Merge release/v2.19.0 into main: FastSync v2.19.0

- Protocol version 2.19.0 (SCRAM-SHA-256 daemon auth replacing the replayable digest)
- Salted PBKDF2 verifier store + --hash-credentials; legacy store hard-rejected
- Persistent anti-enumeration dummy key (<store>.dummykey)
- Verified TLS / opted-in loopback transport required for auth modules
- Secret wiping; carried-over hardening from the security phases
- Add CHANGELOG.md and set the CMake project version

.gitea/workflows/ci.yaml

@@ -4,11 +4,12 @@ on:
   push:
     branches: [main, dev]
   pull_request:
+  workflow_dispatch:
 
 jobs:
   lint:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -19,9 +20,13 @@ jobs:
       - name: cppcheck
         run: cppcheck --enable=warning,style,performance,portability --suppress=missingIncludeSystem --error-exitcode=1 --inline-suppr src/ tests/
 
+  # Fast PR gate: build + unit tests + a representative subset of integration
+  # tests (marked `ci`), parallelized with pytest-xdist.  Only the full coverage
+  # jobs below (sanitizers/fuzz/coverage/valgrind and the FULL integration
+  # 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:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     needs: lint
     steps:
       - name: Checkout
@@ -36,13 +41,19 @@ jobs:
       - name: Unit Tests
         run: ctest --test-dir build --output-on-failure -j$(nproc)
 
-      - name: Integration Tests
-        run: python3 -m pytest tests/integration/ -v --tb=short
+      - name: Integration Tests (PR smoke subset)
+        if: github.event_name == 'pull_request'
+        run: python3 -m pytest tests/integration/ -n 4 --dist=load -m ci --durations=25 --tb=short -q
+
+      - name: Integration Tests (full suite)
+        if: github.event_name == 'push'
+        run: python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv" --durations=25 --tb=short -q
 
   sanitizers:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     needs: lint
+    if: github.event_name == 'push'
     strategy:
       matrix:
         sanitizer: [address, undefined]
@@ -61,8 +72,9 @@ jobs:
 
   fuzz-build:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     needs: lint
+    if: github.event_name == 'push'
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -82,8 +94,9 @@ jobs:
 
   coverage:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     needs: lint
+    if: github.event_name == 'push'
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -105,8 +118,9 @@ jobs:
 
   valgrind:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     needs: lint
+    if: github.event_name == 'push'
     steps:
       - name: Checkout
         uses: actions/checkout@v4

AGENTS.md

@@ -4,28 +4,28 @@ 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:v7`. It contains the full toolchain: gcc/g++, CMake, libzstd-dev, libssl-dev, make, git, cppcheck, clang-format, python3 + pytest, 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: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.
 
 **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:v7
-docker tag gitea.tap-tap.win/taptap/fastsync-ci:v7 fastsync-ci:local
+docker pull gitea.tap-tap.win/taptap/fastsync-ci:v10
+docker tag gitea.tap-tap.win/taptap/fastsync-ci:v10 fastsync-ci:local
 
 # Or build the image from the repo-root Dockerfile
-# (Note: the prebuilt :v7 image reflects the previous Dockerfile state;
+# (Note: the prebuilt :v10 image reflects the previous Dockerfile state;
 #  rebuild from source to pick up any newly added packages like lcov/valgrind.)
 docker build -t fastsync-ci:local .
 
 # Build, run unit tests, and run integration tests inside the container
 docker run --rm -v "$PWD:/workspace" -w /workspace fastsync-ci:local \
-  sh -c 'cmake -B build -S . && cmake --build build -j$(nproc) && ./build/tests && python3 -m pytest tests/'
+  sh -c 'cmake -B build -S . && cmake --build build -j$(nproc) && ./build/tests && python3 -m pytest tests/integration/ -n 4 --dist=load'
 
 # Avoid root-owned build/ artifacts by matching your host UID/GID
 docker run --rm --user "$(id -u):$(id -g)" -v "$PWD:/workspace" \
   -w /workspace fastsync-ci:local \
-  sh -c 'cmake -B build -S . && cmake --build build -j$(nproc) && ./build/tests && python3 -m pytest tests/'
+  sh -c 'cmake -B build -S . && cmake --build build -j$(nproc) && ./build/tests && python3 -m pytest tests/integration/ -n 4 --dist=load'
 ```
 
 > **Note:** The first `cmake configure` (`cmake -B build -S .`) fetches xxHash from GitHub via `FetchContent` — network access is required. Subsequent reconfigures reuse the cached source.
@@ -41,7 +41,7 @@ cmake -B build -S . -DSANITIZER=address           # AddressSanitizer (ASan)
 cmake -B build -S . -DSANITIZER=thread            # ThreadSanitizer (TSan)
 ```
 
-The CI workflow (`.gitea/workflows/ci.yaml`) runs lint (clang-format, cppcheck), build + test (unit + integration), and sanitizer (currently only `address`) jobs sequentially.
+The CI workflow (`.gitea/workflows/ci.yaml`) runs lint (clang-format, cppcheck), then a **fast PR gate** — build + unit + a representative subset of integration tests marked `@pytest.mark.ci`, parallelized with pytest-xdist (`-n 4 --dist=load`). The full coverage jobs (full integration suite as `-m "not setpriv"`, sanitizer, fuzz, coverage, valgrind) run **only on push to `dev`/`main`**; pull requests skip them to keep PR CI under ~3 minutes. The two `setpriv` privilege tests are excluded from CI via a marker because their result depends on the runner/container uid and host mount permissions.
 
 ## Build
 
@@ -53,7 +53,8 @@ cmake -B build -S . && cmake --build build -j$(nproc)
 
 ```bash
 ./build/tests                # unit tests
-python3 -m pytest tests/     # integration 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
 ```
 
 ## CI Workflow — Waiting for Results
@@ -65,14 +66,14 @@ 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 "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v9 \
+docker run --rm -v "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v10 \
   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 "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v9 \
+docker run --rm -v "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v10 \
   sh -c 'cppcheck --enable=warning,style,performance,portability --suppress=missingIncludeSystem --error-exitcode=1 --inline-suppr src/ tests/'
 ```
 

CHANGELOG.md

@@ -0,0 +1,65 @@
+# Changelog
+
+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.
+
+## [2.19.0] - 2026-09-12
+
+### Security
+
+- **Daemon authentication rewritten as SCRAM-SHA-256 challenge/response**
+  (`STATUS_AUTH_CHALLENGE` → `STATUS_AUTH_RESPONSE` → `STATUS_AUTH_OK`/`STATUS_AUTH_FAILED`),
+  replacing the old replayable static `SHA-256(password)` bearer credential.
+  Each proof is bound to a fresh per-connection server nonce plus a client
+  nonce, so a captured response can never be reused.
+- **Salted verifier store.** `--password-file`/`--early-input` now hold
+  `user:$fastsync$1$pbkdf2-sha256$<iters>$<salt>$<stored_key>$<server_key>`
+  (PBKDF2-HMAC-SHA256, default 600000 iterations, range 100000–10000000). The
+  legacy `user:SHA256HEX` form is hard-rejected; there is no auto-upgrade.
+  Generate stores offline with `fastsync-server --hash-credentials FILE
+  [--iterations N]`.
+- **Username-enumeration hardening.** Unknown/off-list users are answered with a
+  dummy verifier whose salt is a deterministic per-username value
+  (`HMAC-SHA256(dummy_key, username)`), using the store-wide uniform iteration
+  count and a constant-time full-length membership scan. The dummy key is
+  persisted in an owner-only `<store>.dummykey` sidecar (atomic publish, exact
+  mode 0600) so challenges are stable across restarts.
+- **Verified transport for auth-required modules.** A module with `auth users`
+  accepts credentials only over verified TLS whose client certificate matches
+  `--client-cn`, or — when `--allow-unauthenticated` is explicitly set —
+  plaintext from a loopback peer. Remote plaintext is refused before any
+  challenge. Clients must use `--tls` to send `--password-file` credentials to a
+  non-loopback daemon; `--client-cn` is mandatory with `--tls`.
+- **Secret hygiene.** The plaintext password, derived keys, nonces/proofs and
+  the dummy key are wiped from memory on every path and never logged.
+- Carried-over hardening: `-K` TOCTOU-safe directory walk
+  (`openat(O_NOFOLLOW)` per component), always shell-quoted SSH remote path,
+  TLS compression/renegotiation disabled, race-free (open-then-`fstat`)
+  `--password-file`/`--early-input` checks, log-injection escaping, and lazy
+  protocol debug escaping.
+
+### Added
+
+- `fastsync-server --hash-credentials FILE [--iterations N]` offline tool.
+- `<store>.dummykey` sidecar (auto-created, owner-only, 0600).
+- Integration tests for auth replay rejection, malformed frames, legacy-store
+  refusal, and the loopback/TLS transport policy; fuzz targets for config
+  receive and daemon-auth parsing.
+
+### Changed
+
+- **Protocol version 2.18.0 → 2.19.0 (breaking).** The config-frame auth block
+  is now `[present][username]` (digest removed) and the auth challenge/response
+  frames are interleaved between the config frame and its `STATUS_OK`. A 2.19.0
+  client and a 2.18.0 server (or vice versa) fail cleanly at the handshake.
+- Daemon modules declaring `auth users` require a configured credential store at
+  startup (fail closed); operators regenerate stores from plaintext with
+  `--hash-credentials`.
+
+### Notes
+
+- First tagged release. FastSync implements rsync-compatible file
+  synchronization over TCP and SSH with TLS (OpenSSL), streaming zstd
+  compression, multithreaded transfers, and incremental sync. See
+  [RSYNC_COMPAT.md](RSYNC_COMPAT.md) for the flag-parity matrix.

CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.22)
 
-project(FastFileTransfer)
+project(FastFileTransfer VERSION 2.19.0)
 
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 set(CMAKE_C_STANDARD 11)
@@ -82,7 +82,7 @@ set(TEST_INCLUDES tests src/shared src/server src/client)
 
 # Monolithic test binary (backward compatible)
 file(GLOB TEST_SRCS "tests/test_*.c" "tests/runner.c")
-add_executable(tests ${TEST_SRCS} ${SHARED_SRCS} ${FILE_STORE_SRCS} ${SERVER_RECEIVER_SRCS} src/client/scanner.c src/client/client_cli.c src/client/client_validation.c src/client/usage.c)
+add_executable(tests ${TEST_SRCS} ${SHARED_SRCS} ${FILE_STORE_SRCS} ${SERVER_RECEIVER_SRCS} src/client/scanner.c src/client/change_list.c src/client/client_cli.c src/client/client_validation.c src/client/usage.c src/server/server_cli.c)
 target_include_directories(tests PRIVATE ${TEST_INCLUDES})
 target_compile_definitions(tests PRIVATE FASTSYNC_TEST_BUILD)
 target_link_libraries(tests PRIVATE ${TEST_LIBS})

Dockerfile

@@ -3,7 +3,7 @@ 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 && \
-    pip3 install --break-system-packages pytest && \
+    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/*

README.md

@@ -6,6 +6,10 @@ source/destination model and rsync-style options while adding optional
 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
+[CHANGELOG.md](CHANGELOG.md) for the history.
+
 The compatibility target is straightforward:
 
 - Existing rsync commands should keep the same meaning.
@@ -63,13 +67,26 @@ replacement for every rsync feature or protocol mode.
 - 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, hard-link, device, and special-file handling is
-  incomplete or unavailable.
-- Sparse-file handling does not yet preserve all holes correctly.
-- `--partial`, `--partial-dir`, `--append`, and `--append-verify` are not yet
-  full rsync-style resumable transfers.
-- Several rsync short options currently have FastSync-specific meanings. Do
-  not assume every short option is interchangeable yet.
+- Owner/group, ACL, xattr, and hard-link handling is incomplete or
+  unavailable.
+- 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).
+- 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).
+- `--partial`, `--partial-dir`, `-P`, `--append`, and `--append-verify` keep
+  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.
+- 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`.
 
 The detailed flag matrix is maintained in
 [`RSYNC_COMPAT.md`](RSYNC_COMPAT.md). It distinguishes implemented,
@@ -84,24 +101,34 @@ partial, alternate, and planned behavior.
 | Argument | Description |
 |----------|-------------|
 | Positional | `<source> <dest>` — automatic SSH detection if dest contains `:` |
-| `-c [level]` | Compression with optional level (1–22, default 5) |
-| `-z [level]` | Alias for `-c` |
-| `-a, --archive` | Archive mode: enables `-c -m -M` (no `-s`) |
-| `-m` | Multithreading mode |
-| `-s` | Chunk serialization (batch all files per chunk) |
-| `-f, --sendfile` | Sendfile zero-copy. Incompatible with `-c` / `-s`. TCP only. |
-| `-M, --preserve` | Preserve supported file metadata (mode and mtime; ownership and atime are unsupported) |
+| `-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) |
+| `-j, --threads` | Multithreading mode |
+| `-m` | rsync `--prune-empty-dirs` (short form now rsync-parity) |
+| `--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 <port>` | SSH port (default: 22) |
+| `-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 |
-| `--delete` | Delete files on receiver not present in source |
+| `-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) |
+| `--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 |
-| `--incremental` | Skip files unchanged since last transfer (size + mtime). Auto-enables `--preserve`. Incompatible with `-s`. |
+| `--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) |
@@ -110,6 +137,7 @@ partial, alternate, and planned behavior.
 | `--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 |
 | `--max-depth <n>` | Maximum directory depth to recurse (0 = unlimited, default: 0) |
 | `--log-file <path>` | Write log messages to file instead of stderr |
 | `--source-dir <path>` | Source directory (overrides `FASTSYNC_SOURCE_DIR`) |
@@ -121,7 +149,7 @@ partial, alternate, and planned behavior.
 | `--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>` | Required TLS client certificate common name |
+| `--client-cn <name>` | TLS client certificate common name; mandatory with `--tls` (a TLS connection always verifies the client CN) |
 
 ### Server
 
@@ -135,7 +163,7 @@ partial, alternate, and planned behavior.
 | `--ca <path>` | TLS CA certificate file for verification (PEM) |
 | `--destination-root <path>` | Authorized destination root (default: `.`) |
 | `--allow-delete` | Permit manifest deletion |
-| `--allow-unauthenticated` | Permit plaintext TCP clients |
+| `--allow-unauthenticated` | Permit plaintext TCP clients. For an `auth users` module this opts in **loopback plaintext only**; remote auth still requires verified TLS, so the flag never permits remote plaintext auth. |
 | `-v, --verbose` | Enable debug logging |
 | `--help` | Show help |
 
@@ -337,14 +365,18 @@ features without changing the meaning of ordinary compatibility options.
 
 | Option | Purpose |
 |---|---|
-| `-m` | Enable the multithreaded scanner/loader/sender pipeline. |
-| `-c [level]`, `-z [level]` | Enable streaming zstd compression, levels 1-22. |
+| `-j`, `--threads` | Enable the multithreaded scanner/loader/sender pipeline. |
+| `-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`. |
+| `--zl <n>` | Alias for `--compress-level`. |
+| `--skip-compress <list>` | Skip compression for comma-separated suffixes; 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. |
-| `-s` | Enable FastSync chunk serialization. |
-| `-f`, `--sendfile` | Use TCP `sendfile()` zero-copy transfer. Incompatible with compression and chunk serialization. |
+| `--chunk-serialization` | Enable FastSync chunk serialization (long form only; `-s` is rsync's `--secluded-args`). |
+| `--sendfile` | Use TCP `sendfile()` zero-copy transfer. Incompatible with compression and chunk serialization. Long form only. |
 | `--delta` | Use FastSync-native block delta transfer. Requires `--incremental`. |
-| `--delta-block <bytes>` | Set the FastSync delta block size. |
+| `--delta-block <bytes>` | Set the FastSync delta block size (`--block-size` is an alias). |
 | `--delta-max <bytes>` | Limit files eligible for FastSync delta transfer. |
 | `--server-host <host>` | Select the TCP server host. |
 | `--server-port <port>` | Select the TCP server port. |
@@ -355,10 +387,18 @@ features without changing the meaning of ordinary compatibility options.
 | `--timeout <seconds>` | Set I/O timeout. |
 | `--contimeout <seconds>` | Set connection timeout. |
 
-Current short-option conflicts are tracked as compatibility work. In
-particular, FastSync currently uses `-p` for SSH port, `-s` for chunk
-serialization, and `-S` for sparse handling. These meanings must be reconciled
-before FastSync can claim full rsync CLI compatibility.
+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`
+is `--remote-option`, `-f` is `--filter`, `-s` is `--secluded-args`, `-p` is
+`--perms`, and `-T` is `--temp-dir`. FastSync's own flags were renamed to
+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`).
+
+`--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
+remote SSH argv is already built injection-safe.
 
 ## Client Options
 
@@ -366,9 +406,13 @@ before FastSync can claim full rsync CLI compatibility.
 
 | Option | Description |
 |---|---|
-| `-a`, `--archive` | Enable current archive preset. Full rsync archive semantics are planned. |
+| `-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. |
+| `--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. |
+| `--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-after` | Explicit delete-after timing: delete only after the transfer succeeded (implies `--delete`). |
 | `--exclude <pattern>` | Exclude matching paths. Repeatable. |
 | `--include <pattern>` | Include matching paths. Repeatable. |
 | `--exclude-from <file>` | Read exclude patterns from a file. |
@@ -379,25 +423,26 @@ before FastSync can claim full rsync CLI compatibility.
 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.With `--partial - dir`,
-    completed files are written there;
-resumable transfers are not implemented.| | `--partial - dir<dir>` |
-    Set a relative partial - transfer directory below the server destination root;
-use with `--partial`. |
+| `--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`. |
 | `--inplace` | Write directly to the destination instead of using a temporary file. |
 
 ### Metadata and links
 
 | Option | Description |
 |---|---|
-| `-M`, `--preserve` | Preserve supported file metadata, currently mode and modification time. |
+| `--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. |
 | `--copy-unsafe-links` | Copy unsafe symlink referents. |
-| `-S`, `--sparse` | Request sparse-file handling; full hole preservation is planned. |
+| `-S`, `--sparse` | Sparse-file handling: receiver preserves holes (zero runs are written as holes; no wire change). |
 
 ### Output and logging
 
@@ -414,7 +459,7 @@ link-target transfer remains incomplete. |
 
 | Option | Description |
 |---|---|
-| `-p <port>` | SSH port in the current CLI. This conflicts with rsync's `-p` permissions option and is planned for correction. |
+| `--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. |
 | `--source-dir <path>` | Set the source directory explicitly. |
 | `--dest-dir <path>` | Set the destination directory explicitly. |
@@ -466,11 +511,57 @@ defaults to the current directory. |
 
 ## Protocol and Security
 
-FastSync protocol version `2.3.0` is shared by the client and server. The
+FastSync protocol version `2.19.0` is shared by the client and server. The
 current protocol is sender-driven and includes configuration negotiation,
-incremental checks, checksums, manifests, keep-alives, abort handling, and
-FastSync-native delta messages. Client and server versions must currently
-match exactly.
+including the maximum allocation limit, incremental checks, checksums,
+manifests, keep-alives, abort handling, per-file remove-source results, and
+FastSync-native delta messages.
+Client and server versions must currently match exactly.
+
+Daemon modules that declare `auth users` authenticate with a SCRAM-SHA-256-style
+challenge/response against a salted PBKDF2 verifier store: no password and no
+replayable bearer credential crosses the wire or is stored on the daemon. All
+store entries share one iteration count, and an unknown user is answered with a
+deterministic per-username dummy challenge, so probing the daemon cannot
+enumerate users. Store lines are generated with
+`fastsync-server --hash-credentials <plaintext-file>` (see `RSYNC_COMPAT.md`);
+redirect that output to an owner-only (mode 0600) file, and note that legacy
+`user:SHA256HEX` stores are rejected. FastSync also maintains an owner-only
+(mode 0600) `<store>.dummykey` sidecar next to the store: it holds the store-wide
+dummy key, is auto-created on first load, and must be preserved across daemon
+restarts so the dummy challenge for an unknown user stays stable (the key is
+never regenerated while the sidecar exists). The sidecar is secret material and
+must be protected like the credential store: keep it owner-only (mode 0600) and
+include it with the store in backups and credential rotation. If the sidecar
+cannot be created (a process-substitution/FIFO store path such as `/dev/fd/N`, a
+read-only filesystem, a missing directory, or a create, write, fsync, link, or
+fchmod failure), the daemon logs a warning and uses a transient key, so the
+cross-restart guarantee does not hold for those deployments. One residual is
+accepted: the store
+iteration count is observable pre-auth by design, since the miss path must match
+a hit.
+
+An `auth users` module accepts credentials only when one of two conditions
+holds: (a) the connection is an encrypted, verified TLS connection whose client
+certificate matches the server's `--client-cn`, or (b) the connection is
+plaintext from a loopback peer **and** the operator explicitly passed
+`--allow-unauthenticated`. A remote plaintext peer is refused before any
+challenge is sent, and `--allow-unauthenticated` never permits remote plaintext
+auth: remote peers still require verified TLS regardless of the flag. Clients
+sending daemon credentials with `--password-file` to a non-loopback daemon must
+therefore use `--tls`; the client rejects a non-local plaintext credential
+destination before any network I/O. Daemon modules are a `--daemon`-only
+feature: the SSH `--stdio` path never loads a daemon config and is not an auth
+transport for them.
+
+Because the loopback allowance trusts whichever peer the kernel reports as
+`127.0.0.1`, it assumes nothing relays remote connections to the daemon. A local
+TCP forwarder or a TLS-terminating proxy in front of an auth-module listener
+makes remote clients appear as loopback and bypasses the mutual-TLS identity
+check, so do not front an auth-module listener with such a relay. `--tls` always
+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

RSYNC_COMPAT.md

@@ -6,11 +6,13 @@ This document maps rsync's full feature set to FastSync's current implementation
 
 | Status | Count | Description |
 |--------|-------|-------------|
-| ✅ Implemented | 35 | Feature works end-to-end |
-| 🔀 Alt Arg | 3 | Functionality exists but under different flag/semantics |
-| ⚠️ Partial | 3 | Flag parsed/stored but behavior incomplete |
-| ❌ Not Implemented | 97 | Flag not recognized or no behavior |
-| **Total** | **138** | |
+| ✅ Implemented | 143 | Feature works end-to-end |
+| 🔀 Alt Arg | 0 | Functionality exists but under different flag/semantics |
+| ⛔ Impossible/Divergence | 4 | Flag is a documented divergence or cannot be implemented on any portable filesystem call |
+| ⚠️ Partial | 0 | Flag parsed/stored but behavior incomplete |
+| 🔄 Compatibility No-op | 0 | Flag is accepted for CLI compatibility but has no effect |
+| ❌ Not Implemented | 0 | Flag not recognized or no behavior |
+| **Total** | **147** | |
 
 ---
 
@@ -18,33 +20,33 @@ This document maps rsync's full feature set to FastSync's current implementation
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `-a`, `--archive` | Archive mode is -rlptgoD | 🔀 Alt Arg | Maps to -c -m -M (compression + multithread + metadata) |
+| `-a`, `--archive` | Archive mode is -rlptgoD | ✅ Implemented | Phase 7 Wave A: real rsync archive. `-a`/`--archive` now implies `--links` + metadata (perms/times/group/owner as FastSync's broad bundle) + `--devices` + `--specials`. FastSync is always recursive, so no `-r` is needed. It no longer implies compression or multithreading (those moved to `-z`/`-j`). The short-option namespace is now rsync-parity (see the Phase 7 note) |
 | `-v`, `--verbose` | Increase verbosity | ✅ Implemented | Sets `log_level=DEBUG` |
-| `-q`, `--quiet` | Suppress non-error messages | ❌ Not Implemented | Removed because it had no effect |
+| `-q`, `--quiet` | Suppress non-error messages | ✅ Implemented | Suppresses client output while preserving errors |
 | `--help` | Show help | ✅ Implemented | Prints usage and exits; `-h` is not accepted |
 | `-V`, `--version` | Print version | ✅ Implemented | |
-| `--info=FLAGS` | Fine-grained info verbosity | ❌ Not Implemented | Removed because it had no effect |
-| `--debug=FLAGS` | Fine-grained debug verbosity | ❌ Not Implemented | Removed because it had no effect |
-| `--stderr=MODE` | Change stderr output mode | ❌ Not Implemented | |
-| `--no-motd` | Suppress daemon MOTD | ❌ Not Implemented | |
+| `--info=FLAGS` | Fine-grained info verbosity | ✅ Implemented | Supports `copy`, `misc`, `skip`, `stats`, `all`, and `none`; explicit flags override `--verbose`, and `none` suppresses info output; unsupported names are rejected |
+| `--debug=FLAGS` | Fine-grained debug verbosity | ✅ Implemented | `io`, `proto`, `pack`, and `util` are supported; `--debug=help` lists flags; other rsync categories are rejected |
+| `--stderr=MODE` | Change stderr output mode | ⛔ Impossible/Divergence | `errors` (default) and `all` are supported; `client` is rejected with a clear error (`--stderr=client is not supported`) because FastSync has no rsync client-message channel — the rejection itself is the documented behavior (Phase 7 Wave B decision). The modes that exist work; the missing rsync channel cannot be emulated without a wire change |
+| `--no-motd` | Suppress daemon MOTD | ✅ Implemented | Client-only display switch (Wave C): the daemon still sends the configured `motd file` on a `host::module/path` connection; the client reads and discards the frame without showing it. Without the flag the MOTD is printed to stdout after the config/auth handshake and escaped so control bytes cannot inject terminal sequences |
 | `--exclude=PATTERN` | Exclude files matching pattern | ✅ Implemented | Glob matching in scanner |
 | `--include=PATTERN` | Include files matching pattern | ✅ Implemented | Glob matching in scanner |
-| `-C`, `--cvs-exclude` | Auto-ignore CVS files | ❌ Not Implemented | Removed because it had no effect |
+| `-C`, `--cvs-exclude` | Auto-ignore CVS files | ✅ Implemented | Applies the well-known rsync default exclude set as exclude rules during scanning (RCS SCCS CVS CVS.adm RCSLOG cvslog.* tags TAGS .make.state .nse_depinfo *~ #* .#* ,* _$* *$ *.old *.bak *.BAK *.orig *.rej .del-* *.a *.olb *.o *.obj *.so *.exe *.Z *.elc *.ln core .svn/ .git/ .hg/ .bzr/); `.git/`-style repo dirs are pruned without descending |
 
 ## 2. Modifying Output
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
 | `--stats` | Give transfer stats | ✅ Implemented | Prints file/byte counts |
-| `-h`, `--human-readable` | Human-readable numbers | ❌ Not Implemented | Removed because it had no effect |
-| `-i`, `--itemize-changes` | Per-file change summary | ❌ Not Implemented | Removed because it had no effect |
+| `-h`, `--human-readable` | Human-readable numbers | ✅ Implemented | Formats transfer byte sizes using binary units |
+| `-i`, `--itemize-changes` | Per-file change summary | ✅ Implemented | Prints rsync-style `>f+++++++++` lines to stdout only for files actually sent (also under `-j`/`--threads`); unchanged files print nothing, matching single-`-i` behavior |
 | `--progress` | Show progress | ✅ Implemented | Progress callback in sender |
-| `-P` | Same as --partial --progress | ❌ Not Implemented | |
-| `--out-format=FORMAT` | Custom output format | ❌ Not Implemented | Removed because it had no effect |
+| `-P` | Same as --partial --progress | ✅ Implemented | Phase 7 Wave B: `-P` parses to `--partial` + `--progress`. On a failed/interrupted write the receiver now retains the already-written temp file at the destination path (best-effort rename instead of unlink when configured), so a later `--append`/`--append-verify` run can resume it; `--partial-dir` still stages completed files under the confined partial dir and installs them atomically. The retention never runs when `--partial` is off, when no data was actually written, or under `--ignore-existing`/`--existing` (the destination is not ours to overwrite), and it only ever renames the already-written temp (never a corrupt blend; a failed rename falls back to the normal unlink). See the `-S`/`--sparse` interplay note (a retained sparse temp has full logical size) |
+| `--out-format=FORMAT` | Custom output format | ✅ Implemented | Per-transfer template on stdout; tokens `%f` `%n` `%l` `%b` `%M` `%%` (`%b` is the source length, always `== %l`; post-compression/delta wire bytes are not counted); unknown escapes preserved |
 | `--log-file=FILE` | Log to file | ✅ Implemented | `log_file` config field |
-| `--log-file-format=FMT` | Log format | ❌ Not Implemented | |
-| `--8-bit-output` | Leave high-bit chars unescaped | ❌ Not Implemented | |
-| `--list-only` | List files instead of copying | ❌ Not Implemented | Removed because it had no effect |
+| `--log-file-format=FMT` | Log format | ✅ Implemented | Requires `--log-file`; writes one template line per transferred file using the same token set as `--out-format` (including `%b` `==` source length) |
+| `--8-bit-output`, `-8` | Leave high-bit chars unescaped | ✅ Implemented | Applies to displayed paths and protocol debug output |
+| `--list-only` | List files instead of copying | ✅ Implemented | `ls -l`-style listing of files that would be transferred; scans the source only, contacts no server, writes nothing; also works with `-n` |
 
 ## 3. File Selection
 
@@ -52,38 +54,40 @@ This document maps rsync's full feature set to FastSync's current implementation
 |------|-------------------|-----------------|-------|
 | `--exclude-from=FILE` | Read exclude patterns from file | ✅ Implemented | Reads patterns from file |
 | `--include-from=FILE` | Read include patterns from file | ✅ Implemented | Reads patterns from file |
-| `--filter=RULE` | Add file-filtering rule | ❌ Not Implemented | Removed because it had no effect |
-| `--files-from=FILE` | Read source file list from file | ❌ Not Implemented | Removed because it had no effect |
-| `-0`, `--from0` | Delimit *-from files with NULs | ❌ Not Implemented | |
+| `--filter=RULE` | Add file-filtering rule | ✅ Implemented | Long option only: rsync's short `-f` conflicts with FastSync sendfile (see FastSync-specific list), so `-f` is not reassigned. Supported subset: `+`/`-` include/exclude, implicit-exclude patterns, `include`/`exclude` word forms, a leading `/` anchor (to the transfer root, or to a `.rsync-filter` file's directory), and a trailing `/` for dir-only rules; first match wins with a default of include inside the filter layer. Filters are an independent layer from `--exclude`/`--include` (an entry must pass both). Rejected with a clear error (no silent no-ops): `merge`/`dir-merge`/`hide`/`show`/`protect`/`risk`/`clear` words, rules that begin with `:`/`.`/`!` (merge/dir-merge/list-clear shorthands), and include/exclude modifiers other than `/` (`! C s r p x`) |
+| `--files-from=FILE` | Read source file list from file | ✅ Implemented | Entries are paths relative to the source root (leading `./` stripped, `..`/absolute entries rejected at parse time, blank lines ignored; NUL-delimited with `-0`). A listed regular file is transferred; a listed directory transfers its whole subtree (FastSync recursion is always on, unlike rsync's non-recursive default). Non-listed paths and their subtrees are pruned by the scanner. A listed entry that does not exist under the source (and an empty list) is a hard error reported before any transfer, unless `--ignore-missing-args` / `--delete-missing-args` is given (see the Safety & Security rows): those flags downgrade the listed-but-missing case to a skip and, for `--delete-missing-args`, a destination deletion; an empty list stays a hard error in every mode. Listing `.` (whole tree) and empty listed directories are fine. Scalability note: `file_list_affects` is O(list size) per scanned entry, so a very large `--files-from` list against a huge tree is quadratic; lists are typically small enough that this is acceptable, but it is the documented bound. The delete manifest still derives from what was actually sent, so `--delete` stays consistent with the subset |
+| `-0`, `--from0` | Delimit *-from files with NULs | ✅ Implemented | `--files-from` entries become NUL-delimited; the flag may appear before or after `--files-from` on the command line. NUL mode preserves entry bytes exactly (trailing CR/LF are part of the name; only newline mode trims them) |
 | `--max-size=SIZE` | Skip files larger than SIZE | ✅ Implemented | `max_size` in scanner |
 | `--min-size=SIZE` | Skip files smaller than SIZE | ✅ Implemented | `min_size` in scanner |
-| `-I`, `--ignore-times` | Don't skip files matching size+time | ❌ Not Implemented | |
-| `--size-only` | Skip based on size only | ❌ Not Implemented | |
-| `-@`, `--modify-window=NUM` | Mod-time comparison accuracy | ❌ Not Implemented | |
+| `-I`, `--ignore-times` | Don't skip files matching size+time | ✅ Implemented | `ignore_times` config field (crosses the wire). Disables the size+mtime quick-check in the `--incremental` per-file handshake and the basis-dir quick-match, forcing the file to be transferred rather than skipped as unchanged. Receiver-side policy: `match_by_metadata` (file_receive.c) is bypassed, so the receiver never replies `STATUS_OK` for a matching size+mtime. Requires `--incremental` to have the handshake to act on (rsync does its quick check by default; FastSync's `-I`/`--size-only`/`--modify-window` only take effect under `--incremental`, exactly like they take effect through the basis check) |
+| `--size-only` | Skip based on size only | ✅ Implemented | With `--incremental`, ignores mtime |
+| `-@`, `--modify-window=NUM` | Mod-time comparison accuracy | ✅ Implemented | Whole-second tolerance with nanosecond-aware comparisons |
 | `--existing` | Skip creating new files on receiver | ✅ Implemented | Existing destination files continue through normal update handling |
-| `--ignore-existing` | Skip updating existing files | ❌ Not Implemented | |
-| `--remove-source-files` | Sender removes synced files | ❌ Not Implemented | |
+| `--ignore-existing` | Skip updating existing files | ✅ Implemented | `ignore_existing` config field (crosses the wire; receiver-side policy). For a destination entry that already exists, the receiver skips the write: in the regular-file path, existing/delay-updates-staged, hardlink-sibling, and special/device handlers all return `FILE_SAVE_SKIPPED` without overwriting (passed as `no_replace` to the write engine), and `--backup` is disabled for skipped files. Note: it is applied at write time, so an existing dest whose size+mtime differ still has its data (or delta) transmitted before the write is discarded — functionally correct, bandwidth-suboptimal vs rsync, which short-circuits earlier. Like rsync, it does not apply to directories/symlinks (those return before the block). Combines with `-j`/`--threads` and `--delay-updates`. See Phase-4/— notes below |
+| `--remove-source-files` | Sender removes regular files after confirmed transfer | ✅ Implemented | |
+| `-x`, `--one-file-system` | Do not cross filesystem boundaries | ✅ Implemented | Sender scanner captures the root device and skips descending into mount-point crossings (`st_dev` differs); cross-filesystem mount-point subdirectories are dropped entirely, matching rsync |
+| `-F` | Add the default `.rsync-filter` rules | ✅ Implemented | Reads one filter rule per line from each directory's `.rsync-filter` file during traversal and applies it to that directory's subtree; the current directory's rules are evaluated before its ancestors', so deeper files override shallower ones and per-directory files override the command-line `--filter`/`-C` base by default (matching rsync's first-match-wins precedence); `.rsync-filter` files are never transferred. The rsync `-FF` behavior (also `.cvsignore`) is out of scope; unsupported rule types inside the file abort with a clear error |
 
 ## 4. Directory Options
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
 | `-r`, `--recursive` | Recurse into directories | ✅ Implemented | Default behavior |
-| `-R`, `--relative` | Use relative path names | ❌ Not Implemented | Removed because it had no effect |
-| `--no-implied-dirs` | Don't send implied dirs with -R | ❌ Not Implemented | |
-| `-d`, `--dirs` | Transfer dirs without recursing | ❌ Not Implemented | |
-| `--mkpath` | Create missing path components | ❌ Not Implemented | |
+| `-R`, `--relative` | Use relative path names | ✅ Implemented | Meaningful together with `--files-from` (FastSync's default full-tree scan always mirrors the full source argument path below the destination root, so -R does not change it). With `-R` + `--files-from` each listed entry is transmitted under its bare relative destination path: an entry `sub/x.txt` lands at `<dest>/sub/x.txt` (its leading components preserved) instead of under the `<dest>/<full source path>` mirror. Only the path sent on the wire changes; the client still reads the absolute source path, and the delete manifest derives from the sent (relative) paths so `--delete` and `--remove-source-files` stay consistent in both layouts. Works single-threaded and under `-j`/`--threads` (including chunk serialization) |
+| `--no-implied-dirs` | Don't send implied dirs with -R | ✅ Implemented | Client-side, meaningful only with `-R` + `--files-from`. rsync would normally create the ancestor directories implied by a listed file so it can be written; with `--no-implied-dirs` a listed file whose parent directory is not itself (or via an ancestor) explicitly listed cannot be placed, and FastSync fails the whole run up front with a clear error (`--no-implied-dirs: cannot place file '...': parent directory '...' is not explicitly listed`). Listing the directory (or an ancestor of it, or the whole tree `.`) permits the file. In every other mode the option has no effect. FastSync has no per-entry skip channel, so the rsync "omit the file" case is surfaced as a hard pre-transfer error |
+| `-d`, `--dirs`, `--old-dirs`, `--old-d` | Transfer dirs without recursing | ✅ Implemented | `-d <dir>` transmits an explicit directory entry for the source-root directory, so the destination mirror is created empty and nothing is descended into. With `--files-from` exactly the listed items are transferred: a listed directory is created empty (no descent) and a listed file is transferred with its content; the dest layout follows the same -R rules as plain files. A new wire frame (`STATUS_MKDIR`) carries each directory entry — the path and, when `--preserve`/`-a` (metadata mode) is negotiated, the directory's metadata; the receiver creates it with the same confined mkdir-parent semantics as regular writes, in single-threaded and `-j`/`--threads` receivers (chunk serialization carries a per-entry type marker). Directory entries appear in the delete manifest so `--delete` prunes correctly. Directory TIMES are transmitted (the `STATUS_DIR_TIMES` frame carries every traversed source directory's captured times, including `--dirs` entries) and applied by the receiver at the END of the transfer, after all children and the delete/publication phases, so a later child write cannot clobber a directory's mtime (`-O`/`--omit-dir-times` skips this application). FastSync divergences: directory modes/ownership are still not applied (only times are), and empty directories are still never created (a `STATUS_DIR_TIMES` entry is record-only), filter/`--exclude` rules are not re-applied to the listed dirs mode (there is no descent during which they would apply), and `-d` never creates the intermediate directories between the destination root and a listed file beyond the usual on-demand parent creation. Under `--delay-updates` only regular files are staged: directory entries are created immediately, so a delayed run that fails part way can leave the already-created empty directories behind (matching rsync, which also creates directories as it processes the file list and only delays regular-file data) |
+| `--mkpath` | Create missing path components | ✅ Implemented | Wire option (client → server). At connection start the server creates the client's destination root directory (and any missing leading components below its own authorized root) when `--mkpath` is set, failing the connection cleanly if it cannot. Without `--mkpath` a destination root that does not exist yet is rejected up front (rsync semantics), so the flag is the only way to transfer into a not-yet-created destination directory. Creation is confined by the same secure mkdir walk as file writes (`O_NOFOLLOW`, no `..`) |
 
 ## 5. Transfer Modifications
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `-u`, `--update` | Skip files newer on receiver | ❌ Not Implemented | Removed because it had no effect |
+| `-u`, `--update` | Skip files newer on receiver | ✅ Implemented | `update` config field (crosses the wire; receiver-side policy, implies `-M` metadata). Before writing a regular file, the receiver checks `file_destination_is_newer_secure()` (via `stat_is_newer`, second-then-nanosecond strict `>` on the existing destination) and skips the write when the destination is newer than the source (`FILE_SAVE_SKIPPED`); equal-or-older destination (or a newer source) is transferred normally. Applied at write time on the regular-file, delay-updates-staged, hardlink-sibling, and special/device paths. Only regular destinations can be guarded (the newer-check requires `S_ISREG`), and like the other write-time policies it does not short-circuit the data transfer for a differing-size dest. `--remove-source-files` correctly respects the receiver's skip outcome so a skipped source is not removed |
 | `--inplace` | Update files in-place | ✅ Implemented | Direct write mode |
-| `--append` | Append data to shorter files | ❌ Not Implemented | Removed because it had no effect |
-| `--append-verify` | Append with old-data checksum | ❌ Not Implemented | Removed because it had no effect |
-| `-W`, `--whole-file` | Copy whole file (no delta) | ❌ Not Implemented | |
-| `--block-size=SIZE` | Force checksum block-size | ⚠️ Partial | Parsed as `--delta-block`; controls delta transfer block size |
+| `--append` | Append data to shorter files | ✅ Implemented | Tail-only resume. When an existing destination file is SHORTER than the source, the receiver negotiates a resume offset with the sender and only the tail is transferred; the receiver rebuilds the full file (retained prefix + tail) and installs it through the normal atomic store path, so the result is byte-identical to the source whenever the retained prefix matches. Plain `--append` does NOT content-verify that prefix (rsync parity): a destination whose prefix differs from the source is resumed anyway, so the result (wrong prefix + correct tail) is NOT byte-identical and the file is effectively left corrupt — the documented rsync-parity risk (use `--append-verify` when the prefix cannot be trusted). Non-content attributes (permissions/ownership/mtime, via `-M`) are still applied. Requires the per-file `STATUS_CHECK` handshake, so it implies `--incremental`; it takes precedence over block delta for a growing file and falls back to delta/full when the destination is not shorter. Incompatible with `-s` (chunk serialization) and `--whole-file` (both rejected up front so the mode never silently degrades to a full transfer). Combines with `--inplace`, `--partial`/`--partial-dir`, and `--delay-updates` (the reconstructed full file flows through those paths unchanged). Divergence: rsync appends in place; FastSync reconstructs and atomically installs, so an interrupted or failed resume never leaves a half-written file at the destination (no corruption window), and `--append` is thus safe to use with the normal atomic path — not only with in-place writes |
+| `--append-verify` | Append with old-data checksum | ✅ Implemented | Like `--append`, but the retained prefix IS verified before resuming: the sender transmits the source prefix checksum and the receiver compares it to the xxHash64 of the retained destination prefix; on a match only the tail is transferred, on a MISMATCH the run falls back to a clean full transfer so the result is always a byte-identical source copy (never a corrupt prefix+tail blend). Wire/protocol: the append handshake adds `STATUS_APPEND` / `STATUS_APPEND_SIG` / `STATUS_APPEND_OK` / `STATUS_APPEND_DATA` frames and `PROTOCOL_VERSION` was bumped **2.9.0 → 2.10.0** (peers must match, and both must be 2.10.0 or the run fails the version check). Same implications/incompatibilities as `--append`; when both spellings are given `--append-verify` wins (the safer semantics). See the Phase-3 append notes below |
+| `-W`, `--whole-file` | Copy whole file (no delta) | ✅ Implemented | `whole_file` config field. Forces a full (whole-file) copy, disabling the block-level delta machinery: the sender only sends `STATUS_NEXT` + full data (client_send.c) and the receiver never requests a delta signature/reconstruction — the receiver's `try_delta = use_delta && !whole_file && ...` short-circuits. `whole_file` crosses the wire folded into `use_delta` (the wire carries `use_delta && !whole_file`), so no separate field/bump is needed. Delta is opt-in (`--delta` needs `--incremental`); `-W` additionally makes `--fuzzy` inert (no similar-file delta basis). `--append`/`--append-verify` are incompatible with `-W` and rejected up front (both sides). See the delta/append notes below |
+| `--block-size=SIZE` | Force checksum block-size | ✅ Implemented | Phase 7 Wave B: `--block-size` is an alias for `--delta-block`; both set `config->delta_block_size` (default `DELTA_BLOCK_SIZE_DEFAULT`, bounds `DELTA_BLOCK_SIZE_MIN..MAX`, out-of-range values are rejected with the default kept). The value is genuinely honored by the delta engine end-to-end: `delta_signature_create_seeded(old, size, config->delta_block_size, seed)` on the sender and receiver, `delta_apply(old, ...)` with the same size, so a non-default block size changes the block count of every signature the harnesses exchange (verified by unit + integration tests) |
 
 ## 6. Destination Handling
 
@@ -93,113 +97,555 @@ This document maps rsync's full feature set to FastSync's current implementation
 | `-b`, `--backup` | Make backups of overwritten files | ✅ Implemented | Backup before overwrite |
 | `--backup-dir=DIR` | Backup directory hierarchy | ✅ Implemented | `backup_dir` config field |
 | `--suffix=SUFFIX` | Backup suffix (default ~) | ✅ Implemented | `suffix` config field |
-| `--delay-updates` | Put updated files in place at end | ❌ Not Implemented | |
+| `--delay-updates` | Put updated files in place at end | ✅ Implemented | Successfully received files are staged under a private 0700 `.fastsync-stage` dir inside the receive root and atomically renamed into their final destinations only after the whole transfer (manifest/delete handling included) succeeds, just before the success/outcome frame is sent. The delete walker deliberately skips the staging dir at the receive root, so `--delete` removes genuine extras but never the staged files (deletion runs before publication; rsync's delete-after ordering is not implemented). `--existing`/`--ignore-existing`/`--update` decide against the final destination path at stage time; `--backup` moves the old file aside at publication. Incompatible with `--inplace` and with `--backup-dir=.fastsync-stage` (the internal staging name is reserved; both are rejected). The staging dir name is fixed, so two simultaneous delayed transfers to the same destination root are serialized with an exclusive advisory lock held for the whole transfer: the second session fails cleanly instead of corrupting the first. Aborting or failing before publication installs nothing and removes the staging tree; a crash between stage and publish leaves staged leftovers that the next delayed run wipes at start (process death releases the lock). A stage→publish failure aborts the transfer (best-effort cleanup of the not-yet-published staged files; already-published files are not rolled back). Works in single-threaded and `-j`/`--threads` modes |
+| `-T`, `--temp-dir=DIR` | Create temporary files in DIR | ✅ Implemented | `--temp-dir` with the rsync short `-T` (Phase 7 Wave A; the timeout alias moved to long-only `--timeout`). Scratch dir is resolved under the receive root; temp copies use a unique name there and are atomically renamed into place. If the scratch dir and destination are on different filesystems the atomic rename fails with EXDEV and the file save fails, which aborts the whole transfer (FastSync has no per-file skip/resume on a save error; rsync's non-atomic copy fallback is deliberately not used). `--inplace` and `--partial-dir` writes bypass the scratch dir |
 
 ## 7. Deletion
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `--delete` | Delete extraneous files from dest | ✅ Implemented | `use_delete` config field |
-| `--delete-before` | Delete before transfer | ❌ Not Implemented | Removed because it had no effect |
-| `--delete-during` | Delete during transfer | ❌ Not Implemented | |
-| `--delete-delay` | Find deletions during, delete after | ❌ Not Implemented | |
-| `--delete-after` | Delete after transfer | ❌ Not Implemented | Removed because it had no effect |
-| `--delete-excluded` | Also delete excluded files | ❌ Not Implemented | Removed because it had no effect |
-| `--max-delete=NUM` | Max files to delete | ❌ Not Implemented | Removed because it had no effect |
-| `--ignore-errors` | Delete even with I/O errors | ❌ Not Implemented | |
-| `--force` | Force deletion of non-empty dirs | ❌ Not Implemented | |
-| `--prune-empty-dirs` | Prune empty dir chains | ❌ Not Implemented | Removed because it had no effect |
+| `--delete` | Delete extraneous files from dest | ✅ Implemented | `use_delete` config field. Deletion is always derived from the transmitted keep-set manifest of the paths the sender sent/keeps (never from unchecked input), runs through the symlink-safe walker bounded by `MAX_SERVER_DELETE_COUNT`, and skips the `.fastsync-stage` staging dir under `--delay-updates`. FastSync's default timing when no timing flag is given is **delete-after** (extras are removed only once the whole transfer succeeded) — intentionally NOT rsync's `--del`/delete-during default, to preserve FastSync's commit-style safety. By default the destination mirror of a path the source scan pruned (filter/exclude/size rules) is **protected** from deletion — matching rsync, which does not delete excluded files under `--delete`; `--delete-excluded` opts back into deleting them (see below). The bounded deletion is **all-or-nothing**: if the destination holds more extras than the effective bound (a client `--max-delete=NUM` or the 100000-entry server bound) nothing is deleted and the run fails with a distinct error instead of silently truncating |
+| `--delete-before` | Delete before transfer | ✅ Implemented | Implies `--delete`. The sender runs a full source pre-scan (paths only) and transmits the keep-set manifest BEFORE any file data; the receiver validates it, removes every destination entry not listed (all-or-nothing bounded walk, staging-dir skip, protected prefixes honored), then acks `STATUS_OK`. The sender only starts streaming after the deletion committed, or aborts if the receiver reported a deletion error. By definition the deletions already happened when a later transfer phase fails — rsync's delete-before is destructive the same way; a subsequent failure does not restore the removed files. Divergence: the keep-set is the pre-scan snapshot, so a file that appears on the source between the pre-scan and the data pass is still transferred but was not protected from deletion |
+| `--del`, `--delete-during` | Delete during transfer | ✅ Implemented | Both spellings accepted; imply `--delete`. FastSync streams the source in a single directory scan and has no per-directory generator pass, so deletions cannot be interleaved per-directory the way rsync's delete-during does. `--delete-during` therefore selects the same early engine mode as `--delete-before` (manifest transmitted before any data, extras removed and acknowledged before data is applied); observable success/failure behaviour equals `--delete-before`. That is the documented divergence from rsync, where `--del` is the default meaning of `--delete` |
+| `--delete-delay` | Find deletions during, delete after | ✅ Implemented | Implies `--delete`. Commit-mode timing: extras are removed only after the whole transfer succeeded. rsync's delete-delay records the deletion list during its scan and applies it at the end; FastSync never snapshots the destination while data flows (the keep-set is the transmitted manifest and the destination is listed only at deletion time), so `--delete-delay` is implemented as the same end-of-transfer commit as `--delete-after` with identical safety. That is the documented divergence |
+| `--delete-after` | Delete after transfer | ✅ Implemented | Implies `--delete`. The delete-after timing is also what plain `--delete` does: the keep-set manifest closes the data stream and the receiver commits the bounded deletion only after the terminal `STATUS_FINISHED` proves the whole transfer (every data frame received and stored) succeeded. A failed or aborted transfer removes nothing |
+| `--delete-excluded` | Also delete excluded files | ✅ Implemented | `delete_excluded` config field. Under `--delete` FastSync now protects (rsync's default) the destination mirror of paths the sender's source scan pruned by user-selection rules — the `--filter`/`-F`/`-C` layer, the legacy `--exclude`/`--include` layer, and `--max-size`/`--min-size`. The sender transmits those concrete pruned paths as **protected prefixes** in the delete-manifest frame (see the Phase-3 notes below); the walker never descends into or removes them. `--delete-excluded` opts back in: the sender sends an empty protected list, so the excluded destination mirrors become ordinary extras and are removed. Divergences (documented): protection is derived only from what the source scan actually pruned — a stray destination-only file that happens to match an exclude rule is not protected (FastSync never re-applies rules to the destination, keeping deletion sender-derived), and `--files-from` subset pruning stays keep-set-only (an unlisted source path is treated as absent and its mirror is deletable, matching the `--files-from` delete note below). The two are orthogonal: `--delete-excluded` removes filter-excluded mirrors; it does not make `--files-from` prune things |
+| `--max-delete=NUM` | Max files to delete | ✅ Implemented | `max_delete` config field (default -1 = no client limit; 0 = delete nothing). NUM bounds a `--delete` run with rsync's all-or-nothing semantics: the receiver rehearses the deletion first and, if the destination holds more than NUM extras, deletes NOTHING and fails the transfer with a distinct `--max-delete` error. A run at or below NUM deletes exactly the extras. NUM only applies together with `--delete` (it is inert otherwise, matching rsync). The hard server bound `MAX_SERVER_DELETE_COUNT` (100000) still caps the walk; a NUM above it never raises that cap, and exceeding the server bound is its own all-or-nothing error. Directories count toward the limit (each removed empty directory is one deletion), like rsync |
+| `--ignore-errors` | Delete even with I/O errors | ✅ Implemented | Sender-side, client-only config field. rsync suppresses `--delete` when the transfer had I/O errors; FastSync's equivalent is a source-scan I/O error (an unreadable directory, e.g. EACCES): by default the scan aborts the run so no deletion happens. With `--ignore-errors` the scan continues past the unreadable directory, the readable tree is transferred and the deletion still runs (the mirror of the unreadable directory is treated as an extra). The run still exits non-zero (the error is reported, matching rsync's error status). Divergence: without the flag FastSync aborts the whole run on the scan error, whereas rsync transfers the rest of the tree and merely skips the deletion; both leave the deletion undone |
+| `--force` | Force deletion of non-empty dirs | ✅ Implemented | `force_delete` receiver config field (crosses the wire). rsync's `--force` lets an incoming non-directory replace a destination directory; FastSync implements exactly that: when a regular file is written to a path that is currently a (possibly non-empty) destination directory, `--force` removes that directory tree first — confined to the receive root and symlink-safe (O_NOFOLLOW fd walk, symlinks removed by name, never followed) — so the atomic install can place the file. Without `--force` such a write fails and the run aborts. Divergence: `--force` acts on the immediate-install path only; under `--delay-updates` a blocking directory is not cleared (publication renames over regular files) |
+| `-m`, `--prune-empty-dirs` | Prune empty dir chains | ✅ Implemented | `-m`/`--prune-empty-dirs` (Phase 7 Wave A freed the rsync short `-m`; FastSync multithreading is now `-j`/`--threads`). FastSync's recursive transfer records directory times but never CREATES an empty directory (a `STATUS_DIR_TIMES` entry is record-only, and `--dirs` empty entries are pruned by this flag), so empty directories are inherently never transferred (which is rsync's `-m` behavior) and truly-empty destination directory chains are removed by `--delete` regardless of this flag. The flag's additional real effect is on the `--dirs` explicit directory-entry generator: a plain `-d <empty-dir>` run omits the empty source directory's entry, so nothing is created at the destination (no `STATUS_MKDIR`, no `-i`/`--out-format` change line, and an existing empty mirror becomes an extra that `--delete` prunes). Explicitly `--files-from`-listed directories always pass through (documented `--files-from` behavior). A directory that still holds an excluded-but-protected file survives, matching the `--delete-excluded` default |
+
+**Deletion-timing implementation notes (Phase 3):** the delete flags above are
+real. Two new config booleans (`delete_during`, `delete_delay`) join the already
+serialized `delete_before`/`delete_after`, so the on-the-wire config layout
+changed and `PROTOCOL_VERSION` was bumped **2.7.0 → 2.8.0** (peers must match).
+The `STATUS_MANIFEST` frame is count-delimited and position-independent: the
+receiver commits the deletion either when the manifest arrives (early modes:
+`--delete-before`/`--delete-during`, which additionally acknowledge with
+`STATUS_OK` before data flows) or after the terminal `STATUS_FINISHED` proves
+the whole transfer succeeded (commit modes: plain `--delete`/`--delete-after`/
+`--delete-delay`). Timing is chosen purely from the config, so server policy
+(`--allow-delete` off) still disables deletion without deadlocking the early
+manifest ack. `--delete-delay` and `--delete-during` are each implemented as
+the closest safe approximation their engine mode allows; the divergences are
+noted in the rows above.
+
+**Deletion-policy notes (Phase 3, delete-policy wave):** this wave made the
+deletion family real — `--delete-excluded`, `--max-delete`, `--ignore-errors`,
+`--force`, `--prune-empty-dirs` — and, to support them, the `STATUS_MANIFEST`
+frame now carries **two sections**: the keep-set paths followed by a list of
+**protected prefixes** (destination-relative paths the source scan pruned by
+user-selection rules, which the walker must never delete unless
+`--delete-excluded` opted out). Two config booleans were added for the wave:
+`force_delete` (crosses the wire; the receiver clears a directory that blocks an
+incoming file) and `ignore_errors` (client-only; the sender's scan continues
+past an unreadable directory). `max_delete`'s default became -1 ("no client
+limit"). These wire/layout changes bumped `PROTOCOL_VERSION` **2.8.0 → 2.9.0**
+(peers must match). All four wire additions — `force_delete`,
+`delete_excluded`, `prune_empty_dirs`, `max_delete` — round-trip unchanged and
+are validated on receive.
+
+**Missing-args note (Phase 3, missing-args wave):** `--ignore-missing-args` and
+`--delete-missing-args` are implemented as described in the Safety & Security
+rows. Wire impact: the `STATUS_MANIFEST` frame now carries a **third section** —
+a list of destination-relative **exact-delete paths** (the missing entries'
+mirrors) — and the config frame gained a `delete_missing_args` boolean
+(`ignore_missing_args` stays client-only, exactly like `ignore_errors`). These
+wire/layout changes bumped `PROTOCOL_VERSION` **2.9.0 → 2.10.0** (peers must
+match). The receiver validates the third section identically to the keep-set
+(non-empty, relative, traversal-free; `MAX_MANIFEST_ENTRIES` per section, a
+single `MAX_MANIFEST_BYTES` budget shared across all three). On commit the
+receiver runs the exact-path deletions FIRST (`manifest_delete_missing_args`:
+confined per-path unlink/rmdir, deep removal only under `--force`/`--delete`,
+staging/basis protected, never blocked by the protected-prefix list) and then
+the ordinary extras walk when `--delete` is active (`manifest_delete_all`). A
+client may request the exact-path deletions without `--delete`; the server's
+`--allow-delete` policy gates them exactly like `--delete`, so an unauthorized
+server ignores the request while the missing entries are still skipped.
+
+The deletion walker is now **all-or-nothing**: before any unlink it rehearses
+the deletion (an fd-relative walk identical to the delete pass, counting every
+regular file it would unlink and every directory it would remove) and refuses to
+start when the extras exceed the effective bound — a client `--max-delete=NUM`
+below the hard bound, or the hard `MAX_SERVER_DELETE_COUNT` (100000) bound
+itself. Previously the walker removed up to `MAX_SERVER_DELETE_COUNT` extras and
+then reported an error (a truncated deletion); it now removes nothing and fails
+with an error naming the bound. Directories count toward the bound. A directory
+that still holds entries the walker leaves in place (a protected excluded file,
+a kept manifest entry, a symlink) is left behind rather than failing the run —
+matching rsync's "cannot delete non-empty directory" behaviour. The
+all-or-nothing guarantee holds only while the destination is not concurrently
+modified: rehearsal and delete are two separate walks, so a concurrent change
+between them (another process adding or removing destination entries) can make
+the actual deletion diverge from the counted set.
+
+Manifest size: the sender's keep-set and protected-prefix collections (streaming
+or early pre-scan) are unbounded, but the receiver rejects a manifest beyond
+`MAX_MANIFEST_ENTRIES` (1 048 576 entries, applied to EACH section — a frame can
+therefore total up to 2 097 152 entries) / `MAX_MANIFEST_BYTES` (16 MB of paths,
+counted across BOTH sections) as a hard protocol error. A heavily filtered
+source whose exclusion list grows large thus fails the run cleanly on the
+receiver (STATUS_ERROR) instead of being silently truncated. In the commit
+modes this only means the deletion is refused after the data already arrived; in
+the early modes (`--delete-before`/`--delete-during`) the manifest is the first
+frame, so an oversized keep-set or protected list aborts the whole transfer
+BEFORE any data is sent. Keep the source tree small enough for the receiver's
+manifest caps when using the early timing.
+
+Early-delete ACK wait: after committing a large deletion (up to
+`MAX_SERVER_DELETE_COUNT` removals) the receiver's `STATUS_OK`/`STATUS_ERROR`
+reply can legitimately take much longer than a normal round trip, so the sender
+waits for that single ACK with an extended explicit deadline (1 hour) instead
+of the default 60 s per-message receive window. A receiver that is genuinely
+gone still aborts the wait via connection close/error; the extended bound only
+protects against aborting after the deletion already committed on the receiver.
+
+Flag-conflict policy: unlike rsync's last-one-wins behaviour, every deletion
+timing flag implies `--delete`, and combining a timing flag with `--no-delete`
+(in either argument order) — or more than one timing flag — is rejected as a
+configuration error rather than silently resolved. Note the check is
+order-independent because it runs over the fully parsed config. The deletion
+POLICY flags (`--delete-excluded`, `--max-delete`, `--ignore-errors`, `--force`)
+do NOT imply `--delete`; without `--delete` they are inert (matching rsync).
+
+**Append-resume notes (Phase 3, append wave):** `--append` and `--append-verify`
+are real. Both are negotiated when an existing destination file is found to be
+**shorter** than the source during the per-file `STATUS_CHECK`; the receiver
+replies with a new `STATUS_APPEND` frame carrying the resume offset (the prefix
+length it already holds) instead of `STATUS_NEXT`/`STATUS_DELTA_SIGNATURE`.
+The sender transmits ONLY the tail. For `--append-verify` it first sends the
+source's prefix xxHash64 in a `STATUS_APPEND_SIG` frame; the receiver compares
+it to the retained prefix and answers `STATUS_APPEND_OK` (transfer the tail) or
+`STATUS_NEXT` (prefix mismatch → the sender falls back to a byte-exact full
+transfer). The tail arrives in a `STATUS_APPEND_DATA` frame (compression and
+metadata still apply). The receiver then rebuilds the full file in memory
+(prefix + tail) and routes it through the existing atomic store engine, so all
+of `--inplace`, `--partial`/`--partial-dir`, `--delay-updates`, `--backup`,
+`--existing`/`--ignore-existing`/`--update` and delete-manifest behaviour is
+unchanged and the result is a byte-identical source copy (given a matching
+prefix). These new frames changed the wire, so `PROTOCOL_VERSION` was bumped
+**2.9.0 → 2.10.0** (peers must match; the pre-existing `append`/`append_verify`
+config booleans already crossed the wire). CLI: both flags imply `--incremental`
+(the handshake needs it); they are incompatible with `-s` (chunk serialization)
+and `--whole-file` (both rejected up front, never a silent full transfer); when
+both spellings are given `--append-verify` wins. The FastSync divergence from
+rsync is intentional and safer: rsync appends in place, whereas FastSync
+reconstructs the whole file and atomically installs it, so an interrupted or
+failed resume never leaves a partial/corrupt file at the destination — this is
+why plain `--append` works on the normal atomic path, not only with `--inplace`.
 
 ## 8. Metadata Preservation
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
 | `-M`, `--preserve` | Preserve file metadata | ✅ Implemented | Mode, uid, gid, mtime |
-| `-p`, `--perms` | Preserve permissions | 🔀 Alt Arg | `-p` means SSH port; permissions preserved via `-M`/`--preserve` |
+| `-p`, `--perms` | Preserve permissions | ✅ Implemented | Phase 7 Wave A: `-p`/`--perms` now preserve permission bits, folded into FastSync's broad metadata bundle (`--preserve`); the SSH port moved to `--ssh-port`. rsync-parity short form |
 | `-o`, `--owner` | Preserve owner | ✅ Implemented | Part of -M |
 | `-g`, `--group` | Preserve group | ✅ Implemented | Part of -M |
 | `-t`, `--times` | Preserve modification times | ✅ Implemented | Part of -M |
-| `-E`, `--executability` | Preserve executability | ❌ Not Implemented | |
-| `--chmod=CHMOD` | Affect file permissions | ❌ Not Implemented | |
-| `-A`, `--acls` | Preserve ACLs | ❌ Not Implemented | Removed because it had no effect |
-| `-X`, `--xattrs` | Preserve extended attributes | ❌ Not Implemented | Removed because it had no effect |
-| `-H`, `--hard-links` | Preserve hard links | ❌ Not Implemented | Removed because it had no effect |
-| `-D` | Same as --devices --specials | ❌ Not Implemented | Removed because device-file handling is not implemented |
-| `--devices` | Preserve device files | ❌ Not Implemented | Removed because it had no effect |
-| `--specials` | Preserve special files | ❌ Not Implemented | |
-| `--copy-devices` | Copy device contents as file | ❌ Not Implemented | |
-| `--write-devices` | Write to devices as files | ❌ Not Implemented | |
-| `-U`, `--atimes` | Preserve access times | ❌ Not Implemented | |
-| `-N`, `--crtimes` | Preserve create times | ❌ Not Implemented | |
-| `-O`, `--omit-dir-times` | Omit dirs from --times | ❌ Not Implemented | |
-| `-J`, `--omit-link-times` | Omit symlinks from --times | ❌ Not Implemented | |
-| `--super` | Receiver attempts super-user activities | ❌ Not Implemented | |
-| `--fake-super` | Store/recover privileged attrs via xattrs | ❌ Not Implemented | |
+| `-E`, `--executability` | Preserve executability | ✅ Implemented | Preserves executable permission bits (implies metadata preservation) |
+| `--chmod=CHMOD` | Affect file permissions | ✅ Implemented | Supports numeric and symbolic `ugo` `rwx` changes; retains receiver safety masking |
+| `-A`, `--acls` | Preserve ACLs | ✅ Implemented | Implemented on Linux via the POSIX-ACL xattr representation: the sender captures the `system.posix_acl_access` / `system.posix_acl_default` xattrs into the same bounded whitelisted set as `-X`, transmits them per-file, and the receiver re-applies them fd-relative. Setting an ACL the receiver is not permitted to set (non-root on a file it does not own, unsupported filesystem) is logged and skipped, never fatal. libacl is **not** required. Only the `system.posix_acl_*` namespaces plus `user.*` are ever applied; privileged namespaces are never applied (see the Phase-4 xattr/ACL notes below). Implies metadata transmission |
+| `-X`, `--xattrs` | Preserve extended attributes | ✅ Implemented | Preserves unprivileged `user.*` extended attributes (Linux `listxattr`/`getxattr` on capture, `fsetxattr` on the written destination fd). Both capture (sender) and application (receiver) are restricted to the `user.*` namespace and the two POSIX ACL xattrs, so a client can **never** force a `security.*`/`trusted.*`/privileged attribute onto the destination; the receiver independently re-validates every incoming name against this whitelist and rejects anything else. Payloads are bounded (per-name ≤255B, per-value ≤1MiB, per-file count ≤256 total bytes ≤4MiB) on both ends, and an oversized/malformed frame is a clean protocol rejection (no OOM). Applied fd-relative to the exact written file. Implies metadata transmission. Incompatible with `-s` (chunk serialization), rejected up front (see the notes); a `--link-dest`/`-H` hard-link copy fallback re-applies the attributes so they are not dropped when a link is refused |
+| `-H`, `--hard-links` | Preserve hard links | ✅ Implemented | Files on the source that share an inode (`st_dev`+`st_ino`, e.g. a `cp -al` tree) are re-created as hard links to one another on the destination, so duplicate links stay deduplicated and only the first member's data is sent (later members are transmitted as payload-less `STATUS_HARDLINK` frames). The receiver links each sibling to the first member's installed file with an atomic link + rename; on `link()` failure it falls back to a byte-identical local copy of the first member, never a partial/corrupt file. Requires the sequential scan for ordering (the first member is always emitted and installed before any sibling is linked). Works single-threaded and under `-j`/`--threads`, `--inplace`, `--delay-updates` (links staged and published by rename) and `--partial`. Crosses the wire (`preserve_hard_links` bool; `PROTOCOL_VERSION` bumped **2.11.0 → 2.12.0**, peers must match). Incompatible with `-s` (chunk serialization) and `--append`/`--append-verify`, rejected up front with a distinct error. See the Phase-4 hard-links notes below |
+| `-D` | Same as --devices --specials | ✅ Implemented | Implies `--devices --specials`. `-D` was unassigned in FastSync (verified: no collision), so it is free to imply both device-node and special-file preservation. See the `--devices`/`--specials` rows and the Phase-4 devices notes below |
+| `--devices` | Preserve device files | ✅ Implemented | Recreates char/block device nodes on the destination via `mknod` instead of transferring content. Type + rdev are validated strictly (S_IFMT from the transmitted mode; major/minor range-checked, non-negative), and creation is **privilege-gated**: `mknod` needs `CAP_MKNOD`, so a non-root receiver (CI runs via setpriv as non-root) logs a warning and **skips the device entry safely** — the whole transfer never aborts just because the node could not be made. The node is created fd-relative below the receive root (`mknodat` on the confined secure parent), so it can never be placed outside the authorized root, never follows a symlink, and never replaces an existing directory. Only a char/block mode is honored. Crosses the wire (a new `STATUS_SPECIAL` frame carries the path + metadata mode + rdev; `PROTOCOL_VERSION` bumped **2.12.0 → 2.13.0**). Divergence: per-entry skip (not a hard error) when the receiver lacks `CAP_MKNOD`, documented in the Phase-4 devices notes |
+| `--specials` | Preserve special files | ⛔ Impossible/Divergence | **FIFO recreation works**: FIFOs are recreated on the destination via `mkfifo` (unprivileged, so this is a real, assertable behavior under CI). **Only socket recreation is impossible**: a socket entry can be created only by `bind(2)` on a live socket, not by any filesystem call, so a source socket is skipped with an explicit note. That one unsupported node kind is why the flag is classified Impossible/Divergence even though FIFO recreation itself works; its normal path is otherwise complete. FIFO creation is privileged-gated only in the sense of graceful skip on any permission failure. Node creation is confined below the receive root (`mkfifoat` on the secure fd-relative parent; no `..`, no symlink follow). Crosses the wire like `--devices` (the `STATUS_SPECIAL` frame; `PROTOCOL_VERSION` bumped **2.12.0 → 2.13.0**). See the Phase-4 devices notes |
+| `--copy-devices` | Copy device contents as file | ✅ Implemented | Copy a device's CONTENT into an ordinary regular file on the destination instead of recreating the node — non-privileged and safe. FastSync scans a device/FIFO as a regular file: its reported size (`st_size`, typically 0 for char devices and FIFOs) is copied, so a FIFO or a non-readable device becomes an empty (or size-bounded) regular file. The default data path is size-bounded and never blocks (it sends exactly `st_size` bytes, never an unbounded pseudo-device stream); with `--sendfile`, a non-regular source (FIFO/device) is detected from its `stat` mode and falls back to that same buffered read, so `--copy-devices --sendfile` cannot hang either. The run always succeeds and never crashes on such input. **Deliberate, safe divergence from rsync's dd-like unbounded device read.** See the Phase-4 devices notes |
+| `--write-devices` | Write to devices as files | ✅ Implemented | Write the received data directly into an **existing** device node on the destination instead of creating a regular file. Restricted and best-effort: the destination must already exist and be a char/block device (opened only under the confined receive root, with `O_NOFOLLOW` + `O_NONBLOCK`); a missing, symlinked, FIFO-with-no-reader (`ENXIO`), non-device destination, or any write failure is **skipped with a warning** rather than allowed, so a run can never clobber the system, never blocks on a special-file target, and never aborts on an unusable target. See the Phase-4 devices notes |
+| `-U`, `--atimes` | Preserve access times | ✅ Implemented | Captures the source access time (from the scanner's pre-read stat, so it is not clobbered by reading the file for transfer) and transmits it over the wire; the receiver restores it together with the mtime via `futimens`/`utimensat`. Implies metadata transmission (the times travel inside the `-M` metadata payload), but does not enable ownership application (that stays opt-in via the identity flags). Wire: new `atime` fields on the metadata frame + a `preserve_atimes` config boolean; `PROTOCOL_VERSION` bumped **2.11.0 → 2.12.0** |
+| `-N`, `--crtimes` | Preserve create times | ⛔ Impossible/Divergence | Birth-times cannot be set by any portable filesystem call (`utimensat`/`futimens` only set atime/mtime), so this row is an explicit **Impossible/Divergence** (Phase 7 Wave B). Capture + transmit stays: `statx(STATX_BTIME)` on Linux records the source birth time as a wire field; the receiver logs a debug note that it cannot be applied and continues — never failing the transfer and never pretending it worked. On platforms without `statx` it parses as a documented no-op (flag accepted; nothing is captured). Implies metadata transmission. Wire: new `crtime` fields + a `preserve_crtimes` config boolean; `PROTOCOL_VERSION` bumped **2.11.0 → 2.12.0** (see the Phase-4 metadata-time notes) |
+| `-O`, `--omit-dir-times` | Omit dirs from --times | ✅ Implemented | Real modifier now that FastSync preserves directory times. With metadata on, the scanner captures every traversed source directory's mtime (and atime under `-U`) and the sender transmits them in trailing `STATUS_DIR_TIMES` frame(s) **after all file data and the optional delete manifest** (chunked at the receiver's `MAX_MANIFEST_ENTRIES` per-frame cap); a dir-time entry only RECORDS metadata and never creates the directory, so empty source directories stay untransferred. The receiver defers applying them until its delete / `--delay-updates` publication phases have committed, so writing or removing a child never clobbers a parent directory's mtime (rsync applies directory times at the end for exactly this reason). When `-O` is set (the boolean crosses the wire) the receiver does not apply any of them; without `-O` an `-a`/`--preserve` transfer now restores directory times (reversing the old "never preserves dir times" divergence). Wire change: the terminal `STATUS_DIR_TIMES` frame; `PROTOCOL_VERSION` bumped **2.16.0 → 2.17.0** |
+| `-J`, `--omit-link-times` | Omit symlinks from --times | ✅ Implemented | Real modifier now that FastSync preserves symlink times. Symlink entries already carried their metadata on `STATUS_SYMLINK`; the receiver now applies it with **no-follow primitives only** (`utimensat(..., AT_SYMLINK_NOFOLLOW)`, plus best-effort `fchmodat(..., AT_SYMLINK_NOFOLLOW)` and policy-gated `fchownat(..., AT_SYMLINK_NOFOLLOW)`), so the link itself is stamped without ever dereferencing it, confined fd-relative below the authorized receive root. A symlink has no children, so the times are applied immediately at creation. When `-J` is set (the boolean crosses the wire) the receiver skips the timestamps (mode/ownership are unaffected); without `-J` an `-a`/`-l` transfer restores symlink mtimes. Wire change alongside `-O`: the shared `STATUS_DIR_TIMES` frame; `PROTOCOL_VERSION` bumped **2.16.0 → 2.17.0** |
+| `--super` | Receiver attempts super-user activities | ✅ Implemented | Phase 7 Wave E: receiver-side **safe-subset + clear-refusal** privilege model, tri-state `super_mode` (auto/on/off). `--super` **permits** the receiver to attempt super-user activities — ownership application and char/block device-node creation — that are already confined fd-relative below the authorized receive root; `--no-super` **forbids** them even when the receiver is root; the default (`auto`) preserves the pre-existing **best-effort** behavior of *attempting* them (not only when already root: an unprivileged attempt is refused by the kernel and skipped per entry, matching FastSync's history). The server additionally accepts an operator-level `--no-super` veto that forces `OFF` for every connection it accepts (so it also refuses any client `--copy-as`/`--super`); the `--fake-super` owner replay and the `--write-devices` write path are gated by the same policy. **FastSync never elevates**: no `setuid`/`seteuid`/`setgid` is ever called, and `--super` never bypasses the confinement floor (`file_open_secure_parent`, `O_NOFOLLOW`, root checks) — it only permits an attempt that is already confined. `--super` does **not** imply `--numeric-ids` and never enables client-chosen ownership on its own: ownership is applied only when an explicit identity policy (`--usermap`/`--groupmap`/`--chown`/`--numeric-ids`/`--copy-as`) is also given. A non-root receiver given `--super` logs exactly one warning at activation and each confined attempt is then refused by the kernel and skipped per entry (never aborts); `--no-super` suppresses ownership, char/block `mknod`, `--write-devices` and the fake-super owner replay, while unprivileged FIFO creation is unaffected. Wire: one trailing `super_mode` int on the config frame (validated 0..2), sent **before** the `--copy-as` block (fixed order: super int, then copy-as presence int + ids); `PROTOCOL_VERSION` bumped **2.17.0 → 2.18.0**. **Documented divergence from rsync:** rsync's `--super` runs the receiver with elevated privilege; FastSync only permits a confined attempt and never elevates |
+| `--fake-super` | Store/recover privileged attrs via xattrs | ✅ Implemented | Phase 7 Wave B: full record **and replay**. The receiver writes the source `uid:gid:mode:mtime_sec:mtime_nsec` into a reserved `user.fastsync.stat` xattr on each written file (best-effort, fd-relative, format unchanged), then immediately re-applies it via `fake_super_restore_fd`: `fchown` (only where privileged — a non-root EPERM/EACCES is skipped silently, matching FastSync's identity philosophy), `fchmod`, and `futimens`. The OWNER leg is additionally skipped unless an explicit ownership identity policy (`--numeric-ids`/`--usermap`/`--groupmap`/`--chown`/`--copy-as`) is active — `--fake-super` on its own only *records* the source owner and must not act as an un-gated chown primitive — when `--no-super` forbids super-user activities (even for root), or when an active `--copy-as` is authoritative, so the recorded source owner can never override a forced `--copy-as` owner; the xattr record is still stored/replayed for a later privileged restore and mode/mtime still apply, so unprivileged `--fake-super` keeps working. The restored mode goes through the same sanitization as the normal metadata path (group/other write bits are never granted, so a recorded 0666 restores as 0644), so fake-super replay can never grant group/other-write that plain `--preserve` would refuse. Absence or a malformed record is a silent no-op, never fatal. The recording format diverges from rsync's `user.rsync.%stat%`; no cross-tool conversion is attempted. Implies metadata transmission so the source uid/gid/mode/mtime are available. Both it and `-X`/`-A` are incompatible with `-s` (chunk serialization), rejected up front |
+| `--open-noatime` | Avoid changing access time when opening files | ✅ Implemented | Sender-side policy: the sender opens source files with `O_NOATIME` (Linux) when reading them for transfer, so the open/read does NOT bump the source's on-disk access time. Degrades safely when `O_NOATIME` is unavailable (not defined) or refused (`EPERM`, since it needs `CAP_FOWNER` or file ownership): the code falls back to a normal open, so the data always transfers — only the atime-bump is skipped. It does not itself capture/preserve atime; it only avoids modifying it. **Client-only, never crosses the wire.** Exposed as `file_open_for_read()` and applied to both the buffered data path and the sendfile path |
+| `--numeric-ids` | Do not map uid/gid by name | ✅ Implemented | Ownership is applied through FastSync's opt-in identity path (see the Phase-4 identity notes below). `--numeric-ids` is a mapping-policy modifier: when applying ownership it uses the transmitted numeric uid/gid directly, skipping the name lookup. Without an ownership-affecting option it is inert (FastSync only applies ownership when the user opts in). It does not need `-M` to be parsed, but ownership is only applied when metadata (hence the source uid/gid) is actually transmitted (see the notes) |
+| `--usermap=STRING` | Map usernames | ✅ Implemented | Opt-in ownership application. rsync subset implemented: comma-separated `FROM:TO` rules evaluated in order, first match wins; `FROM`/`TO` are group/user names (resolved on the SOURCE machine at parse time), `*` (FROM matches any id / TO = the receiving process's current euid), and an `@N` or bare `N` numeric id. Rules are carried over the wire as resolved numeric id pairs; the receiver applies a matching rule (else falls back to `--chown`, `--numeric-ids`, then a best-effort name lookup) via an fd-relative `fchown`. Malformed/unresolvable specs are rejected with a clear error, never a silent no-op. Implies metadata preservation so the source uid/gid travel. Only effective when the receiver can actually change ownership (root or membership); otherwise it warns and continues |
+| `--groupmap=STRING` | Map group names | ✅ Implemented | Same rsync subset and semantics as `--usermap` but for the group (gid) side and the group databases. See the Phase-4 identity notes |
+| `--chown=USER:GROUP` | Map owner and group | ✅ Implemented | Opt-in ownership override applied receiver-side. Forms: `USER:GROUP`, `USER` (owner only), `:GROUP` (group only); a `*` for USER/GROUP means the current/root user or group as appropriate; an `@N`/bare `N` numeric id is accepted. A `:` inside a name may be escaped as `\:`. Equivalent to a trailing `*:*` usermap+groupmap rule (so an explicit `--usermap`/`--groupmap` match wins). Malformed or unresolvable specs are clear parse errors. Implies metadata preservation. Only effective when the receiver has permission to chown; otherwise it warns and continues (rsync parity) |
+| `--copy-as=USER[:GROUP]` | Perform the copy as another user/group | ✅ Implemented | Safe-subset implementation, an explicit divergence from rsync's **real identity switching**. rsync makes the receiving process actually assume USER/GROUP (setuid/setgid); FastSync's receiver is multithreaded, so a real credential drop would be unsafe and is never attempted — FastSync never calls `setuid`/`seteuid`/`setgid`. Instead the receiver FORCES the ownership of every entry it writes to `copy_as_uid`/`copy_as_gid` through the existing confined, fd-relative identity path (the same `fchown`/`fchownat` mechanism as `--chown`/`--usermap`/`--groupmap`; symlinks use `fchownat(..., AT_SYMLINK_NOFOLLOW)`, and directories — including intermediate parents created implicitly while writing a nested file — and char/block/FIFO nodes are owned no-follow too, so a directory never keeps the receiver's owner while its children get the target owner), with `--copy-as` at the **highest priority** — it beats usermap/groupmap/`--chown`/`--numeric-ids` and the best-effort name lookup. This REQUIRES a privileged (root) receiver: an unprivileged receiver REFUSES the whole transfer up front at the config handshake (`server_module_gate`, running inside `config_receive_with_validate` before the `STATUS_OK` ack) with a clear error and no file data exchanged — never a silent wrong-ownership result. A server running with an operator `--no-super` veto also refuses it, and a **daemon** refuses `--copy-as`, like every other client-chosen-ownership request (`--numeric-ids`/`--chown`/`--usermap`/`--groupmap`/`--fake-super`/explicit `--super`), unless the selected module opts in with `client owner = yes`; without that per-module opt-in a daemon must not honor an arbitrary client-selected owner (the standalone listener and SSH `--stdio` server keep honoring these for their single operator-authorized root). `--fake-super` interaction: `--copy-as` is authoritative, so the recorded source owner is never replayed over the forced target owner. If the ownership apply still fails with EPERM/EACCES (capability-restricted root, root-squash, read-only mount) the failure is logged at ERROR and the **entry is reported as failed** rather than written with the wrong owner, which fails the transfer (fail-fast) so overall success is never reported with the wrong owner. USER is resolved on the client against the user database (a name, an `@N`/bare `N` numeric id, or `*` meaning the client's current euid); when `:GROUP` is present it is resolved against the group database (`*` meaning the client's egid). **Group-default rule:** when the group is omitted FastSync uses the user's primary gid (`getpwuid(uid)->pw_gid`); a numeric id with no local passwd entry has no primary gid to look up, so `gid` falls back to `uid` (documented divergence). Malformed/empty/unresolvable specs are clear parse errors, never a silent no-op. Never elevates privileges and never bypasses the confined receive root. Implies metadata preservation (the source uid/gid must be transmitted). Wire: a new trailing config-frame block **sent after** the `--super` int (presence int, then the two int32 ids, both validated `>= 0` on receive; the ids are also rejected if they do not fit int32 at CLI parse time); `PROTOCOL_VERSION` bumped **2.17.0 → 2.18.0** |
+
+**Phase-4 metadata-time notes:** `-U/--atimes`, `-N/--crtimes`,
+`-O/--omit-dir-times`, `-J/--omit-link-times`, and `--open-noatime` are new.
+They change the wire: the per-file metadata frame grows `atime_valid` +
+`atime_sec` + `atime_nsec` and `crtime_valid` + `crtime_sec` + `crtime_nsec`
+(appended after the existing mode/uid/gid/mtime fields, preserving the exact
+positions of every pre-existing field), and the config frame grows four
+booleans — `preserve_atimes`, `preserve_crtimes`, `omit_dir_times`,
+`omit_link_times` — that CROSS the wire so the receiver knows what to apply /
+suppress. `--open-noatime` is **client-only** and is never serialized (it only
+governs the sender's source reads). `PROTOCOL_VERSION` was bumped **2.11.0 →
+2.12.0** (peers must match, exactly as prior phases did).
+
+**Client-vs-wire split:** `-U` and `-N` affect both the sender (capture) and the
+receiver (apply), so they and their metadata fields cross the wire;
+`-O`/`-J` are receiver-side preferences and cross as config booleans;
+`--open-noatime` is purely a client/sender open flag and stays off the wire
+(mirroring the existing convention where `ignore_errors` is client-only while
+`force_delete` crosses the wire).
+
+**Phase-4 xattr/ACL notes (`-X/--xattrs`, `-A/--acls`, `--fake-super`):** these
+are new in protocol 2.13.0 and add a bounded per-file xattr block to the
+per-file metadata frame (count + each `name`/`value`, sent only when xattr
+transport is enabled, i.e. with zero overhead on unaffected runs). The config
+frame carries `preserve_xattrs`, `preserve_acls` (in the existing file-options
+block) and a trailing `fake_super` boolean — all CROSS the wire so the receiver
+knows the negotiated behavior; the derived `use_xattrs` flag is recomputed on
+the receiver. `PROTOCOL_VERSION` was bumped **2.12.0 → 2.13.0** (peers must
+match, exactly as prior phases did).
+
+- **Security model (both `-X` and `-A`):** only `user.*` and the
+  `system.posix_acl_access` / `system.posix_acl_default` namespaces are ever
+  captured (sender) or applied (receiver). `security.*` (SELinux, capabilities,
+  ...), `trusted.*`, and all other `system.*` attributes are never transmitted
+  or applied, so a client can never compel the receiver to set a privileged
+  xattr. The receiver re-validates each incoming name against this whitelist
+  even though the sender already filtered, so a malicious/compromised sender's
+  `security.capability` payload is rejected outright (a clean protocol error),
+  never applied.
+- **Bounds / memory safety:** per-name length ≤ 255 B, per-value ≤ 1 MiB,
+  per-file count ≤ 256 names, per-file name+value total ≤ 4 MiB. Both the
+  sender (during capture) and the receiver (during receive) enforce these; an
+  oversized or malformed frame is rejected, never a large allocation.
+- **Confined application:** xattrs are applied with `fsetxattr` on the exact
+  just-written destination file fd (before the atomic rename), never on a
+  caller-controlled path; this is the same confinement as mode/time restore.
+  The `--link-dest` / `-H` hard-link copy fallback (a byte copy when `link()`
+  is refused) also re-applies the incoming (or, for `-H`, the first member's)
+  xattrs and the `--fake-super` stat, so attributes are preserved rather than
+  silently dropped when the link fails.
+- **Reserved fake-super key is receiver-only:** the `user.fastsync.stat` key is
+  excluded from sender capture AND from receiver application, so it can only be
+  written by the receiver's own `--fake-super` handling. A source file that
+  already carries such a record is never forwarded on a plain `-X` run, so it
+  cannot be spoofed to mislead a later privileged restore.
+- **`-A` requires no libacl** — ACLs travel as the `system.posix_acl_*` xattrs.
+  Applying an ACL is owner-privileged: `fsetxattr` failure (e.g. non-root,
+  unsupported filesystem) is logged (collapsed to one line per file) and never
+  fatal.
+- **`--fake-super`**: see the row above; the reserved key is `user.fastsync.stat`
+  with the documented `uid:gid:mode:mtime_sec:mtime_nsec` (mode octal) format.
+  It is honest but partial — there is no replay, and it does not interoperate
+  with rsync's `user.rsync.%stat%`.
+- **Chunk serialization (`-s`) incompatibility:** the per-file xattr block rides
+  the streaming per-file frame, which `-s` replaces with a fixed buffer format,
+  so `-X` / `-A` combined with `-s` is rejected up front on both ends (mirroring
+  the existing `-H` + `-s` rejection) rather than silently dropping attributes.
+
+**atime capture does not clobber the source atime:** the sender records the
+access time from the **same pre-read stat the scanner already took** (inside
+`file_metadata_create`), before any file data is read for transfer. So `-U`
+alone captures the correct atime even without `--open-noatime`. `--open-noatime`
+is orthogonal: it keeps the source's on-disk atime from being bumped by the read
+that actually ships the data (only honoured where `O_NOATIME` works; it degrades
+to a normal open otherwise, so the data always transfers).
+
+**crtime handling:** `-N` captures the source birth time via `statx`/`STATX_BTIME`
+(guarded `#ifdef STATX_BTIME` on Linux) and transmits it. On the receiver, **no
+portable setter exists** (`utimensat` can only set atime/mtime), so the receiver
+deliberately does **not** apply it: it logs a debug note and continues — it never
+fails the transfer and never pretends the crtime was applied. This is the
+explicit, documented unsupported-attribute handling. On platforms without
+`statx` the flag is accepted but nothing is captured (a documented no-op).
+
+**omit-dir-times / omit-link-times:** `-O` and `-J` are **real modifiers** as of
+P7 Wave D (`🔄 → ✅ Implemented`). FastSync now preserves directory mtimes
+(captured by the scanner, transmitted in trailing `STATUS_DIR_TIMES` frame(s),
+applied only after all children and the delete/publication phases) and symlink
+mtime/owner/mode (no-follow `utimensat`/`fchownat`/`fchmodat` at link creation).
+`-O` makes the receiver skip the directory-time set; `-J` makes it skip the
+symlink timestamps (ownership/mode application is unaffected and stays governed
+by the identity opt-in). Both config booleans already crossed the wire. See the
+`-O`/`-J` rows and the Wave D note below.
+
+**-U/-N and -M interaction:** because FastSync carries all metadata (mode, uid,
+gid, mtime, and now atime/crtime) in one bounded payload that is only sent when
+metadata transmission is on, `-U` and `-N` imply metadata transmission (the
+times travel inside that payload). They do **not** enable ownership application,
+which remains opt-in strictly through the identity flags (`--numeric-ids` /
+`--usermap` / `--groupmap` / `--chown`).
+
+**Phase-4 identity notes:** `--numeric-ids`, `--usermap`, `--groupmap`, and
+`--chown` are real. They introduce a **controlled, opt-in, privilege-gated**
+ownership-application path on the receiver: plain `-M`/`--preserve` still does
+NOT apply client-supplied ownership (FastSync's deliberate conservative
+default, byte-for-byte backward compatible); ownership is only attempted once a
+client explicitly requests an ownership-affecting option. Application goes
+through an fd-relative `fchown()` in the receiver's metadata-restore path (after
+the file is fully written, before timestamps are set), so it is confined and
+symlink-safe — never a path-based `chown`. When the receiver lacks permission
+(typically non-root, e.g. the CI `nobody` user) `EPERM`/`EACCES` is logged as a
+warning and the transfer CONTINUES with exit status success, matching rsync.
+A no-op default means existing transfers are unaffected.
+
+Resolution of the destination uid/gid on the receiver: a matching
+`--usermap`/`--groupmap` rule wins; else the matching `--chown` side; else, with
+`--numeric-ids`, the transmitted numeric id is used raw (no name lookup); else a
+best-effort name lookup on the receiver's own account databases (skipped when
+the transmitted id has no name present there). `--chown` enforces the receiver
+side and is validated at parse time (malformed specs are clear errors, never a
+silent no-op).
+
+Wire/version: the config frame gained `numeric_ids`, `chown_uid_set`,
+`chown_uid`, `chown_gid_set`, `chown_gid`, and the `usermap`/`groupmap` tables
+(count-delimited lists of resolved int32 FROM/TO id pairs), so
+`PROTOCOL_VERSION` was bumped **2.10.0 → 2.11.0** (peers must match). All new
+fields cross `config_send`/`config_receive` with full symmetry and are validated
+on receive (bounded map sizes below `MAX_IDENTITY_MAP`, ids `>=` the `-1`
+sentinels).
+
+Documented divergences from rsync: because FastSync transmits only numeric
+uid/gid (not names) on the wire, name-based values (`--usermap`/`--groupmap`
+names, `--chown` names) are resolved to numbers at CLI parse time against the
+**client (sender) machine's** account databases; this reproduces rsync's
+semantics on a shared-account source/destination and is documented for a
+genuinely different destination. The interesting named-value subset is
+supported (`*` FROM wildcard, `*` TO = current user, `@N`/bare-`N` numerics); a
+lone-`@` "use the FROM value unchanged" rsync form is not implemented. Also
+unlike rsync, plain `-M` never applies ownership and `--usermap`/`--groupmap`/
+`--chown` each imply metadata preservation so the source uid/gid actually travel
+(the flags only take effect where ownership is being preserved/applied).
+
+**Phase-4 hard-links notes:** `-H`/`--hard-links` is real and introduces a
+deduplicating wire path for files whose source entries share a filesystem inode.
+On the sender, the scanner records each distinct `(st_dev, st_ino)` encounter and
+assigns it a stable, run-local link-group id (`HardLinkTable`, mutex-guarded so a
+multi-threaded scan could share one instance). The FIRST member of a group is
+transferred normally and carries the data; each later (sibling) member is
+transmitted as a payload-less `STATUS_HARDLINK` frame carrying its destination
+path, the group id, and the first member's destination-relative wire path.
+Ordering is guaranteed by forcing the sequential scanner whenever `-H` is on
+(even under `-j`/`--threads`), so the first member is always emitted — and, on the receiver's
+single write thread, installed — before any of its siblings; the receiver is
+therefore always able to link to an already-present first member, including the
+"first member already up-to-date/skipped" case (the sibling links to or copies
+the existing file). Asymmetric existence policies are handled gracefully: under
+`--existing`, if the first member's destination is absent (so it is skipped) but
+a sibling's own destination already exists, that existing sibling is left in
+place rather than the transfer aborting on the missing first member. The receiver
+installs each sibling beneath its confined root
+as an atomic hard link (temp link + rename); when `link()` fails (cross-device,
+filesystem refuses links) it falls back to a byte-identical local copy of the
+first member, never a partial/corrupt file. `--delay-updates` stages each sibling
+as a hard link to the first member's STAGED file, so publication's renames
+preserve the shared inode; `--inplace` and `--partial` are unaffected (a sibling
+is a fresh link/copy). Because a hard link shares an inode, metadata is applied
+exactly once on the first member and never re-written through the sibling (whose
+members are byte-identical by construction), so all members agree.
+
+Wire/version: `PROTOCOL_VERSION` was bumped **2.11.0 → 2.12.0** (peers must
+match). The config frame already carried the `preserve_hard_links` boolean
+(round-trips through `config_send`/`config_receive`); the only new wire element
+is the `STATUS_HARDLINK` frame described above. Incompatibilities (rejected up
+front with a distinct error on the client, and re-checked on receive): `-H` with
+`-s` chunk serialization (the chunk wire has no per-file hard-link info) and `-H`
+with `--append`/`--append-verify` (a payload-less sibling cannot be tail-resumed).
+
+**Phase-4 devices notes:** `--devices`, `--specials`, `-D`, `--copy-devices`,
+and `--write-devices` are new. They change the wire: the config frame grows three
+booleans — `preserve_specials`, `copy_devices`, `write_devices` — that CROSS the
+wire (`preserve_devices` already existed), and a new `STATUS_SPECIAL` frame (used
+by `--devices`/`--specials`/`-D`) carries a special/device entry: the destination
+path, the metadata frame (whose mode's S_IFMT bits carry the node kind, requiring
+the flags to imply metadata transmission), and two int32 `rdev` major/minor
+fields. The chunk-serialized wire (`-s`) grows a matching per-file special
+marker + rdev so `--devices/--specials` also work under `-s`. `PROTOCOL_VERSION`
+was bumped **2.12.0 → 2.13.0** (peers must match, exactly as prior phases did).
+
+**Privilege gating (the crux):** making a device node requires `CAP_MKNOD` (root).
+CI runs the integration suite as a NON-ROOT user (via setpriv), so `mknod` fails
+with `EPERM`. The receiver treats this as a graceful, logged *skip of the entry*
+returned as a success/skip outcome — the whole transfer NEVER aborts just because
+the environment cannot create the node. `mkfifo` (FIFOs) is unprivileged, so
+`--specials` FIFO creation is a real, assertable behavior under CI; sockets cannot
+be recreated by any standard filesystem call and are skipped with an explicit
+note. The "device actually created" integration assertions are guarded to run
+only as root. User-facing expectation: point `--devices` at devices and a
+non-root receiver will faithfully skip them while transferring everything else.
+
+**Confinement & validation:** a special/device node is created with
+`mknodat`/`mkfifoat` on the parent directory opened fd-relative below the receive
+root (`file_open_secure_parent`: `O_NOFOLLOW`, no `..` components, root-checked),
+so a node can never be created outside the authorized destination root and never
+through a symlinked parent. The transmitted type is derived ONLY from the
+validated S_IFMT bits of the metadata mode (char/block/FIFO honored, socket
+skipped, regular/dir rejected as an invalid special), and the transmitted rdev is
+validated both on the wire (`file_receive_special`, `chunk_deserialize`) and at
+the creation site (`file_special_rdev_valid`): a negative, oversize, or
+non-device-carrying rdev is rejected outright (receiver aborts the frame), and a
+node is never replaced over an existing directory or unrelated entry (a matching
+existing node is left in place). `--write-devices` is the deliberately restricted
+danger path: it only ever opens an existing char/block node under the confined
+root, and every failure mode (missing, non-device, write error, EPERM) is a
+warning + skip, never a system-clobbering write or an abort.
+
+**Documented divergences (honest subset):**
+- A device entry the receiver cannot create (missing `CAP_MKNOD`) is *skipped*,
+  not a transfer failure — rsync under the same conditions would error.
+- `--copy-devices` copies the device's *reported size* (typically 0 for char
+  devices/FIFOs) into a regular file and never reads an unbounded pseudo-device;
+  this is the safe, non-hanging alternative to rsync's dd-like read.
+- `--write-devices` requires the device to already exist at the destination and
+  never creates it; unsupported/inaccessible targets are skipped, not written.
+- Ownership is not applied to recreated nodes (identity `fchown` needs an fd and
+  would require opening the node); permissions and mtime are applied at
+  creation / via `utimensat`.
 
 ## 9. Symlink Handling
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `-l`, `--links` | Copy symlinks as symlinks | ⚠️ Partial | Scanner includes symlinks; target path not transmitted |
+| `-l`, `--links` | Copy symlinks as symlinks | ✅ Implemented | A symlink is transmitted as a real symlink: its target string crosses the wire (a new `STATUS_SYMLINK` frame / chunk entry type) and the receiver creates it with `symlinkat` beneath the receive root. This makes the previously-`-l`-included-but-targetless symlink handling complete. See the Phase-4 symlink-trust notes |
 | `-L`, `--copy-links` | Transform symlink to referent | ✅ Implemented | `copy_links` config field |
 | `--copy-unsafe-links` | Transform unsafe symlinks | ✅ Implemented | `copy_unsafe_links` config field |
 | `--safe-links` | Ignore symlinks outside tree | ✅ Implemented | `safe_links` config field |
-| `--munge-links` | Munge symlinks for safety | ❌ Not Implemented | |
-| `-k`, `--copy-dirlinks` | Transform symlink to dir | ❌ Not Implemented | |
-| `-K`, `--keep-dirlinks` | Treat symlinked dir as dir | ❌ Not Implemented | |
+| `--munge-links` | Munge symlinks for safety | ✅ Implemented | Sender rewrites each transmitted symlink target with a `#SYMLINK/` marker; a target that could escape the receive root (absolute or containing `..`) is never transmitted (contained/skipped); the receiver strips the marker to restore the real target. See the Phase-4 symlink-trust notes |
+| `-k`, `--copy-dirlinks` | Transform symlink to dir | ✅ Implemented | A symlink whose referent is a directory is dereferenced and recursed as a real directory; a symlink to a regular file stays a symlink. Sender-side only. See the Phase-4 symlink-trust notes |
+| `-K`, `--keep-dirlinks` | Treat symlinked dir as dir | ✅ Implemented | On the receiver, an existing destination symlink-to-a-directory is used as that directory (followed) instead of being replaced; it is followed only when it resolves to a directory that stays beneath the receive root. See the Phase-4 symlink-trust notes |
+
+**Phase-4 symlink-trust notes:** `-l/--links`, `-k/--copy-dirlinks`,
+`-K/--keep-dirlinks`, and `--munge-links` form the "symlink trust boundaries"
+row. Making all three new flags have an observable, security-sane effect
+required transmitting symlink targets, so FastSync's `-l/--links` is now real:
+a symlink-type entry carries its target on the wire (a new `STATUS_SYMLINK`
+frame for the per-file path, and a new entry type `2` in the `-s` chunk
+serializer) and the receiver creates it with `symlinkat` under an `O_NOFOLLOW`
+parent walk, never following the target. Wire changes: `STATUS_SYMLINK`,
+the chunk entry type `2`, a per-entry symlink-target string, and two new config
+booleans that CROSS the wire — `munge_links` and `keep_dirlinks`; `PROTOCOL_VERSION`
+was bumped **2.12.0 → 2.13.0** (peers must match, exactly as prior phases did).
+
+**Per-flag semantics and divergences.**
+- **`-l/--links`** copies a symlink as a symlink: the scanner `readlink`s the
+  target, the sender transmits it, and the receiver `symlinkat`s it. FastSync
+  `-l` never preserved symlink targets before (the flag was documented partial
+  and, in fact, tried to read the referent as file data); it now does, matching
+  rsync. Divergences: because the receiver enforces the symlink containment
+  predicate unconditionally, a plain `-l` sync **refuses to round-trip a
+  legitimate absolute symlink target** (it is dropped, never created pointing
+  outside the root — see the `--munge-links` note for the symmetric trust
+  boundary); a relative in-root target is copied as-is. As of P7 Wave D FastSync
+  also applies the symlink's own metadata with no-follow primitives
+  (`utimensat`/`fchownat`/`fchmodat` with `AT_SYMLINK_NOFOLLOW`), so `-J` is a
+  real omit switch rather than a no-op.
+- **`-k/--copy-dirlinks`** (sender): a symlink whose referent is a directory is
+  dereferenced and recursed into as a real directory; a symlink to a regular
+  file (or any non-directory) is kept as a symlink. This is rsync's `-k`. When
+  `-L/--copy-links` or `--safe-links`/`--copy-unsafe-links` are active, their
+  (dereference) semantics take precedence, so `-k` is subsumed exactly as in
+  rsync.
+- **`-K/--keep-dirlinks`** (receiver, crosses the wire): when a directory is to
+  be created (on-demand parent creation for a child write) and the destination
+  path is already an existing symlink that resolves to a directory *within* the
+  receive root, that symlinked directory is used (followed) instead of being
+  replaced by a real directory; new entries are written beneath it. The follow
+  is confined: it only happens where `realpath` of the symlink resolves to a
+  still-within-root real directory, so a malicious link pointing outside the
+  root is never followed. Scope: `-K` acts on the write path (parent/`mkdir`
+  creation); the delete walker still never follows symlinks (a documented
+  divergence for `--delete` over an existing symlinked dir). Without `-K` the
+  destination symlink is not followed (the O_NOFOLLOW walk fails the write),
+  which is the safe default.
+- **`--munge-links`** (sender security rewrite; crosses the wire so the receiver
+  unmunges): every transmitted symlink target is prefixed with the marker
+  `#SYMLINK/`; the receiver strips the marker (only when the negotiated
+  `munge_links` policy is on — a plain `-l` run never strips the prefix, so a
+  source symlink that genuinely begins with `#SYMLINK/` round-trips verbatim)
+  and restores the exact real target. The trust boundary is **symmetric and
+  enforced receiver-side**, independent of the sender: `file_symlink_at_secure`
+  refuses any target that `file_symlink_target_contained` rejects (absolute
+  `/...` or relative with a `..` component), and `file_save_to_disk_full`
+  contains such an entry (skipped) rather than materializing it. A deliberate confinement trade-off: because the receiver
+  enforces containment unconditionally, a plain `-l` (no `--munge-links`) sync
+  *refuses to round-trip a legitimate absolute symlink target* — such target is
+  dropped, never created pointing outside the root. This is a stricter subset of
+  rsync: rsync stores munged targets on the RECEIVING side and depends on both
+  ends running `--munge-links`; FastSync additionally enforces the containment
+  predicate at the receiver regardless of what the sender transmitted. When no
+  symlink is being transmitted (`-l`/`-k`/`-a` off) `--munge-links` has nothing
+  to rewrite and is inert. -*K/`--keep-dirlinks` policy is installed per
+  connection at config-accept (stable for the whole transfer, never racy under
+  `-j`/`--threads`), and only ever follows an in-root symlink-to-directory.*
+
+**Compatibility (byte-identical when all three are absent):** `-k`, `-K` and
+`--munge-links` are opt-in. Without them the scanner's link handling, the wire
+frames, and the receiver's writes are unchanged for every other option set, so a
+run that previously worked continues to behave identically. `-l/--links` itself
+now transmits targets (the prior behavior was broken/partial); its status moved
+`⚠️ Partial → ✅ Implemented`.
 
 ## 10. Sparse & Device
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `-S`, `--sparse` | Sparse block handling | ⚠️ Partial | Flag is accepted, but full hole preservation is not implemented |
-| `--preallocate` | Allocate dest files before writing | ❌ Not Implemented | |
+| `-S`, `--sparse` | Sparse block handling | ✅ Implemented | Phase 7 Wave B: real hole preservation with no wire change. The receiver's sparse-aware writer (`write_all_sparse`, next to `write_all` in `src/shared/file.c` and `src/shared/file_store.c`) walks the in-memory file image and emits any all-zero run ≥ 4096 bytes as a hole via `lseek(SEEK_CUR)` (the pre-size `ftruncate` guarantees the offset bookkeeping and logical size), `ftruncate(size)` after the last run pins the final size even with a hole tail. Wired into both the atomic temp+rename store and `--inplace` when `sparse` is set; the non-sparse path is byte-identical to before. **Sparse wins over `--preallocate`** (posix_fallocate is skipped when sparse is set, so the holes are not re-allocated). Interplay note: under `--partial` a retained sparse temp already has the full logical size (trailing content is holes), so `--append`'s "shorter destination" resume does not re-run; the retained file is still valid and a normal re-transfer (or `-W`/delta) repairs it — documented so the combination is never surprising |
+| `--preallocate` | Allocate dest files before writing | ✅ Implemented | The receiver preallocates the destination file's full expected space before any data is written, so a transfer that would overflow disk fails fast at allocation time (a clean error, not a half-written file) and the file is laid out contiguously, avoiding fragmentation. Crosses the wire (the config frame carries a `preallocate` boolean; `PROTOCOL_VERSION` bumped **2.10.0 → 2.11.0**, peers must match) so the sender knows the receiver will preallocate and the receiver performs it. **Allocation approach:** `posix_fallocate()` is preferred because it reserves *real* disk blocks (true fail-fast on ENOSPC), falling back to plain `ftruncate()` only when the filesystem reports the allocation is unsupported (`EOPNOTSUPP`/`ENOSYS`); `ftruncate` still extends the logical size so the intent degrades gracefully. **Fallback/error semantics:** `EOPNOTSUPP`/`ENOSYS` → clean fallback to `ftruncate` (best-effort, preallocates the logical size and never fails a transfer on filesystems that lack `posix_fallocate`); a genuine allocation failure (`ENOSPC`/`EDQUOT`/`EFBIG`/…) aborts the file/receive with a distinct `preallocate failed ... transfer aborted` error — it does **not** fall back to a normal non-preallocated write, preserving the fail-fast purpose. **Size-known requirement:** preallocation only runs when the final size is already known up front (the normal regular-file case); unknown-length data is skipped (never failed). **Orthogonality:** applies uniformly across the atomic temp+rename store path, `--inplace`, `--partial`/`--partial-dir`, `--delay-updates` (the staged temp file is preallocated before data flows) and the `--link-dest` copy fallback; it neither implies nor conflicts with `-s`, `--append`, or delta. rsync-divergence: rsync signals that `--preallocate` is ignored with `--sparse`; FastSync gives **sparse precedence** — when both are set, `posix_fallocate` is skipped so the holes the sparse writer creates are not re-allocated (the `ftruncate` presize sizing stays), matching the intent of "sparse wins". See the Phase-4 preallocate notes below |
+
+**Preallocate notes (Phase 4, preallocate wave):** `--preallocate` is implemented as a real receiver-side allocation of the destination file's space before data is written. It is a plain boolean config flag that crosses the wire (serialized in the config frame's selection-options block, mirroring `--inplace`/`--append`/`--force`), so the run requires matching ends: `PROTOCOL_VERSION` was bumped **2.10.0 → 2.11.0** (peers must match or the version check fails). The allocation is performed on the exact destination fd, immediately after it is opened, before any bytes are streamed; `posix_fallocate` (and the `ftruncate` fallback) leave the fd's file offset untouched, so the subsequent data write at offset 0 is unaffected and complete. Because FastSync writes each file's byte payload in one in-memory batch, the "full expected size" is exactly the known `data_size`, which is what gets preallocated. Unknown-length/streamed payloads are skipped rather than failed. A failed allocation logs a distinct `preallocate failed` error and aborts the file (the atomic temp is unlinked, the inplace target is left untrimmed) so the run fails cleanly and never silently degrades to a non-preallocated write — preserving rsync's fail-fast intent on a full disk.
+
 
 ## 11. Checksum & Comparison
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `--checksum` | Skip based on checksum | ✅ Implemented | With `--incremental`, compares xxHash64 content checksums; `-c` remains compression |
-| `--checksum-choice=STR` | Choose checksum algorithm | ❌ Not Implemented | xxHash used internally |
-| `--compare-dest=DIR` | Compare dest files relative to DIR | ❌ Not Implemented | Removed because it had no effect |
-| `--copy-dest=DIR` | Include copies of unchanged files | ❌ Not Implemented | Removed because it had no effect |
-| `--link-dest=DIR` | Hardlink to files when unchanged | ❌ Not Implemented | Removed because it had no effect |
-| `--fuzzy`, `--no-fuzzy` | Find similar file for basis | ❌ Not Implemented | |
+| `--checksum` | Skip based on checksum | ✅ Implemented | With `--incremental`, compares per-file whole-file content digests to skip unchanged files. The digest algorithm is `xxh64` with seed 0 by default and is selectable via `--checksum-choice`/`--cc` (xxh64/xxhash or md5) and `--checksum-seed=NUM` (see those rows); `-c` remains compression |
+| `--checksum-choice=STR`, `--cc=STR` | Choose checksum algorithm | ✅ Implemented | Real algorithm selection for the per-file whole-file digest used by the `--incremental`/`--checksum` handshake and by the basis-dir content verification. FastSync genuinely supports `xxh64` (the default, exact xxHash64, seeded by `--checksum-seed`) and `md5` (via OpenSSL EVP); `xxhash` is accepted as rsync's spelling of xxHash64. Any other name (md4/sha1/sha256/crc32/none/…) is rejected with a clear error at parse time — never a silent no-op. `--cc` is the alias (`--cc=ALG` and space forms both parse). The algorithm id and seed cross the wire with the config frame, so the receiver hashes its on-disk old file with the SAME algorithm+seed the sender used and both agree on a match; the sender's digest and the receiver's comparison live in the per-file `STATUS_CHECK` handshake, which now carries a length-prefixed, bounded (1..16 byte) digest instead of a fixed 64-bit value, and the receiver pins the received length to the negotiated algorithm's digest length (defense-in-depth: a mismatched/malicious length only forces a safe re-transfer). Note: `md5` is a FIPS-non-approved algorithm, so under an OpenSSL build with FIPS mode enabled `--checksum-choice=md5` fails loudly rather than silently falling back. Protocol/layout: `PROTOCOL_VERSION` bumped **2.9.0 → 2.10.0** (peers must match). Defaults preserve the pre-existing behavior byte-for-byte (xxh64, seed 0). Like rsync, the choice only takes effect where a whole-file digest is actually computed (`--checksum` on, or a basis-dir flag); it does not itself enable `--checksum`. Closely-related divergence: the delta BLOCK strong checksum (§11 delta) stays xxHash32 — `--checksum-choice` selects only the whole-file digest, matching rsync where the per-block checksum is independent of the whole-file checksum choice |
+| `--compare-dest=DIR` | Compare dest files relative to DIR | ✅ Implemented | DIR is a receiver-side basis relative to the destination root (confined below it; absolute/`..`/`.` rejected, `//` collapsed and trailing `/` dropped). On the receiver's per-file check (implies `--incremental`) an exact match = same size + mtime (unless `--size-only`; `-I` disables matching) **and** equal xxHash64 of the sender's file; a match suppresses the data transfer. compare-dest never copies: it only skips a file the destination does **not** already hold (sparse destination, rsync parity), and is consulted before the normal delta/full paths. Repeatable; searched in command-line order, first match wins. Divergences: when the destination already holds a *different* version rsync deletes it but FastSync instead transfers the data (keeps the mirror complete; never deletes without `--delete`); attribute-only differences on a match are not re-applied (data is skipped so the sender never sends metadata); content is verified by xxHash64, stricter than rsync's default quick check. Sizing: FastSync's whole-file payload limit is 256 MiB on **every** transfer path (not basis-specific); rsync applies basis dirs to arbitrary sizes, so FastSync refuses a basis run whose source contains a larger file up front with a clear error before any transfer. Wire: a basis-count field is always present on the config frame (protocol 2.9.0, so clients and servers must both be 2.9.0) |
+| `--copy-dest=DIR` | Include copies of unchanged files | ✅ Implemented | Same basis rules as `--compare-dest`, but an exact match materializes a **local copy** of the DIR file into the destination (via the normal atomic temp+rename store path, so `--existing`/`--ignore-existing`/`--update`/`--backup`/`--delay-updates` all still apply) instead of transferring data. Repeatable; command-line order = priority. Content is xxHash64-verified before the copy. Divergences: a basis-hit destination keeps the basis file's own mode/uid/gid and mtime (the sender sends no metadata on a skip), so with `--size-only` its mtime can differ from the source and attribute-only differences are copied with the basis attributes rather than rsync's "copy + fix attributes". Requires `--incremental` (implied); incompatible with `-s`. Wire: protocol 2.9.0 |
+| `--link-dest=DIR` | Hardlink to files when unchanged | ✅ Implemented | Same basis rules as `--copy-dest`, but an exact match installs an atomic **hard link** to the DIR file (temp hard link + rename) so no data or disk space is used; where the link is impossible (basis on another filesystem, filesystem refuses links) it falls back cleanly to a byte-identical local copy, never a corrupt/partial file. `--delay-updates` stages the link and publishes by rename, so the final entry stays a real hard link. Repeatable (searched in command-line order, first match wins). Content is xxHash64-verified before linking. Divergences and caveats: an already up-to-date destination file is not re-linked to a basis file (only files that would otherwise be written are linked); a link keeps the basis inode's own mode/uid/gid and mtime — metadata is never written through the shared inode (that would mutate the basis file), so a later `--inplace` run that rewrites such a destination path **will mutate the basis snapshot** through the shared inode (use `--copy-dest` when the destination must stay independently writable); with `--size-only` the linked mtime can differ from the source; a `--remove-source-files` source satisfied by a basis dir is treated as skipped and therefore **retained** (never removed); basis dirs are excluded from `--delete`. Requires `--incremental` (implied); incompatible with `-s`. Wire: protocol 2.9.0 |
+| `-y`, `--fuzzy`, `--no-fuzzy` | Find similar file for basis | ✅ Implemented | `-y/--fuzzy` is a pure bandwidth optimization on the existing receiver-driven delta path: when a file must be transferred and the destination holds no usable content at the exact path (file absent, or the destination file is outside the delta engine's size bounds), the receiver searches the SAME destination directory for an existing regular file whose basename is similar to the incoming name and uses it as the delta basis, so the sender transmits only the differences instead of the whole file. The output is always byte-exact regardless of which (or whether any) basis is chosen. Decision location: the receiver performs the candidate search inside `receive_incremental_check` and sends the normal `STATUS_DELTA_SIGNATURE`; the sender never learns the basis was a different file, so no new frame type or sender logic was needed — only the config frame grew a `fuzzy` boolean, so `PROTOCOL_VERSION` was bumped **2.8.0 → 2.9.0** (peers must match). Similarity heuristic (deterministic, simpler than rsync's deliberately-fuzzy matching, and documented precisely): candidates are the target's sibling entries in its destination directory, opened `O_NOFOLLOW`/`AT_SYMLINK_NOFOLLOW` under the confined root (symlinks never followed; nothing outside the destination root is ever read or hashed); dotfiles, directories, the target's own name, and the `.fastsync-stage`/temp scratch names are excluded; like the ordinary delta path, the block signature the receiver transmits is derived from on-disk content it may not otherwise send, so a negotiated `--fuzzy` run exposes the destination's sibling files (at block granularity) to the sender as a known-plaintext oracle — the same information class as the normal delta handshake over the file being replaced; the size gate is the delta engine's own bounds (both files ≥ 16 KiB, ≤ `--delta-max`, ratio ≤ 10×) rather than rsync's ~1.5× size window; the name gate is a Levenshtein edit distance between the basenames accepted only when ≤ half the length of the longer basename; the single best candidate (smallest distance, tie-break size closest to the incoming file then lexicographically smaller basename) is read; the directory scan is capped at 4096 entries so a pathological directory cannot stall a transfer. When fuzzy applies: only to files the receiver would otherwise send whole — the destination's own file is always preferred as the delta basis when it exists and fits the delta size bounds, so fuzzy does NOT replace an existing-but-different destination basis; FastSync's 10× delta size-ratio bound means an existing destination file that is too far away in size still lets the fuzzy search run. When no similar candidate exists the transfer falls back to the normal whole-file transfer. rsync-divergence note: rsync's own matching uses a fuzzy name/size rule set; FastSync implements the closest safe deterministic approximation above. Because FastSync's delta machinery is off by default (rsync's is on), `--fuzzy` implies `--incremental` + `--delta` (unless `--whole-file`/`-W` or an explicit `--no-delta` switched delta off, in which case fuzzy is inert — matching rsync where `--whole-file` makes fuzzy irrelevant). Unlike the basis-dir options, `--fuzzy` honors an explicit `--no-incremental` (it does not force the handshake back on); an explicit `--no-incremental` also suppresses the delta implication so no invalid `--delta requires --incremental` config results. `--no-fuzzy` negates it. All surrounding semantics are untouched: a fuzzy-reconstructed file is stored as a normal file, so `--remove-source-files`, itemize/`-i`, `--stats`, `--backup`, `--delay-updates`, `--existing`/`--ignore-existing`/`--update` behave exactly as for a whole-file transfer (the fuzzy delta does not skip the file) |
 
 ## 12. Compression
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `-z`, `--compress` | Compress file data | 🔀 Alt Arg | Always uses zstd (rsync supports multiple algorithms) |
-| `--compress-choice=STR` | Choose compression algorithm | ❌ Not Implemented | Removed because it had no effect; FastSync always uses zstd |
-| `--compress-level=NUM` | Set compression level | ✅ Implemented | 1-22, default 5 |
-| `--compress-threads=NUM` | Set compression threads | ❌ Not Implemented | |
-| `--skip-compress=LIST` | Skip compress for suffixes | ❌ Not Implemented | Internal skip for hardcoded types; not user-configurable |
+| `-z`, `--compress` | Compress file data | ✅ Implemented | Always uses zstd (rsync supports multiple algorithms — a documented divergence, selectable via `--compress-choice`). Phase 7 Wave A: `-z` is now the compression short form; `-c` is rsync's `--checksum` |
+| `--compress-choice=STR`, `--zc=STR` | Choose compression algorithm | ✅ Implemented | FastSync supports `zstd` and `none` |
+| `--compress-level=NUM`, `--zl=NUM` | Set compression level | ✅ Implemented | 1-22, default 5 |
+| `--compress-threads=NUM` | Set compression threads | ✅ Implemented | `compression_threads` config field (client-only; does not cross the wire). Sets the number of worker threads used by the zstd compression pool to NUM (1..64; 0/garbage/oversized rejected up front). Accepted in both `--compress-threads=NUM` and two-argument `--compress-threads NUM` forms. Composes with `-z`/compression; under the `-j`/`--threads` multithreaded pipeline it parallelizes compressed chunk encoding. See test_tcp.py `-z --compress-threads=2` and test_client_cli.c |
+| `--skip-compress=LIST` | Skip compress for suffixes | ✅ Implemented | Comma-separated, case-insensitive suffix list; empty list skips none; incompatible with FastSync chunk serialization (`-s`) |
 
 ## 13. Connectivity
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `-e`, `--rsh=COMMAND` | Remote shell to use | ❌ Not Implemented | Removed; SSH invokes `ssh` directly |
-| `--rsync-path=PROGRAM` | rsync binary on remote | ❌ Not Implemented | Removed; use `--fastsync-server-path` |
-| `--port=PORT` | Alternate daemon port | ✅ Implemented | `server_port` config field |
-| `--sockopts=OPTIONS` | Custom TCP options | ❌ Not Implemented | |
-| `--blocking-io` | Use blocking I/O for remote shell | ❌ Not Implemented | |
-| `--outbuf=N\|L\|B` | Set output buffering | ❌ Not Implemented | |
-| `--address=ADDRESS` | Bind address for outgoing socket | ❌ Not Implemented | Removed because it had no effect |
-| `-4`, `--ipv4` | Prefer IPv4 | ❌ Not Implemented | Removed because it had no effect |
-| `-6`, `--ipv6` | Prefer IPv6 | ❌ Not Implemented | Removed because it had no effect |
+| `-e`, `--rsh=COMMAND` | Remote shell to use | ✅ Implemented | `-e`/`--rsh` (and `--rsh=COMMAND`) select the remote-shell program used to build the SSH child argv, overriding the default `ssh`. The command is whitespace-split into the leading argv words so rsync's `-e "ssh -p 2222"` works; the standard `-o` family, an optional `-p` port, `user@host` and the quoted remote command (`fastsync-server --stdio`) follow. Stored in the `rsh_command` config field. **Client-only, never crosses the wire** (it is a launch concern, not a handshake property) |
+| `--rsync-path=PROGRAM` | rsync binary on remote | ✅ Implemented | Alias for `--fastsync-server-path`: both write the `fastsync_server_path` config field used as the remote-side server program (always quoted as one remote-shell word), which CROSSES the wire as before. Kept separate from `--rsh`, which names the local connecting program |
+| `--port=PORT` | Alternate daemon port | ✅ Implemented | rsync's daemon-port flag maps to the client-side `server_port` config field: a client connects to a TCP/TLS server (incl. `host::module/path` daemon destinations) with `--server-port`, and the `fastsync-server --daemon` listener's port is taken from its config's `port` key (default 873) or overridden by `--dparam port=` / `-p` |
+| `--sockopts=OPTIONS` | Custom TCP options | ✅ Implemented | Comma-separated allowlist of `OPT=VAL` applied via `setsockopt` after `socket()` before `connect()`/`bind()`. Only `TCP_NODELAY`, `SO_KEEPALIVE`, `SO_REUSEADDR` (0/1) and `SO_RCVBUF`/`SO_SNDBUF` (byte count) are accepted; an unknown option name or a bad value is rejected up front, never silently ignored. A value is required for every option (`OPT=VAL`; a bare name is an error). Applied to the outgoing TCP and TLS client socket; absent by default. `SockOptEntry`/`sockopts` config fields. Local socket concern: never crosses the wire |
+| `--blocking-io` | Use blocking I/O for remote shell | ✅ Implemented | With `--blocking-io` the SSH-transport socketpair socket is left without `SO_RCVTIMEO`/`SO_SNDTIMEO`, so the transfer blocks naturally; by default it gets the same read/write timeout as the TCP transport (see `--timeout`). `blocking_io` config bool. **Client-only, never crosses the wire** |
+| `--outbuf=N\|L\|B` | Set output buffering | ✅ Implemented | `N` (none/unbuffered) → `_IONBF`, `L` (line) → `_IOLBF`, `B` (block, the default) → `_IOFBF` via `setvbuf` on stdout and stderr. Garbage values are rejected. `outbuf` config field (`OutbufMode`). **Client-only, never crosses the wire** |
+| `--address=ADDRESS` | Bind address for outgoing socket | ✅ Implemented | Binds the outgoing client socket to a local source address before `connect()` (resolved with the same `-4`/`-6` family hints as the destination). Local socket concern: never crosses the wire |
+| `-4`, `--ipv4` | Prefer IPv4 | ✅ Implemented | Forces `AF_INET` in the `getaddrinfo` hints for client destination/source resolution and the server bind (see the Phase 5, Wave B note). Mutually exclusive with `-6` |
+| `-6`, `--ipv6` | Prefer IPv6 | ✅ Implemented | Forces `AF_INET6` in the `getaddrinfo` hints for client destination/source resolution and the server bind. Mutually exclusive with `-4` |
+| `--remote-option=OPT`, `-M` | Send an option only to the remote side | ✅ Implemented | Each value is appended to the remote server invocation over SSH as an individually single-quote-escaped shell word in `ssh_build_remote_command()`. Values are validated (non-empty, no control characters) and shell metacharacters cannot break out of the quoting (`;`, `&`, `|`, <code>`</code>, `$`, `(`, `)`, quotes are neutralized), so a value cannot inject an arbitrary remote command and a subsequent `--` on the client line cannot be turned into one. The options never cross the binary config frame. Phase 7 Wave A: the short `-M` form is now available (as `-M OPT` and `-M=OPT`), matching rsync; metadata mode moved to long-only `--preserve` |
 
 ## 14. Daemon Mode
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `--daemon` | Run as rsync daemon | ❌ Not Implemented | Removed because it had no effect |
-| `--config=FILE` | Alternate rsyncd.conf file | ❌ Not Implemented | Removed because it had no effect |
-| `--dparam=OVERRIDE` | Override global daemon config | ❌ Not Implemented | |
-| `--no-detach` | Don't detach from parent | ❌ Not Implemented | |
-| `--password-file=FILE` | Read daemon password from file | ❌ Not Implemented | |
-| `--early-input=FILE` | Use FILE for daemon early exec | ❌ Not Implemented | |
+| `--daemon` | Run as rsync daemon | ✅ Implemented | Wave A: a real persistent listener. `fastsync-server --daemon --config FILE` (plus `--no-detach` to stay foreground; without it the listener detaches to the background after binding) reads a FastSync-native module config file and serves each connection confined to the requested module's `path` root (never a client-chosen root; every client-chosen-ownership/super-user request (`--numeric-ids`/`--chown`/`--usermap`/`--groupmap`/`--fake-super`/`--copy-as`/explicit `--super`) is refused unless the module opts in with `client owner = yes`, and the operator `--no-super` veto is honored). TCP/TLS via the existing `--tls` stack; plaintext still requires `--allow-unauthenticated` (same secure default as the standalone server). Client destinations use rsync's `host::module/path` form. Wire/protocol: the config frame gained a trailing daemon-module string and `PROTOCOL_VERSION` was bumped **2.14.0 → 2.15.0** (see the Daemon Mode notes below). Daemon mode is built in FastSync's own protocol/config grammar, not rsync's SMB/daemon option encoding |
+| `--config=FILE` | Alternate rsyncd.conf file | ✅ Implemented | Wave A: selects the daemon config file. Default when omitted (in `--daemon` mode): `~/.config/fastsync/fastsyncd.conf` if it exists, else `/etc/fastsyncd.conf`. The grammar is FastSync-native (documented in the Daemon Mode notes below) and strictly rejects unknown keys so a typo can never silently change what a module serves; requires `--daemon` |
+| `--dparam=OVERRIDE` | Override global daemon config | ✅ Implemented | Wave A: overrides one global scalar from the command line (`--dparam port=8734` and `--dparam=KEY=VALUE` both work). Limited to the global scalar keys the grammar defines (`port`, `motd file`, `address`); keys are case-insensitive and unknown keys/invalid values are rejected. Requires `--daemon` |
+| `--no-detach` | Don't detach from parent | ✅ Implemented | Wave A: with `--daemon`, keeps the listener in the foreground (what integration tests use). Without it the daemonizes (fork/setsid, stdio redirected to /dev/null) after the listening socket is bound. Requires `--daemon` |
+| `--password-file=FILE` | Read daemon password from file | ✅ Implemented | A7 daemon auth. Client: `--password-file` supplies `user:password` for a `host::module/path` destination (the username is taken from this file, so `user@host::module` stays rejected); the literal password is held client-side only for the SCRAM handshake and wiped at teardown. Server (`fastsync-server --daemon --password-file FILE`): the salted-PBKDF2 verifier store that modules with `auth users` are verified against. **Neither the password nor any replayable bearer value crosses the wire or is stored server-side** — the store holds a per-user salt plus derived keys, and the daemon proves the secret with a per-connection nonce challenge. The file must be private to its owner: both the client and server verify the exact inode they read (open-then-`fstat`, so the check cannot be raced) and refuse a `--password-file`/`--early-input` that is not owned by the current user or grants any group/other permission bit (mode 0600), mirroring the TLS private-key check. A process-substitution pipe (`--early-input <(vault ...)`) is still accepted when it satisfies those checks. See the Daemon Mode notes below for the file formats and the plaintext/TLS caveat |
+| `--early-input=FILE` | Use FILE for daemon early exec | ✅ Implemented | Server-only (requires `--daemon`): a second credential-store file, same new-format grammar as `--password-file`, read before the listener accepts connections (a secrets-manager / process-substitution source). Its entries layer over `--password-file`: byte-identical verifiers dedupe, a conflicting verifier for the same user is a startup error. A daemon whose modules declare `auth users` must be given at least one of the two, or it refuses to start (fail closed) |
+| `--hash-credentials=FILE`, `--iterations N` | Hash a plaintext credential file | ✅ Implemented | Server-only offline tool (A7): reads the `user:password` lines of FILE (same owner-only 0600 check) and prints one new-format store line per entry to stdout, then exits. `--iterations` sets the PBKDF2 work factor (default 600000, range 100000–10000000). Dependency-free and does not run a listener. Use its output as `--password-file` for `--daemon`. There is no auto-upgrade: a legacy store line is hard-rejected by the loader and must be regenerated |
+
+**Daemon Mode notes (Wave A protocol 2.15.0; A7 auth protocol 2.19.0; MOTD no bump):** FastSync daemon mode is supported in FastSync's own protocol/config grammar, not rsync's SMB/daemon option encoding.
+
+- **Config grammar** (`fastsyncd.conf`): line-based; an implicit global section first, then `[module]` sections. Keys are case-insensitive, values are trimmed and may be wrapped in one layer of double quotes (`path = "/srv/my dir"`). `#` and `;` at the start of a line (after leading whitespace) are full-line comments; inline comments and `\` continuations are not supported. Lines are bounded (4096 chars). Global keys: `port` (default 873), `motd file` (the daemon sends its bounded, escaped content to a client after the module gate/auth accepts, unless the client passes `--no-motd`), `address` (optional bind address). Module keys: `path` (required; the daemon-side authorized root for that module), `read only` (yes/no/true/false/1/0, default no), `client owner` (yes/no/true/false/1/0, default no; opts the module into client-chosen ownership — see below), `auth users` (comma list). **Unknown keys and malformed lines are parse-and-reject errors** (never silently ignored), so a typo cannot change what a module serves.
+- **Module selection & confinement:** the client requests a module with an rsync-style `host::module[/path]` destination. The module name crosses the wire as a trailing string on the config frame (bumping `PROTOCOL_VERSION` 2.14.0 → 2.15.0; the bump is required because the config-frame layout changed and the strict same-version handshake is what prevents a peer from desynchronizing on the new trailing field). The daemon looks the module up in ITS OWN config and uses the module's `path` as the authorized root through the exact same `configure_authorization` confinement the standalone server applies to `--destination-root` (`file_open_secure_parent`, `has_path_traversal`, `path_is_within`); the client never supplies the root, every client-chosen-ownership/super-user request is refused unless the module declares `client owner = yes` (the daemon's per-module opt-in, see below), and the operator `--no-super` veto forces super-user activities off for every daemon connection. The client's `/path` part is relative inside the module and is rejected if absolute or if it contains `..`. Unknown modules are refused before any data moves (the run fails cleanly at the config handshake). An absolute destination and a module request against a non-daemon server are also refused.
+- **`client owner` (client-chosen-ownership opt-in):** by default a daemon module refuses every request that would let the client pick an owner or ask for super-user activities — `--numeric-ids`, `--chown`, `--usermap`/`--groupmap`, `--fake-super`, `--copy-as`, and an explicit `--super` — at the config handshake (before `STATUS_OK`), because a daemon has no per-module opt-in for client-chosen ownership and any anonymous client could otherwise force arbitrary owner ids inside the module root. `client owner = yes` opts a single module in, allowing those requests within that module's root (the standalone listener and the SSH `--stdio` server always honor them for their single operator-authorized root). Without the opt-in the daemon also forces super-user **device** activity off for that connection — char/block device-node creation (`--devices`) and `--write-devices` — even under the default `AUTO` mode, so a non-opted module can never be made to `mknod` or write a raw device; those entries are skipped (not refused) so an ordinary `-a` push still succeeds without device nodes. The opt-in does **not** lift the privilege requirement: `--copy-as` still needs a root receiver, and the operator `--no-super` veto still forces super-user activities off for every connection. The daemon logs a prominent startup warning for each `client owner = yes` module so the operator's deliberate choice is visible.
+- **`read only` safe default:** every network transfer FastSync currently supports is a push that writes under the module root, so a `read only` module refuses the connection (clear server log "module is read only"; the client exits non-zero, nothing is transferred). A future pull/list operation can be opened up when it exists; the knob is already stored.
+- **`auth users` (A7 SCRAM-SHA-256 authentication):** a module that declares `auth users` requires the client to present credentials. The config frame carries ONLY the username; the daemon answers an auth-required module with `STATUS_AUTH_CHALLENGE` (PBKDF2 iteration count, 16-byte salt, 32-byte server nonce), the client answers with `STATUS_AUTH_RESPONSE` (fresh 32-byte client nonce + a 32-byte ClientProof), and the daemon accepts only when the proof verifies **and** the username is **on the module's `auth users` list** and has a store entry, replying `STATUS_AUTH_OK` with a 32-byte ServerSignature the client verifies before proceeding. Verification is constant-time over fixed 32-byte keys (the compare runs even for a miss), username membership uses a constant-time full-length scan, and an unknown/off-list user still receives a challenge and runs the same math against a dummy verifier: a deterministic per-username salt (`HMAC-SHA256(store dummy key, username)`), the store-wide uniform iteration count and dummy keys. Re-probing the same unknown username therefore yields an identical salt and iteration count while a different username yields a different salt, so there is no user-enumeration or timing oracle. The daemon logs the username but **never the password, proof or keys**. A module WITHOUT `auth users` stays open (legitimate rsync configuration); credentials sent to such a module are ignored. Read-only is orthogonal: even a correctly authenticated push to a `read only` module is still refused (all FastSync network transfers write). Fail-closed policy: a daemon whose config declares `auth users` on any module refuses to start unless a credential store was given (`--password-file` and/or `--early-input`); a missing or empty store is never silently treated as "open". A failed handshake (missing credentials, unknown/off-list user, wrong proof or malformed data) yields a single generic `STATUS_AUTH_FAILED` and the daemon closes before any data moves. The dummy key is persisted in an owner-only `<store_path>.dummykey` sidecar (auto-created on first load, mode 0600) so the dummy salt stays stable across daemon restarts, closing the restart-gated enumeration channel. The sidecar is secret material and must be protected like the credential store (owner-only 0600, included with the store in backups and rotation). It must be preserved across restarts for that guarantee; if it cannot be created (a process-substitution/FIFO store path such as `/dev/fd/N`, a read-only filesystem, a missing directory, or a create/write/fsync/link/fchmod failure), the daemon logs a warning and uses a transient per-run key, so unknown-user challenges change across restarts and the cross-restart guarantee does not hold for that deployment. One residual is accepted: the store iteration count is observable pre-auth by design, since the miss path must match a hit. **Transport policy (hardening A7-3/S1):** an auth-required module accepts credentials only when either (a) the connection is an encrypted, verified TLS connection whose client certificate matches `--client-cn`, or (b) the connection is plaintext from a loopback TCP peer **and** the operator explicitly passed `--allow-unauthenticated`. A remote plaintext peer, and a loopback plaintext peer without that flag, are refused at the config gate before any challenge is sent; `--allow-unauthenticated` never permits remote plaintext auth (remote peers still require verified TLS). Daemon modules are a `--daemon`-only feature — the SSH `--stdio` path never loads a daemon config and is not an auth transport for them. Because the loopback allowance trusts whichever peer the kernel reports as `127.0.0.1`, it assumes nothing relays remote connections to the daemon: a local TCP forwarder or TLS-terminating proxy in front of an auth-module listener makes remote clients appear as loopback and bypasses the mutual-TLS identity check, so do not front an auth-module listener with such a relay.
+- **Credential store format:** server `--password-file`/`--early-input` files are line-based `user:$fastsync$1$pbkdf2-sha256$<iters>$<salt_b64>$<stored_key_b64>$<server_key_b64>`, one per line (standard base64; 16-byte salt, 32-byte keys; `iters` in `[100000, 10000000]`, default 600000). Every entry in the resulting store must agree on `iters` (a store whose entries disagree, or where a layered `--early-input` disagrees with `--password-file`, is rejected). Generate lines with `fastsync-server --hash-credentials FILE [--iterations N]`; the emitted lines are secret material, so redirect them to an owner-only (mode 0600) file (the tool warns on stderr if stdout is a group/other-accessible regular file). Blank lines and lines starting with `#`/`;` are comments; the parser is strict (a malformed line fails the whole load, so a typo can never let a different set of users in). **The legacy `user:SHA256HEX` form is hard-rejected** with an actionable "legacy" error; there is no auto-upgrade, so a replayable bearer digest can never be loaded by a 2.19.0 daemon. The client `--password-file` holds `user:password` on its first meaningful line (the literal password, used only for the handshake then burned); keep both files readable only by their owner (mode 0600). Per-username wire length is bounded (256 chars) and every decoded salt/key length is validated. Loading the store also maintains an owner-only `<store_path>.dummykey` sidecar (auto-created, mode 0600, exactly 32 bytes) holding the store-wide dummy key that shapes unknown-user challenges; persist it across daemon restarts so those challenges stay stable, and treat a sidecar with the wrong owner, a mode other than exactly 0600, the wrong size or the wrong type as a fatal load error (fail closed). If the sidecar cannot be created (e.g. a process-substitution store path such as `/dev/fd/N`, a read-only filesystem, a missing directory, or a create/write/fsync/link/fchmod failure), the daemon logs a warning and uses a transient per-run key, so the cross-restart stability guarantee does not hold there.
+- **Plaintext caveat:** an auth-required module is refused, **before any challenge is sent**, unless the connection is encrypted and verified TLS whose client certificate matches the server's `--client-cn`, or it is plaintext from a loopback TCP peer **and** the operator passed `--allow-unauthenticated`. A remote plaintext peer, and a loopback plaintext peer without that flag, never receive a challenge, and `--allow-unauthenticated` never permits remote plaintext auth (remote peers still require verified TLS). On the loopback plaintext transport that remains permitted, a local sniffer could still read the challenge and response and mount an **offline dictionary attack** against a weak password, so use `--tls` for any real deployment. `--client-cn` matches the certificate CN only (not a subjectAltName), which is acceptable for a private CA. Clients sending daemon credentials with `--password-file` to a non-loopback daemon must use `--tls`; the client rejects such a destination before any network I/O. Unlike the old challenge-less exchange there is **no replay**: the proof is bound to the fresh per-connection server nonce, so a captured `STATUS_AUTH_RESPONSE` cannot be reused on another connection (an integration test proxies the daemon and proves this). TLS client-CN (`--client-cn`) is an independent transport identity check and composes with password auth; because `--tls` already mandates `--client-cn`, a TLS auth connection always verifies the client CN, so both checks necessarily apply together on such a connection.
+- **Wire/protocol:** the config-frame auth block is now `[int present][str_redacted username]` (the old digest field is gone), and the frame stream gains the challenge/response (`STATUS_AUTH_CHALLENGE` → `STATUS_AUTH_RESPONSE` → `STATUS_AUTH_OK`/`STATUS_AUTH_FAILED`) between the config frame and the `STATUS_OK` ack. Both are wire-layout changes, so `PROTOCOL_VERSION` is bumped **2.18.0 → 2.19.0** (see the A7 note in `src/shared/config.h`); the strict same-version handshake keeps a 2.19 client and a 2.18 server from desynchronizing.
+- **Client side:** `host::module/path` selects the TCP transport and connects to `--server-port`; `host:path` stays the SSH transport; plain paths stay local TCP. The daemon username comes from `--password-file` (first `user:password` line), and `--password-file` without a `host::module/path` destination is a client error (fail fast). A `user@host::module` form is rejected with a pointer to `--password-file`. The client's plaintext password is wiped from memory (`config_burn_auth`) at transfer teardown.
+- **MOTD (Wave C):** a daemon configured with a global `motd file` sends that file's content as the first server→client string frame after the config-frame STATUS_OK ack (rsync sends the MOTD as the first thing from the server at the start of a daemon connection). Only the daemon listener path (`host::module`) gets a MOTD; the `--stdio` SSH path never sends or reads one. The server reads the file bounded to 4096 bytes and treats an absent/unreadable file as "no MOTD" (an empty frame, never an error). The exchange is server→client only and does **not** bump `PROTOCOL_VERSION`: every 2.15.0 daemon client reads the frame after the ack, so sender and receiver stay in lockstep (see the Wave C note in `src/shared/config.h`). `--no-motd` is the client-side suppression switch: the client still reads (consumes) the frame to keep the stream in sync but does not display it. The MOTD is printed to stdout with control bytes (ESC included) escaped octal-style while newlines/tabs are preserved, so a hostile server cannot inject terminal escape sequences.
+- **Merge note:** the Wave A module bump (2.15.0) and the MOTD wave did not bump the version, but the A7 auth redesign is a genuine wire-layout change and owns the 2.18.0 → 2.19.0 bump (see the A7 note in `src/shared/config.h`).
 
 ## 15. Safety & Security
 
@@ -210,50 +656,217 @@ This document maps rsync's full feature set to FastSync's current implementation
 | Protocol version check | Verify compatible versions | ✅ Implemented | `config_receive()` |
 | Max data/string/chunk sizes | Prevent OOM attacks | ✅ Implemented | Per-message limits |
 | Per-connection memory limit | 1GB per connection | ✅ Implemented | `MAX_CONNECTION_MEMORY` |
-| `--trust-sender` | Trust remote sender's file list | ❌ Not Implemented | |
-| `--old-args` | Disable modern arg protection | ❌ Not Implemented | |
-| `--ignore-missing-args` | Ignore missing source args | ❌ Not Implemented | |
-| `--delete-missing-args` | Delete missing source args | ❌ Not Implemented | |
+| `--max-alloc=SIZE` | Limit a single memory allocation | ✅ Implemented | Caps the largest single allocation; binary units, default 1G |
+| `--trust-sender` | Trust remote sender's file list | ✅ Implemented | Long-form-only, receiver-local policy that never crosses the wire. The receiver skips its redundant up-front re-validation of the incoming file list (empty/`..` path rejection and the escaping-symlink-target containment), trusting the sender instead of double-checking (fewer checks, faster, potentially unsafe, matching rsync). Off by default. The low-level fd-relative confinement primitives (`file_open_secure_parent`, the O_NOFOLLOW parent walk, leaf/destination confinement) are deliberately KEPT even under `--trust-sender`, so a hostile sender still cannot write or link outside the authorized root (see Phase-5 notes below) |
+| `--old-args` | Disable modern arg protection | ✅ Implemented | SSH-only; accepted for CLI compatibility but is now a **documented no-op**: FastSync always single-quote-escapes the remote server path and each `--remote-option` value (`ssh_build_remote_command`), so a metacharacter-bearing `--rsync-path` can never be interpreted by the remote shell. The flag no longer disables that quoting (the old raw-construction behavior was an injection foot-gun and is removed); the safety-relevant behavior is identical either way |
+| `--ignore-missing-args` | Ignore missing source args | ✅ Implemented | FastSync has a single source-root argument (which always exists), so the "explicitly requested source arguments" are the `--files-from` entries and the flags only ever apply there (inert without `--files-from`, like `-R`). Without the flag a listed-but-missing entry stays a hard pre-transfer error (nothing is transferred). With it each missing entry is skipped: nothing is sent for it, it never enters the keep-set, and the run succeeds for the rest — an all-missing non-empty list succeeds transferring nothing, matching rsync. `--dirs` + `--files-from` missing entries are skipped the same way. Every skipped entry is logged and a per-run warning names the count, so the handling is never a silent no-op. Divergences: an EMPTY `--files-from` file stays a hard error in every mode (no argument was requested at all; rsync likewise reports "no source files specified"); missing-arg skipping only applies to the pre-transfer list validation, so an entry that is present at preflight and vanishes mid-transfer still fails (matching rsync, whose flag "does not affect subsequent vanished-file errors"); `--no-ignore-missing-args` is not a supported negation |
+| `--delete-missing-args` | Delete missing source args | ✅ Implemented | Implies `--ignore-missing-args` (order-independent) and additionally removes each missing entry's destination mirror receiver-side. The mirror is computed exactly like a present sibling's wire path: the bare relative entry under `-R`, otherwise the full source-mirror path below the destination root. rsync parity, verified against the man page: it does **not** imply `--delete` generally and is "independent of any other type of delete processing" — unrelated destination extras are untouched unless `--delete` is also present. Composition with `--delete` + timing: the exact-path deletions commit with the manifest, early for `--delete-before`/`--delete-during`, else only after a fully-successful transfer (delete-after/commit). A non-empty directory mirror is removed only when `--force` or `--delete` is in effect (otherwise it is left with a warning and the run continues, like rsync); an absent mirror is a no-op. An explicitly listed missing arg is a user request, not an excluded file: its deletion is never blocked by the filter-exclusion protection of excluded destination mirrors (a mirror sitting inside a filter-excluded directory is still removed). Safety/policy: gated by the server `--allow-delete` policy like `--delete`; the request paths cross the wire only in the delete-manifest frame and are confined by the same receiver validation as the keep-set (non-empty, relative, traversal-free, bounded by the per-section/per-frame manifest caps); the `--delay-updates` staging directory and basis snapshots are protected exactly as in the extras walker. Divergence: the missing-args deletions are not counted toward `--max-delete` (they are explicit per-path requests, not discovered extras). See the Phase-3 wire note below for the `PROTOCOL_VERSION` bump |
 
 ## 16. Batch Operations
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `--write-batch=FILE` | Write batched update to file | ❌ Not Implemented | |
-| `--only-write-batch=FILE` | Write batch without updating dest | ❌ Not Implemented | |
-| `--read-batch=FILE` | Read batched update from file | ❌ Not Implemented | |
+| `--write-batch=FILE` | Write batched update to file | ✅ Implemented | Phase-6 residual-batch (client-only): runs the normal live transfer AND additionally emits a self-contained single-file batch of the whole source tree. The batch is a magic/format-version header followed by length-prefixed `chunk_serialize` blobs (full file images), replayable byte-identically by `--read-batch` on another machine with no source/server. `--write-batch` drives the single-threaded transfer path (the multithreaded path consumes the config before the separate batch scan pass). See the Phase-6 batch note below |
+| `--only-write-batch=FILE` | Write batch without updating dest | ✅ Implemented | Phase-6 residual-batch: emits the self-contained batch FILE only — NO destination update, NO server connection. Requires a source (scans it and serializes the full tree to FILE). Same single-file format as `--write-batch`, so the file is re-appliable via `--read-batch=FILE DEST`. See the Phase-6 batch note below |
+| `--read-batch=FILE` | Read batched update from file | ✅ Implemented | Phase-6 residual-batch: applies a previously written batch FILE locally to the destination. NO source and NO server — positional args are the destination only. Reads the magic/version header, then length-prefixed records, `chunk_deserialize`, and applies each via the confined `file_save_to_disk_full` path (same O_NOFOLLOW / `..`-rejection / root-confinement as the network receiver, so an attacker-controlled batch cannot escape the destination root). Malformed/truncated/oversized/traversal records are rejected cleanly. See the Phase-6 batch note below |
 
 ## 17. Advanced
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `--stop-after=MINS` | Stop after N minutes | ❌ Not Implemented | |
-| `--stop-at=TIME` | Stop at specified time | ❌ Not Implemented | |
-| `--fsync` | Fsync every written file | ❌ Not Implemented | |
-| `--protocol=NUM` | Force older protocol version | ❌ Not Implemented | |
-| `--iconv=CONVERT_SPEC` | Charset conversion | ❌ Not Implemented | |
-| `--checksum-seed=NUM` | Set checksum seed | ❌ Not Implemented | |
-| `-s`, `--secluded-args` | Use protocol to send args | ❌ Not Implemented | |
-| `--no-OPTION` | Turn off implied option | ❌ Not Implemented | |
+| `--stop-after=MINS` | Stop after N minutes | ✅ Implemented | Client-only sender stop deadline (Phase 6): computing `--stop-after=MINS` (a positive minute count; 0/negative/garbage rejected) and `--stop-at=TIME` (`HH:MM`, `HH:MM:SS`, or `now+N[smhd]`; a past time stops immediately). The transfer stops ELEGANTLY at the next chunk boundary: everything already fully sent is kept and applied, the run returns 0, and --delete (late/delete-after timing) does NOT wipe the destination — when the scan is cut short the partial keep-set manifest is suppressed with a warning (the delete walk is skipped rather than acting on an incomplete keep-set, so unscanned source mirrors survive). `--delete-before`/`--delete-during` still run their complete pre-scan (which ignores the deadline). Local client-only fields: never serialized into the wire config frame, so no PROTOCOL_VERSION bump. `--stop-after` uses CLOCK_MONOTONIC; `--stop-at` uses the wall clock. Works single-threaded and under `-j`/`--threads` (multithreaded). Divergence: rsync computes `--stop-after` from the run start; FastSync likewise. When both are given, the earlier of the two deadlines wins (checked per iteration). See the Phase-6 stop notes below |
+| `--stop-at=TIME` | Stop at specified time | ✅ Implemented | Same feature as `--stop-after` (deadline transfer stop), absolute wall-clock form (`HH:MM[:SS]` or `now+N[smhd]`). See the row above and the Phase-6 stop notes |
+| `--fsync` | Fsync every written file before publication | ✅ Implemented | |
+| `--protocol=NUM` | Force older protocol version | ✅ Implemented | Forces the wire protocol version for this transfer. FastSync has exactly ONE wire format (`PROTOCOL_VERSION`, currently 2.19.0) with no downgrade/backward-compat code paths, so `--protocol=2.19.0` is accepted (it sets the version claim the client sends, which the server already requires to match exactly) and **every other value is rejected up front** with a clear error before any connection — it does not and cannot speak an older or virtual wire format. Divergence from rsync (which negotiates a range and downgrades to an integer 0..31): FastSync's honest contract is force-to-the-one-supported-value; a genuine downgrade would require a per-version compatibility layer that does not exist. Client-only; the server-side exact-match check is unchanged. `--protocol=2.18.0`/`2.18`/`2.17.0`/`2.16.0`/`2.15.0`/`216`/`31`/garbage are all rejected. See the Phase-6 protocol note below |
+| `--iconv=CONVERT_SPEC` | Charset conversion | ✅ Implemented | Charset conversion of FILE NAMES (not content) at the protocol boundary via iconv(3): `--iconv=LOCAL[,REMOTE]` — the sender converts each local filename LOCAL→REMOTE before transmitting, and the receiver converts each wire filename REMOTE→LOCAL before creating/writing. The full CONVERT_SPEC is serialized into the config frame as a new trailing string field so the peer knows the wire charset; **PROTOCOL_VERSION bumped 2.15.0 → 2.16.0**. `LOCAL[,REMOTE]` parse: single charset ⇒ LOCAL==REMOTE (identity both ways); garbage rejected up front. Validation probes BOTH directions (a spec that only opens one way is refused, as is a NUL-emitting target charset like utf-16/utf-32/ucs-2, since filenames cannot contain NUL). An unrepresentable name (EILSEQ/EINVAL) fails that path cleanly with a logged `--iconv: cannot convert file name ...` and is never written mangled/truncated. Conversion is applied at EVERY wire-path site (regular/MKDIR/hardlink path+target/symlink path+target/SPECIAL, the delete manifest, the incremental-check path, and the `-s`/`chunk_serialize` embedded blob path), on both client and server (`--iconv` is also a server/daemon option). Zero overhead when unset. See the Phase-6 iconv notes below |
+| `--checksum-seed=NUM` | Set checksum seed | ✅ Implemented | Sets the seed for FastSync's whole-file xxHash64 digest (full 64-bit seed) and for the delta path's per-block xxHash32 strong checksum (low 32 bits of the seed). An explicit seed deterministically changes every computed digest on BOTH endpoints (sender and receiver share the seed via the config frame, protocol 2.10.0), so identical runs with the same seed skip the same files and a changed seed changes the digests — the explicit-seed path that makes xxHash comparisons deterministic. `--checksum-choice=md5` has no seed and ignores it (documented). The value is a strict decimal 0..2⁶⁴-1 (blank, signed, or non-numeric values are rejected). Like rsync, a seed only matters where a digest is actually computed (`--checksum` or a basis-dir run, or a delta transfer); it does not by itself enable `--checksum`/`--delta`. Divergence from rsync: the default is seed 0, and FastSync never randomizes the seed (rsync uses a random per-transfer seed when `--checksum-seed` is unset); FastSync's unset default therefore reproduces its historical byte-for-byte behavior |
+| `--secluded-args`, `-s` | Use protocol to send args | ⛔ Impossible/Divergence | Accepted for CLI compatibility (including the rsync short `-s`, Phase 7 Wave A) but a documented **no-op / divergence**. rsync's `-s` protects arguments from shell expansion by shipping them over the protocol; FastSync never passes remote arguments through a shell expansion boundary in the first place — its SSH transport builds the remote argv as **single-quote-escaped shell words** (`ssh_build_remote_command`), so the injection/leak that `-s` guards against does not exist and there is nothing to "seclude". Implementing a true arg-send protocol would mean replacing the argv-based SSH launch with an in-band argument channel, a large redesign of the transport that buys no security here. Chunk serialization remains the long-only `--chunk-serialization`. |
+| `--no-OPTION` | Turn off implied option | ✅ Supported | Supported boolean FastSync options and archive-implied options; unsafe or value-taking options are rejected. |
+
+---
+
+## Implementation Difficulty Plan
+
+**Phase 5 notes (remote-option wave):** `--remote-option=OPT` (long form only) and `--trust-sender` landed here.
+- `--remote-option` is CLIENT-only and never serialized into the binary config frame. On the SSH transport the client forwards each value to the remote server by appending it to the remote command line in `ssh_build_remote_command()`, after ` --stdio`, as an individually single-quoted shell word (`'...'` with `'\''` for embedded quotes). Values are validated at CLI parse time (non-empty; no ASCII control characters) and rejected otherwise, and a non-conforming value is refused again in the command builder, so shell metacharacters (`;`, `&`, `|`, backticks, `$()`, quotes) can never break out of the quoting to inject an unrelated remote command — including after a client-side `--` separator, whose arguments are never forwarded anyway. Because the remote options affect the *remote server invocation*, not the transmitted config, the wire frame layout is unchanged, but `PROTOCOL_VERSION` was bumped **2.13.0 → 2.14.0** as the Phase-5 lockstep release marker (a 2.14 client against a 2.13 server fails the version check cleanly rather than the old server rejecting an unfamiliar forwarded argv later). Divergence: rsync's short `-M` form of `--remote-option` was intentionally NOT implemented at that time because `-M` was FastSync metadata mode; **Phase 7 Wave A later freed `-M` for `--remote-option` and moved metadata to long-only `--preserve`** (see the Sending Options table).
+- `--trust-sender` is a receiver-local policy: it never crosses the wire (the sender's value is never serialized, so a wire peer can never enable it). On the receiving process it skips the up-front re-validation of the incoming file list (empty/`..` path rejection and the escaping-symlink-target containment), trusting the sender's list instead of double-checking — fewer checks, faster, and potentially unsafe, matching rsync. It is OFF by default (`config.trust_sender`). As a deliberate safety floor, the low-level fd-relative confinement primitives are NOT disabled: `file_open_secure_parent()` (O_NOFOLLOW walk, `..` rejection, root containment) and leaf/destination confinement still hold, so even under `--trust-sender` a hostile sender cannot write or create a symlink outside the authorized root — the relaxation only removes the redundant list-layer double-checks, never the root-confinement guarantees.
+
+The estimates below cover the currently unimplemented features in this document. They assume one engineer familiar with the codebase, include implementation and focused tests, and exclude production rollout time. A feature should not be marked implemented until its behavior is tested in both local and SSH/TCP paths where applicable.
+
+> **Note:** This plan is a superset snapshot written while several of the listed features were still outstanding. The Summary matrix above is the authoritative record of what is already shipped (for example quiet/info/debug output, `--existing`, `--remove-source-files`, `-h`, and `--size-only` are now implemented on `dev`). Treat the phases as sequencing guidance for the work that remains unimplemented.
+
+| Effort | Typical duration | Meaning |
+|--------|------------------|---------|
+| XS | 0.5-1 day | CLI alias or a local formatting/validation change |
+| S | 1-3 days | Isolated behavior with little or no protocol change |
+| M | 3-7 days | Cross-cutting client, server, or scanner behavior |
+| L | 1-3 weeks | Protocol, filesystem, privilege, or compatibility work |
+| XL | 3+ weeks | New transfer mode, daemon subsystem, or broad interoperability effort |
+
+### Phase 1: Low-Risk CLI and Local Behavior
+
+These are the best first changes because they require limited wire-format work and can be tested with existing transfer fixtures.
+
+| Features | Effort | Implementation plan |
+|----------|--------|--------------------|
+| `--quiet`, `-q`; `--human-readable`, `-h`; `--8-bit-output`, `-8`; `--stderr=MODE`; `--info=FLAGS`; `--debug=FLAGS` | S | Extend logging and output formatting without changing transferred data. |
+| `--no-OPTION`; `--old-args`; `--secluded-args`, `-s` | M | Add option implication/negation and safely serialize or protect remote arguments. `-s` currently has FastSync-specific semantics and needs a compatibility decision. |
+| `-P`; `--del`; `--old-dirs`, `--old-d`; `--cc`; `--zc`; `--zl` | XS | Add aliases and composed behaviors after the underlying options exist. |
+| `--whole-file`, `-W`; `--ignore-times`, `-I`; `--size-only`; `--modify-window`, `-@`; `--update`, `-u` | S | Extend the existing incremental comparison decision. |
+| `--existing`; `--ignore-existing`; `--remove-source-files` | S | Add scanner/receiver eligibility checks and remove successfully synchronized source files. |
+| `--executability`, `-E`; `--chmod=CHMOD` | M | Apply permission transformations safely while preserving current metadata behavior. |
+| `--skip-compress=LIST`; `--compress-threads=NUM` | S | Make compression selection configurable and validate the thread setting against zstd behavior. |
+| `--max-alloc=SIZE`; `--fsync` | S | Reuse existing allocation limits and add an explicit durability step after file writes. |
+
+### Phase 2: Filesystem Selection and Update Semantics
+
+These features are moderate because they affect traversal, temporary files, manifests, or the receiver's update policy.
+
+| Features | Effort | Implementation plan |
+|----------|--------|--------------------|
+| `--one-file-system`, `-x` | M | Track the source device during scanner traversal and skip mount-point crossings. |
+| `--relative`, `-R`; `--no-implied-dirs`; `--dirs`, `-d`; `--mkpath` | M | Extend path-list construction and destination directory creation while preserving traversal safety. |
+| `--temp-dir`, `-T` | M | Separate temporary-file placement from FastSync's timeout alias and define collision, permissions, and cleanup rules. |
+| `--delay-updates` | L | Stage all successful updates and publish them at completion, including crash and cancellation cleanup. |
+| `--files-from=FILE`; `--from0`, `-0`; `--filter=RULE`, `-f`; `-F`; `--cvs-exclude`, `-C` | L | Build a complete filter/parser layer and integrate it with scanner pruning, manifests, and delete behavior. `-f` conflicts with FastSync sendfile mode. |
+| `--list-only`; `--itemize-changes`, `-i`; `--out-format=FORMAT`; `--log-file-format=FMT` | M | Add a structured change-event model so output modes share one source of truth. |
+
+### Phase 3: Deletion, Comparison, and Delta Compatibility
+
+These features require careful interaction with manifests, incremental checks, backups, and the existing delta protocol.
+
+| Features | Effort | Implementation plan |
+|----------|--------|--------------------|
+| `--delete-during`; `--delete-before`; `--delete-after`; `--delete-delay`; `--del` | L | Add deletion timing to the transfer state machine and ensure failures cannot remove files unexpectedly. |
+| `--delete-excluded`; `--max-delete=NUM`; `--ignore-errors`; `--force`; `--prune-empty-dirs`, `-m` | M | Extend delete walks with policy limits, error handling, empty-directory pruning, and the `-m` short-flag conflict. |
+| `--ignore-missing-args`; `--delete-missing-args` | M | Distinguish missing source arguments from traversal errors and apply explicit deletion policy. |
+| `--compare-dest=DIR`; `--copy-dest=DIR`; `--link-dest=DIR` | L | Add alternate basis roots and hard-link handling, including metadata and cross-filesystem failures. |
+| `--fuzzy`, `-y`; `--no-fuzzy` | L | Index candidate files and select a safe similar basis without making transfer time unbounded. |
+| `--append`; `--append-verify` | M | Negotiate file length and verify the retained prefix before resuming. |
+| `--checksum-choice=STR`, `--cc`; `--checksum-seed=NUM` | M | Negotiate checksum algorithms/seeds and preserve compatibility with existing xxHash checks. |
+
+### Phase 4: Metadata, Links, and Devices
+
+These features are platform-sensitive and need Linux permission, ACL, xattr, and special-file integration tests.
+
+| Features | Effort | Implementation plan |
+|----------|--------|--------------------|
+| `--numeric-ids`; `--usermap=STRING`; `--groupmap=STRING`; `--chown=USER:GROUP` | L | Define identity mapping, privilege failures, and wire representation before applying ownership. |
+| `--open-noatime`; `--atimes`, `-U`; `--crtimes`, `-N`; `--omit-dir-times`, `-O`; `--omit-link-times`, `-J` | L | Extend metadata capture/apply with platform capability checks and explicit unsupported-attribute handling. |
+| `--acls`, `-A`; `--xattrs`, `-X`; `--fake-super` | XL | Add portable serialization, size limits, privilege behavior, and security tests for ACL/xattr data. |
+| `--hard-links`, `-H` | L | Preserve inode relationships across the file list and coordinate hard-link creation order. |
+| `--munge-links`; `--copy-dirlinks`, `-k`; `--keep-dirlinks`, `-K` | L | Define symlink trust boundaries and receiver-side directory/link collision behavior. |
+| `--devices`; `--specials`; `-D`; `--copy-devices`; `--write-devices` | XL | Add privileged special-file handling with strict type, path, and authorization checks. |
+| `--super`; `--copy-as=USER[:GROUP]` | XL | Requires a deliberate privilege model, identity switching, and refusal paths; do not implement by blindly elevating the process. |
+| `--preallocate` | S | Use platform allocation APIs before writes and fall back cleanly when unsupported. |
+
+### Phase 5: Connectivity and Daemon Compatibility
+
+These options affect process startup, authentication, sockets, and remote execution. They should follow the filesystem and protocol work rather than being added as parser-only flags.
+
+| Features | Effort | Implementation plan |
+|----------|--------|--------------------|
+| `--rsh=COMMAND`, `-e`; `--rsync-path=PROGRAM`; `--blocking-io`; `--outbuf=N\|L\|B` | M | ✅ Wave A implemented (see the Connectivity table above). SSH argv construction is generalized: `-e`/`--rsh` replaces the hardcoded `ssh` program (whitespace-split, so `-e "ssh -p 2222"` works), `--rsync-path` aliases the existing `fastsync_server_path`, `--blocking-io` drops the SSH socket timeouts, and `--outbuf` maps N/L/B onto `setvbuf`. All four are client-only launch concerns and never cross the wire. |
+| `--address=ADDRESS`; `--ipv4`, `-4`; `--ipv6`, `-6`; `--sockopts=OPTIONS`; `--port=PORT` daemon semantics | M | Add explicit socket-family/bind configuration and validate it independently for TCP client and daemon modes. |
+
+**Phase 5, Wave B (socket/bind) shipping note:** `--sockopts` adds a strict allowlisted `OPT=VAL` socket-option layer applied with correct per-option value types; `--address` binds the outgoing client socket to a local source address; `-4`/`-6` pin the address family via `getaddrinfo` hints on both the client connect and the server bind; and the server bind now honors `--address` plus `-4`/`-6` (falling back to the historical IPv4 `INADDR_ANY` when none are given). All of these are local socket concerns and none cross the wire config frame (only `--port` maps to `server_port`).
+| `--remote-option=OPT`, `-M`; `--trust-sender` | L | Add authenticated remote-option/config negotiation and reject unsafe sender-controlled values. `-M` conflicts with FastSync metadata mode. |
+| `--daemon`; `--config=FILE`; `--dparam=OVERRIDE`; `--no-detach`; `--password-file=FILE`; `--early-input=FILE`; `--no-motd` | XL | Implement a real daemon lifecycle, module configuration, authentication, privilege separation, and process management. |
+
+**Phase 5, Wave A (rsh/ssh) shipping note:** the SSH transport no longer hardcodes `ssh`. `-e`/`--rsh=COMMAND` selects the remote-shell program (whitespace-split into the leading child argv words), `--rsync-path=PROGRAM` aliases `--fastsync-server-path`, `--blocking-io` removes the SSH-socketpair `SO_RCVTIMEO`/`SO_SNDTIMEO` timeouts (by default they now match the TCP transport so a wedged shell cannot hang forever), and `--outbuf=N|L|B` maps onto `setvbuf` (`_IONBF`/`_IOLBF`/`_IOFBF`, garbage rejected). All four are client-only launch concerns and never cross the wire.
+
+**Phase 5, Wave C (remote-option/trust-sender) shipping note (PROTOCOL 2.13.0 → 2.14.0):** `--remote-option=OPT` (long form only; the short `-M` is intentionally left as FastSync metadata mode — documented divergence) appends each validated value to the remote server invocation over SSH as an individually single-quote-escaped shell word, so shell metacharacters cannot break out and a `--` can never be turned into injection; options never cross the binary config frame. `--trust-sender` is a receiver-local policy (never serialized, so a wire peer can't enable it): when requested on the server (via `--remote-option=--trust-sender`), it removes only the redundant receiver/save-layer path re-checking; the low-level floor (`file_open_secure_parent`'s `..` rejection, the O_NOFOLLOW parent walk, leaf/destination confinement) stays enforced. Off by default. The wire config-frame layout is unchanged; the bump reflects that a 2.14 sender composing remote options requires a 2.14 receiver to honor them.
+
+### Phase 6: Batch, Encoding, and Protocol Interoperability
+
+These are the hardest compatibility items because they require durable formats or behavior that must interoperate with rsync itself.
+
+| Features | Effort | Implementation plan |
+|----------|--------|--------------------|
+| `--write-batch=FILE`; `--only-write-batch=FILE`; `--read-batch=FILE` | XL | ✅ Implemented (see the Batch Operations table and Phase-6 batch note below): a versioned self-contained single-file residual-batch format, persisted via the existing chunk codec, with replay, corruption, and partial-application safety tests |
+| `--protocol=NUM` | XL | ✅ Implemented (see the Advanced table and Phase-6 protocol note below): protocol-version forcing without weakening current validation; FastSync's single lockstep wire format means only the current `PROTOCOL_VERSION` is accepted, and everything else is rejected up-front |
+| `--iconv=CONVERT_SPEC` | L | ✅ Implemented (see the Advanced table and Phase-6 iconv notes below): filename charset conversion at the wire boundary with expansion/overflow safety and invalid-sequence test coverage |
+| `--stop-after=MINS`; `--stop-at=TIME` | M | ✅ Implemented (see the Advanced table and Phase-6 stop notes below): deadline propagation and safe early stop with --delete safety |
+| `--early-input=FILE`; `--password-file=FILE` | M | Securely read startup credentials/input with permission checks and no secret disclosure in logs. |
+
+**Phase 6, Wave A (stop deadline) shipping note:** `--stop-after=MINS` and `--stop-at=TIME` are client-only sender stop deadlines. `--stop-after` takes a positive minute count (0/negative/garbage rejected); `--stop-at` takes `HH:MM`, `HH:MM:SS`, or `now+N[smhd]` (a past time stops immediately, a garbage spec is rejected at parse time). The deadline is computed once at the start of the transfer (CLOCK_MONOTONIC for `--stop-after`, wall clock via `time()` for `--stop-at`) and checked at every chunk boundary in both the single-threaded `send_files` loop and the multithreaded `send_chunks_multithreaded` path, and inside the scanner loops so a busy scan itself stops. When it fires, the transfer stops ELEGANTLY: the in-flight chunk completes, the existing completion tail runs (summary, `disconnect`), and the run returns 0 — exactly like rsync's clean early stop. Because the deadline is client-only and never crosses the wire config frame, no PROTOCOL_VERSION bump is required. The safety-critical interaction is with `--delete`: FastSync streams while scanning, so a deadline can cut the source scan short and yield a PARTIAL keep-set manifest; committing that would make the receiver delete destination mirrors of source files not yet scanned. So the sender tracks `scan_stopped_early` and, when it is true on the late/delete-after (`--delete`/`--delete-after`/`--delete-delay`) path, SUPPRESSES the keep-set manifest (logs a warning) so no deletion happens from an incomplete set — this is the safe direction (preserves data; the delete simply does not run). `--delete-before`/`--delete-during` are unaffected: their complete pre-scan runs before any data and ignores the deadline (a stop can be exceeded by that pre-scan). Under `-j`/`--threads` the stop is symmetric and the scanner thread's still-in-progress manifest appends can never race the tail because the tail does not read the manifest on the early-stop path.
+
+**Phase 6, Wave B (iconv) shipping note (PROTOCOL 2.15.0 → 2.16.0):** `--iconv=LOCAL[,REMOTE]` converts file NAMES at the wire boundary (never content). The full CONVERT_SPEC is serialized into the config frame as a new trailing string field (empty→NULL canonicalized), so both ends share the same wire charset interpretation; this required the PROTOCOL bump because the frame is a strict ordered sequence and a peer that does not parse the new trailing field would desynchronize. Each end derives LOCAL (its own charset) and REMOTE (the wire charset): the sender opens LOCAL→REMOTE and converts every transmitted filename; the receiver opens REMOTE→LOCAL and converts every received filename before creating/writing. Conversion is applied at every wire-path site (regular/MKDIR/hardlink path+target/symlink path+target/SPECIAL, the delete manifest keep/protected/missing entries, the incremental-check path, and the embedded `-s`/chunk-blob path). A name it cannot convert (EILSEQ/EINVAL) is failed cleanly with a logged `--iconv: cannot convert file name ...` and is never written truncated/mangled. Validation probes both directions up front (both the sender local→remote and the receiver remote→local, and, for a server/daemon with its own `--iconv`, the client-REMOTE→server-LOCAL pair) so an unusable spec is rejected before the connection rather than mid-transfer, and NUL-emitting target charsets (utf-16/utf-32/ucs-2) are refused because filenames cannot contain NUL. Divergence documented upstream: the receiver does NOT half-swap; the wire charset always comes from the sender's REMOTE half, so a server whose local charset differs from the client's LOCAL must declare it with its own `--iconv`. Conversion is process-global and runs on a single thread per process (sender thread / receiver-loop thread), initialized before worker threads start and freed after they join.
+
+**Phase 6, Wave C (protocol-version) shipping note (no PROTOCOL_VERSION change):** `--protocol=NUM` lets the client force the wire protocol version for a transfer. FastSync's protocol is a single lockstep format: the config frame is a strict ordered sequence and the server requires the client's version string to equal `PROTOCOL_VERSION` exactly (`config_receive_with_validate`, src/shared/config.c) — there are no older-format code paths and no downgrade/negotiation machinery, so a lower/higher/virtual version can never be spoken. The honest contract is therefore: `--protocol=2.19.0` (the current `PROTOCOL_VERSION`, as of the A7 auth redesign) is accepted and stored into the client's `version` claim (which `config_send` already transmits), and every other value — `2.18.0`, `2.18`, `2.17.0`, `2.16.0`, `2.15.0`, `3.0.0`, rsync-integer spellings like `216`/`31`, garbage, empty — is rejected up front in `validate_config()` before any connection, with a clear error that FastSync supports only its current wire protocol and cannot speak an older or virtual one. Implementation is client-only: a server-side `--protocol` is intentionally not added because the server has no negotiation (it only enforces exact match), and it could only ever be the current version. This preserves (and slightly tightens) existing validation: the client now also refuses to launch with a version it cannot actually speak, rather than only the server rejecting it later. A genuine downgrade would require a per-version compatibility layer for every frame/feature added since (append 2.10, preallocate 2.11, hardlinks 2.12, devices/specials/symlink-trust/xattr 2.13, remote-option 2.14, daemon module/auth 2.15, iconv 2.16, dir/symlink times 2.17, privilege flags --super/--copy-as 2.18, SCRAM daemon auth 2.19) and is intentionally out of scope — documented divergences from rsync's integer-negotiated downgrade remain.
+
+**Phase-1/2 selection-and-update status correction (docs):** `-I/--ignore-times`, `--size-only`, `-@/--modify-window`, `--existing`, `--ignore-existing`, `-u/--update`, `-W/--whole-file`, and `--compress-threads` were previously listed as not-implemented in this document but are in fact fully implemented and tested on `dev`. This pass corrects the matrix to match the code. The realistic model of these is that FastSync is a *sender-driven* whole-tree copy, so the size+mtime quick-check and all three receiver-policy skips (`--existing`, `--ignore-existing`, `-u`) are evaluated against the **destination** on the receiver side, and their booleans cross the wire in the config frame. `-I`/`--size-only`/`--modify-window` modify the `--incremental` per-file `STATUS_CHECK` handshake's match predicate (`-I` disables the mtime leg and forces transfer; `--size-only` drops only the mtime leg; `--modify-window` adds tolerance to `metadata_mtime_matches`); they require `--incremental` (or a basis dir) to have a handshake to affect, mirroring how they only matter where a quick-check exists in rsync. `--existing`/`--ignore-existing`/`-u` are receiver write-time policies (skipping the write / newer-destination guard) applied across the regular-file, `--delay-updates`-staged, hardlink-sibling, and special/device paths; `-u` implies `-M` metadata and uses a second-then-nanosecond strict `>` newer check; both correctly influence `--remove-source-files` (a skipped source is not removed). `-W/--whole-file` disables block-level delta (opt-in via `--delta`), folded into the wire `use_delta` so no protocol bump was needed, and makes `--fuzzy` inert; `--append`/`--append-verify` are rejected with `-W`. `--compress-threads=NUM` (1..64, client-only, never crosses the wire) sizes the zstd compression worker pool. No code was changed by this correction; the implementation had landed in earlier merge waves (feat/ignore-times, feat/ignore-existing via the newer `file_to_disk_secure_no_replace`/`linkat EEXIST` path, feat/size-only, feat/modify-window, feat/whole-file, feat/update, compression-threads).
+
+**Phase 6, Wave D (batch) shipping note (no PROTOCOL_VERSION change):** FastSync batch mode is a **client-only, self-contained "residual batch"**: a single file `MAGIC "FSTRESBATCH" + format version 1 + metadata flag`, followed by length-prefixed `chunk_serialize` blobs that store full file images (regular files, dirs, symlinks, specials). It is NOT a raw capture of the live wire, because FastSync's protocol is per-file interactive (`STATUS_CHECK`/`STATUS_DELTA_SIGNATURE`/`STATUS_APPEND` handshake), so a raw sender-stream tee is not deterministically replayable against an arbitrary destination. Storing full residuals via the existing, fuzz-tested chunk codec makes `--read-batch` replay byte-identically by construction. `--write-batch=FILE` runs the normal live transfer AND emits the batch from a separate deterministic scan pass; `--only-write-batch=FILE` emits the batch only (no destination, no server); `--read-batch=FILE DEST` applies it locally (no source, no server; DEST is the only positional arg). Because batch is a local driver concern, it never crosses the wire: no new config-frame field and no `PROTOCOL_VERSION` bump (mirroring `--stop-after`/`--protocol`/`--compress-threads`). The READ side is hardened against untrusted/attacker-controlled batch files: magic+version validated before any record, per-record length bounds checked before allocation (64 MB cap), clean-EOF-after-prefix and truncated/oversized records rejected, and every applied path goes through the same confined `file_save_to_disk_full` machinery as the network receiver (O_NOFOLLOW fd-walk, `..`-rejection, root confinement — a malicious `../` or absolute/symlink path cannot escape the destination root; this was security-reviewed and valgrind/ASan-clean). Divergences from rsync: (1) the batch carries the FULL residual (complete file images) rather than rsync's update-only delta stream — always byte-correct but larger; (2) per-file data is capped at the chunk codec's ~64 MB (`BATCH_MAX_RECORD`), so very large files may be refused by the batch writer with a clean error (never a corrupt/truncated batch); (3) hard-links and xattr/ACL blocks are not represented by `chunk_serialize`, so `-H`/`-X`/`-A` are out of scope for batch; (4) there is no companion `.sh`/`.rsync_argvs` — the batch is invoked directly (`fastsync --read-batch=FILE DEST`, `--only-write-batch=FILE SOURCE`); (5) `--write-batch` drives the single-threaded transfer path. Integration/`-M` note: metadata is captured in the batch when `-M` is used and persisted in the header so it applies consistently regardless of the reading process's own `-M`.
+
+### Phase 7: CLI-Namespace Parity, Filesystem/Output Completion, and Privilege (Final)
+
+These are the last compatibility items and the closing phase toward rsync flag parity. Per the project decision: every rsync flag (short **and** long) that is *possible* gets real rsync-parity behavior; anything physically impossible becomes an explicit **Impossible/Divergence** status (accepted for CLI compatibility, safely inert, with coverage tests proving that); and the two privilege flags (`--super`, `--copy-as`) adopt the deliberately-scoped **safe-subset + clear-refusal** model rather than blind elevation. The remaining `⚠️ Partial`, `🔄 Compatibility No-op`, `🔀 Alt Arg`, and `❌ Not Implemented` rows in the Summary are this phase's scope. All Wave A renames are **client-side only** (the wire config fields `use_compression`/`use_metadata`/`use_sendfile`/`use_chunk_serialization` are unchanged), so they require **no `PROTOCOL_VERSION` bump**.
+
+**Wave A — CLI namespace parity (rename colliding FastSync short flags) — ✅ implemented.** This freed the short letters rsync needs and made the three `🔀 Alt Arg` rows real. `-c`→`--checksum`, `-m`→`--prune-empty-dirs`, `-M`→`--remote-option`, `-f`→`--filter`, `-s`→`--secluded-args`, `-p`→`--perms`, `-T`→`--temp-dir`, `-a`/`--archive`→real `-rlptgoD`. FastSync's own flags moved to long-form-only or new shorts: `-j`/`--threads` (multithreading), `--preserve` (metadata), `--sendfile`, `--chunk-serialization`, `--timeout`, `--ssh-port`. The server's independent little CLI keeps `-p` as its port. All client-side, no wire change, no `PROTOCOL_VERSION` bump. Unit tests 37/37, full integration 400 passed, cppcheck and clang-format clean. Known Wave-A limitation: `--no-perms`/`--no-compress`-style negation of the newly-aliased shorts is not wired into the negatable set (only the long-form `--preserve`/`--compress`/`--no-links` negations exist); `--archive --no-perms` is consequently not supported yet — a minor deviation from rsync, acceptable for Wave A.
+
+| FastSync flag today | rsync wants that name | Proposed rename |
+|---------------------|----------------------|-----------------|
+| `-c` / `--compress` | `-c` = `--checksum` | compression is already aliased as `-z`/`--compress` (rsync parity!) → drop the `-c` short, keep `--compress`/`-z` |
+| `-m` / `--multithreading` | `-m` = `--prune-empty-dirs` | → `-j` / `--threads` |
+| `-M` / `--preserve` | `-M` = `--remote-option` | → `--preserve` (long-only) |
+| `-f` / `--sendfile` | `-f` = `--filter` | → `--sendfile` (long-only) |
+| `-s` / `--chunk-serialization` | `-s` = `--secluded-args`/`--protect-args` | → `--chunk-serialization` (long-only) |
+| `-p` (SSH port) | `-p` = `--perms` | → `--port` (long-only; `--server-port` already exists) |
+| `-T` / `--timeout` | `-T` = `--temp-dir` | → `--timeout` (long-only) |
+| `-a` / `--archive` (= `-c -m -M`) | `-a` = `-rlptgoD` | → becomes **real rsync `-a`** after the renames |
+
+**Wave B — Output & filesystem completion (✅ implemented).** `-S`/`--sparse` (`⚠️→✅`): real hole preservation — a sparse-aware writer (`write_all_sparse`) skips all-zero runs ≥ 4096 bytes with `lseek(SEEK_CUR)` and `ftruncate`s the final size, wired into both the atomic temp+rename store and `--inplace` receiver-side with **no wire change** (the full file image is already in memory; the ftruncate presize is kept). `-P` (`⚠️→✅`): interrupted-write retention — on a save failure after data reached the temp fd, `--partial` now renames the already-written temp to the destination path (best-effort; falls through to the normal unlink on failure, never retains when `--partial` is off) so a later `--append`/`--append-verify` run can resume. `--block-size=SIZE` (`⚠️→✅`): promoted after verification — `--block-size` is now an alias for `--delta-block`, both set `config->delta_block_size`, which the delta engine already honored end-to-end (`delta_signature_create_seeded` + `delta_apply`); out-of-range values keep the default. `--fake-super` (`⚠️→✅`): added `fake_super_restore_fd` to parse and re-apply the recorded `user.fastsync.stat` record fd-relative (fchown best-effort/non-root skipped, fchmod, futimens); a save under `--fake-super` now re-applies the recorded attrs instead of only recording them, with the recording format unchanged. `--stderr=client` (`⚠️→⛔ Impossible/Divergence`): FastSync has no rsync client-message channel, and `client` is rejected at CLI parse — the rejection is the documented behavior (unit-tested). `-N`/`--crtimes` (`⚠️→⛔ Impossible/Divergence`): birth-times cannot be set by any portable fs call (`utimensat` sets only atime/mtime); capture/transmit stays, setting is impossible, the flag is accepted and safely inert. Review-hardening (post-eval): fake-super replay applies the mode through the same sanitization as the normal metadata path (group/other write bits are never granted); `--sparse` takes precedence over `--preallocate` (posix_fallocate skipped so holes survive); `--partial` retention is disabled for `--no_replace` (ignore/existing) and only marks a write-attempt after the actual write begins; `--block-size=SIZE`/`--delta-block=SIZE` inline forms are accepted.
+
+**Wave C — Devices & special files (finalize statuses + tests) (✅ implemented).** The four special-file rows are finalized with coverage tests. `--devices`, `--copy-devices`, and `--write-devices` are **✅ Implemented**, each with a documented, safety-driven divergence: device-node creation is privilege-gated, so a receiver without `CAP_MKNOD` skips that entry with a warning (a per-entry skip, never a transfer failure); `--copy-devices` copies a device/FIFO's reported size into an ordinary regular file (a size-bounded safe divergence from rsync's unbounded dd-like read); `--write-devices` writes only into an existing char/block node under the confined receive root and skips every unusable target rather than clobbering or aborting. `--specials` is classified **⛔ Impossible/Divergence** for one reason only: **FIFO recreation works** (unprivileged `mkfifo`, asserted under CI), but **sockets cannot be recreated by any standard filesystem call**, so a source socket is skipped with an explicit note. Tests assert FIFO recreation, the safe socket skip, the regular-file result of `--copy-devices`, the skipped/missing and non-device `--write-devices` targets, and (root-gated) real device-node creation; a root runner additionally drops the receiver to an unprivileged user to assert the `CAP_MKNOD` skip is graceful.
+
+**Wave D — Times superstructure & arg-protection no-ops (✅ implemented, `--secluded-args` ⛔).** `-O`/`--omit-dir-times` and `-J`/`--omit-link-times` are now **real modifiers** (both `🔄 → ✅ Implemented`), reversing the old "never preserves directory/symlink times" divergence:
+
+- **Directory times.** The recursive scanner captures every traversed source directory's metadata (mtime, plus atime under `-U`) into a per-transfer list — two paths are covered: the sequential `DirectoryScanner` captures each opened directory (including the transfer root), and the parallel scanner captures both the root in `parallel_scanner_create_with_options` and each worker's subdirectories in `open_next_directory` (appends are guarded by a mutex shared with the sender's pipeline context). The sender transmits them in trailing `STATUS_DIR_TIMES` frames (each: int count + count × (wire path, metadata) pairs) sent **after all file data and after the optional delete manifest**, just before `STATUS_FINISHED`. A tree larger than `MAX_MANIFEST_ENTRIES` (1 048 576) directories is chunked into repeated frames, each within the receiver's per-frame bound. A dir-time entry is RECORD-ONLY (`file->dir_time_only`): `file_save_to_disk_full` returns `FILE_SAVE_SKIPPED` without creating anything, so a source directory that was empty (or pruned by `-m/--prune-empty-dirs`) is never resurrected. The receiver accumulates received directory metadata in a `DirTimeList` and applies it only at the very end — after the entire stream, after the commit-style `--delete` deletion, and after `--delay-updates` publication — because creating or removing a child bumps the parent's mtime. Application is fd-relative/walk-confined (`file_open_secure_parent` + `utimensat(..., AT_SYMLINK_NOFOLLOW)`) and best-effort per entry: an absent path (an intentionally uncreated empty dir) is skipped QUIETLY and only a real existing directory is stamped. `-O` (config boolean, already on the wire) makes the receiver skip the whole set. The single-threaded sink applies in `receiver_send_success_frame`; the `-j`/`--threads` sink accumulates in `write_thread` and server.c applies after both threads join and the deletion commits.
+- **Symlink times/owner/mode.** `STATUS_SYMLINK` already carried metadata; the receiver now applies it with no-follow primitives only: `utimensat(..., AT_SYMLINK_NOFOLLOW)`, best-effort `fchmodat(..., AT_SYMLINK_NOFOLLOW)` (honest no-op where unsupported, e.g. Linux), and policy-gated `fchownat(..., AT_SYMLINK_NOFOLLOW)` via a new `identity_apply_ownership_link` that shares the identity resolver with the fd path. `-J` suppresses only the timestamps; ownership stays governed by the identity opt-in (`--numeric-ids`/`--usermap`/`--groupmap`/`--chown`) exactly like regular files. A symlink has no children, so this is applied immediately at creation.
+- **Wire:** the shared `STATUS_DIR_TIMES` frame (and metadata on `STATUS_MKDIR` for `--dirs` entries) is a frame-sequence change, so `PROTOCOL_VERSION` was bumped **2.16.0 → 2.17.0**; every version-sensitive test (`--protocol` accepted/rejected values) was updated. The config-frame layout itself is unchanged (the omit booleans already crossed). Non-metadata and `--no-preserve` transfers send no `STATUS_DIR_TIMES` frame and no directory metadata, keeping them byte-identical.
+
+`--secluded-args` (`🔄 → ⛔ Impossible/Divergence`): a true arg-send protocol would replace the argv-based SSH launch with an in-band channel, and FastSync already builds the remote SSH argv injection-safe (single-quote-escaped shell words), so there is no argument-leak to close; the already-safe behavior is documented in the row and no transport change is made.
+
+**Wave E (LAST) — Privilege: `--super`/`--no-super` and `--copy-as=USER[:GROUP]` (✅ implemented).** FastSync adopts a **safe-subset + clear-refusal** privilege model: it never blind-elevates and never calls `setuid`/`seteuid`/`setgid`. All privileged operations remain fd-relative and confined below the authorized receive root.
+
+`--super`/`--no-super` set a receiver-side tri-state `Config->super_mode` (`SUPER_MODE_AUTO`/`ON`/`OFF`). `privilege_super_permitted()` / `privilege_super_mode_permitted()` (src/shared/identity.c) return true for `ON` and `AUTO` (AUTO preserves FastSync's historical best-effort attempt, where the kernel refuses an unprivileged call and the caller skips it) and false only for `OFF`. The gate covers every super-user activity FastSync performs: ownership application (`identity_apply_ownership`/`_link`), char/block device-node creation (`file_save_special_to_disk`), writes into an existing device (`--write-devices`), and the `--fake-super` owner replay. Unprivileged FIFO creation is deliberately unaffected. `--super` does **not** imply `--numeric-ids`: ownership is applied only when an explicit identity policy (`--usermap`/`--groupmap`/`--chown`/`--numeric-ids`/`--copy-as`) is also given. `--no-super` suppresses those activities even for a root receiver. A non-root receiver given `--super` logs one warning at activation (`identity_set_active`); each confined attempt is then refused by the kernel and skipped, never aborting. The confinement floor is unchanged (`file_open_secure_parent`, `O_NOFOLLOW`, root/path checks). Operator control: the server CLI accepts `--no-super`, a veto that forces `OFF` for every connection, refuses any client `--copy-as`, and neutralizes an explicit `--super` (the connection is accepted but no super-user activity is attempted). On a daemon, a module that has not opted in with `client owner = yes` additionally has super-user device activity forced off (see the Daemon Mode notes).
+
+`--copy-as=USER[:GROUP]` is the safe subset. FastSync's receiver is multithreaded, so a real credential switch is unsafe; instead the receiver forces the ownership of **every entry it writes** — regular files, symlinks, directories (including implicitly-created parents), and special nodes — to the resolved target ids through the confined fd-relative identity path. USER is resolved on the client (name, `@N`/bare N, or `*` = client euid); when `:GROUP` is omitted the user's primary gid is used (falling back to `gid == uid` for a numeric id with no local passwd entry). It requires a privileged (root) receiver: an unprivileged receiver refuses the whole transfer at the config handshake, before `STATUS_OK`, so no data is ever written with the wrong ownership. A `--copy-as` chown failure on a capability-restricted root is logged at ERROR (never silently downgraded). `--copy-as` implies metadata (`--no-preserve` is rejected) and `--fake-super` cannot override it. Daemon policy: a `--daemon` receiver refuses **every** client-chosen-ownership / super-user request — `--numeric-ids`, `--chown`, `--usermap`/`--groupmap`, `--fake-super`, `--copy-as`, and explicit `--super` — unless the selected module opts in with `client owner = yes`; without that per-module opt-in any client could force arbitrary ownership inside the module root (the standalone listener and the SSH-launched `--stdio` server, which each serve one operator-authorized root, honor these requests). A `--copy-as` chown failure on a capability-restricted root marks the entry as failed rather than reporting success with the wrong owner.
+
+**Wire:** two trailing config-frame blocks after the `--iconv` spec, in fixed order — `send_privilege_options`/`receive_privilege_options` (one `super_mode` int, validated `0..2`), then `send_copy_as_options`/`receive_copy_as_options` (presence int + two int32 ids, validated `>= 0`, with `copy_as_set ⇒ use_metadata`). `PROTOCOL_VERSION` bumped **2.17.0 → 2.18.0**. **Divergences from rsync:** rsync's `--super` elevates the receiver and `--copy-as` actually switches its credentials; FastSync never elevates and only permits/forwards confined attempts, and `--copy-as` forces ownership rather than switching identity.
+
+**Post-Phase-7 Summary (after Waves A–E).** ✅143 / 🔀0 / ⛔4 / ⚠️0 / 🔄0 / ❌0 = 147. The 3 `🔀 Alt Arg` rows (`-a`, `-p`, `-z`) are ✅ (Wave A). All 10 prior `⚠️ Partial` rows are resolved to ✅ (`-S`, `-P`, `--block-size`, `--fake-super`, `--devices`, `--copy-devices`, `--write-devices`) or ⛔ (`--stderr=client`, `-N/--crtimes`, `--specials` for the impossible socket case). The 3 `🔄 Compatibility No-op` rows are resolved: `-O`/`-J` are now real ✅ (Wave D), `--secluded-args` is ⛔. The **Impossible/Divergence** bucket holds the 4 physically-impossible/divergent flags: `--stderr=client`, `-N/--crtimes`, `--specials` (sockets), `--secluded-args`. The last two `❌ Not Implemented` rows — `--super` and `--copy-as=USER[:GROUP]` — are now ✅ (Wave E). **No `❌ Not Implemented` rows remain.**
+
+### Recommended Delivery Order
+
+1. Resolve short-option conflicts (`-m`, `-M`, `-T`, `-f`, `-s`) and define the compatibility contract.
+2. Implement Phase 1 comparison, update, output, and alias features with unit and integration coverage.
+3. Implement Phase 2 traversal/filtering and Phase 3 deletion semantics.
+4. Implement metadata and link features that are safe on the supported platforms.
+5. Treat daemon mode, special files, batch mode, and protocol-version compatibility as separate projects.
+
+The existing priority list below is a feature shortlist, not an implementation schedule; this plan supersedes it for effort and sequencing.
 
 ---
 
 ## Recommendations: Top Features to Implement Next
 
-Ranked by user demand, implementation complexity, and interoperability impact:
+Ranked by user demand, implementation complexity, and interoperability impact (_status reflects current `dev`_):
 
 | Priority | Feature | Effort | Impact |
 |----------|---------|--------|--------|
-| 1 | `--whole-file` / `-W` | Low | High — users expect opt-out of delta |
-| 2 | `--ignore-times` / `-I` | Low | Medium — useful for forcing re-transfer |
-| 3 | `--size-only` | Low | Medium — common migration scenario |
-| 4 | `--ignore-existing` | Low | Medium — common sync patterns |
-| 5 | `--remove-source-files` | Low | High — common for moves/backup |
-| 6 | `--delete-during` | Medium | High — performance improvement |
-| 7 | `--delay-updates` | Medium | High — atomic updates |
-| 8 | `--chmod` | Low | Medium — permission flexibility |
-| 9 | `--executability` / `-E` | Low | Low — simple flag |
-| 10 | `--skip-compress` | Low | Medium — performance tuning |
+| 1 | `--whole-file` / `-W` | Low | High — users expect opt-out of delta — **✅ implemented** |
+| 2 | `--ignore-times` / `-I` | Low | Medium — useful for forcing re-transfer — **✅ implemented** |
+| 3 | `--size-only` | Low | Medium — common migration scenario — **✅ implemented** |
+| 4 | `--ignore-existing` | Low | Medium — common sync patterns — **✅ implemented** |
+| 5 | `--existing` | Low | Medium — common sync patterns — **✅ implemented** |
+| 6 | `--remove-source-files` | Low | High — common for moves/backup |
+| 7 | `--delete-during` | Medium | High — performance improvement |
+| 8 | `--delay-updates` | Medium | High — atomic updates |
+| 9 | `--chmod` | Low | Medium — permission flexibility |
+| 10 | `--executability` / `-E` | Low | Low — simple flag |
+| 11 | `--skip-compress` | Low | Medium — performance tuning |
 
 ---
 
@@ -261,10 +874,10 @@ Ranked by user demand, implementation complexity, and interoperability impact:
 
 | Feature | Description |
 |---------|-------------|
-| `-m` | Multithreaded pipeline (scanner/loader/sender) |
-| `-s` | Chunk serialization mode |
-| `-f` / `--sendfile` | Zero-copy sendfile() syscall (TCP only) |
-| `-c [level]` | zstd compression level (1-22) |
+| `-j` / `--threads` | Multithreaded pipeline (scanner/loader/sender) (renamed from `-m` in Phase 7 Wave A; `-m` is now rsync `--prune-empty-dirs`) |
+| `--chunk-serialization` | Chunk serialization mode (long form only; `-s` is now rsync `--secluded-args`) |
+| `--sendfile` | Zero-copy sendfile() syscall (TCP only) (long form only; `-f` is now rsync `--filter`) |
+| `-z [level]` / `--compress` | zstd compression level (1-22) (`-c` is now rsync `--checksum`) |
 | `--chunk-size` | Configurable chunk size |
 | `--tls` | TLS encryption (mutual auth) |
 | `--fastsync-server-path` | Path to fastsync-server binary |

pytest.ini

@@ -0,0 +1,10 @@
+[pytest]
+; Fast integration subset run on every pull request (see .gitea/workflows/ci.yaml).
+markers =
+    ci: fast, representative integration tests run on the PR CI gate
+    setpriv: privilege-dependent tests (drop to an unprivileged user); excluded
+        from CI because their result depends on the runner/container uid and the
+        host mount permissions, but run locally as root
+    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

src/client/change_list.c

@@ -0,0 +1,329 @@
+#include "change_list.h"
+#include "utils.h"
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#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+++++++++"
+
+typedef struct {
+  char* data;
+  size_t length;
+  size_t capacity;
+} StrBuf;
+
+static void strbuf_free(StrBuf* buf) {
+  if (buf == NULL)
+    return;
+  free(buf->data);
+  buf->data = NULL;
+  buf->length = 0;
+  buf->capacity = 0;
+}
+
+static bool strbuf_reserve(StrBuf* buf, size_t extra) {
+  if (buf->length > SIZE_MAX - extra - 1)
+    return false;
+  size_t need = buf->length + extra + 1;
+  if (need <= buf->capacity)
+    return true;
+  size_t capacity = buf->capacity > 0 ? buf->capacity : 32;
+  while (capacity < need) {
+    if (capacity > SIZE_MAX / 2) {
+      capacity = need;
+      break;
+    }
+    capacity *= 2;
+  }
+  char* grown = realloc(buf->data, capacity);
+  if (!grown)
+    return false;
+  buf->data = grown;
+  buf->capacity = capacity;
+  return true;
+}
+
+static bool strbuf_append_char(StrBuf* buf, char c) {
+  if (!strbuf_reserve(buf, 1))
+    return false;
+  buf->data[buf->length++] = c;
+  buf->data[buf->length] = '\0';
+  return true;
+}
+
+static bool strbuf_append(StrBuf* buf, const char* text) {
+  if (text == NULL)
+    return true;
+  size_t length = strlen(text);
+  if (!strbuf_reserve(buf, length))
+    return false;
+  memcpy(buf->data + buf->length, text, length);
+  buf->length += length;
+  buf->data[buf->length] = '\0';
+  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));
+}
+
+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;
+}
+
+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;
+}
+
+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--`. */
+static void mode_to_ls_string(mode_t mode, char out[11]) {
+  out[0] = S_ISDIR(mode)    ? 'd'
+           : S_ISLNK(mode)  ? 'l'
+           : S_ISCHR(mode)  ? 'c'
+           : S_ISBLK(mode)  ? 'b'
+           : S_ISFIFO(mode) ? 'p'
+           : S_ISSOCK(mode) ? 's'
+                            : '-';
+  mode_t bits = mode & 07777;
+  out[1] = (bits & S_IRUSR) ? 'r' : '-';
+  out[2] = (bits & S_IWUSR) ? 'w' : '-';
+  out[3] = (bits & S_IXUSR) ? (bits & S_ISUID ? 's' : 'x') : (bits & S_ISUID ? 'S' : '-');
+  out[4] = (bits & S_IRGRP) ? 'r' : '-';
+  out[5] = (bits & S_IWGRP) ? 'w' : '-';
+  out[6] = (bits & S_IXGRP) ? (bits & S_ISGID ? 's' : 'x') : (bits & S_ISGID ? 'S' : '-');
+  out[7] = (bits & S_IROTH) ? 'r' : '-';
+  out[8] = (bits & S_IWOTH) ? 'w' : '-';
+  out[9] = (bits & S_IXOTH) ? (bits & S_ISVTX ? 't' : 'x') : (bits & S_ISVTX ? 'T' : '-');
+  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), "?");
+  }
+  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 : "");
+  if (!ok) {
+    strbuf_free(&line);
+    return NULL;
+  }
+  return line.data;
+}
+
+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) {
+    fprintf(stream, "%s\n", escaped);
+    free(escaped);
+  } else {
+    fprintf(stream, "%s\n", line);
+  }
+  fflush(stream);
+}
+
+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;
+  if (to_stdout) {
+    char* line = config->out_format != NULL ? change_render_format(config->out_format, event)
+                                            : change_render_itemize(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);
+    if (line != NULL) {
+      print_escaped_line(config->log_file, line, config->eight_bit_output);
+      free(line);
+    }
+  }
+}
+
+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++;
+      continue;
+    }
+    char token = p[1];
+    if (token == '\0')
+      break;
+    if (token == 'M')
+      return true;
+    p += 2;
+  }
+  return false;
+}
+
+void change_emit_file_sent(const Config* config, const File* file) {
+  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.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;
+  }
+  change_emit(config, &event);
+}
+
+/* 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);
+}

src/client/change_list.h

@@ -0,0 +1,78 @@
+#ifndef CHANGE_LIST_H
+#define CHANGE_LIST_H
+
+#include "config.h"
+#include "file_types.h"
+#include <stdbool.h>
+#include <sys/stat.h>
+#include <time.h>
+
+/*
+ * Shared per-file change-event / output model (rsync --itemize-changes,
+ * --out-format, --log-file-format, and --list-only all render from here).
+ *
+ * FastSync is a push-style tool: the client sends files from the source tree
+ * to a server that writes them under the destination root.  Events are
+ * emitted by whichever code path decides a file's fate (the single-threaded
+ * send loop and the `-m` sender thread both call the same per-file sender), so
+ * all change events are emitted by exactly one thread and itemize/out-format
+ * lines never interleave with each other.  They may still interleave with
+ * legacy log messages (log.c) that share the same stdout/log-file stream.
+ */
+
+typedef enum {
+  CHANGE_SENT,       /* file data (full or delta) was transmitted */
+  CHANGE_UP_TO_DATE, /* receiver already had an identical file; skipped */
+} ChangeDecision;
+
+typedef struct {
+  const char* path; /* full source path */
+  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 */
+} 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);
+
+/* 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
+ * Unknown %X sequences are preserved verbatim.  Caller frees the result. */
+char* change_render_format(const char* format, const ChangeEvent* event);
+
+/* Render one --list-only long-listing entry:
+ *   `-rw-r--r--           12 2026/09/06 10:00:00 <path>`
+ * (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);
+
+/* Emit an event to every active destination:
+ *   stdout: --itemize-changes line, or the --out-format expansion when set;
+ *   log file: the --log-file-format expansion (requires --log-file).
+ * 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. */
+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);
+
+#endif

src/client/client_send.h

@@ -9,5 +9,8 @@ int send_chunk(Client* client, Chunk* chunk, Config* config);
 int send_files(Config* config);
 /* Takes ownership only when *config is set to NULL on return. */
 int send_files_multithreaded(Config** config);
+/* 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);
 
 #endif

src/client/client_validation.c

@@ -1,20 +1,61 @@
 #include "client_validation.h"
+#include "charset.h"
+#include "delay_updates.h"
 #include "log.h"
 #include "usage.h"
+#include "utils.h"
+#include <string.h>
 #include <stdio.h>
 
 /* Validate config after parsing. Returns true if valid. */
 bool validate_config(const Config* config) {
-  if (!config->send_directory || !config->receive_root_directory) {
+  /* Phase 6 residual-batch modes relax the normal source+destination pair: the
+     batch driver is local and needs only what it consumes.  --only-write-batch
+     emits a batch from the source (no destination, no server);
+     --read-batch applies a batch to the destination (no source, no server);
+     --write-batch runs the live transfer AND emits a batch, so it keeps the
+     full pair. */
+  bool write_batch = config->write_batch != NULL;
+  bool only_write_batch = config->only_write_batch != NULL;
+  bool read_batch = config->read_batch != NULL;
+  if ((write_batch && only_write_batch) || (write_batch && read_batch) ||
+      (only_write_batch && read_batch)) {
+    log_message(LOG_LEVEL_ERROR,
+                "--write-batch, --only-write-batch, and --read-batch are mutually exclusive");
+    return false;
+  }
+  if (read_batch) {
+    if (!config->receive_root_directory) {
+      log_message(LOG_LEVEL_ERROR, "--read-batch requires a destination directory");
+      print_usage();
+      return false;
+    }
+  } else if (only_write_batch) {
+    if (!config->send_directory) {
+      log_message(LOG_LEVEL_ERROR, "--only-write-batch requires a source directory");
+      print_usage();
+      return false;
+    }
+  } else if (!config->send_directory || !config->receive_root_directory) {
     log_message(LOG_LEVEL_ERROR, "source and destination directories are required");
     print_usage();
     return false;
   }
+  if (config_has_basis(config) && config->use_chunk_serialization) {
+    log_message(LOG_LEVEL_ERROR,
+                "--compare-dest/--copy-dest/--link-dest require per-file incremental checks and "
+                "cannot be combined with -s (chunk serialization)");
+    return false;
+  }
   if (config->use_sendfile && (config->use_chunk_serialization || config->use_compression)) {
     log_message(LOG_LEVEL_ERROR, "-f/--sendfile cannot be combined with -c (compression) or -s "
                                  "(chunk serialization)");
     return false;
   }
+  if (config->compression_threads > 0 && !config->use_compression) {
+    log_message(LOG_LEVEL_ERROR, "--compress-threads requires compression (-c or -z)");
+    return false;
+  }
   if (config->transport == TRANSPORT_SSH && config->use_sendfile) {
     log_message(LOG_LEVEL_ERROR, "-f/--sendfile is not supported with SSH transport");
     return false;
@@ -23,22 +64,71 @@ bool validate_config(const Config* config) {
     log_message(LOG_LEVEL_ERROR, "--incremental is not supported with -s (chunk serialization)");
     return false;
   }
-  if (config->use_delta && !config->use_incremental) {
+  /* -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");
+    return false;
+  }
+  if (config->skip_compress_set && config->use_chunk_serialization) {
+    log_message(LOG_LEVEL_ERROR,
+                "--skip-compress cannot be combined with -s (chunk serialization)");
+    return false;
+  }
+  if (config->use_delta && !config->whole_file && !config->use_incremental) {
     log_message(LOG_LEVEL_ERROR, "--delta requires --incremental");
     return false;
   }
-  if (config->use_delta && config->use_chunk_serialization) {
+  if (config->use_delta && !config->whole_file && config->use_chunk_serialization) {
     log_message(LOG_LEVEL_ERROR, "--delta cannot be combined with -s (chunk serialization)");
     return false;
   }
-  if (config->use_delta && config->use_sendfile) {
+  if (config->use_delta && !config->whole_file && config->use_sendfile) {
     log_message(LOG_LEVEL_ERROR, "--delta cannot be combined with -f (sendfile)");
     return false;
   }
-  if (config->append || config->append_verify) {
-    fprintf(
-        stderr,
-        "Error: --append and --append-verify are not supported yet; refusing to ignore option\n");
+  /* --append / --append-verify resume a shorter existing destination by
+     transmitting only the tail.  The resume needs the per-file STATUS_CHECK
+     handshake (so the dest length is learned), which chunk serialization -s
+     disables; and whole-file is the opposite intent (send everything), so the
+     two would silently make the resume pointless.  Both are rejected up front
+     rather than silently degrading to a full transfer. */
+  if ((config->append || config->append_verify) && config->use_chunk_serialization) {
+    log_message(LOG_LEVEL_ERROR,
+                "--append/--append-verify require the per-file incremental check and cannot be "
+                "combined with -s (chunk serialization)");
+    return false;
+  }
+  if ((config->append || config->append_verify) && config->whole_file) {
+    log_message(LOG_LEVEL_ERROR,
+                "--append/--append-verify are incompatible with --whole-file (which forces a "
+                "full transfer)");
+    return false;
+  }
+  /* --hard-links/-H transmits each later group member as a dedicated per-file
+     STATUS_HARDLINK frame, which chunk serialization -s does not support; and a
+     hard-links sibling carries no payload, so the tail-resume of --append is
+     meaningless for it.  Both combinations are rejected up front rather than
+     silently degrading. */
+  if (config->preserve_hard_links && config->use_chunk_serialization) {
+    log_message(LOG_LEVEL_ERROR,
+                "--hard-links/-H cannot be combined with -s (chunk serialization)");
+    return false;
+  }
+  /* -X/-A ride the per-file metadata frame; the buffer-based chunk-serialization
+     wire format does not carry the xattr block, so the pair is rejected up front
+     (mirroring -H + -s) rather than silently dropping attributes. */
+  if ((config->preserve_xattrs || config->preserve_acls) && config->use_chunk_serialization) {
+    log_message(LOG_LEVEL_ERROR,
+                "--xattrs/-X and --acls/-A cannot be combined with -s (chunk serialization)");
+    return false;
+  }
+  if (config->preserve_hard_links && (config->append || config->append_verify)) {
+    log_message(LOG_LEVEL_ERROR,
+                "--hard-links/-H cannot be combined with --append/--append-verify");
+    return false;
+  }
+  if (config->log_file_format && !config->log_file) {
+    log_message(LOG_LEVEL_ERROR, "--log-file-format requires --log-file");
     return false;
   }
   if (config->use_tls) {
@@ -47,5 +137,58 @@ bool validate_config(const Config* config) {
       return false;
     }
   }
+  /* Daemon credentials (A7, protocol 2.19.0): a --password-file would send the
+     username in the clear and derive a SCRAM proof a network sniffer could
+     attack offline, so it is only allowed over TLS (which itself mandates a
+     verified --cert/--key/--ca set above) or to a loopback destination.  A
+     remote plaintext daemon is refused here, before any network I/O. */
+  if (config->password_file && !config->use_tls && !utils_host_is_loopback(config->server_host)) {
+    log_message(LOG_LEVEL_ERROR, "sending daemon credentials to a non-local server requires --tls");
+    return false;
+  }
+  if (config->delay_updates && config->inplace) {
+    log_message(LOG_LEVEL_ERROR, "--delay-updates does not work with --inplace");
+    return false;
+  }
+  if (config->delay_updates && delay_updates_staging_name_conflict(config->backup_dir)) {
+    log_message(LOG_LEVEL_ERROR,
+                "--backup-dir is reserved when --delay-updates is active (used for the internal "
+                "staging directory)");
+    return false;
+  }
+  if (!config_has_valid_delete_timing(config)) {
+    log_message(LOG_LEVEL_ERROR,
+                "--delete-before/--delete-during/--delete-delay/--delete-after select the delete "
+                "timing; at most one may be given and each implies --delete");
+    return false;
+  }
+  /* --iconv: reject a malformed CONVERT_SPEC or an unsupported charset name at
+     startup (a probe iconv_open is attempted), so a typo'd charset never fails
+     the run mid-transfer with per-file errors. */
+  if (!charset_spec_valid(config->iconv_spec)) {
+    log_message(LOG_LEVEL_ERROR,
+                "--iconv requires LOCAL[,REMOTE] charset names supported by iconv");
+    return false;
+  }
+  /* --protocol: FastSync has exactly one wire format, so the forced version
+     must equal the current PROTOCOL_VERSION exactly.  Rejected here, before any
+     network I/O, rather than letting the server hit its own mismatch check. */
+  if (strcmp(config->version, PROTOCOL_VERSION) != 0) {
+    log_message(LOG_LEVEL_ERROR,
+                "--protocol must be %s (FastSync supports only its current wire "
+                "protocol version and cannot speak an older or virtual one)",
+                PROTOCOL_VERSION);
+    return false;
+  }
+  /* --copy-as pushes the source ids through the metadata path (it implies
+     --preserve).  A later --no-preserve would clear use_metadata, leaving the
+     transfer with nothing to chown while the receiver gate would still pass.
+     Refuse the combination up front rather than silently chowning nothing. */
+  if (config->copy_as_set && !config->use_metadata) {
+    log_message(LOG_LEVEL_ERROR,
+                "--copy-as requires metadata preservation and cannot be combined with "
+                "--no-preserve");
+    return false;
+  }
   return true;
 }

src/client/scanner.h

@@ -2,14 +2,28 @@
 #define SCANNER_H
 
 #include "chunk.h"
+#include "file_list.h"
+#include "filter.h"
+#include "hardlink.h"
+#include "protocol.h"
 #include "queue.h"
+#include "stop_condition.h"
 #include <dirent.h>
 #include <stdbool.h>
-#include <threads.h>
 #include <stdatomic.h>
+#include <sys/types.h>
+#include <threads.h>
 
 typedef struct {
   bool use_metadata;
+  /* Phase 4 metadata capture: -U/--atimes and -N/--crtimes tell the scanner to
+   * capture the source access / birth time into each entry's FileMetadata. */
+  bool preserve_atimes;
+  bool preserve_crtimes;
+  /* Phase 4 xattrs: when preserve_xattrs || preserve_acls is set the scanner
+   * captures each regular file's whitelisted xattr set onto the File. */
+  bool preserve_xattrs;
+  bool preserve_acls;
   unsigned long long chunk_size;
   char** exclude_patterns;
   int exclude_count;
@@ -23,14 +37,94 @@ typedef struct {
   bool copy_links;
   bool safe_links;
   bool copy_unsafe_links;
+  /* Phase 4 symlink-trust sender options: -k/--copy-dirlinks (dereference a
+   * symlink to a directory as a directory, keeping symlinks-to-files as
+   * symlinks) and --munge-links (rewrite each transmitted symlink target with a
+   * marker; escaping targets are never transmitted).  Both are client/sender
+   * side only and never serialized to the wire (keep_dirlinks is the
+   * receiver-side counterpart). */
+  bool copy_dirlinks;
+  bool munge_links;
   bool checksum;
+  bool one_file_system;
+  /* Phase 4 special/devices: whether device nodes (--devices) and special files
+   * (--specials) are preserved via recreation, and whether --copy-devices
+   * copies a device's content as an ordinary regular file. */
+  bool preserve_devices;
+  bool preserve_specials;
+  bool copy_devices;
+  /* Phase 2 (files-from / filter layer). All pointers are shared read-only
+   * across scanner instances and worker threads; ownership stays with the
+   * caller (client_send). */
+  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) */
+  /* --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
+     --files-from-listed directories always pass through.  Recursive transfers
+     never emit empty directories, so the flag has no additional effect there. */
+  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). */
+  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. */
+  bool ignore_io_errors;
+  /* --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
+   * observes a listed-but-missing entry). */
+  bool ignore_missing_args;
+  /* --hard-links (-H): shared, mutable (mutex-guarded) link-group detection
+   * table, NULL when -H is off.  Owned by the caller (client_send), shared
+   * read-only here; the parallel scanner passes it unchanged to every worker so
+   * one table detects every group across all subdirectories. */
+  HardLinkTable* hardlinks;
+  /* Phase 6: optional sender stop deadline.  When non-NULL the scanner checks
+   * it at natural loop boundaries and stops emitting chunks once reached
+   * (without marking the scan as failed), so a busy scan itself stops early.
+   * Client-only, never serialized to the wire. */
+  const StopCondition* stop_condition;
+  /* P7 Wave D (protocol 2.17.0): directory-time capture sink.  When
+   * `capture_dir_times` is true the recursive scan appends one is_dir File
+   * (with metadata, no payload) per source directory it traverses to
+   * `dir_entries`, so the sender can transmit trailing STATUS_DIR_TIMES
+   * frame(s) and the receiver can apply directory mtimes AFTER all children
+   * are written.  `dir_entries_mutex` (optional) guards the list
+   * for the parallel scanner's shared worker threads; the caller owns both.
+   * The --dirs generator does not use this (its directory entries carry their
+   * metadata inline through STATUS_MKDIR). */
+  bool capture_dir_times;
+  ArrayList* dir_entries;
+  mtx_t* dir_entries_mutex;
 } ScannerOptions;
 
+/* Internal per-scanner filter state. FilterNode chains represent the ordered
+ * per-directory .rsync-filter rules that apply below a directory. */
+typedef struct FilterNode FilterNode;
+
 typedef struct {
   Queue* directories;
   DIR* current_dir;
   char* current_path;
   bool use_metadata;
+  bool preserve_atimes;
+  bool preserve_crtimes;
+  bool preserve_xattrs;
+  bool preserve_acls;
   unsigned long long chunk_size;
   char** exclude_patterns;
   int exclude_count;
@@ -44,8 +138,57 @@ typedef struct {
   bool copy_links;
   bool safe_links;
   bool copy_unsafe_links;
+  bool copy_dirlinks;
+  bool munge_links;
   bool checksum;
+  bool one_file_system;
+  dev_t root_dev;
   bool failed;
+  /* Phase 4 special/devices (see ScannerOptions). */
+  bool preserve_devices;
+  bool preserve_specials;
+  bool copy_devices;
+  /* 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) */
+  bool at_seed_dir;         /* next open is the seed directory */
+  FilterNode* seed_node;    /* inherited context of the seed dir, or NULL */
+  FilterNode* current_node; /* filter context of the open directory */
+  ArrayList* filter_nodes;  /* owned FilterNode arena (may be NULL) */
+  const FileListSet* file_list;
+  const FilterRuleList* base_filters;
+  bool per_dir_filters;
+  /* --dirs / -R state for the directory-entry generator (dirs_mode replaces
+     the recursive scan). */
+  bool dirs_mode;
+  bool relative_mode; /* file_list && relative: send bare relative wire paths */
+  bool prune_empty_dirs;
+  bool dirs_root_emitted;
+  int list_index;
+  ArrayList* dirs_batch; /* owned when non-NULL */
+  unsigned long long dirs_batch_size;
+  /* Excluded-path sink (see ScannerOptions). `excluded_mutex` is shared across
+     parallel worker threads. */
+  ArrayList* excluded_paths;
+  mtx_t* excluded_mutex;
+  /* --ignore-errors: continue past unreadable directories (records io_error). */
+  bool ignore_io_errors;
+  /* --ignore-missing-args: --dirs listed-but-missing entries are skipped, not
+     fatal (see ScannerOptions.ignore_missing_args). */
+  bool ignore_missing_args;
+  /* A directory could not be opened (I/O error, e.g. EACCES).  With
+     --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;
+  /* --hard-links (-H): shared link-group detection table (see ScannerOptions).
+     NULL when -H is off. */
+  HardLinkTable* hardlinks;
+  /* Phase 6: sender stop deadline (from ScannerOptions). */
+  const StopCondition* stop_condition;
+  /* P7 Wave D directory-time capture (see ScannerOptions). */
+  bool capture_dir_times;
+  ArrayList* dir_entries;
+  mtx_t* dir_entries_mutex;
 } DirectoryScanner;
 
 typedef struct {
@@ -59,9 +202,13 @@ typedef struct {
   thrd_t* threads;
   bool done;
   bool failed;
+  /* A worker skipped an unreadable directory under --ignore-errors (non-fatal). */
+  bool io_error;
   atomic_bool cancelled;
   int completed;
   Chunk* initial_chunk;
+  ProtocolSession* allocation_session;
+  FilterNode* root_filter_node; /* root .rsync-filter context (owned by ps) */
 } ParallelScanner;
 
 DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_metadata,
@@ -77,10 +224,26 @@ Chunk* directory_scanner_next(DirectoryScanner* scanner);
 bool directory_scanner_failed(const DirectoryScanner* scanner);
 void directory_scanner_destroy(DirectoryScanner* scanner);
 
+/* --one-file-system (-x) decision: a directory entry may be descended into
+ * only when the option is disabled or the entry lives on the same device as
+ * the transfer root. Exposed so tests can exercise the rule directly. */
+bool scanner_same_filesystem(bool one_file_system, dev_t root_device, dev_t entry_device);
+
+/* Relative path of an on-disk path below `root` ("" == the root itself, NULL
+ * when `fs_path` is not under `root`). Handles trailing slashes and a root of
+ * "/". Exposed so tests can exercise the mapping directly. */
+char* scanner_path_relative(const char* root, const char* fs_path);
+
 ParallelScanner* parallel_scanner_create_with_options(const char* root_directory,
-                                                      const ScannerOptions* options);
+                                                      const ScannerOptions* options,
+                                                      ProtocolSession* allocation_session);
 Chunk* parallel_scanner_next(ParallelScanner* scanner);
 bool parallel_scanner_failed(const ParallelScanner* scanner);
+bool parallel_scanner_had_io_error(const ParallelScanner* scanner);
 void parallel_scanner_destroy(ParallelScanner* scanner);
 
+/* True when a directory could not be opened during the scan (an I/O error,
+   recorded even when --ignore-errors keeps the scan going past it). */
+bool directory_scanner_had_io_error(const DirectoryScanner* scanner);
+
 #endif

src/client/usage.c

@@ -11,65 +11,288 @@ void print_usage(void) {
   printf("Destination formats:\n");
   printf("  user@host:/path     SSH transport (rsync-style)\n");
   printf("  host:/path          SSH transport (current user)\n");
+  printf("  host::module/path   Daemon TCP transport (fastsync-server --daemon);\n");
+  printf("                      module names a server-side module, path is relative\n");
+  printf("                      within it (connect with --server-port)\n");
   printf("  /local/path         TCP transport (requires server on localhost:8080)\n");
   printf("\n");
   printf("Options:\n");
-  printf("  -c [level]          Enable compression (level 1-22, default 5)\n");
-  printf("  -z [level]          Alias for -c\n");
-  printf("  -a, --archive       Archive mode (-c -m -M)\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("  -n, --dry-run       Show what would be transferred\n");
-  printf("  -p <port>           SSH port (default: 22)\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("  --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");
+  printf("                      arguments, e.g. -e \"ssh -p 2222\"\n");
+  printf("  --rsync-path <path>  Alias for --fastsync-server-path (path to the\n");
+  printf("                      fastsync server binary on the remote side)\n");
+  printf("  --blocking-io        Leave the SSH transport socket without read/write\n");
+  printf("                      timeouts so it blocks naturally\n");
+  printf("  --outbuf=MODE        stdout/stderr buffering: N (none/unbuffered),\n");
+  printf("                      L (line-buffered), or B (block-buffered, default)\n");
   printf("  --progress          Show transfer progress\n");
+  printf("  -P                  Partial mode with progress (retention incomplete)\n");
+  printf("  -8, --8-bit-output  Leave high-bit characters unescaped in output\n");
+  printf("  --iconv=LOCAL[,REMOTE]  Convert file-NAME charsets at the wire boundary:\n");
+  printf("                      LOCAL is the charset of our file names, REMOTE is the\n");
+  printf("                      remote side's charset (defaults to LOCAL).  Names are\n");
+  printf("                      converted before transmission and back on receipt; a\n");
+  printf("                      name that cannot be represented in the target charset\n");
+  printf("                      fails that transfer cleanly (rsync-compatible)\n");
+  printf("  --protocol=NUM       Force the wire protocol version (must equal the current\n");
+  printf("                       PROTOCOL_VERSION; FastSync cannot speak older/virtual\n");
+  printf("                       wire formats)\n");
+  printf("  --write-batch=FILE    Run the normal live transfer AND also emit a\n");
+  printf("                       self-contained batch file of the whole source tree\n");
+  printf("                       (implies the single-threaded transfer path)\n");
+  printf("  --only-write-batch=FILE\n");
+  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("  --delete            Delete files on receiver not in source\n");
+  printf("                      (default timing: delete only after the whole\n");
+  printf("                      transfer has succeeded)\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("  --del               Alias for --delete-during\n");
+  printf("  --delete-delay      Delete extras only after a successful transfer\n");
+  printf("                      (implies --delete)\n");
+  printf("  --delete-after      Delete only after the whole transfer succeeded\n");
+  printf("                      (the default --delete timing; 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("  --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");
+  printf("  --force             A file may replace a destination directory by removing\n");
+  printf("                      that (non-empty) directory first\n");
+  printf("  --ignore-missing-args  A --files-from entry that does not exist under the\n");
+  printf("                      source is silently skipped instead of failing the run\n");
+  printf("  --delete-missing-args  Implies --ignore-missing-args; also deletes each missing\n");
+  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("  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("  --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");
+  printf("                    recursing into their contents (-d <dir> mirrors the source\n");
+  printf("                    directory empty; with --files-from listed dirs are created\n");
+  printf("                    empty and listed files are transferred)\n");
+  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("  --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("  --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("  -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("  --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("  --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");
+  printf("  -@, --modify-window <sec>  Modification time tolerance\n");
+  printf("  -u, --update        Skip files newer than the source on receiver\n");
   printf("  --existing          Skip files not already present at destination\n");
+  printf("  --compare-dest <dir>  Treat DIR (relative to destination root) as an extra\n");
+  printf("                    comparison basis: unchanged files are not transferred\n");
+  printf("                    (requires --incremental, which is implied)\n");
+  printf("  --copy-dest <dir>   Like --compare-dest, but copies the unchanged file from DIR\n");
+  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("  --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("  --delta             Delta transfer for changed files (requires --incremental)\n");
-  printf("  --delta-block <n>   Delta block size in bytes (default: %d)\n",
-         DELTA_BLOCK_SIZE_DEFAULT);
+  printf("  -W, --whole-file    Transfer changed files without delta processing\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("                    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);
-  printf("  -m                  Enable multithreading\n");
-  printf("  -s                  Enable chunk serialization\n");
-  printf("  -f                  Enable sendfile (TCP only, not with -c or -s)\n");
+  printf("  -j, --threads       Enable multithreading\n");
+  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("  --zc <alg>          Alias for --compress-choice\n");
   printf("  -v, --verbose       Enable debug logging\n");
-  printf("  -M, --preserve      Preserve file metadata\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("  -E, --executability Preserve executable permission bits\n");
+  printf("  -X, --xattrs        Preserve user extended attributes (user.* only;\n");
+  printf("                      privileged security.*/trusted.* namespaces are\n");
+  printf("                      never captured or applied)\n");
+  printf("  -A, --acls          Preserve POSIX ACLs (the system.posix_acl_* xattrs;\n");
+  printf("                      setting an ACL the receiver is not permitted to\n");
+  printf("                      set is warned and skipped, never fatal)\n");
+  printf("  --fake-super        Store the source uid/gid/mode/mtime in a reserved\n");
+  printf("                      user.fastsync.stat xattr on each written file and\n");
+  printf("                      re-apply it (fd-relative) on a privileged run; the\n");
+  printf("                      recording format diverges from rsync's user.rsync.%%stat%%\n");
+  printf("  --super             Permit the receiver to attempt super-user activities\n");
+  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("  --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("  --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("  --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("  --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("                      unprivileged receiver refuses the transfer.  Never\n");
+  printf("                      switches process credentials (safe-subset; see\n");
+  printf("                      RSYNC_COMPAT.md).  A daemon refuses it.\n");
   printf("  --chunk-size <n>    Chunk size in bytes (default: %d)\n", DEFAULT_CHUNK_SIZE);
   printf("  --source-dir <path> Source directory\n");
   printf("  --dest-dir <path>   Destination directory\n");
   printf("  --save-to-disk      Write received files to disk\n");
   printf("  --server-host <ip>  Server IP address (default: 127.0.0.1)\n");
   printf("  --server-port <n>   Server port (default: 8080)\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("  --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("  --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)\n");
-  printf("  -T <sec>            Alias for --timeout\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("  --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("  --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("  --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("  --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("  --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("  --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("  -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("  -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("  -H, --hard-links    Preserve hard-link relationships across the transfer\n");
   printf("  -S, --sparse        Handle sparse files efficiently\n");
+  printf(
+      "  -D                  Preserve device and special files (implies --devices --specials)\n");
+  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("  --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");
+  printf(
+      "  --preallocate       Allocate destination file space up front (fail-fast on full disk)\n");
+  printf("  --append            Resume a shorter destination by appending only its tail\n");
+  printf("                    (prefix is not verified; requires --incremental)\n");
+  printf("  --append-verify     Like --append, but verifies the retained prefix checksum\n");
+  printf("                    before appending (falls back to a full transfer on mismatch)\n");
+  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("  --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");
   printf("  -V, --version       Show version\n");
 }
+
+void print_debug_usage(void) {
+  printf("Supported debug flags: IO,PROTO,PACK,UTIL,ALL,NONE\n");
+  printf("Flags may be comma-separated, for example: --debug=io,proto\n");
+  printf("Other rsync debug flags are unsupported and rejected.\n");
+}

src/client/usage.h

@@ -2,5 +2,6 @@
 #define USAGE_H
 
 void print_usage(void);
+void print_debug_usage(void);
 
 #endif

src/server/receiver.c

@@ -1,12 +1,60 @@
 #include "receiver.h"
 
+#include "charset.h"
 #include "chunk.h"
+#include "config.h"
+#include "delay_updates.h"
+#include "file.h"
+#include "file_receive.h"
 #include "log.h"
+#include "metadata.h"
 #include "protocol.h"
 #include "utils.h"
 #include <stdlib.h>
 #include <sys/stat.h>
 
+bool receiver_outcomes_append(ReceiverOutcomes* outcomes, unsigned char code) {
+  if (!outcomes)
+    return false;
+  if (outcomes->count == outcomes->capacity) {
+    size_t new_capacity = outcomes->capacity == 0 ? 64 : outcomes->capacity * 2;
+    if (new_capacity < outcomes->capacity)
+      return false;
+    unsigned char* grown = realloc(outcomes->entries, new_capacity);
+    if (!grown)
+      return false;
+    outcomes->entries = grown;
+    outcomes->capacity = new_capacity;
+  }
+  outcomes->entries[outcomes->count++] = code;
+  return true;
+}
+
+void receiver_outcomes_destroy(ReceiverOutcomes* outcomes) {
+  if (!outcomes)
+    return;
+  free(outcomes->entries);
+  outcomes->entries = NULL;
+  outcomes->count = 0;
+  outcomes->capacity = 0;
+}
+
+/* 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) {
+  if (!config->remove_source_files)
+    return send_status(fd, STATUS_OK);
+  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);
+}
+
 static bool receiver_process_chunk(Chunk* chunk, const ReceiverSink* sink) {
   if (!chunk || !sink || !sink->store_file)
     return false;
@@ -26,28 +74,55 @@ static bool receiver_process_chunk(Chunk* chunk, const ReceiverSink* sink) {
   return true;
 }
 
+/* P7 Wave D: read one STATUS_DIR_TIMES frame (a count followed by that many
+ * (path, metadata) directory entries) and route every entry through the regular
+ * store_file sink.  A dir-time entry is RECORD-ONLY (file->dir_time_only): the
+ * sink accumulates its metadata for end-of-transfer application but creates
+ * nothing, so an empty/pruned source directory is never resurrected.  A large
+ * tree arrives as repeated frames, each bounded by MAX_MANIFEST_ENTRIES; a
+ * malformed count or entry is a hard error. */
+static bool receiver_process_dir_times(int fd, const Config* config, const ReceiverSink* sink) {
+  int count;
+  if (!receive_int(fd, &count) || count < 0 || count > MAX_MANIFEST_ENTRIES)
+    return false;
+  for (int i = 0; i < count; i++) {
+    File* dir = file_receive_dir_time(fd, config);
+    if (!dir || !sink->store_file(dir, sink->context))
+      return false;
+  }
+  return true;
+}
+
 static bool receiver_process_batch(Config* config, int file_descriptor) {
   int count;
   if (config->checksum || !receive_int(file_descriptor, &count) || count < 0 ||
       count > MAX_MANIFEST_ENTRIES)
     return false;
   for (int i = 0; i < count; i++) {
-    char* check_path = receive_str(file_descriptor);
+    char* check_path = receive_wire_str(file_descriptor);
     if (!check_path)
       return false;
     unsigned long long check_size;
     long long check_mtime;
+    long long check_mtime_nsec;
     if (!receive_n_data(file_descriptor, &check_size, sizeof(check_size)) ||
-        !receive_n_data(file_descriptor, &check_mtime, sizeof(check_mtime))) {
-      free(check_path);
-      return false;
-    }
-    if (!utils_valid_batch_path(check_path)) {
+        !receive_n_data(file_descriptor, &check_mtime, sizeof(check_mtime)) ||
+        !receive_n_data(file_descriptor, &check_mtime_nsec, sizeof(check_mtime_nsec)) ||
+        check_mtime_nsec < 0 || check_mtime_nsec >= 1000000000LL) {
       free(check_path);
       send_status(file_descriptor, STATUS_ERROR);
       return false;
     }
-    if (check_size > MAX_RECEIVE_FILE_SIZE) {
+    /* --trust-sender: accept a ``..``/absolute check path (a trusted sender's
+         odd-but-legit entry) and defer containment to the secure stat below;
+         an empty path is still always rejected. */
+    if (check_path[0] == '\0' ||
+        (!file_get_trust_sender() && !utils_valid_batch_path(check_path))) {
+      free(check_path);
+      send_status(file_descriptor, STATUS_ERROR);
+      return false;
+    }
+    if (check_size > MAX_RECEIVE_WHOLE_FILE_SIZE) {
       free(check_path);
       send_status(file_descriptor, STATUS_ERROR);
       return false;
@@ -60,8 +135,15 @@ static bool receiver_process_batch(Config* config, int file_descriptor) {
     }
     struct stat st;
     bool has_old = file_stat_secure(full_path, &st);
-    bool match = has_old && (unsigned long long)st.st_size == check_size &&
-                 (long long)st.st_mtime == check_mtime;
+    long long old_mtime_nsec = 0;
+    if (has_old) {
+#ifdef __linux__
+      old_mtime_nsec = st.st_mtim.tv_nsec;
+#endif
+    }
+    bool match = !config->ignore_times && has_old && (unsigned long long)st.st_size == check_size &&
+                 metadata_mtime_matches(st.st_mtime, old_mtime_nsec, (time_t)check_mtime,
+                                        (long)check_mtime_nsec, config->modify_window);
     bool sent = send_status(file_descriptor, match ? STATUS_OK : STATUS_NEXT);
     free(full_path);
     free(check_path);
@@ -72,19 +154,41 @@ static bool receiver_process_batch(Config* config, int file_descriptor) {
 }
 
 int receiver_process(Config* config, int file_descriptor, const ReceiverSink* sink) {
+  return receiver_process_pending(config, file_descriptor, sink, 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
+   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. */
+int receiver_process_pending(Config* config, int file_descriptor, const ReceiverSink* sink,
+                             DeleteManifest** pending_manifest) {
   Status status;
   if (!receive_status(file_descriptor, &status))
     return -1;
+  bool early_delete = config_delete_timing_early(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;
   while (status == STATUS_NEXT || status == STATUS_CHUNK || status == STATUS_CHECK ||
-         status == STATUS_KEEPALIVE || status == STATUS_ABORT || status == STATUS_CHECK_BATCH) {
+         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) {
     if (status == STATUS_KEEPALIVE) {
       if (!send_status(file_descriptor, STATUS_KEEPALIVE))
-        return -1;
-      goto next;
+        goto fail;
+      goto next_status;
     }
     if (status == STATUS_ABORT) {
       log_message(LOG_LEVEL_INFO, "Received abort from client, cleaning up");
-      return -1;
+      goto fail;
     }
     if (status == STATUS_CHECK) {
       bool skipped;
@@ -97,8 +201,64 @@ int receiver_process(Config* config, int file_descriptor, const ReceiverSink* si
         goto receive_error;
     } else if (status == STATUS_CHECK_BATCH) {
       if (!receiver_process_batch(config, file_descriptor))
-        return -1;
-      goto next;
+        goto fail;
+      goto next_status;
+    } else if (status == STATUS_MKDIR) {
+      File* dir = file_receive_directory(file_descriptor, config);
+      if (!dir || !sink->store_file(dir, sink->context))
+        goto receive_error;
+    } else if (status == STATUS_DIR_TIMES) {
+      if (!receiver_process_dir_times(file_descriptor, config, sink))
+        goto receive_error;
+    } else if (status == STATUS_HARDLINK) {
+      File* file = file_receive_hardlink(file_descriptor);
+      if (!file || !sink->store_file(file, sink->context))
+        goto receive_error;
+    } else if (status == STATUS_SYMLINK) {
+      File* sym = file_receive_symlink(file_descriptor, config);
+      if (!sym || !sink->store_file(sym, sink->context))
+        goto receive_error;
+    } else if (status == STATUS_SPECIAL) {
+      File* file = file_receive_special(file_descriptor);
+      if (!file || !sink->store_file(file, sink->context))
+        goto receive_error;
+    } else if (status == STATUS_MANIFEST) {
+      DeleteManifest* manifest = receive_manifest_entries(file_descriptor);
+      if (!manifest)
+        goto fail; /* receive_manifest_entries already sent STATUS_ERROR */
+      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_manifest_free(manifest);
+        if (!deletion_ok) {
+          send_status(file_descriptor, STATUS_ERROR);
+          goto fail;
+        }
+        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. */
+        if (deferred_manifest) {
+          log_message(LOG_LEVEL_ERROR, "Received a second delete manifest");
+          delete_manifest_free(deferred_manifest);
+          deferred_manifest = NULL;
+          delete_manifest_free(manifest);
+          send_status(file_descriptor, STATUS_ERROR);
+          goto fail;
+        }
+        deferred_manifest = manifest;
+      } else {
+        delete_manifest_free(manifest);
+      }
+      goto next_status;
     } else {
       File* file = file_receive(config, file_descriptor);
       if (!file) {
@@ -108,35 +268,135 @@ int receiver_process(Config* config, int file_descriptor, const ReceiverSink* si
       if (!sink->store_file(file, sink->context))
         goto receive_error;
     }
-  next:
+  next_status:
     if (!receive_status(file_descriptor, &status))
       goto receive_error;
   }
-  if (status == STATUS_MANIFEST && receive_manifest(file_descriptor, config, &status) != 0)
-    return -1;
   if (status != STATUS_FINISHED) {
     log_message(LOG_LEVEL_ERROR, "Did not receive FINISHED Status");
     goto receive_error;
   }
-  if (sink->send_success && !send_status(file_descriptor, STATUS_OK))
-    return -1;
+  /* Commit-style (late) deletion: every data frame has been received and the
+     sender proved the whole tree with STATUS_FINISHED.  The single-threaded
+     receiver stores files synchronously, so everything is on disk here and the
+     deletion can be committed before the --delay-updates publication in
+     send_success (the walker skips the staging dir, so staged files are never
+     treated as extras).  The -m receiver passes `pending_manifest` because its
+     disk writer may still be draining; the caller commits after the writer has
+     joined so no extra file is removed unless the transfer is known to have
+     succeeded. */
+  if (deferred_manifest) {
+    if (pending_manifest) {
+      *pending_manifest = deferred_manifest;
+      deferred_manifest = NULL;
+    } else {
+      bool deletion_ok = manifest_delete_all(config, deferred_manifest);
+      delete_manifest_free(deferred_manifest);
+      deferred_manifest = NULL;
+      if (!deletion_ok) {
+        send_status(file_descriptor, STATUS_ERROR);
+        goto fail;
+      }
+    }
+  }
+  if (sink->send_success) {
+    if (sink->send_success_frame) {
+      if (!sink->send_success_frame(file_descriptor, sink->context))
+        goto fail;
+    } else if (!send_status(file_descriptor, STATUS_OK)) {
+      goto fail;
+    }
+  }
   return 0;
 
+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. */
+  if (deferred_manifest) {
+    delete_manifest_free(deferred_manifest);
+    deferred_manifest = NULL;
+  }
+  return -1;
+
 receive_error:
+  if (deferred_manifest) {
+    delete_manifest_free(deferred_manifest);
+    deferred_manifest = NULL;
+  }
   if (sink->send_error)
     send_status(file_descriptor, STATUS_ERROR);
   return -1;
 }
 
-static bool receiver_save_file(File* file, void* context) {
-  Config* config = context;
-  bool success =
-      !config->save_to_disk || file_save_to_disk(config->receive_root_directory, file, config);
+/* ---- Single-threaded sink (used by receiver_receive_files) ---- */
+
+typedef struct {
+  Config* config;
+  ReceiverOutcomes outcomes;
+  /* P7 Wave D: directory metadata accumulated during the stream, applied only
+     after the whole transfer (and its delete/publication phases) has run so a
+     child write never clobbers a directory mtime. */
+  DirTimeList dir_times;
+} ReceiverSaveContext;
+
+static bool receiver_save_file(File* file, void* context_pointer) {
+  ReceiverSaveContext* context = context_pointer;
+  FileSaveResult result = FILE_SAVE_ERROR;
+  if (!context->config->save_to_disk) {
+    /* Nothing is stored; report the file as not-written so a
+       --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);
+  }
+  /* 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). */
+  if (result != FILE_SAVE_ERROR && file->is_dir && file->metadata &&
+      context->config->use_metadata && !context->config->omit_dir_times &&
+      !dir_time_list_add(&context->dir_times, file->path, file->metadata)) {
+    file_destroy(file);
+    return false;
+  }
+  if (result != FILE_SAVE_ERROR && context->config->remove_source_files && !file->is_dir &&
+      !file->is_special && !file->skip &&
+      !receiver_outcomes_append(&context->outcomes, (unsigned char)result)) {
+    file_destroy(file);
+    return false;
+  }
   file_destroy(file);
-  return success;
+  return result != FILE_SAVE_ERROR;
+}
+
+static bool receiver_send_success_frame(int fd, void* context_pointer) {
+  ReceiverSaveContext* context = context_pointer;
+  /* --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
+     success/outcome frame tells a --remove-source-files sender it may delete
+     its sources. */
+  if (context->config->delay_updates && context->config->delay_context) {
+    if (!delay_updates_publish(context->config->delay_context, context->config)) {
+      send_status(fd, STATUS_ERROR);
+      return false;
+    }
+  }
+  /* P7 Wave D: every child is now written and the delete / --delay-updates
+     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);
 }
 
 int receiver_receive_files(Config* config, int file_descriptor) {
-  ReceiverSink sink = {receiver_save_file, config, true, true};
-  return receiver_process(config, file_descriptor, &sink);
+  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};
+  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);
+  return ret;
 }

src/server/receiver.h

@@ -3,17 +3,46 @@
 
 #include "config.h"
 #include "file.h"
+#include "file_receive.h"
 
 typedef bool (*ReceiverFileSink)(File* file, void* context);
 
+/* Ordered per-file save outcomes for one connection.  One entry is appended
+   for every data-bearing file the receiver processes (in the order the files
+   were sent) so the sender of a --remove-source-files transfer can be told
+   which sources were actually written versus skipped on the receiver. */
+typedef struct {
+  unsigned char* entries; /* FILE_SAVE_WRITTEN or FILE_SAVE_SKIPPED */
+  size_t count;
+  size_t capacity;
+} ReceiverOutcomes;
+
+typedef bool (*ReceiverSuccessFrame)(int fd, void* context);
+
 typedef struct {
   ReceiverFileSink store_file;
   void* context;
   bool send_error;
   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. */
+  ReceiverSuccessFrame send_success_frame;
 } 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);
+
 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). */
+int receiver_process_pending(Config* config, int file_descriptor, const ReceiverSink* sink,
+                             DeleteManifest** pending_manifest);
 int receiver_receive_files(Config* config, int file_descriptor);
 
 #endif

src/server/server_cli.c

@@ -0,0 +1,281 @@
+#include "server_cli.h"
+#include "charset.h"
+#include "credentials.h"
+#include "utils.h"
+#include <limits.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+
+static void set_error(char* err, size_t err_size, const char* fmt, ...) {
+  if (!err || err_size == 0)
+    return;
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(err, err_size, fmt, args);
+  va_end(args);
+}
+
+void server_cli_options_default(ServerCliOptions* opts) {
+  if (!opts)
+    return;
+  memset(opts, 0, sizeof(*opts));
+  opts->destination_root = ".";
+  opts->port = 8080;
+  opts->bind_family = AF_UNSPEC;
+}
+
+static bool arg_is(const char* arg, const char* name) {
+  return strcmp(arg, name) == 0;
+}
+
+/* Match "--opt" against "--opt=value" / separate-value forms; on the "=" form
+ * *value receives the inline value.  Returns true when the argument is the
+ * named option in either form. */
+static bool arg_has_value(const char* arg, const char* name, const char** value) {
+  if (strcmp(arg, name) == 0)
+    return true; /* separate form; caller takes the next argv slot */
+  size_t name_len = strlen(name);
+  if (strncmp(arg, name, name_len) == 0 && arg[name_len] == '=') {
+    *value = arg + name_len + 1;
+    return true;
+  }
+  return false;
+}
+
+static int parse_port_arg(const char* value, int* port, char* err, size_t err_size) {
+  char* end;
+  long p = strtol(value, &end, 10);
+  if (*end != '\0' || p <= 0 || p > 65535) {
+    char* escaped = output_escape(value, false);
+    set_error(err, err_size, "invalid port '%s' (must be 1-65535)",
+              escaped ? escaped : "<allocation failed>");
+    free(escaped);
+    return -1;
+  }
+  *port = (int)p;
+  return 0;
+}
+
+int server_cli_parse(int argc, char* argv[], ServerCliOptions* opts, char* err, size_t err_size) {
+  if (err && err_size)
+    err[0] = '\0';
+  server_cli_options_default(opts);
+
+  for (int i = 1; i < argc; i++) {
+    const char* inline_value = NULL;
+    if (arg_is(argv[i], "--help")) {
+      opts->show_help = true;
+      return 1;
+    } else if (arg_is(argv[i], "--stdio")) {
+      opts->stdio_mode = true;
+    } else if (arg_is(argv[i], "--daemon")) {
+      opts->daemon_mode = true;
+    } else if (arg_is(argv[i], "--no-detach")) {
+      opts->no_detach = true;
+    } else if (arg_is(argv[i], "-v") || arg_is(argv[i], "--verbose")) {
+      opts->verbose = true;
+    } else if (arg_is(argv[i], "--tls")) {
+      opts->use_tls = true;
+    } else if (arg_is(argv[i], "--cert")) {
+      if (i + 1 >= argc) {
+        set_error(err, err_size, "missing argument for --cert");
+        return -1;
+      }
+      opts->tls_cert = argv[++i];
+    } else if (arg_is(argv[i], "--key")) {
+      if (i + 1 >= argc) {
+        set_error(err, err_size, "missing argument for --key");
+        return -1;
+      }
+      opts->tls_key = argv[++i];
+    } else if (arg_is(argv[i], "--ca")) {
+      if (i + 1 >= argc) {
+        set_error(err, err_size, "missing argument for --ca");
+        return -1;
+      }
+      opts->tls_ca = argv[++i];
+    } else if (arg_is(argv[i], "--client-cn")) {
+      if (i + 1 >= argc) {
+        set_error(err, err_size, "missing argument for --client-cn");
+        return -1;
+      }
+      opts->client_cn = argv[++i];
+    } else if (arg_is(argv[i], "--destination-root")) {
+      if (i + 1 >= argc) {
+        set_error(err, err_size, "missing argument for --destination-root");
+        return -1;
+      }
+      opts->destination_root = argv[++i];
+      opts->destination_root_set = true;
+    } else if (arg_has_value(argv[i], "--password-file", &inline_value)) {
+      if (!inline_value) {
+        if (i + 1 >= argc) {
+          set_error(err, err_size, "missing argument for --password-file");
+          return -1;
+        }
+        inline_value = argv[++i];
+      }
+      opts->password_file = inline_value;
+    } else if (arg_has_value(argv[i], "--early-input", &inline_value)) {
+      if (!inline_value) {
+        if (i + 1 >= argc) {
+          set_error(err, err_size, "missing argument for --early-input");
+          return -1;
+        }
+        inline_value = argv[++i];
+      }
+      opts->early_input_file = inline_value;
+    } else if (arg_has_value(argv[i], "--hash-credentials", &inline_value)) {
+      if (!inline_value) {
+        if (i + 1 >= argc) {
+          set_error(err, err_size, "missing argument for --hash-credentials");
+          return -1;
+        }
+        inline_value = argv[++i];
+      }
+      opts->hash_credentials_file = inline_value;
+    } else if (arg_has_value(argv[i], "--iterations", &inline_value)) {
+      if (!inline_value) {
+        if (i + 1 >= argc) {
+          set_error(err, err_size, "missing argument for --iterations");
+          return -1;
+        }
+        inline_value = argv[++i];
+      }
+      char* end = NULL;
+      long n = strtol(inline_value, &end, 10);
+      if (!end || *end != '\0' || n < (long)CREDENTIAL_MIN_ITERS ||
+          n > (long)CREDENTIAL_MAX_ITERS) {
+        set_error(err, err_size, "--iterations must be in [%u,%u], got '%s'", CREDENTIAL_MIN_ITERS,
+                  CREDENTIAL_MAX_ITERS, inline_value);
+        return -1;
+      }
+      opts->hash_iterations = (uint32_t)n;
+      opts->hash_iterations_set = true;
+    } else if (arg_is(argv[i], "--address")) {
+      if (i + 1 >= argc) {
+        set_error(err, err_size, "missing argument for --address");
+        return -1;
+      }
+      opts->bind_address = argv[++i];
+    } else if (arg_is(argv[i], "-4") || arg_is(argv[i], "--ipv4")) {
+      if (opts->bind_family == AF_INET6) {
+        set_error(err, err_size, "--ipv4 and --ipv6 are mutually exclusive");
+        return -1;
+      }
+      opts->bind_family = AF_INET;
+    } else if (arg_is(argv[i], "-6") || arg_is(argv[i], "--ipv6")) {
+      if (opts->bind_family == AF_INET) {
+        set_error(err, err_size, "--ipv4 and --ipv6 are mutually exclusive");
+        return -1;
+      }
+      opts->bind_family = AF_INET6;
+    } else if (arg_is(argv[i], "--allow-delete")) {
+      opts->allow_delete = true;
+    } else if (arg_is(argv[i], "--trust-sender")) {
+      opts->trust_sender = true;
+    } else if (arg_is(argv[i], "--no-super")) {
+      opts->no_super = true;
+    } else if (arg_is(argv[i], "--allow-unauthenticated")) {
+      opts->allow_unauthenticated = true;
+    } else if (arg_has_value(argv[i], "--iconv", &inline_value)) {
+      if (!inline_value) {
+        if (i + 1 >= argc) {
+          set_error(err, err_size, "missing argument for --iconv");
+          return -1;
+        }
+        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;
+      }
+      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) {
+          if (i + 1 >= argc) {
+            set_error(err, err_size, "missing argument for --config");
+            return -1;
+          }
+          inline_value = argv[++i];
+        }
+        opts->config_path = inline_value;
+      } else if (arg_has_value(argv[i], "--dparam", &inline_value)) {
+        if (!inline_value) {
+          if (i + 1 >= argc) {
+            set_error(err, err_size, "missing argument for --dparam");
+            return -1;
+          }
+          inline_value = argv[++i];
+        }
+        const char** grown =
+            realloc((char**)opts->dparams, (size_t)(opts->dparam_count + 1) * sizeof(const char*));
+        if (!grown) {
+          set_error(err, err_size, "out of memory parsing --dparam");
+          return -1;
+        }
+        opts->dparams = grown;
+        opts->dparams[opts->dparam_count++] = inline_value;
+      } else if (argv[i][0] == '-') {
+        char* escaped = output_escape(argv[i], false);
+        set_error(err, err_size, "unknown option: %s", escaped ? escaped : "<allocation failed>");
+        free(escaped);
+        return -1;
+      } else {
+        set_error(err, err_size, "unexpected argument '%s'", argv[i]);
+        return -1;
+      }
+    }
+  }
+
+  /* Cross-mode validation. */
+  if (opts->stdio_mode && opts->daemon_mode) {
+    set_error(err, err_size, "--stdio and --daemon are mutually exclusive");
+    return -1;
+  }
+  if (opts->daemon_mode && opts->destination_root_set) {
+    set_error(err, err_size,
+              "--destination-root cannot be combined with --daemon (module paths "
+              "replace it)");
+    return -1;
+  }
+  if (!opts->daemon_mode &&
+      (opts->config_path != NULL || opts->dparam_count > 0 || opts->no_detach ||
+       opts->password_file != NULL || opts->early_input_file != NULL)) {
+    set_error(err, err_size,
+              "--config, --dparam, --no-detach, --password-file, and --early-input require "
+              "--daemon");
+    return -1;
+  }
+  if (opts->hash_credentials_file != NULL && (opts->daemon_mode || opts->stdio_mode)) {
+    set_error(err, err_size, "--hash-credentials cannot be combined with --daemon or --stdio");
+    return -1;
+  }
+  if (opts->hash_iterations_set && opts->hash_credentials_file == NULL) {
+    set_error(err, err_size, "--iterations requires --hash-credentials");
+    return -1;
+  }
+  /* --iconv: reject a malformed CONVERT_SPEC or an unsupported charset name at
+     startup (a probe iconv_open is attempted). */
+  if (opts->iconv_spec != NULL && !charset_spec_valid(opts->iconv_spec)) {
+    set_error(err, err_size, "--iconv requires LOCAL[,REMOTE] charset names supported by iconv");
+    return -1;
+  }
+  return 0;
+}
+
+void server_cli_options_free(ServerCliOptions* opts) {
+  if (!opts)
+    return;
+  free((char**)opts->dparams);
+  opts->dparams = NULL;
+  opts->dparam_count = 0;
+}

src/server/server_cli.h

@@ -0,0 +1,68 @@
+#ifndef SERVER_CLI_H
+#define SERVER_CLI_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/* Parsed fastsync-server command line.  All string members are borrowed
+ * pointers into the original argv (valid for the life of the argv array the
+ * caller passed to server_cli_parse); dparams points at the raw --dparam
+ * argument strings.  No member owns heap memory. */
+typedef struct ServerCliOptions {
+  bool stdio_mode;              /* --stdio */
+  bool daemon_mode;             /* --daemon */
+  bool no_detach;               /* --no-detach */
+  bool verbose;                 /* -v / --verbose */
+  bool show_help;               /* --help */
+  bool use_tls;                 /* --tls */
+  const char* tls_cert;         /* --cert */
+  const char* tls_key;          /* --key */
+  const char* tls_ca;           /* --ca */
+  const char* client_cn;        /* --client-cn */
+  bool destination_root_set;    /* an explicit --destination-root was given */
+  const char* destination_root; /* --destination-root value ("." if unset) */
+  bool port_set;                /* an explicit -p was given */
+  int port;                     /* -p value (default 8080 when unset) */
+  const char* config_path;      /* --config value, or NULL */
+  const char* password_file;    /* --password-file value, or NULL (daemon) */
+  const char* early_input_file; /* --early-input value, or NULL (daemon) */
+  /* --hash-credentials=FILE: read `user:password` lines from FILE and print
+   * new-format credential-store lines to stdout, then exit.  Standalone mode
+   * (mutually exclusive with --daemon/--stdio). */
+  const char* hash_credentials_file;
+  bool hash_iterations_set; /* an explicit --iterations was given */
+  uint32_t hash_iterations; /* --iterations value (default CREDENTIAL_DEFAULT_ITERS) */
+  const char** dparams;     /* raw --dparam override strings */
+  int dparam_count;
+  const char* bind_address;   /* --address */
+  int bind_family;            /* AF_UNSPEC / AF_INET / AF_INET6 */
+  bool allow_delete;          /* --allow-delete */
+  bool trust_sender;          /* --trust-sender */
+  bool allow_unauthenticated; /* --allow-unauthenticated */
+  /* --no-super: operator veto forcing SUPER_MODE_OFF for every connection, so
+   * the receiver never attempts super-user activities (ownership application,
+   * device-node creation) even when running as root.  Applies to --stdio and
+   * --daemon alike; also makes the server refuse any client --copy-as. */
+  bool no_super; /* --no-super */
+  /* --iconv=CONVERT_SPEC: the server's own LOCAL charset declaration.  The
+   * client's full spec rides the wire config frame anyway; when the server is
+   * started with its own --iconv, its LOCAL half overrides the local charset
+   * the client assumed so the server converts received names to ITS charset.
+   * Borrowed pointer into argv (never owns heap). */
+  const char* iconv_spec; /* --iconv value, or NULL */
+} ServerCliOptions;
+
+/* Parse argc/argv into *opts.  Zero-initialize *opts before calling (or use
+ * server_cli_options_default).  Returns:
+ *   1  -- --help was requested (opts->show_help set; caller prints usage).
+ *   0  -- parsed successfully.
+ *  -1  -- invalid arguments (err is filled with the reason).
+ */
+void server_cli_options_default(ServerCliOptions* opts);
+int server_cli_parse(int argc, char* argv[], ServerCliOptions* opts, char* err, size_t err_size);
+/* Release the only heap the parsed options own (the dparams pointer array; the
+ * strings it points at are borrowed from argv and are not freed).  Safe to
+ * call on a zero-initialized/defaulted struct. */
+void server_cli_options_free(ServerCliOptions* opts);
+#endif

src/shared/array_list.c

@@ -1,17 +1,18 @@
 #include "log.h"
 #include "array_list.h"
+#include "protocol.h"
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 ArrayList* array_list_create(void (*item_destroyer)(void* item)) {
-  ArrayList* list = (ArrayList*)malloc(sizeof(ArrayList));
+  ArrayList* list = (ArrayList*)protocol_alloc(sizeof(ArrayList));
   if (list == NULL) {
     log_perror("ERROR: Could not allocate memory for array list struct");
     return NULL;
   }
 
-  list->items = malloc(INITIAL_ARRAY_SIZE * sizeof(void*));
+  list->items = protocol_alloc(INITIAL_ARRAY_SIZE * sizeof(void*));
   if (list->items == NULL) {
     free(list);
     return NULL;
@@ -41,7 +42,7 @@ static bool array_list_extend(ArrayList* array_list) {
   int new_capacity = array_list->capacity * 2;
   if (new_capacity == 0)
     new_capacity = INITIAL_ARRAY_SIZE;
-  void* new_items = realloc(array_list->items, new_capacity * sizeof(void*));
+  void* new_items = protocol_realloc(array_list->items, new_capacity * sizeof(void*));
   if (new_items == NULL) {
     log_perror("ERROR: Could not reallocate memory for array list items");
     return false;
@@ -67,7 +68,7 @@ void** array_list_to_array(const ArrayList* array_list) {
   if (array_list == NULL) {
     return NULL;
   }
-  void** array = malloc(array_list->size * sizeof(void*));
+  void** array = protocol_alloc(array_list->size * sizeof(void*));
   if (array == NULL) {
     log_perror("Could not malloc space for array from array list!");
     return NULL;

src/shared/batch.c

@@ -0,0 +1,160 @@
+#include "batch.h"
+#include "data.h"
+#include "file.h"
+#include "file_receive.h"
+#include "log.h"
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+/* 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. */
+static bool batch_metadata_mode = false;
+
+static bool write_all_bytes(int fd, const void* data, size_t size) {
+  const unsigned char* p = (const unsigned char*)data;
+  size_t done = 0;
+  while (done < size) {
+    ssize_t n = write(fd, p + done, size - done);
+    if (n < 0 && errno == EINTR)
+      continue;
+    if (n <= 0)
+      return false;
+    done += (size_t)n;
+  }
+  return true;
+}
+
+bool batch_write_header(int fd, const Config* config) {
+  if (fd < 0)
+    return false;
+  batch_metadata_mode = config != NULL && config->use_metadata;
+  if (!write_all_bytes(fd, BATCH_MAGIC, BATCH_MAGIC_LEN))
+    return false;
+  unsigned char version = BATCH_FORMAT_VERSION;
+  if (!write_all_bytes(fd, &version, 1))
+    return false;
+  unsigned char mode = batch_metadata_mode ? 1 : 0;
+  return write_all_bytes(fd, &mode, 1);
+}
+
+bool batch_write_chunk(int fd, Chunk* chunk) {
+  if (fd < 0 || chunk == NULL)
+    return false;
+  Data* serialized = chunk_serialize(chunk, batch_metadata_mode);
+  if (serialized == NULL)
+    return false;
+  bool ok = false;
+  unsigned long long length = (unsigned long long)serialized->size;
+  if (length > BATCH_MAX_RECORD) {
+    log_message(LOG_LEVEL_ERROR, "batch: record size %llu exceeds the %llu-byte cap", length,
+                (unsigned long long)BATCH_MAX_RECORD);
+  } else if (write_all_bytes(fd, &length, sizeof(length)) &&
+             (length == 0 || write_all_bytes(fd, serialized->data, (size_t)length))) {
+    ok = true;
+  }
+  data_destroy(serialized);
+  return ok;
+}
+
+/* Read exactly `size` bytes.  Returns true on success.  On reaching EOF, sets
+ * *clean_eof only when no bytes had been read yet (a clean boundary) and returns
+ * that value, so a truncated record (EOF mid-read) yields false. */
+static bool read_exact(int fd, void* data, size_t size, bool* clean_eof) {
+  unsigned char* p = (unsigned char*)data;
+  size_t done = 0;
+  while (done < size) {
+    ssize_t n = read(fd, p + done, size - done);
+    if (n < 0 && errno == EINTR)
+      continue;
+    if (n == 0) {
+      if (clean_eof)
+        *clean_eof = done == 0;
+      return done == 0;
+    }
+    if (n < 0)
+      return false;
+    done += (size_t)n;
+  }
+  if (clean_eof)
+    *clean_eof = false;
+  return true;
+}
+
+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;
+
+  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;
+  }
+  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;
+  }
+  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;
+  }
+  bool use_metadata = mode == 1;
+
+  while (1) {
+    unsigned long long length;
+    if (!read_exact(fd, &length, sizeof(length), &eof)) {
+      log_message(LOG_LEVEL_ERROR, "batch: truncated length prefix");
+      return -1;
+    }
+    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;
+    }
+    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;
+    }
+    if (!read_exact(fd, record, (size_t)length, &eof) || eof) {
+      log_message(LOG_LEVEL_ERROR, "batch: truncated chunk record");
+      free(record);
+      return -1;
+    }
+    Data* data = data_create(record, (size_t)length);
+    if (data == NULL)
+      return -1; /* 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;
+    }
+    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) {
+        chunk_destroy(chunk);
+        return -1;
+      }
+    }
+    chunk_destroy(chunk);
+  }
+  return 0;
+}

src/shared/batch.h

@@ -0,0 +1,28 @@
+#ifndef BATCH_H
+#define BATCH_H
+#include "chunk.h"
+#include "config.h"
+
+/* Phase 6 residual-batch codec.  A residual batch is a self-contained
+ * single-file record of a whole source tree: a magic+format-version header
+ * followed by length-prefixed chunk blobs (each built with chunk_serialize),
+ * byte-identical by construction.  The batch is a client-only driver feature:
+ * it never crosses the wire, so there is no PROTOCOL_VERSION bump and no server
+ * change. */
+
+#define BATCH_MAGIC "FSTRESBATCH"
+#define BATCH_MAGIC_LEN 11
+#define BATCH_FORMAT_VERSION 1
+/* Max size of a single length-prefixed record (a whole serialized chunk,
+ * which can span several files).  A single source file near the 64 MB wire
+ * limit plus per-file headers can produce a record slightly over 64 MB, so a
+ * large file just under the wire cap may be refused by the batch writer; this
+ * is documented upstream and the failure is clean (the partial batch is
+ * unlinked), never a truncated/corrupt batch. */
+#define BATCH_MAX_RECORD (64ULL * 1024 * 1024)
+
+bool batch_write_header(int fd, const Config* config);
+bool batch_write_chunk(int fd, Chunk* chunk);
+int batch_read_apply(int fd, const Config* config, const char* dest_root);
+
+#endif

src/shared/charset.c

@@ -0,0 +1,384 @@
+#include "charset.h"
+#include "log.h"
+#include "protocol.h"
+#include "utils.h"
+#include <errno.h>
+#include <iconv.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct {
+  iconv_t cd;
+} CharsetConversion;
+
+/* Process-wide wire conversion descriptor (one direction per process: a client
+ * only sends, a server only receives).  CONCURRENCY CONTRACT: iconv_t is not
+ * guaranteed thread-safe, so every conversion MUST run on a single thread at a
+ * time.  This holds today -- on the client the conversions run on the sender
+ * thread (in the -m pipeline chunk_serialize/send happen on the sender thread
+ * only), on the server on the receive-loop thread; the descriptor is
+ * initialized on one thread before any transfer thread spawns and torn down
+ * (charset_wire_free) only after all threads have joined.  Do not add a
+ * concurrent conversion path (e.g. parallel chunk serialization) without
+ * guarding access with a mutex. */
+static CharsetConversion* g_wire_conv;
+
+/* Grow *buf to double capacity, freeing it on failure.  realloc preserves the
+ * already-written prefix, so the caller only tracks its write offset. */
+static bool grow_charset_buffer(char** buf, size_t* cap) {
+  size_t new_cap = *cap * 2;
+  if (new_cap <= *cap) {
+    free(*buf);
+    *buf = NULL;
+    return false;
+  }
+  char* grown = realloc(*buf, new_cap);
+  if (!grown) {
+    free(*buf);
+    *buf = NULL;
+    return false;
+  }
+  *buf = grown;
+  *cap = new_cap;
+  return true;
+}
+
+/* Throw away any pending shift state so a subsequent conversion starts clean.
+ * The flush output is discarded; for the stateless single-byte/UTF charsets
+ * this feature targets it is a no-op. */
+static void charset_conversion_reset(const CharsetConversion* conv) {
+  char scratch[64];
+  char* sp = scratch;
+  size_t sl = sizeof(scratch);
+  (void)iconv(conv->cd, NULL, NULL, &sp, &sl);
+}
+
+int charset_spec_parse(const char* spec, char** local_out, char** remote_out) {
+  if (!local_out || !remote_out)
+    return -1;
+  *local_out = NULL;
+  *remote_out = NULL;
+  if (!spec || spec[0] == '\0')
+    return -1;
+  char* dup = str_dup(spec);
+  if (!dup)
+    return -1;
+  char* comma = strchr(dup, ',');
+  if (comma) {
+    if (comma == dup || comma[1] == '\0') {
+      free(dup);
+      return -1;
+    }
+    *comma = '\0';
+    *local_out = str_dup(dup);
+    *remote_out = str_dup(comma + 1);
+    free(dup);
+  } else {
+    *local_out = str_dup(dup);
+    *remote_out = str_dup(dup);
+    free(dup);
+  }
+  if (!*local_out || !*remote_out) {
+    free(*local_out);
+    free(*remote_out);
+    *local_out = NULL;
+    *remote_out = NULL;
+    return -1;
+  }
+  return 0;
+}
+
+void* charset_conversion_open(const char* from_charset, const char* to_charset) {
+  if (!from_charset || !to_charset)
+    return NULL;
+  iconv_t cd = iconv_open(to_charset, from_charset);
+  if (cd == (iconv_t)-1)
+    return NULL;
+  CharsetConversion* conv = malloc(sizeof(CharsetConversion));
+  if (!conv) {
+    iconv_close(cd);
+    return NULL;
+  }
+  conv->cd = cd;
+  return conv;
+}
+
+void charset_conversion_close(void* conversion) {
+  if (!conversion)
+    return;
+  CharsetConversion* conv = (CharsetConversion*)conversion;
+  iconv_close(conv->cd);
+  free(conv);
+}
+
+/* Probe a single conversion direction: the from/to charsets both open AND a
+ * representative ASCII name converts to a byte string containing no embedded
+ * NUL (so a target charset like UTF-16 that emits NUL bytes for ordinary ASCII
+ * names is rejected up front -- such an output would be silently truncated by
+ * the C-string wire helpers). */
+static bool direction_probe_valid(const char* from, const char* to) {
+  if (!from || !to)
+    return false;
+  void* conv = charset_conversion_open(from, to);
+  if (!conv)
+    return false;
+  bool ok = true;
+  char input = 'a';
+  char* in_ptr = &input;
+  size_t in_left = 1;
+  char out_buf[64];
+  char* out_ptr = out_buf;
+  size_t out_left = sizeof(out_buf);
+  if (iconv(((CharsetConversion*)conv)->cd, &in_ptr, &in_left, &out_ptr, &out_left) == (size_t)-1)
+    ok = false;
+  char flush_buf[64];
+  char* flush_ptr = flush_buf;
+  size_t flush_left = sizeof(flush_buf);
+  if (ok &&
+      iconv(((CharsetConversion*)conv)->cd, NULL, NULL, &flush_ptr, &flush_left) == (size_t)-1)
+    ok = false;
+  size_t produced = (size_t)(out_ptr - out_buf);
+  if (ok && produced > 0 && memchr(out_buf, '\0', produced) != NULL)
+    ok = false;
+  charset_conversion_close(conv);
+  return ok;
+}
+
+bool charset_pair_valid(const char* local, const char* remote) {
+  /* Both ends convert in opposite directions with the same two charsets, so a
+   * valid spec must open (and be NUL-free) in BOTH directions: the sender
+   * opens local->remote, the receiver opens remote->local. */
+  return direction_probe_valid(local, remote) && direction_probe_valid(remote, local);
+}
+
+bool charset_spec_valid(const char* spec) {
+  if (!spec)
+    return true;
+  char* local;
+  char* remote;
+  if (charset_spec_parse(spec, &local, &remote) != 0)
+    return false;
+  bool ok = charset_pair_valid(local, remote);
+  free(local);
+  free(remote);
+  return ok;
+}
+
+bool charset_spec_valid_direction(const char* from_charset, const char* to_charset) {
+  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
+ * rejected before the connection instead of refusing mid-transfer. */
+bool charset_wire_receiver_spec_valid(const char* spec, const char* server_spec) {
+  if (!spec)
+    return true;
+  char* local;
+  char* remote;
+  if (charset_spec_parse(spec, &local, &remote) != 0)
+    return false;
+  const char* wire = remote;
+  const char* target_local = local;
+  char* server_local = NULL;
+  char* server_remote = NULL;
+  if (server_spec) {
+    if (charset_spec_parse(server_spec, &server_local, &server_remote) != 0) {
+      free(local);
+      free(remote);
+      return false;
+    }
+    target_local = server_local;
+  }
+  bool ok = charset_spec_valid_direction(wire, target_local);
+  free(server_local);
+  free(server_remote);
+  free(local);
+  free(remote);
+  return ok;
+}
+
+char* charset_convert(const void* conversion, const char* in, int* err_out) {
+  if (!conversion || !in)
+    return NULL;
+  const CharsetConversion* conv = (const CharsetConversion*)conversion;
+  size_t in_len = strlen(in);
+  size_t cap = in_len + 16;
+  char* out = malloc(cap);
+  if (!out)
+    return NULL;
+  size_t in_left = in_len;
+  char* in_ptr = (char*)in;
+  size_t out_used = 0;
+
+  while (in_left > 0) {
+    char* out_ptr = out + out_used;
+    size_t out_left = cap - out_used;
+    if (iconv(conv->cd, &in_ptr, &in_left, &out_ptr, &out_left) == (size_t)-1) {
+      if (errno != E2BIG) {
+        if (err_out)
+          *err_out = errno;
+        charset_conversion_reset(conv);
+        free(out);
+        return NULL;
+      }
+      /* Output exhausted but input remains.  E2BIG does not roll the output
+         pointer back: the bytes iconv already emitted before the failure must
+         be preserved, so advance out_used before growing. */
+      out_used = (size_t)(out_ptr - out);
+      if (!grow_charset_buffer(&out, &cap))
+        return NULL;
+      continue;
+    }
+    out_used = (size_t)(out_ptr - out);
+  }
+
+  /* Flush any pending shift state (a no-op for the stateless single-byte and
+     UTF charsets this feature targets, but keeps the descriptor clean). */
+  for (;;) {
+    char* out_ptr = out + out_used;
+    size_t out_left = cap - out_used;
+    if (iconv(conv->cd, NULL, NULL, &out_ptr, &out_left) == (size_t)-1) {
+      if (errno != E2BIG) {
+        if (err_out)
+          *err_out = errno;
+        charset_conversion_reset(conv);
+        free(out);
+        return NULL;
+      }
+      out_used = (size_t)(out_ptr - out);
+      if (!grow_charset_buffer(&out, &cap))
+        return NULL;
+      continue;
+    }
+    out_used = (size_t)(out_ptr - out);
+    break;
+  }
+
+  /* A successful iconv call may legitimately consume the whole buffer (output
+     exactly fills cap), leaving no room for the terminator: guarantee headroom
+     before the final write. */
+  if (out_used >= cap && !grow_charset_buffer(&out, &cap))
+    return NULL;
+
+  /* Defense in depth: a target charset that emits embedded NUL bytes would
+     truncate at the first NUL in the C-string wire helpers; fail cleanly
+     (validation already rejects such charsets up front). */
+  if (memchr(out, '\0', out_used) != NULL) {
+    if (err_out)
+      *err_out = EILSEQ;
+    charset_conversion_reset(conv);
+    free(out);
+    return NULL;
+  }
+
+  out[out_used] = '\0';
+  return out;
+}
+
+bool charset_wire_init_sender(const char* spec) {
+  charset_wire_free();
+  if (!spec)
+    return true;
+  char* local;
+  char* remote;
+  if (charset_spec_parse(spec, &local, &remote) != 0)
+    return false;
+  void* conv = charset_conversion_open(local, remote);
+  free(local);
+  free(remote);
+  if (!conv)
+    return false;
+  g_wire_conv = (CharsetConversion*)conv;
+  return true;
+}
+
+bool charset_wire_init_receiver(const char* spec, const char* server_spec) {
+  charset_wire_free();
+  if (!spec)
+    return true;
+  char* local;
+  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). */
+  const char* wire = remote;
+  const char* target_local = local;
+  char* server_local = NULL;
+  char* server_remote = NULL;
+  if (server_spec) {
+    if (charset_spec_parse(server_spec, &server_local, &server_remote) != 0) {
+      free(local);
+      free(remote);
+      return false;
+    }
+    target_local = server_local;
+  }
+  void* conv = charset_conversion_open(wire, target_local);
+  free(server_local);
+  free(server_remote);
+  free(local);
+  free(remote);
+  if (!conv)
+    return false;
+  g_wire_conv = (CharsetConversion*)conv;
+  return true;
+}
+
+void charset_wire_free(void) {
+  if (g_wire_conv) {
+    charset_conversion_close(g_wire_conv);
+    g_wire_conv = NULL;
+  }
+}
+
+bool charset_wire_active(void) {
+  return g_wire_conv != NULL;
+}
+
+char* charset_wire_apply(const char* path) {
+  if (!g_wire_conv)
+    return str_dup(path);
+  return charset_convert(g_wire_conv, path, NULL);
+}
+
+static void charset_convert_failure_log(const char* path) {
+  char* escaped = output_escape(path, false);
+  log_message(LOG_LEVEL_ERROR, "--iconv: cannot convert file name '%s' to the target charset",
+              escaped ? escaped : "<unprintable>");
+  free(escaped);
+}
+
+bool send_wire_str(int file_descriptor, const char* local_path) {
+  if (!g_wire_conv)
+    return send_str(file_descriptor, local_path);
+  char* wire = charset_wire_apply(local_path);
+  if (!wire) {
+    charset_convert_failure_log(local_path);
+    return false;
+  }
+  bool ok = send_str(file_descriptor, wire);
+  free(wire);
+  return ok;
+}
+
+char* receive_wire_str(int file_descriptor) {
+  char* raw = receive_str(file_descriptor);
+  if (!raw)
+    return NULL;
+  if (!g_wire_conv)
+    return raw;
+  char* local = charset_convert(g_wire_conv, raw, NULL);
+  if (!local) {
+    charset_convert_failure_log(raw);
+    free(raw);
+    return NULL;
+  }
+  free(raw);
+  return local;
+}

src/shared/charset.h

@@ -0,0 +1,85 @@
+#ifndef CHARSET_H
+#define CHARSET_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+/* --iconv=CONVERT_SPEC file-name charset conversion (rsync compatibility).
+ *
+ * CONVERT_SPEC is "LOCAL[,REMOTE]": LOCAL is the charset of our own file
+ * names, REMOTE is the charset of the remote side's file names and defaults
+ * to LOCAL when the comma half is omitted.  The sender converts every local
+ * path from LOCAL to REMOTE before it goes on the wire; the receiver converts
+ * every received path back from REMOTE to LOCAL.  A NULL/disabled spec means
+ * identity with zero overhead (the common path never consults iconv).
+ *
+ * All helpers are friendly to the strict cold path: the wire conversion state
+ * is process-global (one direction per process -- a client only sends, a
+ * server only receives) and is initialized once, before any path is
+ * serialized, so conversion compiles to a single non-NULL check when disabled.
+ */
+
+/* Parse CONVERT_SPEC into malloc'd LOCAL and REMOTE charset names (caller
+ * frees both).  REMOTE is a separate copy of LOCAL when no comma is present.
+ * Returns 0 on success, -1 on a malformed spec (empty halves / missing value /
+ * allocation failure); nothing is allocated on the -1 path.  Both output
+ * pointers are REQUIRED (non-NULL). */
+int charset_spec_parse(const char* spec, char** local_out, char** remote_out);
+
+/* True when a CONVERT_SPEC is well-formed AND its charsets are usable for this
+ * feature: each pair opens in a probe iconv_open in BOTH directions (a sender
+ * converts local->remote, the receiver converts remote->local) and converting
+ * a representative ASCII name emits no embedded NUL byte (a UTF-16-style NUL
+ * emitter would be silently truncated by the C-string wire helpers).  A typo'd
+ * charset name is therefore rejected at startup, not mid-run.  NULL (iconv
+ * disabled) is always valid. */
+bool charset_spec_valid(const char* spec);
+
+/* Probe a concrete from->to conversion pair without keeping the descriptor:
+ * both charsets open AND a representative ASCII name converts with no embedded
+ * NUL.  Used for direction-specific validation (e.g. the receiver's exact
+ * wire->local direction including a server-side charset override). */
+bool charset_spec_valid_direction(const char* from_charset, const char* to_charset);
+bool charset_pair_valid(const char* local, const char* remote);
+
+/* One-shot conversion of a NUL-terminated input to a malloc'd NUL-terminated
+ * result, or NULL on failure.  On failure *err_out (when non-NULL) receives
+ * the iconv errno (EILSEQ/EINVAL = the input is not representable in the
+ * target charset).  The caller must free the result. */
+char* charset_convert(const void* conversion, const char* in, int* err_out);
+
+/* Open a conversion descriptor for direction from_charset -> to_charset.
+ * Returns NULL (errno = EINVAL) when a charset name is unsupported.  Freed
+ * with charset_conversion_close. */
+void* charset_conversion_open(const char* from_charset, const char* to_charset);
+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.
+ * 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);
+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. */
+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
+ * string, or NULL when the name cannot be represented in the target charset. */
+char* charset_wire_apply(const char* path);
+
+/* Convenience wire string I/O: encode+send_str / receive_str+decode.  Both
+ * return false/NULL (logging a clear --iconv error) on conversion failure, so
+ * an unconvertible path FAILS the transfer cleanly instead of silently sending
+ * a mangled name. */
+bool send_wire_str(int file_descriptor, const char* local_path);
+char* receive_wire_str(int file_descriptor);
+
+#endif

src/shared/checksum.c

@@ -0,0 +1,75 @@
+#include "checksum.h"
+#include <openssl/evp.h>
+#include <string.h>
+#include <strings.h>
+
+/* delta.c owns the single XXH_IMPLEMENTATION that provides the xxHash symbols
+ * for the whole binary; this TU only needs the declarations. */
+#include <xxhash.h>
+
+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)
+    return false;
+  if (data == NULL && size != 0)
+    return false;
+
+  if (algo == 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) {
+    /* 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;
+    return true;
+  }
+
+  return false;
+}
+
+int checksum_algo_from_name(const char* name) {
+  if (!name)
+    return -1;
+  if (strcasecmp(name, "xxh64") == 0 || strcasecmp(name, "xxhash") == 0)
+    return (int)CHECKSUM_ALGO_XXH64;
+  if (strcasecmp(name, "md5") == 0)
+    return (int)CHECKSUM_ALGO_MD5;
+  return -1;
+}
+
+const char* checksum_algo_name(ChecksumAlgo algo) {
+  switch (algo) {
+  case CHECKSUM_ALGO_XXH64:
+    return "xxh64";
+  case CHECKSUM_ALGO_MD5:
+    return "md5";
+  }
+  return "<unknown>";
+}
+
+bool checksum_algo_valid(int algo) {
+  return algo == (int)CHECKSUM_ALGO_XXH64 || algo == (int)CHECKSUM_ALGO_MD5;
+}
+
+uint8_t checksum_digest_len(ChecksumAlgo algo) {
+  switch (algo) {
+  case CHECKSUM_ALGO_XXH64:
+    return 8;
+  case CHECKSUM_ALGO_MD5:
+    return 16;
+  }
+  return 0;
+}

src/shared/checksum.h

@@ -0,0 +1,45 @@
+#ifndef CHECKSUM_H
+#define CHECKSUM_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/* 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;
+
+/* md5 digest is 16 bytes, the longest supported. */
+#define CHECKSUM_MAX_DIGEST_LEN 16
+
+/* 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).
+ *  - `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
+ * *out_len.  Returns false on NULL out* or when the digest would not fit.
+ * Never writes more than CHECKSUM_MAX_DIGEST_LEN bytes. */
+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);
+
+/* 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. */
+int checksum_algo_from_name(const char* name);
+
+/* Canonical name of an algorithm (used in CLI error messages). */
+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). */
+uint8_t checksum_digest_len(ChecksumAlgo algo);
+
+#endif /* CHECKSUM_H */

src/shared/chmod.c

@@ -0,0 +1,90 @@
+#include "chmod.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;
+}
+
+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;
+  }
+
+  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')
+      break;
+    begin = end + 1;
+    if (!*begin)
+      return false;
+  }
+  *result = changed;
+  return true;
+}

src/shared/chmod.h

@@ -0,0 +1,10 @@
+#ifndef CHMOD_H
+#define CHMOD_H
+
+#include <stdbool.h>
+#include <sys/stat.h>
+
+/* Apply the supported rsync --chmod syntax to a permission mode. */
+bool chmod_apply(mode_t mode, const char* spec, mode_t* result);
+
+#endif

src/shared/chunk.c

@@ -6,6 +6,7 @@
 #include <string.h>
 
 #include "array_list.h"
+#include "charset.h"
 #include "chunk.h"
 #include "compression.h"
 #include "data.h"
@@ -22,7 +23,7 @@
 Chunk* chunk_create(File** items, int element_count) {
   if (element_count < 0 || (element_count > 0 && items == NULL))
     return NULL;
-  Chunk* chunk = (Chunk*)malloc(sizeof(Chunk));
+  Chunk* chunk = (Chunk*)protocol_alloc(sizeof(Chunk));
   if (chunk == NULL) {
     log_perror("ERROR: Could not allocate memory for chunk structure");
     return NULL;
@@ -35,7 +36,7 @@ Chunk* chunk_create(File** items, int element_count) {
       free(chunk);
       return NULL;
     }
-    chunk->items = (File**)malloc((size_t)element_count * sizeof(File*));
+    chunk->items = (File**)protocol_alloc((size_t)element_count * sizeof(File*));
     if (chunk->items == NULL) {
       free(chunk);
       return NULL;
@@ -63,9 +64,22 @@ void chunk_destroy(void* item) {
   free(chunk);
 }
 
+/* --iconv: a chunk blob carries wire-charset path/target bytes.  Encode the
+ * sender-side path (a no-op copy when iconv is disabled) so the blob is in the
+ * same charset as every other wire string. */
+static char* chunk_encode_wire(const char* path) {
+  if (!charset_wire_active())
+    return str_dup(path);
+  return charset_wire_apply(path);
+}
+
 static unsigned long long per_file_serialize_size(File* file, bool use_metadata) {
   unsigned long long size = sizeof(size_t);
-  size_t path_len = strlen(file->path);
+  char* wire_path = chunk_encode_wire(file_wire_path(file));
+  if (!wire_path)
+    return 0;
+  size_t path_len = strlen(wire_path);
+  free(wire_path);
   unsigned long long metadata_size =
       use_metadata ? sizeof(int) + (file->metadata ? FILE_METADATA_WIRE_SIZE : 0) : 0;
   if ((unsigned long long)path_len > ULLONG_MAX - size)
@@ -74,12 +88,39 @@ static unsigned long long per_file_serialize_size(File* file, bool use_metadata)
   if (metadata_size > ULLONG_MAX - size)
     return 0;
   size += metadata_size;
+  /* Entry type marker: 0 = regular file, 1 = explicit directory entry,
+     2 = symlink entry (carries its target string), 3 = special/device node
+     (recreated by the receiver). */
+  if (sizeof(int) > ULLONG_MAX - size)
+    return 0;
+  size += sizeof(int);
+  /* A special node also carries its rdev major/minor. */
+  if (file->is_special) {
+    if (2 * sizeof(int32_t) > ULLONG_MAX - size)
+      return 0;
+    size += 2 * sizeof(int32_t);
+  }
   if (sizeof(size_t) > ULLONG_MAX - size)
     return 0;
   size += sizeof(size_t);
   if ((unsigned long long)file->data->size > ULLONG_MAX - size)
     return 0;
-  return size + file->data->size;
+  size += file->data->size;
+  /* Symlink entries append the target string (length-prefixed). */
+  if (file->is_symlink) {
+    char* wire_target = chunk_encode_wire(file->symlink_target ? file->symlink_target : "");
+    if (!wire_target)
+      return 0;
+    size_t target_len = strlen(wire_target);
+    free(wire_target);
+    if (sizeof(size_t) > ULLONG_MAX - size)
+      return 0;
+    size += sizeof(size_t);
+    if ((unsigned long long)target_len > ULLONG_MAX - size)
+      return 0;
+    size += target_len;
+  }
+  return size;
 }
 
 Data* chunk_serialize(Chunk* chunk, bool use_metadata) {
@@ -89,7 +130,8 @@ Data* chunk_serialize(Chunk* chunk, bool use_metadata) {
   for (int i = 0; i < chunk->element_count; i++) {
     if (!chunk->items[i] || !chunk->items[i]->path || !chunk->items[i]->data ||
         (chunk->items[i]->data->size > 0 && !chunk->items[i]->data->data) ||
-        chunk->items[i]->path[0] == '\0' || has_path_traversal(chunk->items[i]->path))
+        chunk->items[i]->path[0] == '\0' || has_path_traversal(chunk->items[i]->path) ||
+        (file_wire_path(chunk->items[i]))[0] == '\0')
       return NULL;
     unsigned long long file_size = per_file_serialize_size(chunk->items[i], use_metadata);
     if (file_size == 0 || file_size > ULLONG_MAX - data_size || data_size + file_size > SIZE_MAX)
@@ -104,11 +146,30 @@ Data* chunk_serialize(Chunk* chunk, bool use_metadata) {
   char* data_pointer = data->data;
   for (int i = 0; i < chunk->element_count; i++) {
     File* file = chunk->items[i];
-    size_t path_len = strlen(file->path);
+    char* wire_path = chunk_encode_wire(file_wire_path(file));
+    if (wire_path == NULL) {
+      data_destroy(data);
+      return NULL;
+    }
+    size_t path_len = strlen(wire_path);
     memcpy(data_pointer, &path_len, sizeof(size_t));
     data_pointer += sizeof(size_t);
-    memcpy(data_pointer, file->path, path_len);
+    memcpy(data_pointer, wire_path, path_len);
     data_pointer += path_len;
+    free(wire_path);
+
+    int entry_type = file->is_dir ? 1 : (file->is_symlink ? 2 : (file->is_special ? 3 : 0));
+    memcpy(data_pointer, &entry_type, sizeof(int));
+    data_pointer += sizeof(int);
+
+    if (file->is_special) {
+      int32_t special_major = file->rdev_major;
+      int32_t special_minor = file->rdev_minor;
+      memcpy(data_pointer, &special_major, sizeof(special_major));
+      data_pointer += sizeof(special_major);
+      memcpy(data_pointer, &special_minor, sizeof(special_minor));
+      data_pointer += sizeof(special_minor);
+    }
 
     if (use_metadata)
       metadata_to_buf(&data_pointer, file->metadata);
@@ -116,8 +177,24 @@ Data* chunk_serialize(Chunk* chunk, bool use_metadata) {
     size_t file_data_size = file->data->size;
     memcpy(data_pointer, &file_data_size, sizeof(size_t));
     data_pointer += sizeof(size_t);
-    memcpy(data_pointer, file->data->data, file_data_size);
+    if (file_data_size > 0)
+      memcpy(data_pointer, file->data->data, file_data_size);
     data_pointer += file_data_size;
+
+    if (file->is_symlink) {
+      char* wire_target = chunk_encode_wire(file->symlink_target ? file->symlink_target : "");
+      if (wire_target == NULL) {
+        data_destroy(data);
+        return NULL;
+      }
+      size_t target_len = strlen(wire_target);
+      memcpy(data_pointer, &target_len, sizeof(size_t));
+      data_pointer += sizeof(size_t);
+      if (target_len > 0)
+        memcpy(data_pointer, wire_target, target_len);
+      data_pointer += target_len;
+      free(wire_target);
+    }
   }
   return data;
 }
@@ -158,7 +235,7 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
       array_list_delete(files);
       return NULL;
     }
-    char* path = malloc(path_len + 1);
+    char* path = protocol_alloc(path_len + 1);
     if (path == NULL) {
       log_perror("Could not allocate memory for file path");
       array_list_delete(files);
@@ -174,6 +251,22 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
     data_pointer += path_len;
     remaining_size -= path_len;
 
+    /* --iconv: the blob holds the wire charset; translate it to the receiver's
+       local charset before validation and creation so the destination gets the
+       local name.  A name that cannot be decoded fails the file cleanly. */
+    if (charset_wire_active()) {
+      char* local_path = charset_wire_apply(path);
+      free(path);
+      if (local_path == NULL) {
+        log_message(LOG_LEVEL_ERROR,
+                    "--iconv: received chunk file name cannot be converted to the local charset");
+        array_list_delete(files);
+        return NULL;
+      }
+      path = local_path;
+      path_len = strlen(path);
+    }
+
     if (path_len == 0 || has_path_traversal(path)) {
       free(path);
       array_list_delete(files);
@@ -187,6 +280,54 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
       return NULL;
     }
 
+    if (remaining_size < sizeof(int)) {
+      log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for entry type");
+      file_destroy(file);
+      array_list_delete(files);
+      return NULL;
+    }
+    int entry_type;
+    memcpy(&entry_type, data_pointer, sizeof(int));
+    if (entry_type != 0 && entry_type != 1 && entry_type != 2 && entry_type != 3) {
+      log_message(LOG_LEVEL_ERROR, "Invalid chunk format: bad entry type");
+      file_destroy(file);
+      array_list_delete(files);
+      return NULL;
+    }
+    file->is_dir = entry_type == 1;
+    file->is_symlink = entry_type == 2;
+    file->is_special = entry_type == 3;
+    data_pointer += sizeof(int);
+    remaining_size -= sizeof(int);
+
+    if (file->is_special) {
+      if (remaining_size < 2 * (int32_t)sizeof(int32_t)) {
+        log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for special rdev");
+        file_destroy(file);
+        array_list_delete(files);
+        return NULL;
+      }
+      int32_t special_major, special_minor;
+      memcpy(&special_major, data_pointer, sizeof(special_major));
+      data_pointer += sizeof(special_major);
+      memcpy(&special_minor, data_pointer, sizeof(special_minor));
+      data_pointer += sizeof(special_minor);
+      remaining_size -= 2 * sizeof(int32_t);
+      /* Reject an out-of-range/negative rdev here as a malformed chunk (the
+         same 0xffff / 0x00ffffff bounds file_special_rdev_valid uses), so a
+         bogus large-but-positive rdev is refused cleanly instead of being
+         deferred to the creation site where it would abort after the frame. */
+      if (special_major < 0 || special_minor < 0 || special_major > 0xffff ||
+          special_minor > 0x00ffffff) {
+        log_message(LOG_LEVEL_ERROR, "Invalid chunk format: out-of-range special rdev");
+        file_destroy(file);
+        array_list_delete(files);
+        return NULL;
+      }
+      file->rdev_major = special_major;
+      file->rdev_minor = special_minor;
+    }
+
     if (use_metadata) {
       if (remaining_size < sizeof(int)) {
         log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for metadata");
@@ -245,7 +386,7 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
     }
 
     size_t allocation_size = file_data_size > 0 ? file_data_size : 1;
-    void* file_data = malloc(allocation_size);
+    void* file_data = protocol_alloc(allocation_size);
     if (file_data == NULL) {
       log_perror("Could not allocate memory for file data");
       file_destroy(file);
@@ -264,6 +405,58 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
     data_pointer += file_data_size;
     remaining_size -= file_data_size;
 
+    if (file->is_symlink) {
+      if (remaining_size < sizeof(size_t)) {
+        log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for symlink target");
+        file_destroy(file);
+        array_list_delete(files);
+        return NULL;
+      }
+      size_t target_len;
+      memcpy(&target_len, data_pointer, sizeof(size_t));
+      data_pointer += sizeof(size_t);
+      remaining_size -= sizeof(size_t);
+      if (target_len == 0 || remaining_size < target_len) {
+        log_message(LOG_LEVEL_ERROR, "Invalid chunk format: bad symlink target");
+        file_destroy(file);
+        array_list_delete(files);
+        return NULL;
+      }
+      char* target = protocol_alloc(target_len + 1);
+      if (!target) {
+        log_perror("Could not allocate memory for symlink target");
+        file_destroy(file);
+        array_list_delete(files);
+        return NULL;
+      }
+      memcpy(target, data_pointer, target_len);
+      target[target_len] = '\0';
+      if (memchr(target, '\0', target_len) != NULL) {
+        free(target);
+        file_destroy(file);
+        array_list_delete(files);
+        return NULL;
+      }
+      /* The symlink target also rides the wire charset; decode it to the local
+         charset like the path (a target is a path). */
+      if (charset_wire_active()) {
+        char* local_target = charset_wire_apply(target);
+        free(target);
+        if (local_target == NULL) {
+          log_message(LOG_LEVEL_ERROR,
+                      "--iconv: received chunk symlink target cannot be converted to the local "
+                      "charset");
+          file_destroy(file);
+          array_list_delete(files);
+          return NULL;
+        }
+        target = local_target;
+      }
+      file->symlink_target = target;
+      data_pointer += target_len;
+      remaining_size -= target_len;
+    }
+
     if (!array_list_add(files, file)) {
       file_destroy(file);
       array_list_delete(files);
@@ -290,15 +483,20 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
 }
 
 Data* chunk_compress(Chunk* chunk, int compression_level, bool use_metadata) {
+  return chunk_compress_with_threads(chunk, compression_level, use_metadata, 0);
+}
+
+Data* chunk_compress_with_threads(Chunk* chunk, int compression_level, bool use_metadata,
+                                  int compression_threads) {
   log_message(LOG_LEVEL_DEBUG, "Starting to compress chunk");
   Data* serialized = chunk_serialize(chunk, use_metadata);
   if (serialized == NULL)
     return NULL;
-  Data* compressed = data_compress(serialized, compression_level);
+  Data* compressed = data_compress_with_threads(serialized, compression_level, compression_threads);
   data_destroy(serialized);
   if (compressed == NULL)
     return NULL;
-  log_message(LOG_LEVEL_DEBUG, "Chunk successfully compressed");
+  log_debug_message(LOG_DEBUG_PACK, "Chunk successfully compressed");
   return compressed;
 }
 

src/shared/chunk.h

@@ -19,6 +19,8 @@ void chunk_destroy(void* chunk);
 Data* chunk_serialize(Chunk* chunk, bool use_metadata);
 Chunk* chunk_deserialize(Data* data, bool use_metadata);
 Data* chunk_compress(Chunk* chunk, int compression_level, bool use_metadata);
+Data* chunk_compress_with_threads(Chunk* chunk, int compression_level, bool use_metadata,
+                                  int compression_threads);
 Chunk* receive_chunk_data(int fd, const Config* config);
 
 #endif

src/shared/compression.c

@@ -1,33 +1,53 @@
 #include "compression.h"
 #include "data.h"
 #include "log.h"
+#include "protocol.h"
 #include <stdlib.h>
 #include <limits.h>
 #include <stdint.h>
 #include <string.h>
 #include <strings.h>
+#include <unistd.h>
 #include <zstd.h>
 
 #define INITIAL_DECOMPRESS_BUF_SIZE (1024 * 1024)
 #define MAX_DECOMPRESSED_SIZE (100ULL * 1024 * 1024) /* 100 MB hard ceiling */
 
-static const char* SKIP_COMPRESSION_EXTENSIONS[] = {".jpg", ".jpeg", ".png", ".gif", ".mp4", ".mkv",
-                                                    ".zip", ".gz",   ".xz",  ".zst", NULL};
+static char* SKIP_COMPRESSION_EXTENSIONS[] = {".jpg", ".jpeg", ".png", ".gif", ".mp4", ".mkv",
+                                              ".zip", ".gz",   ".xz",  ".zst", NULL};
 
 bool compression_should_skip(const char* path) {
+  return compression_should_skip_with_suffixes(path, NULL, -1);
+}
+
+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)
     return false;
-  for (int i = 0; SKIP_COMPRESSION_EXTENSIONS[i]; i++) {
-    if (strcasecmp(dot, SKIP_COMPRESSION_EXTENSIONS[i]) == 0)
+  if (count < 0) {
+    suffixes = SKIP_COMPRESSION_EXTENSIONS;
+    count = 0;
+    while (SKIP_COMPRESSION_EXTENSIONS[count])
+      count++;
+  }
+  for (int i = 0; i < count; i++) {
+    if (strcasecmp(dot, suffixes[i]) == 0)
       return true;
   }
   return false;
 }
 
 Data* data_compress(Data* data_to_compress, int compression_level) {
+  return data_compress_with_threads(data_to_compress, compression_level, 0);
+}
+
+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)
+    return NULL;
   log_message(LOG_LEVEL_DEBUG, "Starting to compress data");
   size_t dst_size = ZSTD_compressBound(data_to_compress->size);
   Data* compressed_data = data_create_empty(dst_size);
@@ -49,6 +69,30 @@ Data* data_compress(Data* data_to_compress, int compression_level) {
     return NULL;
   }
 
+  if (compression_threads > 0) {
+    long online_cpus = sysconf(_SC_NPROCESSORS_ONLN);
+    int available_threads = online_cpus > 0 && online_cpus < compression_threads
+                                ? (int)online_cpus
+                                : compression_threads;
+    zret = ZSTD_CCtx_setParameter(cctx, ZSTD_c_nbWorkers, available_threads);
+    if (ZSTD_isError(zret)) {
+      log_message(LOG_LEVEL_ERROR, "Failed to set compression threads: %s",
+                  ZSTD_getErrorName(zret));
+      ZSTD_freeCCtx(cctx);
+      data_destroy(compressed_data);
+      return NULL;
+    }
+    /* Streaming compression needs the source size before threaded mode can end a frame. */
+    zret = ZSTD_CCtx_setPledgedSrcSize(cctx, data_to_compress->size);
+    if (ZSTD_isError(zret)) {
+      log_message(LOG_LEVEL_ERROR, "Failed to set compression source size: %s",
+                  ZSTD_getErrorName(zret));
+      ZSTD_freeCCtx(cctx);
+      data_destroy(compressed_data);
+      return NULL;
+    }
+  }
+
   ZSTD_inBuffer input = {data_to_compress->data, data_to_compress->size, 0};
   ZSTD_outBuffer output = {compressed_data->data, dst_size, 0};
 
@@ -66,8 +110,8 @@ Data* data_compress(Data* data_to_compress, int compression_level) {
   compressed_data->size = output.pos;
   ZSTD_freeCCtx(cctx);
 
-  log_message(LOG_LEVEL_DEBUG, "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",
+                    data_to_compress->size, compressed_data->size);
   return compressed_data;
 }
 
@@ -75,7 +119,7 @@ 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;
-  log_message(LOG_LEVEL_DEBUG, "Start to decompress data");
+  log_debug_message(LOG_DEBUG_UTIL, "Start to decompress data");
   unsigned long long dst_size =
       ZSTD_getFrameContentSize(compressed_data->data, compressed_data->size);
   if (ZSTD_isError(dst_size)) {
@@ -139,7 +183,7 @@ Data* data_decompress_limited(Data* compressed_data, size_t maximum_size) {
       buf_size *= 2;
       if (buf_size > hard_limit)
         buf_size = (size_t)hard_limit;
-      void* new_data = realloc(uncompressed_data->data, buf_size);
+      void* new_data = protocol_realloc(uncompressed_data->data, buf_size);
       if (!new_data) {
         log_message(LOG_LEVEL_ERROR, "Failed to grow decompression buffer");
         ZSTD_freeDCtx(dctx);
@@ -155,7 +199,7 @@ Data* data_decompress_limited(Data* compressed_data, size_t maximum_size) {
   uncompressed_data->size = output.pos;
   ZSTD_freeDCtx(dctx);
 
-  log_message(LOG_LEVEL_DEBUG, "Decompressed data successfully");
+  log_debug_message(LOG_DEBUG_UTIL, "Decompressed data successfully");
   return uncompressed_data;
 }
 

src/shared/compression.h

@@ -4,9 +4,14 @@
 #include "data.h"
 #include <stdbool.h>
 
+#define COMPRESSION_MAX_THREADS 64
+
 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(const char* path);
+bool compression_should_skip_with_suffixes(const char* path, char* const* suffixes, int count);
 
 #endif

src/shared/config.h

@@ -2,12 +2,72 @@
 #define CONFIG_H
 
 #include "array_list.h"
+#include "checksum.h"
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <time.h>
 
 typedef enum { TRANSPORT_TCP, TRANSPORT_SSH } TransportType;
 
+/* --outbuf stdout/stderr buffering style (client-only launch concern, never
+ * crosses the wire).  OUTBUF_BLOCK is the default, matching the stdio default
+ * (fully buffered when output is not a terminal). */
+typedef enum {
+  OUTBUF_BLOCK = 0, /* _IOFBF */
+  OUTBUF_LINE,      /* _IOLBF */
+  OUTBUF_NONE       /* _IONBF */
+} OutbufMode;
+
+/* Receiver-side staging state for --delay-updates.  Forward-declared here so
+   Config can carry it; the concrete type lives in delay_updates.h. */
+typedef struct DelayUpdatesContext DelayUpdatesContext;
+
+/* Alternate basis-directory modes (--compare-dest / --copy-dest /
+ * --link-dest).  Each flag adds one entry to the ordered Config->basis_dirs
+ * list; the receiver consults entries in command-line order and stops at the
+ * first exact match, mirroring rsync's basis-dir priority rules. */
+typedef enum {
+  BASIS_DEST_NONE = 0,
+  BASIS_DEST_COMPARE, /* compare only: never copies, never materializes */
+  BASIS_DEST_COPY,    /* local copy of the matched basis file */
+  BASIS_DEST_LINK     /* hard link to the matched basis file */
+} BasisDestType;
+
+typedef struct BasisDest {
+  BasisDestType type;
+  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). */
+typedef struct {
+  int32_t from;
+  int32_t to;
+} IdentityMap;
+
+/* --sockopts=OPTIONS allowlist.  Only these option names are accepted; anything
+ * else is rejected (never silently ignored).  TCP_NODELAY, SO_KEEPALIVE and
+ * SO_REUSEADDR are boolean options (value 0/1); SO_RCVBUF and SO_SNDBUF take a
+ * non-negative byte count.  All are applied as int-sized setsockopt values. */
+typedef enum {
+  SOCKOPT_TCP_NODELAY = 0,
+  SOCKOPT_SO_KEEPALIVE,
+  SOCKOPT_SO_RCVBUF,
+  SOCKOPT_SO_SNDBUF,
+  SOCKOPT_SO_REUSEADDR,
+  SOCKOPT_COUNT
+} SockOptId;
+
+typedef struct {
+  SockOptId id; /* allowlist index */
+  int value;    /* 0/1 for booleans, byte count for SO_RCVBUF/SO_SNDBUF */
+} SockOptEntry;
+
 typedef struct Config {
   char* version;
   char* send_directory;
@@ -18,23 +78,70 @@ typedef struct Config {
   bool use_compression;
   bool use_sendfile;
   bool use_metadata;
+  bool use_executability;
+  bool metadata_explicitly_disabled;
   bool show_progress;
   bool dry_run;
+  bool remove_source_files;
   bool use_delete;
   int compression_level;
+  int compression_threads;
   unsigned long long chunk_size;
   int ssh_port;
   TransportType transport;
   char* ssh_destination;
+  /* Daemon module selection (Wave A, protocol 2.15.0).  Client-composed from a
+   * host::module/path destination; NULL or "" means "no module" (the ordinary
+   * standalone-server path).  Crosses the wire as a trailing config-frame
+   * string so the daemon can look the module up in its own config and confine
+   * the connection to the module's root (never a client-chosen root). */
+  char* module;
+  /* Daemon password authentication (A7 remediation, protocol 2.19.0).
+   * Client-composed from a --password-file whose first meaningful line is
+   * `user:password`: the client sends ONLY the username in the config frame
+   * (auth_user); the literal password is kept in auth_password CLIENT-SIDE for
+   * the duration of the SCRAM challenge/response and is NEVER serialized.  Both
+   * are NULL when the client has no credentials to present; a module WITHOUT
+   * `auth users` stays open and the server ignores any credentials that do
+   * arrive (the client sends them opportunistically and the server decides). */
+  char* auth_user;
+  char* auth_password;
+  /* Client-only path of --password-file (never crosses the wire; it is read to
+   * populate auth_user/auth_password before connecting). */
+  char* password_file;
   char* fastsync_server_path;
+  /* --iconv=CONVERT_SPEC (protocol 2.16.0, rsync compatibility): convert the
+   * charset of FILE NAMES at the wire boundary.  CONVERT_SPEC is
+   * "LOCAL[,REMOTE]": LOCAL is the charset of our own file names, REMOTE is
+   * the remote side's charset and defaults to LOCAL.  The sender converts
+   * every path LOCAL->REMOTE before transmitting it; the receiver converts
+   * every received path back REMOTE->LOCAL before creating/writing it.  The
+   * FULL SPEC crosses the wire as a trailing config-frame string so each end
+   * derives its own LOCAL and the wire (REMOTE) charset symmetrically.  NULL
+   * (or "") means no conversion: identity with zero overhead.  See charset.c
+   * and the PROTOCOL_VERSION note below. */
+  char* iconv_spec;
   char** exclude_patterns;
   int exclude_count;
   char** include_patterns;
   int include_count;
   unsigned long long max_size;
   unsigned long long min_size;
+  unsigned long long max_alloc;
   bool use_incremental;
+  bool ignore_times;
+  bool size_only;
   bool use_delta;
+  bool whole_file;
+  /* -y/--fuzzy: when a file must be transferred and the destination holds no
+   * usable file at the exact path, the receiver may reuse a SIMILAR-named
+   * existing regular file in the same destination directory as the delta
+   * basis so the sender transmits only the differences.  Crosses the wire
+   * (the receiver performs the candidate search); the CLI implies
+   * --incremental + --delta because the similar-basis only matters on the
+   * receiver-driven delta path.  Off by default. */
+  bool fuzzy;
+  int modify_window;
   uint32_t delta_block_size;
   unsigned long long delta_max_file_size;
   bool use_tls;
@@ -59,6 +166,15 @@ typedef struct Config {
   bool copy_links;
   bool safe_links;
   bool copy_unsafe_links;
+  /* Phase 4 symlink-trust.  -k/--copy-dirlinks and --munge-links are
+   * CLIENT/sender-side only (they decide how the SENDER scans and rewrites
+   * symlinks; the receiver never reads them), so they never cross the wire.
+   * -K/--keep-dirlinks is a RECEIVER-side policy (follow an in-root destination
+   * symlink-to-directory as a directory) and CROSSES the wire along with
+   * --munge-links (so the receiver knows to unmunge). */
+  bool copy_dirlinks; /* client-only, sender-side (-k) */
+  bool munge_links;   /* crosses the wire */
+  bool keep_dirlinks; /* crosses the wire (-K) */
 
   // Issue #121: Extended metadata preservation
   bool preserve_hard_links;
@@ -66,41 +182,135 @@ typedef struct Config {
   bool preserve_xattrs;
   bool preserve_devices;
   bool preserve_sparse;
+  /* Phase 4 special/devices: preserve special files (FIFOs, sockets) and device
+   * nodes on the destination by recreating them (mknod/mkfifo) instead of
+   * transferring content.  preserve_specials mirrors rsync --specials (the
+   * special-file half of -D); preserve_devices mirrors --devices (the device
+   * half of -D); both CROSS the wire so the receiver knows a special/device
+   * entry must be recreated rather than written as a regular file. */
+  bool preserve_specials;
+  /* --copy-devices: copy the CONTENT of a source device as an ordinary regular
+   * file on the destination (rsync's non-privileged safe mode), instead of
+   * recreating the device node.  CROSSES the wire (receiver treats the entry as
+   * a regular file, which is the default, so this is belt-and-braces). */
+  bool copy_devices;
+  /* --write-devices: write the received data directly INTO an existing device
+   * node on the destination instead of creating a regular file.  Dangeroud;
+   * see RSYNC_COMPAT.md for the tight gating.  CROSSES the wire. */
+  bool write_devices;
 
   // Issue #122: Output/logging options
   bool itemize_changes;
   char* out_format;
+  char* log_file_format;
   int info_level;
   int debug_level;
   bool list_only;
   bool human_readable;
+  bool eight_bit_output;
 
   // Issue #127: Transfer modes
   bool existing;
+  bool ignore_existing;
   bool update;
   bool inplace;
+  bool delay_updates;
+  bool use_fsync;
   bool append;
   bool append_verify;
+  /* --preallocate: allocates the destination file's full expected space up
+   * front (before any data is written) so a transfer that would overflow disk
+   * fails fast at allocation time and the file is laid out contiguously,
+   * avoiding fragmentation.  Receiver-side, crosses the wire. */
+  bool preallocate;
 
   // Issue #128: Extended delete options
+  /* --delete-excluded: also delete destination entries that were excluded on
+   * the source.  Default (off) matches rsync: excluded paths are protected from
+   * deletion.  Crosses the wire (the sender encodes the choice by whether it
+   * transmits a protected-prefix list with the keep-set manifest). */
   bool delete_excluded;
   bool delete_after;
+  /* --max-delete=NUM: the receiver refuses to delete more than NUM entries per
+   * run (all-or-nothing: when the extras would exceed NUM nothing is removed and
+   * the transfer fails with a distinct error).  -1 == no client limit (the
+   * server hard bound MAX_SERVER_DELETE_COUNT still applies). */
   int max_delete;
+  /* --ignore-errors (client-only, never serialized): a sender-side source I/O
+   * error (an unreadable directory during the scan) normally aborts the run so
+   * no deletion happens; with --ignore-errors the scan continues and the
+   * (partial) keep-set is still transmitted so the deletion runs. */
+  bool ignore_errors;
+  /* --force (receiver-side): a regular file may replace a destination
+   * directory by removing that (possibly non-empty, symlink-safe) directory
+   * tree first, instead of failing the write.  Crosses the wire. */
+  bool force_delete;
+  /* --ignore-missing-args (client-only, never serialized): a --files-from
+   * entry that does not exist under the source is silently skipped instead of
+   * failing the run.  Sender-side only: nothing is sent for it and it never
+   * enters the keep-set.  Implied by --delete-missing-args. */
+  bool ignore_missing_args;
+  /* --delete-missing-args: implies --ignore-missing-args; additionally each
+   * missing entry's destination mirror (computed like a present entry's wire
+   * path) is deleted receiver-side.  Crosses the wire and is gated by the
+   * server's --allow-delete policy like --delete.  rsync-parity: independent
+   * of ordinary --delete processing (it does not imply --delete); a non-empty
+   * directory mirror is only removed with --force or --delete in effect, and
+   * the missing-args deletions are not counted toward --max-delete. */
+  bool delete_missing_args;
 
-  // Issue #129: Advanced file selection
-  ArrayList* filters;
-  char* files_from;
-  bool cvs_exclude;
+  // 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 */
+  char* files_from;     /* --files-from path (may be NULL) */
+  void* files_from_set; /* parsed FileListSet* allow-set, or NULL */
+  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 */
   bool prune_empty_dirs;
+  bool one_file_system; /* -x/--one-file-system: do not cross filesystem boundaries */
+  /* -R/--relative: crosses the wire; with --files-from listed entries keep
+   * their bare relative destination path (no source-root mirror prefix). */
   bool relative;
+  /* --no-implied-dirs: client-only.  With -R + --files-from, refuse to place a
+   * listed file whose ancestor directory is not itself explicitly listed. */
+  bool no_implied_dirs;
+  /* -d/--dirs: client-only.  Transfer the directory entries named by the
+   * source argument / --files-from list without recursing into contents. */
+  bool dirs;
+  /* --mkpath: crosses the wire.  Tells the server to create the destination
+   * root directory (and missing leading components below its authorized root)
+   * at connection start instead of requiring it to already exist. */
+  bool mkpath;
 
   // Issue #130: Remote shell/connection options
+  /* -e/--rsh: the remote-shell program used to establish the SSH transport.
+   * NULL means the default "ssh".  Client-only launch concern: NEVER crosses
+   * the wire (it is not meaningful to the daemon/server handshake). */
   char* rsh_command;
-  char* rsync_path;
+  /* --blocking-io: leave the SSH transport socket without
+   * SO_RCVTIMEO/SO_SNDTIMEO so it blocks naturally instead of timing out.
+   * Client-only launch concern: NEVER crosses the wire. */
+  bool blocking_io;
+  /* --outbuf mode (OutbufMode): stdout/stderr buffering.  Client-only launch
+   * concern: NEVER crosses the wire. */
+  int outbuf;
+  bool old_args;
   char* temp_dir;
-  char* compare_dest;
-  char* copy_dest;
-  char* link_dest;
+  /* --remote-option=OPT (Phase 5, long form only): one or more extra command-line
+   * options to append to the REMOTE server invocation over SSH.  CLIENT-ONLY:
+   * they are composed into the remote command line by ssh_build_remote_command()
+   * (each valid word is shell-escaped with the same quoting boundary as the
+   * server path), and are NEVER serialized into the binary config frame.  They
+   * do NOT cross the wire and are never parsed on the receiver process. */
+  char** remote_options;
+  int remote_option_count;
+  /* Alternate basis directories, ordered by command-line appearance.  Each
+   * entry's type selects compare/copy/link behavior on an exact match.  These
+   * cross the wire so the receiver can consult them; they are interpreted
+   * relative to the destination root and confined there. */
+  BasisDest* basis_dirs;
+  int basis_count;
 
   // PR #174: Partial transfer resumption
   char* partial_dir;
@@ -111,32 +321,415 @@ typedef struct Config {
   // PR #179: Delete policies
   bool delete_before;
 
+  /* 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
+     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. */
+  bool delete_during;
+  bool delete_delay;
+
   // PR #181: IPv6 and bind address
   char* address;
   char* bind_address;
   bool ipv6;
   bool ipv4;
+  /* --sockopts=OPTIONS (Phase 5, Wave B): strict allowlist of TCP/socket
+   * options applied via setsockopt after socket() and before connect()/bind().
+   * These are LOCAL socket concerns: they never cross the wire config frame.
+   * .address is the outgoing/source bind address (--address); .bind_address is
+   * reserved for daemon-side binding and is not wired yet. */
+  SockOptEntry* sockopts;
+  int sockopt_count;
 
   // PR #182: Daemon/server mode
   bool daemon;
   char* daemon_config;
   bool server_mode;
+  /* --no-motd (Wave C): CLIENT-ONLY, never crosses the wire.  Suppresses
+   * DISPLAY of the daemon's MOTD; the daemon still sends the MOTD frame, so
+   * the client reads and discards it to keep the stream in sync.  rsync's
+   * --no-motd is likewise a client-side display switch.  Default false (the
+   * MOTD is shown when a daemon offers one). */
+  bool no_motd;
 
   // PR #183: Checksum comparison
   bool checksum;
 
   // PR #184: Compression algorithm negotiation
   char* compress_choice;
+  char* chmod_spec;
+
+  /* --checksum-choice / --cc and --checksum-seed.  checksum_algo is the id of
+   * the whole-file content-digest algorithm used by the per-file --incremental
+   * handshake (sender computes it, receiver compares it to skip unchanged
+   * files) and by the basis-dir content verification.  checksum_seed is passed
+   * to xxHash64 (and to the delta block strong hash, low 32 bits); md5 has no
+   * seed so it is ignored there.  Both cross the wire: the receiver MUST hash
+   * the on-disk old file with the same algorithm and seed to reach a matching
+   * digest.  Defaults (XXH64 / seed 0) reproduce the pre-existing behavior
+   * byte-for-byte. */
+  int checksum_algo;      /* ChecksumAlgo, default CHECKSUM_ALGO_XXH64 */
+  uint64_t checksum_seed; /* default 0 */
+
+  char** skip_compress_suffixes;
+  int skip_compress_count;
+  bool skip_compress_set;
+
+  // Issue #131: Identity mapping.  These configure whether and how the receiver
+  // applies ownership when it is actually preserved/applied.  ALL of them cross
+  // the wire (protocol 2.11.0) so the receiver resolves and applies ownership
+  // with the exact policy the client requested.  Plain -M/--preserve still does
+  // NOT apply ownership (FastSync's deliberate conservative default); it is
+  // only attempted when at least one of these is set (see identity.h).
+  /* --numeric-ids: no name lookup, use the transmitted numeric ids raw. */
+  bool numeric_ids;
+  /* --chown USER (owner) override; IDENTITY_CURRENT = the receiver's euid. */
+  bool chown_uid_set;
+  int32_t chown_uid;
+  /* --chown :GROUP (group) override; IDENTITY_CURRENT = the receiver's egid. */
+  bool chown_gid_set;
+  int32_t chown_gid;
+  /* --usermap / --groupmap entries, in order (first match wins). */
+  IdentityMap* usermap;
+  int usermap_count;
+  IdentityMap* groupmap;
+  int groupmap_count;
+
+  /* --super / --no-super (P7 Wave E, protocol 2.18.0): receiver-side privilege
+   * policy for super-user activities confined below the authorized receive
+   * root.  SUPER_MODE_AUTO (default) preserves the pre-existing best-effort
+   * behavior: the confined super-user operation is ALWAYS attempted and an
+   * unprivileged attempt is refused by the kernel and skipped per entry.
+   * SUPER_MODE_ON (--super) explicitly REQUESTS those activities (char/block
+   * device-node creation, --write-devices); it does NOT imply --numeric-ids and
+   * never enables ownership application on its own.  SUPER_MODE_OFF
+   * (--no-super) FORBIDS them even when running as root.  FastSync NEVER
+   * elevates privileges (no setuid/seteuid/setgid) and never bypasses the
+   * 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
+   * identity.h. */
+  int super_mode;
+
+  // Receiver-side runtime staging registry for --delay-updates.  Never sent
+  // over the wire and never set on the sender side.
+  DelayUpdatesContext* delay_context;
+
+  // Phase 4: metadata time preservation.  -U/--atimes and -N/--crtimes capture
+  // and transmit the source access / birth time (both sender and receiver
+  // effect, so they CROSS the wire).  --omit-dir-times/-O and
+  // --omit-link-times/-J are receiver-side prefs (CROSS the wire).  Their
+  // exact capture/transmit/apply semantics are documented in RSYNC_COMPAT.md.
+  /* -U/--atimes: preserve source access times on the destination. */
+  bool preserve_atimes;
+  /* -N/--crtimes: capture+transmit source birth time; see RSYNC_COMPAT for the
+   * receiver not-applied divergence. */
+  bool preserve_crtimes;
+  /* -O/--omit-dir-times: do not apply mtimes to directories. */
+  bool omit_dir_times;
+  /* -J/--omit-link-times: do not apply times to symlinks. */
+  bool omit_link_times;
+  /* --open-noatime: CLIENT-ONLY (never crosses the wire).  The sender opens
+   * source files with O_NOATIME so reading for transfer does not bump the
+   * source access time. */
+  bool open_noatime;
+
+  // Phase 4: xattr / ACL / fake-super preservation.
+  /* -X/--xattrs and -A/--acls toggle the sender's capture and the receiver's
+   * application of per-file extended attributes (xattrs).  Both cross the wire:
+   * the sender only transmits the bounded, whitelisted attribute set it
+   * captures and the receiver re-validates namespaces/sizes before applying
+   * fd-relative.  With neither set (the default) no xattr block is sent, so the
+   * wire is byte-identical to prior protocol versions for unaffected runs. */
+  /* true when preserve_xattrs || preserve_acls; the sender/receiver gate the
+   * xattr wire block on this single flag. */
+  bool use_xattrs;
+  /* --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. */
+  bool fake_super;
+  /* --copy-as=USER[:GROUP] (P7 Wave E, protocol 2.18.0).  Safe-subset
+   * implementation, a documented divergence from rsync's real identity switch:
+   * the receiver does NOT change its process credentials (FastSync's receiver
+   * is multithreaded, so a setuid/seteuid drop would be unsafe).  Instead the
+   * receiver FORCES the ownership of every entry it writes to copy_as_uid /
+   * copy_as_gid through the existing confined, fd-relative identity path
+   * (fchown/fchownat), which REQUIRES receiver privilege (root); an
+   * unprivileged receiver REFUSES the whole transfer up front at the config
+   * handshake (never a silent wrong-ownership result).  All three fields CROSS
+   * the wire as a trailing config-frame block so the receiver learns the
+   * requested ids; see the PROTOCOL_VERSION note below. */
+  bool copy_as_set;
+  int32_t copy_as_uid;
+  int32_t copy_as_gid;
+
+  // Phase 5: --trust-sender
+  /* Long-form-only, receiver-local policy.  rsync's --trust-sender tells the
+   * receiving side to trust that the sender already produced a sane file list,
+   * relaxing the receiver's own up-front re-validation of every incoming path.
+   * In FastSync the receiver normally double-checks each transmitted file-list
+   * entry (empty / ".." path-traversal rejection) and refuses to materialize a
+   * symlink whose target could escape the receive root.  When trust_sender is
+   * set, those redundant list-level re-checks are SKIPPED: the receiving side
+   * trusts the sender's list instead of re-validating it (fewer checks, faster,
+   * potentially unsafe, matching rsync).  It is a LOCAL receiver policy and is
+   * NEVER serialized into the config frame (it exists only on the process that
+   * actually receives the file list).  Even under trust_sender the low-level
+   * fd-relative confinement primitives (file_open_secure_parent, the O_NOFOLLOW
+   * parent walk, leaf/destination confinement) are deliberately KEPT as a hard
+   * floor, so a hostile sender still cannot write or link outside the
+   * authorized root (see the phase-5 notes in RSYNC_COMPAT.md).  Off by
+   * default; only relaxes validation when explicitly requested. */
+  bool trust_sender;
+
+  // Phase 6: --stop-after / --stop-at
+  /* Client-only sender-side transfer stop deadlines.  --stop-after=MINS stops
+   * the transfer after a number of elapsed minutes (checked against
+   * CLOCK_MONOTONIC so clock changes do not skew it); --stop-at=TIME stops at
+   * an absolute wall-clock time (HH:MM, HH:MM:SS, or now+N[smhd]).  At the
+   * deadline the run stops elegantly at the next chunk/file boundary and the
+   * completion tail still runs (exit 0).  Both are LOCAL to the sending
+   * process and are NEVER serialized into the config frame. */
+  int stop_after_mins; /* --stop-after=MINS minutes; 0 when unset */
+  time_t stop_at;      /* --stop-at=... absolute wall-clock deadline */
+  bool stop_at_set;    /* true when --stop-at was given */
+
+  // Phase 6: --write-batch / --only-write-batch / --read-batch
+  /* Client-only residual-batch paths.  A residual batch is a self-contained
+   * single-file record of the whole source tree (full file images using the
+   * chunk codec), independent of any live server.  --write-batch=FILE runs the
+   * normal live transfer AND additionally emits the batch FILE;
+   * --only-write-batch=FILE emits FILE only (no destination, no server);
+   * --read-batch=FILE applies FILE to the destination (no source, no server).
+   * All three are LOCAL to the driving process and are NEVER serialized into
+   * the config frame (the batch paths bypass the transport entirely). */
+  char* write_batch;      /* --write-batch=FILE path, or NULL */
+  char* only_write_batch; /* --only-write-batch=FILE path, or NULL */
+  char* read_batch;       /* --read-batch=FILE path, or NULL */
 } Config;
 
-#define PROTOCOL_VERSION "2.3.0"
+/* Phase 5 (remote-option wave): 2.13.0 -> 2.14.0.
+ *
+ * WHY the bump, grounded in the wire: the binary config-frame layout is
+ * UNCHANGED by this wave (neither --remote-option nor --trust-sender adds a
+ * serialized field; see the field comments above).  --remote-option is
+ * forwarded to the remote server over the SSH remote-command line
+ * (ssh_build_remote_command) and --trust-sender is a purely local receiver
+ * policy, so there is no new frame byte to negotiate.  The bump is still the
+ * correct release marker for Phase 5 because the client-to-server INVOCATION
+ * surface changed: a client that composes remote-options expects a server that
+ * knows how to honor them, and the only safe way to express "this feature set
+ * is one coordinated release" is the strict same-version handshake FastSync
+ * already performs for every release.  A 2.14 client against a 2.13 server
+ * fails the version check cleanly up front (rather than the remote server
+ * rejecting an unfamiliar forwarded argv at a confusing later point), which is
+ * exactly what the lockstep convention of this project requires. */
+/* Daemon Wave A: 2.14.0 -> 2.15.0.
+ *
+ * WHY the bump, grounded in the wire: this wave really does add a serialized
+ * field to the binary config frame.  The client sends its requested daemon
+ * module name (Config->module) as a new trailing string on the frame (sent
+ * after the Phase-4 xattr block and before the STATUS_OK/STATUS_ERROR ack, in
+ * config_send/config_receive), and the daemon reads it to select which module
+ * root confines the connection.  Any config-frame layout change must bump the
+ * protocol version because a peer that does not parse the new trailing bytes
+ * would desynchronize on the frame boundary; the strict same-version handshake
+ * (config_receive rejects a mismatched version before parsing anything else)
+ * is what keeps a 2.15 client and a 2.14 server from ever reaching that state.
+ *
+ * NOTE: daemon module-selection bump owned by Wave A (2.15.0); later daemon
+ * waves (auth, motd) must not bump PROTOCOL_VERSION.  Wave B (auth) added the
+ * credential fields (auth_user + password digest) as further trailing
+ * config-frame strings AFTER the Wave A module string, with a presence int
+ * prefix.  This is not a new frame version: sender and receiver of a 2.15.0
+ * build always read and write the same full layout (the strict same-version
+ * handshake rejects any other version before a byte of the frame is parsed),
+ * so a peer can never desynchronize on the added tail.  The 2.15.0 release
+ * ships Wave A + Wave B together; the bump stays owned by Wave A.
+ *
+ * Wave C (MOTD) adds NO config-frame field and no version bump either.  On the
+ * daemon listener path only, the server sends one MOTD string frame AFTER the
+ * config-frame STATUS_OK (server.c handler), and every 2.15.0 daemon client
+ * reads that frame right after the ack (client_send.c) -- symmetric
+ * server->client in every build, so the strict same-version handshake keeps the
+ * two peers in lockstep and nothing can desynchronize.  The --stdio SSH path
+ * sends/reads no MOTD at all.
+ *
+ * --iconv Wave (P6): 2.15.0 -> 2.16.0.
+ *
+ * WHY the bump, grounded in the wire: the --iconv feature adds a serialized
+ * field to the binary config frame.  The client sends the full CONVERT_SPEC
+ * (Config->iconv_spec) as a new trailing string AFTER the Wave A/B daemon-auth
+ * block (in config_send/config_receive), so the receiver knows the wire charset
+ * (the REMOTE half) before the first file name arrives.  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 2.16 client and a 2.15 server from
+ * ever reaching that state.
+ *
+ * Times Wave (P7 Wave D): 2.16.0 -> 2.17.0.
+ *
+ * WHY the bump, grounded in the wire: this wave makes -O/--omit-dir-times and
+ * -J/--omit-link-times REAL by adding directory and symlink time preservation.
+ * The config-frame LAYOUT is unchanged (the omit flags already crossed the
+ * wire), but the FRAME STREAM gains a new terminal frame: after all file data
+ * and the optional delete manifest, the sender transmits STATUS_DIR_TIMES
+ * frame(s) (each a count followed by (path, metadata) pairs, chunked so no
+ * frame exceeds the receiver's MAX_MANIFEST_ENTRIES bound) carrying every
+ * source directory's captured times, so the receiver can apply them AFTER all of a
+ * directory's children have been written (writing a child bumps the parent's
+ * mtime).  Symlink entries already carry their metadata on the STATUS_SYMLINK
+ * frame; the receiver now applies it (utimensat/lchown with
+ * AT_SYMLINK_NOFOLLOW) unless -J is set.  Any change to the frame sequence must
+ * bump the protocol version: a 2.16 peer that does not know STATUS_DIR_TIMES
+ * would desynchronize on the unknown frame, and the strict same-version
+ * handshake (config_receive rejects a mismatched version before parsing
+ * anything else) is what keeps a 2.17 client and a 2.16 server from ever
+ * reaching that state.
+ *
+ * Privilege Wave (P7 Wave E): 2.17.0 -> 2.18.0.
+ *
+ * WHY the bump, grounded in the wire: this wave adds the receiver-side
+ * privilege flags --super/--no-super and --copy-as=USER[:GROUP].  The
+ * config-frame layout gains two new trailing blocks AFTER the --iconv
+ * CONVERT_SPEC string, in this fixed order: (1) send_privilege_options /
+ * receive_privilege_options send one int (Config->super_mode, 0..2), then
+ * (2) send_copy_as_options / receive_copy_as_options send a presence int and,
+ * when set, the target uid and gid (both int32).  The receiver uses
+ * super_mode to decide whether it may attempt super-user activities
+ * (ownership application, char/block device-node creation) already confined
+ * below the authorized receive root, and the copy-as ids to force the
+ * ownership of every entry it writes (the safe-subset --copy-as model).  The
+ * receiver REQUIRES privilege for copy-as: an unprivileged receiver refuses
+ * the transfer at the config handshake (server_module_gate) instead of silently
+ * ignoring the flag.  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 2.18 client and a 2.17 server from ever reaching that state.
+ * --super never elevates privileges; it only permits a confined attempt, and
+ * --copy-as never switches process credentials (see RSYNC_COMPAT.md).
+ *
+ * A7 Auth Wave: 2.18.0 -> 2.19.0.
+ *
+ * WHY the bump, grounded in the wire: the daemon auth block on the config frame
+ * loses the hard-wired password digest (it becomes `[int present][str_redacted
+ * username]`), and the frame stream gains the SCRAM challenge/response
+ * (STATUS_AUTH_CHALLENGE -> STATUS_AUTH_RESPONSE -> STATUS_AUTH_OK) between the
+ * config frame and the STATUS_OK ack.  A 2.18 peer would desynchronize on both
+ * the shorter auth block and the new status frames, so the strict same-version
+ * handshake (config_receive rejects a mismatched version before parsing
+ * anything else) is what keeps a 2.19 client and a 2.18 server from ever
+ * reaching that state.  SECURITY: a 2.19 store holds a salted PBKDF2 verifier
+ * and cannot verify (and refuses to load) a legacy unsalted-SHA-256 store line,
+ * so an old bearer digest can never be replayed against a 2.19 daemon. */
+#define PROTOCOL_VERSION "2.19.0"
 #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
+
+/* 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). */
+#define IDENTITY_MATCH_ANY (-1)
+#define IDENTITY_CURRENT (-1)
+#define MAX_IDENTITY_MAP 128
+
+/* --super / --no-super tri-state (Config->super_mode).  AUTO (default) and ON
+ * both permit a confined super-user attempt (AUTO preserves FastSync's
+ * historical best-effort behavior; an unprivileged attempt is refused by the
+ * kernel and skipped per entry); OFF forbids the attempt even for root.  See
+ * privilege_super_mode_permitted() in identity.h. */
+#define SUPER_MODE_AUTO 0
+#define SUPER_MODE_ON 1
+#define SUPER_MODE_OFF 2
 
 Config* config_create(void);
 void config_delete(Config* config);
+
+/* Wipe the client-side plaintext auth password (and username) from a Config
+ * before it is freed or handed off.  Safe on a NULL/empty Config and idempotent
+ * (it clears the pointers after burning).  config_delete calls this
+ * automatically; a caller that drops a Config earlier may call it explicitly. */
+void config_burn_auth(Config* config);
+
 bool config_send(int file_descriptor, const Config* config);
 Config* config_receive(int file_descriptor);
 bool config_is_remote_dest(const char* s);
 void config_parse_ssh_dest(Config* config);
 
+/* A ConfigValidateFunc may return this sentinel to tell
+ * config_receive_with_validate that the callback ALREADY sent a terminal status
+ * frame (e.g. STATUS_AUTH_FAILED, then closed) and the frame must be abandoned
+ * without an additional STATUS_ERROR.  A normal rejection returns a message
+ * string (logged, then STATUS_ERROR); NULL accepts. */
+#define CONFIG_VALIDATE_ALREADY_TERMINATED ((const char*)-1)
+
+/* Server-side config-frame gate (daemon module selection, Wave A).  A server
+ * that needs to make an accept/reject decision about a received Config BEFORE
+ * it sends the STATUS_OK ack (so a rejected connection is refused cleanly with
+ * no data transferred) passes a callback here; it runs after the frame parses
+ * and validates but before the STATUS_OK/STATUS_ERROR ack.  Return NULL to
+ * accept the connection; return a non-NULL message to reject it (the message
+ * is logged server-side and STATUS_ERROR is sent in place of STATUS_OK), or the
+ * CONFIG_VALIDATE_ALREADY_TERMINATED sentinel when the callback already sent
+ * its own terminal status.  The callback runs in the connection's own process,
+ * so it may set up per-module process state (e.g. the authorized root) and
+ * drive the daemon auth handshake.  context is an opaque caller pointer. */
+typedef const char* (*ConfigValidateFunc)(const Config* config, void* context);
+Config* config_receive_with_validate(int file_descriptor, ConfigValidateFunc validate,
+                                     void* context);
+
+/* Daemon-destination (host::module[/path]) helpers, Wave A.  config_is_remote_dest
+ * recognizes the ordinary rsync-style single-colon host:path form used by the
+ * SSH transport; config_is_daemon_dest recognizes the double-colon form that
+ * selects a daemon module over TCP.  config_parse_transport_dest is the single
+ * entry point main() uses: it parses a :: destination as a daemon TCP
+ * destination (host -> server_host, module -> config->module, path ->
+ * receive_root_directory) and otherwise falls back to the existing SSH
+ * host:path handling. */
+bool config_is_daemon_dest(const char* s);
+/* Returns 1 when the destination was daemon syntax and was parsed, 0 when it
+ * is not daemon syntax (nothing changed), -1 on an invalid daemon destination
+ * (a message is logged and config is left untouched). */
+int config_parse_daemon_dest(Config* config);
+/* Returns 1/0/-1 mirroring config_parse_daemon_dest when the destination is
+ * daemon syntax; otherwise runs the existing SSH host:path parse and returns
+ * 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
+ * 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). */
+bool config_delete_timing_early(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). */
+bool config_has_valid_delete_timing(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. */
+int config_basis_append(Config* config, BasisDestType type, const char* path);
+/* Validate a client-provided basis-dir path (relative, confined, non-empty). */
+bool config_basis_path_valid(const char* path);
+
+/* Parse and validate a --sockopts=OPTIONS comma-separated "OPT=VAL" list into a
+ * malloc'd array of at most *out_count entries.  Returns 0 on success (the
+ * caller takes ownership of *out), or -1 on the first invalid option name or
+ * value.  Pure/static-analysis friendly: performs no socket calls, so it is
+ * directly unit-testable. */
+int config_sockopts_parse(const char* spec, SockOptEntry** out, int* out_count);
+
 #endif

src/shared/credentials.h

@@ -0,0 +1,203 @@
+#ifndef CREDENTIALS_H
+#define CREDENTIALS_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+
+/* Daemon password authentication (A7 remediation, protocol 2.19.0).
+ *
+ * FastSync authenticates a daemon connection with a SCRAM-SHA-256-style
+ * challenge/response handshake.  The daemon stores only a salted PBKDF2
+ * verifier (never the password, and never a value that can be replayed as a
+ * bearer credential): the client proves knowledge of the password against a
+ * per-connection server nonce, and the server proves the same shared secret
+ * back.  See credentials.c for the exact derivation.
+ *
+ * Server credential store format (--password-file and --early-input): one line
+ * per entry,
+ *   user:$fastsync$1$pbkdf2-sha256$<iters>$<salt_b64>$<stored_key_b64>$<server_key_b64>
+ * with standard base64, a 16-byte salt and 32-byte keys, and iters in
+ * [CREDENTIAL_MIN_ITERS, CREDENTIAL_MAX_ITERS].  Blank lines and lines whose
+ * first non-space character is '#' or ';' are comments.  The parser is STRICT:
+ * a malformed line fails the whole load so a typo can never silently change who
+ * may log in.  A line holding the legacy (unsalted SHA-256 hex) secret is
+ * hard-rejected with an actionable "legacy" error; there is no auto-upgrade.
+ * Use `fastsync-server --hash-credentials` to generate new-format lines.
+ *
+ * Alongside the store, credentials_load maintains an exact-mode-0600
+ * `<store_path>.dummykey` sidecar holding the store-wide random dummy key.  It
+ * is auto-created on first load and MUST be preserved across restarts: it makes
+ * the dummy challenge for an unknown user stable for the life of the store, so
+ * a daemon restart cannot be used as a username-enumeration oracle.  A sidecar
+ * that is not an exact-mode-0600 regular file of exactly 32 bytes fails the load
+ * (fail closed); creation forces exact 0600 with fchmod (so a restrictive umask
+ * cannot leave the sidecar unreadable), and only a create/write/fsync/link or
+ * fchmod failure degrades to a transient per-run key with a warning.  NOTE: the
+ * sidecar requires EXACT 0600, whereas the store / password files only reject
+ * group/other bits (a deliberate difference).
+ *
+ * Client --password-file format: the FIRST meaningful (non-comment, non-blank)
+ * line is `user:password`, holding the literal password.  The client keeps it
+ * only for the duration of the handshake and wipes it at teardown; the file
+ * should be mode 0600 and readable only by its owner. */
+
+/* Longest accepted credential-file line (excluding the trailing newline). */
+#define CREDENTIAL_MAX_LINE 4096
+/* Upper bound on a username in a credential file and on the wire.  Kept well
+ * below MAX_STRING_SIZE so a wire username can never exhaust anything. */
+#define CREDENTIAL_MAX_USER_LEN 256
+/* Upper bound on a client-file password (before derivation). */
+#define CREDENTIAL_MAX_PASSWORD_LEN 1024
+
+/* SCRAM-SHA-256 parameters.  Salt and client nonce sizes are fixed by the
+ * shared-auth-message framing; keys are always 32 bytes (SHA-256). */
+#define CREDENTIAL_SALT_LEN 16
+#define CREDENTIAL_NONCE_LEN 32
+#define CREDENTIAL_KEY_LEN 32
+#define CREDENTIAL_DEFAULT_ITERS 600000u
+#define CREDENTIAL_MIN_ITERS 100000u
+#define CREDENTIAL_MAX_ITERS 10000000u
+/* Buffer size for the full AuthMessage (prefix + three length-prefixed fields).
+ * Worst case: 16 + 4 + 256 + 4 + 32 + 4 + 32. */
+#define CREDENTIAL_AUTH_MESSAGE_MAX                                                                \
+  (16 + 4 + CREDENTIAL_MAX_USER_LEN + 4 + CREDENTIAL_NONCE_LEN + 4 + CREDENTIAL_NONCE_LEN)
+
+typedef struct CredentialStore CredentialStore;
+
+/* One resolved verifier.  `found` is false for an unknown user or a user not on
+ * a module's auth list; the remaining fields then hold a deterministic dummy
+ * salt (HMAC of the store-wide dummy key over the username), the store-wide
+ * uniform iteration count (default for an empty store) and fixed dummy keys, so
+ * the server can run the same challenge/response math with no enumeration or
+ * timing oracle. */
+typedef struct {
+  uint8_t salt[CREDENTIAL_SALT_LEN];
+  uint32_t iters;
+  uint8_t stored_key[CREDENTIAL_KEY_LEN];
+  uint8_t server_key[CREDENTIAL_KEY_LEN];
+  bool found;
+} CredentialVerifier;
+
+/* Load the daemon credential store.
+ *
+ * password_file and early_input_file are both NULL-or-path, matching the
+ * server's --password-file and --early-input options.  A file that cannot be
+ * opened or that fails the strict grammar is a hard error (err filled, NULL
+ * returned) -- the daemon fails CLOSED rather than serving an auth-required
+ * module with a partial store.  Both files may be NULL, which yields an empty
+ * store (every auth-required module then refuses connections).  Every entry in
+ * the resulting store must agree on the iteration count; entries that disagree
+ * (within one file or across the two layered sources) are rejected.  When both
+ * are given, the --early-input file is layered over --password-file: a duplicate
+ * username whose verifier matches is deduplicated; one whose verifier differs
+ * is an error (the two sources disagree), never a silent pick.
+ *
+ * The returned store is heap-owned; free it with credentials_free. */
+CredentialStore* credentials_load(const char* password_file, const char* early_input_file,
+                                  char* err, size_t err_size);
+
+/* Wipe every stored key/salt and free the store. */
+void credentials_free(CredentialStore* store);
+
+/* True when `user` is a single bounded token free of whitespace/control bytes
+ * (the rule applied to store users, client-file users and the module list). */
+bool credentials_username_valid(const char* user);
+
+/* Standard base64.  encode writes NUL-terminated output to out (size out_sz).
+ * decode writes the raw bytes to out (capacity out_sz) and stores the length;
+ * the input must be a well-formed padded base64 string.  Both return false on
+ * NULL arguments, a bad character/length, or insufficient output space. */
+bool credentials_b64_encode(const uint8_t* in, size_t n, char* out, size_t out_sz);
+bool credentials_b64_decode(const char* in, uint8_t* out, size_t out_sz, size_t* out_len);
+
+/* Fill out[0..n) from the CSPRNG (RAND_bytes).  Returns false on failure. */
+bool credentials_random_bytes(uint8_t* out, size_t n);
+
+/* Resolve `user` against the store AND the module's auth-user list.  The list
+ * scan is a constant-time full-length comparison with no early break.  On a
+ * miss, *out is filled with a dummy verifier (a deterministic per-username salt
+ * derived from the store's dummy key, the store-wide uniform iteration count,
+ * fixed dummy keys, found=false).  Returns false on invalid arguments or an
+ * HMAC/crypto primitive failure. */
+bool credentials_get_verifier(const CredentialStore* store, const char* user,
+                              const char* const* module_users, int n, CredentialVerifier* out);
+
+/* Derive the SCRAM keys from a plaintext password:
+ *   K = PBKDF2-HMAC-SHA256(password, salt, iters, 32)
+ *   ClientKey = HMAC-SHA256(K, "Client Key"); StoredKey = SHA256(ClientKey)
+ *   ServerKey = HMAC-SHA256(K, "Server Key")
+ * Any of client_key/stored_key/server_key may be NULL when not needed.
+ * `iters` must lie in [CREDENTIAL_MIN_ITERS, CREDENTIAL_MAX_ITERS]. */
+bool credentials_compute_keys(const char* password, const uint8_t salt[CREDENTIAL_SALT_LEN],
+                              uint32_t iters, uint8_t client_key[CREDENTIAL_KEY_LEN],
+                              uint8_t stored_key[CREDENTIAL_KEY_LEN],
+                              uint8_t server_key[CREDENTIAL_KEY_LEN]);
+
+/* Serialize the shared AuthMessage:
+ *   "FastSync-Auth-v1" || be32(len(user)) || user
+ *                      || be32(32) || server_nonce
+ *                      || be32(32) || client_nonce
+ * out must hold at least CREDENTIAL_AUTH_MESSAGE_MAX bytes.  *out_len receives
+ * the number of bytes written. */
+bool credentials_build_auth_message(const char* user, const uint8_t* snonce, const uint8_t* cnonce,
+                                    uint8_t* out, size_t out_sz, size_t* out_len);
+
+/* Client side: ClientProof = ClientKey XOR HMAC(StoredKey, AuthMessage), and
+ * the expected ServerSignature = HMAC(ServerKey, AuthMessage). */
+bool credentials_client_proof(const uint8_t client_key[CREDENTIAL_KEY_LEN],
+                              const uint8_t stored_key[CREDENTIAL_KEY_LEN],
+                              const uint8_t server_key[CREDENTIAL_KEY_LEN], const uint8_t* auth_msg,
+                              size_t msg_len, uint8_t proof[CREDENTIAL_KEY_LEN],
+                              uint8_t server_sig[CREDENTIAL_KEY_LEN]);
+
+/* Server side: recompute ClientSig' = HMAC(StoredKey, AuthMessage) and
+ * ClientKey' = proof XOR ClientSig', then accept iff v->found AND
+ * SHA256(ClientKey') equals StoredKey (constant-time over the 32-byte keys).
+ * Always computes server_sig_out = HMAC(ServerKey, AuthMessage).  Returns the
+ * accept decision. */
+bool credentials_verify_response(const CredentialVerifier* v, const char* user,
+                                 const uint8_t* snonce, const uint8_t* cnonce,
+                                 const uint8_t proof[CREDENTIAL_KEY_LEN],
+                                 uint8_t server_sig_out[CREDENTIAL_KEY_LEN]);
+
+/* Derive a new-format store line for `user`/`password` and write it (without a
+ * trailing newline) into out.  A random 16-byte salt is used.  On failure err is
+ * filled.  Used by --hash-credentials and by tests. */
+bool credentials_hash_store_line(const char* user, const char* password, uint32_t iters, char* out,
+                                 size_t out_sz, char* err, size_t err_size);
+
+/* Read `user:password` lines from `path` (the same no-group/other-bits check as
+ * the other secret files) and write one new-format store line per entry to
+ * `out`.
+ * Blank/comment lines are skipped; a malformed line fails the whole run.
+ * Returns 0 on success, -1 on error (err filled).  Used by
+ * `--hash-credentials`. */
+int credentials_hash_file(const char* path, uint32_t iters, FILE* out, char* err, size_t err_size);
+
+/* Read the CLIENT-side secret file: the first meaningful line is
+ * `user:password` (the literal password).  *user_out and *password_out are
+ * freshly allocated on success (password is plaintext -- the caller derives the
+ * proof and then burns/frees it); both are NULL on error.  Returns 0 on
+ * success, -1 on failure (err filled: the path is named, never the credential
+ * itself).  Only the line's trailing CR/LF are stripped: the password's bytes
+ * are otherwise preserved exactly, so a password with leading/trailing
+ * whitespace (after the ':') is kept usable.  The username is trimmed of
+ * surrounding space/tabs. */
+int credentials_read_secret_file(const char* path, char** user_out, char** password_out, char* err,
+                                 size_t err_size);
+
+/* Constant-time equality over exactly len bytes. */
+bool credentials_secure_equal(const char* a, const char* b, size_t len);
+
+/* Overwrite secret[0..len) with zeros (best-effort wipe). */
+void credentials_burn(char* secret, size_t len);
+
+/* Number of entries currently in the store (tests/introspection). */
+int credentials_store_size(const CredentialStore* store);
+
+/* Whether the store contains an entry for `user` (tests/introspection). */
+bool credentials_store_has(const CredentialStore* store, const char* user);
+
+#endif

src/shared/daemon_conf.c

@@ -0,0 +1,454 @@
+#include "daemon_conf.h"
+#include "utils.h"
+#include <ctype.h>
+#include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+
+/* ------------------------------------------------------------------ */
+/* helpers                                                             */
+/* ------------------------------------------------------------------ */
+
+static void set_error(char* err, size_t err_size, const char* fmt, ...) {
+  if (!err || err_size == 0)
+    return;
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(err, err_size, fmt, args);
+  va_end(args);
+}
+
+/* Trim leading and trailing ASCII space/tab in place; returns the new start. */
+static char* trim_ws(char* s) {
+  while (*s == ' ' || *s == '\t')
+    s++;
+  size_t len = strlen(s);
+  while (len > 0 && (s[len - 1] == ' ' || s[len - 1] == '\t'))
+    s[--len] = '\0';
+  return s;
+}
+
+/* Case-insensitive equality of a parsed key against a canonical key name. */
+static bool key_equals(const char* key, const char* canonical) {
+  return strcasecmp(key, canonical) == 0;
+}
+
+static bool parse_bool_value(const char* value, bool* out) {
+  if (strcasecmp(value, "yes") == 0 || strcasecmp(value, "true") == 0 || strcmp(value, "1") == 0) {
+    *out = true;
+    return true;
+  }
+  if (strcasecmp(value, "no") == 0 || strcasecmp(value, "false") == 0 || strcmp(value, "0") == 0) {
+    *out = false;
+    return true;
+  }
+  return false;
+}
+
+bool daemon_module_name_valid(const char* name) {
+  if (!name || *name == '\0')
+    return false;
+  size_t len = strlen(name);
+  if (len > DAEMON_MAX_MODULE_NAME)
+    return false;
+  for (size_t i = 0; i < len; i++) {
+    unsigned char c = (unsigned char)name[i];
+    bool alnum = (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9');
+    if (!alnum && c != '.' && c != '_' && c != '-')
+      return false;
+  }
+  return true;
+}
+
+DaemonConf* daemon_conf_create(void) {
+  DaemonConf* conf = calloc(1, sizeof(DaemonConf));
+  if (!conf)
+    return NULL;
+  conf->global.port = DAEMON_CONF_DEFAULT_PORT;
+  return conf;
+}
+
+void daemon_conf_free(DaemonConf* conf) {
+  if (!conf)
+    return;
+  free(conf->global.motd_file);
+  free(conf->global.address);
+  for (int i = 0; i < conf->module_count; i++) {
+    DaemonModule* m = &conf->modules[i];
+    free(m->name);
+    free(m->path);
+    for (int j = 0; j < m->auth_user_count; j++)
+      free(m->auth_users[j]);
+    free(m->auth_users);
+  }
+  free(conf->modules);
+  free(conf);
+}
+
+const DaemonModule* daemon_conf_find_module(const DaemonConf* conf, const char* name) {
+  if (!conf || !name)
+    return NULL;
+  for (int i = 0; i < conf->module_count; i++) {
+    if (strcmp(conf->modules[i].name, name) == 0)
+      return &conf->modules[i];
+  }
+  return NULL;
+}
+
+/* Replace *slot with a str_dup of value; returns false on allocation failure. */
+static bool store_string(char** slot, const char* value) {
+  char* dup = str_dup(value);
+  if (!dup)
+    return false;
+  free(*slot);
+  *slot = dup;
+  return true;
+}
+
+static bool store_port(int* slot, const char* value, char* err, size_t err_size) {
+  char* end;
+  errno = 0;
+  long p = strtol(value, &end, 10);
+  if (errno != 0 || *end != '\0' || *value == '\0' || p <= 0 || p > 65535) {
+    set_error(err, err_size, "invalid port '%s' (must be 1-65535)", value);
+    return false;
+  }
+  *slot = (int)p;
+  return true;
+}
+
+/* Apply a global scalar key/value.  Keys are case-insensitive.  Returns false
+ * (err filled) on an unknown key or an invalid value. */
+static bool apply_global_key(DaemonConf* conf, char* key, const char* value, char* err,
+                             size_t err_size) {
+  if (key_equals(key, "port"))
+    return store_port(&conf->global.port, value, err, err_size);
+  if (key_equals(key, "motd file")) {
+    if (!store_string(&conf->global.motd_file, value)) {
+      set_error(err, err_size, "out of memory parsing 'motd file'");
+      return false;
+    }
+    return true;
+  }
+  if (key_equals(key, "address")) {
+    if (!store_string(&conf->global.address, value)) {
+      set_error(err, err_size, "out of memory parsing 'address'");
+      return false;
+    }
+    return true;
+  }
+  set_error(err, err_size, "unknown global key '%s'", key);
+  return false;
+}
+
+/* Apply a module key/value to the currently-open module.  Returns false (err
+ * filled) on an unknown module key or an invalid value. */
+static bool apply_module_key(DaemonModule* module, char* key, char* value, char* err,
+                             size_t err_size) {
+  if (key_equals(key, "path")) {
+    if (*value == '\0') {
+      set_error(err, err_size, "module '%s': 'path' must not be empty", module->name);
+      return false;
+    }
+    if (!store_string(&module->path, value)) {
+      set_error(err, err_size, "out of memory parsing 'path' for module '%s'", module->name);
+      return false;
+    }
+    return true;
+  }
+  if (key_equals(key, "read only")) {
+    bool parsed;
+    if (!parse_bool_value(value, &parsed)) {
+      set_error(err, err_size,
+                "module '%s': 'read only' must be yes/no (or true/false/1/0), got '%s'",
+                module->name, value);
+      return false;
+    }
+    module->read_only = parsed;
+    return true;
+  }
+  if (key_equals(key, "client owner")) {
+    bool parsed;
+    if (!parse_bool_value(value, &parsed)) {
+      set_error(err, err_size,
+                "module '%s': 'client owner' must be yes/no (or true/false/1/0), got '%s'",
+                module->name, value);
+      return false;
+    }
+    module->client_owner = parsed;
+    return true;
+  }
+  if (key_equals(key, "auth users")) {
+    char* list = str_dup(value);
+    if (!list) {
+      set_error(err, err_size, "out of memory parsing 'auth users' for module '%s'", module->name);
+      return false;
+    }
+    char* save = NULL;
+    for (char* token = strtok_r(list, ",", &save); token; token = strtok_r(NULL, ",", &save)) {
+      const char* user = trim_ws(token);
+      if (*user == '\0')
+        continue;
+      char** grown =
+          realloc(module->auth_users, (size_t)(module->auth_user_count + 1) * sizeof(char*));
+      if (!grown) {
+        free(list);
+        set_error(err, err_size, "out of memory parsing 'auth users' for module '%s'",
+                  module->name);
+        return false;
+      }
+      module->auth_users = grown;
+      char* dup = str_dup(user);
+      if (!dup) {
+        free(list);
+        set_error(err, err_size, "out of memory parsing 'auth users' for module '%s'",
+                  module->name);
+        return false;
+      }
+      module->auth_users[module->auth_user_count++] = dup;
+    }
+    free(list);
+    return true;
+  }
+  set_error(err, err_size, "unknown key '%s' in module '%s'", key, module->name);
+  return false;
+}
+
+static bool module_open_valid(const DaemonModule* module, char* err, size_t err_size) {
+  if (module->path == NULL) {
+    set_error(err, err_size, "module '%s' has no 'path'", module->name);
+    return false;
+  }
+  return true;
+}
+
+/* Validate a [section] header line body (text between the brackets) and set
+ * *name to the module name.  Returns false on a malformed header. */
+static bool parse_section_name(char* body, const char** name_out, char* err, size_t err_size) {
+  char* name = trim_ws(body);
+  if (!daemon_module_name_valid(name)) {
+    set_error(err, err_size, "invalid module name '%s' (must be 1-%d chars of [A-Za-z0-9._-])",
+              name, DAEMON_MAX_MODULE_NAME);
+    return false;
+  }
+  *name_out = name;
+  return true;
+}
+
+/* Open (or switch to) a module section.  Closes any previously open module
+ * (validating it has a path) and appends the new one. */
+static int open_module(DaemonConf* conf, int* current_module, const char* name, char* err,
+                       size_t err_size) {
+  if (*current_module >= 0) {
+    if (!module_open_valid(&conf->modules[*current_module], err, err_size))
+      return -1;
+  }
+  if (daemon_conf_find_module(conf, name)) {
+    set_error(err, err_size, "duplicate module '%s'", name);
+    return -1;
+  }
+  DaemonModule* grown =
+      realloc(conf->modules, (size_t)(conf->module_count + 1) * sizeof(DaemonModule));
+  if (!grown) {
+    set_error(err, err_size, "out of memory adding module '%s'", name);
+    return -1;
+  }
+  conf->modules = grown;
+  memset(&conf->modules[conf->module_count], 0, sizeof(DaemonModule));
+  conf->modules[conf->module_count].name = str_dup(name);
+  if (!conf->modules[conf->module_count].name) {
+    set_error(err, err_size, "out of memory adding module '%s'", name);
+    return -1;
+  }
+  conf->module_count++;
+  *current_module = conf->module_count - 1;
+  return 0;
+}
+
+/* Split a "key = value" line (value pointer returned in *value, pointing into
+ * line).  Returns false when there is no '='. */
+static bool split_key_value(char* line, char** key, char** value) {
+  char* eq = strchr(line, '=');
+  if (!eq)
+    return false;
+  *eq = '\0';
+  *key = trim_ws(line);
+  *value = trim_ws(eq + 1);
+  return true;
+}
+
+/* Strip one layer of surrounding double quotes from a trimmed value.  A value
+ * that starts with '"' but does not end with '"' is an error. */
+static bool unquote_value(char* value, char* err, size_t err_size) {
+  size_t len = strlen(value);
+  if (len == 0 || value[0] != '"')
+    return true;
+  if (len < 2 || value[len - 1] != '"') {
+    set_error(err, err_size, "unterminated quoted value");
+    return false;
+  }
+  memmove(value, value + 1, len - 2);
+  value[len - 2] = '\0';
+  return true;
+}
+
+DaemonConf* daemon_conf_load(const char* path, char* err, size_t err_size) {
+  if (err && err_size)
+    err[0] = '\0';
+  if (!path) {
+    set_error(err, err_size, "no daemon config path");
+    return NULL;
+  }
+  FILE* fp = fopen(path, "r");
+  if (!fp) {
+    set_error(err, err_size, "cannot open daemon config '%s': %s", path, strerror(errno));
+    return NULL;
+  }
+
+  DaemonConf* conf = daemon_conf_create();
+  if (!conf) {
+    fclose(fp);
+    set_error(err, err_size, "out of memory allocating daemon config");
+    return NULL;
+  }
+
+  int current_module = -1;
+  int line_no = 0;
+  char line[DAEMON_CONF_MAX_LINE + 2];
+  bool ok = true;
+
+  while (ok && fgets(line, sizeof(line), fp)) {
+    line_no++;
+    size_t len = strlen(line);
+    if (len == DAEMON_CONF_MAX_LINE + 1 && line[len - 1] != '\n') {
+      /* The read stopped at the buffer edge without a newline and there is
+       * more file to come: the line exceeds the bound. */
+      if (!feof(fp)) {
+        set_error(err, err_size, "line %d exceeds the %d-byte limit", line_no,
+                  DAEMON_CONF_MAX_LINE);
+        ok = false;
+        break;
+      }
+    }
+    if (len > 0 && line[len - 1] == '\n')
+      line[--len] = '\0';
+    if (len > 0 && line[len - 1] == '\r')
+      line[--len] = '\0';
+
+    char* cursor = line;
+    while (*cursor == ' ' || *cursor == '\t')
+      cursor++;
+    if (*cursor == '\0' || *cursor == '#' || *cursor == ';')
+      continue; /* blank or comment line */
+
+    if (*cursor == '[') {
+      char* close = strchr(cursor, ']');
+      if (!close) {
+        set_error(err, err_size, "line %d: unterminated module header", line_no);
+        ok = false;
+        break;
+      }
+      *close = '\0';
+      char* trailing = close + 1;
+      const char* rest = trim_ws(trailing);
+      if (*rest != '\0') {
+        set_error(err, err_size, "line %d: unexpected text after module header", line_no);
+        ok = false;
+        break;
+      }
+      const char* name = NULL;
+      if (!parse_section_name(cursor + 1, &name, err, err_size)) {
+        ok = false;
+        break;
+      }
+      if (open_module(conf, &current_module, name, err, err_size) != 0) {
+        ok = false;
+        break;
+      }
+      continue;
+    }
+
+    char* key;
+    char* value;
+    if (!split_key_value(cursor, &key, &value)) {
+      set_error(err, err_size, "line %d: expected 'key = value'", line_no);
+      ok = false;
+      break;
+    }
+    if (*key == '\0') {
+      set_error(err, err_size, "line %d: empty key", line_no);
+      ok = false;
+      break;
+    }
+    if (!unquote_value(value, err, err_size)) {
+      ok = false;
+      break;
+    }
+    if (current_module >= 0) {
+      if (!apply_module_key(&conf->modules[current_module], key, value, err, err_size)) {
+        ok = false;
+        break;
+      }
+    } else {
+      if (!apply_global_key(conf, key, value, err, err_size)) {
+        ok = false;
+        break;
+      }
+    }
+  }
+
+  if (ok && ferror(fp)) {
+    set_error(err, err_size, "error reading daemon config '%s': %s", path, strerror(errno));
+    ok = false;
+  }
+  fclose(fp);
+
+  if (ok && current_module >= 0 &&
+      !module_open_valid(&conf->modules[current_module], err, err_size)) {
+    ok = false;
+  }
+  if (!ok) {
+    daemon_conf_free(conf);
+    return NULL;
+  }
+  return conf;
+}
+
+int daemon_conf_apply_dparam(DaemonConf* conf, const char* assignment, char* err, size_t err_size) {
+  if (err && err_size)
+    err[0] = '\0';
+  if (!conf || !assignment || *assignment == '\0') {
+    set_error(err, err_size, "--dparam requires a KEY=VALUE override");
+    return -1;
+  }
+  char* copy = str_dup(assignment);
+  if (!copy) {
+    set_error(err, err_size, "out of memory parsing --dparam");
+    return -1;
+  }
+  char* eq = strchr(copy, '=');
+  if (!eq) {
+    free(copy);
+    set_error(err, err_size, "--dparam '%s' has no '=' (expected KEY=VALUE)", assignment);
+    return -1;
+  }
+  *eq = '\0';
+  char* key = trim_ws(copy);
+  const char* value = trim_ws(eq + 1);
+  if (*key == '\0') {
+    free(copy);
+    set_error(err, err_size, "--dparam '%s' has an empty key", assignment);
+    return -1;
+  }
+  if (*value == '\0') {
+    free(copy);
+    set_error(err, err_size, "--dparam '%s' has an empty value", assignment);
+    return -1;
+  }
+  bool ok = apply_global_key(conf, key, value, err, err_size);
+  free(copy);
+  return ok ? 0 : -1;
+}

src/shared/daemon_conf.h

@@ -0,0 +1,107 @@
+#ifndef DAEMON_CONF_H
+#define DAEMON_CONF_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+/* FastSync-native daemon configuration (a FastSync analog of rsyncd.conf).
+ *
+ * This is the config the fastsync-server --daemon listener consumes.  It is
+ * line-based with an implicit global section followed by zero or more
+ * [module] sections.  The full grammar is documented in RSYNC_COMPAT.md
+ * ("Daemon Mode") and summarized below; the parser lives entirely in
+ * daemon_conf.c so it can be unit tested without any socket code.
+ *
+ * The parser is STRICT: an unknown key, a malformed line, a value that does
+ * not parse, a module without a `path`, or a line longer than
+ * DAEMON_CONF_MAX_LINE all fail the whole load with a clear, line-numbered
+ * error instead of being silently ignored.  This keeps a typo from silently
+ * changing what a module serves.
+ */
+
+/* A daemon module's configured root is used exactly like the standalone
+ * server's --destination-root: the daemon confines every connection that
+ * selects this module to this path (file_open_secure_parent /
+ * has_path_traversal / path_is_within all keep the existing confinement, just
+ * per-module).  There is never any client-chosen root: a module path always
+ * stays confined.  A daemon REFUSES every client-chosen ownership / super-user
+ * request by default -- --numeric-ids, --chown, --usermap/--groupmap,
+ * --fake-super, --copy-as and an explicit --super -- because there is no
+ * per-module opt-in unless the operator adds one.  An operator opts a single
+ * module in with `client owner = yes` (DaemonModule.client_owner), which allows
+ * that client to choose ownership within that module's root (the standalone/SSH
+ * server honors such requests for its single operator-authorized root).  The
+ * operator-level --no-super veto additionally forces super-user activities off
+ * for every daemon connection, even an opted-in module.  See server_module_gate
+ * in server.c and RSYNC_COMPAT.md.
+ *
+ * `auth_users` is honored by Wave B daemon authentication: a module that
+ * declares auth users accepts a connection only when the presented username is
+ * on this list AND verifies against the daemon's credential store
+ * (--password-file / --early-input).  An auth-required module with no usable
+ * store refuses (fail closed) rather than falling open; see server.c.  Auth is
+ * never bypassed by ignoring the list. */
+typedef struct DaemonModule {
+  char* name;        /* module name, as the client requests it */
+  char* path;        /* module root (daemon-side authorized root) */
+  bool read_only;    /* `read only = yes/no`; default no */
+  bool client_owner; /* `client owner = yes/no`; default no.  Per-module opt-in
+                        that lets this module's clients choose ownership
+                        (--numeric-ids/--chown/--usermap/--groupmap/--fake-super/
+                        --copy-as) and request explicit --super super-user
+                        activities.  Without it the daemon refuses all of them. */
+  char** auth_users; /* `auth users = a,b`; Wave B credential list */
+  int auth_user_count;
+} DaemonModule;
+
+/* Global (pre-module) scalar keys.  `motd file` is parsed and stored but has
+ * no wire effect yet (MOTD display is Wave C). */
+typedef struct DaemonConfGlobals {
+  int port;        /* `port`, default DAEMON_CONF_DEFAULT_PORT (873) */
+  char* motd_file; /* `motd file`, may be NULL */
+  char* address;   /* `address` (optional bind address), may be NULL */
+} DaemonConfGlobals;
+
+typedef struct DaemonConf {
+  DaemonConfGlobals global;
+  DaemonModule* modules;
+  int module_count;
+} DaemonConf;
+
+#define DAEMON_CONF_DEFAULT_PORT 873
+/* Longest accepted config line (excluding the trailing newline).  Longer lines
+ * are rejected rather than buffered unboundedly. */
+#define DAEMON_CONF_MAX_LINE 4096
+/* Upper bound on a module name.  Kept far below MAX_STRING_SIZE so a wire
+ * module name can never exhaust anything by being long. */
+#define DAEMON_MAX_MODULE_NAME 200
+
+/* Allocate an empty daemon config with defaulted globals (port 873, no
+ * modules, no motd/address).  Never fails for an allocation failure; callers
+ * must still NULL-check. */
+DaemonConf* daemon_conf_create(void);
+
+/* Parse `path` into a freshly allocated DaemonConf.  Returns NULL on any error
+ * and fills `err` (err_size bytes) with a clear, line-numbered message.  The
+ * returned object is heap-owned; free it with daemon_conf_free. */
+DaemonConf* daemon_conf_load(const char* path, char* err, size_t err_size);
+
+void daemon_conf_free(DaemonConf* conf);
+
+/* Case-sensitive exact module lookup by name.  Returns the module or NULL.
+ * Module names are matched exactly (rsync semantics). */
+const DaemonModule* daemon_conf_find_module(const DaemonConf* conf, const char* name);
+
+/* Module-name syntax check: non-empty, at most DAEMON_MAX_MODULE_NAME chars,
+ * and only [A-Za-z0-9._-].  Used by the config parser, the client's
+ * host::module/path destination parser, and (implicitly) by the daemon lookup
+ * (a name that fails this can never match a parsed module). */
+bool daemon_module_name_valid(const char* name);
+
+/* Parse one --dparam=KEY=VALUE (or "--dparam KEY=VALUE") override string and
+ * apply it to the global scalars only.  Keys are case-insensitive and limited
+ * to the global scalar keys defined by the grammar (port, motd file, address).
+ * Returns 0 on success, -1 on error (err filled). */
+int daemon_conf_apply_dparam(DaemonConf* conf, const char* assignment, char* err, size_t err_size);
+
+#endif

src/shared/data.c

@@ -1,11 +1,12 @@
 #include "data.h"
 #include "log.h"
+#include "protocol.h"
 #include <stdlib.h>
 
 Data* data_create_empty(size_t data_size) {
   /* malloc(0) is UB; allocate at least 1 byte but preserve requested size */
   size_t alloc_size = data_size > 0 ? data_size : 1;
-  void* data = malloc(alloc_size);
+  void* data = protocol_alloc(alloc_size);
   if (data == NULL) {
     log_message(LOG_LEVEL_ERROR, "Could not allocate memory for empty data");
     return NULL;
@@ -14,7 +15,7 @@ Data* data_create_empty(size_t data_size) {
 }
 
 Data* data_create_reserve(size_t size) {
-  Data* d = malloc(sizeof(Data));
+  Data* d = protocol_alloc(sizeof(Data));
   if (d == NULL) {
     log_message(LOG_LEVEL_ERROR, "Could not allocate memory for data");
     return NULL;
@@ -26,7 +27,7 @@ Data* data_create_reserve(size_t size) {
 }
 
 Data* data_create(void* data, size_t data_size) {
-  Data* new_data = malloc(sizeof(Data));
+  Data* new_data = protocol_alloc(sizeof(Data));
   if (new_data == NULL) {
     log_message(LOG_LEVEL_ERROR, "Could not allocate memory for data");
     free(data);

src/shared/delay_updates.c

@@ -0,0 +1,338 @@
+#include "delay_updates.h"
+
+#include "config.h"
+#include "file.h"
+#include "log.h"
+#include "utils.h"
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <libgen.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+DelayUpdatesContext* delay_updates_context_create(const char* root_directory) {
+  if (!root_directory)
+    return NULL;
+  DelayUpdatesContext* context = calloc(1, sizeof(DelayUpdatesContext));
+  if (!context)
+    return NULL;
+  context->root_directory = str_dup(root_directory);
+  if (!context->root_directory) {
+    free(context);
+    return NULL;
+  }
+  context->staging_root = path_cat(root_directory, DELAY_UPDATES_STAGING_DIR);
+  if (!context->staging_root) {
+    free(context->root_directory);
+    free(context);
+    return NULL;
+  }
+  context->entries = NULL;
+  context->count = 0;
+  context->capacity = 0;
+  context->prepared = false;
+  context->lock_fd = -1;
+  if (mtx_init(&context->mutex, mtx_plain) != thrd_success) {
+    free(context->staging_root);
+    free(context->root_directory);
+    free(context);
+    return NULL;
+  }
+  return context;
+}
+
+void delay_updates_context_destroy(DelayUpdatesContext* context) {
+  if (!context)
+    return;
+  mtx_destroy(&context->mutex);
+  if (context->lock_fd >= 0)
+    close(context->lock_fd);
+  context->lock_fd = -1;
+  free(context->staging_root);
+  free(context->root_directory);
+  for (size_t i = 0; i < context->count; i++) {
+    free(context->entries[i].staged_path);
+    free(context->entries[i].final_path);
+    free(context->entries[i].file_path);
+  }
+  free(context->entries);
+  free(context);
+}
+
+bool delay_updates_staging_name_conflict(const char* dir) {
+  if (!dir || !*dir)
+    return false;
+  size_t length = strlen(dir);
+  while (length > 0 && dir[length - 1] == '/')
+    length--;
+  size_t reserved_length = strlen(DELAY_UPDATES_STAGING_DIR);
+  if (length != reserved_length)
+    return false;
+  return strncmp(dir, DELAY_UPDATES_STAGING_DIR, length) == 0;
+}
+
+/* Recursively delete every entry inside an open directory (never following
+   symlinks).  The directory itself is left in place.  Mirrors the fd-relative
+   walk used by the delete code so a symlink planted inside the staging tree
+   can never redirect removal outside of it. */
+static bool delay_wipe_dir_fd(int dirfd) {
+  int scanfd = dup(dirfd);
+  if (scanfd < 0)
+    return false;
+  DIR* dir = fdopendir(scanfd);
+  if (!dir) {
+    close(scanfd);
+    return false;
+  }
+  bool operation_ok = true;
+  const struct dirent* entry;
+  while ((entry = readdir(dir)) != NULL) {
+    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
+      continue;
+    struct stat st;
+    if (fstatat(dirfd, entry->d_name, &st, AT_SYMLINK_NOFOLLOW) != 0) {
+      if (errno != ENOENT)
+        operation_ok = false;
+      continue;
+    }
+    if (S_ISDIR(st.st_mode)) {
+      int childfd = openat(dirfd, entry->d_name, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+      bool child_removed = false;
+      if (childfd >= 0) {
+        child_removed = delay_wipe_dir_fd(childfd);
+        close(childfd);
+      } else if (errno != ENOENT) {
+        operation_ok = false;
+      }
+      if (child_removed && unlinkat(dirfd, entry->d_name, AT_REMOVEDIR) != 0 && errno != ENOENT)
+        operation_ok = false;
+    } else {
+      if (unlinkat(dirfd, entry->d_name, 0) != 0 && errno != ENOENT)
+        operation_ok = false;
+    }
+  }
+  closedir(dir);
+  return operation_ok;
+}
+
+bool delay_updates_prepare(DelayUpdatesContext* context) {
+  if (!context)
+    return false;
+  if (context->prepared)
+    return true;
+  int fd = file_open_private_dir(context->staging_root);
+  if (fd < 0) {
+    int saved_errno = errno;
+    char* escaped = output_escape(context->staging_root, false);
+    log_message(LOG_LEVEL_ERROR, "could not create --delay-updates staging directory '%s': %s",
+                escaped ? escaped : "<allocation failed>", strerror(saved_errno));
+    free(escaped);
+    return false;
+  }
+  /* Hold an exclusive advisory lock on the staging directory for the whole
+     transfer.  The staging directory name is fixed, so two simultaneous
+     delayed transfers to the same destination root would otherwise share it
+     and destroy each other's staged files.  The lock makes the second session
+     fail cleanly instead of corrupting the first.  The lock is released when
+     the context (and its file descriptor) is destroyed. */
+  if (flock(fd, LOCK_EX | LOCK_NB) != 0) {
+    int saved_errno = errno;
+    close(fd);
+    if (saved_errno == EWOULDBLOCK || saved_errno == EAGAIN) {
+      char* escaped = output_escape(context->staging_root, false);
+      log_message(LOG_LEVEL_ERROR,
+                  "another --delay-updates transfer to '%s' is already in progress; refusing to "
+                  "share the staging directory",
+                  escaped ? escaped : "<allocation failed>");
+      free(escaped);
+    } else {
+      log_message(LOG_LEVEL_ERROR, "could not lock --delay-updates staging directory '%s': %s",
+                  context->staging_root, strerror(saved_errno));
+    }
+    return false;
+  }
+  context->lock_fd = fd;
+  /* Only now, with exclusive ownership, wipe leftovers from an interrupted
+     earlier transfer; this can never race with a live session. */
+  bool ok = delay_wipe_dir_fd(fd);
+  if (!ok) {
+    log_message(LOG_LEVEL_ERROR, "could not clear stale --delay-updates staging files under '%s'",
+                context->staging_root);
+    close(context->lock_fd);
+    context->lock_fd = -1;
+    return false;
+  }
+  context->prepared = true;
+  return true;
+}
+
+bool delay_updates_record(DelayUpdatesContext* context, const char* staged_path,
+                          const char* final_path, const char* file_path) {
+  if (!context || !staged_path || !final_path || !file_path)
+    return false;
+  char* staged_copy = str_dup(staged_path);
+  char* final_copy = str_dup(final_path);
+  char* file_copy = str_dup(file_path);
+  if (!staged_copy || !final_copy || !file_copy) {
+    free(staged_copy);
+    free(final_copy);
+    free(file_copy);
+    return false;
+  }
+  mtx_lock(&context->mutex);
+  bool ok = true;
+  if (context->count == context->capacity) {
+    size_t new_capacity = context->capacity == 0 ? 64 : context->capacity * 2;
+    if (new_capacity < context->capacity) {
+      ok = false;
+    } else {
+      StagedFileEntry* grown = realloc(context->entries, new_capacity * sizeof(StagedFileEntry));
+      if (!grown) {
+        ok = false;
+      } else {
+        context->entries = grown;
+        context->capacity = new_capacity;
+      }
+    }
+  }
+  if (ok) {
+    context->entries[context->count].staged_path = staged_copy;
+    context->entries[context->count].final_path = final_copy;
+    context->entries[context->count].file_path = file_copy;
+    context->count++;
+  }
+  mtx_unlock(&context->mutex);
+  if (!ok) {
+    free(staged_copy);
+    free(final_copy);
+    free(file_copy);
+  }
+  return ok;
+}
+
+/* Move an existing final destination file aside before the staged replacement
+   is installed.  Deferred from stage time so the final destination is not
+   modified until publication.  Mirrors the immediate-mode backup logic. */
+static bool delay_publish_backup(const DelayUpdatesContext* context, const Config* config,
+                                 const StagedFileEntry* entry) {
+  bool backup_enabled = config && config->backup && !config->ignore_existing;
+  if (!backup_enabled)
+    return true;
+  const char* backup_suffix = (config && config->suffix) ? config->suffix : "~";
+  struct stat backup_stat;
+  if (!file_stat_secure(entry->final_path, &backup_stat))
+    return true; /* nothing to back up */
+
+  char* backup_path = NULL;
+  if (config->backup_dir) {
+    char* confined_backup = path_cat(context->root_directory, config->backup_dir);
+    if (!confined_backup)
+      return false;
+    backup_path = path_cat(confined_backup, entry->file_path);
+    free(confined_backup);
+  } else {
+    size_t path_len = strlen(entry->final_path);
+    size_t suffix_len = strlen(backup_suffix);
+    if (path_len > SIZE_MAX - suffix_len - 1)
+      return false;
+    backup_path = malloc(path_len + suffix_len + 1);
+    if (backup_path) {
+      memcpy(backup_path, entry->final_path, path_len);
+      memcpy(backup_path + path_len, backup_suffix, suffix_len + 1);
+    }
+  }
+  if (!backup_path)
+    return false;
+  char* parent_copy = str_dup(backup_path);
+  if (!parent_copy || !file_ensure_directory_secure(dirname(parent_copy))) {
+    free(parent_copy);
+    free(backup_path);
+    return false;
+  }
+  free(parent_copy);
+  bool ok = file_rename_secure(entry->final_path, backup_path);
+  free(backup_path);
+  return ok;
+}
+
+static bool delay_publish_entry(DelayUpdatesContext* context, const Config* config,
+                                const StagedFileEntry* entry) {
+  if (!delay_publish_backup(context, config, entry))
+    return false;
+  if (!file_rename_secure(entry->staged_path, entry->final_path)) {
+    if (errno == EXDEV) {
+      char* escaped = output_escape(entry->final_path, false);
+      log_message(LOG_LEVEL_ERROR,
+                  "staging directory is on a different filesystem than the destination; cannot "
+                  "atomically install file (EXDEV): %s",
+                  escaped ? escaped : "<allocation failed>");
+      free(escaped);
+    } else {
+      char* escaped = output_escape(entry->final_path, false);
+      log_message(LOG_LEVEL_ERROR, "could not install staged file '%s': %s",
+                  escaped ? escaped : "<allocation failed>", strerror(errno));
+      free(escaped);
+    }
+    return false;
+  }
+  return true;
+}
+
+/* Remove the staging tree (contents plus the directory itself).  Returns true
+   when nothing is left behind (including the case where it never existed). */
+static bool delay_updates_remove_staging_tree(DelayUpdatesContext* context) {
+  int fd = open(context->staging_root, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+  if (fd < 0)
+    return errno == ENOENT;
+  bool ok = delay_wipe_dir_fd(fd);
+  if (close(fd) != 0)
+    ok = false;
+  if (ok && rmdir(context->staging_root) != 0 && errno != ENOENT)
+    ok = false;
+  return ok;
+}
+
+bool delay_updates_publish(DelayUpdatesContext* context, const Config* config) {
+  if (!context)
+    return false;
+  mtx_lock(&context->mutex);
+  bool ok = true;
+  for (size_t i = 0; i < context->count; i++) {
+    if (!delay_publish_entry(context, config, &context->entries[i])) {
+      ok = false;
+      break;
+    }
+  }
+  mtx_unlock(&context->mutex);
+
+  /* Renaming files out of the staging tree leaves the mirrored directories
+     behind, and a mid-publish failure leaves the remaining staged files.
+     Remove whatever is left so a later run starts from a clean staging area
+     and no staged content can linger after a failed publish.  If that cleanup
+     fails, tell the operator: a stale staging directory would otherwise
+     silently accumulate and make the next transfer's prepare-wipe fail. */
+  if (!delay_updates_remove_staging_tree(context)) {
+    log_message(LOG_LEVEL_WARNING,
+                "could not fully remove --delay-updates staging directory '%s' after publish; a "
+                "later --delay-updates transfer to this destination will try to clear it",
+                context->staging_root);
+  }
+  return ok;
+}
+
+void delay_updates_cleanup(DelayUpdatesContext* context) {
+  if (!context)
+    return;
+  /* Only a context that gained exclusive ownership may touch the shared
+     staging directory.  If prepare never succeeded (e.g. lock contention with
+     another live session) the directory belongs to that other session and must
+     be left alone. */
+  if (!context->prepared)
+    return;
+  delay_updates_remove_staging_tree(context);
+}

src/shared/delay_updates.h

@@ -0,0 +1,68 @@
+#ifndef DELAY_UPDATES_H
+#define DELAY_UPDATES_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <threads.h>
+
+/* Forward-declared in config.h; full type needed by file_save_to_disk. */
+typedef struct Config Config;
+
+/* One staged file awaiting publication. */
+typedef struct {
+  char* staged_path; /* full path inside the staging tree */
+  char* final_path;  /* full final destination path */
+  char* file_path;   /* the file path as received on the wire */
+} StagedFileEntry;
+
+/* Receiver-side --delay-updates staging registry.  All successfully written
+   files land under a private staging directory inside the receive root and are
+   atomically renamed into their final destination only at the very end of the
+   transfer.  A single PipelineContextReceiver has exactly one writer thread,
+   but the registry is still mutex-protected so the same object can be safely
+   shared with the publish/cleanup phase that runs after the threads join. */
+typedef struct DelayUpdatesContext {
+  char* root_directory; /* receive root the staging dir lives under */
+  char* staging_root;   /* root_directory/<staging dir name> */
+  mtx_t mutex;
+  StagedFileEntry* entries;
+  size_t count;
+  size_t capacity;
+  bool prepared; /* staging dir created, wiped, and exclusively locked */
+  int lock_fd;   /* advisory exclusive flock held on the staging dir, or -1 */
+} DelayUpdatesContext;
+
+/* Name of the private staging subdirectory created under the receive root. */
+#define DELAY_UPDATES_STAGING_DIR ".fastsync-stage"
+
+/* True when `dir` (ignoring a trailing "/") is the reserved staging directory
+   name.  Used to reject a --backup-dir that would collide with the internal
+   staging area. */
+bool delay_updates_staging_name_conflict(const char* dir);
+
+/* Create an empty staging context rooted below root_directory.  Does not touch
+   the filesystem yet. */
+DelayUpdatesContext* delay_updates_context_create(const char* root_directory);
+void delay_updates_context_destroy(DelayUpdatesContext* context);
+
+/* Create the private 0700 staging directory (on first call) and wipe any
+   leftovers from a previously interrupted delayed transfer.  Idempotent. */
+bool delay_updates_prepare(DelayUpdatesContext* context);
+
+/* Record a fully-written staged file for later publication.  Copies all three
+   paths.  Returns false on allocation failure. */
+bool delay_updates_record(DelayUpdatesContext* context, const char* staged_path,
+                          const char* final_path, const char* file_path);
+
+/* Atomically rename every staged file into its final destination.  Deferred
+   --backup handling runs immediately before each rename.  On any failure the
+   remaining staged files are removed (best effort); already-published files
+   are not rolled back.  Afterwards the staging tree is removed so a successful
+   or failed publish leaves no staging leftovers. */
+bool delay_updates_publish(DelayUpdatesContext* context, const Config* config);
+
+/* Best-effort removal of every staged file and the staging directory itself.
+   Safe to call when nothing was staged or after a successful publish. */
+void delay_updates_cleanup(DelayUpdatesContext* context);
+
+#endif

src/shared/delta.c

@@ -1,5 +1,6 @@
 #include "delta.h"
 #include "log.h"
+#include "protocol.h"
 #include <stdint.h>
 #include <limits.h>
 #include <stdlib.h>
@@ -28,12 +29,21 @@ uint32_t delta_xxhash32(const void* data, uint32_t len) {
   return XXH32(data, len, 0);
 }
 
+uint32_t delta_xxhash32_seeded(const void* data, uint32_t len, uint32_t seed) {
+  return XXH32(data, len, seed);
+}
+
 uint64_t delta_xxhash64(const void* data, size_t len) {
   return XXH64(data, len, 0);
 }
 
 DeltaSignature* delta_signature_create(const void* old_file_data, uint64_t old_file_size,
                                        uint32_t block_size) {
+  return delta_signature_create_seeded(old_file_data, old_file_size, block_size, 0);
+}
+
+DeltaSignature* delta_signature_create_seeded(const void* old_file_data, uint64_t old_file_size,
+                                              uint32_t block_size, uint32_t seed) {
   if (old_file_data == NULL || old_file_size == 0 || block_size == 0)
     return NULL;
 
@@ -43,7 +53,7 @@ DeltaSignature* delta_signature_create(const void* old_file_data, uint64_t old_f
 
   uint32_t block_count = (uint32_t)((old_file_size + block_size - 1) / block_size);
 
-  DeltaSignature* sig = malloc(sizeof(DeltaSignature));
+  DeltaSignature* sig = protocol_alloc(sizeof(DeltaSignature));
   if (!sig)
     return NULL;
 
@@ -54,7 +64,7 @@ DeltaSignature* delta_signature_create(const void* old_file_data, uint64_t old_f
     free(sig);
     return NULL;
   }
-  sig->blocks = malloc((size_t)block_count * sizeof(DeltaBlockSig));
+  sig->blocks = protocol_alloc((size_t)block_count * sizeof(DeltaBlockSig));
   if (!sig->blocks) {
     free(sig);
     return NULL;
@@ -66,7 +76,7 @@ DeltaSignature* delta_signature_create(const void* old_file_data, uint64_t old_f
     uint32_t len =
         (uint32_t)((old_file_size - offset < block_size) ? (old_file_size - offset) : block_size);
     sig->blocks[i].adler32 = delta_adler32(data + offset, len);
-    sig->blocks[i].xxhash = delta_xxhash32(data + offset, len);
+    sig->blocks[i].xxhash = delta_xxhash32_seeded(data + offset, len, seed);
   }
 
   return sig;
@@ -82,7 +92,7 @@ Data* delta_signature_serialize(const DeltaSignature* sig) {
       total > SIZE_MAX)
     return NULL;
 
-  uint8_t* buf = malloc((size_t)total);
+  uint8_t* buf = protocol_alloc((size_t)total);
   if (!buf)
     return NULL;
 
@@ -111,7 +121,7 @@ DeltaSignature* delta_signature_deserialize(const Data* data) {
   const uint8_t* buf = (const uint8_t*)data->data;
   size_t pos = 0;
 
-  DeltaSignature* sig = malloc(sizeof(DeltaSignature));
+  DeltaSignature* sig = protocol_alloc(sizeof(DeltaSignature));
   if (!sig)
     return NULL;
 
@@ -149,7 +159,7 @@ DeltaSignature* delta_signature_deserialize(const Data* data) {
     free(sig);
     return NULL;
   }
-  sig->blocks = malloc((size_t)blocks_size);
+  sig->blocks = protocol_alloc((size_t)blocks_size);
   if (!sig->blocks) {
     free(sig);
     return NULL;
@@ -178,7 +188,7 @@ static bool ensure_capacity(DeltaInstruction** instrs, uint32_t* capacity, uint3
   if (*capacity > MAX_DELTA_INSTRUCTIONS / 2)
     return false;
   uint32_t new_cap = *capacity * 2;
-  DeltaInstruction* tmp = realloc(*instrs, (size_t)new_cap * sizeof(DeltaInstruction));
+  DeltaInstruction* tmp = protocol_realloc(*instrs, (size_t)new_cap * sizeof(DeltaInstruction));
   if (!tmp)
     return false;
   *instrs = tmp;
@@ -195,7 +205,7 @@ static bool flush_literal(DeltaInstruction** instrs, uint32_t* capacity, uint32_
   uint32_t lit_len = (uint32_t)(end - start);
   if (!ensure_capacity(instrs, capacity, *count))
     return false;
-  uint8_t* lit_data = malloc(lit_len);
+  uint8_t* lit_data = protocol_alloc(lit_len);
   if (!lit_data)
     return false;
   memcpy(lit_data, data + start, lit_len);
@@ -215,8 +225,126 @@ static void free_instructions(DeltaInstruction* instrs, uint32_t count) {
   free(instrs);
 }
 
+/* Sentinel meaning "no signature block" in the lookup index chains.  Block
+ * counts are bounded well below UINT32_MAX, so it doubles as a null link. */
+#define DELTA_NO_BLOCK UINT32_MAX
+
+/* Avalanche mix for the rolling checksum so blocks do not cluster in the
+ * bucket table when the weak checksum has little entropy (e.g. all-zero or
+ * patterned files). */
+static uint32_t delta_adler_mix(uint32_t h) {
+  h ^= h >> 16;
+  h *= 0x7feb352dU;
+  h ^= h >> 15;
+  h *= 0x846ca68bU;
+  h ^= h >> 16;
+  return h;
+}
+
+/* Smallest power of two >= v.  v must be non-zero. */
+static uint32_t delta_next_pow2(uint32_t v) {
+  v--;
+  v |= v >> 1;
+  v |= v >> 2;
+  v |= v >> 4;
+  v |= v >> 8;
+  v |= v >> 16;
+  return v + 1;
+}
+
+/* Build a hash index over sig->blocks keyed by the (mixed) rolling checksum.
+ * All blocks sharing an Adler-32 value land in the same bucket; collisions
+ * are chained through a single contiguous allocation:
+ *
+ *   [0, bucket_count)                 heads (first block per bucket)
+ *   [bucket_count, 2*bucket_count)    tails (last block per bucket)
+ *   [2*bucket_count, ...)             per-block chain links
+ *
+ * Blocks are inserted in ascending index order so every bucket chain is
+ * ordered exactly like the historical linear scan.  Returns the base pointer
+ * (also the heads array) or NULL when no index could be allocated; callers
+ * then fall back to the linear scan. */
+static uint32_t* delta_build_index(const DeltaSignature* sig, uint32_t bucket_count) {
+  if (sig->block_count == 0 || bucket_count == 0)
+    return NULL;
+
+  size_t entries = (size_t)2 * bucket_count + sig->block_count;
+  if (entries > SIZE_MAX / sizeof(uint32_t))
+    return NULL;
+
+  uint32_t* index = protocol_alloc(entries * sizeof(uint32_t));
+  if (!index)
+    return NULL;
+
+  uint32_t* heads = index;
+  uint32_t* tails = index + bucket_count;
+  uint32_t* next = index + 2 * bucket_count;
+  uint32_t mask = bucket_count - 1;
+
+  memset(heads, 0xFF, (size_t)bucket_count * sizeof(uint32_t));
+  memset(tails, 0xFF, (size_t)bucket_count * sizeof(uint32_t));
+
+  for (uint32_t j = 0; j < sig->block_count; j++) {
+    uint32_t b = delta_adler_mix(sig->blocks[j].adler32) & mask;
+    if (heads[b] == DELTA_NO_BLOCK)
+      heads[b] = j;
+    else
+      next[tails[b]] = j;
+    tails[b] = j;
+    next[j] = DELTA_NO_BLOCK;
+  }
+  return index;
+}
+
+/* Locate the signature block matching the byte window at new_data[i].
+ *
+ * Mirrors the original per-window behaviour exactly: only a full block_size
+ * window can match, candidates are accepted only when the weak (Adler-32) and
+ * strong (xxHash32) checksums both agree, and the lowest block index wins so
+ * the emitted op stream is byte-identical to the linear scan.  When heads is
+ * non-NULL the candidate set is reached through the bucket index (expected
+ * O(1) per window); otherwise an exact linear scan is used. */
+static uint32_t delta_find_match(const uint8_t* window, uint32_t window_len, uint32_t adler,
+                                 bool full_window, const DeltaSignature* sig, const uint32_t* heads,
+                                 const uint32_t* next, uint32_t mask, uint32_t seed) {
+  if (!full_window || sig->block_count == 0)
+    return DELTA_NO_BLOCK;
+
+  if (heads) {
+    uint32_t b = delta_adler_mix(adler) & mask;
+    uint32_t window_xxh = 0;
+    bool have_xxh = false;
+    for (uint32_t j = heads[b]; j != DELTA_NO_BLOCK; j = next[j]) {
+      if (sig->blocks[j].adler32 != adler)
+        continue;
+      if (!have_xxh) {
+        window_xxh = delta_xxhash32_seeded(window, window_len, seed);
+        have_xxh = true;
+      }
+      if (window_xxh == sig->blocks[j].xxhash)
+        return j;
+    }
+    return DELTA_NO_BLOCK;
+  }
+
+  /* Fallback used when the index could not be allocated. */
+  for (uint32_t j = 0; j < sig->block_count; j++) {
+    if (sig->blocks[j].adler32 == adler) {
+      uint32_t window_xxh = delta_xxhash32_seeded(window, window_len, seed);
+      if (window_xxh == sig->blocks[j].xxhash)
+        return j;
+    }
+  }
+  return DELTA_NO_BLOCK;
+}
+
 Delta* delta_compute(const void* new_file_data, uint64_t new_file_size, const DeltaSignature* sig,
                      uint32_t block_size) {
+  return delta_compute_seeded(new_file_data, new_file_size, sig, block_size, 0);
+}
+
+Delta* delta_compute_seeded(const void* new_file_data, uint64_t new_file_size,
+                            const DeltaSignature* sig, uint32_t block_size, uint32_t seed) {
   if (!new_file_data || !sig || !sig->blocks || new_file_size == 0 || block_size == 0 ||
       block_size > DELTA_BLOCK_SIZE_MAX || sig->block_size != block_size)
     return NULL;
@@ -225,10 +353,29 @@ Delta* delta_compute(const void* new_file_data, uint64_t new_file_size, const De
 
   uint32_t capacity = 64;
   uint32_t count = 0;
-  DeltaInstruction* instrs = malloc((size_t)capacity * sizeof(DeltaInstruction));
+  DeltaInstruction* instrs = protocol_alloc((size_t)capacity * sizeof(DeltaInstruction));
   if (!instrs)
     return NULL;
 
+  /* Build a one-time bucket index over the signature blocks keyed by the weak
+   * checksum.  This turns the per-byte-window candidate lookup from an
+   * O(block_count) linear scan into an expected O(1) probe, which dominates
+   * the cost for large mostly-matching files (the diff steps one byte at a
+   * time through changed regions).  On allocation failure the probe falls back
+   * to the original linear scan, so behaviour is unchanged under memory
+   * pressure. */
+  uint32_t* index = NULL;
+  const uint32_t* chain_next = NULL;
+  uint32_t mask = 0;
+  if (sig->block_count > 0) {
+    uint32_t bucket_count = delta_next_pow2(sig->block_count);
+    index = delta_build_index(sig, bucket_count);
+    if (index) {
+      chain_next = index + 2 * bucket_count;
+      mask = bucket_count - 1;
+    }
+  }
+
   uint64_t literal_start = 0;
   bool has_literal = false;
 
@@ -263,34 +410,32 @@ Delta* delta_compute(const void* new_file_data, uint64_t new_file_size, const De
     }
 
     bool matched = false;
-    for (uint32_t j = 0; j < sig->block_count; j++) {
-      if (adler == sig->blocks[j].adler32 && full_window) {
-        uint32_t xxh = delta_xxhash32(new_data + i, window_len);
-        if (xxh == sig->blocks[j].xxhash) {
-          if (has_literal) {
-            if (!flush_literal(&instrs, &capacity, &count, new_data, literal_start, i)) {
-              free_instructions(instrs, count);
-              return NULL;
-            }
-            has_literal = false;
-          }
-
-          if (!ensure_capacity(&instrs, &capacity, count)) {
-            free_instructions(instrs, count);
-            return NULL;
-          }
-          instrs[count].type = DELTA_INSTR_BLOCK_MATCH;
-          instrs[count].match.block_index = j;
-          instrs[count].match.block_offset = 0;
-          instrs[count].match.length = window_len;
-          count++;
-
-          i += window_len;
-          rolling_valid = false;
-          matched = true;
-          break;
+    uint32_t match_block = delta_find_match(new_data + i, window_len, adler, full_window, sig,
+                                            index, chain_next, mask, seed);
+    if (match_block != DELTA_NO_BLOCK) {
+      if (has_literal) {
+        if (!flush_literal(&instrs, &capacity, &count, new_data, literal_start, i)) {
+          free_instructions(instrs, count);
+          free(index);
+          return NULL;
         }
+        has_literal = false;
       }
+
+      if (!ensure_capacity(&instrs, &capacity, count)) {
+        free_instructions(instrs, count);
+        free(index);
+        return NULL;
+      }
+      instrs[count].type = DELTA_INSTR_BLOCK_MATCH;
+      instrs[count].match.block_index = match_block;
+      instrs[count].match.block_offset = 0;
+      instrs[count].match.length = window_len;
+      count++;
+
+      i += window_len;
+      rolling_valid = false;
+      matched = true;
     }
 
     if (!matched) {
@@ -302,6 +447,8 @@ Delta* delta_compute(const void* new_file_data, uint64_t new_file_size, const De
     }
   }
 
+  free(index);
+
   if (has_literal) {
     if (!flush_literal(&instrs, &capacity, &count, new_data, literal_start, new_file_size)) {
       free_instructions(instrs, count);
@@ -309,7 +456,7 @@ Delta* delta_compute(const void* new_file_data, uint64_t new_file_size, const De
     }
   }
 
-  Delta* delta = malloc(sizeof(Delta));
+  Delta* delta = protocol_alloc(sizeof(Delta));
   if (!delta) {
     free_instructions(instrs, count);
     return NULL;
@@ -355,7 +502,7 @@ Data* delta_serialize(const Delta* delta) {
   if (delta->delta_size > UINT64_MAX - header_size || header_size + delta->delta_size > SIZE_MAX)
     return NULL;
   uint64_t total = header_size + delta->delta_size;
-  uint8_t* buf = malloc((size_t)total);
+  uint8_t* buf = protocol_alloc((size_t)total);
   if (!buf)
     return NULL;
 
@@ -395,7 +542,7 @@ Delta* delta_deserialize(const Data* data) {
   const uint8_t* buf = (const uint8_t*)data->data;
   size_t pos = 0;
 
-  Delta* delta = malloc(sizeof(Delta));
+  Delta* delta = protocol_alloc(sizeof(Delta));
   if (!delta)
     return NULL;
 
@@ -412,9 +559,10 @@ Delta* delta_deserialize(const Data* data) {
     return NULL;
   }
 
-  delta->instructions = delta->instruction_count == 0
-                            ? NULL
-                            : malloc((size_t)delta->instruction_count * sizeof(DeltaInstruction));
+  delta->instructions =
+      delta->instruction_count == 0
+          ? NULL
+          : protocol_alloc((size_t)delta->instruction_count * sizeof(DeltaInstruction));
   if (delta->instruction_count > 0 && !delta->instructions) {
     free(delta);
     return NULL;
@@ -465,7 +613,7 @@ Delta* delta_deserialize(const Data* data) {
         free(delta);
         return NULL;
       }
-      delta->instructions[i].literal.data = malloc(lit_len ? lit_len : 1);
+      delta->instructions[i].literal.data = protocol_alloc(lit_len ? lit_len : 1);
       if (!delta->instructions[i].literal.data) {
         log_message(LOG_LEVEL_ERROR, "Failed to allocate %u bytes for literal data", lit_len);
         free_instructions(delta->instructions, i);
@@ -492,7 +640,7 @@ void* delta_apply(const void* old_data, uint64_t old_size, const Delta* delta,
       delta->new_file_size > DELTA_MAX_FILE_SIZE || delta->new_file_size > SIZE_MAX)
     return NULL;
 
-  void* output = malloc(delta->new_file_size ? (size_t)delta->new_file_size : 1);
+  void* output = protocol_alloc(delta->new_file_size ? (size_t)delta->new_file_size : 1);
   if (!output)
     return NULL;
 

src/shared/delta.h

@@ -56,12 +56,22 @@ typedef struct {
 
 DeltaSignature* delta_signature_create(const void* old_file_data, uint64_t old_file_size,
                                        uint32_t block_size);
+/* Seeded equivalent of delta_signature_create: the per-block strong (xxHash32)
+ * checksum uses `seed` (the low 32 bits of --checksum-seed).  Passing seed 0 is
+ * identical to the unseeded function. */
+DeltaSignature* delta_signature_create_seeded(const void* old_file_data, uint64_t old_file_size,
+                                              uint32_t block_size, uint32_t seed);
 Data* delta_signature_serialize(const DeltaSignature* sig);
 DeltaSignature* delta_signature_deserialize(const Data* data);
 void delta_signature_destroy(DeltaSignature* sig);
 
 Delta* delta_compute(const void* new_file_data, uint64_t new_file_size, const DeltaSignature* sig,
                      uint32_t block_size);
+/* Seeded equivalent of delta_compute: the per-window strong (xxHash32) check
+ * uses `seed` (the low 32 bits of --checksum-seed).  The receiver's signature
+ * must have been built with the same seed for matching. */
+Delta* delta_compute_seeded(const void* new_file_data, uint64_t new_file_size,
+                            const DeltaSignature* sig, uint32_t block_size, uint32_t seed);
 Data* delta_serialize(const Delta* delta);
 Delta* delta_deserialize(const Data* data);
 void* delta_apply(const void* old_data, uint64_t old_size, const Delta* delta, uint32_t block_size);
@@ -72,6 +82,7 @@ bool delta_is_worthwhile(const Delta* delta, uint64_t new_file_size);
 
 uint32_t delta_adler32(const void* data, uint32_t len);
 uint32_t delta_xxhash32(const void* data, uint32_t len);
+uint32_t delta_xxhash32_seeded(const void* data, uint32_t len, uint32_t seed);
 uint64_t delta_xxhash64(const void* data, size_t len);
 
 #endif

src/shared/file.h

@@ -4,6 +4,7 @@
 #include "file_send.h"
 #include "file_receive.h"
 #include "file_types.h"
+#include "checksum.h"
 #include <stdbool.h>
 #include <stdint.h>
 #include <sys/stat.h>
@@ -14,23 +15,130 @@
 File* file_create(const char* path);
 void file_destroy(void* item);
 bool file_load_data(File* file);
-bool file_checksum(File* file, uint64_t* checksum);
+/* Compute the whole-file content digest of `file` with the negotiated
+ * --checksum-choice algorithm and --checksum-seed.  Writes the digest into
+ * `out` (capacity `out_capacity`) and its length into `*out_len`.  Returns
+ * false on read/allocation failure or when the digest would not fit. */
+bool file_checksum(File* file, ChecksumAlgo algo, uint64_t seed, uint8_t* out, size_t out_capacity,
+                   size_t* out_len);
 size_t file_content_to_buffer(File* file);
-FileMetadata* file_metadata_create(const struct stat* stats);
+FileMetadata* file_metadata_create(const char* path, const struct stat* stats, bool capture_atime,
+                                   bool capture_crtime);
 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);
+/* 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/"
+
+char* file_symlink_munge(const char* target);
+/* 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);
+/* Strip a leading SYMLINK_MUNGE_PREFIX from `target` (mutable, in place);
+ * 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`. */
+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. */
+void file_set_keep_dirlinks(bool enable);
+bool file_get_keep_dirlinks(void);
+
+/* --trust-sender receiver process-wide policy (Phase 5).  When set, the
+ * receiver trusts that the sender already produced a clean file list and skips
+ * its own redundant up-front re-validation of incoming paths (the empty/".."
+ * rejection and the escaping-symlink-target containment).  The low-level
+ * fd-relative confinement primitives below are deliberately NOT disabled by
+ * this flag, so a hostile sender still cannot escape the authorized root. */
+void file_set_trust_sender(bool enable);
+bool file_get_trust_sender(void);
+
 /* A configured fd without a canonical identity deliberately rejects paths. */
 bool file_set_authorized_root(int fd, const char* canonical_path);
 
 /* Secure path/filesystem primitives (symlink-safe, O_NOFOLLOW, root-confined). */
 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);
 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);
+/* Remove the whole directory tree at `path` (confined, symlink-safe).  Used by
+   --force to clear a non-empty destination directory that blocks an incoming
+   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. */
+int file_open_private_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. */
 bool file_to_disk_secure(const char* path, const void* data, unsigned long long data_size,
-                         bool inplace, bool sparse, const FileMetadata* metadata);
+                         bool inplace, bool sparse, bool preallocate, const FileMetadata* metadata,
+                         bool preserve_executability, 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);
+/* 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 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 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` /
+ * `no_replace` / `use_fsync` mirror the plain wrappers above; `keep_partial`
+ * 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);
+/* 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).
+   `metadata` is applied only on the copy fallback.  `preallocate` applies to
+   that copy fallback only (a hard-linked file shares the basis inode and is
+   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);
+/* 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,
+                                    bool use_fsync, const FileXattrList* xattrs, bool fake_super,
+                                    const char* temp_dir);
 
 #endif

src/shared/file_list.c

@@ -0,0 +1,191 @@
+#include "file_list.h"
+#include "log.h"
+#include "utils.h"
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct {
+  char** items;
+  int count;
+  int capacity;
+} StringList;
+
+static void string_list_destroy(StringList* list) {
+  if (!list)
+    return;
+  for (int i = 0; i < list->count; i++)
+    free(list->items[i]);
+  free(list->items);
+}
+
+static bool string_list_add(StringList* list, const char* text) {
+  if (list->count == list->capacity) {
+    int new_cap = list->capacity > 0 ? list->capacity * 2 : 16;
+    char** grown = realloc(list->items, (size_t)new_cap * sizeof(char*));
+    if (!grown)
+      return false;
+    list->items = grown;
+    list->capacity = new_cap;
+  }
+  list->items[list->count] = str_dup(text);
+  if (!list->items[list->count])
+    return false;
+  list->count++;
+  return true;
+}
+
+/* Validate and normalize one entry. Returns:
+ *   1 -> added to `out`
+ *   0 -> blank entry, skip
+ *  -1 -> invalid (message set in `err`)
+ * `strip_line_endings` trims a trailing CR/LF (line mode only); NUL mode keeps
+ * the entry bytes verbatim so names ending in CR/LF survive. */
+static int normalize_entry(const char* raw, size_t len, bool strip_line_endings, StringList* out,
+                           char* err, size_t err_size) {
+  if (strip_line_endings) {
+    while (len > 0 && (raw[len - 1] == '\n' || raw[len - 1] == '\r'))
+      len--;
+  }
+  if (len == 0)
+    return 0;
+  if (raw[0] == '/') {
+    snprintf(err, err_size, "absolute path entries are not allowed: '%.*s'", (int)len, raw);
+    return -1;
+  }
+  /* Reject NUL bytes inside a token defensively (NUL-delimited mode splits on
+   * them, so this only guards against embedded garbage). */
+  char* dup = malloc(len + 1);
+  if (!dup) {
+    snprintf(err, err_size, "memory allocation failed");
+    return -1;
+  }
+  memcpy(dup, raw, len);
+  dup[len] = '\0';
+
+  /* Rebuild the path token-by-token: skip '.' and empty segments, reject '..'. */
+  size_t out_len = 0;
+  for (const char* part = dup;;) {
+    const char* slash = strchr(part, '/');
+    size_t part_len = slash ? (size_t)(slash - part) : strlen(part);
+    if (part_len == 1 && part[0] == '.') {
+      /* skip "." segment */
+    } else if (part_len == 2 && part[0] == '.' && part[1] == '.') {
+      snprintf(err, err_size, "path traversal entry is not allowed: '%s'", dup);
+      free(dup);
+      return -1;
+    } else if (part_len > 0) {
+      if (out_len > 0)
+        dup[out_len++] = '/';
+      memmove(dup + out_len, part, part_len);
+      out_len += part_len;
+    }
+    if (!slash)
+      break;
+    part = slash + 1;
+  }
+  dup[out_len] = '\0';
+
+  int result;
+  if (out_len == 0) {
+    /* "." / "./" lists the source root: the whole tree is transferred. */
+    result = string_list_add(out, "") ? 1 : -1;
+    if (result < 0)
+      snprintf(err, err_size, "memory allocation failed");
+  } else {
+    result = string_list_add(out, dup) ? 1 : -1;
+    if (result < 0)
+      snprintf(err, err_size, "memory allocation failed");
+  }
+  free(dup);
+  return result;
+}
+
+static FileListSet* string_list_to_set(StringList* raw, char* err, size_t err_size) {
+  FileListSet* set = malloc(sizeof(FileListSet));
+  if (!set) {
+    snprintf(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  set->count = raw->count;
+  set->entries = raw->items;
+  raw->items = NULL;
+  raw->count = 0;
+  return set;
+}
+
+FileListSet* file_list_load(const char* path, bool null_separated, char* err, size_t err_size) {
+  if (err && err_size > 0)
+    err[0] = '\0';
+  if (!path || !*path) {
+    snprintf(err, err_size, "no file given");
+    return NULL;
+  }
+  FILE* fp = fopen(path, "r");
+  if (!fp) {
+    char* escaped = output_escape(path, false);
+    snprintf(err, err_size, "could not open '%s': %s", escaped ? escaped : path, strerror(errno));
+    free(escaped);
+    return NULL;
+  }
+
+  StringList raw = {0};
+  char* line = NULL;
+  size_t line_cap = 0;
+  ssize_t n;
+  bool ok = true;
+  char delim = null_separated ? '\0' : '\n';
+  while (ok && (n = getdelim(&line, &line_cap, delim, fp)) != -1) {
+    int r = normalize_entry(line, (size_t)n, !null_separated, &raw, err, err_size);
+    if (r < 0) {
+      ok = false;
+      break;
+    }
+  }
+  free(line);
+  fclose(fp);
+  if (!ok) {
+    string_list_destroy(&raw);
+    return NULL;
+  }
+  FileListSet* set = string_list_to_set(&raw, err, err_size);
+  if (!set)
+    string_list_destroy(&raw);
+  return set;
+}
+
+void file_list_destroy(FileListSet* set) {
+  if (!set)
+    return;
+  for (int i = 0; i < set->count; i++)
+    free(set->entries[i]);
+  free(set->entries);
+  free(set);
+}
+
+static bool path_has_prefix(const char* path, const char* prefix) {
+  size_t plen = strlen(prefix);
+  if (strncmp(path, prefix, plen) != 0)
+    return false;
+  return path[plen] == '/' || path[plen] == '\0';
+}
+
+bool file_list_affects(const FileListSet* set, const char* rel) {
+  if (!set)
+    return true;
+  if (!rel)
+    return false;
+  for (int i = 0; i < set->count; i++) {
+    const char* entry = set->entries[i];
+    if (entry[0] == '\0')
+      return true; /* whole tree listed */
+    if (strcmp(rel, entry) == 0)
+      return true; /* the entry itself is listed */
+    if (path_has_prefix(rel, entry))
+      return true; /* rel lives under a listed directory */
+    if (path_has_prefix(entry, rel))
+      return true; /* rel is an ancestor directory of a listed entry */
+  }
+  return false;
+}

src/shared/file_list.h

@@ -0,0 +1,35 @@
+#ifndef FILE_LIST_H
+#define FILE_LIST_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+/* --files-from allow-set. The file lists source paths RELATIVE to the source
+ * root. A listed regular file is transferred; a listed directory transfers its
+ * whole subtree (FastSync's recursion is always on). Blank lines are ignored.
+ *
+ * Entries are normalized: leading "./" and duplicate "/" are removed, an entry
+ * of "." means the whole tree, absolute entries and ".." traversal are
+ * rejected at parse time. The set is immutable and shared read-only across
+ * scanner worker threads.
+ */
+
+typedef struct {
+  char** entries; /* normalized rel paths; "" means the whole tree */
+  int count;
+} FileListSet;
+
+/* Load and validate a --files-from file. When `null_separated` (-0/--from0)
+ * entries are delimited by NUL instead of newlines. Returns NULL with a message
+ * in `err` on open/validation failure. An empty file yields an empty set
+ * (nothing is transferred). */
+FileListSet* file_list_load(const char* path, bool null_separated, char* err, size_t err_size);
+void file_list_destroy(FileListSet* set);
+
+/* True when `rel` (path relative to the source root, "" == root) is a listed
+ * entry, lives under a listed directory, or is an ancestor directory of a
+ * listed entry. Used to prune scanning: directories are descended only when
+ * this returns true, files are transferred only when it returns true. */
+bool file_list_affects(const FileListSet* set, const char* rel);
+
+#endif

src/shared/file_receive.h

@@ -8,8 +8,90 @@
 /* Server-side file receive/save path. */
 
 File* file_receive(const Config* config, int file_descriptor);
+File* file_receive_directory(int file_descriptor, const Config* config);
+File* file_receive_dir_time(int file_descriptor, const Config* config);
+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);
 File* receive_incremental_check(int fd, const Config* config, bool* skipped);
-int receive_manifest(int fd, const Config* config, int* next_status);
+
+/* P7 Wave D directory-time accumulator.  The receiver collects the metadata of
+ * every directory it creates/receives (STATUS_MKDIR with metadata and/or the
+ * trailing STATUS_DIR_TIMES frame(s)) and applies the times only at the END of the
+ * transfer, after all children have been written and after the delete /
+ * --delay-updates phases have committed (writing or removing a child bumps the
+ * 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 */
+  size_t count;
+  size_t capacity;
+} DirTimeList;
+
+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 (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);
+
+/* A received delete-manifest frame: the keep-set (`keeps`, destination-relative
+   paths the sender transferred/keeps) plus `protected`, destination-relative
+   prefixes the sender asks the receiver never to delete (paths excluded on the
+   source, protected at any depth).  When --delete-excluded is given the sender
+   transmits an empty protected list so excluded destination mirrors are treated
+   as ordinary extras.  With --delete-missing-args a third section (`missing`)
+   carries the destination mirrors of explicitly-listed source entries that do
+   not exist: each is an exact deletion request, independent of the ordinary
+   extras walk (never blocked by the protected prefixes) and processed when the
+   manifest is committed. */
+typedef struct DeleteManifest {
+  ArrayList* keeps;
+  ArrayList* protected;
+  ArrayList* missing;
+} 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
+   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);
+/* Remove destination entries under config->receive_root_directory that are not
+   in `manifest` (bounded, all-or-nothing walk; staging-dir, basis-dir and
+   protected-prefix skips).  `--max-delete` and `--force` are honored here.  The
+   caller decides WHEN to run it based on the negotiated delete timing.  Returns
+   false (and the transfer fails) when the deletion cannot be committed. */
+bool manifest_delete_extras(const Config* config, DeleteManifest* manifest);
+/* --delete-missing-args exact-path deletions: remove each destination mirror
+   in `manifest->missing` (never blocked by the protected prefixes, staging dir
+   and basis dirs excluded).  A regular file/symlink is unlinked; an empty
+   directory is removed; a NON-empty directory is removed recursively only when
+   --delete or --force is in effect, otherwise it is left with a warning (rsync
+   parity).  A missing path is a no-op.  Returns false only on a genuine
+   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);
+/* 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);
+
+/* Outcome of a single file_save_to_disk operation.  The receiver needs to
+   distinguish "written" from "skipped" so --remove-source-files can be told
+   which sources were actually stored. */
+typedef enum { FILE_SAVE_ERROR = 0, FILE_SAVE_WRITTEN = 1, FILE_SAVE_SKIPPED = 2 } FileSaveResult;
+
+FileSaveResult file_save_to_disk_full(const char* root_directory, const File* file,
+                                      const Config* config);
 bool file_save_to_disk(const char* root_directory, const File* file, const Config* config);
 
 #endif

src/shared/file_send.c

@@ -10,28 +10,59 @@
 #include <time.h>
 #include <unistd.h>
 
+#include "charset.h"
 #include "compression.h"
 #include "data.h"
 #include "file.h"
 #include "log.h"
 #include "metadata.h"
 #include "protocol.h"
+#include "xattr.h"
+
+/* Transmit a device/special node (--devices / --specials) as a STATUS_SPECIAL
+ * frame: the destination path, the metadata frame (whose mode's S_IFMT bits
+ * carry the node kind) and the device rdev major/minor.  The receiver validates
+ * the kind and rdev and recreates the node (privilege-gating the mknod). */
+bool file_send_special(const File* file, int file_descriptor, bool use_metadata) {
+  if (!file || !file_wire_path(file))
+    return false;
+  if (!send_status(file_descriptor, STATUS_SPECIAL))
+    return false;
+  if (!send_wire_str(file_descriptor, file_wire_path(file)))
+    return false;
+  if (use_metadata && !metadata_send(file_descriptor, file->metadata))
+    return false;
+  int32_t major = file->rdev_major;
+  int32_t minor = file->rdev_minor;
+  return send_n_data(file_descriptor, &major, sizeof(major)) &&
+         send_n_data(file_descriptor, &minor, sizeof(minor));
+}
 
 bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
                             int compression_level, bool send_path) {
+  return file_send_single_calls_with_skip(file, file_descriptor, use_metadata, compression_level,
+                                          send_path, NULL, -1, 0, false);
+}
+
+bool file_send_single_calls_with_skip(File* file, int file_descriptor, bool use_metadata,
+                                      int compression_level, bool send_path,
+                                      char* const* skip_suffixes, int skip_count,
+                                      int compression_threads, bool send_xattrs) {
   if (!file || !file->path || !file->data || (file->data->size != 0 && !file->data->data))
     return false;
   const Data* data_to_send = file->data;
   Data* compressed_data = NULL;
-  if (compression_level > 0 && !compression_should_skip(file->path)) {
-    compressed_data = data_compress(file->data, compression_level);
+  if (compression_level > 0 &&
+      !compression_should_skip_with_suffixes(file->path, skip_suffixes, skip_count)) {
+    compressed_data =
+        data_compress_with_threads(file->data, compression_level, compression_threads);
     if (compressed_data == NULL) {
       log_message(LOG_LEVEL_ERROR, "Failed to compress file data");
       return false;
     }
     data_to_send = compressed_data;
   }
-  if (send_path && !send_str(file_descriptor, file->path)) {
+  if (send_path && !send_wire_str(file_descriptor, file_wire_path(file))) {
     data_destroy(compressed_data);
     return false;
   }
@@ -39,6 +70,10 @@ bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
     data_destroy(compressed_data);
     return false;
   }
+  if (send_xattrs && !xattr_send(file_descriptor, file ? file->xattrs : NULL)) {
+    data_destroy(compressed_data);
+    return false;
+  }
   if (!send_data(file_descriptor, data_to_send)) {
     data_destroy(compressed_data);
     return false;
@@ -49,18 +84,28 @@ bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
 
 bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int compression_level,
                         bool send_path) {
+  return file_send_sendfile_with_skip(file, file_descriptor, use_metadata, compression_level,
+                                      send_path, NULL, -1, 0, false);
+}
+
+bool file_send_sendfile_with_skip(File* file, int file_descriptor, bool use_metadata,
+                                  int compression_level, bool send_path, char* const* skip_suffixes,
+                                  int skip_count, int compression_threads, bool send_xattrs) {
   if (!file || !file->path || !file->data)
     return false;
   if (compression_level > 0)
-    return file_send_single_calls(file, file_descriptor, use_metadata, compression_level,
-                                  send_path);
+    return file_send_single_calls_with_skip(file, file_descriptor, use_metadata, compression_level,
+                                            send_path, skip_suffixes, skip_count,
+                                            compression_threads, send_xattrs);
 
-  if (send_path && !send_str(file_descriptor, file->path))
+  if (send_path && !send_wire_str(file_descriptor, file_wire_path(file)))
     return false;
   if (use_metadata && !metadata_send(file_descriptor, file->metadata))
     return false;
+  if (send_xattrs && !xattr_send(file_descriptor, file ? file->xattrs : NULL))
+    return false;
 
-  int fd = open(file->path, O_RDONLY);
+  int fd = file_open_for_read(file->path);
   if (fd == -1) {
     log_perror("Could not open file for sendfile");
     return false;

src/shared/file_send.h

@@ -6,9 +6,17 @@
 
 /* Client-side file send path. */
 
+bool file_send_special(const File* file, int file_descriptor, bool use_metadata);
 bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
                             int compression_level, bool send_path);
+bool file_send_single_calls_with_skip(File* file, int file_descriptor, bool use_metadata,
+                                      int compression_level, bool send_path,
+                                      char* const* skip_suffixes, int skip_count,
+                                      int compression_threads, bool send_xattrs);
 bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int compression_level,
                         bool send_path);
+bool file_send_sendfile_with_skip(File* file, int file_descriptor, bool use_metadata,
+                                  int compression_level, bool send_path, char* const* skip_suffixes,
+                                  int skip_count, int compression_threads, bool send_xattrs);
 
 #endif

src/shared/file_store.c

@@ -139,8 +139,47 @@ static bool write_all(int fd, const void* data, unsigned long long size) {
   return true;
 }
 
+/* A run of NUL bytes at least this long is emitted as a hole (lseek) rather
+ * than written, so the resulting file is genuinely sparse on the filesystem. */
+#define SPARSE_HOLE_MIN 4096U
+
+/* Sparse-aware writer (--sparse/-S).  Walks `data`; any all-zero run of at
+ * least SPARSE_HOLE_MIN bytes is skipped with lseek(SEEK_CUR) so the block is
+ * never allocated (a real hole on the destination); every other byte is written
+ * normally.  The file is pre-sized with ftruncate by the callers before this
+ * runs, so holes are guaranteed and the offset bookkeeping stays correct
+ * (each lseek advances the fd offset exactly as a write of that many bytes
+ * would).  After the final run, ftruncate(size) guarantees the logical size is
+ * exactly `size` even when the tail was a hole.  The full file image is in
+ * memory, so no wire change is needed.  Returns false on I/O error. */
+bool file_store_write_sparse(int fd, const unsigned char* data, unsigned long long size) {
+  unsigned long long i = 0;
+  while (i < size) {
+    if (data[i] == 0) {
+      unsigned long long run_start = i;
+      while (i < size && data[i] == 0)
+        i++;
+      unsigned long long run_len = i - run_start;
+      if (run_len >= SPARSE_HOLE_MIN) {
+        if (lseek(fd, (off_t)run_len, SEEK_CUR) < 0)
+          return false;
+      } else if (!write_all(fd, data + run_start, run_len)) {
+        return false;
+      }
+    } else {
+      unsigned long long run_start = i;
+      while (i < size && data[i] != 0)
+        i++;
+      if (!write_all(fd, data + run_start, i - run_start))
+        return false;
+    }
+  }
+  return ftruncate(fd, (off_t)size) == 0;
+}
+
 bool file_store_write_secure(const char* path, const void* data, unsigned long long data_size,
-                             bool inplace, bool sparse, const FileMetadata* metadata) {
+                             bool inplace, bool sparse, const FileMetadata* metadata,
+                             bool preserve_executability) {
   char* leaf = NULL;
   int dirfd = file_store_open_secure_parent(path, &leaf);
   if (dirfd < 0)
@@ -150,10 +189,14 @@ bool file_store_write_secure(const char* path, const void* data, unsigned long l
   if (inplace) {
     fd = openat(dirfd, leaf, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC | O_NOFOLLOW, 0644);
     if (fd >= 0) {
-      if (!sparse || data_size == 0 || ftruncate(fd, (off_t)data_size) == 0)
+      if (sparse && data_size > 0) {
+        if (ftruncate(fd, (off_t)data_size) == 0)
+          ok = file_store_write_sparse(fd, data, data_size);
+      } else {
         ok = write_all(fd, data, data_size);
+      }
       if (ok && metadata)
-        ok = file_restore_metadata_fd(fd, metadata);
+        ok = file_restore_metadata_fd(fd, metadata, preserve_executability);
     }
   } else {
     int tmp_size = snprintf(NULL, 0, ".%s.tmp.%ld.%u", leaf, (long)getpid(), 99U);
@@ -176,9 +219,11 @@ bool file_store_write_secure(const char* path, const void* data, unsigned long l
       if (sparse && data_size > 0)
         ok = ftruncate(fd, (off_t)data_size) == 0;
       if (ok || (!sparse || data_size == 0))
-        ok = write_all(fd, data, data_size);
+        ok = (sparse && data_size > 0)
+                 ? file_store_write_sparse(fd, (const unsigned char*)data, data_size)
+                 : write_all(fd, data, data_size);
       if (ok && metadata)
-        ok = file_restore_metadata_fd(fd, metadata);
+        ok = file_restore_metadata_fd(fd, metadata, preserve_executability);
       if (close(fd) != 0)
         ok = false;
       fd = -1;

src/shared/file_store.h

@@ -8,6 +8,14 @@ bool file_store_set_authorized_root(int fd, const char* canonical_path);
 int file_store_open_secure_parent(const char* path, char** leaf_out);
 bool file_store_rename_secure(const char* old_path, const char* new_path);
 bool file_store_write_secure(const char* path, const void* data, unsigned long long data_size,
-                             bool inplace, bool sparse, const FileMetadata* metadata);
+                             bool inplace, bool sparse, const FileMetadata* metadata,
+                             bool preserve_executability);
+/* Sparse-aware write (--sparse/-S): every all-zero run of at least
+ * SPARSE_HOLE_MIN bytes is skipped with lseek(SEEK_CUR) so it becomes a real
+ * hole; every other byte is written.  The caller pre-sizes the file with
+ * ftruncate; this function also ftruncate()s to `size` at the end so a trailing
+ * hole keeps the exact logical length.  Shared by the file_store and file write
+ * paths.  Returns false on write/lseek/ftruncate error. */
+bool file_store_write_sparse(int fd, const unsigned char* data, unsigned long long size);
 
 #endif

src/shared/file_types.h

@@ -2,6 +2,7 @@
 #define FILE_TYPES_H
 
 #include "data.h"
+#include "xattr.h"
 #include <stdbool.h>
 #include <sys/stat.h>
 
@@ -13,13 +14,84 @@ typedef struct {
   gid_t gid;
   time_t mtime_sec;
   long mtime_nsec;
+  /* Optional access time (-U/--atimes) and creation/birth time (-N/--crtimes),
+   * appended for protocol 2.12.0.  The SENDER sets the corresponding *_valid
+   * flag only when the preserve option is active (and, for crtime, only when
+   * the source platform exposed a birth time via statx STATX_BTIME).  The wire
+   * always carries the fields and the flags; a false flag tells the receiver to
+   * ignore the value. */
+  bool atime_valid;
+  time_t atime_sec;
+  long atime_nsec;
+  bool crtime_valid;
+  time_t crtime_sec;
+  long crtime_nsec;
 } FileMetadata;
 
 typedef struct {
   char* path;
+  /* Sender-side override for the path transmitted on the wire (and used for
+   * the delete manifest / change output).  NULL means "use `path`".  With
+   * -R + --files-from this holds the entry's bare relative destination path,
+   * while `path` stays the absolute local source path the client reads from.
+   * Never populated on the receiver. */
+  char* send_path;
   Data* data;
   FileMetadata* metadata;
   bool skip;
+  /* True when this entry is an explicit directory entry (--dirs mode): the
+   * receiver creates the directory instead of writing a regular file. */
+  bool is_dir;
+  /* Receiver-only (P7 Wave D): this is a STATUS_DIR_TIMES entry.  It carries a
+   * traversed source directory's metadata for DEFERRED application, but must
+   * NEVER create the directory: the scanner captures every traversed directory
+   * (including empty ones whose parents no child write created), so creation
+   * would resurrect the empty dirs that FastSync deliberately never transfers.
+   * file_save_to_disk_full short-circuits such an entry as FILE_SAVE_SKIPPED,
+   * and the sink still accumulates the metadata into its DirTimeList. */
+  bool dir_time_only;
+  /* Receiver-only, --link-dest: when set, install the destination entry as a
+   * hard link to this absolute (root-confined) path instead of writing
+   * `data`.  The matching code has already verified the link target's content
+   * 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;
+  /* --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
+   * written normally; every sibling (link_first == false) carries NO data and
+   * hardlink_target holds the first member's wire path so the receiver can link
+   * to (or copy from) the already-installed first member. */
+  int link_group;
+  bool link_first;
+  char* hardlink_target;
+  /* Symlink-type entry (-l/--links, or -k/--copy-dirlinks' keep-as-symlink
+   * branch).  When true, `symlink_target` holds the (sender-munged, if
+   * --munge-links) target string that is carried on the wire; the receiver
+   * creates a symlink to (an unmunged) target instead of writing regular-file
+   * data.  `data` is empty for a symlink entry.  Sender + receiver state. */
+  bool is_symlink;
+  char* symlink_target;
+  /* Phase 4 special/devices: when `is_special` is true this entry is a device
+   * or special node to be RECREATED on the destination (mknod/mkfifo) rather
+   * than written from `data`.  The concrete node kind is derived from the
+   * metadata mode's S_IFMT bits (receiver-validated), and rdev_major/minor
+   * carry the device major/minor numbers for char/block devices.  CROSSES the
+   * wire (protocol 2.13.0). */
+  bool is_special;
+  int32_t rdev_major;
+  int32_t rdev_minor;
+  /* Phase-4 xattrs (-X/--xattrs, -A/--acls).  Sender: captured from the source
+   * file when use_xattrs is set; transmitted in the per-file metadata frame.
+   * Receiver: parsed off the wire, attached here, and applied fd-relative on
+   * the written file.  NULL/0 == the file carries no xattrs. */
+  FileXattrList* xattrs;
 } File;
 
+/* The path that should be sent on the wire and used for the receiver-side
+ * destination layout (see send_path). */
+static inline const char* file_wire_path(const File* file) {
+  return file && file->send_path ? file->send_path : (file ? file->path : NULL);
+}
+
 #endif

src/shared/filter.c

@@ -0,0 +1,427 @@
+#include "filter.h"
+#include "log.h"
+#include "utils.h"
+#include <errno.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;
+}
+
+/* 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;
+}
+
+void filter_rule_free(FilterRule* rule) {
+  if (!rule)
+    return;
+  free(rule->pattern);
+  free(rule->owner);
+  free(rule);
+}
+
+/* ---- Ordered rule lists ---- */
+
+FilterRuleList* filter_rule_list_create(void) {
+  return calloc(1, sizeof(FilterRuleList));
+}
+
+bool filter_rule_list_add(FilterRuleList* list, FilterRule* rule) {
+  if (!list || !rule)
+    return false;
+  if (list->count == list->capacity) {
+    int new_cap = list->capacity > 0 ? list->capacity * 2 : 8;
+    FilterRule** grown = realloc(list->items, (size_t)new_cap * sizeof(FilterRule*));
+    if (!grown)
+      return false;
+    list->items = grown;
+    list->capacity = new_cap;
+  }
+  list->items[list->count++] = 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]);
+  free(list->items);
+  free(list);
+}
+
+static bool set_rule_owner(FilterRule* rule, const char* owner) {
+  char* dup = str_dup(owner ? owner : "");
+  if (!dup)
+    return false;
+  free(rule->owner);
+  rule->owner = dup;
+  return true;
+}
+
+/* ---- CVS default excludes (-C) ---- */
+
+typedef struct {
+  const char* pattern;
+  bool dir_only;
+} CvsDefaultRule;
+
+static const CvsDefaultRule CVS_DEFAULTS[] = {
+    {"RCS", false},         {"SCCS", false},         {"CVS", false},   {"CVS.adm", false},
+    {"RCSLOG", false},      {"cvslog.*", false},     {"tags", false},  {"TAGS", false},
+    {".make.state", false}, {".nse_depinfo", false}, {"*~", false},    {"#*", false},
+    {".#*", false},         {",*", false},           {"_$*", false},   {"*$", false},
+    {"*.old", false},       {"*.bak", false},        {"*.BAK", false}, {"*.orig", false},
+    {"*.rej", false},       {".del-*", false},       {"*.a", false},   {"*.olb", false},
+    {"*.o", false},         {"*.obj", false},        {"*.so", false},  {"*.exe", false},
+    {"*.Z", false},         {"*.elc", false},        {"*.ln", false},  {"core", false},
+    {".svn/", true},        {".git/", true},         {".hg/", true},   {".bzr/", true},
+};
+
+static bool cvs_rule_list_append(FilterRuleList* list) {
+  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->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] == '/')
+      plen--; /* keep the cleaned pattern, matching filter_rule_parse */
+    rule->pattern = malloc(plen + 1);
+    if (!rule->pattern) {
+      free(rule);
+      return false;
+    }
+    memcpy(rule->pattern, CVS_DEFAULTS[i].pattern, plen);
+    rule->pattern[plen] = '\0';
+    if (!set_rule_owner(rule, "")) {
+      filter_rule_free(rule);
+      return false;
+    }
+    if (!filter_rule_list_add(list, rule)) {
+      filter_rule_free(rule);
+      return false;
+    }
+  }
+  return true;
+}
+
+FilterRuleList* filter_base_build(const char* const* rule_texts, int rule_count, bool cvs_exclude,
+                                  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");
+    return NULL;
+  }
+  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) {
+      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)) {
+    filter_rule_list_free(list);
+    snprintf(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  return list;
+}
+
+/* ---- Per-directory .rsync-filter files ---- */
+
+FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, 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 (!filter_path) {
+    snprintf(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  FILE* fp = fopen(filter_path, "r");
+  free(filter_path);
+  if (!fp) {
+    if (errno == ENOENT || errno == ENOTDIR)
+      return filter_rule_list_create();
+    log_message(LOG_LEVEL_WARNING, "Could not read .rsync-filter in %s: %s", dir_path,
+                strerror(errno));
+    return filter_rule_list_create();
+  }
+  if (exists)
+    *exists = true;
+  FilterRuleList* list = filter_rule_list_create();
+  if (!list) {
+    fclose(fp);
+    snprintf(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  char* line = NULL;
+  size_t line_cap = 0;
+  ssize_t n;
+  bool ok = true;
+  while ((n = getline(&line, &line_cap, fp)) != -1) {
+    const char* p = line;
+    while (*p == ' ' || *p == '\t')
+      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");
+      ok = false;
+      break;
+    }
+  }
+  free(line);
+  fclose(fp);
+  if (!ok) {
+    filter_rule_list_free(list);
+    return NULL;
+  }
+  return list;
+}
+
+/* ---- Rule matching ---- */
+
+/* Match a pattern that contains '/' (non-anchored) against the end of the
+ * relative path, starting at any path-component boundary. */
+static bool glob_suffix_match(const char* pattern, const char* str) {
+  if (glob_match(pattern, str))
+    return true;
+  for (const char* slash = strchr(str, '/'); slash; slash = strchr(slash + 1, '/')) {
+    if (glob_match(pattern, slash + 1))
+      return true;
+  }
+  return false;
+}
+
+static FilterAction rule_matches(const FilterRule* rule, const char* rel_path, const char* leaf,
+                                 bool is_dir) {
+  if (!rule || !rule->pattern)
+    return FILTER_ACTION_NONE;
+  if (rule->dir_only && !is_dir)
+    return FILTER_ACTION_NONE;
+  /* A rule applies only to entries below its owner directory. */
+  const char* rel2 = rel_path;
+  if (rule->owner && rule->owner[0] != '\0') {
+    size_t owner_len = strlen(rule->owner);
+    if (strncmp(rule->owner, rel_path, owner_len) != 0)
+      return FILTER_ACTION_NONE;
+    if (rel_path[owner_len] != '/')
+      return FILTER_ACTION_NONE;
+    rel2 = rel_path + owner_len + 1;
+  }
+  if (rel2[0] == '\0')
+    return FILTER_ACTION_NONE;
+  bool matched;
+  if (rule->anchored) {
+    matched = glob_match(rule->pattern, rel2);
+  } else if (strchr(rule->pattern, '/') != NULL) {
+    matched = glob_suffix_match(rule->pattern, rel2);
+  } else {
+    matched = glob_match(rule->pattern, leaf);
+  }
+  return matched ? rule->action : FILTER_ACTION_NONE;
+}
+
+FilterAction filter_rules_apply(const FilterRuleList* list, const char* rel_path, const char* leaf,
+                                bool is_dir) {
+  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);
+    if (action != FILTER_ACTION_NONE)
+      return action;
+  }
+  return FILTER_ACTION_NONE;
+}

src/shared/filter.h

@@ -0,0 +1,83 @@
+#ifndef FILTER_H
+#define FILTER_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+/* rsync-style filter rule engine (client-side file selection).
+ *
+ * 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.
+ */
+
+typedef enum {
+  FILTER_ACTION_NONE = 0, /* no rule matched */
+  FILTER_ACTION_EXCLUDE = -1,
+  FILTER_ACTION_INCLUDE = 1
+} 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;
+
+typedef struct {
+  FilterRule** items; /* owned array of rule pointers */
+  int count;
+  int capacity;
+} FilterRuleList;
+
+/* 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);
+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);
+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).
+ * 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);
+
+/* 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`). */
+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. */
+FilterAction filter_rules_apply(const FilterRuleList* list, const char* rel_path, const char* leaf,
+                                bool is_dir);
+
+#endif

src/shared/hardlink.c

@@ -0,0 +1,127 @@
+#include "hardlink.h"
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "log.h"
+#include "utils.h"
+
+/* ---- Sender-side detection table ---- */
+
+HardLinkTable* hardlink_table_create(void) {
+  HardLinkTable* table = calloc(1, sizeof(HardLinkTable));
+  if (!table)
+    return NULL;
+  if (mtx_init(&table->mutex, mtx_plain) != thrd_success) {
+    free(table);
+    return NULL;
+  }
+  table->next_gid = 1;
+  return table;
+}
+
+static void hardlink_item_destroy(HardLinkItem* item) {
+  if (!item)
+    return;
+  free(item->first_path);
+  item->first_path = NULL;
+}
+
+void hardlink_table_destroy(HardLinkTable* table) {
+  if (!table)
+    return;
+  for (size_t i = 0; i < table->count; i++)
+    hardlink_item_destroy(&table->items[i]);
+  free(table->items);
+  table->items = NULL;
+  table->count = 0;
+  table->capacity = 0;
+  mtx_destroy(&table->mutex);
+  free(table);
+}
+
+static HardLinkItem* hardlink_table_find_locked(HardLinkTable* table, dev_t dev, ino_t ino) {
+  for (size_t i = 0; i < table->count; i++) {
+    if (table->items[i].dev == dev && table->items[i].ino == ino)
+      return &table->items[i];
+  }
+  return NULL;
+}
+
+static bool hardlink_table_add_locked(HardLinkTable* table, dev_t dev, ino_t ino, const char* path,
+                                      int gid, HardLinkItem** out) {
+  if (table->count == table->capacity) {
+    size_t new_capacity = table->capacity == 0 ? 8 : table->capacity * 2;
+    if (new_capacity < table->capacity)
+      return false;
+    HardLinkItem* grown = realloc(table->items, new_capacity * sizeof(HardLinkItem));
+    if (!grown)
+      return false;
+    table->items = grown;
+    table->capacity = new_capacity;
+  }
+  HardLinkItem* item = &table->items[table->count];
+  char* dup = str_dup(path);
+  if (!dup)
+    return false;
+  memset(item, 0, sizeof(*item));
+  item->dev = dev;
+  item->ino = ino;
+  item->gid = gid;
+  item->first_path = dup;
+  table->count++;
+  *out = item;
+  return true;
+}
+
+bool hardlink_table_assign(HardLinkTable* table, const char* wire_path, dev_t dev, ino_t ino,
+                           int* gid, bool* is_first, char** first_path_out) {
+  if (!table || !wire_path || !gid || !is_first || !first_path_out)
+    return false;
+  if (mtx_lock(&table->mutex) != thrd_success)
+    return false;
+  bool ok = true;
+  const HardLinkItem* item = hardlink_table_find_locked(table, dev, ino);
+  int next_gid;
+  if (item) {
+    *is_first = false;
+    char* dup = str_dup(item->first_path);
+    if (!dup) {
+      ok = false;
+    } else {
+      *gid = item->gid;
+      *first_path_out = dup;
+    }
+    next_gid = -1;
+  } else {
+    if (table->next_gid <= 0) {
+      ok = false;
+      next_gid = -1;
+    } else {
+      next_gid = table->next_gid;
+      HardLinkItem* created = NULL;
+      if (!hardlink_table_add_locked(table, dev, ino, wire_path, next_gid, &created)) {
+        ok = false;
+      } else {
+        char* dup = str_dup(wire_path);
+        if (!dup) {
+          hardlink_item_destroy(created);
+          table->count--;
+          ok = false;
+        } else {
+          *is_first = true;
+          *gid = next_gid;
+          *first_path_out = dup;
+        }
+      }
+    }
+  }
+  if (ok && next_gid > 0)
+    table->next_gid++;
+  mtx_unlock(&table->mutex);
+  if (!ok) {
+    log_message(LOG_LEVEL_ERROR, "memory allocation failed while detecting hard links");
+  }
+  return ok;
+}

src/shared/hardlink.h

@@ -0,0 +1,66 @@
+#ifndef HARDLINK_H
+#define HARDLINK_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <sys/types.h>
+#include <threads.h>
+
+/*
+ * --hard-links / -H support.
+ *
+ * Sender side: a HardLinkTable detects regular files on the source that share
+ * an (st_dev, st_ino) identity (a `cp -al`-style hard-linked tree) and assigns
+ * each distinct inode a stable, run-local link-group id.  The first member
+ * encountered carries the file data; every later member is marked as a sibling
+ * (no data payload) that the receiver creates as a hard link to the first
+ * member's destination file.  Grouping is scoped by st_dev so inode reuse
+ * across different filesystems is never conflated.  The table is mutex-guarded
+ * so the parallel (multi-threaded) scanner COULD share one instance across its
+ * worker threads; the first-thread-to-call designates the data-carrying member,
+ * which is safe because a hard-link group's members are byte-identical.  (In
+ * practice the sender forces the sequential scanner whenever -H is on; the
+ * mutex guards the shared table for any path that supplies one.)
+ *
+ * ORDERING (why there is no receiver-side handshake): the receiver stores every
+ * file - including a hard-link group's first member - through a SINGLE writer
+ * thread draining a single FIFO queue driven by a single receive thread, so
+ * wire order == write order and every sibling is processed AFTER its group's
+ * first member.  The sender additionally forces the sequential scanner with -H
+ * so the first-member frame always precedes its siblings on the wire.  Sibling
+ * install therefore needs no present/wait registry: it hard-links to the first
+ * member (or copies it) knowing that path is already installed - or that, if
+ * the first member was skipped (already up to date), its destination still
+ * exists.  This guarantee is REQUIRED; do not introduce a concurrent
+ * multi-writer receiver for -H without re-adding an ordering mechanism.
+ */
+
+typedef struct HardLinkItem {
+  dev_t dev;
+  ino_t ino;
+  int gid;
+  char* first_path; /* wire path of the group's data-carrying first member */
+} HardLinkItem;
+
+typedef struct HardLinkTable {
+  mtx_t mutex;
+  HardLinkItem* items;
+  size_t count;
+  size_t capacity;
+  int next_gid;
+} HardLinkTable;
+
+HardLinkTable* hardlink_table_create(void);
+void hardlink_table_destroy(HardLinkTable* table);
+
+/* Assign a link-group id to the regular file at `wire_path` with (dev, ino).
+ * On the first encounter the file becomes the group's first (data-carrying)
+ * member (*is_first = true) and a fresh gid is allocated.  On a later member
+ * *is_first = false and *first_path_out is set to a malloc'd copy of the first
+ * member's wire path (the caller stores it and owns it; on the first member
+ * path the returned *first_path_out is a malloc'd copy of its own wire path).
+ * Returns false on allocation failure (transfer should abort). */
+bool hardlink_table_assign(HardLinkTable* table, const char* wire_path, dev_t dev, ino_t ino,
+                           int* gid, bool* is_first, char** first_path_out);
+
+#endif

src/shared/identity.c

@@ -0,0 +1,748 @@
+#include "identity.h"
+#include "log.h"
+#include "utils.h"
+#include <errno.h>
+#include <fcntl.h>
+#include <grp.h>
+#include <limits.h>
+#include <pwd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+/* The active identity snapshot lives in a per-process global.  The TCP server
+ * forks one child process per connection, so a connection never shares this
+ * with another; within a connection the multithreaded receiver reads it without
+ * mutation.  This is what lets the fd-relative metadata path consult the
+ * negotiated policy without threading a Config through every write helper. */
+typedef struct {
+  bool numeric_ids;
+  bool chown_uid_set;
+  int32_t chown_uid;
+  bool chown_gid_set;
+  int32_t chown_gid;
+  IdentityMap* usermap;
+  int usermap_count;
+  IdentityMap* groupmap;
+  int groupmap_count;
+  /* --super / --no-super tri-state (SUPER_MODE_AUTO when unset).  Snapshotted
+   * per connection so privilege_super_permitted() can gate super-user
+   * activities without a Config argument. */
+  int super_mode;
+  /* --copy-as=USER[:GROUP]: snapshotted so the ownership resolver can force the
+   * target ids without a Config argument. */
+  bool copy_as_set;
+  int32_t copy_as_uid;
+  int32_t copy_as_gid;
+  bool set;
+} IdentityActive;
+
+static IdentityActive g_identity;
+
+static void identity_active_reset(void) {
+  free(g_identity.usermap);
+  free(g_identity.groupmap);
+  g_identity.usermap = NULL;
+  g_identity.groupmap = NULL;
+  g_identity.usermap_count = 0;
+  g_identity.groupmap_count = 0;
+  g_identity.numeric_ids = false;
+  g_identity.chown_uid_set = false;
+  g_identity.chown_uid = 0;
+  g_identity.chown_gid_set = false;
+  g_identity.chown_gid = 0;
+  g_identity.super_mode = SUPER_MODE_AUTO;
+  g_identity.copy_as_set = false;
+  g_identity.copy_as_uid = 0;
+  g_identity.copy_as_gid = 0;
+  g_identity.set = false;
+}
+
+void identity_clear_active(void) {
+  identity_active_reset();
+}
+
+bool identity_set_active(const Config* config) {
+  identity_active_reset();
+  if (!config)
+    return true;
+  g_identity.numeric_ids = config->numeric_ids;
+  g_identity.chown_uid_set = config->chown_uid_set;
+  g_identity.chown_uid = config->chown_uid;
+  g_identity.chown_gid_set = config->chown_gid_set;
+  g_identity.chown_gid = config->chown_gid;
+  g_identity.super_mode = config->super_mode;
+  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;
+  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));
+    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));
+    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");
+  /* --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
+     once at activation time (never abort) so the operator knows the flag cannot
+     succeed on this host. */
+  if (g_identity.super_mode == SUPER_MODE_ON && geteuid() != 0)
+    log_message(LOG_LEVEL_WARNING,
+                "--super requested but the receiver is not privileged; super-user "
+                "activities (ownership, device nodes) will be attempted but refused "
+                "by the kernel and skipped per entry");
+  return true;
+
+alloc_failed:
+  /* Never proceed with a partial (count-left-zero) map: that would silently
+     apply the WRONG ownership policy.  Fail closed and let the caller refuse
+     the connection. */
+  log_message(LOG_LEVEL_ERROR, "memory allocation failed while activating identity policy");
+  identity_active_reset();
+  return false;
+}
+
+bool privilege_super_permitted(void) {
+  return privilege_super_mode_permitted(g_identity.super_mode);
+}
+
+bool privilege_super_mode_permitted(int mode) {
+  /* AUTO and ON both attempt the confined operation; OFF forbids it even for a
+   * root receiver.  AUTO is the historical FastSync behavior (always attempt
+   * and let the kernel refuse an unprivileged call, which the caller skips), so
+   * it must stay permissive or a group-only chown that a non-root receiver is
+   * allowed to make would regress. */
+  return mode != SUPER_MODE_OFF;
+}
+
+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. */
+  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);
+}
+
+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(). */
+  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;
+}
+
+bool identity_copy_as_active(void) {
+  return g_identity.set && g_identity.copy_as_set;
+}
+
+bool identity_copy_as_refused(const Config* config) {
+  if (!config || !config->copy_as_set)
+    return false;
+  /* The safe-subset --copy-as needs a privileged (root) receiver, and an
+   * operator/--no-super veto forbids the ownership change even for root.  This
+   * is deliberately a pure function of the config and the current effective uid
+   * (never the active snapshot) because the server evaluates it at the
+   * pre-STATUS_OK config gate, before identity_set_active() has run. */
+  return geteuid() != 0 || config->super_mode == SUPER_MODE_OFF;
+}
+
+bool identity_wire_valid(const Config* config) {
+  if (!config)
+    return false;
+  if (config->usermap_count < 0 || config->usermap_count > MAX_IDENTITY_MAP ||
+      config->groupmap_count < 0 || config->groupmap_count > MAX_IDENTITY_MAP)
+    return false;
+  if (config->chown_uid_set && config->chown_uid < IDENTITY_MATCH_ANY)
+    return false;
+  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)
+      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)
+      return false;
+  }
+  /* Defense-in-depth: a --copy-as block must never carry a negative (sentinel)
+   * id into the ownership path.  receive_copy_as_options already rejects them,
+   * but identity_wire_valid is the shared validation used by both the receiver
+   * and unit tests, so re-assert it here. */
+  if (config->copy_as_set && (config->copy_as_uid < 0 || config->copy_as_gid < 0))
+    return false;
+  return true;
+}
+
+/* ---- CLI-time name/number resolution ---- */
+
+/* Parse a single FROM/TO token into an int32 id.  Returns 0 on success, -1 on a
+ * malformed or unresolvable token.  When is_group, name lookups use the group
+ * database; otherwise the user database.  A `*` token returns IDENTITY_MATCH_ANY
+ * / IDENTITY_CURRENT (the same -1 value, disambiguated by the caller's
+ * position).  An `@`-prefixed or bare-decimal token is a numeric id. */
+static int identity_resolve_token(const char* token, bool is_group, int32_t* out) {
+  if (!token || *token == '\0')
+    return -1;
+  if (strcmp(token, "*") == 0) {
+    *out = IDENTITY_MATCH_ANY;
+    return 0;
+  }
+  const char* num = (token[0] == '@') ? token + 1 : token;
+  if (*num != '\0') {
+    bool all_digits = true;
+    for (const char* p = num; *p; p++)
+      if (*p < '0' || *p > '9')
+        all_digits = false;
+    if (all_digits) {
+      char* endptr = NULL;
+      errno = 0;
+      long val = strtol(num, &endptr, 10);
+      if (errno == 0 && endptr && *endptr == '\0' && val >= 0 && val <= INT32_MAX) {
+        *out = (int32_t)val;
+        return 0;
+      }
+      return -1;
+    }
+  }
+  /* A name (or a name-like numeric that failed strict numeric parse). */
+  if (is_group) {
+    struct group* gr = getgrnam(token);
+    if (!gr)
+      return -1;
+    *out = (int32_t)gr->gr_gid;
+    return 0;
+  }
+  struct passwd* pw = getpwnam(token);
+  if (!pw)
+    return -1;
+  *out = (int32_t)pw->pw_uid;
+  return 0;
+}
+
+static int identity_append_rule(IdentityMap** map, int* count, int32_t from, int32_t to) {
+  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;
+  (*count)++;
+  return 0;
+}
+
+int identity_parse_map(Config* config, const char* value, bool is_group) {
+  if (!config || !value || *value == '\0') {
+    log_message(LOG_LEVEL_ERROR, "%smap requires a value", is_group ? "--group" : "--user");
+    return -1;
+  }
+  char* list = str_dup(value);
+  if (!list)
+    return -1;
+  const char* optname = is_group ? "--groupmap" : "--usermap";
+  char* saveptr = NULL;
+  for (char* rule = strtok_r(list, ",", &saveptr); rule; rule = strtok_r(NULL, ",", &saveptr)) {
+    char* colon = strchr(rule, ':');
+    if (!colon || colon == rule) {
+      /* 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);
+      return -1;
+    }
+    *colon = '\0';
+    char* from_token = rule;
+    char* to_token = colon + 1;
+    if (*to_token == '\0') {
+      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) {
+      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) {
+      free(list);
+      log_message(LOG_LEVEL_ERROR, "%s has too many rules (max %d)", optname, MAX_IDENTITY_MAP);
+      return -1;
+    }
+  }
+  free(list);
+  return 0;
+}
+
+/* Split --chown=USER:GROUP on the first UNESCAPED colon, honoring backslash
+ * escapes (a `\:` is a literal colon inside a name; a lone backslash before any
+ * other character is kept verbatim).  Both sides are returned as malloc'd
+ * strings (the absent side is NULL). */
+static int identity_split_chown(const char* value, char** puser, char** pgroup) {
+  size_t len = strlen(value);
+  char* user = malloc(len + 1);
+  char* group = malloc(len + 1);
+  if (!user || !group) {
+    free(user);
+    free(group);
+    return -1;
+  }
+  const char* p = value;
+  size_t ui = 0;
+  bool split_seen = false;
+  size_t gi = 0;
+  while (*p) {
+    if (*p == '\\' && p[1] == ':') {
+      /* an escaped colon: a literal ':' in the current side's name */
+      if (split_seen)
+        group[gi++] = ':';
+      else
+        user[ui++] = ':';
+      p += 2;
+      continue;
+    }
+    if (*p == ':') {
+      split_seen = true;
+      p++;
+      continue;
+    }
+    if (split_seen)
+      group[gi++] = *p;
+    else
+      user[ui++] = *p;
+    p++;
+  }
+  user[ui] = '\0';
+  group[gi] = '\0';
+  char* u = str_dup(user);
+  char* g = str_dup(group);
+  free(user);
+  free(group);
+  if (!u || !g) {
+    free(u);
+    free(g);
+    return -1;
+  }
+  *puser = u;
+  *pgroup = g;
+  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)");
+    return -1;
+  }
+  /* Reject more than one UNESCAPED colon (a name or group may not contain an
+   * unescaped ':' in the spec).  The scan is escape-aware: a `\:` is a literal
+   * colon inside a name, not a field separator. */
+  int colons = 0;
+  bool saw_colon = false;
+  const char* p = value;
+  while (*p) {
+    if (*p == '\\' && p[1] == ':') {
+      p += 2;
+      continue;
+    }
+    if (*p == ':') {
+      colons++;
+      saw_colon = true;
+    }
+    p++;
+  }
+  if (colons > 1) {
+    log_message(LOG_LEVEL_ERROR, "--chown must have at most one ':' (got '%s')", value);
+    return -1;
+  }
+
+  char *user = NULL, *group = NULL;
+  if (identity_split_chown(value, &user, &group) != 0) {
+    log_message(LOG_LEVEL_ERROR, "memory allocation failed for --chown");
+    return -1;
+  }
+  int ret = 0;
+  if (!saw_colon) {
+    /* --chown=USER: owner only. */
+    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);
+      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 (*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 (!*user && !*group) {
+      log_message(LOG_LEVEL_ERROR, "--chown must set a user, a group, or both (got '%s')", value);
+      ret = -1;
+    }
+  }
+done:
+  free(user);
+  free(group);
+  return ret;
+}
+
+/* uid_t/gid_t are unsigned and may hold a value wider than the signed int32 the
+ * wire (and the identity policy) uses.  Reject such an id instead of truncating
+ * it to an out-of-range (possibly negative sentinel) value. */
+static bool identity_id_fits_int32(unsigned long id) {
+  return id <= (unsigned long)INT32_MAX;
+}
+
+/* Resolve one --copy-as id token.  A '*' token means the caller's current
+ * effective uid (user) or gid (group).  Returns 0 on success.  On failure sets
+ * *overflow when a '*' id was wider than int32 so the caller can log the
+ * specific message; otherwise the token was simply unresolvable. */
+static int identity_resolve_copy_as_id(const char* token, bool is_group, int32_t* out,
+                                       bool* overflow) {
+  *overflow = false;
+  if (strcmp(token, "*") == 0) {
+    unsigned long current = is_group ? (unsigned long)getegid() : (unsigned long)geteuid();
+    if (!identity_id_fits_int32(current)) {
+      *overflow = true;
+      return -1;
+    }
+    *out = (int32_t)current;
+    return 0;
+  }
+  return identity_resolve_token(token, is_group, out);
+}
+
+int identity_parse_copy_as(Config* config, const char* value) {
+  if (!config || !value || *value == '\0') {
+    log_message(LOG_LEVEL_ERROR, "--copy-as requires USER[:GROUP]");
+    return -1;
+  }
+  /* --copy-as=USER[:GROUP] is the whole grammar: at most one field separator.
+   * (Unlike --chown there is no escaped-colon form; a name containing ':' is
+   * simply not expressible, and the extra colon is a clear parse error.) */
+  int colons = 0;
+  for (const char* p = value; *p; p++)
+    if (*p == ':')
+      colons++;
+  if (colons > 1) {
+    char* escaped = output_escape(value, false);
+    log_message(LOG_LEVEL_ERROR, "--copy-as must be USER[:GROUP] (got '%s')",
+                escaped ? escaped : "<allocation failed>");
+    free(escaped);
+    return -1;
+  }
+
+  char* spec = str_dup(value);
+  if (!spec) {
+    log_message(LOG_LEVEL_ERROR, "memory allocation failed for --copy-as");
+    return -1;
+  }
+  const char* user_token = spec;
+  const char* group_token = NULL;
+  char* colon = strchr(spec, ':');
+  if (colon) {
+    *colon = '\0';
+    group_token = colon + 1;
+  }
+
+  /* The spec is untrusted user input echoed back in error paths: escape it once
+   * (8-bit-safe) so a control byte cannot forge a log line. */
+  char* escaped_spec = output_escape(value, false);
+  const char* shown = escaped_spec ? escaped_spec : "<allocation failed>";
+  int ret = -1;
+
+  if (*user_token == '\0') {
+    log_message(LOG_LEVEL_ERROR, "--copy-as is missing the user (got '%s')", shown);
+    goto done;
+  }
+  bool overflow = false;
+  int32_t uid;
+  if (identity_resolve_copy_as_id(user_token, false, &uid, &overflow) != 0) {
+    if (overflow)
+      log_message(LOG_LEVEL_ERROR, "--copy-as: current user id %lu exceeds INT32_MAX",
+                  (unsigned long)geteuid());
+    else
+      log_message(LOG_LEVEL_ERROR,
+                  "--copy-as could not resolve user (use a name that exists on the "
+                  "source, '*', or @N): %s",
+                  shown);
+    goto done;
+  }
+
+  int32_t gid;
+  if (group_token) {
+    if (*group_token == '\0') {
+      log_message(LOG_LEVEL_ERROR, "--copy-as group is empty (got '%s')", shown);
+      goto done;
+    }
+    if (identity_resolve_copy_as_id(group_token, true, &gid, &overflow) != 0) {
+      if (overflow)
+        log_message(LOG_LEVEL_ERROR, "--copy-as: current group id %lu exceeds INT32_MAX",
+                    (unsigned long)getegid());
+      else
+        log_message(LOG_LEVEL_ERROR, "--copy-as could not resolve group (got '%s')", shown);
+      goto done;
+    }
+  } else {
+    /* Group omitted: use the user's primary gid.  A numeric id with no local
+     * passwd entry has no primary gid to look up, so fall back to gid == uid
+     * (the rsync-style numeric convention; documented divergence). */
+    struct passwd* pw = getpwuid((uid_t)uid);
+    if (pw) {
+      if (!identity_id_fits_int32((unsigned long)pw->pw_gid)) {
+        log_message(LOG_LEVEL_ERROR,
+                    "--copy-as: primary group id %lu for the requested user exceeds INT32_MAX",
+                    (unsigned long)pw->pw_gid);
+        goto done;
+      }
+      gid = (int32_t)pw->pw_gid;
+    } else {
+      gid = uid;
+    }
+  }
+  /* The group-default and gid==uid fallbacks must never store a negative
+   * (sentinel) value; the explicit numeric path is already capped by
+   * identity_resolve_token. */
+  if (uid < 0 || gid < 0) {
+    log_message(LOG_LEVEL_ERROR, "--copy-as resolved id does not fit in int32 (got '%s')", shown);
+    goto done;
+  }
+
+  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:
+  free(escaped_spec);
+  free(spec);
+  return ret;
+}
+
+/* ---- Receiver-side ownership application ---- */
+
+static bool identity_map_lookup(const IdentityMap* map, int count, int32_t source_id,
+                                int32_t* out_to) {
+  for (int i = 0; i < count; i++) {
+    if (map[i].from == IDENTITY_MATCH_ANY || map[i].from == source_id) {
+      *out_to = map[i].to;
+      return true;
+    }
+  }
+  return false;
+}
+
+/* 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;
+    if (st->st_uid == uid && st->st_gid == gid)
+      return false;
+    *out_uid = uid;
+    *out_gid = gid;
+    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)
+    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)
+    return false;
+  *out_uid = uid;
+  *out_gid = gid;
+  return true;
+}
+
+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
+   * error (EIO/EROFS/ENOSPC/...) is a real failure and must not be silently
+   * downgraded to a warning.
+   *
+   * --copy-as is different: the whole point of the flag is that the target
+   * ownership is REQUIRED (the pre-flight gate already refused an unprivileged
+   * receiver).  If the chown still fails with EPERM/EACCES (a capability-
+   * restricted root, root-squash, or a read-only mount) the run would be
+   * silently producing the WRONG ownership, so surface it at ERROR.  The
+   * caller (identity_apply_ownership*) then reports the ENTRY as failed rather
+   * than as written, which becomes a FILE_SAVE_ERROR and fails the transfer
+   * (fail-fast) instead of reporting overall success with the wrong owner. */
+  if (errno == EPERM || errno == EACCES) {
+    if (identity_copy_as_active())
+      log_message(LOG_LEVEL_ERROR,
+                  "could not apply --copy-as ownership on %s (uid=%ld gid=%ld): %s; "
+                  "entry was written with the wrong owner",
+                  what, (long)uid, (long)gid, strerror(errno));
+    else
+      log_message(LOG_LEVEL_WARNING,
+                  "could not apply ownership (uid=%ld gid=%ld): %s; leaving as-is", (long)uid,
+                  (long)gid, strerror(errno));
+  } else {
+    log_message(LOG_LEVEL_ERROR, "failed to apply ownership on %s (uid=%ld gid=%ld): %s", what,
+                (long)uid, (long)gid, strerror(errno));
+  }
+}
+
+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)
+    return true;
+  struct stat st;
+  if (fstat(fd, &st) != 0)
+    return !identity_copy_as_active();
+  uid_t uid;
+  gid_t gid;
+  if (!identity_resolve_targets(&st, source_uid, source_gid, &uid, &gid))
+    return true;
+  if (fchown(fd, uid, gid) != 0) {
+    identity_log_chown_failure("file", uid, gid);
+    /* A required --copy-as ownership that did not land is a per-entry failure;
+     * every other policy stays best-effort (rsync parity). */
+    return !identity_copy_as_active();
+  }
+  return true;
+}
+
+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)
+    return true;
+  struct stat st;
+  if (fstatat(parent_fd, leaf, &st, AT_SYMLINK_NOFOLLOW) != 0)
+    return !identity_copy_as_active();
+  uid_t uid;
+  gid_t gid;
+  if (!identity_resolve_targets(&st, source_uid, source_gid, &uid, &gid))
+    return true;
+  if (fchownat(parent_fd, leaf, uid, gid, AT_SYMLINK_NOFOLLOW) != 0) {
+    identity_log_chown_failure("no-follow entry", uid, gid);
+    return !identity_copy_as_active();
+  }
+  return true;
+}

src/shared/identity.h

@@ -0,0 +1,133 @@
+#ifndef IDENTITY_H
+#define IDENTITY_H
+
+#include "config.h"
+#include <stdbool.h>
+#include <stdint.h>
+#include <sys/types.h>
+
+/*
+ * Identity mapping: --numeric-ids / --usermap / --groupmap / --chown / --copy-as.
+ *
+ * FastSync transmits uid/gid numerically (int32 on the wire) and, by design,
+ * NEVER applies client-supplied ownership unless a user explicitly opts in with
+ * an identity flag below.  This module is the controlled, opt-in,
+ * privilege-gated path for applying ownership on the receiver: the wire config
+ * is snapshotted once per connection via identity_set_active() and applied
+ * through an fd-relative fchown() in the receiver's metadata-restore path.
+ *
+ * Because only numeric ids cross the wire, name-based values are resolved to
+ * numbers at CLI parse time using the CLIENT (sender) machine's databases.  On
+ * a shared-account source/destination this reproduces rsync's semantics; a
+ * genuinely different destination database is a documented divergence (see
+ * RSYNC_COMPAT.md).
+ */
+
+/* Parse one --usermap= / --groupmap= value (comma-separated FROM:TO rules,
+ * first match wins) into config->usermap / config->groupmap.  is_group selects
+ * the group tables and name databases.  Returns 0 on success, -1 on a
+ * malformed spec or an unresolvable name (never a silent no-op). */
+int identity_parse_map(Config* config, const char* value, bool is_group);
+
+/* Parse --chown=USER:GROUP.  Supports USER:GROUP, USER (owner only), :GROUP
+ * (group only), '*' (current/root as appropriate) and numeric ids.  Returns 0
+ * on success, -1 on a malformed spec / unresolvable name. */
+int identity_parse_chown(Config* config, const char* value);
+
+/* Parse --copy-as=USER[:GROUP] (P7 Wave E).  USER is resolved with the same
+ * user-database rules as --chown (a name, @N/bare N numeric id, or '*' meaning
+ * the client's current euid); when ':GROUP' is present the group is resolved
+ * with the group database ('*' meaning the client's egid).  When the group is
+ * omitted, the user's primary gid is used (getpwuid(uid)->pw_gid); if the
+ * resolved user is a numeric id with no local passwd entry, gid falls back to
+ * uid.  On success sets copy_as_set/copy_as_uid/copy_as_gid and forces
+ * metadata transmission (ownership application needs the metadata path).
+ * Returns 0 on success, -1 on a malformed / empty / unresolvable spec (never a
+ * silent no-op). */
+int identity_parse_copy_as(Config* config, const char* value);
+
+/* True when a --copy-as request is active but the receiver is not permitted to
+ * perform the privileged ownership application it needs.  This is the up-front
+ * refusal predicate: the server rejects the whole transfer at the config
+ * handshake rather than silently ignoring the requested ownership.  It is a
+ * pure function of the config mode and the current effective uid (it does NOT
+ * read the active snapshot, so it is valid at the pre-STATUS_OK gate, before
+ * identity_set_active() has run).  `super_mode` is the EFFECTIVE mode after any
+ * server-side policy veto. */
+bool identity_copy_as_refused(const Config* config);
+
+/* True when the CURRENT per-connection snapshot has a --copy-as active (i.e.
+ * identity_set_active() has run against a config with copy_as_set).  The
+ * --fake-super owner replay consults this so a copy-as run never lets the
+ * recorded source owner overwrite the forced target owner.  Reads the active
+ * snapshot, so call identity_set_active() first (the receiver does, before any
+ * write). */
+bool identity_copy_as_active(void);
+
+/* Receiver-side snapshot of the negotiated identity config.  The server calls
+ * identity_set_active() once per connection (before any file write) using the
+ * config received over the wire; the snapshot is a deep copy so the caller may
+ * free its Config immediately.  identity_clear_active() releases it.
+ *
+ * Returns true on success.  On an allocation failure while deep-copying a
+ * requested usermap/groupmap it logs a LOG_LEVEL_ERROR, leaves the snapshot
+ * cleared (never a partial/wrong policy) and returns false; the caller must
+ * refuse the connection. */
+bool identity_set_active(const Config* config);
+void identity_clear_active(void);
+
+/* True when any ownership-affecting identity option is present in the active
+ * 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. */
+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. */
+bool identity_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
+ * usermap/groupmap rule, then --chown, then --numeric-ids (raw), then a
+ * best-effort name lookup on the receiver's own databases (skipped when the
+ * transmitted id has no name on this system).  Only calls fchown() when the
+ * result differs from the current value.
+ *
+ * Returns false ONLY when an active --copy-as ownership application failed: its
+ * forced ownership is REQUIRED, so the caller must treat the entry as failed
+ * rather than reporting success with the wrong owner.  For every other identity
+ * policy an fchown EPERM/EACCES is logged and ignored and true is returned
+ * (rsync parity: the transfer must not abort).  A no-op when no identity policy
+ * is active returns true. */
+bool identity_apply_ownership(int fd, int32_t source_uid, int32_t source_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
+ * without ever dereferencing it.  A no-op unless an identity flag is active.
+ * The return value follows identity_apply_ownership(): false only when an
+ * active --copy-as application failed. */
+bool identity_apply_ownership_link(int parent_fd, const char* leaf, int32_t source_uid,
+                                   int32_t source_gid);
+
+/* Receiver-side wire validation of the resolved identity fields. */
+bool identity_wire_valid(const Config* config);
+
+/* P7 Wave E receiver-side permission gate for super-user activities (ownership
+ * application and char/block device-node creation).  `privilege_super_permitted`
+ * consults the per-connection snapshot (call identity_set_active() first);
+ * `privilege_super_mode_permitted` is the pure mode predicate and is what
+ * callers holding a Config use (the config-frame gate, file_receive).  Both
+ * return false only for SUPER_MODE_OFF; SUPER_MODE_ON and SUPER_MODE_AUTO (the
+ * default) permit a confined attempt, matching FastSync's historical
+ * best-effort behavior where an unprivileged attempt is refused by the kernel
+ * and skipped.  Neither EVER elevates privileges. */
+bool privilege_super_permitted(void);
+bool privilege_super_mode_permitted(int mode);
+
+#endif

src/shared/log.c

@@ -1,5 +1,6 @@
 #include "log.h"
 #include <errno.h>
+#include <stdbool.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
@@ -7,16 +8,58 @@
 
 static const char* log_level_strings[] = {"DEBUG", "INFO", "WARN", "ERROR"};
 static LogLevel current_log_level = LOG_LEVEL_WARNING;
+static uint32_t current_debug_flags = 0;
+static uint32_t info_flags = 0;
+static bool info_flags_explicit = false;
 static FILE* log_fp = NULL;
+static _Thread_local bool eight_bit_output;
+static LogStderrMode stderr_mode = LOG_STDERR_ERRORS;
 
 void set_log_level(LogLevel level) {
   current_log_level = level;
 }
 
+void set_log_debug_flags(uint32_t flags) {
+  current_debug_flags = flags;
+}
+
+uint32_t get_log_debug_flags(void) {
+  return current_debug_flags;
+}
+
+bool log_debug_enabled(LogDebugFlag flag) {
+  return current_log_level <= LOG_LEVEL_DEBUG && (current_debug_flags & flag) != 0;
+}
+
+void set_log_info_flags(uint32_t flags) {
+  info_flags = flags;
+  info_flags_explicit = true;
+}
+
+uint32_t get_log_info_flags(void) {
+  return info_flags;
+}
+
 void log_set_file(FILE* fp) {
   log_fp = fp;
 }
 
+void log_set_8_bit_output(bool enabled) {
+  eight_bit_output = enabled;
+}
+
+bool log_get_8_bit_output(void) {
+  return eight_bit_output;
+}
+
+void log_set_stderr_mode(LogStderrMode mode) {
+  stderr_mode = mode;
+}
+
+LogStderrMode log_get_stderr_mode(void) {
+  return stderr_mode;
+}
+
 static inline void write_message(FILE* dest_io, LogLevel log_level, struct tm t, const char* format,
                                  va_list args) {
   fprintf(dest_io, "%04d-%02d-%02d %02d:%02d:%02d [%s]: ", t.tm_year + 1900, t.tm_mon + 1,
@@ -37,7 +80,7 @@ void log_message(LogLevel log_level, const char* format, ...) {
     return;
 
   FILE* dest_io = stdout;
-  if (log_level == LOG_LEVEL_ERROR) {
+  if (stderr_mode == LOG_STDERR_ALL || log_level == LOG_LEVEL_ERROR) {
     dest_io = stderr;
   }
 
@@ -53,6 +96,49 @@ void log_message(LogLevel log_level, const char* format, ...) {
   }
 }
 
+void log_debug_message(LogDebugFlag flag, const char* format, ...) {
+  if (current_log_level > LOG_LEVEL_DEBUG || !(current_debug_flags & flag))
+    return;
+
+  time_t now = time(NULL);
+  struct tm t;
+  if (!localtime_r(&now, &t))
+    return;
+
+  va_list args;
+  va_start(args, format);
+  write_message(stdout, LOG_LEVEL_DEBUG, t, format, args);
+  va_end(args);
+
+  if (log_fp) {
+    va_start(args, format);
+    write_message(log_fp, LOG_LEVEL_DEBUG, t, format, args);
+    va_end(args);
+  }
+}
+
+void log_info_message(LogInfoFlag flag, const char* format, ...) {
+  if ((info_flags_explicit && (info_flags & flag) == 0) ||
+      (!info_flags_explicit && current_log_level > LOG_LEVEL_DEBUG))
+    return;
+
+  time_t now = time(NULL);
+  struct tm t;
+  if (!localtime_r(&now, &t))
+    return;
+
+  va_list args;
+  va_start(args, format);
+  write_message(stdout, LOG_LEVEL_INFO, t, format, args);
+  va_end(args);
+
+  if (log_fp) {
+    va_start(args, format);
+    write_message(log_fp, LOG_LEVEL_INFO, t, format, args);
+    va_end(args);
+  }
+}
+
 void log_perror(const char* context) {
   log_message(LOG_LEVEL_ERROR, "%s: %s", context, strerror(errno));
 }

src/shared/log.h

@@ -2,12 +2,45 @@
 #define LOG_H
 
 #include <stdio.h>
+#include <stdbool.h>
+#include <stdint.h>
 
 typedef enum { LOG_LEVEL_DEBUG, LOG_LEVEL_INFO, LOG_LEVEL_WARNING, LOG_LEVEL_ERROR } LogLevel;
+typedef enum { LOG_STDERR_ERRORS, LOG_STDERR_ALL } LogStderrMode;
+
+typedef enum {
+  LOG_DEBUG_IO = 1u << 0,
+  LOG_DEBUG_PROTO = 1u << 1,
+  LOG_DEBUG_PACK = 1u << 2,
+  LOG_DEBUG_UTIL = 1u << 3,
+  LOG_DEBUG_ALL = (1u << 4) - 1,
+} LogDebugFlag;
+
+typedef enum {
+  LOG_INFO_COPY = 1u << 0,
+  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,
+} LogInfoFlag;
 
 void log_message(LogLevel log_level, const char* message, ...);
 void log_perror(const char* context);
 void set_log_level(LogLevel level);
+void set_log_debug_flags(uint32_t flags);
+uint32_t get_log_debug_flags(void);
+/* True when a log_debug_message() call with the same flag would actually emit:
+ * the debug log level is enabled AND the flag is selected.  Hot paths use this
+ * to skip expensive message formatting/escaping when the line is filtered. */
+bool log_debug_enabled(LogDebugFlag flag);
+void log_debug_message(LogDebugFlag flag, const char* message, ...);
+void set_log_info_flags(uint32_t flags);
+uint32_t get_log_info_flags(void);
+void log_info_message(LogInfoFlag flag, const char* message, ...);
 void log_set_file(FILE* fp);
+void log_set_8_bit_output(bool enabled);
+bool log_get_8_bit_output(void);
+void log_set_stderr_mode(LogStderrMode mode);
+LogStderrMode log_get_stderr_mode(void);
 
 #endif

src/shared/metadata.c

@@ -1,7 +1,9 @@
 #include "metadata.h"
 #include "file.h"
+#include "identity.h"
 #include "log.h"
 #include "protocol.h"
+#include "utils.h"
 #include <errno.h>
 #include <fcntl.h>
 #include <stdint.h>
@@ -24,6 +26,29 @@ typedef char static_assert_mode_t_fits[(sizeof(mode_t) <= sizeof(int32_t)) ? 1 :
 typedef char static_assert_uid_t_fits[(sizeof(uid_t) <= sizeof(int32_t)) ? 1 : -1];
 typedef char static_assert_gid_t_fits[(sizeof(gid_t) <= sizeof(int32_t)) ? 1 : -1];
 
+bool metadata_mtime_matches(time_t left_sec, long left_nsec, time_t right_sec, long right_nsec,
+                            int modify_window) {
+  int64_t left = (int64_t)left_sec;
+  int64_t right = (int64_t)right_sec;
+  int64_t seconds;
+  int64_t nanoseconds;
+
+  if (left > right || (left == right && left_nsec >= right_nsec)) {
+    seconds = left - right;
+    nanoseconds = (int64_t)left_nsec - (int64_t)right_nsec;
+  } else {
+    seconds = right - left;
+    nanoseconds = (int64_t)right_nsec - (int64_t)left_nsec;
+  }
+  if (nanoseconds < 0) {
+    seconds--;
+    nanoseconds += 1000000000LL;
+  }
+  if (modify_window == 0)
+    return left == right;
+  return seconds < modify_window || (seconds == modify_window && nanoseconds == 0);
+}
+
 void metadata_to_buf(char** buf, const FileMetadata* m) {
   int32_t present = (m != NULL) ? 1 : 0;
   memcpy(*buf, &present, sizeof(present));
@@ -45,6 +70,24 @@ void metadata_to_buf(char** buf, const FileMetadata* m) {
   int64_t mtime_nsec = (int64_t)m->mtime_nsec;
   memcpy(*buf, &mtime_nsec, sizeof(mtime_nsec));
   *buf += sizeof(mtime_nsec);
+  int32_t atime_valid = m->atime_valid ? 1 : 0;
+  memcpy(*buf, &atime_valid, sizeof(atime_valid));
+  *buf += sizeof(atime_valid);
+  int64_t atime_sec = (int64_t)m->atime_sec;
+  memcpy(*buf, &atime_sec, sizeof(atime_sec));
+  *buf += sizeof(atime_sec);
+  int64_t atime_nsec = (int64_t)m->atime_nsec;
+  memcpy(*buf, &atime_nsec, sizeof(atime_nsec));
+  *buf += sizeof(atime_nsec);
+  int32_t crtime_valid = m->crtime_valid ? 1 : 0;
+  memcpy(*buf, &crtime_valid, sizeof(crtime_valid));
+  *buf += sizeof(crtime_valid);
+  int64_t crtime_sec = (int64_t)m->crtime_sec;
+  memcpy(*buf, &crtime_sec, sizeof(crtime_sec));
+  *buf += sizeof(crtime_sec);
+  int64_t crtime_nsec = (int64_t)m->crtime_nsec;
+  memcpy(*buf, &crtime_nsec, sizeof(crtime_nsec));
+  *buf += sizeof(crtime_nsec);
 }
 
 FileMetadata* metadata_from_buf(char** buf) {
@@ -55,7 +98,7 @@ FileMetadata* metadata_from_buf(char** buf) {
     return NULL;
   if (!present)
     return NULL;
-  FileMetadata* m = malloc(sizeof(FileMetadata));
+  FileMetadata* m = protocol_alloc(sizeof(FileMetadata));
   if (m == NULL)
     return NULL;
   int32_t mode;
@@ -78,8 +121,34 @@ FileMetadata* metadata_from_buf(char** buf) {
   memcpy(&mtime_nsec, *buf, sizeof(mtime_nsec));
   *buf += sizeof(mtime_nsec);
   m->mtime_nsec = (long)mtime_nsec;
+  int32_t atime_valid;
+  memcpy(&atime_valid, *buf, sizeof(atime_valid));
+  *buf += sizeof(atime_valid);
+  int64_t atime_sec;
+  memcpy(&atime_sec, *buf, sizeof(atime_sec));
+  *buf += sizeof(atime_sec);
+  int64_t atime_nsec;
+  memcpy(&atime_nsec, *buf, sizeof(atime_nsec));
+  *buf += sizeof(atime_nsec);
+  int32_t crtime_valid;
+  memcpy(&crtime_valid, *buf, sizeof(crtime_valid));
+  *buf += sizeof(crtime_valid);
+  int64_t crtime_sec;
+  memcpy(&crtime_sec, *buf, sizeof(crtime_sec));
+  *buf += sizeof(crtime_sec);
+  int64_t crtime_nsec;
+  memcpy(&crtime_nsec, *buf, sizeof(crtime_nsec));
+  *buf += sizeof(crtime_nsec);
+  m->atime_valid = atime_valid != 0;
+  m->atime_sec = (time_t)atime_sec;
+  m->atime_nsec = (long)atime_nsec;
+  m->crtime_valid = crtime_valid != 0;
+  m->crtime_sec = (time_t)crtime_sec;
+  m->crtime_nsec = (long)crtime_nsec;
   if (present != 1 || mtime_nsec < 0 || mtime_nsec >= 1000000000LL || mode < 0 || uid < 0 ||
-      gid < 0) {
+      gid < 0 || atime_valid < 0 || atime_valid > 1 || crtime_valid < 0 || crtime_valid > 1 ||
+      (atime_valid && (atime_nsec < 0 || atime_nsec >= 1000000000LL)) ||
+      (crtime_valid && (crtime_nsec < 0 || crtime_nsec >= 1000000000LL))) {
     free(m);
     return NULL;
   }
@@ -97,12 +166,24 @@ bool metadata_send(int file_descriptor, const FileMetadata* m) {
   int32_t gid = (int32_t)m->gid;
   int64_t mtime_sec = (int64_t)m->mtime_sec;
   int64_t mtime_nsec = (int64_t)m->mtime_nsec;
+  int32_t atime_valid = m->atime_valid ? 1 : 0;
+  int64_t atime_sec = (int64_t)m->atime_sec;
+  int64_t atime_nsec = (int64_t)m->atime_nsec;
+  int32_t crtime_valid = m->crtime_valid ? 1 : 0;
+  int64_t crtime_sec = (int64_t)m->crtime_sec;
+  int64_t crtime_nsec = (int64_t)m->crtime_nsec;
   return send_n_data(file_descriptor, &present, sizeof(present)) &&
          send_n_data(file_descriptor, &mode, sizeof(mode)) &&
          send_n_data(file_descriptor, &uid, sizeof(uid)) &&
          send_n_data(file_descriptor, &gid, sizeof(gid)) &&
          send_n_data(file_descriptor, &mtime_sec, sizeof(mtime_sec)) &&
-         send_n_data(file_descriptor, &mtime_nsec, sizeof(mtime_nsec));
+         send_n_data(file_descriptor, &mtime_nsec, sizeof(mtime_nsec)) &&
+         send_n_data(file_descriptor, &atime_valid, sizeof(atime_valid)) &&
+         send_n_data(file_descriptor, &atime_sec, sizeof(atime_sec)) &&
+         send_n_data(file_descriptor, &atime_nsec, sizeof(atime_nsec)) &&
+         send_n_data(file_descriptor, &crtime_valid, sizeof(crtime_valid)) &&
+         send_n_data(file_descriptor, &crtime_sec, sizeof(crtime_sec)) &&
+         send_n_data(file_descriptor, &crtime_nsec, sizeof(crtime_nsec));
 }
 
 FileMetadata* metadata_receive(int file_descriptor, int* ok) {
@@ -122,7 +203,7 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
       *ok = 0;
     return NULL;
   }
-  FileMetadata* m = malloc(sizeof(FileMetadata));
+  FileMetadata* m = protocol_alloc(sizeof(FileMetadata));
   if (m == NULL) {
     if (ok)
       *ok = 0;
@@ -168,7 +249,58 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
     return NULL;
   }
   m->mtime_nsec = (long)mtime_nsec;
-  if (mtime_nsec < 0 || mtime_nsec >= 1000000000LL || mode < 0 || uid < 0 || gid < 0) {
+  int32_t atime_valid;
+  if (!receive_n_data(file_descriptor, &atime_valid, sizeof(atime_valid))) {
+    free(m);
+    if (ok)
+      *ok = 0;
+    return NULL;
+  }
+  int64_t atime_sec;
+  if (!receive_n_data(file_descriptor, &atime_sec, sizeof(atime_sec))) {
+    free(m);
+    if (ok)
+      *ok = 0;
+    return NULL;
+  }
+  int64_t atime_nsec;
+  if (!receive_n_data(file_descriptor, &atime_nsec, sizeof(atime_nsec))) {
+    free(m);
+    if (ok)
+      *ok = 0;
+    return NULL;
+  }
+  int32_t crtime_valid;
+  if (!receive_n_data(file_descriptor, &crtime_valid, sizeof(crtime_valid))) {
+    free(m);
+    if (ok)
+      *ok = 0;
+    return NULL;
+  }
+  int64_t crtime_sec;
+  if (!receive_n_data(file_descriptor, &crtime_sec, sizeof(crtime_sec))) {
+    free(m);
+    if (ok)
+      *ok = 0;
+    return NULL;
+  }
+  int64_t crtime_nsec;
+  if (!receive_n_data(file_descriptor, &crtime_nsec, sizeof(crtime_nsec))) {
+    free(m);
+    if (ok)
+      *ok = 0;
+    return NULL;
+  }
+  m->atime_valid = atime_valid != 0;
+  m->atime_sec = (time_t)atime_sec;
+  m->atime_nsec = (long)atime_nsec;
+  m->crtime_valid = crtime_valid != 0;
+  m->crtime_sec = (time_t)crtime_sec;
+  m->crtime_nsec = (long)crtime_nsec;
+  if (mtime_nsec < 0 || mtime_nsec >= 1000000000LL || mode < 0 || uid < 0 || gid < 0 ||
+      atime_valid < 0 || atime_valid > 1 || crtime_valid < 0 || crtime_valid > 1 ||
+      (atime_valid && (atime_nsec < 0 || atime_nsec >= 1000000000LL)) ||
+      (crtime_valid && (crtime_nsec < 0 || crtime_nsec >= 1000000000LL))) {
     free(m);
     if (ok)
       *ok = 0;
@@ -179,12 +311,27 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
   return m;
 }
 
-void file_restore_metadata(const char* path, const FileMetadata* metadata) {
+static mode_t metadata_mode(const FileMetadata* metadata, mode_t current_mode,
+                            bool preserve_executability) {
+  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);
+}
+
+void file_restore_metadata(const char* path, const FileMetadata* metadata,
+                           bool preserve_executability) {
   if (metadata == NULL)
     return;
-  mode_t safe_mode = metadata->mode & 0777 & ~(S_IWGRP | S_IWOTH);
-  if (chmod(path, safe_mode) != 0)
-    log_message(LOG_LEVEL_WARNING, "Failed to chmod %s: %s", path, strerror(errno));
+  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) {
+    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));
+    free(escaped_path);
+  }
   /* 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];
@@ -192,20 +339,104 @@ void file_restore_metadata(const char* path, const FileMetadata* metadata) {
   times[0].tv_nsec = UTIME_OMIT;
   times[1].tv_sec = metadata->mtime_sec;
   times[1].tv_nsec = metadata->mtime_nsec;
-  if (utimensat(AT_FDCWD, path, times, 0) != 0)
-    log_message(LOG_LEVEL_WARNING, "Failed to set timestamps on %s: %s", path, strerror(errno));
+  if (metadata->atime_valid) {
+    times[0].tv_sec = metadata->atime_sec;
+    times[0].tv_nsec = metadata->atime_nsec;
+  }
+  if (metadata->crtime_valid) {
+    log_message(LOG_LEVEL_DEBUG,
+                "crtime (birth time) %lld.%09ld transmitted for %s but not applied: no portable "
+                "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_metadata_fd(int fd, const FileMetadata* metadata) {
+bool file_restore_symlink_metadata(const char* path, const FileMetadata* metadata,
+                                   bool omit_link_times) {
+  if (path == NULL || metadata == NULL)
+    return !identity_copy_as_active();
+  char* leaf = NULL;
+  int parent_fd = file_open_secure_parent(path, &leaf, false);
+  if (parent_fd < 0)
+    return !identity_copy_as_active();
+  /* Ownership (only when the identity policy is active) via lchown semantics:
+     fchownat with AT_SYMLINK_NOFOLLOW never dereferences the link.  A failed
+     REQUIRED --copy-as ownership marks the entry failed; every other policy is
+     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));
+  }
+  if (!omit_link_times) {
+    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 (utimensat(parent_fd, leaf, times, AT_SYMLINK_NOFOLLOW) != 0) {
+      char* escaped_path = output_escape(path, log_get_8_bit_output());
+      log_message(LOG_LEVEL_WARNING, "Failed to set symlink timestamps on %s: %s",
+                  escaped_path ? escaped_path : "<allocation failed>", strerror(errno));
+      free(escaped_path);
+    }
+  }
+  close(parent_fd);
+  free(leaf);
+  return owned;
+}
+
+bool file_restore_metadata_fd(int fd, const FileMetadata* metadata, bool preserve_executability) {
   if (fd < 0 || metadata == NULL)
     return metadata == NULL;
   bool ok = true;
-  mode_t safe_mode = metadata->mode & 0777 & ~(S_IWGRP | S_IWOTH);
+  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. */
+  /* 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,
+     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
+     for an active --copy-as, whose forced ownership is REQUIRED: a failure
+     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. */
+  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;
+  }
+  /* --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
+   * the receiver deliberately does NOT apply it.  This is explicit, honest
+   * unsupported-attribute handling: log a debug note and continue — never fail
+   * the transfer and never pretend the crtime was applied. */
+  if (metadata->crtime_valid) {
+    log_message(LOG_LEVEL_DEBUG,
+                "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;
   return ok;

src/shared/metadata.h

@@ -5,6 +5,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <sys/stat.h>
+#include <time.h>
 
 /*
  * Wire format (introduced in protocol version 2.0.0):
@@ -14,6 +15,12 @@
  *   int32_t gid     (was gid_t,  platform-dependent)
  *   int64_t mtime_sec (was time_t, platform-dependent)
  *   int64_t mtime_nsec (was long,  platform-dependent)
+ *   int32_t atime_valid   (-U/--atimes; protocol 2.12.0)
+ *   int64_t atime_sec
+ *   int64_t atime_nsec
+ *   int32_t crtime_valid  (-N/--crtimes; protocol 2.12.0)
+ *   int64_t crtime_sec
+ *   int64_t crtime_nsec
  *
  * Prior to 2.0.0 the wire format used the raw platform-dependent types,
  * which broke compatiblity across different systems.  All fields are now
@@ -22,14 +29,29 @@
 
 /* Size of metadata fields on wire, excluding the int32_t `present` field that
  * is always sent first. The total wire size for present metadata is
- * sizeof(int32_t) + FILE_METADATA_WIRE_SIZE (32 bytes on most platforms). */
-#define FILE_METADATA_WIRE_SIZE (sizeof(int32_t) * 3 + sizeof(int64_t) * 2)
+ * sizeof(int32_t) + FILE_METADATA_WIRE_SIZE (68 bytes on most platforms). */
+#define FILE_METADATA_WIRE_SIZE (sizeof(int32_t) * 5 + sizeof(int64_t) * 6)
 
 void metadata_to_buf(char** buf, const FileMetadata* m);
 FileMetadata* metadata_from_buf(char** buf);
 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 file_restore_metadata_fd(int fd, const FileMetadata* metadata);
+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);
+/* 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).
+ * 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);
+
+/* 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,
+                            int modify_window);
 
 #endif

src/shared/motd.c

@@ -0,0 +1,76 @@
+#include "motd.h"
+#include "protocol.h"
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+char* motd_read_file(const char* path) {
+  if (!path || path[0] == '\0')
+    return NULL;
+  FILE* fp = fopen(path, "rb");
+  if (!fp)
+    return NULL;
+  char* buffer = malloc(MOTD_MAX_BYTES + 1);
+  if (!buffer) {
+    fclose(fp);
+    return NULL;
+  }
+  /* fread stops at the bound; a larger file is truncated rather than read
+   * unbounded.  ferror distinguishes a truncated read from an I/O failure. */
+  size_t total = fread(buffer, 1, MOTD_MAX_BYTES, fp);
+  if (ferror(fp)) {
+    free(buffer);
+    fclose(fp);
+    return NULL;
+  }
+  fclose(fp);
+  buffer[total] = '\0';
+  return buffer;
+}
+
+char* motd_render(const char* motd, bool eight_bit_output) {
+  if (!motd)
+    return NULL;
+  size_t length = strlen(motd);
+  if (length > (SIZE_MAX - 1) / 5)
+    return NULL;
+  char* rendered = malloc(length * 5 + 1);
+  if (!rendered)
+    return NULL;
+  size_t out = 0;
+  for (size_t i = 0; i < length; i++) {
+    unsigned char byte = (unsigned char)motd[i];
+    if (byte == '\n' || byte == '\t') {
+      rendered[out++] = (char)byte;
+    } else if ((byte >= 32 && byte <= 126) || (eight_bit_output && byte >= 128)) {
+      rendered[out++] = (char)byte;
+    } else {
+      rendered[out++] = '\\';
+      rendered[out++] = '#';
+      rendered[out++] = (char)('0' + ((byte >> 6) & 7));
+      rendered[out++] = (char)('0' + ((byte >> 3) & 7));
+      rendered[out++] = (char)('0' + (byte & 7));
+    }
+  }
+  rendered[out] = '\0';
+  return rendered;
+}
+
+bool motd_send(int file_descriptor, const char* motd) {
+  return send_str(file_descriptor, motd ? motd : "");
+}
+
+char* motd_receive(int file_descriptor) {
+  char* motd = receive_str(file_descriptor);
+  if (!motd)
+    return NULL;
+  /* Guard against a hostile/oversized peer: receive_str already bounded the
+   * frame at MAX_STRING_SIZE and consumed it, so discarding an over-bound
+   * body here keeps the stream framed while refusing to display it. */
+  if (strlen(motd) > MOTD_MAX_BYTES) {
+    free(motd);
+    return NULL;
+  }
+  return motd;
+}

src/shared/motd.h

@@ -0,0 +1,54 @@
+#ifndef MOTD_H
+#define MOTD_H
+
+#include <stdbool.h>
+
+/* Daemon Message-Of-The-Day (Wave C).
+ *
+ * The daemon listener (fastsync-server --daemon) may advertise a `motd file`
+ * configured in its globals.  When a client connects with a host::module/path
+ * destination and the module gate accepts the connection, the server sends the
+ * MOTD as a single string frame BEFORE any transfer data (rsync sends its MOTD
+ * as the first thing from the server at the start of a daemon connection).
+ * The client reads that frame right after the config/status handshake and
+ * displays it on stdout unless --no-motd was given.
+ *
+ * The MOTD is ordinary display text, never a secret, so it uses the normal
+ * (non-redacted) string primitive.  The exchange is strictly server->client
+ * and happens on the daemon listener path only; the --stdio SSH path has no
+ * MOTD.
+ *
+ * No PROTOCOL_VERSION bump is involved: the frame is sent and read
+ * symmetrically by every 2.15.0 daemon build (the strict same-version
+ * handshake rejects any other version before the frame), so it cannot
+ * desynchronize a peer. */
+
+/* Upper bound on the MOTD bytes the server will read from disk and put on the
+ * wire.  Kept far below MAX_STRING_SIZE (64 KB) so a huge/hostile motd file
+ * can never produce an unbounded frame or allocation. */
+#define MOTD_MAX_BYTES 4096
+
+/* Read a daemon MOTD file, bounded to MOTD_MAX_BYTES.  Returns a malloc'd
+ * NUL-terminated copy of the file content (bytes beyond the bound are
+ * truncated) or NULL when path is NULL/empty, the file cannot be opened or
+ * read, or allocation fails.  An absent or unreadable motd file is NOT an
+ * error: the caller simply sends an empty MOTD frame and continues. */
+char* motd_read_file(const char* path);
+
+/* Render MOTD text for terminal display.  Newlines and tabs are preserved so
+ * a multi-line motd still reads naturally, while every other non-printable /
+ * control byte (ESC included) is escaped with FastSync's `\NNN` octal
+ * convention, so a hostile server cannot inject terminal escape sequences
+ * through the MOTD.  eight_bit_output keeps bytes >= 0x80 verbatim (matching
+ * --8-bit-output).  Returns a malloc'd string or NULL on allocation failure. */
+char* motd_render(const char* motd, bool eight_bit_output);
+
+/* Send/receive the MOTD string frame.  These wrap the normal string
+ * primitive: the MOTD is not a credential, so no redaction is used.  The
+ * receiver additionally rejects an over-bound frame (> MOTD_MAX_BYTES) as a
+ * hostile input guard; the frame itself is always fully consumed first, so the
+ * stream stays framed. */
+bool motd_send(int file_descriptor, const char* motd);
+char* motd_receive(int file_descriptor);
+
+#endif

src/shared/multiprocessing.c

@@ -26,10 +26,27 @@ PipelineContextSender* pipeline_context_sender_create(Config* config, Queue* que
   context->scanner_done = false;
   context->loader_done = false;
   context->manifest = NULL;
+  context->excluded_paths = NULL;
+  context->missing_args = NULL;
+  context->scan_had_io_error = false;
+  context->remove_source_files = NULL;
+  context->early_delete = false;
+  context->scan_stopped_early = false;
+  context->total_files = 0;
   context->progress_bytes = 0;
+  context->total_bytes = 0;
   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;
   int init = 0;
+  if (config->use_metadata) {
+    context->dir_entries = array_list_create(file_destroy);
+    if (!context->dir_entries)
+      goto fail;
+  }
   if (mtx_init(&context->mutex_scanner, mtx_plain) != thrd_success)
     goto fail;
   init++;
@@ -52,10 +69,17 @@ PipelineContextSender* pipeline_context_sender_create(Config* config, Queue* que
     goto fail;
   // cppcheck-suppress unreadVariable
   init++;
+  if (mtx_init(&context->dir_entries_mutex, mtx_plain) != thrd_success)
+    goto fail;
+  context->dir_entries_mutex_init = true;
   return context;
 
 fail:
   log_perror("Error initializing synchronization objects");
+  if (context->dir_entries_mutex_init)
+    mtx_destroy(&context->dir_entries_mutex);
+  if (context->dir_entries)
+    array_list_delete(context->dir_entries);
   if (init >= 6)
     cnd_destroy(&context->condition_not_empty_loader);
   if (init >= 5)
@@ -76,6 +100,16 @@ void pipeline_context_sender_destroy(PipelineContextSender* context) {
   if (context->manifest) {
     array_list_delete(context->manifest);
   }
+  if (context->excluded_paths)
+    array_list_delete(context->excluded_paths);
+  if (context->missing_args)
+    array_list_delete(context->missing_args);
+  if (context->remove_source_files)
+    array_list_delete(context->remove_source_files);
+  if (context->dir_entries)
+    array_list_delete(context->dir_entries);
+  if (context->dir_entries_mutex_init)
+    mtx_destroy(&context->dir_entries_mutex);
   config_delete(context->config);
   queue_destroy(context->queue_scanner);
   queue_destroy(context->queue_loader);
@@ -98,9 +132,16 @@ PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue*
   context->queue = queue;
   context->file_descriptor = file_descriptor;
   context->ssl = ssl;
+  context->outcomes.entries = NULL;
+  context->outcomes.count = 0;
+  context->outcomes.capacity = 0;
+  dir_time_list_init(&context->dir_times);
   protocol_session_init(&context->session, file_descriptor, file_descriptor);
   protocol_session_set_ssl(&context->session, ssl);
   context->receiver_done = false;
+  context->queued_bytes = 0;
+  context->max_queue_bytes = 0;
+  context->deferred_manifest = NULL;
   atomic_init(&context->cancelled, false);
   int init = 0;
   if (mtx_init(&context->mutex, mtx_plain) != thrd_success)
@@ -129,21 +170,84 @@ fail:
 
 void pipeline_context_receiver_destroy(PipelineContextReceiver* context) {
   config_delete(context->config);
+  if (context->deferred_manifest)
+    delete_manifest_free(context->deferred_manifest);
   queue_destroy(context->queue);
+  receiver_outcomes_destroy(&context->outcomes);
+  dir_time_list_free(&context->dir_times);
   mtx_destroy(&context->mutex);
   cnd_destroy(&context->condition_not_full);
   cnd_destroy(&context->condition_not_empty);
   free(context);
 }
 
+void pipeline_context_receiver_set_queue_byte_limit(PipelineContextReceiver* context,
+                                                    size_t max_bytes) {
+  if (context == NULL)
+    return;
+  mtx_lock(&context->mutex);
+  context->max_queue_bytes = max_bytes;
+  context->queued_bytes = 0;
+  cnd_broadcast(&context->condition_not_full);
+  mtx_unlock(&context->mutex);
+}
+
+void pipeline_context_receiver_note_bytes_released(PipelineContextReceiver* context,
+                                                   size_t released_bytes) {
+  if (context == NULL || context->max_queue_bytes == 0 || released_bytes == 0)
+    return;
+  mtx_lock(&context->mutex);
+  if (released_bytes >= context->queued_bytes)
+    context->queued_bytes = 0;
+  else
+    context->queued_bytes -= released_bytes;
+  cnd_signal(&context->condition_not_full);
+  mtx_unlock(&context->mutex);
+}
+
+bool pipeline_context_receiver_enqueue_file(PipelineContextReceiver* context, File* file) {
+  if (context == NULL || file == NULL)
+    return false;
+  size_t file_bytes = file->data ? file->data->size : 0;
+  mtx_lock(&context->mutex);
+  while (!atomic_load(&context->cancelled)) {
+    bool blocked_by_count = queue_is_full(context->queue);
+    bool blocked_by_budget = false;
+    if (context->max_queue_bytes > 0) {
+      size_t budget = context->max_queue_bytes;
+      size_t used = context->queued_bytes;
+      if (used >= budget) {
+        blocked_by_budget = true;
+      } else if (file_bytes > budget - used) {
+        /* A single payload larger than the whole budget (not possible with
+           the per-file receive cap) is only admitted to an empty pipeline so
+           the wait can never deadlock. */
+        blocked_by_budget = used != 0;
+      }
+    }
+    if (!blocked_by_count && !blocked_by_budget)
+      break;
+    cnd_wait(&context->condition_not_full, &context->mutex);
+  }
+  if (atomic_load(&context->cancelled)) {
+    mtx_unlock(&context->mutex);
+    file_destroy(file);
+    return false;
+  }
+  if (!queue_enqueue(context->queue, file)) {
+    mtx_unlock(&context->mutex);
+    file_destroy(file);
+    return false;
+  }
+  context->queued_bytes += file_bytes;
+  cnd_signal(&context->condition_not_empty);
+  mtx_unlock(&context->mutex);
+  return true;
+}
+
 static bool receiver_enqueue_file(File* file, void* context_pointer) {
-  PipelineContextReceiver* context = context_pointer;
-  if (queue_enqueue_multithreaded_cancel(context->queue, file, &context->mutex,
-                                         &context->condition_not_empty,
-                                         &context->condition_not_full, &context->cancelled))
-    return true;
-  file_destroy(file);
-  return false;
+  PipelineContextReceiver* context = (PipelineContextReceiver*)context_pointer;
+  return pipeline_context_receiver_enqueue_file(context, file);
 }
 
 static void receiver_thread_fail(PipelineContextReceiver* context) {
@@ -163,8 +267,9 @@ int receive_thread(void* pipeline_context) {
   const Config* config = context->config;
   mtx_unlock(&context->mutex);
 
-  ReceiverSink sink = {receiver_enqueue_file, context, false, false};
-  if (receiver_process((Config*)config, file_descriptor, &sink) != 0) {
+  ReceiverSink sink = {receiver_enqueue_file, context, false, false, NULL};
+  if (receiver_process_pending((Config*)config, file_descriptor, &sink,
+                               &context->deferred_manifest) != 0) {
     receiver_thread_fail(context);
     protocol_session_unbind();
     return thrd_error;
@@ -179,6 +284,7 @@ int receive_thread(void* pipeline_context) {
 
 int write_thread(void* pipeline_context) {
   PipelineContextReceiver* context = (PipelineContextReceiver*)pipeline_context;
+  protocol_session_bind(&context->session);
   mtx_lock(&context->mutex);
   bool save_to_disk = context->config->save_to_disk;
   char* root_directory = str_dup(context->config->receive_root_directory);
@@ -190,6 +296,7 @@ int write_thread(void* pipeline_context) {
     cnd_broadcast(&context->condition_not_full);
     cnd_broadcast(&context->condition_not_empty);
     mtx_unlock(&context->mutex);
+    protocol_session_unbind();
     return thrd_error;
   }
 
@@ -199,10 +306,35 @@ int write_thread(void* pipeline_context) {
                                     &context->condition_not_full, &context->receiver_done);
     if (file == NULL) {
       free(root_directory);
+      protocol_session_unbind();
       return thrd_success;
     }
-    if (save_to_disk && !file_save_to_disk(root_directory, file, context->config)) {
+    size_t file_bytes = file->data ? file->data->size : 0;
+    FileSaveResult result = FILE_SAVE_SKIPPED;
+    if (save_to_disk) {
+      result = file_save_to_disk_full(root_directory, file, context->config);
+      if (result == FILE_SAVE_ERROR) {
+        file_destroy(file);
+        pipeline_context_receiver_note_bytes_released(context, file_bytes);
+        mtx_lock(&context->mutex);
+        atomic_store(&context->cancelled, true);
+        context->receiver_done = true;
+        cnd_broadcast(&context->condition_not_full);
+        cnd_broadcast(&context->condition_not_empty);
+        mtx_unlock(&context->mutex);
+        free(root_directory);
+        protocol_session_unbind();
+        return thrd_error;
+      }
+    }
+    /* P7 Wave D: a directory's times are never applied inline (a later child
+       write would clobber them); accumulate the metadata here and let the
+       caller apply it once every writer has drained. */
+    if (result != FILE_SAVE_ERROR && file->is_dir && file->metadata &&
+        context->config->use_metadata && !context->config->omit_dir_times &&
+        !dir_time_list_add(&context->dir_times, file->path, file->metadata)) {
       file_destroy(file);
+      pipeline_context_receiver_note_bytes_released(context, file_bytes);
       mtx_lock(&context->mutex);
       atomic_store(&context->cancelled, true);
       context->receiver_done = true;
@@ -210,8 +342,28 @@ int write_thread(void* pipeline_context) {
       cnd_broadcast(&context->condition_not_empty);
       mtx_unlock(&context->mutex);
       free(root_directory);
+      protocol_session_unbind();
+      return thrd_error;
+    }
+    /* Record the per-file outcome so a --remove-source-files sender learns
+       which sources were actually written versus skipped on the receiver.
+       Explicit directory entries and recreated device/special nodes have no
+       source and are never acknowledged (mirrors receiver.c). */
+    if (context->config->remove_source_files && !file->is_dir && !file->is_special && !file->skip &&
+        !receiver_outcomes_append(&context->outcomes, (unsigned char)result)) {
+      file_destroy(file);
+      pipeline_context_receiver_note_bytes_released(context, file_bytes);
+      mtx_lock(&context->mutex);
+      atomic_store(&context->cancelled, true);
+      context->receiver_done = true;
+      cnd_broadcast(&context->condition_not_full);
+      cnd_broadcast(&context->condition_not_empty);
+      mtx_unlock(&context->mutex);
+      free(root_directory);
+      protocol_session_unbind();
       return thrd_error;
     }
     file_destroy(file);
+    pipeline_context_receiver_note_bytes_released(context, file_bytes);
   }
 }

src/shared/multiprocessing.h

@@ -9,6 +9,8 @@
 #include "file.h"
 #include "protocol.h"
 #include "queue.h"
+#include "receiver.h"
+#include "stop_condition.h"
 #include <openssl/ssl.h>
 
 typedef struct {
@@ -24,10 +26,54 @@ typedef struct {
   cnd_t condition_not_empty_loader;
   bool loader_done;
   ArrayList* manifest;
+  /* Protected prefixes (paths the source scan excluded by user rules) sent
+     with the keep-set manifest so --delete leaves them alone unless
+     --delete-excluded is set.  NULL when not collecting.  Populated by the
+     scanner thread (parallel workers append under mutex_scanner via the
+     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;
+  /* --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
+     them in the manifest frame's third section and the receiver deletes each as
+     an explicit request. */
+  ArrayList* missing_args;
+  /* A source I/O error (unreadable directory) was recorded during the scan.
+     Set by the pre-scan (before the threads start) or by the scanner thread
+     under mutex_scanner; the caller turns it into a non-zero exit when
+     --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. */
+  bool early_delete;
   mtx_t mutex_progress;
+  int total_files;
   unsigned long long progress_bytes;
+  unsigned long long total_bytes;
   bool sender_done;
   atomic_bool cancelled;
+  ProtocolSession allocation_session;
+  /* Phase 6: client-only sender stop deadline, computed once before the worker
+   * threads start and shared read-only by the scanner and the sender thread. */
+  StopCondition stop_condition;
+  /* Phase 6: set when the scanner/sender reached the stop deadline before the
+   * scan (and thus the keep-set manifest) completed naturally.  When true the
+   * completion tail must NOT transmit the partial manifest, or the receiver
+   * would delete unscanned source mirrors.  Written by the sender thread
+   * before it reads the manifest, so no additional synchronization is needed
+   * to suppress the manifest. */
+  bool scan_stopped_early;
+  /* P7 Wave D: captured source directory times, filled by the scanner thread
+   * (and its parallel workers, guarded by dir_entries_mutex) and drained by the
+   * sender thread in trailing STATUS_DIR_TIMES frame(s).  Owned by the
+   * context; NULL for non-metadata transfers. */
+  ArrayList* dir_entries;
+  mtx_t dir_entries_mutex;
+  bool dir_entries_mutex_init;
 } PipelineContextSender;
 
 typedef struct PipelineContextReceiver {
@@ -36,11 +82,32 @@ typedef struct PipelineContextReceiver {
   int file_descriptor;
   SSL* ssl;
   ProtocolSession session;
+  ReceiverOutcomes outcomes;
   mtx_t mutex;
   cnd_t condition_not_full;
   cnd_t condition_not_empty;
   bool receiver_done;
   atomic_bool cancelled;
+  /* Aggregate payload bytes that have been received but not yet released by
+     the disk writer (queued or in the writer's hand).  Guarded by `mutex`.
+     When `max_queue_bytes` is non-zero the receiver blocks before enqueuing
+     once this total would exceed it, so decompressed/copied file payloads
+     buffered ahead of a slow disk writer respect the per-connection memory
+     budget instead of growing without bound. */
+  size_t queued_bytes;
+  size_t max_queue_bytes;
+  /* Keep-set manifest for the commit-style (late) deletion
+     (--delete/--delete-after/--delete-delay).  receive_thread parses the whole
+     protocol stream but hands the manifest here instead of deleting while the
+     disk writer may still be draining; the caller (server.c) commits the
+     deletion after both threads have joined, so no extra is removed unless the
+     transfer truly succeeded.  NULL in the early delete modes (which delete at
+     the manifest). */
+  DeleteManifest* deferred_manifest;
+  /* 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;
 } PipelineContextReceiver;
 
 PipelineContextSender* pipeline_context_sender_create(Config* config, Queue* queue_scanner,
@@ -49,6 +116,18 @@ void pipeline_context_sender_destroy(PipelineContextSender* context);
 PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue* queue_receiver,
                                                           int file_descriptor, SSL* ssl);
 void pipeline_context_receiver_destroy(PipelineContextReceiver* context);
+/* Bound the bytes buffered ahead of the disk writer (see max_queue_bytes). */
+void pipeline_context_receiver_set_queue_byte_limit(PipelineContextReceiver* context,
+                                                    size_t max_bytes);
+/* Blocking enqueue used by the receive pipeline sink.  Blocks while the queue
+   is full by element count or when adding `file` would push queued_bytes over
+   the configured byte limit; waits until the disk writer releases bytes.
+   Takes ownership of `file` on success and destroys it on failure/cancel. */
+bool pipeline_context_receiver_enqueue_file(PipelineContextReceiver* context, File* file);
+/* Account for `released_bytes` of payload memory that has been freed by the
+   disk writer, unblocking a receiver that is waiting on the byte limit. */
+void pipeline_context_receiver_note_bytes_released(PipelineContextReceiver* context,
+                                                   size_t released_bytes);
 int receive_thread(void* pipeline_context);
 int write_thread(void* pipeline_context);
 #endif

src/shared/protocol.c

@@ -1,5 +1,6 @@
 #include "protocol.h"
 #include "log.h"
+#include "utils.h"
 #include <errno.h>
 #include <limits.h>
 #include <openssl/ssl.h>
@@ -13,13 +14,13 @@
 
 #define RECEIVE_TIMEOUT_SEC 60 /* 60 second per-message timeout */
 #define SEND_TIMEOUT_SEC 60
-#define MAX_CONNECTION_MEMORY (256ULL * 1024 * 1024) /* bounded cumulative receive budget */
 
 static __thread int io_read_fd = -1;
 static __thread int io_write_fd = -1;
 static __thread SSL* io_ssl;
 static __thread ProtocolSession* bound_session;
-static __thread ProtocolSession legacy_io_session = {.read_fd = -1, .write_fd = -1};
+static __thread ProtocolSession legacy_io_session = {
+    .read_fd = -1, .write_fd = -1, .max_alloc = DEFAULT_MAX_ALLOC};
 
 static unsigned long long io_bwlimit = 0;
 static mtx_t bw_mutex;
@@ -27,12 +28,30 @@ static once_flag bw_mutex_once = ONCE_FLAG_INIT;
 
 static unsigned long long global_bwlimit(void);
 
+static bool protocol_reserve_memory(ProtocolSession* session, size_t charge) {
+  unsigned long long allocated = atomic_load(&session->total_allocated_bytes);
+  while (true) {
+    if (allocated > MAX_CONNECTION_MEMORY ||
+        (unsigned long long)charge > MAX_CONNECTION_MEMORY - allocated)
+      return false;
+    if (atomic_compare_exchange_weak(&session->total_allocated_bytes, &allocated,
+                                     allocated + (unsigned long long)charge))
+      return true;
+  }
+}
+
+static void protocol_release_memory_for_session(ProtocolSession* session, size_t charge) {
+  unsigned long long allocated = atomic_load(&session->total_allocated_bytes);
+  while (true) {
+    unsigned long long remaining = (unsigned long long)charge >= allocated ? 0 : allocated - charge;
+    if (atomic_compare_exchange_weak(&session->total_allocated_bytes, &allocated, remaining))
+      break;
+  }
+}
+
 void protocol_release_memory(size_t charge) {
   ProtocolSession* session = bound_session ? bound_session : &legacy_io_session;
-  if ((unsigned long long)charge >= session->total_allocated_bytes)
-    session->total_allocated_bytes = 0;
-  else
-    session->total_allocated_bytes -= charge;
+  protocol_release_memory_for_session(session, charge);
 }
 void io_set_fds(int read_fd, int write_fd) {
   bound_session = NULL;
@@ -44,7 +63,9 @@ void io_set_fds(int read_fd, int write_fd) {
   legacy_io_session.read_fd = read_fd;
   legacy_io_session.write_fd = write_fd;
   legacy_io_session.ssl = NULL;
-  legacy_io_session.total_allocated_bytes = 0;
+  legacy_io_session.eight_bit_output = false;
+  atomic_store(&legacy_io_session.total_allocated_bytes, 0);
+  legacy_io_session.max_alloc = DEFAULT_MAX_ALLOC;
   protocol_session_set_bwlimit(&legacy_io_session, global_bwlimit());
 }
 
@@ -54,11 +75,46 @@ void protocol_session_init(ProtocolSession* session, int read_fd, int write_fd)
   memset(session, 0, sizeof(*session));
   session->read_fd = read_fd;
   session->write_fd = write_fd;
+  session->max_alloc = DEFAULT_MAX_ALLOC;
+  atomic_init(&session->total_allocated_bytes, 0);
   protocol_session_set_bwlimit(session, global_bwlimit());
 }
 
+void protocol_session_set_max_alloc(ProtocolSession* session, unsigned long long max_alloc) {
+  if (!session)
+    session = bound_session ? bound_session : &legacy_io_session;
+  session->max_alloc = max_alloc;
+}
+
+static bool allocation_allowed(const ProtocolSession* session, size_t size) {
+  return (unsigned long long)size <= session->max_alloc;
+}
+
+static void* protocol_alloc_for_session(const ProtocolSession* session, size_t size) {
+  if (!allocation_allowed(session, size))
+    return NULL;
+  return malloc(size);
+}
+
+static void* protocol_realloc_for_session(const ProtocolSession* session, void* ptr, size_t size) {
+  if (!allocation_allowed(session, size))
+    return NULL;
+  return realloc(ptr, size);
+}
+
+void* protocol_alloc(size_t size) {
+  const ProtocolSession* session = bound_session ? bound_session : &legacy_io_session;
+  return protocol_alloc_for_session(session, size);
+}
+
+void* protocol_realloc(void* ptr, size_t size) {
+  const ProtocolSession* session = bound_session ? bound_session : &legacy_io_session;
+  return protocol_realloc_for_session(session, ptr, size);
+}
+
 void protocol_session_bind(ProtocolSession* session) {
   bound_session = session;
+  log_set_8_bit_output(session && session->eight_bit_output);
 }
 
 void protocol_session_unbind(void) {
@@ -103,6 +159,19 @@ void protocol_session_set_bwlimit(ProtocolSession* session, unsigned long long b
   session->bw_last_refill_nsec = now.tv_nsec;
 }
 
+void protocol_session_set_8_bit_output(ProtocolSession* session, bool enabled) {
+  if (!session)
+    return;
+  session->eight_bit_output = enabled;
+  if (session == bound_session)
+    log_set_8_bit_output(enabled);
+}
+
+void protocol_set_8_bit_output(bool enabled) {
+  ProtocolSession* session = bound_session ? bound_session : &legacy_io_session;
+  protocol_session_set_8_bit_output(session, enabled);
+}
+
 static void bw_throttle_session(ProtocolSession* session, size_t bytes_written) {
   if (session->bwlimit == 0)
     return;
@@ -153,7 +222,8 @@ static ProtocolSession* legacy_session(int read_fd, int write_fd) {
       legacy_io_session.write_fd != target_write_fd) {
     legacy_io_session.read_fd = target_read_fd;
     legacy_io_session.write_fd = target_write_fd;
-    legacy_io_session.total_allocated_bytes = 0;
+    atomic_store(&legacy_io_session.total_allocated_bytes, 0);
+    legacy_io_session.max_alloc = DEFAULT_MAX_ALLOC;
     protocol_session_set_bwlimit(&legacy_io_session, global_bwlimit());
   } else if (legacy_io_session.bwlimit != global_bwlimit()) {
     protocol_session_set_bwlimit(&legacy_io_session, global_bwlimit());
@@ -184,7 +254,7 @@ static int deadline_remaining_ms(const struct timespec* deadline) {
 bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t data_size) {
   if (!data && data_size != 0)
     return false;
-  log_message(LOG_LEVEL_DEBUG, "    Sending n Data: %zu", data_size);
+  log_debug_message(LOG_DEBUG_IO, "    Sending n Data: %zu", data_size);
   if (!session)
     return false;
   int fd = session->write_fd;
@@ -228,19 +298,29 @@ bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t dat
     if (session->ssl)
       wait_events = POLLOUT;
   }
-  log_message(LOG_LEVEL_DEBUG, "    Send n Data: %zu", total_bytes_send);
+  log_debug_message(LOG_DEBUG_IO, "    Send n Data: %zu", total_bytes_send);
   return true;
 }
 
+bool protocol_receive_n_data_timed(ProtocolSession* session, void* data, size_t data_size,
+                                   int timeout_sec);
+
 bool protocol_receive_n_data(ProtocolSession* session, void* data, size_t data_size) {
-  log_message(LOG_LEVEL_DEBUG, "    Receiving n Data: %zu", data_size);
+  return protocol_receive_n_data_timed(session, data, data_size, RECEIVE_TIMEOUT_SEC);
+}
+
+bool protocol_receive_n_data_timed(ProtocolSession* session, void* data, size_t data_size,
+                                   int timeout_sec) {
+  log_debug_message(LOG_DEBUG_IO, "    Receiving n Data: %zu", data_size);
   if (!session)
     return false;
   int fd = session->read_fd;
+  if (timeout_sec <= 0)
+    timeout_sec = RECEIVE_TIMEOUT_SEC;
 
   struct timespec deadline;
   clock_gettime(CLOCK_MONOTONIC, &deadline);
-  deadline.tv_sec += RECEIVE_TIMEOUT_SEC;
+  deadline.tv_sec += timeout_sec;
 
   size_t total_bytes_received = 0;
   short wait_events = POLLIN;
@@ -249,7 +329,7 @@ bool protocol_receive_n_data(ProtocolSession* session, void* data, size_t data_s
       struct pollfd pfd = {.fd = fd, .events = wait_events};
       int poll_result = poll(&pfd, 1, deadline_remaining_ms(&deadline));
       if (poll_result == 0) {
-        log_message(LOG_LEVEL_ERROR, "Receive timeout after %ds", RECEIVE_TIMEOUT_SEC);
+        log_message(LOG_LEVEL_ERROR, "Receive timeout after %ds", timeout_sec);
         return false;
       }
       if (poll_result < 0) {
@@ -287,7 +367,7 @@ bool protocol_receive_n_data(ProtocolSession* session, void* data, size_t data_s
     if (session->ssl)
       wait_events = POLLIN;
   }
-  log_message(LOG_LEVEL_DEBUG, "    Received n Data: %zu", total_bytes_received);
+  log_debug_message(LOG_DEBUG_IO, "    Received n Data: %zu", total_bytes_received);
   return true;
 }
 
@@ -315,12 +395,43 @@ static const char* status_to_string(Status status) {
     return "ABORT";
   case STATUS_CHECK_BATCH:
     return "CHECK_BATCH";
+  case STATUS_MKDIR:
+    return "MKDIR";
+  case STATUS_APPEND:
+    return "APPEND";
+  case STATUS_APPEND_SIG:
+    return "APPEND_SIG";
+  case STATUS_APPEND_OK:
+    return "APPEND_OK";
+  case STATUS_APPEND_DATA:
+    return "APPEND_DATA";
+  case STATUS_HARDLINK:
+    return "HARDLINK";
+  case STATUS_SYMLINK:
+    return "SYMLINK";
+  case STATUS_SPECIAL:
+    return "SPECIAL";
+  case STATUS_DIR_TIMES:
+    return "DIR_TIMES";
+  case STATUS_AUTH_CHALLENGE:
+    return "AUTH_CHALLENGE";
+  case STATUS_AUTH_RESPONSE:
+    return "AUTH_RESPONSE";
+  case STATUS_AUTH_OK:
+    return "AUTH_OK";
+  case STATUS_AUTH_FAILED:
+    return "AUTH_FAILED";
   default:
     return "UNKNOWN";
   }
 }
 
-bool protocol_send_str(ProtocolSession* session, const char* data) {
+/* Shared string send/receive implementation.  `redact` selects whether the
+ * payload body is written to the LOG_DEBUG_PROTO debug log: daemon auth material
+ * (the username and the proof/signature fields) sets it so a --verbose log never
+ * captures a replayable credential, while every other string keeps its normal
+ * debug trace. */
+static bool protocol_send_str_impl(ProtocolSession* session, const char* data, bool redact) {
   if (data == NULL)
     return false;
   size_t size = strlen(data);
@@ -328,21 +439,27 @@ bool protocol_send_str(ProtocolSession* session, const char* data) {
     return false;
   if (!protocol_send_n_data(session, data, size))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Send String: %s", data);
+  if (redact) {
+    log_debug_message(LOG_DEBUG_PROTO, "Send String: <redacted>");
+  } else if (log_debug_enabled(LOG_DEBUG_PROTO)) {
+    char* escaped_data = output_escape(data, log_get_8_bit_output());
+    log_debug_message(LOG_DEBUG_PROTO, "Send String: %s",
+                      escaped_data ? escaped_data : "<allocation failed>");
+    free(escaped_data);
+  }
   return true;
 }
 
-char* protocol_receive_str(ProtocolSession* session) {
+static char* protocol_receive_str_impl(ProtocolSession* session, bool redact) {
   size_t size;
   if (!protocol_receive_n_data(session, &size, sizeof(size_t)))
     return NULL;
-  if (size > MAX_STRING_SIZE || size > SIZE_MAX - 1 ||
-      size + 1 > MAX_CONNECTION_MEMORY - session->total_allocated_bytes) {
+  if (size > MAX_STRING_SIZE || size > SIZE_MAX - 1) {
     log_message(LOG_LEVEL_ERROR, "String size %zu exceeds maximum %llu", size,
                 (unsigned long long)MAX_STRING_SIZE);
     return NULL;
   }
-  char* data = (char*)malloc(size + 1);
+  char* data = (char*)protocol_alloc_for_session(session, size + 1);
   if (data == NULL)
     return NULL;
   if (!protocol_receive_n_data(session, data, size)) {
@@ -355,11 +472,33 @@ char* protocol_receive_str(ProtocolSession* session) {
     return NULL;
   }
   data[size] = '\0';
-  session->total_allocated_bytes += size + 1;
-  log_message(LOG_LEVEL_DEBUG, "Received String: %s", data);
+  if (redact) {
+    log_debug_message(LOG_DEBUG_PROTO, "Received String: <redacted>");
+  } else if (log_debug_enabled(LOG_DEBUG_PROTO)) {
+    char* escaped_data = output_escape(data, log_get_8_bit_output());
+    log_debug_message(LOG_DEBUG_PROTO, "Received String: %s",
+                      escaped_data ? escaped_data : "<allocation failed>");
+    free(escaped_data);
+  }
   return data;
 }
 
+bool protocol_send_str(ProtocolSession* session, const char* data) {
+  return protocol_send_str_impl(session, data, false);
+}
+
+bool protocol_send_str_redacted(ProtocolSession* session, const char* data) {
+  return protocol_send_str_impl(session, data, true);
+}
+
+char* protocol_receive_str(ProtocolSession* session) {
+  return protocol_receive_str_impl(session, false);
+}
+
+char* protocol_receive_str_redacted(ProtocolSession* session) {
+  return protocol_receive_str_impl(session, true);
+}
+
 bool protocol_send_data(ProtocolSession* session, const Data* data) {
   if (!data || (!data->data && data->size != 0))
     return false;
@@ -370,7 +509,7 @@ bool protocol_send_data(ProtocolSession* session, const Data* data) {
     return false;
   if (!protocol_send_n_data(session, data->data, data_size))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Send %lld data", data_size);
+  log_debug_message(LOG_DEBUG_PROTO, "Send %lld data", data_size);
   return true;
 }
 
@@ -385,25 +524,29 @@ Data* protocol_receive_data_limited(ProtocolSession* session, unsigned long long
                 (unsigned long long)MAX_DATA_PAYLOAD_SIZE);
     return NULL;
   }
+  if (size > SIZE_MAX)
+    return NULL;
   size_t allocation_size = size == 0 ? 1 : (size_t)size;
-  if (allocation_size > MAX_CONNECTION_MEMORY - session->total_allocated_bytes) {
+  if (!protocol_reserve_memory(session, allocation_size)) {
     log_message(LOG_LEVEL_ERROR, "Per-connection memory limit exceeded (%llu + %llu > %llu)",
-                (unsigned long long)session->total_allocated_bytes, size,
+                (unsigned long long)atomic_load(&session->total_allocated_bytes), size,
                 (unsigned long long)MAX_CONNECTION_MEMORY);
     return NULL;
   }
-  void* data = malloc(allocation_size);
-  if (data == NULL)
-    return NULL;
-  if (!protocol_receive_n_data(session, data, (size_t)size)) {
-    free(data);
+  void* data = protocol_alloc_for_session(session, allocation_size);
+  if (data == NULL) {
+    protocol_release_memory_for_session(session, allocation_size);
     return NULL;
   }
-  session->total_allocated_bytes += allocation_size;
-  log_message(LOG_LEVEL_DEBUG, "Received %lld data", size);
+  if (!protocol_receive_n_data(session, data, (size_t)size)) {
+    free(data);
+    protocol_release_memory_for_session(session, allocation_size);
+    return NULL;
+  }
+  log_debug_message(LOG_DEBUG_PROTO, "Received %lld data", size);
   Data* result = data_create(data, (size_t)size);
   if (!result) {
-    session->total_allocated_bytes -= allocation_size;
+    protocol_release_memory_for_session(session, allocation_size);
     return NULL;
   }
   result->protocol_charge = allocation_size;
@@ -417,28 +560,39 @@ Data* protocol_receive_data(ProtocolSession* session) {
 bool protocol_send_int(ProtocolSession* session, int data) {
   if (!protocol_send_n_data(session, &data, sizeof(int)))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Send Int: %d", data);
+  log_debug_message(LOG_DEBUG_PROTO, "Send Int: %d", data);
   return true;
 }
 
 bool protocol_receive_int(ProtocolSession* session, int* data) {
   if (!protocol_receive_n_data(session, data, sizeof(int)))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Received Int: %d", *data);
+  log_debug_message(LOG_DEBUG_PROTO, "Received Int: %d", *data);
   return true;
 }
 
 bool protocol_send_status(ProtocolSession* session, Status status) {
   if (!protocol_send_n_data(session, &status, sizeof(Status)))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Send Status: %s", status_to_string(status));
+  log_debug_message(LOG_DEBUG_PROTO, "Send Status: %s", status_to_string(status));
   return true;
 }
 
 bool protocol_receive_status(ProtocolSession* session, Status* status) {
   if (!protocol_receive_n_data(session, status, sizeof(Status)))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Received Status: %s", status_to_string(*status));
+  log_debug_message(LOG_DEBUG_PROTO, "Received Status: %s", status_to_string(*status));
+  return true;
+}
+
+/* protocol_receive_status with an explicit per-message deadline (seconds).
+   Used where a single reply may legitimately take far longer than the default
+   60 s receive window - e.g. the sender waiting for the early-delete ACK after
+   the receiver committed a large (up to MAX_SERVER_DELETE_COUNT) deletion. */
+bool protocol_receive_status_timed(ProtocolSession* session, Status* status, int timeout_sec) {
+  if (!protocol_receive_n_data_timed(session, status, sizeof(Status), timeout_sec))
+    return false;
+  log_debug_message(LOG_DEBUG_PROTO, "Received Status: %s", status_to_string(*status));
   return true;
 }
 
@@ -448,6 +602,15 @@ bool send_str(int fd, const char* data) {
 char* receive_str(int fd) {
   return protocol_receive_str(legacy_session(fd, -1));
 }
+/* Redacted variants: identical framing, but the string body is never written to
+   the debug protocol log.  Used for daemon auth material (username, proof,
+   signature). */
+bool send_str_redacted(int fd, const char* data) {
+  return protocol_send_str_redacted(legacy_session(-1, fd), data);
+}
+char* receive_str_redacted(int fd) {
+  return protocol_receive_str_redacted(legacy_session(fd, -1));
+}
 bool send_data(int fd, const Data* data) {
   return protocol_send_data(legacy_session(-1, fd), data);
 }
@@ -469,3 +632,6 @@ bool send_status(int fd, Status status) {
 bool receive_status(int fd, Status* status) {
   return protocol_receive_status(legacy_session(fd, -1), status);
 }
+bool receive_status_timed(int fd, Status* status, int timeout_sec) {
+  return protocol_receive_status_timed(legacy_session(fd, -1), status, timeout_sec);
+}

src/shared/protocol.h

@@ -4,20 +4,34 @@
 #include "data.h"
 #include <stdbool.h>
 #include <stddef.h>
+#include <stdatomic.h>
 
 /* Maximum allowed string size for receive_str (64 KB) */
 #define MAX_STRING_SIZE (64 * 1024)
 
-/* Maximum allowed data payload size for receive_data (100 MB) */
-#define MAX_DATA_PAYLOAD_SIZE (100ULL * 1024 * 1024)
-/* Maximum uncompressed file payload accepted by the receiver. */
-#define MAX_RECEIVE_FILE_SIZE (64ULL * 1024 * 1024)
+/* Maximum uncompressed file payload accepted by the receiver's whole-file
+ * paths.  A single whole file is charged against the per-connection memory
+ * reservation (MAX_CONNECTION_MEMORY) and against the server allocation
+ * ceiling (MAX_SERVER_ALLOC), so this mirrors those 256 MB bounds rather than
+ * the older 64 MB chunk-era cap.  Chunk-serialized payloads keep their own
+ * 64 MB cap (MAX_CHUNK_SIZE). */
+#define MAX_RECEIVE_WHOLE_FILE_SIZE (256ULL * 1024 * 1024)
+
+/* Maximum allowed data payload size for receive_data (whole-file bound) */
+#define MAX_DATA_PAYLOAD_SIZE MAX_RECEIVE_WHOLE_FILE_SIZE
 
 /* Maximum chunk size (64 MB) — prevents unbounded allocation from the wire */
 #define MAX_CHUNK_SIZE (64ULL * 1024 * 1024)
 #define MAX_MANIFEST_ENTRIES (1024 * 1024)
 /* Aggregate bytes retained by one received deletion manifest. */
 #define MAX_MANIFEST_BYTES (16ULL * 1024 * 1024)
+#define DEFAULT_MAX_ALLOC (1ULL * 1024 * 1024 * 1024)
+/* Server policy ceiling for a client-provided allocation limit. */
+#define MAX_SERVER_ALLOC (256ULL * 1024 * 1024)
+/* 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. */
+#define MAX_CONNECTION_MEMORY (256ULL * 1024 * 1024)
 
 typedef struct ssl_st SSL;
 
@@ -35,7 +49,9 @@ typedef struct ProtocolSession {
   long long bw_tokens;
   long long bw_last_refill_sec;
   long bw_last_refill_nsec;
-  unsigned long long total_allocated_bytes;
+  atomic_ullong total_allocated_bytes;
+  bool eight_bit_output;
+  unsigned long long max_alloc;
 } ProtocolSession;
 
 typedef int Status;
@@ -51,7 +67,66 @@ enum NET_STATUS {
   STATUS_DELTA_DATA,
   STATUS_KEEPALIVE,
   STATUS_ABORT,
-  STATUS_CHECK_BATCH
+  STATUS_CHECK_BATCH,
+  /* An explicit directory entry (--dirs): the sender transmits only the path;
+   * the receiver creates the directory below the receive root. */
+  STATUS_MKDIR,
+  /* --append / --append-verify tail resume.  STATUS_APPEND is sent by the
+   * receiver after a per-file STATUS_CHECK when the existing destination file
+   * is SHORTER than the source and an append mode is negotiated: its payload is
+   * the resume offset (the number of prefix bytes already present), after which
+   * the sender answers either directly with STATUS_APPEND_DATA (plain --append,
+   * prefix not verified) or, for --append-verify, first with STATUS_APPEND_SIG
+   * carrying the xxHash64 of the source prefix; the receiver then replies
+   * STATUS_APPEND_OK (prefix matched -> sender transmits the tail) or
+   * STATUS_NEXT (prefix mismatch -> sender falls back to a full transfer).
+   * STATUS_APPEND_DATA carries the tail bytes (compressed data frame). */
+  STATUS_APPEND,
+  STATUS_APPEND_SIG,
+  STATUS_APPEND_OK,
+  STATUS_APPEND_DATA,
+  /* --hard-links/-H: a sibling (later member) of a source hard-link group.
+   * The sender transmits only the path, the run-local link-group id, and the
+   * first (data-carrying) member's destination-relative wire path; the receiver
+   * creates this entry as a hard link to the first member's installed file
+   * (falling back to a byte-identical copy if link() fails).  Protocol 2.12.0. */
+  STATUS_HARDLINK,
+  /* A symlink-type entry (-l/--links, -k/--copy-dirlinks' keep-as-symlink
+   * branch).  The sender transmits the destination path, the (sender-munged,
+   * if --munge-links) symlink target, and optional metadata; the receiver
+   * creates a symlink to the unmunged target beneath the receive root (see
+   * file_receive_symlink).  Protocol 2.13.0. */
+  STATUS_SYMLINK,
+  /* --devices / --specials (-D): a device or special node the sender wants
+   * recreated (not written from content).  Payload: destination path, the
+   * metadata frame (whose mode's S_IFMT bits carry the node kind), and two
+   * int32 rdev major/minor fields.  The receiver validates the kind and rdev,
+   * confines the node below the receive root, and recreates it (mknod/mkfifo),
+   * privilege-gating the mknod.  Protocol 2.13.0. */
+  STATUS_SPECIAL,
+  /* Directory-time superstructure (P7 Wave D, protocol 2.17.0): one or more
+   * trailing frames sent after all file data (and after the optional delete
+   * manifest) carrying the source directories' captured metadata so the
+   * receiver can apply directory mtimes/atimes AFTER all of a directory's
+   * children have been written.  Payload per frame: an int count, then count
+   * repetitions of (wire path string, metadata frame); an entry count larger
+   * than MAX_MANIFEST_ENTRIES is split across repeated frames.  The receiver
+   * defers the actual utimensat until its own delete/publish phase has
+   * committed, then skips the whole set when -O/--omit-dir-times is set. */
+  STATUS_DIR_TIMES,
+  /* Daemon SCRAM-SHA-256 authentication (A7 remediation, protocol 2.19.0).
+   * STATUS_AUTH_CHALLENGE: the server requires auth and is about to send the
+   * iteration count, the base64 salt and the base64 server nonce.
+   * STATUS_AUTH_RESPONSE: the client's reply, followed by the base64 client
+   * nonce and the base64 ClientProof.  STATUS_AUTH_OK: the client proof
+   * verified, followed by the base64 ServerSignature.  STATUS_AUTH_FAILED:
+   * a single generic refusal (unknown user, off-list user, wrong proof,
+   * missing/malformed credentials) after which the server closes without
+   * writing any data. */
+  STATUS_AUTH_CHALLENGE,
+  STATUS_AUTH_RESPONSE,
+  STATUS_AUTH_OK,
+  STATUS_AUTH_FAILED
 };
 
 void io_set_fds(int read_fd, int write_fd);
@@ -65,10 +140,22 @@ void protocol_session_bind(ProtocolSession* session);
 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);
+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);
+void protocol_set_8_bit_output(bool enabled);
 bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t data_size);
 bool protocol_receive_n_data(ProtocolSession* session, void* data, size_t data_size);
 bool protocol_send_str(ProtocolSession* session, const char* data);
 char* protocol_receive_str(ProtocolSession* session);
+/* Redacted string variants: identical wire framing to protocol_send_str /
+ * protocol_receive_str, but the payload body is replaced by `<redacted>` in the
+ * LOG_DEBUG_PROTO debug log.  Used for daemon auth material (the username and
+ * the proof/signature fields) so a --verbose log can never capture a credential
+ * that could be replayed. */
+bool protocol_send_str_redacted(ProtocolSession* session, const char* data);
+char* protocol_receive_str_redacted(ProtocolSession* session);
 bool protocol_send_data(ProtocolSession* session, const Data* data);
 Data* protocol_receive_data(ProtocolSession* session);
 Data* protocol_receive_data_limited(ProtocolSession* session, unsigned long long maximum_size);
@@ -81,6 +168,9 @@ bool receive_n_data(int file_descriptor, void* data, size_t data_size);
 
 bool send_str(int file_descriptor, const char* data);
 char* receive_str(int file_descriptor);
+/* Redacted fd-level string variants (see protocol_send_str_redacted). */
+bool send_str_redacted(int file_descriptor, const char* data);
+char* receive_str_redacted(int file_descriptor);
 bool send_data(int file_descriptor, const Data* data);
 Data* receive_data(int file_descriptor);
 Data* receive_data_limited(int file_descriptor, unsigned long long maximum_size);
@@ -88,5 +178,10 @@ bool send_int(int file_descriptor, int data);
 bool receive_int(int file_descriptor, int* data);
 bool send_status(int file_descriptor, Status status);
 bool receive_status(int file_descriptor, Status* status);
+/* receive_status with an explicit per-message deadline in seconds, instead of
+   the default RECEIVE_TIMEOUT_SEC.  A reply that may legitimately take longer
+   (e.g. the early-delete ACK after a large receiver-side deletion) must use
+   this so the sender does not abort after the deletion already committed. */
+bool receive_status_timed(int file_descriptor, Status* status, int timeout_sec);
 
 #endif

src/shared/stop_condition.c

@@ -0,0 +1,157 @@
+#include "stop_condition.h"
+#include <errno.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* Parse a strictly positive decimal integer: only ASCII digits, no leading
+ * whitespace, sign or trailing garbage. */
+static bool parse_positive_minutes(const char* value, long* out) {
+  if (!value || *value == '\0')
+    return false;
+  if (*value < '0' || *value > '9')
+    return false;
+  long v = 0;
+  for (const char* p = value; *p != '\0'; p++) {
+    if (*p < '0' || *p > '9')
+      return false;
+    int digit = *p - '0';
+    if (v > (LONG_MAX - digit) / 10)
+      return false;
+    v = v * 10 + digit;
+  }
+  if (v <= 0 || v > INT_MAX)
+    return false;
+  *out = v;
+  return true;
+}
+
+bool stop_parse_after_minutes(const char* value, int* out_minutes) {
+  if (!out_minutes)
+    return false;
+  long minutes = 0;
+  if (!parse_positive_minutes(value, &minutes))
+    return false;
+  *out_minutes = (int)minutes;
+  return true;
+}
+
+/* Two consecutive ASCII digits -> 0..99. */
+static bool parse_two_digits(const char* s, int* out) {
+  if (s[0] < '0' || s[0] > '9' || s[1] < '0' || s[1] > '9')
+    return false;
+  *out = (s[0] - '0') * 10 + (s[1] - '0');
+  return true;
+}
+
+bool stop_parse_at_time(const char* value, time_t now, time_t* out_deadline) {
+  if (!value || !out_deadline)
+    return false;
+
+  /* now+N[smhd]: N whole units from the current wall clock. */
+  if (strncmp(value, "now+", 4) == 0) {
+    const char* p = value + 4;
+    /* The count must be a bare non-negative digit run: reject leading
+       whitespace ('now+ 5s') and a leading sign ('now++5s'). */
+    if (*p < '0' || *p > '9')
+      return false;
+    errno = 0;
+    char* end = NULL;
+    long amount = strtol(p, &end, 10);
+    if (errno != 0 || end == p || amount < 0)
+      return false;
+    long unit_seconds;
+    switch (*end) {
+    case 's':
+      unit_seconds = 1;
+      break;
+    case 'm':
+      unit_seconds = 60;
+      break;
+    case 'h':
+      unit_seconds = 3600;
+      break;
+    case 'd':
+      unit_seconds = 86400;
+      break;
+    default:
+      return false;
+    }
+    if (end[1] != '\0')
+      return false;
+    if (amount > LONG_MAX / unit_seconds)
+      return false;
+    long long delta = (long long)amount * unit_seconds;
+    /* Guard against signed overflow of now + delta. */
+    if ((long long)now > 0 && delta > (long long)LLONG_MAX - (long long)now)
+      return false;
+    if ((long long)now < 0 && delta < (long long)LLONG_MIN - (long long)now)
+      return false;
+    *out_deadline = now + (time_t)delta;
+    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;
+
+  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;
+}
+
+StopCondition stop_condition_make(bool has_after, int after_minutes, bool has_at, time_t at_time,
+                                  struct timespec now_mono) {
+  StopCondition condition;
+  condition.has_monotonic = false;
+  condition.monotonic_deadline.tv_sec = 0;
+  condition.monotonic_deadline.tv_nsec = 0;
+  condition.has_wall = false;
+  condition.wall_deadline = 0;
+  if (has_after && after_minutes > 0) {
+    condition.has_monotonic = true;
+    condition.monotonic_deadline.tv_sec = now_mono.tv_sec + (time_t)after_minutes * 60;
+    condition.monotonic_deadline.tv_nsec = now_mono.tv_nsec;
+  }
+  if (has_at) {
+    condition.has_wall = true;
+    condition.wall_deadline = at_time;
+  }
+  return condition;
+}
+
+bool stop_condition_reached(const StopCondition* condition) {
+  if (!condition)
+    return false;
+  if (condition->has_wall && time(NULL) >= condition->wall_deadline)
+    return true;
+  if (condition->has_monotonic) {
+    struct timespec now;
+    if (clock_gettime(CLOCK_MONOTONIC, &now) != 0)
+      return false;
+    if (now.tv_sec > condition->monotonic_deadline.tv_sec ||
+        (now.tv_sec == condition->monotonic_deadline.tv_sec &&
+         now.tv_nsec >= condition->monotonic_deadline.tv_nsec))
+      return true;
+  }
+  return false;
+}

src/shared/stop_condition.h

@@ -0,0 +1,46 @@
+#ifndef STOP_CONDITION_H
+#define STOP_CONDITION_H
+
+#include <stdbool.h>
+#include <time.h>
+
+/* Client-only transfer stop conditions (--stop-after=MINS / --stop-at=TIME).
+ * Both are local sender-side deadlines: they are never serialized into the
+ * config frame and never bump PROTOCOL_VERSION.  A transfer checks the
+ * condition at natural chunk/file boundaries and, once reached, stops
+ * elegantly (everything already sent is finalized normally, exit 0).
+ *
+ * A condition combines an optional CLOCK_MONOTONIC instant (the relative
+ * --stop-after duration, immune to wall-clock changes) with an optional
+ * wall-clock instant (the absolute --stop-at form).  Either one being reached
+ * ends the transfer. */
+typedef struct StopCondition {
+  bool has_monotonic;
+  struct timespec monotonic_deadline;
+  bool has_wall;
+  time_t wall_deadline;
+} StopCondition;
+
+/* Parse --stop-after=MINS: a positive integer count of minutes.  Zero,
+ * negative, empty and non-numeric values are rejected.  Returns true when
+ * accepted and stores the value in *out_minutes. */
+bool stop_parse_after_minutes(const char* value, int* out_minutes);
+
+/* Parse --stop-at=TIME.  Accepted forms are HH:MM, HH:MM:SS and
+ * now+N[smhd] (seconds/minutes/hours/days from now).  The absolute forms are
+ * resolved against `now` (local wall clock) and written to *out_deadline; a
+ * time already in the past yields a deadline <= now ("stop immediately").
+ * Returns false on any malformed value. */
+bool stop_parse_at_time(const char* value, time_t now, time_t* out_deadline);
+
+/* Build the runtime condition at transfer start.  after_minutes is the
+ * relative --stop-after duration (<= 0 disables it); at_time is the absolute
+ * --stop-at deadline (only consulted when has_at is true); now_mono is the
+ * CLOCK_MONOTONIC reading at start. */
+StopCondition stop_condition_make(bool has_after, int after_minutes, bool has_at, time_t at_time,
+                                  struct timespec now_mono);
+
+/* True once either deadline has passed (wall clock first, then monotonic). */
+bool stop_condition_reached(const StopCondition* condition);
+
+#endif

src/shared/transport_ssh.c

@@ -3,9 +3,11 @@
 #include "utils.h"
 #include <fcntl.h>
 #include <stdio.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
+#include <sys/time.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
@@ -15,6 +17,14 @@ typedef struct {
   char* remote_path;
 } RemoteDest;
 
+/* Writes the exec-failure marker and exits the child.  Marked noreturn so
+ * static analyzers prove the caller's error path never falls through. */
+__attribute__((noreturn)) static void ssh_child_setup_failed(int status_fd) {
+  ssize_t wret = write(status_fd, "x", 1);
+  (void)wret;
+  _exit(1);
+}
+
 static void remote_dest_destroy(RemoteDest* r) {
   free(r->user);
   free(r->host);
@@ -68,10 +78,215 @@ static int parse_remote_dest(const char* dest, RemoteDest* r) {
   return 0;
 }
 
-Client* client_connect_ssh(const char* destination, int port, const char* server_path) {
+char* ssh_build_remote_command(const char* server_path, bool old_args, char* const* remote_options,
+                               int remote_option_count) {
+  const char* path = server_path ? server_path : "fastsync-server";
+  const char* suffix = " --stdio";
+
+  /* Each --remote-option=OPT is appended after " --stdio" as one shell word,
+     escaped with the SAME single-quote boundary used for the server path, so a
+     value containing shell metacharacters (; & | ` $ ()) can never break out of
+     the quoting to inject an unrelated remote command.  Values are already
+     validated at CLI parse time (non-empty, no control characters); this layer
+     only adds the escaping boundary. */
+  size_t path_len = strlen(path);
+  size_t suffix_len = strlen(suffix);
+
+  /* The base command: the server path is ALWAYS quoted as one single-quoted
+     shell word (remote options below reuse the same escaping), then
+     " --stdio".  Quoting the path is the only injection-safe construction: an
+     unquoted path would carry shell metacharacters straight into the remote
+     shell command.  --old-args is kept for CLI/ABI compatibility but no longer
+     disables that protection. */
+  (void)old_args;
+  size_t quote_count = 0;
+  for (const char* p = path; *p; p++)
+    if (*p == '\'')
+      quote_count++;
+  if (path_len > SIZE_MAX - suffix_len - 4 ||
+      quote_count > (SIZE_MAX - path_len - suffix_len - 4) / 4)
+    return NULL;
+  size_t command_len = path_len + quote_count * 4 + suffix_len + 4;
+
+  /* Add each remote option, escaped as one single-quoted word:
+     " '<body>'", i.e. 1 leading space + 1 open quote + body (len + 3 per
+     embedded single quote) + 1 close quote = len + q*3 + 3 bytes.
+     Defense-in-depth against a non-conforming caller: never forward an empty
+     or control-character value, independent of the CLI validation. */
+  for (int i = 0; i < remote_option_count; i++) {
+    const char* opt = remote_options[i];
+    if (!opt || opt[0] == '\0')
+      return NULL;
+    size_t len = 0, q = 0;
+    for (const char* p = opt; *p; p++) {
+      /* Defense-in-depth: never forward a control character (newline/CR/etc.)
+         that could break the single-quoted shell word regardless of the remote
+         shell, independent of the CLI validation. */
+      if ((unsigned char)*p < 0x20 || (unsigned char)*p == 0x7f)
+        return NULL;
+      if (*p == '\'')
+        q++;
+      len++;
+    }
+    if (len > SIZE_MAX - q * 3 || len + q * 3 + 3 > SIZE_MAX - command_len)
+      return NULL;
+    command_len += len + q * 3 + 3;
+  }
+  command_len += 1; /* NUL */
+
+  char* command = malloc(command_len);
+  if (!command)
+    return NULL;
+  char* out = command;
+  *out++ = '\'';
+  for (const char* p = path; *p; p++) {
+    if (*p == '\'') {
+      memcpy(out, "'\\''", 4);
+      out += 4;
+    } else {
+      *out++ = *p;
+    }
+  }
+  *out++ = '\'';
+  memcpy(out, suffix, suffix_len + 1);
+  out += suffix_len;
+  for (int i = 0; i < remote_option_count; i++) {
+    const char* opt = remote_options[i];
+    *out++ = ' ';
+    *out++ = '\'';
+    for (const char* p = opt; *p; p++) {
+      if (*p == '\'') {
+        memcpy(out, "'\\''", 4);
+        out += 4;
+      } else {
+        *out++ = *p;
+      }
+    }
+    *out++ = '\'';
+  }
+  *out = '\0';
+  return command;
+}
+
+/* A heap-owned, NULL-terminated argv whose every string is separately malloc'd
+ * (str_dup'd) so a caller can free arbitrary slots, including argv[0]. */
+char** ssh_build_client_argv(const char* rsh_command, int port, const char* userhost,
+                             const char* remote_command) {
+  const char* rsh = (rsh_command && *rsh_command) ? rsh_command : "ssh";
+
+  /* Whitespace-split the remote-shell command into the leading argv words so
+   * "-e 'ssh -p 2222'" (or "--rsh=ssh -p 2222") works like rsync's rsh.  A
+   * blank command falls back to the default "ssh". */
+  char* copy = str_dup(rsh);
+  if (!copy)
+    return NULL;
+  char* save = NULL;
+  int nwords = 0;
+  char** words = NULL;
+  for (char* tok = strtok_r(copy, " \t", &save); tok; tok = strtok_r(NULL, " \t", &save)) {
+    char** grown = realloc(words, (size_t)(nwords + 1) * sizeof(char*));
+    if (!grown) {
+      for (int i = 0; i < nwords; i++)
+        free(words[i]);
+      free(words);
+      free(copy);
+      return NULL;
+    }
+    words = grown;
+    words[nwords] = str_dup(tok);
+    if (!words[nwords]) {
+      for (int i = 0; i < nwords; i++)
+        free(words[i]);
+      free(words);
+      free(copy);
+      return NULL;
+    }
+    nwords++;
+  }
+  free(copy);
+  if (nwords == 0) {
+    words = malloc(sizeof(char*));
+    if (!words)
+      return NULL;
+    words[0] = str_dup("ssh");
+    if (!words[0]) {
+      free(words);
+      return NULL;
+    }
+    nwords = 1;
+  }
+
+  /* Fixed tail: three -o pairs (6) + optional -p/value (2) + user@host +
+   * remote command + terminating NULL. */
+  int port_extra = (port > 0 && port != 22) ? 2 : 0;
+  size_t total = (size_t)nwords + 6 + (size_t)port_extra + 3;
+  char** argv = calloc(total, sizeof(char*));
+  if (!argv) {
+    for (int i = 0; i < nwords; i++)
+      free(words[i]);
+    free(words);
+    return NULL;
+  }
+  int ac = 0;
+  for (int i = 0; i < nwords; i++)
+    argv[ac++] = words[i];
+  free(words);
+
+  char* tail[] = {"-o", "Compression=no",
+                  "-o", "ControlMaster=auto",
+                  "-o", "ControlPath=~/.cache/fastsync-%r@%h:%p"};
+  for (size_t i = 0; i < sizeof(tail) / sizeof(tail[0]); i++) {
+    argv[ac] = str_dup(tail[i]);
+    if (!argv[ac])
+      goto fail_argv;
+    ac++;
+  }
+  if (port_extra) {
+    char port_str[16];
+    snprintf(port_str, sizeof(port_str), "%d", port);
+    argv[ac] = str_dup("-p");
+    if (!argv[ac])
+      goto fail_argv;
+    ac++;
+    argv[ac] = str_dup(port_str);
+    if (!argv[ac])
+      goto fail_argv;
+    ac++;
+  }
+  argv[ac] = str_dup(userhost);
+  if (!argv[ac])
+    goto fail_argv;
+  ac++;
+  argv[ac] = str_dup(remote_command);
+  if (!argv[ac])
+    goto fail_argv;
+  ac++;
+  argv[ac] = NULL;
+  return argv;
+
+fail_argv:
+  for (int i = 0; i < ac; i++)
+    free(argv[i]);
+  free(argv);
+  return NULL;
+}
+
+void ssh_free_client_argv(char** argv) {
+  if (!argv)
+    return;
+  for (int i = 0; argv[i]; i++)
+    free(argv[i]);
+  free(argv);
+}
+
+Client* client_connect_ssh(const char* destination, int port, const char* server_path,
+                           bool old_args, const char* rsh_command, bool blocking_io,
+                           char* const* remote_options, int remote_option_count) {
   RemoteDest r;
   if (parse_remote_dest(destination, &r) != 0) {
-    fprintf(stderr, "Invalid remote destination: %s\n", destination);
+    char* escaped = output_escape(destination, false);
+    fprintf(stderr, "Invalid remote destination: %s\n", escaped ? escaped : "<allocation failed>");
+    free(escaped);
     return NULL;
   }
 
@@ -88,6 +303,17 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
   setsockopt(sv[1], SOL_SOCKET, SO_SNDBUF, &buf_size, sizeof(buf_size));
   setsockopt(sv[1], SOL_SOCKET, SO_RCVBUF, &buf_size, sizeof(buf_size));
 
+  /* By default the SSH transport socket gets the same read/write timeout as
+   * the TCP transport so a wedged remote shell cannot hang forever.  With
+   * --blocking-io the timeouts are skipped and the socket blocks naturally. */
+  if (!blocking_io) {
+    struct timeval tv;
+    tv.tv_sec = tcp_get_timeout_sec();
+    tv.tv_usec = 0;
+    setsockopt(sv[0], SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
+    setsockopt(sv[0], SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv));
+  }
+
   int exec_pipe[2];
   if (pipe(exec_pipe) < 0) {
     log_perror("pipe failed");
@@ -111,11 +337,12 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
   if (pid == 0) {
     close(sv[0]);
     close(exec_pipe[0]);
-    fcntl(exec_pipe[1], F_SETFD, FD_CLOEXEC);
-    if (sv[1] != STDIN_FILENO)
-      dup2(sv[1], STDIN_FILENO);
-    if (sv[1] != STDOUT_FILENO)
-      dup2(sv[1], STDOUT_FILENO);
+    if (fcntl(exec_pipe[1], F_SETFD, FD_CLOEXEC) < 0)
+      ssh_child_setup_failed(exec_pipe[1]);
+    if (sv[1] != STDIN_FILENO && dup2(sv[1], STDIN_FILENO) < 0)
+      ssh_child_setup_failed(exec_pipe[1]);
+    if (sv[1] != STDOUT_FILENO && dup2(sv[1], STDOUT_FILENO) < 0)
+      ssh_child_setup_failed(exec_pipe[1]);
     if (sv[1] > 1)
       close(sv[1]);
 
@@ -126,36 +353,25 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
       ssh_user_len = strlen(r.host) + 1;
     char* ssh_user = malloc(ssh_user_len);
     if (!ssh_user)
-      _exit(1);
+      ssh_child_setup_failed(exec_pipe[1]);
     if (r.user && r.user[0] != '\0')
       snprintf(ssh_user, ssh_user_len, "%s@%s", r.user, r.host);
     else
       snprintf(ssh_user, ssh_user_len, "%s", r.host);
 
-    char* ssh_argv[16];
-    int ac = 0;
-    char port_str[16];
-    ssh_argv[ac++] = "ssh";
-    ssh_argv[ac++] = "-o";
-    ssh_argv[ac++] = "Compression=no";
-    ssh_argv[ac++] = "-o";
-    ssh_argv[ac++] = "ControlMaster=auto";
-    ssh_argv[ac++] = "-o";
-    ssh_argv[ac++] = "ControlPath=~/.cache/fastsync-%r@%h:%p";
-    if (port > 0 && port != 22) {
-      ssh_argv[ac++] = "-p";
-      snprintf(port_str, sizeof(port_str), "%d", port);
-      ssh_argv[ac++] = port_str;
-    }
-    ssh_argv[ac++] = ssh_user;
-    ssh_argv[ac++] = (char*)(server_path ? server_path : "fastsync-server");
-    ssh_argv[ac++] = "--stdio";
-    ssh_argv[ac] = NULL;
-    execvp("ssh", ssh_argv);
-    log_perror("exec of ssh failed");
-    ssize_t wret = write(exec_pipe[1], "x", 1);
-    (void)wret;
-    _exit(1);
+    char* remote_command =
+        ssh_build_remote_command(server_path, old_args, remote_options, remote_option_count);
+    if (!remote_command)
+      ssh_child_setup_failed(exec_pipe[1]);
+    char** ssh_argv = ssh_build_client_argv(rsh_command, port, ssh_user, remote_command);
+    free(ssh_user);
+    free(remote_command);
+    if (!ssh_argv)
+      ssh_child_setup_failed(exec_pipe[1]);
+    execvp(ssh_argv[0], ssh_argv);
+    log_perror("exec of remote shell failed");
+    ssh_free_client_argv(ssh_argv);
+    ssh_child_setup_failed(exec_pipe[1]);
   }
 
   close(sv[1]);
@@ -165,12 +381,15 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
   ssize_t n = read(exec_pipe[0], &exec_status, 1);
   close(exec_pipe[0]);
 
-  if (n > 0) {
+  if (n != 0) {
     close(sv[0]);
     waitpid(pid, NULL, 0);
     remote_dest_destroy(&r);
+    const char* path = server_path ? server_path : "fastsync-server";
+    char* escaped = output_escape(path, false);
     fprintf(stderr, "Error: could not launch '%s --stdio' on remote\n",
-            server_path ? server_path : "fastsync-server");
+            escaped ? escaped : "<allocation failed>");
+    free(escaped);
     return NULL;
   }
 

src/shared/transport_ssh.h

@@ -3,6 +3,26 @@
 
 #include "transport_tcp.h"
 
-Client* client_connect_ssh(const char* destination, int port, const char* server_path);
+Client* client_connect_ssh(const char* destination, int port, const char* server_path,
+                           bool old_args, const char* rsh_command, bool blocking_io,
+                           char* const* remote_options, int remote_option_count);
+/* Build the escaped remote-shell command string (the server program path always
+ * quoted as one remote-shell word, followed by ` --stdio` and each
+ * --remote-option value appended as an individually single-quoted shell word).
+ * `old_args` is accepted for CLI/ABI compatibility but no longer disables
+ * quoting: the path is always escaped so a metacharacter-bearing
+ * --rsync-path can never be interpreted by the remote shell.  Every
+ * --remote-option value is individually escaped with the '\'' sequence and
+ * values with empty/control characters are rejected at the CLI parse layer. */
+char* ssh_build_remote_command(const char* server_path, bool old_args, char* const* remote_options,
+                               int remote_option_count);
+/* Build the NULL-terminated child argv for the remote-shell client (argv[0] is
+ * the exec/execvp program).  rsh_command is whitespace-split into leading argv
+ * words (NULL or "" selects the default "ssh"); the standard -o family, the
+ * optional -p port, the user@host and the remote command are appended.  Every
+ * string (including argv[0]) is heap-owned; free with ssh_free_client_argv. */
+char** ssh_build_client_argv(const char* rsh_command, int port, const char* userhost,
+                             const char* remote_command);
+void ssh_free_client_argv(char** argv);
 
 #endif

src/shared/transport_tcp.c

@@ -1,9 +1,12 @@
 #include "transport_tcp.h"
 #include "log.h"
 #include "protocol.h"
+#include "utils.h"
 #include <arpa/inet.h>
 #include <errno.h>
 #include <netdb.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
 #include <openssl/ssl.h>
 #include <signal.h>
 #include <stdio.h>
@@ -27,47 +30,91 @@ static void sigchld_handler(int sig) {
   errno = saved_errno;
 }
 
-Server* server_create(int port) {
+/* Map a listen socket's address to its numeric port for logging, independent
+ * of whether it is an IPv4 or IPv6 sockaddr. */
+static unsigned short server_address_port(const struct sockaddr_storage* addr) {
+  if (addr->ss_family == AF_INET6)
+    return ntohs(((const struct sockaddr_in6*)addr)->sin6_port);
+  if (addr->ss_family == AF_INET)
+    return ntohs(((const struct sockaddr_in*)addr)->sin_port);
+  return 0;
+}
+
+Server* server_create_ex(int port, const ServerBindOptions* bind_opts) {
   Server* server = (Server*)malloc(sizeof(Server));
   if (server == NULL) {
     log_perror("Could not allocate space for Server");
     return NULL;
   }
 
-  int file_descriptor = socket(AF_INET, SOCK_STREAM, 0);
-  if (file_descriptor < 0) {
-    log_perror("Could not create Socket!");
-    free(server);
-    return NULL;
-  }
-  server->file_descriptor = file_descriptor;
-  int opt = 1;
-  if (setsockopt(server->file_descriptor, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) {
-    log_perror("Error setting a socket option!");
-    close(server->file_descriptor);
+  /* Effective address family.  preserve the historical default (IPv4 wildcard)
+   * when neither --address nor -4/-6 were given. */
+  int family = (bind_opts && bind_opts->family != AF_UNSPEC) ? bind_opts->family : AF_INET;
+  const char* bind_address = bind_opts ? bind_opts->bind_address : NULL;
+
+  struct addrinfo hints;
+  memset(&hints, 0, sizeof(hints));
+  hints.ai_family = family;
+  hints.ai_socktype = SOCK_STREAM;
+  hints.ai_protocol = IPPROTO_TCP;
+  hints.ai_flags = AI_PASSIVE;
+
+  char port_str[16];
+  snprintf(port_str, sizeof(port_str), "%d", port);
+
+  struct addrinfo* result = NULL;
+  int err = getaddrinfo(bind_address, port_str, &hints, &result);
+  if (err != 0 || result == NULL) {
+    char* escaped = bind_address ? output_escape(bind_address, false) : NULL;
+    fprintf(stderr, "Could not resolve bind address %s (%s)\n", escaped ? escaped : "(wildcard)",
+            gai_strerror(err));
+    free(escaped);
     free(server);
     return NULL;
   }
 
-  server->address.sin_family = AF_INET;
-  server->address.sin_addr.s_addr = INADDR_ANY;
-  server->address.sin_port = htons(port);
-  server->address_length = sizeof(server->address);
+  int file_descriptor = -1;
+  struct addrinfo* rp;
+  for (rp = result; rp != NULL; rp = rp->ai_next) {
+    file_descriptor = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
+    if (file_descriptor < 0)
+      continue;
+    int opt = 1;
+    if (setsockopt(file_descriptor, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) != 0) {
+      log_perror("Error setting a socket option!");
+      close(file_descriptor);
+      file_descriptor = -1;
+      continue;
+    }
+    if (bind(file_descriptor, rp->ai_addr, (socklen_t)rp->ai_addrlen) == 0) {
+      memset(&server->address, 0, sizeof(server->address));
+      memcpy(&server->address, rp->ai_addr, rp->ai_addrlen);
+      server->address_length = rp->ai_addrlen;
+      break;
+    }
+    log_perror("Could not bind server address");
+    close(file_descriptor);
+    file_descriptor = -1;
+  }
+  freeaddrinfo(result);
+
+  if (file_descriptor < 0) {
+    free(server);
+    return NULL;
+  }
+
+  server->file_descriptor = file_descriptor;
   server->ssl_ctx = NULL;
   server->max_connections = 100;
   server->active_connections = 0;
 
-  if (bind(server->file_descriptor, (struct sockaddr*)&server->address, server->address_length) <
-      0) {
-    log_perror("Could not bind server");
-    close(server->file_descriptor);
-    free(server);
-    return NULL;
-  }
-
   return server;
 }
 
+Server* server_create(int port) {
+  return server_create_ex(port, NULL);
+}
+
 void server_delete(Server** server) {
   if (server == NULL || *server == NULL)
     return;
@@ -125,7 +172,7 @@ static void plain_child_fn(int fd, void* ctx) {
 }
 
 bool server_listen(Server* server, void (*handler)(int file_descriptor)) {
-  log_message(LOG_LEVEL_INFO, "Start Listening on Port: %d", ntohs(server->address.sin_port));
+  log_message(LOG_LEVEL_INFO, "Start Listening on Port: %d", server_address_port(&server->address));
   struct plain_ctx ctx = {handler};
   accept_loop(server, plain_child_fn, &ctx, "Received Connection");
   return true;
@@ -133,7 +180,8 @@ bool server_listen(Server* server, void (*handler)(int file_descriptor)) {
 
 void server_accept_loop(Server* server, void (*child_fn)(int, void*), void* child_ctx,
                         const char* log_fmt) {
-  log_message(LOG_LEVEL_INFO, "Start TLS Listening on Port: %d", ntohs(server->address.sin_port));
+  log_message(LOG_LEVEL_INFO, "Start TLS Listening on Port: %d",
+              server_address_port(&server->address));
   accept_loop(server, child_fn, child_ctx, log_fmt);
 }
 
@@ -177,11 +225,100 @@ Client* client_create() {
   return client;
 }
 
-bool tcp_connect_socket(Client* client, char* host, int port) {
+int tcp_connect_family(bool ipv4, bool ipv6) {
+  if (ipv4)
+    return AF_INET;
+  if (ipv6)
+    return AF_INET6;
+  return AF_UNSPEC;
+}
+
+/* The socket-option apply layer maps an allowlist SockOptId to the concrete
+ * level/optname pair and applies it with the correct (int) value type.  The
+ * allowlist bounds what can ever reach this point, so the id-to-name mapping
+ * is total for every SOCKOPT_* value. */
+static int tcp_sockopt_level(SockOptId id) {
+  return id == SOCKOPT_TCP_NODELAY ? IPPROTO_TCP : SOL_SOCKET;
+}
+
+static int tcp_sockopt_name(SockOptId id) {
+  switch (id) {
+  case SOCKOPT_TCP_NODELAY:
+    return TCP_NODELAY;
+  case SOCKOPT_SO_KEEPALIVE:
+    return SO_KEEPALIVE;
+  case SOCKOPT_SO_RCVBUF:
+    return SO_RCVBUF;
+  case SOCKOPT_SO_SNDBUF:
+    return SO_SNDBUF;
+  case SOCKOPT_SO_REUSEADDR:
+    return SO_REUSEADDR;
+  default:
+    return -1;
+  }
+}
+
+static bool tcp_apply_sockopts(int fd, const SockOptEntry* sockopts, int sockopt_count) {
+  for (int i = 0; i < sockopt_count; i++) {
+    int name = tcp_sockopt_name(sockopts[i].id);
+    if (name < 0) { /* unreachable for a validated allowlist, but stay defensive */
+      log_message(LOG_LEVEL_ERROR, "Unsupported socket option requested");
+      return false;
+    }
+    int value = sockopts[i].value;
+    if (setsockopt(fd, tcp_sockopt_level(sockopts[i].id), name, &value, sizeof(value)) != 0) {
+      log_perror("Could not apply socket option");
+      return false;
+    }
+  }
+  return true;
+}
+
+/* Resolve an explicit --address source/bind address into a sockaddr once, so
+ * the per-candidate connect loop can bind() the outgoing socket to it.  The
+ * family follows the same -4/-6 hints as the destination resolution, so a
+ * forced family selects a matching local address; returns 0 on success. */
+static int resolve_bind_address(const char* addr, int family, struct sockaddr_storage* out,
+                                socklen_t* out_len, int* out_family) {
+  struct addrinfo hints;
+  memset(&hints, 0, sizeof(hints));
+  hints.ai_family = family; /* AF_UNSPEC when no -4/-6 */
+  hints.ai_socktype = SOCK_STREAM;
+  hints.ai_protocol = IPPROTO_TCP;
+
+  struct addrinfo* result = NULL;
+  int err = getaddrinfo(addr, NULL, &hints, &result);
+  if (err != 0 || result == NULL) {
+    char* escaped = output_escape(addr, false);
+    fprintf(stderr, "Could not resolve --address %s (%s)\n",
+            escaped ? escaped : "<allocation failed>", gai_strerror(err));
+    free(escaped);
+    return -1;
+  }
+  struct addrinfo* rp;
+  bool found = false;
+  for (rp = result; rp != NULL; rp = rp->ai_next) {
+    if (family != AF_UNSPEC && rp->ai_family != family)
+      continue;
+    memcpy(out, rp->ai_addr, rp->ai_addrlen);
+    *out_len = (socklen_t)rp->ai_addrlen;
+    *out_family = rp->ai_family;
+    found = true;
+    break;
+  }
+  freeaddrinfo(result);
+  return found ? 0 : -1;
+}
+
+bool tcp_connect_socket_ex(Client* client, const char* host, int port,
+                           const TcpConnectOptions* opts) {
   struct addrinfo hints;
   struct addrinfo* result;
   memset(&hints, 0, sizeof(hints));
-  hints.ai_family = AF_UNSPEC;
+  /* TcpConnectOptions.family already encodes -4/-6 (or AF_UNSPEC); feed it
+   * straight into the getaddrinfo hints so the destination resolution is
+   * (optionally) pinned to one address family. */
+  hints.ai_family = opts ? opts->family : AF_UNSPEC;
   hints.ai_socktype = SOCK_STREAM;
   hints.ai_protocol = IPPROTO_TCP;
 
@@ -190,10 +327,25 @@ bool tcp_connect_socket(Client* client, char* host, int port) {
 
   int err = getaddrinfo(host, port_str, &hints, &result);
   if (err != 0 || result == NULL) {
-    fprintf(stderr, "Could not resolve host: %s (%s)\n", host, gai_strerror(err));
+    char* escaped_host = output_escape(host, false);
+    fprintf(stderr, "Could not resolve host: %s (%s)\n",
+            escaped_host ? escaped_host : "<allocation failed>", gai_strerror(err));
+    free(escaped_host);
     return false;
   }
 
+  /* Resolve the optional --address source address once up front. */
+  struct sockaddr_storage bind_addr;
+  socklen_t bind_addr_len = 0;
+  int bind_addr_family = 0;
+  if (opts && opts->bind_address) {
+    if (resolve_bind_address(opts->bind_address, hints.ai_family, &bind_addr, &bind_addr_len,
+                             &bind_addr_family) != 0) {
+      freeaddrinfo(result);
+      return false;
+    }
+  }
+
   struct addrinfo* rp;
   bool connected = false;
   for (rp = result; rp != NULL; rp = rp->ai_next) {
@@ -204,12 +356,33 @@ bool tcp_connect_socket(Client* client, char* host, int port) {
     if (client->file_descriptor < 0)
       continue;
 
+    if (opts && opts->sockopt_count > 0 &&
+        !tcp_apply_sockopts(client->file_descriptor, opts->sockopts, opts->sockopt_count)) {
+      close(client->file_descriptor);
+      client->file_descriptor = -1;
+      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));
 
+    if (bind_addr_family != 0) {
+      if (rp->ai_family != bind_addr_family) {
+        close(client->file_descriptor);
+        client->file_descriptor = -1;
+        continue;
+      }
+      if (bind(client->file_descriptor, (struct sockaddr*)&bind_addr, bind_addr_len) != 0) {
+        log_perror("Could not bind outgoing socket to --address");
+        close(client->file_descriptor);
+        client->file_descriptor = -1;
+        break;
+      }
+    }
+
     memcpy(&client->address, rp->ai_addr, rp->ai_addrlen);
     client->address_length = rp->ai_addrlen;
 
@@ -229,8 +402,19 @@ bool tcp_connect_socket(Client* client, char* host, int port) {
   return true;
 }
 
-bool client_connect(Client* client, char* host, int port) {
-  if (!tcp_connect_socket(client, host, port))
+bool tcp_connect_socket(Client* client, const char* host, int port) {
+  return tcp_connect_socket_ex(client, host, port, NULL);
+}
+
+bool client_connect_ex(Client* client, const char* host, int port, const TcpConnectOptions* opts) {
+  if (!tcp_connect_socket_ex(client, host, port, opts))
+    return false;
+  tcp_apply_socket_timeout(client->file_descriptor);
+  return true;
+}
+
+bool client_connect(Client* client, const char* host, int port) {
+  if (!tcp_connect_socket_ex(client, host, port, NULL))
     return false;
   tcp_apply_socket_timeout(client->file_descriptor);
   return true;

src/shared/transport_tcp.h

@@ -1,12 +1,14 @@
 #ifndef TRANSPORT_TCP_H
 #define TRANSPORT_TCP_H
 
+#include "config.h"
+#include <netdb.h>
 #include <netinet/in.h>
 #include <stdbool.h>
 #include <sys/types.h>
 
 typedef struct Server {
-  struct sockaddr_in address;
+  struct sockaddr_storage address;
   unsigned int address_length;
   int file_descriptor;
   void* ssl_ctx;
@@ -23,18 +25,46 @@ typedef struct Client {
   void* ssl_ctx;
 } Client;
 
+/* Options controlling the server's listening bind (/--address, -4/-6).  When
+ * bind_address is NULL and family is AF_UNSPEC the existing default is used:
+ * an IPv4 wildcard (INADDR_ANY). */
+typedef struct {
+  const char* bind_address; /* explicit address to bind, or NULL for wildcard */
+  int family;               /* AF_INET / AF_INET6, or AF_UNSPEC to use the default */
+} ServerBindOptions;
+
+/* Options controlling an outgoing client connect (--address, -4/-6,
+ * --sockopts).  All fields are client/connection-level and never cross the
+ * wire config frame. */
+typedef struct {
+  const char* bind_address;     /* --address: local source address to bind, or NULL */
+  int family;                   /* AF_INET / AF_INET6 / AF_UNSPEC (from -4 / -6) */
+  const SockOptEntry* sockopts; /* --sockopts allowlist entries */
+  int sockopt_count;
+} TcpConnectOptions;
+
+Server* server_create_ex(int port, const ServerBindOptions* bind_opts);
 Server* server_create(int port);
 bool server_listen(Server* server, void (*handler)(int file_descriptor));
 void server_accept_loop(Server* server, void (*child_fn)(int, void*), void* child_ctx,
                         const char* log_fmt);
 void server_delete(Server** server);
 Client* client_create();
-bool client_connect(Client* client, char* host, int port);
-bool tcp_connect_socket(Client* client, char* host, int port);
+bool client_connect_ex(Client* client, const char* host, int port, const TcpConnectOptions* opts);
+bool client_connect(Client* client, const char* host, int port);
+bool tcp_connect_socket_ex(Client* client, const char* host, int port,
+                           const TcpConnectOptions* opts);
+bool tcp_connect_socket(Client* client, const char* host, int port);
 void client_disconnect(Client* client);
 void client_delete(Client* client);
 void tcp_set_timeouts(int timeout_sec, int contimeout_sec);
 int tcp_get_contimeout_sec(void);
 int tcp_get_timeout_sec(void);
 
+/* Resolve -4/-6 flags to a getaddrinfo ai_family value.  ipv4 wins over ipv6;
+ * when neither is set it returns AF_UNSPEC.  0 means "no preference" and is
+ * therefore never returned; callers that need the "no explicit flag" sentinel
+ * compare the flags directly. */
+int tcp_connect_family(bool ipv4, bool ipv6);
+
 #endif

src/shared/transport_tls.c

@@ -2,6 +2,7 @@
 #include "log.h"
 #include "protocol.h"
 #include "transport_tcp.h"
+#include "utils.h"
 #include <arpa/inet.h>
 #include <openssl/err.h>
 #include <openssl/ssl.h>
@@ -47,6 +48,15 @@ static SSL_CTX* create_ssl_ctx(bool is_server, const char* cert, const char* key
     return NULL;
   }
 
+  /* Harden the context: never negotiate TLS compression (the CRIME attack
+   * vector) and never honour a post-handshake renegotiation request.
+   * SSL_OP_NO_RENEGOTIATION is only available from OpenSSL 1.1.1, so it is
+   * guarded to keep older headers building. */
+  SSL_CTX_set_options(ctx, SSL_OP_NO_COMPRESSION);
+#ifdef SSL_OP_NO_RENEGOTIATION
+  SSL_CTX_set_options(ctx, SSL_OP_NO_RENEGOTIATION);
+#endif
+
   if (SSL_CTX_set_min_proto_version(ctx, TLS1_2_VERSION) != 1) {
     SSL_CTX_free(ctx);
     return NULL;
@@ -65,13 +75,19 @@ static SSL_CTX* create_ssl_ctx(bool is_server, const char* cert, const char* key
       return NULL;
     }
     if (SSL_CTX_use_certificate_file(ctx, cert, SSL_FILETYPE_PEM) <= 0) {
-      log_message(LOG_LEVEL_ERROR, "Failed to load certificate: %s", cert);
+      char* escaped = output_escape(cert, false);
+      log_message(LOG_LEVEL_ERROR, "Failed to load certificate: %s",
+                  escaped ? escaped : "<allocation failed>");
+      free(escaped);
       log_ssl_errors();
       SSL_CTX_free(ctx);
       return NULL;
     }
     if (SSL_CTX_use_PrivateKey_file(ctx, key, SSL_FILETYPE_PEM) <= 0) {
-      log_message(LOG_LEVEL_ERROR, "Failed to load private key: %s", key);
+      char* escaped = output_escape(key, false);
+      log_message(LOG_LEVEL_ERROR, "Failed to load private key: %s",
+                  escaped ? escaped : "<allocation failed>");
+      free(escaped);
       log_ssl_errors();
       SSL_CTX_free(ctx);
       return NULL;
@@ -85,7 +101,10 @@ static SSL_CTX* create_ssl_ctx(bool is_server, const char* cert, const char* key
 
   if (ca_path) {
     if (!SSL_CTX_load_verify_locations(ctx, ca_path, NULL)) {
-      log_message(LOG_LEVEL_ERROR, "Failed to load CA: %s", ca_path);
+      char* escaped = output_escape(ca_path, false);
+      log_message(LOG_LEVEL_ERROR, "Failed to load CA: %s",
+                  escaped ? escaped : "<allocation failed>");
+      free(escaped);
       log_ssl_errors();
       SSL_CTX_free(ctx);
       return NULL;
@@ -176,9 +195,10 @@ bool server_listen_tls(Server* server, void (*handler)(int file_descriptor)) {
   return true;
 }
 
-bool client_connect_tls(Client* client, char* host, int port, const char* cert_path,
-                        const char* key_path, const char* ca_path) {
-  if (!tcp_connect_socket(client, host, port)) {
+bool client_connect_tls_ex(Client* client, const char* host, int port, const char* cert_path,
+                           const char* key_path, const char* ca_path,
+                           const TcpConnectOptions* opts) {
+  if (!tcp_connect_socket_ex(client, host, port, opts)) {
     if (client->file_descriptor >= 0)
       close(client->file_descriptor);
     client->file_descriptor = -1;
@@ -209,3 +229,8 @@ bool client_connect_tls(Client* client, char* host, int port, const char* cert_p
   io_set_ssl(ssl);
   return true;
 }
+
+bool client_connect_tls(Client* client, const char* host, int port, const char* cert_path,
+                        const char* key_path, const char* ca_path) {
+  return client_connect_tls_ex(client, host, port, cert_path, key_path, ca_path, NULL);
+}

src/shared/transport_tls.h

@@ -9,7 +9,10 @@ bool tls_global_init(void);
 bool server_create_tls(Server* server, const char* cert_path, const char* key_path,
                        const char* ca_path);
 bool server_listen_tls(Server* server, void (*handler)(int file_descriptor));
-bool client_connect_tls(Client* client, char* host, int port, const char* cert_path,
+bool client_connect_tls_ex(Client* client, const char* host, int port, const char* cert_path,
+                           const char* key_path, const char* ca_path,
+                           const TcpConnectOptions* opts);
+bool client_connect_tls(Client* client, const char* host, int port, const char* cert_path,
                         const char* key_path, const char* ca_path);
 
 #endif

src/shared/utils.c

@@ -1,13 +1,16 @@
 #include "utils.h"
 #include "array_list.h"
-#include "libgen.h"
+#include "log.h"
+#include <arpa/inet.h>
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <netinet/in.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <stdint.h>
+#include <sys/socket.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
@@ -82,45 +85,6 @@ static int open_authorized_destination(const char* dest_root) {
   return dirfd;
 }
 
-bool mkdir_r(const char* path) {
-  if (!path || *path == '\0')
-    return false;
-  char* duplicate = str_dup(path);
-  if (!duplicate)
-    return false;
-  int dirfd = open(path[0] == '/' ? "/" : ".", O_RDONLY | O_DIRECTORY | O_CLOEXEC | O_NOFOLLOW);
-  if (dirfd < 0) {
-    free(duplicate);
-    return false;
-  }
-  bool ok = true;
-  char* saveptr = NULL;
-  char* component = strtok_r(duplicate, "/", &saveptr);
-  while (component) {
-    if (strcmp(component, "..") == 0) {
-      ok = false;
-      break;
-    }
-    if (strcmp(component, ".") != 0) {
-      int next = openat(dirfd, component, O_RDONLY | O_DIRECTORY | O_CLOEXEC | O_NOFOLLOW);
-      if (next < 0 && errno == ENOENT) {
-        if (mkdirat(dirfd, component, 0755) == 0 || errno == EEXIST)
-          next = openat(dirfd, component, O_RDONLY | O_DIRECTORY | O_CLOEXEC | O_NOFOLLOW);
-      }
-      if (next < 0) {
-        ok = false;
-        break;
-      }
-      close(dirfd);
-      dirfd = next;
-    }
-    component = strtok_r(NULL, "/", &saveptr);
-  }
-  close(dirfd);
-  free(duplicate);
-  return ok;
-}
-
 char* str_dup(const char* string) {
   if (string == NULL)
     return NULL;
@@ -132,6 +96,32 @@ char* str_dup(const char* string) {
   return new_string;
 }
 
+char* output_escape(const char* string, bool eight_bit_output) {
+  if (!string)
+    return NULL;
+  size_t length = strlen(string);
+  if (length > (SIZE_MAX - 1) / 5)
+    return NULL;
+  char* escaped = malloc(length * 5 + 1);
+  if (!escaped)
+    return NULL;
+  size_t out = 0;
+  for (size_t i = 0; i < length; i++) {
+    unsigned char byte = (unsigned char)string[i];
+    if ((byte >= 32 && byte <= 126) || (eight_bit_output && byte >= 128)) {
+      escaped[out++] = (char)byte;
+    } else {
+      escaped[out++] = '\\';
+      escaped[out++] = '#';
+      escaped[out++] = (char)('0' + ((byte >> 6) & 7));
+      escaped[out++] = (char)('0' + ((byte >> 3) & 7));
+      escaped[out++] = (char)('0' + (byte & 7));
+    }
+  }
+  escaped[out] = '\0';
+  return escaped;
+}
+
 /* Match a glob pattern against a string. Supported wildcards:
  *   ?      matches any single character except '/'.
  *   *      matches any sequence of characters within one path component (no '/').
@@ -187,6 +177,25 @@ bool glob_match(const char* pattern, const char* str) {
   return *str == '\0';
 }
 
+bool format_human_bytes(unsigned long long bytes, char* buffer, size_t buffer_size) {
+  static const char* const units[] = {"B", "KB", "MB", "GB", "TB", "PB", "EB"};
+  double value = (double)bytes;
+  size_t unit = 0;
+  int written;
+
+  if (!buffer || buffer_size == 0)
+    return false;
+  while (value >= 1024.0 && unit < sizeof(units) / sizeof(units[0]) - 1) {
+    value /= 1024.0;
+    unit++;
+  }
+  if (unit == 0)
+    written = snprintf(buffer, buffer_size, "%llu %s", bytes, units[unit]);
+  else
+    written = snprintf(buffer, buffer_size, "%.1f %s", value, units[unit]);
+  return written >= 0 && (size_t)written < buffer_size;
+}
+
 static bool is_dir_in_manifest(const char* rel_path, ArrayList* manifest) {
   size_t len = strlen(rel_path);
   for (int i = 0; i < manifest->size; i++) {
@@ -198,9 +207,134 @@ static bool is_dir_in_manifest(const char* rel_path, ArrayList* manifest) {
   return false;
 }
 
+/* True when child_rel is, or lies below, a protected entry.  A prefix "a"
+   therefore protects "a" and "a/b/c" but not "ab".  Entries with top_level_only
+   set only protect DIRECT children of the receive root (at_root); nested
+   directories that share such a name stay ordinary destination content. */
+bool path_under_skip_prefix(const char* child_rel, bool at_root, const DeleteSkipEntry* skips,
+                            int skip_count) {
+  for (int i = 0; i < skip_count; i++) {
+    if (skips[i].top_level_only && !at_root)
+      continue;
+    size_t prefix_len = strlen(skips[i].prefix);
+    if (strncmp(child_rel, skips[i].prefix, prefix_len) == 0 &&
+        (child_rel[prefix_len] == '\0' || child_rel[prefix_len] == '/'))
+      return true;
+  }
+  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, ArrayList* manifest, size_t cap,
+                            size_t* count, bool* exceeds, const DeleteSkipEntry* skips,
+                            int skip_count, bool* survives) {
+  /* 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. */
+  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 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, manifest, cap, count, exceeds, skips,
+                                   skip_count, &child_survives);
+        close(childfd);
+      } else if (errno != ENOENT) {
+        operation_ok = false;
+      }
+      if (!child_ok)
+        operation_ok = false;
+      if (is_dir_in_manifest(child_rel, manifest)) {
+        /* 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 = false;
+      for (int i = 0; i < manifest->size; i++) {
+        if (strcmp((char*)manifest->items[i], child_rel) == 0) {
+          found = true;
+          break;
+        }
+      }
+      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, ArrayList* manifest,
-                             size_t max_delete, size_t* deleted_count) {
-  int scanfd = dup(dirfd);
+                             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);
@@ -218,6 +352,17 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifes
       operation_ok = false;
       continue;
     }
+    /* A --delay-updates run keeps its staging directory as a direct child of
+       the receive root, and basis-dir snapshots live below it too.  Their
+       contents are not manifest entries, so descending into them would delete
+       every staged / basis file as an "extra".  Only the staging name (a
+       top-level-only prefix) and the basis prefixes are protected: a nested
+       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)) {
+      free(child_rel);
+      continue;
+    }
     struct stat st;
     if (fstatat(dirfd, entry->d_name, &st, AT_SYMLINK_NOFOLLOW) != 0) {
       if (errno != ENOENT)
@@ -234,7 +379,8 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifes
       int childfd = openat(dirfd, entry->d_name, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
       bool child_removed = false;
       if (childfd >= 0) {
-        child_removed = delete_extras_fd(childfd, child_rel, manifest, max_delete, deleted_count);
+        child_removed = delete_extras_fd(childfd, child_rel, manifest, max_delete, deleted_count,
+                                         skips, skip_count);
         if (!child_removed)
           operation_ok = false;
         close(childfd);
@@ -246,7 +392,12 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifes
           operation_ok = false;
         } else {
           if (unlinkat(dirfd, entry->d_name, AT_REMOVEDIR) != 0) {
-            if (errno != ENOENT)
+            /* 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)++;
@@ -274,7 +425,9 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifes
         } else {
           (*deleted_count)++;
         }
-        fprintf(stderr, "  Deleted: %s\n", 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);
       }
     }
     free(child_rel);
@@ -283,9 +436,13 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifes
   return operation_ok;
 }
 
-bool delete_extras_limited(const char* dest_root, ArrayList* manifest, size_t max_delete) {
+DeleteWalkResult delete_extras_limited(const char* dest_root, 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 false;
+    return DELETE_WALK_ERROR;
   int rootfd;
   if (authorized_root_fd >= 0) {
     if (authorized_root_path)
@@ -298,16 +455,35 @@ bool delete_extras_limited(const char* dest_root, ArrayList* manifest, size_t ma
     rootfd = open(dest_root, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
   }
   if (rootfd < 0)
-    return false;
+    return DELETE_WALK_ERROR;
+  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, "", manifest, max_delete, &count, &exceeds, skips,
+                                      skip_count, &survives);
+    if (!counted_ok) {
+      close(rootfd);
+      return DELETE_WALK_ERROR;
+    }
+    if (exceeds) {
+      close(rootfd);
+      return DELETE_WALK_LIMIT_EXCEEDED;
+    }
+  }
   size_t deleted_count = 0;
-  bool ok = delete_extras_fd(rootfd, "", manifest, max_delete, &deleted_count);
+  bool ok = delete_extras_fd(rootfd, "", manifest, max_delete, &deleted_count, skips, skip_count);
   if (close(rootfd) != 0)
     ok = false;
-  return ok;
+  if (deleted_out)
+    *deleted_out = deleted_count;
+  return ok ? DELETE_WALK_OK : DELETE_WALK_ERROR;
 }
 
 bool delete_extras(const char* dest_root, ArrayList* manifest) {
-  return delete_extras_limited(dest_root, manifest, SIZE_MAX);
+  return delete_extras_limited(dest_root, manifest, SIZE_MAX, NULL, 0, NULL) == DELETE_WALK_OK;
 }
 
 bool has_path_traversal(const char* path) {
@@ -358,3 +534,81 @@ char* path_cat(const char* path1, const char* path2) {
   new_path[path1_len + path2_len + 1] = '\0';
   return new_path;
 }
+
+bool append_resume_eligible(unsigned long long old_size, unsigned long long check_size) {
+  return old_size < check_size;
+}
+
+bool append_tail_length(unsigned long long old_size, unsigned long long check_size,
+                        unsigned long long* tail_out) {
+  if (!tail_out || !append_resume_eligible(old_size, check_size))
+    return false;
+  *tail_out = check_size - old_size;
+  return true;
+}
+
+/* True when a bound/peer socket address is on the loopback interface: any
+   127.0.0.0/8 IPv4 address, IPv6 ::1, or an IPv4-mapped ::ffff:127.x.x.x.  This
+   is the transport-local test the daemon auth gate uses to decide whether a
+   plaintext connection is a trustworthy local/SSH channel. */
+bool utils_sockaddr_is_loopback(const struct sockaddr* addr) {
+  if (!addr)
+    return false;
+  if (addr->sa_family == AF_INET) {
+    const struct sockaddr_in* v4 = (const struct sockaddr_in*)addr;
+    uint32_t host = ntohl(v4->sin_addr.s_addr);
+    return (host & 0xff000000u) == 0x7f000000u;
+  }
+  if (addr->sa_family == AF_INET6) {
+    const struct sockaddr_in6* v6 = (const struct sockaddr_in6*)addr;
+    if (IN6_IS_ADDR_LOOPBACK(&v6->sin6_addr))
+      return true;
+    /* An IPv4-mapped ::ffff:127.x.x.x is loopback too. */
+    if (IN6_IS_ADDR_V4MAPPED(&v6->sin6_addr) && v6->sin6_addr.s6_addr[12] == 127)
+      return true;
+    return false;
+  }
+  return false;
+}
+
+/* True when the fd's peer is provably a loopback TCP peer: getpeername must
+   succeed AND the returned address must classify as loopback.  Everything else
+   is NOT local, including a non-socket descriptor (pipe/socketpair): a failed
+   getpeername (ENOTSOCK, ENOTCONN, ...) fails closed.  The daemon auth gate
+   must not treat "I cannot tell" as "trusted", and daemon auth modules are
+   daemon-only anyway (the --stdio path never loads a daemon config). */
+bool utils_fd_peer_is_local(int fd) {
+  if (fd < 0)
+    return false;
+  struct sockaddr_storage peer;
+  socklen_t length = sizeof(peer);
+  if (getpeername(fd, (struct sockaddr*)&peer, &length) != 0)
+    return false;
+  return utils_sockaddr_is_loopback((const struct sockaddr*)&peer);
+}
+
+/* True when a client-supplied host string names a loopback destination:
+   "localhost", any 127.0.0.0/8 literal, "::1", or "[::1]". */
+bool utils_host_is_loopback(const char* host) {
+  if (!host || host[0] == '\0')
+    return false;
+  if (strcmp(host, "localhost") == 0)
+    return true;
+  struct in_addr v4;
+  if (inet_pton(AF_INET, host, &v4) == 1)
+    return (ntohl(v4.s_addr) & 0xff000000u) == 0x7f000000u;
+  struct in6_addr addr6;
+  if (host[0] == '[') {
+    size_t len = strlen(host);
+    if (len < 3 || host[len - 1] != ']')
+      return false;
+    /* inet_pton needs the bare address, not the bracketed form. */
+    char bare[INET6_ADDRSTRLEN];
+    if (len - 2 >= sizeof(bare))
+      return false;
+    memcpy(bare, host + 1, len - 2);
+    bare[len - 2] = '\0';
+    return inet_pton(AF_INET6, bare, &addr6) == 1 && IN6_IS_ADDR_LOOPBACK(&addr6);
+  }
+  return inet_pton(AF_INET6, host, &addr6) == 1 && IN6_IS_ADDR_LOOPBACK(&addr6);
+}

src/shared/utils.h

@@ -4,18 +4,78 @@
 #include "array_list.h"
 #include <stddef.h>
 #include <stdbool.h>
+#include <sys/socket.h>
 
-bool mkdir_r(const char* path);
 char* str_dup(const char* string);
+char* output_escape(const char* string, bool eight_bit_output);
 char* path_cat(const char* path1, const char* path2);
 bool glob_match(const char* pattern, const char* str);
+/* Result of a bounded extra-file deletion run. */
+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,
+  /* A traversal or unlink failure aborted the deletion (partial removal is
+     possible, mirroring the delete pass). */
+  DELETE_WALK_ERROR
+} DeleteWalkResult;
+/* One protected entry for the delete walker.  When top_level_only is true the
+   prefix is skipped only as a DIRECT child of dest_root (the --delay-updates
+   staging directory, which must not hide genuine extras inside a nested
+   destination directory that happens to share the staging name); otherwise the
+   prefix is skipped at any depth (the --compare-dest/--copy-dest/--link-dest
+   basis trees, and the sender-side protected filter-excluded prefixes, which
+   are never destination content). */
+typedef struct {
+  const char* prefix;
+  bool top_level_only;
+} DeleteSkipEntry;
+/* True when child_rel is, or lies below, one of the protected entries (a prefix
+   "a" protects "a" and "a/b/c" but not "ab"; top_level_only entries protect
+   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. */
+DeleteWalkResult delete_extras_limited(const char* dest_root, ArrayList* manifest,
+                                       size_t max_delete, const DeleteSkipEntry* skips,
+                                       int skip_count, size_t* deleted_out);
 bool delete_extras(const char* dest_root, ArrayList* manifest);
-bool delete_extras_limited(const char* dest_root, ArrayList* manifest, size_t max_delete);
 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. */
 void utils_set_authorized_root_fd(int fd);
 bool has_path_traversal(const char* path);
 bool utils_valid_batch_path(const char* path);
+bool format_human_bytes(unsigned long long bytes, char* buffer, size_t buffer_size);
+/* --append / --append-verify tail-resume math (pure).  A resume is eligible only
+   when an existing destination file is SHORTER than the source; the tail length
+   is then the difference.  append_resume_eligible answers whether the shorter
+   file makes a resume possible; append_tail_length additionally returns that
+   tail length, refusing (false) the degenerate old_size >= check_size case. */
+bool append_resume_eligible(unsigned long long old_size, unsigned long long check_size);
+bool append_tail_length(unsigned long long old_size, unsigned long long check_size,
+                        unsigned long long* tail_out);
+/* Loopback / local-transport classification for the daemon auth gate and the
+   client credential rule.  utils_sockaddr_is_loopback accepts 127.0.0.0/8,
+   IPv6 ::1 and IPv4-mapped ::ffff:127.x.x.x; utils_host_is_loopback additionally
+   accepts the literal "localhost".  utils_fd_peer_is_local is fail-closed: it is
+   true only when getpeername SUCCEEDS and reports a loopback peer -- a non-socket
+   descriptor (pipe/socketpair) or any getpeername error yields false.  See
+   utils.c for the exact accepted forms. */
+bool utils_sockaddr_is_loopback(const struct sockaddr* addr);
+bool utils_fd_peer_is_local(int fd);
+bool utils_host_is_loopback(const char* host);
 
 #endif

src/shared/xattr.c

@@ -0,0 +1,395 @@
+#define _GNU_SOURCE
+#include "xattr.h"
+#include "identity.h"
+#include "log.h"
+#include "protocol.h"
+#include "utils.h"
+#include "file_types.h"
+#include <errno.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/xattr.h>
+#include <time.h>
+#include <unistd.h>
+
+/* ---- lifecycle ---- */
+
+FileXattrList* xattr_list_new(void) {
+  FileXattrList* list = protocol_alloc(sizeof(FileXattrList));
+  if (!list)
+    return NULL;
+  list->items = NULL;
+  list->count = 0;
+  return list;
+}
+
+void xattr_list_free(FileXattrList* list) {
+  if (!list)
+    return;
+  for (int i = 0; i < list->count; i++) {
+    free(list->items[i].name);
+    free(list->items[i].value);
+  }
+  free(list->items);
+  free(list);
+}
+
+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;
+  if (list->count >= XATTR_MAX_COUNT)
+    return false;
+  FileXattr* grown = realloc(list->items, ((size_t)list->count + 1) * sizeof(FileXattr));
+  if (!grown)
+    return false;
+  list->items = grown;
+  size_t name_len = strlen(name);
+  char* name_copy = malloc(name_len + 1);
+  if (!name_copy) {
+    return false;
+  }
+  unsigned char* value_copy = NULL;
+  if (value_len > 0) {
+    value_copy = malloc(value_len);
+    if (!value_copy) {
+      free(name_copy);
+      return false;
+    }
+    memcpy(value_copy, value, value_len);
+  }
+  memcpy(name_copy, name, name_len);
+  name_copy[name_len] = '\0';
+  list->items[list->count].name = name_copy;
+  list->items[list->count].value = value_copy;
+  list->items[list->count].value_len = value_len;
+  list->count++;
+  return true;
+}
+
+/* ---- namespace / length validation ---- */
+
+/* A Linux xattr name is "namespace.name" with an optional leading "trusted.",
+ * "system.", "security.", "user.", or "trusted." prefix.  We only ever touch
+ * the unprivileged "user.*" namespace and the two POSIX ACL xattrs carried in
+ * the "system." namespace.  Everything else -- especially "security.*" (ACLs,
+ * capabilities, SELinux labels) and "trusted.*" -- is refused so a client can
+ * never compel the receiver to apply a privileged attribute it would not
+ * otherwise be able to set (and which would be a local privilege escalation if
+ * it could). */
+bool xattr_name_appliable(const char* name) {
+  if (!name || name[0] == '\0')
+    return false;
+  size_t len = strlen(name);
+  if (len > XATTR_NAME_MAX)
+    return false;
+  /* The reserved --fake-super key is exclusively the RECEIVER's: it records the
+   * source stat for a later privileged restore.  A plain -X run must never
+   * forward a source file that already carries this key (spoofable) onto the
+   * destination, so it is excluded from capture AND from application.  Only
+   * fake_super_store_fd() writes it. */
+  if (strcmp(name, FAKESUPER_XATTR) == 0)
+    return false;
+  if (strncmp(name, "user.", 5) == 0)
+    return name[5] != '\0';
+  if (strcmp(name, "system.posix_acl_access") == 0)
+    return true;
+  if (strcmp(name, "system.posix_acl_default") == 0)
+    return true;
+  return false;
+}
+
+/* ---- SENDER: capture ---- */
+
+FileXattrList* xattr_capture_path(const char* path) {
+  if (!path)
+    return NULL;
+  ssize_t list_size = listxattr(path, NULL, 0);
+  if (list_size <= 0)
+    return NULL; /* no xattrs, ENOTSUP, or error: nothing appliable */
+  char* names = malloc((size_t)list_size);
+  if (!names)
+    return NULL;
+  ssize_t got = listxattr(path, names, (size_t)list_size);
+  if (got < 0) {
+    free(names);
+    return NULL;
+  }
+  FileXattrList* list = xattr_list_new();
+  if (!list) {
+    free(names);
+    return NULL;
+  }
+  size_t budget = 0;
+  ssize_t offset = 0;
+  while (offset < got) {
+    const char* name = names + offset;
+    size_t name_len = strlen(name);
+    if (name_len == 0)
+      break; /* trailing double NUL not expected; stop */
+    offset += (ssize_t)name_len + 1;
+    if (!xattr_name_appliable(name))
+      continue;
+    ssize_t value_size = getxattr(path, name, NULL, 0);
+    if (value_size < 0)
+      continue;
+    if (value_size > XATTR_VALUE_MAX)
+      continue; /* oversize value is refused up front (bounded capture) */
+    if (name_len + (size_t)value_size > XATTR_TOTAL_MAX - budget)
+      continue; /* would exceed the per-file budget: skip, keep the rest */
+    unsigned char* buffer = malloc(value_size > 0 ? (size_t)value_size : 1);
+    if (!buffer) {
+      xattr_list_free(list);
+      free(names);
+      return NULL;
+    }
+    ssize_t read_len = getxattr(path, name, buffer, (size_t)value_size);
+    if (read_len < 0 || read_len != value_size) {
+      free(buffer);
+      continue;
+    }
+    if (!xattr_list_append(list, name, buffer, (size_t)value_size)) {
+      free(buffer);
+      xattr_list_free(list);
+      free(names);
+      return NULL;
+    }
+    free(buffer);
+    budget += name_len + (size_t)value_size;
+  }
+  free(names);
+  if (list->count == 0) {
+    xattr_list_free(list);
+    return NULL;
+  }
+  return list;
+}
+
+/* ---- WIRE ---- */
+
+bool xattr_send(int fd, const FileXattrList* list) {
+  int count = list ? list->count : 0;
+  if (!send_int(fd, count))
+    return false;
+  for (int i = 0; i < count; i++) {
+    const FileXattr* xa = &list->items[i];
+    size_t name_len = strlen(xa->name);
+    if (name_len > INT32_MAX)
+      return false;
+    int32_t name_len32 = (int32_t)name_len;
+    if (xa->value_len > INT32_MAX)
+      return false;
+    int32_t value_len32 = (int32_t)xa->value_len;
+    if (!send_n_data(fd, &name_len32, sizeof(name_len32)) || !send_n_data(fd, xa->name, name_len) ||
+        !send_n_data(fd, &value_len32, sizeof(value_len32)) ||
+        (value_len32 > 0 && !send_n_data(fd, xa->value, (size_t)value_len32)))
+      return false;
+  }
+  return true;
+}
+
+FileXattrList* xattr_receive(int fd, int* ok) {
+  if (ok)
+    *ok = 0;
+  int count;
+  if (!receive_int(fd, &count))
+    return NULL;
+  if (count < 0 || count > XATTR_MAX_COUNT) {
+    log_message(LOG_LEVEL_ERROR, "rejected xattr block: invalid attribute count %d", count);
+    return NULL;
+  }
+  FileXattrList* list = xattr_list_new();
+  if (!list)
+    return NULL;
+  size_t budget = 0;
+  for (int i = 0; i < count; i++) {
+    int32_t name_len32;
+    if (!receive_n_data(fd, &name_len32, sizeof(name_len32))) {
+      xattr_list_free(list);
+      return NULL;
+    }
+    if (name_len32 <= 0 || name_len32 > XATTR_NAME_MAX) {
+      log_message(LOG_LEVEL_ERROR, "rejected xattr block: invalid name length %d", name_len32);
+      xattr_list_free(list);
+      return NULL;
+    }
+    char* name = protocol_alloc((size_t)name_len32 + 1);
+    if (!name) {
+      xattr_list_free(list);
+      return NULL;
+    }
+    if (!receive_n_data(fd, name, (size_t)name_len32)) {
+      free(name);
+      xattr_list_free(list);
+      return NULL;
+    }
+    name[name_len32] = '\0';
+    if (memchr(name, '\0', (size_t)name_len32) != NULL) {
+      /* embedded NUL in the name: malformed, reject */
+      free(name);
+      xattr_list_free(list);
+      return NULL;
+    }
+    if (!xattr_name_appliable(name)) {
+      log_message(LOG_LEVEL_ERROR, "rejected xattr block: disallowed namespace for '%s'", name);
+      free(name);
+      xattr_list_free(list);
+      return NULL;
+    }
+    int32_t value_len32;
+    if (!receive_n_data(fd, &value_len32, sizeof(value_len32))) {
+      free(name);
+      xattr_list_free(list);
+      return NULL;
+    }
+    if (value_len32 < 0 || value_len32 > XATTR_VALUE_MAX) {
+      log_message(LOG_LEVEL_ERROR, "rejected xattr block: invalid value length %d for '%s'",
+                  value_len32, name);
+      free(name);
+      xattr_list_free(list);
+      return NULL;
+    }
+    if ((size_t)name_len32 + (size_t)value_len32 > XATTR_TOTAL_MAX - budget) {
+      log_message(LOG_LEVEL_ERROR, "rejected xattr block: total size budget exceeded for '%s'",
+                  name);
+      free(name);
+      xattr_list_free(list);
+      return NULL;
+    }
+    unsigned char* value = NULL;
+    if (value_len32 > 0) {
+      value = protocol_alloc((size_t)value_len32);
+      if (!value) {
+        free(name);
+        xattr_list_free(list);
+        return NULL;
+      }
+      if (!receive_n_data(fd, value, (size_t)value_len32)) {
+        free(value);
+        free(name);
+        xattr_list_free(list);
+        return NULL;
+      }
+    }
+    if (!xattr_list_append(list, name, value, (size_t)value_len32)) {
+      free(value);
+      free(name);
+      xattr_list_free(list);
+      return NULL;
+    }
+    free(value);
+    free(name);
+    budget += (size_t)name_len32 + (size_t)value_len32;
+  }
+  if (ok)
+    *ok = 1;
+  return list;
+}
+
+/* ---- RECEIVER: apply (fd-relative, best-effort) ---- */
+
+bool xattr_apply_fd(int fd, const FileXattrList* list) {
+  if (fd < 0 || !list)
+    return false;
+  bool warned = false;
+  int first_errno = 0;
+  for (int i = 0; i < list->count; i++) {
+    const FileXattr* xa = &list->items[i];
+    /* Defense in depth: even a hand-crafted list can never apply the reserved
+       --fake-super key (only fake_super_store_fd may write it). */
+    if (strcmp(xa->name, FAKESUPER_XATTR) == 0)
+      continue;
+    if (fsetxattr(fd, xa->name, xa->value, xa->value_len, 0) != 0) {
+      if (!warned) {
+        warned = true;
+        first_errno = errno;
+      }
+    }
+  }
+  /* Collapse potentially many per-attribute failures into one per-file warning
+     so a run with many unsettable attributes does not spam the log. */
+  if (warned)
+    log_message(LOG_LEVEL_WARNING, "could not set one or more xattrs on the destination file: %s",
+                strerror(first_errno));
+  return true;
+}
+
+/* ---- --fake-super: park ownership/mode/mtime in a reserved xattr ---- */
+
+void fake_super_store_fd(int fd, uint32_t uid, uint32_t gid, uint32_t mode, int64_t mtime_sec,
+                         int64_t mtime_nsec) {
+  if (fd < 0)
+    return;
+  char record[128];
+  int len =
+      snprintf(record, sizeof(record), "%lu:%lu:%03o:%lld:%ld", (unsigned long)uid,
+               (unsigned long)gid, (unsigned)mode & 0777U, (long long)mtime_sec, (long)mtime_nsec);
+  if (len <= 0 || (size_t)len >= sizeof(record))
+    return;
+  if (fsetxattr(fd, FAKESUPER_XATTR, record, (size_t)len, 0) != 0) {
+    log_message(LOG_LEVEL_WARNING, "--fake-super: could not store %s on destination file: %s",
+                FAKESUPER_XATTR, strerror(errno));
+  }
+}
+
+/* --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) {
+  if (fd < 0)
+    return false;
+  char record[128];
+  ssize_t len = fgetxattr(fd, FAKESUPER_XATTR, record, sizeof(record) - 1);
+  if (len < 0)
+    return false; /* absent or filesystem without xattrs: silent no-op */
+  record[len] = '\0';
+  unsigned long ul_uid, ul_gid, ul_mode;
+  long long mtime_sec;
+  long mtime_nsec;
+  if (sscanf(record, "%lu:%lu:%lo:%lld:%ld", &ul_uid, &ul_gid, &ul_mode, &mtime_sec, &mtime_nsec) !=
+      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));
+  return true;
+}

src/shared/xattr.h

@@ -0,0 +1,101 @@
+#ifndef XATTR_H
+#define XATTR_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/*
+ * Portable extended-attribute (xattr) and POSIX-ACL preservation (Phase 4,
+ * protocol 2.13.0).  --xattrs/-X and --acls/-A are implemented on top of the
+ * xattr machinery: the SENDER captures a bounded, namespace-whitelisted set of
+ * `name = value` pairs per file, transmits them in a per-file wire block, and
+ * the RECEIVER re-applies them fd-relative on the just-written file.  Linux
+ * xattr syscalls are used; libacl is NOT required (ACLs travel as the
+ * system.posix_acl_access / system.posix_acl_default xattrs).
+ *
+ * Security model:
+ *   * A client can never force a `security.*` / privileged xattr onto the
+ *     destination: both capture (sender) and apply (receiver) are restricted to
+ *     the unprivileged `user.*` namespace and the two POSIX ACL xattrs.  The
+ *     receiver independently re-validates every incoming name against this
+ *     whitelist, so a malicious sender's `security.capability` payload is
+ *     rejected, not applied.
+ *   * Payloads are bounded (per-name length, per-value length, per-file count
+ *     and total bytes) on BOTH ends to prevent OOM/memory abuse; an oversized
+ *     or malformed frame is a clean protocol rejection, never an allocation
+ *     blowup.
+ *   * Application is confined to the exact destination file descriptor
+ *     (fsetxattr on the just-written fd), never a caller-controlled path.
+ */
+
+/* Reserved key used by --fake-super to park the source's privileged ownership
+ * / mode / mtime on the destination file as an unprivileged user.* xattr, so a
+ * later privileged restore could re-apply them.  Exact documented format:
+ *   uid:gid:mode:mtime_sec:mtime_nsec           (decimal, decimal, octal, dec, dec)
+ * e.g. "1000:1000:644:1765238400:0". */
+#define FAKESUPER_XATTR "user.fastsync.stat"
+
+/* --- bounds --- */
+#define XATTR_NAME_MAX 255                /* xattr names are limited to 255 bytes */
+#define XATTR_VALUE_MAX (1024 * 1024)     /* per-value cap (1 MiB) */
+#define XATTR_TOTAL_MAX (4 * 1024 * 1024) /* per-file total name+value bytes */
+#define XATTR_MAX_COUNT 256
+
+typedef struct {
+  char* name;           /* owned, NUL-terminated */
+  unsigned char* value; /* owned, may hold embedded NULs */
+  size_t value_len;
+} FileXattr;
+
+typedef struct {
+  FileXattr* items;
+  int count;
+} FileXattrList;
+
+FileXattrList* xattr_list_new(void);
+void xattr_list_free(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);
+
+/* True when `name` is a well-formed xattr name AND belongs to a namespace this
+ * build is authorized to apply (user.* or the two POSIX ACL xattrs).  Used for
+ * both capture and receiver-side validation. */
+bool xattr_name_appliable(const char* name);
+
+/* Sender: read the whitelisted xattrs of `path` into a new list.  Returns NULL
+ * when the path has no appliable xattrs (or the filesystem has no xattr
+ * support); an empty-but-valid list is never returned distinct from NULL. */
+FileXattrList* xattr_capture_path(const char* path);
+
+/* Wire: bounded serialization.  xattr_send returns false on write failure; an
+ * empty/NULL list transmits a zero-count block.  xattr_receive returns NULL and
+ * sets *ok = 0 on any malformed / oversized / non-whitelisted entry. */
+bool xattr_send(int fd, const FileXattrList* list);
+FileXattrList* xattr_receive(int fd, int* ok);
+
+/* Receiver: apply every entry fd-relative (fsetxattr) to the just-written file
+ * descriptor.  A per-attribute failure (e.g. ACL set refused for non-root on a
+ * file the process does not own) is logged and skipped, never fatal.  Returns
+ * true when apply was attempted (allowing callers to treat it as best-effort). */
+bool xattr_apply_fd(int fd, const FileXattrList* list);
+
+/* --fake-super: write the source uid/gid/mode/mtime record into the reserved
+ * FAKESUPER_XATTR on `fd`.  Best-effort (logged, never fatal).  Only meaningful
+ * when metadata was transmitted so the values exist. */
+void fake_super_store_fd(int fd, uint32_t uid, uint32_t gid, uint32_t mode, int64_t mtime_sec,
+                         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);
+
+#endif

tests/conftest.py

@@ -1,17 +1,31 @@
 """Shared pytest configuration for integration tests."""
 import os
+import shutil
 import sys
 import pytest
 
 sys.path.insert(0, os.path.join(os.path.dirname(__file__), "integration"))
 
-from common import ServerManager
+from common import ServerManager, TEST_DATA_DIR
 
 
 @pytest.fixture(scope="session")
 def shared_server():
-    """One server for the entire test session. Avoids 27+ server start/stop cycles."""
+    """One server for the entire test session. Avoids 27+ server start/stop cycles.
+
+    Under pytest-xdist this session fixture is instantiated once per worker
+    process, so each worker gets its own server on an ephemeral port."""
     server = ServerManager()
     server.start()
     yield server
     server.stop()
+
+
+@pytest.fixture(scope="session", autouse=True)
+def _cleanup_worker_test_data():
+    """Remove this (worker-keyed) TEST_DATA_DIR at the end of the session.
+
+    Modules clean only their own rows; this final pass ensures the per-worker
+    directory never lingers in the working tree."""
+    yield
+    shutil.rmtree(TEST_DATA_DIR, ignore_errors=True)

tests/fuzz/fuzz_config_receive.c

@@ -0,0 +1,346 @@
+/*
+ * Fuzz the binary config-frame receive path: Config* config_receive(int fd).
+ *
+ * The frame is a length-prefixed stream of strings/ints/bools, so the receiver
+ * stops at the first malformed field.  Feeding raw fuzz bytes alone therefore
+ * almost never reaches the deep P8 trailing blocks (--super / --copy-as) or the
+ * identity-map block, because every preceding wire bool must be exactly 0 or 1.
+ *
+ * To exercise those paths we first build one canonical, fully-valid frame with
+ * the production sender and then feed the receiver four shapes:
+ *
+ *   1. raw     : the raw fuzz bytes as the whole frame (version gate included).
+ *   2. general : the valid version-string prefix + the raw fuzz bytes, so the
+ *                fuzzer can walk the early/core/selection blocks from arbitrary
+ *                input while staying past the version gate.
+ *   3. tail    : the valid frame up to its last P8_TAIL_BYTES (super_mode +
+ *                copy-as presence/uid/gid) + the raw fuzz bytes, so the fuzzer
+ *                directly mutates super_mode and the copy-as ids and truncates
+ *                the tail at any byte.
+ *   4. map     : the valid frame up to the --usermap count + the raw fuzz bytes,
+ *                so the fuzzer directly drives the map count (huge/extreme) and
+ *                the map entries.
+ *
+ * The canonical frame is captured by running config_send once, writing the
+ * frame into a pipe whose read end is drained afterwards; the STATUS_OK ack is
+ * pre-loaded into a second pipe so a single thread suffices.
+ */
+#include "config.h"
+#include "credentials.h"
+#include "protocol.h"
+#include "utils.h"
+#include <errno.h>
+#include <fcntl.h>
+#include <openssl/evp.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+/* super_mode (4) + copy-as presence (4) + uid (4) + gid (4) = the P8 tail. */
+#define P8_TAIL_BYTES 16
+
+/* Distinctive --usermap entry used to locate the map-count field in the
+ * canonical frame without duplicating the wire layout here. */
+#define MAP_FROM 0x11223344
+#define MAP_TO 0x55667788
+
+static unsigned char* g_frame;
+static size_t g_frame_len;
+static size_t g_version_len;       /* length of the leading version-string frame */
+static size_t g_usermap_count_off; /* offset of the usermap count int, 0 = unknown */
+static size_t g_auth_off;          /* offset of the auth presence int, 0 = unknown */
+static bool g_auth_found;          /* whether g_auth_off is valid */
+static bool g_frame_ready;
+
+/* Read the canonical frame from the send peer.  The producer shuts down its
+ * write half first, so a blocking read drains the frame and then sees EOF. */
+static unsigned char* drain_frame(int fd, size_t* out_len) {
+  size_t cap = 4096;
+  size_t len = 0;
+  unsigned char* buf = malloc(cap);
+  if (!buf)
+    return NULL;
+  for (;;) {
+    if (len == cap) {
+      size_t grown = cap * 2;
+      unsigned char* bigger = realloc(buf, grown);
+      if (!bigger) {
+        free(buf);
+        return NULL;
+      }
+      buf = bigger;
+      cap = grown;
+    }
+    ssize_t n = read(fd, buf + len, cap - len);
+    if (n > 0) {
+      len += (size_t)n;
+      continue;
+    }
+    if (n < 0 && errno == EINTR)
+      continue;
+    break; /* 0 (EOF) or error */
+  }
+  *out_len = len;
+  return buf;
+}
+
+/* Serialize a valid Config with the real sender.  The frame is written into a
+ * pipe (64 KiB kernel buffer, far larger than one config frame) whose read end
+ * is drained afterwards; the STATUS_OK ack is pre-loaded into a second pipe so
+ * a single thread suffices (config_send writes the whole frame before it reads
+ * the ack). */
+static void build_canonical_frame(void) {
+  g_frame_ready = true;
+
+  Config* cfg = config_create();
+  if (!cfg)
+    return;
+  cfg->send_directory = str_dup("/src");
+  cfg->receive_root_directory = str_dup("/dst");
+  /* Force the shortened auth block (`[present][username]`) to be present so the
+   * fuzzer can mutate it. */
+  cfg->auth_user = str_dup("alice");
+  cfg->auth_password = str_dup("alice-s3cret");
+  /* Force the three P8 tail fields to be present (copy-as requires metadata). */
+  cfg->copy_as_set = true;
+  cfg->copy_as_uid = 0;
+  cfg->copy_as_gid = 0;
+  cfg->use_metadata = true;
+  /* Force one usermap entry with a locatable sentinel. */
+  cfg->usermap = malloc(sizeof(IdentityMap));
+  if (cfg->usermap) {
+    cfg->usermap_count = 1;
+    cfg->usermap[0].from = MAP_FROM;
+    cfg->usermap[0].to = MAP_TO;
+  }
+  if (!cfg->send_directory || !cfg->receive_root_directory || !cfg->usermap) {
+    config_delete(cfg);
+    return;
+  }
+
+  int frame_pipe[2] = {-1, -1};
+  int status_pipe[2] = {-1, -1};
+  if (pipe(frame_pipe) != 0 || pipe(status_pipe) != 0)
+    goto out;
+
+  int ack = STATUS_OK;
+  if (write(status_pipe[1], &ack, sizeof(ack)) != (ssize_t)sizeof(ack))
+    goto out;
+
+  io_set_fds(status_pipe[0], frame_pipe[1]);
+  io_set_bwlimit(0);
+  bool sent = config_send(frame_pipe[1], cfg);
+  close(frame_pipe[1]);
+  frame_pipe[1] = -1;
+  close(status_pipe[0]);
+  status_pipe[0] = -1;
+  close(status_pipe[1]);
+  status_pipe[1] = -1;
+
+  if (sent)
+    g_frame = drain_frame(frame_pipe[0], &g_frame_len);
+
+out:
+  if (frame_pipe[0] != -1)
+    close(frame_pipe[0]);
+  if (frame_pipe[1] != -1)
+    close(frame_pipe[1]);
+  if (status_pipe[0] != -1)
+    close(status_pipe[0]);
+  if (status_pipe[1] != -1)
+    close(status_pipe[1]);
+  config_delete(cfg);
+  if (!g_frame || g_frame_len == 0) {
+    free(g_frame);
+    g_frame = NULL;
+    g_frame_len = 0;
+    return;
+  }
+
+  g_version_len = sizeof(size_t) + strlen(PROTOCOL_VERSION);
+  if (g_version_len > g_frame_len)
+    g_version_len = g_frame_len;
+
+  /* Locate the usermap entry sentinel; its count int sits 4 bytes before it. */
+  int32_t from = MAP_FROM;
+  int32_t to = MAP_TO;
+  unsigned char pattern[8];
+  memcpy(pattern, &from, sizeof(from));
+  memcpy(pattern + sizeof(from), &to, sizeof(to));
+  if (g_frame_len >= sizeof(pattern)) {
+    for (size_t i = 4; i + sizeof(pattern) <= g_frame_len; i++) {
+      if (memcmp(g_frame + i, pattern, sizeof(pattern)) == 0) {
+        g_usermap_count_off = i - sizeof(int32_t);
+        break;
+      }
+    }
+  }
+
+  /* Locate the auth username string (a size_t length followed by its bytes);
+   * the presence int sits one int before the length.  The username bytes cannot
+   * start before sizeof(size_t)+sizeof(int) without the presence-int offset
+   * underflowing, so begin the scan there. */
+  const char* auth_name = "alice";
+  size_t auth_name_len = strlen(auth_name);
+  if (g_frame_len >= sizeof(size_t) + auth_name_len + sizeof(int)) {
+    for (size_t i = sizeof(size_t) + sizeof(int); i + auth_name_len <= g_frame_len; i++) {
+      if (memcmp(g_frame + i, auth_name, auth_name_len) != 0)
+        continue;
+      size_t found_len = 0;
+      memcpy(&found_len, g_frame + i - sizeof(size_t), sizeof(size_t));
+      if (found_len == auth_name_len) {
+        g_auth_off = i - sizeof(size_t) - sizeof(int);
+        g_auth_found = true;
+        break;
+      }
+    }
+  }
+}
+
+/* Fuzz the A7 auth crypto primitives directly: arbitrary bytes through the
+ * base64 decoder, plus a self-consistent SCRAM property (a proof built from a
+ * chosen client key must verify, while a tampered proof, a proof replayed
+ * against a different nonce, and a not-found verifier must all be refused). */
+static uint8_t pick_byte(const uint8_t* data, size_t size, size_t index) {
+  return size ? data[index % size] : 0;
+}
+
+static void fuzz_credentials(const uint8_t* data, size_t size) {
+  char b64[300];
+  size_t n = size < sizeof(b64) - 1 ? size : sizeof(b64) - 1;
+  memcpy(b64, data, n);
+  b64[n] = '\0';
+  uint8_t decoded[64];
+  size_t decoded_len = 0;
+  (void)credentials_b64_decode(b64, decoded, sizeof(decoded), &decoded_len);
+
+  uint8_t client_key[CREDENTIAL_KEY_LEN];
+  uint8_t stored_key[CREDENTIAL_KEY_LEN];
+  uint8_t server_key[CREDENTIAL_KEY_LEN];
+  uint8_t snonce[CREDENTIAL_NONCE_LEN];
+  uint8_t cnonce[CREDENTIAL_NONCE_LEN];
+  for (size_t i = 0; i < CREDENTIAL_KEY_LEN; i++) {
+    client_key[i] = pick_byte(data, size, i);
+    server_key[i] = pick_byte(data, size, i + CREDENTIAL_KEY_LEN);
+  }
+  for (size_t i = 0; i < CREDENTIAL_NONCE_LEN; i++) {
+    snonce[i] = pick_byte(data, size, i + 2 * CREDENTIAL_KEY_LEN);
+    cnonce[i] = pick_byte(data, size, i + 2 * CREDENTIAL_KEY_LEN + CREDENTIAL_NONCE_LEN);
+  }
+  unsigned int stored_len = 0;
+  if (EVP_Digest(client_key, sizeof(client_key), stored_key, &stored_len, EVP_sha256(), NULL) !=
+          1 ||
+      stored_len != CREDENTIAL_KEY_LEN)
+    return;
+  uint8_t auth_msg[CREDENTIAL_AUTH_MESSAGE_MAX];
+  size_t msg_len = 0;
+  if (!credentials_build_auth_message("alice", snonce, cnonce, auth_msg, sizeof(auth_msg),
+                                      &msg_len))
+    return;
+  uint8_t proof[CREDENTIAL_KEY_LEN];
+  uint8_t server_sig[CREDENTIAL_KEY_LEN];
+  if (!credentials_client_proof(client_key, stored_key, server_key, auth_msg, msg_len, proof,
+                                server_sig))
+    return;
+  CredentialVerifier verifier;
+  memset(&verifier, 0, sizeof(verifier));
+  verifier.found = true;
+  verifier.iters = CREDENTIAL_DEFAULT_ITERS;
+  memcpy(verifier.stored_key, stored_key, CREDENTIAL_KEY_LEN);
+  memcpy(verifier.server_key, server_key, CREDENTIAL_KEY_LEN);
+  uint8_t out_sig[CREDENTIAL_KEY_LEN];
+  if (!credentials_verify_response(&verifier, "alice", snonce, cnonce, proof, out_sig))
+    abort();
+  if (memcmp(out_sig, server_sig, CREDENTIAL_KEY_LEN) != 0)
+    abort();
+  uint8_t bad_proof[CREDENTIAL_KEY_LEN];
+  memcpy(bad_proof, proof, CREDENTIAL_KEY_LEN);
+  bad_proof[pick_byte(data, size, 0) % CREDENTIAL_KEY_LEN] ^= 0x01;
+  if (credentials_verify_response(&verifier, "alice", snonce, cnonce, bad_proof, out_sig))
+    abort();
+  uint8_t other_cnonce[CREDENTIAL_NONCE_LEN];
+  memcpy(other_cnonce, cnonce, CREDENTIAL_NONCE_LEN);
+  other_cnonce[pick_byte(data, size, 1) % CREDENTIAL_NONCE_LEN] ^= 0x80;
+  if (credentials_verify_response(&verifier, "alice", snonce, other_cnonce, proof, out_sig))
+    abort();
+  verifier.found = false;
+  if (credentials_verify_response(&verifier, "alice", snonce, cnonce, proof, out_sig))
+    abort();
+}
+
+/* Best-effort non-blocking write: an oversized fuzz input is truncated rather
+ * than stalling the harness. */
+static void write_best_effort(int fd, const void* data, size_t size) {
+  const unsigned char* p = data;
+  size_t off = 0;
+  while (off < size) {
+    ssize_t n = write(fd, p + off, size - off);
+    if (n > 0) {
+      off += (size_t)n;
+      continue;
+    }
+    if (n < 0 && errno == EINTR)
+      continue;
+    break;
+  }
+}
+
+/* Build prefix ++ data as a stream and drive config_receive over it. */
+static void receive_stream(const unsigned char* prefix, size_t prefix_len, const uint8_t* data,
+                           size_t size) {
+  int sv[2];
+  if (socketpair(AF_UNIX, SOCK_STREAM, 0, sv) != 0)
+    return;
+
+  int flags = fcntl(sv[0], F_GETFL, 0);
+  if (flags != -1)
+    (void)fcntl(sv[0], F_SETFL, flags | O_NONBLOCK);
+
+  if (prefix_len > 0)
+    write_best_effort(sv[0], prefix, prefix_len);
+  if (size > 0)
+    write_best_effort(sv[0], data, size);
+  /* Signal EOF without closing the read half, so the receiver's STATUS_ERROR
+   * replies do not hit EPIPE. */
+  shutdown(sv[0], SHUT_WR);
+
+  io_set_fds(sv[1], sv[1]);
+  io_set_bwlimit(0);
+  Config* cfg = config_receive(sv[1]);
+  config_delete(cfg);
+
+  close(sv[0]);
+  close(sv[1]);
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  fuzz_credentials(data, size);
+
+  if (!g_frame_ready)
+    build_canonical_frame();
+
+  /* Raw bytes as the whole frame (version gate and all). */
+  receive_stream(NULL, 0, data, size);
+
+  if (g_frame) {
+    /* Keep the valid version prefix, fuzz everything after it. */
+    receive_stream(g_frame, g_version_len, data, size);
+
+    /* Keep the valid frame up to the shortened auth block, fuzz it. */
+    if (g_auth_found)
+      receive_stream(g_frame, g_auth_off, data, size);
+
+    /* Keep the valid frame up to the P8 tail, fuzz super_mode + copy-as. */
+    if (g_frame_len > P8_TAIL_BYTES)
+      receive_stream(g_frame, g_frame_len - P8_TAIL_BYTES, data, size);
+
+    /* Keep the valid frame up to the usermap count, fuzz the count + entries. */
+    if (g_usermap_count_off > 0)
+      receive_stream(g_frame, g_usermap_count_off, data, size);
+  }
+  return 0;
+}

tests/fuzz/fuzz_identity_parse.c

@@ -0,0 +1,58 @@
+/*
+ * Fuzz the CLI-time identity parsers (identity.h):
+ *   - identity_parse_copy_as
+ *   - identity_parse_map (user and group variants)
+ *   - identity_parse_chown
+ *
+ * Each parser mutates a Config, so every input gets a fresh config_create()
+ * (freed afterwards).  After a successful parse the shared wire validator and
+ * the ownership predicate are also exercised on the mutated config.  The input
+ * is NUL-terminated; embedded NULs simply shorten the effective spec, which is
+ * fine for a parser fuzzer.
+ */
+#include "config.h"
+#include "identity.h"
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+static void exercise(Config* c, const char* spec, int which) {
+  if (!c)
+    return;
+  switch (which) {
+  case 0:
+    (void)identity_parse_copy_as(c, spec);
+    break;
+  case 1:
+    (void)identity_parse_map(c, spec, false);
+    break;
+  case 2:
+    (void)identity_parse_map(c, spec, true);
+    break;
+  default:
+    (void)identity_parse_chown(c, spec);
+    break;
+  }
+  (void)identity_wire_valid(c);
+  (void)identity_ownership_requested(c);
+  config_delete(c);
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  if (size == 0)
+    return 0;
+
+  char* spec = malloc(size + 1);
+  if (!spec)
+    return 0;
+  memcpy(spec, data, size);
+  spec[size] = '\0';
+
+  exercise(config_create(), spec, 0);
+  exercise(config_create(), spec, 1);
+  exercise(config_create(), spec, 2);
+  exercise(config_create(), spec, 3);
+
+  free(spec);
+  return 0;
+}

tests/integration/common.py

@@ -6,13 +6,19 @@ import socket
 import subprocess
 import sys
 import tempfile
+import threading
 import time
 
 PROJECT_ROOT = os.path.abspath(os.path.join(os.path.dirname(__file__), "..", ".."))
 BUILD_DIR = os.path.join(PROJECT_ROOT, "build")
 SERVER_CMD = [os.path.join(BUILD_DIR, "server")]
 CLIENT_CMD = [os.path.join(BUILD_DIR, "client")]
-TEST_DATA_DIR = os.path.join(PROJECT_ROOT, "test_data")
+# Under pytest-xdist each worker process gets its own PYTEST_XDIST_WORKER id
+# ('gw0', 'gw1', ...).  Worker-key the transient working dir so concurrent
+# workers on the shared filesystem never collide on fixtures.  Outside xdist
+# (or with -n1) this stays the historical 'test_data' path.
+_WORKER = os.environ.get("PYTEST_XDIST_WORKER")
+TEST_DATA_DIR = os.path.join(PROJECT_ROOT, f"test_data-{_WORKER}" if _WORKER else "test_data")
 
 
 class ServerManager:
@@ -53,6 +59,78 @@ class ServerManager:
         self.stop()
 
 
+class CountingProxy:
+    """One-shot TCP forwarder that counts the bytes flowing in each direction
+    between one client and the real server.
+
+    Client output and --stats report SOURCE lengths, so a delta/fuzzy transfer
+    that moves only a few percent of the file is invisible in normal output.
+    Routing the client through this proxy makes the actual wire usage
+    observable: client_to_server counts every byte the client sent (config,
+    paths, and file/delta payloads), server_to_client counts the reply bytes
+    (including the receiver's delta signatures).
+    """
+
+    def __init__(self, target_port):
+        self.target_port = target_port
+        self._listener = socket.socket()
+        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(30)
+        self.port = self._listener.getsockname()[1]
+        self.client_to_server = 0
+        self.server_to_client = 0
+
+    @staticmethod
+    def _pump(src, dst, counter):
+        while True:
+            try:
+                data = src.recv(65536)
+            except OSError:
+                return
+            if not data:
+                try:
+                    dst.shutdown(socket.SHUT_WR)
+                except OSError:
+                    pass
+                return
+            try:
+                dst.sendall(data)
+            except OSError:
+                return
+            counter[0] += len(data)
+
+    def run(self, cmd):
+        """Forward one client run (the full command list) to the real server and
+        return the CompletedProcess after the counts have settled."""
+
+        def serve():
+            try:
+                client_sock, _ = self._listener.accept()
+                server_sock = socket.create_connection(("127.0.0.1", self.target_port),
+                                                       timeout=10)
+            except OSError:
+                self._listener.close()
+                return
+            c2s, s2c = [0], [0]
+            a = threading.Thread(target=self._pump, args=(client_sock, server_sock, c2s))
+            b = threading.Thread(target=self._pump, args=(server_sock, client_sock, s2c))
+            a.start()
+            b.start()
+            a.join()
+            b.join()
+            self.client_to_server = c2s[0]
+            self.server_to_client = s2c[0]
+            self._listener.close()
+
+        thread = threading.Thread(target=serve)
+        thread.start()
+        result = subprocess.run(cmd, capture_output=True, text=True, timeout=180)
+        thread.join(20)
+        return result
+
+
 def run_client(source_dir, dest_dir, flags=None, port=None, extra_args=None):
     """Run the client and return (result, duration)."""
     cmd = CLIENT_CMD + ["--source-dir", source_dir, "--dest-dir", dest_dir, "--save-to-disk"]

tests/integration/test_append.py

@@ -0,0 +1,144 @@
+"""--append / --append-verify tail-resume integration tests.
+
+A shorter existing destination file is resumed by transferring only the tail:
+--append sends it without verifying the retained prefix (rsync parity: a wrong
+prefix is kept, so the result can differ from the source), while --append-verify
+checksums the retained prefix against the source and, on a mismatch, falls back
+to a clean full transfer so the result is always a byte-identical source copy.
+"""
+import os
+import random
+import shutil
+
+import pytest
+
+from common import (
+    TEST_DATA_DIR,
+    run_client, CountingProxy, clean_dir,
+    get_dest_received_dir, CLIENT_CMD,
+)
+
+REL = "sub/grow.dat"
+
+
+def _grow_payload(prefix_size, added_size, seed=99):
+    r = random.Random(seed)
+    return bytes(r.randbytes(prefix_size)), bytes(r.randbytes(added_size))
+
+
+class TestAppend:
+    def _make(self, tag):
+        source = os.path.join(TEST_DATA_DIR, f"append_{tag}_src")
+        dest = os.path.join(TEST_DATA_DIR, f"append_{tag}_dst")
+        clean_dir(source)
+        shutil.rmtree(dest, ignore_errors=True)
+        return source, dest
+
+    def _place(self, root, rel, data):
+        p = os.path.join(root, rel)
+        os.makedirs(os.path.dirname(p), exist_ok=True)
+        with open(p, "wb") as fh:
+            fh.write(data)
+        return p
+
+    def _read(self, root, rel):
+        with open(os.path.join(root, rel), "rb") as fh:
+            return fh.read()
+
+    def _dest_file(self, source, dest, rel):
+        return os.path.join(get_dest_received_dir(dest, source), rel)
+
+    @pytest.mark.ci
+    def test_append_resumes_short_dest_atomically(self, shared_server):
+        """A shorter dest with a MATCHING prefix is resumed; the reconstructed
+        file is byte-identical to the source."""
+        source, dest = self._make("atomic")
+        prefix, added = _grow_payload(1 * 1024 * 1024, 64 * 1024)
+        self._place(source, REL, prefix + added)
+        self._place(self._dest_file(source, dest, ""), REL, prefix)
+
+        result, _ = run_client(source, dest, flags=["--append"], port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--append failed: {(result.stderr or result.stdout)[:400]}"
+        assert self._read(self._dest_file(source, dest, ""), REL) == prefix + added
+
+    def test_append_verify_matching_prefix_succeeds(self, shared_server):
+        source, dest = self._make("verify_ok")
+        prefix, added = _grow_payload(512 * 1024, 32 * 1024)
+        self._place(source, REL, prefix + added)
+        self._place(self._dest_file(source, dest, ""), REL, prefix)
+
+        result, _ = run_client(source, dest, flags=["--append-verify"], port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--append-verify failed: {(result.stderr or result.stdout)[:400]}"
+        assert self._read(self._dest_file(source, dest, ""), REL) == prefix + added
+
+    def test_append_sends_only_tail(self, shared_server):
+        """Sorted transfer moves only the tail: wire bytes stay well below the
+        full source size (incompressible payload, no -c)."""
+        source, dest = self._make("tail")
+        prefix, added = _grow_payload(4 * 1024 * 1024, 8 * 1024, seed=7)
+        full = prefix + added
+        self._place(source, REL, full)
+        self._place(self._dest_file(source, dest, ""), REL, prefix)
+
+        proxy = CountingProxy(shared_server.port)
+        cmd = (CLIENT_CMD + ["--source-dir", source, "--dest-dir", dest,
+                             "--save-to-disk", "--server-port", str(proxy.port), "--append"])
+        result = proxy.run(cmd)
+        assert result.returncode == 0, \
+            f"--append failed: {(result.stderr or result.stdout)[:400]}"
+        assert self._read(self._dest_file(source, dest, ""), REL) == full
+        assert proxy.client_to_server < full.__len__() // 2, \
+            f"expected a tail-only transfer, sent {proxy.client_to_server}B for {full.__len__()}B"
+
+    def test_plain_append_wrong_prefix_is_rsync_parity(self, shared_server):
+        """--append does NOT verify the retained prefix: a wrong prefix is kept,
+        so the result is prefix+tail (differs from the source).  This is the
+        documented rsync-parity risk of plain --append."""
+        source, dest = self._make("plain_wrong")
+        correct_prefix, added = _grow_payload(256 * 1024, 32 * 1024, seed=1)
+        wrong_prefix = bytes(b ^ 0xFF for b in correct_prefix)
+        self._place(source, REL, correct_prefix + added)
+        self._place(self._dest_file(source, dest, ""), REL, wrong_prefix)
+
+        result, _ = run_client(source, dest, flags=["--append"], port=shared_server.port)
+        assert result.returncode == 0
+        assert self._read(self._dest_file(source, dest, ""), REL) == wrong_prefix + added
+
+    def test_append_verify_wrong_prefix_never_corrupts(self, shared_server):
+        """--append-verify detects the retained prefix mismatch and falls back to
+        a full transfer, so the result is a byte-identical source copy."""
+        source, dest = self._make("verify_wrong")
+        correct_prefix, added = _grow_payload(256 * 1024, 32 * 1024, seed=2)
+        wrong_prefix = bytes(b ^ 0xFF for b in correct_prefix)
+        self._place(source, REL, correct_prefix + added)
+        self._place(self._dest_file(source, dest, ""), REL, wrong_prefix)
+
+        result, _ = run_client(source, dest, flags=["--append-verify"], port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--append-verify mismatch fallback failed: {(result.stderr or result.stdout)[:400]}"
+        assert self._read(self._dest_file(source, dest, ""), REL) == correct_prefix + added
+
+    def test_append_with_inplace(self, shared_server):
+        source, dest = self._make("inplace")
+        prefix, added = _grow_payload(128 * 1024, 16 * 1024, seed=3)
+        self._place(source, REL, prefix + added)
+        self._place(self._dest_file(source, dest, ""), REL, prefix)
+
+        result, _ = run_client(source, dest, flags=["--append", "--inplace"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--append --inplace failed: {(result.stderr or result.stdout)[:400]}"
+        assert self._read(self._dest_file(source, dest, ""), REL) == prefix + added
+
+    def test_append_multithreaded(self, shared_server):
+        source, dest = self._make("mthread")
+        prefix, added = _grow_payload(512 * 1024, 32 * 1024, seed=4)
+        self._place(source, REL, prefix + added)
+        self._place(self._dest_file(source, dest, ""), REL, prefix)
+
+        result, _ = run_client(source, dest, flags=["--append", "--threads"], port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--append -m failed: {(result.stderr or result.stdout)[:400]}"
+        assert self._read(self._dest_file(source, dest, ""), REL) == prefix + added

tests/integration/test_batch.py

@@ -0,0 +1,120 @@
+"""Residual-batch (client-only) driver tests.
+
+--write-batch / --only-write-batch emit a self-contained batch file of a whole
+source tree; --read-batch applies one locally.  None of these cross the wire (no
+PROTOCOL_VERSION bump, no config-frame field, no server flag): only --write-batch
+also performs a live transfer and so needs a server.
+"""
+import os
+import shutil
+import subprocess
+import sys
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (
+    TEST_DATA_DIR,
+    run_client,
+    generate_test_files,
+    verify_transfer,
+    clean_dir,
+    get_dest_received_dir,
+    CLIENT_CMD,
+)
+
+SOURCE_DIR = os.path.join(TEST_DATA_DIR, "batch_source")
+DEST1 = os.path.join(TEST_DATA_DIR, "batch_dest1")
+DEST2 = os.path.join(TEST_DATA_DIR, "batch_dest2")
+BATCH_FILE = os.path.join(TEST_DATA_DIR, "batch.bin")
+
+BATCH_MAGIC = b"FSTRESBATCH"
+
+
+@pytest.fixture(scope="module", autouse=True)
+def setup_test_data():
+    generate_test_files(SOURCE_DIR, full=False)
+    clean_dir(DEST1)
+    clean_dir(DEST2)
+    yield
+    shutil.rmtree(SOURCE_DIR, ignore_errors=True)
+    shutil.rmtree(DEST1, ignore_errors=True)
+    shutil.rmtree(DEST2, ignore_errors=True)
+    for p in (BATCH_FILE,):
+        if os.path.exists(p):
+            os.unlink(p)
+
+
+def _run(args):
+    return CLIENT_CMD + args
+
+
+def test_write_batch_no_server():
+    """--only-write-batch emits a batch from the source with no destination and
+    no server connection."""
+    if os.path.exists(BATCH_FILE):
+        os.unlink(BATCH_FILE)
+    cmd = _run(["--only-write-batch", BATCH_FILE, SOURCE_DIR])
+    result = subprocess.run(cmd, capture_output=True, text=True, timeout=180)
+    assert result.returncode == 0, (result.stdout, result.stderr)
+    with open(BATCH_FILE, "rb") as f:
+        assert f.read(len(BATCH_MAGIC)) == BATCH_MAGIC
+    # No destination was touched (nothing was created next to the batch).
+    assert not os.path.exists(os.path.join(DEST1, "small.txt"))
+
+
+def test_read_batch_roundtrip_no_source():
+    """--read-batch applies an emitted batch to a fresh destination with no
+    source and no server; the tree is byte-identical to the source."""
+    received = get_dest_received_dir(DEST2, SOURCE_DIR)
+    clean_dir(DEST2)
+    cmd = _run(["--read-batch", BATCH_FILE, DEST2])
+    result = subprocess.run(cmd, capture_output=True, text=True, timeout=180)
+    assert result.returncode == 0, (result.stdout, result.stderr)
+    mismatches, missing = verify_transfer(SOURCE_DIR, received)
+    assert not missing, f"Missing: {missing[:5]}"
+    assert not mismatches, f"Mismatch: {mismatches[:5]}"
+
+
+def test_write_batch_with_transfer(shared_server):
+    """--write-batch runs a live transfer to a server AND emits the batch file."""
+    if os.path.exists(BATCH_FILE):
+        os.unlink(BATCH_FILE)
+    clean_dir(DEST1)
+    result, _ = run_client(
+        SOURCE_DIR, DEST1,
+        flags=["--write-batch", BATCH_FILE], port=shared_server.port)
+    assert result.returncode == 0, (result.stdout, result.stderr)
+    with open(BATCH_FILE, "rb") as f:
+        assert f.read(len(BATCH_MAGIC)) == BATCH_MAGIC
+    received = get_dest_received_dir(DEST1, SOURCE_DIR)
+    mismatches, missing = verify_transfer(SOURCE_DIR, received)
+    assert not missing, f"Missing: {missing[:5]}"
+    assert not mismatches, f"Mismatch: {mismatches[:5]}"
+
+
+def test_read_batch_requires_destination():
+    """--read-batch with no positional destination fails cleanly."""
+    cmd = _run(["--read-batch", BATCH_FILE])
+    result = subprocess.run(cmd, capture_output=True, text=True, timeout=180)
+    assert result.returncode != 0
+
+
+def test_only_write_batch_requires_source():
+    """--only-write-batch with no source fails cleanly."""
+    cmd = _run(["--only-write-batch", BATCH_FILE])
+    result = subprocess.run(cmd, capture_output=True, text=True, timeout=180)
+    assert result.returncode != 0
+
+
+def test_batch_modes_conflict():
+    """The three batch flags are mutually exclusive."""
+    combos = [
+        ["--write-batch", BATCH_FILE, "--only-write-batch", BATCH_FILE],
+        ["--write-batch", BATCH_FILE, "--read-batch", BATCH_FILE],
+        ["--only-write-batch", BATCH_FILE, "--read-batch", BATCH_FILE],
+    ]
+    for flags in combos:
+        cmd = _run(["--source-dir", SOURCE_DIR, "--dest-dir", DEST1] + flags)
+        result = subprocess.run(cmd, capture_output=True, text=True, timeout=180)
+        assert result.returncode != 0, \
+            f"expected conflict failure for {flags}: {result.stderr}"

tests/integration/test_iconv.py

@@ -0,0 +1,250 @@
+"""--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).
+"""
+import os
+import shutil
+
+import pytest
+
+from common import TEST_DATA_DIR, run_client, clean_dir, ServerManager
+
+LATIN1_NAME = b"caf\xe9.txt"
+UTF8_NAME = "caf\u00e9.txt".encode("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")
+    clean_dir(source)
+    shutil.rmtree(dest, ignore_errors=True)
+    # The destination ROOT must pre-exist on the receiver (the --mkpath contract:
+    # without --mkpath the server requires the root directory to exist).
+    os.makedirs(dest, exist_ok=True)
+    return source, dest
+
+
+def _place_bytes(root, name_bytes, data=b"latin1 payload\n"):
+    full = os.path.join(os.fsencode(root), name_bytes)
+    os.makedirs(os.path.dirname(full), exist_ok=True)
+    with open(full, "wb") as fh:
+        fh.write(data)
+    return full
+
+
+def _dest_file(source, dest, name):
+    base = os.path.join(dest, os.path.abspath(source).lstrip(os.sep))
+    return os.path.join(os.fsencode(base), 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)."""
+    source, dest = _make("latin1")
+    _place_bytes(source, LATIN1_NAME)
+
+    result, _ = run_client(
+        source, dest, flags=["--iconv=iso-8859-1,utf-8"], port=shared_server.port
+    )
+    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}"
+
+
+@pytest.mark.ci
+def test_iconv_to_utf8_on_wire(shared_server):
+    """--iconv=utf-8 (single, identity both ways) on an ascii filename transfers
+    cleanly with no error."""
+    source, dest = _make("utf8")
+    src_path = os.path.join(source, "plain.txt")
+    with open(src_path, "wb") as fh:
+        fh.write(b"identity\n")
+
+    result, _ = run_client(source, dest, flags=["--iconv=utf-8"], port=shared_server.port)
+    assert result.returncode == 0, (result.stderr or result.stdout)[:400]
+
+    dst = _dest_file(source, dest, os.fsencode("plain.txt"))
+    assert os.path.exists(dst)
+
+
+@pytest.mark.ci
+def test_iconv_passthrough_identity(shared_server):
+    """No --iconv flag: the transfer is unchanged (regression guard -- the common
+    path must not go through iconv at all)."""
+    source, dest = _make("identity")
+    for name, data in (("a.txt", b"aaa\n"), ("sub/b.txt", b"bbb\n")):
+        p = os.path.join(source, name)
+        os.makedirs(os.path.dirname(p), exist_ok=True)
+        with open(p, "wb") as fh:
+            fh.write(data)
+
+    result, _ = run_client(source, dest, port=shared_server.port)
+    assert result.returncode == 0, (result.stderr or result.stdout)[:400]
+
+    for name in ("a.txt", "sub/b.txt"):
+        assert os.path.exists(_dest_file(source, dest, os.fsencode(name)))
+
+
+@pytest.mark.ci
+def test_iconv_receiver_own_charset(shared_server):
+    """A dedicated server started with its OWN --iconv converts received names
+    to ITS charset: the source holds a latin1-named file, the wire carries it
+    as UTF-8 (from the client's spec), and the receiver re-decodes it to UTF-8
+    on disk.  This discriminates a real wire conversion from a no-op passthrough
+    (a latin1 byte sequence is not valid UTF-8, so the receiver decoding it as
+    UTF-8 would fail the transfer)."""
+    with ServerManager() as server:
+        server.start(extra_args=["--iconv=utf-8"])
+        source, dest = _make("recv_charset")
+        _place_bytes(source, LATIN1_NAME)
+
+        result, _ = run_client(
+            source, dest, flags=["--iconv=iso-8859-1,utf-8"], port=server.port
+        )
+        assert result.returncode == 0, (result.stderr or result.stdout)[:400]
+
+        dst = _dest_file(source, dest, UTF8_NAME)
+        assert os.path.exists(dst), f"dest UTF-8-named file not found under {dest}"
+
+
+@pytest.mark.ci
+def test_iconv_invalid_charset_rejected(shared_server):
+    """An unsupported charset name is rejected at startup with a nonzero exit."""
+    source, dest = _make("badcharset")
+    src_path = os.path.join(source, "f.txt")
+    with open(src_path, "wb") as fh:
+        fh.write(b"x")
+
+    result, _ = run_client(
+        source, dest, flags=["--iconv=no-such-charset,utf-8"], port=shared_server.port
+    )
+    assert result.returncode != 0
+
+
+@pytest.mark.ci
+def test_iconv_garbage_spec_rejected(shared_server):
+    """A malformed CONVERT_SPEC is rejected at startup with a nonzero exit."""
+    source, dest = _make("garbage")
+    src_path = os.path.join(source, "f.txt")
+    with open(src_path, "wb") as fh:
+        fh.write(b"x")
+
+    result, _ = run_client(source, dest, flags=["--iconv=,,,"], port=shared_server.port)
+    assert result.returncode != 0
+
+
+@pytest.mark.ci
+def test_iconv_expanding_name_growth(shared_server):
+    """A long latin1 name whose UTF-8 encoding expands past the initial output
+    buffer exercises the E2BIG growth path in charset_convert (each high-bit
+    latin1 byte doubles in UTF-8), and must land unchanged on the destination."""
+    source, dest = _make("growth")
+    name_bytes = b"a" * 40 + bytes(range(0x80, 0x80 + 40)) + b".txt"
+    _place_bytes(source, name_bytes, data=b"growth\n")
+
+    result, _ = run_client(
+        source, dest, flags=["--iconv=iso-8859-1,utf-8"], port=shared_server.port
+    )
+    assert result.returncode == 0, (result.stderr or result.stdout)[:400]
+
+    assert os.path.exists(_dest_file(source, dest, name_bytes))
+
+
+def test_iconv_symlink_path_and_target(shared_server):
+    """A latin1-named symlink pointing at a latin1-named target survives the
+    transfer: both the link name and the link target are wire-converted and
+    re-decoded on the destination (-l preserves links)."""
+    source, dest = _make("symlink")
+    target = b"target\xe9.dat"
+    _place_bytes(source, target, data=b"t\n")
+    os.symlink(target, os.path.join(os.fsencode(source), b"link\xe9"))
+
+    result, _ = run_client(
+        source, dest, flags=["--iconv=iso-8859-1,utf-8", "--links"], port=shared_server.port
+    )
+    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"
+    with open(dst_link, "rb") as fh:
+        assert fh.read() == b"t\n"
+
+
+def test_iconv_hardlink_path_and_target(shared_server):
+    """A latin1-named hard-linked pair is preserved: -H transmits later group
+    members as a path+target link to the first member, so both the member name
+    and the target wire-convert (the two destination names must stay one
+    inode)."""
+    source, dest = _make("hardlink")
+    a = b"hl_a\xe9.txt"
+    b = b"hl_b\xe9.txt"
+    src_a = os.path.join(os.fsencode(source), a)
+    with open(src_a, "wb") as fh:
+        fh.write(b"shared\n")
+    os.link(src_a, os.path.join(os.fsencode(source), b))
+
+    result, _ = run_client(
+        source, dest, flags=["--iconv=iso-8859-1,utf-8", "--hard-links"],
+        port=shared_server.port,
+    )
+    assert result.returncode == 0, (result.stderr or result.stdout)[:400]
+
+    dst_a = _dest_file(source, dest, a)
+    dst_b = _dest_file(source, dest, 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"
+
+
+def test_iconv_delete_manifest_consistent(shared_server):
+    """Combining --iconv with --delete: the delete manifest's keep-set paths are
+    wire-converted on send and disk-converted on receive, so the receiver's
+    delete walker compares like with like and removes exactly the missing
+    latin1-named file (never a wrong-named mirror)."""
+    source, dest = _make("delete")
+    keep = b"keep\xe9.txt"
+    gone = b"gone\xe9.txt"
+    _place_bytes(source, keep, data=b"k\n")
+    _place_bytes(source, gone, data=b"g\n")
+
+    with ServerManager() as server:
+        server.start(extra_args=["--allow-delete"])
+        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))
+
+        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)), \
+            "missing file was not deleted"
+
+
+def test_iconv_chunk_serialization_blob(shared_server):
+    """-s (chunk serialization) embeds paths and symlink targets inside the
+    serialized chunk blob rather than as separate frames; a latin1 name must
+    still wire-convert and re-decoded on the destination."""
+    source, dest = _make("chunk")
+    name = b"\xe9\xe9\xe9\xe9\xe9\xe9\xe9\xe9\xe9\xe9\xe9\xe9\xe9\xe9\xe9\xe9.txt"
+    _place_bytes(source, name, data=b"blob\n")
+
+    result, _ = run_client(
+        source, dest, flags=["--iconv=iso-8859-1,utf-8", "--chunk-serialization"], port=shared_server.port
+    )
+    assert result.returncode == 0, (result.stderr or result.stdout)[:400]
+
+    assert os.path.exists(_dest_file(source, dest, name))

tests/integration/test_preflight.py

@@ -2,10 +2,11 @@
 import subprocess
 import sys
 import os
+import shutil
 import pytest
 
 sys.path.insert(0, os.path.dirname(__file__))
-from common import BUILD_DIR, CLIENT_CMD, SERVER_CMD
+from common import BUILD_DIR, CLIENT_CMD, SERVER_CMD, TEST_DATA_DIR, run_client, verify_transfer
 
 
 class TestHelp:
@@ -79,3 +80,58 @@ class TestServerPort:
         finally:
             proc.terminate()
             proc.wait(timeout=5)
+
+
+def _seed_protocol_source(source):
+    os.makedirs(source, exist_ok=True)
+    with open(os.path.join(source, "p.txt"), "w") as fh:
+        fh.write("protocol test\n")
+    os.makedirs(os.path.join(source, "nested"), exist_ok=True)
+    with open(os.path.join(source, "nested", "deep.txt"), "w") as fh:
+        fh.write("deep file\n")
+
+
+class TestProtocol:
+    @pytest.mark.ci
+    def test_protocol_current_version_accepted(self, shared_server):
+        """--protocol=2.19.0 (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=2.19.0"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--protocol current run failed: {(result.stderr or result.stdout)[:400]}"
+        received = os.path.join(dest, os.path.abspath(source).lstrip(os.sep))
+        mismatches, missing = verify_transfer(source, received)
+        assert not mismatches and not missing, \
+            f"transfer mismatch: missing={missing} mismatches={mismatches}"
+
+    @pytest.mark.ci
+    def test_protocol_rejects_other_versions(self, shared_server):
+        """Other versions are rejected up front, before connecting."""
+        source = os.path.join(TEST_DATA_DIR, "proto_reject_src")
+        dest = os.path.join(TEST_DATA_DIR, "proto_reject_dst")
+        shutil.rmtree(dest, ignore_errors=True)
+        os.makedirs(dest)
+        _seed_protocol_source(source)
+        for bad in ("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"
+
+    @pytest.mark.ci
+    def test_protocol_rejects_garbage(self, shared_server):
+        """Garbage/empty --protocol values are rejected up front."""
+        source = os.path.join(TEST_DATA_DIR, "proto_garbage_src")
+        dest = os.path.join(TEST_DATA_DIR, "proto_garbage_dst")
+        shutil.rmtree(dest, ignore_errors=True)
+        os.makedirs(dest)
+        _seed_protocol_source(source)
+        for bad in ("abc", ""):
+            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_ssh.py

@@ -60,14 +60,16 @@ def setup_test_data():
         generate_test_files(SOURCE_DIR, full=False)
         clean_dir(DEST_DIR)
     yield
-    shutil.rmtree(TEST_DATA_DIR, ignore_errors=True)
+    shutil.rmtree(SOURCE_DIR, ignore_errors=True)
+    shutil.rmtree(DEST_DIR, ignore_errors=True)
 
 
-def _run_ssh_test(name, flags, expected_missing=None):
+def _run_ssh_test(name, flags, expected_missing=None, path_args=None):
     ssh_dest = f"localhost:{DEST_DIR}"
     clean_dir(DEST_DIR)
-    cmd = CLIENT_CMD + [SOURCE_DIR, ssh_dest, "--save-to-disk",
-                        "--fastsync-server-path", os.path.join(BUILD_DIR, "server")] + flags
+    if not path_args:
+        path_args = ["--fastsync-server-path", os.path.join(BUILD_DIR, "server")]
+    cmd = CLIENT_CMD + [SOURCE_DIR, ssh_dest, "--save-to-disk"] + path_args + flags
     start = __import__("time").monotonic()
     result = subprocess.run(cmd, text=True, capture_output=True)
     duration = __import__("time").monotonic() - start
@@ -95,31 +97,31 @@ class TestSSHStandard:
         assert r["status"] == "Success", r["error"]
 
     def test_multithreading(self):
-        r = _run_ssh_test("SSH Multithreading (-m)", ["-m"])
+        r = _run_ssh_test("SSH Multithreading (--threads)", ["--threads"])
         assert r["status"] == "Success", r["error"]
 
     def test_compression(self):
-        r = _run_ssh_test("SSH Compression (-c)", ["-c"])
+        r = _run_ssh_test("SSH Compression (-z)", ["-z"])
         assert r["status"] == "Success", r["error"]
 
     def test_chunk_serialization(self):
-        r = _run_ssh_test("SSH Chunk Serialization (-s)", ["-s"])
+        r = _run_ssh_test("SSH Chunk Serialization (--chunk-serialization)", ["--chunk-serialization"])
         assert r["status"] == "Success", r["error"]
 
     def test_compression_chunk(self):
-        r = _run_ssh_test("SSH Compression + Chunk (-c -s)", ["-c", "-s"])
+        r = _run_ssh_test("SSH Compression + Chunk (-z --chunk-serialization)", ["-z", "--chunk-serialization"])
         assert r["status"] == "Success", r["error"]
 
     def test_multithread_compression(self):
-        r = _run_ssh_test("SSH Multithread + Compression (-m -c)", ["-m", "-c"])
+        r = _run_ssh_test("SSH Multithread + Compression (--threads -z)", ["--threads", "-z"])
         assert r["status"] == "Success", r["error"]
 
     def test_multithread_chunk(self):
-        r = _run_ssh_test("SSH Multithread + Chunk (-m -s)", ["-m", "-s"])
+        r = _run_ssh_test("SSH Multithread + Chunk (--threads --chunk-serialization)", ["--threads", "--chunk-serialization"])
         assert r["status"] == "Success", r["error"]
 
     def test_all_flags(self):
-        r = _run_ssh_test("SSH All Flags (-m -c -s)", ["-m", "-c", "-s"])
+        r = _run_ssh_test("SSH All Flags (--threads -z --chunk-serialization)", ["--threads", "-z", "--chunk-serialization"])
         assert r["status"] == "Success", r["error"]
 
 
@@ -137,3 +139,89 @@ class TestSSHFeatures:
         r = _run_ssh_test("SSH Exclude (--exclude small.txt)",
                           ["--exclude", "small.txt"], expected_missing=["small.txt"])
         assert r["status"] == "Success", r["error"]
+
+    def test_preallocate(self):
+        r = _run_ssh_test("SSH Preallocate (--preallocate)", ["--preallocate"])
+        assert r["status"] == "Success", r["error"]
+
+class TestSSHConnectivity:
+    """Phase 5 connectivity options: -e/--rsh, --rsync-path, --blocking-io,
+    --outbuf.  These are client-side launch concerns, so each must parse and
+    still drive a real SSH transfer to completion."""
+
+    @pytest.fixture(autouse=True)
+    def require_ssh(self):
+        if not SSH_AVAILABLE:
+            pytest.skip(SSH_SKIP_REASON)
+
+    def test_rsh_short_form_selects_ssh(self):
+        r = _run_ssh_test("SSH -e ssh", ["-e", "ssh"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_rsh_long_form_selects_ssh(self):
+        r = _run_ssh_test("SSH --rsh=ssh", ["--rsh=ssh"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_rsync_path_aliases_server_path(self):
+        r = _run_ssh_test("SSH --rsync-path",
+                          [],
+                          path_args=["--rsync-path", os.path.join(BUILD_DIR, "server")])
+        assert r["status"] == "Success", r["error"]
+
+    def test_blocking_io(self):
+        r = _run_ssh_test("SSH --blocking-io", ["--blocking-io"])
+        assert r["status"] == "Success", r["error"]
+
+    @pytest.mark.parametrize("mode", ["N", "L", "B"])
+    def test_outbuf_mode(self, mode):
+        r = _run_ssh_test(f"SSH --outbuf={mode}", [f"--outbuf={mode}"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_blocking_io_with_compression(self):
+        r = _run_ssh_test("SSH --blocking-io -c", ["--blocking-io", "-z"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_trust_sender(self):
+        r = _run_ssh_test("SSH Trust Sender (--trust-sender)", ["--trust-sender"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_remote_option_reaches_server(self):
+        """--remote-option=OPT appends OPT to the remote server command line and
+        the server honors it.  Over SSH the server is launched without
+        --allow-delete, so a bare --delete is inert (nothing is removed).  If
+        --remote-option=--allow-delete really reaches the remote server, the
+        receiver's deletion policy becomes permissive and the stale destination
+        file IS removed.  Asserting the file is gone is therefore a positive
+        proof the forwarded option was honored by the server."""
+        src = SOURCE_DIR
+        if os.path.exists(src):
+            shutil.rmtree(src)
+        os.makedirs(src)
+        with open(os.path.join(src, "keep.txt"), "w") as f:
+            f.write("kept\n")
+        with open(os.path.join(src, "stale.txt"), "w") as f:
+            f.write("stale\n")
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+
+        # Initial push so the destination mirrors the source.
+        clean_dir(DEST_DIR)
+        ssh_dest = f"localhost:{DEST_DIR}"
+        base = CLIENT_CMD + [src, ssh_dest, "--save-to-disk",
+                             "--fastsync-server-path", os.path.join(BUILD_DIR, "server")]
+        first = subprocess.run(base, text=True, capture_output=True)
+        assert first.returncode == 0, f"initial push failed: {(first.stderr or first.stdout)[:200]}"
+        assert os.path.exists(os.path.join(received, "stale.txt"))
+
+        # Remove stale.txt from the source and re-push with --delete +
+        # --remote-option=--allow-delete.  Forwarding --allow-delete to the
+        # server is what makes the deletion actually happen.
+        os.remove(os.path.join(src, "stale.txt"))
+        second = subprocess.run(base + ["--delete", "--remote-option=--allow-delete"],
+                                text=True, capture_output=True)
+        assert second.returncode == 0, \
+            f"second push failed: {(second.stderr or second.stdout)[:200]}"
+        assert not os.path.exists(os.path.join(received, "stale.txt")), (
+            "stale.txt still present: --allow-delete (forwarded via "
+            "--remote-option) did not reach the remote server"
+        )
+        assert os.path.exists(os.path.join(received, "keep.txt"))

tests/integration/test_stop.py

@@ -0,0 +1,241 @@
+"""--stop-after / --stop-at deadline-stop integration tests.
+
+These cover the client-only sender stop conditions: --stop-after=MINS stops
+after N elapsed minutes, --stop-at=HH:MM[:SS] or now+N[smhd] stops at an
+absolute (or relative) wall-clock time.  A reached deadline ends the transfer
+elegantly at the next chunk/file boundary -- whatever was already transferred is
+kept, the completion tail still runs, and the exit code is 0 (like rsync's
+clean "stopped early" behavior).  Malformed values are rejected up front.
+"""
+import filecmp
+import os
+import shutil
+import time
+
+import pytest
+
+from common import (
+    TEST_DATA_DIR,
+    run_client,
+    clean_dir,
+    get_dest_received_dir,
+    verify_transfer,
+)
+
+
+def _make(self_prefix):
+    source = os.path.join(TEST_DATA_DIR, f"stop_{self_prefix}_src")
+    dest = os.path.join(TEST_DATA_DIR, f"stop_{self_prefix}_dst")
+    clean_dir(source)
+    shutil.rmtree(dest, ignore_errors=True)
+    os.makedirs(dest)
+    return source, dest
+
+
+def _received_files(root):
+    """All files under `root`, relative paths."""
+    if not os.path.isdir(root):
+        return []
+    return [
+        os.path.relpath(os.path.join(dirpath, name), root)
+        for dirpath, _, names in os.walk(root)
+        for name in names
+    ]
+
+
+def _seed_source(source):
+    """Create a handful of regular and nested files."""
+    files = {
+        "small.txt": b"hello world\n",
+        "medium.txt": b"the quick brown fox jumps over the lazy dog\n" * 400,
+        "binary.bin": bytes(range(256)) * 100,
+        "nested/deep.txt": b"deeply nested file\n",
+        "nested/another.txt": b"another nested file\n" * 40,
+    }
+    for rel, content in files.items():
+        path = os.path.join(source, rel)
+        os.makedirs(os.path.dirname(path), exist_ok=True)
+        with open(path, "wb") as fh:
+            fh.write(content)
+
+
+def _seed_many(source, count=40, size=32 * 1024):
+    """Create `count` same-size regular files (enough to span several chunks)."""
+    blob = os.urandom(size)
+    for i in range(count):
+        with open(os.path.join(source, f"f{i:04d}.dat"), "wb") as fh:
+            fh.write(blob)
+
+
+def _seed_dest_by_transfer(source, dest, port, extra=None):
+    """Do a plain full transfer source->dest so dest exactly mirrors source."""
+    run_client(source, dest, flags=(extra or []), port=port)
+
+
+def _received_subset_matches(source, received):
+    """Every file under `received` exists under `source` with identical bytes."""
+    if not os.path.isdir(received):
+        return not _received_files(received)
+    rels = _received_files(received)
+    for rel in rels:
+        src = os.path.join(source, rel)
+        dst = os.path.join(received, rel)
+        if not os.path.isfile(src) or not filecmp.cmp(src, dst, shallow=False):
+            return False
+    return True
+
+
+class TestStopAfter:
+    @pytest.mark.ci
+    def test_stop_after_within_window(self, shared_server):
+        """A --stop-after set well past the run's duration lets it finish fully."""
+        source, dest = _make("within")
+        _seed_source(source)
+        result, _ = run_client(source, dest, flags=["--stop-after=60"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--stop-after full run failed: {(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, \
+            f"full transfer mismatch: missing={missing} mismatches={mismatches}"
+
+    @pytest.mark.ci
+    def test_stop_after_rejects_nonpositive(self, shared_server):
+        """0 and negative minutes are invalid (must be a positive integer)."""
+        source, dest = _make("reject")
+        _seed_source(source)
+        for bad in ("0", "-1"):
+            result, _ = run_client(source, dest, flags=[f"--stop-after={bad}"],
+                                   port=shared_server.port)
+            assert result.returncode != 0, f"--stop-after={bad} should be rejected"
+
+
+class TestStopAt:
+    @pytest.mark.ci
+    def test_stop_at_past(self, shared_server):
+        """A --stop-at already in the past stops the transfer immediately but
+        cleanly (exit 0, nothing transferred)."""
+        source, dest = _make("past")
+        _seed_source(source)
+        # Use a same-day HH:MM two minutes in the past when that cannot roll
+        # over into the previous day (which would parse as a FUTURE time today);
+        # otherwise fall back to now+0s which is deterministically immediate.
+        lt = time.localtime()
+        if lt.tm_hour * 60 + lt.tm_min >= 3:
+            past = time.localtime(time.time() - 120)
+            stop_value = f"{past.tm_hour:02d}:{past.tm_min:02d}"
+        else:
+            stop_value = "now+0s"
+        result, _ = run_client(source, dest, flags=[f"--stop-at={stop_value}"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--stop-at past run failed (rc {result.returncode}): " \
+            f"{(result.stderr or result.stdout)[:400]}"
+        received = get_dest_received_dir(dest, source)
+        assert _received_files(received) == [], \
+            f"expected nothing transferred, got {_received_files(received)}"
+
+    @pytest.mark.ci
+    def test_stop_at_now_plus_stops_immediately(self, shared_server):
+        """now+0s resolves to the current instant, so the transfer stops at once."""
+        source, dest = _make("nowplus")
+        _seed_source(source)
+        result, _ = run_client(source, dest, flags=["--stop-at=now+0s"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--stop-at=now+0s should stop cleanly: " \
+            f"{(result.stderr or result.stdout)[:400]}"
+        received = get_dest_received_dir(dest, source)
+        assert _received_files(received) == [], \
+            f"expected nothing transferred, got {_received_files(received)}"
+
+    @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"):
+            result, _ = run_client(source, dest, flags=[flag],
+                                   port=shared_server.port)
+            assert result.returncode != 0, f"{flag} should be rejected"
+
+
+class TestStopPartial:
+    """A genuine mid-transfer stop leaves a valid, strict non-empty prefix."""
+
+    @pytest.mark.ci
+    def test_stop_mid_transfer_leaves_valid_partial(self, shared_server):
+        """With --bwlimit a real deadline cuts the transfer mid-way: what WAS
+        transferred is byte-identical, not everything is transferred, and the
+        run returns 0 without corrupting any file."""
+        source, dest = _make("partial")
+        _seed_many(source, count=60, size=32 * 1024)
+        flags = ["--chunk-size", "262144", "--bwlimit", "100", "--stop-at=now+3s"]
+        result, _ = run_client(source, dest, flags=flags, port=shared_server.port)
+        assert result.returncode == 0, \
+            f"mid-transfer stop failed (rc {result.returncode}): " \
+            f"{(result.stderr or result.stdout)[:400]}"
+        received = get_dest_received_dir(dest, source)
+        got = _received_files(received)
+        assert len(got) > 0, "expected an early stop to still transfer a prefix"
+        assert len(got) < 60, \
+            f"expected a PARTIAL transfer (all 60 arrived): stopped too late"
+        assert _received_subset_matches(source, received), \
+            f"received files are not a byte-identical subset of the source"
+
+
+class TestStopDelete:
+    """--delete must never wipe the destination when the scan is cut short."""
+
+    def _seed(self, prefix, port, many=False):
+        source, dest = _make(prefix)
+        if many:
+            _seed_many(source, count=40, size=96 * 1024)
+        else:
+            _seed_source(source)
+        _seed_dest_by_transfer(source, dest, port)
+        return source, dest
+
+    @pytest.mark.ci
+    def test_stop_delete_immediate_preserves_source_mirrors(self, shared_server):
+        """Immediate stop + --delete: the incomplete/empty keep-set must NOT
+        delete the seeded source mirrors (returncode 0, files survive)."""
+        source, dest = self._seed("del_imm", shared_server.port)
+        result, _ = run_client(source, dest, flags=["--delete", "--stop-at=now+0s"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--delete immediate stop failed: {(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, \
+            f"--delete wiped source mirrors: missing={missing} mismatches={mismatches}"
+
+    @pytest.mark.ci
+    def test_stop_delete_midscan_preserves_source_mirrors(self, shared_server):
+        """A mid-scan stop + --delete must suppress the partial keep-set so all
+        seeded source mirrors survive."""
+        source, dest = self._seed("del_mid", shared_server.port, many=True)
+        flags = ["--delete", "--chunk-size", "262144", "--bwlimit", "300", "--stop-at=now+3s"]
+        result, _ = run_client(source, dest, flags=flags, port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--delete mid-scan stop failed: {(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, \
+            f"--delete mid-scan wiped source mirrors: missing={missing} mismatches={mismatches}"
+
+    @pytest.mark.ci
+    def test_stop_delete_multithreaded_preserves_source_mirrors(self, shared_server):
+        """-m immediate stop + --delete: the completion tail must not read the
+        still-appendable manifest (no race) and must not delete the mirrors."""
+        source, dest = self._seed("del_mt", shared_server.port, many=True)
+        result, _ = run_client(source, dest, flags=["--threads", "--delete", "--stop-at=now+0s"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--threads --delete immediate stop failed: {(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, \
+            f"--threads --delete wiped source mirrors: missing={missing} mismatches={mismatches}"

tests/integration/test_tcp.py

@@ -21,7 +21,8 @@ def setup_test_data():
     generate_test_files(SOURCE_DIR, full=False)
     clean_dir(DEST_DIR)
     yield
-    shutil.rmtree(TEST_DATA_DIR, ignore_errors=True)
+    shutil.rmtree(SOURCE_DIR, ignore_errors=True)
+    shutil.rmtree(DEST_DIR, ignore_errors=True)
 
 
 def _run_tcp_test(name, port, flags, use_metadata=True, posix=False):
@@ -29,11 +30,11 @@ def _run_tcp_test(name, port, flags, use_metadata=True, posix=False):
     clean_dir(DEST_DIR)
     if posix:
         result, dur = run_client_posix(SOURCE_DIR, DEST_DIR,
-                                       flags=(["-M"] if use_metadata else []) + flags,
+                                       flags=(["--preserve"] if use_metadata else []) + flags,
                                        port=port)
     else:
         result, dur = run_client(SOURCE_DIR, DEST_DIR,
-                                 flags=(["-M"] if use_metadata else []) + flags,
+                                 flags=(["--preserve"] if use_metadata else []) + flags,
                                  port=port)
 
     if result.returncode != 0:
@@ -49,10 +50,12 @@ def _run_tcp_test(name, port, flags, use_metadata=True, posix=False):
 
 
 class TestTCPStandard:
+    @pytest.mark.ci
     def test_standard(self, shared_server):
         r = _run_tcp_test("Standard", shared_server.port, [])
         assert r["status"] == "Success", r["error"]
 
+    @pytest.mark.ci
     def test_posix_args(self, shared_server):
         r = _run_tcp_test("Posix Args", shared_server.port, [], posix=True)
         assert r["status"] == "Success", r["error"]
@@ -63,40 +66,76 @@ class TestTCPStandard:
 
 
 class TestTCPFlags:
+    @pytest.mark.ci
     def test_multithreading(self, shared_server):
-        r = _run_tcp_test("Multithreading (-m)", shared_server.port, ["-m"])
+        r = _run_tcp_test("Multithreading (--threads)", shared_server.port, ["--threads"])
         assert r["status"] == "Success", r["error"]
 
+    @pytest.mark.ci
     def test_compression(self, shared_server):
-        r = _run_tcp_test("Compression (-c)", shared_server.port, ["-c"])
+        r = _run_tcp_test("Compression (-z)", shared_server.port, ["-z"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_compression_threads(self, shared_server):
+        r = _run_tcp_test("Compression threads (-z --compress-threads=2)", shared_server.port,
+                          ["-z", "--compress-threads=2"])
         assert r["status"] == "Success", r["error"]
 
     def test_chunk_serialization(self, shared_server):
-        r = _run_tcp_test("Chunk Serialization (-s)", shared_server.port, ["-s"])
+        r = _run_tcp_test("Chunk Serialization (--chunk-serialization)", shared_server.port, ["--chunk-serialization"])
         assert r["status"] == "Success", r["error"]
 
     def test_compression_chunk(self, shared_server):
-        r = _run_tcp_test("Compression + Chunk (-c -s)", shared_server.port, ["-c", "-s"])
+        r = _run_tcp_test("Compression + Chunk (-z --chunk-serialization)", shared_server.port, ["-z", "--chunk-serialization"])
         assert r["status"] == "Success", r["error"]
 
     def test_multithread_compression(self, shared_server):
-        r = _run_tcp_test("Multithreading + Compression (-m -c)", shared_server.port, ["-m", "-c"])
+        r = _run_tcp_test("Multithreading + Compression (--threads -z)", shared_server.port, ["--threads", "-z"])
         assert r["status"] == "Success", r["error"]
 
     def test_multithread_chunk(self, shared_server):
-        r = _run_tcp_test("Multithreading + Chunk (-m -s)", shared_server.port, ["-m", "-s"])
+        r = _run_tcp_test("Multithreading + Chunk (--threads --chunk-serialization)", shared_server.port, ["--threads", "--chunk-serialization"])
         assert r["status"] == "Success", r["error"]
 
     def test_all_flags(self, shared_server):
-        r = _run_tcp_test("Multithread + Compression + Chunk (-m -c -s)", shared_server.port, ["-m", "-c", "-s"])
+        r = _run_tcp_test("Multithread + Compression + Chunk (--threads -z --chunk-serialization)", shared_server.port, ["--threads", "-z", "--chunk-serialization"])
         assert r["status"] == "Success", r["error"]
 
     def test_sendfile(self, shared_server):
-        r = _run_tcp_test("Sendfile (-f)", shared_server.port, ["-f"])
+        r = _run_tcp_test("Sendfile (--sendfile)", shared_server.port, ["--sendfile"])
         assert r["status"] == "Success", r["error"]
 
     def test_sendfile_multithread(self, shared_server):
-        r = _run_tcp_test("Sendfile + Multithreading (-f -m)", shared_server.port, ["-f", "-m"])
+        r = _run_tcp_test("Sendfile + Multithreading (--sendfile --threads)", shared_server.port, ["--sendfile", "--threads"])
+        assert r["status"] == "Success", r["error"]
+
+
+class TestTCPSocketOptions:
+    """--sockopts, -4/-6 and --address: rsync-compatible socket/bind options.
+
+    These are purely local (client-side) socket concerns that never cross the
+    wire, so each is exercised by a normal transfer succeeding end-to-end."""
+
+    @pytest.mark.ci
+    def test_sockopts_apply(self, shared_server):
+        r = _run_tcp_test("Sockopts (TCP_NODELAY=1,SO_KEEPALIVE=1)", shared_server.port,
+                          ["--sockopts=TCP_NODELAY=1,SO_KEEPALIVE=1"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_sockopts_buffer_sizes(self, shared_server):
+        r = _run_tcp_test("Sockopts buffer sizes (SO_RCVBUF/SO_SNDBUF)", shared_server.port,
+                          ["--sockopts=SO_RCVBUF=131072,SO_SNDBUF=131072"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_ipv4_forced(self, shared_server):
+        r = _run_tcp_test("Force IPv4 (-4)", shared_server.port, ["-4"])
+        assert r["status"] == "Success", r["error"]
+
+    @pytest.mark.skipif(shutil.which("ip") is None,
+                        reason="requires ip tooling to enumerate a usable local address")
+    def test_address_source_bind(self, shared_server):
+        r = _run_tcp_test("Source bind (--address=127.0.0.1)", shared_server.port,
+                          ["--address", "127.0.0.1"])
         assert r["status"] == "Success", r["error"]
 
 

tests/integration/test_tls.py

@@ -92,10 +92,12 @@ def setup_test_data():
     generate_test_files(SOURCE_DIR, full=False)
     clean_dir(DEST_DIR)
     yield
-    shutil.rmtree(TEST_DATA_DIR, ignore_errors=True)
+    shutil.rmtree(SOURCE_DIR, ignore_errors=True)
+    shutil.rmtree(DEST_DIR, ignore_errors=True)
 
 
 class TestTLSBasic:
+    @pytest.mark.ci
     def test_tls_server_client(self, certs):
         """Basic TLS: server with cert/key, client with cert/key + CA."""
         clean_dir(DEST_DIR)
@@ -130,7 +132,7 @@ class TestTLSBasic:
             ])
             result, dur = run_client(
                 SOURCE_DIR, DEST_DIR,
-                flags=["-c", "--tls",
+                flags=["-z", "--tls",
                        "--cert", certs["client_cert"], "--key", certs["client_key"],
                        "--ca", certs["ca"]],
                 port=server.port,
@@ -155,7 +157,7 @@ class TestTLSBasic:
             ])
             result, dur = run_client(
                 SOURCE_DIR, DEST_DIR,
-                flags=["-m", "--tls",
+                flags=["--threads", "--tls",
                        "--cert", certs["client_cert"], "--key", certs["client_key"],
                        "--ca", certs["ca"]],
                 port=server.port,