected from --delete (PROTECT) or explicitly left at risk
+   * (RISK). */
+  FILTER_ACTION_PROTECT = 2,
+  FILTER_ACTION_RISK = 3,
 } FilterAction;
 
-typedef struct {
-  FilterAction action;
-  bool anchored; /* pattern anchored to the rule's owner directory */
-  bool dir_only; /* pattern had a trailing '/': matches directories only */
-  char* owner;   /* owning directory rel path ("" == transfer root) */
-  char* pattern; /* cleaned glob pattern (no leading '/', no trailing '/') */
-} FilterRule;
+#define FILTER_SIDE_SENDER 1u
+#define FILTER_SIDE_RECEIVER 2u
 
 typedef struct {
+  FilterAction action; /* EXCLUDE or INCLUDE (the base pattern action) */
+  unsigned sides;      /* FILTER_SIDE_SENDER | FILTER_SIDE_RECEIVER */
+  bool anchored;       /* pattern anchored to the rule's owner directory */
+  bool dir_only;       /* pattern had a trailing '/': matches directories only */
+  bool negate;         /* '!' modifier: match succeeds when the pattern does not */
+  bool perishable;     /* 'p' modifier (ignored in deleted directories) */
+  char* owner;         /* owning directory rel path ("" == transfer root) */
+  char* pattern;       /* cleaned glob pattern (no leading '/', no trailing '/') */
+} FilterRule;
+
+typedef struct FilterRuleList {
   FilterRule** items; /* owned array of rule pointers */
   int count;
   int capacity;
+  /* Per-directory merge-file basenames registered by "dir-merge NAME"/": NAME"
+   * or by -F (.rsync-filter).  Owned strings; the scanner reads each name in
+   * every directory it traverses. */
+  char** dir_merge_names;
+  int dir_merge_count;
+  int dir_merge_capacity;
 } FilterRuleList;
 
+/* Context needed while parsing a rule list (merge files, --delete-excluded). */
+typedef struct {
+  bool delete_excluded; /* --delete-excluded: default sides become sender-only */
+  bool cvs_exclude;     /* -C: expand the CVS default excludes */
+} FilterParseOptions;
+
 /* Parse a single filter-rule line (no trailing newline required). Returns an
- * owned rule, or NULL on unsupported/invalid syntax with a message in `err`. */
-FilterRule* filter_rule_parse(const char* line, char* err, size_t err_size);
+ * owned rule, or NULL on unsupported/invalid syntax with a message in `err`.
+ * `opts` may be NULL (no merge expansion / no delete-excluded). */
+FilterRule* filter_rule_parse(const char* line, const FilterParseOptions* opts, char* err,
+                              size_t err_size);
 void filter_rule_free(FilterRule* rule);
 
 FilterRuleList* filter_rule_list_create(void);
 /* Append a fully-parsed rule (takes ownership). Returns false on OOM. */
 bool filter_rule_list_add(FilterRuleList* list, FilterRule* rule);
-/* Parse `line` and append it. Returns false and fills `err` on bad syntax. */
-bool filter_rule_list_parse_append(FilterRuleList* list, const char* line, char* err,
-                                   size_t err_size);
+/* Register a per-directory merge-file basename (idempotent). Returns false on
+ * OOM.  Used by the scanner to read custom "dir-merge" files. */
+bool filter_rule_list_add_dir_merge(FilterRuleList* list, const char* name);
+/* Parse `line` and append it.  Handles "clear"/"!" (resets the list), "merge
+ * FILE"/". FILE" (splices the file's rules) and "dir-merge NAME"/": NAME"
+ * (registers a per-directory filename).  Returns false and fills `err` on bad
+ * syntax or an unreadable merge file.  `merge_base_dir` resolves a relative
+ * merge-file path (NULL means the process working directory). */
+bool filter_rule_list_parse_append(FilterRuleList* list, const char* line,
+                                   const FilterParseOptions* opts, const char* merge_base_dir,
+                                   char* err, size_t err_size);
 void filter_rule_list_free(FilterRuleList* list);
 
 /* Build the command-line filter set: `rule_texts` (--filter=RULE in the order
  * given, 0..rule_count) followed by the -C CVS default excludes when
- * cvs_exclude is true. All rules are owned by "" (the transfer root).
+ * cvs_exclude is true.  All rules are owned by "" (the transfer root).
  * Returns NULL on unsupported rule text (message in `err`). */
 FilterRuleList* filter_base_build(const char* const* rule_texts, int rule_count, bool cvs_exclude,
-                                  char* err, size_t err_size);
+                                  bool delete_excluded, char* err, size_t err_size);
 
-/* Read "<dir_path>/.rsync-filter" and return its rules, each owned by
- * `owner_rel`. A missing file yields an empty list with *exists=false; an
- * unreadable file is treated as missing. Returns NULL only on parse or
- * allocation failure (message in `err`). */
+/* Read "<dir_path>/<name>" and return its rules, each owned by `owner_rel`.  A
+ * missing file yields an empty list with *exists=false; an unreadable file is
+ * treated as missing.  Returns NULL only on parse or allocation failure
+ * (message in `err`).  `opts` may be NULL. */
+FilterRuleList* filter_file_read_named(const char* dir_path, const char* name,
+                                       const char* owner_rel, const FilterParseOptions* opts,
+                                       bool* exists, char* err, size_t err_size);
+
+/* Append the rules of "<dir_path>/<name>" into an existing list (each owned by
+ * `owner_rel`).  A missing file yields *exists=false and no error.  Returns
+ * false only on parse/allocation failure (message in `err`). */
+bool filter_file_append(FilterRuleList* list, const char* dir_path, const char* name,
+                        const char* owner_rel, const FilterParseOptions* opts, bool* exists,
+                        char* err, size_t err_size);
+
+/* filter_file_read_named with the default ".rsync-filter" name. */
 FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, bool* exists,
                                  char* err, size_t err_size);
 
-/* Evaluate an entry against one ordered rule list. Returns FILTER_ACTION_NONE
- * when no rule matched, otherwise the first matching rule's action.
- * `rel_path` is the entry's path relative to the transfer root ("" == root),
- * `leaf` its final name, `is_dir` whether it is a directory. */
+/* Evaluate an entry against one ordered rule list for one side.  Returns
+ * FILTER_ACTION_NONE when no rule matched, otherwise the first matching rule's
+ * action (for the receiver side an EXCLUDE is reported as
+ * FILTER_ACTION_PROTECT and an INCLUDE as FILTER_ACTION_RISK).  `rel_path` is
+ * the entry's path relative to the transfer root ("" == root), `leaf` its final
+ * name, `is_dir` whether it is a directory. */
+FilterAction filter_rules_apply_side(const FilterRuleList* list, const char* rel_path,
+                                     const char* leaf, bool is_dir, unsigned side);
+
+/* Sender-side convenience wrapper (kept for callers/tests that only need the
+ * transfer decision). */
 FilterAction filter_rules_apply(const FilterRuleList* list, const char* rel_path, const char* leaf,
                                 bool is_dir);
 

src/shared/format.c

@@ -0,0 +1,131 @@
+#include "format.h"
+#include "protocol.h"
+#include <stdio.h>
+#include <string.h>
+
+bool format_human_size_decimal(unsigned long long bytes, char* buffer, size_t buffer_size) {
+  if (!buffer || buffer_size == 0)
+    return false;
+  if (bytes < 1000ULL) {
+    int written = snprintf(buffer, buffer_size, "%llu", bytes);
+    return written >= 0 && (size_t)written < buffer_size;
+  }
+  static const char units[] = "KMGTPE";
+  double value = (double)bytes;
+  size_t divisions = 0;
+  while (value >= 1000.0 && divisions < sizeof(units) - 1) {
+    value /= 1000.0;
+    divisions++;
+  }
+  int written = snprintf(buffer, buffer_size, "%.2f%c", value, units[divisions - 1]);
+  return written >= 0 && (size_t)written < buffer_size;
+}
+
+bool format_big_num(unsigned long long value, bool human_readable, char* buffer,
+                    size_t buffer_size) {
+  if (human_readable)
+    return format_human_size_decimal(value, buffer, buffer_size);
+  char digits[32];
+  int written = snprintf(digits, sizeof(digits), "%llu", value);
+  if (written < 0 || (size_t)written >= sizeof(digits))
+    return false;
+  size_t len = (size_t)written;
+  size_t separators = len > 1 ? (len - 1) / 3 : 0;
+  size_t total = len + separators;
+  if (total + 1 > buffer_size)
+    return false;
+  size_t out = total;
+  buffer[out] = '\0';
+  size_t digits_since_sep = 0;
+  for (size_t i = len; i > 0; i--) {
+    buffer[--out] = digits[i - 1];
+    digits_since_sep++;
+    if (digits_since_sep == 3 && i > 1) {
+      buffer[--out] = ',';
+      digits_since_sep = 0;
+    }
+  }
+  return true;
+}
+
+bool format_rsync_datetime(time_t when, bool dash, char* buffer, size_t buffer_size) {
+  if (!buffer || buffer_size == 0)
+    return false;
+  struct tm broken_down;
+  if (localtime_r(&when, &broken_down) == NULL)
+    return false;
+  const char* format = dash ? "%Y/%m/%d-%H:%M:%S" : "%Y/%m/%d %H:%M:%S";
+  return strftime(buffer, buffer_size, format, &broken_down) != 0;
+}
+
+bool format_dest_state_send(int fd, const OutputDestState* state) {
+  if (!state)
+    return false;
+  int32_t has_old = state->existed ? 1 : 0;
+  uint64_t size = (uint64_t)state->size;
+  int64_t mtime = (int64_t)state->mtime_sec;
+  int64_t mtime_nsec = state->mtime_nsec;
+  uint32_t mode = state->mode;
+  int32_t uid = state->uid;
+  int32_t gid = state->gid;
+  return send_n_data(fd, &has_old, sizeof(has_old)) && send_n_data(fd, &size, sizeof(size)) &&
+         send_n_data(fd, &mtime, sizeof(mtime)) &&
+         send_n_data(fd, &mtime_nsec, sizeof(mtime_nsec)) && send_n_data(fd, &mode, sizeof(mode)) &&
+         send_n_data(fd, &uid, sizeof(uid)) && send_n_data(fd, &gid, sizeof(gid));
+}
+
+bool format_dest_state_receive(int fd, OutputDestState* state) {
+  if (!state)
+    return false;
+  int32_t has_old = 0;
+  uint64_t size = 0;
+  int64_t mtime = 0;
+  int64_t mtime_nsec = 0;
+  uint32_t mode = 0;
+  int32_t uid = 0;
+  int32_t gid = 0;
+  if (!receive_n_data(fd, &has_old, sizeof(has_old)) || !receive_n_data(fd, &size, sizeof(size)) ||
+      !receive_n_data(fd, &mtime, sizeof(mtime)) ||
+      !receive_n_data(fd, &mtime_nsec, sizeof(mtime_nsec)) ||
+      !receive_n_data(fd, &mode, sizeof(mode)) || !receive_n_data(fd, &uid, sizeof(uid)) ||
+      !receive_n_data(fd, &gid, sizeof(gid)))
+    return false;
+  memset(state, 0, sizeof(*state));
+  state->known = true;
+  state->existed = has_old != 0;
+  state->size = size;
+  state->mtime_sec = mtime;
+  state->mtime_nsec = mtime_nsec;
+  state->mode = mode;
+  state->uid = uid;
+  state->gid = gid;
+  return true;
+}
+
+bool format_stats_send(int fd, const ReceiverStats* stats) {
+  if (!stats)
+    return false;
+  unsigned long long fields[8] = {
+      stats->matched_data, stats->deleted_files, stats->would_delete_count, stats->literal_bytes,
+      stats->created_reg,  stats->created_dir,   stats->created_link,       stats->created_special,
+  };
+  return send_n_data(fd, fields, sizeof(fields));
+}
+
+bool format_stats_receive(int fd, ReceiverStats* stats) {
+  if (!stats)
+    return false;
+  unsigned long long fields[8] = {0};
+  if (!receive_n_data(fd, fields, sizeof(fields)))
+    return false;
+  memset(stats, 0, sizeof(*stats));
+  stats->matched_data = fields[0];
+  stats->deleted_files = fields[1];
+  stats->would_delete_count = fields[2];
+  stats->literal_bytes = fields[3];
+  stats->created_reg = fields[4];
+  stats->created_dir = fields[5];
+  stats->created_link = fields[6];
+  stats->created_special = fields[7];
+  return true;
+}

src/shared/format.h

@@ -0,0 +1,111 @@
+#ifndef FORMAT_H
+#define FORMAT_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <time.h>
+
+/* Low-level output-formatting primitives shared by the change-event model
+ * (change_list.c) and the transfer driver (client_send.c).
+ *
+ * The functions here are pure/string-level except for the STATUS_DEST_INFO
+ * codec, which lets the receiver report the pre-transfer destination entry so
+ * the sender can render rsync-accurate --itemize-changes / --out-format
+ * columns (see protocol.h). */
+
+/* Pre-transfer destination snapshot, reported by the receiver when the wire
+ * config carries report_dest_info.  `known` distinguishes "no report was
+ * requested/received" from "the destination did not exist" (`existed == false`
+ * with `known == true`). */
+typedef struct {
+  bool known;
+  bool existed;
+  unsigned long long size;
+  long long mtime_sec;
+  long long mtime_nsec;
+  uint32_t mode;
+  int32_t uid;
+  int32_t gid;
+} OutputDestState;
+
+/* rsync's -h/--human-readable size (decimal, base 1000): integers below 1000
+ * print verbatim; larger values use the largest unit that keeps the value
+ * below 1000 (K/M/G/T/P/E) with exactly two decimals, so 1500000 -> "1.50M"
+ * and 999999 -> "1000.00K" (matching rsync's human_num).  Returns false when
+ * the buffer is too small (nothing is written). */
+bool format_human_size_decimal(unsigned long long bytes, char* buffer, size_t buffer_size);
+
+/* rsync's general number formatting (big_num).  When `human_readable` is true
+ * this is format_human_size_decimal; otherwise the integer is rendered with a
+ * ',' thousands separator every three digits (rsync's separator in the C
+ * locale).  Returns false on an undersized buffer. */
+bool format_big_num(unsigned long long value, bool human_readable, char* buffer,
+                    size_t buffer_size);
+
+/* rsync's %M/%t timestamp.  When `dash` is true the separator between the date
+ * and the time is '-' (the %M form: "YYYY/MM/DD-HH:MM:SS"); otherwise it is a
+ * space (the %t form: "YYYY/MM/DD HH:MM:SS").  Local time.  Returns false on a
+ * bad time or an undersized buffer. */
+bool format_rsync_datetime(time_t when, bool dash, char* buffer, size_t buffer_size);
+
+/* Fixed-width STATUS_DEST_INFO record codec (int32 has_old, uint64 size,
+ * int64 mtime, int64 mtime_nsec, uint32 mode, int32 uid, int32 gid).  The
+ * status frame itself is sent/received by the caller.  Returns false on I/O
+ * failure. */
+bool format_dest_state_send(int fd, const OutputDestState* state);
+bool format_dest_state_receive(int fd, OutputDestState* state);
+
+/* End-of-transfer receiver counters reported through STATUS_STATS (protocol
+ * 2.25.0, extended in 2.28.0) when the wire config carries report_stats.
+ * `would_delete_count` is the number of destination-relative paths the receiver
+ * would have deleted in a -n/--dry-run --delete run; that many wire strings
+ * immediately follow the fixed record (sent/read by the caller).
+ *
+ * Protocol 2.28.0 adds the receiver-observed counters the sender cannot see:
+ * `literal_bytes` is the file data the receiver actually stored literally
+ * (whole files plus the literal fragments of a delta) and the four `created_*`
+ * counters split the destination entries the receiver newly created by type,
+ * reproducing rsync's `Number of created files` breakdown and an exact
+ * `Literal data` for a delta run. */
+typedef struct {
+  unsigned long long matched_data;
+  unsigned long long deleted_files;
+  unsigned long long would_delete_count;
+  unsigned long long literal_bytes;
+  unsigned long long created_reg;
+  unsigned long long created_dir;
+  unsigned long long created_link;
+  unsigned long long created_special;
+} ReceiverStats;
+
+/* Fixed-width STATUS_STATS counter record.  The status frame and the optional
+ * would-delete path list are sent/received by the caller.  Returns false on I/O
+ * failure. */
+bool format_stats_send(int fd, const ReceiverStats* stats);
+bool format_stats_receive(int fd, ReceiverStats* stats);
+
+/* Sender-side file-list accounting for rsync's `--stats` block.  Filled while
+ * the scan/send loops walk each entry: the flist counters describe every
+ * scanned source entry (transferred or skipped), while the transferred/literal
+ * counters describe only the regular files the receiver actually stored.  The
+ * type split lets the client print rsync's `Number of files` breakdown; the
+ * receiver-only counters (matched data, deleted, created) come from
+ * STATUS_STATS. */
+typedef struct {
+  unsigned long long flist_reg;
+  unsigned long long flist_dir;
+  unsigned long long flist_link;
+  unsigned long long flist_special;
+  unsigned long long total_file_size;       /* sum of entry sizes (link target len) */
+  unsigned long long transferred_regular;   /* regular files actually stored */
+  unsigned long long transferred_file_size; /* source size of those files */
+  /* Whole-file accuracy: the `--stats` "Literal data" row.  The sender counts
+   * the source size of every stored file, so a whole-file transfer matches
+   * rsync.  A delta run actually ships only the literal fragments of the diff
+   * (the rest is matched/copied), so here the value is an upper bound, not
+   * rsync's literal-byte total; see RSYNC_COMPAT.md's `--stats` row. */
+  unsigned long long literal_data;
+} TransferStats;
+
+#endif

src/shared/identity.c

@@ -36,14 +36,34 @@ typedef struct {
   bool copy_as_set;
   int32_t copy_as_uid;
   int32_t copy_as_gid;
+  /* -o/--owner and -g/--group: preserve the source owner/group through the
+   * normal name/identity resolution path.  Split out of the former
+   * use_metadata bundle; unlike --numeric-ids/--chown/--usermap/--groupmap/-a
+   * these are a preserve-source request, not an arbitrary client-chosen owner,
+   * so they are tracked separately from the explicit ownership gate. */
+  bool preserve_owner;
+  bool preserve_group;
+  /* --fake-super: when active the receiver must only RECORD the (resolved)
+   * ownership in the reserved xattr, never perform a real chown.  Snapshotted
+   * so the fd-relative ownership helpers can suppress the chown without a
+   * Config argument. */
+  bool fake_super;
   bool set;
 } IdentityActive;
 
 static IdentityActive g_identity;
 
 static void identity_active_reset(void) {
-  free(g_identity.usermap);
-  free(g_identity.groupmap);
+  if (g_identity.usermap) {
+    for (int i = 0; i < g_identity.usermap_count; i++)
+      free(g_identity.usermap[i].to_name);
+    free(g_identity.usermap);
+  }
+  if (g_identity.groupmap) {
+    for (int i = 0; i < g_identity.groupmap_count; i++)
+      free(g_identity.groupmap[i].to_name);
+    free(g_identity.groupmap);
+  }
   g_identity.usermap = NULL;
   g_identity.groupmap = NULL;
   g_identity.usermap_count = 0;
@@ -57,6 +77,9 @@ static void identity_active_reset(void) {
   g_identity.copy_as_set = false;
   g_identity.copy_as_uid = 0;
   g_identity.copy_as_gid = 0;
+  g_identity.preserve_owner = false;
+  g_identity.preserve_group = false;
+  g_identity.fake_super = false;
   g_identity.set = false;
 }
 
@@ -77,32 +100,57 @@ bool identity_set_active(const Config* config) {
   g_identity.copy_as_set = config->copy_as_set;
   g_identity.copy_as_uid = config->copy_as_uid;
   g_identity.copy_as_gid = config->copy_as_gid;
+  g_identity.preserve_owner = config->preserve_owner;
+  g_identity.preserve_group = config->preserve_group;
+  g_identity.fake_super = config->fake_super;
   if (config->usermap_count > 0) {
     g_identity.usermap = calloc((size_t)config->usermap_count, sizeof(IdentityMap));
     if (!g_identity.usermap)
       goto alloc_failed;
-    memcpy(g_identity.usermap, config->usermap,
-           (size_t)config->usermap_count * sizeof(IdentityMap));
+    for (int i = 0; i < config->usermap_count; i++) {
+      g_identity.usermap[i] = config->usermap[i];
+      g_identity.usermap[i].to_name =
+          config->usermap[i].to_name ? str_dup(config->usermap[i].to_name) : NULL;
+      if (config->usermap[i].to_name && !g_identity.usermap[i].to_name) {
+        g_identity.usermap_count = i; /* free only the entries already duplicated */
+        goto alloc_failed;
+      }
+    }
     g_identity.usermap_count = config->usermap_count;
   }
   if (config->groupmap_count > 0) {
     g_identity.groupmap = calloc((size_t)config->groupmap_count, sizeof(IdentityMap));
     if (!g_identity.groupmap)
       goto alloc_failed;
-    memcpy(g_identity.groupmap, config->groupmap,
-           (size_t)config->groupmap_count * sizeof(IdentityMap));
+    for (int i = 0; i < config->groupmap_count; i++) {
+      g_identity.groupmap[i] = config->groupmap[i];
+      g_identity.groupmap[i].to_name =
+          config->groupmap[i].to_name ? str_dup(config->groupmap[i].to_name) : NULL;
+      if (config->groupmap[i].to_name && !g_identity.groupmap[i].to_name) {
+        g_identity.groupmap_count = i;
+        goto alloc_failed;
+      }
+    }
     g_identity.groupmap_count = config->groupmap_count;
   }
   g_identity.set = true;
   /* A root receiver would honor any client-supplied ownership request (a
-     --usermap/--groupmap/--chown/--copy-as, or raw ids under --numeric-ids).
-     Surface that prominently; a privileged daemon applying arbitrary client
-     ownership is a deliberate, opt-in choice the operator should be aware of. */
-  if (geteuid() == 0)
-    log_message(LOG_LEVEL_WARNING,
-                "identity mapping active and running as root: client-supplied "
-                "ownership (usermap/groupmap/chown/numeric-ids) will be honored; "
-                "run the daemon as an unprivileged user unless intended");
+     --usermap/--groupmap/--chown/--copy-as, or raw ids under --numeric-ids)
+     ONLY when super-user activities are permitted.  --no-super (or a daemon
+     veto that forced SUPER_MODE_OFF) forbids the chown even for root, so do
+     not claim the ownership will be honored in that case. */
+  if (geteuid() == 0) {
+    if (privilege_super_mode_permitted(g_identity.super_mode))
+      log_message(LOG_LEVEL_WARNING,
+                  "identity mapping active and running as root: client-supplied "
+                  "ownership (usermap/groupmap/chown/numeric-ids) will be honored; "
+                  "run the daemon as an unprivileged user unless intended");
+    else
+      log_message(LOG_LEVEL_WARNING,
+                  "identity mapping active and running as root, but super-user activities are "
+                  "disabled (--no-super): requested ownership will NOT be applied; run the "
+                  "daemon as an unprivileged user unless intended");
+  }
   /* --super explicitly requests super-user activities, but FastSync never
      elevates privileges: when the receiver is not already root the kernel will
      refuse those confined attempts and each is skipped per entry.  Warn exactly
@@ -138,25 +186,55 @@ bool privilege_super_mode_permitted(SuperMode mode) {
 }
 
 bool identity_active_enabled(void) {
-  /* numeric_ids is included: this set only gates identity_apply_ownership,
-     which runs only when metadata is present (a -M/--preserve transfer).  A
-     standalone --numeric-ids (no ownership-affecting flag) carries no
-     metadata, never reaches identity_apply_ownership, and therefore correctly
-     stays inert; combined with -M it activates raw-id application.  --super /
-     --no-super does NOT enable ownership: it only permits or forbids the
-     already-requested super-user activities, so a --super with no explicit
-     identity flag must never silently apply client-chosen ownership. */
+  /* --numeric-ids is deliberately NOT included: it is a mapping MODIFIER (use
+   * the transmitted numeric id raw instead of a name lookup), not a request to
+   * change ownership.  rsync's --numeric-ids on its own never chowns anything;
+   * it only changes how an already-requested -o/-g/map resolves.  Ownership is
+   * activated only by an explicit request: --chown/--usermap/--groupmap/
+   * --copy-as or a preserve-source -o/--owner / -g/--group.  --super/--no-super
+   * likewise does NOT enable ownership: it only permits or forbids the
+   * already-requested super-user activities. */
   return g_identity.set &&
-         (g_identity.numeric_ids || g_identity.chown_uid_set || g_identity.chown_gid_set ||
-          g_identity.usermap_count > 0 || g_identity.groupmap_count > 0 || g_identity.copy_as_set);
+         (g_identity.chown_uid_set || g_identity.chown_gid_set || g_identity.usermap_count > 0 ||
+          g_identity.groupmap_count > 0 || g_identity.copy_as_set || g_identity.preserve_owner ||
+          g_identity.preserve_group);
+}
+
+bool identity_owner_requested(void) {
+  return g_identity.set && (g_identity.copy_as_set || g_identity.chown_uid_set ||
+                            g_identity.preserve_owner || g_identity.usermap_count > 0);
+}
+
+bool identity_group_requested(void) {
+  return g_identity.set && (g_identity.copy_as_set || g_identity.chown_gid_set ||
+                            g_identity.preserve_group || g_identity.groupmap_count > 0);
 }
 
 bool identity_ownership_requested(const Config* config) {
   if (!config)
     return false;
-  /* Every value that makes the receiver act on a client-chosen owner, plus an
-   * explicit --super (super-user device-node activities).  Pure config, so the
-   * daemon gate can evaluate it before identity_set_active(). */
+  /* General-awareness predicate: every value that makes the receiver act on a
+   * client-chosen owner, plus an explicit --super (super-user device-node
+   * activities) and the preserve-source -o/-g requests.  Pure config, so callers
+   * can evaluate it before identity_set_active().  The daemon module gate uses
+   * the narrower identity_explicit_ownership_requested() below, which treats a
+   * plain -o/-g/-a as a preserve-source request rather than arbitrary
+   * client-chosen ownership. */
+  return config->numeric_ids || config->chown_uid_set || config->chown_gid_set ||
+         config->usermap_count > 0 || config->groupmap_count > 0 || config->copy_as_set ||
+         config->preserve_owner || config->preserve_group || config->fake_super ||
+         config->super_mode == SUPER_MODE_ON;
+}
+
+bool identity_explicit_ownership_requested(const Config* config) {
+  if (!config)
+    return false;
+  /* The narrow set the daemon gate refuses for a non-opted module: a request
+   * that lets the CLIENT choose an arbitrary owner/group (rather than preserve
+   * the source's own).  Deliberately EXCLUDES preserve_owner/preserve_group so a
+   * plain -a/-o/-g push is not refused; for those the gate instead forces
+   * super-user ownership activity off (no chown happens) unless the module has
+   * `client owner = yes`. */
   return config->numeric_ids || config->chown_uid_set || config->chown_gid_set ||
          config->usermap_count > 0 || config->groupmap_count > 0 || config->copy_as_set ||
          config->fake_super || config->super_mode == SUPER_MODE_ON;
@@ -177,6 +255,29 @@ bool identity_copy_as_refused(const Config* config) {
   return geteuid() != 0 || config->super_mode == SUPER_MODE_OFF;
 }
 
+/* Validate one received FROM:TO map rule.  `from` is a single id, the LOW end
+ * of an inclusive range, IDENTITY_MATCH_ANY, or IDENTITY_MATCH_UNNAMED; a
+ * sentinel FROM must carry the same value in from_hi.  `to` is a non-negative
+ * id, IDENTITY_CURRENT, or ignored when a bounded receiver-resolved `to_name`
+ * is present. */
+static bool identity_wire_map_valid(const IdentityMap* map) {
+  if (!map)
+    return false;
+  if (map->from < IDENTITY_MATCH_UNNAMED)
+    return false;
+  if (map->from < 0) {
+    if (map->from_hi != map->from)
+      return false;
+  } else if (map->from_hi < map->from) {
+    return false;
+  }
+  if (map->to < IDENTITY_CURRENT)
+    return false;
+  if (map->to_name && strlen(map->to_name) > 255)
+    return false;
+  return true;
+}
+
 bool identity_wire_valid(const Config* config) {
   if (!config)
     return false;
@@ -188,11 +289,11 @@ bool identity_wire_valid(const Config* config) {
   if (config->chown_gid_set && config->chown_gid < IDENTITY_MATCH_ANY)
     return false;
   for (int i = 0; i < config->usermap_count; i++) {
-    if (config->usermap[i].from < IDENTITY_MATCH_ANY || config->usermap[i].to < IDENTITY_CURRENT)
+    if (!identity_wire_map_valid(&config->usermap[i]))
       return false;
   }
   for (int i = 0; i < config->groupmap_count; i++) {
-    if (config->groupmap[i].from < IDENTITY_MATCH_ANY || config->groupmap[i].to < IDENTITY_CURRENT)
+    if (!identity_wire_map_valid(&config->groupmap[i]))
       return false;
   }
   /* Defense-in-depth: a --copy-as block must never carry a negative (sentinel)
@@ -250,15 +351,137 @@ static int identity_resolve_token(const char* token, bool is_group, int32_t* out
   return 0;
 }
 
-static int identity_append_rule(IdentityMap** map, int* count, int32_t from, int32_t to) {
+static bool identity_all_digits(const char* token) {
+  if (!token || *token == '\0')
+    return false;
+  for (const char* p = token; *p; p++)
+    if (*p < '0' || *p > '9')
+      return false;
+  return true;
+}
+
+static bool identity_token_has_glob(const char* token) {
+  return token && (strchr(token, '*') || strchr(token, '?') || strchr(token, '['));
+}
+
+/* Parse a --usermap/--groupmap FROM token into a matcher (from/from_hi).  rsync
+ * accepts a name, a numeric id, an inclusive LOW-HIGH range, '*' (any id), or an
+ * empty token (ids with no name on the sender).  Returns 0 on success, -1 on a
+ * malformed token or an unresolvable sender-side name. */
+static int identity_parse_from(const char* token, bool is_group, int32_t* out_from,
+                               int32_t* out_hi) {
+  if (token[0] == '\0') {
+    *out_from = IDENTITY_MATCH_UNNAMED;
+    *out_hi = IDENTITY_MATCH_UNNAMED;
+    return 0;
+  }
+  if (strcmp(token, "*") == 0) {
+    *out_from = IDENTITY_MATCH_ANY;
+    *out_hi = IDENTITY_MATCH_ANY;
+    return 0;
+  }
+  const char* num = token[0] == '@' ? token + 1 : token;
+  if (identity_all_digits(num)) {
+    int32_t id;
+    if (identity_resolve_token(token, is_group, &id) != 0)
+      return -1;
+    *out_from = id;
+    *out_hi = id;
+    return 0;
+  }
+  /* An inclusive LOW-HIGH numeric range. */
+  const char* dash = strchr(num, '-');
+  if (dash && dash != num && dash[1] != '\0' && strchr(dash + 1, '-') == NULL) {
+    size_t lo_len = (size_t)(dash - num);
+    size_t hi_len = strlen(dash + 1);
+    char low[16];
+    char high[16];
+    if (lo_len < sizeof(low) && hi_len < sizeof(high)) {
+      memcpy(low, num, lo_len);
+      low[lo_len] = '\0';
+      memcpy(high, dash + 1, hi_len);
+      high[hi_len] = '\0';
+      if (identity_all_digits(low) && identity_all_digits(high)) {
+        char* endptr = NULL;
+        errno = 0;
+        long lo = strtol(low, &endptr, 10);
+        if (errno != 0 || !endptr || *endptr != '\0')
+          return -1;
+        errno = 0;
+        long hi = strtol(high, &endptr, 10);
+        if (errno != 0 || !endptr || *endptr != '\0' || hi < lo || hi > INT32_MAX)
+          return -1;
+        *out_from = (int32_t)lo;
+        *out_hi = (int32_t)hi;
+        return 0;
+      }
+    }
+    /* Not a numeric LOW-HIGH range: fall through and treat as a name (a
+     * hyphenated account name like "wayne-smith" must still resolve). */
+  }
+  /* A sender-side name.  A wildcard other than the bare '*' is matched by rsync
+   * against the sender's names; because FastSync transmits numeric ids only, the
+   * receiver cannot evaluate it, so reject rather than silently mis-match. */
+  if (identity_token_has_glob(token)) {
+    log_message(LOG_LEVEL_ERROR,
+                "%smap FROM '%s': name wildcards other than '*' are not supported "
+                "(FastSync transmits numeric ids, so sender names are unavailable on the "
+                "receiver)",
+                is_group ? "--group" : "--user", token);
+    return -1;
+  }
+  int32_t id;
+  if (identity_resolve_token(token, is_group, &id) != 0)
+    return -1;
+  *out_from = id;
+  *out_hi = id;
+  return 0;
+}
+
+/* Parse a --usermap/--groupmap TO token.  '*', a bare numeric id, or an @N id is
+ * stored numerically; every other non-empty token is a NAME resolved on the
+ * RECEIVER at apply time (rsync resolves TO names against the receiving side).
+ * Returns 0 on success, -1 on an empty/malformed token. */
+static int identity_parse_to(const char* token, bool is_group, int32_t* out_to, char** out_name) {
+  if (token[0] == '\0') {
+    log_message(LOG_LEVEL_ERROR, "%smap TO value is missing", is_group ? "--group" : "--user");
+    return -1;
+  }
+  if (strcmp(token, "*") == 0) {
+    *out_to = IDENTITY_CURRENT;
+    *out_name = NULL;
+    return 0;
+  }
+  const char* num = token[0] == '@' ? token + 1 : token;
+  if (identity_all_digits(num)) {
+    int32_t id;
+    if (identity_resolve_token(token, is_group, &id) != 0)
+      return -1;
+    *out_to = id;
+    *out_name = NULL;
+    return 0;
+  }
+  if (identity_token_has_glob(token)) {
+    log_message(LOG_LEVEL_ERROR, "%smap TO '%s' may not contain a wildcard",
+                is_group ? "--group" : "--user", token);
+    return -1;
+  }
+  char* name = str_dup(token);
+  if (!name)
+    return -1;
+  *out_to = 0;
+  *out_name = name;
+  return 0;
+}
+
+static int identity_append_rule(IdentityMap** map, int* count, const IdentityMap* rule) {
   if (*count >= MAX_IDENTITY_MAP)
     return -1;
   IdentityMap* grown = realloc(*map, (size_t)(*count + 1) * sizeof(IdentityMap));
   if (!grown)
     return -1;
   *map = grown;
-  (*map)[*count].from = from;
-  (*map)[*count].to = to;
+  (*map)[*count] = *rule;
   (*count)++;
   return 0;
 }
@@ -275,7 +498,7 @@ int identity_parse_map(Config* config, const char* value, bool is_group) {
   char* saveptr = NULL;
   for (char* rule = strtok_r(list, ",", &saveptr); rule; rule = strtok_r(NULL, ",", &saveptr)) {
     char* colon = strchr(rule, ':');
-    if (!colon || colon == rule) {
+    if (!colon) {
       /* Log before freeing: `rule` points into the str_dup'd list. */
       log_message(LOG_LEVEL_ERROR, "%s rules must be FROM:TO (got '%s')", optname, rule);
       free(list);
@@ -284,25 +507,25 @@ int identity_parse_map(Config* config, const char* value, bool is_group) {
     *colon = '\0';
     char* from_token = rule;
     char* to_token = colon + 1;
-    if (*to_token == '\0') {
+    IdentityMap parsed;
+    memset(&parsed, 0, sizeof(parsed));
+    if (identity_parse_from(from_token, is_group, &parsed.from, &parsed.from_hi) != 0) {
+      log_message(LOG_LEVEL_ERROR,
+                  "%s could not resolve FROM '%s' in '%s' (a name must exist on the "
+                  "source; use @N for a numeric id)",
+                  optname, from_token, value);
       free(list);
-      log_message(LOG_LEVEL_ERROR, "%s rule 'FROM:' is missing the TO value (got '%s')", optname,
-                  value);
       return -1;
     }
-    int32_t from_id, to_id;
-    if (identity_resolve_token(from_token, is_group, &from_id) != 0 ||
-        identity_resolve_token(to_token, is_group, &to_id) != 0) {
+    if (identity_parse_to(to_token, is_group, &parsed.to, &parsed.to_name) != 0) {
+      log_message(LOG_LEVEL_ERROR, "%s could not parse TO '%s' in '%s'", optname, to_token, value);
       free(list);
-      log_message(LOG_LEVEL_ERROR,
-                  "%s could not resolve '%s' (name must exist on the source; use "
-                  "@N for a numeric id)",
-                  optname, value);
       return -1;
     }
     if (identity_append_rule(is_group ? &config->groupmap : &config->usermap,
-                             is_group ? &config->groupmap_count : &config->usermap_count, from_id,
-                             to_id) != 0) {
+                             is_group ? &config->groupmap_count : &config->usermap_count,
+                             &parsed) != 0) {
+      free(parsed.to_name);
       free(list);
       log_message(LOG_LEVEL_ERROR, "%s has too many rules (max %d)", optname, MAX_IDENTITY_MAP);
       return -1;
@@ -366,6 +589,67 @@ static int identity_split_chown(const char* value, char** puser, char** pgroup)
   return 0;
 }
 
+/* --chown is rsync's shorthand for "--usermap=*:USER --groupmap=*:GROUP", so a
+ * name TO value must be resolved on the RECEIVER, not on the sender.  Append the
+ * equivalent map rule (FROM matches every id).  The numeric/'*' forms are stored
+ * numerically exactly as rsync's id_parse/user_to_uid would.  Returns 0 on
+ * success, -1 on a malformed numeric token or allocation failure. */
+static int identity_append_chown_rule(Config* config, bool is_group, const char* token) {
+  IdentityMap rule;
+  memset(&rule, 0, sizeof(rule));
+  rule.from = IDENTITY_MATCH_ANY;
+  rule.from_hi = IDENTITY_MATCH_ANY;
+  if (strcmp(token, "*") == 0) {
+    rule.to = IDENTITY_CURRENT;
+  } else if (identity_all_digits(token[0] == '@' ? token + 1 : token)) {
+    if (identity_resolve_token(token, is_group, &rule.to) != 0) {
+      log_message(LOG_LEVEL_ERROR, "--chown numeric id is out of range: %s", token);
+      return -1;
+    }
+  } else {
+    rule.to = 0;
+    rule.to_name = str_dup(token);
+    if (!rule.to_name)
+      return -1;
+  }
+  if (identity_append_rule(is_group ? &config->groupmap : &config->usermap,
+                           is_group ? &config->groupmap_count : &config->usermap_count,
+                           &rule) != 0) {
+    free(rule.to_name);
+    log_message(LOG_LEVEL_ERROR, "--chown has too many rules (max %d)", MAX_IDENTITY_MAP);
+    return -1;
+  }
+  return 0;
+}
+
+/* Resolve/record one --chown side.  The source-side numeric value is kept in
+ * chown_uid/chown_gid purely as a fallback (the appended map rule resolves the
+ * name on the receiver and wins); a name that does not exist on the sender is
+ * accepted and left to receiver-side resolution, matching rsync. */
+static int identity_parse_chown_side(Config* config, bool is_group, const char* token) {
+  if (identity_append_chown_rule(config, is_group, token) != 0)
+    return -1;
+  bool numeric = identity_all_digits(token[0] == '@' ? token + 1 : token);
+  int32_t resolved;
+  if (identity_resolve_token(token, is_group, &resolved) == 0) {
+    if (is_group) {
+      config->chown_gid = resolved;
+      config->chown_gid_set = true;
+    } else {
+      config->chown_uid = resolved;
+      config->chown_uid_set = true;
+    }
+    return 0;
+  }
+  if (numeric) {
+    log_message(LOG_LEVEL_ERROR, "--chown could not resolve numeric id '%s'", token);
+    return -1;
+  }
+  /* Unknown sender-side name: rsync accepts it and resolves it (or warns) on
+   * the receiver; do the same instead of failing the whole run. */
+  return 0;
+}
+
 int identity_parse_chown(Config* config, const char* value) {
   if (!config || !value || *value == '\0') {
     log_message(LOG_LEVEL_ERROR, "--chown requires a value (USER:GROUP, USER, or :GROUP)");
@@ -404,32 +688,18 @@ int identity_parse_chown(Config* config, const char* value) {
     if (*user == '\0') {
       log_message(LOG_LEVEL_ERROR, "--chown requires a user or group (got '%s')", value);
       ret = -1;
-    } else if (identity_resolve_token(user, false, &config->chown_uid) != 0) {
-      log_message(LOG_LEVEL_ERROR,
-                  "--chown could not resolve user '%s' (use a name that exists "
-                  "on the source, '*', or @N)",
-                  value);
+    } else if (identity_parse_chown_side(config, false, user) != 0) {
       ret = -1;
-    } else {
-      config->chown_uid_set = true;
     }
   } else {
     /* --chown=USER:GROUP, --chown=:GROUP, --chown=USER: */
-    if (*user != '\0') {
-      if (identity_resolve_token(user, false, &config->chown_uid) != 0) {
-        log_message(LOG_LEVEL_ERROR, "--chown could not resolve user '%s'", value);
-        ret = -1;
-        goto done;
-      }
-      config->chown_uid_set = true;
+    if (*user != '\0' && identity_parse_chown_side(config, false, user) != 0) {
+      ret = -1;
+      goto done;
     }
-    if (*group != '\0') {
-      if (identity_resolve_token(group, true, &config->chown_gid) != 0) {
-        log_message(LOG_LEVEL_ERROR, "--chown could not resolve group '%s'", value);
-        ret = -1;
-        goto done;
-      }
-      config->chown_gid_set = true;
+    if (*group != '\0' && identity_parse_chown_side(config, true, group) != 0) {
+      ret = -1;
+      goto done;
     }
     if (!*user && !*group) {
       log_message(LOG_LEVEL_ERROR, "--chown must set a user, a group, or both (got '%s')", value);
@@ -567,9 +837,6 @@ int identity_parse_copy_as(Config* config, const char* value) {
   config->copy_as_set = true;
   config->copy_as_uid = uid;
   config->copy_as_gid = gid;
-  /* Ownership application needs the metadata path (the source uid/gid must be
-   * transmitted); imply it exactly like --chown/--usermap/--groupmap. */
-  config->use_metadata = true;
   ret = 0;
 
 done:
@@ -580,34 +847,120 @@ done:
 
 /* ---- Receiver-side ownership application ---- */
 
-static bool identity_map_lookup(const IdentityMap* map, int count, int32_t source_id,
+/* True when a map rule's FROM matcher accepts `id`.  A sentinel FROM never
+ * carries a range.  IDENTITY_MATCH_UNNAMED mirrors rsync's empty FROM: it
+ * matches only ids that have no name in the account database (rsync matches the
+ * sender's names; FastSync transmits numeric ids only, so it approximates this
+ * with the receiver's database -- documented in RSYNC_COMPAT.md). */
+static bool identity_map_from_matches(const IdentityMap* map, int32_t id, bool is_group) {
+  if (map->from == IDENTITY_MATCH_ANY)
+    return true;
+  if (map->from == IDENTITY_MATCH_UNNAMED)
+    return is_group ? (getgrgid((gid_t)id) == NULL) : (getpwuid((uid_t)id) == NULL);
+  return id >= map->from && id <= map->from_hi;
+}
+
+/* First matching rule wins.  A rule whose TO is a receiver-side name resolves it
+ * against the receiver's account database here; an unresolvable TO name is
+ * skipped with a warning and the next rule is considered (rsync prints "Unknown
+ * --usermap name on receiver" and leaves the id unmapped rather than aborting). */
+static bool identity_map_lookup(const IdentityMap* map, int count, int32_t source_id, bool is_group,
                                 int32_t* out_to) {
   for (int i = 0; i < count; i++) {
-    if (map[i].from == IDENTITY_MATCH_ANY || map[i].from == source_id) {
+    if (!identity_map_from_matches(&map[i], source_id, is_group))
+      continue;
+    if (map[i].to_name) {
+      if (is_group) {
+        struct group* gr = getgrnam(map[i].to_name);
+        if (!gr) {
+          log_message(LOG_LEVEL_WARNING, "Unknown --groupmap name on receiver: %s", map[i].to_name);
+          continue;
+        }
+        *out_to = (int32_t)gr->gr_gid;
+      } else {
+        struct passwd* pw = getpwnam(map[i].to_name);
+        if (!pw) {
+          log_message(LOG_LEVEL_WARNING, "Unknown --usermap name on receiver: %s", map[i].to_name);
+          continue;
+        }
+        *out_to = (int32_t)pw->pw_uid;
+      }
+    } else {
       *out_to = map[i].to;
-      return true;
     }
+    return true;
   }
   return false;
 }
 
+/* Resolve the owner side from the negotiated policy.  Sets *out and returns
+ * true when an owner-affecting request is active (a usermap, --chown USER, or
+ * -o/--owner); returns false (leaving *out untouched) when the owner side is
+ * not requested, so callers can pass (uid_t)-1 to fchown and leave it as-is.
+ * --numeric-ids only changes the RESOLUTION (raw id instead of a name lookup);
+ * it never makes the side requested. */
+static bool identity_resolve_owner(int32_t source_uid, uid_t* out) {
+  if (!(g_identity.chown_uid_set || g_identity.preserve_owner || g_identity.usermap_count > 0))
+    return false;
+  int32_t target;
+  if (identity_map_lookup(g_identity.usermap, g_identity.usermap_count, source_uid, false,
+                          &target)) {
+    *out = target == IDENTITY_CURRENT ? geteuid() : (uid_t)target;
+  } else if (g_identity.chown_uid_set) {
+    *out = g_identity.chown_uid == IDENTITY_CURRENT ? geteuid() : (uid_t)g_identity.chown_uid;
+  } else if (g_identity.numeric_ids) {
+    *out = (uid_t)source_uid;
+  } else {
+    /* Best-effort name mapping against the receiver's own database.  When the
+     * transmitted (numeric) id has no name here, fall back to the raw numeric id
+     * so -o still preserves the source owner. */
+    struct passwd* pw = getpwuid((uid_t)source_uid);
+    if (pw) {
+      const struct passwd* mapped = getpwnam(pw->pw_name);
+      *out = mapped ? mapped->pw_uid : (uid_t)source_uid;
+    } else {
+      *out = (uid_t)source_uid;
+    }
+  }
+  return true;
+}
+
+/* Group-side counterpart of identity_resolve_owner(). */
+static bool identity_resolve_group(int32_t source_gid, gid_t* out) {
+  if (!(g_identity.chown_gid_set || g_identity.preserve_group || g_identity.groupmap_count > 0))
+    return false;
+  int32_t target;
+  if (identity_map_lookup(g_identity.groupmap, g_identity.groupmap_count, source_gid, true,
+                          &target)) {
+    *out = target == IDENTITY_CURRENT ? getegid() : (gid_t)target;
+  } else if (g_identity.chown_gid_set) {
+    *out = g_identity.chown_gid == IDENTITY_CURRENT ? getegid() : (gid_t)g_identity.chown_gid;
+  } else if (g_identity.numeric_ids) {
+    *out = (gid_t)source_gid;
+  } else {
+    struct group* gr = getgrgid((gid_t)source_gid);
+    if (gr) {
+      const struct group* mapped = getgrnam(gr->gr_name);
+      *out = mapped ? mapped->gr_gid : (gid_t)source_gid;
+    } else {
+      *out = (gid_t)source_gid;
+    }
+  }
+  return true;
+}
+
 /* Resolve the target ownership from the negotiated policy against the entry's
  * current stat.  Shared by the fd (regular file) and no-follow (symlink) apply
  * paths.  Returns false when no side is to be changed. */
 static bool identity_resolve_targets(const struct stat* st, int32_t source_uid, int32_t source_gid,
                                      uid_t* out_uid, gid_t* out_gid) {
-  bool set_uid = false;
-  bool set_gid = false;
-  uid_t uid = 0;
-  gid_t gid = 0;
-
   /* --copy-as (P7 Wave E) has the highest priority: it forces BOTH the owner
    * and group of every written entry to the requested ids, beating usermap /
    * groupmap / --chown / --numeric-ids and the best-effort name lookup.  Only
    * skip when the entry already carries exactly those ids. */
   if (g_identity.copy_as_set) {
-    uid = (uid_t)g_identity.copy_as_uid;
-    gid = (gid_t)g_identity.copy_as_gid;
+    uid_t uid = (uid_t)g_identity.copy_as_uid;
+    gid_t gid = (gid_t)g_identity.copy_as_gid;
     if (st->st_uid == uid && st->st_gid == gid)
       return false;
     *out_uid = uid;
@@ -615,67 +968,52 @@ static bool identity_resolve_targets(const struct stat* st, int32_t source_uid,
     return true;
   }
 
-  int32_t target;
-  if (identity_map_lookup(g_identity.usermap, g_identity.usermap_count, source_uid, &target)) {
-    uid = target == IDENTITY_CURRENT ? geteuid() : (uid_t)target;
-    set_uid = true;
-  } else if (g_identity.chown_uid_set) {
-    uid = g_identity.chown_uid == IDENTITY_CURRENT ? geteuid() : (uid_t)g_identity.chown_uid;
-    set_uid = true;
-  } else if (g_identity.numeric_ids) {
-    uid = (uid_t)source_uid;
-    set_uid = true;
-  } else {
-    /* Best-effort name mapping against the receiver's own database: if the
-     * transmitted (numeric) id resolves to a name present on this machine,
-     * re-resolve it.  On a shared-account host this is the identity operation;
-     * when the id has no name here, the user side is left alone. */
-    struct passwd* pw = getpwuid((uid_t)source_uid);
-    if (pw) {
-      const struct passwd* mapped = getpwnam(pw->pw_name);
-      if (mapped) {
-        uid = mapped->pw_uid;
-        set_uid = true;
-      }
-    }
-  }
-
-  if (identity_map_lookup(g_identity.groupmap, g_identity.groupmap_count, source_gid, &target)) {
-    gid = target == IDENTITY_CURRENT ? getegid() : (gid_t)target;
-    set_gid = true;
-  } else if (g_identity.chown_gid_set) {
-    gid = g_identity.chown_gid == IDENTITY_CURRENT ? getegid() : (gid_t)g_identity.chown_gid;
-    set_gid = true;
-  } else if (g_identity.numeric_ids) {
-    gid = (gid_t)source_gid;
-    set_gid = true;
-  } else {
-    struct group* gr = getgrgid((gid_t)source_gid);
-    if (gr) {
-      const struct group* mapped = getgrnam(gr->gr_name);
-      if (mapped) {
-        gid = mapped->gr_gid;
-        set_gid = true;
-      }
-    }
-  }
-
-  if (!set_uid && !set_gid)
+  /* Each side is resolved independently: -o/-g and the explicit identity flags
+   * request the owner/group respectively, and a side that is NOT requested must
+   * be left exactly as it is (`-1` to fchown on that side).  This is what lets
+   * plain -g change only the group, or -o only the owner. */
+  uid_t uid = (uid_t)-1;
+  gid_t gid = (gid_t)-1;
+  bool owner_requested = identity_resolve_owner(source_uid, &uid);
+  bool group_requested = identity_resolve_group(source_gid, &gid);
+  if (!owner_requested && !group_requested)
     return false;
-  /* An unset side keeps the file's current id so the other side can change. */
-  if (!set_uid)
-    uid = st->st_uid;
-  if (!set_gid)
-    gid = st->st_gid;
-  /* Only change ownership when the target differs (avoid needless syscalls and
-   * any chance of clearing setuid/setgid on an already-correct entry). */
-  if (st->st_uid == uid && st->st_gid == gid)
+
+  /* Only change ownership when a requested side actually differs (avoid
+   * needless syscalls and any chance of clearing setuid/setgid on an
+   * already-correct entry). */
+  bool changed = (owner_requested && uid != st->st_uid) || (group_requested && gid != st->st_gid);
+  if (!changed)
     return false;
   *out_uid = uid;
   *out_gid = gid;
   return true;
 }
 
+/* --fake-super storage resolution: the receiver records the ownership it WOULD
+ * have applied.  A requested side uses the resolved mapping (--copy-as /
+ * usermap / --chown / -o/-g, with --numeric-ids as the raw-id modifier); a side
+ * that was not requested keeps the source's own id, so a plain --fake-super run
+ * records the source owner untouched. */
+void identity_resolve_storage_ids(int32_t source_uid, int32_t source_gid, uint32_t* out_uid,
+                                  uint32_t* out_gid) {
+  if (g_identity.copy_as_set) {
+    *out_uid = (uint32_t)g_identity.copy_as_uid;
+    *out_gid = (uint32_t)g_identity.copy_as_gid;
+    return;
+  }
+  uid_t uid = (uid_t)source_uid;
+  gid_t gid = (gid_t)source_gid;
+  uid_t resolved_uid;
+  gid_t resolved_gid;
+  if (identity_resolve_owner(source_uid, &resolved_uid))
+    uid = resolved_uid;
+  if (identity_resolve_group(source_gid, &resolved_gid))
+    gid = resolved_gid;
+  *out_uid = (uint32_t)uid;
+  *out_gid = (uint32_t)gid;
+}
+
 static void identity_log_chown_failure(const char* what, uid_t uid, gid_t gid) {
   /* EPERM/EACCES are expected when the receiver is not privileged (e.g. the CI
    * `nobody` user): warn and continue, never abort the transfer.  Any other
@@ -710,8 +1048,12 @@ bool identity_apply_ownership(int fd, int32_t source_uid, int32_t source_gid) {
   /* Ownership application is OFF unless the client requested an identity flag.
    * This is the controlled gate: a default (or plain -M) transfer never changes
    * ownership, byte-for-byte preserving FastSync's existing behavior.  --no-super
-   * additionally forbids it even when the receiver is root. */
-  if (!identity_active_enabled() || !privilege_super_permitted() || fd < 0)
+   * additionally forbids it even when the receiver is root.  --fake-super never
+   * performs a REAL chown: that would defeat the point of the flag (record the
+   * source ownership on an unprivileged receiver for a later privileged
+   * restore); the resolved ownership is stored in the reserved xattr instead by
+   * fake_super_store_fd(). */
+  if (!identity_active_enabled() || g_identity.fake_super || !privilege_super_permitted() || fd < 0)
     return true;
   struct stat st;
   if (fstat(fd, &st) != 0)
@@ -731,7 +1073,8 @@ bool identity_apply_ownership(int fd, int32_t source_uid, int32_t source_gid) {
 
 bool identity_apply_ownership_link(int parent_fd, const char* leaf, int32_t source_uid,
                                    int32_t source_gid) {
-  if (!identity_active_enabled() || !privilege_super_permitted() || parent_fd < 0 || !leaf)
+  if (!identity_active_enabled() || g_identity.fake_super || !privilege_super_permitted() ||
+      parent_fd < 0 || !leaf)
     return true;
   struct stat st;
   if (fstatat(parent_fd, leaf, &st, AT_SYMLINK_NOFOLLOW) != 0)

src/shared/identity.h

@@ -80,16 +80,37 @@ void identity_clear_active(void);
  * snapshot.  Ownership stays OFF ("do not apply") for every transfer that
  * requests none of them, preserving FastSync's existing behavior.  --super /
  * --no-super alone does NOT enable ownership; an explicit identity flag
- * (--numeric-ids / --chown / --usermap / --groupmap / --copy-as) is required. */
+ * (--numeric-ids / --chown / --usermap / --groupmap / --copy-as) or a
+ * preserve-source -o/--owner / -g/--group request is required. */
 bool identity_active_enabled(void);
 
-/* Pure, config-only predicate: true when the client requested ANY
- * client-chosen ownership or super-user activity (--numeric-ids, --chown,
- * --usermap/--groupmap, --copy-as, --fake-super, or an explicit --super).  Used
- * by the daemon module gate to decide whether a module's per-module opt-in is
- * required; it never reads the per-connection snapshot. */
+/* Per-side predicates over the ACTIVE per-connection snapshot (call
+ * identity_set_active() first).  They mirror the owner_requested /
+ * group_requested conditions inside identity_resolve_targets() exactly, so
+ * callers that must apply only one side (e.g. the --fake-super owner replay)
+ * can pass (uid_t)-1 / (gid_t)-1 for the side that was NOT requested and leave
+ * it untouched.  The owner side is requested by --copy-as, --chown USER,
+ * --numeric-ids, -o/--owner, or a non-empty --usermap; the group side by
+ * --copy-as, --chown :GROUP, --numeric-ids, -g/--group, or a non-empty
+ * --groupmap. */
+bool identity_owner_requested(void);
+bool identity_group_requested(void);
+
+/* Pure, config-only predicate: true when the client requested ANY client-chosen
+ * ownership or super-user activity (--numeric-ids, --chown, --usermap/--groupmap,
+ * --copy-as, --fake-super, an explicit --super, or a preserve-source -o/-g).
+ * General awareness only; the daemon module gate uses the narrower
+ * identity_explicit_ownership_requested() below.  Never reads the snapshot. */
 bool identity_ownership_requested(const Config* config);
 
+/* Pure, config-only predicate for the narrow set that lets the CLIENT choose an
+ * arbitrary owner/group: --numeric-ids, --chown, --usermap/--groupmap,
+ * --copy-as, --fake-super, or an explicit --super.  Deliberately EXCLUDES a
+ * plain -o/--owner / -g/--group (or -a) preserve-source request, which the
+ * daemon gate handles by forcing super-user ownership activity off rather than
+ * refusing the whole transfer.  Never reads the snapshot. */
+bool identity_explicit_ownership_requested(const Config* config);
+
 /* Apply the negotiated ownership to an already-written file descriptor.
  * source_uid/source_gid are the transmitted numeric ids.  Resolution order:
  * --copy-as (highest priority, forces both ids), then a matching
@@ -106,6 +127,14 @@ bool identity_ownership_requested(const Config* config);
  * is active returns true. */
 bool identity_apply_ownership(int fd, int32_t source_uid, int32_t source_gid);
 
+/* Resolve the ownership that --fake-super should RECORD in the reserved xattr
+ * (rather than chown for real).  A requested side (--copy-as / usermap /
+ * --chown / -o / -g, with --numeric-ids as the raw-id modifier) yields the
+ * resolved target; a side that was not requested keeps the transmitted source
+ * id.  Must be called after identity_set_active(). */
+void identity_resolve_storage_ids(int32_t source_uid, int32_t source_gid, uint32_t* out_uid,
+                                  uint32_t* out_gid);
+
 /* P7 Wave D: the no-follow (symlink) counterpart.  Resolves the same
  * usermap/groupmap/chown/numeric-ids/copy-as policy but applies it with
  * fchownat(..., AT_SYMLINK_NOFOLLOW) so a symlink's own ownership is changed

src/shared/log.h

@@ -21,7 +21,26 @@ typedef enum {
   LOG_INFO_MISC = 1u << 1,
   LOG_INFO_SKIP = 1u << 2,
   LOG_INFO_STATS = 1u << 3,
-  LOG_INFO_ALL = LOG_INFO_COPY | LOG_INFO_MISC | LOG_INFO_SKIP | LOG_INFO_STATS,
+  /* rsync categories that map to a FastSync event (emitted in rsync's line
+   * format): del (deletions), remove (sender-side source removal), name
+   * (transferred entry names), flist (file-list header), nonreg (skipped
+   * non-regular files), progress (per-file progress).  rsync's `backup`
+   * category is accepted for CLI parity but stays silent: the receiver does the
+   * backing-up and FastSync has no backup event to report from the sender. */
+  LOG_INFO_DEL = 1u << 4,
+  LOG_INFO_REMOVE = 1u << 5,
+  LOG_INFO_NAME = 1u << 6,
+  LOG_INFO_FLIST = 1u << 7,
+  LOG_INFO_NONREG = 1u << 8,
+  LOG_INFO_PROGRESS = 1u << 9,
+  /* Marker for `--info=name2` and higher: also print rsync's
+     "NAME is uptodate" line for entries the receiver already has.  It rides in
+     the info_level bitset (there is no separate Config field) and is never set
+     by --info=all (which selects level 1). */
+  LOG_INFO_NAME_UPTODATE = 1u << 10,
+  LOG_INFO_ALL = LOG_INFO_COPY | LOG_INFO_MISC | LOG_INFO_SKIP | LOG_INFO_STATS | LOG_INFO_DEL |
+                 LOG_INFO_REMOVE | LOG_INFO_NAME | LOG_INFO_FLIST | LOG_INFO_NONREG |
+                 LOG_INFO_PROGRESS,
 } LogInfoFlag;
 
 void log_message(LogLevel log_level, const char* message, ...);

src/shared/metadata.c

@@ -209,22 +209,58 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
   return m;
 }
 
-static mode_t metadata_mode(const FileMetadata* metadata, mode_t current_mode,
-                            bool preserve_executability) {
+bool metadata_mode_for_policy(mode_t source_mode, mode_t current_mode, FileAttrPolicy policy,
+                              mode_t* out_mode) {
   const mode_t execute_bits = S_IXUSR | S_IXGRP | S_IXOTH;
-  if (preserve_executability)
-    return (current_mode & 0777 & ~execute_bits) | (metadata->mode & execute_bits);
-  return metadata->mode & 0777 & ~(S_IWGRP | S_IWOTH);
+  if (policy.perms) {
+    /* rsync --perms copies the source's permission and special bits exactly,
+     * including group/other write and setuid/setgid/sticky.  The kernel may
+     * still clear setgid when the receiver is not in the file's group; the
+     * caller logs a failed chmod rather than silently masking the bits here. */
+    *out_mode = source_mode & (mode_t)(S_ISUID | S_ISGID | S_ISVTX | 0777);
+    return true;
+  }
+  if (policy.executability) {
+    /* -E/--executability (rsync 3.4 rule): do NOT copy the source's execute
+     * bits per class.  If the source is executable at all, derive the execute
+     * bits from the DESTINATION's own read bits (so a class that can read may
+     * execute); otherwise clear every execute bit.  This runs on the
+     * destination-derived base (pre-existing dest mode, or source&~umask for a
+     * new file), and leaves the special bits untouched.  --perms wins when both
+     * are set (handled above). */
+    mode_t base = current_mode & (mode_t)(S_ISUID | S_ISGID | S_ISVTX | 0777);
+    if (source_mode & 0111)
+      *out_mode = base | ((base & 0444) >> 2);
+    else
+      *out_mode = base & ~execute_bits;
+    return true;
+  }
+  /* Neither requested: no source mode is applied at all. */
+  return false;
 }
 
-void file_restore_metadata(const char* path, const FileMetadata* metadata,
-                           bool preserve_executability) {
+FileAttrPolicy file_attr_policy_from_config(const Config* config) {
+  FileAttrPolicy policy = {false, false, false, false};
+  if (config) {
+    policy.perms = config->preserve_perms;
+    policy.times = config->preserve_times;
+    policy.atimes = config->preserve_atimes;
+    policy.executability = config->use_executability;
+  }
+  return policy;
+}
+
+void file_restore_metadata(const char* path, const FileMetadata* metadata, FileAttrPolicy policy) {
   if (metadata == NULL)
     return;
-  struct stat current;
-  mode_t current_mode = stat(path, &current) == 0 ? current.st_mode : 0;
-  mode_t safe_mode = metadata_mode(metadata, current_mode, preserve_executability);
-  if (chmod(path, safe_mode) != 0) {
+  bool apply_mode = false;
+  mode_t safe_mode = 0;
+  if (policy.perms || policy.executability) {
+    struct stat current;
+    mode_t current_mode = stat(path, &current) == 0 ? current.st_mode : 0;
+    apply_mode = metadata_mode_for_policy(metadata->mode, current_mode, policy, &safe_mode);
+  }
+  if (apply_mode && chmod(path, safe_mode) != 0) {
     char* escaped_path = output_escape(path, log_get_8_bit_output());
     log_message(LOG_LEVEL_WARNING, "Failed to chmod %s: %s",
                 escaped_path ? escaped_path : "<allocation failed>", strerror(errno));
@@ -232,14 +268,23 @@ void file_restore_metadata(const char* path, const FileMetadata* metadata,
   }
   /* Never apply client-supplied ownership.  The descriptor API below is the
      receiver write path; retain this legacy API only for compatibility. */
-  struct timespec times[2];
-  times[0].tv_sec = 0;
-  times[0].tv_nsec = UTIME_OMIT;
-  times[1].tv_sec = metadata->mtime_sec;
-  times[1].tv_nsec = metadata->mtime_nsec;
-  if (metadata->atime_valid) {
-    times[0].tv_sec = metadata->atime_sec;
-    times[0].tv_nsec = metadata->atime_nsec;
+  if (policy.times || (policy.atimes && metadata->atime_valid)) {
+    struct timespec times[2] = {{.tv_sec = 0, .tv_nsec = UTIME_OMIT},
+                                {.tv_sec = 0, .tv_nsec = UTIME_OMIT}};
+    if (policy.times) {
+      times[1].tv_sec = metadata->mtime_sec;
+      times[1].tv_nsec = metadata->mtime_nsec;
+    }
+    if (policy.atimes && metadata->atime_valid) {
+      times[0].tv_sec = metadata->atime_sec;
+      times[0].tv_nsec = metadata->atime_nsec;
+    }
+    if (utimensat(AT_FDCWD, path, times, 0) != 0) {
+      char* escaped_path = output_escape(path, log_get_8_bit_output());
+      log_message(LOG_LEVEL_WARNING, "Failed to set timestamps on %s: %s",
+                  escaped_path ? escaped_path : "<allocation failed>", strerror(errno));
+      free(escaped_path);
+    }
   }
   if (metadata->crtime_valid) {
     log_message(LOG_LEVEL_DEBUG,
@@ -247,16 +292,10 @@ void file_restore_metadata(const char* path, const FileMetadata* metadata,
                 "setter exists",
                 (long long)metadata->crtime_sec, metadata->crtime_nsec, path);
   }
-  if (utimensat(AT_FDCWD, path, times, 0) != 0) {
-    char* escaped_path = output_escape(path, log_get_8_bit_output());
-    log_message(LOG_LEVEL_WARNING, "Failed to set timestamps on %s: %s",
-                escaped_path ? escaped_path : "<allocation failed>", strerror(errno));
-    free(escaped_path);
-  }
 }
 
 bool file_restore_symlink_metadata(const char* path, const FileMetadata* metadata,
-                                   bool omit_link_times) {
+                                   FileAttrPolicy policy, bool omit_link_times) {
   if (path == NULL || metadata == NULL)
     return !identity_copy_as_active();
   char* leaf = NULL;
@@ -269,18 +308,25 @@ bool file_restore_symlink_metadata(const char* path, const FileMetadata* metadat
      best-effort. */
   bool owned = identity_apply_ownership_link(parent_fd, leaf, (int32_t)metadata->uid,
                                              (int32_t)metadata->gid);
-  /* Symlink mode: not settable on Linux (fchmodat AT_SYMLINK_NOFOLLOW returns
-     EOPNOTSUPP/ENOTSUP); attempt it for platforms that support it and quietly
-     ignore the unsupported case so the transfer never fails over it. */
-  mode_t link_mode = metadata->mode & 0777;
-  if (fchmodat(parent_fd, leaf, link_mode, AT_SYMLINK_NOFOLLOW) != 0 && errno != EOPNOTSUPP &&
-      errno != ENOTSUP && errno != ENOSYS) {
-    log_message(LOG_LEVEL_DEBUG, "Could not set symlink mode on %s: %s", path, strerror(errno));
+  /* Symlink mode: only when -p is in effect.  It is not settable on Linux
+     (fchmodat AT_SYMLINK_NOFOLLOW returns EOPNOTSUPP/ENOTSUP); attempt it for
+     platforms that support it and quietly ignore the unsupported case so the
+     transfer never fails over it. */
+  if (policy.perms) {
+    mode_t link_mode = metadata->mode & (mode_t)(S_ISUID | S_ISGID | S_ISVTX | 0777);
+    if (fchmodat(parent_fd, leaf, link_mode, AT_SYMLINK_NOFOLLOW) != 0 && errno != EOPNOTSUPP &&
+        errno != ENOTSUP && errno != ENOSYS) {
+      log_message(LOG_LEVEL_DEBUG, "Could not set symlink mode on %s: %s", path, strerror(errno));
+    }
   }
-  if (!omit_link_times) {
+  if (!omit_link_times && (policy.times || (policy.atimes && metadata->atime_valid))) {
     struct timespec times[2] = {{.tv_sec = 0, .tv_nsec = UTIME_OMIT},
-                                {.tv_sec = metadata->mtime_sec, .tv_nsec = metadata->mtime_nsec}};
-    if (metadata->atime_valid) {
+                                {.tv_sec = 0, .tv_nsec = UTIME_OMIT}};
+    if (policy.times) {
+      times[1].tv_sec = metadata->mtime_sec;
+      times[1].tv_nsec = metadata->mtime_nsec;
+    }
+    if (policy.atimes && metadata->atime_valid) {
       times[0].tv_sec = metadata->atime_sec;
       times[0].tv_nsec = metadata->atime_nsec;
     }
@@ -296,19 +342,13 @@ bool file_restore_symlink_metadata(const char* path, const FileMetadata* metadat
   return owned;
 }
 
-bool file_restore_metadata_fd(int fd, const FileMetadata* metadata, bool preserve_executability) {
+bool file_restore_metadata_fd(int fd, const FileMetadata* metadata, FileAttrPolicy policy) {
   if (fd < 0 || metadata == NULL)
     return metadata == NULL;
   bool ok = true;
-  struct stat current;
-  if (fstat(fd, &current) != 0)
-    return false;
-  mode_t safe_mode = metadata_mode(metadata, current.st_mode, preserve_executability);
-  if (fchmod(fd, safe_mode) != 0)
-    ok = false;
   /* Client uid/gid values are deliberately not authoritative UNLESS the client
      explicitly opted in with an identity flag (--numeric-ids / --usermap /
-     --groupmap / --chown).  identity_apply_ownership is the controlled,
+     --groupmap / --chown / -o/-g).  identity_apply_ownership is the controlled,
      privilege-gated path: it consults the negotiated policy, resolves the
      target ids, and applies them via an fd-relative fchown() that is confined
      to the just-written file (EPERM/EACCES are logged, never fatal) -- EXCEPT
@@ -316,14 +356,19 @@ bool file_restore_metadata_fd(int fd, const FileMetadata* metadata, bool preserv
      marks this entry as failed instead of reporting a wrong-owner write as
      success.  With no identity flag set it is a no-op, so a default or plain -M
      transfer keeps FastSync's existing behavior of never applying client
-     ownership. */
+     ownership.  Ownership runs BEFORE the mode because a chown clears
+     setuid/setgid; rsync likewise chowns first and then restores the source
+     mode (including its special bits). */
   if (!identity_apply_ownership(fd, (int32_t)metadata->uid, (int32_t)metadata->gid))
     ok = false;
-  struct timespec times[2] = {{.tv_sec = 0, .tv_nsec = UTIME_OMIT},
-                              {.tv_sec = metadata->mtime_sec, .tv_nsec = metadata->mtime_nsec}};
-  if (metadata->atime_valid) {
-    times[0].tv_sec = metadata->atime_sec;
-    times[0].tv_nsec = metadata->atime_nsec;
+  if (policy.perms || policy.executability) {
+    struct stat current;
+    if (fstat(fd, &current) != 0)
+      return false;
+    mode_t safe_mode = 0;
+    bool apply_mode = metadata_mode_for_policy(metadata->mode, current.st_mode, policy, &safe_mode);
+    if (apply_mode && fchmod(fd, safe_mode) != 0)
+      ok = false;
   }
   /* --crtimes captures and transmits the source birth time, but there is no
    * portable way to set a birth time (utimensat can only set atime/mtime), so
@@ -335,7 +380,19 @@ bool file_restore_metadata_fd(int fd, const FileMetadata* metadata, bool preserv
                 "crtime (birth time) %lld.%09ld transmitted but not applied: no portable setter",
                 (long long)metadata->crtime_sec, metadata->crtime_nsec);
   }
-  if (futimens(fd, times) != 0)
-    ok = false;
+  if (policy.times || (policy.atimes && metadata->atime_valid)) {
+    struct timespec times[2] = {{.tv_sec = 0, .tv_nsec = UTIME_OMIT},
+                                {.tv_sec = 0, .tv_nsec = UTIME_OMIT}};
+    if (policy.times) {
+      times[1].tv_sec = metadata->mtime_sec;
+      times[1].tv_nsec = metadata->mtime_nsec;
+    }
+    if (policy.atimes && metadata->atime_valid) {
+      times[0].tv_sec = metadata->atime_sec;
+      times[0].tv_nsec = metadata->atime_nsec;
+    }
+    if (futimens(fd, times) != 0)
+      ok = false;
+  }
   return ok;
 }

src/shared/metadata.h

@@ -2,6 +2,7 @@
 #define METADATA_H
 
 #include "file.h"
+#include "file_attr.h"
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
@@ -49,19 +50,31 @@ void metadata_to_buf(char** buf, const FileMetadata* m);
 FileMetadata* metadata_from_buf(const uint8_t* buf, size_t len);
 bool metadata_send(int file_descriptor, const FileMetadata* m);
 FileMetadata* metadata_receive(int file_descriptor, int* ok);
-void file_restore_metadata(const char* path, const FileMetadata* metadata,
-                           bool preserve_executability);
-bool file_restore_metadata_fd(int fd, const FileMetadata* metadata, bool preserve_executability);
+void file_restore_metadata(const char* path, const FileMetadata* metadata, FileAttrPolicy policy);
+bool file_restore_metadata_fd(int fd, const FileMetadata* metadata, FileAttrPolicy policy);
+
+/* Shared mode-policy helper: the single source of truth for the receiver's
+ * mode rule.  Given a source mode and the destination's CURRENT mode, returns
+ * true and stores the exact mode to apply in *out_mode when `policy` requests
+ * a change, or false when it requests neither --perms nor --executability (the
+ * caller then leaves the destination mode alone).  --perms wins over -E; the
+ * -E rule derives exec bits from the destination's read bits (rsync 3.4);
+ * group/other write is never granted from a client-supplied mode.  Shared by
+ * file_restore_metadata_fd() and the --fake-super replay so the two cannot
+ * diverge. */
+bool metadata_mode_for_policy(mode_t source_mode, mode_t current_mode, FileAttrPolicy policy,
+                              mode_t* out_mode);
 /* P7 Wave D: apply a SYMLINK's own metadata using no-follow primitives only
  * (utimensat/lchown/fchmodat with AT_SYMLINK_NOFOLLOW), confined fd-relative
- * under the authorized root.  `omit_link_times` (-J/--omit-link-times)
- * suppresses the timestamps; the link's mode/ownership are still attempted
- * (ownership stays gated by the identity policy and by default is not applied).
+ * under the authorized root.  The link's mode is applied only when policy.perms;
+ * policy.times (further suppressed by `omit_link_times` for -J) applies the
+ * mtime with policy.atimes controlling the atime slot; ownership stays gated by
+ * the identity policy and by default is not applied.
  * A null metadata or an unfollowable parent is a harmless no-op.  Returns false
  * only when a REQUIRED --copy-as ownership application failed, so the caller can
  * report the entry as failed instead of claiming a wrong-owner success. */
 bool file_restore_symlink_metadata(const char* path, const FileMetadata* metadata,
-                                   bool omit_link_times);
+                                   FileAttrPolicy policy, bool omit_link_times);
 
 /* Compare timestamps using rsync's whole-second modification window. */
 bool metadata_mtime_matches(time_t left_sec, long left_nsec, time_t right_sec, long right_nsec,

src/shared/multiprocessing.c

@@ -30,20 +30,27 @@ PipelineContextSender* pipeline_context_sender_create(Config* config, Queue* que
   context->max_queue_bytes = 0;
   context->manifest = NULL;
   context->excluded_paths = NULL;
+  context->size_skipped_paths = NULL;
+  context->synced_dirs = NULL;
+  context->plan_dirs = NULL;
   context->missing_args = NULL;
   context->scan_had_io_error = false;
   context->remove_source_files = NULL;
   context->early_delete = false;
+  context->delete_plans = NULL;
+  context->delete_suppressed = false;
   context->scan_stopped_early = false;
   context->total_files = 0;
   context->progress_bytes = 0;
   context->total_bytes = 0;
+  memset(&context->stats, 0, sizeof(context->stats));
   context->sender_done = false;
   atomic_init(&context->cancelled, false);
   protocol_session_init(&context->allocation_session, -1, -1);
   protocol_session_set_max_alloc(&context->allocation_session, config->max_alloc);
   context->dir_entries = NULL;
   context->dir_entries_mutex_init = false;
+  context->delete_limit = false;
   int init = 0;
   if (config->use_metadata) {
     context->dir_entries = array_list_create(file_destroy);
@@ -184,8 +191,16 @@ void pipeline_context_sender_destroy(PipelineContextSender* context) {
   if (context->manifest) {
     array_list_delete(context->manifest);
   }
+  if (context->delete_plans)
+    delete_plan_sender_destroy(context->delete_plans);
   if (context->excluded_paths)
     array_list_delete(context->excluded_paths);
+  if (context->size_skipped_paths)
+    array_list_delete(context->size_skipped_paths);
+  if (context->synced_dirs)
+    array_list_delete(context->synced_dirs);
+  if (context->plan_dirs)
+    array_list_delete(context->plan_dirs);
   if (context->missing_args)
     array_list_delete(context->missing_args);
   if (context->remove_source_files)

src/shared/multiprocessing.h

@@ -7,7 +7,9 @@
 #include "array_list.h"
 #include "chunk.h"
 #include "config.h"
+#include "delete_plan.h"
 #include "file.h"
+#include "format.h"
 #include "protocol.h"
 #include "queue.h"
 #include "stop_condition.h"
@@ -42,6 +44,23 @@ typedef struct {
      scanner's exclusion sink) or, in the early modes, by the path-only pre-scan
      on the calling thread before the pipeline starts. */
   ArrayList* excluded_paths;
+  /* --max-size/--min-size pruned source paths.  These are ALWAYS sent as
+     protected prefixes (even with --delete-excluded), so the destination
+     mirrors of size-skipped files survive --delete like rsync.  Populated by
+     the scanner thread (workers append under mutex_scanner) or, in the early
+     modes, by the path-only pre-scan on the calling thread. */
+  ArrayList* size_skipped_paths;
+  /* Destination-relative paths of the directories the source scan synchronized
+     for this run (the receive root is the "." sentinel).  Sent with the
+     manifest so the receiver confines its extras walk to them, matching rsync's
+     "delete only in synchronized directories" (notably for --files-from).
+     Populated by the scanner thread or the early pre-scan. */
+  ArrayList* synced_dirs;
+  /* Destination-relative paths of every traversed source directory, for the
+     per-directory delete plan keep set (so an empty source directory survives
+     --delete rather than being removed as an extra).  Prebuilt by the path-only
+     pre-scan on the calling thread. */
+  ArrayList* plan_dirs;
   /* --delete-missing-args: the destination-relative mirrors of the --files-from
      entries that are missing under the source.  Computed by the preflight on
      the calling thread before the pipeline starts; the sender thread transmits
@@ -54,15 +73,32 @@ typedef struct {
      --ignore-errors kept the run going. */
   bool scan_had_io_error;
   ArrayList* remove_source_files;
-  /* True when --delete-before/--delete-during require the keep-set manifest to
-     be transmitted before any file data: context->manifest is then prebuilt by
-     a path-only pre-scan on the calling thread and the pipeline scanner must
-     not append to it.  Set once before the worker threads start. */
+  /* True when --delete-before requires the whole-tree keep-set manifest to be
+     transmitted before any file data: context->manifest is then prebuilt by a
+     path-only pre-scan on the calling thread and the pipeline scanner must not
+     append to it.  Set once before the worker threads start. */
   bool early_delete;
+  /* Non-NULL for --delete-during/--delete-delay: the per-directory plan set
+     prebuilt by the path-only pre-scan on the calling thread.  The sender
+     thread transmits the root plan before any data and the remaining plans
+     alongside the chunks.  Set once before the worker threads start. */
+  DeletePlanSender* delete_plans;
+  /* A scan I/O error without --ignore-errors suppressed deletion: the prebuilt
+     keep-set/plans were dropped, and the streaming scanner must not build a
+     fresh manifest or re-send the per-directory plans.  Set once before the
+     worker threads start. */
+  bool delete_suppressed;
   mtx_t mutex_progress;
   int total_files;
   unsigned long long progress_bytes;
   unsigned long long total_bytes;
+  /* Per-type flist / transferred accounting for the rsync --stats breakdown and
+     the progress `to-chk` denominator.  Owned by the sender thread: it is the
+     only writer (the entry/transfer notes in send_chunks_multithreaded) and it
+     reads the totals in its completion tail, so no lock is needed.  This is NOT
+     guarded by mutex_progress (which covers total_files/progress_bytes/
+     total_bytes/sender_done). */
+  TransferStats stats;
   bool sender_done;
   atomic_bool cancelled;
   ProtocolSession allocation_session;
@@ -83,6 +119,10 @@ typedef struct {
   ArrayList* dir_entries;
   mtx_t dir_entries_mutex;
   bool dir_entries_mutex_init;
+  /* Set by the sender thread when the receiver reported a --max-delete-capped
+     deletion (STATUS_DELETE_LIMIT): the transfer succeeded and the process must
+     exit 25 like rsync.  Read by the caller after the sender thread is joined. */
+  bool delete_limit;
 } PipelineContextSender;
 
 /* `config` is borrowed and must outlive the context: destroy does NOT free it,

src/shared/protocol.c

@@ -12,8 +12,7 @@
 #include <time.h>
 #include <unistd.h>
 
-#define RECEIVE_TIMEOUT_SEC 60 /* 60 second per-message timeout */
-#define SEND_TIMEOUT_SEC 60
+#define RECEIVE_TIMEOUT_SEC 60 /* built-in fallback for explicit -timed calls only */
 
 static __thread int io_read_fd = -1;
 static __thread int io_write_fd = -1;
@@ -30,6 +29,13 @@ static unsigned long long io_bwlimit = 0;
 static mtx_t bw_mutex;
 static once_flag bw_mutex_once = ONCE_FLAG_INIT;
 
+/* Process-wide wire byte counters, used by the client to render rsync's
+ * --stats/--progress totals and the --out-format %b/%c tokens.  The zero-copy
+ * sendfile path bypasses protocol_send_n_data, so it reports its bytes through
+ * protocol_note_bytes_written. */
+static atomic_ullong io_bytes_written = 0;
+static atomic_ullong io_bytes_read = 0;
+
 static unsigned long long global_bwlimit(void);
 
 static bool protocol_reserve_memory(ProtocolSession* session, size_t charge) {
@@ -99,8 +105,14 @@ void protocol_session_set_io_timeout(ProtocolSession* session, int sec) {
 
 int protocol_get_io_timeout_sec(void) {
   const ProtocolSession* session = bound_session ? bound_session : &legacy_io_session;
-  int sec = session->io_timeout_sec;
-  return sec > 0 ? sec : RECEIVE_TIMEOUT_SEC;
+  /* 0 (or negative) means the session timeout is disabled, matching rsync's
+   * --timeout=0 default.  Callers must treat a non-positive result as "wait
+   * without a deadline" instead of substituting a built-in window. */
+  return session->io_timeout_sec > 0 ? session->io_timeout_sec : 0;
+}
+
+int protocol_server_io_timeout_sec(int client_timeout) {
+  return client_timeout > 0 ? client_timeout : SERVER_IO_TIMEOUT_SEC;
 }
 
 void protocol_session_set_max_alloc(ProtocolSession* session, unsigned long long max_alloc) {
@@ -110,7 +122,8 @@ void protocol_session_set_max_alloc(ProtocolSession* session, unsigned long long
 }
 
 static bool allocation_allowed(const ProtocolSession* session, size_t size) {
-  return (unsigned long long)size <= session->max_alloc;
+  /* max_alloc == 0 is rsync's --max-alloc=0 "no limit". */
+  return session->max_alloc == 0 || (unsigned long long)size <= session->max_alloc;
 }
 
 static void* protocol_alloc_for_session(const ProtocolSession* session, size_t size) {
@@ -170,12 +183,28 @@ void io_set_bwlimit(unsigned long long bytes_per_sec) {
   mtx_unlock(&bw_mutex);
 }
 
+unsigned long long io_get_bwlimit(void) {
+  return global_bwlimit();
+}
+
+/* rsync's throttle (io.c sleep_for_bwlimit) sleeps once its unslept debt
+ * reaches ~100 ms of bandwidth, so its effective initial burst is about 0.1 s
+ * worth of bytes, not a full second.  FastSync models the same with a token
+ * bucket whose capacity is bwlimit/10, so a throttled run paces like rsync
+ * instead of sending a full second's worth up front. */
+static long long bw_burst_capacity(unsigned long long bwlimit) {
+  if (bwlimit == 0)
+    return 0;
+  long long burst = (long long)(bwlimit / 10);
+  return burst > 0 ? burst : 1;
+}
+
 void protocol_session_set_bwlimit(ProtocolSession* session, unsigned long long bytes_per_sec) {
   if (!session)
     return;
   session->bwlimit =
       bytes_per_sec > (unsigned long long)LLONG_MAX ? (unsigned long long)LLONG_MAX : bytes_per_sec;
-  session->bw_tokens = (long long)session->bwlimit;
+  session->bw_tokens = bw_burst_capacity(session->bwlimit);
   struct timespec now;
   clock_gettime(CLOCK_MONOTONIC, &now);
   session->bw_last_refill_sec = now.tv_sec;
@@ -209,8 +238,9 @@ static void bw_throttle_session(ProtocolSession* session, size_t bytes_written)
 
   long long tokens_to_add = (long long)((double)session->bwlimit * elapsed_ns / 1000000000.0);
   session->bw_tokens += tokens_to_add;
-  if (session->bw_tokens > (long long)session->bwlimit)
-    session->bw_tokens = (long long)session->bwlimit;
+  long long burst = bw_burst_capacity(session->bwlimit);
+  if (session->bw_tokens > burst)
+    session->bw_tokens = burst;
 
   session->bw_tokens -= bytes_written;
 
@@ -221,7 +251,11 @@ static void bw_throttle_session(ProtocolSession* session, size_t bytes_written)
       poll(NULL, 0, (int)(deficit_us / 1000));
     else
       usleep((useconds_t)deficit_us);
+    /* Reset the bucket AFTER the sleep: crediting the sleep duration as elapsed
+       refill time would cancel half the throttle (the next call would see the
+       whole sleep as refill and immediately grant a fresh burst). */
     session->bw_tokens = 0;
+    clock_gettime(CLOCK_MONOTONIC, &now);
     session->bw_last_refill_sec = now.tv_sec;
     session->bw_last_refill_nsec = now.tv_nsec;
   }
@@ -236,6 +270,18 @@ SSL* io_get_ssl(void) {
   return io_ssl;
 }
 
+unsigned long long protocol_bytes_written(void) {
+  return atomic_load(&io_bytes_written);
+}
+
+unsigned long long protocol_bytes_read(void) {
+  return atomic_load(&io_bytes_read);
+}
+
+void protocol_note_bytes_written(unsigned long long bytes) {
+  atomic_fetch_add(&io_bytes_written, bytes);
+}
+
 static ProtocolSession* legacy_session(int read_fd, int write_fd) {
   if (bound_session)
     return bound_session;
@@ -280,11 +326,15 @@ bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t dat
   log_debug_message(LOG_DEBUG_IO, "    Sending n Data: %zu", data_size);
   if (!session)
     return false;
-  int timeout_sec = session->io_timeout_sec > 0 ? session->io_timeout_sec : SEND_TIMEOUT_SEC;
+  /* A non-positive session timeout disables the deadline entirely (rsync's
+   * --timeout=0 default); poll then blocks until the socket becomes writable. */
+  int timeout_sec = session->io_timeout_sec > 0 ? session->io_timeout_sec : 0;
   int fd = session->write_fd;
   struct timespec deadline;
-  clock_gettime(CLOCK_MONOTONIC, &deadline);
-  deadline.tv_sec += timeout_sec;
+  if (timeout_sec > 0) {
+    clock_gettime(CLOCK_MONOTONIC, &deadline);
+    deadline.tv_sec += timeout_sec;
+  }
   short wait_events = POLLOUT;
   ssize_t total_bytes_send = 0;
   while ((size_t)total_bytes_send < data_size) {
@@ -292,7 +342,7 @@ bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t dat
     if (session->bwlimit > 0 && chunk > 65536)
       chunk = 65536;
     struct pollfd pfd = {.fd = fd, .events = wait_events};
-    int poll_result = poll(&pfd, 1, deadline_remaining_ms(&deadline));
+    int poll_result = poll(&pfd, 1, timeout_sec > 0 ? deadline_remaining_ms(&deadline) : -1);
     if (poll_result == 0 || (poll_result < 0 && errno != EINTR)) {
       log_message(LOG_LEVEL_ERROR, "Send timeout or poll failure");
       return false;
@@ -333,17 +383,27 @@ bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t dat
       wait_events = POLLOUT;
   }
   log_debug_message(LOG_DEBUG_IO, "    Send n Data: %zu", total_bytes_send);
+  atomic_fetch_add(&io_bytes_written, (unsigned long long)total_bytes_send);
   return true;
 }
 
 bool protocol_receive_n_data_timed(ProtocolSession* session, void* data, size_t data_size,
                                    int timeout_sec);
+static bool protocol_receive_n_data_until(ProtocolSession* session, void* data, size_t data_size,
+                                          const struct timespec* deadline);
 
 bool protocol_receive_n_data(ProtocolSession* session, void* data, size_t data_size) {
-  /* Honor the session's configured deadline; protocol_receive_n_data_timed
-   * re-applies the built-in 60 s default when the value is <= 0. */
-  int timeout_sec = session ? session->io_timeout_sec : 0;
-  return protocol_receive_n_data_timed(session, data, data_size, timeout_sec);
+  /* Honor the session's configured deadline.  A non-positive value disables the
+   * deadline (rsync's --timeout=0 default): wait without a poll timeout.  The
+   * explicit _timed variants keep their own 0 -> built-in-default contract. */
+  if (!session)
+    return false;
+  if (session->io_timeout_sec <= 0)
+    return protocol_receive_n_data_until(session, data, data_size, NULL);
+  struct timespec deadline;
+  clock_gettime(CLOCK_MONOTONIC, &deadline);
+  deadline.tv_sec += session->io_timeout_sec;
+  return protocol_receive_n_data_until(session, data, data_size, &deadline);
 }
 
 /* Read exactly `data_size` bytes from `session` before `deadline` elapses
@@ -353,7 +413,7 @@ bool protocol_receive_n_data(ProtocolSession* session, void* data, size_t data_s
 static bool protocol_receive_n_data_until(ProtocolSession* session, void* data, size_t data_size,
                                           const struct timespec* deadline) {
   log_debug_message(LOG_DEBUG_IO, "    Receiving n Data: %zu", data_size);
-  if (!session || !deadline)
+  if (!session)
     return false;
   int fd = session->read_fd;
 
@@ -362,7 +422,8 @@ static bool protocol_receive_n_data_until(ProtocolSession* session, void* data,
   while (total_bytes_received < data_size) {
     if (!session->ssl || SSL_pending(session->ssl) == 0) {
       struct pollfd pfd = {.fd = fd, .events = wait_events};
-      int poll_result = poll(&pfd, 1, deadline_remaining_ms(deadline));
+      /* A NULL deadline means "wait indefinitely" (timeout disabled). */
+      int poll_result = poll(&pfd, 1, deadline ? deadline_remaining_ms(deadline) : -1);
       if (poll_result == 0) {
         log_message(LOG_LEVEL_ERROR, "Receive timeout");
         return false;
@@ -410,6 +471,7 @@ static bool protocol_receive_n_data_until(ProtocolSession* session, void* data,
       wait_events = POLLIN;
   }
   log_debug_message(LOG_DEBUG_IO, "    Received n Data: %zu", total_bytes_received);
+  atomic_fetch_add(&io_bytes_read, (unsigned long long)total_bytes_received);
   return true;
 }
 
@@ -479,6 +541,10 @@ static const char* status_to_string(Status status) {
     return "ERROR_DETAIL";
   case STATUS_DRY_RUN_TRANSFER:
     return "DRY_RUN_TRANSFER";
+  case STATUS_DELETE_LIMIT:
+    return "DELETE_LIMIT";
+  case STATUS_DEST_INFO:
+    return "DEST_INFO";
   default:
     return "UNKNOWN";
   }
@@ -702,13 +768,16 @@ static bool protocol_capture_error_detail(ProtocolSession* session, Status* stat
 bool protocol_receive_status(ProtocolSession* session, Status* status) {
   if (!session || !status)
     return false;
-  int timeout_sec = session->io_timeout_sec > 0 ? session->io_timeout_sec : RECEIVE_TIMEOUT_SEC;
   struct timespec deadline;
-  clock_gettime(CLOCK_MONOTONIC, &deadline);
-  deadline.tv_sec += timeout_sec;
-  if (!protocol_receive_n_data_until(session, status, sizeof(Status), &deadline))
+  const struct timespec* deadline_ptr = NULL;
+  if (session->io_timeout_sec > 0) {
+    clock_gettime(CLOCK_MONOTONIC, &deadline);
+    deadline.tv_sec += session->io_timeout_sec;
+    deadline_ptr = &deadline;
+  }
+  if (!protocol_receive_n_data_until(session, status, sizeof(Status), deadline_ptr))
     return false;
-  if (!protocol_capture_error_detail(session, status, &deadline, NULL))
+  if (!protocol_capture_error_detail(session, status, deadline_ptr, NULL))
     return false;
   log_debug_message(LOG_DEBUG_PROTO, "Received Status: %s", status_to_string(*status));
   return true;
@@ -747,8 +816,8 @@ static bool protocol_read_status_until(ProtocolSession* session, Status* status,
   short wait_events = POLLIN;
   while (got < sizeof(Status)) {
     if (!session->ssl || SSL_pending(session->ssl) == 0) {
-      int remaining_ms = deadline_remaining_ms(deadline);
-      if (remaining_ms <= 0) {
+      int remaining_ms = deadline ? deadline_remaining_ms(deadline) : -1;
+      if (remaining_ms == 0) {
         log_message(LOG_LEVEL_ERROR, "Receive timeout while reading status");
         return false;
       }

src/shared/protocol.h

@@ -34,6 +34,11 @@
 #define DEFAULT_MAX_ALLOC (1ULL * 1024 * 1024 * 1024)
 /* Server policy ceiling for a client-provided allocation limit. */
 #define MAX_SERVER_ALLOC (256ULL * 1024 * 1024)
+/* Server-owned floor for the per-message I/O deadline.  A client --timeout=0
+   (rsync's default) disables the client's own deadlines, but a server session
+   must never be held open forever by a silent peer (slow-loris), so the server
+   floors the effective deadline at this value. */
+#define SERVER_IO_TIMEOUT_SEC 60
 /* Bounded cumulative per-connection receive budget.  In-flight wire buffers,
    decompression buffers and queued (not yet written) file payloads for a
    connection must stay within this ceiling. */
@@ -59,10 +64,12 @@ typedef struct ProtocolSession {
   bool eight_bit_output;
   unsigned long long max_alloc;
   /* Per-session deadline (seconds) applied to every protocol send/receive by
-   * protocol_send_n_data / protocol_receive_n_data.  Defaults to the built-in
-   * 60 s window; a value <= 0 falls back to that default.  Set from the
-   * negotiated Config->timeout so --timeout is honored by the poll()-driven
-   * protocol I/O, not just the socket SO_RCVTIMEO/SO_SNDTIMEO. */
+   * protocol_send_n_data / protocol_receive_n_data.  The initialized default is
+   * the built-in 60 s window; a value <= 0 disables the deadline (rsync's
+   * --timeout=0).  Set from the negotiated Config->timeout so --timeout is
+   * honored by the poll()-driven protocol I/O, not just the socket
+   * SO_RCVTIMEO/SO_SNDTIMEO.  The server does not propagate a client 0 here: it
+   * installs protocol_server_io_timeout_sec() so its sessions keep a floor. */
   int io_timeout_sec;
 } ProtocolSession;
 
@@ -155,14 +162,65 @@ enum NET_STATUS {
    * (the receiver reads none in dry-run).  STATUS_OK keeps its meaning in this
    * path ("already up to date / nothing to do").  Appended after
    * STATUS_ERROR_DETAIL so no existing status is renumbered. */
-  STATUS_DRY_RUN_TRANSFER
+  STATUS_DRY_RUN_TRANSFER,
+  /* --max-delete budget exhausted (protocol 2.23.0).  Sent by the receiver as
+   * the terminal success status INSTEAD of STATUS_OK when a --delete/
+   * --delete-missing-args commit removed up to the --max-delete bound but had
+   * to skip further extras.  The transfer itself succeeded and all file data is
+   * stored; the sender maps this to rsync's exit code 25 ("the --max-delete
+   * limit stopped deletions").  Appended after STATUS_DRY_RUN_TRANSFER so no
+   * existing status is renumbered. */
+  STATUS_DELETE_LIMIT,
+  /* Destination-state report for output parity (protocol 2.23.0).  When the
+   * wire config carries report_dest_info=true, the receiver answers every
+   * per-file STATUS_CHECK request with STATUS_DEST_INFO FIRST, followed by a
+   * fixed record describing the pre-transfer destination entry
+   * (int32 has_old; uint64 size; int64 mtime; int64 mtime_nsec; uint32 mode;
+   * int32 uid; int32 gid).  The ordinary STATUS_OK/STATUS_NEXT/... verdict
+   * follows, so the sender can render rsync-accurate -i/--out-format columns
+   * (new vs modified, and which of size/time/perms/owner/group differ) without
+   * changing the transfer decision itself.  Appended after
+   * STATUS_DELETE_LIMIT so no existing status is renumbered. */
+  STATUS_DEST_INFO,
+  /* Per-directory delete plan (protocol 2.24.0).  The sender of a
+   * --delete-during/--delete-delay transfer streams one frame per source
+   * directory in directory order instead of a single whole-tree keep-set
+   * manifest.  The receiver applies the plan when it arrives
+   * (--delete-during removes that directory's extras immediately) or records
+   * the extras and applies them only after the whole transfer succeeded
+   * (--delete-delay).  Payload: an int32 has_config flag (1 on the first plan
+   * of the run, 0 afterwards); when set, the three global config sections
+   * (protected-prefix count+paths, size-skipped count+paths, missing-args
+   * count+paths); then an int32 apply flag (1 for a real plan, 0 for a
+   * config-only carrier frame that must not walk a directory); then the
+   * destination-relative directory path wire string
+   * ("." for the receive root); then the child-directory count + names and the
+   * child-file count + names that must be kept.  Appended after
+   * STATUS_DEST_INFO so no existing status is renumbered. */
+  STATUS_DELETE_PLAN,
+  /* End-of-transfer receiver counter report (protocol 2.25.0).  When the wire
+   * config carries report_stats=true, the receiver sends this status once,
+   * immediately before its terminal success status, followed by a fixed stats
+   * record (see format_stats_send/receive in format.h) and, when the run is a
+   * --dry-run with --delete, the would-delete path list.  Appended after
+   * STATUS_DELETE_PLAN so no existing status is renumbered. */
+  STATUS_STATS
 };
 
 void io_set_fds(int read_fd, int write_fd);
 void io_set_bwlimit(unsigned long long bytes_per_sec);
+unsigned long long io_get_bwlimit(void);
 void io_set_ssl(SSL* ssl);
 SSL* io_get_ssl(void);
 
+/* Process-wide wire byte counters.  protocol_send_n_data/protocol_receive_n_data
+ * update them; the zero-copy sendfile path reports through
+ * protocol_note_bytes_written.  Used by the client to render rsync's
+ * --stats/--progress totals and the --out-format %b/%c tokens. */
+unsigned long long protocol_bytes_written(void);
+unsigned long long protocol_bytes_read(void);
+void protocol_note_bytes_written(unsigned long long bytes);
+
 void protocol_session_init(ProtocolSession* session, int read_fd, int write_fd);
 /* Transitional bridge for helpers whose signatures still carry only an fd. */
 void protocol_session_bind(ProtocolSession* session);
@@ -170,15 +228,20 @@ void protocol_session_unbind(void);
 void protocol_session_set_ssl(ProtocolSession* session, SSL* ssl);
 void protocol_session_set_bwlimit(ProtocolSession* session, unsigned long long bytes_per_sec);
 void protocol_session_set_max_alloc(ProtocolSession* session, unsigned long long max_alloc);
-/* Override the per-message send/receive deadline for this session.
- * `sec` <= 0 restores the built-in 60 s default (used for --timeout=0/unset).
- * An explicit long deadline (e.g. the delete-ack wait) is applied per-call by
- * protocol_receive_status_timed and is unaffected by this setter. */
+/* Override the per-message send/receive deadline for this session.  The value
+ * is stored verbatim: a positive value sets the deadline, `sec` <= 0 disables
+ * it (rsync's --timeout=0).  An explicit long deadline (e.g. the delete-ack
+ * wait) is applied per-call by protocol_receive_status_timed and is unaffected
+ * by this setter. */
 void protocol_session_set_io_timeout(ProtocolSession* session, int sec);
-/* Effective per-message I/O deadline (seconds) for the currently-bound session,
- * falling back to the built-in default.  Used by the plaintext sendfile path
- * which bypasses the protocol send primitive. */
+/* Effective per-message I/O deadline (seconds) for the currently-bound session.
+ * Zero means the deadline is disabled (rsync's --timeout=0).  Used by the
+ * plaintext sendfile path which bypasses the protocol send primitive. */
 int protocol_get_io_timeout_sec(void);
+/* The server-side effective deadline for a client-requested timeout: a positive
+ * client value is honored, otherwise the SERVER_IO_TIMEOUT_SEC floor applies so
+ * a silent peer can never hold a session open forever. */
+int protocol_server_io_timeout_sec(int client_timeout);
 void* protocol_alloc(size_t size);
 void* protocol_realloc(void* ptr, size_t size);
 void protocol_session_set_8_bit_output(ProtocolSession* session, bool enabled);

src/shared/stop_condition.c

@@ -44,6 +44,181 @@ static bool parse_two_digits(const char* s, int* out) {
   return true;
 }
 
+/* True when the current character of the cursor is a decimal digit. */
+static bool is_digit(const char* cp) {
+  return *cp >= '0' && *cp <= '9';
+}
+
+/* rsync 3.4.1's flexible --stop-at date parser (ported from
+ * options.c:parse_time).  Returns a time_t, or (time_t)-1 on a malformed value.
+ * Accepted forms include Y-M-DTh:m, Y/M/DTh:m, Y-M-D, M-D, D, h:m, :m and
+ * "T h:m"; a 1- or 2-digit year and omitted fields are resolved to the next
+ * matching point in time in the local timezone.  Seconds are NOT accepted
+ * (rsync rejects them too); FastSync keeps its own HH:MM:SS spelling as an
+ * extension handled by the caller.  `now` is passed in so tests are
+ * deterministic; production passes time(NULL). */
+static time_t parse_time_rsync(const char* value, time_t now) {
+  const char* cp;
+  time_t val;
+  struct tm today;
+  if (!localtime_r(&now, &today))
+    return (time_t)-1;
+  struct tm t;
+  int in_date, old_mday, n;
+
+  memset(&t, 0, sizeof t);
+  t.tm_year = t.tm_mon = t.tm_mday = -1;
+  t.tm_hour = t.tm_min = t.tm_isdst = -1;
+  cp = value;
+  if (*cp == 'T' || *cp == 't' || *cp == ':') {
+    in_date = *cp == ':' ? 0 : -1;
+    cp++;
+  } else
+    in_date = 1;
+  for (;; cp++) {
+    if (!is_digit(cp))
+      return (time_t)-1;
+    n = 0;
+    do {
+      n = n * 10 + *cp++ - '0';
+    } while (is_digit(cp));
+    if (*cp == ':')
+      in_date = 0;
+    if (in_date > 0) {
+      if (t.tm_year != -1)
+        return (time_t)-1;
+      t.tm_year = t.tm_mon;
+      t.tm_mon = t.tm_mday;
+      t.tm_mday = n;
+      if (!*cp)
+        break;
+      if (*cp == 'T' || *cp == 't') {
+        if (!cp[1])
+          break;
+        in_date = -1;
+      } else if (*cp != '-' && *cp != '/')
+        return (time_t)-1;
+      continue;
+    }
+    if (t.tm_hour != -1)
+      return (time_t)-1;
+    t.tm_hour = t.tm_min;
+    t.tm_min = n;
+    if (!*cp) {
+      if (in_date < 0)
+        return (time_t)-1;
+      break;
+    }
+    if (*cp != ':')
+      return (time_t)-1;
+    in_date = 0;
+  }
+
+  in_date = 0;
+  if (t.tm_year < 0) {
+    t.tm_year = today.tm_year;
+    in_date = 1;
+  } else if (t.tm_year < 100) {
+    while (t.tm_year < today.tm_year)
+      t.tm_year += 100;
+  } else
+    t.tm_year -= 1900;
+  if (t.tm_mon < 0) {
+    t.tm_mon = today.tm_mon;
+    in_date = 2;
+  } else
+    t.tm_mon--;
+  if (t.tm_mday < 0) {
+    t.tm_mday = today.tm_mday;
+    in_date = 3;
+  }
+
+  n = 0;
+  if (t.tm_min < 0) {
+    t.tm_hour = t.tm_min = 0;
+  } else if (t.tm_hour < 0) {
+    if (in_date != 3)
+      return (time_t)-1;
+    in_date = 0;
+    t.tm_hour = today.tm_hour;
+    n = 60 * 60;
+  }
+
+  /* mktime() may roll a too-large tm_mday into the following month; undo that
+   * in the "next match" loop below. */
+  old_mday = t.tm_mday;
+  if (t.tm_hour > 23 || t.tm_min > 59 || t.tm_mon < 0 || t.tm_mon >= 12 || t.tm_mday < 1 ||
+      t.tm_mday > 31 || (val = mktime(&t)) == (time_t)-1)
+    return (time_t)-1;
+
+  while (in_date && (val <= now || t.tm_mday < old_mday)) {
+    switch (in_date) {
+    case 3:
+      old_mday = ++t.tm_mday;
+      break;
+    case 2:
+      if (t.tm_mday < old_mday)
+        t.tm_mday = old_mday; /* the month already got bumped forward */
+      else if (++t.tm_mon == 12) {
+        t.tm_mon = 0;
+        t.tm_year++;
+      }
+      break;
+    case 1:
+      if (t.tm_mday < old_mday) {
+        /* mon==1 mday==29 got bumped to mon==2 */
+        if (t.tm_mon != 2 || old_mday != 29)
+          return (time_t)-1;
+        t.tm_mon = 1;
+        t.tm_mday = 29;
+      }
+      t.tm_year++;
+      break;
+    }
+    if ((val = mktime(&t)) == (time_t)-1) {
+      if (in_date != 3 || t.tm_mday <= 28)
+        return (time_t)-1;
+      t.tm_mday = old_mday = 1;
+      in_date = 2;
+    }
+  }
+  if (n) {
+    while (val <= now)
+      val += n;
+  }
+  return val;
+}
+
+/* FastSync's HH:MM or HH:MM:SS spelling on the current local day.  rsync's own
+ * --stop-at accepts only HH:MM, so this is a strict superset extension. */
+static bool parse_clock_time(const char* value, time_t now, time_t* out_deadline) {
+  size_t len = strlen(value);
+  if (len != 5 && len != 8)
+    return false;
+  if (value[2] != ':' || (len == 8 && value[5] != ':'))
+    return false;
+  int hh, mm, ss = 0;
+  if (!parse_two_digits(value, &hh) || !parse_two_digits(value + 3, &mm))
+    return false;
+  if (len == 8 && !parse_two_digits(value + 6, &ss))
+    return false;
+  if (hh > 23 || mm > 59 || ss > 59)
+    return false;
+
+  struct tm today;
+  if (!localtime_r(&now, &today))
+    return false;
+  today.tm_hour = hh;
+  today.tm_min = mm;
+  today.tm_sec = ss;
+  today.tm_isdst = -1;
+  time_t deadline = mktime(&today);
+  if (deadline == (time_t)-1)
+    return false;
+  *out_deadline = deadline;
+  return true;
+}
+
 bool stop_parse_at_time(const char* value, time_t now, time_t* out_deadline) {
   if (!value || !out_deadline)
     return false;
@@ -91,28 +266,13 @@ bool stop_parse_at_time(const char* value, time_t now, time_t* out_deadline) {
     return true;
   }
 
-  /* HH:MM or HH:MM:SS on the current local day. */
-  size_t len = strlen(value);
-  if (len != 5 && len != 8)
-    return false;
-  if (value[2] != ':' || (len == 8 && value[5] != ':'))
-    return false;
-  int hh, mm, ss = 0;
-  if (!parse_two_digits(value, &hh) || !parse_two_digits(value + 3, &mm))
-    return false;
-  if (len == 8 && !parse_two_digits(value + 6, &ss))
-    return false;
-  if (hh > 23 || mm > 59 || ss > 59)
-    return false;
+  /* HH:MM or HH:MM:SS on the current local day (FastSync extension). */
+  if (parse_clock_time(value, now, out_deadline))
+    return true;
 
-  struct tm today;
-  if (!localtime_r(&now, &today))
-    return false;
-  today.tm_hour = hh;
-  today.tm_min = mm;
-  today.tm_sec = ss;
-  today.tm_isdst = -1;
-  time_t deadline = mktime(&today);
+  /* rsync's full/partial date-and-time form (e.g. 2000-12-31T23:59, 12-31,
+   * 14:00, :59, 1, 1-30). */
+  time_t deadline = parse_time_rsync(value, now);
   if (deadline == (time_t)-1)
     return false;
   *out_deadline = deadline;

src/shared/transport_tcp.c

@@ -289,14 +289,14 @@ void server_accept_loop(Server* server, void (*child_fn)(int, void*), void* chil
   accept_loop(server, child_fn, child_ctx, log_fmt);
 }
 
-static int g_timeout_sec = 30;
-static int g_contimeout_sec = 10;
+/* rsync defaults: --timeout=0 (disabled) and --contimeout=60.  A non-positive
+ * value means "no timeout" rather than "leave the built-in value in place". */
+static int g_timeout_sec = 0;
+static int g_contimeout_sec = 60;
 
 void tcp_set_timeouts(int timeout_sec, int contimeout_sec) {
-  if (timeout_sec > 0)
-    g_timeout_sec = timeout_sec;
-  if (contimeout_sec > 0)
-    g_contimeout_sec = contimeout_sec;
+  g_timeout_sec = timeout_sec > 0 ? timeout_sec : 0;
+  g_contimeout_sec = contimeout_sec > 0 ? contimeout_sec : 0;
 }
 
 int tcp_get_contimeout_sec(void) {
@@ -308,6 +308,10 @@ int tcp_get_timeout_sec(void) {
 }
 
 static void tcp_apply_socket_timeout(int fd) {
+  /* timeout 0 means no timeout: leave the socket in its default (blocking)
+   * mode instead of installing a zero SO_RCVTIMEO/SO_SNDTIMEO. */
+  if (g_timeout_sec <= 0)
+    return;
   struct timeval tv;
   tv.tv_sec = g_timeout_sec;
   tv.tv_usec = 0;
@@ -483,11 +487,15 @@ bool tcp_connect_socket_ex(Client* client, const char* host, int port,
       break;
     }
 
-    struct timeval ct;
-    ct.tv_sec = g_contimeout_sec;
-    ct.tv_usec = 0;
-    setsockopt(client->file_descriptor, SOL_SOCKET, SO_RCVTIMEO, &ct, sizeof(ct));
-    setsockopt(client->file_descriptor, SOL_SOCKET, SO_SNDTIMEO, &ct, sizeof(ct));
+    /* --contimeout=0 disables the connect timeout: skip the pre-connect socket
+     * timeouts entirely. */
+    if (g_contimeout_sec > 0) {
+      struct timeval ct;
+      ct.tv_sec = g_contimeout_sec;
+      ct.tv_usec = 0;
+      setsockopt(client->file_descriptor, SOL_SOCKET, SO_RCVTIMEO, &ct, sizeof(ct));
+      setsockopt(client->file_descriptor, SOL_SOCKET, SO_SNDTIMEO, &ct, sizeof(ct));
+    }
 
     if (bind_addr_family != 0) {
       if (rp->ai_family != bind_addr_family) {

src/shared/utils.c

@@ -2,6 +2,7 @@
 #include "array_list.h"
 #include "log.h"
 #include <arpa/inet.h>
+#include <ctype.h>
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -52,6 +53,31 @@ bool path_is_within_root(const char* root, const char* path) {
   return strncmp(root, path, root_len) == 0 && (path[root_len] == '\0' || path[root_len] == '/');
 }
 
+/* Borrowed transfer-relative view of `path`: strip any leading '/' and then a
+ * `root` prefix (its own leading/trailing slashes tolerated), returning a
+ * pointer into `path`.  Non-allocating, so it is safe on the hot scan/print
+ * paths.  A NULL/empty root, or a path not under `root`, leaves only the
+ * leading-slash strip.  `path` must be NUL-terminated and live in the caller. */
+const char* utils_strip_transfer_root(const char* path, const char* root) {
+  if (path == NULL)
+    return NULL;
+  const char* rel = path;
+  while (*rel == '/')
+    rel++;
+  if (root == NULL)
+    return rel;
+  while (*root == '/')
+    root++;
+  size_t root_len = strlen(root);
+  while (root_len > 0 && root[root_len - 1] == '/')
+    root_len--;
+  if (root_len == 0)
+    return rel;
+  if (strncmp(rel, root, root_len) == 0 && (rel[root_len] == '/' || rel[root_len] == '\0'))
+    return rel + root_len + (rel[root_len] == '/' ? 1 : 0);
+  return rel;
+}
+
 /* Open the destination root directory itself, confined to the authorized root.
  * NOTE (do not merge with file_open_secure_parent): this walk opens dest_root
  * (a directory that must already exist) and returns its fd, whereas
@@ -60,7 +86,7 @@ bool path_is_within_root(const char* root, const char* path) {
  * two differ in create-vs-no-create, in what path component they stop at, and
  * in the extra receiver policies they apply, so they are intentionally kept
  * separate.  Both rely on the shared lexical path_is_within_root check. */
-static int open_authorized_destination(const char* dest_root) {
+int utils_open_authorized_destination(const char* dest_root) {
   int root_fd = utils_get_authorized_root_fd();
   const char* root_path = utils_get_authorized_root_path();
   if (root_fd < 0 || !root_path || !dest_root || !path_is_within_root(root_path, dest_root))
@@ -117,6 +143,47 @@ char* str_dup(const char* string) {
   return new_string;
 }
 
+int env_choice_first(const char* env_name, int (*resolve)(const char*), bool* specified) {
+  if (specified)
+    *specified = false;
+  if (!env_name || !resolve)
+    return -1;
+  const char* env = getenv(env_name);
+  if (!env)
+    return -1;
+
+  bool saw_nonblank = false;
+  const char* p = env;
+  while (*p) {
+    if (*p == '&')
+      break;
+    if (isspace((unsigned char)*p)) {
+      p++;
+      continue;
+    }
+    saw_nonblank = true;
+    char token[64];
+    size_t len = 0;
+    while (*p && *p != '&' && !isspace((unsigned char)*p)) {
+      if (len < sizeof(token) - 1)
+        token[len++] = *p;
+      p++;
+    }
+    token[len] = '\0';
+    if (len > 0) {
+      int id = resolve(token);
+      if (id >= 0) {
+        if (specified)
+          *specified = true;
+        return id;
+      }
+    }
+  }
+  if (specified)
+    *specified = saw_nonblank;
+  return -1;
+}
+
 #define STR_HASH_SET_MIN_CAPACITY 16
 
 static size_t str_hash_set_hash(const char* key, size_t len) {
@@ -584,22 +651,43 @@ bool path_under_skip_prefix(const char* child_rel, bool at_root, const DeleteSki
   return false;
 }
 
-/* All-or-nothing max-delete needs to know BEFORE any unlink whether the run
-   would delete more than max_delete entries.  This rehearsal pass walks the
-   destination with the same decisions as the delete pass but never touches the
-   filesystem: it counts every regular file the delete pass would unlink and
-   every directory it would rmdir (a directory is removed only once every entry
-   below it has been removed and nothing the walker leaves in place survives).
-   Entries the walker never removes (symlinks, manifest-listed files, protected
-   prefixes) mark the enclosing directory as surviving, exactly as they would
-   make a real rmdir fail with ENOTEMPTY.  Stops early once *count reaches the
-   cap (sets *exceeds).  Returns false on a traversal error. */
-static bool count_extras_fd(int dirfd, const char* rel_path, const PathIndex* keep, size_t cap,
-                            size_t* count, bool* exceeds, const DeleteSkipEntry* skips,
-                            int skip_count, bool* survives) {
+/* Per-run deletion budget and tallies.  `max_delete` is the cap on the number
+   of entries the walker may remove (SIZE_MAX = unlimited); once it is reached
+   the remaining extras are counted in `skipped` and left in place, matching
+   rsync's partial --max-delete behavior. */
+typedef struct {
+  size_t max_delete;
+  size_t deleted;
+  size_t skipped;
+  bool limit_hit;
+} DeleteBudget;
+
+/* True when direct children of the directory named by `rel` may be removed.
+   With no synchronization info (dirs == NULL) the whole tree is deletable; when
+   a dirs index is supplied only its exact entries are (the receive root is the
+   "." sentinel). */
+static bool is_synced_dir(const PathIndex* dirs, const char* rel) {
+  if (!dirs)
+    return true;
+  return path_index_contains(dirs, rel[0] == '\0' ? "." : rel);
+}
+
+/* Remove the extras directly inside the directory open on `dirfd`, recursing
+   into every child directory so kept content below a synchronized prefix is
+   reached.  `all_removed` reports whether every child entry was removed (so the
+   caller may rmdir this directory).  A child directory is never removed when it
+   is itself a synchronized directory or holds kept content; with a dirs index
+   supplied, direct children of a non-synchronized directory are never extras at
+   all (they are left in place but still descended into).  Symlinks are unlinked
+   like any other non-directory extra (never followed). */
+static bool delete_extras_fd(int dirfd, const char* rel_path, const PathIndex* keep,
+                             const PathIndex* dirs, DeleteBudget* budget,
+                             const DeleteSkipEntry* skips, int skip_count,
+                             const FilterRuleList* protect_rules, bool parent_deletable,
+                             bool* all_removed, DeletePathObserver observer,
+                             void* observer_context) {
   /* openat(dirfd, ".") opens an independent file description: a dup() would
-     share dirfd's file offset, and a prior rehearsal pass must not have drained
-     this directory's stream before the delete pass reads it again. */
+     share dirfd's file offset and a prior pass could leave the stream drained. */
   int scanfd = openat(dirfd, ".", O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
   if (scanfd < 0)
     return false;
@@ -610,93 +698,10 @@ static bool count_extras_fd(int dirfd, const char* rel_path, const PathIndex* ke
   }
   bool operation_ok = true;
   bool local_survives = false;
-  bool at_root = rel_path[0] == '\0';
-  const struct dirent* entry;
-  while ((entry = readdir(dir)) != NULL) {
-    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
-      continue;
-    if (*exceeds)
-      break;
-    char* child_rel = path_cat((char*)rel_path, entry->d_name);
-    if (!child_rel) {
-      operation_ok = false;
-      continue;
-    }
-    if (path_under_skip_prefix(child_rel, at_root, skips, skip_count)) {
-      local_survives = true;
-      free(child_rel);
-      continue;
-    }
-    struct stat st;
-    if (fstatat(dirfd, entry->d_name, &st, AT_SYMLINK_NOFOLLOW) != 0) {
-      if (errno != ENOENT)
-        operation_ok = false;
-      free(child_rel);
-      continue;
-    }
-    if (S_ISLNK(st.st_mode)) {
-      local_survives = true;
-      free(child_rel);
-      continue;
-    }
-    if (S_ISDIR(st.st_mode)) {
-      int childfd = openat(dirfd, entry->d_name, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
-      bool child_ok = true;
-      bool child_survives = true;
-      if (childfd >= 0) {
-        child_ok = count_extras_fd(childfd, child_rel, keep, cap, count, exceeds, skips, skip_count,
-                                   &child_survives);
-        close(childfd);
-      } else if (errno != ENOENT) {
-        operation_ok = false;
-      }
-      if (!child_ok)
-        operation_ok = false;
-      if (keep_is_dir(keep, child_rel)) {
-        /* A directory with kept content below it is never removed. */
-        local_survives = true;
-      } else if (child_survives) {
-        /* The directory still holds entries the walker leaves in place, so an
-           rmdir would fail with ENOTEMPTY; the delete pass leaves it behind
-           rather than reporting an error (matching rsync). */
-        local_survives = true;
-      } else {
-        if (*count >= cap) {
-          *exceeds = true;
-        } else {
-          (*count)++;
-        }
-      }
-    } else {
-      bool found = keep_is_file(keep, child_rel);
-      if (!found) {
-        if (*count >= cap) {
-          *exceeds = true;
-        } else {
-          (*count)++;
-        }
-      }
-    }
-    free(child_rel);
-  }
-  closedir(dir);
-  *survives = local_survives;
-  return operation_ok;
-}
-
-static bool delete_extras_fd(int dirfd, const char* rel_path, const PathIndex* keep,
-                             size_t max_delete, size_t* deleted_count, const DeleteSkipEntry* skips,
-                             int skip_count) {
-  /* Independent file description (see count_extras_fd). */
-  int scanfd = openat(dirfd, ".", O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
-  if (scanfd < 0)
-    return false;
-  DIR* dir = fdopendir(scanfd);
-  if (!dir) {
-    close(scanfd);
-    return false;
-  }
-  bool operation_ok = true;
+  /* A directory is deletable when it or ANY ancestor is synchronized; the
+     `parent_deletable` flag carries that down the recursion so dest-only
+     directories below a synchronized root are removed wholesale. */
+  bool deletable = parent_deletable || is_synced_dir(dirs, rel_path);
   const struct dirent* entry;
   while ((entry = readdir(dir)) != NULL) {
     if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
@@ -714,6 +719,7 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, const PathIndex* k
        destination directory that happens to be called .fastsync-stage is
        ordinary content. */
     if (path_under_skip_prefix(child_rel, rel_path[0] == '\0', skips, skip_count)) {
+      local_survives = true;
       free(child_rel);
       continue;
     }
@@ -724,55 +730,73 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, const PathIndex* k
       free(child_rel);
       continue;
     }
-    // Skip symlinks to prevent following them outside the destination tree
-    if (S_ISLNK(st.st_mode)) {
+    bool is_dir = S_ISDIR(st.st_mode);
+    if (protect_rules && filter_rules_apply_side(protect_rules, child_rel, entry->d_name, is_dir,
+                                                 FILTER_SIDE_RECEIVER) == FILTER_ACTION_PROTECT) {
+      /* A first-match protect rule shields the extra; for a directory the whole
+         subtree is shielded (rsync prunes an excluded directory), so do not
+         descend. */
+      local_survives = true;
       free(child_rel);
       continue;
     }
-    if (S_ISDIR(st.st_mode)) {
+    if (is_dir) {
       int childfd = openat(dirfd, entry->d_name, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
-      bool child_removed = false;
+      bool child_all_removed = false;
       if (childfd >= 0) {
-        child_removed = delete_extras_fd(childfd, child_rel, keep, max_delete, deleted_count, skips,
-                                         skip_count);
-        if (!child_removed)
+        if (!delete_extras_fd(childfd, child_rel, keep, dirs, budget, skips, skip_count,
+                              protect_rules, deletable, &child_all_removed, observer,
+                              observer_context))
           operation_ok = false;
         close(childfd);
       } else if (errno != ENOENT) {
         operation_ok = false;
       }
-      if (child_removed && !keep_is_dir(keep, child_rel)) {
-        if (*deleted_count >= max_delete) {
-          operation_ok = false;
+      bool child_synced = dirs && path_index_contains(dirs, child_rel);
+      if (child_synced || keep_is_dir(keep, child_rel)) {
+        /* A synchronized directory and a directory holding kept content are
+           never removed. */
+        local_survives = true;
+      } else if (child_all_removed && deletable) {
+        if (budget->deleted >= budget->max_delete) {
+          budget->limit_hit = true;
+          budget->skipped++;
+          local_survives = true;
+        } else if (unlinkat(dirfd, entry->d_name, AT_REMOVEDIR) != 0) {
+          /* ENOENT: already gone (fine).  ENOTEMPTY/EEXIST: the directory
+             still holds entries the walker leaves in place (a protected
+             excluded prefix, a kept file the manifest protects, a symlink);
+             rsync leaves such a directory behind, so this is not an error.
+             Only genuine I/O failures abort the deletion. */
+          if (errno != ENOENT && errno != ENOTEMPTY && errno != EEXIST)
+            operation_ok = false;
+          local_survives = true;
         } else {
-          if (unlinkat(dirfd, entry->d_name, AT_REMOVEDIR) != 0) {
-            /* ENOENT: already gone (fine).  ENOTEMPTY/EEXIST: the directory
-               still holds entries the walker leaves in place (a protected
-               excluded prefix, a kept file the manifest protects, a symlink);
-               rsync leaves such a directory behind, so this is not an error.
-               Only genuine I/O failures abort the deletion. */
-            if (errno != ENOENT && errno != ENOTEMPTY && errno != EEXIST)
-              operation_ok = false;
-          } else {
-            (*deleted_count)++;
-          }
+          budget->deleted++;
+          if (observer)
+            observer(observer_context, child_rel);
         }
+      } else {
+        local_survives = true;
       }
     } else {
-      // Check if relative path is in manifest
       bool found = keep_is_file(keep, child_rel);
-      if (!found) {
-        if (*deleted_count >= max_delete) {
+      if (found || !deletable) {
+        /* Kept file, or a child of a directory that is not synchronized: never
+           an extra for this run. */
+        local_survives = true;
+      } else if (budget->deleted >= budget->max_delete) {
+        budget->limit_hit = true;
+        budget->skipped++;
+        local_survives = true;
+      } else if (unlinkat(dirfd, entry->d_name, 0) != 0) {
+        if (errno != ENOENT)
           operation_ok = false;
-          free(child_rel);
-          continue;
-        }
-        if (unlinkat(dirfd, entry->d_name, 0) != 0) {
-          if (errno != ENOENT)
-            operation_ok = false;
-        } else {
-          (*deleted_count)++;
-        }
+        local_survives = true;
+      } else {
+        budget->deleted++;
+        if (observer)
+          observer(observer_context, child_rel);
         char* escaped_path = output_escape(child_rel, log_get_8_bit_output());
         fprintf(stderr, "  Deleted: %s\n", escaped_path ? escaped_path : "<allocation failed>");
         free(escaped_path);
@@ -781,26 +805,135 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, const PathIndex* k
     free(child_rel);
   }
   closedir(dir);
+  *all_removed = !local_survives;
   return operation_ok;
 }
 
-DeleteWalkResult delete_extras_limited(const char* dest_root, const ArrayList* manifest,
-                                       size_t max_delete, const DeleteSkipEntry* skips,
-                                       int skip_count, size_t* deleted_out) {
-  if (deleted_out)
-    *deleted_out = 0;
-  if (!manifest)
-    return DELETE_WALK_ERROR;
-  /* Index the keep-set once so both passes answer membership in O(path length)
-     instead of scanning every manifest entry for every destination entry. */
+/* Read-only mirror of delete_extras_fd: records the paths that WOULD be removed
+   without unlinking anything.  A child directory is reported after its own
+   reportable children (depth-first), matching the delete pass's ordering. */
+static bool list_extras_fd(int dirfd, const char* rel_path, const PathIndex* keep,
+                           const PathIndex* dirs, ArrayList* out, size_t* recorded,
+                           const DeleteSkipEntry* skips, int skip_count,
+                           const FilterRuleList* protect_rules, bool parent_deletable,
+                           bool* all_removed) {
+  int scanfd = openat(dirfd, ".", O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+  if (scanfd < 0)
+    return false;
+  DIR* dir = fdopendir(scanfd);
+  if (!dir) {
+    close(scanfd);
+    return false;
+  }
+  bool operation_ok = true;
+  bool local_survives = false;
+  bool deletable = parent_deletable || is_synced_dir(dirs, rel_path);
+  const struct dirent* entry;
+  while ((entry = readdir(dir)) != NULL) {
+    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
+      continue;
+    char* child_rel = path_cat((char*)rel_path, entry->d_name);
+    if (!child_rel) {
+      operation_ok = false;
+      continue;
+    }
+    if (path_under_skip_prefix(child_rel, rel_path[0] == '\0', skips, skip_count)) {
+      local_survives = true;
+      free(child_rel);
+      continue;
+    }
+    struct stat st;
+    if (fstatat(dirfd, entry->d_name, &st, AT_SYMLINK_NOFOLLOW) != 0) {
+      if (errno != ENOENT)
+        operation_ok = false;
+      free(child_rel);
+      continue;
+    }
+    bool is_dir = S_ISDIR(st.st_mode);
+    if (protect_rules && filter_rules_apply_side(protect_rules, child_rel, entry->d_name, is_dir,
+                                                 FILTER_SIDE_RECEIVER) == FILTER_ACTION_PROTECT) {
+      /* Mirror the delete walk: a protected entry is never reported as a
+         would-delete and a protected directory's subtree is not enumerated. */
+      local_survives = true;
+      free(child_rel);
+      continue;
+    }
+    if (is_dir) {
+      int childfd = openat(dirfd, entry->d_name, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+      bool child_all_removed = false;
+      if (childfd >= 0) {
+        if (!list_extras_fd(childfd, child_rel, keep, dirs, out, recorded, skips, skip_count,
+                            protect_rules, deletable, &child_all_removed))
+          operation_ok = false;
+        close(childfd);
+      } else if (errno != ENOENT) {
+        operation_ok = false;
+      }
+      bool child_synced = dirs && path_index_contains(dirs, child_rel);
+      if (child_synced || keep_is_dir(keep, child_rel)) {
+        local_survives = true;
+      } else if (child_all_removed && deletable) {
+        size_t len = strlen(child_rel);
+        char* copy = malloc(len + 2);
+        if (!copy) {
+          operation_ok = false;
+        } else {
+          memcpy(copy, child_rel, len);
+          copy[len] = '/';
+          copy[len + 1] = '\0';
+          if (!array_list_add(out, copy)) {
+            free(copy);
+            operation_ok = false;
+          } else {
+            (*recorded)++;
+          }
+        }
+      } else {
+        local_survives = true;
+      }
+    } else {
+      bool found = keep_is_file(keep, child_rel);
+      if (found || !deletable) {
+        local_survives = true;
+      } else {
+        char* copy = str_dup(child_rel);
+        if (!copy || !array_list_add(out, copy)) {
+          free(copy);
+          operation_ok = false;
+        } else {
+          (*recorded)++;
+        }
+      }
+    }
+    free(child_rel);
+  }
+  closedir(dir);
+  *all_removed = !local_survives;
+  return operation_ok;
+}
+
+bool delete_extras_list(const char* dest_root, const ArrayList* manifest,
+                        const ArrayList* synced_dirs, const DeleteSkipEntry* skips, int skip_count,
+                        const FilterRuleList* protect_rules, ArrayList* out, size_t* count_out) {
+  if (count_out)
+    *count_out = 0;
+  if (!manifest || !out)
+    return false;
   PathIndex keep;
   if (!build_keep_index(manifest, &keep))
-    return DELETE_WALK_ERROR;
+    return false;
+  PathIndex dirs;
+  bool have_dirs = synced_dirs != NULL;
+  if (have_dirs &&
+      !path_index_build(&dirs, (const char* const*)synced_dirs->items, (size_t)synced_dirs->size)) {
+    path_index_free(&keep);
+    return false;
+  }
   int rootfd;
   int root_fd = utils_get_authorized_root_fd();
   if (root_fd >= 0) {
     if (utils_get_authorized_root_path())
-      rootfd = open_authorized_destination(dest_root);
+      rootfd = utils_open_authorized_destination(dest_root);
     else if (dest_root == NULL)
       rootfd = dup(root_fd);
     else
@@ -810,39 +943,100 @@ DeleteWalkResult delete_extras_limited(const char* dest_root, const ArrayList* m
   }
   if (rootfd < 0) {
     path_index_free(&keep);
-    return DELETE_WALK_ERROR;
+    if (have_dirs)
+      path_index_free(&dirs);
+    return false;
   }
-  if (max_delete != SIZE_MAX) {
-    /* Rehearse the deletion first so a run that would exceed the cap removes
-       nothing (rsync's all-or-nothing --max-delete contract). */
-    size_t count = 0;
-    bool exceeds = false;
-    bool survives = false;
-    bool counted_ok = count_extras_fd(rootfd, "", &keep, max_delete, &count, &exceeds, skips,
-                                      skip_count, &survives);
-    if (!counted_ok) {
-      close(rootfd);
-      path_index_free(&keep);
-      return DELETE_WALK_ERROR;
-    }
-    if (exceeds) {
-      close(rootfd);
-      path_index_free(&keep);
-      return DELETE_WALK_LIMIT_EXCEEDED;
-    }
-  }
-  size_t deleted_count = 0;
-  bool ok = delete_extras_fd(rootfd, "", &keep, max_delete, &deleted_count, skips, skip_count);
+  bool all_removed = false;
+  size_t recorded = 0;
+  bool ok = list_extras_fd(rootfd, "", &keep, have_dirs ? &dirs : NULL, out, &recorded, skips,
+                           skip_count, protect_rules, false, &all_removed);
   if (close(rootfd) != 0)
     ok = false;
   path_index_free(&keep);
+  if (have_dirs)
+    path_index_free(&dirs);
+  if (count_out)
+    *count_out = recorded;
+  return ok;
+}
+
+DeleteWalkResult delete_extras_limited_observed(const char* dest_root, const ArrayList* manifest,
+                                                const ArrayList* synced_dirs, size_t max_delete,
+                                                const DeleteSkipEntry* skips, int skip_count,
+                                                const FilterRuleList* protect_rules,
+                                                size_t* deleted_out, size_t* skipped_out,
+                                                DeletePathObserver observer,
+                                                void* observer_context) {
   if (deleted_out)
-    *deleted_out = deleted_count;
-  return ok ? DELETE_WALK_OK : DELETE_WALK_ERROR;
+    *deleted_out = 0;
+  if (skipped_out)
+    *skipped_out = 0;
+  if (!manifest)
+    return DELETE_WALK_ERROR;
+  /* Index the keep-set (and the synchronized-dir set, when supplied) once so
+     membership is answered in O(path length) instead of scanning every entry
+     for every destination entry. */
+  PathIndex keep;
+  if (!build_keep_index(manifest, &keep))
+    return DELETE_WALK_ERROR;
+  PathIndex dirs;
+  bool have_dirs = synced_dirs != NULL;
+  if (have_dirs &&
+      !path_index_build(&dirs, (const char* const*)synced_dirs->items, (size_t)synced_dirs->size)) {
+    path_index_free(&keep);
+    return DELETE_WALK_ERROR;
+  }
+  int rootfd;
+  int root_fd = utils_get_authorized_root_fd();
+  if (root_fd >= 0) {
+    if (utils_get_authorized_root_path())
+      rootfd = utils_open_authorized_destination(dest_root);
+    else if (dest_root == NULL)
+      rootfd = dup(root_fd);
+    else
+      rootfd = -1;
+  } else {
+    rootfd = open(dest_root, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+  }
+  if (rootfd < 0) {
+    path_index_free(&keep);
+    if (have_dirs)
+      path_index_free(&dirs);
+    return DELETE_WALK_ERROR;
+  }
+  DeleteBudget budget = {.max_delete = max_delete, .deleted = 0, .skipped = 0, .limit_hit = false};
+  bool all_removed = false;
+  bool ok =
+      delete_extras_fd(rootfd, "", &keep, have_dirs ? &dirs : NULL, &budget, skips, skip_count,
+                       protect_rules, false, &all_removed, observer, observer_context);
+  if (close(rootfd) != 0)
+    ok = false;
+  path_index_free(&keep);
+  if (have_dirs)
+    path_index_free(&dirs);
+  if (deleted_out)
+    *deleted_out = budget.deleted;
+  if (skipped_out)
+    *skipped_out = budget.skipped;
+  if (!ok)
+    return DELETE_WALK_ERROR;
+  return budget.limit_hit ? DELETE_WALK_LIMIT_REACHED : DELETE_WALK_OK;
+}
+
+DeleteWalkResult delete_extras_limited(const char* dest_root, const ArrayList* manifest,
+                                       const ArrayList* synced_dirs, size_t max_delete,
+                                       const DeleteSkipEntry* skips, int skip_count,
+                                       const FilterRuleList* protect_rules, size_t* deleted_out,
+                                       size_t* skipped_out) {
+  return delete_extras_limited_observed(dest_root, manifest, synced_dirs, max_delete, skips,
+                                        skip_count, protect_rules, deleted_out, skipped_out, NULL,
+                                        NULL);
 }
 
 bool delete_extras(const char* dest_root, const ArrayList* manifest) {
-  return delete_extras_limited(dest_root, manifest, SIZE_MAX, NULL, 0, NULL) == DELETE_WALK_OK;
+  return delete_extras_limited(dest_root, manifest, NULL, SIZE_MAX, NULL, 0, NULL, NULL, NULL) ==
+         DELETE_WALK_OK;
 }
 
 bool has_path_traversal(const char* path) {

src/shared/utils.h

@@ -2,6 +2,7 @@
 #define UTILS_H
 
 #include "array_list.h"
+#include "filter.h"
 #include <stddef.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -81,6 +82,17 @@ bool path_index_has_descendant(const PathIndex* index, const char* path);
 
 char* str_dup(const char* string);
 char* output_escape(const char* string, bool eight_bit_output);
+
+/* Resolve the first supported name from a rsync algorithm-preference
+ * environment variable (RSYNC_COMPRESS_LIST / RSYNC_CHECKSUM_LIST).  `resolve`
+ * maps a case-insensitive name to an algorithm id (>= 0) or -1 for an unknown
+ * name.  rsync's syntax is a whitespace-separated list (comma/colon are NOT
+ * separators); the client-side half ends at '&'.  Unknown entries are skipped
+ * and the first resolvable one wins.  *specified is set true when the variable
+ * holds at least one non-blank character.  Returns the first resolvable id, or
+ * -1 when the variable is unset/blank or names no supported algorithm. */
+int env_choice_first(const char* env_name, int (*resolve)(const char*), bool* specified);
+
 /* Upper bound on one line/token read from a local list file (--files-from,
  * --exclude-from/--include-from, .rsync-filter).  Mirrors MAX_STRING_SIZE and
  * stops a hostile multi-gigabyte line from forcing unbounded allocation. */
@@ -98,10 +110,10 @@ bool glob_match(const char* pattern, const char* str);
 typedef enum {
   /* Every extra entry was removed (or there were none). */
   DELETE_WALK_OK = 0,
-  /* The destination holds more extras than the numeric cap for this run.  With
-     the all-or-nothing max-delete semantics NOTHING was removed (the walker
-     counts first and refuses to start when the run would exceed the limit). */
-  DELETE_WALK_LIMIT_EXCEEDED,
+  /* The numeric cap for this run was reached before every extra was removed.
+     The walker removed exactly the entries the cap allowed and skipped (without
+     removing) the rest, matching rsync's partial --max-delete behavior. */
+  DELETE_WALK_LIMIT_REACHED,
   /* A traversal or unlink failure aborted the deletion (partial removal is
      possible, mirroring the delete pass). */
   DELETE_WALK_ERROR
@@ -122,20 +134,56 @@ typedef struct {
    only DIRECT children of the destination root, i.e. child_rel has no '/'). */
 bool path_under_skip_prefix(const char* child_rel, bool at_root, const DeleteSkipEntry* skips,
                             int skip_count);
-/* Remove files/dirs under dest_root that are not listed in manifest without
-   ever descending into a protected prefix (see DeleteSkipEntry).  When
-   max_delete is not SIZE_MAX the run is all-or-nothing: extras are counted
-   first and DELETE_WALK_LIMIT_EXCEEDED is returned (with nothing removed) when
-   the count would exceed the cap.  `deleted_out` optionally receives the number
-   of entries actually removed.  The all-or-nothing guarantee holds only while
-   the destination tree is not being concurrently modified: the rehearsal pass
-   and the delete pass are two separate walks, so a concurrent change between
-   them (another process adding/removing entries) can make the second pass
-   delete a different set than the first one counted. */
+/* Remove files/dirs/symlinks under dest_root that are not listed in manifest
+   without ever descending into a protected prefix (see DeleteSkipEntry).  When
+   `synced_dirs` is non-NULL, extras are only removed directly inside a directory
+   whose destination-relative path is an exact entry in that list (the receive
+   root is the "." sentinel); directories outside the synchronized set are still
+   descended into so kept content below a listed directory is preserved, but
+   nothing in them is removed.  A NULL `synced_dirs` keeps the legacy behavior of
+   treating the whole destination tree as deletable.  `max_delete` caps the
+   number of removed entries (SIZE_MAX = unlimited): the walker removes up to the
+   cap and returns DELETE_WALK_LIMIT_REACHED when more extras remained.
+   `deleted_out`/`skipped_out` optionally receive the number of entries removed
+   and the number skipped because of the cap. */
 DeleteWalkResult delete_extras_limited(const char* dest_root, const ArrayList* manifest,
-                                       size_t max_delete, const DeleteSkipEntry* skips,
-                                       int skip_count, size_t* deleted_out);
+                                       const ArrayList* synced_dirs, size_t max_delete,
+                                       const DeleteSkipEntry* skips, int skip_count,
+                                       const FilterRuleList* protect_rules, size_t* deleted_out,
+                                       size_t* skipped_out);
+
+/* Optional per-deletion observer: called for each destination-relative path
+   actually removed (a file, symlink, or directory), in removal order, so the
+   receiver can stream rsync's `--info=del`/`--info=remove` lines. */
+typedef void (*DeletePathObserver)(void* context, const char* rel_path);
+
+/* `delete_extras_limited_observed` is delete_extras_limited with an optional
+ * observer; the observer is invoked only for entries truly removed.  When
+ * `protect_rules` is non-NULL its receiver-side verdict is evaluated for every
+ * candidate extra: a first-match PROTECT leaves the entry (and, for a
+ * directory, its whole subtree) in place, while RISK/NONE fall through to the
+ * ordinary skip-prefix/keep-set logic. */
+DeleteWalkResult delete_extras_limited_observed(const char* dest_root, const ArrayList* manifest,
+                                                const ArrayList* synced_dirs, size_t max_delete,
+                                                const DeleteSkipEntry* skips, int skip_count,
+                                                const FilterRuleList* protect_rules,
+                                                size_t* deleted_out, size_t* skipped_out,
+                                                DeletePathObserver observer,
+                                                void* observer_context);
+/* Read-only companion to delete_extras_limited: walk the destination exactly as
+   the delete pass would and APPEND (strdup'd) destination-relative paths that
+   WOULD be removed, without touching disk.  Used for -n/--dry-run --delete
+   would-delete reporting.  Returns true on a clean walk; the caller owns the
+   strings appended to `out` and receives their count in *count_out. */
+bool delete_extras_list(const char* dest_root, const ArrayList* manifest,
+                        const ArrayList* synced_dirs, const DeleteSkipEntry* skips, int skip_count,
+                        const FilterRuleList* protect_rules, ArrayList* out, size_t* count_out);
 bool delete_extras(const char* dest_root, const ArrayList* manifest);
+/* Open the existing destination directory at `dest_root`, confined to the
+   authorized root with an O_NOFOLLOW component walk (the same confinement the
+   deletion walker uses for its root).  Returns a new fd the caller owns, or -1
+   on error (including a destination that does not exist). */
+int utils_open_authorized_destination(const char* dest_root);
 bool utils_set_authorized_root(int fd, const char* canonical_path);
 /* The fd-only compatibility form is fail-closed for path-based operations;
  * callers should use utils_set_authorized_root with the canonical identity. */
@@ -161,6 +209,11 @@ const char* utils_get_authorized_root_path(void);
  * callers guarantee this); this is containment by string, not by resolved
  * symlinks.  Shared by the utils and file secure-walk root confinement. */
 bool path_is_within_root(const char* root, const char* path);
+/* Non-allocating transfer-relative view of `path`: strip any leading '/' and
+ * then a `root` prefix (leading/trailing slashes tolerated), returning a
+ * borrowed pointer into `path`.  A NULL/empty root, or a path not under
+ * `root`, yields just the leading-slash strip.  `path`/`root` must stay alive. */
+const char* utils_strip_transfer_root(const char* path, const char* root);
 /* True when `path` contains a ".." component.  This is a purely lexical
  * dot-dot check: an absolute path is NOT rejected here, because default
  * (non-relative) transfers legitimately put the sender's absolute source path

src/shared/xattr.c

@@ -2,6 +2,7 @@
 #include "xattr.h"
 #include "identity.h"
 #include "log.h"
+#include "metadata.h"
 #include "protocol.h"
 #include "utils.h"
 #include "file_types.h"
@@ -37,6 +38,22 @@ void xattr_list_free(FileXattrList* list) {
   free(list);
 }
 
+FileXattrList* xattr_list_clone(const FileXattrList* list) {
+  if (!list)
+    return NULL;
+  FileXattrList* clone = xattr_list_new();
+  if (!clone)
+    return NULL;
+  for (int i = 0; i < list->count; i++) {
+    if (!xattr_list_append(clone, list->items[i].name, list->items[i].value,
+                           list->items[i].value_len)) {
+      xattr_list_free(clone);
+      return NULL;
+    }
+  }
+  return clone;
+}
+
 bool xattr_list_append(FileXattrList* list, const char* name, const void* value, size_t value_len) {
   if (!list || !name || (!value && value_len != 0))
     return false;
@@ -364,26 +381,12 @@ void fake_super_store_fd(int fd, uint32_t uid, uint32_t gid, uint32_t mode, int6
   }
 }
 
-/* --fake-super replay: read the freshly-stored record and re-apply the source
- * stat fd-relative.  A privileged (root) run can actually change the owner;
- * a non-root run silently skips the fchown on EPERM/EACCES (never fatal,
- * mirroring the normal metadata identity path; other errors are logged) and
- * still applies mode/mtime where permitted.
- *
- * The OWNER leg additionally honors three policies:
- *   - an explicit ownership identity policy must be active (numeric-ids /
- *     chown / usermap / groupmap / copy-as).  --fake-super on its own only
- *     RECORDS the source owner; replaying that owner as a live chown without an
- *     explicit ownership opt-in would be an un-gated client-chosen-ownership
- *     primitive.
- *   - --no-super (privilege_super_permitted() false) suppresses it even for a
- *     root receiver, exactly like the normal metadata identity path.
- *   - an active --copy-as is AUTHORITATIVE: the identity path already forced the
- *     target owner, so replaying the recorded source owner here would silently
- *     override it.  The xattr record is still stored/replayed for a later
- *     privileged restore; only the live chown is skipped.  Mode/mtime remain
- *     applied either way so unprivileged --fake-super still works. */
-bool fake_super_restore_fd(int fd) {
+/* --fake-super replay: read the freshly-stored record and re-apply mode/mtime
+ * fd-relative.  The recorded uid/gid are retained for a later privileged
+ * restore but are NEVER chowned here: --fake-super only RECORDS ownership, it
+ * must not real-chown the recorded (resolved) owner.  Mode/mtime still apply so
+ * unprivileged --fake-super keeps working. */
+bool fake_super_restore_fd(int fd, FileAttrPolicy policy) {
   if (fd < 0)
     return false;
   char record[128];
@@ -398,28 +401,37 @@ bool fake_super_restore_fd(int fd) {
       5)
     return false; /* malformed record: skip, never fatal */
 
-  /* Owner is applied best-effort only: a non-root process cannot chown and
-     must not abort the transfer for that reason (FastSync identity philosophy).
-     EPERM/EACCES (expected for a non-root receiver) are skipped silently; a
-     genuine EINVAL (an impossible stored id) is logged so the corruption is
-     not hidden.  --no-super suppresses the owner leg even for root, and an
-     active --copy-as is authoritative so its forced owner must not be
-     overwritten by the recorded source owner. */
-  if (identity_active_enabled() && privilege_super_permitted() && !identity_copy_as_active() &&
-      fchown(fd, (uid_t)ul_uid, (gid_t)ul_gid) != 0 && errno != EPERM && errno != EACCES)
-    log_message(LOG_LEVEL_WARNING, "--fake-super: could not restore owner on destination file: %s",
-                strerror(errno));
-  /* Mode is applied through the same sanitization the normal metadata path
-     uses (metadata_mode): group/other write bits are never granted, so a
-     recorded source mode of 0666 restores as 0644 — identical to a non-fake-
-     super --preserve run, never a privilege-granting regression. */
-  if (fchmod(fd, (mode_t)(ul_mode & 0777U & ~(S_IWGRP | S_IWOTH))) != 0)
-    log_message(LOG_LEVEL_WARNING, "--fake-super: could not restore mode on destination file: %s",
-                strerror(errno));
-  struct timespec times[2] = {{.tv_sec = 0, .tv_nsec = UTIME_OMIT},
-                              {.tv_sec = (time_t)mtime_sec, .tv_nsec = mtime_nsec}};
-  if (futimens(fd, times) != 0)
-    log_message(LOG_LEVEL_WARNING, "--fake-super: could not restore mtime on destination file: %s",
-                strerror(errno));
+  /* --fake-super NEVER performs a real chown: that would defeat the whole
+     point of the flag (record privileged ownership on an unprivileged receiver
+     for a later privileged restore).  The uid/gid parsed above are retained in
+     the record for that later restore, but no ownership change happens here. */
+  (void)ul_uid;
+  (void)ul_gid;
+  /* Mode is applied only when the per-attribute policy asks for it, through the
+     SAME shared helper the normal metadata path uses (metadata_mode_for_policy):
+     under --perms the recorded source mode is copied exactly, including
+     group/other write and setuid/setgid/sticky bits (rsync parity), and the -E
+     rule derives exec bits from the destination's read bits exactly like
+     file_restore_metadata_fd. */
+  if (policy.perms || policy.executability) {
+    struct stat cur;
+    mode_t want = 0;
+    if (fstat(fd, &cur) != 0) {
+      log_message(LOG_LEVEL_WARNING, "--fake-super: could not read destination mode: %s",
+                  strerror(errno));
+    } else if (metadata_mode_for_policy((mode_t)ul_mode, cur.st_mode, policy, &want)) {
+      if (fchmod(fd, want) != 0)
+        log_message(LOG_LEVEL_WARNING,
+                    "--fake-super: could not restore mode on destination file: %s",
+                    strerror(errno));
+    }
+  }
+  if (policy.times) {
+    struct timespec times[2] = {{.tv_sec = 0, .tv_nsec = UTIME_OMIT},
+                                {.tv_sec = (time_t)mtime_sec, .tv_nsec = mtime_nsec}};
+    if (futimens(fd, times) != 0)
+      log_message(LOG_LEVEL_WARNING,
+                  "--fake-super: could not restore mtime on destination file: %s", strerror(errno));
+  }
   return true;
-}
+}

src/shared/xattr.h

@@ -1,6 +1,7 @@
 #ifndef XATTR_H
 #define XATTR_H
 
+#include "file_attr.h"
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
@@ -55,6 +56,8 @@ typedef struct {
 
 FileXattrList* xattr_list_new(void);
 void xattr_list_free(FileXattrList* list);
+/* Deep-copy `list` (NULL in, NULL out).  Returns NULL on allocation failure. */
+FileXattrList* xattr_list_clone(const FileXattrList* list);
 /* Append one entry (deep copy).  Returns false on allocation failure. */
 bool xattr_list_append(FileXattrList* list, const char* name, const void* value, size_t value_len);
 
@@ -95,15 +98,17 @@ void fake_super_store_fd(int fd, uint32_t uid, uint32_t gid, uint32_t mode, int6
                          int64_t mtime_nsec);
 
 /* --fake-super replay: parse the FAKESUPER_XATTR record previously written on
- * `fd` by fake_super_store_fd and re-apply uid/gid/mode/mtime fd-relative.
- * Best-effort: absence of the xattr or a malformed record is a silent no-op
- * that never fails the transfer.  The OWNER leg is applied only when an explicit
- * ownership identity policy is active (numeric-ids/chown/usermap/groupmap/
- * copy-as), when super-user activities are permitted, and when --copy-as is not
- * authoritative; a non-root EPERM/EACCES is skipped silently, matching
- * FastSync's identity philosophy.  The mode is sanitized exactly like the normal
- * metadata path (group/other write bits never granted).  Returns true when the
- * xattr was present and parsed. */
-bool fake_super_restore_fd(int fd);
+ * `fd` by fake_super_store_fd and re-apply mode/mtime fd-relative.  The
+ * recorded uid/gid are deliberately NOT chowned for real: --fake-super only
+ * RECORDS ownership (the caller stores the resolved mapping via
+ * identity_resolve_storage_ids), it never performs a real chown.  Best-effort:
+ * absence of the xattr or a malformed record is a silent no-op that never fails
+ * the transfer.  The MODE leg is applied only when policy.perms||policy.
+ * executability and the MTIME leg only when policy.times, so the fake-super
+ * replay cannot bypass the per-attribute split; the mode follows the normal
+ * metadata path exactly (under --perms the source mode is copied verbatim,
+ * special and group/other write bits included).
+ * Returns true when the xattr was present and parsed. */
+bool fake_super_restore_fd(int fd, FileAttrPolicy policy);
 
 #endif

test_data-manual/dst/f.bin

@@ -0,0 +1 @@
+OLDDEST

test_data-manual/dst/test_data-manual/src/f.bin

@@ -0,0 +1 @@
+NEWCONTENT

test_data-manual/src/f.bin

@@ -0,0 +1 @@
+NEWCONTENT

tests/fuzz/fuzz_config_receive.c

@@ -115,7 +115,16 @@ static void build_canonical_frame(void) {
   if (cfg->usermap) {
     cfg->usermap_count = 1;
     cfg->usermap[0].from = MAP_FROM;
+    cfg->usermap[0].from_hi = MAP_FROM;
     cfg->usermap[0].to = MAP_TO;
+    cfg->usermap[0].to_name = NULL;
+  }
+  /* Force a non-empty receiver delete-protection block so the fuzzer mutates
+   * its rule count, action/sides codes and pattern strings. */
+  cfg->filters = array_list_create(free);
+  if (cfg->filters) {
+    array_list_add(cfg->filters, str_dup("P *.log"));
+    array_list_add(cfg->filters, str_dup("+r keep/**"));
   }
   if (!cfg->send_directory || !cfg->receive_root_directory || !cfg->usermap) {
     config_delete(cfg);

tests/integration/README.md

@@ -0,0 +1,80 @@
+# Integration tests
+
+The integration suite drives the built `build/server` and `build/client`
+against local corpora. Unit tests live in `tests/` (the custom C framework);
+the Python suite here covers the full transfer pipeline, transports, features,
+and rsync parity.
+
+## Running
+
+```bash
+# Full suite (excludes privilege-dependent tests on CI runners)
+python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"
+
+# Fast PR subset only
+python3 -m pytest tests/integration/ -n 4 --dist=load -m ci
+```
+
+The tests expect `build/server` and `build/client` (configure/build with CMake
+first); `common.py` derives `BUILD_DIR` from the repository root.
+
+## Differential rsync-parity gate
+
+`test_differential_parity.py` runs the **same** transfer with real
+`rsync 3.4.1` and with FastSync over separate destinations, then compares:
+
+- the destination trees — relative paths, file content hashes, symlink
+  targets, modes (where the case is about perms), and hard-link grouping;
+- the normalized stdout for output-oriented flags (`-i`,
+  `--out-format=...`, `--stats`), after stripping volatile fields
+  (timings, rates, wire byte counts) and directory-only itemize lines that
+  FastSync's recursive scanner documents as absent.
+
+FastSync mirrors the absolute source path under its receive root (see
+`get_dest_received_dir`); the harness normalizes that layout (and the
+`-R`/`--files-from` layouts) before comparing.
+
+```bash
+# Fast subset that guards the ✅ surface on pull requests
+python3 -m pytest tests/integration/test_differential_parity.py -n 4 --dist=load -m parity_ci
+
+# Full differential case table (`_CASES`): every row is marked `parity`, and a
+# case with an allowlisted residual in `parity_caveats.py` is included too.
+python3 -m pytest tests/integration/test_differential_parity.py -n 4 --dist=load -m parity
+```
+
+`-m parity` selects only the `_CASES` table in this module. Differential
+coverage for options outside that table (`--temp-dir`, `--delay-updates`,
+`--dry-run`, `--fuzzy`, the basis-dir options, `-M` over daemon/TCP, and
+receiver filter-protect) lives in dedicated modules (`test_option_parity.py`,
+`test_parity_blockers.py`, `test_parity_quickwins.py`, ...) and is not part of
+this gate. The suite skips cleanly when `rsync` is not installed.
+
+## Allowlist (`parity_caveats.py`)
+
+`parity_caveats.py` is the single data-driven allowlist of known differences.
+Each entry maps a case id to the aspects that may differ (`tree`, `stdout`,
+`extra`, `rc`) and cites the governing row in `RSYNC_COMPAT.md`:
+
+```python
+CAVEATS = {
+    # no known residuals at present -- the burn-down reached zero
+    # "some_case_id": {"tree": "documented residual ... ref: RSYNC_COMPAT.md ..."},
+}
+```
+
+A differential mismatch in an aspect that is **not** listed fails the gate with
+a readable tree/stdout diff.
+
+If a case is allowlisted but now matches rsync, the gate emits a loud warning
+naming the stale entry — that is the parity burn-down signal. Run with
+`FASTSYNC_PARITY_STRICT=1` to make stale entries fail instead (the full CI
+parity job sets this). To add a residual:
+
+1. Reproduce it with `-m parity` and read the failure's tree/stdout diff.
+2. Confirm it is a documented `⚠️`/`❌` residual (or get the `✅` row
+   reclassified) and cite the row.
+3. Add the case id and aspect(s) to `CAVEATS`, keeping the reason concise.
+
+Do not allowlist an undocumented divergence from a `✅` row — fix it or get the
+row reclassified first.

tests/integration/common.py

@@ -101,9 +101,15 @@ class CountingProxy:
                 return
             counter[0] += len(data)
 
-    def run(self, cmd):
+    def run(self, cmd, join_timeout=20):
         """Forward one client run (the full command list) to the real server and
-        return the CompletedProcess after the counts have settled."""
+        return the CompletedProcess after the counts have settled.
+
+        ``join_timeout`` bounds how long to wait for the forwarding threads.  The
+        client->server count is published as soon as the client side reaches EOF
+        (i.e. once the client process has exited), so callers that only need that
+        count can pass a small value instead of waiting for the server to close
+        its idle socket."""
 
         def serve():
             try:
@@ -119,15 +125,15 @@ class CountingProxy:
             a.start()
             b.start()
             a.join()
-            b.join()
             self.client_to_server = c2s[0]
+            b.join()
             self.server_to_client = s2c[0]
             self._listener.close()
 
-        thread = threading.Thread(target=serve)
+        thread = threading.Thread(target=serve, daemon=True)
         thread.start()
         result = subprocess.run(cmd, capture_output=True, text=True, timeout=180)
-        thread.join(20)
+        thread.join(join_timeout)
         return result
 
 
@@ -254,6 +260,13 @@ def _wait_for_port(port, timeout=5):
 
 
 def _wait_proc(proc, timeout=5):
+    """Stop a long-lived subprocess promptly.  The server installs a SIGTERM
+    handler, so signal first and only escalate to SIGKILL if it does not exit;
+    waiting without signalling would burn the full timeout on every stop."""
+    if proc.poll() is not None:
+        proc.wait()
+        return
+    proc.terminate()
     try:
         proc.wait(timeout=timeout)
     except subprocess.TimeoutExpired:

tests/integration/parity_caveats.py

@@ -0,0 +1,34 @@
+"""Data-driven allowlist for the differential rsync-parity gate.
+
+Every entry maps a case id (see ``test_differential_parity.py``) to the aspects
+that are *known* to differ from ``rsync 3.4.1`` and the documented reason.  A
+differential mismatch in an aspect that is **not** listed here fails the gate.
+
+Aspect keys
+-----------
+``tree``    destination tree differs (paths, file hashes, symlink targets,
+            modes, hardlink grouping)
+``stdout``  normalized output for ``-i`` / ``--stats`` / ``--out-format``
+``extra``   a case-specific assertion differs (basis/inode checks, ...)
+``rc``      exit status differs
+
+Burn-down
+---------
+If a case is listed here but now matches rsync, the gate emits a loud
+``pytest`` warning naming the stale entry: delete the entry (and, when the
+underlying row in ``RSYNC_COMPAT.md`` is now parity, update that row).  Set
+``FASTSYNC_PARITY_STRICT=1`` to turn stale entries into failures in CI.
+
+Keep the values concise but cite the governing row so the entry can be
+re-triaged when the row moves.
+"""
+
+# case id -> {aspect: "reason (ref: RSYNC_COMPAT.md ...)"}
+CAVEATS = {}
+
+# Accepted aspect names (guards against typos in this file).
+ASPECTS = ("tree", "stdout", "extra", "rc")
+
+
+def caveat_for(case_id: str) -> dict:
+    return CAVEATS.get(case_id, {})

tests/integration/parity_harness.py

@@ -0,0 +1,584 @@
+"""Differential rsync-parity harness.
+
+Runs the SAME transfer with real ``rsync`` and with FastSync over separate
+destinations and compares the resulting trees and (optionally) normalized
+stdout.  ``test_differential_parity.py`` drives this module with a table of
+cases; ``parity_caveats.py`` is the data-driven allowlist of documented
+residuals.
+
+Design notes
+------------
+FastSync mirrors the *absolute* source path below its receive root, while
+rsync copies the source contents directly into the destination.  ``Case.layout``
+tells the harness which pair of directory roots to compare:
+
+* ``MIRROR``     -- rsync ``DEST/`` vs FastSync ``DEST/<abs-src>/`` (the common
+  case; matches ``common.get_dest_received_dir``).
+* ``MIRROR_ABS`` -- ``rsync -R`` without a cut lays the full absolute path
+  under the destination, so rsync ``DEST/<abs-src>/`` is compared against the
+  same FastSync mirror path.
+* ``RELATIVE``   -- ``rsync -R --files-from`` lays bare relative paths under the
+  destination and FastSync does the same, so both destination roots compare
+  directly.
+
+Only ``tests/integration/common.py`` is used to reach the build products and the
+server manager; the harness never duplicates that plumbing.
+"""
+import difflib
+import hashlib
+import os
+import re
+import shutil
+import subprocess
+import sys
+from dataclasses import dataclass
+from typing import Callable, Dict, List, Optional, Tuple
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (  # noqa: E402  (path bootstrap above)
+    TEST_DATA_DIR,
+    clean_dir,
+    get_dest_received_dir,
+    run_client,
+)
+
+RSYNC = shutil.which("rsync")
+
+# Comparison layouts (see module docstring).
+MIRROR = "mirror"
+MIRROR_ABS = "mirror_abs"
+RELATIVE = "relative"
+
+# stdout comparators.
+STDOUT_NONE = None
+STDOUT_ITEMIZE = "itemize"
+STDOUT_OUTFMT = "outfmt"
+STDOUT_STATS = "stats"
+STDOUT_PROGRESS = "progress"
+
+# rsync --stats lines that are protocol-independent and must match exactly.
+# `Number of files` and `Number of created files` carry rsync's per-type
+# breakdown; protocol 2.28.0 reports the receiver-created split over
+# STATUS_STATS.  Deliberately excluded: Total bytes sent/received (protocol
+# framing differs, see the `--stats` row in RSYNC_COMPAT.md).
+STATS_KEYS = (
+    "Number of files",
+    "Number of created files",
+    "Number of deleted files",
+    "Number of regular files transferred",
+    "Total file size",
+    "Total transferred file size",
+    "Literal data",
+    "Matched data",
+    "File list size",
+)
+
+_ITEMIZE_RE = re.compile(r"^(<|>|c|h|\.|\*)[fdLDS][.+\-][.+\-][.+\-][.+\-]")
+_PROGRESS_TOTAL_RE = re.compile(r"to-chk=\d+/(\d+)")
+_PROGRESS_XFR_RE = re.compile(r"xfr#(\d+)")
+
+
+@dataclass
+class Case:
+    """One differential scenario: a corpus, a flag set, and how to compare."""
+
+    id: str
+    corpus: str
+    flags: List[str]
+    fastsync_flags: Optional[List[str]] = None
+    layout: str = MIRROR
+    server_args: Tuple[str, ...] = ("--allow-super",)
+    seed: Optional[Callable] = None
+    stdout: Optional[str] = STDOUT_NONE
+    compare_modes: bool = False
+    compare_hardlinks: bool = False
+    ignore_paths: Tuple[str, ...] = ()
+    extra_check: Optional[Callable] = None
+    files_from: Optional[Tuple[str, ...]] = None
+    # rsync receives ``src + "/"``; FastSync mirrors the path it is given, so a
+    # trailing-slash-sensitive case must hand FastSync the same form.
+    fs_src_suffix: str = ""
+    # Some cases have an unspecified result (e.g. which extras survive a
+    # partial --max-delete abort): assert the case-specific invariants via
+    # extra_check and skip the exact-tree comparison.
+    compare_tree: bool = True
+    ci: bool = False
+    ref: str = ""
+
+    def fs_flags(self) -> List[str]:
+        return list(self.flags if self.fastsync_flags is None else self.fastsync_flags)
+
+
+# ---------------------------------------------------------------------------
+# Corpora
+# ---------------------------------------------------------------------------
+
+# Deterministic mtimes so quick-check decisions are reproducible.
+_SRC_MTIME = 1_600_000_000
+
+
+def _write(path: str, data: bytes, mode: Optional[int] = None) -> None:
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    with open(path, "wb") as fh:
+        fh.write(data)
+    os.utime(path, (_SRC_MTIME, _SRC_MTIME))
+    if mode is not None:
+        os.chmod(path, mode)
+
+
+def _set_mode(path: str, mode: int) -> None:
+    os.chmod(path, mode)
+
+
+def corpus_basic(root: str) -> None:
+    """Regular files + nested dirs (dirs are implied by their files)."""
+    clean_dir(root)
+    _write(os.path.join(root, "a.txt"), b"hello world\n")
+    _write(os.path.join(root, "sub", "b.bin"),
+           bytes((i * 7) & 0xFF for i in range(5000)))
+    _write(os.path.join(root, "sub", "deep", "c.txt"), "w\u00f6rld\n".encode())
+
+
+def corpus_unicode(root: str) -> None:
+    clean_dir(root)
+    _write(os.path.join(root, "uni \u00f1\u6587.txt"), b"unicode\n")
+    _write(os.path.join(root, "sub", "sp ace \u00e9.dat"), b"spaced\n")
+    _set_mode(os.path.join(root, "sub"), 0o750)
+
+
+def corpus_links(root: str) -> None:
+    corpus_basic(root)
+    os.symlink("a.txt", os.path.join(root, "rel_link"))
+    os.symlink("/etc/hostname", os.path.join(root, "abs_link"))
+    os.symlink("nowhere/target", os.path.join(root, "broken_link"))
+
+
+def corpus_hardlinks(root: str) -> None:
+    clean_dir(root)
+    _write(os.path.join(root, "h1.txt"), b"hardlinked payload\n")
+    os.link(os.path.join(root, "h1.txt"), os.path.join(root, "h2.txt"))
+    _write(os.path.join(root, "other.txt"), b"other\n")
+
+
+def corpus_sparse(root: str) -> None:
+    clean_dir(root)
+    _write(os.path.join(root, "small.txt"), b"small\n")
+    sparse = os.path.join(root, "sparse.bin")
+    with open(sparse, "wb") as fh:
+        fh.seek(1024 * 1024 - 1)
+        fh.write(b"\0")
+    os.utime(sparse, (_SRC_MTIME, _SRC_MTIME))
+
+
+def corpus_filters(root: str) -> None:
+    clean_dir(root)
+    _write(os.path.join(root, "keep.txt"), b"keep\n")
+    _write(os.path.join(root, "drop.log"), b"log\n")
+    _write(os.path.join(root, "sub", "keep2.txt"), b"keep2\n")
+    _write(os.path.join(root, "sub", "drop2.log"), b"log2\n")
+    _write(os.path.join(root, "sub", "data.bin"), b"bin\n")
+
+
+def corpus_empty_dir(root: str) -> None:
+    clean_dir(root)
+    _write(os.path.join(root, "keep.txt"), b"keep\n")
+    os.makedirs(os.path.join(root, "emptydir"), exist_ok=True)
+    os.utime(os.path.join(root, "emptydir"), (_SRC_MTIME, _SRC_MTIME))
+    _write(os.path.join(root, "nonempty", "f.txt"), b"f\n")
+
+
+def corpus_multidir(root: str) -> None:
+    """Multi-directory tree for the --progress file-list naming/denominator.
+
+    Nested files, a directory-only branch, an empty directory and a symlink
+    exercise every file-list entry type rsync counts in `to-chk` but FastSync's
+    streaming scanner never emits as a transfer entry.
+    """
+    clean_dir(root)
+    _write(os.path.join(root, "a.txt"), b"alpha\n")
+    _write(os.path.join(root, "b.txt"), b"bravo\n")
+    _write(os.path.join(root, "sub1", "c.txt"), b"charlie\n")
+    _write(os.path.join(root, "sub1", "deep", "d.txt"), b"delta\n")
+    _write(os.path.join(root, "sub2", "e.txt"), b"echo\n")
+    os.symlink("a.txt", os.path.join(root, "link1"))
+    os.makedirs(os.path.join(root, "emptydir"), exist_ok=True)
+    os.utime(os.path.join(root, "emptydir"), (_SRC_MTIME, _SRC_MTIME))
+
+
+def corpus_relative(root: str) -> None:
+    """Tree for the -R/--files-from cases."""
+    clean_dir(root)
+    _write(os.path.join(root, "a.txt"), b"a\n")
+    _write(os.path.join(root, "b.txt"), b"b\n")
+    _write(os.path.join(root, "sub", "x.txt"), b"x\n")
+    _write(os.path.join(root, "sub", "y.txt"), b"y\n")
+    os.makedirs(os.path.join(root, "dir1"), exist_ok=True)
+    os.utime(os.path.join(root, "dir1"), (_SRC_MTIME, _SRC_MTIME))
+    _write(os.path.join(root, "dir1", "keep.txt"), b"keep\n")
+
+
+def corpus_iconv(root: str) -> None:
+    """Latin-1 (ISO-8859-1) encoded filenames, matching the --iconv direction."""
+    clean_dir(root)
+    for rel, data in ((b"caf\xe9.txt", b"caf\xe9\n"),
+                      (os.path.join(b"sub", b"\xfcber.txt"), b"\xfcber\n")):
+        full = os.path.join(os.fsencode(root), rel)
+        os.makedirs(os.path.dirname(full), exist_ok=True)
+        with open(full, "wb") as fh:
+            fh.write(data)
+        os.utime(full, (_SRC_MTIME, _SRC_MTIME))
+
+
+# Payload for the --fuzzy basis corpus: large enough for the delta engine's
+# 16 KiB minimum and with repeated content so a coinciding basis yields a
+# non-zero (and identical) Matched data count in both tools.
+FUZZY_PAYLOAD = (b"the quick brown fox jumps over the lazy dog\n" * 2000)[:65536]
+
+
+def corpus_fuzzy(root: str) -> None:
+    """A named regular file; the `fuzzy` seed adds the similar-suffix sibling."""
+    clean_dir(root)
+    _write(os.path.join(root, "report_v2.txt"), FUZZY_PAYLOAD)
+
+
+CORPORA: Dict[str, Callable[[str], None]] = {
+    "basic": corpus_basic,
+    "unicode": corpus_unicode,
+    "links": corpus_links,
+    "hardlinks": corpus_hardlinks,
+    "sparse": corpus_sparse,
+    "filters": corpus_filters,
+    "empty_dir": corpus_empty_dir,
+    "multidir": corpus_multidir,
+    "relative": corpus_relative,
+    "iconv": corpus_iconv,
+    "fuzzy": corpus_fuzzy,
+}
+
+
+# ---------------------------------------------------------------------------
+# Tree snapshotting / comparison
+# ---------------------------------------------------------------------------
+
+def snapshot(root: str, compare_modes: bool = False) -> Dict[str, tuple]:
+    """Map relative path -> descriptor for every entry below ``root``.
+
+    Files hash their contents with SHA-256 (structural comparison, so differing
+    quick-check metadata cannot mask a payload difference).  Symlinks record
+    their target.  Empty directories are included (as ``("dir", ...)``) so the
+    recursive-empty-directory residual is observable.
+    """
+    out: Dict[str, tuple] = {}
+    if not os.path.isdir(root):
+        return out
+
+    def describe(path: str) -> Optional[tuple]:
+        st = os.lstat(path)
+        if os.path.islink(path):
+            return ("link", os.readlink(path))
+        if os.path.isdir(path):
+            mode = oct(st.st_mode & 0o7777) if compare_modes else None
+            return ("dir", mode)
+        h = hashlib.sha256()
+        with open(path, "rb") as fh:
+            for chunk in iter(lambda: fh.read(65536), b""):
+                h.update(chunk)
+        mode = oct(st.st_mode & 0o7777) if compare_modes else None
+        return ("file", h.hexdigest()[:16], mode)
+
+    # The comparison root itself is not part of the tree diff: a no-transfer
+    # result legitimately leaves FastSync's mirror directory absent while rsync
+    # leaves an existing (empty) destination root.
+    for dirpath, dirnames, filenames in os.walk(root, followlinks=False):
+        dirnames.sort()
+        for name in sorted(dirnames):
+            p = os.path.join(dirpath, name)
+            rel = os.path.relpath(p, root)
+            if os.path.islink(p):
+                out[rel] = ("link", os.readlink(p))
+                dirnames.remove(name)
+            else:
+                out[rel] = describe(p)
+        for name in sorted(filenames):
+            p = os.path.join(dirpath, name)
+            out[os.path.relpath(p, root)] = describe(p)
+    return out
+
+
+def _hardlink_groups(root: str) -> Dict[str, str]:
+    """Assign a stable group letter to each inode shared by >1 regular file."""
+    inodes: Dict[tuple, List[str]] = {}
+    for dirpath, _dirs, filenames in os.walk(root, followlinks=False):
+        for name in filenames:
+            p = os.path.join(dirpath, name)
+            if os.path.islink(p):
+                continue
+            st = os.lstat(p)
+            if st.st_nlink > 1:
+                inodes.setdefault((st.st_dev, st.st_ino), []).append(
+                    os.path.relpath(p, root))
+    groups: Dict[str, str] = {}
+    for i, (_key, members) in enumerate(sorted(inodes.items())):
+        for rel in members:
+            groups[rel] = chr(ord("A") + i)
+    return groups
+
+
+def _drop_ignored(tree: Dict[str, tuple], ignore_paths) -> Dict[str, tuple]:
+    if not ignore_paths:
+        return tree
+    out = {}
+    for rel, desc in tree.items():
+        if any(rel == ig or rel.startswith(ig.rstrip("/") + "/") for ig in ignore_paths):
+            continue
+        out[rel] = desc
+    return out
+
+
+def tree_diff(rsync_root: str, fs_root: str, case: Case) -> List[str]:
+    """Return a list of human-readable differences (empty when identical)."""
+    rtree = _drop_ignored(snapshot(rsync_root, case.compare_modes), case.ignore_paths)
+    ftree = _drop_ignored(snapshot(fs_root, case.compare_modes), case.ignore_paths)
+    if case.compare_hardlinks:
+        rgroups = _hardlink_groups(rsync_root)
+        fgroups = _hardlink_groups(fs_root)
+    else:
+        rgroups = fgroups = {}
+    diffs: List[str] = []
+    for rel in sorted(set(rtree) | set(ftree)):
+        r = rtree.get(rel)
+        f = ftree.get(rel)
+        if r == f:
+            continue
+        if r is None:
+            diffs.append(f"+ fastsync-only: {rel!r} {f}")
+        elif f is None:
+            diffs.append(f"- rsync-only:    {rel!r} {r}")
+        else:
+            diffs.append(f"~ differs:       {rel!r} rsync={r} fastsync={f}")
+    if case.compare_hardlinks:
+        for rel in sorted(set(rgroups) | set(fgroups)):
+            if rgroups.get(rel) != fgroups.get(rel):
+                diffs.append(
+                    f"~ hardlink group: {rel!r} rsync={rgroups.get(rel)} "
+                    f"fastsync={fgroups.get(rel)}")
+    return diffs
+
+
+# ---------------------------------------------------------------------------
+# stdout normalization
+# ---------------------------------------------------------------------------
+
+def _parse_bytes(text: str) -> str:
+    m = re.match(r"([\d,]+)", text.strip())
+    return m.group(1).replace(",", "") if m else text.strip()
+
+
+def normalize_stdout(text: str, mode: Optional[str]) -> object:
+    if mode == STDOUT_ITEMIZE:
+        lines = []
+        for line in (text or "").splitlines():
+            line = line.rstrip()
+            if not line:
+                continue
+            if line.startswith("*deleting"):
+                lines.append(line)
+                continue
+            if not _ITEMIZE_RE.match(line):
+                continue
+            # Directories are not transfer entries in FastSync's recursive
+            # scanner, so rsync's `cd+++++++++ name/` lines have no counterpart
+            # (documented recursive-empty-dir residual).  Compare file/link
+            # itemization only.
+            if line.rsplit(" ", 1)[-1].endswith("/"):
+                continue
+            lines.append(line)
+        return sorted(lines)
+    if mode == STDOUT_OUTFMT:
+        lines = []
+        for line in (text or "").splitlines():
+            line = line.rstrip()
+            if not line:
+                continue
+            # Directory entries are emitted by rsync but not by FastSync's
+            # recursive scanner (documented residual).  Tokens are either
+            # `%n %l` (path first) or `%i %n` (path last); drop a line when
+            # either end-token is a directory path.
+            first = line.split(" ", 1)[0]
+            last = line.rsplit(" ", 1)[-1]
+            if first.endswith("/") or last.endswith("/"):
+                continue
+            lines.append(line)
+        return sorted(lines)
+    if mode == STDOUT_STATS:
+        found = {}
+        for line in (text or "").splitlines():
+            for key in STATS_KEYS:
+                if line.startswith(key + ":"):
+                    found[key] = _parse_bytes(line.split(":", 1)[1])
+        return found
+    if mode == STDOUT_PROGRESS:
+        # rsync prints the file-list entries in sorted depth-first order while
+        # FastSync's streaming scan emits them in readdir/BFS order; only the
+        # entry set and deterministic fields are compared.  The transfer-root
+        # `./` line's trigger condition is a separate documented residual, and
+        # the per-frame rate/elapsed/xfr#/to-chk numerator are wall-clock- or
+        # order-dependent, so only the `to-chk` denominator and the name set are
+        # asserted.
+        names = []
+        totals = set()
+        max_xfr = 0
+        for line in (text or "").splitlines():
+            line = line.rstrip()
+            if not line:
+                continue
+            if "%" in line:
+                m = _PROGRESS_TOTAL_RE.search(line)
+                if m:
+                    totals.add(int(m.group(1)))
+                mx = _PROGRESS_XFR_RE.search(line)
+                if mx:
+                    max_xfr = max(max_xfr, int(mx.group(1)))
+                continue
+            if line == "sending incremental file list":
+                continue
+            if line.startswith("created directory "):
+                continue
+            if line == "./":
+                continue
+            names.append(line)
+        return {"names": sorted(names), "total": sorted(totals), "xfr": max_xfr}
+    # raw
+    return sorted(l.rstrip() for l in (text or "").splitlines() if l.strip())
+
+
+def stdout_diff(rsync_out: str, fs_out: str, mode: Optional[str]) -> List[str]:
+    r = normalize_stdout(rsync_out, mode)
+    f = normalize_stdout(fs_out, mode)
+    if r == f:
+        return []
+    if mode == STDOUT_STATS:
+        return [f"stats rsync={r}", f"stats fastsync={f}"]
+    if mode == STDOUT_PROGRESS:
+        return [f"progress rsync={r}", f"progress fastsync={f}"]
+    return list(difflib.unified_diff(
+        [str(x) for x in r], [str(x) for x in f],
+        fromfile="rsync", tofile="fastsync", lineterm=""))
+
+
+# ---------------------------------------------------------------------------
+# Running one case
+# ---------------------------------------------------------------------------
+
+def run_rsync(src: str, rdst: str, flags: List[str]) -> subprocess.CompletedProcess:
+    args = [RSYNC] + list(flags) + [src + "/", rdst + "/"]
+    return subprocess.run(
+        args, capture_output=True, text=True,
+        env=dict(os.environ, LC_ALL="C"), timeout=180)
+
+
+def run_fastsync(src: str, fdst: str, flags: List[str], port: int):
+    return run_client(src, fdst, flags=list(flags), port=port)
+
+
+def run_differential(  # noqa: PLR0913 (explicit scenario parameters)
+    src: str,
+    rdst: str,
+    fdst: str,
+    rs_flags: List[str],
+    fs_flags: List[str],
+    server,
+    layout: str = MIRROR,
+    seed: Optional[Callable] = None,
+    stdout: Optional[str] = STDOUT_NONE,
+    compare_modes: bool = False,
+    compare_hardlinks: bool = False,
+    ignore_paths: Tuple[str, ...] = (),
+    extra_check: Optional[Callable] = None,
+    files_from: Optional[Tuple[str, ...]] = None,
+    fs_src_suffix: str = "",
+    compare_tree: bool = True,
+) -> Dict[str, object]:
+    """Run one rsync/FastSync pair and return the diff aspects.
+
+    Returned dict keys: ``rsync_rc``, ``fastsync_rc``, ``rsync_stderr``,
+    ``fastsync_stderr``, ``tree``, ``stdout``, ``extra``.
+    """
+    clean_dir(rdst)
+    clean_dir(fdst)
+    abs_src = os.path.abspath(src)
+    rel = abs_src.lstrip(os.sep)
+    if layout == RELATIVE:
+        rroot, froot = rdst, fdst
+    elif layout == MIRROR_ABS:
+        rroot, froot = os.path.join(rdst, rel), get_dest_received_dir(fdst, src)
+    else:
+        rroot, froot = rdst, get_dest_received_dir(fdst, src)
+    # rsync's destination root always exists (clean_dir created it).  FastSync's
+    # logical transfer root is the mirror path below the destination argument,
+    # so pre-create it too: `Number of created files` counts the root only when
+    # it is genuinely absent, and the two tools must start from the same state.
+    os.makedirs(froot, exist_ok=True)
+    if seed:
+        seed(src, rroot, froot)
+
+    rs_flags = list(rs_flags)
+    fs_flags = list(fs_flags)
+    if files_from is not None:
+        list_path = os.path.join(TEST_DATA_DIR, "parity_" +
+                                 os.path.basename(src) + ".list")
+        write_list(list_path, files_from)
+        rs_flags.append(f"--files-from={list_path}")
+        fs_flags.append(f"--files-from={list_path}")
+
+    rs = run_rsync(src, rdst, rs_flags)
+    fs_result, _ = run_fastsync(src + fs_src_suffix, fdst, fs_flags, server.port)
+
+    class _View:
+        """Adapter so tree_diff/extra_check keep the Case-shaped interface."""
+
+        def __init__(self) -> None:
+            self.compare_modes = compare_modes
+            self.compare_hardlinks = compare_hardlinks
+            self.ignore_paths = ignore_paths
+
+    result = {
+        "rsync_rc": rs.returncode,
+        "fastsync_rc": fs_result.returncode,
+        "rsync_stderr": rs.stderr,
+        "fastsync_stderr": fs_result.stderr or fs_result.stdout,
+        "tree": tree_diff(rroot, froot, _View()) if compare_tree else [],
+        "stdout": [],
+        "extra": [],
+    }
+    if stdout is not None:
+        result["stdout"] = stdout_diff(rs.stdout, fs_result.stdout, stdout)
+    if extra_check:
+        result["extra"] = list(extra_check(src, rroot, froot, rs, fs_result) or [])
+    return result
+
+
+def execute_case(case: Case, server) -> Dict[str, object]:
+    """Run a table-driven case and return the diff aspects."""
+    tag = case.id
+    src = os.path.join(TEST_DATA_DIR, f"parity_{tag}_src")
+    rdst = os.path.join(TEST_DATA_DIR, f"parity_{tag}_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, f"parity_{tag}_fdst")
+    CORPORA[case.corpus](src)
+    return run_differential(
+        src, rdst, fdst,
+        case.flags, case.fs_flags(), server,
+        layout=case.layout, seed=case.seed, stdout=case.stdout,
+        compare_modes=case.compare_modes, compare_hardlinks=case.compare_hardlinks,
+        ignore_paths=case.ignore_paths, extra_check=case.extra_check,
+        files_from=case.files_from, fs_src_suffix=case.fs_src_suffix,
+        compare_tree=case.compare_tree,
+    )
+
+
+def write_list(path: str, entries) -> str:
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    with open(path, "w", encoding="utf-8") as fh:
+        for e in entries:
+            fh.write(e + "\n")
+    return path

tests/integration/test_client_cli.py

@@ -0,0 +1,213 @@
+"""Differential tests for the client CLI's codec defaults and env lists.
+
+Track 3a of the rsync-parity plan pins two rsync 3.4.1 behaviors that are
+resolved entirely on the client:
+
+* the per-codec default ``--compress-level`` (zstd 3, zlib/zlibx 6, lz4
+  ignored) applied when the user omits ``--compress-level``/``--zl``, with an
+  explicit level clamped to the codec's range; and
+* the ``RSYNC_COMPRESS_LIST`` / ``RSYNC_CHECKSUM_LIST`` preference lists that
+  rsync's ``auto`` consults before its compiled-in order (whitespace-separated,
+  unknown names skipped, first supported wins, all-unknown is exit 4).
+
+The rsync side is observed through ``--debug=NSTR1``; FastSync publishes its
+resolved codec/level through ``--debug=util``.  The checksum side is confirmed
+byte-for-byte through ``--out-format %C``.  The rsync-based tests skip cleanly
+when rsync is not installed.
+"""
+import os
+import re
+import shutil
+import subprocess
+import sys
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (
+    TEST_DATA_DIR,
+    run_client,
+    clean_dir,
+    get_dest_received_dir,
+)
+
+RSYNC = shutil.which("rsync")
+requires_rsync = pytest.mark.skipif(RSYNC is None, reason="rsync 3.4.1 not installed")
+
+CODEC_ROOT = os.path.join(TEST_DATA_DIR, "cli_differential")
+
+_COMPRESS_RE = re.compile(r"compress(?:ion)?: (\w+) \(level (-?\d+)\)")
+
+
+def _rsync(args):
+    env = dict(os.environ, LC_ALL="C")
+    return subprocess.run([RSYNC] + args, capture_output=True, text=True, env=env, timeout=120)
+
+
+def _scratch(tag):
+    path = os.path.join(CODEC_ROOT, tag)
+    clean_dir(path)
+    os.makedirs(path, exist_ok=True)
+    return path
+
+
+def _make_corpus(root):
+    clean_dir(root)
+    os.makedirs(root, exist_ok=True)
+    with open(os.path.join(root, "big.bin"), "wb") as fh:
+        fh.write(b"FastSync codec payload " * 4096)
+    with open(os.path.join(root, "small.txt"), "wb") as fh:
+        fh.write(b"hello codec world\n" * 32)
+    return root
+
+
+def _rsync_compress_level(choice, level):
+    src = _make_corpus(_scratch(f"lvl_src_{choice}_{level}"))
+    dst = _scratch(f"lvl_rsync_{choice}_{level}")
+    args = ["-a", "-z", f"--zc={choice}"]
+    if level is not None:
+        args.append(f"--zl={level}")
+    args += ["--debug=NSTR1", src + "/", dst + "/"]
+    result = _rsync(args)
+    assert result.returncode == 0, result.stderr
+    match = _COMPRESS_RE.search(result.stdout + result.stderr)
+    assert match, (result.stdout, result.stderr)
+    return match.group(1), int(match.group(2))
+
+
+def _fastsync_compress_level(choice, level, shared_server):
+    src = _make_corpus(_scratch(f"lvl_src_fs_{choice}_{level}"))
+    dst = _scratch(f"lvl_fs_{choice}_{level}")
+    args = ["-a", "-z", f"--zc={choice}"]
+    if level is not None:
+        args.append(f"--zl={level}")
+    args += ["-v", "--debug=util"]
+    result, _ = run_client(src, dst, flags=args, port=shared_server.port)
+    assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+    match = _COMPRESS_RE.search(result.stdout)
+    assert match, result.stdout[:500]
+    return match.group(1), int(match.group(2))
+
+
+class TestPerCodecCompressionLevelDefaults:
+    """``--compress-level`` defaults and clamping match rsync per codec."""
+
+    # FastSync uses a positive lz4 placeholder because its "level > 0" gate
+    # enables compression; lz4_compress ignores the value, so rsync's level 0
+    # and FastSync's level 1 produce the same bytes.
+    CASES = [
+        ("zstd", None, 3),
+        ("zlib", None, 6),
+        ("zlibx", None, 6),
+        ("lz4", None, 1),
+        ("zstd", 10, 10),
+        ("zlib", 15, 9),
+        ("zlib", 3, 3),
+        ("lz4", 15, 1),
+    ]
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("choice,level,fs_level", CASES)
+    def test_level_matches_rsync(self, choice, level, fs_level, shared_server):
+        rsync_algo, rsync_level = _rsync_compress_level(choice, level)
+        fs_algo, fs_level_actual = _fastsync_compress_level(choice, level, shared_server)
+        assert rsync_algo == choice
+        assert fs_algo == choice
+        if choice == "lz4":
+            assert rsync_level == 0 and fs_level_actual > 0
+        else:
+            assert rsync_level == fs_level
+            assert fs_level_actual == fs_level
+
+
+class TestEnvPreferenceLists:
+    """``RSYNC_COMPRESS_LIST`` / ``RSYNC_CHECKSUM_LIST`` drive auto like rsync."""
+
+    # (env value, expected codec, rsync level, FastSync level)
+    COMPRESS_CASES = [
+        ("zlib lz4", "zlib", 6, 6),
+        ("lz4 zstd", "lz4", 0, 1),
+        ("bogus zstd zlib", "zstd", 3, 3),
+        ("   ", "zstd", 3, 3),
+    ]
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("env,algo,rsync_level,fs_level", COMPRESS_CASES)
+    def test_compress_list_matches_rsync(self, env, algo, rsync_level, fs_level, shared_server,
+                                         monkeypatch):
+        monkeypatch.setenv("RSYNC_COMPRESS_LIST", env)
+        src = _make_corpus(_scratch(f"envc_src_{algo}"))
+        rdst = _scratch(f"envc_rsync_{algo}")
+        rs = _rsync(["-a", "-z", "--debug=NSTR1", src + "/", rdst + "/"])
+        assert rs.returncode == 0, rs.stderr
+        rm = _COMPRESS_RE.search(rs.stdout + rs.stderr)
+        assert rm, (rs.stdout, rs.stderr)
+        assert rm.group(1) == algo
+        assert int(rm.group(2)) == rsync_level
+
+        fdst = _scratch(f"envc_fs_{algo}")
+        result, _ = run_client(src, fdst, flags=["-a", "-z", "-v", "--debug=util"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        fm = _COMPRESS_RE.search(result.stdout)
+        assert fm, result.stdout[:500]
+        assert fm.group(1) == algo
+        assert int(fm.group(2)) == fs_level
+        received = get_dest_received_dir(fdst, src)
+        assert _tree_bytes(received) == _tree_bytes(src)
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("env,algo", [("md5", "md5"), ("sha1", "sha1"), ("xxh3 md5", "xxh3")])
+    def test_checksum_list_matches_rsync(self, env, algo, shared_server, monkeypatch):
+        monkeypatch.setenv("RSYNC_CHECKSUM_LIST", env)
+        src = _make_corpus(_scratch(f"envcc_src_{algo}"))
+        rdst = _scratch(f"envcc_rsync_{algo}")
+        rs = _rsync(["-a", "--checksum", "--out-format=%C %n", src + "/", rdst + "/"])
+        assert rs.returncode == 0, rs.stderr
+        rs_digests = _digests(rs.stdout)
+
+        fdst = _scratch(f"envcc_fs_{algo}")
+        result, _ = run_client(src, fdst, flags=["-a", "--checksum", "--out-format=%C %n"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        assert _digests(result.stdout) == rs_digests
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_all_unknown_lists_fail_like_rsync(self, shared_server, monkeypatch):
+        src = _make_corpus(_scratch("envbad_src"))
+        monkeypatch.setenv("RSYNC_COMPRESS_LIST", "bogus")
+        rs = _rsync(["-a", "-z", src + "/", _scratch("envbad_rsync_c") + "/"])
+        assert rs.returncode == 4, rs.stderr
+        result, _ = run_client(src, _scratch("envbad_fs_c"), flags=["-a", "-z"],
+                               port=shared_server.port)
+        assert result.returncode == 4, (result.stderr or result.stdout)[:200]
+
+        monkeypatch.setenv("RSYNC_CHECKSUM_LIST", "bogus")
+        rs = _rsync(["-a", src + "/", _scratch("envbad_rsync_s") + "/"])
+        assert rs.returncode == 4, rs.stderr
+        result, _ = run_client(src, _scratch("envbad_fs_s"), flags=["-a"],
+                               port=shared_server.port)
+        assert result.returncode == 4, (result.stderr or result.stdout)[:200]
+
+
+def _tree_bytes(root):
+    out = {}
+    for dirpath, _dirs, files in os.walk(root):
+        for name in files:
+            path = os.path.join(dirpath, name)
+            with open(path, "rb") as fh:
+                out[os.path.relpath(path, root)] = fh.read()
+    return out
+
+
+def _digests(output):
+    out = {}
+    for line in output.splitlines():
+        parts = line.split()
+        if len(parts) == 2 and parts[0]:
+            out[parts[1]] = parts[0]
+    return out

tests/integration/test_codecs.py

@@ -0,0 +1,367 @@
+"""Differential tests for --checksum-choice / --compress-choice against rsync 3.4.1.
+
+These pin the accepted/rejected algorithm matrix and exit codes to real rsync,
+and verify that every codec FastSync now offers still transfers byte-exactly.
+The rsync-based tests skip cleanly when rsync is not installed.
+
+The FastSync server confines transfers to its authorized root (the project
+directory when the shared test server is launched), so every scratch tree lives
+under ``TEST_DATA_DIR`` rather than pytest's ``tmp_path``.
+"""
+import os
+import random
+import shutil
+import subprocess
+import sys
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (
+    TEST_DATA_DIR,
+    run_client,
+    clean_dir,
+    get_dest_received_dir,
+)
+
+RSYNC = shutil.which("rsync")
+requires_rsync = pytest.mark.skipif(RSYNC is None, reason="rsync 3.4.1 not installed")
+
+CHECKSUM_NAMES = ["xxh128", "xxh3", "xxh64", "md5", "md4", "sha1"]
+COMPRESS_NAMES = ["zstd", "lz4", "zlib", "zlibx"]
+
+CODEC_ROOT = os.path.join(TEST_DATA_DIR, "codec_differential")
+
+
+def _rsync(args):
+    env = dict(os.environ, LC_ALL="C")
+    return subprocess.run([RSYNC] + args, capture_output=True, text=True, env=env, timeout=120)
+
+
+def _scratch(tag):
+    """A confined, uniquely named scratch directory under the project tree."""
+    path = os.path.join(CODEC_ROOT, tag)
+    clean_dir(path)
+    os.makedirs(path, exist_ok=True)
+    return path
+
+
+def _make_corpus(root):
+    clean_dir(root)
+    os.makedirs(os.path.join(root, "sub"), exist_ok=True)
+    # Highly compressible payload so each codec is actually exercised.
+    with open(os.path.join(root, "big.bin"), "wb") as fh:
+        fh.write(b"FastSync codec payload " * 4096)
+    with open(os.path.join(root, "sub", "text.txt"), "wb") as fh:
+        fh.write(b"hello codec world\n" * 128)
+    with open(os.path.join(root, "empty"), "wb"):
+        pass
+    return root
+
+
+def _tree_bytes(root):
+    out = {}
+    for dirpath, _dirs, files in os.walk(root):
+        for name in files:
+            path = os.path.join(dirpath, name)
+            with open(path, "rb") as fh:
+                out[os.path.relpath(path, root)] = fh.read()
+    return out
+
+
+_CC_DELTA_T0 = 1_600_000_000
+_CC_DELTA_T1 = 1_600_000_100
+
+_DELTA_STATS_KEYS = (
+    "Number of created files",
+    "Number of regular files transferred",
+    "Total transferred file size",
+    "Literal data",
+    "Matched data",
+)
+
+
+def _pin_tree(root, mtime):
+    for dirpath, dirnames, filenames in os.walk(root):
+        for name in dirnames + filenames:
+            path = os.path.join(dirpath, name)
+            if not os.path.islink(path):
+                os.utime(path, (mtime, mtime))
+    os.utime(root, (mtime, mtime))
+
+
+def _make_delta_basis(src, size=512 * 1024):
+    """Build a source and a matching pre-modification basis tree.
+
+    The source's ``big.bin`` is then modified in a few disjoint places and given
+    a newer mtime so both tools take the delta path.  Returns the basis dir.
+    """
+    clean_dir(src)
+    original = random.Random(20240101).randbytes(size)
+    with open(os.path.join(src, "big.bin"), "wb") as fh:
+        fh.write(original)
+    with open(os.path.join(src, "small.txt"), "wb") as fh:
+        fh.write(b"hello world\n")
+    _pin_tree(src, _CC_DELTA_T0)
+
+    basis = src.rstrip("/") + "_basis"
+    clean_dir(basis)
+    shutil.copy2(os.path.join(src, "big.bin"), os.path.join(basis, "big.bin"))
+    shutil.copy2(os.path.join(src, "small.txt"), os.path.join(basis, "small.txt"))
+    _pin_tree(basis, _CC_DELTA_T0)
+
+    modified = bytearray(original)
+    for off in (0, size // 3, 2 * size // 3, size - 64):
+        for i in range(32):
+            modified[off + i] ^= 0x5A
+    with open(os.path.join(src, "big.bin"), "wb") as fh:
+        fh.write(bytes(modified))
+    os.utime(os.path.join(src, "big.bin"), (_CC_DELTA_T1, _CC_DELTA_T1))
+    return basis
+
+
+def _seed_from_basis(basis, target):
+    clean_dir(target)
+    for name in os.listdir(basis):
+        shutil.copy2(os.path.join(basis, name), os.path.join(target, name))
+
+
+def _delta_stats(text):
+    found = {}
+    for line in text.splitlines():
+        for key in _DELTA_STATS_KEYS:
+            if line.startswith(key + ":"):
+                found[key] = line.split(":", 1)[1].strip()
+    return found
+
+
+def _big_bin_outfmt(text):
+    """The ``(c, C)`` pair from the ``big.bin`` out-format line (`%c|%C %n`)."""
+    for line in text.splitlines():
+        stripped = line.strip()
+        if "|" not in stripped or not stripped.endswith("big.bin"):
+            continue
+        c_field, rest = stripped.split("|", 1)
+        fields = rest.split()
+        return c_field.strip(), (fields[0] if fields else "")
+    return None, None
+
+
+class TestCodecChoiceMatrix:
+    """The CLI accept/reject set and exit codes must match rsync 3.4.1."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("name", CHECKSUM_NAMES)
+    def test_checksum_names_accepted_by_both(self, name, shared_server):
+        src = _make_corpus(_scratch(f"cc_src_{name}"))
+        rdst = _scratch(f"cc_rsync_{name}")
+        rsync_result = _rsync(["-a", f"--cc={name}", src + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+
+        fdst = _scratch(f"cc_fs_{name}")
+        result, _ = run_client(src, fdst, flags=[f"--cc={name}"], port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("name", COMPRESS_NAMES)
+    def test_compress_names_accepted_by_both(self, name, shared_server):
+        src = _make_corpus(_scratch(f"zc_src_{name}"))
+        rdst = _scratch(f"zc_rsync_{name}")
+        rsync_result = _rsync(["-az", f"--zc={name}", src + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+
+        fdst = _scratch(f"zc_fs_{name}")
+        result, _ = run_client(src, fdst, flags=["-z", f"--zc={name}"], port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("choice", ["md4,sha1", "sha1,md4", "auto,md5", "none,md5"])
+    def test_checksum_two_name_accepted_by_both(self, choice, shared_server):
+        tag = choice.replace(",", "_")
+        src = _make_corpus(_scratch(f"two_src_{tag}"))
+        rdst = _scratch(f"two_rsync_{tag}")
+        rsync_result = _rsync(["-a", "--checksum", f"--cc={choice}", src + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+
+        fdst = _scratch(f"two_fs_{tag}")
+        result, _ = run_client(src, fdst, flags=["--checksum", f"--cc={choice}"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("name", ["sha256", "crc32", "md5,", "md4,md5,sha1"])
+    def test_unknown_checksum_rejected_exit_4_both(self, name, shared_server):
+        src = _make_corpus(_scratch(f"badcc_src_{name.replace(',', '_').replace(':', '_')}"))
+        rdst = _scratch(f"badcc_rsync_{name.replace(',', '_').replace(':', '_')}")
+        rsync_result = _rsync(["-a", f"--cc={name}", src + "/", rdst + "/"])
+        assert rsync_result.returncode == 4, rsync_result.stderr
+
+        fdst = _scratch(f"badcc_fs_{name.replace(',', '_').replace(':', '_')}")
+        result, _ = run_client(src, fdst, flags=[f"--cc={name}"], port=shared_server.port)
+        assert result.returncode == 4, (result.stderr or result.stdout)[:200]
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("choice", ["none", "md5,none"])
+    def test_checksum_none_with_checksum_rejected_exit_4_both(self, choice, shared_server):
+        tag = choice.replace(",", "_")
+        src = _make_corpus(_scratch(f"nonecc_src_{tag}"))
+        rdst = _scratch(f"nonecc_rsync_{tag}")
+        rsync_result = _rsync(["-a", "--checksum", f"--cc={choice}", src + "/", rdst + "/"])
+        assert rsync_result.returncode == 4, rsync_result.stderr
+
+        fdst = _scratch(f"nonecc_fs_{tag}")
+        result, _ = run_client(src, fdst, flags=["--checksum", f"--cc={choice}"],
+                               port=shared_server.port)
+        assert result.returncode == 4, (result.stderr or result.stdout)[:200]
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("name", ["bogus", "zstd,lz4"])
+    def test_unknown_compress_rejected_exit_4_both(self, name, shared_server):
+        tag = name.replace(",", "_")
+        src = _make_corpus(_scratch(f"badzc_src_{tag}"))
+        rdst = _scratch(f"badzc_rsync_{tag}")
+        rsync_result = _rsync(["-az", f"--zc={name}", src + "/", rdst + "/"])
+        assert rsync_result.returncode == 4, rsync_result.stderr
+
+        fdst = _scratch(f"badzc_fs_{tag}")
+        result, _ = run_client(src, fdst, flags=["-z", f"--zc={name}"], port=shared_server.port)
+        assert result.returncode == 4, (result.stderr or result.stdout)[:200]
+
+
+class TestCodecTransferDifferential:
+    """Each codec lands the same bytes rsync lands."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("name", COMPRESS_NAMES + ["none"])
+    def test_compress_codec_matches_rsync_bytes(self, name, shared_server):
+        src = _make_corpus(_scratch(f"byteszc_src_{name}"))
+        rsync_dst = _scratch(f"byteszc_rsync_{name}")
+        rsync_result = _rsync(["-a", "-z", f"--zc={name}", src + "/", rsync_dst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+
+        fs_dst = _scratch(f"byteszc_fs_{name}")
+        result, _ = run_client(src, fs_dst, flags=["-a", "-z", f"--zc={name}"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        received = get_dest_received_dir(fs_dst, src)
+        assert _tree_bytes(received) == _tree_bytes(rsync_dst)
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("name", CHECKSUM_NAMES)
+    def test_checksum_codec_matches_rsync_bytes(self, name, shared_server):
+        src = _make_corpus(_scratch(f"bytescc_src_{name}"))
+        rsync_dst = _scratch(f"bytescc_rsync_{name}")
+        rsync_result = _rsync(["-a", "--checksum", f"--cc={name}", src + "/", rsync_dst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+
+        fs_dst = _scratch(f"bytescc_fs_{name}")
+        result, _ = run_client(src, fs_dst, flags=["-a", "--checksum", f"--cc={name}"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        received = get_dest_received_dir(fs_dst, src)
+        assert _tree_bytes(received) == _tree_bytes(rsync_dst)
+
+
+class TestChecksumChoiceDeltaSurface:
+    """--checksum-choice does not move the delta-transfer parity surface.
+
+    FastSync's delta BLOCK strong checksum is a fixed xxHash32, so the
+    negotiated algorithm only selects the whole-file comparison digest (and the
+    ``%C`` transfer digest).  A pre-seeded delta transfer must therefore land
+    byte-identical bytes and report the same counters for every choice, while
+    ``%C`` -- the one token that tracks the choice -- stays byte-identical to
+    rsync.  This pins the Track-3b reclassification in RSYNC_COMPAT.md.
+    """
+
+    CHOICES = ["xxh64", "xxh128", "xxh3", "md5", "md4", "sha1",
+               "xxh64,sha1", "sha1,xxh64"]
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_delta_surface_invariant_to_checksum_choice(self, shared_server):
+        src = _scratch("ccdelta_src")
+        basis = _make_delta_basis(src)
+        source_bytes = _tree_bytes(src)
+
+        rsync_c, fastsync_c, digests = {}, {}, {}
+        rsync_stats, fastsync_stats = {}, {}
+        for choice in self.CHOICES:
+            tag = choice.replace(",", "_")
+            rsync_dst = _scratch(f"ccdelta_rs_{tag}")
+            fs_dst = _scratch(f"ccdelta_fs_{tag}")
+            fs_root = get_dest_received_dir(fs_dst, src)
+            _seed_from_basis(basis, rsync_dst)
+            _seed_from_basis(basis, fs_root)
+
+            # Pin the block size on both ends so the literal/matched split is
+            # comparable (rsync's adaptive default would otherwise differ from
+            # FastSync's 8192-byte default).
+            rsync_result = _rsync(["-a", "--no-whole-file", "-B8192", "--stats",
+                                   "--out-format=%c|%C %n", f"--cc={choice}",
+                                   src + "/", rsync_dst + "/"])
+            assert rsync_result.returncode == 0, rsync_result.stderr
+            result, _ = run_client(
+                src, fs_dst,
+                flags=["-a", "--incremental", "--delta", "-B8192", "--stats",
+                       "--out-format=%c|%C %n", f"--cc={choice}"],
+                port=shared_server.port)
+            assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+
+            assert _tree_bytes(rsync_dst) == source_bytes, choice
+            assert _tree_bytes(fs_root) == source_bytes, choice
+            assert _delta_stats(rsync_result.stdout) == _delta_stats(result.stdout), choice
+
+            rs_c, rs_C = _big_bin_outfmt(rsync_result.stdout)
+            fs_c, fs_C = _big_bin_outfmt(result.stdout)
+            assert rs_C == fs_C, f"{choice}: %C rsync={rs_C!r} fastsync={fs_C!r}"
+            rsync_c[choice] = rs_c
+            fastsync_c[choice] = fs_c
+            digests[choice] = fs_C
+            rsync_stats[choice] = _delta_stats(rsync_result.stdout)
+            fastsync_stats[choice] = _delta_stats(result.stdout)
+
+        # The choice is only observable in %C, and it is effective (the digests
+        # are not all the same algorithm's output).
+        assert len(set(digests.values())) > 1, digests
+        # The compared --stats counters are invariant across choices in each tool
+        # (and were asserted equal cross-tool inside the loop).
+        assert len({tuple(sorted(s.items())) for s in rsync_stats.values()}) == 1, rsync_stats
+        assert len({tuple(sorted(s.items())) for s in fastsync_stats.values()}) == 1, fastsync_stats
+        # The block-checksum token (%c) is invariant across choices in each tool.
+        assert len(set(rsync_c.values())) == 1, rsync_c
+        assert len(set(fastsync_c.values())) == 1, fastsync_c
+
+
+class TestCodecNegotiationFallback:
+    """FastSync's auto negotiation and deterministic fallback order."""
+
+    @pytest.mark.ci
+    def test_default_checksum_and_compression_agree(self, shared_server):
+        """A default transfer (auto on both peers) succeeds; the negotiated
+        default is xxh128 + zstd."""
+        src = _make_corpus(_scratch("auto_src"))
+        fdst = _scratch("auto_fs")
+        result, _ = run_client(src, fdst, flags=["-a", "-z"], port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        received = get_dest_received_dir(fdst, src)
+        assert _tree_bytes(received) == _tree_bytes(src)
+
+    @pytest.mark.ci
+    def test_explicit_choice_overrides_auto(self, shared_server):
+        """An explicit --zc/--cc wins over the negotiated default on both ends,
+        so the receiver decodes with the sender's codec."""
+        src = _make_corpus(_scratch("explicit_src"))
+        fdst = _scratch("explicit_fs")
+        result, _ = run_client(src, fdst, flags=["-a", "-z", "--zc=lz4", "--cc=sha1"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        received = get_dest_received_dir(fdst, src)
+        assert _tree_bytes(received) == _tree_bytes(src)

tests/integration/test_delete_delay_budget_parity.py

@@ -0,0 +1,185 @@
+"""Differential coverage for ``--delete-delay`` + ``--max-delete`` with a
+refilled deferred directory.
+
+FastSync snapshots a directory's extras at plan time (``defer_add``) but charges
+``--max-delete`` only when a path is actually removed, and its deferred commit
+re-scans a queued directory and removes content created after the plan -- the
+same rules as rsync.  These tests run both tools on the same fixture and assert
+both sides remove the late content (recursively) and bound the deletion with
+``--max-delete`` identically.
+
+They are not part of the fast PR gate because the rsync side needs a wide
+real-time injection window (a throttled transfer), while the FastSync side uses
+the existing byte-deterministic slicing proxy.
+
+The refilled directory sits at the transfer ROOT, whose delete plan is always
+processed before any subdirectory's, so the budget is deterministically charged
+to the refilled entry; the second extra lives under ``b`` and is skipped.
+"""
+import os
+import shutil
+import subprocess
+import sys
+import threading
+import time
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (  # noqa: E402
+    TEST_DATA_DIR,
+    ServerManager,
+    clean_dir,
+    get_dest_received_dir,
+    run_client,
+)
+from test_delete_timing_parity import _SlicingProxy  # noqa: E402
+
+RSYNC = shutil.which("rsync")
+requires_rsync = pytest.mark.skipif(RSYNC is None, reason="rsync 3.4.1 not installed")
+
+BIG_BYTES = 8 * 1024 * 1024
+MID_TRANSFER_BYTES = 256 * 1024
+PROXY_THROTTLE = 0.001
+# rsync is driven locally, so the refill is injected on a wall-clock delay while
+# a throttled ~8 s transfer is in flight.  1.5 s is safely after rsync's plan
+# scan (t=0) and well before the deferred commit at the end.
+RSYNC_BWLIMIT = 1024  # 1 MiB/s
+RSYNC_INJECT_DELAY = 1.5
+
+
+def _write(path, content):
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    with open(path, "wb") as fh:
+        fh.write(content)
+
+
+def _seed_source(tag):
+    source = os.path.join(TEST_DATA_DIR, f"ddb_{tag}_src")
+    clean_dir(source)
+    _write(os.path.join(source, "a", "keep.bin"), b"B" * BIG_BYTES)
+    _write(os.path.join(source, "b", "keep.txt"), b"keep\n")
+    return source
+
+
+def _seed_fastsync(tag):
+    """FastSync mirrors the absolute source path under its receive root, so the
+    extras live below ``received``."""
+    source = _seed_source(tag)
+    dest = os.path.join(TEST_DATA_DIR, f"ddb_{tag}_dst")
+    clean_dir(dest)
+    received = get_dest_received_dir(dest, source)
+    os.makedirs(os.path.join(received, "xdir"), exist_ok=True)
+    os.makedirs(os.path.join(received, "b", "ydir"), exist_ok=True)
+    return source, dest, received
+
+
+def _seed_rsync(tag):
+    """rsync mirrors the source contents directly into the destination, so the
+    extras are flat under ``rsync_dst``."""
+    source = _seed_source(tag)
+    rsync_dst = os.path.join(TEST_DATA_DIR, f"ddb_{tag}_dst")
+    clean_dir(rsync_dst)
+    os.makedirs(os.path.join(rsync_dst, "xdir"), exist_ok=True)
+    os.makedirs(os.path.join(rsync_dst, "b", "ydir"), exist_ok=True)
+    return source, rsync_dst
+
+
+def _deleted_count(text):
+    for line in text.splitlines():
+        if line.startswith("Number of deleted files:"):
+            return int(line.split(":", 1)[1].split()[0])
+    return None
+
+
+def _rsync(args, timeout=120):
+    env = dict(os.environ, LC_ALL="C")
+    return subprocess.run([RSYNC] + args, capture_output=True, text=True, env=env, timeout=timeout)
+
+
+class TestDeleteDelayRefilledDirVsRsync:
+    """Both tools charge --max-delete on actual removals and recurse."""
+
+    def _fastsync_refilled(self, tag, max_delete=None):
+        """Run FastSync with the refill injected deterministically by the proxy
+        hook (fired once the receiver has processed the plan frames)."""
+        source, dest, received = _seed_fastsync(tag)
+        late = os.path.join(received, "xdir", "new.txt")
+
+        def hook():
+            _write(late, b"created mid-transfer\n")
+
+        flags = ["--delete-delay", "--incremental", "--ignore-times", "--stats"]
+        if max_delete is not None:
+            flags.append(f"--max-delete={max_delete}")
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            proxy = _SlicingProxy(server.port, hook=hook, hook_after=MID_TRANSFER_BYTES,
+                                  throttle=PROXY_THROTTLE, wait_for_reply=True)
+            result, _ = run_client(source, dest, flags=flags, port=proxy.port)
+            proxy.finish()
+        assert proxy.hook_called.is_set(), "refill hook never fired"
+        return result, received, late
+
+    @requires_rsync
+    def test_max_delete_budget_bound_matches(self):
+        # --- FastSync: the one actual removal is the late file; dirs survive ---
+        result, received, late = self._fastsync_refilled("budget_fs", max_delete=1)
+        assert result.returncode == 25, (result.stderr or result.stdout)[:300]
+        assert _deleted_count(result.stdout) == 1, result.stdout
+        assert not os.path.exists(late), "FastSync kept the late content of a queued dir"
+        assert os.path.isdir(os.path.join(received, "xdir"))
+        assert os.path.isdir(os.path.join(received, "b", "ydir")), (
+            "FastSync did not bound the deletion with --max-delete=1"
+        )
+
+        # --- rsync: same budget rule and recursive removal ---
+        source, rsync_dst = _seed_rsync("budget_rsync")
+
+        def inject():
+            time.sleep(RSYNC_INJECT_DELAY)
+            _write(os.path.join(rsync_dst, "xdir", "new.txt"), b"created mid-transfer\n")
+
+        t = threading.Thread(target=inject)
+        t.start()
+        rsync_result = _rsync(
+            ["-a", "--delete-delay", "--max-delete=1", "--stats",
+             f"--bwlimit={RSYNC_BWLIMIT}", source + "/", rsync_dst + "/"]
+        )
+        t.join()
+        assert rsync_result.returncode == 25, rsync_result.stderr
+        assert _deleted_count(rsync_result.stdout) == _deleted_count(result.stdout)
+        assert not os.path.exists(os.path.join(rsync_dst, "xdir", "new.txt")), (
+            "rsync kept late content inside a queued directory"
+        )
+        assert os.path.isdir(os.path.join(rsync_dst, "b", "ydir")), (
+            "rsync did not bound the deletion with --max-delete=1"
+        )
+        assert os.path.isdir(os.path.join(received, "b", "ydir"))
+
+    @requires_rsync
+    def test_refilled_extra_dir_recursive_removal_matches(self):
+        """Without --max-delete both tools remove the refilled extra directory
+        (and its late content)."""
+        result, received, late = self._fastsync_refilled("recur_fs")
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        assert not os.path.exists(late), "FastSync kept the refilled directory's late content"
+        assert not os.path.isdir(os.path.join(received, "xdir"))
+
+        source, rsync_dst = _seed_rsync("recur_rsync")
+
+        def inject():
+            time.sleep(RSYNC_INJECT_DELAY)
+            _write(os.path.join(rsync_dst, "xdir", "new.txt"), b"created mid-transfer\n")
+
+        t = threading.Thread(target=inject)
+        t.start()
+        rsync_result = _rsync(
+            ["-a", "--delete-delay", "--stats", f"--bwlimit={RSYNC_BWLIMIT}",
+             source + "/", rsync_dst + "/"]
+        )
+        t.join()
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        assert not os.path.exists(os.path.join(rsync_dst, "xdir")), (
+            "rsync did not recursively remove the refilled extra directory"
+        )

tests/integration/test_delete_timing_parity.py

@@ -0,0 +1,539 @@
+"""Differential + regression coverage for rsync's delete timing.
+
+``--delete-during``/``--delete-delay`` stream a per-directory delete plan instead
+of one whole-tree manifest, so the timing is observable:
+
+  * ``--delete-during`` removes a directory's extras as it processes that
+    directory (so an interrupted transfer has already removed the extras of the
+    directories it reached);
+  * ``--delete-delay`` snapshots those extras while scanning and commits the
+    removals only after a fully-successful transfer (so an extra created in the
+    destination after its directory's plan survives, and a failed transfer
+    removes nothing);
+  * ``--delete-after`` re-scans the destination at the end (so that same
+    late-created extra is removed).
+
+The final-state tests compare against real ``rsync 3.4.1`` where a deterministic
+comparison exists; the timing tests use a byte-slicing proxy to force a
+mid-transfer failure or to create a destination entry while the transfer is in
+flight.
+"""
+import os
+import select
+import shutil
+import socket
+import struct
+import subprocess
+import sys
+import threading
+import time
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (  # noqa: E402
+    BUILD_DIR,
+    TEST_DATA_DIR,
+    ServerManager,
+    clean_dir,
+    get_dest_received_dir,
+    run_client,
+)
+
+# Every test here is deterministic (the proxy throttles until the delete-plan
+# frames are processed), so the PR gate runs the whole module.
+pytestmark = pytest.mark.ci
+
+RSYNC = shutil.which("rsync")
+requires_rsync = pytest.mark.skipif(RSYNC is None, reason="rsync 3.4.1 not installed")
+
+BIG_BYTES = 8 * 1024 * 1024
+# Forward/cut this far into the stream: past the (small) delete-plan frames and
+# well into the big payload, so the receiver has already processed the plan.
+MID_TRANSFER_BYTES = 256 * 1024
+# Throttle the proxy so the receiver keeps up with the (fast) client and the
+# plan frames are provably processed before the hook/cut offset is reached.
+PROXY_THROTTLE = 0.001
+
+
+def _write(path, content):
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    with open(path, "wb") as fh:
+        fh.write(content)
+
+
+def _seed_pair(tag, big=False):
+    """Create a source tree and a destination mirror seeded with extras.
+
+    The tree is a single directory ``d`` containing the transferred files plus,
+    in the destination, an extra ``d/old_extra``.
+    """
+    source = os.path.join(TEST_DATA_DIR, f"dtp_{tag}_src")
+    dest = os.path.join(TEST_DATA_DIR, f"dtp_{tag}_dst")
+    clean_dir(source)
+    clean_dir(dest)
+    _write(os.path.join(source, "d", "keep.txt"), b"kept payload\n")
+    if big:
+        _write(os.path.join(source, "d", "big.bin"), b"B" * BIG_BYTES)
+    received = get_dest_received_dir(dest, source)
+    os.makedirs(os.path.join(received, "d"), exist_ok=True)
+    _write(os.path.join(received, "d", "old_extra"), b"stale extra\n")
+    return source, dest, received
+
+
+def _tree(root):
+    """Sorted relative paths of every entry below root (files and dirs)."""
+    out = []
+    for dirpath, dirs, files in os.walk(root):
+        for name in dirs:
+            out.append(os.path.relpath(os.path.join(dirpath, name), root))
+        for name in files:
+            out.append(os.path.relpath(os.path.join(dirpath, name), root))
+    return sorted(out)
+
+
+def _rsync(args):
+    env = dict(os.environ, LC_ALL="C")
+    return subprocess.run([RSYNC] + args, capture_output=True, text=True, env=env, timeout=120)
+
+
+class _SlicingProxy:
+    """Forward the client stream to a server, optionally cutting it or invoking a
+    hook after a byte threshold.  ``forward_limit`` mode resets both ends after
+    that many client bytes (a mid-transfer failure).  ``hook`` mode calls the
+    hook once and keeps forwarding to completion.
+
+    With ``wait_for_reply`` the hook is a real barrier, not a timing guess: it
+    fires only after the server has sent *any* reply, which the receiver does
+    only after it has consumed the frames that precede the payload (the
+    per-directory delete plan for ``--delete-delay``).  The caller pairs it with
+    ``--incremental`` so a per-file handshake reply is guaranteed mid-transfer.
+    """
+
+    def __init__(self, target_port, forward_limit=None, hook=None, hook_after=0,
+                 throttle=0.0, wait_for_reply=False):
+        self.target = ("127.0.0.1", target_port)
+        self.forward_limit = forward_limit
+        self.hook = hook
+        self.hook_after = hook_after
+        self.throttle = throttle
+        self.wait_for_reply = wait_for_reply
+        self.server_replied = threading.Event()
+        self.hook_called = threading.Event()
+        self.listener = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        self.listener.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        self.listener.bind(("127.0.0.1", 0))
+        self.listener.listen(1)
+        self.listener.settimeout(20)
+        self.port = self.listener.getsockname()[1]
+        self._thread = threading.Thread(target=self._serve, daemon=True)
+        self._thread.start()
+
+    def _serve(self):
+        try:
+            client, _ = self.listener.accept()
+        except OSError:
+            return
+        try:
+            backend = socket.create_connection(self.target, timeout=10)
+        except OSError:
+            client.close()
+            return
+        client.settimeout(20)
+        backend.settimeout(20)
+        forwarded = 0
+        socks = [client, backend]
+        try:
+            while socks:
+                ready, _, _ = select.select(socks, [], [], 20)
+                if not ready:
+                    break
+                for sock in ready:
+                    data = sock.recv(65536)
+                    if not data:
+                        socks.remove(sock)
+                        peer = backend if sock is client else client
+                        try:
+                            peer.shutdown(socket.SHUT_WR)
+                        except OSError:
+                            pass
+                        continue
+                    if sock is client:
+                        if self.forward_limit is not None:
+                            room = self.forward_limit - forwarded
+                            if room <= 0:
+                                socks = []
+                                break
+                            data = data[:room]
+                        backend.sendall(data)
+                        forwarded += len(data)
+                        self._maybe_hook(forwarded)
+                        if self.forward_limit is not None and forwarded >= self.forward_limit:
+                            socks = []
+                            break
+                        if self.throttle > 0:
+                            time.sleep(self.throttle)
+                    else:
+                        client.sendall(data)
+                        # Any server reply proves the receiver consumed the
+                        # frames that precede it, so the hook barrier is met.
+                        self.server_replied.set()
+                        self._maybe_hook(forwarded)
+        except OSError:
+            pass
+        for sock in (client, backend):
+            try:
+                sock.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, struct.pack("ii", 1, 0))
+            except OSError:
+                pass
+            try:
+                sock.close()
+            except OSError:
+                pass
+        try:
+            self.listener.close()
+        except OSError:
+            pass
+
+    def _maybe_hook(self, forwarded):
+        """Fire the one-shot hook once its barrier is satisfied: enough client
+        bytes have been forwarded and, when ``wait_for_reply`` is set, the
+        server has sent a reply proving it processed the preceding frames."""
+        if self.hook is None or self.hook_called.is_set():
+            return
+        if forwarded < self.hook_after:
+            return
+        if self.wait_for_reply and not self.server_replied.is_set():
+            return
+        self.hook()
+        self.hook_called.set()
+
+    def finish(self):
+        self._thread.join(30)
+        try:
+            self.listener.close()
+        except OSError:
+            pass
+
+
+class TestDeleteTimingFinalStateParity:
+    """On a successful transfer the per-directory timings match rsync's result.
+
+    Plain ``--delete`` has no rsync-incompatible spelling: it defaults to
+    delete-during on both tools, so it is compared against rsync's own default.
+    ``--delete-commit`` is FastSync-only and selects the late whole-tree commit,
+    which is rsync's ``--delete-after`` timing.
+    """
+
+    # (fastsync flag, rsync flag)
+    PAIRS = [
+        ("--delete", "--delete"),
+        ("--delete-during", "--delete-during"),
+        ("--delete-delay", "--delete-delay"),
+        ("--delete-commit", "--delete-after"),
+    ]
+
+    def _run_fastsync(self, tag, timing):
+        source, dest, received = _seed_pair(tag)
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest, flags=[timing], port=server.port)
+        return result, received
+
+    @pytest.mark.parametrize("fs_timing,rs_timing", PAIRS)
+    @requires_rsync
+    def test_success_final_state_matches_rsync(self, fs_timing, rs_timing):
+        # Worker-safe names: xdist may run the parametrizations concurrently, so
+        # the flags are part of every fixture path.
+        label = f"{fs_timing.lstrip('-')}_vs_{rs_timing.lstrip('-')}"
+        # Build the rsync fixture from the same seed so both sides start equal.
+        source, dest, received = _seed_pair(f"parity_rsync_{label}")
+        source2 = source
+        rsync_dst = os.path.join(TEST_DATA_DIR, f"dtp_rsync_{label}_dst")
+        clean_dir(rsync_dst)
+        # rsync mirrors src/ into dst/; seed the same extra.
+        _write(os.path.join(rsync_dst, "d", "old_extra"), b"stale extra\n")
+
+        rsync_result = _rsync(["-a", rs_timing, source2 + "/", rsync_dst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_tree = _tree(rsync_dst)
+
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest, flags=[fs_timing], port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        fastsync_tree = _tree(received)
+        assert fastsync_tree == rsync_tree, (
+            f"{fs_timing} vs rsync {rs_timing}: fastsync tree {fastsync_tree} != "
+            f"rsync tree {rsync_tree}"
+        )
+
+
+class TestDeleteTimingTypeConflictParity:
+    """A destination entry whose type differs from the source is replaced, in
+    both per-directory timings and in both directions, exactly like rsync."""
+
+    @pytest.mark.parametrize("timing", ["--delete-during", "--delete-delay"])
+    @requires_rsync
+    def test_type_conflicts_match_rsync(self, timing):
+        label = timing.lstrip("-")
+        source = os.path.join(TEST_DATA_DIR, f"dtc_{label}_src")
+        clean_dir(source)
+        _write(os.path.join(source, "foo"), b"now a file\n")
+        _write(os.path.join(source, "bar", "inner.txt"), b"now a dir\n")
+
+        def seed_dest(root):
+            clean_dir(root)
+            _write(os.path.join(root, "foo", "inner.txt"), b"was a dir\n")
+            _write(os.path.join(root, "bar"), b"was a file\n")
+
+        rsync_dst = os.path.join(TEST_DATA_DIR, f"dtc_{label}_rsync_dst")
+        seed_dest(rsync_dst)
+        rsync_result = _rsync(["-a", timing, source + "/", rsync_dst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_tree = _tree(rsync_dst)
+
+        dest = os.path.join(TEST_DATA_DIR, f"dtc_{label}_dst")
+        clean_dir(dest)
+        received = get_dest_received_dir(dest, source)
+        seed_dest(received)
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest, flags=[timing], port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        assert _tree(received) == rsync_tree, (
+            f"{timing}: fastsync tree {_tree(received)} != rsync tree {rsync_tree}"
+        )
+
+
+class TestDeleteTimingFailure:
+    """A mid-transfer failure distinguishes the during timings from the late
+    commit timings.
+
+    Plain ``--delete`` must behave like ``--delete-during`` (the rsync default),
+    removing the extras of the directories already reached; ``--delete-commit``
+    must behave like ``--delete-after`` and remove nothing until the transfer
+    has fully succeeded.
+    """
+
+    @pytest.mark.parametrize("mt", [False, True])
+    def test_during_removes_delay_preserves_on_failure(self, mt):
+        source, dest, received = _seed_pair(f"failure_mt{int(mt)}", big=True)
+        extra = os.path.join(received, "d", "old_extra")
+        assert os.path.exists(extra)
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            for timing, expect_removed in (
+                    ("--delete-during", True),
+                    ("--delete", True),
+                    ("--delete-delay", False),
+                    ("--delete-commit", False),
+                    ("--delete-after", False)):
+                # Re-seed the extra before each run.
+                _write(extra, b"stale extra\n")
+                proxy = _SlicingProxy(server.port, forward_limit=MID_TRANSFER_BYTES, throttle=PROXY_THROTTLE)
+                flags = [timing] + (["--threads"] if mt else [])
+                result, _ = run_client(source, dest, flags=flags, port=proxy.port)
+                proxy.finish()
+                assert result.returncode != 0, f"{timing}: truncated transfer succeeded"
+                present = os.path.exists(extra)
+                assert present != expect_removed, (
+                    f"{timing} (mt={mt}): extra present={present}, expected "
+                    f"removed={expect_removed}"
+                )
+
+
+class TestDeleteDelayDeletedCount:
+    """The reported deleted count must reflect entries actually removed."""
+
+    def test_refilled_deferred_dir_is_recursively_removed_and_counted(self):
+        """A directory snapshotted into a --delete-delay plan that is refilled
+        before the commit is re-scanned and removed recursively (rsync parity):
+        the late file and the directory are both counted as deleted."""
+        source = os.path.join(TEST_DATA_DIR, "ddc_src")
+        dest = os.path.join(TEST_DATA_DIR, "ddc_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        _write(os.path.join(source, "d", "keep.txt"), b"kept payload\n")
+        _write(os.path.join(source, "d", "big.bin"), b"B" * BIG_BYTES)
+        received = get_dest_received_dir(dest, source)
+        extra_dir = os.path.join(received, "d", "extradir")
+        os.makedirs(extra_dir, exist_ok=True)
+
+        def hook():
+            # Runs while big.bin is in flight, after d's delete plan was processed.
+            _write(os.path.join(extra_dir, "new.txt"), b"created mid-transfer\n")
+
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            proxy = _SlicingProxy(server.port, hook=hook, hook_after=MID_TRANSFER_BYTES,
+                                  throttle=PROXY_THROTTLE, wait_for_reply=True)
+            flags = ["--delete-delay", "--incremental", "--ignore-times", "--stats"]
+            result, _ = run_client(source, dest, flags=flags, port=proxy.port)
+            proxy.finish()
+        assert result.returncode == 0, (result.stderr or result.stdout)[:400]
+        assert proxy.hook_called.is_set(), "hook never fired"
+        assert not os.path.exists(os.path.join(extra_dir, "new.txt")), "late file survived"
+        assert not os.path.isdir(extra_dir), "refilled extra dir survived"
+        deleted = None
+        for line in result.stdout.splitlines():
+            if line.startswith("Number of deleted files:"):
+                deleted = int(line.split(":", 1)[1].split()[0])
+        assert deleted == 2, (deleted, result.stdout)
+
+
+class TestDeleteDelayMaxDeleteParity:
+    """--max-delete with --delete-delay: a partial deletion still reports the
+    number of entries actually removed, matching rsync (the exact surviving set
+    can differ; only the count is compared)."""
+
+    @requires_rsync
+    def test_max_delete_count_matches_rsync(self):
+        source = os.path.join(TEST_DATA_DIR, "ddm_src")
+        rsync_dst = os.path.join(TEST_DATA_DIR, "ddm_rsync_dst")
+        clean_dir(source)
+        clean_dir(rsync_dst)
+        _write(os.path.join(source, "d", "keep.txt"), b"keep\n")
+        for i in range(1, 6):
+            _write(os.path.join(rsync_dst, "d", f"e{i}.txt"), f"extra{i}\n".encode())
+
+        rsync_result = _rsync(["-a", "--delete-delay", "--max-delete=2", "--stats",
+                               source + "/", rsync_dst + "/"])
+        # rsync exits 25 ("the --max-delete limit stopped deletions").
+        assert rsync_result.returncode == 25, rsync_result.stderr
+        rsync_count = _deleted_count(rsync_result.stdout)
+        assert rsync_count == 2, rsync_result.stdout
+
+        dest = os.path.join(TEST_DATA_DIR, "ddm_dst")
+        clean_dir(dest)
+        received = get_dest_received_dir(dest, source)
+        for i in range(1, 6):
+            _write(os.path.join(received, "d", f"e{i}.txt"), f"extra{i}\n".encode())
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(
+                source, dest,
+                flags=["--delete-delay", "--max-delete=2", "--stats"],
+                port=server.port,
+            )
+        # A capped --max-delete commit is a successful transfer that both tools
+        # report with exit 25.
+        assert result.returncode == 25, (result.stderr or result.stdout)[:300]
+        assert _deleted_count(result.stdout) == rsync_count, result.stdout
+
+
+def _deleted_count(text):
+    for line in text.splitlines():
+        if line.startswith("Number of deleted files:"):
+            return int(line.split(":", 1)[1].split()[0])
+    return None
+
+
+class TestDeleteDelayVsAfterSnapshot:
+    """A destination entry created after its directory's scan survives under
+    --delete-delay but is removed by --delete-after's fresh end scan."""
+
+    @pytest.mark.parametrize("mt", [False, True])
+    def test_late_created_extra_survives_delay_not_after(self, mt):
+        source, dest, received = _seed_pair(f"latecreate_mt{int(mt)}", big=True)
+        old_extra = os.path.join(received, "d", "old_extra")
+        new_extra = os.path.join(received, "d", "new_extra")
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            for timing, new_survives in (("--delete-delay", True),
+                                         ("--delete-after", False)):
+                _write(old_extra, b"stale extra\n")
+                if os.path.exists(new_extra):
+                    os.unlink(new_extra)
+
+                def hook():
+                    # Runs on the proxy thread while the big file is in flight,
+                    # after the directory's plan (delay) has been processed.
+                    _write(new_extra, b"created mid-transfer\n")
+
+                # --incremental gives the receiver a mid-transfer handshake
+                # reply; the proxy waits for it (wait_for_reply) so the hook is
+                # causally after the plan frame, never a timing guess.
+                # --ignore-times forces the big file to transfer on the second
+                # timing too (the first run already installed it), keeping the
+                # mid-transfer reply present in both iterations.
+                proxy = _SlicingProxy(server.port, hook=hook,
+                                      hook_after=MID_TRANSFER_BYTES,
+                                      throttle=PROXY_THROTTLE, wait_for_reply=True)
+                flags = [timing, "--incremental", "--ignore-times"] + (["--threads"] if mt else [])
+                result, _ = run_client(source, dest, flags=flags, port=proxy.port)
+                proxy.finish()
+                assert result.returncode == 0, (
+                    f"{timing}: {(result.stderr or result.stdout)[:300]}"
+                )
+                assert proxy.hook_called.is_set(), f"{timing}: hook never fired"
+                assert not os.path.exists(old_extra), f"{timing}: old extra survived"
+                assert os.path.exists(new_extra) == new_survives, (
+                    f"{timing} (mt={mt}): new_extra present="
+                    f"{os.path.exists(new_extra)}, expected survives={new_survives}"
+                )
+
+
+class TestDeleteAfterThreadsKeepSet:
+    """Regression: -j/--threads must still transmit the delete keep-set in every
+    timing.  PipelineContextSender.delete_suppressed was left uninitialized, so a
+    garbage true silently skipped the late keep-set manifest under --threads.
+    Plain --delete now uses the per-directory plans, while --delete-commit /
+    --delete-after keep exercising the late whole-tree manifest."""
+
+    @pytest.mark.parametrize("delete_flag", ["--delete", "--delete-commit", "--delete-after"])
+    def test_threads_delete_after_sends_keep_set(self, delete_flag):
+        source, dest, received = _seed_pair("mtkeep")
+        extra = os.path.join(received, "d", "old_extra")
+        assert os.path.exists(extra)
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest, flags=["--threads", delete_flag],
+                                   port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        assert not os.path.exists(extra), (
+            f"{delete_flag} --threads did not remove an extra: delete keep-set was suppressed"
+        )
+
+class TestDeleteDelayMaxDeleteRefilledDir:
+    """--delete-delay charges the --max-delete budget on ACTUAL removals: the
+    refilled directory's late content is removed first (consuming the one slot),
+    so the directory itself and a later extra are skipped, matching rsync.
+
+    The refilled directory is at the destination ROOT (its plan is always sent
+    first) and the skipped extra is under a separate source directory, so the
+    ordering that decides the budget charge is deterministic -- not readdir
+    order.  The refill is injected through the byte-barrier proxy so it is
+    causally after the plan frame."""
+
+    def test_budget_charged_on_actual_removal(self):
+        source = os.path.join(TEST_DATA_DIR, "ddmb_src")
+        dest = os.path.join(TEST_DATA_DIR, "ddmb_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        _write(os.path.join(source, "a", "keep.bin"), b"B" * BIG_BYTES)
+        _write(os.path.join(source, "b", "keep.txt"), b"keep\n")
+        received = get_dest_received_dir(dest, source)
+        refilled_dir = os.path.join(received, "xdir")
+        os.makedirs(refilled_dir, exist_ok=True)
+        later_dir = os.path.join(received, "b", "ydir")
+        os.makedirs(later_dir, exist_ok=True)
+
+        def hook():
+            _write(os.path.join(refilled_dir, "new.txt"), b"created mid-transfer\n")
+
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            proxy = _SlicingProxy(server.port, hook=hook, hook_after=MID_TRANSFER_BYTES,
+                                  throttle=PROXY_THROTTLE, wait_for_reply=True)
+            flags = ["--delete-delay", "--max-delete=1", "--incremental", "--ignore-times", "--stats"]
+            result, _ = run_client(source, dest, flags=flags, port=proxy.port)
+            proxy.finish()
+        assert result.returncode == 25, (result.stderr or result.stdout)[:400]
+        assert proxy.hook_called.is_set(), "hook never fired"
+        # The late content consumes the single budget slot; the refilled
+        # directory itself and the later extra are skipped.
+        assert not os.path.exists(os.path.join(refilled_dir, "new.txt")), "late file survived"
+        assert os.path.isdir(later_dir), "later extra was not skipped by the budget"
+        # The one actual removal is reported.
+        assert _deleted_count(result.stdout) == 1, result.stdout

tests/integration/test_differential_parity.py

@@ -0,0 +1,719 @@
+"""Differential rsync-parity gate.
+
+Runs real ``rsync 3.4.1`` and FastSync over the same corpora and flags, then
+compares the destination trees and the normalized output of the
+output-oriented flags.  This is the executable counterpart of
+``RSYNC_COMPAT.md``: the fast subset (``-m parity_ci``) guards the ✅ surface on
+every pull request, and the full set (``-m parity``) burns the documented
+⚠️/❌ residuals down.
+
+Known, documented differences live in ``parity_caveats.py``; anything else
+fails with a readable tree/stdout diff.  A stale allowlist entry is reported
+loudly (and fails when ``FASTSYNC_PARITY_STRICT=1``).
+
+Run locally::
+
+    python3 -m pytest tests/integration/test_differential_parity.py -n 4 --dist=load -m parity_ci
+    python3 -m pytest tests/integration/test_differential_parity.py -n 4 --dist=load -m parity
+"""
+import os
+import shutil
+import sys
+import warnings
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (  # noqa: E402
+    ServerManager,
+    TEST_DATA_DIR,
+    clean_dir,
+    get_dest_received_dir,
+)
+from parity_caveats import ASPECTS, caveat_for  # noqa: E402
+import parity_harness as H  # noqa: E402
+
+RSYNC = shutil.which("rsync")
+requires_rsync = pytest.mark.skipif(RSYNC is None, reason="rsync 3.4.1 not installed")
+
+# `--allow-super` matches the rest of the integration suite; `--allow-delete`
+# is needed only by the delete cases.
+SUPER = ("--allow-super",)
+DELETE = ("--allow-super", "--allow-delete")
+_OLD_MTIME = 1_500_000_000
+
+parity = pytest.mark.parity
+parity_ci = pytest.mark.parity_ci
+
+
+@pytest.fixture(scope="session")
+def parity_server_factory():
+    """Lazily start one server per distinct extra-argument set, per xdist worker."""
+    servers = {}
+
+    def get(extra):
+        key = tuple(extra)
+        if key not in servers:
+            s = ServerManager()
+            s.start(extra_args=list(extra))
+            servers[key] = s
+        return servers[key]
+
+    yield get
+    for s in servers.values():
+        s.stop()
+
+
+def _pin(path, mtime):
+    os.utime(path, (mtime, mtime))
+
+
+def _mk(path, data, mtime=None):
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    with open(path, "wb") as fh:
+        fh.write(data)
+    if mtime is not None:
+        _pin(path, mtime)
+
+
+# --- destination seeds ------------------------------------------------------
+
+def seed_extras(_src, rroot, froot):
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "extra.txt"), b"extra\n")
+        _mk(os.path.join(root, "extradir", "z.txt"), b"z\n")
+
+
+def seed_update(_src, rroot, froot):
+    for root in (rroot, froot):
+        p = os.path.join(root, "a.txt")
+        _mk(p, b"destination is newer and longer\n", 2_000_000_000)
+
+
+def seed_ignore_existing(_src, rroot, froot):
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "a.txt"), b"destination-kept\n", _OLD_MTIME)
+
+
+def seed_append(_src, rroot, froot):
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "a.txt"), b"hello ", _OLD_MTIME)
+
+
+def seed_backup(_src, rroot, froot):
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "a.txt"), b"OLD-CONTENT\n", _OLD_MTIME)
+
+
+def seed_size_only(_src, rroot, froot):
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "a.txt"), b"XXXXXXXXXXX\n", _OLD_MTIME)
+
+
+def seed_delete_excluded(_src, rroot, froot):
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "drop.log"), b"stale log\n", _OLD_MTIME)
+        _mk(os.path.join(root, "extra.txt"), b"extra\n", _OLD_MTIME)
+        _mk(os.path.join(root, "keep.txt"), b"keep\n", _OLD_MTIME)
+
+
+def seed_filter_protect(_src, rroot, froot):
+    """Destination-only entries, including nested ones, for the receiver-side
+    `protect` rule: the `.log` extras must survive --delete, the rest go."""
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "extra.log"), b"dest-only log\n", _OLD_MTIME)
+        _mk(os.path.join(root, "other.txt"), b"dest-only other\n", _OLD_MTIME)
+        _mk(os.path.join(root, "sub", "extra2.log"), b"nested dest-only log\n", _OLD_MTIME)
+        _mk(os.path.join(root, "sub", "other2.txt"), b"nested dest-only other\n", _OLD_MTIME)
+
+
+def seed_max_delete(_src, rroot, froot):
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "extra1.txt"), b"e1\n", _OLD_MTIME)
+        _mk(os.path.join(root, "extra2.txt"), b"e2\n", _OLD_MTIME)
+
+
+def fuzzy_basis_seed(_src, rroot, froot):
+    """Seed a same-suffix sibling whose name is one edit from the source and
+    whose content matches it, with a DIFFERENT mtime so rsync's exact
+    size+mtime pass cannot fire: both tools must select it via the
+    name-distance pass.  Where the two tools' basis choices coincide the
+    block-level results are identical when the block size is pinned."""
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "report_v1.txt"), H.FUZZY_PAYLOAD, _OLD_MTIME)
+
+
+def max_delete_count_check(_src, rroot, froot, _rs, _fs):
+    """The exact survivor set is order-dependent; the count must still match."""
+    r = H.snapshot(rroot)
+    f = H.snapshot(froot)
+    if len(r) != len(f):
+        return [f"survivor count differs: rsync={len(r)} fastsync={len(f)}"]
+    return []
+
+
+# --- case table -------------------------------------------------------------
+
+_CASES = [
+    # --- core archive / recursion -----------------------------------------
+    H.Case("archive", "basic", ["-a"], ci=True, ref="-a/--archive"),
+    H.Case("recursive", "basic", ["-r"], ci=True, ref="-r/--recursive"),
+    H.Case("unicode_names", "unicode", ["-a"], ci=True, ref="-a unicode names"),
+    H.Case("links_archive", "links", ["-a"], ci=True, ref="-l/--links"),
+    H.Case("copy_links", "links", ["-aL"], ref="-L/--copy-links"),
+    H.Case("hardlinks", "hardlinks", ["-a", "-H"], compare_hardlinks=True,
+           ci=True, ref="-H/--hard-links"),
+    H.Case("hardlinks_without_H", "hardlinks", ["-a"], compare_hardlinks=True,
+           ref="hardlinks without -H"),
+    H.Case("sparse", "sparse", ["-a", "-S"], ref="-S/--sparse"),
+
+    # --- compression / checksums ------------------------------------------
+    H.Case("compress_zstd", "basic", ["-a", "-z"], ci=True, ref="-z/--compress"),
+    H.Case("checksum", "basic", ["-a", "-c"], ref="-c/--checksum"),
+    H.Case("checksum_choice_xxh64", "basic",
+           ["-a", "-c", "--checksum-choice=xxh64"], ref="--checksum-choice"),
+
+    # --- selection --------------------------------------------------------
+    H.Case("exclude", "filters", ["-a", "--exclude=*.log"], ci=True,
+           ref="--exclude"),
+    H.Case("include_exclude", "filters",
+           ["-a", "--include=*.txt", "--exclude=*"], ci=True,
+           ref="--include/--exclude ordering"),
+    H.Case("filter_rules", "filters",
+           ["-a", "-f", "- *.log", "-f", "+ *.txt", "-f", "- *"],
+           ref="--filter/-f grammar"),
+    H.Case("max_size", "basic", ["-a", "--max-size=1000"], ref="--max-size"),
+    H.Case("min_size", "basic", ["-a", "--min-size=1000"], ref="--min-size"),
+
+    # --- output-oriented --------------------------------------------------
+    H.Case("stats", "basic", ["-a", "--stats"], stdout=H.STDOUT_STATS,
+           ci=True, ref="--stats"),
+    H.Case("itemize", "links", ["-a", "-i"], stdout=H.STDOUT_ITEMIZE,
+           ci=True, ref="-i/--itemize-changes"),
+    H.Case("out_format_n_l", "basic", ["-a", "--out-format=%n %l"],
+           stdout=H.STDOUT_OUTFMT, ref="--out-format %n %l"),
+    H.Case("out_format_i_n", "basic", ["-a", "--out-format=%i %n"],
+           stdout=H.STDOUT_OUTFMT, ref="--out-format %i %n"),
+    H.Case("progress", "multidir", ["-a", "--progress"], stdout=H.STDOUT_PROGRESS,
+           ci=True, ref="--progress multi-directory file list"),
+    H.Case("progress_threads", "multidir", ["-a", "--progress"],
+           fastsync_flags=["-a", "--progress", "--threads"],
+           stdout=H.STDOUT_PROGRESS, ci=True,
+           ref="--progress multi-directory file list (--threads)"),
+
+    # --- transfer modifications -------------------------------------------
+    H.Case("update", "basic", ["-a", "--update"], seed=seed_update,
+           ref="-u/--update"),
+    H.Case("ignore_existing", "basic", ["-a", "--ignore-existing"],
+           seed=seed_ignore_existing, ci=True, ref="--ignore-existing"),
+    H.Case("size_only", "basic",
+           ["-a", "--size-only"], fastsync_flags=["-a", "--incremental", "--size-only"],
+           seed=seed_size_only, ref="--size-only"),
+    H.Case("append", "basic", ["-a", "--append"], seed=seed_append,
+           ref="--append"),
+    H.Case("append_verify", "basic", ["-a", "--append-verify"], seed=seed_append,
+           ref="--append-verify"),
+    H.Case("backup", "basic", ["-a", "--backup"], seed=seed_backup,
+           ref="--backup"),
+    H.Case("chmod", "basic", ["-a", "--chmod=Fu+rwx"], compare_modes=True,
+           ci=True, ref="--chmod"),
+
+    # --- delta / similar-file basis (--fuzzy) -----------------------------
+    # Basis choices coincide here (same-suffix sibling, name distance one edit,
+    # content identical); with the block size pinned both tools report the same
+    # Matched/Literal/transferred counters.  The residual (FastSync's narrower
+    # delta size window) is covered by TestFuzzy in test_parity_quickwins.py.
+    H.Case("fuzzy_basis", "fuzzy",
+           ["-a", "--no-whole-file", "--fuzzy", "--stats", "-B8192"],
+           fastsync_flags=["-a", "--incremental", "--delta", "--fuzzy",
+                           "--stats", "--delta-block=8192"],
+           seed=fuzzy_basis_seed, stdout=H.STDOUT_STATS, ci=True,
+           ref="-y/--fuzzy similar-file basis"),
+
+    # --- deletion ---------------------------------------------------------
+    H.Case("delete", "basic", ["-a", "--delete"], seed=seed_extras,
+           server_args=DELETE, ci=True, ref="--delete"),
+    H.Case("delete_before", "basic", ["-a", "--delete-before"], seed=seed_extras,
+           server_args=DELETE, ref="--delete-before"),
+    H.Case("delete_during", "basic", ["-a", "--delete-during"], seed=seed_extras,
+           server_args=DELETE, ref="--delete-during"),
+    H.Case("delete_delay", "basic", ["-a", "--delete-delay"], seed=seed_extras,
+           server_args=DELETE, ref="--delete-delay"),
+    H.Case("delete_after", "basic", ["-a", "--delete-after"], seed=seed_extras,
+           server_args=DELETE, ref="--delete-after"),
+    H.Case("delete_commit", "basic", ["-a", "--delete-after"], seed=seed_extras,
+           fastsync_flags=["-a", "--delete-commit"], server_args=DELETE,
+           ref="FastSync-only --delete-commit == rsync --delete-after"),
+    H.Case("delete_excluded", "filters",
+           ["-a", "--delete", "--delete-excluded", "--exclude=*.log"],
+           seed=seed_delete_excluded, server_args=DELETE, ref="--delete-excluded"),
+    H.Case("exclude_protect_dest_only", "filters",
+           ["-a", "--delete", "--exclude=*.log"],
+           seed=seed_delete_excluded, server_args=DELETE, ci=True,
+           ref="--delete protects a destination-only excluded entry like rsync"),
+    H.Case("max_delete", "basic", ["-a", "--delete", "--max-delete=1"],
+           seed=seed_max_delete, server_args=DELETE,
+           extra_check=max_delete_count_check, compare_tree=False,
+           ref="--max-delete"),
+    H.Case("filter_protect", "filters",
+           ["-a", "--delete", "--filter=P *.log"],
+           seed=seed_filter_protect, server_args=DELETE, ci=True,
+           ref="--filter P/--protect receiver-side delete protection (default during)"),
+    H.Case("filter_protect_during", "filters",
+           ["-a", "--delete-during", "--filter=P *.log"],
+           seed=seed_filter_protect, server_args=DELETE, ci=True,
+           ref="--filter P/--protect under --delete-during"),
+    H.Case("filter_protect_delay", "filters",
+           ["-a", "--delete-delay", "--filter=P *.log"],
+           seed=seed_filter_protect, server_args=DELETE, ci=True,
+           ref="--filter P/--protect under --delete-delay"),
+    H.Case("filter_protect_after", "filters",
+           ["-a", "--delete-after", "--filter=P *.log"],
+           seed=seed_filter_protect, server_args=DELETE, ci=True,
+           ref="--filter P/--protect under the whole-tree --delete-after commit"),
+
+    # --- relative / dirs --------------------------------------------------
+    H.Case("relative_general", "basic", ["-a", "-R"], layout=H.MIRROR_ABS,
+           compare_modes=True, ref="-R/--relative"),
+    H.Case("relative_no_implied_dirs", "basic",
+           ["-a", "-R", "--no-implied-dirs"], layout=H.MIRROR_ABS,
+           compare_modes=True, ref="--no-implied-dirs"),
+    H.Case("files_from", "relative", ["--dirs", "-R"],
+           files_from=("dir1", "sub/x.txt"), layout=H.RELATIVE, ci=True,
+           ref="-d/--dirs + --files-from"),
+    H.Case("dirs_plain", "basic", ["-d"], fs_src_suffix="/",
+           ref="-d/--dirs (plain)"),
+    H.Case("empty_dirs_recursive", "empty_dir", ["-a"],
+           ref="recursive empty-directory residual"),
+    H.Case("empty_dirs_files_from", "empty_dir", ["--dirs", "-R"],
+           files_from=("emptydir",), layout=H.RELATIVE, ci=True,
+           ref="-d/--dirs explicit empty directory"),
+
+    # --- codecs -----------------------------------------------------------
+    H.Case("iconv_identity", "basic", ["-a", "--iconv=UTF-8,UTF-8"],
+           ref="--iconv identity"),
+    H.Case("iconv_convert", "iconv",
+           ["-a", "--iconv=ISO-8859-1,UTF-8"],
+           server_args=("--allow-super", "--iconv=UTF-8"),
+           ref="--iconv conversion (receiver declares its own charset)"),
+    # rsync's spec is LOCAL,REMOTE and the destination end's charset is REMOTE
+    # on a push, so a default server writes the wire (UTF-8) names verbatim.
+    H.Case("iconv_default_server", "iconv",
+           ["-a", "--iconv=ISO-8859-1,UTF-8"],
+           ref="--iconv push direction (default receiver charset = REMOTE)"),
+
+    # --- partial ----------------------------------------------------------
+    H.Case("partial_complete", "basic", ["-a", "--partial"], ref="--partial"),
+]
+
+# Cases that must always be tolerated (documented ⚠️/❌ residuals) get an
+# allowlist entry; the table below stays the exact ✅ surface.
+ALL_CASES = _CASES
+
+
+def _params():
+    out = []
+    for case in ALL_CASES:
+        marks = [parity]
+        if case.ci:
+            marks.append(parity_ci)
+        out.append(pytest.param(case, id=case.id, marks=marks))
+    return out
+
+
+def _aspects_to_check(result):
+    return {
+        "tree": result["tree"],
+        "stdout": result["stdout"],
+        "extra": result["extra"],
+    }
+
+
+def _assert_no_unexpected(case_id, mismatches, caveat, ref=""):
+    unexpected = {a: v for a, v in mismatches.items() if v and a not in caveat}
+    if unexpected:
+        lines = [f"differential parity mismatch for case {case_id!r}:"]
+        lines.append(f"  ref: {ref or 'see RSYNC_COMPAT.md'}")
+        for aspect, detail in unexpected.items():
+            lines.append(f"  --- {aspect} ---")
+            lines.extend("  " + str(d) for d in detail)
+        lines.append("If this is a documented residual, add it to "
+                     "tests/integration/parity_caveats.py with a RSYNC_COMPAT.md "
+                     "reference.  Do not allowlist an undocumented divergence.")
+        pytest.fail("\n".join(lines))
+
+    stale = [a for a in ASPECTS
+             if a in caveat and a != "rc" and not mismatches.get(a)]
+    if stale:
+        msg = (f"stale parity allowlist entry for case {case_id!r}, aspect(s) "
+               f"{stale}: FastSync now matches rsync. Remove it from "
+               f"parity_caveats.py (and update RSYNC_COMPAT.md if the row moved).")
+        if os.environ.get("FASTSYNC_PARITY_STRICT") == "1":
+            pytest.fail(msg)
+        warnings.warn(msg, stacklevel=2)
+
+
+@requires_rsync
+@pytest.mark.parametrize("case", _params())
+def test_differential_case(case, parity_server_factory):
+    server = parity_server_factory(case.server_args)
+    result = H.execute_case(case, server)
+    caveat = caveat_for(case.id)
+
+    mismatches = _aspects_to_check(result)
+    if result["rsync_rc"] != result["fastsync_rc"]:
+        mismatches["rc"] = [
+            f"rsync rc={result['rsync_rc']} fastsync rc={result['fastsync_rc']} "
+            f"(rsync stderr: {result['rsync_stderr'][:200]!r}, "
+            f"fastsync stderr: {result['fastsync_stderr'][:200]!r})"]
+    _assert_no_unexpected(case.id, mismatches, caveat, ref=case.ref)
+
+
+# ---------------------------------------------------------------------------
+# Multi-run and setup-heavy scenarios (kept as explicit tests)
+# ---------------------------------------------------------------------------
+
+def _result_aspects(result):
+    return _aspects_to_check(result)
+
+
+_STANDALONE_REFS = {
+    "incremental_modified": "-i/--itemize-changes + incremental second run",
+    "compare_dest": "--compare-dest",
+    "copy_dest": "--copy-dest",
+    "link_dest": "--link-dest",
+    "link_dest_stats": "--link-dest + --stats",
+    "verify_basis": "--verify-basis (FastSync-only)",
+    "verify_basis_default": "--verify-basis (default quick-check vs rsync)",
+    "added_and_deleted": "--delete across two runs",
+    "added_and_deleted_seed": "--delete across two runs",
+    "one_file_system": "-x/--one-file-system",
+}
+
+
+def _run_and_check(case_id, result, ref=""):
+    mismatches = _result_aspects(result)
+    if result["rsync_rc"] != result["fastsync_rc"]:
+        mismatches["rc"] = [
+            f"rsync rc={result['rsync_rc']} fastsync rc={result['fastsync_rc']} "
+            f"(rsync stderr: {result['rsync_stderr'][:200]!r}, "
+            f"fastsync stderr: {result['fastsync_stderr'][:200]!r})"]
+    _assert_no_unexpected(case_id, mismatches, caveat_for(case_id),
+                          ref=ref or _STANDALONE_REFS.get(case_id, ""))
+
+
+@requires_rsync
+@parity
+def test_incremental_modified_file(parity_server_factory):
+    """A second run sends only the modified file; destinations stay identical."""
+    case_id = "incremental_modified"
+    src = os.path.join(TEST_DATA_DIR, "parity_inc_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_inc_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_inc_fdst")
+    H.CORPORA["basic"](src)
+    server = parity_server_factory(SUPER)
+
+    # Seed both destinations with the initial content.
+    H.run_differential(src, rdst, fdst, ["-a"], ["-a"], server,
+                       extra_check=lambda *a: [])
+    with open(os.path.join(src, "a.txt"), "wb") as fh:
+        fh.write(b"hello world, now modified and longer\n")
+    _pin(os.path.join(src, "a.txt"), 1_650_000_000)
+
+    result = H.run_differential(
+        src, rdst, fdst, ["-a", "-i"], ["-a", "-i", "--incremental"], server,
+        stdout=H.STDOUT_ITEMIZE)
+    _run_and_check(case_id, result)
+
+
+def _seed_basis(rel_entries):
+    def seed(src, rroot, froot):
+        for root in (rroot, froot):
+            os.makedirs(root, exist_ok=True)
+            for rel, data in rel_entries.items():
+                _mk(os.path.join(root, rel), data)
+    return seed
+
+
+@requires_rsync
+@parity
+def test_compare_dest_skips_basis(parity_server_factory):
+    """--compare-dest: a file present in the basis is not copied."""
+    case_id = "compare_dest"
+    src = os.path.join(TEST_DATA_DIR, "parity_cmpd_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_cmpd_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_cmpd_fdst")
+    clean_dir(src)
+    _mk(os.path.join(src, "f.txt"), b"basis-content\n")
+    _pin(os.path.join(src, "f.txt"), _OLD_MTIME)
+    server = parity_server_factory(SUPER)
+    rel = os.path.abspath(src).lstrip(os.sep)
+
+    # rsync resolves --compare-dest relative to the destination dir; FastSync
+    # resolves it under the receive root and appends the mirrored source path.
+    # Both rely on rsync's size+mtime quick-check, so the basis mtime is pinned
+    # to the source's to keep the match deterministic across a second boundary.
+    def seed(_src, rroot, froot):
+        _mk(os.path.join(rroot, "basis", "f.txt"), b"basis-content\n", _OLD_MTIME)
+        _mk(os.path.join(fdst, "basis", rel, "f.txt"), b"basis-content\n", _OLD_MTIME)
+
+    def extra(_src, rroot, froot, _rs, _fs):
+        out = []
+        for label, root in (("rsync", rroot), ("fastsync", froot)):
+            if os.path.exists(os.path.join(root, "f.txt")):
+                out.append(f"{label} copied a file that is present in the "
+                           f"compare basis")
+        return out
+
+    result = H.run_differential(
+        src, rdst, fdst,
+        ["-a", "--compare-dest=basis"],
+        ["-a", f"--compare-dest={os.path.join(fdst, 'basis')}", "--incremental"],
+        server, seed=seed, ignore_paths=("basis",), extra_check=extra)
+    _run_and_check(case_id, result)
+
+
+@requires_rsync
+@parity
+def test_link_dest_hardlinks_basis(parity_server_factory):
+    """--link-dest: an unchanged file is hard-linked to the basis, not copied."""
+    case_id = "link_dest"
+    src = os.path.join(TEST_DATA_DIR, "parity_linkd_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_linkd_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_linkd_fdst")
+    clean_dir(src)
+    _mk(os.path.join(src, "f.txt"), b"link-basis-content\n")
+    _pin(os.path.join(src, "f.txt"), _OLD_MTIME)
+    server = parity_server_factory(SUPER)
+    rel = os.path.abspath(src).lstrip(os.sep)
+
+    def seed(_src, rroot, froot):
+        _mk(os.path.join(rroot, "basis", "f.txt"), b"link-basis-content\n", _OLD_MTIME)
+        _mk(os.path.join(fdst, "basis", rel, "f.txt"), b"link-basis-content\n", _OLD_MTIME)
+
+    def extra(_src, rroot, froot, _rs, _fs):
+        r_basis = os.stat(os.path.join(rroot, "basis", "f.txt")).st_ino
+        f_basis = os.stat(os.path.join(fdst, "basis", rel, "f.txt")).st_ino
+        out = []
+        for label, root, basis in (("rsync", rroot, r_basis),
+                                   ("fastsync", froot, f_basis)):
+            target = os.path.join(root, "f.txt")
+            if not os.path.exists(target):
+                out.append(f"{label}: f.txt missing")
+            elif os.stat(target).st_ino != basis:
+                out.append(f"{label}: f.txt is not hard-linked to the basis")
+        return out
+
+    result = H.run_differential(
+        src, rdst, fdst,
+        ["-a", "--link-dest=basis"],
+        ["-a", f"--link-dest={os.path.join(fdst, 'basis')}", "--incremental"],
+        server, seed=seed, ignore_paths=("basis",), extra_check=extra)
+    _run_and_check(case_id, result)
+
+
+@requires_rsync
+@parity
+def test_link_dest_stats_matches_rsync(parity_server_factory):
+    """A basis hit must not be counted as created or literal data: rsync reports
+    zero for both, so FastSync's receiver tallies must too (regression for the
+    basis materialization over-report)."""
+    case_id = "link_dest_stats"
+    src = os.path.join(TEST_DATA_DIR, "parity_linkds_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_linkds_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_linkds_fdst")
+    clean_dir(src)
+    _mk(os.path.join(src, "f.txt"), b"link-basis-content\n")
+    _pin(os.path.join(src, "f.txt"), _OLD_MTIME)
+    server = parity_server_factory(SUPER)
+    rel = os.path.abspath(src).lstrip(os.sep)
+
+    def seed(_src, rroot, froot):
+        _mk(os.path.join(rroot, "basis", "f.txt"), b"link-basis-content\n", _OLD_MTIME)
+        _mk(os.path.join(fdst, "basis", rel, "f.txt"), b"link-basis-content\n", _OLD_MTIME)
+
+    result = H.run_differential(
+        src, rdst, fdst,
+        ["-a", "--link-dest=basis", "--stats"],
+        ["-a", f"--link-dest={os.path.join(fdst, 'basis')}", "--incremental", "--stats"],
+        server, seed=seed, ignore_paths=("basis",), stdout=H.STDOUT_STATS)
+    _run_and_check(case_id, result, ref="--link-dest + --stats")
+
+
+@requires_rsync
+@parity
+def test_copy_dest_copies_basis(parity_server_factory):
+    """--copy-dest: a basis match is materialized as an independent copy with the
+    source's attributes, matching rsync (copy then fix attributes)."""
+    case_id = "copy_dest"
+    src = os.path.join(TEST_DATA_DIR, "parity_copyd_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_copyd_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_copyd_fdst")
+    clean_dir(src)
+    _mk(os.path.join(src, "f.txt"), b"copy-basis-content\n")
+    _pin(os.path.join(src, "f.txt"), 1_600_000_000)
+    os.chmod(os.path.join(src, "f.txt"), 0o755)
+    server = parity_server_factory(SUPER)
+    rel = os.path.abspath(src).lstrip(os.sep)
+
+    def seed(_src, rroot, froot):
+        # Basis content matches the source; give the basis a different mode so a
+        # wrong "keep basis attributes" implementation is visible.
+        _mk(os.path.join(rroot, "basis", "f.txt"), b"copy-basis-content\n",
+            1_600_000_000)
+        os.chmod(os.path.join(rroot, "basis", "f.txt"), 0o644)
+        _mk(os.path.join(fdst, "basis", rel, "f.txt"), b"copy-basis-content\n",
+            1_600_000_000)
+        os.chmod(os.path.join(fdst, "basis", rel, "f.txt"), 0o644)
+
+    def extra(_src, rroot, froot, _rs, _fs):
+        out = []
+        bases = {"rsync": os.path.join(rroot, "basis", "f.txt"),
+                 "fastsync": os.path.join(fdst, "basis", rel, "f.txt")}
+        for label, root in (("rsync", rroot), ("fastsync", froot)):
+            target = os.path.join(root, "f.txt")
+            if not os.path.exists(target):
+                out.append(f"{label}: f.txt missing")
+                continue
+            if os.stat(target).st_ino == os.stat(bases[label]).st_ino:
+                out.append(f"{label}: f.txt is hard-linked, not copied")
+            if (os.stat(target).st_mode & 0o777) != 0o755:
+                out.append(f"{label}: f.txt mode "
+                           f"{oct(os.stat(target).st_mode & 0o777)} != 0o755")
+        return out
+
+    result = H.run_differential(
+        src, rdst, fdst,
+        ["-a", "--copy-dest=basis"],
+        ["-a", f"--copy-dest={os.path.join(fdst, 'basis')}", "--incremental"],
+        server, seed=seed, ignore_paths=("basis",), extra_check=extra,
+        compare_modes=True)
+    _run_and_check(case_id, result)
+
+
+@requires_rsync
+@parity
+def test_verify_basis_restores_strict_content(parity_server_factory):
+    """Default matches rsync's metadata quick-check; FastSync-only
+    `--verify-basis` restores strict content equality and transfers the source
+    when a same-size/different-content basis would otherwise be trusted."""
+    case_id = "verify_basis"
+    src = os.path.join(TEST_DATA_DIR, "parity_vbasis_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_vbasis_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_vbasis_fdst")
+    clean_dir(src)
+    _mk(os.path.join(src, "f.txt"), b"AAAA\n")
+    _pin(os.path.join(src, "f.txt"), _OLD_MTIME)
+    server = parity_server_factory(SUPER)
+    rel = os.path.abspath(src).lstrip(os.sep)
+
+    def seed(_src, rroot, froot):
+        # Same size and mtime as the source, different bytes: a metadata
+        # quick-check trusts it; --verify-basis must not.
+        for root, basis_rel in ((rroot, os.path.join("basis", "f.txt")),
+                                (fdst, os.path.join("basis", rel, "f.txt"))):
+            _mk(os.path.join(root, basis_rel), b"BBBB\n", _OLD_MTIME)
+
+    # Default: both tools trust the basis (rsync's quick check), so the
+    # destination carries the basis bytes and the trees match.
+    result = H.run_differential(
+        src, rdst, fdst,
+        ["-a", "--link-dest=basis"],
+        ["-a", f"--link-dest={os.path.join(fdst, 'basis')}", "--incremental"],
+        server, seed=seed, ignore_paths=("basis",))
+    _run_and_check(case_id + "_default", result)
+
+    # --verify-basis (FastSync only): the digest mismatch rejects the basis and
+    # the source is transferred, so the destination is the source bytes.  rsync
+    # has no such flag; assert the FastSync outcome directly against the source.
+    fdst2 = os.path.join(TEST_DATA_DIR, "parity_vbasis_fdst2")
+    clean_dir(fdst2)
+    for root, basis_rel in ((fdst2, os.path.join("basis", rel, "f.txt")),):
+        _mk(os.path.join(root, basis_rel), b"BBBB\n", _OLD_MTIME)
+    result, _ = H.run_fastsync(src, fdst2,
+                               ["-a", f"--link-dest={os.path.join(fdst2, 'basis')}",
+                                "--incremental", "--verify-basis"], server.port)
+    assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+    target = os.path.join(get_dest_received_dir(fdst2, src), "f.txt")
+    with open(target, "rb") as fh:
+        assert fh.read() == b"AAAA\n", \
+            "--verify-basis must reject the same-size/different-content basis"
+
+
+@requires_rsync
+@parity
+def test_added_and_deleted_between_runs(parity_server_factory):
+    """A source deletion and addition sync correctly under --delete."""
+    case_id = "added_and_deleted"
+    src = os.path.join(TEST_DATA_DIR, "parity_addel_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_addel_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_addel_fdst")
+    server = parity_server_factory(DELETE)
+    H.CORPORA["basic"](src)
+
+    seed = seed_extras
+    result = H.run_differential(
+        src, rdst, fdst, ["-a", "--delete"], ["-a", "--delete"], server,
+        seed=seed)
+    _run_and_check(case_id + "_seed", result)
+
+    os.remove(os.path.join(src, "a.txt"))
+    _mk(os.path.join(src, "added.txt"), b"added between runs\n")
+    result = H.run_differential(
+        src, rdst, fdst, ["-a", "--delete", "-i"],
+        ["-a", "--delete", "-i", "--incremental"], server,
+        stdout=H.STDOUT_ITEMIZE)
+    _run_and_check(case_id, result)
+
+
+@requires_rsync
+@parity
+def test_one_file_system(parity_server_factory):
+    """-x emits the mount-point directory but not its contents."""
+    case_id = "one_file_system"
+    local = os.stat(".")
+    shm = "/dev/shm"
+    if not os.path.isdir(shm):
+        pytest.skip("/dev/shm not available")
+    if os.stat(shm).st_dev == local.st_dev:
+        pytest.skip("no cross-device filesystem available")
+
+    src = os.path.join(TEST_DATA_DIR, "parity_ofs_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_ofs_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_ofs_fdst")
+    clean_dir(src)
+    _mk(os.path.join(src, "keep.txt"), b"keep\n")
+    probe = os.path.join(shm, f"fastsync_ofs_{os.getpid()}")
+    shutil.rmtree(probe, ignore_errors=True)
+    os.makedirs(probe)
+    _mk(os.path.join(probe, "inside.txt"), b"cross\n")
+    try:
+        os.symlink(probe, os.path.join(src, "nested_link"))
+        server = parity_server_factory(SUPER)
+        result = H.run_differential(
+            src, rdst, fdst,
+            ["-a", "--copy-links", "-x"],
+            ["-a", "--copy-links", "-x"], server)
+        _run_and_check(case_id, result)
+    finally:
+        shutil.rmtree(probe, ignore_errors=True)
+
+
+@requires_rsync
+@parity
+def test_parity_caveats_reference_known_cases():
+    """Every allowlist entry must name a real case id and aspect."""
+    from parity_caveats import CAVEATS
+    known = {c.id for c in ALL_CASES} | {
+        "incremental_modified", "compare_dest", "link_dest",
+        "added_and_deleted", "added_and_deleted_seed", "one_file_system",
+    }
+    problems = []
+    for case_id, entry in CAVEATS.items():
+        if case_id not in known:
+            problems.append(f"unknown case id in parity_caveats.py: {case_id!r}")
+        for aspect in entry:
+            if aspect not in ASPECTS:
+                problems.append(
+                    f"{case_id!r}: unknown aspect {aspect!r} (expected {ASPECTS})")
+    assert not problems, "\n".join(problems)

tests/integration/test_fault_injection.py

@@ -36,7 +36,7 @@ from common import (  # noqa: E402
     verify_transfer,
 )
 
-PROTOCOL_VERSION = b"2.21.0"
+PROTOCOL_VERSION = b"2.28.0"
 STATUS_MANIFEST = 5
 STATUS_OK = 0
 
@@ -59,6 +59,10 @@ def _seed_source():
     if os.path.exists(SOURCE_DIR):
         shutil.rmtree(SOURCE_DIR)
     os.makedirs(os.path.join(SOURCE_DIR, "nested"))
+    # The receiver rejects a destination root that does not exist, and the
+    # capture fixture can run before any test that creates it, so create it
+    # here (test order/distribution must not matter).
+    os.makedirs(DEST_DIR, exist_ok=True)
     with open(os.path.join(SOURCE_DIR, "hello.txt"), "wb") as fh:
         fh.write(b"fault injection payload\n" * 64)
     with open(os.path.join(SOURCE_DIR, "nested", "deep.bin"), "wb") as fh:

tests/integration/test_iconv.py

@@ -1,10 +1,12 @@
 """--iconv=CONVERT_SPEC file-NAME charset conversion integration tests.
 
-The client converts every source file name from LOCAL to REMOTE before it goes
-on the wire, and the receiver converts it back from REMOTE to LOCAL, so a
-source tree using one charset can be written into a destination tree using
-another (rsync compatibility; content bytes are never touched).
+rsync's spec is ``--iconv=LOCAL,REMOTE`` (the order is the same push or pull).
+The sender converts each source name from LOCAL to REMOTE for the wire, and on
+a PUSH the receiver's charset is the spec's REMOTE half, so it writes the wire
+bytes verbatim (only a server with its own ``--iconv`` declares a different
+destination charset and re-converts).  Content bytes are never touched.
 """
+import codecs
 import os
 import shutil
 
@@ -16,6 +18,11 @@ LATIN1_NAME = b"caf\xe9.txt"
 UTF8_NAME = "caf\u00e9.txt".encode("utf-8")
 
 
+def _to_utf8(name_bytes):
+    """The UTF-8 encoding of a name that is stored as ISO-8859-1 bytes."""
+    return codecs.encode(codecs.decode(name_bytes, "iso-8859-1"), "utf-8")
+
+
 def _make(tag):
     source = os.path.join(TEST_DATA_DIR, f"iconv_{tag}_src")
     dest = os.path.join(TEST_DATA_DIR, f"iconv_{tag}_dst")
@@ -41,10 +48,10 @@ def _dest_file(source, dest, name):
 
 
 @pytest.mark.ci
-def test_iconv_latin1_roundtrip(shared_server):
-    """A source file whose name is ISO-8859-1 bytes is transferred with
-    --iconv=iso-8859-1,utf-8 and lands on the destination with the ORIGINAL
-    latin1 name (the wire carried it as UTF-8)."""
+def test_iconv_latin1_to_utf8_dest(shared_server):
+    """rsync push parity: --iconv=iso-8859-1,utf-8 converts a latin1 source name
+    to the spec's REMOTE (UTF-8) on the wire and the default receiver writes it
+    verbatim, so the destination name is UTF-8 (not the source's latin1)."""
     source, dest = _make("latin1")
     _place_bytes(source, LATIN1_NAME)
 
@@ -53,8 +60,10 @@ def test_iconv_latin1_roundtrip(shared_server):
     )
     assert result.returncode == 0, (result.stderr or result.stdout)[:400]
 
-    dst = _dest_file(source, dest, LATIN1_NAME)
-    assert os.path.exists(dst), f"dest latin1-named file not found under {dest}"
+    dst = _dest_file(source, dest, UTF8_NAME)
+    assert os.path.exists(dst), f"dest UTF-8-named file not found under {dest}"
+    assert not os.path.exists(_dest_file(source, dest, LATIN1_NAME)), \
+        "destination kept the latin1 name instead of the wire (UTF-8) charset"
 
 
 @pytest.mark.ci
@@ -153,7 +162,7 @@ def test_iconv_expanding_name_growth(shared_server):
     )
     assert result.returncode == 0, (result.stderr or result.stdout)[:400]
 
-    assert os.path.exists(_dest_file(source, dest, name_bytes))
+    assert os.path.exists(_dest_file(source, dest, _to_utf8(name_bytes)))
 
 
 def test_iconv_symlink_path_and_target(shared_server):
@@ -170,11 +179,13 @@ def test_iconv_symlink_path_and_target(shared_server):
     )
     assert result.returncode == 0, (result.stderr or result.stdout)[:400]
 
-    dst_target = _dest_file(source, dest, target)
-    dst_link = _dest_file(source, dest, b"link\xe9")
-    assert os.path.exists(dst_target), "dest latin1 target file missing"
-    assert os.path.islink(dst_link), "dest latin1 symlink missing"
-    assert os.readlink(dst_link) == target, "symlink target not preserved/decoded"
+    utf8_target = _to_utf8(target)
+    utf8_link = _to_utf8(b"link\xe9")
+    dst_target = _dest_file(source, dest, utf8_target)
+    dst_link = _dest_file(source, dest, utf8_link)
+    assert os.path.exists(dst_target), "dest UTF-8 target file missing"
+    assert os.path.islink(dst_link), "dest UTF-8 symlink missing"
+    assert os.readlink(dst_link) == utf8_target, "symlink target not wire-converted"
     with open(dst_link, "rb") as fh:
         assert fh.read() == b"t\n"
 
@@ -198,8 +209,8 @@ def test_iconv_hardlink_path_and_target(shared_server):
     )
     assert result.returncode == 0, (result.stderr or result.stdout)[:400]
 
-    dst_a = _dest_file(source, dest, a)
-    dst_b = _dest_file(source, dest, b)
+    dst_a = _dest_file(source, dest, _to_utf8(a))
+    dst_b = _dest_file(source, dest, _to_utf8(b))
     assert os.path.exists(dst_a) and os.path.exists(dst_b)
     assert os.stat(dst_a).st_ino == os.stat(dst_b).st_ino, \
         "hard-link relationship not preserved across the transfer"
@@ -221,16 +232,16 @@ def test_iconv_delete_manifest_consistent(shared_server):
         flags = ["--iconv=iso-8859-1,utf-8"]
         result, _ = run_client(source, dest, flags=flags, port=server.port)
         assert result.returncode == 0, (result.stderr or result.stdout)[:400]
-        assert os.path.exists(_dest_file(source, dest, keep))
-        assert os.path.exists(_dest_file(source, dest, gone))
+        assert os.path.exists(_dest_file(source, dest, _to_utf8(keep)))
+        assert os.path.exists(_dest_file(source, dest, _to_utf8(gone)))
 
         os.remove(os.path.join(os.fsencode(source), gone))
         result, _ = run_client(
             source, dest, flags=flags + ["--delete"], port=server.port
         )
         assert result.returncode == 0, (result.stderr or result.stdout)[:400]
-        assert os.path.exists(_dest_file(source, dest, keep)), "kept file deleted"
-        assert not os.path.exists(_dest_file(source, dest, gone)), \
+        assert os.path.exists(_dest_file(source, dest, _to_utf8(keep))), "kept file deleted"
+        assert not os.path.exists(_dest_file(source, dest, _to_utf8(gone))), \
             "missing file was not deleted"
 
 
@@ -247,4 +258,4 @@ def test_iconv_chunk_serialization_blob(shared_server):
     )
     assert result.returncode == 0, (result.stderr or result.stdout)[:400]
 
-    assert os.path.exists(_dest_file(source, dest, name))
+    assert os.path.exists(_dest_file(source, dest, _to_utf8(name)))

tests/integration/test_option_parity.py

@@ -0,0 +1,538 @@
+"""Differential parity tests for the option wave (bwlimit, --info=*, -M,
+--ignore-errors, --filter protect).
+
+Every differential here runs the SAME scenario with real ``rsync 3.4.1`` and
+with fastsync and compares the observable result, so the modules are skipped
+when rsync is unavailable.  The privilege-dependent --ignore-errors differential
+drops the client to an unprivileged uid so a mode-000 source directory is
+genuinely unreadable; it is marked ``setpriv`` (run as root locally, excluded
+from the root PR gate exactly like the other privilege tests).
+"""
+import os
+import shutil
+import subprocess
+import sys
+import time
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (  # noqa: E402
+    CLIENT_CMD,
+    TEST_DATA_DIR,
+    ServerManager,
+    clean_dir,
+    get_dest_received_dir,
+    run_client,
+)
+
+RSYNC = shutil.which("rsync")
+requires_rsync = pytest.mark.skipif(RSYNC is None, reason="rsync 3.4.1 not installed")
+
+
+def _rsync(args, timeout=120, as_nobody=False):
+    env = dict(os.environ, LC_ALL="C")
+    cmd = [RSYNC] + args
+    if as_nobody:
+        cmd = ["setpriv", "--reuid=65534", "--regid=65534", "--clear-groups"] + cmd
+    return subprocess.run(cmd, capture_output=True, text=True, env=env, timeout=timeout)
+
+
+def _write(path, content):
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    with open(path, "wb") as fh:
+        fh.write(content)
+
+
+class TestBwlimitParity:
+    """--bwlimit must accept rsync 3.4.1's spellings and pace like it."""
+
+    ACCEPTED = ["100", "0", "1.5", "100K", "100KB", "100KiB", "1M", "1MB", "1m", "1G", "512"]
+    REJECTED = ["-1", "abc", "1x", "1 000"]
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_parse_acceptance_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "bwp_src")
+        clean_dir(source)
+        _write(os.path.join(source, "f.txt"), b"payload\n")
+
+        for value in self.ACCEPTED + self.REJECTED:
+            rdst = os.path.join(TEST_DATA_DIR, "bwp_rdst")
+            clean_dir(rdst)
+            rsync_result = _rsync(["-a", "--bwlimit=" + value, source + "/", rdst + "/"])
+            dest = os.path.join(TEST_DATA_DIR, "bwp_dst")
+            clean_dir(dest)
+            result, _ = run_client(source, dest, flags=["-a", "--bwlimit=" + value],
+                                   port=shared_server.port)
+            assert (result.returncode == 0) == (rsync_result.returncode == 0), (
+                f"--bwlimit={value}: fastsync rc={result.returncode} "
+                f"({(result.stderr or result.stdout)[:120]!r}) "
+                f"rsync rc={rsync_result.returncode} ({rsync_result.stderr[:120]!r})"
+            )
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_throttle_rate_matches_rsync(self, shared_server):
+        """A 4 MiB transfer at --bwlimit=2048 (2 MiB/s) must take about the same
+        wall-clock time for both tools (~2 s with rsync's leaky bucket)."""
+        source = os.path.join(TEST_DATA_DIR, "bwt_src")
+        clean_dir(source)
+        _write(os.path.join(source, "big.bin"), os.urandom(4 * 1024 * 1024))
+        dest = os.path.join(TEST_DATA_DIR, "bwt_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "bwt_rdst")
+
+        clean_dir(rdst)
+        start = time.monotonic()
+        rsync_result = _rsync(["-a", "--bwlimit=2048", source + "/", rdst + "/"])
+        rsync_secs = time.monotonic() - start
+        assert rsync_result.returncode == 0, rsync_result.stderr
+
+        clean_dir(dest)
+        result, fast_secs = run_client(source, dest, flags=["-a", "--bwlimit=2048"],
+                                       port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+        # 4 MiB at 2 MiB/s rendezvous near 2 s.  Use a coarse band on each side
+        # (an unthrottled transfer finishes well under 1.5 s) plus a generous
+        # cross-tolerance so a loaded CI runner cannot flake the parity assert.
+        lo, hi = 1.5, 4.5
+        assert lo <= fast_secs <= hi, f"fastsync throttle out of band: {fast_secs:.2f}s"
+        assert lo <= rsync_secs <= hi, f"rsync throttle out of band: {rsync_secs:.2f}s"
+        assert abs(fast_secs - rsync_secs) < 2.0, (
+            f"fastsync {fast_secs:.2f}s vs rsync {rsync_secs:.2f}s"
+        )
+
+
+def _output_tree(root):
+    clean_dir(root)
+    os.makedirs(os.path.join(root, "sub"))
+    _write(os.path.join(root, "a.txt"), b"top\n")
+    _write(os.path.join(root, "sub", "b.txt"), b"nested\n")
+    os.symlink("a.txt", os.path.join(root, "link"))
+
+
+class TestInfoParity:
+    """The --info categories that map to a FastSync event must print rsync's
+    line format."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_info_flist_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "inf_fl_src")
+        dest = os.path.join(TEST_DATA_DIR, "inf_fl_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "inf_fl_rdst")
+        _output_tree(source)
+        clean_dir(dest)
+        clean_dir(rdst)
+        rsync_result = _rsync(["-a", "--info=flist", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["-a", "--info=flist"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+        assert "sending incremental file list" in result.stdout
+        assert "sending incremental file list" in rsync_result.stdout
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_info_name_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "inf_nm_src")
+        dest = os.path.join(TEST_DATA_DIR, "inf_nm_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "inf_nm_rdst")
+        _output_tree(source)
+        clean_dir(dest)
+        clean_dir(rdst)
+        rsync_result = _rsync(["-a", "--info=name", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["-a", "--info=name"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+
+        def entries(text):
+            # Compare the transferred entries only: rsync also prints the
+            # transfer-root `./` and every directory (FastSync records dirs),
+            # which are a separate documented divergence.
+            out = []
+            for line in text.splitlines():
+                if not line or line.startswith("sending ") or line.startswith("created "):
+                    continue
+                if line == "./" or line.endswith("/"):
+                    continue
+                out.append(line)
+            return sorted(out)
+
+        assert entries(result.stdout) == entries(rsync_result.stdout), (
+            f"rsync={entries(rsync_result.stdout)} fastsync={entries(result.stdout)}"
+        )
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_info_name_root_line_matches_rsync(self, shared_server):
+        """A fresh destination: rsync prints `created directory`, then the
+        transfer-root `./` name line before the entries; FastSync must emit the
+        same `./` line."""
+        source = os.path.join(TEST_DATA_DIR, "inf_root_src")
+        dest = os.path.join(TEST_DATA_DIR, "inf_root_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "inf_root_rdst")
+        clean_dir(source)
+        _write(os.path.join(source, "f.bin"), b"payload\n")
+        clean_dir(dest)
+        shutil.rmtree(rdst, ignore_errors=True)
+        rsync_result = _rsync(["-a", "--info=name", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["-a", "--info=name"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+
+        def names(text):
+            return [l for l in text.splitlines()
+                    if l and not l.startswith("created directory")
+                    and not (l.endswith("/") and l != "./")]
+
+        assert names(rsync_result.stdout) == ["./", "f.bin"], names(rsync_result.stdout)
+        assert names(result.stdout) == ["./", "f.bin"], names(result.stdout)
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_info_name2_uptodate_matches_rsync(self, shared_server):
+        """--info=name2 prints `NAME is uptodate` for entries the receiver
+        already has, matching rsync byte-for-byte."""
+        source = os.path.join(TEST_DATA_DIR, "inf_up_src")
+        dest = os.path.join(TEST_DATA_DIR, "inf_up_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "inf_up_rdst")
+        clean_dir(source)
+        os.makedirs(os.path.join(source, "sub"))
+        _write(os.path.join(source, "a.txt"), b"a\n")
+        _write(os.path.join(source, "sub", "b.txt"), b"b\n")
+        clean_dir(rdst)
+        assert _rsync(["-a", source + "/", rdst + "/"]).returncode == 0
+        rsync_result = _rsync(["-a", "--info=name2", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+
+        clean_dir(dest)
+        seed, _ = run_client(source, dest, flags=["-a", "--incremental"],
+                             port=shared_server.port)
+        assert seed.returncode == 0, (seed.stderr or seed.stdout)[:200]
+        result, _ = run_client(source, dest, flags=["-a", "--incremental", "--info=name2"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+        rsync_lines = sorted(l for l in rsync_result.stdout.splitlines()
+                             if l.endswith("is uptodate"))
+        fast_lines = sorted(l for l in result.stdout.splitlines()
+                            if l.endswith("is uptodate"))
+        assert fast_lines == rsync_lines, (rsync_lines, fast_lines)
+        assert fast_lines == ["a.txt is uptodate", "sub/b.txt is uptodate"], fast_lines
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_info_nonreg_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "inf_nr_src")
+        dest = os.path.join(TEST_DATA_DIR, "inf_nr_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "inf_nr_rdst")
+        clean_dir(source)
+        os.mkfifo(os.path.join(source, "fifo"))
+        _write(os.path.join(source, "a.txt"), b"a\n")
+        clean_dir(dest)
+        clean_dir(rdst)
+        rsync_result = _rsync(["-rlt", "--info=nonreg", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["-rlt", "--info=nonreg"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+        rsync_lines = sorted(l for l in rsync_result.stdout.splitlines()
+                             if l.startswith("skipping non-regular"))
+        fast_lines = sorted(l for l in result.stdout.splitlines()
+                            if l.startswith("skipping non-regular"))
+        assert fast_lines == rsync_lines, (rsync_lines, fast_lines)
+        assert fast_lines, "no non-regular skip line emitted"
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_info_del_real_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "inf_dl_src")
+        dest = os.path.join(TEST_DATA_DIR, "inf_dl_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "inf_dl_rdst")
+        clean_dir(source)
+        _write(os.path.join(source, "keep.txt"), b"keep\n")
+        clean_dir(rdst)
+        _write(os.path.join(rdst, "extra.txt"), b"x\n")
+        _write(os.path.join(rdst, "extra2.txt"), b"y\n")
+        rsync_result = _rsync(["-a", "--delete", "--info=del", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_lines = sorted(l for l in rsync_result.stdout.splitlines()
+                             if l.startswith("deleting "))
+
+        clean_dir(dest)
+        received = get_dest_received_dir(dest, source)
+        _write(os.path.join(received, "extra.txt"), b"x\n")
+        _write(os.path.join(received, "extra2.txt"), b"y\n")
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest, flags=["-a", "--delete", "--info=del"],
+                                   port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+        fast_lines = sorted(l for l in result.stdout.splitlines()
+                            if l.startswith("deleting "))
+        assert fast_lines == rsync_lines, (rsync_lines, fast_lines)
+        assert fast_lines, "no deletion lines emitted"
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_info_del_itemize_real_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "inf_di_src")
+        dest = os.path.join(TEST_DATA_DIR, "inf_di_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "inf_di_rdst")
+        clean_dir(source)
+        _write(os.path.join(source, "keep.txt"), b"keep\n")
+        clean_dir(rdst)
+        _write(os.path.join(rdst, "extra.txt"), b"x\n")
+        rsync_result = _rsync(["-a", "-i", "--delete", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_lines = sorted(l for l in rsync_result.stdout.splitlines()
+                             if l.startswith("*deleting"))
+
+        clean_dir(dest)
+        received = get_dest_received_dir(dest, source)
+        _write(os.path.join(received, "extra.txt"), b"x\n")
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest, flags=["-a", "-i", "--delete"],
+                                   port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+        fast_lines = sorted(l for l in result.stdout.splitlines()
+                            if l.startswith("*deleting"))
+        assert fast_lines == rsync_lines, (rsync_lines, fast_lines)
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_info_del_dry_run_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "inf_dd_src")
+        dest = os.path.join(TEST_DATA_DIR, "inf_dd_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "inf_dd_rdst")
+        clean_dir(source)
+        _write(os.path.join(source, "keep.txt"), b"keep\n")
+        clean_dir(rdst)
+        _write(os.path.join(rdst, "extra.txt"), b"x\n")
+        rsync_result = _rsync(["-a", "-n", "--delete", "--info=del", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_lines = sorted(l for l in rsync_result.stdout.splitlines()
+                             if l.startswith("deleting "))
+
+        clean_dir(dest)
+        received = get_dest_received_dir(dest, source)
+        _write(os.path.join(received, "extra.txt"), b"x\n")
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest, flags=["-a", "-n", "--delete", "--info=del"],
+                                   port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+        fast_lines = sorted(l for l in result.stdout.splitlines()
+                            if l.startswith("deleting "))
+        assert fast_lines == rsync_lines, (rsync_lines, fast_lines)
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_info_remove_matches_rsync(self, shared_server):
+        tag = "inf_rm"
+        rsync_src = os.path.join(TEST_DATA_DIR, f"{tag}_rsrc")
+        rsync_dst = os.path.join(TEST_DATA_DIR, f"{tag}_rdst")
+        fast_src = os.path.join(TEST_DATA_DIR, f"{tag}_fsrc")
+        fast_dst = os.path.join(TEST_DATA_DIR, f"{tag}_fdst")
+        for root in (rsync_src, rsync_dst, fast_src, fast_dst):
+            clean_dir(root)
+        _write(os.path.join(rsync_src, "a.txt"), b"a\n")
+        _write(os.path.join(rsync_src, "sub", "b.txt"), b"b\n")
+        _write(os.path.join(fast_src, "a.txt"), b"a\n")
+        _write(os.path.join(fast_src, "sub", "b.txt"), b"b\n")
+
+        rsync_result = _rsync(["-a", "--remove-source-files", "--info=remove",
+                               rsync_src + "/", rsync_dst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_lines = sorted(l for l in rsync_result.stdout.splitlines()
+                             if l.startswith("sender removed "))
+
+        result, _ = run_client(fast_src, fast_dst,
+                               flags=["-a", "--remove-source-files", "--info=remove"],
+                               port=shared_server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+        fast_lines = sorted(l for l in result.stdout.splitlines()
+                            if l.startswith("sender removed "))
+        assert fast_lines == rsync_lines, (rsync_lines, fast_lines)
+        assert fast_lines, "no source-removal lines emitted"
+
+
+class TestIgnoreErrorsParity:
+    """--ignore-errors: a source I/O error skips deletion by default; the flag
+    lets deletion proceed.  Both exit 23.  Run the client as an unprivileged user
+    so the mode-000 directory is genuinely unreadable."""
+
+    @pytest.mark.setpriv
+    def test_delete_after_io_error_matches_rsync(self):
+        if os.geteuid() != 0 or shutil.which("setpriv") is None:
+            pytest.skip("requires root + setpriv to drop privileges for the client")
+        tag = f"ie_{os.getpid()}"
+        source = os.path.join(TEST_DATA_DIR, f"{tag}_src")
+        rsync_dst = os.path.join(TEST_DATA_DIR, f"{tag}_rdst")
+        dest = os.path.join(TEST_DATA_DIR, f"{tag}_dst")
+        clean_dir(source)
+        clean_dir(rsync_dst)
+        clean_dir(dest)
+        _write(os.path.join(source, "top.txt"), b"top\n")
+        _write(os.path.join(source, "locked", "blocked.txt"), b"blocked\n")
+        os.chmod(os.path.join(source, "locked"), 0)
+        os.chmod(TEST_DATA_DIR, 0o777)
+        os.chmod(source, 0o755)
+        os.chmod(rsync_dst, 0o777)
+        os.chmod(dest, 0o777)
+        try:
+            for ignore in (False, True):
+                flags = ["-a", "--delete-after"] + (["--ignore-errors"] if ignore else [])
+                # rsync side
+                _write(os.path.join(rsync_dst, "extra.txt"), b"x\n")
+                os.chmod(os.path.join(rsync_dst, "extra.txt"), 0o666)
+                rres = _rsync(flags + [source + "/", rsync_dst + "/"], as_nobody=True)
+                rsync_extra = os.path.exists(os.path.join(rsync_dst, "extra.txt"))
+
+                # fastsync side
+                received = get_dest_received_dir(dest, source)
+                _write(os.path.join(received, "extra.txt"), b"x\n")
+                os.chmod(os.path.join(received, "extra.txt"), 0o666)
+                with ServerManager() as server:
+                    server.start(extra_args=["--allow-delete"])
+                    fflags = (["--delete", "--ignore-errors"] if ignore else ["--delete"])
+                    cmd = CLIENT_CMD + ["--source-dir", source, "--dest-dir", dest,
+                                        "--save-to-disk", "--server-port", str(server.port)] + fflags
+                    fres = subprocess.run(
+                        ["setpriv", "--reuid=65534", "--regid=65534", "--clear-groups"] + cmd,
+                        text=True, capture_output=True)
+                fast_extra = os.path.exists(os.path.join(received, "extra.txt"))
+
+                assert rres.returncode == 23, (ignore, rres.returncode, rres.stderr[:200])
+                assert fres.returncode == 23, (ignore, fres.returncode, fres.stderr[:200])
+                assert rsync_extra == fast_extra, (
+                    f"ignore_errors={ignore}: rsync extra={rsync_extra} fastsync extra={fast_extra}"
+                )
+                assert fast_extra is (not ignore), (ignore, fast_extra)
+        finally:
+            os.chmod(os.path.join(source, "locked"), 0o755)
+
+
+class TestRemoteOptionDaemon:
+    """rsync forwards -M/--remote-option to its remote process over a daemon
+    connection; FastSync's daemon has no per-connection argv channel and rejects
+    it.  This pins the documented divergence with evidence."""
+
+    @requires_rsync
+    def test_rsync_forwards_M_over_daemon_and_fastsync_rejects(self, tmp_path):
+        import socket
+
+        with socket.socket() as probe:
+            probe.bind(("127.0.0.1", 0))
+            port = probe.getsockname()[1]
+
+        module_root = tmp_path / "mod"
+        module_root.mkdir()
+        os.chmod(module_root, 0o777)
+        source = tmp_path / "src"
+        source.mkdir()
+        (source / "a.txt").write_bytes(b"hello\n")
+        conf = tmp_path / "rsyncd.conf"
+        conf.write_text(
+            f"port = {port}\nuse chroot = no\n[m]\npath = {module_root}\nread only = no\n"
+        )
+        daemon = subprocess.Popen(
+            [RSYNC, "--daemon", "--no-detach", "--port", str(port), "--config", str(conf)],
+            stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+        try:
+            deadline = time.monotonic() + 5
+            while time.monotonic() < deadline:
+                try:
+                    with socket.create_connection(("127.0.0.1", port), timeout=0.3):
+                        break
+                except OSError:
+                    time.sleep(0.05)
+            else:
+                pytest.skip("rsync daemon did not start")
+
+            # A well-formed -M option is forwarded and accepted by the daemon...
+            ok = _rsync(["-a", "-M--safe-links", source.as_posix() + "/",
+                         f"rsync://127.0.0.1:{port}/m/"])
+            # ...and a bogus one is rejected ON THE REMOTE with "unknown option",
+            # which proves the option reached the daemon's parser.
+            bogus = _rsync(["-a", "-M--totally-bogus", source.as_posix() + "/",
+                            f"rsync://127.0.0.1:{port}/m/"])
+            assert bogus.returncode != 0
+            assert "unknown option" in (bogus.stderr + bogus.stdout), bogus.stderr
+            del ok
+        finally:
+            daemon.terminate()
+            try:
+                daemon.wait(timeout=5)
+            except subprocess.TimeoutExpired:
+                daemon.kill()
+
+        # FastSync rejects -M for a non-SSH transport up front.
+        dest = os.path.join(TEST_DATA_DIR, "ro_dst")
+        clean_dir(dest)
+        result, _ = run_client(source.as_posix(), dest, flags=["-a", "-M--safe-links"])
+        assert result.returncode != 0
+        assert "remote-option" in (result.stderr + result.stdout)
+
+
+class TestFilterProtect:
+    """Receiver-derived delete protection: a `protect`/`P` rule is compiled by
+    the sender and sent on the config frame, so the receiver shields a
+    destination-only entry that never appeared on the sender, matching rsync."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_protect_dest_only_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "fpd_src")
+        dest = os.path.join(TEST_DATA_DIR, "fpd_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "fpd_rdst")
+        clean_dir(source)
+        _write(os.path.join(source, "keep.txt"), b"keep\n")
+        clean_dir(rdst)
+        _write(os.path.join(rdst, "extra.log"), b"extra\n")
+        _write(os.path.join(rdst, "other.txt"), b"other\n")
+
+        rsync_result = _rsync(["-a", "--delete", "--filter=P *.log", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        assert os.path.exists(os.path.join(rdst, "extra.log")), "rsync did not protect extra.log"
+        assert not os.path.exists(os.path.join(rdst, "other.txt")), "rsync did not delete other.txt"
+
+        clean_dir(dest)
+        received = get_dest_received_dir(dest, source)
+        _write(os.path.join(received, "extra.log"), b"extra\n")
+        _write(os.path.join(received, "other.txt"), b"other\n")
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest,
+                                   flags=["-a", "--delete", "--filter=P *.log"],
+                                   port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:200]
+        assert os.path.exists(os.path.join(received, "extra.log")), (
+            "FastSync must protect a destination-only P match like rsync")
+        assert not os.path.exists(os.path.join(received, "other.txt"))
+
+    @pytest.mark.ci
+    def test_protect_dest_only_dry_run_enumeration(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "fpd_nd_src")
+        dest = os.path.join(TEST_DATA_DIR, "fpd_nd_dst")
+        clean_dir(source)
+        _write(os.path.join(source, "keep.txt"), b"keep\n")
+        received = get_dest_received_dir(dest, source)
+        clean_dir(received)
+        _write(os.path.join(received, "keep.txt"), b"keep\n")
+        _write(os.path.join(received, "extra.log"), b"extra\n")
+        _write(os.path.join(received, "other.txt"), b"other\n")
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest,
+                                   flags=["-a", "-n", "--delete", "--out-format=%n",
+                                          "--filter=P *.log"],
+                                   port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        assert "other.txt" in result.stdout, result.stdout
+        assert "extra.log" not in result.stdout, result.stdout
+        assert os.path.exists(os.path.join(received, "extra.log"))
+        assert os.path.exists(os.path.join(received, "other.txt"))

tests/integration/test_output_parity.py

@@ -0,0 +1,808 @@
+"""Output-parity tests (#291 selection/output, #292 output formatting).
+
+These tests exercise rsync-style selection ordering and output formatting.  The
+differential tests run the SAME transfer with real ``rsync 3.4.1`` and with
+fastsync and compare stdout, so they are skipped when rsync is unavailable.
+"""
+import os
+import re
+import shutil
+import subprocess
+import sys
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import TEST_DATA_DIR, run_client, clean_dir, get_dest_received_dir, ServerManager
+
+RSYNC = shutil.which("rsync")
+requires_rsync = pytest.mark.skipif(RSYNC is None, reason="rsync 3.4.1 not installed")
+
+
+def _rsync(args):
+    env = dict(os.environ, LC_ALL="C")
+    return subprocess.run(
+        [RSYNC] + args, capture_output=True, text=True, env=env, timeout=120
+    )
+
+
+def _make_selection_tree(root):
+    clean_dir(root)
+    os.makedirs(os.path.join(root, "sub"))
+    with open(os.path.join(root, "a.txt"), "wb") as fh:
+        fh.write(b"top text\n")
+    with open(os.path.join(root, "b.log"), "wb") as fh:
+        fh.write(b"log data\n")
+    with open(os.path.join(root, "sub", "c.txt"), "wb") as fh:
+        fh.write(b"nested text\n")
+    with open(os.path.join(root, "sub", "d.log"), "wb") as fh:
+        fh.write(b"nested log\n")
+
+
+class TestSelectionOrdering:
+    """#291: --include/--exclude compile into one ordered rule list."""
+
+    @pytest.mark.ci
+    def test_include_then_exclude_keeps_only_matching(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "out_inc_src")
+        dest = os.path.join(TEST_DATA_DIR, "out_inc_dst")
+        _make_selection_tree(source)
+        clean_dir(dest)
+        result, _ = run_client(
+            source, dest,
+            flags=["--preserve", "--include=*.txt", "--exclude=*"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"include/exclude failed: {result.stderr[:300]}"
+        received = get_dest_received_dir(dest, source)
+        assert os.path.exists(os.path.join(received, "a.txt"))
+        # `*` also excludes the directory, so nothing below sub/ is sent.
+        assert not os.path.exists(os.path.join(received, "b.log"))
+        assert not os.path.exists(os.path.join(received, "sub", "c.txt"))
+
+    @pytest.mark.ci
+    def test_include_dirs_then_files_idiom(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "out_inc2_src")
+        dest = os.path.join(TEST_DATA_DIR, "out_inc2_dst")
+        _make_selection_tree(source)
+        clean_dir(dest)
+        result, _ = run_client(
+            source, dest,
+            flags=["--preserve", "--include=*/", "--include=*.txt", "--exclude=*"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"include/exclude failed: {result.stderr[:300]}"
+        received = get_dest_received_dir(dest, source)
+        assert os.path.exists(os.path.join(received, "a.txt"))
+        assert os.path.exists(os.path.join(received, "sub", "c.txt"))
+        assert not os.path.exists(os.path.join(received, "b.log"))
+        assert not os.path.exists(os.path.join(received, "sub", "d.log"))
+
+    @requires_rsync
+    def test_include_idiom_matches_rsync_selection(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "out_inc3_src")
+        dest = os.path.join(TEST_DATA_DIR, "out_inc3_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "out_inc3_rdst")
+        _make_selection_tree(source)
+        clean_dir(dest)
+        clean_dir(rdst)
+        flags = ["--include=*/", "--include=*.txt", "--exclude=*"]
+        rsync_result = _rsync(["-a"] + flags + [source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["--preserve"] + flags,
+                               port=shared_server.port)
+        assert result.returncode == 0
+        received = get_dest_received_dir(dest, source)
+        assert os.path.exists(os.path.join(received, "a.txt"))
+        assert os.path.exists(os.path.join(received, "sub", "c.txt"))
+        assert not os.path.exists(os.path.join(received, "b.log"))
+        # rsync -a src/ dst/ writes directly into dst/
+        assert os.path.exists(os.path.join(rdst, "a.txt"))
+        assert os.path.exists(os.path.join(rdst, "sub", "c.txt"))
+        assert not os.path.exists(os.path.join(rdst, "b.log"))
+
+
+class TestOneFileSystem:
+    """#291: -x emits the mount-point directory but not its contents."""
+
+    def test_one_file_system_emits_mount_point_dir(self, shared_server):
+        local = os.stat(".")
+        shm = "/dev/shm"
+        try:
+            shm_stat = os.stat(shm)
+        except OSError:
+            pytest.skip("/dev/shm not available")
+        if shm_stat.st_dev == local.st_dev:
+            pytest.skip("no cross-device filesystem available")
+
+        source = os.path.join(TEST_DATA_DIR, "out_ofs_src")
+        dest = os.path.join(TEST_DATA_DIR, "out_ofs_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        os.makedirs(os.path.join(source, "nested"))
+        os.makedirs(os.path.join(shm, "fastsync_ofs_probe"), exist_ok=True)
+        with open(os.path.join(source, "keep.txt"), "wb") as fh:
+            fh.write(b"keep\n")
+        with open(os.path.join(shm, "fastsync_ofs_probe", "inside.txt"), "wb") as fh:
+            fh.write(b"cross\n")
+        link = os.path.join(source, "nested", "link")
+        try:
+            os.symlink(os.path.join(shm, "fastsync_ofs_probe"), link)
+        except OSError:
+            pytest.skip("cannot create symlink")
+
+        try:
+            result, _ = run_client(
+                source, dest,
+                flags=["--preserve", "--copy-links", "-x"],
+                port=shared_server.port,
+            )
+            assert result.returncode == 0, f"-x failed: {result.stderr[:300]}"
+            received = get_dest_received_dir(dest, source)
+            assert os.path.exists(os.path.join(received, "keep.txt"))
+            # The mount-point directory entry is created but its contents are not.
+            assert os.path.isdir(os.path.join(received, "nested", "link"))
+            assert not os.path.exists(os.path.join(received, "nested", "link", "inside.txt"))
+        finally:
+            shutil.rmtree(os.path.join(shm, "fastsync_ofs_probe"), ignore_errors=True)
+
+
+def _make_output_tree(root):
+    clean_dir(root)
+    os.makedirs(os.path.join(root, "sub"))
+    with open(os.path.join(root, "a.txt"), "wb") as fh:
+        fh.write(b"hello\n")
+    with open(os.path.join(root, "sub", "b.txt"), "wb") as fh:
+        fh.write("wörld\n".encode("utf-8"))
+    os.symlink("a.txt", os.path.join(root, "link"))
+
+
+class TestItemizeParity:
+    """#292: -i output matches rsync 3.4.1 for the cases fastsync can observe."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_itemize_first_transfer_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "out_item_src")
+        dest = os.path.join(TEST_DATA_DIR, "out_item_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "out_item_rdst")
+        _make_output_tree(source)
+        clean_dir(dest)
+        clean_dir(rdst)
+        rsync_result = _rsync(["-a", "-i", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_lines = sorted(
+            line for line in rsync_result.stdout.splitlines()
+            if line.startswith(">f") or line.startswith("cL")
+        )
+        result, _ = run_client(source, dest, flags=["-a", "-i"],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        fast_lines = sorted(
+            line for line in result.stdout.splitlines()
+            if line.startswith(">f") or line.startswith("cL")
+        )
+        assert fast_lines == rsync_lines, f"rsync={rsync_lines} fastsync={fast_lines}"
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_itemize_modified_file_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "out_item2_src")
+        dest = os.path.join(TEST_DATA_DIR, "out_item2_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "out_item2_rdst")
+        _make_output_tree(source)
+        clean_dir(dest)
+        clean_dir(rdst)
+        seed = run_client(source, dest, flags=["-a"], port=shared_server.port)
+        assert seed[0].returncode == 0, seed[0].stderr[:300]
+        assert _rsync(["-a", source + "/", rdst + "/"]).returncode == 0
+
+        with open(os.path.join(source, "a.txt"), "wb") as fh:
+            fh.write(b"hello changed and longer\n")
+        # Pin the source mtime so rsync's `t` column is deterministic (a write
+        # that lands in the same whole second as the seed would not show `t`).
+        os.utime(os.path.join(source, "a.txt"), (1000000000, 1000000000))
+
+        rsync_result = _rsync(["-a", "-i", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_lines = sorted(
+            line for line in rsync_result.stdout.splitlines() if line.startswith(">f")
+        )
+        result, _ = run_client(source, dest,
+                               flags=["-a", "-i", "--incremental"],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        fast_lines = sorted(
+            line for line in result.stdout.splitlines() if line.startswith(">f")
+        )
+        assert fast_lines == rsync_lines, f"rsync={rsync_lines} fastsync={fast_lines}"
+
+
+class TestOutFormatParity:
+    @requires_rsync
+    @pytest.mark.ci
+    def test_out_format_n_l_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "out_fmt_src")
+        dest = os.path.join(TEST_DATA_DIR, "out_fmt_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "out_fmt_rdst")
+        _make_output_tree(source)
+        clean_dir(dest)
+        clean_dir(rdst)
+        fmt = "%n %l"
+        rsync_result = _rsync(["-a", "--out-format=" + fmt, source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_lines = sorted(
+            line for line in rsync_result.stdout.splitlines()
+            if line and not line.split(" ", 1)[0].endswith("/")
+        )
+        result, _ = run_client(source, dest,
+                               flags=["-a", "--out-format=" + fmt],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        fast_lines = sorted(
+            line for line in result.stdout.splitlines()
+            if line and not line.split(" ", 1)[0].endswith("/")
+        )
+        assert fast_lines == rsync_lines, f"rsync={rsync_lines} fastsync={fast_lines}"
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_out_format_M_datetime_shape(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "out_M_src")
+        dest = os.path.join(TEST_DATA_DIR, "out_M_dst")
+        _make_output_tree(source)
+        clean_dir(dest)
+        result, _ = run_client(source, dest,
+                               flags=["-a", "--out-format=%M %f"],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        import re
+        pattern = re.compile(r"^\d{4}/\d{2}/\d{2}-\d{2}:\d{2}:\d{2} ")
+        for line in result.stdout.splitlines():
+            if line:
+                assert pattern.match(line), f"bad %M format: {line!r}"
+
+
+class TestListOnlyParity:
+    @requires_rsync
+    @pytest.mark.ci
+    def test_list_only_matches_rsync(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "out_list_src")
+        dest = os.path.join(TEST_DATA_DIR, "out_list_dst")
+        _make_output_tree(source)
+        clean_dir(dest)
+        rsync_result = _rsync(["-r", "--list-only", source + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_lines = sorted(rsync_result.stdout.splitlines())
+        result, _ = run_client(source, dest, flags=["--list-only", "-l"],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        fast_lines = sorted(result.stdout.splitlines())
+        assert fast_lines == rsync_lines, (
+            f"rsync={rsync_lines}\nfastsync={fast_lines}"
+        )
+
+
+def _make_one_file(root, name="f.bin", size=100):
+    clean_dir(root)
+    with open(os.path.join(root, name), "wb") as fh:
+        fh.write(bytes((i * 7 + 3) & 0xFF for i in range(size)))
+
+
+def _make_multidir_tree(root):
+    """Multi-directory corpus for the --progress file-list tests: nested files,
+    a directory-only branch, an empty directory and a symlink."""
+    clean_dir(root)
+    for rel, data in (("a.txt", b"alpha\n"), ("b.txt", b"bravo\n"),
+                      ("sub1/c.txt", b"charlie\n"), ("sub1/deep/d.txt", b"delta\n"),
+                      ("sub2/e.txt", b"echo\n")):
+        path = os.path.join(root, rel)
+        os.makedirs(os.path.dirname(path), exist_ok=True)
+        with open(path, "wb") as fh:
+            fh.write(data)
+    os.symlink("a.txt", os.path.join(root, "link1"))
+    os.makedirs(os.path.join(root, "emptydir"), exist_ok=True)
+
+
+def _parse_progress(text):
+    """Name lines and the `to-chk` denominators from a --progress run."""
+    names = []
+    totals = set()
+    for line in text.splitlines():
+        line = line.rstrip()
+        if not line or line == "sending incremental file list":
+            continue
+        if "%" in line:
+            match = re.search(r"to-chk=\d+/(\d+)", line)
+            if match:
+                totals.add(int(match.group(1)))
+            continue
+        if line == "./":  # root-line trigger is a separate documented residual
+            continue
+        names.append(line)
+    return sorted(names), totals
+
+
+def _pick_stats(text, keys):
+    out = {}
+    for line in text.splitlines():
+        for key in keys:
+            if line.startswith(key + ":"):
+                out[key] = line
+    return out
+
+
+class TestWireStatsParity:
+    """Wire-counter output parity: --out-format %b/%c/%C, --progress and
+    --stats versus real rsync 3.4.1."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_out_format_checksum_matches_rsync(self, shared_server):
+        """%C (whole-file xxh128, seed 0) is protocol-independent, so the full
+        `%C %l %n` line must be byte-identical to rsync."""
+        source = os.path.join(TEST_DATA_DIR, "wire_ck_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_ck_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_ck_rdst")
+        _make_one_file(source, "f.bin", 200000)
+        clean_dir(dest)
+        clean_dir(rdst)
+        fmt = "%C %l %n"
+        rsync_result = _rsync(["-a", "--out-format=" + fmt, source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["-a", "--out-format=" + fmt],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+
+        def file_lines(text):
+            # Ignore the root directory entry: fastsync does not transfer the
+            # source-root dir itself (a separate pre-existing divergence).
+            return [
+                line for line in text.splitlines() if not line.rsplit(" ", 1)[-1].endswith("/")
+            ]
+
+        assert file_lines(result.stdout) == file_lines(rsync_result.stdout), (
+            f"rsync={rsync_result.stdout!r} fastsync={result.stdout!r}"
+        )
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_out_format_b_is_wire_bytes(self, shared_server):
+        """%b is the bytes actually transferred (wire), not the source length.
+
+        A differential run against rsync confirms both implementations report a
+        framed value greater than %l.  The exact numbers are not compared: each
+        counts its own protocol framing and checksum trailer, so the two are
+        protocol-specific and cannot be numerically equal (documented
+        divergence)."""
+        source = os.path.join(TEST_DATA_DIR, "wire_b_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_b_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_b_rdst")
+        _make_one_file(source, "f.bin", 5000)
+        clean_dir(dest)
+        clean_dir(rdst)
+        fmt = "%b %l"
+        rsync_result = _rsync(["-a", "--out-format=" + fmt, source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["-a", "--out-format=" + fmt],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        rb, rl = (int(x) for x in rsync_result.stdout.split()[:2])
+        fb, fl = (int(x) for x in result.stdout.split()[:2])
+        assert rl == fl == 5000, (rsync_result.stdout, result.stdout)
+        assert rb > rl, f"rsync %b must include framing: {rsync_result.stdout!r}"
+        assert fb > fl, f"fastsync %b must include framing: {result.stdout!r}"
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_out_format_c_whole_file_matches_rsync(self, shared_server):
+        """%c is the block-checksum bytes received.  rsync reports its 16-byte
+        sum header even for a whole-file transfer (no basis), so `%c` must match
+        rsync exactly for the whole-file case."""
+        source = os.path.join(TEST_DATA_DIR, "wire_c_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_c_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_c_rdst")
+        _make_one_file(source, "f.bin", 5000)
+        clean_dir(dest)
+        clean_dir(rdst)
+        fmt = "%c %l %n"
+        rsync_result = _rsync(["-a", "--out-format=" + fmt, source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["-a", "--out-format=" + fmt],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+
+        def file_lines(text):
+            return [
+                line for line in text.splitlines()
+                if line and not line.rsplit(" ", 1)[-1].endswith("/")
+            ]
+
+        assert file_lines(result.stdout) == file_lines(rsync_result.stdout), (
+            f"rsync={rsync_result.stdout!r} fastsync={result.stdout!r}"
+        )
+        assert result.stdout.split()[0] == rsync_result.stdout.split()[0] == "16", (
+            f"%c must be rsync's 16-byte sum header: {result.stdout!r}"
+        )
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_out_format_c_delta_mode_divergence(self, shared_server):
+        """Documented residual: with delta enabled, rsync's %c is its 16-byte sum
+        header plus one checksum entry per block (protocol-specific, so it grows
+        with the basis size), while FastSync's %c is the bytes of its own delta
+        handshake.  FastSync's delta %c therefore cannot match rsync numerically;
+        only the whole-file case is aligned.  Pinned here so a future change is
+        noticed."""
+        source = os.path.join(TEST_DATA_DIR, "wire_cd_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_cd_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_cd_rdst")
+        _make_one_file(source, "f.bin", 5000)
+        clean_dir(dest)
+        clean_dir(rdst)
+        fmt = "%c %l"
+        # rsync local default is whole-file; force the block-delta path.
+        rsync_result = _rsync(["-a", "--no-whole-file", "--out-format=" + fmt,
+                               source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest,
+                               flags=["-a", "--incremental", "--delta",
+                                      "--out-format=" + fmt],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        rs_c = int(rsync_result.stdout.split()[0])
+        fs_c = int(result.stdout.split()[0])
+        # No basis exists, so rsync still reports only its sum header.
+        assert rs_c == 16, rsync_result.stdout
+        # FastSync reports its own handshake bytes and is not aligned.
+        assert fs_c > 16, (
+            f"FastSync delta %c changed to {fs_c}; the documented divergence "
+            "may be closable now"
+        )
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [False, True])
+    @pytest.mark.parametrize("progress_flag", ["--progress", "-P"])
+    def test_progress_first_frame_matches_rsync(self, shared_server, progress_flag, mt):
+        """For a sub-32 KiB file the first --progress/-P frame is deterministic
+        (0.00 kB/s, 0:00:00) and must be byte-identical to rsync's, in both the
+        single-threaded and --threads send paths."""
+        source = os.path.join(TEST_DATA_DIR, "wire_pg_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_pg_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_pg_rdst")
+        _make_one_file(source, "f.bin", 100)
+        clean_dir(dest)
+        clean_dir(rdst)
+        rsync_result = _rsync(["-a", progress_flag, source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        flags = ["-a", progress_flag] + (["--threads"] if mt else [])
+        result, _ = run_client(source, dest, flags=flags, port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+
+        def frames(text):
+            # subprocess text mode normalizes \r to \n (universal newlines).
+            return [p for p in text.split("\n") if "%" in p]
+
+        rsync_frames = frames(rsync_result.stdout)
+        fast_frames = frames(result.stdout)
+        assert rsync_frames and fast_frames, (rsync_result.stdout, result.stdout)
+        assert fast_frames[0] == rsync_frames[0], (rsync_frames[0], fast_frames[0])
+        assert "(xfr#1," in fast_frames[-1], fast_frames[-1]
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_progress_leading_root_line_and_to_chk_match_rsync(self, shared_server):
+        """A single-file transfer: rsync emits the transfer-root `./` name line
+        and a `to-chk=0/2` denominator that counts that root entry.  Both must
+        match FastSync byte-for-byte for the deterministic frames."""
+        source = os.path.join(TEST_DATA_DIR, "wire_pgroot_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_pgroot_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_pgroot_rdst")
+        _make_one_file(source, "f.bin", 100)
+        clean_dir(dest)
+        # rsync prints the `./` root line only when the transfer root itself is
+        # created, so make the rsync destination absent.  The "created directory"
+        # line it then emits has no FastSync counterpart (different mirror
+        # layout), so only the name/frame lines are compared.
+        shutil.rmtree(rdst, ignore_errors=True)
+        rsync_result = _rsync(["-a", "--progress", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["-a", "--progress"],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+
+        # subprocess text mode normalizes \r to \n (universal newlines).
+        def lines_of(text):
+            return [ln for ln in text.splitlines() if ln and not ln.startswith("created directory")]
+
+        rsync_lines = lines_of(rsync_result.stdout)
+        fast_lines = lines_of(result.stdout)
+        rsync_names = [ln for ln in rsync_lines if "%" not in ln]
+        fast_names = [ln for ln in fast_lines if "%" not in ln]
+
+        assert rsync_names == ["sending incremental file list", "./", "f.bin"], rsync_names
+        assert fast_names == rsync_names, (rsync_names, fast_names)
+        # The final frame's to-chk denominator must include the source-root entry.
+        assert "to-chk=0/2" in fast_lines[-1], fast_lines[-1]
+        assert fast_lines[-1] == rsync_lines[-1], (rsync_lines[-1], fast_lines[-1])
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [False, True])
+    def test_progress_multidir_file_list_matches_rsync(self, shared_server, mt):
+        """A multi-directory tree: the paths-only pre-count must reproduce
+        rsync's file-list set and `to-chk` denominator.  Per-directory name
+        lines are emitted for directories, symlinks and the empty directory; the
+        name set and the denominator (every entry plus the transfer root) match
+        rsync, while the emitted *order* remains a documented residual (rsync
+        sorts depth-first, FastSync streams in readdir/BFS order)."""
+        source = os.path.join(TEST_DATA_DIR, "wire_pgmd_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_pgmd_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_pgmd_rdst")
+        _make_multidir_tree(source)
+        clean_dir(dest)
+        clean_dir(rdst)
+
+        rsync_result = _rsync(["-a", "--progress", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        flags = ["-a", "--progress"] + (["--threads"] if mt else [])
+        result, _ = run_client(source, dest, flags=flags, port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+
+        rsync_names, rsync_totals = _parse_progress(rsync_result.stdout)
+        fast_names, fast_totals = _parse_progress(result.stdout)
+        assert sorted(rsync_names) == [
+            "a.txt", "b.txt", "emptydir/", "link1 -> a.txt", "sub1/",
+            "sub1/c.txt", "sub1/deep/", "sub1/deep/d.txt", "sub2/", "sub2/e.txt",
+        ], rsync_names
+        assert fast_names == rsync_names, (rsync_names, fast_names)
+        # 10 entries + the transfer-root "." counted by rsync's file list.
+        assert rsync_totals == {11}, rsync_totals
+        assert fast_totals == rsync_totals, (rsync_totals, fast_totals)
+
+    @pytest.mark.ci
+    def test_progress_delete_during_reuses_pre_scan(self):
+        """--delete-during + --progress reuses the keep-set pre-scan instead of
+        walking the tree a second time: the file-list total and directory name
+        lines are identical to a plain --progress run."""
+        source = os.path.join(TEST_DATA_DIR, "wire_pgdel_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_pgdel_dst")
+        _make_multidir_tree(source)
+        clean_dir(dest)
+        server = ServerManager()
+        server.start(extra_args=["--allow-super", "--allow-delete"])
+        try:
+            result, _ = run_client(source, dest, flags=["-a", "--progress", "--delete-during"],
+                                   port=server.port)
+        finally:
+            server.stop()
+        assert result.returncode == 0, result.stderr[:300]
+        names, totals = _parse_progress(result.stdout)
+        assert totals == {11}, totals
+        assert "sub1/" in names and "sub1/deep/" in names and "emptydir/" in names, names
+        assert "link1 -> a.txt" in names, names
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [False, True])
+    def test_stats_selected_lines_match_rsync(self, shared_server, mt):
+        """The protocol-independent --stats lines must match rsync exactly, in
+        both the single-threaded and --threads (multithreaded) send paths."""
+        source = os.path.join(TEST_DATA_DIR, "wire_st_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_st_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_st_rdst")
+        _make_one_file(source, "f.bin", 6000)
+        clean_dir(dest)
+        clean_dir(rdst)
+        # Start both tools from the same state: rsync's destination root exists,
+        # so pre-create FastSync's mirrored logical root as well.
+        os.makedirs(get_dest_received_dir(dest, source), exist_ok=True)
+        rsync_result = _rsync(["-a", "--stats", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        flags = ["-a", "--stats"] + (["--threads"] if mt else [])
+        result, _ = run_client(source, dest, flags=flags, port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        keys = (
+            "Number of regular files transferred",
+            "Total file size",
+            "Total transferred file size",
+            "Literal data",
+            "Matched data",
+            "Number of deleted files",
+            "File list size",
+        )
+
+        def pick(text):
+            out = {}
+            for line in text.splitlines():
+                for key in keys:
+                    if line.startswith(key + ":"):
+                        out[key] = line
+            return out
+
+        assert pick(result.stdout) == pick(rsync_result.stdout), (
+            f"rsync={pick(rsync_result.stdout)} fastsync={pick(result.stdout)}"
+        )
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_stats_file_count_breakdown_matches_rsync(self, shared_server):
+        """`Number of files` and `Number of created files` both carry rsync's
+        per-type breakdown (protocol 2.28.0 reports the receiver-created
+        reg/dir/link/special split over STATUS_STATS)."""
+        source = os.path.join(TEST_DATA_DIR, "wire_stc_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_stc_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_stc_rdst")
+        _make_one_file(source, "f.bin", 6000)
+        clean_dir(dest)
+        clean_dir(rdst)
+        # Start both tools from the same state: rsync's destination root exists,
+        # so pre-create FastSync's mirrored logical root as well.
+        os.makedirs(get_dest_received_dir(dest, source), exist_ok=True)
+        rsync_result = _rsync(["-a", "--stats", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["-a", "--stats"],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+
+        def stats_line(text, key):
+            for line in text.splitlines():
+                if line.startswith(key + ":"):
+                    return line
+            return None
+
+        r_files = stats_line(rsync_result.stdout, "Number of files")
+        r_created = stats_line(rsync_result.stdout, "Number of created files")
+        f_files = stats_line(result.stdout, "Number of files")
+        f_created = stats_line(result.stdout, "Number of created files")
+
+        assert re.match(r"Number of files: 2 \(reg: 1, dir: 1\)$", r_files), r_files
+        assert r_files == f_files, (r_files, f_files)
+        assert re.match(r"Number of created files: 1 \(reg: 1\)$", r_created), r_created
+        assert f_created == r_created, (r_created, f_created)
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [False, True])
+    def test_stats_created_and_literal_fresh_update_delta(self, shared_server, mt):
+        """The receiver-observed counters must match rsync for the three
+        transfer shapes: a fresh create (created breakdown + whole-file literal),
+        an update (created == 0, whole-file literal), and a delta update (only
+        the literal delta fragments are counted, not the whole file)."""
+        source = os.path.join(TEST_DATA_DIR, "wire_stcd_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_stcd_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_stcd_rdst")
+        clean_dir(source)
+        clean_dir(dest)
+        clean_dir(rdst)
+        os.makedirs(source, exist_ok=True)
+        os.makedirs(get_dest_received_dir(dest, source), exist_ok=True)
+        with open(os.path.join(source, "big.bin"), "wb") as fh:
+            fh.write(bytes(range(256)) * 4096)  # 1 MiB
+        mt_flag = ["--threads"] if mt else []
+
+        def compare(tag):
+            # Pin the delta block size on both ends: rsync's adaptive block size
+            # would otherwise make the literal/matched split non-comparable.
+            rsync_result = _rsync(["-a", "--stats", "--no-whole-file", "-B8192",
+                                   source + "/", rdst + "/"])
+            assert rsync_result.returncode == 0, rsync_result.stderr
+            result, _ = run_client(
+                source, dest,
+                flags=["-a", "--stats", "--incremental", "--delta", "-B8192"] + mt_flag,
+                port=shared_server.port)
+            assert result.returncode == 0, result.stderr[:300]
+            keys = ("Number of created files", "Literal data", "Matched data",
+                    "Total transferred file size")
+            r = _pick_stats(rsync_result.stdout, keys)
+            f = _pick_stats(result.stdout, keys)
+            assert r == f, f"{tag}: rsync={r} fastsync={f}"
+            return r
+
+        fresh = compare("fresh")
+        assert re.match(r"Number of created files: 1 \(reg: 1\)$",
+                        fresh["Number of created files"]), fresh
+
+        # Update the source and re-run: the destination already exists.
+        sleep_mtime = os.path.getmtime(os.path.join(source, "big.bin")) + 2
+        with open(os.path.join(source, "big.bin"), "r+b") as fh:
+            fh.seek(100)
+            fh.write(b"XXXXXXXXXX")
+        os.utime(os.path.join(source, "big.bin"), (sleep_mtime, sleep_mtime))
+        update = compare("update")
+        assert update["Number of created files"] == "Number of created files: 0", update
+
+        # Second delta update: change bytes far apart, so rsync ships only the
+        # literal fragments and FastSync must report the same Literal data.
+        sleep_mtime = os.path.getmtime(os.path.join(source, "big.bin")) + 2
+        with open(os.path.join(source, "big.bin"), "r+b") as fh:
+            fh.seek(500000)
+            fh.write(b"YYYYYYYYYY")
+        os.utime(os.path.join(source, "big.bin"), (sleep_mtime, sleep_mtime))
+        delta = compare("delta")
+        assert delta["Number of created files"] == "Number of created files: 0", delta
+        lit = int(delta["Literal data"].split(":", 1)[1].strip().split()[0].replace(",", ""))
+        assert 0 < lit < 1024 * 1024, delta
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("choice", ["xxh128", "xxh64", "xxh3", "md5", "md4", "sha1", "none"])
+    def test_out_format_C_selected_algorithm_matches_rsync(self, shared_server, choice):
+        """`%C` must use the algorithm selected by --checksum-choice, not always
+        xxh128, and render it exactly like rsync (big-endian for the 64-bit
+        hashes, high-then-low for xxh128, standard hex for md5/md4/sha1)."""
+        source = os.path.join(TEST_DATA_DIR, f"wire_cc_{choice}_src")
+        dest = os.path.join(TEST_DATA_DIR, f"wire_cc_{choice}_dst")
+        rdst = os.path.join(TEST_DATA_DIR, f"wire_cc_{choice}_rdst")
+        _make_one_file(source, "f.bin", 200000)
+        clean_dir(dest)
+        clean_dir(rdst)
+        fmt = "%C %l %n"
+        rsync_result = _rsync(["-a", "--checksum-choice=" + choice,
+                               "--out-format=" + fmt, source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest,
+                               flags=["-a", "--checksum-choice=" + choice,
+                                      "--out-format=" + fmt],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+
+        def file_lines(text):
+            return [line for line in text.splitlines()
+                    if line and not line.rsplit(" ", 1)[-1].endswith("/")]
+
+        assert file_lines(result.stdout) == file_lines(rsync_result.stdout), (
+            f"choice={choice}: rsync={rsync_result.stdout!r} fastsync={result.stdout!r}"
+        )
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [False, True])
+    def test_dry_run_delete_lines_match_rsync(self, mt):
+        """-n --delete emits transfer-relative `*deleting` lines like rsync
+        (single-threaded and --threads)."""
+        source = os.path.join(TEST_DATA_DIR, "wire_del_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_del_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_del_rdst")
+        clean_dir(source)
+        clean_dir(dest)
+        clean_dir(rdst)
+        with open(os.path.join(source, "a.txt"), "wb") as fh:
+            fh.write(b"a\n")
+        for root, entries in (
+            (rdst, {"extra.txt": b"x\n"}),
+            (rdst, {"sub/y.txt": b"y\n", "extradir/z.txt": b"z\n"}),
+        ):
+            for rel, data in entries.items():
+                full = os.path.join(root, rel)
+                os.makedirs(os.path.dirname(full), exist_ok=True)
+                with open(full, "wb") as fh:
+                    fh.write(data)
+        # FastSync mirrors the source's absolute path under dest.
+        received = get_dest_received_dir(dest, source)
+        for rel, data in (
+            ("extra.txt", b"x\n"),
+            ("sub/y.txt", b"y\n"),
+            ("extradir/z.txt", b"z\n"),
+        ):
+            full = os.path.join(received, rel)
+            os.makedirs(os.path.dirname(full), exist_ok=True)
+            with open(full, "wb") as fh:
+                fh.write(data)
+
+        rsync_result = _rsync(["-a", "-n", "--delete", "-i", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_del = sorted(
+            line for line in rsync_result.stdout.splitlines() if line.startswith("*deleting")
+        )
+        # The shared session server refuses deletion; start one that allows it.
+        flags = ["-a", "-n", "--delete", "-i"] + (["--threads"] if mt else [])
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest, flags=flags, port=server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        fast_del = sorted(
+            line for line in result.stdout.splitlines() if line.startswith("*deleting")
+        )
+        assert fast_del == rsync_del, f"rsync={rsync_del}\nfastsync={fast_del}"

tests/integration/test_parity_blockers.py

@@ -0,0 +1,299 @@
+"""Differential/regression coverage for the parity-completion review blockers.
+
+Each test pins a fix against real ``rsync 3.4.1`` where a deterministic
+comparison exists; the differential tests skip cleanly when rsync is absent.
+"""
+import os
+import shutil
+import subprocess
+import sys
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (  # noqa: E402
+    TEST_DATA_DIR,
+    ServerManager,
+    clean_dir,
+    get_dest_received_dir,
+    run_client,
+)
+
+RSYNC = shutil.which("rsync")
+requires_rsync = pytest.mark.skipif(RSYNC is None, reason="rsync 3.4.1 not installed")
+
+
+def _write(path, content):
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    with open(path, "wb") as fh:
+        fh.write(content)
+
+
+def _tree(root):
+    """Sorted relative paths of every entry below root (files and dirs)."""
+    out = []
+    for dirpath, dirs, files in os.walk(root):
+        for name in dirs:
+            out.append(os.path.relpath(os.path.join(dirpath, name), root))
+        for name in files:
+            out.append(os.path.relpath(os.path.join(dirpath, name), root))
+    return sorted(out)
+
+
+def _rsync(args):
+    env = dict(os.environ, LC_ALL="C")
+    return subprocess.run([RSYNC] + args, capture_output=True, text=True, env=env, timeout=120)
+
+
+class TestRelativePerDirDeleteScope:
+    """Blocker #1: -R --delete-during/--delete-delay must not delete destination
+    content outside the transferred prefix (rsync keeps sibling directories)."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [False, True])
+    @pytest.mark.parametrize("timing", ["--delete-during", "--delete-delay"])
+    def test_prefix_scoped_delete_matches_rsync(self, timing, mt):
+        source = os.path.join(TEST_DATA_DIR, f"delblk_src{int(mt)}")
+        clean_dir(source)
+        _write(os.path.join(source, "foo", "a.txt"), b"payload\n")
+        spec = source + "/./foo"
+
+        def seed(root):
+            clean_dir(root)
+            _write(os.path.join(root, "foo", "extra.txt"), b"stale\n")
+            _write(os.path.join(root, "unrelated", "keep.txt"), b"keep\n")
+
+        rdst = os.path.join(TEST_DATA_DIR, f"delblk_rdst{int(mt)}")
+        dest = os.path.join(TEST_DATA_DIR, f"delblk_dst{int(mt)}")
+        seed(rdst)
+        seed(dest)
+        r = _rsync(["-aR", timing, spec, rdst + "/"])
+        assert r.returncode == 0, r.stderr
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            flags = ["-a", "-R", timing] + (["--threads"] if mt else [])
+            result, _ = run_client(spec, dest, flags=flags, port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+#The prefix's parent-directory sibling survives on both sides.
+        assert os.path.isfile(os.path.join(dest, "unrelated", "keep.txt"))
+        assert os.path.isfile(os.path.join(rdst, "unrelated", "keep.txt"))
+#The in - scope extra is removed on both sides.
+        assert not os.path.exists(os.path.join(dest, "foo", "extra.txt"))
+        assert not os.path.exists(os.path.join(rdst, "foo", "extra.txt"))
+        assert _tree(dest) == _tree(rdst)
+
+
+def _stats_value(text, label):
+    for line in text.splitlines():
+        if line.startswith(label + ":"):
+            return int(line.split(":", 1)[1].strip().split()[0].replace(",", ""))
+    return None
+
+
+def _seed_delta_pair(tag):
+    """Source file plus a same-size/basis destination file whose mtime differs,
+    and an extra destination file to be deleted."""
+    source = os.path.join(TEST_DATA_DIR, f"stats_{tag}_src")
+    dest = os.path.join(TEST_DATA_DIR, f"stats_{tag}_dst")
+    rdst = os.path.join(TEST_DATA_DIR, f"stats_{tag}_rdst")
+    clean_dir(source)
+    clean_dir(dest)
+    clean_dir(rdst)
+    payload = (b"0123456789abcdef" * 16384)[:200000]
+    _write(os.path.join(source, "f.bin"), payload)
+#Destination basis : same length, one byte changed, deliberately older.
+    basis = bytearray(payload)
+    basis[100000] ^= 0xFF
+    received = get_dest_received_dir(dest, source)
+    for root in (rdst, received):
+        _write(os.path.join(root, "f.bin"), bytes(basis))
+        _write(os.path.join(root, "extra.txt"), b"delete me\n")
+        old = 1000000
+        os.utime(os.path.join(root, "f.bin"), (old, old))
+    return source, dest, rdst
+
+
+class TestReceiverWireStats:
+    """Blocker #3/#4: the receiver must populate the STATUS_STATS counters
+    (matched data, deleted files) on both the single-threaded and -m paths."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("threads", [False, True])
+    def test_stats_reports_matched_and_deleted(self, threads):
+        source, dest, rdst = _seed_delta_pair(f"mt{int(threads)}")
+        rsync_result = _rsync(["-a", "--stats", "--delete", "--no-whole-file", source + "/",
+                               rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        assert _stats_value(rsync_result.stdout, "Matched data") > 0
+        assert _stats_value(rsync_result.stdout, "Number of deleted files") == 1
+
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            flags = ["-a", "--stats", "--delete", "--delta", "--incremental"]
+            if threads:
+                flags.append("--threads")
+            result, _ = run_client(source, dest, flags=flags, port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        assert _stats_value(result.stdout, "Matched data") > 0, result.stdout
+        assert _stats_value(result.stdout, "Number of deleted files") == 1, result.stdout
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_threads_dry_run_delete_lines_match_rsync(self):
+        """-n --delete --threads must emit transfer-relative `*deleting` lines."""
+        source = os.path.join(TEST_DATA_DIR, "stats_drydel_src")
+        dest = os.path.join(TEST_DATA_DIR, "stats_drydel_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "stats_drydel_rdst")
+        clean_dir(source)
+        clean_dir(dest)
+        clean_dir(rdst)
+        _write(os.path.join(source, "a.txt"), b"a\n")
+        for root in (rdst, get_dest_received_dir(dest, source)):
+            _write(os.path.join(root, "extra.txt"), b"x\n")
+            _write(os.path.join(root, "sub", "y.txt"), b"y\n")
+        rsync_result = _rsync(["-a", "-n", "--delete", "-i", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        rsync_del = sorted(
+            line for line in rsync_result.stdout.splitlines() if line.startswith("*deleting")
+        )
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest,
+                                   flags=["-a", "-n", "--delete", "-i", "--threads"],
+                                   port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        fast_del = sorted(
+            line for line in result.stdout.splitlines() if line.startswith("*deleting")
+        )
+        assert fast_del and fast_del == rsync_del, f"rsync={rsync_del}\nfastsync={fast_del}"
+
+
+class TestRelativeFilesFromProtect:
+    """Blocker #9: a -R + --files-from receiver-protect rule must record the bare
+    relative wire path so the protected destination mirror survives --delete."""
+
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [False, True])
+    def test_hidden_protected_mirror_survives_delete(self, mt):
+        source = os.path.join(TEST_DATA_DIR, "rfprot_src")
+        dest = os.path.join(TEST_DATA_DIR, "rfprot_dst")
+        clean_dir(source)
+        clean_dir(dest)
+#Root - level entry exercises the parallel root scanner; the nested one
+#exercises the sequential worker scanner.
+        _write(os.path.join(source, "root_secret.tmp"), b"root\n")
+        _write(os.path.join(source, "sub", "nested_secret.tmp"), b"nested\n")
+        _write(os.path.join(source, "sub", "keep.txt"), b"keep\n")
+        listfile = os.path.join(TEST_DATA_DIR, "rfprot.list")
+        with open(listfile, "w") as fh:
+            fh.write(".\n")
+#H hides from the sender, P protects the receiver mirror from-- delete.
+        filters = ["--filter=H root_secret.tmp", "--filter=P root_secret.tmp",
+                   "--filter=H sub/nested_secret.tmp", "--filter=P sub/nested_secret.tmp"]
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            seed = ["--files-from", listfile, "-R"] + (["--threads"] if mt else [])
+            result, _ = run_client(source, dest, flags=seed, port=server.port)
+            assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+            assert os.path.isfile(os.path.join(dest, "root_secret.tmp"))
+            assert os.path.isfile(os.path.join(dest, "sub", "nested_secret.tmp"))
+            _write(os.path.join(dest, "extra.txt"), b"extra\n")
+            _write(os.path.join(dest, "sub", "extra.txt"), b"extra\n")
+            flags = seed + ["--delete"] + filters
+            result, _ = run_client(source, dest, flags=flags, port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        assert os.path.isfile(os.path.join(dest, "root_secret.tmp")), \
+            "root-level protected mirror was deleted"
+        assert os.path.isfile(os.path.join(dest, "sub", "nested_secret.tmp")), \
+            "nested protected mirror was deleted"
+        assert not os.path.exists(os.path.join(dest, "extra.txt"))
+        assert not os.path.exists(os.path.join(dest, "sub", "extra.txt"))
+
+
+class TestInvalidPerDirFilter:
+    """Blocker #8: a per-directory filter file that fails to parse must fail the
+    scan even when an earlier merge file in the same directory existed."""
+
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [False, True])
+    def test_invalid_dir_filter_fails_scan(self, mt):
+        source = os.path.join(TEST_DATA_DIR, "badfilter_src")
+        dest = os.path.join(TEST_DATA_DIR, "badfilter_dst")
+        clean_dir(source)
+        clean_dir(dest)
+#A valid.rsync - filter makes any_exists true for the directory; the
+#invalid.rules must not then be silently ignored.
+        _write(os.path.join(source, ".rsync-filter"), b"- *.bak\n")
+        _write(os.path.join(source, ".rules"), b"protect\n")
+        _write(os.path.join(source, "a.txt"), b"a\n")
+        flags = ["-a", "-F", "--filter=: .rules"]
+        if mt:
+            flags.append("--threads")
+        with ServerManager() as server:
+            result, _ = run_client(source, dest, flags=flags, port=server.port)
+        assert result.returncode != 0, "invalid per-directory filter was silently ignored"
+        assert "invalid per-directory filter" in (result.stderr + result.stdout)
+
+
+class TestWouldDeleteEscaping:
+    """Blocker #5: -n --delete --out-format must escape control bytes in a
+    peer-supplied would-delete path so it cannot forge output lines."""
+
+    @pytest.mark.ci
+    def test_out_format_escapes_control_chars(self):
+        source = os.path.join(TEST_DATA_DIR, "esc_src")
+        dest = os.path.join(TEST_DATA_DIR, "esc_dst")
+        clean_dir(source)
+        _write(os.path.join(source, "a.txt"), b"a\n")
+        received = get_dest_received_dir(dest, source)
+        clean_dir(received)
+        _write(os.path.join(received, "a.txt"), b"a\n")
+#A newline in a destination filename must not split the printed line.
+        with open(os.path.join(received, "evil\nname.txt"), "wb") as fh:
+            fh.write(b"x\n")
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest,
+                                   flags=["-a", "-n", "--delete", "--out-format=%n"],
+                                   port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        assert "\\#012" in result.stdout, result.stdout
+        assert "evil\nname.txt" not in result.stdout, result.stdout
+
+
+class TestEmptySourceDirectoryDelete:
+    """Blocker #10: an empty in-scope source directory must survive
+    --delete-during/--delete-delay (rsync keeps it) while its extras are still
+    removed."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [False, True])
+    @pytest.mark.parametrize("timing", ["--delete-during", "--delete-delay"])
+    def test_empty_source_dir_survives_matches_rsync(self, timing, mt):
+        source = os.path.join(TEST_DATA_DIR, f"emptydir_src{int(mt)}")
+        dest = os.path.join(TEST_DATA_DIR, f"emptydir_dst{int(mt)}")
+        rdst = os.path.join(TEST_DATA_DIR, f"emptydir_rdst{int(mt)}")
+        clean_dir(source)
+        os.makedirs(os.path.join(source, "empty"))
+        _write(os.path.join(source, "keep.txt"), b"keep\n")
+        received = get_dest_received_dir(dest, source)
+        for root in (rdst, received):
+            clean_dir(root)
+            _write(os.path.join(root, "keep.txt"), b"keep\n")
+            _write(os.path.join(root, "empty", "extra.txt"), b"extra\n")
+        rsync_result = _rsync(["-a", timing, source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        assert os.path.isdir(os.path.join(rdst, "empty"))
+        assert not os.path.exists(os.path.join(rdst, "empty", "extra.txt"))
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            flags = ["-a", timing] + (["--threads"] if mt else [])
+            result, _ = run_client(source, dest, flags=flags, port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        assert os.path.isdir(os.path.join(received, "empty")), \
+            "empty source directory was removed"
+        assert not os.path.exists(os.path.join(received, "empty", "extra.txt"))
+        assert _tree(received) == _tree(rdst)

tests/integration/test_parity_selection.py

@@ -0,0 +1,326 @@
+"""rsync 3.4.1 parity for selection/path semantics and client option aliases.
+
+Each test pins behaviour against real ``rsync 3.4.1``; the differential tests
+skip cleanly when rsync is not installed.
+"""
+import os
+import shutil
+import subprocess
+import sys
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (
+    TEST_DATA_DIR,
+    CLIENT_CMD,
+    ServerManager,
+    run_client,
+    clean_dir,
+    get_dest_received_dir,
+)
+
+RSYNC = shutil.which("rsync")
+requires_rsync = pytest.mark.skipif(RSYNC is None, reason="rsync 3.4.1 not installed")
+
+
+def _tree(root):
+    """Sorted relative paths of directories (``D ``) and files (``F ``)."""
+    out = []
+    for dirpath, dirs, files in os.walk(root):
+        rel = os.path.relpath(dirpath, root)
+        for d in dirs:
+            out.append("D " + (d if rel == "." else os.path.join(rel, d)))
+        for f in files:
+            out.append("F " + (f if rel == "." else os.path.join(rel, f)))
+    return sorted(out)
+
+
+def _rsync(args):
+    env = dict(os.environ, LC_ALL="C")
+    return subprocess.run([RSYNC] + args, capture_output=True, text=True, env=env, timeout=120)
+
+
+def _make_tree(root):
+    clean_dir(root)
+    for rel, content in {
+        "top.txt": b"top\n",
+        "foo/bar/baz/f.txt": b"deep\n",
+        "sub/x.txt": b"x\n",
+    }.items():
+        full = os.path.join(root, rel)
+        os.makedirs(os.path.dirname(full), exist_ok=True)
+        with open(full, "wb") as fh:
+            fh.write(content)
+    return root
+
+
+class TestRelativeGeneral:
+    """#11: -R without --files-from uses rsync's '/./' cut and relative
+    reconstruction instead of always mirroring the full source path."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("suffix", ["", "/./foo", "/./foo/bar", "/./"])
+    def test_relative_cut_matches_rsync(self, shared_server, suffix):
+        source = _make_tree(os.path.join(TEST_DATA_DIR, "sel_rel_src"))
+        dest = os.path.join(TEST_DATA_DIR, "sel_rel_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "sel_rel_rdst")
+        clean_dir(dest)
+        clean_dir(rdst)
+        spec = source + suffix
+        r = _rsync(["-aR", spec, rdst + "/"])
+        assert r.returncode == 0, r.stderr
+        result, _ = run_client(spec, dest, flags=["-R"], port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        assert _tree(rdst) == _tree(dest), f"layout mismatch for {spec!r}"
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_no_implied_dirs_matches_rsync(self, shared_server):
+        source = _make_tree(os.path.join(TEST_DATA_DIR, "sel_nid_src"))
+        a = os.path.join(source, "foo")
+        b = os.path.join(source, "foo", "bar")
+        os.chmod(a, 0o700)
+        os.chmod(b, 0o711)
+        os.utime(a, (978307200, 978307200))
+        os.utime(b, (978307200, 978307200))
+        spec = source + "/./foo/bar"
+        for extra in ([], ["--no-implied-dirs"]):
+            dest = os.path.join(TEST_DATA_DIR, "sel_nid_dst")
+            rdst = os.path.join(TEST_DATA_DIR, "sel_nid_rdst")
+            clean_dir(dest)
+            clean_dir(rdst)
+            r = _rsync(["-aR"] + extra + [spec, rdst + "/"])
+            assert r.returncode == 0, r.stderr
+            result, _ = run_client(spec, dest, flags=["-a", "-R"] + extra,
+                                   port=shared_server.port)
+            assert result.returncode == 0, result.stderr[:300]
+            for rel in ("foo", "foo/bar"):
+                rs = os.stat(os.path.join(rdst, rel))
+                fs = os.stat(os.path.join(dest, rel))
+                assert (rs.st_mode & 0o7777) == (fs.st_mode & 0o7777), \
+                    f"mode mismatch for {rel} with {extra}"
+                if extra == ["--no-implied-dirs"]:
+                    # The implied parent directory is created at run time (no
+                    # metadata applied), so rsync's and FastSync's separate runs
+                    # can differ by a second; compare with a tolerance.
+                    assert abs(rs.st_mtime - fs.st_mtime) <= 2, \
+                        f"mtime mismatch for {rel} with {extra}"
+                else:
+                    assert int(rs.st_mtime) == int(fs.st_mtime), \
+                        f"mtime mismatch for {rel} with {extra}"
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_no_implied_dirs_files_from_matches_rsync(self, shared_server):
+        """-R --no-implied-dirs --files-from: a listed file whose parent is not
+        itself listed still transfers; the implied parent is created with
+        default attributes (rsync 3.4.1 parity)."""
+        source = _make_tree(os.path.join(TEST_DATA_DIR, "sel_nidff_src"))
+        # Make the implied parent unmistakably non-default on the source so a
+        # wrongly-applied attribute would be observable.
+        os.chmod(os.path.join(source, "foo"), 0o700)
+        os.chmod(os.path.join(source, "foo", "bar"), 0o711)
+        os.utime(os.path.join(source, "foo"), (978307200, 978307200))
+        os.utime(os.path.join(source, "foo", "bar"), (978307200, 978307200))
+        lst = os.path.join(TEST_DATA_DIR, "sel_nidff_list")
+        with open(lst, "w") as fh:
+            fh.write("foo/bar/baz/f.txt\n")
+        dest = os.path.join(TEST_DATA_DIR, "sel_nidff_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "sel_nidff_rdst")
+        clean_dir(dest)
+        clean_dir(rdst)
+        r = _rsync(["-rlpt", "-R", "--no-implied-dirs", "--files-from=" + lst,
+                    source + "/", rdst + "/"])
+        assert r.returncode == 0, r.stderr
+        result, _ = run_client(source, dest, flags=[
+            "-rlpt", "-R", "--no-implied-dirs", "--files-from", lst],
+            port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        assert _tree(rdst) == _tree(dest), "implied-parent layout mismatch"
+        # The implied parents exist on both sides and carry the run-time default
+        # attributes, not the source's (non-default) ones.
+        for rel in ("foo", "foo/bar", "foo/bar/baz"):
+            rs = os.stat(os.path.join(rdst, rel))
+            fs = os.stat(os.path.join(dest, rel))
+            assert (rs.st_mode & 0o7777) == (fs.st_mode & 0o7777), \
+                f"mode mismatch for implied {rel}"
+        # The listed file is transferred with its content.
+        with open(os.path.join(dest, "foo", "bar", "baz", "f.txt"), "rb") as fh:
+            assert fh.read() == b"deep\n"
+
+
+class TestDirsOneLevel:
+    """#13: -d with a trailing slash (or '.') lists the source's immediate
+    contents; FastSync mirrors them below the source-root mirror, so compare
+    rsync's destination tree against that mirror."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_dirs_trailing_slash_matches_rsync(self, shared_server):
+        source = _make_tree(os.path.join(TEST_DATA_DIR, "sel_dirs_src"))
+        os.makedirs(os.path.join(source, "empty"), exist_ok=True)
+        dest = os.path.join(TEST_DATA_DIR, "sel_dirs_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "sel_dirs_rdst")
+        clean_dir(dest)
+        clean_dir(rdst)
+        r = _rsync(["-d", source + "/", rdst + "/"])
+        assert r.returncode == 0, r.stderr
+        result, _ = run_client(source + "/", dest, flags=["-d"], port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        mirror = get_dest_received_dir(dest, source)
+        assert _tree(rdst) == _tree(mirror)
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_dirs_relative_matches_rsync(self, shared_server):
+        source = _make_tree(os.path.join(TEST_DATA_DIR, "sel_dirsr_src"))
+        dest = os.path.join(TEST_DATA_DIR, "sel_dirsr_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "sel_dirsr_rdst")
+        clean_dir(dest)
+        clean_dir(rdst)
+        spec = source + "/./foo"
+        r = _rsync(["-d", "-R", spec, rdst + "/"])
+        assert r.returncode == 0, r.stderr
+        result, _ = run_client(spec, dest, flags=["-d", "-R"], port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        assert _tree(rdst) == _tree(dest)
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_relative_delete_scope_matches_rsync(self):
+        """-R --delete must be confined to the transferred prefix subtree so a
+        sibling destination directory survives (rsync parity)."""
+        source = _make_tree(os.path.join(TEST_DATA_DIR, "sel_delscope_src"))
+        dest = os.path.join(TEST_DATA_DIR, "sel_delscope_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "sel_delscope_rdst")
+        spec = source + "/./foo"
+        for root in (dest, rdst):
+            clean_dir(root)
+            os.makedirs(os.path.join(root, "foo"))
+            with open(os.path.join(root, "foo", "extra.txt"), "wb") as fh:
+                fh.write(b"extra\n")
+            os.makedirs(os.path.join(root, "unrelated"))
+            with open(os.path.join(root, "unrelated", "keep.txt"), "wb") as fh:
+                fh.write(b"keep\n")
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            r = _rsync(["-aR", "--delete", spec, rdst + "/"])
+            assert r.returncode == 0, r.stderr
+            result, _ = run_client(spec, dest, flags=["-a", "-R", "--delete"],
+                                   port=server.port)
+            assert result.returncode == 0, result.stderr[:300]
+        assert (os.path.isfile(os.path.join(dest, "unrelated", "keep.txt"))
+                == os.path.isfile(os.path.join(rdst, "unrelated", "keep.txt")))
+        assert _tree(dest) == _tree(rdst)
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [False, True])
+    def test_relative_delete_protects_excluded_mirror(self, mt):
+        """-R --delete with --exclude must protect the destination mirror of an
+        excluded source path (recorded as a prefix-relative wire path)."""
+        source = _make_tree(os.path.join(TEST_DATA_DIR, "sel_delexc_src"))
+        with open(os.path.join(source, "foo", "secret.tmp"), "wb") as fh:
+            fh.write(b"secret\n")
+        dest = os.path.join(TEST_DATA_DIR, "sel_delexc_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "sel_delexc_rdst")
+        for root in (dest, rdst):
+            clean_dir(root)
+            os.makedirs(os.path.join(root, "foo"))
+            with open(os.path.join(root, "foo", "secret.tmp"), "wb") as fh:
+                fh.write(b"secret\n")
+            with open(os.path.join(root, "foo", "extra.txt"), "wb") as fh:
+                fh.write(b"extra\n")
+        spec = source + "/./foo"
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            r = _rsync(["-aR", "--delete", "--exclude=*.tmp", spec, rdst + "/"])
+            assert r.returncode == 0, r.stderr
+            flags = ["-a", "-R", "--delete", "--exclude=*.tmp"] + (["--threads"] if mt else [])
+            result, _ = run_client(spec, dest, flags=flags, port=server.port)
+            assert result.returncode == 0, result.stderr[:300]
+        assert _tree(dest) == _tree(rdst)
+        assert os.path.isfile(os.path.join(dest, "foo", "secret.tmp"))
+        assert not os.path.exists(os.path.join(dest, "foo", "extra.txt"))
+
+
+class TestClientAliases:
+    """#5: safe rsync option aliases accepted client-side."""
+
+    def _seed(self):
+        source = _make_tree(os.path.join(TEST_DATA_DIR, "sel_alias_src"))
+        return source
+
+    @pytest.mark.parametrize(
+        "flag",
+        [
+            "--ignore-non-existing",
+            "--protect-args",
+            "--msgs2stderr",
+            "--no-msgs2stderr",
+            "--no-iconv",
+            "--iconv=.",
+            "--iconv=-",
+        ],
+    )
+    def test_alias_accepted(self, shared_server, flag):
+        source = self._seed()
+        dest = os.path.join(TEST_DATA_DIR, "sel_alias_dst")
+        clean_dir(dest)
+        result, _ = run_client(source, dest, flags=[flag], port=shared_server.port)
+        assert result.returncode == 0, f"{flag} rejected: {result.stderr[:300]}"
+
+    def test_lone_h_prints_help(self):
+        result = subprocess.run([CLIENT_CMD[0], "-h"], capture_output=True, text=True,
+                                timeout=30)
+        assert result.returncode == 0, result.stderr
+        assert "Usage" in (result.stdout + result.stderr)
+
+    def test_h_with_args_still_human_readable(self, shared_server):
+        source = self._seed()
+        dest = os.path.join(TEST_DATA_DIR, "sel_h_dst")
+        clean_dir(dest)
+        result, _ = run_client(source, dest, flags=["-h"], port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        received = get_dest_received_dir(dest, source)
+        assert os.path.isfile(os.path.join(received, "top.txt"))
+
+
+class TestFilesFromEdges:
+    """#8/#58: --files-from empty list succeeds; rsync 3.4.1 rejects the
+    --no-ignore-missing-args negation, so FastSync must reject it too."""
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_empty_files_from_list_succeeds(self, shared_server):
+        source = _make_tree(os.path.join(TEST_DATA_DIR, "sel_ff_src"))
+        dest = os.path.join(TEST_DATA_DIR, "sel_ff_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "sel_ff_rdst")
+        clean_dir(dest)
+        clean_dir(rdst)
+        lst = os.path.join(TEST_DATA_DIR, "sel_ff_empty")
+        with open(lst, "w") as fh:
+            fh.write("")
+        r = _rsync(["-a", "--files-from=" + lst, source + "/", rdst + "/"])
+        assert r.returncode == 0, r.stderr
+        result, _ = run_client(source, dest, flags=["--files-from", lst],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        assert _tree(rdst) == []
+        assert _tree(dest) == []
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_no_ignore_missing_args_rejected_like_rsync(self):
+        source = _make_tree(os.path.join(TEST_DATA_DIR, "sel_nima_src"))
+        r = _rsync(["-a", "--no-ignore-missing-args", source + "/",
+                    os.path.join(TEST_DATA_DIR, "sel_nima_rdst") + "/"])
+        assert r.returncode != 0, "rsync unexpectedly accepted --no-ignore-missing-args"
+
+        cmd = CLIENT_CMD + ["--source-dir", source, "--dest-dir",
+                            os.path.join(TEST_DATA_DIR, "sel_nima_dst"), "--save-to-disk",
+                            "--no-ignore-missing-args"]
+        result = subprocess.run(cmd, capture_output=True, text=True, timeout=30)
+        assert result.returncode != 0, "FastSync unexpectedly accepted the negation"

tests/integration/test_preflight.py

@@ -94,14 +94,14 @@ def _seed_protocol_source(source):
 class TestProtocol:
     @pytest.mark.ci
     def test_protocol_current_version_accepted(self, shared_server):
-        """--protocol=2.21.0 (the current PROTOCOL_VERSION) is accepted and the
+        """--protocol=2.28.0 (the current PROTOCOL_VERSION) is accepted and the
         transfer completes normally."""
         source = os.path.join(TEST_DATA_DIR, "proto_ok_src")
         dest = os.path.join(TEST_DATA_DIR, "proto_ok_dst")
         shutil.rmtree(dest, ignore_errors=True)
         os.makedirs(dest)
         _seed_protocol_source(source)
-        result, _ = run_client(source, dest, flags=["--protocol=2.21.0"],
+        result, _ = run_client(source, dest, flags=["--protocol=2.28.0"],
                                port=shared_server.port)
         assert result.returncode == 0, \
             f"--protocol current run failed: {(result.stderr or result.stdout)[:400]}"
@@ -118,7 +118,8 @@ class TestProtocol:
         shutil.rmtree(dest, ignore_errors=True)
         os.makedirs(dest)
         _seed_protocol_source(source)
-        for bad in ("2.20.0", "2.19.0", "2.18.0", "2.17.0", "2.15.0", "2.16.0", "216", "31"):
+        for bad in ("2.27.0", "2.26.0", "2.25.0", "2.24.0", "2.23.0", "2.22.0", "2.21.0", "2.20.0",
+                    "2.19.0", "2.18.0", "2.17.0", "2.15.0", "2.16.0", "216", "31"):
             result, _ = run_client(source, dest, flags=[f"--protocol={bad}"],
                                    port=shared_server.port)
             assert result.returncode != 0, f"--protocol={bad} should be rejected"

tests/integration/test_preserve_attrs.py

@@ -0,0 +1,489 @@
+"""Wave 2b: per-attribute preservation split (-p/-t/-o/-g and their negations).
+
+The receiver applies each attribute independently (see src/shared/file_attr.h).
+These tests cover the per-flag behavior end-to-end, the CLI negations, directory
+modes, and the unprivileged best-effort / root-only ownership paths.  They reuse
+the established helpers from common.py.
+
+The `-s` spelling is rsync's --secluded-args no-op in FastSync; chunk
+serialization is the long-form --chunk-serialization, which is what the feature
+matrix below exercises.
+"""
+import os
+import stat
+import sys
+import time
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (
+    TEST_DATA_DIR,
+    run_client,
+    clean_dir,
+    get_dest_received_dir,
+    ServerManager,
+)
+
+DISTINCT_MTIME = 1_000_000_000  # 2001-09-09T01:46:40Z, a whole second
+
+
+def _process_umask():
+    current = os.umask(0)
+    os.umask(current)
+    return current
+
+
+def _seed_file(source, dest, name, content, mode, mtime=None):
+    """Create a one-file source tree at an explicit mode (and mtime), and a
+    clean destination.  Returns the source file path."""
+    clean_dir(source)
+    clean_dir(dest)
+    path = os.path.join(source, name)
+    with open(path, "wb") as fh:
+        fh.write(content)
+    os.chmod(path, mode)
+    if mtime is not None:
+        os.utime(path, (mtime, mtime))
+    return path
+
+
+def _received(dest, source, name):
+    return os.path.join(get_dest_received_dir(dest, source), name)
+
+
+class TestPreservePerms:
+    @pytest.mark.ci
+    def test_p_applies_source_mode(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "perms_p_src")
+        dest = os.path.join(TEST_DATA_DIR, "perms_p_dst")
+        _seed_file(source, dest, "f.txt", b"perms\n", 0o750)
+
+        result, _ = run_client(source, dest, flags=["-p"], port=shared_server.port)
+        assert result.returncode == 0, \
+            f"-p failed: {(result.stderr or result.stdout)[:300]}"
+        got = os.stat(_received(dest, source, "f.txt")).st_mode & 0o777
+        assert got == 0o750, f"-p must apply the source mode, got {oct(got)}"
+
+    @pytest.mark.ci
+    def test_without_p_preexisting_dest_keeps_mode(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "perms_nop_exist_src")
+        dest = os.path.join(TEST_DATA_DIR, "perms_nop_exist_dst")
+        src_file = _seed_file(source, dest, "f.txt", b"one\n", 0o750)
+
+        # Seed the destination.
+        result, _ = run_client(source, dest, flags=["-p"], port=shared_server.port)
+        assert result.returncode == 0, f"seed failed: {(result.stderr or '')[:200]}"
+
+        # Give the destination a distinguishable mode, then re-transfer without
+        # -p (but with -t so metadata still travels).
+        dst_file = _received(dest, source, "f.txt")
+        os.chmod(dst_file, 0o600)
+        with open(src_file, "wb") as fh:
+            fh.write(b"two, changed content\n")
+
+        result, _ = run_client(source, dest, flags=["-t"], port=shared_server.port)
+        assert result.returncode == 0, f"re-run failed: {(result.stderr or '')[:200]}"
+        got = os.stat(dst_file).st_mode & 0o777
+        assert got == 0o600, \
+            f"without -p a pre-existing destination must keep its mode, got {oct(got)}"
+        with open(dst_file, "rb") as fh:
+            assert fh.read() == b"two, changed content\n"
+
+    @pytest.mark.ci
+    def test_without_p_new_dest_gets_source_and_umask(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "perms_nop_new_src")
+        dest = os.path.join(TEST_DATA_DIR, "perms_nop_new_dst")
+        # 0664 has group/other bits that the umask strips, so the result is not
+        # just the source mode.  Under strict rsync parity the source mode is
+        # masked only by the umask (group/other write is no longer force-cleared
+        # on top of it).
+        _seed_file(source, dest, "f.txt", b"new\n", 0o664)
+
+        result, _ = run_client(source, dest, flags=["-t"], port=shared_server.port)
+        assert result.returncode == 0, f"-t failed: {(result.stderr or result.stdout)[:300]}"
+        want = 0o664 & ~_process_umask()
+        got = os.stat(_received(dest, source, "f.txt")).st_mode & 0o777
+        assert got == want, \
+            f"new no--p destination mode: want {oct(want)}, got {oct(got)}"
+
+
+class TestPreserveTimes:
+    @pytest.mark.ci
+    def test_t_applies_mtime(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "times_t_src")
+        dest = os.path.join(TEST_DATA_DIR, "times_t_dst")
+        _seed_file(source, dest, "f.txt", b"times\n", 0o644, mtime=DISTINCT_MTIME)
+
+        result, _ = run_client(source, dest, flags=["-t"], port=shared_server.port)
+        assert result.returncode == 0, f"-t failed: {(result.stderr or '')[:300]}"
+        dst_m = os.stat(_received(dest, source, "f.txt")).st_mtime
+        assert abs(dst_m - DISTINCT_MTIME) < 2, \
+            f"-t must apply the source mtime, got {dst_m}"
+
+    @pytest.mark.ci
+    def test_without_t_dest_mtime_differs(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "times_not_src")
+        dest = os.path.join(TEST_DATA_DIR, "times_not_dst")
+        _seed_file(source, dest, "f.txt", b"times\n", 0o644, mtime=DISTINCT_MTIME)
+
+        # -p transmits metadata but must not apply the source mtime.
+        result, _ = run_client(source, dest, flags=["-p"], port=shared_server.port)
+        assert result.returncode == 0, f"-p failed: {(result.stderr or '')[:300]}"
+        dst_m = os.stat(_received(dest, source, "f.txt")).st_mtime
+        assert abs(dst_m - DISTINCT_MTIME) > 24 * 3600, \
+            f"without -t the destination mtime must not be the source mtime ({dst_m})"
+
+    @pytest.mark.ci
+    def test_incremental_t_retransfers_after_no_t(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "times_incr_src")
+        dest = os.path.join(TEST_DATA_DIR, "times_incr_dst")
+        _seed_file(source, dest, "f.txt", b"retransfer\n", 0o644, mtime=DISTINCT_MTIME)
+
+        # First run without -t: the destination mtime becomes "now", differing
+        # from the pinned source mtime.
+        result, _ = run_client(source, dest, flags=["-p"], port=shared_server.port)
+        assert result.returncode == 0, f"seed failed: {(result.stderr or '')[:200]}"
+        dst_file = _received(dest, source, "f.txt")
+        assert abs(os.stat(dst_file).st_mtime - DISTINCT_MTIME) > 24 * 3600
+
+        # The incremental quick-check now sees a mtime mismatch, so the file is
+        # re-transferred and -t stamps the source time.
+        result, _ = run_client(source, dest, flags=["--incremental", "-t"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"incremental -t failed: {(result.stderr or '')[:300]}"
+        dst_m = os.stat(dst_file).st_mtime
+        assert abs(dst_m - DISTINCT_MTIME) < 2, \
+            f"second --incremental -t run must re-transfer and stamp the mtime, got {dst_m}"
+
+
+class TestPreserveNegations:
+    @pytest.mark.ci
+    def test_a_no_owner_no_group_keeps_perms_and_times(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "neg_owner_group_src")
+        dest = os.path.join(TEST_DATA_DIR, "neg_owner_group_dst")
+        _seed_file(source, dest, "f.txt", b"neg\n", 0o750, mtime=DISTINCT_MTIME)
+
+        result, _ = run_client(source, dest, flags=["-a", "--no-owner", "--no-group"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"-a --no-owner --no-group: {(result.stderr or '')[:300]}"
+        st = os.stat(_received(dest, source, "f.txt"))
+        assert st.st_mode & 0o777 == 0o750, "perms must survive the owner/group negation"
+        assert abs(st.st_mtime - DISTINCT_MTIME) < 2, "times must survive the owner/group negation"
+
+    @pytest.mark.ci
+    def test_a_no_perms_keeps_times_and_dest_mode(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "neg_perms_src")
+        dest = os.path.join(TEST_DATA_DIR, "neg_perms_dst")
+        src_file = _seed_file(source, dest, "f.txt", b"one\n", 0o750, mtime=DISTINCT_MTIME)
+
+        result, _ = run_client(source, dest, flags=["-a"], port=shared_server.port)
+        assert result.returncode == 0, f"seed failed: {(result.stderr or '')[:200]}"
+        dst_file = _received(dest, source, "f.txt")
+        os.chmod(dst_file, 0o600)
+        with open(src_file, "wb") as fh:
+            fh.write(b"changed\n")
+        # Rewriting the source bumped its mtime; restore the pinned value so the
+        # --no-perms run still has a distinct source time to apply.
+        os.utime(src_file, (DISTINCT_MTIME, DISTINCT_MTIME))
+
+        result, _ = run_client(source, dest, flags=["-a", "--no-perms"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"-a --no-perms: {(result.stderr or '')[:300]}"
+        st = os.stat(dst_file)
+        assert st.st_mode & 0o777 == 0o600, \
+            f"--no-perms must keep the destination mode, got {oct(st.st_mode & 0o777)}"
+        assert abs(st.st_mtime - DISTINCT_MTIME) < 2, "--no-perms must not disable times"
+
+    @pytest.mark.ci
+    def test_a_no_times_keeps_perms_but_not_mtime(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "neg_times_src")
+        dest = os.path.join(TEST_DATA_DIR, "neg_times_dst")
+        _seed_file(source, dest, "f.txt", b"neg times\n", 0o750, mtime=DISTINCT_MTIME)
+
+        result, _ = run_client(source, dest, flags=["-a", "--no-times"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"-a --no-times: {(result.stderr or '')[:300]}"
+        st = os.stat(_received(dest, source, "f.txt"))
+        assert st.st_mode & 0o777 == 0o750, "--no-times must not disable perms"
+        assert abs(st.st_mtime - DISTINCT_MTIME) > 24 * 3600, \
+            "--no-times must not apply the source mtime"
+
+    @pytest.mark.ci
+    def test_preserve_no_preserve_clears_all(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "neg_bundle_src")
+        dest = os.path.join(TEST_DATA_DIR, "neg_bundle_dst")
+        _seed_file(source, dest, "f.txt", b"bundle\n", 0o750, mtime=DISTINCT_MTIME)
+
+        result, _ = run_client(source, dest, flags=["--preserve", "--no-preserve"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"--preserve --no-preserve: {(result.stderr or '')[:300]}"
+        dst_file = _received(dest, source, "f.txt")
+        with open(dst_file, "rb") as fh:
+            assert fh.read() == b"bundle\n"
+        st = os.stat(dst_file)
+        # No metadata travels at all: a new file gets the fixed safe 0644 and
+        # the source mtime is not applied.
+        assert st.st_mode & 0o777 == 0o644, \
+            f"--no-preserve must not apply the source mode, got {oct(st.st_mode & 0o777)}"
+        assert abs(st.st_mtime - DISTINCT_MTIME) > 24 * 3600, \
+            "--no-preserve must not apply the source mtime"
+
+
+class TestDirectoryModes:
+    def _tree(self, name, dir_mode, pin_mtime):
+        source = os.path.join(TEST_DATA_DIR, name + "_src")
+        dest = os.path.join(TEST_DATA_DIR, name + "_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        sub = os.path.join(source, "sub")
+        os.makedirs(sub)
+        with open(os.path.join(sub, "file.txt"), "wb") as fh:
+            fh.write(b"dir mode content\n")
+        os.chmod(sub, dir_mode)
+        if pin_mtime:
+            os.utime(sub, (DISTINCT_MTIME, DISTINCT_MTIME))
+        return source, dest, sub
+
+    @pytest.mark.ci
+    def test_p_applies_directory_mode(self, shared_server):
+        source, dest, _ = self._tree("dirmode_p", 0o750, pin_mtime=False)
+        result, _ = run_client(source, dest, flags=["-p"], port=shared_server.port)
+        assert result.returncode == 0, f"-p failed: {(result.stderr or result.stdout)[:300]}"
+        got = os.stat(os.path.join(get_dest_received_dir(dest, source), "sub")).st_mode & 0o777
+        assert got == 0o750, f"-p must apply the source directory mode, got {oct(got)}"
+
+    @pytest.mark.ci
+    def test_p_preserves_directory_group_other_write(self, shared_server):
+        # Strict rsync parity: -p copies the source directory mode exactly,
+        # including group/other write (the old sanitization is gone).
+        source, dest, _ = self._tree("dirmode_go_write", 0o777, pin_mtime=False)
+        result, _ = run_client(source, dest, flags=["-p"], port=shared_server.port)
+        assert result.returncode == 0, f"-p failed: {(result.stderr or result.stdout)[:300]}"
+        mode = os.stat(os.path.join(get_dest_received_dir(dest, source), "sub")).st_mode & 0o777
+        assert mode == 0o777, \
+            f"-p must preserve the source directory mode exactly, got {oct(mode)}"
+
+    @pytest.mark.ci
+    def test_omit_dir_times_suppresses_times_not_modes(self, shared_server):
+        source, dest, _ = self._tree("dirmode_omit", 0o750, pin_mtime=True)
+        result, _ = run_client(source, dest, flags=["-a", "-O"], port=shared_server.port)
+        assert result.returncode == 0, f"-a -O failed: {(result.stderr or result.stdout)[:300]}"
+        st = os.stat(os.path.join(get_dest_received_dir(dest, source), "sub"))
+        assert st.st_mode & 0o777 == 0o750, \
+            f"-O must suppress only dir times, not dir modes (got {oct(st.st_mode & 0o777)})"
+        assert abs(st.st_mtime - DISTINCT_MTIME) > 5, \
+            f"-O must not apply the directory mtime (got {st.st_mtime})"
+
+
+class TestOwnershipBestEffort:
+    """-o/-g/-a must succeed with correct content even when the receiver cannot
+    chown (the unprivileged CI case).  Ownership is deliberately not asserted."""
+
+    @pytest.mark.ci
+    @pytest.mark.parametrize("flags", [["-o"], ["-g"], ["-a"]])
+    def test_ownership_flags_succeed_unprivileged(self, shared_server, flags):
+        tag = flags[0].strip("-")
+        source = os.path.join(TEST_DATA_DIR, f"best_effort_{tag}_src")
+        dest = os.path.join(TEST_DATA_DIR, f"best_effort_{tag}_dst")
+        _seed_file(source, dest, "f.txt", b"best effort ownership\n", 0o640)
+
+        result, _ = run_client(source, dest, flags=flags, port=shared_server.port)
+        assert result.returncode == 0, \
+            f"{flags} exit {result.returncode}: {(result.stderr or result.stdout)[:300]}"
+        with open(_received(dest, source, "f.txt"), "rb") as fh:
+            assert fh.read() == b"best effort ownership\n"
+
+
+@pytest.mark.skipif(os.geteuid() != 0, reason="only root can change ownership")
+class TestOwnershipRoot:
+    """Root-only per-attribute ownership application.  Not marked ci: the PR
+    gate runs as an unprivileged user."""
+
+    def _seed_owned(self, tag, uid, gid):
+        source = os.path.join(TEST_DATA_DIR, f"root_owner_{tag}_src")
+        dest = os.path.join(TEST_DATA_DIR, f"root_owner_{tag}_dst")
+        path = _seed_file(source, dest, "f.txt", b"root ownership\n", 0o644)
+        os.chown(path, uid, gid)
+        return source, dest
+
+    def test_o_applies_owner_only(self, shared_server):
+        source, dest = self._seed_owned("o", 12345, 12346)
+        result, _ = run_client(source, dest, flags=["-o"], port=shared_server.port)
+        assert result.returncode == 0, f"-o failed: {(result.stderr or '')[:300]}"
+        st = os.stat(_received(dest, source, "f.txt"))
+        assert st.st_uid == 12345, f"-o must apply the owner, got uid={st.st_uid}"
+        assert st.st_gid != 12346, "-o must not change the group"
+
+    def test_g_applies_group_only(self, shared_server):
+        source, dest = self._seed_owned("g", 12345, 54321)
+        result, _ = run_client(source, dest, flags=["-g"], port=shared_server.port)
+        assert result.returncode == 0, f"-g failed: {(result.stderr or '')[:300]}"
+        st = os.stat(_received(dest, source, "f.txt"))
+        assert st.st_gid == 54321, f"-g must apply the group, got gid={st.st_gid}"
+        assert st.st_uid != 12345, "-g must not change the owner"
+
+    def test_a_applies_owner_and_group(self, shared_server):
+        source, dest = self._seed_owned("a", 12345, 54321)
+        result, _ = run_client(source, dest, flags=["-a"], port=shared_server.port)
+        assert result.returncode == 0, f"-a failed: {(result.stderr or '')[:300]}"
+        st = os.stat(_received(dest, source, "f.txt"))
+        assert (st.st_uid, st.st_gid) == (12345, 54321), \
+            f"-a must apply owner+group, got uid={st.st_uid} gid={st.st_gid}"
+
+    def test_chown_overrides_o(self, shared_server):
+        source, dest = self._seed_owned("chown", 11111, 22222)
+        result, _ = run_client(source, dest, flags=["-o", "--chown=@33333:@44444"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"-o --chown failed: {(result.stderr or '')[:300]}"
+        st = os.stat(_received(dest, source, "f.txt"))
+        assert (st.st_uid, st.st_gid) == (33333, 44444), \
+            f"--chown must override -o, got uid={st.st_uid} gid={st.st_gid}"
+
+    def test_fake_super_o_does_not_real_chown(self, shared_server):
+        # #294: --fake-super only RECORDS ownership; it must never real-chown the
+        # recorded source owner (that defeats the point of the flag).  With -o the
+        # resolved owner is parked in the reserved xattr and the on-disk owner is
+        # left as the receiver's.
+        source, dest = self._seed_owned("fake_o", 12345, 54321)
+        result, _ = run_client(source, dest, flags=["--fake-super", "-o"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"--fake-super -o failed: {(result.stderr or '')[:300]}"
+        dst = _received(dest, source, "f.txt")
+        st = os.stat(dst)
+        assert st.st_uid != 12345, \
+            f"--fake-super -o must NOT real-chown the source owner, got uid={st.st_uid}"
+        record = os.getxattr(dst, "user.fastsync.stat").decode()
+        fields = record.split(":")
+        assert fields[0] == "12345", \
+            f"--fake-super must record the resolved owner, got {fields[0]}"
+
+    def test_o_applies_directory_owner(self, shared_server):
+        """#286.2: -o must apply the source owner to DIRECTORIES too (the
+        deferred directory-metadata application now runs the identity path)."""
+        source = os.path.join(TEST_DATA_DIR, "root_dir_o_src")
+        dest = os.path.join(TEST_DATA_DIR, "root_dir_o_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        os.makedirs(os.path.join(source, "sub", "deep"))
+        with open(os.path.join(source, "sub", "deep", "f.txt"), "wb") as fh:
+            fh.write(b"dir owner\n")
+        os.chown(os.path.join(source, "sub"), 12345, 12346)
+        os.chown(os.path.join(source, "sub", "deep"), 23456, 34567)
+
+        result, _ = run_client(source, dest, flags=["-o", "-t"], port=shared_server.port)
+        assert result.returncode == 0, f"-o dir failed: {(result.stderr or '')[:300]}"
+        received = get_dest_received_dir(dest, source)
+        sub = os.stat(os.path.join(received, "sub"))
+        deep = os.stat(os.path.join(received, "sub", "deep"))
+        assert sub.st_uid == 12345, f"dir 'sub' owner not applied: {sub.st_uid}"
+        assert deep.st_uid == 23456, f"dir 'sub/deep' owner not applied: {deep.st_uid}"
+        # -o alone must not change the group.
+        assert sub.st_gid != 12346
+
+    def test_a_applies_directory_owner_and_group(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "root_dir_a_src")
+        dest = os.path.join(TEST_DATA_DIR, "root_dir_a_dst")
+        clean_dir(source)
+        clean_dir(dest)
+        os.makedirs(os.path.join(source, "sub"))
+        with open(os.path.join(source, "sub", "f.txt"), "wb") as fh:
+            fh.write(b"dir owner group\n")
+        os.chown(os.path.join(source, "sub"), 12345, 54321)
+
+        result, _ = run_client(source, dest, flags=["-a"], port=shared_server.port)
+        assert result.returncode == 0, f"-a dir failed: {(result.stderr or '')[:300]}"
+        received = get_dest_received_dir(dest, source)
+        st = os.stat(os.path.join(received, "sub"))
+        assert (st.st_uid, st.st_gid) == (12345, 54321), \
+            f"-a must apply dir owner+group, got uid={st.st_uid} gid={st.st_gid}"
+
+    def test_numeric_ids_alone_does_not_chown(self, shared_server):
+        """#286.1: --numeric-ids is a mapping modifier, not an ownership request.
+        `-t --numeric-ids` must leave the receiver's ownership untouched."""
+        source, dest = self._seed_owned("num_only", 12345, 54321)
+        result, _ = run_client(source, dest, flags=["-t", "--numeric-ids"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"-t --numeric-ids failed: {(result.stderr or '')[:300]}"
+        st = os.stat(_received(dest, source, "f.txt"))
+        assert st.st_uid != 12345, \
+            f"--numeric-ids alone must not chown, got uid={st.st_uid}"
+
+    def test_numeric_ids_with_o_uses_raw_id(self, shared_server):
+        source, dest = self._seed_owned("num_o", 12345, 54321)
+        result, _ = run_client(source, dest, flags=["-o", "-t", "--numeric-ids"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"-o --numeric-ids failed: {(result.stderr or '')[:300]}"
+        st = os.stat(_received(dest, source, "f.txt"))
+        assert st.st_uid == 12345, \
+            f"-o --numeric-ids must apply the raw id, got uid={st.st_uid}"
+
+
+class TestPreserveFeatureMatrix:
+    """A representative per-attribute check under the alternate transfer engines
+    (chunk serialization, --delay-updates, and the multithreaded scanner)."""
+
+    @pytest.mark.ci
+    @pytest.mark.parametrize("extra", ["--chunk-serialization", "--delay-updates", "--threads"])
+    def test_p_and_t_hold_under_engine(self, shared_server, extra):
+        tag = extra.strip("-").replace("-", "_")
+        source = os.path.join(TEST_DATA_DIR, f"matrix_{tag}_src")
+        dest = os.path.join(TEST_DATA_DIR, f"matrix_{tag}_dst")
+        _seed_file(source, dest, "f.txt", b"matrix\n", 0o750, mtime=DISTINCT_MTIME)
+
+        result, _ = run_client(source, dest, flags=["-p", "-t", extra],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"-p -t {extra} failed: {(result.stderr or result.stdout)[:300]}"
+        st = os.stat(_received(dest, source, "f.txt"))
+        assert st.st_mode & 0o777 == 0o750, f"mode lost under {extra}"
+        assert abs(st.st_mtime - DISTINCT_MTIME) < 2, f"mtime lost under {extra}"
+
+
+class TestSpecialNodeModes:
+    """Strict rsync parity: with -p the source FIFO mode is copied exactly,
+    including group/other write.  Without -p the node follows the same
+    source & ~umask base as any other new entry.  FIFOs are created
+    unprivileged via mkfifo."""
+
+    @pytest.mark.ci
+    def test_specials_p_preserves_fifo_mode(self):
+        source = os.path.join(TEST_DATA_DIR, "specialmode_src")
+        dest = os.path.join(TEST_DATA_DIR, "specialmode_dst")
+        clean_dir(source)
+        clean_dir(dest)
+
+        src_fifo = os.path.join(source, "world.fifo")
+        os.mkfifo(src_fifo)
+        os.chmod(src_fifo, 0o777)
+        assert os.stat(src_fifo).st_mode & 0o777 == 0o777
+
+        # Production daemonizes with umask(0) (server.c) so the source mode is
+        # what reaches mkfifo.  The session server runs in the foreground and
+        # would inherit the runner's umask, which alone would strip the write
+        # bits and mask a regression.  Start a dedicated foreground server under
+        # umask(0) to exercise the real path.
+        server = ServerManager()
+        saved_umask = os.umask(0)
+        try:
+            server.start(extra_args=["--allow-super"])
+        finally:
+            os.umask(saved_umask)
+        try:
+            result, _ = run_client(source, dest, flags=["--specials", "-p"],
+                                   port=server.port)
+        finally:
+            server.stop()
+
+        assert result.returncode == 0, \
+            f"--specials -p failed: {(result.stderr or result.stdout)[:300]}"
+
+        received = _received(dest, source, "world.fifo")
+        assert os.path.lexists(received), "source FIFO was not recreated on the destination"
+        st = os.lstat(received)
+        assert stat.S_ISFIFO(st.st_mode), f"received entry is not a FIFO: {oct(st.st_mode)}"
+        mode = st.st_mode & 0o777
+        assert mode == 0o777, \
+            f"-p must preserve the source FIFO mode exactly (want 0o777), got {oct(mode)}"

tests/integration/test_readme_consistency.py

@@ -0,0 +1,262 @@
+"""Guard the README against drifting from the real CLI.
+
+This test parses README.md and checks it against the actual sources of truth
+instead of against a hand-maintained copy:
+
+  * client ``--help`` output  -> ``src/client/usage.c`` (``print_usage``)
+  * server ``--help`` output  -> ``src/server/server.c`` (``print_server_usage``)
+  * ``FASTSYNC_*`` env vars   -> ``getenv("...")`` call sites under ``src/``
+
+It is deliberately offline and read-only: no server is started, no transfer is
+performed.  Each binary is invoked at most once per test session and the result
+is cached.
+"""
+
+import functools
+import os
+import re
+import subprocess
+import sys
+
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import BUILD_DIR, PROJECT_ROOT
+
+pytestmark = pytest.mark.ci
+
+README_PATH = os.path.join(PROJECT_ROOT, "README.md")
+SRC_DIR = os.path.join(PROJECT_ROOT, "src")
+
+# ---------------------------------------------------------------------------
+# Markdown helpers
+# ---------------------------------------------------------------------------
+
+_HEADING_RE = re.compile(r"^(#+)\s+(.*?)\s*$")
+_BACKTICK_RE = re.compile(r"`([^`]*)`")
+# A documented option may carry an argument annotation that is not part of the
+# option name itself: ``--out=FILE``, ``--exclude <pattern>``, ``--threads[=N]``,
+# ``--copy-as=USER[:GROUP]``.  Cut the name loose from the first such marker.
+_OPTION_SUFFIX_RE = re.compile(r"[=\s<\[(].*$")
+_OPTION_TOKEN_RE = re.compile(r"^--?[A-Za-z][A-Za-z0-9-]*$")
+
+
+def _readme_lines():
+    with open(README_PATH, encoding="utf-8") as fh:
+        return fh.read().splitlines()
+
+
+def _heading_level(line):
+    match = _HEADING_RE.match(line)
+    return len(match.group(1)) if match else 0
+
+
+def _section(lines, heading):
+    """Return ``(lineno, line)`` pairs under the first exact ``heading``.
+
+    The section runs until the next heading of the same or higher level, so a
+    ``##`` section includes its ``###`` subsections.  Line numbers are 1-based
+    to match what a reader sees in an editor.
+    """
+    target_level = _heading_level(heading)
+    for index, line in enumerate(lines):
+        if line.strip() != heading:
+            continue
+        start = index + 1
+        for end in range(start, len(lines)):
+            level = _heading_level(lines[end])
+            if level and level <= target_level:
+                return [(n + 1, lines[n]) for n in range(start, end)]
+        return [(n + 1, lines[n]) for n in range(start, len(lines))]
+    raise AssertionError(
+        f"README heading not found (has the README been restructured?): {heading!r}"
+    )
+
+
+def _first_column_spans(section_lines):
+    """Backticked spans from the first column of every markdown table row."""
+    spans = []
+    for lineno, line in section_lines:
+        stripped = line.strip()
+        if not stripped.startswith("|"):
+            continue
+        cells = stripped.split("|")
+        if len(cells) < 2:
+            continue
+        first = cells[1]
+        if set(first.strip()) <= set("-: "):
+            continue  # header separator row, e.g. |---|---|
+        for match in _BACKTICK_RE.finditer(first):
+            spans.append((match.group(1), lineno))
+    return spans
+
+
+def _documented_option_tokens(section_lines):
+    """``(token, lineno, raw_cell)`` for each CLI option in a section's tables."""
+    found = []
+    for raw, lineno in _first_column_spans(section_lines):
+        for piece in re.split(r"[,\s]+", raw):
+            name = _OPTION_SUFFIX_RE.sub("", piece).strip()
+            if _OPTION_TOKEN_RE.match(name):
+                found.append((name, lineno, raw))
+    return found
+
+
+# ---------------------------------------------------------------------------
+# Sources of truth
+# ---------------------------------------------------------------------------
+
+_GETENV_RE = re.compile(r'getenv\s*\(\s*"([^"]+)"\s*\)')
+_FASTSYNC_ENV_RE = re.compile(r"FASTSYNC_[A-Z0-9_]+")
+
+
+def _getenv_names():
+    """Every string literal passed to ``getenv()`` anywhere under ``src/``."""
+    names = set()
+    for root, _dirs, files in os.walk(SRC_DIR):
+        for filename in files:
+            if not filename.endswith((".c", ".h")):
+                continue
+            path = os.path.join(root, filename)
+            with open(path, encoding="utf-8", errors="replace") as fh:
+                names.update(_GETENV_RE.findall(fh.read()))
+    return names
+
+
+@functools.lru_cache(maxsize=None)
+def _help_stdout(binary_name):
+    """Cached ``<binary> --help`` stdout; skipped (not failed) if unbuilt."""
+    binary = os.path.join(BUILD_DIR, binary_name)
+    if not (os.path.isfile(binary) and os.access(binary, os.X_OK)):
+        pytest.skip(
+            f"{binary} is not built; run "
+            "`cmake -B build -S . && cmake --build build` first"
+        )
+    try:
+        result = subprocess.run(
+            [binary, "--help"], capture_output=True, text=True, timeout=30
+        )
+    except OSError as exc:
+        pytest.skip(f"could not execute {binary}: {exc}")
+    assert result.returncode == 0, (
+        f"{binary} --help exited {result.returncode}: "
+        f"{(result.stderr or result.stdout).strip()[:200]}"
+    )
+    return result.stdout
+
+
+def _mentions_option(help_text, token):
+    """True when ``token`` appears as a standalone option in ``help_text``.
+
+    A plain substring test would let a removed token hide behind a longer one
+    (``--del`` inside ``--delete``); requiring a non-word boundary on both sides
+    keeps every documented token individually accountable.
+    """
+    return (
+        re.search(r"(?<![\w-])" + re.escape(token) + r"(?![\w-])", help_text)
+        is not None
+    )
+
+
+# Options the help text intentionally expresses only as a family (for example
+# the generic ``--no-OPTION`` entry) rather than by spelling every member out.
+# Add an entry here only with a one-line justification; prefer fixing the
+# extractor first.  Currently empty: every option the README documents is
+# printed verbatim by the matching ``--help`` (including ``--no-super`` and
+# ``--no-detach``).
+_FAMILY_FORM_ALLOWLIST = frozenset()
+
+
+# ---------------------------------------------------------------------------
+# Tests
+# ---------------------------------------------------------------------------
+
+
+def test_documented_env_vars_exist():
+    """Every ``FASTSYNC_*`` in the README env table has a ``getenv()`` site.
+
+    Both directions are checked so the documented set and the source set stay
+    identical: a documented variable with no call site is a README defect, and a
+    new ``FASTSYNC_*`` call site without documentation is a README gap.
+    """
+    documented = _documented_env_vars()
+    assert documented, "no FASTSYNC_* variables found in the README env table"
+
+    getenv_names = _getenv_names()
+    documented_names = {name for name, _lineno in documented}
+
+    missing_in_source = [
+        (name, lineno) for name, lineno in documented if name not in getenv_names
+    ]
+    if missing_in_source:
+        details = "; ".join(
+            f"`{name}` (README.md line {lineno})"
+            for name, lineno in sorted(missing_in_source, key=lambda item: item[1])
+        )
+        pytest.fail(
+            "README documents environment variable(s) with no getenv() call "
+            f"site under src/: {details}"
+        )
+
+    fastsync_getenv = {name for name in getenv_names if name.startswith("FASTSYNC_")}
+    undocumented = sorted(fastsync_getenv - documented_names)
+    assert not undocumented, (
+        "src/ reads FASTSYNC_* environment variable(s) that the README does not "
+        f"document in '## Environment Variables': {', '.join(undocumented)}"
+    )
+
+
+def test_documented_client_flags_exist_in_help():
+    """Client options in README tables must appear in ``client --help``."""
+    _assert_documented_flags(
+        "client",
+        ["### Client", "## Client Options", "## FastSync Extensions"],
+    )
+
+
+def test_documented_server_flags_exist_in_help():
+    """Server options in README tables must appear in ``server --help``."""
+    _assert_documented_flags("server", ["### Server", "## Server Options"])
+
+
+# ---------------------------------------------------------------------------
+# Implementation helpers for the tests above
+# ---------------------------------------------------------------------------
+
+
+def _documented_env_vars():
+    """``(name, lineno)`` for each ``FASTSYNC_*`` token in the env table."""
+    lines = _readme_lines()
+    section = _section(lines, "## Environment Variables")
+    found = []
+    for raw, lineno in _first_column_spans(section):
+        for match in _FASTSYNC_ENV_RE.finditer(raw):
+            found.append((match.group(0), lineno))
+    return found
+
+
+def _assert_documented_flags(binary_name, headings):
+    help_text = _help_stdout(binary_name)
+    readme_lines = _readme_lines()
+
+    failures = []
+    for heading in headings:
+        for token, lineno, raw in _documented_option_tokens(
+            _section(readme_lines, heading)
+        ):
+            if token in _FAMILY_FORM_ALLOWLIST:
+                continue
+            if not _mentions_option(help_text, token):
+                failures.append((lineno, token, heading, raw))
+
+    if failures:
+        failures.sort()
+        shown = "\n".join(
+            f"  {token}  (README.md line {lineno}, section {heading!r}, "
+            f"table cell `{raw}`)"
+            for lineno, token, heading, raw in failures
+        )
+        pytest.fail(
+            f"README documents option(s) missing from `{binary_name} --help`:\n"
+            f"{shown}"
+        )

tests/integration/test_stop.py

@@ -150,13 +150,36 @@ class TestStopAt:
         assert _received_files(received) == [], \
             f"expected nothing transferred, got {_received_files(received)}"
 
+    @pytest.mark.ci
+    def test_stop_at_rsync_date_form(self, shared_server):
+        """rsync's full date form (Y-M-DTh:m) is accepted; a deadline well in the
+        future lets the transfer complete normally."""
+        source, dest = _make("dateform")
+        _seed_source(source)
+        stamp = time.strftime("%Y-%m-%dT%H:%M", time.localtime(time.time() + 3600))
+        result, _ = run_client(source, dest, flags=[f"--stop-at={stamp}"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--stop-at={stamp} should be accepted: " \
+            f"{(result.stderr or result.stdout)[:400]}"
+        received = get_dest_received_dir(dest, source)
+        mismatches, missing = verify_transfer(source, received)
+        assert not mismatches and not missing
+
+        # The slash-separated date spelling is accepted too.
+        slash = time.strftime("%Y/%m/%dT%H:%M", time.localtime(time.time() + 3600))
+        result, _ = run_client(source, dest, flags=[f"--stop-at={slash}"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"--stop-at={slash} should be accepted"
+
     @pytest.mark.ci
     def test_stop_rejects_garbage(self, shared_server):
         """Malformed --stop-at/--stop-after values are rejected up front."""
         source, dest = _make("garbage")
         _seed_source(source)
-        for flag in ("--stop-after=abc", "--stop-at=12:99", "--stop-at=12",
-                     "--stop-at=now+5x", "--stop-at=now-5s"):
+        for flag in ("--stop-after=abc", "--stop-at=12:99", "--stop-at=1234",
+                     "--stop-at=now+5x", "--stop-at=now-5s",
+                     "--stop-at=2000-13-45", "--stop-at=2030-12-31T23:59:59"):
             result, _ = run_client(source, dest, flags=[flag],
                                    port=shared_server.port)
             assert result.returncode != 0, f"{flag} should be rejected"

tests/runner.c

@@ -11,10 +11,12 @@
 #include "test_daemon_conf.h"
 #include "test_daemon_limits.h"
 #include "test_delay_updates.h"
+#include "test_delete_plan.h"
 #include "test_delta.h"
 #include "test_file.h"
 #include "test_file_list.h"
 #include "test_file_sendfile.h"
+#include "test_format.h"
 #include "test_fuzz_smoke.h"
 #include "test_glob.h"
 #include "test_hardlink.h"
@@ -41,6 +43,7 @@
 #include "test_utils.h"
 #include "test_xattr.h"
 #include <stdio.h>
+#include <stdlib.h>
 #include <signal.h>
 
 // Define global test state variables
@@ -50,6 +53,11 @@ bool current_test_failed = false;
 
 int main() {
   signal(SIGPIPE, SIG_IGN);
+  /* The codec/checksum resolvers consult rsync's preference-list environment
+   * variables; clear them so a developer's shell cannot change test outcomes.
+   * The env-specific tests set and restore their own values. */
+  unsetenv("RSYNC_COMPRESS_LIST");
+  unsetenv("RSYNC_CHECKSUM_LIST");
   printf("\033[1;36m=== RUNNING UNIT TESTS ===\033[0m\n\n");
 
   RUN_TEST(test_queue);
@@ -58,12 +66,14 @@ int main() {
   RUN_TEST(test_chunk);
   RUN_TEST(test_batch);
   RUN_TEST(test_change_list);
+  RUN_TEST(test_format);
   RUN_TEST(test_config);
   RUN_TEST(test_credentials);
   RUN_TEST(test_compression);
   RUN_TEST(test_scanner);
   RUN_TEST(test_checksum);
   RUN_TEST(test_delta);
+  RUN_TEST(test_delete_plan);
   RUN_TEST(test_data);
   RUN_TEST(test_protocol);
   RUN_TEST(test_protocol_error);

tests/test_change_list.c

@@ -1,5 +1,6 @@
 #include "test_change_list.h"
 #include "change_list.h"
+#include "config.h"
 #include "test_utils.h"
 #include "utils.h"
 #include <stdlib.h>
@@ -9,64 +10,150 @@
 static ChangeEvent sample_event(void) {
   ChangeEvent event;
   memset(&event, 0, sizeof(event));
-  event.path = "/srv/root/sub/file.txt";
+  event.path = "src/sub/file.txt";
+  event.name = "sub/file.txt";
   event.decision = CHANGE_SENT;
   event.is_directory = false;
   event.size = 12345;
   event.bytes_sent = 999;
   event.mtime_sec = 1700000000;
+  event.mtime_nsec = 0;
+  event.mode = 0100644;
+  event.uid = 1000;
+  event.gid = 1000;
   return event;
 }
 
+/* Expected %M expansion computed independently with localtime_r. */
+static void expected_mtime(time_t when, char out[32]) {
+  struct tm broken_down;
+  localtime_r(&when, &broken_down);
+  strftime(out, 32, "%Y/%m/%d-%H:%M:%S", &broken_down);
+}
+
 static void test_format_tokens() {
   ChangeEvent event = sample_event();
-  char* line = change_render_format("%f %n %l %b %M %%", &event);
+  Config* config = config_create();
+  char when[32];
+  expected_mtime(event.mtime_sec, when);
+  char* line = change_render_format("%f %n %l %b %M %%", config, &event);
   EXPECT_NOT_NULL(line);
-  EXPECT_EQ_STR(line, "/srv/root/sub/file.txt file.txt 12345 999 1700000000 %");
+  char expected[256];
+  snprintf(expected, sizeof(expected), "src/sub/file.txt sub/file.txt 12345 999 %s %%", when);
+  EXPECT_EQ_STR(line, expected);
   free(line);
+  config_delete(config);
 }
 
 static void test_format_unknown_tokens_preserved() {
   ChangeEvent event = sample_event();
-  char* line = change_render_format("x%q=%f%z", &event);
+  Config* config = config_create();
+  char* line = change_render_format("x%q=%f%z", config, &event);
   EXPECT_NOT_NULL(line);
-  EXPECT_EQ_STR(line, "x%q=/srv/root/sub/file.txt%z");
+  EXPECT_EQ_STR(line, "x%q=src/sub/file.txt%z");
   free(line);
+  config_delete(config);
 }
 
-static void test_format_leaf_name() {
+static void test_format_directory_name_has_trailing_slash() {
   ChangeEvent event = sample_event();
-  event.path = "bare.txt";
-  char* line = change_render_format("%n|%f", &event);
+  event.is_directory = true;
+  event.path = "src/sub";
+  event.name = "sub";
+  Config* config = config_create();
+  char* line = change_render_format("%n|%f", config, &event);
   EXPECT_NOT_NULL(line);
-  EXPECT_EQ_STR(line, "bare.txt|bare.txt");
+  EXPECT_EQ_STR(line, "sub/|src/sub");
   free(line);
+  config_delete(config);
 }
 
 static void test_render_itemize_sent_file() {
   ChangeEvent event = sample_event();
-  char* line = change_render_itemize(&event);
+  Config* config = config_create();
+  char* line = change_render_itemize(config, &event);
   EXPECT_NOT_NULL(line);
-  EXPECT_EQ_STR(line, ">f+++++++++ /srv/root/sub/file.txt");
+  EXPECT_EQ_STR(line, ">f+++++++++ sub/file.txt");
   free(line);
+  config_delete(config);
+}
+
+static void test_render_itemize_directory() {
+  ChangeEvent event = sample_event();
+  event.is_directory = true;
+  event.path = "src/sub";
+  event.name = "sub";
+  Config* config = config_create();
+  char* line = change_render_itemize(config, &event);
+  EXPECT_NOT_NULL(line);
+  EXPECT_EQ_STR(line, "cd+++++++++ sub/");
+  free(line);
+  config_delete(config);
+}
+
+static void test_render_itemize_symlink() {
+  ChangeEvent event = sample_event();
+  event.is_symlink = true;
+  event.path = "src/link";
+  event.name = "link";
+  event.symlink_target = "a.txt";
+  Config* config = config_create();
+  char* line = change_render_itemize(config, &event);
+  EXPECT_NOT_NULL(line);
+  EXPECT_EQ_STR(line, "cL+++++++++ link -> a.txt");
+  free(line);
+  config_delete(config);
+}
+
+static void test_render_itemize_compares_destination() {
+  ChangeEvent event = sample_event();
+  Config* config = config_create();
+  config->preserve_perms = true;
+  config->preserve_owner = true;
+  config->preserve_group = true;
+  event.dest.known = true;
+  event.dest.existed = true;
+  event.dest.size = 1;
+  event.dest.mtime_sec = 1700000000;
+  event.dest.mtime_nsec = 0;
+  event.dest.mode = 0100600;
+  event.dest.uid = 1;
+  event.dest.gid = 2;
+  char* line = change_render_itemize(config, &event);
+  EXPECT_NOT_NULL(line);
+  /* size, perms, owner and group differ; time matches. */
+  EXPECT_EQ_STR(line, ">f.s.pog... sub/file.txt");
+  free(line);
+  config_delete(config);
 }
 
 static void test_render_itemize_up_to_date_is_empty() {
   ChangeEvent event = sample_event();
+  Config* config = config_create();
   event.decision = CHANGE_UP_TO_DATE;
-  char* line = change_render_itemize(&event);
+  char* line = change_render_itemize(config, &event);
   EXPECT_NOT_NULL(line);
   EXPECT_EQ_STR(line, "");
   free(line);
+  config_delete(config);
 }
 
 static void test_render_list_line() {
-  char* line = change_render_list_line(0100644, 4096, 1700000000, "/srv/x.txt");
+  ChangeEvent event;
+  memset(&event, 0, sizeof(event));
+  Config* config = config_create();
+  event.name = "sub/x.txt";
+  event.path = "sub/x.txt";
+  event.mode = 0100644;
+  event.size = 4096;
+  event.mtime_sec = 1700000000;
+  char* line = change_render_list_line(config, &event);
   EXPECT_NOT_NULL(line);
   EXPECT_TRUE(strncmp(line, "-rw-r--r--", 10) == 0);
-  EXPECT_TRUE(strstr(line, "4096") != NULL);
-  EXPECT_TRUE(strstr(line, "/srv/x.txt") != NULL);
+  EXPECT_TRUE(strstr(line, "4,096") != NULL);
+  EXPECT_TRUE(strstr(line, "sub/x.txt") != NULL);
   free(line);
+  config_delete(config);
 }
 
 static void test_change_list_enabled() {
@@ -90,12 +177,50 @@ static void test_change_list_enabled() {
   config_delete(config); /* closes config->log_file */
 }
 
+/* %C uses the negotiated TRANSFER checksum's column width (not the pre-transfer
+ * whole-file digest), and `none` renders as a blank 2-char column, matching
+ * rsync.  A not-yet-filled checksum renders as spaces. */
+static void test_format_C_padding_uses_transfer_algo() {
+  ChangeEvent event = sample_event();
+  Config* config = config_create();
+  EXPECT_NOT_NULL(config);
+  /* Deliberately different pre-transfer algorithm: the transfer one must win. */
+  config->checksum_algo = (int)CHECKSUM_ALGO_MD4;
+  struct {
+    int algo;
+    int width;
+  } cases[] = {
+      {CHECKSUM_ALGO_XXH128, 32}, {CHECKSUM_ALGO_XXH64, 16}, {CHECKSUM_ALGO_XXH3, 16},
+      {CHECKSUM_ALGO_MD5, 32},    {CHECKSUM_ALGO_MD4, 32},   {CHECKSUM_ALGO_SHA1, 40},
+      {CHECKSUM_ALGO_NONE, 2},
+  };
+  for (size_t i = 0; i < sizeof(cases) / sizeof(cases[0]); i++) {
+    config->checksum_transfer_algo = cases[i].algo;
+    char expected[64];
+    size_t n = 0;
+    expected[n++] = '[';
+    for (int j = 0; j < cases[i].width; j++)
+      expected[n++] = ' ';
+    expected[n++] = ']';
+    expected[n] = '\0';
+    char* line = change_render_format("[%C]", config, &event);
+    EXPECT_NOT_NULL(line);
+    EXPECT_EQ_STR(line, expected);
+    free(line);
+  }
+  config_delete(config);
+}
+
 void test_change_list() {
   test_format_tokens();
   test_format_unknown_tokens_preserved();
-  test_format_leaf_name();
+  test_format_directory_name_has_trailing_slash();
   test_render_itemize_sent_file();
+  test_render_itemize_directory();
+  test_render_itemize_symlink();
+  test_render_itemize_compares_destination();
   test_render_itemize_up_to_date_is_empty();
   test_render_list_line();
   test_change_list_enabled();
+  test_format_C_padding_uses_transfer_algo();
 }

tests/test_checksum.c

@@ -1,7 +1,9 @@
 #include "test_checksum.h"
 #include "checksum.h"
 #include "test_utils.h"
+#include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 /* Known xxHash64 vector (seed 0) for the empty string and a literal.
  * The md5 vectors are the standard NIST/RFC1321 test strings.  These pin the
@@ -91,6 +93,63 @@ static void test_checksum_md5_seed_ignored() {
   EXPECT_TRUE(memcmp(a, b, alen) == 0);
 }
 
+static void test_checksum_md4_vectors() {
+  uint8_t out[CHECKSUM_MAX_DIGEST_LEN];
+  size_t len = 0;
+  /* RFC 1320 / RFC 1321 test vectors. */
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_MD4, 0, "", 0, out, sizeof(out), &len));
+  EXPECT_TRUE(len == (size_t)16);
+  const uint8_t expect_empty[16] = {0x31, 0xd6, 0xcf, 0xe0, 0xd1, 0x6a, 0xe9, 0x31,
+                                    0xb7, 0x3c, 0x59, 0xd7, 0xe0, 0xc0, 0x89, 0xc0};
+  EXPECT_TRUE(memcmp(out, expect_empty, 16) == 0);
+
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_MD4, 0, "abc", 3, out, sizeof(out), &len));
+  const uint8_t expect_abc[16] = {0xa4, 0x48, 0x01, 0x7a, 0xaf, 0x21, 0xd8, 0x52,
+                                  0x5f, 0xc1, 0x0a, 0xe8, 0x7a, 0xa6, 0x72, 0x9d};
+  EXPECT_TRUE(memcmp(out, expect_abc, 16) == 0);
+
+  /* A longer input exercises the block loop and the padding boundary. */
+  const char* msg =
+      "12345678901234567890123456789012345678901234567890123456789012345678901234567890";
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_MD4, 0, msg, strlen(msg), out, sizeof(out), &len));
+  const uint8_t expect_long[16] = {0xe3, 0x3b, 0x4d, 0xdc, 0x9c, 0x38, 0xf2, 0x19,
+                                   0x9c, 0x3e, 0x7b, 0x16, 0x4f, 0xcc, 0x05, 0x36};
+  EXPECT_TRUE(memcmp(out, expect_long, 16) == 0);
+}
+
+static void test_checksum_sha1_vectors() {
+  uint8_t out[CHECKSUM_MAX_DIGEST_LEN];
+  size_t len = 0;
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_SHA1, 0, "abc", 3, out, sizeof(out), &len));
+  EXPECT_TRUE(len == (size_t)20);
+  const uint8_t expect_abc[20] = {0xa9, 0x99, 0x3e, 0x36, 0x47, 0x06, 0x81, 0x6a, 0xba, 0x3e,
+                                  0x25, 0x71, 0x78, 0x50, 0xc2, 0x6c, 0x9c, 0xd0, 0xd8, 0x9d};
+  EXPECT_TRUE(memcmp(out, expect_abc, 20) == 0);
+
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_SHA1, 0, "", 0, out, sizeof(out), &len));
+  EXPECT_TRUE(len == (size_t)20);
+  const uint8_t expect_empty[20] = {0xda, 0x39, 0xa3, 0xee, 0x5e, 0x6b, 0x4b, 0x0d, 0x32, 0x55,
+                                    0xbf, 0xef, 0x95, 0x60, 0x18, 0x90, 0xaf, 0xd8, 0x07, 0x09};
+  EXPECT_TRUE(memcmp(out, expect_empty, 20) == 0);
+
+  /* sha1 has no seed: the digest is seed-independent (documented). */
+  uint8_t seeded[CHECKSUM_MAX_DIGEST_LEN];
+  size_t seeded_len = 0;
+  EXPECT_TRUE(
+      checksum_digest(CHECKSUM_ALGO_SHA1, 12345, "abc", 3, seeded, sizeof(seeded), &seeded_len));
+  EXPECT_TRUE(seeded_len == (size_t)20);
+  EXPECT_TRUE(memcmp(expect_abc, seeded, 20) == 0);
+}
+
+/* "none" is a successful no-digest: length 0, nothing written. */
+static void test_checksum_none_digest() {
+  uint8_t out[CHECKSUM_MAX_DIGEST_LEN];
+  size_t len = 99;
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_NONE, 0, "data", 4, out, sizeof(out), &len));
+  EXPECT_EQ_INT((int)len, 0);
+  EXPECT_EQ_INT((int)checksum_digest_len(CHECKSUM_ALGO_NONE), 0);
+}
+
 static void test_checksum_algo_name_mapping() {
   EXPECT_EQ_INT(checksum_algo_from_name("xxh64"), (int)CHECKSUM_ALGO_XXH64);
   EXPECT_EQ_INT(checksum_algo_from_name("XXH64"), (int)CHECKSUM_ALGO_XXH64);
@@ -98,18 +157,58 @@ static void test_checksum_algo_name_mapping() {
   EXPECT_EQ_INT(checksum_algo_from_name("XXHASH"), (int)CHECKSUM_ALGO_XXH64);
   EXPECT_EQ_INT(checksum_algo_from_name("md5"), (int)CHECKSUM_ALGO_MD5);
   EXPECT_EQ_INT(checksum_algo_from_name("MD5"), (int)CHECKSUM_ALGO_MD5);
+  EXPECT_EQ_INT(checksum_algo_from_name("xxh3"), (int)CHECKSUM_ALGO_XXH3);
+  EXPECT_EQ_INT(checksum_algo_from_name("XXH3"), (int)CHECKSUM_ALGO_XXH3);
+  EXPECT_EQ_INT(checksum_algo_from_name("xxh128"), (int)CHECKSUM_ALGO_XXH128);
+  EXPECT_EQ_INT(checksum_algo_from_name("XXH128"), (int)CHECKSUM_ALGO_XXH128);
+  EXPECT_EQ_INT(checksum_algo_from_name("md4"), (int)CHECKSUM_ALGO_MD4);
+  EXPECT_EQ_INT(checksum_algo_from_name("MD4"), (int)CHECKSUM_ALGO_MD4);
+  EXPECT_EQ_INT(checksum_algo_from_name("sha1"), (int)CHECKSUM_ALGO_SHA1);
+  EXPECT_EQ_INT(checksum_algo_from_name("SHA1"), (int)CHECKSUM_ALGO_SHA1);
+  EXPECT_EQ_INT(checksum_algo_from_name("none"), (int)CHECKSUM_ALGO_NONE);
+  /* Names rsync does not offer (or FastSync cannot compute) are rejected. */
   EXPECT_TRUE(checksum_algo_from_name("sha256") < 0);
   EXPECT_TRUE(checksum_algo_from_name("crc32") < 0);
-  EXPECT_TRUE(checksum_algo_from_name("none") < 0);
-  EXPECT_TRUE(checksum_algo_from_name("xxh3") < 0);
   EXPECT_TRUE(checksum_algo_from_name("") < 0);
   EXPECT_TRUE(checksum_algo_from_name(NULL) < 0);
 
   EXPECT_TRUE(checksum_algo_valid((int)CHECKSUM_ALGO_XXH64));
   EXPECT_TRUE(checksum_algo_valid((int)CHECKSUM_ALGO_MD5));
+  EXPECT_TRUE(checksum_algo_valid((int)CHECKSUM_ALGO_XXH3));
+  EXPECT_TRUE(checksum_algo_valid((int)CHECKSUM_ALGO_XXH128));
+  EXPECT_TRUE(checksum_algo_valid((int)CHECKSUM_ALGO_MD4));
+  EXPECT_TRUE(checksum_algo_valid((int)CHECKSUM_ALGO_SHA1));
+  EXPECT_TRUE(checksum_algo_valid((int)CHECKSUM_ALGO_NONE));
   EXPECT_FALSE(checksum_algo_valid(99));
   EXPECT_EQ_STR(checksum_algo_name(CHECKSUM_ALGO_XXH64), "xxh64");
   EXPECT_EQ_STR(checksum_algo_name(CHECKSUM_ALGO_MD5), "md5");
+  EXPECT_EQ_STR(checksum_algo_name(CHECKSUM_ALGO_XXH3), "xxh3");
+  EXPECT_EQ_STR(checksum_algo_name(CHECKSUM_ALGO_XXH128), "xxh128");
+  EXPECT_EQ_STR(checksum_algo_name(CHECKSUM_ALGO_MD4), "md4");
+  EXPECT_EQ_STR(checksum_algo_name(CHECKSUM_ALGO_SHA1), "sha1");
+  EXPECT_EQ_STR(checksum_algo_name(CHECKSUM_ALGO_NONE), "none");
+
+  /* rsync 3.4.1 auto-negotiates xxh128 first. */
+  EXPECT_EQ_INT((int)checksum_negotiate_default(), (int)CHECKSUM_ALGO_XXH128);
+}
+
+/* xxh3 is 8 bytes and seed-aware; xxh128 is 16 bytes and differs from both
+ * xxh64 and md5 for the same input. */
+static void test_checksum_xxh3_xxh128() {
+  EXPECT_EQ_INT((int)checksum_digest_len(CHECKSUM_ALGO_XXH3), 8);
+  EXPECT_EQ_INT((int)checksum_digest_len(CHECKSUM_ALGO_XXH128), 16);
+
+  uint8_t a[CHECKSUM_MAX_DIGEST_LEN], b[CHECKSUM_MAX_DIGEST_LEN];
+  size_t alen = 0, blen = 0;
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_XXH3, 0, "payload", 7, a, sizeof(a), &alen));
+  EXPECT_TRUE(alen == (size_t)8);
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_XXH3, 5, "payload", 7, b, sizeof(b), &blen));
+  EXPECT_TRUE(memcmp(a, b, alen) != 0);
+
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_XXH128, 0, "payload", 7, a, sizeof(a), &alen));
+  EXPECT_TRUE(alen == (size_t)16);
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_XXH128, 0, "payload", 7, b, sizeof(b), &blen));
+  EXPECT_TRUE(memcmp(a, b, blen) == 0);
 }
 
 static void test_checksum_truncated_buffer_rejected() {
@@ -133,15 +232,76 @@ static void test_checksum_null_empty_digest() {
   EXPECT_TRUE(memcmp(a, b, alen) == 0);
 }
 
+/* Every algorithm checksum_digest_file() claims to support must produce the
+ * SAME digest as the in-memory one-shot, including the newly added md4/sha1/
+ * none.  A 200000-byte payload forces several 64 KiB streaming reads. */
+static void test_checksum_digest_file_matches_oneshot(void) {
+  static const ChecksumAlgo algos[] = {
+      CHECKSUM_ALGO_XXH64, CHECKSUM_ALGO_XXH3, CHECKSUM_ALGO_XXH128, CHECKSUM_ALGO_MD5,
+      CHECKSUM_ALGO_MD4,   CHECKSUM_ALGO_SHA1, CHECKSUM_ALGO_NONE,
+  };
+  enum { SIZE = 200000 };
+  uint8_t* data = malloc(SIZE);
+  EXPECT_NOT_NULL(data);
+  for (int i = 0; i < SIZE; i++)
+    data[i] = (uint8_t)((i * 7 + 3) & 0xff);
+  char path[] = "/tmp/fastsync_ck_XXXXXX";
+  int fd = mkstemp(path);
+  EXPECT_TRUE(fd >= 0);
+  ssize_t written = write(fd, data, SIZE);
+  close(fd);
+  EXPECT_EQ_INT((int)written, SIZE);
+  for (size_t a = 0; a < sizeof(algos) / sizeof(algos[0]); a++) {
+    ChecksumAlgo algo = algos[a];
+    uint8_t one[CHECKSUM_MAX_DIGEST_LEN];
+    uint8_t file[CHECKSUM_MAX_DIGEST_LEN];
+    size_t one_len = 0, file_len = 0;
+    EXPECT_TRUE(checksum_digest(algo, 0, data, SIZE, one, sizeof(one), &one_len));
+    EXPECT_TRUE(checksum_digest_file(algo, 0, path, file, sizeof(file), &file_len));
+    EXPECT_EQ_INT((int)file_len, (int)one_len);
+    EXPECT_TRUE(memcmp(one, file, one_len) == 0);
+  }
+  unlink(path);
+  free(data);
+}
+
+/* RSYNC_CHECKSUM_LIST precedence, syntax and fallback. */
+static void test_checksum_choice_env_list() {
+  unsetenv("RSYNC_CHECKSUM_LIST");
+  EXPECT_EQ_INT(checksum_choice_resolve(), (int)CHECKSUM_ALGO_XXH128);
+  EXPECT_EQ_INT((int)checksum_negotiate_default(), (int)CHECKSUM_ALGO_XXH128);
+
+  setenv("RSYNC_CHECKSUM_LIST", "bogus md5 xxh3", 1);
+  EXPECT_EQ_INT(checksum_choice_resolve(), (int)CHECKSUM_ALGO_MD5);
+
+  setenv("RSYNC_CHECKSUM_LIST", "SHA1", 1);
+  EXPECT_EQ_INT(checksum_choice_resolve(), (int)CHECKSUM_ALGO_SHA1);
+
+  /* Whitespace-separated only: comma is not a separator in rsync's syntax. */
+  setenv("RSYNC_CHECKSUM_LIST", "md5,xxh3", 1);
+  EXPECT_EQ_INT(checksum_choice_resolve(), -1);
+
+  setenv("RSYNC_CHECKSUM_LIST", "  ", 1);
+  EXPECT_EQ_INT(checksum_choice_resolve(), (int)CHECKSUM_ALGO_XXH128);
+
+  unsetenv("RSYNC_CHECKSUM_LIST");
+}
+
 void test_checksum(void) {
   test_checksum_xxh64_seed0();
   test_checksum_xxh64_empty();
   test_checksum_xxh64_seed_changes_digest();
   test_checksum_xxh64_seed_deterministic();
   test_checksum_md5_vectors();
+  test_checksum_md4_vectors();
+  test_checksum_sha1_vectors();
+  test_checksum_none_digest();
   test_checksum_algo_lengths_distinct();
   test_checksum_md5_seed_ignored();
   test_checksum_algo_name_mapping();
+  test_checksum_xxh3_xxh128();
   test_checksum_truncated_buffer_rejected();
   test_checksum_null_empty_digest();
-}
+  test_checksum_digest_file_matches_oneshot();
+  test_checksum_choice_env_list();
+}