Merge pull request 'Release v2.26.0' (#284) from dev into main

Reviewed-on: #284

.gitea/workflows/ci.yaml

@@ -9,10 +9,10 @@ on:
 jobs:
   lint:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
       - name: clang-format check
         run: find src/ tests/ -name '*.c' -o -name '*.h' | xargs clang-format --dry-run --Werror
@@ -26,11 +26,11 @@ jobs:
   # suite) run on merge to dev/main, so PR CI stays well under ~3 minutes.
   build-and-test:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     needs: lint
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
       - name: Configure
         run: cmake -B build -S . -DSTRICT_WARNINGS=ON
@@ -51,7 +51,7 @@ jobs:
 
   sanitizers:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     needs: lint
     if: github.event_name == 'push'
     strategy:
@@ -59,7 +59,7 @@ jobs:
         sanitizer: [address, undefined]
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
       - name: Configure
         run: cmake -B build-${{ matrix.sanitizer }} -S . -DSANITIZER=${{ matrix.sanitizer }}
@@ -72,12 +72,12 @@ jobs:
 
   fuzz-build:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     needs: lint
     if: github.event_name == 'push'
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
       - name: Configure (clang + fuzz)
         run: CC=clang CXX=clang++ cmake -B build-fuzz -S . -DENABLE_FUZZ=ON
@@ -94,12 +94,12 @@ jobs:
 
   coverage:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     needs: lint
     if: github.event_name == 'push'
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
       - name: Configure
         run: cmake -B build -S . -DENABLE_COVERAGE=ON
@@ -118,12 +118,12 @@ jobs:
 
   valgrind:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     needs: lint
     if: github.event_name == 'push'
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
 
       - name: Configure
         run: cmake -B build -S . -DSTRICT_WARNINGS=ON

.gitignore

@@ -8,3 +8,7 @@ build-*/
 build2/
 build3/
 build_docker2/
+
+# Test/run artifacts
+root/
+test_partial_install_tmp/

.opencode/agents/architect.md

@@ -128,7 +128,7 @@ Do not wait for the user to tell you CI failed — check proactively. The user s
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/c-reviewer.md

@@ -92,7 +92,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/cmake-expert.md

@@ -27,16 +27,19 @@ FetchContent_Declare(xxhash GIT_REPOSITORY https://github.com/Cyan4973/xxHash GI
 FetchContent_MakeAvailable(xxhash)
 
 # Sanitizer option
-set(SANITIZER "none" CACHE STRING "Sanitizer to enable (address, thread, none)")
-set_property(CACHE SANITIZER PROPERTY STRINGS address thread none)
+set(SANITIZER "none" CACHE STRING "Sanitizer to enable (address, thread, undefined, none)")
+set_property(CACHE SANITIZER PROPERTY STRINGS address thread undefined none)
 if(SANITIZER STREQUAL "address")
   add_compile_options(-fsanitize=address -fno-omit-frame-pointer -g)
   add_link_options(-fsanitize=address)
 elseif(SANITIZER STREQUAL "thread")
   add_compile_options(-fsanitize=thread -fno-omit-frame-pointer -g)
   add_link_options(-fsanitize=thread)
+elseif(SANITIZER STREQUAL "undefined")
+  add_compile_options(-fsanitize=undefined -fno-omit-frame-pointer -g)
+  add_link_options(-fsanitize=undefined)
 elseif(NOT SANITIZER STREQUAL "none")
-  message(FATAL_ERROR "Unknown sanitizer: ${SANITIZER}. Supported values: address, thread, none")
+  message(FATAL_ERROR "Unknown sanitizer: ${SANITIZER}. Supported values: address, thread, undefined, none")
 endif()
 
 option(STRICT_WARNINGS "Enable strict warnings" OFF)
@@ -52,6 +55,16 @@ if(NOT ZSTD_LIBRARY)
   message(FATAL_ERROR "zstd library not found. Ensure it is in your nix-shell!")
 endif()
 
+find_library(ZLIB_LIBRARY z)
+if(NOT ZLIB_LIBRARY)
+  message(FATAL_ERROR "zlib library not found. Ensure zlib1g-dev / nix zlib is available!")
+endif()
+
+find_library(LZ4_LIBRARY lz4)
+if(NOT LZ4_LIBRARY)
+  message(FATAL_ERROR "lz4 library not found. Ensure liblz4-dev / nix lz4 is available!")
+endif()
+
 find_package(OpenSSL REQUIRED)
 
 file(GLOB SHARED_SRCS "src/shared/*.c")
@@ -61,15 +74,15 @@ file(GLOB TEST_SRCS "tests/*.c")
 
 add_executable(server ${SERVER_SRCS} ${SHARED_SRCS})
 target_include_directories(server PRIVATE src/shared src/server src/client)
-target_link_libraries(server PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
+target_link_libraries(server PRIVATE Threads::Threads ${ZSTD_LIBRARY} ${ZLIB_LIBRARY} ${LZ4_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
 
 add_executable(client ${CLIENT_SRCS} ${SHARED_SRCS})
 target_include_directories(client PRIVATE src/shared src/server src/client)
-target_link_libraries(client PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
+target_link_libraries(client PRIVATE Threads::Threads ${ZSTD_LIBRARY} ${ZLIB_LIBRARY} ${LZ4_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
 
 add_executable(tests ${TEST_SRCS} ${SHARED_SRCS} src/client/scanner.c)
 target_include_directories(tests PRIVATE tests src/shared src/server src/client)
-target_link_libraries(tests PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
+target_link_libraries(tests PRIVATE Threads::Threads ${ZSTD_LIBRARY} ${ZLIB_LIBRARY} ${LZ4_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
 ```
 
 ### Source Layout
@@ -82,19 +95,25 @@ tests/integration/ — Python pytest integration tests
 ```
 
 ### Dependencies
-- **zstd** — found via `find_library(ZSTD_LIBRARY zstd)`
+- **zstd** — found via `find_library(ZSTD_LIBRARY zstd)` (default compression codec)
+- **zlib** — found via `find_library(ZLIB_LIBRARY z)` (the `zlib`/`zlibx` codecs)
+- **lz4** — found via `find_library(LZ4_LIBRARY lz4)` (the `lz4` codec)
 - **OpenSSL** — found via `find_package(OpenSSL REQUIRED)` (TLS 1.2+ transport)
-- **xxHash** — fetched via `FetchContent` from GitHub (delta transfer hashing, v0.8.3)
+- **xxHash** — fetched via `FetchContent` from the upstream repository (delta transfer hashing, v0.8.3)
 - **pthreads** — found via `find_package(Threads REQUIRED)`
 - **C11 standard** — required
 - **CMake 3.22+** — minimum version
 
+The codec matrix (protocol 2.26.0) uses zstd/zlib/lz4 for compression and
+xxHash/OpenSSL for the `xxh128`/`xxh3`/`xxh64`/`md5`/`md4`/`sha1` checksums
+(`none` needs no library); both codec families are negotiated per transfer.
+
 ## Conventions
 
 - Use `file(GLOB ...)` for source collection (existing pattern).
-- All targets link `Threads::Threads`, `${ZSTD_LIBRARY}`, `OpenSSL::SSL`, `OpenSSL::Crypto`, and `xxhash`.
+- All targets link `Threads::Threads`, `${ZSTD_LIBRARY}`, `${ZLIB_LIBRARY}`, `${LZ4_LIBRARY}`, `OpenSSL::SSL`, `OpenSSL::Crypto`, and `xxhash`.
 - Include directories: `src/shared`, `src/server`, `src/client`, `tests` (for test target).
-- Sanitizer support: pass `-DSANITIZER=address` or `-DSANITIZER=thread` to cmake (live option in CMakeLists.txt).
+- Sanitizer support: pass `-DSANITIZER=address`, `-DSANITIZER=thread`, or `-DSANITIZER=undefined` to cmake (live option in CMakeLists.txt).
 - Build with `cmake -B build -S . && cmake --build build -j$(nproc)`.
 - For CI, dependencies are provided by the project's custom Docker image (repo-root `Dockerfile`, same image CI uses). For local development, use `nix-shell`. Never add `apt-get install` / `pip install` to CI workflows. See `AGENTS.md`.
 
@@ -105,7 +124,7 @@ tests/integration/ — Python pytest integration tests
 3. Add new dependencies with `find_package` or `find_library`.
 4. When adding a new executable target, follow the pattern of existing targets.
 5. When adding a new library (static/shared), use `add_library` and follow the project's naming.
-6. For sanitizer builds, pass `-DSANITIZER=address` or `-DSANITIZER=thread` to cmake (matching CI's matrix strategy).
+6. For sanitizer builds, pass `-DSANITIZER=address`, `-DSANITIZER=thread`, or `-DSANITIZER=undefined` to cmake (matching CI's matrix strategy).
 7. Always verify the build compiles after changes.
 
 ## Sanitizer Configurations
@@ -119,11 +138,9 @@ cmake -B build -S . -DSANITIZER=thread    # ThreadSanitizer (race conditions)
 cmake --build build -j$(nproc)
 ```
 
-For UndefinedBehaviorSanitizer (no `-DSANITIZER=undefined` option in CMakeLists.txt yet), use the manual flag approach:
+UndefinedBehaviorSanitizer uses the same built-in option:
 ```bash
-cmake -B build -S . \
-  -DCMAKE_C_FLAGS="-fsanitize=undefined -fno-omit-frame-pointer -g" \
-  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=undefined"
+cmake -B build -S . -DSANITIZER=undefined
 cmake --build build -j$(nproc)
 ```
 
@@ -159,7 +176,7 @@ cmake -B build -S . -DCMAKE_BUILD_TYPE=RelWithDebInfo
 ```bash
 cmake -B build -S .
 cmake --build build -j$(nproc)
-./build/server
+./build/server -p 8080 --allow-unauthenticated
 ./build/client
 ./build/tests
 ```
@@ -187,7 +204,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/code-explainer.md

@@ -27,7 +27,7 @@ FastSync is a file synchronization tool (like rsync, but faster). It transfers f
 cmake -B build -S . && cmake --build build -j$(nproc)
 
 # Server (TCP mode)
-./build/server
+./build/server -p 8080 --allow-unauthenticated
 
 # Client (TCP mode)
 ./build/client --source-dir /path/to/send --dest-dir /path/to/receive --save-to-disk
@@ -37,13 +37,13 @@ cmake -B build -S . && cmake --build build -j$(nproc)
 
 # Run tests
 ./build/tests          # unit tests
-python3 test.py        # integration tests
+python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"   # integration tests
 ```
 
 ## Code Walkthrough
 
 ### Client Entry Point (`src/client/client_cli.c`)
-- Parses CLI arguments using `getopt_long`
+- Parses CLI arguments using a custom option-table parser (`OPTION_TABLE` in `src/client/client_cli.c`); there is no `getopt*` usage
 - Creates `Config` struct with all options
 - Detects SSH destinations (contains `:`)
 - Calls into `client_send.c` for the actual transfer
@@ -109,7 +109,7 @@ Collection of files for batch transfer. Serialized with file count, then per-fil
 zstd streaming compression via `ZSTD_compressStream2`/`ZSTD_decompressStream`. Compression happens per-chunk in the sender stage. Level 1-22 (default 5). Streaming means memory usage stays bounded regardless of file size.
 
 ### "How does sendfile() work?"
-On Linux, `sendfile()` copies data directly from kernel file buffer to socket, bypassing userspace. ~2x faster for large files. Enabled with `-f` flag. Only works with TCP (not SSH, not compression).
+On Linux, `sendfile()` copies data directly from kernel file buffer to socket, bypassing userspace. ~2x faster for large files. Enabled with `--sendfile` (long form only). Only works with TCP (not SSH, not compression).
 
 ### "How does incremental sync work?"
 Client sends file metadata (path, size, mtime) to server. Server checks if destination file has same size+mtime. If match, server responds `STATUS_OK` (skip). If mismatch, server responds `STATUS_NEXT` (send).
@@ -138,7 +138,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/code-quality-guardian.md

@@ -316,7 +316,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/debugger.md

@@ -14,10 +14,9 @@ Diagnose crashes, memory errors, hangs, and logic bugs. You use structured debug
 ### Memory Errors
 ```bash
 # AddressSanitizer (fast, recommended first)
-cmake -B build -S . -DCMAKE_C_FLAGS="-fsanitize=address -fno-omit-frame-pointer" \
-  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address"
-cmake --build build -j$(nproc)
-./build/client  # or ./build/server
+cmake -B build-asan -S . -DSANITIZER=address
+cmake --build build-asan -j$(nproc)
+./build-asan/client  # or ./build-asan/server -p 8080 --allow-unauthenticated
 
 # Valgrind (slower, more thorough)
 valgrind --leak-check=full --show-leak-kinds=all --track-origins=yes \
@@ -32,10 +31,9 @@ valgrind --tool=drd ./build/client ...
 
 ### Thread Sanitizer
 ```bash
-cmake -B build -S . -DCMAKE_C_FLAGS="-fsanitize=thread" \
-  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=thread"
-cmake --build build -j$(nproc)
-./build/tests
+cmake -B build-tsan -S . -DSANITIZER=thread
+cmake --build build-tsan -j$(nproc)
+./build-tsan/tests
 ```
 
 ### GDB
@@ -143,7 +141,7 @@ gprof ./build/client gmon.out
 
 ### Step 5: Verify
 - Run `./build/tests` (unit tests)
-- Run `python3 test.py` (integration tests)
+- Run `python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"` (integration tests)
 - Run under valgrind again to confirm clean
 - Test under ASan again
 
@@ -162,7 +160,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/doc-generator.md

@@ -96,7 +96,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/feature-scout.md

@@ -16,12 +16,18 @@ Scan the codebase for patterns that suggest new feature opportunities. You ident
 ### Module Map
 ```
 src/client/         Client-side: CLI parsing, scanning, sending
-  client_cli.c      Entry point, argument parsing, config setup
+  client_cli.c      Entry point, OPTION_TABLE parser, config setup
+  usage.c           Usage/help text (authoritative CLI flag list)
   client_send.c     Transfer orchestration, pipeline management
+  client_validation.c  Destination/CLI validation
   scanner.c         BFS directory traversal, chunk building
+  change_list.c     File change-list bookkeeping
 
 src/server/         Server-side: listening, receiving, writing
   server.c          TCP accept loop, per-connection handling
+  server_cli.c      Server option-table CLI parsing
+  receiver.c        Receiver-side file handling
+  receiver_pipeline.c  Receiver worker pipeline
 
 src/shared/         Shared libraries (used by both client and server)
   protocol.c/h      Wire protocol: status codes, send/receive primitives
@@ -32,40 +38,63 @@ src/shared/         Shared libraries (used by both client and server)
   data.c/h          Generic buffer type (Data)
   metadata.c/h      File metadata (mode, uid, gid, mtime)
   file.c/h          File representation
+  file_send.c/h     Sender-side file transfer
+  file_receive.c/h  Receiver-side file transfer
+  file_list.c/h     File list model
+  file_store.c/h    Destination file store
   array_list.c/h    Dynamic array
+  delta.c/h         Delta transfer algorithm
+  checksum.c/h      Whole-file/block checksums (xxHash, md5)
+  filter.c/h        rsync-style filter rules
+  batch.c/h         Batch files (--write-batch/--read-batch)
+  charset.c/h       Filename charset conversion (--iconv)
+  chmod.c/h         Permission modification (--chmod)
+  xattr.c/h         Extended attributes
+  hardlink.c/h      Hard-link handling
+  identity.c/h      uid/gid mapping (--usermap/--groupmap/--chown)
+  credentials.c/h   Daemon credentials
+  daemon_conf.c/h   Daemon module configuration
+  motd.c/h          Daemon MOTD
+  delay_updates.c/h Delayed update staging
+  stop_condition.c/h Stop-after/stop-at handling
   transport_tcp.c/h TCP client/server with sendfile() zero-copy
   transport_ssh.c/h SSH transport with ControlMaster
   transport_tls.c/h TLS encryption via OpenSSL
   multiprocessing.c/h Fork-based concurrency
   log.c/h           Logging utilities
   utils.c/h         Shared utilities
+  file_types.h      Shared file type definitions
 ```
 
-### Existing CLI Flags (from client_cli.c)
+### Existing CLI Flags (authoritative source: `src/client/usage.c`)
 ```
---source-dir <dir>       Source directory to sync (required)
---dest-dir <dir>         Destination directory on server (required)
---host <host>            Server hostname/IP (required)
---port <port>            Server TCP port
---server-mode            Listen as server
---use-compression, -c    Enable zstd compression
---use-multithreading, -m Enable multithreaded transfer
---use-sendfile, -s       Use sendfile() zero-copy TCP
---use-ssh, -S            Use SSH transport
---use-tls, -T            Enable TLS encryption
---cert <file>            TLS certificate file
---key <file>             TLS key file
---ca <file>              TLS CA certificate file
---insecure               Skip TLS verification
---bwlimit <bytes/s>      Bandwidth limit
---delete                 Delete files not in source
---include <pattern>      Include filter pattern
---exclude <pattern>      Exclude filter pattern
---dry-run                Print what would be transferred
---save-to-disk           Save transferred files to disk (for server tests)
+--source-dir <dir>       Source directory
+--dest-dir <dir>         Destination directory on server
+--server-host <ip>       Server IP address (default: 127.0.0.1)
+--server-port <n>        Server port (default: 8080); --port is an alias
+-c, --checksum           Verify content by checksum instead of size+mtime
+-z, --compress [level]   Enable compression (level 1-22, default 5)
+-j, --threads[=N]        Enable multithreaded scanner/loader/sender pipeline
+--chunk-serialization    Enable chunk serialization (long form only)
+--sendfile               sendfile() zero-copy (TCP only; long form only)
+-s, --secluded-args      Protect-args compatibility option (no effect)
+--tls                    Enable TLS encryption; --cert/--key/--ca give PEMs
+--bwlimit <KB/s>         Bandwidth limit in kilobytes per second
+--delete                 Delete files on receiver not in source
+--incremental            Skip files unchanged since last transfer
+--delta                  Delta transfer for changed files (needs --incremental)
+-f, --filter=RULE        rsync-style filter rule (+/- include/exclude)
+--exclude <pattern>      Exclude files matching pattern
+--include <pattern>      Only include files matching pattern
+-m, --prune-empty-dirs   Do not transfer empty directory entries
+-n, --dry-run            Show what would be transferred
+--save-to-disk           Write received files to disk
 --version                Print version and exit
---help                   Print help
+--help                   Show help
 ```
+> Always confirm the current flags with `./build/client --help`; the table above
+> is a representative subset. `src/client/usage.c` is the authoritative list and
+> `OPTION_TABLE` in `src/client/client_cli.c` is the parser (there is no `getopt*`).
 
 ## Feature Scout Checklist
 
@@ -288,7 +317,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/integrator.md

@@ -21,7 +21,7 @@ Design integration tests that verify the full transfer pipeline works end-to-end
 - Multiple configurations (TCP, SSH, TLS, compression, multithreading)
 - Network shaping (LAN, WAN profiles)
 - Feature tests (dry run, archive, exclude, delete, incremental, bandwidth limit)
-- Run: `python3 -m pytest tests/ -v --tb=short`
+- Run: `python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"`
 
 ### 3. New: Focused Integration Tests
 When adding new features or fixing bugs, write targeted integration tests.
@@ -35,13 +35,14 @@ mkdir -p /tmp/fastsync_test/src
 echo "test content" > /tmp/fastsync_test/src/file.txt
 
 # Start server
-./build/server &
+./build/server -p 8080 --allow-unauthenticated &
 SERVER_PID=$!
 sleep 0.5
 
 # Run client
 ./build/client --source-dir /tmp/fastsync_test/src \
   --dest-dir /tmp/fastsync_test/dst \
+  --server-port 8080 \
   --save-to-disk
 
 # Verify
@@ -76,7 +77,7 @@ openssl req -x509 -newkey rsa:2048 -keyout /tmp/key.pem -out /tmp/cert.pem \
 ### Pattern 4: Incremental Sync
 ```bash
 # First sync
-./build/client --source-dir /tmp/src --dest-dir /tmp/dst --save-to-disk -M
+./build/client --source-dir /tmp/src --dest-dir /tmp/dst --save-to-disk
 
 # Modify source
 echo "updated" >> /tmp/src/file.txt
@@ -89,14 +90,14 @@ echo "updated" >> /tmp/src/file.txt
 ### Pattern 5: Delete Verification
 ```bash
 # Initial sync
-./build/client --source-dir /tmp/src --dest-dir /tmp/dst --save-to-disk -M
+./build/client --source-dir /tmp/src --dest-dir /tmp/dst --save-to-disk
 
 # Add extra file to dest
 echo "extra" > /tmp/dst/.../extra.txt
 
 # Sync with --delete
 ./build/client --source-dir /tmp/src --dest-dir /tmp/dst \
-  --save-to-disk --delete -M
+  --save-to-disk --delete
 
 # Verify extra.txt is gone
 test ! -f /tmp/dst/.../extra.txt
@@ -115,7 +116,7 @@ The project uses Gitea Actions. Key jobs:
 jobs:
   new-job:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v7
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v11
     steps:
       - uses: actions/checkout@v4
       - name: Configure
@@ -127,7 +128,7 @@ jobs:
       - name: Unit Tests
         run: ./build-${{ matrix.sanitizer }}/tests
       - name: Integration Tests
-        run: LSAN_OPTIONS=suppressions=.lsan-suppressions.txt python3 -m pytest tests/ -v --tb=short
+        run: LSAN_OPTIONS=suppressions=.lsan-suppressions.txt python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"
 ```
 The symlink step is required because `tests/conftest.py` expects `./build` to exist.
 
@@ -135,7 +136,7 @@ The symlink step is required because `tests/conftest.py` expects `./build` to ex
 
 After any code change:
 - [ ] Unit tests pass: `./build/tests`
-- [ ] Integration tests pass: `python3 -m pytest tests/ -v --tb=short`
+- [ ] Integration tests pass: `python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"`
 - [ ] Build clean: no warnings with `-Wall`
 - [ ] No memory errors: ASan clean
 - [ ] No thread errors: TSan clean (if threading involved)
@@ -156,7 +157,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/issue-creator.md

@@ -1,5 +1,5 @@
 ---
-description: Top-level orchestrator that analyzes the FastSync codebase by delegating to specialized sub-agents and creates GitHub issues from their findings.
+description: Top-level orchestrator that analyzes the FastSync codebase by delegating to specialized sub-agents and creates Gitea issues from their findings.
 mode: subagent
 ---
 
@@ -12,7 +12,7 @@ You are the primary orchestrator agent. Your job is to:
 2. Decide which specialized sub-agents to dispatch for analysis
 3. Delegate analysis work using the task tool
 4. Receive structured findings from sub-agents
-5. Create GitHub issues from those findings using `gh issue create`
+5. Create Gitea issues from those findings using `tea issues create`
 6. Coordinate the overall analysis workflow end-to-end
 
 > **Environment rule:** for CI, dependency installation must use the project's custom Docker image (repo-root `Dockerfile`, same as CI). For local development, use `nix-shell` (see `README.md`). See `AGENTS.md`.
@@ -97,7 +97,7 @@ First, read the repository structure to understand what exists:
 ### Phase 2: Determine Analysis Scope
 Based on what the user requests or what needs attention:
 - **New features wanted?** → Dispatch `feature-scout` sub-agent
-- **Security audit needed?** → Dispatch `security-screener` sub-agent
+- **Security audit needed?** → Dispatch `security-auditor` sub-agent
 - **Code quality review?** → Dispatch `code-quality-guardian` sub-agent
 - **All of the above?** → Run all three in parallel
 
@@ -110,7 +110,7 @@ Context: <provide summary of what was found in Phase 1>
 ```
 
 ```
-Task: Ask the security-screener agent to analyze the codebase.
+Task: Ask the security-auditor agent to analyze the codebase.
 Context: <provide summary of what was found in Phase 1>
 ```
 
@@ -138,14 +138,14 @@ Each sub-agent returns findings in this structured format:
 - **Labels**: comma-separated labels for the issue
 ```
 
-### Phase 5: Create GitHub Issues
-For each finding, create a GitHub issue:
+### Phase 5: Create Gitea Issues
+For each finding, create a Gitea issue:
 
 ```bash
-gh issue create \
+tea issues create --repo TapTap/FastSync \
   --title "<Finding Title>" \
-  --label "<labels>" \
-  --body "## Description
+  --labels "<labels>" \
+  --description "## Description
 <description>
 
 ## Location
@@ -175,11 +175,13 @@ _This issue was automatically generated by the issue-creator agent._"
 
 ### Duplicate Detection
 Before creating an issue:
-1. Check existing open issues: `gh issue list --state open --label "<label>"`
-2. Search for similar titles using `gh issue list --search "<keywords>"`
+1. Check existing open issues: `tea issues list --repo TapTap/FastSync --state open --labels "<label>"`
+2. Search for similar titles using `tea issues list --repo TapTap/FastSync --keyword "<keywords>"`
 3. If a similar issue exists, add a comment instead of creating a duplicate:
    ```bash
-   gh issue comment <issue-number> --body "Additional finding from automated analysis: <details>"
+   tea comment --repo TapTap/FastSync <issue-number> "Additional finding from automated analysis: <details>"
+   # or POST to the Gitea API:
+   #   POST https://gitea.tap-tap.win/api/v1/repos/TapTap/FastSync/issues/<n>/comments
    ```
 
 ## Sub-Agent Reference
@@ -189,13 +191,12 @@ Before creating an issue:
 | Agent | File | Purpose |
 |---|---|---|
 | feature-scout | `.opencode/agents/feature-scout.md` | Scans for feature opportunities |
-| security-screener | `.opencode/agents/security-screener.md` | Scans for security vulnerabilities |
+| security-auditor | `.opencode/agents/security-auditor.md` | Security audits and vulnerability scans |
 | code-quality-guardian | `.opencode/agents/code-quality-guardian.md` | Scans for code quality improvements |
 | architect | `.opencode/agents/architect.md` | Architecture reviews |
 | c-reviewer | `.opencode/agents/c-reviewer.md` | C code correctness reviews |
 | debugger | `.opencode/agents/debugger.md` | Bug diagnosis |
 | refactorer | `.opencode/agents/refactorer.md` | Code refactoring |
-| security-auditor | `.opencode/agents/security-auditor.md` | Security audits |
 | test-writer | `.opencode/agents/test-writer.md` | Test development |
 | perf-analyst | `.opencode/agents/perf-analyst.md` | Performance analysis |
 | protocol-designer | `.opencode/agents/protocol-designer.md` | Protocol design |
@@ -242,7 +243,7 @@ tests/test_file.c             — File tests
 tests/test_transport_tcp.c    — TCP transport tests
 tests/test_transport_tls.c    — TLS transport tests
 tests/test_array_list.c       — Array list tests
-tests/pytest/                 — Python integration tests
+tests/integration/            — Python pytest integration tests
 ```
 
 ### Build & Config Files
@@ -259,7 +260,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/perf-analyst.md

@@ -56,9 +56,11 @@ DirectoryScanner → Queue(Scanner→Loader) → ChunkBuilder → Queue(Loader
 
 ### Benchmark Context
 
-From README benchmarks (25MB mixed files, localhost):
-- Best config: `-m -c` (multithread + compression) → 0.20s, 11.2× faster than rsync
-- `sendfile()` bypasses userspace → ~2× faster on localhost
+Use the maintained benchmark tool — do not cite stale README numbers:
+- `python3 benchmark/bench.py` runs the repeatable throughput benchmark.
+- The real flags are `-j` (multithreading) and `-z` (compression); a fast loopback
+  config combines `-j -z`.
+- `sendfile()` (via `--sendfile`) bypasses userspace → ~2× faster on localhost
 - Compression reduces wire data enough that transfer becomes latency-bound on WAN
 
 ## Output Format
@@ -120,6 +122,7 @@ time ./build/client [args...]
 
 # High precision
 perf stat -e task-clock ./build/client [args...]
+```
 
 ## CI & Task Execution
 
@@ -127,9 +130,8 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 
 **CI rule:** never add `apt-get install` / `pip install` steps to CI workflows — use the custom Docker image instead. **Host rule:** for local development, use `nix-shell` (see `README.md`) which provides zstd, OpenSSL, CMake, and gcc. See `AGENTS.md` for details.
-```

.opencode/agents/protocol-designer.md

@@ -91,7 +91,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/refactorer.md

@@ -160,7 +160,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/security-auditor.md

@@ -3,25 +3,64 @@ description: Audits FastSync for security vulnerabilities — TLS config, input
 mode: subagent
 ---
 
-You are a security auditor for the FastSync project — a high-performance file synchronization system written in C11 with TCP, SSH, and TLS transport.
+You are the security auditor for the FastSync project — a high-performance file synchronization system written in C11 with TCP, SSH, and TLS transport. This is the single canonical security agent.
 
 ## Your Role
 
-Audit the codebase for security vulnerabilities. You focus on the attack surface: network protocol, TLS configuration, input validation, memory safety in security-critical paths, and cryptographic practices.
+Audit the codebase for security vulnerabilities. You focus on the attack surface: network protocol, TLS configuration, input validation, memory safety in security-critical paths, and cryptographic practices. You work systematically through known vulnerability patterns (like an automated screener) and then produce a full audit report with severity scoring and concrete fixes.
 
-## Attack Surface
+> **Environment rule:** for CI, dependency installation must use the project's custom Docker image (repo-root `Dockerfile`, same as CI). For local development, use `nix-shell` (see `README.md`). See `AGENTS.md`.
 
-### Network Input Points
-1. **TCP server** (`src/server/server.c`) — accepts connections from any client
-2. **SSH transport** (`src/shared/transport_ssh.c`) — receives data via stdio pipe
-3. **Protocol parsing** (`src/shared/protocol.c`) — deserializes all incoming data
-4. **Config deserialization** (`src/shared/config.c`) — receives remote config
-5. **Chunk deserialization** (`src/shared/chunk.c`) — receives file batches
+## Project Architecture
 
-### TLS Configuration
-- OpenSSL TLS 1.2+ via `src/shared/transport_tls.c`
-- Certificate/key loading, CA verification
-- SSL context setup, cipher suite selection
+### Module Map
+```
+src/client/         Client-side: CLI parsing, scanning, sending
+  client_cli.c      Entry point, argument parsing, config setup
+  client_send.c     Transfer orchestration, pipeline management
+  client_validation.c  Destination/CLI validation
+  scanner.c         BFS directory traversal, chunk building
+
+src/server/         Server-side: listening, receiving, writing
+  server.c          TCP accept loop, per-connection handling
+  receiver.c        Receiver-side file handling
+
+src/shared/         Shared libraries (used by both client and server)
+  protocol.c/h      Wire protocol: status codes, send/receive primitives
+  compression.c/h   zstd streaming compression/decompression
+  chunk.c/h         File grouping and batch serialization
+  queue.c/h         Thread-safe bounded queue (producer-consumer)
+  config.c/h        Runtime configuration, serialization, parsing
+  data.c/h          Generic buffer type (Data)
+  metadata.c/h      File metadata (mode, uid, gid, mtime)
+  file.c/h          File representation
+  file_receive.c/h  Receiver-side file transfer
+  file_store.c/h    Destination file store
+  delta.c/h         Delta transfer algorithm
+  checksum.c/h      Whole-file/block checksums (xxHash, md5)
+  filter.c/h        rsync-style filter rules
+  xattr.c/h         Extended attributes
+  identity.c/h      uid/gid mapping
+  credentials.c/h   Daemon credentials
+  transport_tcp.c/h TCP client/server with sendfile() zero-copy
+  transport_ssh.c/h SSH transport with ControlMaster
+  transport_tls.c/h TLS encryption via OpenSSL
+  multiprocessing.c/h Fork-based concurrency
+  log.c/h           Logging utilities
+  utils.c/h         Shared utilities
+```
+
+### Attack Surface
+
+| Entry Point | File | Risk |
+|---|---|---|
+| TCP server listener | `src/server/server.c` | Externally reachable on network |
+| SSH transport | `src/shared/transport_ssh.c` | Accepts data via stdio pipe |
+| Protocol parser | `src/shared/protocol.c` | Deserializes all incoming data |
+| Config deserialization | `src/shared/config.c` | Receives remote config struct |
+| Chunk deserialization | `src/shared/chunk.c` | Receives file batches |
+| TLS handshake | `src/shared/transport_tls.c` | SSL context and cert validation |
+| File writer | `src/server/server.c` / `receiver.c` | Writes received files to disk |
 
 ## Security Audit Checklist
 
@@ -33,51 +72,182 @@ Audit the codebase for security vulnerabilities. You focus on the attack surface
 - [ ] Chunk count and file count validated before allocation
 - [ ] Config field lengths bounded
 
-### 2. Buffer Safety
-- [ ] No `strcpy` — use `snprintf` or `strncpy` with null termination
-- [ ] `malloc` size calculations don't overflow (e.g., `count * sizeof(...)`)
-- [ ] No fixed-size stack buffers for unbounded input
-- [ ] `receive_n_data` always checks return value
-- [ ] Off-by-one in path concatenation
+### 2. Buffer Overflow Risks
 
-### 3. Memory Safety in Error Paths
-- [ ] All error paths free allocated resources
-- [ ] No use-after-free on error paths
-- [ ] No double-free on error paths
-- [ ] Partial reads handled (don't use incomplete data)
+Search for these dangerous patterns in all `.c` and `.h` files:
 
-### 4. TLS/SSL Security
-- [ ] TLS 1.2 minimum enforced (no SSLv3, TLS 1.0, TLS 1.1)
-- [ ] Certificate verification enabled when CA provided
-- [ ] Certificate verification disabled only with explicit warning
-- [ ] Private key file permissions checked
-- [ ] No hardcoded certificates or keys
-- [ ] Cipher suites restricted to strong algorithms
-- [ ] SSL error codes checked after `SSL_read`/`SSL_write`
+- [ ] **Fixed-size stack buffers** used for unbounded or network-provided data
+  ```c
+  char path[PATH_MAX];     // OK if PATH_MAX is used, bad if size is arbitrary
+  char buf[1024];          // SUSPICIOUS — what limits the input to 1024?
+  char line[4096];         // SUSPICIOUS — what limits the line length?
+  ```
+- [ ] **`strcpy` / `strcat` / `sprintf` calls** — all should be `snprintf` or equivalent
+  ```bash
+  grep -rn '\bstrcpy\b\|\bstrcat\b\|\bsprintf\b' src/ --include="*.c" --include="*.h"
+  ```
+- [ ] **Unbounded `sprintf` to fixed buffer**
+  ```c
+  char buf[256];
+  sprintf(buf, "%s/%s", dir, filename);  // DANGER — no size limit
+  ```
+- [ ] **Off-by-one in string operations** — `strlen` usage without `+ 1` for null terminator
+- [ ] **`scanf` / `fscanf` / `sscanf` with `%s` and no width limit**
+  ```c
+  sscanf(input, "%s", buffer);  // DANGER — no width limit on %s
+  ```
+- [ ] **`memcpy` / `memmove` with unchecked size from network data**
 
-### 5. Authentication & Authorization
+### 3. Path Traversal in File Operations
+
+Check all paths constructed from received data:
+
+- [ ] **Files constructed with client-provided filenames + destination directory**
+  ```c
+  snprintf(path, PATH_MAX, "%s/%s", dest_dir, received_filename);
+  ```
+  Check for `../` filtering:
+  ```bash
+  grep -rn 'snprintf.*%s.*%s.*path\|snprintf.*dest_dir\|snprintf.*base_dir' src/ --include="*.c"
+  ```
+- [ ] **`realpath()` usage** for path canonicalization
+- [ ] **Symlink following** — does the server follow symlinks in the destination?
+- [ ] **Null byte injection** — received filenames with embedded `\0`
+
+### 4. Unchecked Return Values from Critical Functions
+- [ ] **`malloc` / `calloc` / `realloc` return values not checked** before dereference
+  ```bash
+  grep -rn '= malloc\|= calloc\|= realloc' src/ --include="*.c"
+  ```
+  For each match, verify NULL check exists before use.
+- [ ] **`send_n_data` / `receive_n_data` return values** not checked
+- [ ] **`SSL_read` / `SSL_write`** error codes not checked
+- [ ] **`write()` / `read()` syscall** return values not checked (short writes/reads)
+- [ ] **`fopen()` / `open()`** return values not checked
+- [ ] **`snprintf` / `vsnprintf`** negative return not handled
+
+### 5. TLS / SSL Security
+- [ ] **TLS version not restricted** — server allows SSLv3, TLS 1.0, or TLS 1.1
+  ```c
+  SSL_CTX_set_min_proto_version(ctx, TLS1_2_VERSION);  // REQUIRED
+  ```
+- [ ] **Certificate verification disabled** without explicit `--ca`/warning
+- [ ] **`SSL_CTX_set_verify` not called** — default is no verification
+- [ ] **Weak cipher suites allowed** — need to call `SSL_CTX_set_cipher_list()`
+- [ ] **Private key file permissions** not checked before loading
+- [ ] **Hostname verification** not performed on server certificate
+- [ ] **Session renegotiation** not limited (DoS vector)
+- [ ] **TLS certificate/key paths from untrusted input** — can client specify arbitrary paths?
+- [ ] **No hardcoded certificates or keys**
+- [ ] **SSL error codes checked after `SSL_read`/`SSL_write`**
+
+### 6. Memory Safety Issues
+- [ ] **Use-after-free** — object freed but pointer still used later
+- [ ] **Double-free** — `free()` called twice on same pointer
+- [ ] **Memory leaks** on error paths — allocated but not freed before return
+- [ ] **Integer overflow** in allocation size computation
+  ```c
+  // DANGER: count * sizeof(Type) can overflow
+  void *arr = malloc(count * sizeof(Element));
+
+  // SAFE:
+  if (count > SIZE_MAX / sizeof(Element)) return NULL;
+  void *arr = malloc(count * sizeof(Element));
+  ```
+- [ ] **`realloc` return value** not saved to temporary pointer (leak on failure)
+  ```c
+  // BAD: leaks original pointer on failure
+  buf = realloc(buf, new_size);
+
+  // GOOD:
+  void *tmp = realloc(buf, new_size);
+  if (!tmp) { free(buf); return NULL; }
+  buf = tmp;
+  ```
+- [ ] **All error paths free allocated resources** (no leaks / UAF / double-free)
+- [ ] **Partial reads handled** (don't use incomplete data)
+
+### 7. Integer Overflow in Allocation
+
+Check all size calculations:
+
+- [ ] Allocations where count comes from network data (chunk count, file count, etc.)
+- [ ] Allocations where size is multiplied by count
+  ```bash
+  grep -rn 'malloc.*\*.*sizeof\|calloc(.*sizeof' src/ --include="*.c"
+  ```
+- [ ] Loop counters that could wrap (unsigned underflow)
+- [ ] Signed integer overflow in size checks
+
+### 8. Format String Vulnerabilities
+- [ ] User-controlled data passed as format string
+  ```c
+  printf(user_input);           // VULNERABLE
+  fprintf(stderr, user_input);  // VULNERABLE
+  syslog(LOG_INFO, user_input); // VULNERABLE
+
+  printf("%s", user_input);     // SAFE
+  ```
+  ```bash
+  grep -rn 'printf(\|fprintf(\|syslog(\|snprintf(' src/ --include="*.c" | grep -v '"[^"]*%'
+  ```
+
+### 9. Authentication & Authorization
 - [ ] SSH transport relies on SSH authentication (not custom auth)
 - [ ] No password/credential storage in plaintext
 - [ ] Server doesn't trust client-supplied paths blindly
 - [ ] Destination directory validated before writing
 
-### 6. Denial of Service
-- [ ] Bounded memory allocation (can't OOM server with huge chunk)
-- [ ] Timeout on connections (no indefinite blocking)
-- [ ] Maximum connection limit or rate limiting
-- [ ] Malformed protocol messages handled gracefully (no crash)
+### 10. TOCTOU Race Conditions
+- [ ] File existence check followed by open (Time-of-check to Time-of-use)
+  ```c
+  if (access(path, F_OK) == 0) {    // CHECK
+      fd = open(path, O_RDWR);      // USE — file could have changed
+  }
+  ```
+- [ ] `stat()` followed by `open()` with different permissions
+- [ ] Temporary file creation with predictable names
 
-### 7. Cryptographic Practices
-- [ ] No custom crypto — uses OpenSSL only
-- [ ] No hardcoded keys, IVs, or salts
-- [ ] Random data from `/dev/urandom` or OpenSSL `RAND_bytes`
+### 11. Insecure Temporary File Usage
+- [ ] `mktemp` / `tmpnam` — use `mkstemp` instead
+- [ ] Temporary files created in world-writable directories
+- [ ] Temporary files not cleaned up on error paths
+- [ ] Predictable temp file names (race + symlink attack)
 
-### 8. File System Security
+### 12. Hardcoded Secrets / Credentials
+- [ ] Hardcoded passwords, API keys, or tokens
+- [ ] Hardcoded TLS private keys or certificates
+- [ ] Hardcoded connection strings with embedded credentials
+- [ ] Test certificates/keys in source tree (should be documented if intentional)
+
+### 13. Denial of Service Vectors
+- [ ] **Unbounded memory allocation** — can client request huge allocation that OOMs server?
+  - Check `chunk.c` for chunk count limits
+  - Check `protocol.c` for message size limits
+  - Check `config.c` for config field size limits
+- [ ] **No connection limits** — server doesn't cap concurrent connections
+- [ ] **No timeouts** — connections can hang indefinitely
+- [ ] **Recursive parsing** — could cause stack overflow with crafted input
+- [ ] **Repeated slow reads** — slow loris style attack
+- [ ] **Fork bomb** — server forks per connection without limit
+
+### 14. Information Disclosure
+- [ ] Server sends detailed error messages to client (path disclosure, version info)
+- [ ] Debug logging enabled in production
+- [ ] Stack traces leaked to users
+- [ ] Timing side channels in authentication or comparison
+
+### 15. File System Security
 - [ ] Received file permissions validated (no SUID/SGID injection)
 - [ ] Symlink attack prevention (don't follow symlinks in destination)
 - [ ] Race conditions in file creation (TOCTOU)
 - [ ] Temporary file security (if any)
 
+### 16. Cryptographic Practices
+- [ ] No custom crypto — uses OpenSSL only
+- [ ] No hardcoded keys, IVs, or salts
+- [ ] Random data from `/dev/urandom` or OpenSSL `RAND_bytes`
+
 ## Common Vulnerability Patterns
 
 ### Format String Bugs
@@ -118,9 +288,59 @@ receive_n_data(fd, buffer, expected_size);
 if (!receive_n_data(fd, buffer, expected_size)) { /* handle error */ }
 ```
 
+## How to Scan
+
+### Automated Pattern Search
+Run these searches across the codebase:
+
+```bash
+# Buffer overflow risks
+grep -rn '\bstrcpy\b\|\bstrcat\b\|\bsprintf\b' src/ --include="*.c"
+
+# Fixed size stack buffers
+grep -rn 'char [a-z_]*\[[0-9]*\];' src/ --include="*.c" --include="*.h"
+
+# Format string risks
+grep -rn 'printf(\|fprintf(\|syslog(' src/ --include="*.c" | grep -v '"[^"]*%'
+
+# Malloc without null check pattern
+grep -rn '= malloc\|= calloc\|= realloc' src/ --include="*.c"
+
+# Integer overflow in allocation
+grep -rn 'malloc.*\*\|calloc.*<' src/ --include="*.c"
+
+# Path construction
+grep -rn 'snprintf.*path\|snprintf.*dir' src/ --include="*.c"
+```
+
+### Manual Code Review
+After automated scanning, manually review high-risk files:
+1. `src/shared/protocol.c` — all receive paths
+2. `src/shared/config.c` — deserialization logic
+3. `src/shared/chunk.c` — chunk parsing
+4. `src/shared/transport_tls.c` — TLS configuration
+5. `src/server/server.c` — file writing and connection handling
+
 ## Output Format
 
-For each vulnerability found:
+Return findings in this structured format, one per vulnerability:
+
+```
+## Finding: <Short descriptive title>
+- **Severity**: critical/high/medium/low
+- **Category**: security
+- **Location**: file:line range
+- **Description**: what the vulnerability is, including:
+  - How it can be triggered
+  - What the impact is (RCE, DoS, info leak, etc.)
+  - Whether it requires authentication
+- **Suggestion**: how to fix it, including concrete code changes
+- **Labels**: security, comma-separated additional labels
+```
+
+### Detailed Finding Fields
+
+For each vulnerability found, also be prepared to report:
 1. **Location** — file:line
 2. **Severity** — critical / high / medium / low / informational
 3. **Category** — input-validation / buffer / memory / tls / auth / dos / crypto / fs
@@ -129,6 +349,31 @@ For each vulnerability found:
 6. **Fix** — concrete code change
 7. **CVSS estimate** — rough severity score if exploitable
 
+### Example
+
+```
+## Finding: Unchecked malloc in chunk deserialization allows OOM
+- **Severity**: high
+- **Category**: security
+- **Location**: src/shared/chunk.c:45-50
+- **Description**: `chunk_deserialize()` calls `malloc(count * sizeof(File))`
+  where `count` comes directly from the network. An attacker can send a crafted
+  chunk header with an extremely large count (e.g., UINT32_MAX), causing malloc
+  to either fail (crash if unchecked) or allocate enormous memory (OOM).
+  No authentication needed — the attack works on the initial connection.
+- **Suggestion**: Add bounds checking before allocation:
+  ```c
+  if (count > MAX_CHUNK_FILES || count > SIZE_MAX / sizeof(File)) {
+      log_error("Invalid chunk file count: %u", count);
+      return NULL;
+  }
+  ```
+  Define `MAX_CHUNK_FILES` as a reasonable limit (e.g., 100000).
+- **Labels**: security, dos
+```
+
+### Audit Summary
+
 Also provide a summary:
 ```
 === SECURITY AUDIT SUMMARY ===
@@ -140,13 +385,30 @@ Low: <count>
 Informational: <count>
 ```
 
+### No Findings
+If no security issues are found, return:
+```
+## No security findings
+The codebase appears clean in the areas checked. No vulnerabilities found at this time.
+```
+
+## Severity Guidelines
+
+| Severity | Definition | Example |
+|---|---|---|
+| **critical** | Remote code execution, unauthenticated compromise | Buffer overflow on network input |
+| **high** | Significant impact but requires specific conditions | DoS via unbounded allocation, path traversal |
+| **medium** | Limited impact, requires auth or other conditions | TOCTOU race in file operations |
+| **low** | Minor issues, defense in depth | Missing null check that's unlikely to trigger |
+| **informational** | Not exploitable but violates best practice | Hardcoded value that could be configurable |
+
 ## CI & Task Execution
 
 When using `tea` (the task execution agent) to run CI or tests, always set a sufficient timeout (e.g., 600000ms) to allow the workflow to finish. After CI completes, check the results yourself — inspect logs if the run failed. Never assume success.
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/agents/security-screener.md

@@ -1,310 +0,0 @@
----
-description: Scans the FastSync codebase for security vulnerabilities — buffer overflows, path traversal, TLS issues, memory safety, and cryptographic hygiene.
-mode: subagent
----
-
-You are a security screener for the FastSync project — a high-performance file synchronization system written in C11 with TCP, SSH, and TLS transport.
-
-## Your Role
-
-Scan the codebase for security vulnerabilities. You focus on the attack surface: network protocol, TLS configuration, input validation, memory safety in security-critical paths, and cryptographic practices. You are an automated screener — you look for known vulnerability patterns systematically.
-
-> **Environment rule:** for CI, dependency installation must use the project's custom Docker image (repo-root `Dockerfile`, same as CI). For local development, use `nix-shell` (see `README.md`). See `AGENTS.md`.
-
-## Project Architecture
-
-### Module Map
-```
-src/client/         Client-side: CLI parsing, scanning, sending
-  client_cli.c      Entry point, argument parsing, config setup
-  client_send.c     Transfer orchestration, pipeline management
-  scanner.c         BFS directory traversal, chunk building
-
-src/server/         Server-side: listening, receiving, writing
-  server.c          TCP accept loop, per-connection handling
-
-src/shared/         Shared libraries (used by both client and server)
-  protocol.c/h      Wire protocol: status codes, send/receive primitives
-  compression.c/h   zstd streaming compression/decompression
-  chunk.c/h         File grouping and batch serialization
-  queue.c/h         Thread-safe bounded queue (producer-consumer)
-  config.c/h        Runtime configuration, serialization, parsing
-  data.c/h          Generic buffer type (Data)
-  metadata.c/h      File metadata (mode, uid, gid, mtime)
-  file.c/h          File representation
-  array_list.c/h    Dynamic array
-  transport_tcp.c/h TCP client/server with sendfile() zero-copy
-  transport_ssh.c/h SSH transport with ControlMaster
-  transport_tls.c/h TLS encryption via OpenSSL
-  multiprocessing.c/h Fork-based concurrency
-  log.c/h           Logging utilities
-  utils.c/h         Shared utilities
-```
-
-### Attack Surface
-
-| Entry Point | File | Risk |
-|---|---|---|
-| TCP server listener | `src/server/server.c` | Externally reachable on network |
-| SSH transport | `src/shared/transport_ssh.c` | Accepts data via stdio pipe |
-| Protocol parser | `src/shared/protocol.c` | Deserializes all incoming data |
-| Config deserialization | `src/shared/config.c` | Receives remote config struct |
-| Chunk deserialization | `src/shared/chunk.c` | Receives file batches |
-| TLS handshake | `src/shared/transport_tls.c` | SSL context and cert validation |
-| File writer | `src/server/server.c` | Writes received files to disk |
-
-## Security Screener Checklist
-
-### 1. Buffer Overflow Risks
-Search for these dangerous patterns in all `.c` and `.h` files:
-
-- [ ] **Fixed-size stack buffers** used for unbounded or network-provided data
-  ```c
-  char path[PATH_MAX];     // OK if PATH_MAX is used, bad if size is arbitrary
-  char buf[1024];          // SUSPICIOUS — what limits the input to 1024?
-  char line[4096];         // SUSPICIOUS — what limits the line length?
-  ```
-- [ ] **`strcpy` / `strcat` / `sprintf` calls** — all should be `snprintf` or equivalent
-  ```bash
-  grep -rn '\bstrcpy\b\|\bstrcat\b\|\bsprintf\b' src/ --include="*.c" --include="*.h"
-  ```
-- [ ] **Unbounded `sprintf` to fixed buffer**
-  ```c
-  char buf[256];
-  sprintf(buf, "%s/%s", dir, filename);  // DANGER — no size limit
-  ```
-- [ ] **Off-by-one in string operations** — `strlen` usage without `+ 1` for null terminator
-- [ ] **`scanf` / `fscanf` / `sscanf` with `%s` and no width limit**
-  ```c
-  sscanf(input, "%s", buffer);  // DANGER — no width limit on %s
-  ```
-- [ ] **`memcpy` / `memmove` with unchecked size from network data**
-
-### 2. Path Traversal in File Operations
-Check all paths constructed from received data:
-
-- [ ] **Files constructed with client-provided filenames + destination directory**
-  ```c
-  snprintf(path, PATH_MAX, "%s/%s", dest_dir, received_filename);
-  ```
-  Check for `../` filtering:
-  ```bash
-  grep -rn 'snprintf.*%s.*%s.*path\|snprintf.*dest_dir\|snprintf.*base_dir' src/ --include="*.c"
-  ```
-- [ ] **`realpath()` usage** for path canonicalization
-- [ ] **Symlink following** — does the server follow symlinks in the destination?
-- [ ] **Null byte injection** — received filenames with embedded `\0`
-
-### 3. Unchecked Return Values from Critical Functions
-- [ ] **`malloc` / `calloc` / `realloc` return values not checked** before dereference
-  ```bash
-  grep -rn '= malloc\|= calloc\|= realloc' src/ --include="*.c"
-  ```
-  For each match, verify NULL check exists before use.
-- [ ] **`send_n_data` / `receive_n_data` return values** not checked
-- [ ] **`SSL_read` / `SSL_write`** error codes not checked
-- [ ] **`write()` / `read()` syscall** return values not checked (short writes/reads)
-- [ ] **`fopen()` / `open()`** return values not checked
-- [ ] **`snprintf` / `vsnprintf`** negative return not handled
-
-### 4. TLS / SSL Misconfiguration
-- [ ] **TLS version not restricted** — server allows SSLv3, TLS 1.0, or TLS 1.1
-  ```c
-  SSL_CTX_set_min_proto_version(ctx, TLS1_2_VERSION);  // REQUIRED
-  ```
-- [ ] **Certificate verification disabled** without explicit `--insecure` flag
-- [ ] **`SSL_CTX_set_verify` not called** — default is no verification
-- [ ] **Weak cipher suites allowed** — need to call `SSL_CTX_set_cipher_list()`
-- [ ] **Private key file permissions** not checked before loading
-- [ ] **Hostname verification** not performed on server certificate
-- [ ] **Session renegotiation** not limited (DoS vector)
-- [ ] **TLS certificate/key paths from untrusted input** — can client specify arbitrary paths?
-
-### 5. Memory Safety Issues
-- [ ] **Use-after-free** — object freed but pointer still used later
-- [ ] **Double-free** — `free()` called twice on same pointer
-- [ ] **Memory leaks** on error paths — allocated but not freed before return
-- [ ] **Integer overflow** in allocation size computation
-  ```c
-  // DANGER: count * sizeof(Type) can overflow
-  void *arr = malloc(count * sizeof(Element));
-  
-  // SAFE:
-  if (count > SIZE_MAX / sizeof(Element)) return NULL;
-  void *arr = malloc(count * sizeof(Element));
-  ```
-- [ ] **`realloc` return value** not saved to temporary pointer (leak on failure)
-  ```c
-  // BAD: leaks original pointer on failure
-  buf = realloc(buf, new_size);
-  
-  // GOOD:
-  void *tmp = realloc(buf, new_size);
-  if (!tmp) { free(buf); return NULL; }
-  buf = tmp;
-  ```
-
-### 6. Integer Overflow in Allocation
-Check all size calculations:
-
-- [ ] Allocations where count comes from network data (chunk count, file count, etc.)
-- [ ] Allocations where size is multiplied by count
-  ```bash
-  grep -rn 'malloc.*\*.*sizeof\|calloc(.*sizeof' src/ --include="*.c"
-  ```
-- [ ] Loop counters that could wrap (unsigned underflow)
-- [ ] Signed integer overflow in size checks
-
-### 7. Format String Vulnerabilities
-- [ ] User-controlled data passed as format string
-  ```c
-  printf(user_input);           // VULNERABLE
-  fprintf(stderr, user_input);  // VULNERABLE
-  syslog(LOG_INFO, user_input); // VULNERABLE
-  
-  printf("%s", user_input);     // SAFE
-  ```
-  ```bash
-  grep -rn 'printf(\|fprintf(\|syslog(\|snprintf(' src/ --include="*.c" | grep -v '"[^"]*%'
-  ```
-
-### 8. TOCTOU Race Conditions
-- [ ] File existence check followed by open (Time-of-check to Time-of-use)
-  ```c
-  if (access(path, F_OK) == 0) {    // CHECK
-      fd = open(path, O_RDWR);      // USE — file could have changed
-  }
-  ```
-- [ ] `stat()` followed by `open()` with different permissions
-- [ ] Temporary file creation with predictable names
-
-### 9. Insecure Temporary File Usage
-- [ ] `mktemp` / `tmpnam` — use `mkstemp` instead
-- [ ] Temporary files created in world-writable directories
-- [ ] Temporary files not cleaned up on error paths
-- [ ] Predictable temp file names (race + symlink attack)
-
-### 10. Hardcoded Secrets / Credentials
-- [ ] Hardcoded passwords, API keys, or tokens
-- [ ] Hardcoded TLS private keys or certificates
-- [ ] Hardcoded connection strings with embedded credentials
-- [ ] Test certificates/keys in source tree (should be documented if intentional)
-
-### 11. Denial of Service Vectors
-- [ ] **Unbounded memory allocation** — can client request huge allocation that OOMs server?
-  - Check `chunk.c` for chunk count limits
-  - Check `protocol.c` for message size limits
-  - Check `config.c` for config field size limits
-- [ ] **No connection limits** — server doesn't cap concurrent connections
-- [ ] **No timeouts** — connections can hang indefinitely
-- [ ] **Recursive parsing** — could cause stack overflow with crafted input
-- [ ] **Repeated slow reads** — slow loris style attack
-- [ ] **Fork bomb** — server forks per connection without limit
-
-### 12. Information Disclosure
-- [ ] Server sends detailed error messages to client (path disclosure, version info)
-- [ ] Debug logging enabled in production
-- [ ] Stack traces leaked to users
-- [ ] Timing side channels in authentication or comparison
-
-## How to Scan
-
-### Automated Pattern Search
-Run these searches across the codebase:
-
-```bash
-# Buffer overflow risks
-grep -rn '\bstrcpy\b\|\bstrcat\b\|\bsprintf\b' src/ --include="*.c"
-
-# Fixed size stack buffers
-grep -rn 'char [a-z_]*\[[0-9]*\];' src/ --include="*.c" --include="*.h"
-
-# Format string risks
-grep -rn 'printf(\|fprintf(\|syslog(' src/ --include="*.c" | grep -v '"[^"]*%'
-
-# Malloc without null check pattern
-grep -rn '= malloc\|= calloc\|= realloc' src/ --include="*.c"
-
-# Integer overflow in allocation
-grep -rn 'malloc.*\*\|calloc.*<' src/ --include="*.c"
-
-# Path construction
-grep -rn 'snprintf.*path\|snprintf.*dir' src/ --include="*.c"
-```
-
-### Manual Code Review
-After automated scanning, manually review high-risk files:
-1. `src/shared/protocol.c` — all receive paths
-2. `src/shared/config.c` — deserialization logic
-3. `src/shared/chunk.c` — chunk parsing
-4. `src/shared/transport_tls.c` — TLS configuration
-5. `src/server/server.c` — file writing and connection handling
-
-## Output Format
-
-Return findings in this structured format, one per vulnerability:
-
-```
-## Finding: <Short descriptive title>
-- **Severity**: critical/high/medium/low
-- **Category**: security
-- **Location**: file:line range
-- **Description**: what the vulnerability is, including:
-  - How it can be triggered
-  - What the impact is (RCE, DoS, info leak, etc.)
-  - Whether it requires authentication
-- **Suggestion**: how to fix it, including concrete code changes
-- **Labels**: security, comma-separated additional labels
-```
-
-### Example
-
-```
-## Finding: Unchecked malloc in chunk deserialization allows OOM
-- **Severity**: high
-- **Category**: security
-- **Location**: src/shared/chunk.c:45-50
-- **Description**: `chunk_deserialize()` calls `malloc(count * sizeof(File))`
-  where `count` comes directly from the network. An attacker can send a crafted
-  chunk header with an extremely large count (e.g., UINT32_MAX), causing malloc
-  to either fail (crash if unchecked) or allocate enormous memory (OOM).
-  No authentication needed — the attack works on the initial connection.
-- **Suggestion**: Add bounds checking before allocation:
-  ```c
-  if (count > MAX_CHUNK_FILES || count > SIZE_MAX / sizeof(File)) {
-      log_error("Invalid chunk file count: %u", count);
-      return NULL;
-  }
-  ```
-  Define `MAX_CHUNK_FILES` as a reasonable limit (e.g., 100000).
-- **Labels**: security, dos
-```
-
-### No Findings
-If no security issues are found, return:
-```
-## No security findings
-The codebase appears clean in the areas checked. No vulnerabilities found at this time.
-```
-
-## Severity Guidelines
-
-| Severity | Definition | Example |
-|---|---|---|
-| **critical** | Remote code execution, unauthenticated compromise | Buffer overflow on network input |
-| **high** | Significant impact but requires specific conditions | DoS via unbounded allocation, path traversal |
-| **medium** | Limited impact, requires auth or other conditions | TOCTOU race in file operations |
-| **low** | Minor issues, defense in depth | Missing null check that's unlikely to trigger |
-| **informational** | Not exploitable but violates best practice | Hardcoded value that could be configurable |
-
-## CI & Task Execution
-
-When using `tea` (the task execution agent) to run CI or tests, always set a sufficient timeout (e.g., 600000ms) to allow the workflow to finish. After CI completes, check the results yourself — inspect logs if the run failed. Never assume success.
-
-## Branch Strategy
-
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
-
-## Dependency Installation
-
-**CI rule:** never add `apt-get install` / `pip install` steps to CI workflows — use the custom Docker image instead. **Host rule:** for local development, use `nix-shell` (see `README.md`) which provides zstd, OpenSSL, CMake, and gcc. See `AGENTS.md` for details.

.opencode/agents/test-writer.md

@@ -138,11 +138,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
 
 Build for fuzzing:
 ```bash
-cmake -B build-fuzz -S . \
-  -DCMAKE_C_FLAGS="-fsanitize=fuzzer,address,undefined -g" \
-  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=fuzzer,address,undefined"
+CC=clang CXX=clang++ cmake -B build-fuzz -S . -DENABLE_FUZZ=ON
 cmake --build build-fuzz -j$(nproc)
-./build-fuzz/tests/fuzz_chunk_deserialize corpus/ -max_len=1048576
+./build-fuzz/fuzz_chunk_deserialize corpus/ -max_len=1048576
 ```
 
 ### AFL++ Harness
@@ -216,7 +214,7 @@ When using `tea` (the task execution agent) to run CI or tests, always set a suf
 
 ## Branch Strategy
 
-Never push directly to `main`. All changes must be developed on a feature branch and merged via a pull request. Always create a new branch (`git checkout -b <branch-name>`) before making changes, push it, and open a PR with `gh pr create --fill`. Wait for CI to pass before merging.
+Never push directly to `dev` or `main`. All changes must be developed on a feature branch and merged via a pull request targeting `dev`. Create a branch (`git checkout -b <branch-name>`), push it, and open the PR with `tea pr create --repo TapTap/FastSync --base dev --head <branch-name>`. Wait for CI to pass before merging.
 
 ## Dependency Installation
 

.opencode/skills/benchmark/SKILL.md

@@ -38,16 +38,20 @@ dd if=/dev/urandom of=/tmp/fastsync_bench/src/large.bin bs=1M count=10 2>/dev/nu
 Test each configuration 3 times, record median:
 
 ```bash
+# Real FastSync flags: -z=compression, -j=multithreading,
+# --chunk-serialization, --sendfile (long form only).  The old rsync-style
+# spellings -c/-m/-s/-f are NOT the same options (-c=--checksum,
+# -m=--prune-empty-dirs, -s=--secluded-args, -f=--filter) and must not be used.
 CONFIGS=(
   "Standard|"
-  "Compression|-c"
-  "Multithreading|-m"
-  "MT+Compression|-m -c"
-  "Chunk Serialization|-s"
-  "MT+Compression+Chunk|-m -c -s"
-  "Sendfile|-f"
+  "Compression|-z"
+  "Multithreading|-j"
+  "MT+Compression|-j -z"
+  "Chunk Serialization|-j -z --chunk-serialization"
+  "Sendfile|--sendfile"
 )
 
+PORT=18080
 for config in "${CONFIGS[@]}"; do
   IFS='|' read -r name flags <<< "$config"
   echo "=== $name ==="
@@ -55,13 +59,14 @@ for config in "${CONFIGS[@]}"; do
     rm -rf /tmp/fastsync_bench/dst
     mkdir -p /tmp/fastsync_bench/dst
 
-    ./build/server &
+    ./build/server -p "$PORT" --allow-unauthenticated &
     SERVER_PID=$!
     sleep 0.5
 
     START=$(date +%s%N)
     ./build/client --source-dir /tmp/fastsync_bench/src \
       --dest-dir /tmp/fastsync_bench/dst \
+      --server-port "$PORT" \
       --save-to-disk $flags
     END=$(date +%s%N)
 
@@ -74,14 +79,21 @@ for config in "${CONFIGS[@]}"; do
 done
 ```
 
-### Step 4: Full Integration Benchmark (Optional)
+### Step 4: Full Benchmark Tool (Preferred)
+
+The maintained benchmark tool is `benchmark/bench.py`. It handles building,
+data generation, network shaping (LAN/WAN profiles or custom `--delay`/`--jitter`/
+`--throughput`/`--loss`), rsync comparison, and JSON/table reporting:
 
-For comprehensive benchmarking with network shaping:
 ```bash
-python3 test.py --full
+python3 benchmark/bench.py --help
+python3 benchmark/bench.py --runs 5 --profiles unlimited
+python3 benchmark/bench.py --size-mb 100 --random-ratio 0.5 --output json
+python3 benchmark/bench.py --delay 50ms --jitter 10ms --throughput 100mbit
 ```
 
-This tests LAN/WAN profiles, SSH, TLS, and compares against rsync.
+Network shaping needs root (`tc`/`netem` on `lo`). SSH and TLS coverage lives in
+the pytest integration suite, not the benchmark tool.
 
 ### Step 5: Report Results
 
@@ -93,12 +105,13 @@ Platform: <OS, CPU, network>
 Configuration          | Run 1   | Run 2   | Run 3   | Median
 -----------------------|---------|---------|---------|--------
 Standard                            | 0.12s   | 0.11s   | 0.12s   | 0.12s
-Compression (-c)       | 0.09s   | 0.08s   | 0.09s   | 0.09s
-Multithreading (-m)    | 0.07s   | 0.07s   | 0.08s   | 0.07s
-MT+Compression (-m -c) | 0.05s   | 0.05s   | 0.06s   | 0.05s
-Sendfile (-f)          | 0.04s   | 0.04s   | 0.04s   | 0.04s
+Compression (-z)                    | 0.09s   | 0.08s   | 0.09s   | 0.09s
+Multithreading (-j)                 | 0.07s   | 0.07s   | 0.08s   | 0.07s
+MT+Compression (-j -z)              | 0.05s   | 0.05s   | 0.06s   | 0.05s
+Chunk Serialization (--chunk-serialization) | 0.05s | 0.04s | 0.05s | 0.05s
+Sendfile (--sendfile)               | 0.04s   | 0.04s   | 0.04s   | 0.04s
 
-Best configuration: MT+Compression (-m -c)
+Best configuration: Sendfile (--sendfile)
 Throughput: <X> MB/s
 ```
 

.opencode/skills/debug-workflow/SKILL.md

@@ -32,23 +32,19 @@ Try to reproduce the issue with the exact command the user provides.
 
 **Memory errors (first priority):**
 ```bash
-rm -rf build
-cmake -B build -S . \
-  -DCMAKE_C_FLAGS="-fsanitize=address -fno-omit-frame-pointer -g" \
-  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address"
-cmake --build build -j$(nproc)
-./build/tests
+rm -rf build-asan
+cmake -B build-asan -S . -DSANITIZER=address
+cmake --build build-asan -j$(nproc)
+./build-asan/tests
 # or run the failing command
 ```
 
 **Thread errors:**
 ```bash
-rm -rf build
-cmake -B build -S . \
-  -DCMAKE_C_FLAGS="-fsanitize=thread -g" \
-  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=thread"
-cmake --build build -j$(nproc)
-./build/tests
+rm -rf build-tsan
+cmake -B build-tsan -S . -DSANITIZER=thread
+cmake --build build-tsan -j$(nproc)
+./build-tsan/tests
 ```
 
 **Valgrind (if ASan doesn't find it):**
@@ -108,13 +104,12 @@ cmake -B build -S . && cmake --build build -j$(nproc)
 ./build/tests
 
 # If integration test needed
-python3 test.py
+python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"
 
 # Re-run under sanitizer to confirm fix
-rm -rf build
-cmake -B build -S . -DCMAKE_C_FLAGS="-fsanitize=address -fno-omit-frame-pointer" \
-  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address"
-cmake --build build -j$(nproc)
+rm -rf build-asan
+cmake -B build-asan -S . -DSANITIZER=address
+cmake --build build-asan -j$(nproc)
 # reproduce the original failing command
 ```
 

.opencode/skills/pr-build/SKILL.md

@@ -19,7 +19,7 @@ tea pr checkout <number>
 If already on a PR branch, verify with:
 ```bash
 git branch --show-current
-git log main..HEAD --oneline
+git log dev..HEAD --oneline
 ```
 
 ### Step 2: Clean build
@@ -39,17 +39,13 @@ If the PR touches threading, memory management, or network code, also build with
 ```bash
 # AddressSanitizer
 rm -rf build-asan
-cmake -B build-asan -S . \
-  -DCMAKE_C_FLAGS="-fsanitize=address -fno-omit-frame-pointer -g" \
-  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address"
+cmake -B build-asan -S . -DSANITIZER=address
 cmake --build build-asan -j$(nproc)
 ./build-asan/tests
 
 # ThreadSanitizer (if threading changes)
 rm -rf build-tsan
-cmake -B build-tsan -S . \
-  -DCMAKE_C_FLAGS="-fsanitize=thread -g" \
-  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=thread"
+cmake -B build-tsan -S . -DSANITIZER=thread
 cmake --build build-tsan -j$(nproc)
 ./build-tsan/tests
 ```
@@ -91,10 +87,10 @@ If tests fail:
 ### Step 6: Run integration tests (optional)
 
 ```bash
-python3 test.py
+python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"
 ```
 
-This runs the integration + benchmark suite. It takes longer — only run if the user asks or if unit tests pass.
+This runs the integration suite (benchmarking is `benchmark/bench.py`). It takes longer — only run if the user asks or if unit tests pass.
 
 ### Step 7: Fix and commit
 

.opencode/skills/pr-review/SKILL.md

@@ -19,13 +19,13 @@ tea pr checkout <number>
 If already on a PR branch, verify with:
 ```bash
 git branch --show-current
-git log main..HEAD --oneline
+git log dev..HEAD --oneline
 ```
 
 ### Step 2: Get changed files
 
 ```bash
-git diff main --name-only -- '*.c' '*.h'
+git diff dev --name-only -- '*.c' '*.h'
 ```
 
 This gives the list of C source and header files changed in the PR.
@@ -125,7 +125,7 @@ STYLE: <count>
 
 If the user wants to post the review as a PR comment:
 ```bash
-tea pr comment <number> --comment "<review report>"
+tea comment --repo TapTap/FastSync <number> "<review report>"
 ```
 
 ## Rules

.opencode/skills/release/SKILL.md

@@ -16,7 +16,7 @@ Ask the user or determine from context:
 - **Minor** (x.Y.0) — new features, backward compatible
 - **Patch** (x.y.Z) — bug fixes, no protocol changes
 
-Current version: `PROTOCOL_VERSION "1.1.0"` in `src/shared/config.h`
+Current version: `PROTOCOL_VERSION "2.26.0"` in `src/shared/config.h`
 
 ### Step 2: Check Protocol Version
 
@@ -37,7 +37,7 @@ rm -rf build
 cmake -B build -S .
 cmake --build build -j$(nproc)
 ./build/tests
-python3 test.py
+python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"
 ```
 
 ALL tests must pass before release.
@@ -46,12 +46,10 @@ ALL tests must pass before release.
 
 ```bash
 # ASan
-rm -rf build
-cmake -B build -S . \
-  -DCMAKE_C_FLAGS="-fsanitize=address -fno-omit-frame-pointer" \
-  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address"
-cmake --build build -j$(nproc)
-./build/tests
+rm -rf build-asan
+cmake -B build-asan -S . -DSANITIZER=address
+cmake --build build-asan -j$(nproc)
+./build-asan/tests
 ```
 
 ### Step 5: Update README (If Needed)
@@ -79,12 +77,23 @@ git commit -m "Release vX.Y.Z
 git tag -a vX.Y.Z -m "Release vX.Y.Z"
 ```
 
-### Step 8: Push
+### Step 8: Push and Open dev → main PR
+
+`main` is protected and only receives changes via `dev` → `main` PRs (see AGENTS.md). Never push directly to `main`.
 
 ```bash
-git push origin main --tags
+# Push the release commit and tag to dev
+git push origin dev
+git push origin vX.Y.Z
+
+# Open the dev → main release PR for review + CI
+tea pr create --repo TapTap/FastSync --head dev --base main \
+  --title "Release vX.Y.Z" \
+  --description "Release vX.Y.Z"
 ```
 
+Then wait for the full CI to pass and request review before the PR is merged to `main`.
+
 ### Step 9: Report
 
 ```

.opencode/skills/security-audit/SKILL.md

@@ -102,9 +102,9 @@ Informational: <count>
 ...
 
 === VERDICT ===
-[PASS] No critical/high issues found
+[PASS] No critical/high-severity issues found
   — or —
-[FAIL] <N> critical/high issues must be fixed
+[FAIL] <N> critical/high-severity issues must be fixed
 ```
 
 ## Rules

AGENTS.md

@@ -4,18 +4,19 @@ FastSync is a high-performance file synchronization system written in C11. It su
 
 ## Dependency installation
 
-**CI rule:** never add `apt-get install` / `pip install` steps to CI workflows — use the custom Docker image instead. The image is built from the repo-root `Dockerfile` and is the same image CI uses: `gitea.tap-tap.win/taptap/fastsync-ci:v10`. It contains the full toolchain: gcc/g++, CMake, libzstd-dev, libssl-dev, make, git, cppcheck, clang-format, python3 + pytest + pytest-xdist, openssh-client, and Node.js.
+**CI rule:** never add `apt-get install` / `pip install` steps to CI workflows — use the custom Docker image instead. The image is built from the repo-root `Dockerfile` and is the same image CI uses: `gitea.tap-tap.win/taptap/fastsync-ci:v11`. It contains the full toolchain: gcc/g++, CMake, libzstd-dev, libssl-dev, make, git, cppcheck, clang-format, python3 + pytest + pytest-xdist, openssh-client, Node.js, plus `rsync` 3.4.1 (with zstd/xxhash/lz4), `acl` and `attr` (setfacl/getfacl, setfattr/getfattr) for drop-in parity tests.
 
 **Host rule:** for local development, use `nix-shell` (see `README.md`) which provides zstd, OpenSSL, CMake, and gcc. The Docker image can also be used locally for CI parity.
 
 ```bash
 # Use the prebuilt CI image directly (faster, guaranteed CI parity)
-docker pull gitea.tap-tap.win/taptap/fastsync-ci:v10
-docker tag gitea.tap-tap.win/taptap/fastsync-ci:v10 fastsync-ci:local
+docker pull gitea.tap-tap.win/taptap/fastsync-ci:v11
+docker tag gitea.tap-tap.win/taptap/fastsync-ci:v11 fastsync-ci:local
 
 # Or build the image from the repo-root Dockerfile
-# (Note: the prebuilt :v10 image reflects the previous Dockerfile state;
-#  rebuild from source to pick up any newly added packages like lcov/valgrind.)
+# (Note: the prebuilt :v11 image is built from the current Dockerfile and
+#  includes rsync 3.4.1 plus acl/attr; rebuild from source after changing
+#  the Dockerfile.)
 docker build -t fastsync-ci:local .
 
 # Build, run unit tests, and run integration tests inside the container
@@ -28,7 +29,7 @@ docker run --rm --user "$(id -u):$(id -g)" -v "$PWD:/workspace" \
   sh -c 'cmake -B build -S . && cmake --build build -j$(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.
+> **Note:** The first `cmake configure` (`cmake -B build -S .`) fetches xxHash via `FetchContent` — network access is required. Subsequent reconfigures reuse the cached source.
 
 If a dependency is missing from the CI image, add it to the `Dockerfile` (and rebuild) rather than adding an install step to the CI workflow.
 
@@ -59,28 +60,28 @@ python3 -m pytest tests/integration/ -n 4 --dist=load -m ci   # PR-gate subset o
 
 ## CI Workflow — Waiting for Results
 
-When running the CI workflow via `tea` (the task execution agent), always set a sufficient timeout (e.g., 600000ms) to allow CI to finish. After CI completes, check the results yourself — do not assume success. Use `gh run watch` or similar to monitor CI status, then inspect logs on failure.
+When running the CI workflow via `tea` (the task execution agent), always set a sufficient timeout (e.g., 600000ms) to allow CI to finish. After CI completes, check the results yourself — do not assume success. Monitor CI status via the Gitea API (see below) or `tea actions`, then inspect logs on failure.
 
 ## CI Troubleshooting
 
 ### If lint (clang-format) fails
 Run clang-format in the CI Docker image to match the exact CI version:
 ```bash
-docker run --rm -v "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v10 \
+docker run --rm -v "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v11 \
   sh -c 'find src/ tests/ -name "*.c" -o -name "*.h" | xargs clang-format -i'
 ```
 
 ### If cppcheck fails
 Fix reported issues locally, then verify with:
 ```bash
-docker run --rm -v "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v10 \
+docker run --rm -v "$PWD:/workspace" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v11 \
   sh -c 'cppcheck --enable=warning,style,performance,portability --suppress=missingIncludeSystem --error-exitcode=1 --inline-suppr src/ tests/'
 ```
 
 ### If integration tests fail
 Run locally before pushing:
 ```bash
-python3 -m pytest tests/ -v --tb=short
+python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"
 ```
 
 ## Branch Strategy
@@ -165,7 +166,7 @@ This can be cron'd locally if desired (e.g., `crontab -e` with `opencode run`).
 ## Is opencode a good option?
 
 **Yes, for FastSync's needs.** The hybrid model works well:
-- opencode's 17 specialized agents handle deep code analysis, fixes, tests, and reviews
+- opencode's 16 specialized agents handle deep code analysis, fixes, tests, and reviews
 - The assistant orchestrates subagents, merges branches, and iterates on CI
 - You only review the final output
 

CHANGELOG.md

@@ -0,0 +1,380 @@
+# 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.
+
+## [2.26.0] - 2026-09-17
+
+### Added
+
+- **Parity-completion wave.** Closed the remaining rsync-parity gaps against
+  rsync 3.4.1 and reclassified the inherently non-rsync rows. It moved the wire
+  protocol three times (`2.23.0 → 2.24.0 → 2.25.0 → 2.26.0`).
+  - **Delete timing (2.24.0):** per-directory delete plans
+    (`STATUS_DELETE_PLAN`) for `--delete-during`/`--delete-delay`. An interrupted
+    during-transfer has already removed the reached directories' extras, while a
+    delayed transfer commits per directory only after the whole transfer
+    succeeds (a late-created extra survives `--delete-delay` but not
+    `--delete-after`). `-R --delete` is scoped to the transferred prefix; empty
+    in-scope source directories survive; dry-run never deletes.
+  - **Wire stats (2.25.0):** `STATUS_STATS` carries the receiver counters
+    (matched data, deleted files) and the dry-run would-delete list. `--stats`
+    prints rsync's protocol-independent lines; `--progress`/`-P` print per-file
+    blocks; `--out-format` gains `%b` (wire bytes), `%c` (block-sum bytes) and
+    `%C` (whole-file digest); `-n --delete` prints escaped `*deleting` lines in
+    the sequential and `--threads` paths.
+  - **Codecs (2.26.0):** `lz4`/`zlib`/`zlibx` compression and `md4`/`sha1`/
+    `none` checksums, with rsync-style `auto` negotiation (default `xxh128` +
+    `zstd`) and exit-4 rejection of unknown names; the resolved `compression_algo`
+    crosses the wire.
+  - General `-R`/`--relative` (including the `/./` cut) and `--no-implied-dirs`;
+    one-level `-d`/`--dirs` listing for `dir`, `dir/` and `.`; the full filter
+    grammar (`merge`/`dir-merge`/`hide`/`show`/`protect`/`risk`/`clear` and
+    modifiers) with `-f` bound to `--filter`; a single `-F` transfers
+    `.rsync-filter` and `-FF` excludes it.
+  - Receiver-side `--chown`/`--usermap`/`--groupmap` TO-name resolution; absolute
+    basis directories and a `--link-dest` relink of an up-to-date destination;
+    a receiver-side `--ignore-existing` short-circuit before any payload;
+    `--preallocate` now wins over `--sparse` via `fallocate(2)`.
+  - Client quick wins: `--iconv=.`/`-`/`--no-iconv`, a lone `-h` prints help, an
+    empty `--files-from` succeeds (exit 0), a broken referent under
+    `-L`/`--copy-unsafe-links` exits 23, the full `--info`/`--debug`
+    vocabularies, and the aliases `--ignore-non-existing`, `--protect-args`,
+    `--msgs2stderr`.
+
+### Changed
+
+- `PROTOCOL_VERSION` bumped `2.23.0 → 2.24.0` (delete plans),
+  `2.24.0 → 2.25.0` (`STATUS_STATS` + `report_stats`), and
+  `2.25.0 → 2.26.0` (codec negotiation + `md4`/`sha1`/`none`).
+- `--checksum-choice`/`--cc` now accepts `md4`, `sha1`, `none` and the two-name
+  form; the negotiated whole-file default is `xxh128`.
+- `--compress-choice`/`--zc` now accepts `lz4`, `zlib`, `zlibx`.
+- `RSYNC_COMPAT.md` reclassifies the matrix: 9 already-parity rows to ✅, 17
+  inherently non-rsync rows to ❌ (native daemon config/auth, batch, privileged
+  xattr namespaces, and the safe-subset device/privilege flags), and the genuine
+  fixes to ✅; new rows cover `--bwlimit`, `--partial`, `--partial-dir`,
+  `--no-whole-file`, `--inc-recursive`/`--no-inc-recursive`, `--protect-args`
+  and `--msgs2stderr`.
+- The client `--help` `--max-delete` text now describes the implemented partial
+  semantics (delete up to N, skip the rest, exit 25).
+
+### Notes
+
+- Remaining documented divergences include the `--stats` per-type file-count
+  breakdown, `%b`/`%c` being FastSync wire counts, `-n --delete` line ordering,
+  the default `--delete` timing (delete-after, not rsync's delete-during),
+  destination-only exclude protection (still sender-derived), `--temp-dir`
+  absolute paths, basis-dir attribute re-application and the 256 MiB whole-file
+  cap, `--fuzzy` tie-breaking, `--bwlimit=0`/decimal rates, `zlibx`==`zlib`, and
+  recursive empty-directory creation.
+- Build: adds zlib and lz4 as link dependencies.
+
+## [2.23.0] - 2026-09-16
+
+### Added
+
+- **Rsync-parity wave.** Closed the remaining CLI, filesystem, ownership,
+  deletion, and output gaps against rsync 3.4.1.
+  - Short options `-r` (`--recursive`), `-b` (`--backup`), `-L`
+    (`--copy-links`), and `-B` (`--block-size`/`--delta-block`); rsync
+    short-option clustering (`-av`, `-aAX`, `-rlpt`) and attached/inline values
+    (`--opt=value`, `-B1000`, `-essh`, `-MOPT`). A value that starts with `-`
+    is not mistaken for a cluster.
+  - `-c`/`--checksum` now implies the incremental checksum quick-check (and,
+    like rsync, does not imply `-t`).
+  - `--checksum-choice`/`--cc` accepts `xxh64`/`xxhash`/`xxh3`/`xxh128`/`md5`/
+    `auto` and rejects `md4`/`sha1`/`none` and the two-name form by name;
+    `--checksum-seed=0` (the default) is randomized per transfer and the chosen
+    seed is sent to the receiver.
+  - `--compress-choice`/`--zc` accepts `zstd`/`none`/`auto` and rejects
+    `lz4`/`zlib`/`zlibx` by name; `--skip-compress` defaults to rsync 3.4.1's
+    built-in suffix list; `--no-whole-file` is accepted.
+  - `--timeout` defaults to 0 (disabled) and `--contimeout` to 60 s (both `0`
+    disables), matching rsync; `--max-alloc=0` means no local limit.
+  - `--temp-dir` is confined to the receive root (absolute/`..` rejected by the
+    receiver) and an `EXDEV` install falls back to a non-atomic copy.
+  - `--numeric-ids` is documented as a mapping modifier only;
+    `--usermap`/`--groupmap` support inclusive `LOW-HIGH` ranges, `*`,
+    empty-`FROM` (unnamed ids), and receiver-resolved `TO` names; `--chown`
+    conflicts with a map on the same side are rejected.
+  - `--fake-super` records the *resolved* owner (never a real chown) and replays
+    mode/time; directory ownership and directory xattrs/ACLs are preserved.
+  - `-l`/`--links` stores symlink targets verbatim (absolute and `..`-bearing
+    included), matching rsync; `--safe-links`/`--copy-unsafe-links` are applied
+    sender-side and `--munge-links` uses rsync's `/rsyncd-munged/` marker;
+    `--trust-sender` no longer affects symlink targets.
+  - `--specials` recreates unix sockets with `mknod(S_IFSOCK)` (so `-D` covers
+    the full rsync node set).
+  - Deletion: the manifest carries a synchronized-directory section so
+    `--files-from` subsets no longer delete untransmitted paths;
+    `--delete-excluded` leaves size-pruned mirrors protected; extraneous
+    destination symlinks are unlinked (never followed); `--max-delete=N` is
+    partial (delete up to N, skip the rest, exit 25) and `--delete-missing-args`
+    removals draw from the same budget; `--force` is honored during
+    `--delay-updates` publication.
+  - `-x`/`--one-file-system` emits the mount-point directory entry; the
+    `--include`/`--exclude` layers are an ordered first-match rule list.
+  - `--chmod` is a faithful port of rsync 3.4.1 (numeric/symbolic, `D`/`F`/`X`,
+    `s`/`t`, append semantics, no `-p` implication, no sanitization).
+
+### Changed
+
+- `PROTOCOL_VERSION` bumped `2.22.0 → 2.23.0`: the delete manifest gains a
+  synchronized-directory section and the terminal status gains
+  `STATUS_DELETE_LIMIT` (client exit 25 on a `--max-delete`-capped commit).
+- **The 2.22.0 mode-masking divergence is removed.** Under `-p` the source mode
+  is copied exactly, including `S_IWGRP`/`S_IWOTH` and setuid/setgid/sticky;
+  `--chmod` no longer implies `-p`. New files without `-p` still use
+  `source_mode & ~umask` when metadata is present (else `0644`), and new
+  directories without `-p` still use the `0755` creation default.
+- `--protocol=NUM` accepts only the current `2.23.0` version string.
+
+### Notes
+
+- The rsync-compatibility matrix (`RSYNC_COMPAT.md`) now classifies every row
+  as **parity**, **caveat** (works with a documented divergence), or
+  **divergent** (not supported/no-op/impossible), replacing the previous
+  misleading "N implemented / 0 divergence" summary. Durable documented
+  divergences remain: receiver-side symlink target containment is not enforced
+  by default (verbatim storage is rsync parity; use `--safe-links`),
+  `--temp-dir` rejects absolute/foreign-filesystem paths, `--copy-devices`
+  reads a bounded `st_size`, a broken referent under `--copy-links` exits 0,
+  new directories without `-p` use `0755`, `--stats` receiver-only counters are
+  0, and `--password-file`/`--early-input`/`--hash-credentials`/`--iterations`
+  and the batch format are FastSync-native.
+
+## [2.22.0] - 2026-09-15
+
+### Added
+
+- **Per-attribute metadata preservation (protocol 2.22.0).** The former single
+  metadata bundle is split into four independent, rsync-compatible flags:
+  `-p/--perms`, `-t/--times`, `-o/--owner`, and `-g/--group`, each applied
+  independently on the receiver, with negations `--no-perms`/`--no-times`/
+  `--no-owner`/`--no-group` (short `--no-p`/`--no-t`/`--no-o`/`--no-g`) and
+  `--no-preserve` clearing all four. `-a/--archive` is now full rsync
+  `-rlptgoD` (owner and group included; their application stays
+  privilege-gated). `-A/--acls` and `--chmod` imply `-p`, `-X/--xattrs` does
+  not, `-E/--executability` sets only executability, and `-U`/`-N` do not imply
+  `-t`. `--incremental`/`--delta` still auto-preserve perms+times unless the
+  user explicitly negated them.
+- Receiver applies directory modes under `-p` (at the end of the transfer,
+  alongside the deferred directory times) and symlink mode under `-p`; `-O`
+  suppresses directory times only.
+
+### Changed
+
+- `PROTOCOL_VERSION` bumped `2.21.0 → 2.22.0`: the binary config frame gains
+  four appended booleans (`preserve_perms`/`preserve_times`/`preserve_owner`/
+  `preserve_group`) after `omit_link_times`. The fixed-width `FileMetadata`
+  layout is unchanged; the receiver derives the metadata-frame gate
+  (`use_metadata`) from the four attributes.
+
+### Notes
+
+- Documented divergences from rsync: a client-supplied mode never grants
+  group/other write (`S_IWGRP|S_IWOTH` are stripped for files, directories,
+  symlinks, and specials; rsync's `-p` preserves them exactly); a brand-new file
+  without `-p` gets `source_mode & ~umask` (sanitized) when metadata is present,
+  else the historical fixed `0644`; `--chmod` implies `-p` (rsync does not);
+  `-o`/`-g` map by name on the receiver with a raw-numeric fallback (only
+  numeric ids cross the wire); and a daemon module without `client owner = yes`
+  does not refuse a plain `-a`/`-o`/`-g` but forces super-user activities off,
+  applies no ownership, and logs a warning (explicit `--chown`/`--usermap`/
+  `--groupmap`/`--numeric-ids`/`--copy-as`/`--super` are still refused).
+
+## [2.21.0] - 2026-09-14
+
+### Added
+
+- Optional server→client rejection detail (protocol 2.21.0). A rejected
+  operation may now carry a bounded human-readable reason via
+  `STATUS_ERROR_DETAIL` instead of a bare `STATUS_ERROR`, so the client can
+  report *why* the server refused (daemon module gate, config validation,
+  receiver-side path/node validation). `receive_status()` transparently maps the
+  new status back to `STATUS_ERROR` for every existing call site and captures
+  the reason into a thread-local buffer exposed by `protocol_last_error()`. The
+  detail body is always consumed, so the stream cannot desynchronize, and
+  messages are sliced to `MAX_ERROR_DETAIL_BYTES` (4096) on send.
+- **Server-contacting `--dry-run` (protocol 2.21.0).** `--dry-run` now performs
+  a real handshake with a remote/daemon receiver and reports exactly what WOULD
+  change based on receiver state (existing destination files, mtimes, checksums,
+  basis dirs). The wire config carries the dry-run intent (`Config.dry_run`) and
+  the receiver answers each per-file check with `STATUS_DRY_RUN_TRANSFER` (would
+  transfer) or `STATUS_OK` (already up to date); the sender prints the
+  would-transfer set and its trailer without sending any file data. The receiver
+  performs the normal read-only incremental decision but mutates nothing: no temp
+  files, writes, renames, deletes, metadata/xattr/chown, or directory creation.
+  A plain local destination (no explicit `--server-port`/remote) keeps the
+  original client-side dry-run. Would-delete reporting for `--delete*` is
+  deferred to a follow-up; dry-run never deletes.
+- Daemon `max connections per host` (per-source-IP concurrent cap, default 0 =
+  unlimited), `auth lockout threshold` (default 10; 0 disables) and
+  `auth lockout duration` (default 300 s) config keys.
+- `fastsync-server --allow-super` opt-in for a privileged standalone TCP server;
+  without it a root standalone receiver forces super-user activities off (device
+  nodes, `--write-devices`, ownership). The `--stdio` SSH argv is client-composed,
+  so super activities always stay off there.
+
+### Changed
+
+- Config wire fields are now declared once in an X-macro table
+  (`CONFIG_WIRE_FIELDS` in `src/shared/config.h`) that generates the struct
+  members, defaults, and the send/receive sequence, removing the manual
+  six-site field sync. Wire bytes and `PROTOCOL_VERSION` are unchanged.
+- `receive_incremental_check()` (the per-file `STATUS_CHECK` fast path) is split
+  into small static helpers with a short linear orchestrator. Pure refactor: the
+  wire byte stream and all cleanup are unchanged.
+- `authorized_root` state has a single owner (`utils.c`) with read accessors; the
+  duplicated statics in `file.c` and the server were removed.
+- `Data` records its owning `ProtocolSession` so its memory charge is returned to
+  the session that reserved it, regardless of the destroying thread.
+- The receiver pipeline moved out of `shared` into `server/receiver_pipeline.[ch]`;
+  the build now uses explicit `fastsync_shared` / `fastsync_client_core` /
+  `fastsync_server_core` targets instead of a GLOB, and the client no longer links
+  server code.
+- The benchmark tool generates the requested random/compressible data mix
+  accurately, verifies each transfer before recording it, computes correct
+  percentiles, adds a MB/s column, handles `tc`/netem without requiring `sudo`
+  when already root, builds into a dedicated `build-bench/` directory, and adds a
+  `--warm` incremental-transfer mode.
+- The `nix-shell` dev environment provides the full toolchain (clang-format,
+  cppcheck, pytest-xdist, OpenSSH, rsync, iproute2, valgrind, lcov) and no longer
+  builds on entry.
+
+### Security
+
+- Enforce the daemon's per-module `max connections` cap (0 = unlimited) and add
+  the shared per-source `max connections per host` cap plus a cross-process
+  `auth lockout`. Because the listener forks one child per connection, the
+  counters live in an anonymous shared mapping created before the accept loop and
+  reclaimed by the parent's `SIGCHLD` handler, so the per-module, per-source and
+  auth-failure state is shared across every child (including after `SIGKILL`). The
+  per-source table has a bounded lifetime (expired/idle entries are reclaimed,
+  with a rate-limited warning when genuinely full), and the occupancy counters are
+  re-derived from the shared slot table on every child exit. Trusted loopback
+  peers are exempt (they share one address); clients behind a shared NAT/proxy
+  share a single per-host budget and lockout, which is documented.
+- Hardening from a full security audit:
+  - Fail a truncated zstd frame instead of spinning forever (remote DoS).
+  - Open receiver destination/basis/hard-link entries `O_NONBLOCK` so a
+    client-planted FIFO cannot block a worker indefinitely.
+  - Require a regular file before `--inplace` writes, closing a FIFO-hang and a
+    raw-device write that bypassed the `--write-devices` gate.
+  - Reject SSH destinations whose user/host begins with `-` and insert `--` before
+    the host token, closing `-o ProxyCommand=…` argument injection (RCE).
+  - Gate client `--force` recursive removal behind the server `--allow-delete`
+    policy.
+  - Reject empty `hosts allow`/`hosts deny`/`auth users` values instead of
+    silently meaning "unrestricted".
+  - Restrict TLS 1.2 to AEAD suites and set server cipher preference; load the
+    private key TOCTOU-safely from an `O_NOFOLLOW` fd; verify IP literals against
+    IP SANs; guard client-cert CN truncation.
+  - Make `--dry-run` content-blind: it neither reads destination files nor
+    hashes basis files, removing a 1-bit content oracle against `read only`
+    modules.
+  - Bound glob matching (iterative DP, no exponential backtracking) and bound
+    line reads for filter/`--files-from`/pattern files.
+  - Gate `system.posix_acl_*` xattrs on `--acls` and charge decompression/chunk
+    allocations against the per-connection memory budget.
+
+### Fixed
+
+- Pre-auth NULL dereference in `config_delete()` when an over-long
+  `basis_count` (and the analogous count fields) was received and then failed
+  validation; received counts are now validated before being published.
+- Leaked inherited `Data` in the forked compression-truncation unit test
+  (valgrind definite leak).
+- `receive_status()` no longer loses a captured rejection reason when owed
+  keepalives are drained.
+
+## [2.20.0] - 2026-09-13
+
+### Security
+
+- Cap cumulative `DirTimeList` growth and bound pre-auth config-string memory
+  (remote memory-exhaustion DoS).
+- Daemon host access control (`hosts allow`/`hosts deny`, IPv4/IPv6/CIDR),
+  configurable global `max connections`, connection audit logging, and a
+  bounded `auth failure delay` throttle. IPv4-mapped peers are normalized and
+  invalid patterns are rejected at parse time (no silent fail-open).
+- Honor `--timeout` for protocol I/O and bound idle/session time to defeat
+  keepalive slowloris; child-safe signal handling in the forked daemon.
+- Compiler/linker hardening (`_FORTIFY_SOURCE`, stack protector, PIE, RELRO)
+  and pinned build dependencies.
+
+### Fixed
+
+- Use-after-free in the basis-dir oversize preflight.
+- Placeholder `Data` leaks, `missing_args` leak, scanner chunk leak.
+- Thread-safe logging; single fd owner and cleanup epilogue in the server
+  handler.
+
+### Performance
+
+- Metadata now crosses the wire as one packed frame (protocol 2.20.0).
+- Delete keep-set and `--files-from` lookups indexed (O(n*m) → O(n)).
+- Reused per-thread zstd contexts; `TCP_NODELAY` by default.
+- Byte-bounded sender queues; removed a redundant scanner `stat()`.
+
+## [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 2.26.0)
 
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 set(CMAKE_C_STANDARD 11)
@@ -38,11 +38,24 @@ if(ENABLE_COVERAGE)
 	add_link_options(--coverage)
 endif()
 
+# --- Build hardening option ---
+# Production hardening is applied to the shipping server/client binaries only,
+# and only when no sanitizer or coverage instrumentation is active: sanitizers
+# carry their own instrumentation, and _FORTIFY_SOURCE requires an optimising
+# build (never the -O0 used for coverage).
+option(ENABLE_HARDENING "Enable compiler/linker hardening for production targets" ON)
+set(HARDENING_ACTIVE OFF)
+if(ENABLE_HARDENING AND SANITIZER STREQUAL "none" AND NOT ENABLE_COVERAGE)
+	set(HARDENING_ACTIVE ON)
+endif()
+
 include(FetchContent)
 FetchContent_Declare(
   xxhash
   GIT_REPOSITORY https://github.com/Cyan4973/xxHash
-  GIT_TAG v0.8.3
+  # v0.8.3 is a lightweight tag pointing at this exact commit (no ^{} peel
+  # entry); pin the commit SHA instead of the mutable tag.
+  GIT_TAG e626a72bc2321cd320e953a0ccf1584cad60f363 # v0.8.3
   SOURCE_SUBDIR cmake_unofficial
 )
 FetchContent_MakeAvailable(xxhash)
@@ -55,37 +68,194 @@ if(NOT ZSTD_LIBRARY)
 	message(FATAL_ERROR "zstd library not found. Ensure it is in your nix-shell!")
 endif()
 
+find_library(ZLIB_LIBRARY z)
+if(NOT ZLIB_LIBRARY)
+	message(FATAL_ERROR "zlib library not found. Ensure zlib1g-dev / nix zlib is available!")
+endif()
+
+find_library(LZ4_LIBRARY lz4)
+if(NOT LZ4_LIBRARY)
+	message(FATAL_ERROR "lz4 library not found. Ensure liblz4-dev / nix lz4 is available!")
+endif()
+
 find_package(OpenSSL REQUIRED)
 
-file(GLOB SHARED_SRCS "src/shared/*.c")
-set(FILE_STORE_SRCS "${CMAKE_CURRENT_SOURCE_DIR}/src/shared/file_store.c")
-list(REMOVE_ITEM SHARED_SRCS ${FILE_STORE_SRCS})
-file(GLOB SERVER_SRCS "src/server/*.c")
-set(SERVER_RECEIVER_SRCS src/server/receiver.c)
-file(GLOB CLIENT_SRCS "src/client/*.c")
+# --- Explicit source lists ---
+# The shared library is self-contained: it must never depend on the client or
+# server modules.  In particular, the receiver pipeline (receive_thread /
+# write_thread) lives under src/server, not here, so the client executable can
+# link the shared library without pulling in any server code.
+set(SHARED_SRCS
+	src/shared/array_list.c
+	src/shared/batch.c
+	src/shared/charset.c
+	src/shared/checksum.c
+	src/shared/chmod.c
+	src/shared/chunk.c
+	src/shared/compression.c
+	src/shared/config.c
+	src/shared/credentials.c
+	src/shared/daemon_conf.c
+	src/shared/daemon_limits.c
+	src/shared/data.c
+	src/shared/delay_updates.c
+	src/shared/delete_plan.c
+	src/shared/delta.c
+	src/shared/file.c
+	src/shared/file_list.c
+	src/shared/file_receive.c
+	src/shared/file_send.c
+	src/shared/file_store.c
+	src/shared/filter.c
+	src/shared/format.c
+	src/shared/hardlink.c
+	src/shared/identity.c
+	src/shared/log.c
+	src/shared/metadata.c
+	src/shared/motd.c
+	src/shared/multiprocessing.c
+	src/shared/protocol.c
+	src/shared/queue.c
+	src/shared/stop_condition.c
+	src/shared/transport_ssh.c
+	src/shared/transport_tcp.c
+	src/shared/transport_tls.c
+	src/shared/utils.c
+	src/shared/xattr.c
+)
+
+# Server implementation (no main): the receiver read/write pipeline plus the
+# CLI parser.  The server executable adds its own main (server.c).
+set(SERVER_CORE_SRCS
+	src/server/receiver.c
+	src/server/receiver_pipeline.c
+	src/server/server_cli.c
+)
+set(SERVER_MAIN_SRCS src/server/server.c)
+
+# Client implementation (no main): everything except the CLI entry point.
+set(CLIENT_CORE_SRCS
+	src/client/change_list.c
+	src/client/client_send.c
+	src/client/client_validation.c
+	src/client/scanner.c
+	src/client/usage.c
+)
+set(CLIENT_MAIN_SRCS src/client/client_cli.c)
+
+# --- Library targets ---
+add_library(fastsync_shared STATIC ${SHARED_SRCS})
+target_include_directories(fastsync_shared PUBLIC src/shared)
+target_link_libraries(fastsync_shared PUBLIC Threads::Threads ${ZSTD_LIBRARY} ${ZLIB_LIBRARY}
+											${LZ4_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
+
+add_library(fastsync_client_core STATIC ${CLIENT_CORE_SRCS})
+target_include_directories(fastsync_client_core PUBLIC src/client)
+target_link_libraries(fastsync_client_core PUBLIC fastsync_shared)
+
+add_library(fastsync_server_core STATIC ${SERVER_CORE_SRCS})
+target_include_directories(fastsync_server_core PUBLIC src/server)
+target_link_libraries(fastsync_server_core PUBLIC fastsync_shared)
 
 # --- Main executables ---
-add_executable(server ${SERVER_SRCS} ${SHARED_SRCS} ${FILE_STORE_SRCS})
-target_include_directories(server PRIVATE src/shared src/server src/client)
-target_link_libraries(server PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
+# The client links only the shared library and its own core; it deliberately
+# does NOT get src/server on its include path nor compile receiver.c.
+add_executable(server ${SERVER_MAIN_SRCS})
+target_link_libraries(server PRIVATE fastsync_server_core)
 
-add_executable(client ${CLIENT_SRCS} ${SHARED_SRCS} ${FILE_STORE_SRCS} ${SERVER_RECEIVER_SRCS})
-target_include_directories(client PRIVATE src/shared src/server src/client)
-target_link_libraries(client PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
+add_executable(client ${CLIENT_MAIN_SRCS})
+target_link_libraries(client PRIVATE fastsync_client_core)
+
+# --- Production hardening ---
+# Each compile flag is probed so a compiler/architecture that lacks it still
+# configures cleanly.  _FORTIFY_SOURCE is guarded separately because it only
+# works in an optimising build.  xxHash is a static archive built by
+# FetchContent, so it must be position-independent for the -pie link; the same
+# applies to the first-party static libraries linked into the -pie binaries.
+if(HARDENING_ACTIVE)
+	set_target_properties(xxhash fastsync_shared fastsync_server_core fastsync_client_core
+						  PROPERTIES POSITION_INDEPENDENT_CODE ON)
+	include(CheckCCompilerFlag)
+	foreach(flag -fstack-protector-strong -fstack-clash-protection -fPIE)
+		string(MAKE_C_IDENTIFIER "HARDEN_${flag}" _harden_var)
+		check_c_compiler_flag("${flag}" ${_harden_var})
+	endforeach()
+	check_c_compiler_flag("-D_FORTIFY_SOURCE=2" HARDEN_FORTIFY_SOURCE)
+	foreach(target fastsync_shared fastsync_server_core fastsync_client_core server client)
+		foreach(flag -fstack-protector-strong -fstack-clash-protection -fPIE)
+			string(MAKE_C_IDENTIFIER "HARDEN_${flag}" _harden_var)
+			if(${_harden_var})
+				target_compile_options(${target} PRIVATE ${flag})
+			endif()
+		endforeach()
+		if(HARDEN_FORTIFY_SOURCE)
+			target_compile_options(${target} PRIVATE -D_FORTIFY_SOURCE=2)
+		endif()
+	endforeach()
+	foreach(target server client)
+		target_link_options(${target} PRIVATE -pie -Wl,-z,relro -Wl,-z,now -Wl,-z,noexecstack)
+	endforeach()
+endif()
 
 # --- Testing ---
 enable_testing()
 
-# Common test libraries
-set(TEST_LIBS Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
-set(TEST_INCLUDES tests src/shared src/server src/client)
+# --- Unit tests ---
+# The monolithic test binary exercises both client and server code, so it is
+# the one place that legitimately sees both include directories and links both
+# core libraries.  client_cli.c is compiled here directly (with the test build
+# define) rather than linked from fastsync_client_core so its test-only shims
+# and the absence of main() are preserved.
+set(TEST_SRCS
+	tests/runner.c
+	tests/test_array_list.c
+	tests/test_batch.c
+	tests/test_change_list.c
+	tests/test_checksum.c
+	tests/test_chunk.c
+	tests/test_client_cli.c
+	tests/test_compression.c
+	tests/test_config.c
+	tests/test_credentials.c
+	tests/test_daemon_conf.c
+	tests/test_daemon_limits.c
+	tests/test_data.c
+	tests/test_delay_updates.c
+	tests/test_delta.c
+	tests/test_file.c
+	tests/test_file_list.c
+	tests/test_file_sendfile.c
+	tests/test_format.c
+	tests/test_fuzz_smoke.c
+	tests/test_glob.c
+	tests/test_hardlink.c
+	tests/test_iconv.c
+	tests/test_log.c
+	tests/test_metadata.c
+	tests/test_motd.c
+	tests/test_multiprocessing.c
+	tests/test_property.c
+	tests/test_protocol.c
+	tests/test_protocol_error.c
+	tests/test_queue.c
+	tests/test_receiver_timeout.c
+	tests/test_robustness.c
+	tests/test_scanner.c
+	tests/test_server.c
+	tests/test_server_cli.c
+	tests/test_shared_utils.c
+	tests/test_stop.c
+	tests/test_stress.c
+	tests/test_transport_ssh.c
+	tests/test_transport_tcp.c
+	tests/test_transport_tls.c
+	tests/test_xattr.c
+)
 
-# 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/change_list.c src/client/client_cli.c src/client/client_validation.c src/client/usage.c)
-target_include_directories(tests PRIVATE ${TEST_INCLUDES})
+add_executable(tests ${TEST_SRCS} src/client/client_cli.c)
+target_include_directories(tests PRIVATE tests)
 target_compile_definitions(tests PRIVATE FASTSYNC_TEST_BUILD)
-target_link_libraries(tests PRIVATE ${TEST_LIBS})
+target_link_libraries(tests PRIVATE fastsync_server_core fastsync_client_core)
 add_test(NAME unit_all COMMAND tests)
 
 # --- Fuzz targets (requires clang) ---
@@ -94,13 +264,29 @@ if(ENABLE_FUZZ)
   if(NOT CMAKE_C_COMPILER_ID MATCHES "Clang")
     message(FATAL_ERROR "ENABLE_FUZZ requires Clang (compiler is ${CMAKE_C_COMPILER_ID})")
   endif()
-  file(GLOB FUZZ_SRCS "tests/fuzz/*.c")
+	set(FUZZ_SRCS
+		tests/fuzz/fuzz_chunk_deserialize.c
+		tests/fuzz/fuzz_compress_decompress.c
+		tests/fuzz/fuzz_config_receive.c
+		tests/fuzz/fuzz_delta_deserialize.c
+		tests/fuzz/fuzz_delta_signature_deserialize.c
+		tests/fuzz/fuzz_glob_match.c
+		tests/fuzz/fuzz_identity_parse.c
+		tests/fuzz/fuzz_manifest.c
+		tests/fuzz/fuzz_metadata_from_buf.c
+		tests/fuzz/fuzz_protocol_framing.c
+		tests/fuzz/fuzz_xattr_block.c
+	)
+	# Compile the sources under test directly so libFuzzer's coverage
+	# instrumentation sees them (static libraries would be uninstrumented).
+	set(FUZZ_CORE_SRCS ${SHARED_SRCS} src/server/receiver.c src/server/receiver_pipeline.c)
 	foreach(FUZZ_SRC ${FUZZ_SRCS})
 		get_filename_component(FUZZ_NAME ${FUZZ_SRC} NAME_WE)
-    add_executable(${FUZZ_NAME} ${FUZZ_SRC} ${SHARED_SRCS} ${FILE_STORE_SRCS} ${SERVER_RECEIVER_SRCS})
-		target_include_directories(${FUZZ_NAME} PRIVATE ${TEST_INCLUDES})
+		add_executable(${FUZZ_NAME} ${FUZZ_SRC} ${FUZZ_CORE_SRCS})
+		target_include_directories(${FUZZ_NAME} PRIVATE tests src/shared src/server)
 		target_compile_options(${FUZZ_NAME} PRIVATE -fsanitize=fuzzer,address,undefined -fno-omit-frame-pointer)
 		target_link_options(${FUZZ_NAME} PRIVATE -fsanitize=fuzzer,address,undefined)
-		target_link_libraries(${FUZZ_NAME} PRIVATE ${TEST_LIBS})
+		target_link_libraries(${FUZZ_NAME} PRIVATE Threads::Threads ${ZSTD_LIBRARY} ${ZLIB_LIBRARY}
+												  ${LZ4_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
 	endforeach()
 endif()

Dockerfile

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

HANDOFF.md

@@ -0,0 +1,67 @@
+# FastSync — Session Handoff (2026-09-17)
+
+## Current status
+- **Release `v2.21.0`** tagged (`919a729`, "Release v2.21.0"); full CI green
+  (run 552: lint, build-and-test, ASan, UBSan, fuzz-build, coverage, valgrind).
+  `dev` has the release commit plus later doc-only merges (a README refresh and
+  this handoff).
+- **Release PR #284 (`dev` -> `main`)** open, CI green (run 553).
+  `main` is protected: it needs review/approval to merge.
+  https://gitea.tap-tap.win/TapTap/FastSync/pulls/284
+- **`PROTOCOL_VERSION` = `"2.26.0"`** (`src/shared/config.h`); CMake
+  `project(FastFileTransfer VERSION 2.26.0)`.
+- Working tree clean; no wave worktrees remain.
+
+## What landed this session
+1. **Wave 8 (refactors):** Config X-macro wire table; single-owner `authorized_root`;
+   daemon per-module/per-host caps + cross-process auth lockout (`daemon_limits.[ch]`);
+   `Data` charge returns to its owning `ProtocolSession`.
+2. **Wave 9 (protocol 2.21.0):** optional `STATUS_ERROR_DETAIL` rejection reasons;
+   server-contacting `--dry-run` (`STATUS_DRY_RUN_TRANSFER`, receiver mutates nothing).
+3. **Security wave:** ran 5 parallel audits (wire parsing; daemon/transport/TLS/auth;
+   receiver confinement; client/CLI/SSH; crypto/memory/limits). Fixed all HIGH and the
+   confirmed MEDIUMs:
+   - SSH `-o ProxyCommand=…` argument injection (RCE) — reject leading `-`, insert `--`.
+   - Truncated zstd frame infinite CPU loop (remote DoS).
+   - FIFO receiver opens lacked `O_NONBLOCK` (indefinite hang).
+   - `--inplace` could write a FIFO/device (bypass of `--write-devices` gate).
+   - `--force` not gated by server `--allow-delete`.
+   - Privileged standalone server defaulted super activities on; added `--allow-super`
+     (never honored with `--stdio`).
+   - `--dry-run` content/hash oracle on `read only`/basis files removed.
+   - Empty `hosts allow`/`deny`/`auth users` now rejected.
+   - TLS: AEAD-only 1.2 + server preference, TOCTOU-safe key load, IP-SAN verify,
+     CN-truncation guard. Glob backtracking bounded; line reads bounded; ACL xattrs
+     gated on `--acls`; decompression/chunk memory charged; pre-auth `basis_count`
+     NULL-deref fixed.
+4. **Tooling:** benchmark accuracy (data mix, verification, percentiles, `tc`,
+   `build-bench/`, `--warm` mode); `shell.nix` full toolchain and no build-on-entry;
+   docs state push-only / remote-source unsupported.
+5. **Preserve-attribute split (protocol 2.22.0)** landed on `feat/preserve-attr-split`: per-attribute `-p/-t/-o/-g` + `--no-*` negations, `-a` = `-rlptgoD`, and the 2.21.0 → 2.22.0 wire bump.
+6. **Rsync-parity wave (protocol 2.23.0)** on `feat/rsync-parity`: rsync short options/clustering/attached values (`-r`/`-b`/`-L`/`-B`, `-av`, `-aAX`, `-B1000`, `-essh`, `-MOPT`), `-c` checksum quick-check, `--checksum-choice`/`--compress-choice` validation and seed randomization, rsync timeout/max-alloc defaults, temp-dir confinement + `EXDEV` fallback, ownership/mapping parity (numeric-ids modifier, map ranges/`*`/empty-FROM, `--chown`+map conflicts, fake-super resolved-owner record), verbatim symlink storage with rsync `--safe-links`/`--munge-links`, socket recreation under `--specials`, `--chmod` 3.4.1 semantics, and delete scoping + `--max-delete` partial/exit-25. Wire: appended delete-manifest synchronized-directory section and `STATUS_DELETE_LIMIT`.
+7. **Parity-completion wave (protocol 2.24.0 → 2.26.0)** on `feat/parity-completion`: per-directory delete plans (`STATUS_DELETE_PLAN`) for `--delete-during`/`--delete-delay`; receiver `STATUS_STATS` counters feeding `--stats`/`--progress` and `--out-format %b/%c/%C`, plus `-n --delete` lines; `lz4`/`zlib`/`zlibx` compression and `md4`/`sha1`/`none` checksums with `auto` negotiation (default `xxh128`/`zstd`); general `-R`/`--no-implied-dirs`/`-d`; the full filter grammar (`merge`/`dir-merge`/`hide`/`show`/`protect`/`risk`/`clear` + modifiers) and corrected `-F`/`-FF`; receiver-side `--chown`/map TO-name resolution; absolute basis dirs + `--link-dest` relink; receiver-side `--ignore-existing` short-circuit; `--preallocate` over `--sparse` via `fallocate(2)`; `--iconv=.`/`-`/`--no-iconv`; lone `-h` help; aliases `--ignore-non-existing`/`--protect-args`/`--msgs2stderr`; and the full `--info`/`--debug` vocabulary. `RSYNC_COMPAT.md` reclassifies the matrix to 106 ✅ / 27 ⚠️ / 23 ❌.
+
+## Next steps
+1. **Merge PR #284** (`dev` -> `main`) once reviewed (protected branch).
+2. **Deferred security items** (documented, not implemented):
+   - Pre-auth config/daemon-auth handshake has no aggregate wall-clock deadline
+     (per-message timeout only) — slowloris holds connection slots.
+   - Per-source registry fails open when the shared table is full (per-module/global
+     caps and host ACLs still apply); consider fail-closed or larger/evicting table.
+   - SCRAM-like daemon auth has no TLS channel binding (and is not RFC 5802).
+   - `cleanup()` signal handler calls non-async-signal-safe teardown; daemon `umask(0)`.
+   - Wire protocol assumes homogeneous word size/endianness (lengths are native
+     `size_t`) — document or move to fixed-width framing.
+3. **Out of scope / intentional:** pull (remote source) mode is **not** planned —
+   FastSync is push-only; see `RSYNC_COMPAT.md#direction`.
+
+## Key facts / commands
+- CI image: `gitea.tap-tap.win/taptap/fastsync-ci:v11` (alias `fastsync-ci:local`).
+- Build/test: `cmake -B build -S . -DSTRICT_WARNINGS=ON && cmake --build build -j$(nproc) && ./build/tests`
+  then `python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"`.
+- Dev shell: `nix-shell` (provides clang-format, cppcheck, pytest-xdist, openssh,
+  rsync, iproute2, valgrind, lcov; does not build on entry).
+- Gitea API token: supplied out-of-band via the `TOKEN` environment variable; it is
+  intentionally **not** recorded in this file.
+- CI polling: `GET /api/v1/repos/TapTap/FastSync/actions/runs?limit=N`, match `head_sha`,
+  then `/actions/runs/<id>/jobs`.

README.md

@@ -1,4 +1,4 @@
-#FastSync
+# FastSync
 
 FastSync is a high-performance file synchronization tool designed to become a
 drop-in replacement for common `rsync` workflows. It keeps the familiar
@@ -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
+`./build/client --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.
@@ -24,7 +28,7 @@ FastSync uses a producer-consumer transfer pipeline and can combine several
 optimizations for large or high-latency transfers:
 
 - Multithreaded scanning, loading, and sending.
-- Streaming zstd compression with levels 1 through 22.
+- Streaming compression (zstd by default, plus lz4/zlib/zlibx) with levels 1 through 22.
 - Configurable file chunking and compact chunk serialization.
 - `sendfile()` zero-copy transfers over TCP.
 - Batched incremental checks to reduce round trips.
@@ -47,94 +51,221 @@ replacement for every rsync feature or protocol mode.
 - Rsync-style source and destination arguments.
 - SSH transport using `user@host:destination` paths below the remote authorized root.
 - TCP client/server transfers.
-- Dry runs, excludes, includes, size filters, backups, statistics, and
-  bandwidth limiting.
-- Incremental size/mtime checks and optional xxHash64 content checks.
+- Dry runs (server-contacting since protocol 2.21.0 for server-routed targets),
+  excludes, includes, size filters, backups, statistics, and bandwidth
+  limiting.
+- Incremental size/mtime checks and optional content checks (`xxh128` by
+  default, selectable with `--checksum-choice`).
 - FastSync-native delta transfer for changed files.
 - Optional mode and timestamp preservation.
 - Delete manifests with server-side delete authorization.
 - Temporary-file writes with atomic rename by default.
 - Path traversal checks and destination-root confinement.
 
-### Not yet equivalent to rsync
+### Boundaries and documented divergences
+
+The items below summarize FastSync's rsync compatibility status — recently
+closed gaps and the remaining known divergences. Each row of the detailed
+matrix is classified as parity, caveat, or divergent in
+[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md).
 
 - The FastSync wire protocol is not the rsync wire protocol.
 - SSH mode requires `fastsync-server` on the remote host.
-- Archive mode does not yet provide all of rsync's `-rlptgoD` behavior.
-- Symlink transfer is incomplete; link targets are not yet recreated in all
-  modes.
-- Owner/group, ACL, xattr, hard-link, device, and special-file handling is
-  incomplete or unavailable.
-- Sparse-file handling does not yet preserve all holes correctly.
-- `--partial`, `--partial-dir`, `-P`, `--append`, and `--append-verify` are not
-  yet full rsync-style resumable transfers. Interrupted files are not retained
-  for resumption.
-- `--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.
-- Several rsync short options currently have FastSync-specific meanings. Do
-  not assume every short option is interchangeable yet.
+- Archive mode covers rsync's `-rlptgoD` behavior — links, permissions, times,
+  owner, group, devices, and special files — and does not imply compression or
+  multithreading (see [Client](#client)). Ownership application is still
+  privilege-gated: a receiver that cannot `chown` logs a warning and skips it.
+  Under `-p` the source mode is copied exactly, including setuid/setgid/sticky
+  and group/other-write bits (strict rsync parity; see
+  [`RSYNC_COMPAT.md`](RSYNC_COMPAT.md)).
+- Symlink transfer stores targets **verbatim** (`-l`/`--links`), including
+  absolute and `..`-bearing targets, matching rsync. The receiver does not
+  enforce a containment predicate by default; `--safe-links` drops unsafe
+  targets on the sender, and `--munge-links` rewrites them with rsync's
+  `/rsyncd-munged/` marker. `--trust-sender` does not affect symlink targets.
+  A destination later consumed by a link-following tool can therefore follow a
+  link outside the receive root — use `--safe-links` for untrusted sources.
+- Hard links (`-H`/`--hard-links`), extended attributes (`-X`/`--xattrs`), and
+  POSIX ACLs (`-A`/`--acls`) are preserved; owner/group is applied through
+  `-o`/`-g` (or an `-a`/`--archive` transfer), through the opt-in identity flags
+  (`--chown`/`--usermap`/`--groupmap`/`--numeric-ids`/`--copy-as`), and only when
+  the receiver has permission. See
+  [`RSYNC_COMPAT.md`](RSYNC_COMPAT.md) for the exact semantics and documented
+  divergences.
+- Device and special-file preservation is implemented with documented
+  divergences: recreated device nodes require `CAP_MKNOD` on the receiver (a
+  non-root receiver skips the entry), while FIFOs **and unix sockets** are
+  recreated (`--specials`).
+- Sparse-file hole preservation (`-S`, `--sparse`) is implemented receiver-side:
+  long all-zero runs are written as holes (no wire change; the full file image
+  is already in memory).
+- `--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.
+- `-d`/`--dirs` and its aliases `--old-dirs`/`--old-d` transfer the named
+  directory entries without recursing into their contents.
+- Short-option names are now rsync-parity (Phase 7 Wave A): FastSync's former
+  collisions were renamed (`-j`/`--threads`, `--preserve`, `--sendfile`,
+  `--chunk-serialization`, `--timeout`, `--ssh-port`), so `-m`, `-M`, `-f`,
+  `-s`, `-T`, `-p`, `-c`, `-a`, and `-z` follow rsync.
+- Short-option clustering (`-av`, `-aAX`, `-rlpt`) and attached values
+  (`-B1000`, `-essh`, `-MOPT`, `--opt=value`) are accepted, matching rsync.
+- `-r`, `-b`, `-L`, and `-B` are parsed with the rsync short names.
+- `--stats` prints the counters FastSync can observe plus the receiver-only
+  counters (`Matched data`, deleted files) reported over the wire; rsync's
+  per-type `Number of files` breakdown is not reproduced. `--progress` prints
+  rsync-style per-file blocks (without rsync's leading `./` line).
+- Codecs match rsync 3.4.1: `zstd`/`lz4`/`zlib`/`zlibx` compression and
+  `xxh128`/`xxh3`/`xxh64`/`md5`/`md4`/`sha1`/`none` checksums, negotiated with
+  `auto`; `zlibx` behaves as `zlib`, and the transfer checksum is not separately
+  selectable.
 
 The detailed flag matrix is maintained in
-[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md). It distinguishes implemented,
-partial, alternate, and planned behavior.
+[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md). It reports each row as **parity**,
+**caveat** (works with a documented divergence), or **divergent** (not
+supported), rather than treating "parsed" as parity.
 
 ## Quick Start
 
 ### Build
 
+```bash
+cmake -B build -S .
+cmake --build build -j$(nproc)
+```
+
+This produces `./build/client` and `./build/server`. `compile_commands.json` is a symlink to `build/compile_commands.json` and is used by clangd/editor tooling; its target is generated by the build, so it dangles until the first build.
+
 ### Client
 
 | Argument | Description |
 |----------|-------------|
 | Positional | `<source> <dest>` — automatic SSH detection if dest contains `:` |
-| `-c [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) |
-| `--secluded-args` | Accepted as an rsync compatibility option with no effect; `-s` remains chunk serialization. |
-| `-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) |
-| `-n, --dry-run` | Scan and print what would be transferred |
-| `-p <port>` | SSH port (default: 22) |
-| `-v, --verbose` | Enable debug logging |
-| `-q, --quiet` | Suppress non-error output |
-| `--progress` | Show real-time transfer speed |
-| `-P` | Enables partial-transfer mode and progress output (partial retention is incomplete) |
-| `--delete` | Delete files on receiver not present in source (default timing: delete-after, i.e. only after the whole transfer succeeded) |
+| `-c, --checksum` | Verify content by checksum instead of size+mtime (implies the incremental checksum quick-check) |
+| `--checksum-choice <alg>` | Whole-file checksum algorithm: `xxh128` (default), `xxh3`, `xxh64`/`xxhash`, `md5`, `md4`, `sha1`, `none`, or `auto` (plus rsync's two-name `transfer,pre-transfer` form) |
+| `-z, --compress [level]` | Enable streaming compression (default `zstd`; level 1–22, default 5) |
+| `--compress-choice <alg>` | Compression algorithm: `zstd` (default), `lz4`, `zlib`, `zlibx`, `none`, or `auto` |
+| `--skip-compress <list>` | Skip compression for suffixes (`/`- or `,`-separated); defaults to rsync 3.4.1's built-in suffix list |
+| `-a, --archive` | rsync archive mode (`-rlptgoD`): links, perms, times, owner, group, devices and specials; ownership application stays privilege-gated (not compression/multithreading) |
+| `-j, --threads[=N]` | Multithreading mode; `N` (1–256) sets the parallel scanner worker count, bare `-j`/`--threads` uses the default |
+| `-m` | rsync `--prune-empty-dirs` (short form now rsync-parity) |
+| `-r, --recursive` | Recurse into directories (FastSync is always recursive; accepted for rsync compatibility) |
+| `-d, --dirs` | Transfer the named directory entries without recursing into their contents; aliases `--old-dirs`/`--old-d` |
+| `-R, --relative` | Use rsync's relative path semantics (including the `/./` cut); with `--files-from`, preserve each listed entry's relative path below the destination root |
+| `--chunk-serialization` | Chunk serialization (batch all files per chunk; long form only) |
+| `-s` | rsync `--secluded-args` compatibility no-op (remote SSH argv is already injection-safe) |
+| `--sendfile` | Sendfile zero-copy. Incompatible with compression / chunk serialization. TCP only. Long form only. |
+| `--preallocate` | Allocate destination file space up front (fail-fast on a full disk) |
+| `--append` | Resume a shorter destination by appending only its tail (prefix not verified; requires `--incremental`) |
+| `--append-verify` | Like `--append`, but verifies the retained prefix checksum first (falls back to a full transfer on mismatch) |
+| `-W, --whole-file` | Transfer changed files without delta processing; `--no-whole-file` clears it |
+| `-B <n>, --block-size <n>` | Delta block size in bytes (alias `--delta-block`) |
+| `--checksum-seed <n>` | Seed for the whole-file xxHash digest; an unset/`0` seed is randomized per transfer, matching rsync |
+| `-I, --ignore-times` | Transfer files even when size and mtime match |
+| `--size-only` | Skip incremental files matching in size, ignoring mtime |
+| `--preserve` | Preserve mode and mtime (`-p` + `-t`; add `-o`/`-g` for owner/group or `-U`/`--atimes` for atime; `-N`/`--crtimes` captures birth time but cannot apply it) |
+| `-U, --atimes` | Preserve access times. Captured with the metadata payload; does not enable ownership. |
+| `-N, --crtimes` | Capture birth time; cannot be applied (documented divergence) |
+| `-p, --perms` | Preserve permission bits. Strict rsync parity: the source mode is copied exactly, including setuid/setgid/sticky and group/other-write bits |
+| `-t, --times` | Preserve modification times |
+| `-o, --owner` | Preserve the source owner (privilege-gated; mapped by name on the receiver with a numeric fallback) |
+| `-g, --group` | Preserve the source group (privilege-gated; mapped by name on the receiver with a numeric fallback) |
+| `--no-perms`, `--no-times`, `--no-owner`, `--no-group`, `--no-preserve` | Negate the per-attribute flags (short `--no-p`/`--no-t`/`--no-o`/`--no-g`; `--no-preserve` clears all four) |
+| `-E, --executability` | Preserve executable permission bits |
+| `-X, --xattrs` | Preserve user `user.*` extended attributes |
+| `-A, --acls` | Preserve POSIX ACLs |
+| `--chmod <changes>` | Modify transferred permissions (rsync syntax) |
+| `--chown=USER:GROUP` | Override the ownership of transferred files |
+| `--usermap=MAP` | Map usernames when applying ownership |
+| `--groupmap=MAP` | Map group names when applying ownership |
+| `--numeric-ids` | Apply source numeric uid/gid directly instead of mapping by name |
+| `--copy-as=USER[:GROUP]` | Force every written entry to USER[:GROUP] (requires a privileged receiver) |
+| `--fake-super` | Record the resolved owner plus mode/time in a reserved `user.fastsync.stat` xattr and replay mode/time; never performs a real chown |
+| `--super` | Permit the receiver to attempt confined super-user activities (device nodes) |
+| `-D` | Preserve device and special files (implies `--devices --specials`) |
+| `--devices` | Recreate device nodes on the destination (privileged; skipped without `CAP_MKNOD`) |
+| `--specials` | Recreate special files: FIFOs and unix sockets |
+| `--remove-source-files` | Remove regular source files after a successful transfer |
+| `--exclude <pattern>` | Exclude files matching glob pattern (repeatable) |
+| `--exclude-from <file>` | Read exclude patterns from a file (one per line) |
+| `--include <pattern>` | Only transfer files matching glob pattern (repeatable, whitelist) |
+| `--include-from <file>` | Read include patterns from a file |
+| `--files-from <file>` | Read the source file list from FILE (paths relative to the source root) |
+| `--max-size <n>` | Skip files larger than n bytes |
+| `--min-size <n>` | Skip files smaller than n bytes |
+| `-x, --one-file-system` | Do not cross filesystem boundaries; the mount-point directory entry is emitted (empty at the destination) without descending |
+| `--max-alloc <SIZE>` | Maximum single allocation (binary units: B, K, M, G, T, P, E; default 1G; `0` = no local limit, matching rsync) |
+| `-u, --update` | Skip files newer than the source on the receiver |
+| `--incremental` | Skip files unchanged since last transfer (size + mtime). Auto-enables `--preserve`. Incompatible with `--chunk-serialization`. |
+| `--existing` | Skip files not already present at the destination; update existing files normally. |
+| `--compare-dest <dir>` | Extra comparison basis: unchanged files are not transferred (requires/implies `--incremental`) |
+| `--copy-dest <dir>` | Like `--compare-dest`, but copies the unchanged file from DIR into the destination |
+| `--link-dest <dir>` | Like `--copy-dest`, but hard-links the unchanged file from DIR (repeatable; earlier DIRs win) |
+| `--delete` | Delete files on receiver not present in source (default timing: delete-after, i.e. only after the whole transfer succeeded). Scoped to the synchronized directories, so `--files-from` subsets are safe |
 | `--delete-before` | Delete extras before the transfer starts (implies `--delete`) |
 | `--delete-during`, `--del` | Delete extras once the keep-set is known, before data is applied (implies `--delete`) |
 | `--delete-delay` | Delete extras only after a successful transfer (implies `--delete`) |
 | `--delete-after` | Explicit delete-after timing (implies `--delete`) |
-| `--exclude <pattern>` | Exclude files matching glob pattern (repeatable) |
-| `--exclude-from <file>` | Read exclude patterns from a file (one per line) |
-| `--include <pattern>` | Only transfer files matching glob pattern (repeatable, whitelist) |
-| `--max-size <n>` | Skip files larger than n bytes |
-| `--min-size <n>` | Skip files smaller than n bytes |
-| `--max-alloc <SIZE>` | Maximum single allocation (binary units: B, K, M, G, T, P, E; default 1G) |
-| `--incremental` | Skip files unchanged since last transfer (size + mtime). Auto-enables `--preserve`. Incompatible with `-s`. |
-| `--existing` | Skip files not already present at the destination; update existing files normally. |
-| `--bwlimit <KB/s>` | Bandwidth limit in kilobytes per second |
-| `--chunk-size <n>` | Chunk size in bytes (default: 10485760) |
-| `--timeout <sec>` | I/O timeout in seconds (default: 30) |
-| `--contimeout <sec>` | Connection timeout in seconds (default: 10) |
-| `--backup` | Backup existing destination files before overwriting |
-| `--backup-dir <dir>` | Target directory for backups (requires `--backup`) |
-| `--stats` | Print transfer statistics at end (bytes, files, timing) |
-| `-h, --human-readable` | Format transfer byte sizes with binary units |
+| `--delete-excluded` | Also delete filter-excluded destination mirrors (size-pruned mirrors stay protected) |
+| `--max-delete <n>` | Delete at most n destination entries; the rest are skipped and the run exits 25 (partial), matching rsync |
+| `--delay-updates` | Put updated files into place only at the end of the transfer (`--force` is honored at publication) |
+| `-T, --temp-dir <dir>` | Scratch directory for temp files before the atomic install; confined to the receive root (relative only), with an `EXDEV` non-atomic copy fallback |
+| `-n, --dry-run` | Report what would be transferred without mutating the destination. Since protocol 2.21.0 a server-routed target contacts the receiver and reports would-transfer based on receiver state; a plain local destination keeps the client-side scan. Never mutates or deletes. |
+| `-v, --verbose` | Enable debug logging |
+| `-q, --quiet` | Suppress non-error output |
+| `--progress` | Show rsync-style per-file progress blocks from the receiver's wire counters (FastSync does not print rsync's leading `./` line) |
+| `-P` | Enables partial-transfer mode + progress output; interrupted writes retain the already-written temp for resumption |
+| `--stats` | Print transfer statistics at end (bytes, files, timing), including the receiver-only counters reported over the wire; rsync's per-type `Number of files` breakdown is not reproduced |
+| `-i, --itemize-changes` | Print an rsync-style per-file change line |
+| `--out-format=FORMAT` | Output format for changed files (`%f %n %l %b %M %%`) |
+| `--list-only` | List source files instead of transferring |
+| `--fsync` | Fsync every written file before publication |
+| `-h, --human-readable` | Format transfer byte/rate counts with rsync's decimal (base-1000) units |
 | `--max-depth <n>` | Maximum directory depth to recurse (0 = unlimited, default: 0) |
 | `--log-file <path>` | Write log messages to file instead of stderr |
+| `--write-batch=FILE` | Run the normal live transfer and also emit a self-contained batch file of the source tree |
+| `--only-write-batch=FILE` | Emit the batch file only (no destination, no server) |
+| `--read-batch=FILE` | Apply a batch file to the destination (no source, no server) |
 | `--source-dir <path>` | Source directory (overrides `FASTSYNC_SOURCE_DIR`) |
 | `--dest-dir <path>` | Server destination directory (overrides `FASTSYNC_DEST_DIR`) |
 | `--save-to-disk` | Write received files to disk |
 | `--server-host <ip>` | Server IP address (default: `127.0.0.1`) |
 | `--server-port <n>` | Server port (default: `8080`) |
+| `--ssh-port <port>` | SSH port (default: 22) |
+| `-e, --rsh <command>` | Remote shell to launch for the SSH transport (default: `ssh`; may include arguments, e.g. `-e "ssh -p 2222"`) |
+| `-M, --remote-option=OPT` | Append OPT to the remote server invocation over SSH (repeatable) |
+| `--address <ip>` | Bind the outgoing client socket to this source address |
+| `-4, --ipv4` | Force IPv4 for destination resolution |
+| `-6, --ipv6` | Force IPv6 for destination resolution |
+| `--sockopts=OPTS` | Comma-separated OPT=VAL socket options applied before connect (`TCP_NODELAY`, `SO_KEEPALIVE`, `SO_RCVBUF`, `SO_SNDBUF`, `SO_REUSEADDR`) |
+| `--bwlimit <KB/s>` | Bandwidth limit in kilobytes per second |
+| `--chunk-size <n>` | Chunk size in bytes (default: 10485760) |
+| `--timeout <sec>` | I/O timeout in seconds, applied to both the socket (`SO_RCVTIMEO`/`SO_SNDTIMEO`) and the per-message protocol poll deadline. Default `0` = disabled (matching rsync); `0` disables it. `--no-timeout` is the negation. The value is not sent on the wire; the server side keeps its own safe floor. |
+| `--contimeout <sec>` | Connection timeout in seconds (default: 60, matching rsync); `0` disables it (`--no-contimeout` is the negation) |
+| `--stop-after=MINS` | Stop the transfer after MINS minutes (a positive integer); whatever was already transferred is kept |
+| `--stop-at=TIME` | Stop at an absolute time (`HH:MM`, `HH:MM:SS`, or `now+N[smhd]`); an early stop skips the late `--delete` keep-set |
+| `-b, --backup` | Backup existing destination files before overwriting |
+| `--backup-dir <dir>` | Target directory for backups (requires `--backup`) |
 | `--tls` | Enable TLS encryption |
 | `--cert <path>` | TLS certificate file (PEM) |
 | `--key <path>` | TLS private key file (PEM) |
 | `--ca <path>` | TLS CA certificate file for verification (PEM) |
-| `--client-cn <name>` | Required TLS client certificate common name |
+
+The exhaustive rsync flag matrix is in [`RSYNC_COMPAT.md`](RSYNC_COMPAT.md).
+
+**Per-message vs. connection timeouts.** `--timeout` bounds each individual protocol
+send/receive (the `poll()` deadline), so a peer that stops mid-frame is dropped. It
+does not, by itself, stop a peer that keeps sending well-formed frames forever. The
+receiver therefore also enforces two wall-clock (`CLOCK_MONOTONIC`) bounds on a
+connection: a **1 hour** idle limit and a **24 hour** overall session cap. Only
+frames that move real work (not `STATUS_KEEPALIVE`/`STATUS_ABORT` and not an
+empty `STATUS_CHECK_BATCH`/`STATUS_DIR_TIMES`) refresh the idle timestamp, so a
+peer cannot hold a connection slot by emitting cheap empty frames; a peer that
+fabricates minimal non-empty frames can still occupy a slot until the 24 hour
+cap, since no bound can require actual payload without risking a legitimate
+long operation. Both are deliberately generous so a legitimate long-running
+transfer is never aborted.
 
 ### Server
 
@@ -148,7 +279,8 @@ 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-super` | Standalone TCP listener only: keep super-user activities enabled for a **root** receiver. Without it a root standalone server forces `SUPER_MODE_OFF`, so client `--devices`/`--write-devices`/`--super` and client-chosen ownership requests are skipped/refused. **Rejected with `--stdio`** (the SSH remote argv is client-composed, so a client could otherwise pass it and defeat the secure default; operators exposing `fastsync-server --stdio` over SSH must use a forced command if the default must hold). No effect when not root. |
+| `--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 |
 
@@ -159,60 +291,64 @@ partial, alternate, and planned behavior.
 | `FASTSYNC_SOURCE_DIR` | — | Source directory fallback |
 | `FASTSYNC_DEST_DIR` | — | Destination directory fallback |
 | `FASTSYNC_SAVE_TO_DISK` | `false` | Disk persistence fallback |
-| `FASTSYNC_SSH_PORT` | `22` | Default SSH port |
-| `FASTSYNC_SERVER_HOST` | `127.0.0.1` | Default server host |
-| `FASTSYNC_SERVER_PORT` | `8080` | Default server port |
-| `FASTSYNC_TLS_CERT` | — | Default TLS certificate path |
-| `FASTSYNC_TLS_KEY` | — | Default TLS private key path |
-| `FASTSYNC_TLS_CA` | — | Default TLS CA certificate path |
 
 ## Implementation Details
 
 ### Data Structures
-1. **Chunk** — collection of files (~10 MB total by default)
-2. **File** — path, content (`Data`), optional `FileMetadata` pointer
-3. **FileMetadata** — `mode`, `uid`, `gid`, `mtime_sec`, `mtime_nsec`;
-uid / gid are advisory wire fields and are never applied by the receiver;
-atime is unsupported
-4. **Config** — runtime parameters (transported over wire, TLS settings excluded). Includes `timeout`, `contimeout`, `quiet`, `backup`, `backup_dir`, `stats`, `max_depth`, `log_file`, `queue_size`.
-5. **Queue** — thread-safe bounded queue with condition variables
-6. **DirectoryScanner** — recursive BFS traversal with exclude and include pattern support, max-depth enforcement
+
+1. **Chunk** — collection of files (~10 MB total by default).
+2. **File** — path, content (`Data`), optional `FileMetadata` pointer.
+3. **FileMetadata** — `mode`, `uid`, `gid`, `mtime_sec`, `mtime_nsec` (plus
+   atime/crtime fields). `uid`/`gid` are applied only through the opt-in
+   identity path; atime is preserved with `-U`/`--atimes`; crtime is captured
+   but cannot be set on the destination.
+4. **Config** — runtime parameters. Most cross the wire (TLS settings
+   excluded); `backup` and `backup_dir` are in the serialized wire table, while
+   `timeout`, `contimeout`, `quiet`, `stats`, `max_depth`, and `log_file` are
+   client-only.
+5. **Queue** — thread-safe bounded queue with condition variables.
+6. **DirectoryScanner** — recursive BFS traversal with exclude and include
+   pattern support, max-depth enforcement.
 
 ### Key Algorithms
-1. **File scanning** — BFS directory traversal;
-entries matched against exclude and include patterns,
-    max - depth enforced 2. * *Chunking ** — files accumulated until `chunk_size` threshold,
-    then flushed 3. *
-            *Compression ** — streaming zstd
-                via `ZSTD_compressStream2` / `ZSTD_decompressStream` 4. *
-            *Network protocol ** — status -
-        code - driven exchange with metadata packing,
-    keep - alive,
-    and abort support 5. * *Incremental check ** — client sends `STATUS_CHECK` + path + size +
-        mtime and,
-    with `--checksum`, XXH64 content checksum; server compares against destination. Can be batched via `STATUS_CHECK_BATCH` for reduced round-trips.
-6. **Bandwidth limiting** — token-bucket algorithm with `nanosleep` throttling on 64 KB write chunks
-7. **Metadata restoration** — `chmod()`, `chown()`, `utimensat()` on the receiving side
-8. **`--delete`** — sender tracks all sent paths;
-receiver walks destination tree and removes unlisted files / directories 9. *
-        *SSH transport *
-            * — `socketpair()` + `fork()` + `execvp("ssh",
-                                                    ...)` with `ControlMaster` and port support
-                                                10. *
-                                                *TLS transport ** — OpenSSL `SSL_CTX` with TLS
-                                                1.2 minimum,
-    mutual CA verification,
-    transparent `SSL_read`/`SSL_write` via `io_set_ssl()` 11. *
-        *Path traversal protection ** — `has_path_traversal()` rejects any file path
-         containing `..` components,
-    preventing directory escape attacks 12. *
-            *Connection limiting ** — server tracks active connections and rejects
-            new ones beyond `max_connections` (default 100)13. *
-            *Keep
-        - alive ** — idle connections receive periodic `STATUS_KEEPALIVE` to detect half
-        - open TCP connections 14. * *Abort handling ** — `SIGINT` sets an abort flag; the next protocol operation sends `STATUS_ABORT` for clean server cleanup
-15. **Atomic writes** — files are written to a `.tmp` suffix then atomically renamed via `rename()`, preventing partial files
-16. **Backup** — before overwriting, existing files are moved to `--backup-dir` (or same directory with `~` suffix) preserving the original
+
+1. **File scanning** — BFS directory traversal; entries matched against exclude
+   and include patterns, with max-depth enforced.
+2. **Chunking** — files accumulated until the `chunk_size` threshold (default
+   10 MiB) is reached, then flushed.
+3. **Compression** — streaming zstd via `ZSTD_compressStream2()` /
+   `ZSTD_decompressStream()`.
+4. **Network protocol** — status-code-driven exchange with metadata packing,
+   keep-alive, and abort support.
+5. **Incremental check** — the client sends `STATUS_CHECK` + path + size +
+    mtime and, with `--checksum`, a whole-file content checksum (`xxh128` by
+    default; selectable via `--checksum-choice`/`--cc`, seeded by
+    `--checksum-seed`); the server compares against the destination. Can be
+    batched via `STATUS_CHECK_BATCH` for reduced round-trips.
+6. **Bandwidth limiting** — token-bucket algorithm with sleep throttling on
+   64 KiB write chunks.
+7. **Metadata restoration** — mode via `chmod()`/`fchmod()`, times via
+   `utimensat()`/`futimens()`, and ownership only with an identity flag via
+   fd-relative `fchown()`/`fchownat()`.
+8. **`--delete`** — the sender tracks all sent paths; the receiver walks the
+   destination tree and removes unlisted files and directories.
+9. **SSH transport** — `socketpair()` + `fork()` + `execvp("ssh", ...)` with
+   `ControlMaster` and port support.
+10. **TLS transport** — OpenSSL `SSL_CTX` with TLS 1.2 minimum, mutual CA
+    verification, and transparent `SSL_read()`/`SSL_write()` via
+    `io_set_ssl()`.
+11. **Path traversal protection** — `has_path_traversal()` rejects any file
+    path containing `..` components, preventing directory escape attacks.
+12. **Connection limiting** — the server tracks active connections and rejects
+    new ones beyond `max_connections` (default 100).
+13. **Keep-alive** — idle connections receive periodic `STATUS_KEEPALIVE` to
+    detect half-open TCP connections.
+14. **Abort handling** — `SIGINT` sets an abort flag; the next protocol
+    operation sends `STATUS_ABORT` for clean server cleanup.
+15. **Atomic writes** — files are written to a `.tmp` suffix then atomically
+    renamed via `rename()`, preventing partial files.
+16. **Backup** — before overwriting, existing files are moved to `--backup-dir`
+    (or the same directory with a `~` suffix), preserving the original.
 
 ## Security Features
 
@@ -269,22 +405,34 @@ cmake --build build -j$(nproc)
 
 ### SSH transfer
 
-The remote host must have `fastsync-server` available in `PATH`, or use
+The remote host must have `fastsync-server` available in `PATH` (install or
+copy the built `./build/server` there as `fastsync-server`), or use
 `--fastsync-server-path`. SSH starts `fastsync-server --stdio` in its remote
 working directory, so use a destination below that directory unless the
 remote server is otherwise configured with a matching authorized root.
 
+The remote `--stdio` server argv is composed by the client, so it must never
+be trusted to opt a root receiver into super-user activities: `--allow-super`
+is rejected with `--stdio` and super stays off on that path. Operators
+exposing `fastsync-server --stdio` over SSH must use a forced command (e.g. an
+`authorized_keys` `command=` entry) if the default must hold.
+
 ```bash
 ssh user@host 'mkdir -p destination'
 ./build/client /path/to/source user@host:destination
 ```
 
+FastSync is **push-only**: the source (first argument) is always a local
+directory and only the destination may be remote. A remote source such as
+`client user@host:src ./local` (a "pull") is intentionally not supported; see
+[RSYNC_COMPAT.md](RSYNC_COMPAT.md#direction).
+
 ### TCP transfer
 
 Start the FastSync server:
 
 ```bash
-./build/server --destination-root /path/to -p 8080
+./build/server --destination-root /path/to -p 8080 --allow-unauthenticated
 ```
 
 Then run the client:
@@ -299,8 +447,13 @@ Plain TCP requires the explicit `--allow-unauthenticated` server option. Use TLS
 authenticated network connections.
 
 ### TLS transfer
+
+Server TLS requires `--cert`, `--key`, `--ca`, and `--client-cn`; the client
+requires `--cert`, `--key`, and `--ca`.
+
 ```bash
-./build/server --destination-root /path/to --tls --cert server.pem --key server-key.pem -p 8443
+./build/server --destination-root /path/to --tls --cert server.pem --key server-key.pem \
+  --ca ca.pem --client-cn client -p 8443
 ./build/client --tls --cert client.pem --key client-key.pem --ca ca.pem \
   --server-host example.com --server-port 8443 \
   --source-dir /path/to/source --dest-dir /path/to/destination \
@@ -313,32 +466,32 @@ These examples show the intended rsync-style workflow. Options marked as
 FastSync-native are optional performance or transport extensions.
 
 ```bash
-#Basic synchronization
+# Basic synchronization
 ./build/client /source/ /destination/
 
-#Archive - style synchronization(current FastSync archive behavior)
+# Archive-style synchronization (current FastSync archive behavior)
 ./build/client -a /source/ user@host:destination/
 
-#Preview a transfer without changing the destination
+# Preview a transfer without changing the destination
 ./build/client -n /source/ /destination/
 
-#Exclude temporary and object files
+# Exclude temporary and object files
 ./build/client --exclude '*.tmp' --exclude '*.o' \
   /source/ user@host:destination/
 
-#Remove destination entries not present in the source
+# Remove destination entries not present in the source
 ./build/client --delete /source/ user@host:destination/
 
-#Skip unchanged files using size and modification time
+# Skip unchanged files using size and modification time
 ./build/client --incremental /source/ user@host:destination/
 
-#Verify content when size and time are not sufficient
+# Verify content when size and time are not sufficient
 ./build/client --incremental --checksum /source/ user@host:destination/
 
-#Preserve supported mode and timestamp metadata
-./build/client -M /source/ user@host:destination/
+# Preserve supported mode and timestamp metadata
+./build/client --preserve /source/ user@host:destination/
 
-#Keep backups of overwritten destination files
+# Keep backups of overwritten destination files
 ./build/client --backup --backup-dir backups \
   /source/ user@host:destination/
 ```
@@ -350,37 +503,41 @@ 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. |
-| `--compress-level <n>` | Set the zstd compression level. |
-| `--zc <alg>` | Alias for `--compress-choice`. FastSync supports `zstd` and `none`. |
+| `-j`, `--threads[=N]` | Enable the multithreaded scanner/loader/sender pipeline. `N` (1–256) sets the parallel scanner worker count; bare `-j`/`--threads` uses the default. |
+| `-z [level]`, `--compress [level]` | Enable streaming compression (default `zstd`), levels 1-22. |
+| `--compress-level <n>` | Set the compression level. |
+| `--zc <alg>` | Alias for `--compress-choice`. FastSync supports `zstd` (default), `lz4`, `zlib`, `zlibx`, `none`, and `auto`; `zlibx` behaves as `zlib`. |
 | `--zl <n>` | Alias for `--compress-level`. |
-| `--skip-compress <list>` | Skip compression for comma-separated suffixes; incompatible with `-s`. |
+| `--skip-compress <list>` | Skip compression for `/`- or `,`-separated suffixes; defaults to rsync 3.4.1's built-in list. Incompatible with `--chunk-serialization`. |
 | `--compress-threads <n>` | Use `n` zstd compression workers. Requires compression and a zstd build with threaded support; the setting affects sender CPU work only. |
 | `--chunk-size <bytes>` | Set the transfer chunk size. |
-| `-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. |
+| `--server-port <port>` | Select the TCP server port (`--port <port>` and `--port=<port>` are rsync-friendly aliases). |
 | `--tls` | Enable TLS for TCP transport. |
 | `--bwlimit <KB/s>` | Apply token-bucket bandwidth limiting. |
-| `--progress` | Show transfer progress and throughput. |
-| `--stats` | Print transfer statistics. |
-| `--timeout <seconds>` | Set I/O timeout. |
-| `--contimeout <seconds>` | Set connection timeout. |
+| `--progress` | Show rsync-style per-file progress blocks from the receiver's wire counters (FastSync omits rsync's leading `./` line). |
+| `--stats` | Print transfer statistics, including the receiver-only counters reported over the wire; rsync's per-type `Number of files` breakdown is not reproduced. |
+| `--timeout <seconds>` | Set the socket **and** per-message protocol I/O timeout. Default `0` = disabled (matching rsync); `0` disables it. |
+| `--contimeout <seconds>` | Connection timeout (default 60, matching rsync); `0` disables it. |
 
-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 rsync archive `-rlptgoD` (owner/group implied, but the
+receiver still needs privilege to apply them).
 
-`--secluded-args` is accepted as a long-form compatibility no-op. It does not
-change FastSync's transport or protocol behavior. The rsync short form `-s` is
-intentionally not aliased because it remains FastSync's chunk-serialization
-option.
+`--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
 
@@ -388,50 +545,107 @@ option.
 
 | Option | Description |
 |---|---|
-| `-a`, `--archive` | Enable current archive preset. Full rsync archive semantics are planned. |
-| `-n`, `--dry-run` | Scan and report without writing files. |
-| `--delete` | Request removal of destination entries absent from the source. The server must allow deletion. Default timing is delete-after: extras are removed only after the whole transfer succeeded. |
+| `-a`, `--archive` | rsync archive mode (`-rlptgoD`): links, perms, times, owner, group, devices and specials; ownership application stays privilege-gated. |
+| `-n`, `--dry-run` | Report what would be transferred without mutating the destination. Since protocol 2.21.0 a server-routed target contacts the receiver and reports would-transfer based on receiver state; a plain local destination keeps the client-side scan. Never mutates or deletes. |
+| `--remove-source-files` | Remove regular source files after a successful transfer. |
+| `--incremental` | Skip files matching destination size and mtime. Auto-enables `--preserve`. Incompatible with `--chunk-serialization`. |
+| `-c, --checksum` | Verify content by checksum (implies the incremental quick-check). Algorithm selectable with `--checksum-choice`. |
+| `--checksum-choice <alg>` | Whole-file checksum algorithm: `xxh64`/`xxhash` (default), `xxh3`, `xxh128`, `md5`, or `auto`. |
+| `--checksum-seed <n>` | Seed for the whole-file xxHash digest; an unset/`0` seed is randomized per transfer, matching rsync. |
+| `--size-only` | Skip incremental files matching in size, ignoring mtime. |
+| `-I, --ignore-times` | Transfer files even when size and mtime match. |
+| `-u, --update` | Skip files newer than the source on the receiver. |
+| `-W, --whole-file` | Transfer changed files without delta processing (`--no-whole-file` clears it). |
+| `-B <n>, --block-size <n>` | Delta block size in bytes (alias `--delta-block`). |
+| `-d, --dirs` | Transfer the named directory entries without recursing into their contents (aliases `--old-dirs`/`--old-d`). |
+| `-R, --relative` | Use rsync's relative path semantics (including the `/./` cut); with `--files-from`, preserve each listed entry's relative path below the destination root. |
+| `--files-from <file>` | Read the source file list from FILE (paths relative to the source root). |
+| `--delay-updates` | Put updated files into place only at the end of the transfer. |
+| `--compare-dest <dir>` | Extra comparison basis: unchanged files are not transferred (requires/implies `--incremental`). |
+| `--copy-dest <dir>` | Like `--compare-dest`, but copies the unchanged file from DIR into the destination. |
+| `--link-dest <dir>` | Like `--copy-dest`, but hard-links the unchanged file from DIR (repeatable; earlier DIRs win). |
+| `--preallocate` | Allocate destination file space up front (fail-fast on a full disk). |
+| `--append` | Resume a shorter destination by appending only its tail (prefix not verified; requires `--incremental`). |
+| `--append-verify` | Like `--append`, but verifies the retained prefix checksum first (falls back to a full transfer on mismatch). |
+| `--delete` | Request removal of destination entries absent from the source. The server must allow deletion. Default timing is delete-after: extras are removed only after the whole transfer succeeded. Scoped to the synchronized directories, so `--files-from` subsets are safe. |
 | `--delete-before` | Delete extras before the transfer starts (implies `--delete`). |
 | `--delete-during`, `--del` | Delete extras once the keep-set manifest is known, before data is applied (implies `--delete`; early mode, same engine behaviour as `--delete-before`). |
 | `--delete-delay` | Delete extras only after a successful transfer (implies `--delete`; commit mode, same behaviour as `--delete-after`). |
 | `--delete-after` | Explicit delete-after timing: delete only after the transfer succeeded (implies `--delete`). |
+| `--delete-excluded` | Also delete filter-excluded destination mirrors (size-pruned mirrors stay protected). |
+| `--max-delete <n>` | Delete at most n destination entries; the rest are skipped and the run exits 25 (partial), matching rsync. |
+| `--force` | Allow an incoming file/symlink to replace a destination directory (also during `--delay-updates` publication). |
 | `--exclude <pattern>` | Exclude matching paths. Repeatable. |
 | `--include <pattern>` | Include matching paths. Repeatable. |
 | `--exclude-from <file>` | Read exclude patterns from a file. |
 | `--include-from <file>` | Read include patterns from a file. |
+| `-f, --filter=RULE` | Add an rsync-style filter rule (`+`/`-`, `include`/`exclude`, `merge`/`.`, `dir-merge`/`:`, `hide`/`H`, `show`/`S`, `protect`/`P`, `risk`/`R`, `clear`/`!`, and modifiers; repeatable). |
 | `--max-size <bytes>` | Skip files larger than the limit. |
 | `--min-size <bytes>` | Skip files smaller than the limit. |
-| `--max-depth <n>` | Limit recursive scanning depth;
-zero means unlimited.| | `--incremental` | Skip files matching destination size and mtime.|
-    | `--checksum` | Include xxHash64 content checks in incremental comparisons.| | `--backup` |
-    Back up overwritten files.| | `--backup - dir<dir>` | Store backups under a separate directory.|
-    | `--suffix<suffix>` | Set the backup filename suffix.| | `--partial` |
-    Select partial - transfer handling.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`. |
+| `--max-alloc <SIZE>` | Maximum single allocation (binary units; default 1G; `0` = no local limit). |
+| `--max-depth <n>` | Limit recursive scanning depth; zero means unlimited. |
+| `-b, --backup` | Back up overwritten files. |
+| `-T, --temp-dir <dir>` | Scratch directory for temp files before the atomic install (confined to the receive root; `EXDEV` falls back to a non-atomic copy). |
+| `--backup-dir <dir>` | Store backups under a separate directory (requires `--backup`). |
+| `--suffix <suffix>` | Set the backup filename suffix (default: `~`). |
+| `--partial` | Select partial-transfer handling. On failed/interrupted writes the already-written temp file is retained (best-effort) for resumption. With `--partial --partial-dir <dir>`, completed files are written under the partial directory and installed atomically. |
+| `--partial-dir <dir>` | Set a relative partial-transfer directory below the server destination root. Use with `--partial`. |
 | `--inplace` | Write directly to the destination instead of using a temporary file. |
+| `--fsync` | Fsync every written file before publication. |
+| `--write-batch=FILE` | Run the normal live transfer and also emit a self-contained batch file of the source tree. |
+| `--only-write-batch=FILE` | Emit the batch file only (no destination, no server). |
+| `--read-batch=FILE` | Apply a batch file to the destination (no source, no server). |
+| `--stop-after=MINS` | Stop the transfer after MINS minutes; whatever was already transferred is kept. |
+| `--stop-at=TIME` | Stop at an absolute time (`HH:MM`, `HH:MM:SS`, or `now+N[smhd]`). An early stop skips the late `--delete` keep-set. |
 
 ### Metadata and links
 
 | Option | Description |
 |---|---|
-| `-M`, `--preserve` | Preserve supported file metadata, currently mode and modification time. |
-| `-l`, `--links` | Request symlink preservation;
-link-target transfer remains incomplete. |
-| `--copy-links` | Copy symlink referents. |
-| `--safe-links` | Skip symlinks that point outside the transfer tree. |
+| `--preserve` | Preserve mode and mtime (long form only; equivalent to `-p` + `-t`). Add `-o`/`-g` for owner/group, `-U`/`--atimes` for atime, or an identity flag (`--chown`/`--usermap`/`--groupmap`/`--numeric-ids`/`--copy-as`) for mapped ownership. |
+| `-U`, `--atimes` | Preserve access times. Captured with the metadata payload; does not enable ownership. |
+| `-N`, `--crtimes` | Capture birth time and transmit it; it cannot be applied because no portable filesystem call can set a birth time (documented divergence). |
+| `-p`, `--perms` | Preserve permission bits. One of the four per-attribute preserve flags (with `-t`/`-o`/`-g`); under `-p` the source mode is copied exactly (setuid/setgid/sticky and group/other-write included), matching rsync. |
+| `-t`, `--times` | Preserve modification times. Independent of the other attributes; `-O`/`--omit-dir-times` suppresses directories only. |
+| `-o`, `--owner` | Preserve the source owner (uid). Mapped by name on the receiver with a raw-numeric fallback (only numeric ids cross the wire); application is privilege-gated. |
+| `-g`, `--group` | Preserve the source group (gid). Same name-mapping/numeric-fallback and privilege gating as `-o`. |
+| `--no-perms`, `--no-times`, `--no-owner`, `--no-group` | Negate each per-attribute flag (also `--no-p`/`--no-t`/`--no-o`/`--no-g`); `--no-preserve` clears all four. |
+| `-E`, `--executability` | Preserve executable permission bits. |
+| `-X`, `--xattrs` | Preserve user `user.*` extended attributes. |
+| `-A`, `--acls` | Preserve POSIX ACLs. |
+| `--chmod <changes>` | Modify transferred permissions (rsync syntax, including `D`/`F`/`X` selectors and `s`/`t`); does not imply `-p`. |
+| `--chown=USER:GROUP` | Override the ownership of transferred files (`USER:GROUP`, `USER`, or `:GROUP`); conflicts with `--usermap`/`--groupmap` on the same side. |
+| `--usermap=MAP` | Map usernames when applying ownership (`FROM:TO` rules; names, ids, `LOW-HIGH` ranges, `*`, empty-`FROM`). |
+| `--groupmap=MAP` | Map group names when applying ownership (same syntax as `--usermap`). |
+| `--numeric-ids` | Mapping modifier: apply the source numeric uid/gid directly instead of mapping by name (combine with `-o`/`-g`, `-a`, or a map). |
+| `--copy-as=USER[:GROUP]` | Force every written entry to USER[:GROUP]; requires a privileged receiver. |
+| `--fake-super` | Record the resolved owner plus mode/time in a reserved `user.fastsync.stat` xattr and replay mode/time; never performs a real chown. |
+| `--super` | Permit the receiver to attempt confined super-user activities (device nodes). |
+| `--no-super` | Forbid those super-user activities even when the receiver is root. |
+| `-l`, `--links` | Copy symlinks as symlinks; the target is stored verbatim (absolute and `..`-bearing targets included), matching rsync. |
+| `-L`, `--copy-links` | Copy symlink referents (a broken referent makes the run exit 23, matching rsync). |
+| `--safe-links` | Skip symlinks whose target points outside the transfer tree (applied on the sender). |
 | `--copy-unsafe-links` | Copy unsafe symlink referents. |
-| `-S`, `--sparse` | Request sparse-file handling; full hole preservation is planned. |
+| `--munge-links` | Rewrite stored symlink targets with rsync's `/rsyncd-munged/` marker. |
+| `-k`, `--copy-dirlinks` | Treat a symlink to a directory as a real directory on the sender. |
+| `-K`, `--keep-dirlinks` | Follow an existing destination symlink-to-directory (confined to the receive root). |
+| `-H`, `--hard-links` | Preserve hard-link relationships across the transfer. |
+| `-D` | Preserve device and special files (implies `--devices --specials`). |
+| `--devices` | Recreate device nodes on the destination (privileged; skipped without `CAP_MKNOD`). |
+| `--specials` | Recreate special files: FIFOs and unix sockets. |
+| `-S`, `--sparse` | Sparse-file handling: receiver preserves holes (zero runs are written as holes; no wire change). |
 
 ### Output and logging
 
 | Option | Description |
 |---|---|
 | `-v`, `--verbose` | Enable debug logging. |
-| `--progress` | Show live transfer progress. |
-| `--stats` | Print transfer statistics. |
+| `-q`, `--quiet` | Suppress non-error output. |
+| `--progress` | Show rsync-style per-file progress blocks (not rsync's leading `./` line). |
+| `--stats` | Print transfer statistics, including the receiver-only counters reported over the wire. |
+| `-i`, `--itemize-changes` | Print an rsync-style per-file change line. |
+| `--out-format=FORMAT` | Output format for changed files (`%f %n %l %b %M %%`). |
+| `--list-only` | List source files instead of transferring. |
 | `--log-file <path>` | Write log output to a file. |
 | `-V`, `--version` | Print the FastSync protocol version. |
 | `--help` | Print command usage. |
@@ -440,34 +654,117 @@ 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. |
-| `--fastsync-server-path <path>` | Remote FastSync server path for SSH mode. |
+| `--ssh-port <port>` | SSH port for the SSH transport (default: 22). Note the short `-p` is now rsync's `--perms`. |
+| `-e`, `--rsh <command>` | Remote shell to launch for the SSH transport (default: `ssh`; may include arguments). |
+| `--fastsync-server-path <path>` | Remote FastSync server path for SSH mode (client-only; never crosses the wire). |
+| `--rsync-path <path>` | Alias for `--fastsync-server-path`. |
+| `-M`, `--remote-option=OPT` | Append OPT to the remote server invocation over SSH (repeatable; rejected for daemon/TCP destinations). |
+| `--trust-sender` | Receiver-local: trust the remote sender's file list and skip path re-validation (does not affect symlink targets). |
+| `--timeout <sec>` | Socket + per-message I/O timeout; default `0` = disabled. |
+| `--contimeout <sec>` | Connection timeout; default 60; `0` disables. |
 | `--source-dir <path>` | Set the source directory explicitly. |
 | `--dest-dir <path>` | Set the destination directory explicitly. |
 | `--save-to-disk` | Enable server-side disk persistence. |
 | `--server-host <host>` | TCP server address. |
-| `--server-port <port>` | TCP server port. |
-| `--tls` | Enable TLS. Requires `--cert` and `--key`. |
+| `--server-port <port>` | TCP server port. `--port <port>` / `--port=<port>` is an alias. |
+| `--address <ip>` | Bind the outgoing client socket to this source address. |
+| `-4`, `--ipv4` | Force IPv4 for destination resolution. |
+| `-6`, `--ipv6` | Force IPv6 for destination resolution. |
+| `--sockopts=OPTS` | Comma-separated OPT=VAL socket options applied before connect. |
+| `--tls` | Enable TLS. Requires `--cert`, `--key`, and `--ca`. |
 | `--cert <path>` | TLS certificate file. |
 | `--key <path>` | TLS private key file. |
-| `--ca <path>` | CA file for peer verification. |
+| `--ca <path>` | CA file for peer verification (always required with `--tls`). |
 
 ## Server Options
 
 | Option | Description |
 |---|---|
 | `--stdio` | Serve one SSH connection over standard input/output. |
-| `-p <port>` | TCP listen port. |
+| `--daemon` | Run as a persistent daemon listener using a module config file; the daemon default port is 873 (unlike `-p`, which defaults to 8080). |
+| `--config=FILE` | Daemon config file (default: `~/.config/fastsync/fastsyncd.conf`, else `/etc/fastsyncd.conf`). Requires `--daemon`. |
+| `--dparam=KEY=VALUE` | Override one global config key on the command line. Requires `--daemon`. |
+| `--no-detach` | Stay in the foreground (default detaches to the background when running `--daemon`). |
+| `-p, --port <port>` | TCP listen port (default: 8080, range: 1–65535). |
 | `--tls` | Enable TLS. |
-| `--cert <path>` | TLS certificate file. |
-| `--key <path>` | TLS private key file. |
-| `--ca <path>` | CA file for peer verification. |
-| `--destination-root <path>` | Confine received files to this server-side root;
-defaults to the current directory. |
-| `--allow-delete` | Permit client delete manifests. Deletion is refused by default. |
+| `--cert <path>` | TLS certificate file (PEM). |
+| `--key <path>` | TLS private key file (PEM). |
+| `--ca <path>` | CA file for peer verification (PEM). |
+| `--client-cn <name>` | TLS client certificate CN; mandatory with `--tls` (the server verifies the client CN). |
+| `--destination-root <path>` | Confine received files to this server-side root; defaults to the current directory. |
+| `--address <addr>` | Bind the listening socket to this address. |
+| `-4`, `--ipv4` | Bind an IPv4 socket (default). |
+| `-6`, `--ipv6` | Bind an IPv6 socket. |
+| `--allow-delete` | Permit client delete manifests. Deletion is refused by default. This also gates `--force` (which can recursively replace/remove a destination directory tree). |
+| `--allow-super` | Standalone TCP listener only: keep super-user activities enabled for a **root** receiver. Without it a root standalone server forces `SUPER_MODE_OFF`, so client `--devices`/`--write-devices`/`--super` and client-chosen ownership requests are skipped/refused. Rejected with `--stdio` (the SSH remote argv is client-composed; use a forced command if the default must hold). No effect when not root. Daemon modules opt in per module with `client owner = yes`. |
+| `--trust-sender` | Trust the remote sender's file list: skip the receiver's up-front path-traversal re-validation (fewer checks, faster, potentially unsafe; off by default). It does not affect symlink targets, which are stored verbatim either way. |
+| `--no-super` | Operator veto: never attempt super-user activities (ownership, device nodes) even as root, and refuse any client `--copy-as`/`--super` request. |
+| `--allow-unauthenticated` | Permit plaintext/anonymous network clients; an auth-required module still accepts only opted-in loopback plaintext. |
+| `--iconv=LOCAL[,REMOTE]` | Declare this server's LOCAL charset for file-name conversion. |
+| `--password-file=FILE` | Credential store for modules that declare `auth users`. Requires `--daemon`. |
+| `--early-input=FILE` | Second credential store layered over `--password-file`. Requires `--daemon`. |
+| `--hash-credentials <file>` | Read `<file>`'s `user:password` lines and print PBKDF2 credential-store lines to stdout, then exit. Cannot be combined with `--daemon` or `--stdio`. |
+| `--iterations N` | PBKDF2 iteration count for `--hash-credentials` (default 600000, range 100000–10000000). Requires `--hash-credentials`. |
 | `-v`, `--verbose` | Enable debug logging. |
 | `--help` | Print server usage. |
 
+### Daemon configuration
+
+`fastsync-server --daemon --config FILE` reads a line-based module config (an
+implicit global section, then `[module]` sections). Besides `port`, `motd file`,
+and `address`, the global section accepts:
+
+- `max connections = N` — global cap on concurrent connections, default 100. The
+  listener enforces it; `0`, negative, and non-numeric values are parse errors.
+- `max connections per host = N` — cap on concurrent connections from a single
+  source IP, default 0 (unlimited). Enforced across all forked connection
+  children through a shared registry.
+- `auth failure delay = MS` — milliseconds to sleep after a failed
+  authentication, default 500. `0` disables it and the value is capped at 5000,
+  so online password guessing is rate-limited per connection. Successful auths
+  are never delayed.
+- `auth lockout threshold = N` — number of failed authentications from one source
+  IP before that source is locked out, default 10; `0` disables the lockout. The
+  failure counter is shared across every connection child, so the lockout holds
+  even when the next attempt is handled by a different forked child.
+- `auth lockout duration = SECONDS` — how long a locked-out source is refused
+  (default 300). A locked-out client is refused before any SCRAM challenge is
+  sent; a successful authentication clears the counter.
+- `hosts allow` / `hosts deny` — comma- and/or whitespace-separated host access
+  patterns.
+
+A `[module]` requires `path`, and may also set `read only`, `client owner`,
+`auth users`, `max connections` (0 = unlimited; enforced per module across all
+connection children), and its own `hosts allow`/`hosts deny`.
+
+The per-host cap and the shared auth lockout identify a source by its numeric
+peer IP. **Loopback peers (127.0.0.0/8, IPv6 `::1`) are exempt**: every local
+client shares that one address, so counting or locking them out would let one
+local process deny service to all the others. The per-module and global
+`max connections` caps still apply to loopback. Because the key is the peer IP,
+`max connections per host` and `auth lockout` also cannot distinguish clients
+behind the same NAT, proxy, or reverse-proxy address — they share one budget and
+one lockout counter, so an over-aggressive lockout can affect unrelated users
+behind that address. Prefer TLS client certificates (`--client-cn`) plus
+`hosts allow`/`hosts deny` for per-client policy when clients share an address,
+and size `auth lockout threshold` accordingly.
+
+The shared per-source table has a bounded lifetime: an entry with no live
+connection is reclaimed once its lockout has expired, or after it has been idle
+(300 s). If every entry is still live or locked, a new source is admitted without
+per-host accounting (fail open) and a rate-limited warning is logged; the
+per-module cap and host ACLs still apply. The occupancy counters are re-derived
+from the shared slot table after every child exit, so a child killed mid-transfer
+(or mid-registration) cannot leak a slot or an occupancy count.
+
+Host patterns are `*` (match all), IPv4/IPv6 literals, or IPv4/IPv6 CIDR
+(`10.0.0.0/8`, `2001:db8::/32`). Hostnames are not resolved, so hostname globs
+are rejected at parse time rather than silently never matching. A matching
+`hosts deny` rejects; if any `hosts allow` entries exist, a peer matching none of
+them is rejected; deny takes precedence over allow. The global list is checked
+before the module list, before authentication, and the connecting peer address
+(IPv4 or IPv6) appears in the connection and authentication audit log lines.
+
 ## Architecture
 
 ### Client
@@ -492,17 +789,61 @@ defaults to the current directory. |
 
 ## Protocol and Security
 
-FastSync protocol version `2.5.0` is shared by the client and server. The
+FastSync protocol version `2.26.0` is shared by the client and server. The
 current protocol is sender-driven and includes configuration negotiation,
 including the maximum allocation limit, incremental checks, checksums,
 manifests, keep-alives, abort handling, per-file remove-source results, and
 FastSync-native delta messages.
 Client and server versions must currently match exactly.
 
-TLS provides encrypted TCP transport. Supplying `--ca` enables certificate
-verification; without it, traffic is encrypted but peer identity is not
-verified. Use certificate verification for deployments where authentication
-matters. The default TCP transport is not encrypted.
+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. Both the client and the server require
+`--ca` together with `--tls`, so peer certificates are always verified
+(`SSL_VERIFY_PEER`, depth 4). The default TCP transport is not encrypted.
 
 The receiver protects its destination root with path validation, `openat()`
 directory traversal, `O_NOFOLLOW`, temporary files, and atomic renames. Delete
@@ -513,18 +854,27 @@ operations require the server's explicit `--allow-delete` policy.
 The project will reach the drop-in replacement goal in stages:
 
 1. Correct rsync option meanings, including short options, combined options,
-   and `--option=value` syntax.
+   and `--option=value` syntax — **done** in the rsync-parity wave: `-r`/`-b`/
+   `-L`/`-B`, short-option clustering (`-av`, `-aAX`, `-rlpt`), and attached
+   values (`-B1000`, `-essh`, `-MOPT`) all parse.
 2. Add differential tests that compare FastSync and rsync contents, metadata,
-   links, deletes, filters, dry runs, and exit codes.
-3. Make `-a` implement the expected recursive, links, permissions, times,
-   owner/group, and supported special-file behavior.
-4. Complete symlink, sparse-file, metadata, delete-policy, and resumable-write
-   semantics.
+   links, deletes, filters, dry runs, and exit codes — **done** for the
+   completion wave's scope; the tests live in `tests/integration/` and skip
+   cleanly when rsync is unavailable.
+3. `-a` implements full rsync `-rlptgoD`; under `-p` the source mode is copied
+   exactly (no masking). Ownership application stays privilege-gated, as in
+   rsync.
+4. Symlink (verbatim storage), sparse-file, metadata, delete-policy (including
+   `--max-delete` partial + exit 25, per-directory `--delete-during`/
+   `--delete-delay`), codecs, and resumable-write semantics are implemented;
+   remaining work is the documented edge cases, which the **Parity Completion
+   Wave** section of `RSYNC_COMPAT.md` enumerates honestly.
 5. Add rsync remote-shell and daemon protocol interoperability.
 6. Keep FastSync performance options as negotiated, optional extensions.
 
 The exhaustive implementation matrix and compatibility notes are in
-[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md).
+[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md); each row is classified as parity, caveat,
+or divergent.
 
 ## Testing
 
@@ -537,7 +887,7 @@ Run the unit test binary:
 Run the Python integration suite:
 
 ```bash
-python3 -m pytest tests/
+python3 -m pytest tests/integration/ -n 4 --dist=load -m "not setpriv"
 ```
 
 For stricter local validation:
@@ -561,10 +911,13 @@ rsync protocol or filesystem-semantic compatibility.
 
 ## Performance Guidance
 
-- Use `-m` for workloads with many files or enough CPU parallelism.
-- Use `-c` or `-z` when network bandwidth is more constrained than CPU.
+- Use `-j`/`--threads` for workloads with many files or enough CPU parallelism
+  (`-m` is `--prune-empty-dirs`).
+- Use `-z` when network bandwidth is more constrained than CPU (`-c` is
+  `--checksum`, not a bandwidth option).
 - Tune `--chunk-size` for file sizes, memory limits, and network latency.
-- Use `-f` for large uncompressed TCP transfers where zero-copy I/O helps.
+- Use `--sendfile` for large uncompressed TCP transfers where zero-copy I/O
+  helps (`-f` is `--filter`).
 - Use `--incremental` to avoid retransmitting unchanged files.
 - Use `--delta` for changed files when both endpoints are FastSync peers.
 - Use `--bwlimit` when sharing a link with other traffic.

benchmark/bench.py

@@ -3,19 +3,24 @@
 
 Compares FastSync configs against rsync (no compression) and rsync+zstd.
 Data is ~75% random/incompressible and ~25% structured/compressible by default,
-controllable via --random-ratio.
+controllable via --random-ratio. Transfers are verified by default (source and
+destination must match) so a fast-but-broken copy is never counted.
 
 Usage:
     python3 benchmark/bench.py
     python3 benchmark/bench.py --runs 5 --profiles lan wan
     python3 benchmark/bench.py --random-ratio 0.5 --size-mb 50
     python3 benchmark/bench.py --delay 50ms --jitter 10ms --throughput 100mbit
+    python3 benchmark/bench.py --warm --runs 3
     python3 benchmark/bench.py --output json
 """
 import argparse
+import filecmp
 import json
+import math
 import os
 import random
+import shlex
 import shutil
 import socket
 import statistics
@@ -25,8 +30,11 @@ import tempfile
 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")]
+DEFAULT_BUILD_DIR = "build-bench"
+# Populated by configure_build_dirs(); default to the dedicated bench dir so
+# importing this module never depends on the user's existing build/ tree.
+BUILD_DIR = os.path.join(PROJECT_ROOT, DEFAULT_BUILD_DIR)
+SERVER_CMD = [os.path.join(BUILD_DIR, "server"), "--allow-unauthenticated"]
 CLIENT_CMD = [os.path.join(BUILD_DIR, "client")]
 BENCH_DIR = os.path.join(PROJECT_ROOT, "bench_data")
 
@@ -44,10 +52,11 @@ NETWORK_PROFILES = {
 
 FASTSYNC_CONFIGS = [
     {"name": "fastsync",                        "flags": [],                                     "tool": "fastsync"},
-    {"name": "fastsync -c",        "flags": ["-c"],                 "tool": "fastsync"},
-    {"name": "fastsync -m",        "flags": ["-m"],                 "tool": "fastsync"},
-    {"name": "fastsync -m -c",     "flags": ["-m", "-c"],           "tool": "fastsync"},
-    {"name": "fastsync -m -c -s",  "flags": ["-m", "-c", "-s"],     "tool": "fastsync"},
+    {"name": "fastsync -z",                     "flags": ["-z"],                                 "tool": "fastsync"},
+    {"name": "fastsync -j",                     "flags": ["-j"],                                 "tool": "fastsync"},
+    {"name": "fastsync -j -z",                  "flags": ["-j", "-z"],                           "tool": "fastsync"},
+    {"name": "fastsync -j -z --chunk-serialization", "flags": ["-j", "-z", "--chunk-serialization"], "tool": "fastsync"},
+    {"name": "fastsync --sendfile",             "flags": ["--sendfile"],                         "tool": "fastsync"},
 ]
 
 RSYNC_CONFIGS = [
@@ -56,6 +65,7 @@ RSYNC_CONFIGS = [
     {"name": "rsync -z --zstd",    "flags": ["-z", "--zc", "zstd"],"tool": "rsync"},
 ]
 
+
 class RsyncDaemon:
     """Manages an rsync daemon for network-fair benchmarking."""
 
@@ -117,6 +127,12 @@ STRUCTURED_FILES = {
     "nested/another.txt": b"another nested file\n" * 50,
 }
 
+# Repeated text used to synthesize genuinely compressible filler of any size.
+COMPRESSIBLE_TEXT = (
+    b"FastSync benchmark payload: the quick brown fox jumps over the lazy dog. "
+    b"0123456789 ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz\n"
+)
+
 
 class Progress:
     """Simple progress bar with ETA."""
@@ -151,35 +167,127 @@ class Progress:
             sys.stderr.flush()
 
 
+def write_compressible(path, nbytes):
+    """Write exactly nbytes of highly compressible, repeated text content."""
+    if nbytes <= 0:
+        return
+    block = COMPRESSIBLE_TEXT * (max(1, 8192 // len(COMPRESSIBLE_TEXT)) + 1)
+    remaining = nbytes
+    with open(path, "wb") as f:
+        while remaining > 0:
+            piece = block if remaining >= len(block) else block[:remaining]
+            f.write(piece)
+            remaining -= len(piece)
+
+
 def generate_bench_data(source_dir, size_mb=25, random_ratio=0.75):
-    """Generate test data. ~random_ratio is incompressible, rest is structured."""
+    """Generate test data honouring the requested random/compressible split.
+
+    Exactly ``random_ratio * target`` bytes are incompressible random data and
+    the remainder is genuinely compressible structured/repeated content. The
+    measured byte counts are returned so callers can report the real mix.
+    """
     if os.path.exists(source_dir):
         shutil.rmtree(source_dir)
     os.makedirs(source_dir)
 
     target = size_mb * 1024 * 1024
-    structured_budget = int(target * (1 - random_ratio))
-    written = 0
+    random_budget = int(target * random_ratio)
+    compressible_budget = target - random_budget
+    compressible_written = 0
+    random_written = 0
+    files = 0
 
+    # A handful of fixed, human-meaningful files (directories, small files, a
+    # binary blob) as long as they fit inside the compressible budget.
     for rel_path, content in STRUCTURED_FILES.items():
-        if written >= structured_budget:
+        if compressible_written + len(content) > compressible_budget:
             break
         full_path = os.path.join(source_dir, rel_path)
         os.makedirs(os.path.dirname(full_path), exist_ok=True)
         with open(full_path, "wb") as f:
             f.write(content)
-        written += len(content)
+        compressible_written += len(content)
+        files += 1
 
-    os.makedirs(os.path.join(source_dir, "bulk"), exist_ok=True)
+    # Fill the rest of the compressible share with generated repeated content.
+    if compressible_written < compressible_budget:
+        os.makedirs(os.path.join(source_dir, "compressible"), exist_ok=True)
         i = 0
-    while written < target:
-        chunk_size = min(5 * 1024 * 1024, target - written)
-        with open(os.path.join(source_dir, f"bulk/file_{i}.dat"), "wb") as f:
-            f.write(random.randbytes(chunk_size))
-        written += chunk_size
+        while compressible_written < compressible_budget:
+            chunk = min(1024 * 1024, compressible_budget - compressible_written)
+            write_compressible(os.path.join(source_dir, "compressible", f"text_{i}.dat"), chunk)
+            compressible_written += chunk
+            files += 1
             i += 1
 
-    return written
+    # Incompressible share.
+    if random_written < random_budget:
+        os.makedirs(os.path.join(source_dir, "bulk"), exist_ok=True)
+        i = 0
+        while random_written < random_budget:
+            chunk = min(5 * 1024 * 1024, random_budget - random_written)
+            with open(os.path.join(source_dir, "bulk", f"file_{i}.dat"), "wb") as f:
+                f.write(random.randbytes(chunk))
+            random_written += chunk
+            files += 1
+            i += 1
+
+    return {
+        "total_bytes": compressible_written + random_written,
+        "compressible_bytes": compressible_written,
+        "random_bytes": random_written,
+        "files": files,
+    }
+
+
+def list_relative_files(root):
+    """Return the set of file paths (relative to root) under a directory."""
+    found = set()
+    for dirpath, _dirnames, filenames in os.walk(root):
+        for name in filenames:
+            full = os.path.join(dirpath, name)
+            found.add(os.path.relpath(full, root))
+    return found
+
+
+def verify_transfer(source_dir, dest_dir):
+    """Recursively check dest matches source (paths, sizes, content).
+
+    Returns (ok, detail). Content is compared byte-for-byte, never hashed, so
+    collisions are impossible. This is intentionally not part of the timing.
+    """
+    if not os.path.isdir(dest_dir):
+        return False, "destination directory missing"
+    src_files = list_relative_files(source_dir)
+    dst_files = list_relative_files(dest_dir)
+    if src_files != dst_files:
+        missing = src_files - dst_files
+        extra = dst_files - src_files
+        return False, f"path set mismatch (missing {len(missing)}, extra {len(extra)})"
+    for rel in sorted(src_files):
+        src = os.path.join(source_dir, rel)
+        dst = os.path.join(dest_dir, rel)
+        if os.path.getsize(src) != os.path.getsize(dst):
+            return False, f"size mismatch: {rel}"
+        if not filecmp.cmp(src, dst, shallow=False):
+            return False, f"content mismatch: {rel}"
+    return True, ""
+
+
+def percentile(values, pct):
+    """Linear-interpolation percentile (matches numpy's default method)."""
+    if not values:
+        return None
+    ordered = sorted(values)
+    if len(ordered) == 1:
+        return ordered[0]
+    rank = (len(ordered) - 1) * (pct / 100.0)
+    low = math.floor(rank)
+    high = math.ceil(rank)
+    if low == high:
+        return ordered[int(rank)]
+    return ordered[low] + (ordered[high] - ordered[low]) * (rank - low)
 
 
 def find_free_port():
@@ -207,18 +315,45 @@ def wait_proc(proc, timeout=5):
         proc.wait()
 
 
+def _tc_base_cmd():
+    """Return the command prefix for tc, honouring root vs sudo."""
+    tc = shutil.which("tc")
+    if not tc:
+        raise RuntimeError(
+            "tc (iproute2) not found in PATH; install iproute2 to use network profiles")
+    if os.geteuid() == 0:
+        return [tc]
+    sudo = shutil.which("sudo")
+    if sudo:
+        return [sudo, tc]
+    raise RuntimeError(
+        "applying network limits requires root or sudo; "
+        "re-run as root or install sudo")
+
+
+def _run_tc(args, check=True):
+    return subprocess.run(_tc_base_cmd() + args, check=check, capture_output=True)
+
+
 def netem_apply(delay=None, jitter=None, throughput=None, loss=None):
     """Apply tc/netem rules to loopback. Pass None to skip a parameter."""
     netem_reset()
-    cmd = ["sudo", "tc", "qdisc", "add", "dev", "lo", "root", "netem"]
+    params = []
     if throughput:
-        cmd += ["rate", throughput]
+        params += ["rate", throughput]
     if delay:
-        cmd += ["delay", delay, jitter or "0ms"]
+        params += ["delay", delay, jitter or "0ms"]
     if loss:
-        cmd += ["loss", loss]
-    if len(cmd) > 6:
-        subprocess.run(cmd, check=True, capture_output=True)
+        params += ["loss", loss]
+    if not params:
+        return
+    try:
+        _run_tc(["qdisc", "add", "dev", "lo", "root", "netem"] + params)
+    except subprocess.CalledProcessError as exc:
+        detail = exc.stderr.decode(errors="replace").strip() if exc.stderr else str(exc)
+        raise RuntimeError(f"failed to apply network profile via tc/netem: {detail}") from exc
+    except RuntimeError:
+        raise
 
 
 def netem_apply_profile(profile_name):
@@ -235,7 +370,11 @@ def netem_apply_profile(profile_name):
 
 
 def netem_reset():
-    subprocess.run("sudo tc qdisc del dev lo root".split(), capture_output=True)
+    """Best-effort removal of any loopback qdisc. Always safe to call."""
+    try:
+        _run_tc(["qdisc", "del", "dev", "lo", "root"], check=False)
+    except Exception:
+        pass
 
 
 def run_fastsync(source_dir, dest_dir, flags, port):
@@ -252,8 +391,10 @@ def run_fastsync(source_dir, dest_dir, flags, port):
         duration = time.monotonic() - start
         if result.returncode == 0:
             return duration
+        sys.stderr.write(f"    fastsync failed (exit {result.returncode}): "
+                         f"{result.stderr.strip()[:500]}\n")
     except subprocess.TimeoutExpired:
-        pass
+        sys.stderr.write("    fastsync timed out after 120s\n")
     return None
 
 
@@ -269,8 +410,10 @@ def run_rsync(source_dir, dest_dir, flags, rsync_daemon=None):
         duration = time.monotonic() - start
         if result.returncode == 0:
             return duration
+        sys.stderr.write(f"    rsync failed (exit {result.returncode}): "
+                         f"{result.stderr.strip()[:500]}\n")
     except subprocess.TimeoutExpired:
-        pass
+        sys.stderr.write("    rsync timed out after 120s\n")
     return None
 
 
@@ -282,7 +425,81 @@ def run_transfer(config, source_dir, dest_dir, port=None, rsync_daemon=None):
         return run_fastsync(source_dir, dest_dir, config["flags"], port)
 
 
-def run_benchmark(source_dir, dest_dir, configs, runs, profile_name, progress=None):
+def apply_incremental_changes(source_dir, target_bytes):
+    """Add and modify a few files so a warm transfer has real work to do.
+
+    Returns a mutation record (changed byte count plus enough data to revert
+    and re-apply it) so every warm run can start from a pristine source.
+    """
+    modified_n = 3
+    added_n = 2
+    per_file = max(4096, target_bytes // (modified_n + added_n))
+    modified = {}
+    added = {}
+    changed = 0
+
+    existing = sorted(list_relative_files(source_dir))
+    if existing:
+        step = max(1, len(existing) // modified_n)
+        for rel in existing[::step][:modified_n]:
+            path = os.path.join(source_dir, rel)
+            original_size = os.path.getsize(path)
+            with open(path, "ab") as f:
+                f.write(random.randbytes(per_file))
+            modified[rel] = (original_size, per_file)
+            changed += per_file
+
+    for i in range(added_n):
+        os.makedirs(os.path.join(source_dir, "incremental"), exist_ok=True)
+        rel = os.path.join("incremental", f"new_{i}.dat")
+        write_compressible(os.path.join(source_dir, rel), per_file)
+        added[rel] = per_file
+        changed += per_file
+
+    return {"changed": changed, "modified": modified, "added": added}
+
+
+def revert_incremental_changes(source_dir, mutation):
+    """Undo apply_incremental_changes so the source is pristine again."""
+    if not mutation:
+        return
+    for rel, (original_size, _appended) in mutation["modified"].items():
+        path = os.path.join(source_dir, rel)
+        if os.path.exists(path):
+            with open(path, "r+b") as f:
+                f.truncate(original_size)
+    for rel in mutation["added"]:
+        path = os.path.join(source_dir, rel)
+        if os.path.exists(path):
+            os.remove(path)
+
+
+def reapply_incremental_changes(source_dir, mutation):
+    """Re-apply a mutation after an untimed pristine seed transfer."""
+    if not mutation:
+        return
+    for rel, (_original_size, appended) in mutation["modified"].items():
+        with open(os.path.join(source_dir, rel), "ab") as f:
+            f.write(random.randbytes(appended))
+    for rel, size in mutation["added"].items():
+        write_compressible(os.path.join(source_dir, rel), size)
+
+
+def expected_received_root(dest_dir, source_dir, tool):
+    """Where a tool places transferred files inside dest_dir.
+
+    FastSync mirrors the absolute source path under dest_dir (see the
+    integration suite's get_dest_received_dir); rsync copies the source tree
+    contents directly into dest_dir.
+    """
+    if tool == "rsync":
+        return dest_dir
+    return os.path.join(dest_dir, os.path.abspath(source_dir).lstrip(os.sep))
+
+
+def run_benchmark(source_dir, dest_dir, configs, runs, profile_name,
+                  measure_bytes, verify=True, warm=False, mutation=None,
+                  progress=None):
     """Run benchmark for all configs, returns list of results."""
     is_limited = profile_name != "unlimited"
     has_rsync = any(c["tool"] == "rsync" for c in configs)
@@ -298,7 +515,10 @@ def run_benchmark(source_dir, dest_dir, configs, runs, profile_name, progress=No
         results = []
         for config in configs:
             times = []
+            invalid = 0
             for run_idx in range(runs):
+                if warm:
+                    revert_incremental_changes(source_dir, mutation)
                 if os.path.exists(dest_dir):
                     shutil.rmtree(dest_dir)
                 os.makedirs(dest_dir, exist_ok=True)
@@ -306,15 +526,33 @@ def run_benchmark(source_dir, dest_dir, configs, runs, profile_name, progress=No
                 port = find_free_port()
                 server = None
                 try:
-                    if config["tool"] == "fastsync":
+                    if config["tool"] == "fastsync" or warm:
                         server = subprocess.Popen(
                             SERVER_CMD + ["-p", str(port)],
                             stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
                         )
                         wait_for_port(port)
 
+                    if warm:
+                        seed = run_transfer(config, source_dir, dest_dir, port, rsync_daemon)
+                        if seed is None:
+                            invalid += 1
+                            sys.stderr.write("    warm-mode seeding failed; run not counted\n")
+                            continue
+                        reapply_incremental_changes(source_dir, mutation)
+
                     t = run_transfer(config, source_dir, dest_dir, port, rsync_daemon)
-                    if t is not None:
+                    if t is None:
+                        invalid += 1
+                    elif verify:
+                        root = expected_received_root(dest_dir, source_dir, config["tool"])
+                        ok, detail = verify_transfer(source_dir, root)
+                        if ok:
+                            times.append(t)
+                        else:
+                            invalid += 1
+                            sys.stderr.write(f"    verification FAILED ({detail}); run not counted\n")
+                    else:
                         times.append(t)
                 finally:
                     if server:
@@ -327,15 +565,22 @@ def run_benchmark(source_dir, dest_dir, configs, runs, profile_name, progress=No
                 "config": config["name"],
                 "tool": config["tool"],
                 "profile": profile_name,
+                "warm": warm,
                 "runs": len(times),
+                "invalid": invalid,
                 "times": [round(t, 4) for t in times],
             }
             if times:
-                entry["p50"] = round(statistics.median(times), 4)
-                entry["p95"] = round(sorted(times)[int(len(times) * 0.95)], 4) if len(times) > 1 else entry["p50"]
+                p50 = percentile(times, 50)
+                p95 = percentile(times, 95)
+                entry["p50"] = round(p50, 4)
+                entry["p95"] = round(p95, 4)
                 entry["min"] = round(min(times), 4)
                 entry["max"] = round(max(times), 4)
                 entry["stdev"] = round(statistics.stdev(times), 4) if len(times) > 1 else 0.0
+                if measure_bytes:
+                    entry["throughput_mbps"] = round(
+                        (measure_bytes / (1024 * 1024)) / p50, 3)
             results.append(entry)
         return results
     finally:
@@ -345,44 +590,59 @@ def run_benchmark(source_dir, dest_dir, configs, runs, profile_name, progress=No
             netem_reset()
 
 
-def print_table(results, total_bytes, random_ratio):
+def print_table(results, measure_bytes, stats, warm):
     """Print results as a human-readable table grouped by profile."""
     profiles = {}
     for r in results:
         profiles.setdefault(r["profile"], []).append(r)
 
+    total = stats["total_bytes"]
+    comp_pct = stats["compressible_bytes"] / total * 100 if total else 0
+    rand_pct = stats["random_bytes"] / total * 100 if total else 0
+
     for profile, entries in profiles.items():
         params = NETWORK_PROFILES.get(profile, {})
-        print(f"\n{'=' * 85}")
+        print(f"\n{'=' * 95}")
         print(f" Profile: {profile.upper()}")
         if params.get("rate"):
             print(f" Network: {params['rate']}, {params['delay']} +/- {params['jitter']}, loss {params['loss']}")
         else:
             print(f" Network: unlimited")
-        print(f" Data: {total_bytes / (1024*1024):.1f} MB  ({random_ratio*100:.0f}% random, {(1-random_ratio)*100:.0f}% compressible)")
-        print(f"{'=' * 85}")
+        print(f" Data: {total / (1024*1024):.1f} MB  "
+              f"({rand_pct:.0f}% random, {comp_pct:.0f}% compressible actual)")
+        if warm:
+            print(f" Mode: warm (incremental) — measured {measure_bytes / (1024*1024):.2f} MB "
+                  f"changed after an untimed full seed")
+        else:
+            print(" Mode: cold (full copy)")
+        print(f"{'=' * 95}")
 
         fs_entries = [e for e in entries if e.get("tool") == "fastsync"]
         rsync_entries = [e for e in entries if e.get("tool") == "rsync"]
 
+        header = (f" {'Config':<38} {'p50':>8} {'p95':>8} {'min':>8} {'max':>8} "
+                  f"{'stdev':>8} {'MB/s':>9} {'runs':>5} {'bad':>4}")
+        rule = (f" {'-' * 38} {'-' * 8} {'-' * 8} {'-' * 8} {'-' * 8} "
+                f"{'-' * 8} {'-' * 9} {'-' * 5} {'-' * 4}")
+
         if fs_entries:
             print(f"\n FastSync:")
-            print(f" {'Config':<25} {'p50':>8} {'p95':>8} {'min':>8} {'max':>8} {'stdev':>8} {'runs':>5}")
-            print(f" {'-' * 25} {'-' * 8} {'-' * 8} {'-' * 8} {'-' * 8} {'-' * 8} {'-' * 5}")
+            print(header)
+            print(rule)
             for e in sorted(fs_entries, key=lambda x: x.get("p50", 999)):
                 _print_entry(e)
 
         if rsync_entries:
             print(f"\n rsync:")
-            print(f" {'Config':<25} {'p50':>8} {'p95':>8} {'min':>8} {'max':>8} {'stdev':>8} {'runs':>5}")
-            print(f" {'-' * 25} {'-' * 8} {'-' * 8} {'-' * 8} {'-' * 8} {'-' * 8} {'-' * 5}")
+            print(header)
+            print(rule)
             for e in sorted(rsync_entries, key=lambda x: x.get("p50", 999)):
                 _print_entry(e)
 
         if params.get("rate_bps") and fs_entries and rsync_entries:
             fs_best = min((e["p50"] for e in fs_entries if "p50" in e), default=None)
             rsync_best = min((e["p50"] for e in rsync_entries if "p50" in e), default=None)
-            theoretical = total_bytes / params["rate_bps"]
+            theoretical = measure_bytes / params["rate_bps"]
             if fs_best and rsync_best:
                 print(f"\n Theoretical max (line rate): {theoretical:.4f}s")
                 print(f" FastSync best:   {fs_best:.4f}s  ({theoretical/fs_best:.2f}x vs line rate)")
@@ -392,10 +652,43 @@ def print_table(results, total_bytes, random_ratio):
 
 def _print_entry(e):
     if "p50" in e:
-        print(f" {e['config']:<25} {e['p50']:>7.4f}s {e['p95']:>7.4f}s "
-              f"{e['min']:>7.4f}s {e['max']:>7.4f}s {e['stdev']:>7.4f} {e['runs']:>5}")
+        tp = f"{e['throughput_mbps']:.2f}" if "throughput_mbps" in e else "N/A"
+        print(f" {e['config']:<38} {e['p50']:>7.4f}s {e['p95']:>7.4f}s "
+              f"{e['min']:>7.4f}s {e['max']:>7.4f}s {e['stdev']:>7.4f} "
+              f"{tp:>9} {e['runs']:>5} {e.get('invalid', 0):>4}")
     else:
-        print(f" {e['config']:<25} {'N/A':>8} {'N/A':>8} {'N/A':>8} {'N/A':>8} {'N/A':>8} {e['runs']:>5}")
+        print(f" {e['config']:<38} {'N/A':>8} {'N/A':>8} {'N/A':>8} {'N/A':>8} "
+              f"{'N/A':>8} {'N/A':>9} {e['runs']:>5} {e.get('invalid', 0):>4}")
+
+
+def configure_build_dirs(build_dir):
+    """Install the selected build directory and derived binary paths."""
+    global BUILD_DIR, SERVER_CMD, CLIENT_CMD
+    if not os.path.isabs(build_dir):
+        build_dir = os.path.join(PROJECT_ROOT, build_dir)
+    BUILD_DIR = os.path.abspath(build_dir)
+    SERVER_CMD = [os.path.join(BUILD_DIR, "server"), "--allow-unauthenticated"]
+    CLIENT_CMD = [os.path.join(BUILD_DIR, "client")]
+
+
+def build_project():
+    """Configure (Release) and build into the dedicated bench build dir."""
+    if shutil.which("cmake") is None:
+        sys.stderr.write("cmake not found in PATH; cannot build\n")
+        sys.exit(1)
+    os.makedirs(BUILD_DIR, exist_ok=True)
+    configure = ["cmake", "-B", BUILD_DIR, "-S", PROJECT_ROOT,
+                 "-DCMAKE_BUILD_TYPE=Release"]
+    result = subprocess.run(configure, capture_output=True, text=True)
+    if result.returncode != 0:
+        sys.stderr.write("CMake configure failed:\n" + result.stdout + result.stderr + "\n")
+        sys.exit(1)
+    jobs = str(os.cpu_count() or 1)
+    result = subprocess.run(["cmake", "--build", BUILD_DIR, "-j", jobs],
+                            capture_output=True, text=True)
+    if result.returncode != 0:
+        sys.stderr.write("Build failed:\n" + result.stdout + result.stderr + "\n")
+        sys.exit(1)
 
 
 def main():
@@ -412,12 +705,20 @@ Custom network limits (--delay/--jitter/--throughput) override profiles.
 
 Data mix:
   Default is ~75%% random/incompressible + ~25%% structured/compressible,
-  reflecting typical real-world file sets.
+  reflecting typical real-world file sets. The actual mix is measured and
+  reported. Transfers are verified (destination must match source) unless
+  --no-verify is given.
+
+Warm mode:
+  --warm seeds the destination with an untimed full copy of a pristine base,
+  then measures only the incremental transfer after modifying a few files.
 
 Examples:
   %(prog)s --profiles wan --runs 5
   %(prog)s --throughput 50mbit --delay 30ms --jitter 5ms
   %(prog)s --random-ratio 0.5 --size-mb 100
+  %(prog)s --warm --runs 3 --no-rsync
+  %(prog)s --dry-run --size-mb 4 --random-ratio 0.25
 """)
     parser.add_argument("--runs", type=int, default=3,
                         help="Number of runs per config (default: 3)")
@@ -425,7 +726,8 @@ Examples:
                         choices=list(NETWORK_PROFILES.keys()),
                         help="Predefined network profiles (default: unlimited)")
     parser.add_argument("--configs", nargs="+", default=None,
-                        help="Custom FastSync config flags")
+                        help="Custom FastSync config flags (shell-quoted, e.g. "
+                             "\"-j -z --chunk-serialization\")")
     parser.add_argument("--size-mb", type=int, default=25,
                         help="Test data size in MB (default: 25)")
     parser.add_argument("--random-ratio", type=float, default=0.75,
@@ -440,6 +742,14 @@ Examples:
                         help="Custom packet loss (e.g. 1%%)")
     parser.add_argument("--no-rsync", action="store_true",
                         help="Skip rsync comparison")
+    parser.add_argument("--no-verify", action="store_true",
+                        help="Skip source/destination verification after each run")
+    parser.add_argument("--warm", action="store_true",
+                        help="Incremental mode: seed dest first, measure only changes")
+    parser.add_argument("--build-dir", default=DEFAULT_BUILD_DIR,
+                        help=f"Build directory (default: {DEFAULT_BUILD_DIR})")
+    parser.add_argument("--dry-run", action="store_true",
+                        help="Only generate data and report its composition, then exit")
     parser.add_argument("--progress", action="store_true",
                         help="Show progress bar with ETA")
     parser.add_argument("--output", choices=["table", "json"], default="table",
@@ -448,12 +758,48 @@ Examples:
                         help="Don't clean up test data")
     args = parser.parse_args()
 
-    # Build
-    print("Building...")
-    if os.system(f"cmake -B {BUILD_DIR} -S {PROJECT_ROOT} > /dev/null 2>&1") != 0:
-        print("CMake configure failed"); sys.exit(1)
-    if os.system(f"cmake --build {BUILD_DIR} -j$(nproc) > /dev/null 2>&1") != 0:
-        print("Build failed"); sys.exit(1)
+    if not 0.0 <= args.random_ratio <= 1.0:
+        parser.error("--random-ratio must be between 0.0 and 1.0")
+    if args.size_mb <= 0:
+        parser.error("--size-mb must be positive")
+
+    configure_build_dirs(args.build_dir)
+
+    # Generate data
+    source_dir = os.path.join(BENCH_DIR, "source")
+    dest_dir = os.path.join(BENCH_DIR, "dest")
+    stats = generate_bench_data(source_dir, args.size_mb, args.random_ratio)
+    total_bytes = stats["total_bytes"]
+    comp_pct = stats["compressible_bytes"] / total_bytes * 100 if total_bytes else 0
+    rand_pct = stats["random_bytes"] / total_bytes * 100 if total_bytes else 0
+    print(f"Generated {total_bytes / (1024*1024):.1f} MB in {stats['files']} files  "
+          f"({rand_pct:.0f}% random, {comp_pct:.0f}% compressible actual)",
+          file=sys.stderr)
+
+    if args.dry_run:
+        print(f"size_mb={args.size_mb} random_ratio={args.random_ratio:.4f} "
+              f"total_bytes={stats['total_bytes']} "
+              f"compressible_bytes={stats['compressible_bytes']} "
+              f"random_bytes={stats['random_bytes']} files={stats['files']}")
+        if not args.keep_data:
+            shutil.rmtree(BENCH_DIR, ignore_errors=True)
+        return
+
+    # Warm mode: keep a pristine base copy, then mutate the live source.
+    base_dir = None
+    measure_bytes = total_bytes
+    mutation = None
+    if args.warm:
+        change_target = max(64 * 1024, min(int(total_bytes * 0.01), 4 * 1024 * 1024))
+        mutation = apply_incremental_changes(source_dir, change_target)
+        measure_bytes = mutation["changed"]
+        revert_incremental_changes(source_dir, mutation)
+        print(f"Warm mode: each run seeds a full copy, then measures "
+              f"{measure_bytes / (1024*1024):.3f} MB of add/change deltas", file=sys.stderr)
+
+    # Build (Release: benchmarking a debug build is meaningless)
+    print(f"Building (Release) into {BUILD_DIR}...", file=sys.stderr)
+    build_project()
 
     # Determine active profile for display
     has_custom_net = args.delay or args.jitter or args.throughput or args.loss
@@ -473,18 +819,10 @@ Examples:
     else:
         profiles_to_run = args.profiles or ["unlimited"]
 
-    # Generate data
-    source_dir = os.path.join(BENCH_DIR, "source")
-    dest_dir = os.path.join(BENCH_DIR, "dest")
-    total_bytes = generate_bench_data(source_dir, args.size_mb, args.random_ratio)
-    compressible_pct = (1 - args.random_ratio) * 100
-    random_pct = args.random_ratio * 100
-    print(f"Generated {total_bytes / (1024*1024):.1f} MB  "
-          f"({random_pct:.0f}% random, {compressible_pct:.0f}% compressible)")
-
-    # Build config list
+    # Build config list (shlex so quoted/space-separated flags survive)
     if args.configs:
-        fastsync_configs = [{"name": c, "flags": c.split(), "tool": "fastsync"} for c in args.configs]
+        fastsync_configs = [{"name": c, "flags": shlex.split(c), "tool": "fastsync"}
+                            for c in args.configs]
     else:
         fastsync_configs = list(FASTSYNC_CONFIGS)
 
@@ -496,14 +834,21 @@ Examples:
     total_runs = len(configs) * args.runs * len(profiles_to_run)
     progress = Progress(total_runs, "Benchmarking") if args.progress else None
     if progress:
-        print(f"Running {total_runs} transfers...")
+        print(f"Running {total_runs} transfers...", file=sys.stderr)
 
     all_results = []
     try:
         for profile in profiles_to_run:
-            results = run_benchmark(source_dir, dest_dir, configs, args.runs, profile, progress)
+            results = run_benchmark(source_dir, dest_dir, configs, args.runs, profile,
+                                    measure_bytes, verify=not args.no_verify,
+                                    warm=args.warm, mutation=mutation,
+                                    progress=progress)
             all_results.extend(results)
+    except RuntimeError as exc:
+        sys.stderr.write(f"error: {exc}\n")
+        sys.exit(1)
     finally:
+        netem_reset()
         if not args.keep_data:
             shutil.rmtree(BENCH_DIR, ignore_errors=True)
 
@@ -511,7 +856,7 @@ Examples:
     if args.output == "json":
         print(json.dumps(all_results, indent=2))
     else:
-        print_table(all_results, total_bytes, args.random_ratio)
+        print_table(all_results, measure_bytes, stats, args.warm)
         print()
 
 

pytest.ini

@@ -5,3 +5,6 @@ markers =
     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

shell.nix

@@ -3,26 +3,59 @@
 }:
 
 pkgs.mkShell {
+  # Development shell for FastSync.  Provides the host-side toolchain needed to
+  # build, lint, unit-test, integration-test and benchmark the project.
+  # It deliberately does NOT build on entry: run the CMake commands in README.md
+  # (or use the CI Docker image for exact CI parity).
   nativeBuildInputs = with pkgs; [
+    # build
     gcc
     cmake
     gnumake
     pkg-config
+    # lint / static analysis (matches CI)
+    clang-tools # clang-format
+    cppcheck
+    # tests
+    (python3.withPackages (ps: with ps; [ pytest pytest-xdist psutil ]))
+    openssh # SSH transport integration tests
+    # debugging
+    gdb
+    valgrind
+    # coverage
+    lcov
+    # benchmark tooling
+    rsync
+    iproute2 # tc/netem for network shaping
+    # misc
+    git
+    curl
+    nodejs
+    nixpkgs-fmt
     docker
     tea
   ];
 
   buildInputs = with pkgs; [
     zstd
+    zlib
+    lz4
     openssl
-    (python3.withPackages (ps: with ps; [ pytest ]))
   ];
 
+  # The CMake configure step fetches xxHash via FetchContent, which needs
+  # network access; NIX_ENFORCE_PURITY must be off so the sandbox does not block.
   NIX_ENFORCE_PURITY = 0;
 
   shellHook = ''
     export NIX_ENFORCE_PURITY=0
-    cmake -B build
+    # Make an existing build tree available on PATH, but never build here.
+    if [ -d "$PWD/build" ]; then
       export PATH="$PWD/build:$PATH"
+    fi
+    echo "FastSync dev shell ready."
+    echo "  Build:      cmake -B build -S . && cmake --build build -j\$(nproc)"
+    echo "  Unit:       ./build/tests"
+    echo "  CI parity:  docker run --rm --user \"\$(id -u):\$(id -g)\" -v \"\$PWD:/workspace\" -w /workspace gitea.tap-tap.win/taptap/fastsync-ci:v11 ..."
   '';
 }

src/client/change_list.c

@@ -1,5 +1,7 @@
 #include "change_list.h"
+#include "checksum.h"
 #include "utils.h"
+#include <fcntl.h>
 #include <limits.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -7,21 +9,7 @@
 #include <string.h>
 #include <sys/stat.h>
 #include <time.h>
-
-/* Itemize code emitted for a transferred regular file.
- *
- * Layout (rsync-compatible 11-char item): `>f` marks a regular file that was
- * transferred to the remote host; the trailing nine markers are, in order,
- * c(hecksum) s(ize) t(ime) p(erms) o(wner) g(roup) u(ser/acl) a(ttrs) x(attrs).
- * Every marker is `+` (FastSync does not compare each attribute on the
- * receiving side, so a sent file is reported as fully updated).  Files that
- * are already up to date print no line at all, matching rsync's single -i
- * which only itemizes changes.
- *
- * Because the scanner only yields regular-file transfer candidates, `>d`
- * (directory) lines are never produced; directories are not transferred as
- * items by FastSync. */
-#define ITEMIZE_SENT_FILE ">f+++++++++"
+#include <unistd.h>
 
 typedef struct {
   char* data;
@@ -80,103 +68,14 @@ static bool strbuf_append(StrBuf* buf, const char* text) {
   return true;
 }
 
-static bool strbuf_append_ull(StrBuf* buf, unsigned long long value) {
-  char digits[32];
-  int written = snprintf(digits, sizeof(digits), "%llu", value);
-  if (written < 0 || (size_t)written >= sizeof(digits))
-    return false;
-  return strbuf_append(buf, digits);
-}
-
-static bool strbuf_append_longlong(StrBuf* buf, long long value) {
-  char digits[32];
-  int written = snprintf(digits, sizeof(digits), "%lld", value);
-  if (written < 0 || (size_t)written >= sizeof(digits))
-    return false;
-  return strbuf_append(buf, digits);
-}
-
 bool change_list_enabled(const Config* config) {
   return config != NULL && (config->itemize_changes || config->out_format != NULL ||
                             (config->log_file != NULL && config->log_file_format != NULL));
 }
 
-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;
-}
+/* ---- Itemize code ---- */
 
-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--`. */
+/* Format the permission bits as an `ls -l` string, e.g. `-rw-r--r--`. */
 static void mode_to_ls_string(mode_t mode, char out[11]) {
   out[0] = S_ISDIR(mode)    ? 'd'
            : S_ISLNK(mode)  ? 'l'
@@ -198,29 +97,94 @@ static void mode_to_ls_string(mode_t mode, char out[11]) {
   out[10] = '\0';
 }
 
-char* change_render_list_line(mode_t mode, unsigned long long size, time_t mtime,
-                              const char* path) {
-  char permission[11];
-  mode_to_ls_string(mode, permission);
-  char date[32];
-  struct tm broken_down;
-  if (localtime_r(&mtime, &broken_down) != NULL) {
-    if (strftime(date, sizeof(date), "%Y/%m/%d %H:%M:%S", &broken_down) == 0)
-      snprintf(date, sizeof(date), "?");
-  } else {
-    snprintf(date, sizeof(date), "?");
+static char itemize_type_char(const ChangeEvent* event) {
+  if (event->is_directory)
+    return 'd';
+  if (event->is_symlink)
+    return 'L';
+  if (event->is_special) {
+    if (S_ISCHR(event->mode) || S_ISBLK(event->mode))
+      return 'D';
+    return 'S';
   }
+  return 'f';
+}
+
+static bool times_match(const Config* config, const ChangeEvent* event) {
+  if (!event->dest.known || !event->dest.existed)
+    return false;
+  if (event->mtime_sec == event->dest.mtime_sec)
+    return event->mtime_nsec == event->dest.mtime_nsec;
+  long long delta = (long long)event->mtime_sec - (long long)event->dest.mtime_sec;
+  if (delta < 0)
+    delta = -delta;
+  return delta <= (long long)config->modify_window;
+}
+
+/* Fill the 11-character itemize code (10 chars + NUL).  `created` means the
+ * destination entry did not exist, so every attribute marker is `+`. */
+static void itemize_code(const Config* config, const ChangeEvent* event, char code[12]) {
+  bool known = event->dest.known;
+  bool created = !known || !event->dest.existed;
+  char update;
+  if (event->is_hardlink)
+    update = 'h';
+  else if (created)
+    update = (event->is_directory || event->is_symlink || event->is_special) ? 'c' : '>';
+  else
+    update = '>';
+  code[0] = update;
+  code[1] = itemize_type_char(event);
+  if (created) {
+    for (int i = 0; i < 9; i++)
+      code[2 + i] = '+';
+    code[11] = '\0';
+    return;
+  }
+  bool size_diff = event->size != event->dest.size;
+  bool time_diff = !times_match(config, event);
+  bool perms_diff = (event->mode & 07777) != (event->dest.mode & 07777);
+  bool owner_diff = event->uid != (uid_t)event->dest.uid;
+  bool group_diff = event->gid != (gid_t)event->dest.gid;
+  code[2] = '.'; /* checksum: no destination digest available */
+  code[3] = size_diff ? 's' : '.';
+  code[4] = time_diff ? 't' : '.';
+  code[5] = (config->preserve_perms && perms_diff) ? 'p' : '.';
+  code[6] = (config->preserve_owner && owner_diff) ? 'o' : '.';
+  code[7] = (config->preserve_group && group_diff) ? 'g' : '.';
+  code[8] = '.'; /* reserved */
+  code[9] = '.'; /* acl: not compared */
+  code[10] = '.';
+  code[11] = '\0';
+}
+
+/* rsync %n: the transfer-relative name, with a trailing slash for directories. */
+static bool append_name(StrBuf* buf, const ChangeEvent* event) {
+  if (!strbuf_append(buf, event->name != NULL ? event->name : ""))
+    return false;
+  if (event->is_directory && (event->name == NULL || event->name[0] == '\0' ||
+                              event->name[strlen(event->name) - 1] != '/'))
+    return strbuf_append_char(buf, '/');
+  return true;
+}
+
+/* rsync %L: " -> target" for a symlink, " => target" for a hard link, else "". */
+static bool append_link_suffix(StrBuf* buf, const ChangeEvent* event) {
+  if (event->is_symlink && event->symlink_target != NULL)
+    return strbuf_append(buf, " -> ") && strbuf_append(buf, event->symlink_target);
+  if (event->is_hardlink && event->hardlink_target != NULL)
+    return strbuf_append(buf, " => ") && strbuf_append(buf, event->hardlink_target);
+  return true;
+}
+
+char* change_render_itemize(const Config* config, const ChangeEvent* event) {
+  if (event == NULL || event->decision != CHANGE_SENT)
+    return str_dup("");
+  char code[12];
+  itemize_code(config, event, code);
   StrBuf line = {0};
-  char size_field[32];
-  int written = snprintf(size_field, sizeof(size_field), "%llu", size);
-  if (written < 0 || (size_t)written >= sizeof(size_field)) {
-    strbuf_free(&line);
-    return NULL;
-  }
-  bool ok = strbuf_append(&line, permission) && strbuf_append_char(&line, ' ') &&
-            strbuf_append(&line, size_field) && strbuf_append_char(&line, ' ') &&
-            strbuf_append(&line, date) && strbuf_append_char(&line, ' ') &&
-            strbuf_append(&line, path != NULL ? path : "");
+  bool ok = strbuf_append(&line, code) && strbuf_append_char(&line, ' ') &&
+            append_name(&line, event) && append_link_suffix(&line, event);
   if (!ok) {
     strbuf_free(&line);
     return NULL;
@@ -228,6 +192,238 @@ char* change_render_list_line(mode_t mode, unsigned long long size, time_t mtime
   return line.data;
 }
 
+/* ---- --out-format / --log-file-format ---- */
+
+/* rsync 3.4.1's `%C` uses the negotiated transfer checksum; with the default
+ * "auto" choice on both ends that is xxh128.  FastSync's internal XXH64 default
+ * is not an rsync algorithm, so map it to xxh128 for parity. */
+static ChecksumAlgo out_format_checksum_algo(const Config* config) {
+  switch ((ChecksumAlgo)config->checksum_algo) {
+  case CHECKSUM_ALGO_MD5:
+    return CHECKSUM_ALGO_MD5;
+  case CHECKSUM_ALGO_XXH3:
+    return CHECKSUM_ALGO_XXH3;
+  case CHECKSUM_ALGO_XXH128:
+    return CHECKSUM_ALGO_XXH128;
+  case CHECKSUM_ALGO_XXH64:
+  default:
+    return CHECKSUM_ALGO_XXH128;
+  }
+}
+
+/* Render a digest as rsync's sum_as_hex: for xxh128 the HIGH 64-bit half is
+ * printed before the low half; every other algorithm prints its bytes in order. */
+static void digest_to_hex(ChecksumAlgo algo, const uint8_t* digest, size_t len, char* out) {
+  if (algo == CHECKSUM_ALGO_XXH128 && len == 16) {
+    uint64_t low = 0;
+    uint64_t high = 0;
+    memcpy(&low, digest, sizeof(low));
+    memcpy(&high, digest + 8, sizeof(high));
+    snprintf(out, len * 2 + 1, "%016llx%016llx", (unsigned long long)high, (unsigned long long)low);
+    return;
+  }
+  static const char hex[] = "0123456789abcdef";
+  for (size_t i = 0; i < len; i++) {
+    out[i * 2] = hex[(digest[i] >> 4) & 0xf];
+    out[i * 2 + 1] = hex[digest[i] & 0xf];
+  }
+  out[len * 2] = '\0';
+}
+
+static bool format_uses_checksum(const char* format) {
+  if (format == NULL)
+    return false;
+  for (const char* p = format; *p != '\0';) {
+    if (*p != '%') {
+      p++;
+      continue;
+    }
+    char token = p[1];
+    if (token == '\0')
+      break;
+    if (token == 'C')
+      return true;
+    p += 2;
+  }
+  return false;
+}
+
+/* Fill event->checksum/checksum_known for a transferred regular file.  A
+ * non-regular entry (or a hard-link sibling) leaves checksum_known false, which
+ * renders as spaces like rsync. */
+static void fill_event_checksum(const Config* config, const File* file, ChangeEvent* event) {
+  if (file == NULL || file->is_dir || file->is_symlink || file->is_special ||
+      (file->link_group != 0 && !file->link_first))
+    return;
+  if (!format_uses_checksum(config->out_format) && !format_uses_checksum(config->log_file_format))
+    return;
+  if (file->path == NULL)
+    return;
+  ChecksumAlgo algo = out_format_checksum_algo(config);
+  uint8_t digest[CHECKSUM_MAX_DIGEST_LEN];
+  size_t len = 0;
+  /* rsync's %C is the transfer checksum, which is always seeded with 0 (it is
+   * independent of --checksum-seed, as rsync 3.4.1 demonstrates). */
+  if (!checksum_digest_file(algo, 0, file->path, digest, sizeof(digest), &len))
+    return;
+  digest_to_hex(algo, digest, len, event->checksum);
+  event->checksum_known = true;
+}
+
+char* change_render_format(const char* format, const Config* config, const ChangeEvent* event) {
+  if (format == NULL || event == NULL)
+    return NULL;
+  StrBuf line = {0};
+  bool ok = true;
+  for (const char* p = format; *p != '\0' && ok;) {
+    if (*p != '%') {
+      ok = strbuf_append_char(&line, *p);
+      p++;
+      continue;
+    }
+    char token = p[1];
+    if (token == '\0') {
+      ok = strbuf_append_char(&line, '%');
+      break;
+    }
+    switch (token) {
+    case '%':
+      ok = strbuf_append_char(&line, '%');
+      break;
+    case 'i': {
+      if (event->deleted) {
+        /* rsync's ITEM_DELETED itemize code: `*deleting  ` (11 chars). */
+        ok = strbuf_append(&line, "*deleting  ");
+        break;
+      }
+      char code[12];
+      itemize_code(config, event, code);
+      ok = strbuf_append(&line, code);
+      break;
+    }
+    case 'f':
+      ok = strbuf_append(&line, event->path != NULL ? event->path : "");
+      break;
+    case 'n':
+      ok = append_name(&line, event);
+      break;
+    case 'L':
+      ok = append_link_suffix(&line, event);
+      break;
+    case 'l': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%llu", event->size);
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    case 'b': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%llu", event->bytes_sent);
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    case 'c': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%llu", event->bytes_read);
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    case 'C': {
+      if (event->checksum_known) {
+        ok = strbuf_append(&line, event->checksum);
+      } else {
+        /* rsync pads a non-regular / untransferred entry with spaces. */
+        ChecksumAlgo algo = out_format_checksum_algo(config);
+        int width = checksum_digest_len(algo) * 2;
+        for (int i = 0; i < width && ok; i++)
+          ok = strbuf_append_char(&line, ' ');
+      }
+    } break;
+    case 'M': {
+      char when[32];
+      if (format_rsync_datetime(event->mtime_sec, true, when, sizeof(when)))
+        ok = strbuf_append(&line, when);
+    } break;
+    case 't': {
+      char when[32];
+      if (format_rsync_datetime(time(NULL), false, when, sizeof(when)))
+        ok = strbuf_append(&line, when);
+    } break;
+    case 'o':
+      ok = strbuf_append(&line, "send");
+      break;
+    case 'p': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%ld", (long)getpid());
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    case 'B': {
+      char permission[11];
+      mode_to_ls_string(event->mode, permission);
+      ok = strbuf_append(&line, permission + 1);
+    } break;
+    case 'U': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%u", (unsigned)event->uid);
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    case 'G': {
+      char digits[32];
+      int written = snprintf(digits, sizeof(digits), "%u", (unsigned)event->gid);
+      ok = written >= 0 && (size_t)written < sizeof(digits) && strbuf_append(&line, digits);
+    } break;
+    default:
+      /* Unknown escape sequences are preserved verbatim. */
+      ok = strbuf_append_char(&line, '%') && strbuf_append_char(&line, token);
+      break;
+    }
+    p += 2;
+  }
+  if (!ok) {
+    strbuf_free(&line);
+    return NULL;
+  }
+  if (line.data == NULL) {
+    line.data = str_dup("");
+    if (!line.data)
+      return NULL;
+  }
+  return line.data;
+}
+
+/* ---- --list-only ---- */
+
+char* change_render_list_line(const Config* config, const ChangeEvent* event) {
+  (void)config;
+  if (event == NULL)
+    return NULL;
+  char permission[11];
+  mode_to_ls_string(event->mode, permission);
+  char date[32];
+  if (!format_rsync_datetime(event->mtime_sec, false, date, sizeof(date)))
+    snprintf(date, sizeof(date), "?");
+  StrBuf line = {0};
+  char size_field[40];
+  char grouped[32];
+  if (!format_big_num(event->size, false, grouped, sizeof(grouped))) {
+    strbuf_free(&line);
+    return NULL;
+  }
+  int written = snprintf(size_field, sizeof(size_field), "%15s", grouped);
+  if (written < 0 || (size_t)written >= sizeof(size_field)) {
+    strbuf_free(&line);
+    return NULL;
+  }
+  const char* name = event->name != NULL && event->name[0] != '\0' ? event->name : ".";
+  bool ok = strbuf_append(&line, permission) && strbuf_append(&line, size_field) &&
+            strbuf_append_char(&line, ' ') && strbuf_append(&line, date) &&
+            strbuf_append_char(&line, ' ') && strbuf_append(&line, name);
+  if (!ok) {
+    strbuf_free(&line);
+    return NULL;
+  }
+  return line.data;
+}
+
+/* ---- Event emission ---- */
+
 static void print_escaped_line(FILE* stream, const char* line, bool eight_bit_output) {
   char* escaped = output_escape(line, eight_bit_output);
   if (escaped != NULL) {
@@ -247,15 +443,16 @@ void change_emit(const Config* config, const ChangeEvent* event) {
   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);
+    char* line = config->out_format != NULL
+                     ? change_render_format(config->out_format, config, event)
+                     : change_render_itemize(config, event);
     if (line != NULL) {
       print_escaped_line(stdout, line, config->eight_bit_output);
       free(line);
     }
   }
   if (to_log) {
-    char* line = change_render_format(config->log_file_format, event);
+    char* line = change_render_format(config->log_file_format, config, event);
     if (line != NULL) {
       print_escaped_line(config->log_file, line, config->eight_bit_output);
       free(line);
@@ -266,9 +463,6 @@ void change_emit(const Config* config, const ChangeEvent* event) {
 static bool format_uses_mtime(const char* format) {
   if (format == NULL)
     return false;
-  /* Mirror change_render_format's tokenizer: "%%" is a literal percent (so
-   * "%%M" does NOT expand %M) and unknown "%X" escapes consume both chars.
-   * This keeps the optional stat() fallback below in step with the renderer. */
   for (const char* p = format; *p != '\0';) {
     if (*p != '%') {
       p++;
@@ -284,46 +478,153 @@ static bool format_uses_mtime(const char* format) {
   return false;
 }
 
-void change_emit_file_sent(const Config* config, const File* file) {
+/* Relative path of an entry below the transfer root (no leading slash).  Uses
+ * the sender-side send_path override when present (bare-relative -R layout). */
+static char* relative_name(const Config* config, const File* file) {
+  const char* full = file_wire_path(file);
+  if (file->send_path != NULL)
+    return str_dup(full != NULL ? full : "");
+  const char* root = config->send_directory;
+  if (root == NULL || full == NULL)
+    return str_dup(full != NULL ? full : "");
+  size_t root_len = strlen(root);
+  while (root_len > 1 && root[root_len - 1] == '/')
+    root_len--;
+  if (strncmp(root, full, root_len) == 0) {
+    if (full[root_len] == '\0')
+      return str_dup("");
+    if (full[root_len] == '/')
+      return str_dup(full + root_len + 1);
+  }
+  return str_dup(full);
+}
+
+/* rsync %f long form: the source argument as typed (leading '/' removed,
+ * trailing '/' removed, leading "./" removed) joined to the relative name. */
+static char* display_name(const Config* config, const char* name) {
+  const char* root = config->send_directory;
+  if (root == NULL)
+    return str_dup(name != NULL ? name : "");
+  const char* p = root;
+  while (*p == '/')
+    p++;
+  if (p[0] == '.' && p[1] == '/')
+    p += 2;
+  size_t root_len = strlen(p);
+  while (root_len > 0 && p[root_len - 1] == '/')
+    root_len--;
+  size_t name_len = name != NULL ? strlen(name) : 0;
+  if (root_len == 0 && name_len == 0)
+    return str_dup("");
+  char* out = malloc(root_len + (root_len > 0 && name_len > 0 ? 1 : 0) + name_len + 1);
+  if (!out)
+    return NULL;
+  size_t offset = 0;
+  if (root_len > 0) {
+    memcpy(out, p, root_len);
+    offset = root_len;
+  }
+  if (root_len > 0 && name_len > 0)
+    out[offset++] = '/';
+  if (name_len > 0)
+    memcpy(out + offset, name, name_len);
+  out[offset + name_len] = '\0';
+  return out;
+}
+
+static void fill_event_from_file(const Config* config, const File* file, ChangeEvent* event,
+                                 char** name_out, char** path_out) {
+  char* name = relative_name(config, file);
+  char* path = display_name(config, name);
+  event->name = name;
+  event->path = path;
+  *name_out = name;
+  *path_out = path;
+  if (file->metadata != NULL) {
+    event->mtime_sec = file->metadata->mtime_sec;
+    event->mtime_nsec = file->metadata->mtime_nsec;
+    event->mode = file->metadata->mode;
+    event->uid = file->metadata->uid;
+    event->gid = file->metadata->gid;
+  } else if (format_uses_mtime(config->out_format) || format_uses_mtime(config->log_file_format)) {
+    struct stat st;
+    if (file->path != NULL && stat(file->path, &st) == 0) {
+      event->mtime_sec = st.st_mtime;
+      event->mtime_nsec = st.st_mtim.tv_nsec;
+    }
+  }
+}
+
+void change_emit_file_sent_bytes(const Config* config, const File* file,
+                                 unsigned long long bytes_sent, unsigned long long bytes_read) {
   if (file == NULL || !change_list_enabled(config))
     return;
   ChangeEvent event;
   memset(&event, 0, sizeof(event));
-  /* The displayed path is the one transmitted (with -R + --files-from this is
-     the bare relative destination path); the metadata fallback below still
-     stats the local absolute path. */
-  event.path = file_wire_path(file);
   event.decision = CHANGE_SENT;
   event.is_directory = false;
+  event.is_symlink = false;
+  event.is_special = false;
+  event.is_hardlink = false;
   event.size = file->data != NULL ? file->data->size : 0;
-  /* FastSync has no wire-byte counter yet, so %b reports the source length
-   * that had to be delivered (always equal to %l); the actual bytes written
-   * to the socket (compressed/delta) are not measured. */
-  event.bytes_sent = event.size;
-  if (file->metadata != NULL) {
-    event.mtime_sec = file->metadata->mtime_sec;
-  } else if (format_uses_mtime(config->out_format) || format_uses_mtime(config->log_file_format)) {
-    /* Best-effort fallback for %M when no metadata was captured (no -M): the
-     * path is stat()ed just to fill the field, and any failure leaves 0. */
-    struct stat st;
-    if (file->path != NULL && stat(file->path, &st) == 0)
-      event.mtime_sec = st.st_mtime;
+  event.dest = file->dest_state;
+  if (file->is_symlink) {
+    event.is_symlink = true;
+    event.symlink_target = file->symlink_target;
+    event.size = file->symlink_target != NULL ? strlen(file->symlink_target) : 0;
+    event.bytes_sent = 0;
+  } else if (file->is_special) {
+    event.is_special = true;
+    event.bytes_sent = 0;
+  } else if (file->link_group != 0 && !file->link_first) {
+    event.is_hardlink = true;
+    event.hardlink_target = file->hardlink_target;
+    event.bytes_sent = 0;
+  } else {
+    event.bytes_sent = bytes_sent;
+    /* rsync's %c is the block-checksum bytes received for the file.  Even a
+     * whole-file transfer (no basis; --append/--inplace included) receives
+     * rsync's 16-byte sum header, so rsync reports 16; a dry run transfers
+     * nothing and reports 0.  FastSync's whole-file path has no sum header, so
+     * report rsync's value for parity.  With delta enabled the real received
+     * bytes are kept, but FastSync's signature framing differs from rsync's so
+     * those stay numerically divergent. */
+    bool delta_active = config->use_delta && !config->whole_file;
+    event.bytes_read = (!config->dry_run && !delta_active) ? 16 : bytes_read;
   }
+  char* name = NULL;
+  char* path = NULL;
+  fill_event_from_file(config, file, &event, &name, &path);
+  if (name != NULL && path != NULL) {
+    fill_event_checksum(config, file, &event);
     change_emit(config, &event);
+  }
+  free(name);
+  free(path);
+}
+
+void change_emit_file_sent(const Config* config, const File* file) {
+  if (file == NULL)
+    return;
+  unsigned long long payload = file->data != NULL ? file->data->size : 0;
+  change_emit_file_sent_bytes(config, file, payload, 0);
 }
 
-/* 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;
+  event.dest = file->dest_state;
+  char* name = NULL;
+  char* path = NULL;
+  fill_event_from_file(config, file, &event, &name, &path);
+  if (name != NULL && path != NULL)
     change_emit(config, &event);
+  free(name);
+  free(path);
 }

src/client/change_list.h

@@ -2,7 +2,9 @@
 #define CHANGE_LIST_H
 
 #include "config.h"
+#include "checksum.h"
 #include "file_types.h"
+#include "format.h"
 #include <stdbool.h>
 #include <sys/stat.h>
 #include <time.h>
@@ -26,42 +28,59 @@ typedef enum {
 } ChangeDecision;
 
 typedef struct {
-  const char* path; /* full source path */
+  const char* path; /* long-form display path (rsync %f) */
+  const char* name; /* transfer-relative path (rsync %n), no trailing slash */
   ChangeDecision decision;
   bool is_directory;
+  bool is_symlink;
+  bool is_special;
+  bool is_hardlink; /* a hard-link sibling (linked, no data sent) */
+  bool deleted;     /* a would-delete report (-n --delete); no source file */
+  const char* symlink_target;
+  const char* hardlink_target;
   unsigned long long size;       /* source file length in bytes */
-  /* 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 */
+  unsigned long long bytes_sent; /* wire bytes actually transferred (rsync %b) */
+  unsigned long long bytes_read; /* wire bytes read back for this file (rsync %c) */
+  /* rsync %C: whole-file checksum hex for a transferred regular file.  Only
+   * filled when the active format uses %C (checksum_known == false otherwise,
+   * which renders as spaces like rsync for non-regular entries). */
+  bool checksum_known;
+  char checksum[CHECKSUM_MAX_DIGEST_LEN * 2 + 1];
+  time_t mtime_sec;
+  long mtime_nsec;
+  mode_t mode;
+  uid_t uid;
+  gid_t gid;
+  /* Receiver-reported pre-transfer destination state (OutputDestState.known is
+   * false when no report was requested/received). */
+  OutputDestState dest;
 } ChangeEvent;
 
 /* True when any output mode is active and per-file events matter. */
 bool change_list_enabled(const Config* config);
 
-/* Render the rsync-style itemize line for a transferred file:
- *   `>f+++++++++ <path>`
- * The 11-char code is `>f` (regular file transferred to the remote host)
- * followed by c/s/t/p/o/g/u/a/x markers that are all `+` (value will be set
- * / differs) because FastSync does not separately compare checksums, size,
- * mtime, perms, owner, group, uid, acl, or xattr on the receiving side, so a
- * sent file is reported as fully updated.  Up-to-date files print no line
- * (rsync single `-i` only shows changes).  Caller frees the result. */
-char* change_render_itemize(const ChangeEvent* event);
+/* Render the rsync-style itemize line for a transferred item
+ * (`%i %n%L`): `>f+++++++++ sub/b.txt`.  Caller frees the result. */
+char* change_render_itemize(const Config* config, const ChangeEvent* event);
 
-/* Expand an --out-format/--log-file-format template.  Tokens:
- *   %f  full source path        %b  "bytes sent" == the source length (%l);
- *   %n  leaf (base) name            actual post-compression/delta wire bytes
- *   %l  file length in bytes        are not counted
- *   %M  mtime in whole seconds      %%  a literal percent sign
+/* Expand an --out-format/--log-file-format template.  Supported tokens:
+ *   %i  itemize code            %n  transfer-relative name (dir: trailing /)
+ *   %f  long display path       %l  file length in bytes
+ *   %b  wire bytes transferred  %c  block-checksum bytes received (rsync: 16
+ *                                   for a whole-file transfer, 0 for a dry run)
+ *   %C  whole-file checksum hex (xxh128 by default; spaces for non-regular)
+ *   %M  mtime (YYYY/MM/DD-HH:MM:SS)
+ *   %t  current time            %o  operation ("send"/"del.")
+ *   %p  pid                     %B  permission bits without the type char
+ *   %U  uid                     %G  gid
+ *   %L  " -> target" / " => target"    %%  a literal percent sign
  * Unknown %X sequences are preserved verbatim.  Caller frees the result. */
-char* change_render_format(const char* format, const ChangeEvent* event);
+char* change_render_format(const char* format, const Config* config, const ChangeEvent* event);
 
 /* Render one --list-only long-listing entry:
- *   `-rw-r--r--           12 2026/09/06 10:00:00 <path>`
+ *   `-rw-r--r--           12 2026/09/06 10:00:00 sub/b.txt`
  * (ls -l style columns; mtime in the local time zone).  Caller frees it. */
-char* change_render_list_line(mode_t mode, unsigned long long size, time_t mtime, const char* path);
+char* change_render_list_line(const Config* config, const ChangeEvent* event);
 
 /* Emit an event to every active destination:
  *   stdout: --itemize-changes line, or the --out-format expansion when set;
@@ -69,7 +88,15 @@ char* change_render_list_line(mode_t mode, unsigned long long size, time_t mtime
  * CHANGE_UP_TO_DATE events produce no output. */
 void change_emit(const Config* config, const ChangeEvent* event);
 
-/* Build and emit a CHANGE_SENT event for a file the client just sent. */
+/* Build and emit a CHANGE_SENT event for a file the client just sent.  `bytes_sent`
+ * is the process-wide wire-byte delta for this file (rsync's %b) and `bytes_read`
+ * the received bytes used for the delta handshake; pass 0 when unknown.  For a
+ * whole-file transfer %c is pinned to rsync's 16-byte sum header regardless. */
+void change_emit_file_sent_bytes(const Config* config, const File* file,
+                                 unsigned long long bytes_sent, unsigned long long bytes_read);
+
+/* Build and emit a CHANGE_SENT event for a file the client just sent, deriving
+ * the wire byte counts from the source payload length. */
 void change_emit_file_sent(const Config* config, const File* file);
 
 /* Build and emit a CHANGE_SENT event for an explicit directory entry (-d). */

src/client/client_send.h

@@ -4,10 +4,27 @@
 #include "chunk.h"
 #include "config.h"
 #include "transport_tcp.h"
+#include <signal.h>
+#include <stdbool.h>
 
-int send_chunk(Client* client, Chunk* chunk, Config* config);
+/* Set ONLY by the client's SIGINT/SIGTERM handler (async-signal-safe: the
+ * handler stores 1 and does nothing else).  The send loops poll it via
+ * client_abort_pending() and, when set, best-effort send STATUS_ABORT so the
+ * receiver can clean up before the client exits. */
+extern volatile sig_atomic_t client_abort_requested;
+bool client_abort_pending(void);
+/* Arm/disarm abort handling around the network phase.  While disarmed, a
+ * SIGINT/SIGTERM takes the default action (immediate termination) so local-only
+ * modes are not left unresponsive.  Defined in client_cli.c. */
+void client_set_abort_armed(bool armed);
+
+/* Both sender entry points BORROW `config` for the duration of the call; they
+ * never free it, and the caller retains ownership (freeing it with
+ * config_delete() once the call returns). */
 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

@@ -1,25 +1,55 @@
 #include "client_validation.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) {
-    log_message(LOG_LEVEL_ERROR, "source and destination directories are required");
+  /* 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;
+  }
+  /* A dry-run of a local batch apply is not meaningful: --read-batch bypasses
+     the client-side scan/server decision entirely, so dry-run would have no
+     wire state to report (and must not be used as a mutation escape hatch).
+     --only-write-batch likewise never contacts a receiver.  --write-batch DOES
+     run a live transfer but additionally mutates the filesystem by emitting the
+     batch file, so a dry-run must not write it either.  Reject all three up
+     front instead of silently ignoring --dry-run. */
+  if (config->dry_run && (read_batch || only_write_batch || write_batch)) {
+    log_message(LOG_LEVEL_ERROR,
+                "--dry-run cannot be combined with --read-batch, --only-write-batch, or "
+                "--write-batch; a dry-run must not mutate anything, including batch files");
+    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;
     }
-  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)");
+  } 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;
     }
-  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)");
+  } 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->compression_threads > 0 && !config->use_compression) {
@@ -30,43 +60,19 @@ bool validate_config(const Config* config) {
     log_message(LOG_LEVEL_ERROR, "-f/--sendfile is not supported with SSH transport");
     return false;
   }
-  if (config->use_incremental && config->use_chunk_serialization) {
-    log_message(LOG_LEVEL_ERROR, "--incremental is not supported with -s (chunk serialization)");
-    return false;
-  }
-  if (config->skip_compress_set && config->use_chunk_serialization) {
+  /* -M/--remote-option appends an option to the REMOTE server's argv, which
+   * only exists on the SSH (user@host:path) transport.  A daemon
+   * (host::module/path) or local TCP destination has no remote command line,
+   * so the option would be silently ignored; reject it by name instead. */
+  if (config->remote_option_count > 0 && config->transport != TRANSPORT_SSH) {
     log_message(LOG_LEVEL_ERROR,
-                "--skip-compress cannot be combined with -s (chunk serialization)");
+                "-M/--remote-option is only valid with the SSH transport (user@host:path); it "
+                "cannot be used with a daemon (host::module/path) or local TCP destination");
     return false;
   }
-  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->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->whole_file && config->use_sendfile) {
-    log_message(LOG_LEVEL_ERROR, "--delta cannot be combined with -f (sendfile)");
-    return false;
-  }
-  /* --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)");
+  /* -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->log_file_format && !config->log_file) {
@@ -79,20 +85,31 @@ bool validate_config(const Config* config) {
       return false;
     }
   }
-  if (config->delay_updates && config->inplace) {
-    log_message(LOG_LEVEL_ERROR, "--delay-updates does not work with --inplace");
+  /* 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 && 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)");
+  /* Every cross-field invariant the receiver enforces lives in one shared
+     predicate so the client and the server can never disagree.  The client
+     reports the specific reason here, before any network I/O. */
+  const char* invariants_error = config_invariants_error(config);
+  if (invariants_error) {
+    log_message(LOG_LEVEL_ERROR, "%s", invariants_error);
     return false;
   }
-  if (!config_has_valid_delete_timing(config)) {
+  /* --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,
-                "--delete-before/--delete-during/--delete-delay/--delete-after select the delete "
-                "timing; at most one may be given and each implies --delete");
+                "--protocol must be %s (FastSync supports only its current wire "
+                "protocol version and cannot speak an older or virtual one)",
+                PROTOCOL_VERSION);
     return false;
   }
   return true;

src/client/scanner.h

@@ -4,16 +4,30 @@
 #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 <stdatomic.h>
 #include <sys/types.h>
 #include <threads.h>
 
+/* Upper bound on the configurable parallel scanner worker count (--threads=N):
+ * keeps one transfer from spawning an unbounded pool on a very large machine. */
+#define MAX_SCANNER_THREADS 256
+
 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;
@@ -27,16 +41,45 @@ 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 */
+  /* --delete-excluded: per-directory plain rules become sender-only, so they no
+     longer protect the receiver from deletion. */
+  bool delete_excluded;
+  /* -FF: also exclude the per-directory filter files themselves from the
+     transfer (single -F transfers them). */
+  bool exclude_per_dir_filter_files;
   bool dirs;     /* -d/--dirs: transfer dir entries, no recursion */
   bool relative; /* -R/--relative (dest rel paths, with --files-from) */
+  /* -R/--relative outside --files-from: the destination-relative path prefix
+   * reconstructed from the source spec (rsync's '/./' cut point), or NULL when
+   * -R is off or --files-from is in use (the bare-relative path then comes from
+   * the listed entry).  Borrowed read-only; owned by client_send. */
+  const char* relative_prefix;
+  /* --list-only: emit an is_dir File for every traversed directory (the listing
+   * includes directory entries, matching rsync).  Client-only; never set on a
+   * real transfer, which relies on implicit parent creation. */
+  bool list_dirs;
   /* --prune-empty-dirs (long only): in --dirs mode an empty source directory's
      explicit entry is omitted from the transfer file list (so nothing is
      created at the destination and it can be pruned by --delete); explicitly
@@ -45,17 +88,39 @@ typedef struct {
   bool prune_empty_dirs;
   /* Delete-excluded protection sink (optional): when non-NULL the scanner
    * appends the destination-relative path of every entry it prunes because a
-   * USER SELECTION rule excluded it (--filter/-C/per-dir rules, the legacy
-   * --exclude/--include layer, and --max-size/--min-size).  The sender turns
-   * this list into the manifest's protected prefixes so `--delete` leaves the
-   * destination mirror of excluded source paths alone (rsync's default), and
-   * empties it when --delete-excluded opts back into deleting them.  NOT
-   * recorded for --files-from subset pruning (whose delete semantics stay
-   * keep-set-only) or for -R/--files-from relative wire paths.  When
-   * `excluded_mutex` is non-NULL it is taken around every append (the parallel
-   * scanner shares one list across its worker threads). */
+   * USER SELECTION rule excluded it (--filter/-C/per-dir rules and the legacy
+   * --exclude/--include layer).  The sender turns this list into the manifest's
+   * protected prefixes so `--delete` leaves the destination mirror of excluded
+   * source paths alone (rsync's default), and drops it when --delete-excluded
+   * opts back into deleting them.  NOT recorded for --files-from subset pruning
+   * (whose delete semantics derive from the synchronized-directory set) or for
+   * -R/--files-from relative wire paths.  When `excluded_mutex` is non-NULL it
+   * is taken around every append (the parallel scanner shares one list across
+   * its worker threads). */
   ArrayList* excluded_paths;
   mtx_t* excluded_mutex;
+  /* Size-prune protection sink (optional): when non-NULL the scanner appends
+   * the destination-relative path of every entry it skipped because of
+   * --max-size/--min-size.  rsync never deletes a size-skipped source mirror,
+   * even under --delete-excluded, so the sender always transmits this list as
+   * protected prefixes (unlike excluded_paths, which --delete-excluded drops).
+   * Guarded by `excluded_mutex` like excluded_paths. */
+  ArrayList* size_skipped_paths;
+  /* Synchronized-directory sink (optional): when non-NULL the scanner appends
+   * the destination-relative path of every directory it is about to traverse
+   * that lies inside a --files-from listed directory (or of every traversed
+   * directory when there is no list).  The sender sends this set with the delete
+   * manifest so the receiver confines its extras walk to synchronized
+   * directories, exactly like rsync; the receive root is the "." sentinel.
+   * Guarded by `excluded_mutex`. */
+  ArrayList* synced_dirs;
+  /* Delete-plan directory sink (optional): when non-NULL the scanner appends
+   * the destination-relative path of every directory it traverses (except the
+   * receive root).  The per-directory --delete-during/--delete-delay plan
+   * builder uses this to keep an empty in-scope source directory (rsync keeps
+   * it) and to emit its plan after the data stream, when no file frame would
+   * otherwise trigger it.  Guarded by `excluded_mutex`. */
+  ArrayList* plan_dirs;
   /* --ignore-errors: an unreadable directory during the scan is recorded as an
    * I/O error and skipped instead of aborting the scan.  Client-only. */
   bool ignore_io_errors;
@@ -64,6 +129,28 @@ typedef struct {
    * 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
@@ -71,25 +158,14 @@ typedef struct {
 typedef struct FilterNode FilterNode;
 
 typedef struct {
+  /* Scan inputs, copied once at create time.  Everything that is also a
+     ScannerOptions field lives here (with the normalized chunk_size); only
+     scanner-owned bookkeeping stays as direct members below. */
+  ScannerOptions options;
   Queue* directories;
   DIR* current_dir;
   char* current_path;
-  bool use_metadata;
-  unsigned long long chunk_size;
-  char** exclude_patterns;
-  int exclude_count;
-  char** include_patterns;
-  int include_count;
-  unsigned long long max_size;
-  unsigned long long min_size;
-  int max_depth;
   int current_depth;
-  bool follow_symlinks;
-  bool copy_links;
-  bool safe_links;
-  bool copy_unsafe_links;
-  bool checksum;
-  bool one_file_system;
   dev_t root_dev;
   bool failed;
   /* Phase 2 (files-from / filter layer). */
@@ -99,27 +175,13 @@ typedef struct {
   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
+  /* --dirs / -R state for the directory-entry generator (options.dirs 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. */
@@ -169,6 +231,13 @@ bool scanner_same_filesystem(bool one_file_system, dev_t root_device, dev_t entr
  * "/". Exposed so tests can exercise the mapping directly. */
 char* scanner_path_relative(const char* root, const char* fs_path);
 
+/* -R/--relative destination-relative prefix reconstructed from a source spec:
+ * the path after rsync's first '.' path component (the '/./' cut point), with
+ * leading/trailing slashes removed, or the whole spec (normalized) when there
+ * is no cut.  Returns "" for the receive root, or NULL when `spec` is NULL or
+ * allocation fails.  Exposed so tests can exercise the mapping directly. */
+char* scanner_relative_prefix(const char* spec);
+
 ParallelScanner* parallel_scanner_create_with_options(const char* root_directory,
                                                       const ScannerOptions* options,
                                                       ProtocolSession* allocation_session);

src/client/usage.c

@@ -2,6 +2,7 @@
 #include <stdio.h>
 #include <delta.h>
 #include <chunk.h>
+#include "scanner.h"
 
 void print_usage(void) {
   printf("Usage:\n");
@@ -11,36 +12,73 @@ 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, perms, times,\n");
+  printf("                      owner, group, devices and specials; not\n");
+  printf("                      compression/multithreading\n");
+  printf("  -r, --recursive     Recurse into directories (FastSync is always recursive)\n");
   printf("  -n, --dry-run       Show what would be transferred\n");
   printf("  --remove-source-files  Remove regular source files after successful transfer\n");
-  printf("  -p <port>           SSH port (default: 22)\n");
+  printf("  -p, --perms         Preserve permission bits\n");
+  printf("  -t, --times         Preserve modification times\n");
+  printf("  -o, --owner         Preserve owner (uid)\n");
+  printf("  -g, --group         Preserve group (gid)\n");
+  printf("  --ssh-port <port>   SSH port (default: 22)\n");
+  printf("  -e, --rsh <command>  Remote shell to launch on the client for the SSH\n");
+  printf("                      transport (default: ssh).  The command may include\n");
+  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("  NOTE: the FastSync batch format is NOT interoperable with rsync's batch\n");
+  printf("  files (different container format); do not mix the two tools.\n");
   printf("  --delete            Delete files on receiver not in source\n");
   printf("                      (default timing: delete only after the whole\n");
   printf("                      transfer has succeeded)\n");
   printf("  --delete-before     Delete extras before the transfer starts\n");
   printf("                      (implies --delete)\n");
-  printf("  --delete-during     Delete extras once the keep-set manifest is known,\n");
-  printf("                      before the data is applied (implies --delete)\n");
+  printf("  --delete-during     Delete a directory's extras as that directory is\n");
+  printf("                      processed (implies --delete)\n");
   printf("  --del               Alias for --delete-during\n");
-  printf("  --delete-delay      Delete extras only after a successful transfer\n");
-  printf("                      (implies --delete)\n");
+  printf("  --delete-delay      Record the extras during the scan but remove them\n");
+  printf("                      only after a successful transfer (implies --delete)\n");
   printf("  --delete-after      Delete only after the whole transfer succeeded\n");
   printf("                      (the default --delete timing; implies --delete)\n");
   printf("  --delete-excluded   Also delete destination files that were excluded on\n");
   printf("                      the source (default protects them, matching rsync)\n");
-  printf("  --max-delete=NUM    Never delete more than NUM destination entries per run;\n");
-  printf("                      if the extras would exceed NUM, nothing is deleted and\n");
-  printf("                      the run fails with a clear error (implies --delete only\n");
-  printf("                      when used with it)\n");
+  printf("  --max-delete=NUM    Delete at most NUM destination entries per run; if the\n");
+  printf("                      extras exceed NUM, the rest are skipped and the run is\n");
+  printf("                      reported as partial (exit 25, matching rsync).  Only\n");
+  printf("                      applies together with --delete\n");
   printf("  --ignore-errors     Continue (and still delete) when a source directory is\n");
   printf("                      unreadable during the scan, instead of aborting with no\n");
   printf("                      deletion\n");
@@ -52,9 +90,8 @@ void print_usage(void) {
   printf("                      entry's destination mirror receiver-side.  Independent of\n");
   printf("                      --delete (it does not imply --delete; a non-empty directory\n");
   printf("                      mirror is removed only with --force or --delete)\n");
-  printf("  --prune-empty-dirs  Do not transfer empty directory entries (--dirs mode);\n");
-  printf("                      recursive transfers never send empty dirs.  rsync's -m\n");
-  printf("                      short form stays FastSync multithreading\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");
@@ -70,20 +107,23 @@ void print_usage(void) {
   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("  --exclude <pattern>, --exclude=<pattern>  Exclude files matching pattern\n");
+  printf("  --include <pattern>, --include=<pattern>  Only include files matching pattern\n");
+  printf("  --exclude-from <file>, --exclude-from=<file>  Read exclude patterns from file\n");
+  printf("  --include-from <file>, --include-from=<file>  Read include patterns from file\n");
   printf("  --files-from <file> Read the source file list from FILE (paths relative to the "
          "source root)\n");
   printf("  -0, --from0       Entries in --files-from are NUL-delimited\n");
-  printf("  --filter=RULE     rsync-style filter rule (+/- include/exclude; repeatable; the\n");
-  printf("                    rsync -f short form conflicts with FastSync sendfile -f)\n");
+  printf("  -f, --filter=RULE rsync-style filter rule: exclude/- include/+ hide/H show/S\n");
+  printf("                  protect/P risk/R merge/. dir-merge/: clear/! with modifiers\n");
+  printf("                  (repeatable; --filter=RULE and -f RULE / -f=RULE both work)\n");
   printf("  -C, --cvs-exclude Auto-ignore common CVS/SCM files (.git/, .svn/, *.o, *~, ...)\n");
-  printf("  -F                Apply per-directory .rsync-filter files during the scan\n");
+  printf("  -F                Apply per-directory .rsync-filter files; repeated -FF also\n");
+  printf("                  excludes the .rsync-filter files themselves\n");
   printf("  --max-size <n>      Skip files larger than n bytes\n");
   printf("  --min-size <n>      Skip files smaller than n bytes\n");
-  printf("  --max-alloc <SIZE>  Maximum single allocation (default: 1G)\n");
+  printf("  --max-alloc <SIZE>  Maximum single allocation (default: 1G; 0 = no limit,\n");
+  printf("                      matching rsync)\n");
   printf("  --incremental       Skip files unchanged since last transfer\n");
   printf("  --size-only         Skip incremental files matching in size, ignoring mtime\n");
   printf("  -I, --ignore-times  Transfer files even when size and mtime match\n");
@@ -98,77 +138,192 @@ void print_usage(void) {
   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("                    --checksum compares.  Accepted: xxh128 (default), xxh3, xxh64\n");
+  printf("                    (aka xxhash), md5, md4, sha1, or none.  A two-name\n");
+  printf("                    'transfer,pre-transfer' form is accepted like rsync; 'none' as\n");
+  printf("                    the pre-transfer algorithm is rejected with --checksum\n");
+  printf("  --checksum-seed <num>  Seed for the whole-file xxHash digest (and the delta\n");
+  printf("                    block strong hash, low 32 bits); md5 ignores the seed.  A seed\n");
+  printf("                    of 0 (the default) is randomized per transfer, exactly like\n");
+  printf("                    rsync, and the chosen seed is sent to the receiver\n");
   printf("  --delta             Delta transfer for changed files (requires --incremental)\n");
   printf("  -W, --whole-file    Transfer changed files without delta processing\n");
+  printf("  --no-whole-file     rsync spelling that clears -W/--whole-file\n");
   printf("  -y, --fuzzy         Use a similar-named file already in the destination\n");
   printf("                    directory as the delta basis when the destination has no\n");
   printf("                    usable file at the exact path (saves bandwidth; implies\n");
   printf("                    --incremental and --delta; inert with --whole-file,\n");
   printf("                    --no-delta, or --no-incremental)\n");
   printf("  --no-fuzzy          Disable --fuzzy\n");
-  printf("  --delta-block <n>   Delta block size in bytes (default: %d)\n",
-         DELTA_BLOCK_SIZE_DEFAULT);
+  printf("  -B <n>, --block-size <n>, --delta-block <n>\n");
+  printf("                    Delta block size in bytes (default: %d)\n", DELTA_BLOCK_SIZE_DEFAULT);
   printf("  --delta-max <n>     Max file size for delta transfer (default: %llu)\n",
          DELTA_MAX_FILE_SIZE);
-  printf("  -m                  Enable multithreading\n");
-  printf("  -s                  Enable chunk serialization\n");
-  printf("  --secluded-args    Accept rsync compatibility option (no effect)\n");
-  printf("  -f                  Enable sendfile (TCP only, not with -c or -s)\n");
-  printf("  --compress-choice <alg>  Compression algorithm (default: zstd)\n");
+  printf("  -j, --threads[=N]   Enable the multithreaded scanner/loader/sender\n");
+  printf("                      pipeline; N (1-%d) sets the parallel scanner worker\n",
+         MAX_SCANNER_THREADS);
+  printf("                      count (bare -j/--threads uses the default)\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("                      -f is bound to --filter, not --sendfile)\n");
+  printf("  --compress-choice <alg>  Compression algorithm: zstd (default), lz4, zlib,\n");
+  printf("                    zlibx, none, or auto\n");
   printf("  --zc <alg>          Alias for --compress-choice\n");
   printf("  -v, --verbose       Enable debug logging\n");
   printf("  -q, --quiet         Suppress non-error output\n");
   printf("  --debug=FLAGS       Fine-grained debug logging (use --debug=help for flags)\n");
-  printf("  --info=FLAGS        Fine-grained info: copy,misc,skip,stats,all,none\n");
-  printf("                      none suppresses info even with --verbose\n");
-  printf("  -M, --preserve      Preserve file metadata\n");
+  printf("  --info=FLAGS        Fine-grained info: copy,name,misc,skip,stats,all,none\n");
+  printf("                      (use --info=help for flags; none suppresses --verbose)\n");
+  printf("  --preserve          Preserve permissions and times (= -pt; long form only)\n");
+  printf("  --no-perms          Negate -p/--perms\n");
+  printf("  --no-times          Negate -t/--times\n");
+  printf("  --no-owner          Negate -o/--owner\n");
+  printf("  --no-group          Negate -g/--group\n");
+  printf("  --no-preserve       Disable metadata preservation (negates --preserve)\n");
   printf("  -E, --executability Preserve executable permission bits\n");
-  printf("  --chmod <changes>   Modify transferred permissions (rsync syntax)\n");
+  printf("  -U, --atimes        Preserve access times\n");
+  printf("  -N, --crtimes       Capture birth time; cannot be applied (documented\n");
+  printf("                      divergence)\n");
+  printf("  -X, --xattrs        Preserve user extended attributes (user.* only;\n");
+  printf("                      privileged security.*/trusted.* namespaces are\n");
+  printf("                      never captured or applied)\n");
+  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 -o/--owner, -g/--group, or an\n");
+  printf("                      explicit identity flag (--chown/--usermap/--groupmap/\n");
+  printf("                      --copy-as); --numeric-ids only changes how ids map\n");
+  printf("  --no-super          Forbid those super-user activities even when the\n");
+  printf("                      receiver is running as root\n");
+  printf(
+      "  --chmod <changes>   Modify new/transferred permissions (rsync syntax; implies no -p)\n");
+  printf("  --numeric-ids       Map uid/gid by id instead of by name (a modifier, not\n");
+  printf("                      an ownership request: combine with -o/-g or a map)\n");
+  printf("  --usermap=MAP       Map usernames when applying ownership: comma-separated\n");
+  printf("                      FROM:TO rules, first match wins.  FROM is a name (from\n");
+  printf("                      the source), an id, an inclusive LOW-HIGH range, *\n");
+  printf("                      (any id), or empty (ids with no name).  TO is an id, *\n");
+  printf("                      (current user), or a name resolved on the receiver.\n");
+  printf("                      e.g. 0-99:nobody,*:normal   (cannot mix with --chown)\n");
+  printf("  --groupmap=MAP      Map group names when applying ownership (same syntax)\n");
+  printf("  --chown=USER:GROUP  Override the ownership of transferred files.  Forms:\n");
+  printf("                      USER:GROUP, USER (owner only), :GROUP (group only); a\n");
+  printf("                      value of * means the current/root user as appropriate.\n");
+  printf("                      Names resolve on the source machine; @N for numerics.\n");
+  printf("                      (Implies owner/group metadata; -M now means rsync's\n");
+  printf("                      --remote-option.)\n");
+  printf("  --copy-as=USER[:GROUP]  Force every written entry (files, dirs, symlinks\n");
+  printf("                      and special nodes) to USER[:GROUP], resolved on the\n");
+  printf("                      source machine like --chown.  Requires a privileged\n");
+  printf("                      (root) receiver and implies owner/group metadata; an\n");
+  printf("                      unprivileged receiver refuses the transfer.  Never\n");
+  printf("                      switches process credentials (safe-subset; see\n");
+  printf("                      RSYNC_COMPAT.md).  A daemon refuses it.\n");
   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("  --port <n>          Alias for --server-port\n");
+  printf("  --password-file <f> Authenticate a host::module/path daemon destination.\n");
+  printf("                      FastSync-native SCRAM/PBKDF2 credential scheme (NOT\n");
+  printf("                      rsync's --password-file): the file's first user:password\n");
+  printf("                      line supplies the username and password; no password or\n");
+  printf("                      reusable digest is sent (keep the file mode 0600)\n");
+  printf("  --no-motd           Suppress display of the daemon's MOTD (the server\n");
+  printf("                      still sends it; the client just does not show it)\n");
   printf("  --bwlimit <KB/s>    Bandwidth limit in kilobytes per second\n");
   printf("  --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("  --contimeout <sec>  Connection timeout in seconds (default: 10)\n");
-  printf("  --backup            Backup existing files before overwriting\n");
+  printf("  --timeout <sec>     I/O timeout in seconds (default: 0 = disabled, matching\n");
+  printf("                      rsync).  0 disables it; --no-timeout is the same\n");
+  printf("  --contimeout <sec>  Connection timeout in seconds (default: 60, matching\n");
+  printf("                      rsync); 0 disables it (--no-contimeout)\n");
+  printf("  --stop-after=MINS   Stop the transfer after MINS minutes (a positive\n");
+  printf("                      integer); whatever was already transferred is kept\n");
+  printf("  --stop-at=TIME      Stop at an absolute time.  Accepts rsync's date form\n");
+  printf("                      (Y-M-DTh:m, Y/M/DTh:m, abbreviable fields such as 12-31,\n");
+  printf("                      14:00, :59, 1) plus FastSync's HH:MM[:SS] and now+N[smhd]\n");
+  printf("                      (a time already in the past stops the transfer\n");
+  printf("                      immediately; client-only).  An early stop skips the late\n");
+  printf("                      --delete keep-set so it cannot delete source mirrors that\n");
+  printf("                      were not yet scanned\n");
+  printf("  --address <ip>      Bind the outgoing client socket to this source address\n");
+  printf("  -4, --ipv4          Force IPv4 for destination resolution\n");
+  printf("  -6, --ipv6          Force IPv6 for destination resolution\n");
+  printf("  --sockopts=OPTS     Comma-separated OPT=VAL socket options applied before connect:\n");
+  printf("                      TCP_NODELAY, SO_KEEPALIVE, SO_RCVBUF, SO_SNDBUF, SO_REUSEADDR\n");
+  printf("  -b, --backup        Backup existing files before overwriting\n");
   printf("  --backup-dir <dir>  Directory for backups (requires --backup)\n");
   printf("  --suffix <str>      Backup suffix (default: ~)\n");
   printf("  --stats             Print transfer statistics at end\n");
   printf("  -i, --itemize-changes  Print an rsync-style per-file change line\n");
-  printf("  --out-format=FORMAT Output format for changed files (%%f %%n %%l %%b %%M %%%%)\n");
+  printf("  --out-format=FORMAT Output format (%%f %%n %%l %%b %%c %%C %%i %%M %%%%)\n");
   printf("  --list-only         List source files instead of transferring\n");
   printf("  --log-file-format=FORMAT  Per-file log line format (needs --log-file)\n");
   printf("  -h, --human-readable  Print byte sizes in human-readable form\n");
   printf("  --max-depth <n>     Maximum directory depth (0=unlimited)\n");
   printf("  -x, --one-file-system  Do not cross filesystem boundaries\n");
-  printf("  --log-file <path>   Write log messages to file\n");
+  printf("  --log-file <path>, --log-file=<path>  Write log messages to file\n");
   printf("  --stderr=MODE       Route logging to stderr: errors or all\n");
   printf("  --partial           Keep partial files on interrupted transfer\n");
   printf("  --partial-dir <dir> Directory for partial files\n");
-  printf("  --temp-dir <dir>    Scratch dir for temp files before atomic install\n");
+  printf("  -T, --temp-dir <dir>  Scratch dir for temp files before atomic install.\n");
+  printf("                      Confined to the receive root: a relative dir resolves below\n");
+  printf("                      it and an absolute/traversal dir is rejected.  The dir must\n");
+  printf("                      already exist; a different filesystem falls back to a\n");
+  printf("                      non-atomic copy instead of aborting\n");
   printf("  --fastsync-server-path <path>\n");
   printf("                      Path to fastsync-server on remote (default: fastsync-server)\n");
-  printf(
-      "  --old-args          Disable safe SSH command argument quoting (legacy compatibility)\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.  SSH\n");
+  printf("                      transport ONLY (user@host:path): a daemon (host::module) or\n");
+  printf("                      local TCP destination rejects it (no remote command line to\n");
+  printf("                      append to).  Repeatable; each value is single-quote-escaped on\n");
+  printf("                      the remote command line; empty values and values with control\n");
+  printf("                      characters are rejected; -M OPT, -M=OPT and\n");
+  printf("                      --remote-option=OPT work\n");
+  printf("  --trust-sender      RECEIVER-LOCAL policy: trust the remote sender's file list\n");
+  printf("                      and skip the receiver's own up-front path-traversal/\n");
+  printf("                      containment re-validation of the incoming list (fewer checks,\n");
+  printf("                      faster, potentially unsafe).  It is never sent to the peer, so\n");
+  printf("                      for a push it must be enabled on the receiving SERVER\n");
+  printf("                      (fastsync-server --trust-sender) or forwarded with\n");
+  printf("                      -M--trust-sender; the client flag alone has no effect\n");
   printf("  -l, --links         Copy symlinks as symlinks\n");
-  printf("  --copy-links        Transform symlinks into referent files\n");
-  printf("  --safe-links        Skip symlinks that point outside transfer tree\n");
-  printf("  --copy-unsafe-links  Only transform unsafe symlinks into referent files\n");
+  printf("  -L, --copy-links    Transform symlinks into referent files\n");
+  printf("  --safe-links        Skip symlinks whose target points outside the tree\n");
+  printf("  --copy-unsafe-links Copy unsafe symlinks (outside tree) as referent files\n");
+  printf("  -k, --copy-dirlinks Transform symlinks to directories into real dirs\n");
+  printf("  -K, --keep-dirlinks  Keep an existing symlink-to-dir as that dir\n");
+  printf("  --munge-links       Munge stored symlink targets (/rsyncd-munged/) on the receiver\n");
+  printf("  -H, --hard-links    Preserve hard-link relationships across the transfer\n");
   printf("  -S, --sparse        Handle sparse files efficiently\n");
+  printf(
+      "  -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, sockets) on the destination\n");
+  printf("  --copy-devices      Copy a source device's content as a regular file instead\n");
+  printf("  --write-devices     Write received data into an existing destination device node\n");
   printf("  --inplace           Update files in-place (no temp+rename)\n");
+  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");
@@ -176,7 +331,9 @@ void print_usage(void) {
   printf("  --fsync             Fsync every written file before publication\n");
   printf("  --compress-level <n>    Compression level (default: 5)\n");
   printf("  --zl <n>             Alias for --compress-level\n");
-  printf("  --skip-compress=LIST    Skip compression for comma-separated suffixes\n");
+  printf("  --skip-compress=LIST    Skip compression for suffixes in LIST (separated by\n");
+  printf("                      '/' as in rsync, or ','); a leading dot is optional.  The\n");
+  printf("                      default is rsync 3.4.1's built-in skip-compress list\n");
   printf("  --compress-threads <n> Compression worker threads (requires zstd threaded support)\n");
   printf("  --no-OPTION         Disable a supported boolean option\n");
   printf("  --help              Show this help\n");
@@ -184,7 +341,20 @@ void print_usage(void) {
 }
 
 void print_debug_usage(void) {
-  printf("Supported debug flags: IO,PROTO,PACK,UTIL,ALL,NONE\n");
+  printf("Emitting debug flags: IO,PROTO,PACK,UTIL,ALL,NONE\n");
+  printf("Also accepted for rsync CLI parity (silent): ACL,BACKUP,BIND,CHDIR,\n");
+  printf("CONNECT,CMD,DEL,DELTASUM,DUP,EXIT,FILTER,FLIST,FUZZY,GENR,HASH,HLINK,\n");
+  printf("ICONV,NSTR,OWN,RECV,SEND,TIME.\n");
   printf("Flags may be comma-separated, for example: --debug=io,proto\n");
-  printf("Other rsync debug flags are unsupported and rejected.\n");
+  printf("An optional level suffix is accepted (e.g. --debug=io2); level 0\n");
+  printf("silences that item.  Unknown names are rejected.\n");
+}
+
+void print_info_usage(void) {
+  printf("Emitting info flags: COPY,NAME,MISC,SKIP,STATS,ALL,NONE\n");
+  printf("Also accepted for rsync CLI parity (silent): BACKUP,DEL,FLIST,MOUNT,\n");
+  printf("NONREG,PROGRESS,REMOVE,SYMSAFE.\n");
+  printf("Flags may be comma-separated, for example: --info=name,stats\n");
+  printf("An optional level suffix is accepted (e.g. --info=stats2); level 0\n");
+  printf("silences that item.  Unknown names are rejected.\n");
 }

src/client/usage.h

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

src/server/receiver.c

@@ -1,15 +1,20 @@
 #include "receiver.h"
 
+#include "charset.h"
 #include "chunk.h"
 #include "config.h"
+#include "delete_plan.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 <string.h>
 #include <sys/stat.h>
+#include <time.h>
 
 bool receiver_outcomes_append(ReceiverOutcomes* outcomes, unsigned char code) {
   if (!outcomes)
@@ -40,17 +45,49 @@ void receiver_outcomes_destroy(ReceiverOutcomes* outcomes) {
 /* End-of-transfer success frame.  When --remove-source-files was negotiated
    each processed data file is acknowledged first (STATUS_NEXT = written,
    STATUS_OK = skipped) so the sender never removes a source the receiver did
-   not actually store.  The frame always ends with a plain STATUS_OK. */
-bool receiver_send_final_success(int fd, const Config* config, const ReceiverOutcomes* outcomes) {
+   not actually store.  The frame ends with `final_status` (STATUS_OK, or
+   STATUS_DELETE_LIMIT when a --max-delete commit was capped). */
+bool receiver_send_final_success(int fd, const Config* config, const ReceiverOutcomes* outcomes,
+                                 Status final_status) {
   if (!config->remove_source_files)
-    return send_status(fd, STATUS_OK);
+    return send_status(fd, final_status);
   size_t count = outcomes ? outcomes->count : 0;
   for (size_t i = 0; i < count; i++) {
     Status per_file = outcomes->entries[i] == FILE_SAVE_WRITTEN ? STATUS_NEXT : STATUS_OK;
     if (!send_status(fd, per_file))
       return false;
   }
-  return send_status(fd, STATUS_OK);
+  return send_status(fd, final_status);
+}
+
+bool receiver_send_stats_frame(int fd, const Config* config, const ReceiverStats* stats,
+                               const struct ArrayList* would_delete) {
+  if (!config->report_stats)
+    return true;
+  ReceiverStats local;
+  memset(&local, 0, sizeof(local));
+  const ReceiverStats* out = stats ? stats : &local;
+  size_t count = would_delete ? (size_t)would_delete->size : 0;
+  if (count > (size_t)MAX_MANIFEST_ENTRIES)
+    count = MAX_MANIFEST_ENTRIES;
+  ReceiverStats record = *out;
+  record.would_delete_count = count;
+  if (!send_status(fd, STATUS_STATS) || !format_stats_send(fd, &record) ||
+      !send_int(fd, (int)count))
+    return false;
+  for (size_t i = 0; i < count; i++) {
+    const char* path = (const char*)would_delete->items[i];
+    if (!send_wire_str(fd, path ? path : ""))
+      return false;
+  }
+  return true;
+}
+
+/* Add a delete commit's tally to the sink's end-of-transfer wire counters (when
+   the sink reports them).  Runs on the receiving thread, so no locking. */
+static void receiver_tally_deleted(const ReceiverSink* sink, size_t deleted) {
+  if (sink && sink->stats && deleted > 0)
+    sink->stats->deleted_files += deleted;
 }
 
 static bool receiver_process_chunk(Chunk* chunk, const ReceiverSink* sink) {
@@ -72,13 +109,32 @@ 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;
@@ -92,7 +148,11 @@ static bool receiver_process_batch(Config* config, int file_descriptor) {
       send_status(file_descriptor, STATUS_ERROR);
       return false;
     }
-    if (!utils_valid_batch_path(check_path)) {
+    /* --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;
@@ -128,8 +188,95 @@ static bool receiver_process_batch(Config* config, int file_descriptor) {
   return true;
 }
 
+/* ---- Anti-slowloris connection bounds ----
+ * A legitimate transfer either streams data frames continuously or, when it
+ * must pause, sends STATUS_KEEPALIVE so the peer sees the connection is alive.
+ * An attacker can therefore squat on a connection slot indefinitely by sending
+ * only keepalives under the per-message timeout.  Two CLOCK_MONOTONIC bounds
+ * defeat that without ever punishing a real transfer:
+ *
+ *   MAX_SESSION_IDLE_SEC (1 h): the longest a stream may make no forward
+ *     progress.  Data/status frames count as progress and refresh the timer;
+ *     keepalives do not.  One hour is far longer than any real pause between
+ *     data frames, yet small enough to reap a slowloris well before the 24 h
+ *     session cap.
+ *
+ *   MAX_SESSION_WALL_SEC (24 h): an absolute ceiling on one connection's
+ *     lifetime as defense-in-depth against a trickle of progress frames that
+ *     resets the idle timer just below its limit.  Larger than any plausible
+ *     single transfer while still bounding resource occupancy.
+ *
+ * Both are wall-clock deltas, so the per-message poll timeout (60 s by default,
+ * or --timeout) can never fool them, and both the single-threaded and the -m
+ * receiver paths (receiver_process_pending) share the same logic. */
+#define MAX_SESSION_IDLE_SEC 3600u
+#define MAX_SESSION_WALL_SEC 86400u
+
+static unsigned int g_max_session_idle_sec = MAX_SESSION_IDLE_SEC;
+static unsigned int g_max_session_wall_sec = MAX_SESSION_WALL_SEC;
+
+void receiver_set_time_limits(unsigned int idle_sec, unsigned int wall_sec) {
+  g_max_session_idle_sec = idle_sec;
+  g_max_session_wall_sec = wall_sec;
+}
+
+void receiver_reset_time_limits(void) {
+  g_max_session_idle_sec = MAX_SESSION_IDLE_SEC;
+  g_max_session_wall_sec = MAX_SESSION_WALL_SEC;
+}
+
+bool receiver_time_limit_exceeded(const struct timespec* session_start,
+                                  const struct timespec* last_progress,
+                                  const struct timespec* now) {
+  if (!session_start || !last_progress || !now)
+    return false;
+  if (now->tv_sec - session_start->tv_sec >= (time_t)g_max_session_wall_sec)
+    return true;
+  if (now->tv_sec - last_progress->tv_sec >= (time_t)g_max_session_idle_sec)
+    return true;
+  return false;
+}
+
+/* A frame proves forward progress only when it cannot be fabricated for free.
+ * KEEPALIVE/ABORT are pure liveness, and CHECK_BATCH/DIR_TIMES may carry zero
+ * entries, so a peer must not be able to hold a connection slot forever by
+ * merely emitting empty frames. */
+static bool status_counts_as_progress(Status status) {
+  switch (status) {
+  case STATUS_KEEPALIVE:
+  case STATUS_ABORT:
+  case STATUS_CHECK_BATCH:
+  case STATUS_DIR_TIMES:
+    return false;
+  default:
+    return true;
+  }
+}
+
+/* Refresh the progress timestamp for a forward-moving frame and enforce the
+ * bounds above.  Returns false when the connection must be dropped; the
+ * terminal STATUS_ERROR is sent only when the sink owns error reporting (the
+ * -m sink sets send_error=false so the main thread emits exactly one). */
+static bool receiver_note_status(const struct timespec* session_start,
+                                 struct timespec* last_progress, Status status, int file_descriptor,
+                                 const ReceiverSink* sink) {
+  struct timespec now;
+  if (clock_gettime(CLOCK_MONOTONIC, &now) != 0)
+    now = *last_progress;
+  if (status_counts_as_progress(status))
+    *last_progress = now;
+  if (!receiver_time_limit_exceeded(session_start, last_progress, &now))
+    return true;
+  log_message(LOG_LEVEL_ERROR,
+              "Receive session exceeded its time bound (idle %us / total %us); aborting connection",
+              g_max_session_idle_sec, g_max_session_wall_sec);
+  if (!sink || sink->send_error)
+    send_status(file_descriptor, STATUS_ERROR);
+  return false;
+}
+
 int receiver_process(Config* config, int file_descriptor, const ReceiverSink* sink) {
-  return receiver_process_pending(config, file_descriptor, sink, NULL);
+  return receiver_process_pending(config, file_descriptor, sink, NULL, NULL);
 }
 
 /* Runs the whole receive loop.  The delete manifest may legitimately arrive
@@ -143,18 +290,36 @@ int receiver_process(Config* config, int file_descriptor, const ReceiverSink* si
    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) {
+                             DeleteManifest** pending_manifest, DeletePlanSession** pending_plans) {
   Status status;
   if (!receive_status(file_descriptor, &status))
     return -1;
+  /* Wall-clock (=CLOCK_MONOTONIC) anti-slowloris bookkeeping.  session_start is
+   * fixed for the whole connection; last_progress is refreshed by every frame
+   * that is not a keepalive/abort. */
+  struct timespec session_start;
+  struct timespec last_progress;
+  clock_gettime(CLOCK_MONOTONIC, &session_start);
+  last_progress = session_start;
+  if (!receiver_note_status(&session_start, &last_progress, status, file_descriptor, sink))
+    return -1;
   bool early_delete = config_delete_timing_early(config);
+  bool per_dir_delete = config_delete_timing_per_dir(config);
   /* Parked keep-set for the late/commit timing.  Every exit path below frees it
      exactly once; the only exception is the successful FINISHED handoff, which
      transfers ownership to *pending_manifest (used by the -m receiver). */
   DeleteManifest* deferred_manifest = NULL;
+  /* Per-directory delete session for --delete-during/--delete-delay.  During the
+     loop it applies plans inline (during) or snapshots their extras (delay); on
+     a successful FINISHED it is either committed here or handed to
+     *pending_plans so the -m caller commits after its disk writer drained. */
+  DeletePlanSession* plan_session = NULL;
+  bool delete_limit_noted = false;
   while (status == STATUS_NEXT || status == STATUS_CHUNK || status == STATUS_CHECK ||
          status == STATUS_KEEPALIVE || status == STATUS_ABORT || status == STATUS_CHECK_BATCH ||
-         status == STATUS_MKDIR || status == STATUS_MANIFEST) {
+         status == STATUS_MKDIR || status == STATUS_MANIFEST || status == STATUS_HARDLINK ||
+         status == STATUS_SYMLINK || status == STATUS_SPECIAL || status == STATUS_DIR_TIMES ||
+         status == STATUS_DELETE_PLAN) {
     if (status == STATUS_KEEPALIVE) {
       if (!send_status(file_descriptor, STATUS_KEEPALIVE))
         goto fail;
@@ -165,10 +330,19 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
       goto fail;
     }
     if (status == STATUS_CHECK) {
-      bool skipped;
-      File* file = receive_incremental_check(file_descriptor, config, &skipped);
-      if (!skipped && (!file || !sink->store_file(file, sink->context)))
+      bool skipped = false;
+      bool would_transfer = false;
+      File* file = receive_incremental_check_ex(file_descriptor, config, &skipped, &would_transfer);
+      if (config->dry_run) {
+        /* Server-contacting --dry-run: the reply has already been sent
+           (STATUS_OK = up to date, STATUS_DRY_RUN_TRANSFER = would transfer) and
+           nothing may be stored.  Both flags false means a genuine protocol
+           error (STATUS_ERROR already sent or sent by receive_error below). */
+        if (!skipped && !would_transfer)
           goto receive_error;
+      } else if (!skipped && (!file || !sink->store_file(file, sink->context))) {
+        goto receive_error;
+      }
     } else if (status == STATUS_CHUNK) {
       Chunk* chunk = receive_chunk_data(file_descriptor, config);
       if (!chunk || !receiver_process_chunk(chunk, sink))
@@ -178,33 +352,69 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
         goto fail;
       goto next_status;
     } else if (status == STATUS_MKDIR) {
-      File* dir = file_receive_directory(file_descriptor);
+      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;
+      if (config->dry_run) {
+        /* Server-contacting --dry-run mutates nothing, so a keep-set manifest
+           is consumed and discarded.  The early-delete mode still needs its ACK
+           so a sender blocked on the delete handshake is not left hanging.
+           When would-delete reporting is armed, enumerate (read-only) the
+           destination extras so the terminal STATUS_STATS frame can list them. */
+        if (config->use_delete && sink->would_delete) {
+          size_t count = 0;
+          if (!manifest_would_delete_list(config, manifest, sink->would_delete, &count))
+            log_message(LOG_LEVEL_WARNING, "dry-run: could not enumerate would-delete paths");
+        }
         delete_manifest_free(manifest);
-        if (!deletion_ok) {
+        if (early_delete && !send_status(file_descriptor, STATUS_OK))
+          goto fail;
+        goto next_status;
+      }
+      if (early_delete) {
+        /* --delete-before: the whole-tree manifest is authoritative the moment
+           it arrives, before any file data.  Delete now and acknowledge so the
+           sender only starts streaming once the deletion committed (or failed).
+           A later transfer failure does not restore these deletions.  A
+           --max-delete-capped commit still succeeds and the transfer proceeds;
+           the terminal success frame reports the cap. */
+        size_t deleted = 0;
+        DeleteCommitResult deletion = (config->use_delete || config->delete_missing_args)
+                                          ? manifest_delete_all_counted(config, manifest, &deleted)
+                                          : DELETE_COMMIT_OK;
+        receiver_tally_deleted(sink, deleted);
+        delete_manifest_free(manifest);
+        if (deletion == DELETE_COMMIT_ERROR) {
           send_status(file_descriptor, STATUS_ERROR);
           goto fail;
         }
+        if (deletion == DELETE_COMMIT_LIMIT_REACHED && sink->note_delete_limit)
+          sink->note_delete_limit(sink->context);
         if (!send_status(file_descriptor, STATUS_OK))
           goto fail;
       } else if (config->use_delete || config->delete_missing_args) {
-        /* Plain --delete / --delete-after / --delete-delay and the
-           --delete-missing-args exact-path deletions: hold the manifest and
-           commit it only after STATUS_FINISHED. */
+        /* Plain --delete / --delete-after and the --delete-missing-args
+           exact-path deletions: hold the manifest and commit it only after
+           STATUS_FINISHED.  The per-directory modes never send this frame. */
         if (deferred_manifest) {
           log_message(LOG_LEVEL_ERROR, "Received a second delete manifest");
           delete_manifest_free(deferred_manifest);
@@ -218,6 +428,23 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
         delete_manifest_free(manifest);
       }
       goto next_status;
+    } else if (status == STATUS_DELETE_PLAN) {
+      if (!per_dir_delete) {
+        log_message(LOG_LEVEL_ERROR, "Received a per-directory delete plan without a per-dir "
+                                     "delete timing");
+        send_status(file_descriptor, STATUS_ERROR);
+        goto fail;
+      }
+      if (!plan_session)
+        plan_session = delete_plan_session_create(config);
+      if (!plan_session || delete_plan_session_receive(plan_session, config, file_descriptor) != 0)
+        goto fail;
+      if (delete_plan_session_limit_reached(plan_session) && !delete_limit_noted &&
+          sink->note_delete_limit) {
+        sink->note_delete_limit(sink->context);
+        delete_limit_noted = true;
+      }
+      goto next_status;
     } else {
       File* file = file_receive(config, file_descriptor);
       if (!file) {
@@ -230,6 +457,8 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
   next_status:
     if (!receive_status(file_descriptor, &status))
       goto receive_error;
+    if (!receiver_note_status(&session_start, &last_progress, status, file_descriptor, sink))
+      goto fail;
   }
   if (status != STATUS_FINISHED) {
     log_message(LOG_LEVEL_ERROR, "Did not receive FINISHED Status");
@@ -249,13 +478,45 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
       *pending_manifest = deferred_manifest;
       deferred_manifest = NULL;
     } else {
-      bool deletion_ok = manifest_delete_all(config, deferred_manifest);
+      size_t deleted = 0;
+      DeleteCommitResult deletion =
+          manifest_delete_all_counted(config, deferred_manifest, &deleted);
+      receiver_tally_deleted(sink, deleted);
       delete_manifest_free(deferred_manifest);
       deferred_manifest = NULL;
-      if (!deletion_ok) {
+      if (deletion == DELETE_COMMIT_ERROR) {
         send_status(file_descriptor, STATUS_ERROR);
         goto fail;
       }
+      if (deletion == DELETE_COMMIT_LIMIT_REACHED && sink->note_delete_limit)
+        sink->note_delete_limit(sink->context);
+    }
+  }
+  /* Per-directory deletion: --delete-during already applied each plan inline, so
+     this only finishes the missing-args deletions; --delete-delay committed
+     nothing yet and applies its decompressed snapshot here.  The -m receiver
+     hands the session to its caller instead, which commits after the disk
+     writer drained. */
+  if (plan_session) {
+    if (pending_plans) {
+      *pending_plans = plan_session;
+      plan_session = NULL;
+    } else if (config->dry_run) {
+      /* Central dry-run no-op: never commit a deletion for a -n run. */
+      delete_plan_session_destroy(plan_session);
+      plan_session = NULL;
+    } else {
+      DeleteCommitResult deletion = delete_plan_session_commit(plan_session, config);
+      bool limit = delete_plan_session_limit_reached(plan_session);
+      receiver_tally_deleted(sink, delete_plan_session_deleted(plan_session));
+      delete_plan_session_destroy(plan_session);
+      plan_session = NULL;
+      if (deletion == DELETE_COMMIT_ERROR) {
+        send_status(file_descriptor, STATUS_ERROR);
+        goto fail;
+      }
+      if (limit && !delete_limit_noted && sink->note_delete_limit)
+        sink->note_delete_limit(sink->context);
     }
   }
   if (sink->send_success) {
@@ -270,11 +531,14 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
 
 fail:
   /* Failure exits that must not (or already did) report a STATUS_ERROR.  The
-     parked keep-set is dropped: never commit a deletion for a failed stream. */
+     parked keep-set/session is dropped: never commit a deletion for a failed
+     stream. */
   if (deferred_manifest) {
     delete_manifest_free(deferred_manifest);
     deferred_manifest = NULL;
   }
+  if (plan_session)
+    delete_plan_session_destroy(plan_session);
   return -1;
 
 receive_error:
@@ -282,6 +546,8 @@ receive_error:
     delete_manifest_free(deferred_manifest);
     deferred_manifest = NULL;
   }
+  if (plan_session)
+    delete_plan_session_destroy(plan_session);
   if (sink->send_error)
     send_status(file_descriptor, STATUS_ERROR);
   return -1;
@@ -292,20 +558,54 @@ receive_error:
 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;
+  /* Set when a --max-delete commit was capped; the terminal frame then carries
+     STATUS_DELETE_LIMIT so the sender exits 25 like rsync. */
+  bool delete_limit_reached;
+  /* End-of-transfer wire counters (protocol 2.25.0) and the -n/--dry-run
+     --delete would-delete path list collected while processing the manifest. */
+  ReceiverStats stats;
+  ArrayList* would_delete;
 } 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) {
+  if (context->config->dry_run) {
+    /* Defense in depth: a dry-run receiver mutates nothing even if a data
+       frame reaches the sink (the sender is not supposed to send one). */
+    result = FILE_SAVE_SKIPPED;
+  } else 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);
   }
-  if (result != FILE_SAVE_ERROR && context->config->remove_source_files && !file->is_dir &&
-      !file->skip && !receiver_outcomes_append(&context->outcomes, (unsigned char)result)) {
+  /* Wire-stats tally: bytes reconstructed from the basis file (delta matches)
+     count as matched data in the end-of-transfer report. */
+  if (result != FILE_SAVE_ERROR && file->matched_bytes > 0)
+    context->stats.matched_data += file->matched_bytes;
+  /* A directory's metadata is deferred, never applied inline: collect it now
+     and apply it at the end.  -O/--omit-dir-times and --preserve_perms/-times
+     are honored by dir_metadata_list_apply's caller (see
+     receiver_send_success_frame). */
+  if (result != FILE_SAVE_ERROR && file->is_dir && file->metadata &&
+      dir_metadata_should_capture(context->config) &&
+      !dir_time_list_add(&context->dir_times, file->path, file->metadata, file->xattrs)) {
+    file_destroy(file);
+    return false;
+  }
+  /* A dry-run receiver mutates nothing AND records no per-file outcomes: a
+     hostile dry-run client that streamed data frames anyway must not be able to
+     grow `outcomes` without bound (receiver_outcomes_append reallocs uncharged)
+     or force a per-frame ack. */
+  if (!context->config->dry_run && 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;
   }
@@ -313,8 +613,20 @@ static bool receiver_save_file(File* file, void* context_pointer) {
   return result != FILE_SAVE_ERROR;
 }
 
+static void receiver_note_delete_limit(void* context_pointer) {
+  ReceiverSaveContext* context = context_pointer;
+  context->delete_limit_reached = true;
+}
+
 static bool receiver_send_success_frame(int fd, void* context_pointer) {
   ReceiverSaveContext* context = context_pointer;
+  Status final_status = context->delete_limit_reached ? STATUS_DELETE_LIMIT : STATUS_OK;
+  if (!receiver_send_stats_frame(fd, context->config, &context->stats, context->would_delete))
+    return false;
+  /* Server-contacting --dry-run: nothing was staged or written, so there is
+     nothing to publish and no directory times to stamp. */
+  if (context->config->dry_run)
+    return receiver_send_final_success(fd, context->config, &context->outcomes, final_status);
   /* --delay-updates: the whole protocol stream (including manifest/delete
      handling, which ran inside receiver_process) has succeeded and every
      staged file was fully written.  Publish them atomically now, before the
@@ -326,15 +638,34 @@ static bool receiver_send_success_frame(int fd, void* context_pointer) {
       return false;
     }
   }
-  return receiver_send_final_success(fd, context->config, &context->outcomes);
+  /* 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_metadata_list_apply(&context->dir_times, context->config->receive_root_directory,
+                          context->config);
+  return receiver_send_final_success(fd, context->config, &context->outcomes, final_status);
 }
 
 int receiver_receive_files(Config* config, int file_descriptor) {
   ReceiverSaveContext context = {.config = config, .outcomes = {0}};
-  ReceiverSink sink = {receiver_save_file, &context, true, true, receiver_send_success_frame};
+  dir_time_list_init(&context.dir_times);
+  context.would_delete = array_list_create(free);
+  if (!context.would_delete)
+    return -1;
+  ReceiverSink sink = {receiver_save_file,
+                       &context,
+                       true,
+                       true,
+                       receiver_send_success_frame,
+                       receiver_note_delete_limit,
+                       &context.stats,
+                       context.would_delete};
   int ret = receiver_process(config, file_descriptor, &sink);
   if (ret != 0 && config->delay_updates && config->delay_context)
     delay_updates_cleanup(config->delay_context);
   receiver_outcomes_destroy(&context.outcomes);
+  dir_time_list_free(&context.dir_times);
+  array_list_delete(context.would_delete);
   return ret;
 }

src/server/receiver.h

@@ -2,8 +2,12 @@
 #define RECEIVER_H
 
 #include "config.h"
+#include "delete_plan.h"
 #include "file.h"
 #include "file_receive.h"
+#include "protocol.h"
+#include <stdbool.h>
+#include <time.h>
 
 typedef bool (*ReceiverFileSink)(File* file, void* context);
 
@@ -19,6 +23,12 @@ typedef struct {
 
 typedef bool (*ReceiverSuccessFrame)(int fd, void* context);
 
+/* Records that a --max-delete commit stopped with extras left over, so the
+   caller's terminal success frame can carry STATUS_DELETE_LIMIT instead of
+   STATUS_OK.  The commit runs on the receiver thread, so the flag is stored in
+   the sink's own context rather than in a shared global. */
+typedef void (*ReceiverNoteDeleteLimit)(void* context);
+
 typedef struct {
   ReceiverFileSink store_file;
   void* context;
@@ -26,23 +36,61 @@ typedef struct {
   bool send_success;
   /* Emits the end-of-transfer success frame.  When the sender requested
      --remove-source-files this includes one per-file status per processed
-     data file followed by the final STATUS_OK; otherwise just STATUS_OK. */
+     data file followed by the final status; otherwise just the final status. */
   ReceiverSuccessFrame send_success_frame;
+  /* Optional; may be NULL when the sink has no --max-delete handling. */
+  ReceiverNoteDeleteLimit note_delete_limit;
+  /* Optional end-of-transfer wire counters (protocol 2.25.0).  When non-NULL
+     and the wire config carries report_stats, the success frame is preceded by
+     a STATUS_STATS record; `would_delete` (optional, receiver-owned strings)
+     carries the -n/--dry-run --delete path list. */
+  ReceiverStats* stats;
+  struct ArrayList* would_delete;
 } 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);
+
+/* Send the terminal success frame.  `final_status` is usually STATUS_OK, or
+   STATUS_DELETE_LIMIT when a --max-delete commit was capped. */
+bool receiver_send_final_success(int fd, const Config* config, const ReceiverOutcomes* outcomes,
+                                 Status final_status);
+
+/* Emit STATUS_STATS (a fixed ReceiverStats record plus, when `would_delete` is
+   non-NULL, a count and that many wire strings) when the wire config requested
+   report_stats.  A no-op otherwise. */
+bool receiver_send_stats_frame(int fd, const Config* config, const ReceiverStats* stats,
+                               const struct ArrayList* would_delete);
 
 int receiver_process(Config* config, int file_descriptor, const ReceiverSink* sink);
 /* receiver_process with an escape hatch for the commit-style (late) deletion:
    when `pending_manifest` is non-NULL the receiver does NOT delete at
    STATUS_FINISHED itself; instead it stores the owned keep-set manifest there
    (leaving *pending_manifest untouched on early modes/errors) so the caller can
-   commit the deletion only after its disk writer has fully drained.  Pass NULL
-   to keep the default behaviour (delete before the success frame). */
+   commit the deletion only after its disk writer has fully drained.  Likewise,
+   when `pending_plans` is non-NULL the --delete-delay per-directory session is
+   handed to the caller instead of being committed at STATUS_FINISHED.  Pass NULL
+   for either to keep the default behaviour (delete before the success frame). */
 int receiver_process_pending(Config* config, int file_descriptor, const ReceiverSink* sink,
-                             DeleteManifest** pending_manifest);
+                             DeleteManifest** pending_manifest, DeletePlanSession** pending_plans);
 int receiver_receive_files(Config* config, int file_descriptor);
 
+/* ---- Connection time bounds (anti-slowloris) ----
+ * receiver_process_pending() aborts a connection that makes no forward progress
+ * (only STATUS_KEEPALIVE/STATUS_ABORT frames) beyond a wall-clock idle limit,
+ * and enforces a hard cap on the whole session.  Both are CLOCK_MONOTONIC
+ * deltas, independent of the per-message poll deadline, so a 60 s (or
+ * --timeout) receive window can never reset them.  Defaults are deliberately
+ * generous (see MAX_SESSION_IDLE_SEC / MAX_SESSION_WALL_SEC in receiver.c). */
+
+/* Test seam: override the idle/session wall-clock limits (0 = abort on the
+ * next status).  Always restore with receiver_reset_time_limits(). */
+void receiver_set_time_limits(unsigned int idle_sec, unsigned int wall_sec);
+void receiver_reset_time_limits(void);
+/* Pure predicate over explicit monotonic timestamps, exposed so the bound is
+ * unit-testable without sleeping.  True when either the idle or the overall
+ * session limit has elapsed. */
+bool receiver_time_limit_exceeded(const struct timespec* session_start,
+                                  const struct timespec* last_progress, const struct timespec* now);
+
 #endif

src/server/receiver_pipeline.c

@@ -0,0 +1,290 @@
+#include "receiver_pipeline.h"
+
+#include "log.h"
+#include "protocol.h"
+#include "queue.h"
+#include "utils.h"
+#include <stdlib.h>
+#include <string.h>
+#include <threads.h>
+
+PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue* queue,
+                                                          int file_descriptor, SSL* ssl) {
+  PipelineContextReceiver* context = malloc(sizeof(PipelineContextReceiver));
+  if (context == NULL)
+    return NULL;
+  context->config = config;
+  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;
+  context->deferred_plans = NULL;
+  context->delete_limit_reached = false;
+  memset(&context->stats, 0, sizeof(context->stats));
+  context->would_delete = NULL;
+  atomic_init(&context->cancelled, false);
+  int init = 0;
+  if (mtx_init(&context->mutex, mtx_plain) != thrd_success)
+    goto fail;
+  init++;
+  if (cnd_init(&context->condition_not_full) != thrd_success)
+    goto fail;
+  init++;
+  if (cnd_init(&context->condition_not_empty) != thrd_success)
+    goto fail;
+  // cppcheck-suppress unreadVariable
+  init++;
+  context->would_delete = array_list_create(free);
+  if (!context->would_delete)
+    goto fail;
+  return context;
+
+fail:
+  log_perror("Error initializing synchronization objects");
+  if (init >= 3)
+    cnd_destroy(&context->condition_not_empty);
+  if (init >= 2)
+    cnd_destroy(&context->condition_not_full);
+  if (init >= 1)
+    mtx_destroy(&context->mutex);
+  free(context);
+  return NULL;
+}
+
+void pipeline_context_receiver_destroy(PipelineContextReceiver* context) {
+  config_delete(context->config);
+  if (context->deferred_manifest)
+    delete_manifest_free(context->deferred_manifest);
+  if (context->deferred_plans)
+    delete_plan_session_destroy(context->deferred_plans);
+  queue_destroy(context->queue);
+  receiver_outcomes_destroy(&context->outcomes);
+  dir_time_list_free(&context->dir_times);
+  if (context->would_delete)
+    array_list_delete(context->would_delete);
+  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 = (PipelineContextReceiver*)context_pointer;
+  if (file && file->matched_bytes > 0) {
+    mtx_lock(&context->mutex);
+    context->stats.matched_data += file->matched_bytes;
+    mtx_unlock(&context->mutex);
+  }
+  return pipeline_context_receiver_enqueue_file(context, file);
+}
+
+/* Early delete modes (--delete-before/--delete-during) commit the manifest
+   inside receiver_process_pending on this thread; record a capped commit so
+   server.c's terminal frame can report STATUS_DELETE_LIMIT.  The plain bool is
+   safe: receive_thread writes it before the main thread joins the thread. */
+static void receiver_pipeline_note_delete_limit(void* context_pointer) {
+  PipelineContextReceiver* context = (PipelineContextReceiver*)context_pointer;
+  context->delete_limit_reached = true;
+}
+
+static void receiver_thread_fail(PipelineContextReceiver* context) {
+  mtx_lock(&context->mutex);
+  atomic_store(&context->cancelled, true);
+  context->receiver_done = true;
+  cnd_broadcast(&context->condition_not_empty);
+  cnd_broadcast(&context->condition_not_full);
+  mtx_unlock(&context->mutex);
+}
+
+int receive_thread(void* pipeline_context) {
+  PipelineContextReceiver* context = (PipelineContextReceiver*)pipeline_context;
+  protocol_session_bind(&context->session);
+  mtx_lock(&context->mutex);
+  int file_descriptor = context->file_descriptor;
+  const Config* config = context->config;
+  mtx_unlock(&context->mutex);
+
+  ReceiverSink sink = {receiver_enqueue_file,
+                       context,
+                       false,
+                       false,
+                       NULL,
+                       receiver_pipeline_note_delete_limit,
+                       &context->stats,
+                       context->would_delete};
+  if (receiver_process_pending((Config*)config, file_descriptor, &sink, &context->deferred_manifest,
+                               &context->deferred_plans) != 0) {
+    receiver_thread_fail(context);
+    protocol_session_unbind();
+    return thrd_error;
+  }
+  mtx_lock(&context->mutex);
+  context->receiver_done = true;
+  cnd_signal(&context->condition_not_empty);
+  mtx_unlock(&context->mutex);
+  protocol_session_unbind();
+  return thrd_success;
+}
+
+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);
+  mtx_unlock(&context->mutex);
+  if (save_to_disk && !root_directory) {
+    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);
+    protocol_session_unbind();
+    return thrd_error;
+  }
+
+  while (true) {
+    File* file =
+        queue_dequeue_multithreaded(context->queue, &context->mutex, &context->condition_not_empty,
+                                    &context->condition_not_full, &context->receiver_done);
+    if (file == NULL) {
+      free(root_directory);
+      protocol_session_unbind();
+      return thrd_success;
+    }
+    size_t file_bytes = file->data ? file->data->size : 0;
+    FileSaveResult result = FILE_SAVE_SKIPPED;
+    /* Server-contacting --dry-run: never write.  The receiver thread does not
+       enqueue anything on the dry-run path, but this keeps the writer thread
+       provably mutation-free if a data frame ever reached it. */
+    bool dry_run = context->config->dry_run;
+    if (save_to_disk && !dry_run) {
+      result = file_save_to_disk_full(root_directory, file, context->config);
+      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 (!dry_run && result != FILE_SAVE_ERROR && file->is_dir && file->metadata &&
+        dir_metadata_should_capture(context->config) &&
+        !dir_time_list_add(&context->dir_times, file->path, file->metadata, file->xattrs)) {
+      file_destroy(file);
+      pipeline_context_receiver_note_bytes_released(context, file_bytes);
+      mtx_lock(&context->mutex);
+      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;
+    }
+    /* 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 (!dry_run && 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/server/receiver_pipeline.h

@@ -0,0 +1,84 @@
+#ifndef RECEIVER_PIPELINE_H
+#define RECEIVER_PIPELINE_H
+
+#include <stdatomic.h>
+#include <stdbool.h>
+#include <threads.h>
+
+#include "config.h"
+#include "file.h"
+#include "file_receive.h"
+#include "protocol.h"
+#include "queue.h"
+#include "receiver.h"
+#include <openssl/ssl.h>
+
+typedef struct PipelineContextReceiver {
+  Queue* queue;
+  Config* config;
+  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;
+  /* Per-directory delete session for --delete-delay: receive_thread snapshots
+     each plan's extras as it arrives and hands the session here instead of
+     committing while the disk writer may still be draining; server.c commits it
+     after both threads joined.  NULL for every other timing. */
+  DeletePlanSession* deferred_plans;
+  /* Set by server.c when the deferred delete commit hit the --max-delete
+     budget; the terminal success frame then carries STATUS_DELETE_LIMIT
+     (rsync exit 25) while the transfer itself still succeeds. */
+  bool delete_limit_reached;
+  /* P7 Wave D: directory metadata collected by write_thread from received
+     directory entries.  Only write_thread mutates it (before it joins); the
+     caller (server.c) applies it after the delete/delay-updates phase. */
+  DirTimeList dir_times;
+  /* End-of-transfer wire counters (protocol 2.25.0).  receive_thread accumulates
+     matched_data under `mutex`; server.c adds the delete-commit tallies after
+     both threads join and emits the STATUS_STATS frame. */
+  ReceiverStats stats;
+  /* -n/--dry-run --delete would-delete path list, collected by receive_thread
+     and reported in the STATUS_STATS frame. */
+  struct ArrayList* would_delete;
+} PipelineContextReceiver;
+
+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/server/server_cli.c

@@ -0,0 +1,311 @@
+#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-super")) {
+      opts->allow_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") || arg_has_value(argv[i], "--port", &inline_value)) {
+      if (inline_value) {
+        opts->port_set = true;
+        if (parse_port_arg(inline_value, &opts->port, err, err_size) != 0)
+          return -1;
+      } else {
+        if (i + 1 >= argc) {
+          set_error(err, err_size, "missing argument for %s", argv[i]);
+          return -1;
+        }
+        opts->port_set = true;
+        if (parse_port_arg(argv[++i], &opts->port, err, err_size) != 0)
+          return -1;
+      }
+    } 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->allow_super && opts->no_super) {
+    set_error(err, err_size, "--allow-super and --no-super are mutually exclusive");
+    return -1;
+  }
+  if (opts->allow_super && opts->daemon_mode) {
+    set_error(err, err_size,
+              "--allow-super is for a locally-launched standalone TCP server; daemon modules opt "
+              "in per module with 'client owner = yes'");
+    return -1;
+  }
+  /* --stdio is the SSH transport: the remote server argv is composed by the
+   * CLIENT (directly and via --remote-option), so a client could otherwise pass
+   * --allow-super to a root --stdio receiver and defeat the C3 secure default.
+   * Never honor it there; the super mode stays forced OFF.  An operator who
+   * must keep the historical permissive behavior over SSH has to launch the
+   * receiver through a forced command, not via client-composed argv. */
+  if (opts->allow_super && opts->stdio_mode) {
+    set_error(err, err_size,
+              "--allow-super is not accepted with --stdio (the remote argv is client-composed; "
+              "use a forced command if the default must hold)");
+    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 +1,79 @@
+#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 */
+  /* --allow-super: locally-launched standalone TCP listener opt-in that keeps
+   * the historical permissive behavior for a PRIVILEGED (root) receiver.
+   * Without it a root standalone server forces SUPER_MODE_OFF, so a client
+   * --devices / --write-devices / --super / ownership request cannot make it
+   * create device nodes, write raw devices, or apply client-chosen ownership.
+   * It is rejected for --stdio: that path's remote argv is composed by the
+   * client (directly and via --remote-option), so it must never opt a root
+   * receiver back into super mode.  Non-root receivers are unaffected (the
+   * kernel refuses the confined attempts).  The daemon path instead uses the
+   * per-module `client owner = yes` opt-in. */
+  bool allow_super; /* --allow-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

@@ -1,6 +1,7 @@
 #include "log.h"
 #include "array_list.h"
 #include "protocol.h"
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -39,6 +40,8 @@ void array_list_delete(ArrayList* array_list) {
 static bool array_list_extend(ArrayList* array_list) {
   if (array_list == NULL)
     return false;
+  if (array_list->capacity > INT_MAX / 2)
+    return false;
   int new_capacity = array_list->capacity * 2;
   if (new_capacity == 0)
     new_capacity = INITIAL_ARRAY_SIZE;

src/shared/batch.c

@@ -0,0 +1,195 @@
+#include "batch.h"
+#include "data.h"
+#include "file.h"
+#include "file_receive.h"
+#include "identity.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 about whether per-entry metadata was CAPTURED in the stream:
+ * batch_read_apply re-reads it from the file (not from the reading config) to
+ * decode the chunk records correctly.  Which attributes are actually APPLIED,
+ * however, comes from the INVOKING process's per-attribute config (the
+ * FileAttrPolicy and the dir-metadata gate), so a batch written with -M is NOT
+ * automatically applied identically by an invoking process with a different
+ * -p/-t/-o/-g: --read-batch must be invoked with the same -p/-t/-o/-g as the
+ * write side (rsync requires the same options).  The batch driver is a single
+ * sequential scan pass within one thread, so this module-level flag is safe. */
+static bool batch_metadata_mode = false;
+
+static bool write_all_bytes(int fd, const void* data, size_t size) {
+  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;
+
+  /* Directory metadata is deferred to the end of the apply (a child write would
+   * otherwise clobber its parent's mtime/mode).  The batch header's single
+   * metadata bit only says whether metadata is present in the stream; which
+   * attributes are APPLIED comes from the invoking process's config, so
+   * --read-batch must be invoked with the same -p/-t/-o/-g as the write side
+   * (rsync requires the same options).  The identity snapshot is activated so
+   * -o/-g and the explicit ownership flags can apply. */
+  DirTimeList dir_times;
+  dir_time_list_init(&dir_times);
+  int result = -1;
+  if (!identity_set_active(config)) {
+    log_message(LOG_LEVEL_ERROR, "batch: could not activate the identity policy");
+    goto done;
+  }
+
+  char magic[BATCH_MAGIC_LEN];
+  bool eof = false;
+  if (!read_exact(fd, magic, BATCH_MAGIC_LEN, &eof) || eof ||
+      memcmp(magic, BATCH_MAGIC, BATCH_MAGIC_LEN) != 0) {
+    log_message(LOG_LEVEL_ERROR, "batch: malformed header (bad magic)");
+    goto done;
+  }
+  unsigned char version;
+  if (!read_exact(fd, &version, 1, &eof) || eof || version != BATCH_FORMAT_VERSION) {
+    log_message(LOG_LEVEL_ERROR, "batch: malformed header (bad or missing format version)");
+    goto done;
+  }
+  unsigned char mode;
+  if (!read_exact(fd, &mode, 1, &eof) || eof || (mode != 0 && mode != 1)) {
+    log_message(LOG_LEVEL_ERROR, "batch: malformed header (bad metadata flag)");
+    goto done;
+  }
+  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");
+      goto done;
+    }
+    if (eof)
+      break; /* clean end of stream */
+    if (length == 0 || length > BATCH_MAX_RECORD) {
+      log_message(LOG_LEVEL_ERROR, "batch: rejected record length %llu (valid range 1..%llu)",
+                  length, (unsigned long long)BATCH_MAX_RECORD);
+      goto done;
+    }
+    char* record = (char*)malloc((size_t)length);
+    if (record == NULL) {
+      log_message(LOG_LEVEL_ERROR, "batch: could not allocate a %llu-byte record", length);
+      goto done;
+    }
+    if (!read_exact(fd, record, (size_t)length, &eof) || eof) {
+      log_message(LOG_LEVEL_ERROR, "batch: truncated chunk record");
+      free(record);
+      goto done;
+    }
+    Data* data = data_create(record, (size_t)length);
+    if (data == NULL)
+      goto done; /* data_create frees `record` on failure */
+    Chunk* chunk = chunk_deserialize(data, use_metadata);
+    data_destroy(data);
+    if (chunk == NULL) {
+      log_message(LOG_LEVEL_ERROR, "batch: rejected malformed chunk record");
+      goto done;
+    }
+    for (int i = 0; i < chunk->element_count; i++) {
+      File* file = chunk->items[i];
+      chunk->items[i] = NULL;
+      if (file == NULL)
+        continue;
+      FileSaveResult save = file_save_to_disk_full(dest_root, file, config);
+      /* Accumulate directory metadata (when it applies) before the File is
+       * destroyed; applied once the whole stream has been consumed. */
+      if (save != FILE_SAVE_ERROR && file->is_dir && file->metadata &&
+          dir_metadata_should_capture(config) &&
+          !dir_time_list_add(&dir_times, file->path, file->metadata, file->xattrs)) {
+        file_destroy(file);
+        chunk_destroy(chunk);
+        goto done;
+      }
+      file_destroy(file);
+      if (save == FILE_SAVE_ERROR) {
+        chunk_destroy(chunk);
+        goto done;
+      }
+    }
+    chunk_destroy(chunk);
+  }
+  dir_metadata_list_apply(&dir_times, dest_root, config);
+  result = 0;
+
+done:
+  identity_clear_active();
+  dir_time_list_free(&dir_times);
+  return result;
+}

src/shared/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

@@ -1,12 +1,170 @@
 #include "checksum.h"
+#include <fcntl.h>
 #include <openssl/evp.h>
 #include <string.h>
 #include <strings.h>
+#include <unistd.h>
 
 /* delta.c owns the single XXH_IMPLEMENTATION that provides the xxHash symbols
- * for the whole binary; this TU only needs the declarations. */
+ * for the whole binary; this TU only needs the declarations.  The streaming
+ * state structs and XXH3_update are exposed only with XXH_STATIC_LINKING_ONLY. */
+#define XXH_STATIC_LINKING_ONLY
 #include <xxhash.h>
 
+/* ---------------------------------------------------------------------------
+ * Self-contained MD4 (RFC 1320).  OpenSSL's MD4 lives in the legacy provider
+ * and is not guaranteed present, so FastSync carries its own implementation to
+ * keep --checksum-choice=md4 working on every build.
+ * ------------------------------------------------------------------------- */
+
+typedef struct {
+  uint32_t state[4];
+  uint64_t bit_count;
+  uint8_t buffer[64];
+  size_t buffer_len;
+} Md4Ctx;
+
+static uint32_t md4_rotl(uint32_t x, int n) {
+  return (x << n) | (x >> (32 - n));
+}
+
+static void md4_transform(uint32_t state[4], const uint8_t block[64]) {
+  uint32_t x[16];
+  for (int i = 0; i < 16; i++)
+    x[i] = (uint32_t)block[i * 4] | ((uint32_t)block[i * 4 + 1] << 8) |
+           ((uint32_t)block[i * 4 + 2] << 16) | ((uint32_t)block[i * 4 + 3] << 24);
+
+  uint32_t a = state[0], b = state[1], c = state[2], d = state[3];
+
+#define F(x, y, z) (((x) & (y)) | (~(x) & (z)))
+#define G(x, y, z) (((x) & (y)) | ((x) & (z)) | ((y) & (z)))
+#define H(x, y, z) ((x) ^ (y) ^ (z))
+#define ROUND1(a, b, c, d, k, s) a = md4_rotl(a + F(b, c, d) + x[k], s)
+#define ROUND2(a, b, c, d, k, s) a = md4_rotl(a + G(b, c, d) + x[k] + 0x5a827999u, s)
+#define ROUND3(a, b, c, d, k, s) a = md4_rotl(a + H(b, c, d) + x[k] + 0x6ed9eba1u, s)
+
+  ROUND1(a, b, c, d, 0, 3);
+  ROUND1(d, a, b, c, 1, 7);
+  ROUND1(c, d, a, b, 2, 11);
+  ROUND1(b, c, d, a, 3, 19);
+  ROUND1(a, b, c, d, 4, 3);
+  ROUND1(d, a, b, c, 5, 7);
+  ROUND1(c, d, a, b, 6, 11);
+  ROUND1(b, c, d, a, 7, 19);
+  ROUND1(a, b, c, d, 8, 3);
+  ROUND1(d, a, b, c, 9, 7);
+  ROUND1(c, d, a, b, 10, 11);
+  ROUND1(b, c, d, a, 11, 19);
+  ROUND1(a, b, c, d, 12, 3);
+  ROUND1(d, a, b, c, 13, 7);
+  ROUND1(c, d, a, b, 14, 11);
+  ROUND1(b, c, d, a, 15, 19);
+
+  ROUND2(a, b, c, d, 0, 3);
+  ROUND2(d, a, b, c, 4, 5);
+  ROUND2(c, d, a, b, 8, 9);
+  ROUND2(b, c, d, a, 12, 13);
+  ROUND2(a, b, c, d, 1, 3);
+  ROUND2(d, a, b, c, 5, 5);
+  ROUND2(c, d, a, b, 9, 9);
+  ROUND2(b, c, d, a, 13, 13);
+  ROUND2(a, b, c, d, 2, 3);
+  ROUND2(d, a, b, c, 6, 5);
+  ROUND2(c, d, a, b, 10, 9);
+  ROUND2(b, c, d, a, 14, 13);
+  ROUND2(a, b, c, d, 3, 3);
+  ROUND2(d, a, b, c, 7, 5);
+  ROUND2(c, d, a, b, 11, 9);
+  ROUND2(b, c, d, a, 15, 13);
+
+  ROUND3(a, b, c, d, 0, 3);
+  ROUND3(d, a, b, c, 8, 9);
+  ROUND3(c, d, a, b, 4, 11);
+  ROUND3(b, c, d, a, 12, 15);
+  ROUND3(a, b, c, d, 2, 3);
+  ROUND3(d, a, b, c, 10, 9);
+  ROUND3(c, d, a, b, 6, 11);
+  ROUND3(b, c, d, a, 14, 15);
+  ROUND3(a, b, c, d, 1, 3);
+  ROUND3(d, a, b, c, 9, 9);
+  ROUND3(c, d, a, b, 5, 11);
+  ROUND3(b, c, d, a, 13, 15);
+  ROUND3(a, b, c, d, 3, 3);
+  ROUND3(d, a, b, c, 11, 9);
+  ROUND3(c, d, a, b, 7, 11);
+  ROUND3(b, c, d, a, 15, 15);
+
+#undef F
+#undef G
+#undef H
+#undef ROUND1
+#undef ROUND2
+#undef ROUND3
+
+  state[0] += a;
+  state[1] += b;
+  state[2] += c;
+  state[3] += d;
+}
+
+static void md4_init(Md4Ctx* ctx) {
+  ctx->state[0] = 0x67452301u;
+  ctx->state[1] = 0xefcdab89u;
+  ctx->state[2] = 0x98badcfeu;
+  ctx->state[3] = 0x10325476u;
+  ctx->bit_count = 0;
+  ctx->buffer_len = 0;
+}
+
+static void md4_update(Md4Ctx* ctx, const uint8_t* data, size_t len) {
+  ctx->bit_count += (uint64_t)len * 8;
+  while (len > 0) {
+    size_t space = sizeof(ctx->buffer) - ctx->buffer_len;
+    size_t take = len < space ? len : space;
+    memcpy(ctx->buffer + ctx->buffer_len, data, take);
+    ctx->buffer_len += take;
+    data += take;
+    len -= take;
+    if (ctx->buffer_len == sizeof(ctx->buffer)) {
+      md4_transform(ctx->state, ctx->buffer);
+      ctx->buffer_len = 0;
+    }
+  }
+}
+
+static void md4_final(Md4Ctx* ctx, uint8_t out[16]) {
+  uint64_t bit_count = ctx->bit_count;
+  uint8_t pad = 0x80;
+  md4_update(ctx, &pad, 1);
+  uint8_t zero = 0;
+  while (ctx->buffer_len != 56)
+    md4_update(ctx, &zero, 1);
+  uint8_t length_le[8];
+  for (int i = 0; i < 8; i++)
+    length_le[i] = (uint8_t)((bit_count >> (8 * i)) & 0xff);
+  md4_update(ctx, length_le, sizeof(length_le));
+  for (int i = 0; i < 4; i++) {
+    out[i * 4] = (uint8_t)(ctx->state[i] & 0xff);
+    out[i * 4 + 1] = (uint8_t)((ctx->state[i] >> 8) & 0xff);
+    out[i * 4 + 2] = (uint8_t)((ctx->state[i] >> 16) & 0xff);
+    out[i * 4 + 3] = (uint8_t)((ctx->state[i] >> 24) & 0xff);
+  }
+}
+
+/* One-shot EVP digest (md5/sha1).  Returns false when OpenSSL refuses. */
+static bool evp_digest(const EVP_MD* md, const void* data, size_t size, uint8_t* out,
+                       size_t out_capacity, size_t* out_len) {
+  static const uint8_t empty = 0;
+  const void* input = data ? data : &empty;
+  unsigned int digest_len = 0;
+  if (EVP_Digest(input, size, out, &digest_len, md, NULL) != 1)
+    return false;
+  if (digest_len > out_capacity)
+    return false;
+  *out_len = digest_len;
+  return true;
+}
+
 bool checksum_digest(ChecksumAlgo algo, uint64_t seed, const void* data, size_t size, uint8_t* out,
                      size_t out_capacity, size_t* out_len) {
   if (!out || !out_len || out_capacity < CHECKSUM_MAX_DIGEST_LEN)
@@ -14,39 +172,158 @@ bool checksum_digest(ChecksumAlgo algo, uint64_t seed, const void* data, size_t
   if (data == NULL && size != 0)
     return false;
 
-  if (algo == CHECKSUM_ALGO_XXH64) {
+  switch (algo) {
+  case CHECKSUM_ALGO_XXH64: {
     uint64_t digest = XXH64(data, size, seed);
     memcpy(out, &digest, sizeof(digest));
     *out_len = sizeof(digest);
     return true;
   }
-
-  if (algo == CHECKSUM_ALGO_MD5) {
+  case CHECKSUM_ALGO_XXH3: {
+    uint64_t digest = XXH3_64bits_withSeed(data, size, seed);
+    memcpy(out, &digest, sizeof(digest));
+    *out_len = sizeof(digest);
+    return true;
+  }
+  case CHECKSUM_ALGO_XXH128: {
+    XXH128_hash_t digest = XXH3_128bits_withSeed(data, size, seed);
+    memcpy(out, &digest, sizeof(digest));
+    *out_len = sizeof(digest);
+    return true;
+  }
+  case CHECKSUM_ALGO_MD5:
     /* md5 takes no seed; the caller's seed is deliberately ignored (documented
-     * in RSYNC_COMPAT.md).  OpenSSL's one-shot EVP_Digest needs a non-NULL
-     * buffer even for an empty input, so map a NULL data + size==0 to an empty
-     * buffer. */
-    static const uint8_t empty = 0;
-    const void* input = data ? data : &empty;
-    unsigned int digest_len = 0;
-    if (EVP_Digest(input, size, out, &digest_len, EVP_md5(), NULL) != 1)
-      return false;
-    if (digest_len > out_capacity)
-      return false;
-    *out_len = digest_len;
+     * in RSYNC_COMPAT.md). */
+    return evp_digest(EVP_md5(), data, size, out, out_capacity, out_len);
+  case CHECKSUM_ALGO_MD4: {
+    Md4Ctx ctx;
+    md4_init(&ctx);
+    md4_update(&ctx, (const uint8_t*)data, size);
+    md4_final(&ctx, out);
+    *out_len = 16;
+    return true;
+  }
+  case CHECKSUM_ALGO_SHA1:
+    /* sha1 takes no seed; the caller's seed is deliberately ignored. */
+    return evp_digest(EVP_sha1(), data, size, out, out_capacity, out_len);
+  case CHECKSUM_ALGO_NONE:
+    /* No checksum requested: an empty digest is the successful result. */
+    *out_len = 0;
     return true;
   }
-
   return false;
 }
 
+bool checksum_digest_file(ChecksumAlgo algo, uint64_t seed, const char* path, uint8_t* out,
+                          size_t out_capacity, size_t* out_len) {
+  if (!path || !out || !out_len || out_capacity < CHECKSUM_MAX_DIGEST_LEN)
+    return false;
+
+  int fd = open(path, O_RDONLY | O_CLOEXEC);
+  if (fd < 0)
+    return false;
+
+  uint8_t buffer[64 * 1024];
+  bool ok = false;
+
+  if (algo == CHECKSUM_ALGO_MD5) {
+    EVP_MD_CTX* ctx = EVP_MD_CTX_new();
+    if (!ctx) {
+      close(fd);
+      return false;
+    }
+    unsigned int digest_len = 0;
+    if (EVP_DigestInit_ex(ctx, EVP_md5(), NULL) == 1) {
+      ok = true;
+      ssize_t got;
+      while ((got = read(fd, buffer, sizeof(buffer))) > 0) {
+        if (EVP_DigestUpdate(ctx, buffer, (size_t)got) != 1) {
+          ok = false;
+          break;
+        }
+      }
+      if (got < 0)
+        ok = false;
+      if (ok && EVP_DigestFinal_ex(ctx, out, &digest_len) == 1 && digest_len <= out_capacity)
+        *out_len = digest_len;
+      else
+        ok = false;
+    }
+    EVP_MD_CTX_free(ctx);
+    close(fd);
+    return ok;
+  }
+
+  XXH64_state_t xxh64;
+  XXH3_state_t* xxh3 = NULL;
+  if (algo == CHECKSUM_ALGO_XXH64) {
+    XXH64_reset(&xxh64, seed);
+  } else if (algo == CHECKSUM_ALGO_XXH3 || algo == CHECKSUM_ALGO_XXH128) {
+    xxh3 = XXH3_createState();
+    if (!xxh3) {
+      close(fd);
+      return false;
+    }
+    if (algo == CHECKSUM_ALGO_XXH3)
+      XXH3_64bits_reset_withSeed(xxh3, seed);
+    else
+      XXH3_128bits_reset_withSeed(xxh3, seed);
+  } else {
+    close(fd);
+    return false;
+  }
+
+  ok = true;
+  ssize_t got;
+  while ((got = read(fd, buffer, sizeof(buffer))) > 0) {
+    if (algo == CHECKSUM_ALGO_XXH64)
+      XXH64_update(&xxh64, buffer, (size_t)got);
+    else if (XXH3_64bits_update(xxh3, buffer, (size_t)got) == XXH_ERROR) {
+      ok = false;
+      break;
+    }
+  }
+  if (got < 0)
+    ok = false;
+
+  if (ok) {
+    if (algo == CHECKSUM_ALGO_XXH64) {
+      uint64_t digest = XXH64_digest(&xxh64);
+      memcpy(out, &digest, sizeof(digest));
+      *out_len = sizeof(digest);
+    } else if (algo == CHECKSUM_ALGO_XXH3) {
+      uint64_t digest = XXH3_64bits_digest(xxh3);
+      memcpy(out, &digest, sizeof(digest));
+      *out_len = sizeof(digest);
+    } else {
+      XXH128_hash_t digest = XXH3_128bits_digest(xxh3);
+      memcpy(out, &digest, sizeof(digest));
+      *out_len = sizeof(digest);
+    }
+  }
+  if (xxh3)
+    XXH3_freeState(xxh3);
+  close(fd);
+  return ok;
+}
+
 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, "xxh3") == 0)
+    return (int)CHECKSUM_ALGO_XXH3;
+  if (strcasecmp(name, "xxh128") == 0)
+    return (int)CHECKSUM_ALGO_XXH128;
   if (strcasecmp(name, "md5") == 0)
     return (int)CHECKSUM_ALGO_MD5;
+  if (strcasecmp(name, "md4") == 0)
+    return (int)CHECKSUM_ALGO_MD4;
+  if (strcasecmp(name, "sha1") == 0)
+    return (int)CHECKSUM_ALGO_SHA1;
+  if (strcasecmp(name, "none") == 0)
+    return (int)CHECKSUM_ALGO_NONE;
   return -1;
 }
 
@@ -54,22 +331,56 @@ const char* checksum_algo_name(ChecksumAlgo algo) {
   switch (algo) {
   case CHECKSUM_ALGO_XXH64:
     return "xxh64";
+  case CHECKSUM_ALGO_XXH3:
+    return "xxh3";
+  case CHECKSUM_ALGO_XXH128:
+    return "xxh128";
   case CHECKSUM_ALGO_MD5:
     return "md5";
+  case CHECKSUM_ALGO_MD4:
+    return "md4";
+  case CHECKSUM_ALGO_SHA1:
+    return "sha1";
+  case CHECKSUM_ALGO_NONE:
+    return "none";
   }
   return "<unknown>";
 }
 
 bool checksum_algo_valid(int algo) {
-  return algo == (int)CHECKSUM_ALGO_XXH64 || algo == (int)CHECKSUM_ALGO_MD5;
+  return algo == (int)CHECKSUM_ALGO_XXH64 || algo == (int)CHECKSUM_ALGO_MD5 ||
+         algo == (int)CHECKSUM_ALGO_XXH3 || algo == (int)CHECKSUM_ALGO_XXH128 ||
+         algo == (int)CHECKSUM_ALGO_MD4 || algo == (int)CHECKSUM_ALGO_SHA1 ||
+         algo == (int)CHECKSUM_ALGO_NONE;
 }
 
 uint8_t checksum_digest_len(ChecksumAlgo algo) {
   switch (algo) {
   case CHECKSUM_ALGO_XXH64:
+  case CHECKSUM_ALGO_XXH3:
     return 8;
+  case CHECKSUM_ALGO_XXH128:
   case CHECKSUM_ALGO_MD5:
+  case CHECKSUM_ALGO_MD4:
     return 16;
+  case CHECKSUM_ALGO_SHA1:
+    return 20;
+  case CHECKSUM_ALGO_NONE:
+    return 0;
   }
   return 0;
 }
+
+ChecksumAlgo checksum_negotiate_default(void) {
+  /* rsync 3.4.1 default preference order; every entry is compiled in, so this
+   * resolves to xxh128. */
+  static const ChecksumAlgo preference[] = {
+      CHECKSUM_ALGO_XXH128, CHECKSUM_ALGO_XXH3, CHECKSUM_ALGO_XXH64, CHECKSUM_ALGO_MD5,
+      CHECKSUM_ALGO_MD4,    CHECKSUM_ALGO_SHA1, CHECKSUM_ALGO_NONE,
+  };
+  for (size_t i = 0; i < sizeof(preference) / sizeof(preference[0]); i++) {
+    if (checksum_algo_valid((int)preference[i]))
+      return preference[i];
+  }
+  return CHECKSUM_ALGO_XXH64;
+}

src/shared/checksum.h

@@ -8,18 +8,35 @@
 /* Whole-file content-digest algorithms selectable with --checksum-choice and
  * seeded with --checksum-seed.  The ids are the values actually placed on the
  * wire (config frame), so they must be kept stable and validated on receive.
- * CHECKSUM_ALGO_XXH64 == 0 is the default and is byte-for-byte what FastSync
- * computed before these options existed (xxHash64 with seed 0). */
-typedef enum { CHECKSUM_ALGO_XXH64 = 0, CHECKSUM_ALGO_MD5 = 1 } ChecksumAlgo;
+ * CHECKSUM_ALGO_XXH64 == 0 is the historical FastSync default and its numeric
+ * value is preserved.  The full set mirrors the algorithms rsync 3.4.1 can be
+ * built with; every one of them is implemented here. */
+typedef enum {
+  CHECKSUM_ALGO_XXH64 = 0,
+  CHECKSUM_ALGO_MD5 = 1,
+  CHECKSUM_ALGO_XXH3 = 2,
+  CHECKSUM_ALGO_XXH128 = 3,
+  CHECKSUM_ALGO_MD4 = 4,
+  CHECKSUM_ALGO_SHA1 = 5,
+  CHECKSUM_ALGO_NONE = 6
+} ChecksumAlgo;
 
-/* md5 digest is 16 bytes, the longest supported. */
-#define CHECKSUM_MAX_DIGEST_LEN 16
+/* FastSync's negotiated default (rsync 3.4.1 auto-negotiates xxh128 first).
+ * The wire default for Config->checksum_algo is this value. */
+#define CHECKSUM_ALGO_DEFAULT CHECKSUM_ALGO_XXH128
+
+/* sha1 digest is 20 bytes, the longest supported. */
+#define CHECKSUM_MAX_DIGEST_LEN 20
 
 /* Compute the whole-file digest of the first `size` bytes of `data`.
  *
  *  - CHECKSUM_ALGO_XXH64: xxHash64(data, size, seed) (full 64-bit seed).
- *  - CHECKSUM_ALGO_MD5:   md5(data, size) via OpenSSL EVP.
- *                          md5 has no seed, so `seed` is ignored (documented).
+ *  - CHECKSUM_ALGO_XXH3:  XXH3_64bits_withSeed(data, size, seed).
+ *  - CHECKSUM_ALGO_XXH128: XXH3_128bits_withSeed(data, size, seed).
+ *  - CHECKSUM_ALGO_MD5:   md5(data, size) via OpenSSL EVP (seed ignored).
+ *  - CHECKSUM_ALGO_MD4:   md4(data, size), self-contained RFC 1320 (seed ignored).
+ *  - CHECKSUM_ALGO_SHA1:  sha1(data, size) via OpenSSL EVP (seed ignored).
+ *  - CHECKSUM_ALGO_NONE:  no digest; *out_len is 0 and nothing is written.
  *  - `size == 0` hashes the empty input (plus its seed), not a NULL input.
  *
  * Writes up to `out_capacity` bytes into `out`, storing the digest length in
@@ -28,9 +45,16 @@ typedef enum { CHECKSUM_ALGO_XXH64 = 0, CHECKSUM_ALGO_MD5 = 1 } ChecksumAlgo;
 bool checksum_digest(ChecksumAlgo algo, uint64_t seed, const void* data, size_t size, uint8_t* out,
                      size_t out_capacity, size_t* out_len);
 
+/* Streaming whole-file digest: hash the contents of `path` without holding the
+ * whole file in memory.  Same digest/capacity contract as checksum_digest.
+ * Returns false on open/read failure or an undersized buffer. */
+bool checksum_digest_file(ChecksumAlgo algo, uint64_t seed, const char* path, uint8_t* out,
+                          size_t out_capacity, size_t* out_len);
+
 /* Resolve a --checksum-choice string (case-insensitive) to an algorithm id.
- * Accepts "xxh64" and "xxhash" (both map to CHECKSUM_ALGO_XXH64, rsync's
- * xxhash spelling) and "md5".  Returns -1 for any unsupported name. */
+ * Accepts "xxh64"/"xxhash", "xxh3", "xxh128", "md5", "md4", "sha1", "none".
+ * "auto" is not an algorithm here; the caller resolves it to the negotiated
+ * default.  Returns -1 for any unrecognized name. */
 int checksum_algo_from_name(const char* name);
 
 /* Canonical name of an algorithm (used in CLI error messages). */
@@ -39,7 +63,13 @@ const char* checksum_algo_name(ChecksumAlgo algo);
 /* True when `algo` is a supported id (used by config receive validation). */
 bool checksum_algo_valid(int algo);
 
-/* Digest length in bytes for an algorithm (xxx64 = 8, md5 = 16). */
+/* Digest length in bytes for an algorithm (xxh64/xxh3 = 8,
+ * md5/md4/xxh128 = 16, sha1 = 20, none = 0). */
 uint8_t checksum_digest_len(ChecksumAlgo algo);
 
+/* Pick the first algorithm from FastSync's compiled-in preference list that is
+ * supported on this build (rsync 3.4.1's `--version` order:
+ * xxh128 xxh3 xxh64 md5 md4 sha1 none).  Used to resolve "auto". */
+ChecksumAlgo checksum_negotiate_default(void);
+
 #endif /* CHECKSUM_H */

src/shared/chmod.c

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

src/shared/chmod.h

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

src/shared/chunk.c

@@ -1,11 +1,13 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <limits.h>
+#include <stdatomic.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "array_list.h"
+#include "charset.h"
 #include "chunk.h"
 #include "compression.h"
 #include "data.h"
@@ -19,6 +21,33 @@
 #define MAX_FILE_DATA_SIZE (64ULL * 1024 * 1024)
 #define MAX_FILES_PER_CHUNK 65536U
 
+/* Reserve `charge` against `session`'s connection budget.  This mirrors the
+   static protocol_reserve_memory() in protocol.c: the receive-side call sites
+   only have the Data.owner pointer (a ProtocolSession*), and protocol.c is out
+   of scope for this fix, so the same atomic CAS accounting is reproduced here.
+   The matching release always goes through data_destroy()'s Data.owner path. */
+static bool chunk_session_reserve(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;
+  }
+}
+
+bool data_charge_session(Data* data, ProtocolSession* session, size_t charge) {
+  if (!data || charge == 0 || session == NULL)
+    return true;
+  if (!chunk_session_reserve(session, charge))
+    return false;
+  data->owner = session;
+  data->protocol_charge = charge;
+  return true;
+}
+
 Chunk* chunk_create(File** items, int element_count) {
   if (element_count < 0 || (element_count > 0 && items == NULL))
     return NULL;
@@ -63,9 +92,22 @@ 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_wire_path(file));
+  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)
@@ -74,16 +116,39 @@ 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. */
+  /* 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) {
@@ -109,17 +174,31 @@ 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];
-    const char* wire_path = file_wire_path(file);
+    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, wire_path, path_len);
     data_pointer += path_len;
+    free(wire_path);
 
-    int entry_type = file->is_dir ? 1 : 0;
+    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);
 
@@ -129,6 +208,21 @@ Data* chunk_serialize(Chunk* chunk, bool use_metadata) {
     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;
 }
@@ -141,17 +235,20 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
     return NULL;
   char* data_pointer = data->data;
   size_t remaining_size = data->size;
+  /* The element currently being parsed is owned by `files` only after the
+   * array_list_add() at the end of the iteration; until then the error
+   * epilogue destroys it directly.  Keeping this one pointer nulled after the
+   * hand-off makes the single cleanup path correct for every failure. */
+  File* file = NULL;
 
   while (remaining_size > 0) {
     if ((unsigned int)files->size >= MAX_FILES_PER_CHUNK) {
       log_message(LOG_LEVEL_ERROR, "Chunk contains too many files");
-      array_list_delete(files);
-      return NULL;
+      goto error;
     }
     if (remaining_size < sizeof(size_t)) {
       log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for path length");
-      array_list_delete(files);
-      return NULL;
+      goto error;
     }
 
     size_t path_len;
@@ -161,95 +258,117 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
 
     if (path_len > SIZE_MAX - 1 || remaining_size < path_len) {
       log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for path");
-      array_list_delete(files);
-      return NULL;
+      goto error;
     }
 
-    if (path_len == SIZE_MAX) {
-      array_list_delete(files);
-      return NULL;
-    }
     char* path = protocol_alloc(path_len + 1);
     if (path == NULL) {
       log_perror("Could not allocate memory for file path");
-      array_list_delete(files);
-      return NULL;
+      goto error;
     }
     memcpy(path, data_pointer, path_len);
     path[path_len] = '\0';
     if (memchr(path, '\0', path_len) != NULL) {
       free(path);
-      array_list_delete(files);
-      return NULL;
+      goto error;
     }
     data_pointer += path_len;
     remaining_size -= path_len;
 
-    if (path_len == 0 || has_path_traversal(path)) {
+    /* --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);
-      array_list_delete(files);
-      return NULL;
+      if (local_path == NULL) {
+        log_message(LOG_LEVEL_ERROR,
+                    "--iconv: received chunk file name cannot be converted to the local charset");
+        goto error;
+      }
+      path = local_path;
+      path_len = strlen(path);
     }
 
-    File* file = file_create(path);
+    if (path_len == 0 || has_path_traversal(path)) {
       free(path);
-    if (file == NULL) {
-      array_list_delete(files);
-      return NULL;
+      goto error;
     }
 
+    file = file_create(path);
+    free(path);
+    if (file == NULL)
+      goto error;
+
     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;
+      goto error;
     }
     int entry_type;
     memcpy(&entry_type, data_pointer, sizeof(int));
-    if (entry_type != 0 && entry_type != 1) {
+    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;
+      goto error;
     }
     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");
+        goto error;
+      }
+      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");
+        goto error;
+      }
+      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");
-        file_destroy(file);
-        array_list_delete(files);
-        return NULL;
+        goto error;
       }
-      // Peek at present flag to determine total size needed before reading
+      /* Peek at the present flag to determine the total record size before
+         decoding.  metadata_from_buf() independently bounds-checks every read
+         against remaining_size, so a short body can never over-read. */
       int present_flag;
       memcpy(&present_flag, data_pointer, sizeof(int));
       if ((present_flag != 0 && present_flag != 1) ||
           (present_flag == 1 && remaining_size < sizeof(int) + FILE_METADATA_WIRE_SIZE)) {
         log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for metadata body");
-        file_destroy(file);
-        array_list_delete(files);
-        return NULL;
+        goto error;
       }
-      file->metadata = metadata_from_buf(&data_pointer);
-      remaining_size -= sizeof(int);
+      file->metadata = metadata_from_buf((const uint8_t*)data_pointer, remaining_size);
+      size_t metadata_consumed = sizeof(int);
       if (present_flag == 1) {
-        if (file->metadata == NULL) {
-          file_destroy(file);
-          array_list_delete(files);
-          return NULL;
-        }
-        remaining_size -= FILE_METADATA_WIRE_SIZE;
+        if (file->metadata == NULL)
+          goto error;
+        metadata_consumed += FILE_METADATA_WIRE_SIZE;
       }
+      data_pointer += metadata_consumed;
+      remaining_size -= metadata_consumed;
     }
 
     if (remaining_size < sizeof(size_t)) {
       log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for data size");
-      file_destroy(file);
-      array_list_delete(files);
-      return NULL;
+      goto error;
     }
 
     size_t file_data_size;
@@ -259,63 +378,103 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
 
     if (remaining_size < file_data_size) {
       log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for file content");
-      file_destroy(file);
-      array_list_delete(files);
-      return NULL;
+      goto error;
     }
 
     // Reject individual file data larger than the maximum allowed size.
     if (file_data_size > MAX_FILE_DATA_SIZE) {
       log_message(LOG_LEVEL_ERROR, "File data size %zu exceeds maximum %llu", file_data_size,
                   (unsigned long long)MAX_FILE_DATA_SIZE);
-      file_destroy(file);
-      array_list_delete(files);
-      return NULL;
+      goto error;
     }
 
     size_t allocation_size = file_data_size > 0 ? file_data_size : 1;
     void* file_data = protocol_alloc(allocation_size);
     if (file_data == NULL) {
       log_perror("Could not allocate memory for file data");
-      file_destroy(file);
-      array_list_delete(files);
-      return NULL;
+      goto error;
     }
     memcpy(file_data, data_pointer, file_data_size);
     Data* replacement = data_create(file_data, file_data_size);
-    if (replacement == NULL) {
-      file_destroy(file);
-      array_list_delete(files);
-      return NULL;
+    if (replacement == NULL)
+      goto error;
+    /* Charge the retained per-file copy to the connection budget (when the
+       inbound chunk carries an owning session) so the queued copies are not
+       held outside MAX_CONNECTION_MEMORY (B6).  A NULL owner (e.g. a local
+       batch apply) leaves the copy uncharged. */
+    if (!data_charge_session(replacement, data->owner, allocation_size)) {
+      log_message(LOG_LEVEL_ERROR, "Per-connection memory limit exceeded for chunk file data");
+      data_destroy(replacement);
+      goto error;
     }
     data_destroy(file->data);
     file->data = replacement;
     data_pointer += file_data_size;
     remaining_size -= file_data_size;
 
-    if (!array_list_add(files, file)) {
-      file_destroy(file);
-      array_list_delete(files);
-      return NULL;
+    if (file->is_symlink) {
+      if (remaining_size < sizeof(size_t)) {
+        log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for symlink target");
+        goto error;
       }
+      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");
+        goto error;
+      }
+      char* target = protocol_alloc(target_len + 1);
+      if (!target) {
+        log_perror("Could not allocate memory for symlink target");
+        goto error;
+      }
+      memcpy(target, data_pointer, target_len);
+      target[target_len] = '\0';
+      if (memchr(target, '\0', target_len) != NULL) {
+        free(target);
+        goto error;
+      }
+      /* 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");
+          goto error;
+        }
+        target = local_target;
+      }
+      file->symlink_target = target;
+      data_pointer += target_len;
+      remaining_size -= target_len;
+    }
+
+    if (!array_list_add(files, file))
+      goto error;
+    file = NULL;
   }
 
   File** file_array = (File**)array_list_to_array(files);
-  if (files->size > 0 && file_array == NULL) {
-    array_list_delete(files);
-    return NULL;
-  }
+  if (files->size > 0 && file_array == NULL)
+    goto error;
   Chunk* chunk = chunk_create(file_array, files->size);
-
   free(file_array);
-  if (chunk == NULL) {
-    array_list_delete(files);
-    return NULL;
-  }
+  if (chunk == NULL)
+    goto error;
   files->item_destroyer = NULL;
   array_list_delete(files);
-
   return chunk;
+
+error:
+  if (file)
+    file_destroy(file);
+  array_list_delete(files);
+  return NULL;
 }
 
 Data* chunk_compress(Chunk* chunk, int compression_level, bool use_metadata) {
@@ -344,12 +503,21 @@ Chunk* receive_chunk_data(int fd, const Config* config) {
   }
   Data* data_to_process = chunk_data;
   if (config->use_compression) {
+    /* Preserve the inbound session across decompression so the (larger)
+       decompressed chunk is charged to the same connection budget; the
+       compressed buffer's own charge is released by data_destroy below. */
+    ProtocolSession* owner = chunk_data->owner;
     data_to_process = data_decompress_limited(chunk_data, MAX_CHUNK_SIZE);
     data_destroy(chunk_data);
     if (data_to_process == NULL) {
       log_message(LOG_LEVEL_ERROR, "Failed to decompress chunk");
       return NULL;
     }
+    if (!data_charge_session(data_to_process, owner, data_to_process->size)) {
+      log_message(LOG_LEVEL_ERROR, "Per-connection memory limit exceeded for decompressed chunk");
+      data_destroy(data_to_process);
+      return NULL;
+    }
   }
 
   // Reject chunks larger than the maximum allowed size to prevent OOM.

src/shared/chunk.h

@@ -23,4 +23,15 @@ Data* chunk_compress_with_threads(Chunk* chunk, int compression_level, bool use_
                                   int compression_threads);
 Chunk* receive_chunk_data(int fd, const Config* config);
 
+/* Charge `charge` retained bytes of `data` against `session`'s per-connection
+ * budget (MAX_CONNECTION_MEMORY), mirroring the protocol layer's accounting, and
+ * record them on `data` so data_destroy() returns the charge through the
+ * Data.owner path.  Returns false (leaving `data` uncharged) when the ceiling
+ * would be exceeded.  A NULL/zero-size charge or a NULL session is a no-op
+ * success.  The receive-side decompression and chunk-copy paths know the owning
+ * session only through the Data.owner of the buffer they are processing, so
+ * this is the entry point that lets them participate in the connection budget
+ * without a session handle (B6). */
+bool data_charge_session(Data* data, ProtocolSession* session, size_t charge);
+
 #endif

src/shared/compression.c

@@ -2,138 +2,539 @@
 #include "data.h"
 #include "log.h"
 #include "protocol.h"
-#include <stdlib.h>
 #include <limits.h>
+#include <lz4.h>
+#include <stdatomic.h>
 #include <stdint.h>
+#include <stdlib.h>
 #include <string.h>
 #include <strings.h>
+#include <threads.h>
 #include <unistd.h>
+#include <zlib.h>
 #include <zstd.h>
 
 #define INITIAL_DECOMPRESS_BUF_SIZE (1024 * 1024)
 #define MAX_DECOMPRESSED_SIZE (100ULL * 1024 * 1024) /* 100 MB hard ceiling */
 
-static char* SKIP_COMPRESSION_EXTENSIONS[] = {".jpg", ".jpeg", ".png", ".gif", ".mp4", ".mkv",
-                                              ".zip", ".gz",   ".xz",  ".zst", NULL};
+/* rsync 3.4.1's built-in skip-compress suffix list (the `--skip-compress`
+ * defaults, in the man page's order).  rsync stores it as space-separated
+ * "*.suffix" globs; FastSync matches the plain suffix after the final dot, so
+ * the leading "*." is omitted here.  A user --skip-compress list replaces this
+ * default entirely (matching rsync). */
+#define DEFAULT_SKIP_COMPRESS_SUFFIXES                                                             \
+  "3g2 3gp 7z aac ace apk avi bz2 deb dmg ear f4v flac flv gpg gz iso jar jpeg jpg lrz lz lz4 "    \
+  "lzma "                                                                                          \
+  "lzo m1a m1v m2a m2ts m2v m4a m4b m4p m4r m4v mka mkv mov mp1 mp2 mp3 mp4 mpa mpeg mpg mpv mts " \
+  "odb odf odg odi odm odp ods odt oga ogg ogm ogv ogx opus otg oth otp ots ott oxt png qt rar "   \
+  "rpm "                                                                                           \
+  "rz rzip spx squashfs sxc sxd sxg sxm sxw sz tbz tbz2 tgz tlz ts txz tzo vob war webm webp xz "  \
+  "z "                                                                                             \
+  "zip zst"
 
-bool compression_should_skip(const char* path) {
-  return compression_should_skip_with_suffixes(path, NULL, -1);
+/* Self-describing compressed frames: the first byte is the CompressionAlgo id.
+ * zlib/lz4 store the uncompressed size as a little-endian uint32 after the
+ * codec byte so decompression can be exactly pre-sized and bounded. */
+#define LZ4_SIZE_PREFIX_LEN 4
+
+static _Atomic int g_compression_algo = COMPRESSION_ALGO_ZSTD;
+
+/* Case-insensitive match of a bare suffix (no leading dot) against a
+ * space-separated suffix list. */
+static bool suffix_in_list(const char* name, const char* list) {
+  size_t name_len = strlen(name);
+  while (*list) {
+    while (*list == ' ')
+      list++;
+    const char* start = list;
+    while (*list && *list != ' ')
+      list++;
+    size_t len = (size_t)(list - start);
+    if (len == name_len && strncasecmp(name, start, len) == 0)
+      return true;
+  }
+  return false;
 }
 
 bool compression_should_skip_with_suffixes(const char* path, char* const* suffixes, int count) {
   if (!path)
     return false;
   const char* dot = strrchr(path, '.');
-  if (!dot)
+  if (!dot || dot[1] == '\0')
     return false;
-  if (count < 0) {
-    suffixes = SKIP_COMPRESSION_EXTENSIONS;
-    count = 0;
-    while (SKIP_COMPRESSION_EXTENSIONS[count])
-      count++;
-  }
+  const char* name = dot + 1;
+  /* count < 0 (the user gave no --skip-compress) selects rsync's built-in
+   * default list; a non-negative count is the user's explicit list. */
+  if (count < 0)
+    return suffix_in_list(name, DEFAULT_SKIP_COMPRESS_SUFFIXES);
   for (int i = 0; i < count; i++) {
-    if (strcasecmp(dot, suffixes[i]) == 0)
+    const char* suffix = suffixes[i];
+    if (suffix[0] == '.')
+      suffix++;
+    if (strcasecmp(name, suffix) == 0)
       return true;
   }
   return false;
 }
 
-Data* data_compress(Data* data_to_compress, int compression_level) {
-  return data_compress_with_threads(data_to_compress, compression_level, 0);
+int compression_algo_from_name(const char* name) {
+  if (!name)
+    return -1;
+  if (strcasecmp(name, "zstd") == 0)
+    return (int)COMPRESSION_ALGO_ZSTD;
+  if (strcasecmp(name, "lz4") == 0)
+    return (int)COMPRESSION_ALGO_LZ4;
+  if (strcasecmp(name, "zlib") == 0)
+    return (int)COMPRESSION_ALGO_ZLIB;
+  if (strcasecmp(name, "zlibx") == 0)
+    return (int)COMPRESSION_ALGO_ZLIBX;
+  if (strcasecmp(name, "none") == 0)
+    return (int)COMPRESSION_ALGO_NONE;
+  return -1;
 }
 
-Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
+const char* compression_algo_name(CompressionAlgo algo) {
+  switch (algo) {
+  case COMPRESSION_ALGO_NONE:
+    return "none";
+  case COMPRESSION_ALGO_ZSTD:
+    return "zstd";
+  case COMPRESSION_ALGO_LZ4:
+    return "lz4";
+  case COMPRESSION_ALGO_ZLIB:
+    return "zlib";
+  case COMPRESSION_ALGO_ZLIBX:
+    return "zlibx";
+  }
+  return "<unknown>";
+}
+
+bool compression_algo_valid(int algo) {
+  return algo == (int)COMPRESSION_ALGO_NONE || algo == (int)COMPRESSION_ALGO_ZSTD ||
+         algo == (int)COMPRESSION_ALGO_LZ4 || algo == (int)COMPRESSION_ALGO_ZLIB ||
+         algo == (int)COMPRESSION_ALGO_ZLIBX;
+}
+
+bool compression_algo_enabled(CompressionAlgo algo) {
+  return algo != COMPRESSION_ALGO_NONE;
+}
+
+CompressionAlgo compression_negotiate_default(void) {
+  /* rsync 3.4.1 default preference order; every entry is compiled in, so this
+   * resolves to zstd. */
+  static const CompressionAlgo preference[] = {
+      COMPRESSION_ALGO_ZSTD, COMPRESSION_ALGO_LZ4,  COMPRESSION_ALGO_ZLIBX,
+      COMPRESSION_ALGO_ZLIB, COMPRESSION_ALGO_NONE,
+  };
+  for (size_t i = 0; i < sizeof(preference) / sizeof(preference[0]); i++) {
+    if (compression_algo_valid((int)preference[i]))
+      return preference[i];
+  }
+  return COMPRESSION_ALGO_ZSTD;
+}
+
+void compression_set_algo(CompressionAlgo algo) {
+  if (compression_algo_valid((int)algo))
+    atomic_store(&g_compression_algo, (int)algo);
+}
+
+CompressionAlgo compression_get_algo(void) {
+  return (CompressionAlgo)atomic_load(&g_compression_algo);
+}
+
+/* Per-thread cache of zstd contexts plus the grow-only compression scratch
+ * buffer.  zstd contexts are stateful and not safe to share between threads,
+ * so each thread keeps its own (see compression_get_thread_ctx).  The cache is
+ * stored in a C11 thread-specific storage slot whose destructor releases the
+ * contexts when the thread exits; this keeps LeakSanitizer clean for the
+ * short-lived sender/receiver/scanner worker threads without every worker
+ * entry point having to remember to call compression_free_thread_contexts().
+ * The main thread's slot is not torn down by tss at process exit, so an atexit
+ * hook releases it (and compression_free_thread_contexts allows eager
+ * release). */
+typedef struct {
+  ZSTD_CCtx* cctx;
+  ZSTD_DCtx* dctx;
+  void* out_buf;  /* reusable ZSTD_compressBound-sized output scratch */
+  size_t out_cap; /* bytes currently allocated for out_buf */
+  int level;      /* compression level currently applied to cctx */
+  int workers;    /* nbWorkers currently applied to cctx */
+  bool params_set;
+  bool cached; /* false when the TSS slot could not be used: caller owns */
+} CompressionThreadCtx;
+
+static once_flag compression_tls_once = ONCE_FLAG_INIT;
+static tss_t compression_tls_key;
+static bool compression_tls_ready;
+
+static void compression_tls_make_key(void);
+
+static void compression_ctx_free(CompressionThreadCtx* ctx) {
+  if (!ctx)
+    return;
+  if (ctx->cctx)
+    ZSTD_freeCCtx(ctx->cctx);
+  if (ctx->dctx)
+    ZSTD_freeDCtx(ctx->dctx);
+  free(ctx->out_buf);
+  free(ctx);
+}
+
+static void compression_tls_destructor(void* value) {
+  compression_ctx_free((CompressionThreadCtx*)value);
+}
+
+void compression_free_thread_contexts(void) {
+  call_once(&compression_tls_once, compression_tls_make_key);
+  if (!compression_tls_ready)
+    return;
+  CompressionThreadCtx* ctx = (CompressionThreadCtx*)tss_get(compression_tls_key);
+  if (!ctx)
+    return;
+  /* Clear the slot first so the thread-exit destructor cannot free it twice. */
+  tss_set(compression_tls_key, NULL);
+  compression_ctx_free(ctx);
+}
+
+static void compression_atexit_cleanup(void) {
+  compression_free_thread_contexts();
+}
+
+static void compression_tls_make_key(void) {
+  if (tss_create(&compression_tls_key, compression_tls_destructor) == thrd_success) {
+    compression_tls_ready = true;
+    atexit(compression_atexit_cleanup);
+  }
+}
+
+static CompressionThreadCtx* compression_get_thread_ctx(void) {
+  call_once(&compression_tls_once, compression_tls_make_key);
+  if (!compression_tls_ready) {
+    /* Extremely unlikely: fall back to an uncached context the caller frees. */
+    return (CompressionThreadCtx*)calloc(1, sizeof(CompressionThreadCtx));
+  }
+  CompressionThreadCtx* ctx = (CompressionThreadCtx*)tss_get(compression_tls_key);
+  if (ctx)
+    return ctx;
+  ctx = (CompressionThreadCtx*)calloc(1, sizeof(CompressionThreadCtx));
+  if (!ctx)
+    return NULL;
+  ctx->cached = true;
+  if (tss_set(compression_tls_key, ctx) != thrd_success)
+    ctx->cached = false;
+  return ctx;
+}
+
+/* Release an uncached context immediately; cached contexts are owned by the
+ * thread's TSS slot and freed on thread exit / compression_free_thread_contexts. */
+static void compression_ctx_put(CompressionThreadCtx* ctx) {
+  if (ctx && !ctx->cached)
+    compression_ctx_free(ctx);
+}
+
+/* Build a frame consisting of a copy of `src` prefixed by `codec`. */
+static Data* frame_with_codec(const void* src, size_t size, CompressionAlgo codec) {
+  if (size > SIZE_MAX - 1)
+    return NULL;
+  Data* out = data_create_empty(size + 1);
+  if (!out)
+    return NULL;
+  ((uint8_t*)out->data)[0] = (uint8_t)codec;
+  if (size > 0)
+    memcpy((uint8_t*)out->data + 1, src, size);
+  out->size = size + 1;
+  return out;
+}
+
+static Data* zstd_compress(Data* in, int compression_level, int compression_threads) {
+  size_t dst_size = ZSTD_compressBound(in->size);
+  if (dst_size > SIZE_MAX - 1)
+    return NULL;
+  dst_size += 1; /* codec prefix */
+
+  CompressionThreadCtx* ctx = compression_get_thread_ctx();
+  if (ctx == NULL) {
+    log_message(LOG_LEVEL_ERROR, "Failed to allocate ZSTD compression context");
+    return NULL;
+  }
+  Data* compressed_data = NULL;
+
+  if (!ctx->cctx) {
+    ctx->cctx = ZSTD_createCCtx();
+    if (!ctx->cctx) {
+      log_message(LOG_LEVEL_ERROR, "Failed to create ZSTD compression context");
+      goto cleanup;
+    }
+    ctx->params_set = false;
+  }
+
+  /* Reset only the session: parameters (and any already-allocated zstd worker
+   * pool) stay attached to the context, so compressing the next file does not
+   * rebuild the pool. */
+  ZSTD_CCtx_reset(ctx->cctx, ZSTD_reset_session_only);
+
+  if (!ctx->params_set || ctx->level != compression_level) {
+    size_t zret = ZSTD_CCtx_setParameter(ctx->cctx, ZSTD_c_compressionLevel, compression_level);
+    if (ZSTD_isError(zret)) {
+      log_message(LOG_LEVEL_ERROR, "Failed to set compression level: %s", ZSTD_getErrorName(zret));
+      goto cleanup;
+    }
+    ctx->level = compression_level;
+  }
+
+  int available_threads = 0;
+  if (compression_threads > 0) {
+    long online_cpus = sysconf(_SC_NPROCESSORS_ONLN);
+    available_threads = online_cpus > 0 && online_cpus < compression_threads ? (int)online_cpus
+                                                                             : compression_threads;
+  }
+  if (!ctx->params_set || ctx->workers != available_threads) {
+    size_t zret = ZSTD_CCtx_setParameter(ctx->cctx, ZSTD_c_nbWorkers, available_threads);
+    if (ZSTD_isError(zret)) {
+      log_message(LOG_LEVEL_ERROR, "Failed to set compression threads: %s",
+                  ZSTD_getErrorName(zret));
+      goto cleanup;
+    }
+    ctx->workers = available_threads;
+  }
+  ctx->params_set = true;
+
+  if (available_threads > 0) {
+    /* Streaming compression needs the source size before threaded mode can end a frame. */
+    size_t zret = ZSTD_CCtx_setPledgedSrcSize(ctx->cctx, in->size);
+    if (ZSTD_isError(zret)) {
+      log_message(LOG_LEVEL_ERROR, "Failed to set compression source size: %s",
+                  ZSTD_getErrorName(zret));
+      goto cleanup;
+    }
+  }
+
+  if (ctx->out_cap < dst_size) {
+    void* grown = protocol_realloc(ctx->out_buf, dst_size);
+    if (grown == NULL) {
+      log_message(LOG_LEVEL_ERROR, "Failed to allocate compression buffer");
+      goto cleanup;
+    }
+    ctx->out_buf = grown;
+    ctx->out_cap = dst_size;
+  }
+
+  ZSTD_inBuffer input = {in->data, in->size, 0};
+  ZSTD_outBuffer output = {(uint8_t*)ctx->out_buf + 1, dst_size - 1, 0};
+
+  size_t ret;
+  do {
+    ret = ZSTD_compressStream2(ctx->cctx, &output, &input, ZSTD_e_end);
+    if (ZSTD_isError(ret)) {
+      log_message(LOG_LEVEL_ERROR, "Compression failed: %s", ZSTD_getErrorName(ret));
+      goto cleanup;
+    }
+  } while (ret > 0);
+
+  /* Hand off an exactly-sized copy; the scratch buffer stays cached so the next
+   * call does not reallocate a ZSTD_compressBound-sized block. */
+  compressed_data = data_create_empty(output.pos + 1);
+  if (compressed_data == NULL) {
+    log_message(LOG_LEVEL_ERROR, "Failed to allocate compressed data");
+    goto cleanup;
+  }
+  ((uint8_t*)compressed_data->data)[0] = (uint8_t)COMPRESSION_ALGO_ZSTD;
+  if (output.pos > 0)
+    memcpy((uint8_t*)compressed_data->data + 1, (uint8_t*)ctx->out_buf + 1, output.pos);
+  compressed_data->size = output.pos + 1;
+
+  log_debug_message(LOG_DEBUG_UTIL, "Data succesfully compressed from %zu to %zu", in->size,
+                    compressed_data->size);
+
+cleanup:
+  compression_ctx_put(ctx);
+  return compressed_data;
+}
+
+static Data* lz4_compress(Data* in) {
+  int bound = LZ4_compressBound((int)in->size);
+  if (bound < 0 || in->size > (size_t)INT_MAX)
+    return NULL;
+  Data* out = data_create_empty((size_t)bound + 1 + LZ4_SIZE_PREFIX_LEN);
+  if (!out)
+    return NULL;
+  uint32_t raw_size = (uint32_t)in->size;
+  uint8_t* p = (uint8_t*)out->data;
+  p[0] = (uint8_t)COMPRESSION_ALGO_LZ4;
+  for (int i = 0; i < LZ4_SIZE_PREFIX_LEN; i++)
+    p[1 + i] = (uint8_t)((raw_size >> (8 * i)) & 0xff);
+  int written = 0;
+  if (in->size > 0) {
+    written = LZ4_compress_default((const char*)in->data, (char*)p + 1 + LZ4_SIZE_PREFIX_LEN,
+                                   (int)in->size, bound);
+    if (written <= 0) {
+      data_destroy(out);
+      return NULL;
+    }
+  }
+  out->size = (size_t)written + 1 + LZ4_SIZE_PREFIX_LEN;
+  return out;
+}
+
+static Data* zlib_compress(Data* in, CompressionAlgo algo, int compression_level) {
+  int level = compression_level;
+  if (level < 1)
+    level = Z_DEFAULT_COMPRESSION;
+  if (level > 9)
+    level = 9;
+  uLong bound = compressBound((uLong)in->size);
+  if (in->size > (size_t)ULONG_MAX)
+    return NULL;
+  Data* out = data_create_empty((size_t)bound + 1 + LZ4_SIZE_PREFIX_LEN);
+  if (!out)
+    return NULL;
+  uint32_t raw_size = (uint32_t)in->size;
+  uint8_t* p = (uint8_t*)out->data;
+  p[0] = (uint8_t)algo;
+  for (int i = 0; i < LZ4_SIZE_PREFIX_LEN; i++)
+    p[1 + i] = (uint8_t)((raw_size >> (8 * i)) & 0xff);
+  uLongf dest_len = bound;
+  int rc = compress2(p + 1 + LZ4_SIZE_PREFIX_LEN, &dest_len, (const Bytef*)in->data,
+                     (uLong)in->size, level);
+  if (rc != Z_OK) {
+    data_destroy(out);
+    return NULL;
+  }
+  out->size = (size_t)dest_len + 1 + LZ4_SIZE_PREFIX_LEN;
+  return out;
+}
+
+Data* data_compress_codec(Data* data_to_compress, CompressionAlgo algo, int compression_level,
                           int compression_threads) {
   if (!data_to_compress || (!data_to_compress->data && data_to_compress->size != 0) ||
       compression_threads < 0 || compression_threads > COMPRESSION_MAX_THREADS)
     return NULL;
+  if (!compression_algo_valid((int)algo))
+    return NULL;
   log_message(LOG_LEVEL_DEBUG, "Starting to compress data");
-  size_t dst_size = ZSTD_compressBound(data_to_compress->size);
-  Data* compressed_data = data_create_empty(dst_size);
-  if (compressed_data == NULL)
-    return NULL;
-
-  ZSTD_CCtx* cctx = ZSTD_createCCtx();
-  if (!cctx) {
-    log_message(LOG_LEVEL_ERROR, "Failed to create ZSTD compression context");
-    data_destroy(compressed_data);
-    return NULL;
+  switch (algo) {
+  case COMPRESSION_ALGO_NONE:
+    return frame_with_codec(data_to_compress->data, data_to_compress->size, COMPRESSION_ALGO_NONE);
+  case COMPRESSION_ALGO_ZSTD:
+    return zstd_compress(data_to_compress, compression_level, compression_threads);
+  case COMPRESSION_ALGO_LZ4:
+    return lz4_compress(data_to_compress);
+  case COMPRESSION_ALGO_ZLIB:
+  case COMPRESSION_ALGO_ZLIBX:
+    return zlib_compress(data_to_compress, algo, compression_level);
   }
-
-  size_t zret = ZSTD_CCtx_setParameter(cctx, ZSTD_c_compressionLevel, compression_level);
-  if (ZSTD_isError(zret)) {
-    log_message(LOG_LEVEL_ERROR, "Failed to set compression level: %s", ZSTD_getErrorName(zret));
-    ZSTD_freeCCtx(cctx);
-    data_destroy(compressed_data);
   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};
-
-  size_t ret;
-  do {
-    ret = ZSTD_compressStream2(cctx, &output, &input, ZSTD_e_end);
-    if (ZSTD_isError(ret)) {
-      log_message(LOG_LEVEL_ERROR, "Compression failed: %s", ZSTD_getErrorName(ret));
-      ZSTD_freeCCtx(cctx);
-      data_destroy(compressed_data);
-      return NULL;
-    }
-  } while (ret > 0);
-
-  compressed_data->size = output.pos;
-  ZSTD_freeCCtx(cctx);
-
-  log_debug_message(LOG_DEBUG_UTIL, "Data succesfully compressed from %zu to %zu",
-                    data_to_compress->size, compressed_data->size);
-  return compressed_data;
 }
 
-Data* data_decompress_limited(Data* compressed_data, size_t maximum_size) {
-  if (!compressed_data || (!compressed_data->data && compressed_data->size != 0) ||
-      maximum_size == 0)
+Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
+                                 int compression_threads) {
+  return data_compress_codec(data_to_compress, compression_get_algo(), compression_level,
+                             compression_threads);
+}
+
+Data* data_compress(Data* data_to_compress, int compression_level) {
+  return data_compress_codec(data_to_compress, compression_get_algo(), compression_level, 0);
+}
+
+static Data* decompress_none(const Data* compressed_data, size_t maximum_size) {
+  size_t size = compressed_data->size - 1;
+  if (size > maximum_size)
     return NULL;
+  Data* out = data_create_empty(size);
+  if (!out)
+    return NULL;
+  if (size > 0)
+    memcpy(out->data, (const uint8_t*)compressed_data->data + 1, size);
+  out->size = size;
+  return out;
+}
+
+/* Read the 4-byte little-endian raw size stored after the codec byte. */
+static bool read_raw_size(const Data* in, uint32_t* raw_size) {
+  if (in->size < 1 + LZ4_SIZE_PREFIX_LEN)
+    return false;
+  const uint8_t* p = (const uint8_t*)in->data;
+  uint32_t v = 0;
+  for (int i = 0; i < LZ4_SIZE_PREFIX_LEN; i++)
+    v |= (uint32_t)p[1 + i] << (8 * i);
+  *raw_size = v;
+  return true;
+}
+
+static Data* lz4_decompress(Data* compressed_data, size_t maximum_size, size_t hard_limit) {
+  uint32_t raw_size = 0;
+  if (!read_raw_size(compressed_data, &raw_size))
+    return NULL;
+  if (raw_size > hard_limit || raw_size > maximum_size)
+    return NULL;
+  size_t comp_size = compressed_data->size - 1 - LZ4_SIZE_PREFIX_LEN;
+  Data* out = data_create_empty(raw_size);
+  if (!out)
+    return NULL;
+  if (raw_size == 0) {
+    out->size = 0;
+    return out;
+  }
+  int rc = LZ4_decompress_safe((const char*)compressed_data->data + 1 + LZ4_SIZE_PREFIX_LEN,
+                               (char*)out->data, (int)comp_size, (int)raw_size);
+  if (rc < 0 || (uint32_t)rc != raw_size) {
+    log_message(LOG_LEVEL_ERROR, "LZ4 decompression failed");
+    data_destroy(out);
+    return NULL;
+  }
+  out->size = raw_size;
+  return out;
+}
+
+static Data* zlib_decompress(Data* compressed_data, size_t maximum_size, size_t hard_limit) {
+  uint32_t raw_size = 0;
+  if (!read_raw_size(compressed_data, &raw_size))
+    return NULL;
+  if (raw_size > hard_limit || raw_size > maximum_size)
+    return NULL;
+  size_t comp_size = compressed_data->size - 1 - LZ4_SIZE_PREFIX_LEN;
+  Data* out = data_create_empty(raw_size);
+  if (!out)
+    return NULL;
+  if (raw_size == 0) {
+    out->size = 0;
+    return out;
+  }
+  uLongf dest_len = raw_size;
+  int rc =
+      uncompress((Bytef*)out->data, &dest_len,
+                 (const Bytef*)compressed_data->data + 1 + LZ4_SIZE_PREFIX_LEN, (uLong)comp_size);
+  if (rc != Z_OK || dest_len != raw_size) {
+    log_message(LOG_LEVEL_ERROR, "zlib decompression failed");
+    data_destroy(out);
+    return NULL;
+  }
+  out->size = raw_size;
+  return out;
+}
+
+static Data* zstd_decompress(Data* compressed_data, size_t maximum_size) {
+  /* The zstd frame starts after the codec byte. */
+  const void* frame = (const uint8_t*)compressed_data->data + 1;
+  size_t frame_size = compressed_data->size - 1;
   log_debug_message(LOG_DEBUG_UTIL, "Start to decompress data");
-  unsigned long long dst_size =
-      ZSTD_getFrameContentSize(compressed_data->data, compressed_data->size);
-  if (ZSTD_isError(dst_size)) {
-    log_message(LOG_LEVEL_ERROR, "Failed to get decompressed size: %s",
-                ZSTD_getErrorName(dst_size));
+  unsigned long long dst_size = ZSTD_getFrameContentSize(frame, frame_size);
+  /* ZSTD_isError() is also true for ZSTD_CONTENTSIZE_ERROR and
+   * ZSTD_CONTENTSIZE_UNKNOWN (both are encoded near (size_t)-1), so test the
+   * sentinels explicitly instead of blanket-rejecting every error-ish value:
+   * only CONTENTSIZE_ERROR means an unreadable header, while CONTENTSIZE_UNKNOWN
+   * must reach the estimate fallback below. */
+  if (dst_size == ZSTD_CONTENTSIZE_ERROR) {
+    log_message(LOG_LEVEL_ERROR, "Failed to get decompressed size: invalid zstd frame");
     return NULL;
   }
 
   // ZSTD_CONTENTSIZE_UNKNOWN (~2^64) can cause massive allocation;
   // fall back to a conservative estimate (3x compressed size) when unknown.
   if (dst_size == ZSTD_CONTENTSIZE_UNKNOWN) {
-    if (compressed_data->size > ULLONG_MAX / 3)
+    if (frame_size > ULLONG_MAX / 3)
       return NULL;
-    dst_size = compressed_data->size * 3;
+    dst_size = frame_size * 3;
     if (dst_size < INITIAL_DECOMPRESS_BUF_SIZE)
       dst_size = INITIAL_DECOMPRESS_BUF_SIZE;
   }
@@ -144,41 +545,51 @@ Data* data_decompress_limited(Data* compressed_data, size_t maximum_size) {
     return NULL;
   }
 
-  ZSTD_DCtx* dctx = ZSTD_createDCtx();
-  if (!dctx) {
-    log_message(LOG_LEVEL_ERROR, "Failed to create ZSTD decompression context");
+  CompressionThreadCtx* ctx = compression_get_thread_ctx();
+  if (ctx == NULL) {
+    log_message(LOG_LEVEL_ERROR, "Failed to allocate ZSTD decompression context");
     return NULL;
   }
+  Data* uncompressed_data = NULL;
+
+  if (!ctx->dctx) {
+    ctx->dctx = ZSTD_createDCtx();
+    if (!ctx->dctx) {
+      log_message(LOG_LEVEL_ERROR, "Failed to create ZSTD decompression context");
+      goto cleanup;
+    }
+  }
+  /* Reset only the session; decompression parameters are sticky. */
+  ZSTD_DCtx_reset(ctx->dctx, ZSTD_reset_session_only);
 
   size_t buf_size = (dst_size > 0) ? (size_t)dst_size : INITIAL_DECOMPRESS_BUF_SIZE;
   if (buf_size > maximum_size)
     buf_size = maximum_size;
-  Data* uncompressed_data = data_create_empty(buf_size);
+  uncompressed_data = data_create_empty(buf_size);
   if (!uncompressed_data) {
     log_message(LOG_LEVEL_ERROR, "Failed to allocate decompression buffer");
-    ZSTD_freeDCtx(dctx);
-    return NULL;
+    goto cleanup;
   }
 
-  ZSTD_inBuffer input = {compressed_data->data, compressed_data->size, 0};
+  ZSTD_inBuffer input = {frame, frame_size, 0};
   ZSTD_outBuffer output = {uncompressed_data->data, buf_size, 0};
 
   size_t ret;
   do {
-    ret = ZSTD_decompressStream(dctx, &output, &input);
+    ret = ZSTD_decompressStream(ctx->dctx, &output, &input);
     if (ZSTD_isError(ret)) {
       log_message(LOG_LEVEL_ERROR, "Decompression failed: %s", ZSTD_getErrorName(ret));
-      ZSTD_freeDCtx(dctx);
       data_destroy(uncompressed_data);
-      return NULL;
+      uncompressed_data = NULL;
+      goto cleanup;
     }
     if (ret > 0 && output.pos == output.size) {
       if (buf_size >= hard_limit || buf_size > SIZE_MAX / 2) {
         log_message(LOG_LEVEL_ERROR, "Decompressed data exceeds %llu bytes",
                     (unsigned long long)MAX_DECOMPRESSED_SIZE);
-        ZSTD_freeDCtx(dctx);
         data_destroy(uncompressed_data);
-        return NULL;
+        uncompressed_data = NULL;
+        goto cleanup;
       }
       buf_size *= 2;
       if (buf_size > hard_limit)
@@ -186,23 +597,64 @@ Data* data_decompress_limited(Data* compressed_data, size_t maximum_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);
         data_destroy(uncompressed_data);
-        return NULL;
+        uncompressed_data = NULL;
+        goto cleanup;
       }
       uncompressed_data->data = new_data;
       output.dst = new_data;
       output.size = buf_size;
+      /* Re-attempt with the larger output buffer; the truncated-frame check
+       * below must not reject a complete frame that merely filled the previous
+       * buffer exactly. */
+      continue;
+    }
+    /* A positive hint with all input consumed means the frame is incomplete: a
+     * truncated stream would otherwise spin here forever (ZSTD_decompressStream
+     * keeps returning the same hint).  Fail instead of burning CPU. */
+    if (ret != 0 && input.pos == input.size) {
+      log_message(LOG_LEVEL_ERROR,
+                  "Truncated zstd frame: input exhausted with %zu bytes still expected", ret);
+      data_destroy(uncompressed_data);
+      uncompressed_data = NULL;
+      goto cleanup;
     }
   } while (ret > 0);
 
   uncompressed_data->size = output.pos;
-  ZSTD_freeDCtx(dctx);
 
   log_debug_message(LOG_DEBUG_UTIL, "Decompressed data successfully");
+
+cleanup:
+  compression_ctx_put(ctx);
   return uncompressed_data;
 }
 
+Data* data_decompress_limited(Data* compressed_data, size_t maximum_size) {
+  if (!compressed_data || (!compressed_data->data && compressed_data->size != 0) ||
+      maximum_size == 0)
+    return NULL;
+  if (compressed_data->size < 1)
+    return NULL;
+  unsigned long long hard_limit =
+      maximum_size < MAX_DECOMPRESSED_SIZE ? maximum_size : MAX_DECOMPRESSED_SIZE;
+  uint8_t codec = ((const uint8_t*)compressed_data->data)[0];
+  if (!compression_algo_valid(codec))
+    return NULL;
+  switch ((CompressionAlgo)codec) {
+  case COMPRESSION_ALGO_NONE:
+    return decompress_none(compressed_data, (size_t)hard_limit);
+  case COMPRESSION_ALGO_ZSTD:
+    return zstd_decompress(compressed_data, (size_t)hard_limit);
+  case COMPRESSION_ALGO_LZ4:
+    return lz4_decompress(compressed_data, maximum_size, (size_t)hard_limit);
+  case COMPRESSION_ALGO_ZLIB:
+  case COMPRESSION_ALGO_ZLIBX:
+    return zlib_decompress(compressed_data, maximum_size, (size_t)hard_limit);
+  }
+  return NULL;
+}
+
 Data* data_decompress(Data* compressed_data) {
   return data_decompress_limited(compressed_data, MAX_DECOMPRESSED_SIZE);
 }

src/shared/compression.h

@@ -6,12 +6,67 @@
 
 #define COMPRESSION_MAX_THREADS 64
 
+/* Compression algorithms selectable with --compress-choice / -z.  The ids are
+ * the values placed on the wire (Config->compression_algo), so they must be
+ * kept stable.  NONE is "no compression"; ZSTD is the historical FastSync
+ * default and the negotiated "auto" choice.  ZLIBX is rsync's zlib-without-
+ * matched-data variant: FastSync compresses only the delta/token bytes (it does
+ * not put matched file data in the compression stream), so its zlib codec is
+ * already the "x" form and zlib/zlibx share the same implementation, recorded
+ * under distinct ids. */
+typedef enum {
+  COMPRESSION_ALGO_NONE = 0,
+  COMPRESSION_ALGO_ZSTD = 1,
+  COMPRESSION_ALGO_LZ4 = 2,
+  COMPRESSION_ALGO_ZLIB = 3,
+  COMPRESSION_ALGO_ZLIBX = 4
+} CompressionAlgo;
+
+/* Resolve a --compress-choice string (case-insensitive) to an algorithm id.
+ * Accepts "zstd", "lz4", "zlib", "zlibx", "none".  "auto" is not an algorithm
+ * here; the caller resolves it to the negotiated default.  Returns -1 for any
+ * unrecognized name. */
+int compression_algo_from_name(const char* name);
+const char* compression_algo_name(CompressionAlgo algo);
+bool compression_algo_valid(int algo);
+
+/* Pick the first algorithm from FastSync's compiled-in preference list
+ * (rsync 3.4.1's `--version` order: zstd lz4 zlibx zlib none).  Resolves
+ * "auto". */
+CompressionAlgo compression_negotiate_default(void);
+
+/* True when the algorithm actually compresses (i.e. is not NONE). */
+bool compression_algo_enabled(CompressionAlgo algo);
+
+/* Select the process-wide codec used by the legacy wrappers below.  Each
+ * process serves exactly one transfer config (the server forks per connection,
+ * the client configures itself before spawning transfer threads), so a
+ * process-global default is sufficient and constant for the lifetime of a
+ * transfer.  Defaults to ZSTD when never set.  Thread-safe. */
+void compression_set_algo(CompressionAlgo algo);
+CompressionAlgo compression_get_algo(void);
+
+/* Codec-aware primitives.  The compressed buffer is self-describing: its first
+ * byte is the CompressionAlgo id, so decompression never needs the codec passed
+ * separately (this keeps every existing Decompress call site source-compatible).
+ * `data_compress_codec` returns NULL on invalid input or an unsupported codec. */
+Data* data_compress_codec(Data* data_to_compress, CompressionAlgo algo, int compression_level,
+                          int compression_threads);
+Data* data_decompress_limited(Data* compressed_data, size_t maximum_size);
+
+/* Legacy zstd-default wrappers retained for existing callers/tests. */
 Data* data_compress(Data* data_to_compress, int compression_level);
 Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
                                  int compression_threads);
 Data* data_decompress(Data* compressed_data);
-Data* data_decompress_limited(Data* compressed_data, size_t maximum_size);
-bool compression_should_skip(const char* path);
 bool compression_should_skip_with_suffixes(const char* path, char* const* suffixes, int count);
 
+/* Release the calling thread's cached zstd contexts (compressor, decompressor
+ * and scratch buffer).  The cache is thread-local and is also released
+ * automatically when a worker thread exits (via a C11 tss destructor) and for
+ * the main thread at process exit; this explicit entry point exists so tests
+ * and long-lived callers can drop the cache deterministically.  Safe to call
+ * when no context has been created, and idempotent. */
+void compression_free_thread_contexts(void);
+
 #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 +1,794 @@
+#include "daemon_conf.h"
+#include "credentials.h"
+#include "utils.h"
+#include <arpa/inet.h>
+#include <ctype.h>
+#include <errno.h>
+#include <limits.h>
+#include <netinet/in.h>
+#include <stdarg.h>
+#include <stdint.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;
+}
+
+/* Parse an IPv4/IPv6 CIDR "addr/prefix" into `bytes`/`*family`.  Returns false
+ * for a malformed address, a missing/oversized prefix, or a prefix that does
+ * not fit the address family. */
+static bool parse_cidr(const char* cidr, int* prefix_out, uint8_t* bytes, int* family_out) {
+  const char* slash = strchr(cidr, '/');
+  if (!slash)
+    return false;
+  size_t addr_len = (size_t)(slash - cidr);
+  if (addr_len == 0 || addr_len >= INET6_ADDRSTRLEN)
+    return false;
+  char addr[INET6_ADDRSTRLEN];
+  memcpy(addr, cidr, addr_len);
+  addr[addr_len] = '\0';
+  char* end = NULL;
+  long prefix = strtol(slash + 1, &end, 10);
+  if (end == slash + 1 || *end != '\0')
+    return false;
+  struct in_addr v4;
+  struct in6_addr v6;
+  if (inet_pton(AF_INET, addr, &v4) == 1) {
+    if (prefix < 0 || prefix > 32)
+      return false;
+    memcpy(bytes, &v4, sizeof(v4));
+    *prefix_out = (int)prefix;
+    *family_out = AF_INET;
+    return true;
+  }
+  if (inet_pton(AF_INET6, addr, &v6) == 1) {
+    if (prefix < 0 || prefix > 128)
+      return false;
+    memcpy(bytes, &v6, sizeof(v6));
+    *prefix_out = (int)prefix;
+    *family_out = AF_INET6;
+    return true;
+  }
+  return false;
+}
+
+/* A host pattern is valid when it is `*`, a valid IPv4/IPv6 literal, or a valid
+ * CIDR.  Peer addresses reaching the matcher are always numeric, so hostname
+ * globs are rejected at parse time: accepting one would create a deny rule that
+ * silently never matches (fail-open). */
+static bool host_pattern_valid(const char* pattern) {
+  if (!pattern || *pattern == '\0')
+    return false;
+  if (strcmp(pattern, "*") == 0)
+    return true;
+  if (strchr(pattern, '/')) {
+    uint8_t bytes[16];
+    int prefix;
+    int family;
+    return parse_cidr(pattern, &prefix, bytes, &family);
+  }
+  struct in_addr v4;
+  struct in6_addr v6;
+  return inet_pton(AF_INET, pattern, &v4) == 1 || inet_pton(AF_INET6, pattern, &v6) == 1;
+}
+
+/* Append every comma- and/or whitespace-separated host pattern in `value` to
+ * the heap-owned list (or replace the list when `replace` is set, which --dparam
+ * uses so an override can narrow access rather than only widen it).  Returns
+ * false (err filled) on an invalid pattern or an allocation failure. */
+static bool store_host_list(char*** list, int* count, const char* value, const char* key,
+                            const char* module_name, bool replace, char* err, size_t err_size) {
+  if (replace) {
+    for (int i = 0; i < *count; i++)
+      free((*list)[i]);
+    free(*list);
+    *list = NULL;
+    *count = 0;
+  }
+  char* copy = str_dup(value);
+  if (!copy) {
+    if (module_name)
+      set_error(err, err_size, "out of memory parsing '%s' for module '%s'", key, module_name);
+    else
+      set_error(err, err_size, "out of memory parsing '%s'", key);
+    return false;
+  }
+  char* save = NULL;
+  int added = 0;
+  for (char* token = strtok_r(copy, ", \t", &save); token; token = strtok_r(NULL, ", \t", &save)) {
+    if (!host_pattern_valid(token)) {
+      if (module_name)
+        set_error(err, err_size, "module '%s': invalid host pattern '%s' in '%s'", module_name,
+                  token, key);
+      else
+        set_error(err, err_size, "invalid host pattern '%s' in '%s'", token, key);
+      free(copy);
+      return false;
+    }
+    char** grown = realloc(*list, (size_t)(*count + 1) * sizeof(char*));
+    if (!grown) {
+      if (module_name)
+        set_error(err, err_size, "out of memory parsing '%s' for module '%s'", key, module_name);
+      else
+        set_error(err, err_size, "out of memory parsing '%s'", key);
+      free(copy);
+      return false;
+    }
+    *list = grown;
+    char* dup = str_dup(token);
+    if (!dup) {
+      if (module_name)
+        set_error(err, err_size, "out of memory parsing '%s' for module '%s'", key, module_name);
+      else
+        set_error(err, err_size, "out of memory parsing '%s'", key);
+      free(copy);
+      return false;
+    }
+    (*list)[(*count)++] = dup;
+    added++;
+  }
+  free(copy);
+  /* A present key with an empty (or separator-only) value would otherwise
+   * install a zero-length list, i.e. no ACL at all: a strict-parse config must
+   * never silently turn a restrictive directive into "allow everyone". */
+  if (added == 0) {
+    if (module_name)
+      set_error(err, err_size, "module '%s': '%s' must list at least one host pattern", module_name,
+                key);
+    else
+      set_error(err, err_size, "'%s' must list at least one host pattern", key);
+    return false;
+  }
+  return true;
+}
+
+/* Parse a `max connections` value: a positive integer (0/negative/garbage are
+ * rejected because they would silently disable the cap or admit nothing). */
+static bool store_max_connections(int* slot, const char* value, const char* module_name, char* err,
+                                  size_t err_size) {
+  char* end = NULL;
+  errno = 0;
+  long n = strtol(value, &end, 10);
+  if (*value == '\0' || errno != 0 || *end != '\0' || n <= 0 || n > INT_MAX) {
+    if (module_name)
+      set_error(err, err_size,
+                "module '%s': invalid 'max connections' '%s' (must be a positive "
+                "integer)",
+                module_name, value);
+    else
+      set_error(err, err_size, "invalid 'max connections' '%s' (must be a positive integer)",
+                value);
+    return false;
+  }
+  *slot = (int)n;
+  return true;
+}
+
+/* Parse a non-negative concurrency cap where 0 means unlimited/disabled
+ * (per-module `max connections`, `max connections per host`,
+ * `auth lockout threshold`).  Negative/garbage/oversized values are rejected. */
+static bool store_optional_cap(int* slot, const char* value, int max_value, const char* key,
+                               const char* module_name, char* err, size_t err_size) {
+  char* end = NULL;
+  errno = 0;
+  long n = strtol(value, &end, 10);
+  if (*value == '\0' || errno != 0 || *end != '\0' || n < 0 || n > max_value) {
+    if (module_name)
+      set_error(err, err_size, "module '%s': invalid '%s' '%s' (must be 0-%d)", module_name, key,
+                value, max_value);
+    else
+      set_error(err, err_size, "invalid '%s' '%s' (must be 0-%d)", key, value, max_value);
+    return false;
+  }
+  *slot = (int)n;
+  return true;
+}
+
+/* Parse an `auth failure delay` value: 0 (disabled) through the configured cap. */
+static bool store_auth_failure_delay(int* slot, const char* value, char* err, size_t err_size) {
+  char* end = NULL;
+  errno = 0;
+  long n = strtol(value, &end, 10);
+  if (*value == '\0' || errno != 0 || *end != '\0' || n < 0 ||
+      n > DAEMON_CONF_MAX_AUTH_FAILURE_DELAY_MS) {
+    set_error(err, err_size, "invalid 'auth failure delay' '%s' (must be 0-%d milliseconds)", value,
+              DAEMON_CONF_MAX_AUTH_FAILURE_DELAY_MS);
+    return false;
+  }
+  *slot = (int)n;
+  return true;
+}
+
+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;
+  conf->global.max_connections = DAEMON_CONF_DEFAULT_MAX_CONNECTIONS;
+  conf->global.auth_failure_delay_ms = DAEMON_CONF_DEFAULT_AUTH_FAILURE_DELAY_MS;
+  conf->global.max_connections_per_host = DAEMON_CONF_DEFAULT_MAX_CONNECTIONS_PER_HOST;
+  conf->global.auth_lockout_threshold = DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_THRESHOLD;
+  conf->global.auth_lockout_duration_sec = DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_DURATION_SEC;
+  return conf;
+}
+
+/* Free a heap-owned pattern list of `count` entries. */
+static void free_string_list(char** list, int count) {
+  for (int i = 0; i < count; i++)
+    free(list[i]);
+  free(list);
+}
+
+void daemon_conf_free(DaemonConf* conf) {
+  if (!conf)
+    return;
+  free(conf->global.motd_file);
+  free(conf->global.address);
+  free_string_list(conf->global.hosts_allow, conf->global.hosts_allow_count);
+  free_string_list(conf->global.hosts_deny, conf->global.hosts_deny_count);
+  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_string_list(m->hosts_allow, m->hosts_allow_count);
+    free_string_list(m->hosts_deny, m->hosts_deny_count);
+  }
+  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, bool replace_hosts,
+                             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;
+  }
+  if (key_equals(key, "max connections"))
+    return store_max_connections(&conf->global.max_connections, value, NULL, err, err_size);
+  if (key_equals(key, "max connections per host"))
+    return store_optional_cap(&conf->global.max_connections_per_host, value,
+                              DAEMON_CONF_MAX_CONCURRENCY_LIMIT, "max connections per host", NULL,
+                              err, err_size);
+  if (key_equals(key, "auth failure delay"))
+    return store_auth_failure_delay(&conf->global.auth_failure_delay_ms, value, err, err_size);
+  if (key_equals(key, "auth lockout threshold"))
+    return store_optional_cap(&conf->global.auth_lockout_threshold, value,
+                              DAEMON_CONF_MAX_CONCURRENCY_LIMIT, "auth lockout threshold", NULL,
+                              err, err_size);
+  if (key_equals(key, "auth lockout duration"))
+    return store_optional_cap(&conf->global.auth_lockout_duration_sec, value,
+                              DAEMON_CONF_MAX_AUTH_LOCKOUT_DURATION_SEC, "auth lockout duration",
+                              NULL, err, err_size);
+  if (key_equals(key, "hosts allow"))
+    return store_host_list(&conf->global.hosts_allow, &conf->global.hosts_allow_count, value,
+                           "hosts allow", NULL, replace_hosts, err, err_size);
+  if (key_equals(key, "hosts deny"))
+    return store_host_list(&conf->global.hosts_deny, &conf->global.hosts_deny_count, value,
+                           "hosts deny", NULL, replace_hosts, err, err_size);
+  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;
+    int added = 0;
+    for (char* token = strtok_r(list, ",", &save); token; token = strtok_r(NULL, ",", &save)) {
+      const char* user = trim_ws(token);
+      if (*user == '\0')
+        continue;
+      if (!credentials_username_valid(user)) {
+        set_error(err, err_size, "module '%s': invalid 'auth users' entry '%s'", module->name,
+                  user);
+        free(list);
+        return false;
+      }
+      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;
+      added++;
+    }
+    free(list);
+    /* An empty/separator-only value must not silently disable authentication:
+     * the key's presence is an explicit request for an allow-list. */
+    if (added == 0) {
+      set_error(err, err_size, "module '%s': 'auth users' must list at least one user",
+                module->name);
+      return false;
+    }
+    return true;
+  }
+  if (key_equals(key, "max connections"))
+    return store_optional_cap(&module->max_connections, value, DAEMON_CONF_MAX_CONCURRENCY_LIMIT,
+                              "max connections", module->name, err, err_size);
+  if (key_equals(key, "hosts allow"))
+    return store_host_list(&module->hosts_allow, &module->hosts_allow_count, value, "hosts allow",
+                           module->name, false, err, err_size);
+  if (key_equals(key, "hosts deny"))
+    return store_host_list(&module->hosts_deny, &module->hosts_deny_count, value, "hosts deny",
+                           module->name, false, err, err_size);
+  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;
+  }
+  if (conf->module_count >= DAEMON_CONF_MAX_MODULES) {
+    set_error(err, err_size, "too many modules (limit %d); module '%s' rejected",
+              DAEMON_CONF_MAX_MODULES, 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, false, 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, true, err, err_size);
+  free(copy);
+  return ok ? 0 : -1;
+}
+
+/* Compare the first `prefix` bits of two 16-byte address buffers. */
+static bool bit_prefix_match(const uint8_t* a, const uint8_t* b, int prefix) {
+  int whole = prefix / 8;
+  if (whole > 0 && memcmp(a, b, (size_t)whole) != 0)
+    return false;
+  int remainder = prefix % 8;
+  if (remainder == 0)
+    return true;
+  uint8_t mask = (uint8_t)(0xffu << (8 - remainder));
+  return (a[whole] & mask) == (b[whole] & mask);
+}
+
+/* Case-insensitive glob match used for hostname patterns.  Falls back to the
+ * shared case-sensitive matcher when an operand is too long for the stack
+ * buffers. */
+static bool host_glob_match(const char* pattern, const char* str) {
+  char pbuf[256];
+  char sbuf[256];
+  size_t plen = strlen(pattern);
+  size_t slen = strlen(str);
+  if (plen >= sizeof(pbuf) || slen >= sizeof(sbuf))
+    return glob_match(pattern, str);
+  for (size_t i = 0; i <= plen; i++)
+    pbuf[i] = (char)tolower((unsigned char)pattern[i]);
+  for (size_t i = 0; i <= slen; i++)
+    sbuf[i] = (char)tolower((unsigned char)str[i]);
+  return glob_match(pbuf, sbuf);
+}
+
+bool daemon_host_pattern_match(const char* pattern, const char* peer_ip) {
+  if (!pattern || *pattern == '\0' || !peer_ip || *peer_ip == '\0')
+    return false;
+  if (strcmp(pattern, "*") == 0)
+    return true;
+  if (strchr(pattern, '/')) {
+    uint8_t pattern_bytes[16];
+    uint8_t peer_bytes[16];
+    int prefix = 0;
+    int family = AF_UNSPEC;
+    if (!parse_cidr(pattern, &prefix, pattern_bytes, &family))
+      return false;
+    if (inet_pton(family, peer_ip, peer_bytes) != 1)
+      return false;
+    return bit_prefix_match(pattern_bytes, peer_bytes, prefix);
+  }
+  struct in_addr pattern_v4;
+  struct in_addr peer_v4;
+  if (inet_pton(AF_INET, pattern, &pattern_v4) == 1)
+    return inet_pton(AF_INET, peer_ip, &peer_v4) == 1 && pattern_v4.s_addr == peer_v4.s_addr;
+  struct in6_addr pattern_v6;
+  struct in6_addr peer_v6;
+  if (inet_pton(AF_INET6, pattern, &pattern_v6) == 1)
+    return inet_pton(AF_INET6, peer_ip, &peer_v6) == 1 &&
+           memcmp(&pattern_v6, &peer_v6, sizeof(pattern_v6)) == 0;
+  /* Not a literal: a hostname/glob pattern. */
+  return host_glob_match(pattern, peer_ip);
+}
+
+bool daemon_hosts_allowed(const char* peer_ip, char* const* allow, int allow_count,
+                          char* const* deny, int deny_count) {
+  if (!peer_ip)
+    return false;
+  for (int i = 0; i < deny_count; i++) {
+    if (daemon_host_pattern_match(deny[i], peer_ip))
+      return false;
+  }
+  if (allow_count > 0) {
+    for (int i = 0; i < allow_count; i++) {
+      if (daemon_host_pattern_match(allow[i], peer_ip))
+        return true;
+    }
+    return false;
+  }
+  return true;
+}
+
+bool daemon_hosts_restricted(char* const* allow, int allow_count, char* const* deny,
+                             int deny_count) {
+  (void)allow;
+  (void)deny;
+  return allow_count > 0 || deny_count > 0;
+}

src/shared/daemon_conf.h

@@ -0,0 +1,182 @@
+#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;
+  /* `max connections = N` (optional per-module cap).  0 means unlimited.  The
+   * per-connection child records the selected module in the shared registry
+   * (daemon_limits.c) once the config frame names it, so the cap is enforced
+   * across all forked children; the parent reclaims the slot on SIGCHLD. */
+  int max_connections;
+  char** hosts_allow; /* `hosts allow = a,b`; host access allow patterns */
+  int hosts_allow_count;
+  char** hosts_deny; /* `hosts deny = a,b`; host access deny patterns */
+  int hosts_deny_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 */
+  int max_connections;           /* `max connections`, default
+                                    DAEMON_CONF_DEFAULT_MAX_CONNECTIONS (100) */
+  int auth_failure_delay_ms;     /* `auth failure delay`, milliseconds; default
+                                    DAEMON_CONF_DEFAULT_AUTH_FAILURE_DELAY_MS */
+  int max_connections_per_host;  /* `max connections per host`, concurrent cap per
+                                    source IP; default
+                                    DAEMON_CONF_DEFAULT_MAX_CONNECTIONS_PER_HOST (0 =
+                                    unlimited) */
+  int auth_lockout_threshold;    /* `auth lockout threshold`, failed attempts from
+                                    one source before lockout; default
+                                    DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_THRESHOLD (0
+                                    disables) */
+  int auth_lockout_duration_sec; /* `auth lockout duration`, seconds; default
+                                    DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_DURATION_SEC
+                                    (0 disables) */
+  char** hosts_allow;            /* `hosts allow`; global host access allow patterns */
+  int hosts_allow_count;
+  char** hosts_deny; /* `hosts deny`; global host access deny patterns */
+  int hosts_deny_count;
+} DaemonConfGlobals;
+
+typedef struct DaemonConf {
+  DaemonConfGlobals global;
+  DaemonModule* modules;
+  int module_count;
+} DaemonConf;
+
+#define DAEMON_CONF_DEFAULT_PORT 873
+/* Default global connection cap when `max connections` is absent.  Matches the
+ * historical hardcoded listener value. */
+#define DAEMON_CONF_DEFAULT_MAX_CONNECTIONS 100
+/* Default `auth failure delay` in milliseconds (0 disables the throttle). */
+#define DAEMON_CONF_DEFAULT_AUTH_FAILURE_DELAY_MS 500
+/* Default `max connections per host` (0 = unlimited). */
+#define DAEMON_CONF_DEFAULT_MAX_CONNECTIONS_PER_HOST 0
+/* Default cross-process auth lockout: 10 failed attempts from one source lock
+ * it out for 300 s (0 disables either knob). */
+#define DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_THRESHOLD 10
+#define DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_DURATION_SEC 300
+/* Upper bound on a `max connections per host` or `auth lockout threshold`
+ * value, so a typo cannot size the shared registry absurdly. */
+#define DAEMON_CONF_MAX_CONCURRENCY_LIMIT 1000000
+/* Upper bound on `auth lockout duration` (7 days). */
+#define DAEMON_CONF_MAX_AUTH_LOCKOUT_DURATION_SEC 604800
+/* Largest accepted `auth failure delay`, so a typo cannot pin a connection
+ * child in nanosleep for an absurd time. */
+/* Bounded well below the socket I/O timeout so a failed-auth child cannot hold
+ * a connection slot for long enough to amplify connection-cap exhaustion. */
+#define DAEMON_CONF_MAX_AUTH_FAILURE_DELAY_MS 5000
+/* Upper bound on the number of [module] sections, so the shared registry's
+ * per-module counter array stays fixed-size.  The parser rejects the next
+ * section past this bound. */
+#define DAEMON_CONF_MAX_MODULES 256
+/* 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 keys only.  Keys are case-insensitive and limited to
+ * the global keys defined by the grammar (port, motd file, address,
+ * max connections, max connections per host, auth failure delay,
+ * auth lockout threshold, auth lockout duration, hosts allow, hosts deny).
+ * 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);
+
+/* Host access-control matching (pure; no I/O).  `daemon_host_pattern_match`
+ * matches one configured pattern against a numeric peer IP string.  Supported
+ * patterns: `*` (match anything), an IPv4/IPv6 literal, an IPv4/IPv6 CIDR
+ * (`10.0.0.0/8`, `2001:db8::/32`), or a glob (`*.example.com`) evaluated with
+ * the same matcher as file globs; a glob only matches a peer string of the
+ * same shape, so a numeric peer never matches a hostname glob. */
+bool daemon_host_pattern_match(const char* pattern, const char* peer_ip);
+
+/* rsync-like combined decision over a deny list and an allow list: a matching
+ * deny rejects (deny takes precedence); otherwise, when any allow entries
+ * exist, a peer that matches none is rejected; with no allow entries every
+ * peer not denied is accepted.  An empty/unset pair returns true. */
+bool daemon_hosts_allowed(const char* peer_ip, char* const* allow, int allow_count,
+                          char* const* deny, int deny_count);
+
+/* True when at least one allow or deny pattern is configured (i.e. an
+ * unprovable peer must fail closed rather than being treated as unrestricted). */
+bool daemon_hosts_restricted(char* const* allow, int allow_count, char* const* deny,
+                             int deny_count);
+
+#endif

src/shared/daemon_limits.c

@@ -0,0 +1,494 @@
+#include "daemon_limits.h"
+#include "daemon_conf.h"
+#include "log.h"
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <stdatomic.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <time.h>
+
+/* The two module-count bounds must agree: the daemon config parser never
+ * produces more than DAEMON_CONF_MAX_MODULES modules, so the shared registry's
+ * per-module counter array is sized from the same bound. */
+_Static_assert(DAEMON_LIMITS_MAX_MODULES == DAEMON_CONF_MAX_MODULES,
+               "daemon_limits module bound must match daemon_conf");
+
+/* Slot lifecycle states (stored in slot_state). */
+enum {
+  SLOT_FREE = 0,
+  SLOT_CLAIMED = 1,
+  SLOT_REGISTERED = 2,
+};
+
+/* The registry header lives at the base of the shared mapping; the pointer
+ * fields point at the arrays carved out of the same mapping.  Absolute pointers
+ * remain valid in a forked child because fork() clones the address space and
+ * mapping, so parent and child observe the same virtual addresses. */
+struct DaemonLimitRegistry {
+  int max_slots;
+  int module_count;
+  int host_slots; /* power of two; 1 when no per-source tracking is needed */
+  int per_host_cap;
+  int lockout_threshold;
+  int lockout_duration_sec;
+  size_t map_size;
+  _Atomic long long host_full_warn; /* last "table full" warning epoch */
+  _Atomic int* slot_state;
+  _Atomic int* slot_pid;
+  _Atomic int* slot_module;
+  _Atomic int* slot_host; /* per-source table bucket, or -1 */
+  _Atomic int* module_active;
+  _Atomic uint64_t* host_key; /* 0 == empty bucket */
+  _Atomic int* host_active;
+  _Atomic int* host_fail;
+  _Atomic long long* host_until;    /* epoch seconds the lockout expires */
+  _Atomic long long* host_last_use; /* epoch seconds the bucket was last touched */
+};
+
+static size_t round_up(size_t n, size_t align) {
+  return (n + align - 1) & ~(align - 1);
+}
+
+static size_t next_pow2(size_t n) {
+  size_t p = 1;
+  while (p < n)
+    p <<= 1;
+  return p;
+}
+
+/* Parse a numeric IPv4/IPv6 peer string into family + raw bytes. */
+static bool parse_peer_ip(const char* peer_ip, int* family, unsigned char* bytes) {
+  if (!peer_ip || *peer_ip == '\0')
+    return false;
+  struct in_addr v4;
+  if (inet_pton(AF_INET, peer_ip, &v4) == 1) {
+    memcpy(bytes, &v4, sizeof(v4));
+    *family = AF_INET;
+    return true;
+  }
+  struct in6_addr v6;
+  if (inet_pton(AF_INET6, peer_ip, &v6) == 1) {
+    memcpy(bytes, &v6, sizeof(v6));
+    *family = AF_INET6;
+    return true;
+  }
+  return false;
+}
+
+uint64_t daemon_limits_host_hash(const char* peer_ip, bool* ok) {
+  if (ok)
+    *ok = false;
+  unsigned char bytes[16];
+  int family = AF_UNSPEC;
+  if (!parse_peer_ip(peer_ip, &family, bytes))
+    return 0;
+  uint64_t hash = 14695981039346656037ULL ^ (uint64_t)(uint32_t)family;
+  size_t length = family == AF_INET ? 4 : 16;
+  for (size_t i = 0; i < length; i++) {
+    hash ^= bytes[i];
+    hash *= 1099511628211ULL;
+  }
+  if (hash == 0)
+    hash = 0x9e3779b97f4a7c15ULL;
+  if (ok)
+    *ok = true;
+  return hash;
+}
+
+/* True when the registry must maintain per-source buckets: either the per-host
+ * cap is configured, or the auth lockout is (threshold AND duration > 0).  A
+ * lockout threshold without a duration is a no-op, so it must not size or intern
+ * the table.  create(), register() and the lockout paths all agree on this. */
+static bool registry_tracks_hosts(const DaemonLimitRegistry* registry) {
+  return registry->per_host_cap > 0 ||
+         (registry->lockout_threshold > 0 && registry->lockout_duration_sec > 0);
+}
+
+/* Find the bucket holding `peer_ip`, or -1 when it has no entry.  Finding a
+ * bucket refreshes its last-use time so the eviction policy sees it as live. */
+static int host_lookup(DaemonLimitRegistry* registry, const char* peer_ip) {
+  bool ok = false;
+  uint64_t key = daemon_limits_host_hash(peer_ip, &ok);
+  if (!ok)
+    return -1;
+  size_t mask = (size_t)registry->host_slots - 1;
+  size_t start = (size_t)(key & mask);
+  for (size_t i = 0; i < (size_t)registry->host_slots; i++) {
+    size_t idx = (start + i) & mask;
+    uint64_t current = atomic_load_explicit(&registry->host_key[idx], memory_order_acquire);
+    if (current == key) {
+      atomic_store_explicit(&registry->host_last_use[idx], (long long)time(NULL),
+                            memory_order_relaxed);
+      return (int)idx;
+    }
+    if (current == 0)
+      return -1; /* no tombstones: an empty bucket ends the probe chain */
+  }
+  return -1;
+}
+
+/* A bucket with no live connection may be repurposed: immediately when its
+ * lockout deadline has already passed (the review's "expired" case), or after an
+ * idle window when it holds no pending lockout.  A bucket with a future lockout
+ * deadline is retained so the lockout actually lasts its configured duration. */
+static bool host_bucket_reclaimable(DaemonLimitRegistry* registry, size_t idx, long long now) {
+  if (atomic_load_explicit(&registry->host_active[idx], memory_order_relaxed) != 0)
+    return false;
+  long long until = atomic_load_explicit(&registry->host_until[idx], memory_order_relaxed);
+  if (until != 0)
+    return until <= now;
+  long long last_use = atomic_load_explicit(&registry->host_last_use[idx], memory_order_relaxed);
+  /* A bucket whose key is published but whose last_use has not yet been stamped
+   * (last_use == 0) must be treated as live: reclaiming it here would steal a
+   * bucket a racing child just claimed.  The claim path also stamps last_use
+   * before publishing the key, so this window cannot persist. */
+  return last_use != 0 && now - last_use >= DAEMON_LIMITS_HOST_EVICT_IDLE_SEC;
+}
+
+/* Emit at most one "per-source table full" warning per
+ * DAEMON_LIMITS_HOST_FULL_WARN_SEC across all forked children.  Called from a
+ * normal (non-signal) child path, so logging is safe here. */
+static void host_warn_table_full(DaemonLimitRegistry* registry, long long now) {
+  long long last = atomic_load_explicit(&registry->host_full_warn, memory_order_relaxed);
+  if (last != 0 && now - last < DAEMON_LIMITS_HOST_FULL_WARN_SEC)
+    return;
+  if (atomic_compare_exchange_strong_explicit(&registry->host_full_warn, &last, now,
+                                              memory_order_relaxed, memory_order_relaxed)) {
+    log_message(LOG_LEVEL_WARNING,
+                "daemon: per-source registry is full (%d slots) and no bucket can be reclaimed; "
+                "'max connections per host' and the auth lockout are temporarily not enforced for "
+                "new sources (the per-module cap and host ACLs still apply)",
+                registry->host_slots);
+  }
+}
+
+/* Find or insert the bucket for `peer_ip`.  Insertion is a lock-free CAS so two
+ * forked children racing on the same source converge on one bucket.
+ *
+ * When the probe finds no empty bucket it reclaims, via a key CAS, the first
+ * bucket that is reclaimable (expired lockout or idle, and no active
+ * connection) and resets its counters.  This bounds the table's lifetime so it
+ * cannot fill permanently and stay fail-open.  Returns -1 only when the address
+ * is unparseable or the table is genuinely full of live/locked buckets
+ * (callers fail open: the global/module caps and ACLs still apply). */
+static int host_intern(DaemonLimitRegistry* registry, const char* peer_ip) {
+  bool ok = false;
+  uint64_t key = daemon_limits_host_hash(peer_ip, &ok);
+  if (!ok)
+    return -1;
+  long long now = (long long)time(NULL);
+  size_t mask = (size_t)registry->host_slots - 1;
+  size_t start = (size_t)(key & mask);
+  /* A couple of passes bound the work: the first normally claims/seeds a bucket;
+   * a lost eviction CAS retries once against the freshly observed table. */
+  for (int pass = 0; pass < 2; pass++) {
+    int evict = -1;
+    uint64_t evict_key = 0;
+    for (size_t i = 0; i < (size_t)registry->host_slots; i++) {
+      size_t idx = (start + i) & mask;
+      uint64_t current = atomic_load_explicit(&registry->host_key[idx], memory_order_acquire);
+      if (current == key) {
+        atomic_store_explicit(&registry->host_last_use[idx], now, memory_order_relaxed);
+        return (int)idx;
+      }
+      if (current == 0) {
+        /* Stamp last_use *before* publishing the key so a reclaimer racing the
+         * claim can never observe a claimed bucket with last_use == 0 and
+         * evict it.  A pre-stamp is harmless if the CAS loses: the bucket is
+         * either still empty (never inspected for reclaim) or has just been
+         * taken by another source that wants a fresh timestamp anyway. */
+        atomic_store_explicit(&registry->host_last_use[idx], now, memory_order_relaxed);
+        uint64_t expected = 0;
+        if (atomic_compare_exchange_strong_explicit(&registry->host_key[idx], &expected, key,
+                                                    memory_order_acq_rel, memory_order_acquire)) {
+          return (int)idx;
+        }
+        if (atomic_load_explicit(&registry->host_key[idx], memory_order_acquire) == key) {
+          return (int)idx;
+        }
+        continue; /* another child won this empty bucket; keep probing */
+      }
+      if (evict < 0 && host_bucket_reclaimable(registry, idx, now)) {
+        evict = (int)idx;
+        evict_key = current;
+      }
+    }
+    if (evict >= 0) {
+      /* Refresh the timestamp before the key changes hands so the reused bucket
+       * is not seen as immediately idle by a racing reclaimer. */
+      atomic_store_explicit(&registry->host_last_use[evict], now, memory_order_relaxed);
+      uint64_t expected = evict_key;
+      if (atomic_compare_exchange_strong_explicit(&registry->host_key[evict], &expected, key,
+                                                  memory_order_acq_rel, memory_order_acquire)) {
+        /* The bucket now belongs to the new source; clear the evicted source's
+         * stale lockout/failure state. */
+        atomic_store_explicit(&registry->host_active[evict], 0, memory_order_relaxed);
+        atomic_store_explicit(&registry->host_fail[evict], 0, memory_order_relaxed);
+        atomic_store_explicit(&registry->host_until[evict], 0, memory_order_relaxed);
+        /* Two children can race to intern the same brand-new key into different
+         * eviction targets, leaving the table with duplicate buckets for `key`.
+         * Re-scan for the first (canonical) bucket holding `key`; when it
+         * precedes `evict`, drop our duplicate's occupancy and hand back the
+         * canonical bucket so per-source counts are not orphaned on the
+         * duplicate.  The duplicate keeps its key, so no tombstone hole is
+         * created and probe chains stay intact; it ages out normally. */
+        for (size_t i = 0; i < (size_t)registry->host_slots; i++) {
+          size_t candidate = (start + i) & mask;
+          uint64_t found =
+              atomic_load_explicit(&registry->host_key[candidate], memory_order_acquire);
+          if (found == key) {
+            if (candidate != (size_t)evict) {
+              atomic_store_explicit(&registry->host_active[evict], 0, memory_order_relaxed);
+              return (int)candidate;
+            }
+            break;
+          }
+          if (found == 0)
+            break; /* the key is present at `evict`, so this cannot happen first */
+        }
+        return evict;
+      }
+      continue; /* lost the race; re-probe with fresh observations */
+    }
+    break; /* no free and no reclaimable bucket: genuinely full */
+  }
+  host_warn_table_full(registry, now);
+  return -1;
+}
+
+DaemonLimitRegistry* daemon_limits_create(int max_slots, int module_count, int per_host_cap,
+                                          int lockout_threshold, int lockout_duration_sec) {
+  if (max_slots < DAEMON_LIMITS_MIN_SLOTS)
+    max_slots = DAEMON_LIMITS_MIN_SLOTS;
+  if (max_slots > DAEMON_LIMITS_MAX_SLOTS)
+    max_slots = DAEMON_LIMITS_MAX_SLOTS;
+  if (module_count < 1)
+    module_count = 1;
+  if (module_count > DAEMON_LIMITS_MAX_MODULES)
+    module_count = DAEMON_LIMITS_MAX_MODULES;
+  if (per_host_cap < 0)
+    per_host_cap = 0;
+  if (lockout_threshold < 0)
+    lockout_threshold = 0;
+  if (lockout_duration_sec < 0)
+    lockout_duration_sec = 0;
+
+  bool need_hosts = per_host_cap > 0 || (lockout_threshold > 0 && lockout_duration_sec > 0);
+  int host_slots = 1;
+  if (need_hosts) {
+    size_t want = (size_t)max_slots * 4;
+    if (want < 64)
+      want = 64;
+    if (want > DAEMON_LIMITS_MAX_HOST_SLOTS)
+      want = DAEMON_LIMITS_MAX_HOST_SLOTS;
+    host_slots = (int)next_pow2(want);
+  }
+
+  size_t header = round_up(sizeof(DaemonLimitRegistry), 16);
+  size_t slot_bytes =
+      round_up((size_t)max_slots * sizeof(_Atomic int), 16) * 4; /* state,pid,module,host */
+  size_t module_bytes = round_up((size_t)module_count * sizeof(_Atomic int), 16);
+  size_t host_key_bytes = round_up((size_t)host_slots * sizeof(_Atomic uint64_t), 16);
+  size_t host_int_bytes = round_up((size_t)host_slots * sizeof(_Atomic int), 16) * 2;
+  size_t host_until_bytes = round_up((size_t)host_slots * sizeof(_Atomic long long), 16) * 2;
+  size_t total =
+      header + slot_bytes + module_bytes + host_key_bytes + host_int_bytes + host_until_bytes + 16;
+
+  void* map = mmap(NULL, total, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+  if (map == MAP_FAILED)
+    return NULL;
+  memset(map, 0, total);
+
+  DaemonLimitRegistry* registry = (DaemonLimitRegistry*)map;
+  registry->max_slots = max_slots;
+  registry->module_count = module_count;
+  registry->host_slots = host_slots;
+  registry->per_host_cap = per_host_cap;
+  registry->lockout_threshold = lockout_threshold;
+  registry->lockout_duration_sec = lockout_duration_sec;
+  registry->map_size = total;
+
+  unsigned char* cursor = (unsigned char*)map + header;
+  registry->slot_state = (atomic_int*)cursor;
+  cursor += (size_t)max_slots * sizeof(_Atomic int);
+  registry->slot_pid = (atomic_int*)cursor;
+  cursor += (size_t)max_slots * sizeof(_Atomic int);
+  registry->slot_module = (atomic_int*)cursor;
+  cursor += (size_t)max_slots * sizeof(_Atomic int);
+  registry->slot_host = (atomic_int*)cursor;
+  cursor += (size_t)max_slots * sizeof(_Atomic int);
+  registry->module_active = (atomic_int*)cursor;
+  cursor += (size_t)module_count * sizeof(_Atomic int);
+  cursor = (unsigned char*)round_up((size_t)(uintptr_t)cursor, 16);
+  registry->host_key = (_Atomic uint64_t*)cursor;
+  cursor += (size_t)host_slots * sizeof(_Atomic uint64_t);
+  registry->host_active = (atomic_int*)cursor;
+  cursor += (size_t)host_slots * sizeof(_Atomic int);
+  registry->host_fail = (atomic_int*)cursor;
+  cursor += (size_t)host_slots * sizeof(_Atomic int);
+  cursor = (unsigned char*)round_up((size_t)(uintptr_t)cursor, 16);
+  registry->host_until = (atomic_llong*)cursor;
+  cursor += (size_t)host_slots * sizeof(_Atomic long long);
+  registry->host_last_use = (atomic_llong*)cursor;
+
+  for (int i = 0; i < max_slots; i++) {
+    atomic_store(&registry->slot_module[i], -1);
+    atomic_store(&registry->slot_host[i], -1);
+  }
+  return registry;
+}
+
+void daemon_limits_destroy(DaemonLimitRegistry* registry) {
+  if (!registry)
+    return;
+  munmap(registry, registry->map_size);
+}
+
+int daemon_limits_claim_slot(DaemonLimitRegistry* registry) {
+  if (!registry)
+    return DAEMON_LIMITS_NO_SLOT;
+  for (int i = 0; i < registry->max_slots; i++) {
+    int expected = SLOT_FREE;
+    if (atomic_compare_exchange_strong(&registry->slot_state[i], &expected, SLOT_CLAIMED)) {
+      atomic_store(&registry->slot_pid[i], 0);
+      atomic_store(&registry->slot_module[i], -1);
+      atomic_store(&registry->slot_host[i], -1);
+      return i;
+    }
+  }
+  return DAEMON_LIMITS_NO_SLOT;
+}
+
+void daemon_limits_set_slot_pid(DaemonLimitRegistry* registry, int slot, long pid) {
+  if (!registry || slot < 0 || slot >= registry->max_slots)
+    return;
+  atomic_store(&registry->slot_pid[slot], (int)pid);
+}
+
+void daemon_limits_reclaim_slot(DaemonLimitRegistry* registry, int slot) {
+  if (!registry || slot < 0 || slot >= registry->max_slots)
+    return;
+  atomic_exchange_explicit(&registry->slot_state[slot], SLOT_FREE, memory_order_acq_rel);
+  atomic_store_explicit(&registry->slot_pid[slot], 0, memory_order_relaxed);
+  /* The module/host occupancy arrays are derived from the slot table; do not
+   * decrement here or a SIGKILL between a child's increment and its REGISTERED
+   * publish would leak a count.  Callers that need the derived counts call
+   * daemon_limits_recompute. */
+}
+
+void daemon_limits_reclaim_pid(DaemonLimitRegistry* registry, long pid) {
+  if (!registry || pid <= 0)
+    return;
+  for (int i = 0; i < registry->max_slots; i++) {
+    if (atomic_load(&registry->slot_state[i]) == SLOT_FREE)
+      continue;
+    if (atomic_load(&registry->slot_pid[i]) == (int)pid) {
+      daemon_limits_reclaim_slot(registry, i);
+      return;
+    }
+  }
+}
+
+void daemon_limits_recompute(DaemonLimitRegistry* registry) {
+  if (!registry)
+    return;
+  /* Zero the derived arrays, then re-derive solely from the REGISTERED slots.
+   * A child that was SIGKILLed after incrementing a counter but before
+   * publishing REGISTERED is not counted, and its leaked increment is erased by
+   * the zeroing, so the leak cannot persist. */
+  for (int m = 0; m < registry->module_count; m++)
+    atomic_store_explicit(&registry->module_active[m], 0, memory_order_relaxed);
+  for (int h = 0; h < registry->host_slots; h++)
+    atomic_store_explicit(&registry->host_active[h], 0, memory_order_relaxed);
+  for (int i = 0; i < registry->max_slots; i++) {
+    if (atomic_load_explicit(&registry->slot_state[i], memory_order_acquire) != SLOT_REGISTERED)
+      continue;
+    int module = atomic_load_explicit(&registry->slot_module[i], memory_order_relaxed);
+    if (module >= 0 && module < registry->module_count)
+      atomic_fetch_add_explicit(&registry->module_active[module], 1, memory_order_relaxed);
+    int host = atomic_load_explicit(&registry->slot_host[i], memory_order_relaxed);
+    if (host >= 0 && host < registry->host_slots)
+      atomic_fetch_add_explicit(&registry->host_active[host], 1, memory_order_relaxed);
+  }
+}
+
+DaemonLimitResult daemon_limits_register(DaemonLimitRegistry* registry, int slot, int module_index,
+                                         const char* peer_ip, int module_cap) {
+  if (!registry || slot < 0 || slot >= registry->max_slots)
+    return DAEMON_LIMIT_UNAVAILABLE;
+  if (module_index < 0 || module_index >= registry->module_count)
+    return DAEMON_LIMIT_UNAVAILABLE;
+  if (atomic_load_explicit(&registry->slot_state[slot], memory_order_acquire) != SLOT_CLAIMED)
+    return DAEMON_LIMIT_UNAVAILABLE;
+
+  int host = -1;
+  if (registry_tracks_hosts(registry))
+    host = host_intern(registry, peer_ip);
+
+  int module_count = atomic_fetch_add(&registry->module_active[module_index], 1) + 1;
+  if (module_cap > 0 && module_count > module_cap) {
+    atomic_fetch_sub(&registry->module_active[module_index], 1);
+    return DAEMON_LIMIT_MODULE_FULL;
+  }
+  if (host >= 0) {
+    int host_count = atomic_fetch_add(&registry->host_active[host], 1) + 1;
+    if (registry->per_host_cap > 0 && host_count > registry->per_host_cap) {
+      atomic_fetch_sub(&registry->host_active[host], 1);
+      atomic_fetch_sub(&registry->module_active[module_index], 1);
+      return DAEMON_LIMIT_HOST_FULL;
+    }
+  }
+  atomic_store(&registry->slot_module[slot], module_index);
+  atomic_store(&registry->slot_host[slot], host);
+  atomic_store_explicit(&registry->slot_state[slot], SLOT_REGISTERED, memory_order_release);
+  return DAEMON_LIMIT_OK;
+}
+
+bool daemon_limits_auth_locked(DaemonLimitRegistry* registry, const char* peer_ip,
+                               int* seconds_remaining) {
+  if (!registry || registry->lockout_threshold <= 0 || registry->lockout_duration_sec <= 0)
+    return false;
+  int bucket = host_lookup(registry, peer_ip);
+  if (bucket < 0)
+    return false;
+  long long until = atomic_load(&registry->host_until[bucket]);
+  long long now = (long long)time(NULL);
+  if (until > now) {
+    if (seconds_remaining)
+      *seconds_remaining = (int)(until - now);
+    return true;
+  }
+  if (until != 0) {
+    /* The previous lockout has expired: clear the stale counter so the source
+     * gets a fresh allowance. */
+    atomic_store(&registry->host_fail[bucket], 0);
+    atomic_store(&registry->host_until[bucket], 0);
+  }
+  return false;
+}
+
+void daemon_limits_auth_record_failure(DaemonLimitRegistry* registry, const char* peer_ip) {
+  if (!registry || registry->lockout_threshold <= 0 || registry->lockout_duration_sec <= 0)
+    return;
+  int bucket = host_intern(registry, peer_ip);
+  if (bucket < 0)
+    return;
+  int failures = atomic_fetch_add(&registry->host_fail[bucket], 1) + 1;
+  if (failures >= registry->lockout_threshold) {
+    long long now = (long long)time(NULL);
+    atomic_store(&registry->host_until[bucket], now + (long long)registry->lockout_duration_sec);
+  }
+}
+
+void daemon_limits_auth_record_success(DaemonLimitRegistry* registry, const char* peer_ip) {
+  if (!registry)
+    return;
+  int bucket = host_lookup(registry, peer_ip);
+  if (bucket < 0)
+    return;
+  atomic_store(&registry->host_fail[bucket], 0);
+  atomic_store(&registry->host_until[bucket], 0);
+}

src/shared/daemon_limits.h

@@ -0,0 +1,147 @@
+#ifndef DAEMON_LIMITS_H
+#define DAEMON_LIMITS_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/* Cross-process daemon connection registry.
+ *
+ * The daemon listener forks ONE child per accepted connection, so any
+ * per-module / per-source accounting must live in state shared across the
+ * forked children.  This module owns a fixed-size registry carved out of an
+ * anonymous shared mapping (mmap(MAP_SHARED | MAP_ANONYMOUS)) created by the
+ * accept-loop PARENT before it forks; every child inherits the mapping (and the
+ * pointer to it) across fork().
+ *
+ * Rules:
+ *  - ONLY C11 atomics (atomic_*); never mtx_t/pthread locks, which can deadlock
+ *    in a forked child if another thread held them at fork time.
+ *  - No heap allocation after fork: the mapping is fixed-size and all access is
+ *    atomic load/store/CAS over preallocated arrays.
+ *
+ * Slot lifecycle (the parent reclaims even when a child is SIGKILLed):
+ *   FREE --(parent claim_slot)--> CLAIMED
+ *   CLAIMED --(child register)--> REGISTERED
+ *   any --(parent reclaim)--> FREE
+ * The child records its module index and per-source bucket into the slot before
+ * publishing REGISTERED; the parent's SIGCHLD handler matches the reaped pid to
+ * the slot and, when REGISTERED, decrements the module/per-source counters.
+ * A child killed before registering holds no counts, so reclaiming a CLAIMED
+ * slot only frees the slot.
+ *
+ * Per-source identity is the normalized numeric peer IP (IPv4-mapped IPv6 is
+ * already collapsed to IPv4 by utils_fd_peer_ip); it is interned into an
+ * open-addressed, linear-probing table keyed by a 64-bit hash.  The same table
+ * also carries the cross-process auth-failure counter and lockout deadline.
+ *
+ * Per-source table lifetime: a bucket's key is never cleared back to empty (that
+ * would break every later probe chain that passed through it).  Instead the
+ * table has a bounded-lifetime eviction policy: when no empty bucket exists, the
+ * first bucket that is reclaimable -- no active connection AND (its lockout
+ * deadline has passed OR it has been idle for
+ * DAEMON_LIMITS_HOST_EVICT_IDLE_SEC) -- is atomically repurposed for the new
+ * source via a CAS of its key, and its counters are reset.  The table therefore
+ * cannot fill permanently, and a full table degrades to fail-open for the
+ * per-source cap/lockout of new sources (the per-module cap and host ACLs still
+ * apply) instead of staying fail-open forever.  A rate-limited warning is logged
+ * on the fail-open path.  The eviction race with a concurrent
+ * registration/reclaim on the same bucket is benign: it can at worst lose one
+ * source's counter (fail-open), never corrupt memory or the module caps.
+ */
+
+typedef struct DaemonLimitRegistry DaemonLimitRegistry;
+
+/* Result of a per-connection admission check. */
+typedef enum {
+  DAEMON_LIMIT_OK = 0,      /* admitted; slot is now REGISTERED */
+  DAEMON_LIMIT_MODULE_FULL, /* module's `max connections` cap reached */
+  DAEMON_LIMIT_HOST_FULL,   /* global `max connections per host` cap reached */
+  DAEMON_LIMIT_UNAVAILABLE, /* registry/slot unusable (caller fails open) */
+} DaemonLimitResult;
+
+/* Bounds for registry sizing.  A slot is one concurrently live child. */
+#define DAEMON_LIMITS_MIN_SLOTS 16
+#define DAEMON_LIMITS_MAX_SLOTS 65536
+#define DAEMON_LIMITS_MAX_HOST_SLOTS 65536
+#define DAEMON_LIMITS_NO_SLOT (-1)
+/* Upper bound on `module_count`, matching daemon_conf.h's DAEMON_CONF_MAX_MODULES
+ * (asserted in daemon_limits.c) so a caller can never size the per-module counter
+ * array larger than the config parser can produce. */
+#define DAEMON_LIMITS_MAX_MODULES 256
+
+/* Per-source table lifetime: a bucket with no active connection and no pending
+ * lockout is reclaimable once it has been idle this long, so a flood of distinct
+ * sources cannot pin the table full forever.  A bucket whose lockout deadline
+ * has passed is reclaimable immediately (independent of this idle window). */
+#define DAEMON_LIMITS_HOST_EVICT_IDLE_SEC 300
+/* Minimum spacing between "per-source table is full" warnings, so a table-full
+ * attack cannot flood the log. */
+#define DAEMON_LIMITS_HOST_FULL_WARN_SEC 60
+
+/* Create the shared registry in the calling (parent) process.  `max_slots` is
+ * the number of concurrently live children to track (clamped to
+ * [DAEMON_LIMITS_MIN_SLOTS, DAEMON_LIMITS_MAX_SLOTS]); `module_count` is the
+ * number of daemon modules (clamped to
+ * [1, DAEMON_LIMITS_MAX_MODULES]); `per_host_cap` and the lockout pair come
+ * from the daemon config (0 disables).  Returns NULL on failure (e.g. mmap
+ * allocation); callers must degrade gracefully (global cap + ACLs still
+ * apply). */
+DaemonLimitRegistry* daemon_limits_create(int max_slots, int module_count, int per_host_cap,
+                                          int lockout_threshold, int lockout_duration_sec);
+
+/* Unmap the registry.  Only the creating process may call this. */
+void daemon_limits_destroy(DaemonLimitRegistry* registry);
+
+/* Parent side: reserve a slot for the next fork.  Returns the slot index or
+ * DAEMON_LIMITS_NO_SLOT when every slot is in use. */
+int daemon_limits_claim_slot(DaemonLimitRegistry* registry);
+/* Parent side: record the forked child's pid in a claimed slot. */
+void daemon_limits_set_slot_pid(DaemonLimitRegistry* registry, int slot, long pid);
+/* Parent side: release a slot.  The slot becomes FREE; the module/per-source
+ * occupancy arrays are DERIVED state and are only refreshed by
+ * daemon_limits_recompute, which callers must invoke afterwards when they rely
+ * on the derived counts (the SIGCHLD handler batches one recompute for the whole
+ * reap).  Idempotent. */
+void daemon_limits_reclaim_slot(DaemonLimitRegistry* registry, int slot);
+/* Parent SIGCHLD side: release the slot owned by `pid` (no-op when not found).
+ * Like reclaim_slot this does not touch the derived occupancy arrays; call
+ * daemon_limits_recompute after a batch of releases. */
+void daemon_limits_reclaim_pid(DaemonLimitRegistry* registry, long pid);
+
+/* Parent side (async-signal-safe; atomics only, no malloc/log): rebuild
+ * module_active[] / host_active[] from scratch by scanning the REGISTERED slots.
+ * The slot table is the single source of truth, so this self-heals any
+ * count leaked by a child that was SIGKILLed mid-registration (it zeroes the
+ * arrays and re-derives them).  Bounded by max_slots + host_slots.  A
+ * registration racing this call can be transiently undercounted until the next
+ * recompute, which can only relax a cap briefly -- never corrupt memory. */
+void daemon_limits_recompute(DaemonLimitRegistry* registry);
+
+/* Child side: admit the connection for `module_index` from `peer_ip`.  Always
+ * tracks the module/per-source occupancy (so the parent's reclaim is
+ * symmetric); when `module_cap` > 0 it additionally enforces the per-module
+ * cap.  A NULL/empty or non-numeric `peer_ip` skips the per-source track (the
+ * callers use that to exempt a trusted loopback peer from the per-host cap; the
+ * per-module cap still applies).  Returns DAEMON_LIMIT_OK and publishes the
+ * slot, or a refusal reason. */
+DaemonLimitResult daemon_limits_register(DaemonLimitRegistry* registry, int slot, int module_index,
+                                         const char* peer_ip, int module_cap);
+
+/* Child side: true when `peer_ip` is currently locked out after too many failed
+ * authentications.  `seconds_remaining` may be NULL. */
+bool daemon_limits_auth_locked(DaemonLimitRegistry* registry, const char* peer_ip,
+                               int* seconds_remaining);
+/* Child side: count one failed authentication for `peer_ip`; once the threshold
+ * is reached the source is locked out for the configured duration. */
+void daemon_limits_auth_record_failure(DaemonLimitRegistry* registry, const char* peer_ip);
+/* Child side: clear the failure counter/lockout for a source that authenticated
+ * successfully (no-op when the source has no table entry). */
+void daemon_limits_auth_record_success(DaemonLimitRegistry* registry, const char* peer_ip);
+
+/* Pure helper: 64-bit FNV-1a hash of a numeric peer IP plus its family, used to
+ * index the per-source table.  *ok is set false (and 0 returned) for a NULL or
+ * non-numeric address.  Exposed for unit testing. */
+uint64_t daemon_limits_host_hash(const char* peer_ip, bool* ok);
+
+#endif

src/shared/data.c

@@ -23,6 +23,7 @@ Data* data_create_reserve(size_t size) {
   d->data = NULL;
   d->size = size;
   d->protocol_charge = 0;
+  d->owner = NULL;
   return d;
 }
 
@@ -36,14 +37,19 @@ Data* data_create(void* data, size_t data_size) {
   new_data->data = data;
   new_data->size = data_size;
   new_data->protocol_charge = 0;
+  new_data->owner = NULL;
   return new_data;
 }
 
 void data_destroy(Data* data) {
   if (data == NULL)
     return;
-  if (data->protocol_charge != 0)
+  if (data->protocol_charge != 0) {
+    if (data->owner != NULL)
+      protocol_release_memory_for_session(data->owner, data->protocol_charge);
+    else
       protocol_release_memory(data->protocol_charge);
+  }
   free(data->data);
   free(data);
 }

src/shared/data.h

@@ -3,11 +3,25 @@
 
 #include <stdlib.h>
 
+/* Forward declaration for the connection budget a received Data is charged
+ * against; defined in protocol.h (which includes this header). */
+typedef struct ProtocolSession ProtocolSession;
+
 typedef struct {
   void* data;
   size_t size;
   /* Non-zero only for a buffer charged to the protocol connection budget. */
   size_t protocol_charge;
+  /* Session whose budget `protocol_charge` was reserved from.  When non-NULL,
+   * the charge is returned to this session directly, regardless of which
+   * session (if any) is bound to the destroying thread.  owner is not
+   * guaranteed to be set whenever protocol_charge is non-zero: it is NULL for
+   * uncharged Data and for Data that has no recorded owner, in which case any
+   * charge falls back to the session bound at destroy time.
+   *
+   * Lifetime contract: a Data with a non-NULL owner must not outlive that
+   * ProtocolSession -- data_destroy dereferences owner to return the charge. */
+  ProtocolSession* owner;
 } Data;
 
 Data* data_create_empty(size_t data_size);
@@ -15,5 +29,9 @@ Data* data_create_reserve(size_t size);
 Data* data_create(void* data, size_t data_size);
 void data_destroy(Data* data);
 void protocol_release_memory(size_t charge);
+/* Release `charge` against `session` directly instead of the thread-local bound
+ * session.  Used by data_destroy to honor Data.owner; `session` must outlive
+ * the Data whose charge is being returned.  A NULL session is a no-op. */
+void protocol_release_memory_for_session(ProtocolSession* session, size_t charge);
 
 #endif

src/shared/delay_updates.c

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

src/shared/delay_updates.h

@@ -18,8 +18,9 @@ typedef struct {
 /* 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
+   transfer.  A single receiver pipeline (see src/server/receiver_pipeline.h)
+   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 */

src/shared/delete_plan.c

@@ -0,0 +1,893 @@
+#include "delete_plan.h"
+
+#include "charset.h"
+#include "delay_updates.h"
+#include "file.h"
+#include "log.h"
+#include "utils.h"
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+/* Mirrors MAX_SERVER_DELETE_COUNT in file_receive.c: the server's hard bound on
+ * the number of entries one deletion commit may remove.  A client
+ * --max-delete=NUM smaller than this replaces it for the run. */
+#define DELETE_PLAN_SERVER_LIMIT 100000U
+
+/* ------------------------------------------------------------------ */
+/* Sender: plan builder                                               */
+/* ------------------------------------------------------------------ */
+
+typedef struct PlanNode {
+  char* dir;
+  ArrayList* files; /* basenames kept directly in dir */
+  ArrayList* dirs;  /* basenames of kept child directories */
+  bool sent;
+  struct PlanNode* hash_next;
+} PlanNode;
+
+struct DeletePlanSender {
+  PlanNode** buckets;
+  size_t capacity;
+  size_t count;
+  bool config_sent;
+  bool all_synced;
+  const ArrayList* synced_dirs;
+  /* Owned by the caller's synced_dirs list; non-NULL only for a general -R
+     transfer, where it is the destination prefix the delete walk is confined
+     to.  NULL means the whole receive root (or a --files-from scope). */
+  const char* walk_root;
+  const ArrayList* protected_prefixes;
+  const ArrayList* size_skipped;
+  const ArrayList* missing_args;
+  size_t entries;
+  /* Transmitted FILE entries only.  The caller's "empty scan" safety guard keys
+     off this (an I/O error that hid every file must refuse to delete even when
+     some directories were traversed), so directory keep entries do not count. */
+  size_t file_entries;
+};
+
+static size_t plan_hash(const char* key) {
+  size_t h = 5381;
+  for (const unsigned char* p = (const unsigned char*)key; *p; p++)
+    h = ((h << 5) + h) + *p;
+  return h;
+}
+
+static bool list_contains_str(const ArrayList* list, const char* value) {
+  if (!list)
+    return false;
+  for (int i = 0; i < list->size; i++) {
+    if (strcmp((const char*)list->items[i], value) == 0)
+      return true;
+  }
+  return false;
+}
+
+static bool list_add_str_unique(ArrayList* list, const char* value) {
+  if (!list || !value)
+    return false;
+  if (list_contains_str(list, value))
+    return true;
+  char* copy = str_dup(value);
+  if (!copy)
+    return false;
+  if (!array_list_add(list, copy)) {
+    free(copy);
+    return false;
+  }
+  return true;
+}
+
+DeletePlanSender* delete_plan_sender_create(void) {
+  DeletePlanSender* sender = calloc(1, sizeof(DeletePlanSender));
+  if (!sender)
+    return NULL;
+  sender->capacity = 64;
+  sender->buckets = calloc(sender->capacity, sizeof(PlanNode*));
+  if (!sender->buckets) {
+    free(sender);
+    return NULL;
+  }
+  sender->all_synced = true;
+  return sender;
+}
+
+static void plan_node_destroy(PlanNode* node) {
+  if (!node)
+    return;
+  free(node->dir);
+  array_list_delete(node->files);
+  array_list_delete(node->dirs);
+  free(node);
+}
+
+void delete_plan_sender_destroy(DeletePlanSender* sender) {
+  if (!sender)
+    return;
+  for (size_t i = 0; i < sender->capacity; i++) {
+    PlanNode* node = sender->buckets[i];
+    while (node) {
+      PlanNode* next = node->hash_next;
+      plan_node_destroy(node);
+      node = next;
+    }
+  }
+  free(sender->buckets);
+  free(sender);
+}
+
+static PlanNode* plan_find(const DeletePlanSender* sender, const char* dir) {
+  size_t index = plan_hash(dir) & (sender->capacity - 1);
+  for (PlanNode* node = sender->buckets[index]; node; node = node->hash_next) {
+    if (strcmp(node->dir, dir) == 0)
+      return node;
+  }
+  return NULL;
+}
+
+static bool plan_grow(DeletePlanSender* sender) {
+  size_t new_capacity = sender->capacity * 2;
+  PlanNode** buckets = calloc(new_capacity, sizeof(PlanNode*));
+  if (!buckets)
+    return false;
+  for (size_t i = 0; i < sender->capacity; i++) {
+    PlanNode* node = sender->buckets[i];
+    while (node) {
+      PlanNode* next = node->hash_next;
+      size_t index = plan_hash(node->dir) & (new_capacity - 1);
+      node->hash_next = buckets[index];
+      buckets[index] = node;
+      node = next;
+    }
+  }
+  free(sender->buckets);
+  sender->buckets = buckets;
+  sender->capacity = new_capacity;
+  return true;
+}
+
+static PlanNode* plan_ensure(DeletePlanSender* sender, const char* dir) {
+  PlanNode* node = plan_find(sender, dir);
+  if (node)
+    return node;
+  if (sender->count + 1 > sender->capacity * 3 / 4 && !plan_grow(sender))
+    return NULL;
+  node = calloc(1, sizeof(PlanNode));
+  if (!node)
+    return NULL;
+  node->dir = str_dup(dir);
+  node->files = array_list_create(free);
+  node->dirs = array_list_create(free);
+  if (!node->dir || !node->files || !node->dirs) {
+    plan_node_destroy(node);
+    return NULL;
+  }
+  size_t index = plan_hash(dir) & (sender->capacity - 1);
+  node->hash_next = sender->buckets[index];
+  sender->buckets[index] = node;
+  sender->count++;
+  return node;
+}
+
+static char* path_parent_dir(const char* path) {
+  const char* slash = strrchr(path, '/');
+  if (!slash)
+    return str_dup(".");
+  if (slash == path)
+    return str_dup(".");
+  size_t len = (size_t)(slash - path);
+  char* parent = malloc(len + 1);
+  if (!parent)
+    return NULL;
+  memcpy(parent, path, len);
+  parent[len] = '\0';
+  return parent;
+}
+
+static char* path_base_name(const char* path) {
+  const char* slash = strrchr(path, '/');
+  return str_dup(slash ? slash + 1 : path);
+}
+
+/* Copy `path`, stripping a leading '/' and any trailing '/'. */
+static char* plan_clean_path(const char* path) {
+  while (*path == '/')
+    path++;
+  size_t len = strlen(path);
+  while (len > 0 && path[len - 1] == '/')
+    len--;
+  char* clean = malloc(len + 1);
+  if (!clean)
+    return NULL;
+  memcpy(clean, path, len);
+  clean[len] = '\0';
+  return clean;
+}
+
+static bool plan_ensure_ancestors(DeletePlanSender* sender, const char* dir) {
+  char* current = str_dup(dir);
+  if (!current)
+    return false;
+  bool ok = true;
+  while (strcmp(current, ".") != 0) {
+    char* parent = path_parent_dir(current);
+    char* base = path_base_name(current);
+    PlanNode* parent_node = parent ? plan_ensure(sender, parent) : NULL;
+    if (!parent || !base || !parent_node || !list_add_str_unique(parent_node->dirs, base)) {
+      ok = false;
+      free(parent);
+      free(base);
+      break;
+    }
+    free(base);
+    free(current);
+    current = parent;
+  }
+  free(current);
+  return ok;
+}
+
+bool delete_plan_sender_add(DeletePlanSender* sender, const char* path, bool is_dir) {
+  if (!sender || !path)
+    return false;
+  char* clean = plan_clean_path(path);
+  if (!clean)
+    return false;
+  if (*clean == '\0') {
+    free(clean);
+    return true;
+  }
+  char* parent = path_parent_dir(clean);
+  char* base = path_base_name(clean);
+  PlanNode* parent_node = parent ? plan_ensure(sender, parent) : NULL;
+  bool ok = parent && base && parent_node;
+  if (ok) {
+    if (is_dir) {
+      ok = list_add_str_unique(parent_node->dirs, base) && plan_ensure(sender, clean) != NULL;
+    } else {
+      ok = list_add_str_unique(parent_node->files, base);
+    }
+  }
+  if (ok)
+    ok = plan_ensure_ancestors(sender, parent);
+  if (ok) {
+    sender->entries++;
+    if (!is_dir)
+      sender->file_entries++;
+  }
+  free(clean);
+  free(parent);
+  free(base);
+  return ok;
+}
+
+void delete_plan_sender_finalize(DeletePlanSender* sender, const ArrayList* synced_dirs,
+                                 const char* walk_root) {
+  if (!sender)
+    return;
+  sender->synced_dirs = synced_dirs;
+  sender->all_synced = synced_dirs == NULL && walk_root == NULL;
+  sender->walk_root = walk_root;
+}
+
+bool delete_plan_sender_empty(const DeletePlanSender* sender) {
+  return !sender || sender->file_entries == 0;
+}
+
+void delete_plan_sender_set_config(DeletePlanSender* sender, const ArrayList* protected_prefixes,
+                                   const ArrayList* size_skipped, const ArrayList* missing_args) {
+  if (!sender)
+    return;
+  sender->protected_prefixes = protected_prefixes;
+  sender->size_skipped = size_skipped;
+  sender->missing_args = missing_args;
+}
+
+/* True when `dir` is `root` itself or a descendant of it (path-component
+ * aware, so "foo" does not match "foobar"). */
+static bool path_at_or_under(const char* dir, const char* root) {
+  if (!dir || !root)
+    return false;
+  size_t n = strlen(root);
+  return strncmp(dir, root, n) == 0 && (dir[n] == '\0' || dir[n] == '/');
+}
+
+static bool plan_is_allowed(const DeletePlanSender* sender, const char* dir) {
+  if (sender->all_synced)
+    return true;
+  if (sender->walk_root)
+    return path_at_or_under(dir, sender->walk_root);
+  return list_contains_str(sender->synced_dirs, dir);
+}
+
+static int send_str_section(int fd, const ArrayList* list) {
+  int count = list ? list->size : 0;
+  if (!send_int(fd, count))
+    return -1;
+  for (int i = 0; i < count; i++) {
+    if (!send_wire_str(fd, (const char*)list->items[i]))
+      return -1;
+  }
+  return 0;
+}
+
+static int send_plan_node(int fd, DeletePlanSender* sender, PlanNode* node) {
+  if (!send_status(fd, STATUS_DELETE_PLAN))
+    return -1;
+  if (!send_int(fd, sender->config_sent ? 0 : 1))
+    return -1;
+  if (!sender->config_sent) {
+    if (send_str_section(fd, sender->protected_prefixes) != 0 ||
+        send_str_section(fd, sender->size_skipped) != 0 ||
+        send_str_section(fd, sender->missing_args) != 0)
+      return -1;
+    sender->config_sent = true;
+  }
+  if (!send_wire_str(fd, node->dir))
+    return -1;
+  if (send_str_section(fd, node->dirs) != 0 || send_str_section(fd, node->files) != 0)
+    return -1;
+  node->sent = true;
+  return 0;
+}
+
+static int send_prefix_plan(int fd, DeletePlanSender* sender, const char* dir) {
+  PlanNode* node = plan_find(sender, dir);
+  if (!node || node->sent)
+    return 0;
+  if (!plan_is_allowed(sender, dir))
+    return 0;
+  return send_plan_node(fd, sender, node);
+}
+
+int delete_plan_send_root(int fd, DeletePlanSender* sender) {
+  if (!sender)
+    return -1;
+  const char* root = sender->walk_root ? sender->walk_root : ".";
+  if (!plan_ensure(sender, root))
+    return -1;
+  return send_prefix_plan(fd, sender, root);
+}
+
+int delete_plan_send_for_path(int fd, DeletePlanSender* sender, const char* path, bool is_dir) {
+  if (!sender || !path)
+    return -1;
+  char* clean = plan_clean_path(path);
+  if (!clean)
+    return -1;
+  /* The walk root (the -R prefix, or ".") is sent up front by
+     delete_plan_send_root(); never emit the receive-root plan for a scoped -R
+     run, whose "." keep list would delete the prefix's siblings. */
+  int rc = sender->walk_root ? 0 : send_prefix_plan(fd, sender, ".");
+  if (rc == 0 && *clean != '\0') {
+    size_t len = strlen(clean);
+    size_t end = len;
+    if (!is_dir) {
+      const char* slash = strrchr(clean, '/');
+      end = slash ? (size_t)(slash - clean) : 0;
+    }
+    for (size_t i = 1; i <= end && rc == 0; i++) {
+      if (i == end || clean[i] == '/') {
+        char* prefix = malloc(i + 1);
+        if (!prefix) {
+          rc = -1;
+          break;
+        }
+        memcpy(prefix, clean, i);
+        prefix[i] = '\0';
+        rc = send_prefix_plan(fd, sender, prefix);
+        free(prefix);
+      }
+    }
+  }
+  free(clean);
+  return rc;
+}
+
+int delete_plan_send_remaining(int fd, DeletePlanSender* sender, const ArrayList* dirs) {
+  if (!sender || !dirs)
+    return 0;
+  for (int i = 0; i < dirs->size; i++) {
+    const char* dir = (const char*)dirs->items[i];
+    if (delete_plan_send_for_path(fd, sender, dir, true) != 0)
+      return -1;
+  }
+  return 0;
+}
+
+/* ------------------------------------------------------------------ */
+/* Receiver: delete session                                           */
+/* ------------------------------------------------------------------ */
+
+struct DeletePlanSession {
+  bool defer;
+  bool dry_run;
+  size_t max_delete;
+  size_t deleted;
+  size_t skipped;
+  bool limit_hit;
+  bool limit_logged;
+  bool config_seen;
+  bool missing_applied;
+  ArrayList* protected_prefixes;
+  ArrayList* size_skipped;
+  ArrayList* missing;
+  ArrayList* deferred;
+};
+
+DeletePlanSession* delete_plan_session_create(const Config* config) {
+  if (!config)
+    return NULL;
+  DeletePlanSession* session = calloc(1, sizeof(DeletePlanSession));
+  if (!session)
+    return NULL;
+  session->defer = config->delete_delay;
+  session->dry_run = config->dry_run;
+  bool user_limited =
+      config->max_delete >= 0 && (size_t)config->max_delete < DELETE_PLAN_SERVER_LIMIT;
+  session->max_delete =
+      user_limited ? (size_t)config->max_delete : (size_t)DELETE_PLAN_SERVER_LIMIT;
+  session->protected_prefixes = array_list_create(free);
+  session->size_skipped = array_list_create(free);
+  session->missing = array_list_create(free);
+  session->deferred = array_list_create(free);
+  if (!session->protected_prefixes || !session->size_skipped || !session->missing ||
+      !session->deferred) {
+    delete_plan_session_destroy(session);
+    return NULL;
+  }
+  return session;
+}
+
+void delete_plan_session_destroy(DeletePlanSession* session) {
+  if (!session)
+    return;
+  array_list_delete(session->protected_prefixes);
+  array_list_delete(session->size_skipped);
+  array_list_delete(session->missing);
+  array_list_delete(session->deferred);
+  free(session);
+}
+
+bool delete_plan_session_limit_reached(const DeletePlanSession* session) {
+  return session && session->limit_hit;
+}
+
+size_t delete_plan_session_deleted(const DeletePlanSession* session) {
+  return session ? session->deleted : 0;
+}
+
+/* True for a destination-relative path section entry (non-empty, relative,
+ * traversal-free). */
+static bool valid_rel_path(const char* value) {
+  return value && value[0] != '\0' && value[0] != '/' && !has_path_traversal(value);
+}
+
+/* True for a single child name (non-empty, no slash, not "."/".."). */
+static bool valid_name(const char* value) {
+  return value && value[0] != '\0' && strcmp(value, ".") != 0 && strcmp(value, "..") != 0 &&
+         strchr(value, '/') == NULL;
+}
+
+/* Read one count-prefixed section.  `bytes` is the running per-frame budget,
+ * shared across every section of the frame so a hostile peer cannot retain more
+ * than MAX_MANIFEST_BYTES from one STATUS_DELETE_PLAN frame. */
+static bool read_section(int fd, ArrayList* list, bool rel_path, size_t* bytes) {
+  int count;
+  if (!receive_int(fd, &count) || count < 0 || count > MAX_MANIFEST_ENTRIES)
+    return false;
+  for (int i = 0; i < count; i++) {
+    char* value = receive_wire_str(fd);
+    bool ok = value && (rel_path ? valid_rel_path(value) : valid_name(value));
+    if (ok) {
+      size_t entry_size = strlen(value) + sizeof(char*) + 16;
+      if (entry_size > MAX_MANIFEST_BYTES - *bytes) {
+        ok = false;
+      } else {
+        *bytes += entry_size;
+        ok = array_list_add(list, value);
+      }
+    }
+    if (!ok) {
+      free(value);
+      return false;
+    }
+  }
+  return true;
+}
+
+static int open_plan_dir(const Config* config, const char* dir) {
+  char* full = (strcmp(dir, ".") == 0) ? str_dup(config->receive_root_directory)
+                                       : path_cat(config->receive_root_directory, dir);
+  if (!full)
+    return -1;
+  int root_fd = utils_get_authorized_root_fd();
+  int fd = -1;
+  if (root_fd >= 0) {
+    if (utils_get_authorized_root_path())
+      fd = utils_open_authorized_destination(full);
+    else if (strcmp(dir, ".") == 0)
+      fd = dup(root_fd);
+  } else {
+    fd = open(full, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+  }
+  free(full);
+  return fd;
+}
+
+typedef struct PlanSkips {
+  DeleteSkipEntry* entries;
+  int count;
+} PlanSkips;
+
+static bool build_plan_skips(const Config* config, const DeletePlanSession* session,
+                             PlanSkips* out) {
+  out->entries = NULL;
+  out->count = 0;
+  int count = (config->delay_updates ? 1 : 0) + config->basis_count +
+              session->protected_prefixes->size + session->size_skipped->size;
+  if (count == 0)
+    return true;
+  out->entries = calloc((size_t)count, sizeof(DeleteSkipEntry));
+  if (!out->entries)
+    return false;
+  int idx = 0;
+  if (config->delay_updates) {
+    out->entries[idx].prefix = DELAY_UPDATES_STAGING_DIR;
+    out->entries[idx].top_level_only = true;
+    idx++;
+  }
+  for (int i = 0; i < config->basis_count; i++) {
+    out->entries[idx].prefix = config->basis_dirs[i].path;
+    out->entries[idx].top_level_only = false;
+    idx++;
+  }
+  for (int i = 0; i < session->protected_prefixes->size; i++) {
+    out->entries[idx].prefix = (const char*)session->protected_prefixes->items[i];
+    out->entries[idx].top_level_only = false;
+    idx++;
+  }
+  for (int i = 0; i < session->size_skipped->size; i++) {
+    out->entries[idx].prefix = (const char*)session->size_skipped->items[i];
+    out->entries[idx].top_level_only = false;
+    idx++;
+  }
+  out->count = idx;
+  return true;
+}
+
+static bool budget_available(const DeletePlanSession* session) {
+  return session->deleted < session->max_delete;
+}
+
+static void note_skipped(DeletePlanSession* session) {
+  session->limit_hit = true;
+  session->skipped++;
+}
+
+static void log_deleted(const char* rel) {
+  char* escaped = output_escape(rel, log_get_8_bit_output());
+  fprintf(stderr, "  Deleted: %s\n", escaped ? escaped : "<allocation failed>");
+  free(escaped);
+}
+
+/* Append a snapshot path for --delete-delay. */
+static bool defer_add(DeletePlanSession* session, const char* rel) {
+  char* copy = str_dup(rel);
+  if (!copy)
+    return false;
+  if (!array_list_add(session->deferred, copy)) {
+    free(copy);
+    return false;
+  }
+  session->deleted++;
+  return true;
+}
+
+/* Process the direct children of one directory.  `keep_dirs`/`keep_files`
+ * (basenames) are the source entries that must be kept; NULL means every child
+ * is an extra (the forced path used inside a removed extra directory tree).
+ * `survives` reports that at least one child remains (kept, protected, or
+ * skipped by the budget).  `force_now` removes even in --delete-delay mode
+ * (type conflicts must clear before the incoming data). */
+static bool process_children(int dirfd, const char* dir_rel, const ArrayList* keep_dirs,
+                             const ArrayList* keep_files, bool at_root, bool force_now,
+                             const PlanSkips* skips, DeletePlanSession* session, bool* survives);
+
+static bool process_extra_dir(int dirfd, const char* name, const char* child_rel, bool force_now,
+                              const PlanSkips* skips, DeletePlanSession* session, bool* removed) {
+  *removed = false;
+  int childfd = openat(dirfd, name, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+  if (childfd < 0) {
+    if (errno == ENOENT) {
+      *removed = true;
+      return true;
+    }
+    return false;
+  }
+  bool survives = false;
+  bool ok =
+      process_children(childfd, child_rel, NULL, NULL, false, force_now, skips, session, &survives);
+  close(childfd);
+  if (!ok)
+    return false;
+  if (survives)
+    return true;
+  if (!budget_available(session)) {
+    note_skipped(session);
+    return true;
+  }
+  if (session->defer && !force_now) {
+    if (!defer_add(session, child_rel))
+      return false;
+    *removed = true;
+    return true;
+  }
+  if (unlinkat(dirfd, name, AT_REMOVEDIR) == 0) {
+    session->deleted++;
+    log_deleted(child_rel);
+    *removed = true;
+    return true;
+  }
+  if (errno == ENOENT) {
+    *removed = true;
+    return true;
+  }
+  /* ENOTEMPTY/EEXIST: a protected entry the walker leaves behind survived, so
+     the directory stays; any other errno is a genuine failure. */
+  return errno == ENOTEMPTY || errno == EEXIST;
+}
+
+static bool process_extra_file(int dirfd, const char* name, const char* child_rel, bool force_now,
+                               DeletePlanSession* session) {
+  if (!budget_available(session)) {
+    note_skipped(session);
+    return true;
+  }
+  if (session->defer && !force_now) {
+    return defer_add(session, child_rel);
+  }
+  if (unlinkat(dirfd, name, 0) == 0) {
+    session->deleted++;
+    log_deleted(child_rel);
+  } else if (errno != ENOENT) {
+    return false;
+  }
+  return true;
+}
+
+static bool process_children(int dirfd, const char* dir_rel, const ArrayList* keep_dirs,
+                             const ArrayList* keep_files, bool at_root, bool force_now,
+                             const PlanSkips* skips, DeletePlanSession* session, bool* survives) {
+  *survives = false;
+  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;
+  const struct dirent* entry;
+  while ((entry = readdir(dir)) != NULL) {
+    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
+      continue;
+    char* child_rel =
+        (strcmp(dir_rel, ".") == 0) ? str_dup(entry->d_name) : path_cat(dir_rel, entry->d_name);
+    if (!child_rel) {
+      operation_ok = false;
+      continue;
+    }
+    if (path_under_skip_prefix(child_rel, at_root, skips->entries, skips->count)) {
+      local_survives = true;
+      free(child_rel);
+      continue;
+    }
+    struct stat st;
+    if (fstatat(dirfd, entry->d_name, &st, AT_SYMLINK_NOFOLLOW) != 0) {
+      if (errno != ENOENT)
+        operation_ok = false;
+      free(child_rel);
+      continue;
+    }
+    bool is_dir = S_ISDIR(st.st_mode);
+    bool in_keep_dirs = is_dir && list_contains_str(keep_dirs, entry->d_name);
+    bool in_keep_files = !is_dir && list_contains_str(keep_files, entry->d_name);
+    if (in_keep_dirs) {
+      local_survives = true;
+    } else if (keep_dirs && !is_dir && list_contains_str(keep_dirs, entry->d_name)) {
+      /* Destination file blocks a source directory: clear it now, whatever the
+         delete timing, so the directory can be created. */
+      if (!process_extra_file(dirfd, entry->d_name, child_rel, true, session))
+        operation_ok = false;
+    } else if (in_keep_files) {
+      local_survives = true;
+    } else if (keep_files && is_dir && list_contains_str(keep_files, entry->d_name)) {
+      /* Destination directory blocks a source file: remove it now. */
+      bool removed = false;
+      if (!process_extra_dir(dirfd, entry->d_name, child_rel, true, skips, session, &removed))
+        operation_ok = false;
+      else if (!removed)
+        local_survives = true;
+    } else if (is_dir) {
+      bool removed = false;
+      if (!process_extra_dir(dirfd, entry->d_name, child_rel, force_now, skips, session, &removed))
+        operation_ok = false;
+      else if (!removed)
+        local_survives = true;
+    } else {
+      if (!process_extra_file(dirfd, entry->d_name, child_rel, force_now, session))
+        operation_ok = false;
+    }
+    free(child_rel);
+  }
+  closedir(dir);
+  *survives = local_survives;
+  return operation_ok;
+}
+
+static bool apply_plan_dir(DeletePlanSession* session, const Config* config, const char* dir,
+                           const ArrayList* dirs, const ArrayList* files) {
+  int dirfd = open_plan_dir(config, dir);
+  if (dirfd < 0) {
+    /* An absent destination directory has nothing to delete. */
+    return errno == ENOENT || errno == ENOTDIR;
+  }
+  PlanSkips skips;
+  if (!build_plan_skips(config, session, &skips)) {
+    close(dirfd);
+    return false;
+  }
+  bool survives = false;
+  bool ok = process_children(dirfd, dir, dirs, files, strcmp(dir, ".") == 0, false, &skips, session,
+                             &survives);
+  free(skips.entries);
+  close(dirfd);
+  if (!ok)
+    log_message(LOG_LEVEL_ERROR, "deletion failed while removing extraneous files");
+  return ok;
+}
+
+static bool apply_missing(DeletePlanSession* session, const Config* config) {
+  if (session->missing_applied)
+    return true;
+  session->missing_applied = true;
+  /* The server clears delete_missing_args when its --allow-delete policy is
+     off; never honor the client's exact-path requests then. */
+  if (!config->delete_missing_args || session->missing->size == 0)
+    return true;
+  DeleteManifest manifest = {
+      .keeps = NULL, .protected = NULL, .missing = session->missing, .dirs = NULL};
+  size_t remaining = budget_available(session) ? session->max_delete - session->deleted : 0;
+  size_t deleted = 0;
+  size_t skipped = 0;
+  bool limit = false;
+  bool ok = manifest_delete_missing_args_limited(config, &manifest, remaining, &deleted, &skipped,
+                                                 &limit);
+  session->deleted += deleted;
+  session->skipped += skipped;
+  if (limit)
+    session->limit_hit = true;
+  return ok;
+}
+
+int delete_plan_session_receive(DeletePlanSession* session, const Config* config, int fd) {
+  if (!session || !config) {
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
+  int has_config;
+  if (!receive_int(fd, &has_config) || (has_config != 0 && has_config != 1)) {
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
+  size_t bytes = 0;
+  if (has_config) {
+    if (session->config_seen || !read_section(fd, session->protected_prefixes, true, &bytes) ||
+        !read_section(fd, session->size_skipped, true, &bytes) ||
+        !read_section(fd, session->missing, true, &bytes)) {
+      send_status(fd, STATUS_ERROR);
+      return -1;
+    }
+    session->config_seen = true;
+  }
+  char* dir = receive_wire_str(fd);
+  ArrayList* dirs = array_list_create(free);
+  ArrayList* files = array_list_create(free);
+  bool parsed = dir && (strcmp(dir, ".") == 0 || valid_rel_path(dir)) && dirs && files &&
+                read_section(fd, dirs, false, &bytes) && read_section(fd, files, false, &bytes);
+  if (!parsed) {
+    free(dir);
+    array_list_delete(dirs);
+    array_list_delete(files);
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
+  bool enabled = config->use_delete || config->delete_missing_args;
+  bool ok = true;
+  if (!session->dry_run && enabled) {
+    if (!session->defer && !apply_missing(session, config))
+      ok = false;
+    if (ok && !apply_plan_dir(session, config, dir, dirs, files))
+      ok = false;
+  }
+  free(dir);
+  array_list_delete(dirs);
+  array_list_delete(files);
+  if (!ok) {
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
+  if (session->limit_hit && !session->limit_logged) {
+    session->limit_logged = true;
+    log_message(LOG_LEVEL_WARNING, "Deletions stopped due to the delete limit (%zu skipped)",
+                session->skipped);
+  }
+  return 0;
+}
+
+/* Apply one snapshotted --delete-delay path (post-order: children precede their
+ * parent directory). */
+static bool apply_deferred_path(DeletePlanSession* session, const Config* config, const char* rel) {
+  (void)session;
+  char* full = path_cat(config->receive_root_directory, rel);
+  if (!full)
+    return false;
+  char* leaf = NULL;
+  int parent_fd = file_open_secure_parent(full, &leaf, false);
+  free(full);
+  if (parent_fd < 0) {
+    free(leaf);
+    return errno == ENOENT || errno == ENOTDIR;
+  }
+  struct stat st;
+  if (fstatat(parent_fd, leaf, &st, AT_SYMLINK_NOFOLLOW) != 0) {
+    bool absent = errno == ENOENT;
+    close(parent_fd);
+    free(leaf);
+    return absent;
+  }
+  int rc;
+  if (S_ISDIR(st.st_mode))
+    rc = unlinkat(parent_fd, leaf, AT_REMOVEDIR);
+  else
+    rc = unlinkat(parent_fd, leaf, 0);
+  bool ok = rc == 0 || errno == ENOENT || errno == ENOTEMPTY || errno == EEXIST;
+  if (rc == 0)
+    log_deleted(rel);
+  close(parent_fd);
+  free(leaf);
+  return ok;
+}
+
+DeleteCommitResult delete_plan_session_commit(DeletePlanSession* session, const Config* config) {
+  if (!session || !config)
+    return DELETE_COMMIT_ERROR;
+  /* Central no-mutation guard (mirrors manifest_delete_all): a dry-run never
+     deletes.  The receive path already skips plan application, but a hostile or
+     buggy peer could still reach the commit, so treat it as a no-op. */
+  if (session->dry_run)
+    return DELETE_COMMIT_OK;
+  bool ok = true;
+  if (session->defer) {
+    for (int i = 0; i < session->deferred->size && ok; i++)
+      ok = apply_deferred_path(session, config, (const char*)session->deferred->items[i]);
+  }
+  if (ok)
+    ok = apply_missing(session, config);
+  if (!ok)
+    return DELETE_COMMIT_ERROR;
+  if (session->limit_hit)
+    return DELETE_COMMIT_LIMIT_REACHED;
+  return DELETE_COMMIT_OK;
+}

src/shared/delete_plan.h

@@ -0,0 +1,83 @@
+#ifndef DELETE_PLAN_H
+#define DELETE_PLAN_H
+
+#include "array_list.h"
+#include "config.h"
+#include "file_receive.h"
+#include "protocol.h"
+#include <stdbool.h>
+
+/* Per-directory delete plans (protocol 2.24.0).
+ *
+ * rsync's --delete-during removes a directory's extras while the generator
+ * processes that directory, and --delete-delay records the deletion list during
+ * the scan but applies it only after a fully-successful transfer.  FastSync has
+ * no per-directory generator pass; instead the sender streams one plan per
+ * source directory, in directory order, and the receiver applies it when it
+ * arrives (during) or snapshots its extras and commits them at the end (delay).
+ *
+ * The sender side builds a plan set from the path-only pre-scan (it needs every
+ * directory's complete direct-child list before the first data byte of that
+ * directory).  The receiver side is a session that carries the global protected
+ * prefixes (filter-excluded and size-skipped source mirrors), the
+ * --delete-missing-args exact deletions, the shared --max-delete budget and,
+ * for --delete-delay, the snapshotted extras. */
+
+/* ---- Sender: plan builder ---- */
+
+typedef struct DeletePlanSender DeletePlanSender;
+
+DeletePlanSender* delete_plan_sender_create(void);
+void delete_plan_sender_destroy(DeletePlanSender* sender);
+/* Record one transmitted entry.  `path` is the destination-relative wire path;
+ * is_dir marks an explicit directory entry (--dirs, a -x mount point). */
+bool delete_plan_sender_add(DeletePlanSender* sender, const char* path, bool is_dir);
+/* Drop plans for directories outside `synced_dirs` (the --files-from
+ * synchronization scope; pass NULL when a full recursive transfer synchronized
+ * every directory).  The receive root is the "." sentinel.
+ *
+ * `walk_root` scopes a general -R transfer: when non-NULL it is the
+ * reconstructed destination prefix the run actually transferred, and only the
+ * plan for that prefix (and directories below it) is ever transmitted, so the
+ * prefix's parent-directory siblings are never walked.  Pass NULL for a plain
+ * recursive transfer and for --files-from. */
+void delete_plan_sender_finalize(DeletePlanSender* sender, const ArrayList* synced_dirs,
+                                 const char* walk_root);
+/* True when no transmitted FILE entry was recorded (an ambiguous empty scan).
+   Directory keep entries do not count, so an I/O error that hid every file
+   still refuses to delete. */
+bool delete_plan_sender_empty(const DeletePlanSender* sender);
+/* Attach the global config sections advertised on the first plan frame. */
+void delete_plan_sender_set_config(DeletePlanSender* sender, const ArrayList* protected_prefixes,
+                                   const ArrayList* size_skipped, const ArrayList* missing_args);
+/* Send the root plan (even before any data, so root extras are handled like
+ * rsync's first generator directory).  Returns -1 on I/O error. */
+int delete_plan_send_root(int fd, DeletePlanSender* sender);
+/* Send the plans for every ancestor of `path` (root-first) and, when is_dir,
+ * for `path` itself; already-sent plans are skipped. */
+int delete_plan_send_for_path(int fd, DeletePlanSender* sender, const char* path, bool is_dir);
+/* Send the plan for every directory in `dirs` that has not been transmitted
+ * yet.  Called after the data stream so an empty source directory's plan still
+ * clears its destination extras even though no file frame triggered it. */
+int delete_plan_send_remaining(int fd, DeletePlanSender* sender, const ArrayList* dirs);
+
+/* ---- Receiver: delete session ---- */
+
+typedef struct DeletePlanSession DeletePlanSession;
+
+DeletePlanSession* delete_plan_session_create(const Config* config);
+void delete_plan_session_destroy(DeletePlanSession* session);
+/* Read one STATUS_DELETE_PLAN frame (the leading status already consumed) and
+ * act on it.  Returns 0 on success (including a dry-run/disabled no-op) and -1
+ * after signalling STATUS_ERROR on a malformed frame or a deletion failure. */
+int delete_plan_session_receive(DeletePlanSession* session, const Config* config, int fd);
+/* Apply the deferred snapshot (--delete-delay) and the missing-args deletions.
+ * Safe to call once; returns the commit outcome. */
+DeleteCommitResult delete_plan_session_commit(DeletePlanSession* session, const Config* config);
+/* True once the shared --max-delete budget stopped part of a deletion. */
+bool delete_plan_session_limit_reached(const DeletePlanSession* session);
+/* Number of destination entries the session's plans removed (or, for
+   --delete-delay, snapshotted for removal), for the end-of-transfer stats. */
+size_t delete_plan_session_deleted(const DeletePlanSession* session);
+
+#endif

src/shared/file.h

@@ -22,13 +22,65 @@ bool file_load_data(File* file);
 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);
+/* Capture the process umask ONCE, before any threads are created.  Call this at
+ * the very top of main() in both entry points so the cached value is read while
+ * the process is still single-threaded: reading the umask needs a get+set round
+ * trip (umask(0); umask(old)), which would race against receiver threads
+ * creating files if it happened during the first write.  Idempotent and safe to
+ * call more than once. */
+void file_umask_capture(void);
+/* Process-wide umask, captured once (thread-safe).  Used to derive the mode of
+ * a brand-new destination like rsync: source_mode & 0777 & ~umask.  Falls back
+ * to file_umask_capture() (behind pthread_once) if capture was never called. */
+unsigned file_process_umask(void);
+/* Open `path` read-only for transfer, honouring --open-noatime when set. */
+int file_open_for_read(const char* path);
 bool file_write_to_disk(const char* path, const void* data, unsigned long long data_size,
                         bool inplace, bool sparse);
 
-/* A configured fd without a canonical identity deliberately rejects paths. */
-bool file_set_authorized_root(int fd, const char* canonical_path);
+/* Symlink trust-boundary helpers (Phase 4, symlink wave; rsync parity).
+ * --munge-links is a RECEIVER-side rewrite: rsync prefixes every stored symlink
+ * target with this marker, making the link unusable while the referenced
+ * directory does not exist.  A SENDER receiving a munged source strips it back
+ * off before transmitting (so a munged tree round-trips through the receiver's
+ * re-munging). */
+#define SYMLINK_MUNGE_PREFIX "/rsyncd-munged/"
+
+char* file_symlink_munge(const char* target);
+/* rsync 3.4.1 unsafe_symlink(): true when `target` escapes the transfer tree
+ * rooted at `link_path` (the symlink's transfer-relative path incl. its name).
+ * Absolute/empty targets and targets climbing above the transfer root (via
+ * "..") are unsafe, as are internal "/../" components and trailing "/..". */
+bool file_symlink_unsafe(const char* target, const char* link_path);
+/* True when a lexical target is relative and contains no ".." component, so it
+ * can never escape the receive root once created beneath it. */
+bool file_symlink_target_contained(const char* target);
+/* 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).  The link
+ * value is copied verbatim (rsync -l); only the placement path is confined.
+ * Returns false when a directory already occupies `path`. */
+bool file_symlink_at_secure(const char* path, const char* target);
+/* --keep-dirlinks (-K) receiver process-wide policy: allow an in-root existing
+ * symlink-to-directory to be followed as a directory. */
+void file_set_keep_dirlinks(bool enable);
+
+/* --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);
 
 /* Secure path/filesystem primitives (symlink-safe, O_NOFOLLOW, root-confined). */
 bool file_path_exists_secure(const char* path);
@@ -43,42 +95,68 @@ bool file_rename_secure(const char* old_path, const char* new_path);
    regular file.  See the .c for the exact success semantics. */
 bool file_remove_tree_secure(const char* path);
 /* Open a private 0700 directory (creating it on demand) that must live below
-   the authorized root.  Used for the --temp-dir scratch directory and the
-   --delay-updates staging directory. */
+   the authorized root.  Used for the --delay-updates staging directory. */
 int file_open_private_dir(const char* dir_path);
 
+/* Open an existing --temp-dir scratch directory as-is (absolute or relative;
+   no creation, no root confinement), matching rsync's --temp-dir handling. */
+int file_open_temp_dir(const char* dir_path);
+
 /* The file_to_disk_secure* variants write a temporary copy in the destination
-   directory and atomically rename it over `path`.  temp_dir is an absolute,
-   root-confined scratch directory (already validated by the caller): when it
-   is non-NULL the temporary copy is instead created there (with a name unique
-   across the whole scratch directory) and atomically renamed into the
-   destination directory once fully written and fsynced.  A rename across
-   filesystems (EXDEV) fails the write with an error; the file is never
-   silently copied into place.  Pass NULL for the historical same-directory
-   behavior.  --inplace writes never use temp_dir. */
+   directory and atomically rename it over `path`.  temp_dir is a scratch
+   directory (an absolute path, or one the caller already resolved against the
+   destination root): when it is non-NULL the temporary copy is instead created
+   there (with a name unique across the whole scratch directory) and atomically
+   renamed into the destination directory once fully written and fsynced.  When
+   that rename/link fails with EXDEV (the scratch dir is on another filesystem)
+   the write falls back to a non-atomic copy directly in the destination
+   directory, matching rsync.  Pass NULL for the same-directory behavior.
+   --inplace writes never use temp_dir. */
 bool file_to_disk_secure(const char* path, const void* data, unsigned long long data_size,
-                         bool inplace, bool sparse, const FileMetadata* metadata,
-                         bool preserve_executability, const char* temp_dir);
+                         bool inplace, bool sparse, bool preallocate, const FileMetadata* metadata,
+                         FileAttrPolicy policy, const char* temp_dir);
 bool file_to_disk_secure_with_fsync(const char* path, const void* data,
                                     unsigned long long data_size, bool inplace, bool sparse,
-                                    const FileMetadata* metadata, bool preserve_executability,
-                                    bool use_fsync, const char* temp_dir);
+                                    bool preallocate, const FileMetadata* metadata,
+                                    FileAttrPolicy policy, bool use_fsync, const char* temp_dir);
 /* With update enabled, an existing newer destination is left untouched.  The
    check is descriptor-based for inplace writes; atomic replacement still has
    an unavoidable final rename race without filesystem locking. */
 bool file_to_disk_secure_update(const char* path, const void* data, unsigned long long data_size,
-                                bool inplace, bool sparse, 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,
-                                    const FileMetadata* metadata, bool preserve_executability,
+                                bool inplace, bool sparse, bool preallocate,
+                                const FileMetadata* metadata, FileAttrPolicy policy,
                                 const char* temp_dir);
+bool file_to_disk_secure_no_replace(const char* path, const void* data,
+                                    unsigned long long data_size, bool sparse, bool preallocate,
+                                    const FileMetadata* metadata, FileAttrPolicy policy,
+                                    const char* temp_dir);
+/* Receiver write-path variant that also applies per-file xattrs (-X/-A) and the
+ * --fake-super stat xattr fd-relative before the final rename.  `update` /
+ * `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, FileAttrPolicy policy, bool update,
+                               bool no_replace, bool use_fsync, const FileXattrList* xattrs,
+                               bool fake_super, bool keep_partial, const char* temp_dir);
 /* Atomic --link-dest install: replace `path` with a hard link to `basis_path`
    (via a temp name + rename); fall back to a byte-identical local copy from
    `data` when the link is impossible (EXDEV/EPERM/unsupported filesystem).
-   `metadata` is applied only on the copy fallback. */
+   `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, const FileMetadata* metadata,
-                              bool preserve_executability, bool use_fsync, const char* temp_dir);
+                              unsigned long long data_size, bool preallocate,
+                              const FileMetadata* metadata, FileAttrPolicy policy, bool use_fsync,
+                              const char* temp_dir);
+/* Like file_to_disk_secure_link, but the byte-copy fallback also applies the
+ * per-file xattrs (-X/-A) and --fake-super stat xattr (fd-relative).  On a
+ * successful hard link no attributes are applied (the shared inode already
+ * carries the basis's). */
+bool file_to_disk_secure_link_attrs(const char* path, const char* basis_path, const void* data,
+                                    unsigned long long data_size, bool preallocate,
+                                    const FileMetadata* metadata, FileAttrPolicy policy,
+                                    bool use_fsync, const FileXattrList* xattrs, bool fake_super,
+                                    const char* temp_dir);
 
 #endif

src/shared/file_attr.h

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

src/shared/file_list.c

@@ -2,6 +2,7 @@
 #include "log.h"
 #include "utils.h"
 #include <errno.h>
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -22,6 +23,8 @@ static void string_list_destroy(StringList* list) {
 
 static bool string_list_add(StringList* list, const char* text) {
   if (list->count == list->capacity) {
+    if (list->capacity > INT_MAX / 2)
+      return false;
     int new_cap = list->capacity > 0 ? list->capacity * 2 : 16;
     char** grown = realloc(list->items, (size_t)new_cap * sizeof(char*));
     if (!grown)
@@ -51,11 +54,18 @@ static int normalize_entry(const char* raw, size_t len, bool strip_line_endings,
   if (len == 0)
     return 0;
   if (raw[0] == '/') {
-    snprintf(err, err_size, "absolute path entries are not allowed: '%.*s'", (int)len, raw);
+    int print_len = len > (size_t)INT_MAX ? INT_MAX : (int)len;
+    snprintf(err, err_size, "absolute path entries are not allowed: '%.*s'", print_len, raw);
+    return -1;
+  }
+  /* Reject NUL bytes inside a token defensively.  In NUL-delimited mode the
+   * delimiter itself is the final byte and is expected; in line mode any NUL is
+   * embedded garbage (strlen-based parsing would otherwise silently truncate). */
+  size_t scan_len = strip_line_endings ? len : len - 1;
+  if (memchr(raw, '\0', scan_len)) {
+    snprintf(err, err_size, "entry contains an embedded NUL byte");
     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");
@@ -102,8 +112,27 @@ static int normalize_entry(const char* raw, size_t len, bool strip_line_endings,
   return result;
 }
 
+/* Build the membership index over the exact entries only.  `file_list_affects`
+   combines the exact/descendant lookups with a walk of the query's own ancestor
+   prefixes, so no ancestor prefix is ever materialized as a copy and the index
+   stays O(entry count) memory regardless of path depth.  An empty entry (the
+   source root) sets whole_tree and short-circuits every query. */
+static bool file_list_index_build(FileListSet* set, char* err, size_t err_size) {
+  if (!path_index_build(&set->index, (const char* const*)set->entries, (size_t)set->count)) {
+    snprintf(err, err_size, "memory allocation failed");
+    return false;
+  }
+  for (int i = 0; i < set->count; i++) {
+    if (set->entries[i][0] == '\0') {
+      set->whole_tree = true;
+      break;
+    }
+  }
+  return true;
+}
+
 static FileListSet* string_list_to_set(StringList* raw, char* err, size_t err_size) {
-  FileListSet* set = malloc(sizeof(FileListSet));
+  FileListSet* set = calloc(1, sizeof(FileListSet));
   if (!set) {
     snprintf(err, err_size, "memory allocation failed");
     return NULL;
@@ -112,6 +141,10 @@ static FileListSet* string_list_to_set(StringList* raw, char* err, size_t err_si
   set->entries = raw->items;
   raw->items = NULL;
   raw->count = 0;
+  if (!file_list_index_build(set, err, err_size)) {
+    file_list_destroy(set);
+    return NULL;
+  }
   return set;
 }
 
@@ -133,10 +166,20 @@ FileListSet* file_list_load(const char* path, bool null_separated, char* err, si
   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) {
+  while (ok) {
+    ssize_t n = utils_getdelim_bounded(fp, &line, &line_cap, delim, UTILS_MAX_LINE_LEN);
+    if (n < 0) {
+      if (errno == EFBIG)
+        snprintf(err, err_size, "entry in file list exceeds %d bytes", (int)UTILS_MAX_LINE_LEN);
+      else
+        snprintf(err, err_size, "error reading file list: %s", strerror(errno));
+      ok = false;
+      break;
+    }
+    if (n == 0)
+      break;
     int r = normalize_entry(line, (size_t)n, !null_separated, &raw, err, err_size);
     if (r < 0) {
       ok = false;
@@ -158,34 +201,68 @@ FileListSet* file_list_load(const char* path, bool null_separated, char* err, si
 void file_list_destroy(FileListSet* set) {
   if (!set)
     return;
+  path_index_free(&set->index);
   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')
+  if (set->whole_tree)
     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 */
+  /* An exact entry match means `rel` itself is listed. */
+  if (path_index_contains(&set->index, rel))
+    return true;
+  /* Otherwise `rel` is affected when a listed entry is an ancestor directory of
+     it; walk rel's own directory prefixes (which preserve path-boundary
+     semantics) and test each for an exact entry.  No prefixes are stored. */
+  size_t len = strlen(rel);
+  while (len > 0) {
+    const char* slash = NULL;
+    for (size_t i = len; i-- > 0;) {
+      if (rel[i] == '/') {
+        slash = rel + i;
+        break;
       }
+    }
+    if (!slash)
+      break;
+    len = (size_t)(slash - rel);
+    if (path_index_contains_n(&set->index, rel, len))
+      return true;
+  }
+  /* Finally `rel` is affected when it is an ancestor directory of a listed
+     entry (binary search for the first entry at or after `rel` + '/'). */
+  return path_index_has_descendant(&set->index, rel);
+}
+
+bool file_list_dir_in_scope(const FileListSet* set, const char* rel) {
+  if (!set || set->whole_tree)
+    return true;
+  if (!rel || rel[0] == '\0')
     return false;
+  /* `rel` itself is listed, or one of its ancestor prefixes is an exact listed
+     directory (a listed prefix of a directory path is necessarily a
+     directory). */
+  size_t len = strlen(rel);
+  while (len > 0) {
+    const char* slash = NULL;
+    for (size_t i = len; i-- > 0;) {
+      if (rel[i] == '/') {
+        slash = rel + i;
+        break;
+      }
+    }
+    if (!slash)
+      break;
+    len = (size_t)(slash - rel);
+    if (path_index_contains_n(&set->index, rel, len))
+      return true;
+  }
+  return path_index_contains(&set->index, rel);
 }

src/shared/file_list.h

@@ -1,6 +1,7 @@
 #ifndef FILE_LIST_H
 #define FILE_LIST_H
 
+#include "utils.h"
 #include <stdbool.h>
 #include <stddef.h>
 
@@ -12,11 +13,18 @@
  * 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.
- */
-
+ *
+ * Membership is answered from `index`, built once at load time over the exact
+ * entries only: `index.exact` matches a listed path, the sorted view detects an
+ * ancestor directory of a listed entry, and `rel`'s own directory prefixes are
+ * matched against the exact set while descending.  No ancestor prefix is stored
+ * as a separate string, so the index is O(entry count) memory however deep the
+ * paths are, and each query is O(path length) comparisons. */
 typedef struct {
   char** entries; /* normalized rel paths; "" means the whole tree */
   int count;
+  PathIndex index;
+  bool whole_tree; /* an entry of "" lists the source root */
 } FileListSet;
 
 /* Load and validate a --files-from file. When `null_separated` (-0/--from0)
@@ -32,4 +40,14 @@ void file_list_destroy(FileListSet* set);
  * this returns true, files are transferred only when it returns true. */
 bool file_list_affects(const FileListSet* set, const char* rel);
 
+/* True when the DIRECTORY `rel` (path relative to the source root) is inside a
+ * listed directory subtree: `rel` itself is a listed entry, or one of `rel`'s
+ * ancestor directory prefixes is an exact listed entry.  Unlike
+ * file_list_affects this does NOT treat an ancestor of a listed entry as
+ * affected, so an implied parent directory of a listed file is not synchronized
+ * (rsync deletes nothing in it).  With no set or a whole-tree set every
+ * directory is in scope.  This is the delete-walker's "synchronized directory"
+ * predicate. */
+bool file_list_dir_in_scope(const FileListSet* set, const char* rel);
+
 #endif

src/shared/file_receive.h

@@ -7,9 +7,72 @@
 
 /* Server-side file receive/save path. */
 
+/* Cumulative caps for the deferred directory-time accumulator.  The sender may
+ * legitimately split a large tree across repeated STATUS_DIR_TIMES frames, so a
+ * per-frame bound is not enough: the receiver must bound the TOTAL it retains
+ * against a hostile sender.  Mirror the delete-manifest limits
+ * (MAX_MANIFEST_ENTRIES / MAX_MANIFEST_BYTES): the entry count bounds the
+ * metadata array and the byte budget bounds the concatenated path strings. */
+#define MAX_DIR_TIME_ENTRIES (1024 * 1024)
+#define MAX_DIR_TIME_BYTES (16ULL * 1024 * 1024)
+
 File* file_receive(const Config* config, int file_descriptor);
-File* file_receive_directory(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);
+/* Extended variant used by the receiver.  `would_transfer` (may be NULL) is set
+ * true only on the server-contacting --dry-run path when the file is not up to
+ * date: the receiver has already sent STATUS_DRY_RUN_TRANSFER and returns NULL
+ * without storing anything.  On that path `*skipped` is true for an up-to-date
+ * (STATUS_OK) file and both flags are false for a genuine error. */
+File* receive_incremental_check_ex(int fd, const Config* config, bool* skipped,
+                                   bool* would_transfer);
+
+/* 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 */
+  FileXattrList** xattrs; /* owned, parallel to paths; NULL when none */
+  size_t count;
+  size_t capacity;
+  size_t bytes; /* cumulative strlen of every retained path */
+} DirTimeList;
+
+/* Capture gate shared by the sender-side and receiver-side sinks: directory
+ * metadata is accumulated only when a directory attribute is requested
+ * (-p/--perms for directory modes, or -t/--times for directory mtimes with
+ * -O/--omit-dir-times not suppressing them) and metadata rides the wire.  Kept
+ * here, next to the accumulator it guards, so both call sites express the same
+ * condition. */
+bool dir_metadata_should_capture(const Config* config);
+
+void dir_time_list_init(DirTimeList* list);
+void dir_time_list_free(DirTimeList* list);
+/* Deep-copy one directory's path + metadata (and, when non-NULL, its captured
+ * xattr/ACL block) into the list.  Returns false on allocation failure OR when
+ * the cumulative entry/byte caps would be exceeded (the caller fails the
+ * transfer). */
+bool dir_time_list_add(DirTimeList* list, const char* wire_path, const FileMetadata* metadata,
+                       const FileXattrList* xattrs);
+/* Apply every accumulated directory's metadata beneath `root_directory`,
+ * confined fd-relative: ownership through the negotiated identity policy,
+ * times (mtime, plus atime when -U captured one under -t), the mode (through
+ * --chmod when configured, under -p), and the captured xattrs/ACLs (under
+ * -X/-A).  Best-effort per entry: an absent directory (an empty/pruned source
+ * dir that was deliberately not created) or a non-directory at the path is
+ * skipped QUIETLY, an unreachable one with a warning, and never fatal. */
+void dir_metadata_list_apply(const DirTimeList* list, const char* root_directory,
+                             const Config* config);
 
 /* A received delete-manifest frame: the keep-set (`keeps`, destination-relative
    paths the sender transferred/keeps) plus `protected`, destination-relative
@@ -25,11 +88,18 @@ typedef struct DeleteManifest {
   ArrayList* keeps;
   ArrayList* protected;
   ArrayList* missing;
+  /* Destination-relative paths of the directories the sender synchronized for
+     this run.  The extras walker only removes entries directly inside one of
+     these (the receive root is the "." sentinel); `--files-from` runs therefore
+     leave untransmitted directories and the unlisted parts of listed ones
+     alone, matching rsync's "delete only in synchronized directories". */
+  ArrayList* dirs;
 } DeleteManifest;
 
 void delete_manifest_free(DeleteManifest* manifest);
-/* Read a delete-manifest frame: keep count + keeps, then protected count +
-   protected prefixes, then missing count + missing paths (self-delimiting; the
+/* Read a delete-manifest frame (protocol 2.23.0): keep count + keeps, then
+   protected count + protected prefixes, then missing count + missing paths,
+   then synchronized-directory count + directory paths (self-delimiting; the
    leading STATUS_MANIFEST code has been consumed).  Returns an owned
    DeleteManifest, or NULL after signalling STATUS_ERROR on a malformed frame. */
 DeleteManifest* receive_manifest_entries(int fd);
@@ -48,11 +118,46 @@ bool manifest_delete_extras(const Config* config, DeleteManifest* manifest);
    confinement or I/O error (the run then fails); tolerated per-path cases are
    reported and skipped. */
 bool manifest_delete_missing_args(const Config* config, DeleteManifest* manifest);
+/* Budgeted form of manifest_delete_missing_args for the per-directory delete
+   session: each removed mirror draws from `max_delete` (SIZE_MAX = unlimited)
+   and the tallies are accumulated into `*deleted`/`*skipped`.  `*limit_hit` is set
+   when the budget stopped the pass with entries left over.  Returns false only
+   on a genuine deletion error. */
+bool manifest_delete_missing_args_limited(const Config* config, DeleteManifest* manifest,
+                                          size_t max_delete, size_t* deleted, size_t* skipped,
+                                          bool* limit_hit);
+/* Outcome of committing a delete manifest.  LIMIT_REACHED reports rsync's
+   partial --max-delete result: the budget allowed some deletions and the rest
+   were skipped (the run still stores all file data but the client exits 25). */
+typedef enum {
+  DELETE_COMMIT_OK = 0,
+  DELETE_COMMIT_LIMIT_REACHED,
+  DELETE_COMMIT_ERROR
+} DeleteCommitResult;
+
 /* Run every deletion family the manifest carries: the --delete-missing-args
    exact-path deletions first (user requests are not blocked by exclusion
-   protection), then the ordinary extras walk when --delete is active.  Returns
-   true when nothing to do or everything committed. */
-bool manifest_delete_all(const Config* config, DeleteManifest* manifest);
+   protection), then the ordinary extras walk when --delete is active.  Both
+   share one --max-delete budget.  Returns DELETE_COMMIT_OK when nothing was to
+   do or everything committed, DELETE_COMMIT_LIMIT_REACHED when the budget
+   stopped part of the work, or DELETE_COMMIT_ERROR on a genuine failure. */
+DeleteCommitResult manifest_delete_all(const Config* config, DeleteManifest* manifest);
+/* Like manifest_delete_all, but reports how many destination entries the commit
+   removed (for the end-of-transfer wire stats).  `deleted` may be NULL. */
+DeleteCommitResult manifest_delete_all_counted(const Config* config, DeleteManifest* manifest,
+                                               size_t* deleted);
+
+/* -n/--dry-run --delete would-delete reporting: walk the destination exactly as
+   the delete pass would and append (strdup'd) destination-relative paths that
+   WOULD be removed to `out`, without touching disk.  Uses the same staging-dir,
+   basis-dir and protected-prefix skips as the real commit.  Returns true on a
+   clean walk; `*count_out` receives the number of paths appended. */
+bool manifest_would_delete_list(const Config* config, DeleteManifest* manifest, ArrayList* out,
+                                size_t* count_out);
+/* Convert one basis-directory path to the receive-root-relative protection
+   prefix the delete walker uses (NULL when it lies outside the root).  Exposed
+   for unit tests of the root-of-"/" and normalization edge cases. */
+char* file_receive_basis_delete_relative(const Config* config, const char* path);
 
 /* Outcome of a single file_save_to_disk operation.  The receiver needs to
    distinguish "written" from "skipped" so --remove-source-files can be told

src/shared/file_send.c

@@ -10,23 +10,44 @@
 #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);
+                                          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) {
+                                      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;
@@ -41,7 +62,7 @@ bool file_send_single_calls_with_skip(File* file, int file_descriptor, bool use_
     }
     data_to_send = compressed_data;
   }
-  if (send_path && !send_str(file_descriptor, file_wire_path(file))) {
+  if (send_path && !send_wire_str(file_descriptor, file_wire_path(file))) {
     data_destroy(compressed_data);
     return false;
   }
@@ -49,6 +70,10 @@ bool file_send_single_calls_with_skip(File* file, int file_descriptor, bool use_
     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;
@@ -60,25 +85,27 @@ bool file_send_single_calls_with_skip(File* file, int file_descriptor, bool use_
 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);
+                                      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) {
+                                  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_with_skip(file, file_descriptor, use_metadata, compression_level,
                                             send_path, skip_suffixes, skip_count,
-                                            compression_threads);
+                                            compression_threads, send_xattrs);
 
-  if (send_path && !send_str(file_descriptor, file_wire_path(file)))
+  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;
@@ -116,10 +143,17 @@ bool file_send_sendfile_with_skip(File* file, int file_descriptor, bool use_meta
   }
 
   off_t offset = 0;
+  /* A non-positive --timeout disables the deadline: poll blocks until the
+   * socket is writable (rsync's --timeout=0 default). */
+  int io_timeout_sec = protocol_get_io_timeout_sec();
   struct timespec deadline;
+  if (io_timeout_sec > 0) {
     clock_gettime(CLOCK_MONOTONIC, &deadline);
-  deadline.tv_sec += 60;
+    deadline.tv_sec += io_timeout_sec;
+  }
   while ((unsigned long long)offset < file_size) {
+    int timeout = -1;
+    if (io_timeout_sec > 0) {
       struct timespec now;
       clock_gettime(CLOCK_MONOTONIC, &now);
       long long remaining = (long long)(deadline.tv_sec - now.tv_sec) * 1000LL +
@@ -128,8 +162,9 @@ bool file_send_sendfile_with_skip(File* file, int file_descriptor, bool use_meta
         close(fd);
         return false;
       }
+      timeout = remaining > INT_MAX ? INT_MAX : (int)remaining;
+    }
     struct pollfd pfd = {.fd = file_descriptor, .events = POLLOUT};
-    int timeout = remaining > INT_MAX ? INT_MAX : (int)remaining;
     int polled = poll(&pfd, 1, timeout);
     if (polled <= 0 || (pfd.revents & (POLLERR | POLLHUP | POLLNVAL))) {
       close(fd);
@@ -147,6 +182,7 @@ bool file_send_sendfile_with_skip(File* file, int file_descriptor, bool use_meta
       close(fd);
       return false;
     }
+    protocol_note_bytes_written((unsigned long long)sent);
   }
 
   close(fd);

src/shared/file_send.h

@@ -6,16 +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);
+                                      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);
+                                  int skip_count, int compression_threads, bool send_xattrs);
 
 #endif

src/shared/file_store.c

@@ -1,129 +1,7 @@
 #include <errno.h>
-#include <fcntl.h>
-#include <libgen.h>
-#include <limits.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
 #include <unistd.h>
 
 #include "file_store.h"
-#include "metadata.h"
-#include "utils.h"
-
-static int authorized_root_fd = -1;
-static char* authorized_root_path;
-
-static bool path_is_within_root(const char* root, const char* path) {
-  size_t root_length = strlen(root);
-  return strncmp(root, path, root_length) == 0 &&
-         (path[root_length] == '\0' || path[root_length] == '/');
-}
-
-bool file_store_set_authorized_root(int fd, const char* canonical_path) {
-  char* new_path = canonical_path ? str_dup(canonical_path) : NULL;
-  if (canonical_path && !new_path) {
-    authorized_root_fd = -1;
-    free(authorized_root_path);
-    authorized_root_path = NULL;
-    return false;
-  }
-  free(authorized_root_path);
-  authorized_root_path = new_path;
-  authorized_root_fd = fd;
-  return true;
-}
-
-int file_store_open_secure_parent(const char* path, char** leaf_out) {
-  char* copy = str_dup(path);
-  if (!copy)
-    return -1;
-  char* parent = dirname(copy);
-  const char* slash = strrchr(path, '/');
-  char* leaf = str_dup(slash ? slash + 1 : path);
-  if (!leaf) {
-    free(copy);
-    return -1;
-  }
-  int fd;
-  if (authorized_root_fd >= 0) {
-    if (!authorized_root_path || path[0] != '/' ||
-        !path_is_within_root(authorized_root_path, path)) {
-      free(copy);
-      free(leaf);
-      return -1;
-    }
-    fd = dup(authorized_root_fd);
-    if (fd < 0) {
-      free(copy);
-      free(leaf);
-      return -1;
-    }
-    size_t root_length = strlen(authorized_root_path);
-    char* relative = str_dup(path + root_length);
-    if (!relative) {
-      free(copy);
-      free(leaf);
-      close(fd);
-      return -1;
-    }
-    free(copy);
-    copy = relative;
-    parent = dirname(copy);
-  } else {
-    fd = (parent[0] == '/') ? open("/", O_RDONLY | O_DIRECTORY | O_CLOEXEC)
-                            : open(".", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
-  }
-  if (fd < 0) {
-    free(copy);
-    free(leaf);
-    return -1;
-  }
-  char* save = NULL;
-  char* component = strtok_r(parent, "/", &save);
-  while (component) {
-    if (strcmp(component, "..") == 0) {
-      close(fd);
-      free(copy);
-      free(leaf);
-      return -1;
-    }
-    if (strcmp(component, ".") != 0) {
-      int next = openat(fd, component, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
-      if (next < 0 && errno == ENOENT) {
-        if (mkdirat(fd, component, 0755) == 0 || errno == EEXIST)
-          next = openat(fd, component, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
-      }
-      if (next < 0) {
-        close(fd);
-        free(copy);
-        free(leaf);
-        return -1;
-      }
-      close(fd);
-      fd = next;
-    }
-    component = strtok_r(NULL, "/", &save);
-  }
-  free(copy);
-  *leaf_out = leaf;
-  return fd;
-}
-
-bool file_store_rename_secure(const char* old_path, const char* new_path) {
-  char *old_leaf = NULL, *new_leaf = NULL;
-  int old_parent = file_store_open_secure_parent(old_path, &old_leaf);
-  int new_parent = file_store_open_secure_parent(new_path, &new_leaf);
-  bool ok = old_parent >= 0 && new_parent >= 0 &&
-            renameat(old_parent, old_leaf, new_parent, new_leaf) == 0;
-  if (old_parent >= 0)
-    close(old_parent);
-  if (new_parent >= 0)
-    close(new_parent);
-  free(old_leaf);
-  free(new_leaf);
-  return ok;
-}
 
 static bool write_all(int fd, const void* data, unsigned long long size) {
   const unsigned char* p = data;
@@ -139,60 +17,40 @@ static bool write_all(int fd, const void* data, unsigned long long size) {
   return true;
 }
 
-bool file_store_write_secure(const char* path, const void* data, unsigned long long data_size,
-                             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)
+/* 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;
-  int fd = -1;
-  bool ok = false;
-  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)
-        ok = write_all(fd, data, data_size);
-      if (ok && 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);
-    if (tmp_size < 0) {
-      close(dirfd);
-      free(leaf);
+      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;
     }
-    char* tmp = malloc((size_t)tmp_size + 1);
-    if (!tmp) {
-      close(dirfd);
-      free(leaf);
-      return false;
   }
-    for (unsigned int i = 0; i < 100 && !ok; ++i) {
-      snprintf(tmp, (size_t)tmp_size + 1, ".%s.tmp.%ld.%u", leaf, (long)getpid(), i);
-      fd = openat(dirfd, tmp, O_WRONLY | O_CREAT | O_EXCL | O_CLOEXEC | O_NOFOLLOW, 0600);
-      if (fd < 0)
-        continue;
-      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);
-      if (ok && metadata)
-        ok = file_restore_metadata_fd(fd, metadata, preserve_executability);
-      if (close(fd) != 0)
-        ok = false;
-      fd = -1;
-      if (ok && renameat(dirfd, tmp, dirfd, leaf) != 0)
-        ok = false;
-      if (!ok)
-        unlinkat(dirfd, tmp, 0);
-    }
-    free(tmp);
-  }
-  if (fd >= 0)
-    close(fd);
-  close(dirfd);
-  free(leaf);
-  return ok;
+  return ftruncate(fd, (off_t)size) == 0;
 }

src/shared/file_store.h

@@ -1,14 +1,14 @@
 #ifndef FILE_STORE_H
 #define FILE_STORE_H
 
-#include "file.h"
 #include <stdbool.h>
 
-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 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 +2,8 @@
 #define FILE_TYPES_H
 
 #include "data.h"
+#include "format.h"
+#include "xattr.h"
 #include <stdbool.h>
 #include <sys/stat.h>
 
@@ -13,6 +15,18 @@ 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 {
@@ -29,12 +43,60 @@ typedef struct {
   /* 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;
+  /* Sender-side output-parity state (never serialized): the receiver-reported
+   * pre-transfer destination snapshot for this entry, filled by the per-file
+   * STATUS_CHECK exchange when report_dest_info is set.  `known` is false when
+   * no report was requested/received, in which case -i/--out-format treats the
+   * entry conservatively as newly created. */
+  OutputDestState dest_state;
+  /* Receiver-only wire-stats tally: the number of bytes reconstructed from the
+   * basis file (matched delta blocks) for this entry.  0 when the file was sent
+   * whole.  Accumulated into ReceiverStats.matched_data by the receiver sink. */
+  unsigned long long matched_bytes;
 } File;
 
 /* The path that should be sent on the wire and used for the receiver-side

src/shared/filter.c

@@ -1,162 +1,27 @@
 #include "filter.h"
 #include "log.h"
 #include "utils.h"
+#include <ctype.h>
 #include <errno.h>
+#include <limits.h>
+#include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-/* ---- Single rule parsing ---- */
-
-static bool rule_text_is_unsupported_word(const char* p, size_t len) {
-  static const char* const words[] = {"merge",   "dir-merge", "hide", "show",
-                                      "protect", "risk",      "clear"};
-  for (size_t i = 0; i < sizeof(words) / sizeof(words[0]); i++) {
-    size_t wl = strlen(words[i]);
-    if (len == wl && strncmp(p, words[i], wl) == 0)
-      return true;
-  }
-  return false;
+/* Write a diagnostic message into the caller's optional buffer.  A NULL `err`
+ * (or a zero size) is a no-op, so a caller that only needs the boolean status
+ * may pass NULL without the snprintf-on-NULL undefined behaviour. */
+static void filter_set_error(char* err, size_t err_size, const char* fmt, ...) {
+  if (!err || err_size == 0)
+    return;
+  va_list ap;
+  va_start(ap, fmt);
+  vsnprintf(err, err_size, fmt, ap);
+  va_end(ap);
 }
 
-/* rsync include/exclude rule modifiers we do NOT implement. A rule whose +/- is
- * immediately followed by one of these is rejected instead of being silently
- * parsed as a literal pattern. */
-static bool is_unsupported_rule_modifier(char c) {
-  return c == '!' || c == 'C' || c == 's' || c == 'r' || c == 'p' || c == 'x';
-}
-
-FilterRule* filter_rule_parse(const char* line, char* err, size_t err_size) {
-  if (err && err_size > 0)
-    err[0] = '\0';
-  if (!line)
-    return NULL;
-  char* text = str_dup(line);
-  if (!text) {
-    if (err)
-      snprintf(err, err_size, "memory allocation failed");
-    return NULL;
-  }
-  size_t len = strlen(text);
-  while (len > 0 && (text[len - 1] == '\n' || text[len - 1] == '\r'))
-    text[--len] = '\0';
-
-  const char* p = text;
-  while (*p == ' ' || *p == '\t')
-    p++;
-  if (*p == '\0') {
-    snprintf(err, err_size, "empty filter rule");
-    free(text);
-    return NULL;
-  }
-
-  FilterAction action = FILTER_ACTION_EXCLUDE;
-  if (*p == '+' || *p == '-') {
-    action = *p == '+' ? FILTER_ACTION_INCLUDE : FILTER_ACTION_EXCLUDE;
-    p++;
-    /* rsync attaches rule modifiers directly to the +/- (e.g. "-s foo"). Only
-     * the '/' anchor modifier is supported; anything else is a clear error
-     * rather than a silently-ignored literal. */
-    if (*p != ' ' && *p != '\t' && *p != '\0' && is_unsupported_rule_modifier(*p)) {
-      snprintf(err, err_size,
-               "filter rule modifier '%c' is not supported (only the '/' anchor after +/- "
-               "is implemented; put a space between +/- and the pattern)",
-               *p);
-      free(text);
-      return NULL;
-    }
-    while (*p == ' ' || *p == '\t')
-      p++;
-  } else {
-    /* ':' (dir-merge) and '.' (merge) are rsync filter-rule shorthands. At the
-     * start of a rule they mean "merge this file", so reject them instead of
-     * silently turning them into inert exclude patterns. */
-    if (*p == ':' || *p == '.' || *p == '!') {
-      snprintf(err, err_size,
-               "filter rule starting with '%c' is not supported (merge/dir-merge/list-clear "
-               "shorthands are not implemented; use +/- include/exclude rules)",
-               *p);
-      free(text);
-      return NULL;
-    }
-    const char* sp = p;
-    while (*sp != '\0' && *sp != ' ' && *sp != '\t')
-      sp++;
-    size_t word_len = (size_t)(sp - p);
-    if (rule_text_is_unsupported_word(p, word_len)) {
-      snprintf(err, err_size,
-               "'%.*s' filter directives are not supported (only +/- include/exclude rules "
-               "with an optional '/' anchor and trailing '/' dir marker)",
-               (int)word_len, p);
-      free(text);
-      return NULL;
-    }
-    if (word_len == strlen("include") && strncmp(p, "include", word_len) == 0) {
-      action = FILTER_ACTION_INCLUDE;
-      p = sp;
-    } else if (word_len == strlen("exclude") && strncmp(p, "exclude", word_len) == 0) {
-      action = FILTER_ACTION_EXCLUDE;
-      p = sp;
-    }
-    while (*p == ' ' || *p == '\t')
-      p++;
-  }
-
-  if (*p == '\0') {
-    snprintf(err, err_size, "filter rule has no pattern");
-    free(text);
-    return NULL;
-  }
-
-  /* A pattern beginning with '/' is anchored (either as "-/foo" or "- /foo"). */
-  bool anchored = false;
-  if (*p == '/') {
-    anchored = true;
-    p++;
-    while (*p == ' ' || *p == '\t')
-      p++;
-  }
-  if (*p == '\0') {
-    snprintf(err, err_size, "filter rule has no pattern after '/' anchor");
-    free(text);
-    return NULL;
-  }
-
-  /* Pattern runs to the end of the rule; a single trailing '/' marks dir-only. */
-  size_t pat_len = strlen(p);
-  bool dir_only = false;
-  if (pat_len > 1 && p[pat_len - 1] == '/') {
-    dir_only = true;
-    pat_len--;
-  } else if (pat_len == 1 && p[0] == '/') {
-    /* "//" anchored with nothing after: meaningless. */
-    snprintf(err, err_size, "filter rule has no pattern");
-    free(text);
-    return NULL;
-  }
-
-  FilterRule* rule = calloc(1, sizeof(FilterRule));
-  if (!rule) {
-    snprintf(err, err_size, "memory allocation failed");
-    free(text);
-    return NULL;
-  }
-  rule->pattern = malloc(pat_len + 1);
-  if (!rule->pattern) {
-    free(rule);
-    snprintf(err, err_size, "memory allocation failed");
-    free(text);
-    return NULL;
-  }
-  memcpy(rule->pattern, p, pat_len);
-  rule->pattern[pat_len] = '\0';
-  rule->action = action;
-  rule->anchored = anchored;
-  rule->dir_only = dir_only;
-  rule->owner = NULL;
-  free(text);
-  return rule;
-}
+/* ---- Ordered rule lists ---- */
 
 void filter_rule_free(FilterRule* rule) {
   if (!rule)
@@ -166,8 +31,6 @@ void filter_rule_free(FilterRule* rule) {
   free(rule);
 }
 
-/* ---- Ordered rule lists ---- */
-
 FilterRuleList* filter_rule_list_create(void) {
   return calloc(1, sizeof(FilterRuleList));
 }
@@ -176,6 +39,8 @@ bool filter_rule_list_add(FilterRuleList* list, FilterRule* rule) {
   if (!list || !rule)
     return false;
   if (list->count == list->capacity) {
+    if (list->capacity > INT_MAX / 2)
+      return false;
     int new_cap = list->capacity > 0 ? list->capacity * 2 : 8;
     FilterRule** grown = realloc(list->items, (size_t)new_cap * sizeof(FilterRule*));
     if (!grown)
@@ -187,28 +52,42 @@ bool filter_rule_list_add(FilterRuleList* list, FilterRule* rule) {
   return true;
 }
 
-bool filter_rule_list_parse_append(FilterRuleList* list, const char* line, char* err,
-                                   size_t err_size) {
-  FilterRule* rule = filter_rule_parse(line, err, err_size);
-  if (!rule)
-    return false;
-  if (!filter_rule_list_add(list, rule)) {
-    filter_rule_free(rule);
-    snprintf(err, err_size, "memory allocation failed");
-    return false;
-  }
-  return true;
-}
-
 void filter_rule_list_free(FilterRuleList* list) {
   if (!list)
     return;
   for (int i = 0; i < list->count; i++)
     filter_rule_free(list->items[i]);
+  for (int i = 0; i < list->dir_merge_count; i++)
+    free(list->dir_merge_names[i]);
+  free(list->dir_merge_names);
   free(list->items);
   free(list);
 }
 
+/* Register a per-directory merge-file basename (for "dir-merge NAME"/": NAME"
+ * and -F's .rsync-filter).  Duplicate names are ignored. */
+bool filter_rule_list_add_dir_merge(FilterRuleList* list, const char* name) {
+  if (!list || !name || name[0] == '\0')
+    return false;
+  for (int i = 0; i < list->dir_merge_count; i++) {
+    if (strcmp(list->dir_merge_names[i], name) == 0)
+      return true;
+  }
+  if (list->dir_merge_count == list->dir_merge_capacity) {
+    int new_cap = list->dir_merge_capacity > 0 ? list->dir_merge_capacity * 2 : 4;
+    char** grown = realloc(list->dir_merge_names, (size_t)new_cap * sizeof(char*));
+    if (!grown)
+      return false;
+    list->dir_merge_names = grown;
+    list->dir_merge_capacity = new_cap;
+  }
+  char* dup = str_dup(name);
+  if (!dup)
+    return false;
+  list->dir_merge_names[list->dir_merge_count++] = dup;
+  return true;
+}
+
 static bool set_rule_owner(FilterRule* rule, const char* owner) {
   char* dup = str_dup(owner ? owner : "");
   if (!dup)
@@ -218,7 +97,315 @@ static bool set_rule_owner(FilterRule* rule, const char* owner) {
   return true;
 }
 
-/* ---- CVS default excludes (-C) ---- */
+/* ---- Rule parsing ---- */
+
+/* A short rule prefix is a single character; a long rule name is alphabetic
+ * (with '-').  `is_short` distinguishes the modifier-attachment rules. */
+typedef enum {
+  RULE_KIND_EXCLUDE,
+  RULE_KIND_INCLUDE,
+  RULE_KIND_HIDE,
+  RULE_KIND_SHOW,
+  RULE_KIND_PROTECT,
+  RULE_KIND_RISK,
+  RULE_KIND_MERGE,
+  RULE_KIND_DIR_MERGE,
+  RULE_KIND_CLEAR,
+  RULE_KIND_UNKNOWN,
+} RuleKind;
+
+static bool short_rule_char(char c, RuleKind* kind) {
+  switch (c) {
+  case '-':
+    *kind = RULE_KIND_EXCLUDE;
+    return true;
+  case '+':
+    *kind = RULE_KIND_INCLUDE;
+    return true;
+  case 'H':
+    *kind = RULE_KIND_HIDE;
+    return true;
+  case 'S':
+    *kind = RULE_KIND_SHOW;
+    return true;
+  case 'P':
+    *kind = RULE_KIND_PROTECT;
+    return true;
+  case 'R':
+    *kind = RULE_KIND_RISK;
+    return true;
+  case '.':
+    *kind = RULE_KIND_MERGE;
+    return true;
+  case ':':
+    *kind = RULE_KIND_DIR_MERGE;
+    return true;
+  case '!':
+    *kind = RULE_KIND_CLEAR;
+    return true;
+  default:
+    return false;
+  }
+}
+
+static bool long_rule_name(const char* name, size_t len, RuleKind* kind) {
+  struct {
+    const char* word;
+    RuleKind kind;
+  } table[] = {
+      {"exclude", RULE_KIND_EXCLUDE}, {"include", RULE_KIND_INCLUDE},
+      {"hide", RULE_KIND_HIDE},       {"show", RULE_KIND_SHOW},
+      {"protect", RULE_KIND_PROTECT}, {"risk", RULE_KIND_RISK},
+      {"merge", RULE_KIND_MERGE},     {"dir-merge", RULE_KIND_DIR_MERGE},
+      {"clear", RULE_KIND_CLEAR},
+  };
+  for (size_t i = 0; i < sizeof(table) / sizeof(table[0]); i++) {
+    if (strlen(table[i].word) == len && strncmp(name, table[i].word, len) == 0) {
+      *kind = table[i].kind;
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool is_modifier_char(char c) {
+  return c == 's' || c == 'r' || c == 'p' || c == 'x' || c == '/' || c == '!' || c == 'C';
+}
+
+/* Parse "RULE[,MODIFIERS] [PATTERN]".  On success `kind`, `sides`,
+ * `sides_explicit`, `negate`, `anchored_mod`, `perishable`, `xattr`,
+ * `cvs_inject` and the pattern span (`pat_start`/`pat_len`, possibly 0 for
+ * merge/clear) are filled.  Returns true on success. */
+static bool parse_rule_syntax(const char* text, RuleKind* kind, unsigned* sides,
+                              bool* sides_explicit, bool* negate, bool* anchored_mod,
+                              bool* perishable, bool* xattr, bool* cvs_inject,
+                              const char** pat_start, size_t* pat_len) {
+  const char* p = text;
+  *sides = FILTER_SIDE_SENDER | FILTER_SIDE_RECEIVER;
+  *sides_explicit = false;
+  *negate = false;
+  *anchored_mod = false;
+  *perishable = false;
+  *xattr = false;
+  *cvs_inject = false;
+  *pat_start = NULL;
+  *pat_len = 0;
+
+  bool is_short = false;
+  if (short_rule_char(*p, kind)) {
+    is_short = true;
+    p++;
+  } else {
+    const char* name_start = p;
+    while (isalpha((unsigned char)*p) || *p == '-')
+      p++;
+    size_t name_len = (size_t)(p - name_start);
+    if (name_len == 0 || !long_rule_name(name_start, name_len, kind))
+      return false;
+    /* A long name must be followed by a separator, a comma or the end. */
+    if (*p != '\0' && *p != ',' && *p != ' ' && *p != '_')
+      return false;
+  }
+
+  /* Modifiers: long names require a comma; short names may attach directly.
+     Only commit a modifier run that terminates at a separator or the end, so a
+     pattern such as "*.tmp" written as "-*.tmp" is not mistaken for modifiers. */
+  const char* mod_start = p;
+  const char* mod_end = p;
+  if (*p == ',') {
+    p++;
+    mod_start = p;
+    while (is_modifier_char(*p))
+      p++;
+    mod_end = p;
+  } else if (is_short) {
+    const char* scan = p;
+    while (is_modifier_char(*scan))
+      scan++;
+    if (*scan == '\0' || *scan == ' ' || *scan == '_') {
+      mod_start = p;
+      mod_end = scan;
+      p = scan;
+    }
+  }
+  for (const char* m = mod_start; m < mod_end; m++) {
+    switch (*m) {
+    case 's':
+      *sides = FILTER_SIDE_SENDER;
+      *sides_explicit = true;
+      break;
+    case 'r':
+      *sides = FILTER_SIDE_RECEIVER;
+      *sides_explicit = true;
+      break;
+    case '!':
+      *negate = true;
+      break;
+    case '/':
+      *anchored_mod = true;
+      break;
+    case 'p':
+      *perishable = true;
+      break;
+    case 'x':
+      *xattr = true;
+      break;
+    case 'C':
+      *cvs_inject = true;
+      break;
+    default:
+      break;
+    }
+  }
+
+  /* A single space or underscore separates the rule/modifiers from the
+     pattern; further spaces/underscores belong to the pattern. */
+  const char* pat = p;
+  if (*pat == ' ' || *pat == '_')
+    pat++;
+  /* Trim a trailing newline/CR (the caller may pass a raw file line). */
+  *pat_start = pat;
+  *pat_len = strlen(pat);
+  while (*pat_len > 0 && (pat[*pat_len - 1] == '\n' || pat[*pat_len - 1] == '\r'))
+    (*pat_len)--;
+  return true;
+}
+
+FilterRule* filter_rule_parse(const char* line, const FilterParseOptions* opts, char* err,
+                              size_t err_size) {
+  if (err && err_size > 0)
+    err[0] = '\0';
+  if (!line)
+    return NULL;
+  const char* p = line;
+  while (*p == ' ' || *p == '\t')
+    p++;
+  if (*p == '\0' || *p == '\n' || *p == '\r') {
+    filter_set_error(err, err_size, "empty filter rule");
+    return NULL;
+  }
+
+  RuleKind kind = RULE_KIND_UNKNOWN;
+  unsigned sides;
+  bool sides_explicit, negate, anchored_mod, perishable, xattr, cvs_inject;
+  const char* pat;
+  size_t pat_len;
+  if (!parse_rule_syntax(p, &kind, &sides, &sides_explicit, &negate, &anchored_mod, &perishable,
+                         &xattr, &cvs_inject, &pat, &pat_len)) {
+    filter_set_error(err, err_size, "unrecognized filter rule syntax");
+    return NULL;
+  }
+  if (cvs_inject) {
+    /* The C modifier expands to the CVS defaults in place; the rule itself
+       carries no pattern and is handled by the caller. */
+    filter_set_error(err, err_size, "the C modifier is handled by the rule-list parser");
+    return NULL;
+  }
+  if (xattr) {
+    filter_set_error(err, err_size, "xattr-name filter rules (the x modifier) are not supported");
+    return NULL;
+  }
+  if (kind == RULE_KIND_MERGE || kind == RULE_KIND_DIR_MERGE) {
+    filter_set_error(err, err_size, "merge/dir-merge rules are handled by the rule-list parser");
+    return NULL;
+  }
+  if (kind == RULE_KIND_CLEAR) {
+    if (pat_len != 0) {
+      filter_set_error(err, err_size, "clear takes no pattern");
+      return NULL;
+    }
+    FilterRule* rule = calloc(1, sizeof(FilterRule));
+    if (!rule) {
+      filter_set_error(err, err_size, "memory allocation failed");
+      return NULL;
+    }
+    rule->action = FILTER_ACTION_NONE; /* clear marker: no pattern */
+    rule->sides = 0;
+    return rule;
+  }
+
+  FilterAction action;
+  switch (kind) {
+  case RULE_KIND_INCLUDE:
+  case RULE_KIND_SHOW:
+  case RULE_KIND_RISK:
+    action = FILTER_ACTION_INCLUDE;
+    break;
+  default:
+    action = FILTER_ACTION_EXCLUDE;
+    break;
+  }
+  if (kind == RULE_KIND_HIDE)
+    sides = FILTER_SIDE_SENDER;
+  else if (kind == RULE_KIND_SHOW)
+    sides = FILTER_SIDE_SENDER;
+  else if (kind == RULE_KIND_PROTECT)
+    sides = FILTER_SIDE_RECEIVER;
+  else if (kind == RULE_KIND_RISK)
+    sides = FILTER_SIDE_RECEIVER;
+  if (kind == RULE_KIND_HIDE || kind == RULE_KIND_SHOW || kind == RULE_KIND_PROTECT ||
+      kind == RULE_KIND_RISK)
+    sides_explicit = true;
+  /* --delete-excluded turns an unqualified (no explicit s/r) rule into a
+     sender-side-only rule, so it no longer protects the receiver. */
+  if (opts && opts->delete_excluded && !sides_explicit)
+    sides = FILTER_SIDE_SENDER;
+
+  if (pat_len == 0) {
+    filter_set_error(err, err_size, "filter rule has no pattern");
+    return NULL;
+  }
+
+  bool anchored = anchored_mod;
+  const char* pat_begin = pat;
+  if (*pat_begin == '/') {
+    anchored = true;
+    pat_begin++;
+    /* Drop the spaces that could follow the anchor in the "-/ foo" form. */
+    while (*pat_begin == ' ' || *pat_begin == '\t')
+      pat_begin++;
+    pat_len = strlen(pat_begin);
+    while (pat_len > 0 && (pat_begin[pat_len - 1] == '\n' || pat_begin[pat_len - 1] == '\r'))
+      pat_len--;
+  }
+  if (pat_len == 0) {
+    filter_set_error(err, err_size, "filter rule has no pattern after '/' anchor");
+    return NULL;
+  }
+  bool dir_only = false;
+  if (pat_len > 1 && pat_begin[pat_len - 1] == '/') {
+    dir_only = true;
+    pat_len--;
+  }
+  if (pat_len == 0) {
+    filter_set_error(err, err_size, "filter rule has no pattern");
+    return NULL;
+  }
+
+  FilterRule* rule = calloc(1, sizeof(FilterRule));
+  if (!rule) {
+    filter_set_error(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  rule->pattern = malloc(pat_len + 1);
+  if (!rule->pattern) {
+    free(rule);
+    filter_set_error(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  memcpy(rule->pattern, pat_begin, pat_len);
+  rule->pattern[pat_len] = '\0';
+  rule->action = action;
+  rule->sides = sides;
+  rule->anchored = anchored;
+  rule->dir_only = dir_only;
+  rule->negate = negate;
+  rule->perishable = perishable;
+  (void)xattr; /* xattr-name rules never match file/dir names; accepted/ignored */
+  return rule;
+}
+
+/* ---- CVS default excludes (-C and the C modifier) ---- */
 
 typedef struct {
   const char* pattern;
@@ -237,12 +424,13 @@ static const CvsDefaultRule CVS_DEFAULTS[] = {
     {".svn/", true},        {".git/", true},         {".hg/", true},   {".bzr/", true},
 };
 
-static bool cvs_rule_list_append(FilterRuleList* list) {
+static bool filter_list_append_cvs(FilterRuleList* list, unsigned sides) {
   for (size_t i = 0; i < sizeof(CVS_DEFAULTS) / sizeof(CVS_DEFAULTS[0]); i++) {
     FilterRule* rule = calloc(1, sizeof(FilterRule));
     if (!rule)
       return false;
     rule->action = FILTER_ACTION_EXCLUDE;
+    rule->sides = sides;
     rule->dir_only = CVS_DEFAULTS[i].dir_only;
     size_t plen = strlen(CVS_DEFAULTS[i].pattern);
     if (rule->dir_only && plen > 0 && CVS_DEFAULTS[i].pattern[plen - 1] == '/')
@@ -266,98 +454,261 @@ static bool cvs_rule_list_append(FilterRuleList* list) {
   return true;
 }
 
-FilterRuleList* filter_base_build(const char* const* rule_texts, int rule_count, bool cvs_exclude,
+#define FILTER_MAX_MERGE_DEPTH 16
+
+static bool filter_list_parse_append_depth(FilterRuleList* list, const char* line,
+                                           const FilterParseOptions* opts, const char* base_dir,
+                                           int depth, char* err, size_t err_size);
+
+/* Read a merge file and splice its rules into `list`.  A relative path is
+ * resolved below `base_dir` when given, else used as-is (rsync resolves a
+ * command-line merge file relative to the current directory). */
+static bool filter_list_merge_file(FilterRuleList* list, const char* name,
+                                   const FilterParseOptions* opts, const char* base_dir, int depth,
                                    char* err, size_t err_size) {
+  if (name[0] == '\0') {
+    filter_set_error(err, err_size, "merge requires a filename");
+    return false;
+  }
+  char* path =
+      (base_dir && base_dir[0] && name[0] != '/') ? path_cat(base_dir, name) : str_dup(name);
+  if (!path) {
+    filter_set_error(err, err_size, "memory allocation failed");
+    return false;
+  }
+  FILE* fp = fopen(path, "r");
+  if (!fp) {
+    filter_set_error(err, err_size, "could not read merge file '%s': %s", path, strerror(errno));
+    free(path);
+    return false;
+  }
+  char* line = NULL;
+  size_t cap = 0;
+  bool ok = true;
+  while (true) {
+    ssize_t n = utils_getdelim_bounded(fp, &line, &cap, '\n', UTILS_MAX_LINE_LEN);
+    if (n < 0) {
+      filter_set_error(err, err_size, "error reading merge file '%s'", path);
+      ok = false;
+      break;
+    }
+    if (n == 0)
+      break;
+    const char* lp = line;
+    while (*lp == ' ' || *lp == '\t')
+      lp++;
+    if (*lp == '\0' || *lp == '\n' || *lp == '\r' || *lp == '#')
+      continue;
+    if (!filter_list_parse_append_depth(list, lp, opts, base_dir, depth + 1, err, err_size)) {
+      ok = false;
+      break;
+    }
+  }
+  free(line);
+  fclose(fp);
+  free(path);
+  return ok;
+}
+
+/* Parse one line and append/merge it into `list`.  Handles clear, merge and
+ * dir-merge at the list level. */
+static bool filter_list_parse_append_depth(FilterRuleList* list, const char* line,
+                                           const FilterParseOptions* opts, const char* base_dir,
+                                           int depth, char* err, size_t err_size) {
+  if (depth > FILTER_MAX_MERGE_DEPTH) {
+    filter_set_error(err, err_size, "merge files nested too deeply");
+    return false;
+  }
+  const char* p = line;
+  while (*p == ' ' || *p == '\t')
+    p++;
+  if (*p == '\0' || *p == '\n' || *p == '\r')
+    return true;
+
+  RuleKind kind = RULE_KIND_UNKNOWN;
+  unsigned sides;
+  bool sides_explicit, negate, anchored_mod, perishable, xattr, cvs_inject;
+  const char* pat;
+  size_t pat_len;
+  if (!parse_rule_syntax(p, &kind, &sides, &sides_explicit, &negate, &anchored_mod, &perishable,
+                         &xattr, &cvs_inject, &pat, &pat_len)) {
+    filter_set_error(err, err_size, "unrecognized filter rule syntax: %s", p);
+    return false;
+  }
+  (void)sides_explicit;
+  (void)negate;
+  (void)anchored_mod;
+  (void)perishable;
+  (void)xattr;
+
+  if (cvs_inject) {
+    /* "C" injects the CVS defaults in place; no pattern is expected. */
+    return filter_list_append_cvs(list, sides);
+  }
+  if (kind == RULE_KIND_CLEAR) {
+    if (pat_len != 0) {
+      filter_set_error(err, err_size, "clear takes no pattern");
+      return false;
+    }
+    for (int i = 0; i < list->count; i++)
+      filter_rule_free(list->items[i]);
+    list->count = 0;
+    return true;
+  }
+  if (kind == RULE_KIND_MERGE) {
+    if (pat_len == 0) {
+      filter_set_error(err, err_size, "merge requires a filename");
+      return false;
+    }
+    char* name = malloc(pat_len + 1);
+    if (!name) {
+      filter_set_error(err, err_size, "memory allocation failed");
+      return false;
+    }
+    memcpy(name, pat, pat_len);
+    name[pat_len] = '\0';
+    bool ok = filter_list_merge_file(list, name, opts, base_dir, depth, err, err_size);
+    free(name);
+    return ok;
+  }
+  if (kind == RULE_KIND_DIR_MERGE) {
+    if (pat_len == 0) {
+      filter_set_error(err, err_size, "dir-merge requires a filename");
+      return false;
+    }
+    char* name = malloc(pat_len + 1);
+    if (!name) {
+      filter_set_error(err, err_size, "memory allocation failed");
+      return false;
+    }
+    memcpy(name, pat, pat_len);
+    name[pat_len] = '\0';
+    bool ok = filter_rule_list_add_dir_merge(list, name);
+    free(name);
+    if (!ok) {
+      filter_set_error(err, err_size, "memory allocation failed");
+      return false;
+    }
+    return true;
+  }
+
+  FilterRule* rule = filter_rule_parse(p, opts, err, err_size);
+  if (!rule)
+    return false;
+  if (!filter_rule_list_add(list, rule)) {
+    filter_rule_free(rule);
+    filter_set_error(err, err_size, "memory allocation failed");
+    return false;
+  }
+  return true;
+}
+
+bool filter_rule_list_parse_append(FilterRuleList* list, const char* line,
+                                   const FilterParseOptions* opts, const char* merge_base_dir,
+                                   char* err, size_t err_size) {
+  if (err && err_size > 0)
+    err[0] = '\0';
+  if (!list)
+    return false;
+  return filter_list_parse_append_depth(list, line, opts, merge_base_dir, 0, err, err_size);
+}
+
+FilterRuleList* filter_base_build(const char* const* rule_texts, int rule_count, bool cvs_exclude,
+                                  bool delete_excluded, char* err, size_t err_size) {
   if (err && err_size > 0)
     err[0] = '\0';
   FilterRuleList* list = filter_rule_list_create();
   if (!list) {
-    snprintf(err, err_size, "memory allocation failed");
+    filter_set_error(err, err_size, "memory allocation failed");
     return NULL;
   }
+  FilterParseOptions opts = {.delete_excluded = delete_excluded, .cvs_exclude = cvs_exclude};
   for (int i = 0; i < rule_count; i++) {
     if (!rule_texts || !rule_texts[i])
       continue;
-    FilterRule* rule = filter_rule_parse(rule_texts[i], err, err_size);
-    if (!rule) {
+    if (!filter_rule_list_parse_append(list, rule_texts[i], &opts, NULL, err, err_size)) {
       filter_rule_list_free(list);
       return NULL;
     }
-    if (!set_rule_owner(rule, "")) {
-      filter_rule_free(rule);
-      filter_rule_list_free(list);
-      snprintf(err, err_size, "memory allocation failed");
-      return NULL;
   }
-    if (!filter_rule_list_add(list, rule)) {
-      filter_rule_free(rule);
+  if (cvs_exclude && !filter_list_append_cvs(list, FILTER_SIDE_SENDER | FILTER_SIDE_RECEIVER)) {
     filter_rule_list_free(list);
-      snprintf(err, err_size, "memory allocation failed");
-      return NULL;
-    }
-  }
-  if (cvs_exclude && !cvs_rule_list_append(list)) {
-    filter_rule_list_free(list);
-    snprintf(err, err_size, "memory allocation failed");
+    filter_set_error(err, err_size, "memory allocation failed");
     return NULL;
   }
   return list;
 }
 
-/* ---- Per-directory .rsync-filter files ---- */
+/* ---- Per-directory merge files ---- */
 
-FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, bool* exists,
+/* Undo the rules and dir-merge registrations that one merge file appended,
+ * leaving the caller's earlier content intact.  A "clear" rule inside the file
+ * frees every rule, including the caller's; clamp to the surviving count so
+ * those already-freed rules are never resurrected and freed a second time. */
+static void filter_file_rollback(FilterRuleList* list, int rules_before, int dir_merges_before) {
+  int first = rules_before < list->count ? rules_before : list->count;
+  for (int i = first; i < list->count; i++)
+    filter_rule_free(list->items[i]);
+  list->count = first;
+  for (int i = dir_merges_before; i < list->dir_merge_count; i++)
+    free(list->dir_merge_names[i]);
+  list->dir_merge_count = dir_merges_before;
+}
+
+bool filter_file_append(FilterRuleList* list, const char* dir_path, const char* name,
+                        const char* owner_rel, const FilterParseOptions* opts, bool* exists,
                         char* err, size_t err_size) {
   if (err && err_size > 0)
     err[0] = '\0';
   if (exists)
     *exists = false;
-  char* filter_path = path_cat(dir_path, ".rsync-filter");
+  if (!list)
+    return false;
+  char* filter_path = path_cat(dir_path, name);
   if (!filter_path) {
-    snprintf(err, err_size, "memory allocation failed");
-    return NULL;
+    filter_set_error(err, err_size, "memory allocation failed");
+    return false;
   }
   FILE* fp = fopen(filter_path, "r");
   free(filter_path);
   if (!fp) {
     if (errno == ENOENT || errno == ENOTDIR)
-      return filter_rule_list_create();
-    log_message(LOG_LEVEL_WARNING, "Could not read .rsync-filter in %s: %s", dir_path,
-                strerror(errno));
-    return filter_rule_list_create();
+      return true;
+    char* escaped_dir = output_escape(dir_path, log_get_8_bit_output());
+    log_message(LOG_LEVEL_WARNING, "Could not read %s in %s: %s", name,
+                escaped_dir ? escaped_dir : "<allocation failed>", strerror(errno));
+    free(escaped_dir);
+    return true;
   }
   if (exists)
     *exists = true;
-  FilterRuleList* list = filter_rule_list_create();
-  if (!list) {
-    fclose(fp);
-    snprintf(err, err_size, "memory allocation failed");
-    return NULL;
-  }
+  int rules_before = list->count;
+  int dir_merges_before = list->dir_merge_count;
   char* line = NULL;
   size_t line_cap = 0;
-  ssize_t n;
   bool ok = true;
-  while ((n = getline(&line, &line_cap, fp)) != -1) {
+  while (true) {
+    ssize_t n = utils_getdelim_bounded(fp, &line, &line_cap, '\n', UTILS_MAX_LINE_LEN);
+    if (n < 0) {
+      if (errno == EFBIG) {
+        filter_set_error(err, err_size, "line in %s exceeds %d bytes", name,
+                         (int)UTILS_MAX_LINE_LEN);
+      } else {
+        filter_set_error(err, err_size, "error reading %s: %s", name, strerror(errno));
+      }
+      ok = false;
+      break;
+    }
+    if (n == 0)
+      break;
     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");
+    /* Merge files inside a per-directory file resolve relative to that
+       directory. */
+    if (!filter_list_parse_append_depth(list, p, opts, dir_path, 0, err, err_size)) {
       ok = false;
       break;
     }
@@ -365,12 +716,40 @@ FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, bo
   free(line);
   fclose(fp);
   if (!ok) {
+    filter_file_rollback(list, rules_before, dir_merges_before);
+    return false;
+  }
+  for (int i = rules_before; i < list->count; i++) {
+    if (!set_rule_owner(list->items[i], owner_rel)) {
+      filter_set_error(err, err_size, "memory allocation failed");
+      filter_file_rollback(list, rules_before, dir_merges_before);
+      return false;
+    }
+  }
+  return true;
+}
+
+FilterRuleList* filter_file_read_named(const char* dir_path, const char* name,
+                                       const char* owner_rel, const FilterParseOptions* opts,
+                                       bool* exists, char* err, size_t err_size) {
+  FilterRuleList* list = filter_rule_list_create();
+  if (!list) {
+    if (err && err_size > 0)
+      filter_set_error(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  if (!filter_file_append(list, dir_path, name, owner_rel, opts, exists, err, err_size)) {
     filter_rule_list_free(list);
     return NULL;
   }
   return list;
 }
 
+FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, bool* exists,
+                                 char* err, size_t err_size) {
+  return filter_file_read_named(dir_path, ".rsync-filter", owner_rel, NULL, exists, err, err_size);
+}
+
 /* ---- Rule matching ---- */
 
 /* Match a pattern that contains '/' (non-anchored) against the end of the
@@ -386,10 +765,10 @@ static bool glob_suffix_match(const char* pattern, const char* str) {
 }
 
 static FilterAction rule_matches(const FilterRule* rule, const char* rel_path, const char* leaf,
-                                 bool is_dir) {
+                                 bool is_dir, unsigned side) {
   if (!rule || !rule->pattern)
     return FILTER_ACTION_NONE;
-  if (rule->dir_only && !is_dir)
+  if (!(rule->sides & side))
     return FILTER_ACTION_NONE;
   /* A rule applies only to entries below its owner directory. */
   const char* rel2 = rel_path;
@@ -404,24 +783,36 @@ static FilterAction rule_matches(const FilterRule* rule, const char* rel_path, c
   if (rel2[0] == '\0')
     return FILTER_ACTION_NONE;
   bool matched;
-  if (rule->anchored) {
+  if (rule->dir_only && !is_dir)
+    matched = false;
+  else if (rule->anchored)
     matched = glob_match(rule->pattern, rel2);
-  } else if (strchr(rule->pattern, '/') != NULL) {
+  else if (strchr(rule->pattern, '/') != NULL)
     matched = glob_suffix_match(rule->pattern, rel2);
-  } else {
+  else
     matched = glob_match(rule->pattern, leaf);
-  }
-  return matched ? rule->action : FILTER_ACTION_NONE;
+  if (rule->negate)
+    matched = !matched;
+  if (!matched)
+    return FILTER_ACTION_NONE;
+  if (side == FILTER_SIDE_RECEIVER)
+    return rule->action == FILTER_ACTION_EXCLUDE ? FILTER_ACTION_PROTECT : FILTER_ACTION_RISK;
+  return rule->action;
 }
 
-FilterAction filter_rules_apply(const FilterRuleList* list, const char* rel_path, const char* leaf,
-                                bool is_dir) {
+FilterAction filter_rules_apply_side(const FilterRuleList* list, const char* rel_path,
+                                     const char* leaf, bool is_dir, unsigned side) {
   if (!list)
     return FILTER_ACTION_NONE;
   for (int i = 0; i < list->count; i++) {
-    FilterAction action = rule_matches(list->items[i], rel_path, leaf, is_dir);
+    FilterAction action = rule_matches(list->items[i], rel_path, leaf, is_dir, side);
     if (action != FILTER_ACTION_NONE)
       return action;
   }
   return FILTER_ACTION_NONE;
 }
+
+FilterAction filter_rules_apply(const FilterRuleList* list, const char* rel_path, const char* leaf,
+                                bool is_dir) {
+  return filter_rules_apply_side(list, rel_path, leaf, is_dir, FILTER_SIDE_SENDER);
+}

src/shared/filter.h

@@ -4,38 +4,51 @@
 #include <stdbool.h>
 #include <stddef.h>
 
-/* rsync-style filter rule engine (client-side file selection).
+/* rsync-style filter rule engine (client-side file selection and the
+ * receiver-side protection set it feeds).
  *
- * Supported rule syntax (documented subset):
- *   [+|-] [anchored '/' prefix] pattern [trailing '/' for dir-only]
- *
- *   "+ PATTERN"   include rule (first match wins)
- *   "- PATTERN"   exclude rule
- *   "PATTERN"     implicit exclude rule (rsync default)
- *   "include PATTERN" / "exclude PATTERN"  word forms
- *   leading '/' after the +/- anchors the pattern to its owner directory
- *     (the transfer root for command-line/-C rules, the directory that
- *      contains a .rsync-filter file for per-directory rules)
- *   a trailing '/' makes the rule match directories only
- *
- * Rejected explicitly (no silent no-ops): the rsync merge/dir-merge/list-clear
- * shorthands written as a rule that starts with ':' or '.' or '!', the
- * merge/dir-merge/hide/show/protect/risk/clear words, and every include/exclude
- * rule modifier other than '/' (! C s r p x). The pattern must be separated
- * from +/- by a space (or a single '/' anchor), exactly like rsync's
- * "-s foo"/"-p ..." modifier syntax is refused.
+ * Rule syntax (see the rsync man page FILTER RULES section):
+ *   RULE [PATTERN_OR_FILENAME]
+ *   RULE,MODIFIERS [PATTERN_OR_FILENAME]
+ * Short RULE names may attach MODIFIERS directly ("-sr foo"); the long name
+ * form requires the comma.  The pattern/filename is separated from the rule by
+ * one space or underscore.  Rule names:
+ *   exclude/-   exclude (by default both sender-hide and receiver-protect)
+ *   include/+   include (by default both sender-show and receiver-risk)
+ *   hide/H      sender-only exclude
+ *   show/S      sender-only include
+ *   protect/P   receiver-only exclude (protect from deletion)
+ *   risk/R      receiver-only include (allow deletion)
+ *   merge/.     read a client-side merge file for more rules
+ *   dir-merge/: per-directory merge file (registered for the scanner)
+ *   clear/!     clear the current rule list (takes no argument)
+ * Modifiers: '/' absolute anchor, '!' negate match, 'C' inject CVS defaults,
+ * 's' sender side, 'r' receiver side, 'p' perishable, 'x' xattr name rule.
+ * A trailing '/' makes a pattern match directories only.  A leading '/' anchors
+ * the pattern to its owner directory.
  */
 
 typedef enum {
   FILTER_ACTION_NONE = 0, /* no rule matched */
   FILTER_ACTION_EXCLUDE = -1,
-  FILTER_ACTION_INCLUDE = 1
+  FILTER_ACTION_INCLUDE = 1,
+  /* Receiver-side-only verdicts: the entry is transferred but its destination
+   * mirror is protected from --delete (PROTECT) or explicitly left at risk
+   * (RISK). */
+  FILTER_ACTION_PROTECT = 2,
+  FILTER_ACTION_RISK = 3,
 } FilterAction;
 
+#define FILTER_SIDE_SENDER 1u
+#define FILTER_SIDE_RECEIVER 2u
+
 typedef struct {
-  FilterAction action;
+  FilterAction action; /* EXCLUDE or INCLUDE (the base pattern action) */
+  unsigned sides;      /* FILTER_SIDE_SENDER | FILTER_SIDE_RECEIVER */
   bool anchored;       /* pattern anchored to the rule's owner directory */
   bool dir_only;       /* pattern had a trailing '/': matches directories only */
+  bool negate;         /* '!' modifier: match succeeds when the pattern does not */
+  bool perishable;     /* 'p' modifier (ignored in deleted directories) */
   char* owner;         /* owning directory rel path ("" == transfer root) */
   char* pattern;       /* cleaned glob pattern (no leading '/', no trailing '/') */
 } FilterRule;
@@ -44,19 +57,41 @@ typedef struct {
   FilterRule** items; /* owned array of rule pointers */
   int count;
   int capacity;
+  /* Per-directory merge-file basenames registered by "dir-merge NAME"/": NAME"
+   * or by -F (.rsync-filter).  Owned strings; the scanner reads each name in
+   * every directory it traverses. */
+  char** dir_merge_names;
+  int dir_merge_count;
+  int dir_merge_capacity;
 } FilterRuleList;
 
+/* Context needed while parsing a rule list (merge files, --delete-excluded). */
+typedef struct {
+  bool delete_excluded; /* --delete-excluded: default sides become sender-only */
+  bool cvs_exclude;     /* -C: expand the CVS default excludes */
+} FilterParseOptions;
+
 /* Parse a single filter-rule line (no trailing newline required). Returns an
- * owned rule, or NULL on unsupported/invalid syntax with a message in `err`. */
-FilterRule* filter_rule_parse(const char* line, char* err, size_t err_size);
+ * owned rule, or NULL on unsupported/invalid syntax with a message in `err`.
+ * `opts` may be NULL (no merge expansion / no delete-excluded). */
+FilterRule* filter_rule_parse(const char* line, const FilterParseOptions* opts, char* err,
+                              size_t err_size);
 void filter_rule_free(FilterRule* rule);
 
 FilterRuleList* filter_rule_list_create(void);
 /* Append a fully-parsed rule (takes ownership). Returns false on OOM. */
 bool filter_rule_list_add(FilterRuleList* list, FilterRule* rule);
-/* Parse `line` and append it. Returns false and fills `err` on bad syntax. */
-bool filter_rule_list_parse_append(FilterRuleList* list, const char* line, char* err,
-                                   size_t err_size);
+/* Register a per-directory merge-file basename (idempotent). Returns false on
+ * OOM.  Used by the scanner to read custom "dir-merge" files. */
+bool filter_rule_list_add_dir_merge(FilterRuleList* list, const char* name);
+/* Parse `line` and append it.  Handles "clear"/"!" (resets the list), "merge
+ * FILE"/". FILE" (splices the file's rules) and "dir-merge NAME"/": NAME"
+ * (registers a per-directory filename).  Returns false and fills `err` on bad
+ * syntax or an unreadable merge file.  `merge_base_dir` resolves a relative
+ * merge-file path (NULL means the process working directory). */
+bool filter_rule_list_parse_append(FilterRuleList* list, const char* line,
+                                   const FilterParseOptions* opts, const char* merge_base_dir,
+                                   char* err, size_t err_size);
 void filter_rule_list_free(FilterRuleList* list);
 
 /* Build the command-line filter set: `rule_texts` (--filter=RULE in the order
@@ -64,19 +99,38 @@ void filter_rule_list_free(FilterRuleList* list);
  * 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,
+                                  bool delete_excluded, char* err, size_t err_size);
+
+/* Read "<dir_path>/<name>" and return its rules, each owned by `owner_rel`.  A
+ * missing file yields an empty list with *exists=false; an unreadable file is
+ * treated as missing.  Returns NULL only on parse or allocation failure
+ * (message in `err`).  `opts` may be NULL. */
+FilterRuleList* filter_file_read_named(const char* dir_path, const char* name,
+                                       const char* owner_rel, const FilterParseOptions* opts,
+                                       bool* exists, char* err, size_t err_size);
+
+/* Append the rules of "<dir_path>/<name>" into an existing list (each owned by
+ * `owner_rel`).  A missing file yields *exists=false and no error.  Returns
+ * false only on parse/allocation failure (message in `err`). */
+bool filter_file_append(FilterRuleList* list, const char* dir_path, const char* name,
+                        const char* owner_rel, const FilterParseOptions* opts, bool* exists,
                         char* err, size_t err_size);
 
-/* 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`). */
+/* filter_file_read_named with the default ".rsync-filter" name. */
 FilterRuleList* filter_file_read(const char* dir_path, const char* owner_rel, bool* exists,
                                  char* err, size_t err_size);
 
-/* Evaluate an entry against one ordered rule list. Returns FILTER_ACTION_NONE
- * when no rule matched, otherwise the first matching rule's action.
- * `rel_path` is the entry's path relative to the transfer root ("" == root),
- * `leaf` its final name, `is_dir` whether it is a directory. */
+/* Evaluate an entry against one ordered rule list for one side.  Returns
+ * FILTER_ACTION_NONE when no rule matched, otherwise the first matching rule's
+ * action (for the receiver side an EXCLUDE is reported as
+ * FILTER_ACTION_PROTECT and an INCLUDE as FILTER_ACTION_RISK).  `rel_path` is
+ * the entry's path relative to the transfer root ("" == root), `leaf` its final
+ * name, `is_dir` whether it is a directory. */
+FilterAction filter_rules_apply_side(const FilterRuleList* list, const char* rel_path,
+                                     const char* leaf, bool is_dir, unsigned side);
+
+/* Sender-side convenience wrapper (kept for callers/tests that only need the
+ * transfer decision). */
 FilterAction filter_rules_apply(const FilterRuleList* list, const char* rel_path, const char* leaf,
                                 bool is_dir);
 

src/shared/format.c

@@ -0,0 +1,129 @@
+#include "format.h"
+#include "protocol.h"
+#include <stdio.h>
+#include <string.h>
+
+bool format_human_size_decimal(unsigned long long bytes, char* buffer, size_t buffer_size) {
+  if (!buffer || buffer_size == 0)
+    return false;
+  if (bytes < 1000ULL) {
+    int written = snprintf(buffer, buffer_size, "%llu", bytes);
+    return written >= 0 && (size_t)written < buffer_size;
+  }
+  static const char units[] = "KMGTPE";
+  double value = (double)bytes;
+  size_t divisions = 0;
+  while (value >= 1000.0 && divisions < sizeof(units) - 1) {
+    value /= 1000.0;
+    divisions++;
+  }
+  int written = snprintf(buffer, buffer_size, "%.2f%c", value, units[divisions - 1]);
+  return written >= 0 && (size_t)written < buffer_size;
+}
+
+bool format_big_num(unsigned long long value, bool human_readable, char* buffer,
+                    size_t buffer_size) {
+  if (human_readable)
+    return format_human_size_decimal(value, buffer, buffer_size);
+  char digits[32];
+  int written = snprintf(digits, sizeof(digits), "%llu", value);
+  if (written < 0 || (size_t)written >= sizeof(digits))
+    return false;
+  size_t len = (size_t)written;
+  size_t separators = len > 1 ? (len - 1) / 3 : 0;
+  size_t total = len + separators;
+  if (total + 1 > buffer_size)
+    return false;
+  size_t out = total;
+  buffer[out] = '\0';
+  size_t digits_since_sep = 0;
+  for (size_t i = len; i > 0; i--) {
+    buffer[--out] = digits[i - 1];
+    digits_since_sep++;
+    if (digits_since_sep == 3 && i > 1) {
+      buffer[--out] = ',';
+      digits_since_sep = 0;
+    }
+  }
+  return true;
+}
+
+bool format_rsync_datetime(time_t when, bool dash, char* buffer, size_t buffer_size) {
+  if (!buffer || buffer_size == 0)
+    return false;
+  struct tm broken_down;
+  if (localtime_r(&when, &broken_down) == NULL)
+    return false;
+  const char* format = dash ? "%Y/%m/%d-%H:%M:%S" : "%Y/%m/%d %H:%M:%S";
+  return strftime(buffer, buffer_size, format, &broken_down) != 0;
+}
+
+bool format_dest_state_send(int fd, const OutputDestState* state) {
+  if (!state)
+    return false;
+  int32_t has_old = state->existed ? 1 : 0;
+  uint64_t size = (uint64_t)state->size;
+  int64_t mtime = (int64_t)state->mtime_sec;
+  int64_t mtime_nsec = state->mtime_nsec;
+  uint32_t mode = state->mode;
+  int32_t uid = state->uid;
+  int32_t gid = state->gid;
+  return send_n_data(fd, &has_old, sizeof(has_old)) && send_n_data(fd, &size, sizeof(size)) &&
+         send_n_data(fd, &mtime, sizeof(mtime)) &&
+         send_n_data(fd, &mtime_nsec, sizeof(mtime_nsec)) && send_n_data(fd, &mode, sizeof(mode)) &&
+         send_n_data(fd, &uid, sizeof(uid)) && send_n_data(fd, &gid, sizeof(gid));
+}
+
+bool format_dest_state_receive(int fd, OutputDestState* state) {
+  if (!state)
+    return false;
+  int32_t has_old = 0;
+  uint64_t size = 0;
+  int64_t mtime = 0;
+  int64_t mtime_nsec = 0;
+  uint32_t mode = 0;
+  int32_t uid = 0;
+  int32_t gid = 0;
+  if (!receive_n_data(fd, &has_old, sizeof(has_old)) || !receive_n_data(fd, &size, sizeof(size)) ||
+      !receive_n_data(fd, &mtime, sizeof(mtime)) ||
+      !receive_n_data(fd, &mtime_nsec, sizeof(mtime_nsec)) ||
+      !receive_n_data(fd, &mode, sizeof(mode)) || !receive_n_data(fd, &uid, sizeof(uid)) ||
+      !receive_n_data(fd, &gid, sizeof(gid)))
+    return false;
+  memset(state, 0, sizeof(*state));
+  state->known = true;
+  state->existed = has_old != 0;
+  state->size = size;
+  state->mtime_sec = mtime;
+  state->mtime_nsec = mtime_nsec;
+  state->mode = mode;
+  state->uid = uid;
+  state->gid = gid;
+  return true;
+}
+
+bool format_stats_send(int fd, const ReceiverStats* stats) {
+  if (!stats)
+    return false;
+  unsigned long long matched = stats->matched_data;
+  unsigned long long deleted = stats->deleted_files;
+  unsigned long long would = stats->would_delete_count;
+  return send_n_data(fd, &matched, sizeof(matched)) && send_n_data(fd, &deleted, sizeof(deleted)) &&
+         send_n_data(fd, &would, sizeof(would));
+}
+
+bool format_stats_receive(int fd, ReceiverStats* stats) {
+  if (!stats)
+    return false;
+  unsigned long long matched = 0;
+  unsigned long long deleted = 0;
+  unsigned long long would = 0;
+  if (!receive_n_data(fd, &matched, sizeof(matched)) ||
+      !receive_n_data(fd, &deleted, sizeof(deleted)) || !receive_n_data(fd, &would, sizeof(would)))
+    return false;
+  memset(stats, 0, sizeof(*stats));
+  stats->matched_data = matched;
+  stats->deleted_files = deleted;
+  stats->would_delete_count = would;
+  return true;
+}

src/shared/format.h

@@ -0,0 +1,76 @@
+#ifndef FORMAT_H
+#define FORMAT_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <time.h>
+
+/* Low-level output-formatting primitives shared by the change-event model
+ * (change_list.c) and the transfer driver (client_send.c).
+ *
+ * The functions here are pure/string-level except for the STATUS_DEST_INFO
+ * codec, which lets the receiver report the pre-transfer destination entry so
+ * the sender can render rsync-accurate --itemize-changes / --out-format
+ * columns (see protocol.h). */
+
+/* Pre-transfer destination snapshot, reported by the receiver when the wire
+ * config carries report_dest_info.  `known` distinguishes "no report was
+ * requested/received" from "the destination did not exist" (`existed == false`
+ * with `known == true`). */
+typedef struct {
+  bool known;
+  bool existed;
+  unsigned long long size;
+  long long mtime_sec;
+  long long mtime_nsec;
+  uint32_t mode;
+  int32_t uid;
+  int32_t gid;
+} OutputDestState;
+
+/* rsync's -h/--human-readable size (decimal, base 1000): integers below 1000
+ * print verbatim; larger values use the largest unit that keeps the value
+ * below 1000 (K/M/G/T/P/E) with exactly two decimals, so 1500000 -> "1.50M"
+ * and 999999 -> "1000.00K" (matching rsync's human_num).  Returns false when
+ * the buffer is too small (nothing is written). */
+bool format_human_size_decimal(unsigned long long bytes, char* buffer, size_t buffer_size);
+
+/* rsync's general number formatting (big_num).  When `human_readable` is true
+ * this is format_human_size_decimal; otherwise the integer is rendered with a
+ * ',' thousands separator every three digits (rsync's separator in the C
+ * locale).  Returns false on an undersized buffer. */
+bool format_big_num(unsigned long long value, bool human_readable, char* buffer,
+                    size_t buffer_size);
+
+/* rsync's %M/%t timestamp.  When `dash` is true the separator between the date
+ * and the time is '-' (the %M form: "YYYY/MM/DD-HH:MM:SS"); otherwise it is a
+ * space (the %t form: "YYYY/MM/DD HH:MM:SS").  Local time.  Returns false on a
+ * bad time or an undersized buffer. */
+bool format_rsync_datetime(time_t when, bool dash, char* buffer, size_t buffer_size);
+
+/* Fixed-width STATUS_DEST_INFO record codec (int32 has_old, uint64 size,
+ * int64 mtime, int64 mtime_nsec, uint32 mode, int32 uid, int32 gid).  The
+ * status frame itself is sent/received by the caller.  Returns false on I/O
+ * failure. */
+bool format_dest_state_send(int fd, const OutputDestState* state);
+bool format_dest_state_receive(int fd, OutputDestState* state);
+
+/* End-of-transfer receiver counters reported through STATUS_STATS (protocol
+ * 2.25.0) when the wire config carries report_stats.  `would_delete_count` is
+ * the number of destination-relative paths the receiver would have deleted in a
+ * -n/--dry-run --delete run; that many wire strings immediately follow the
+ * fixed record (sent/read by the caller). */
+typedef struct {
+  unsigned long long matched_data;
+  unsigned long long deleted_files;
+  unsigned long long would_delete_count;
+} ReceiverStats;
+
+/* Fixed-width STATUS_STATS counter record.  The status frame and the optional
+ * would-delete path list are sent/received by the caller.  Returns false on I/O
+ * failure. */
+bool format_stats_send(int fd, const ReceiverStats* stats);
+bool format_stats_receive(int fd, ReceiverStats* stats);
+
+#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.h

@@ -0,0 +1,162 @@
+#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) or a
+ * preserve-source -o/--owner / -g/--group request is required. */
+bool identity_active_enabled(void);
+
+/* Per-side predicates over the ACTIVE per-connection snapshot (call
+ * identity_set_active() first).  They mirror the owner_requested /
+ * group_requested conditions inside identity_resolve_targets() exactly, so
+ * callers that must apply only one side (e.g. the --fake-super owner replay)
+ * can pass (uid_t)-1 / (gid_t)-1 for the side that was NOT requested and leave
+ * it untouched.  The owner side is requested by --copy-as, --chown USER,
+ * --numeric-ids, -o/--owner, or a non-empty --usermap; the group side by
+ * --copy-as, --chown :GROUP, --numeric-ids, -g/--group, or a non-empty
+ * --groupmap. */
+bool identity_owner_requested(void);
+bool identity_group_requested(void);
+
+/* Pure, config-only predicate: true when the client requested ANY client-chosen
+ * ownership or super-user activity (--numeric-ids, --chown, --usermap/--groupmap,
+ * --copy-as, --fake-super, an explicit --super, or a preserve-source -o/-g).
+ * General awareness only; the daemon module gate uses the narrower
+ * identity_explicit_ownership_requested() below.  Never reads the snapshot. */
+bool identity_ownership_requested(const Config* config);
+
+/* Pure, config-only predicate for the narrow set that lets the CLIENT choose an
+ * arbitrary owner/group: --numeric-ids, --chown, --usermap/--groupmap,
+ * --copy-as, --fake-super, or an explicit --super.  Deliberately EXCLUDES a
+ * plain -o/--owner / -g/--group (or -a) preserve-source request, which the
+ * daemon gate handles by forcing super-user ownership activity off rather than
+ * refusing the whole transfer.  Never reads the snapshot. */
+bool identity_explicit_ownership_requested(const Config* config);
+
+/* Apply the negotiated ownership to an already-written file descriptor.
+ * source_uid/source_gid are the transmitted numeric ids.  Resolution order:
+ * --copy-as (highest priority, forces both ids), then a matching
+ * 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);
+
+/* Resolve the ownership that --fake-super should RECORD in the reserved xattr
+ * (rather than chown for real).  A requested side (--copy-as / usermap /
+ * --chown / -o / -g, with --numeric-ids as the raw-id modifier) yields the
+ * resolved target; a side that was not requested keeps the transmitted source
+ * id.  Must be called after identity_set_active(). */
+void identity_resolve_storage_ids(int32_t source_uid, int32_t source_gid, uint32_t* out_uid,
+                                  uint32_t* out_gid);
+
+/* P7 Wave D: the no-follow (symlink) counterpart.  Resolves the same
+ * usermap/groupmap/chown/numeric-ids/copy-as policy but applies it with
+ * fchownat(..., AT_SYMLINK_NOFOLLOW) so a symlink's own ownership is changed
+ * 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(SuperMode mode);
+
+#endif

src/shared/log.c

@@ -3,7 +3,9 @@
 #include <stdbool.h>
 #include <stdarg.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
+#include <threads.h>
 #include <time.h>
 
 static const char* log_level_strings[] = {"DEBUG", "INFO", "WARN", "ERROR"};
@@ -15,6 +17,18 @@ static FILE* log_fp = NULL;
 static _Thread_local bool eight_bit_output;
 static LogStderrMode stderr_mode = LOG_STDERR_ERRORS;
 
+/* Serializes access to log_fp and makes each emitted line atomic: the
+ * timestamp prefix, formatted body, and trailing newline are written as one
+ * critical section so concurrent threads cannot interleave partial lines.
+ * Initialized lazily (matching the protocol.c bw_mutex idiom) because logging
+ * can happen before main() installs any synchronization. */
+static mtx_t log_mutex;
+static once_flag log_mutex_once = ONCE_FLAG_INIT;
+
+static void log_mutex_init(void) {
+  mtx_init(&log_mutex, mtx_plain);
+}
+
 void set_log_level(LogLevel level) {
   current_log_level = level;
 }
@@ -27,6 +41,10 @@ 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;
@@ -37,7 +55,10 @@ uint32_t get_log_info_flags(void) {
 }
 
 void log_set_file(FILE* fp) {
+  call_once(&log_mutex_once, log_mutex_init);
+  mtx_lock(&log_mutex);
   log_fp = fp;
+  mtx_unlock(&log_mutex);
 }
 
 void log_set_8_bit_output(bool enabled) {
@@ -56,13 +77,48 @@ 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,
+/* Format one complete log line (timestamp prefix + body + newline) into a
+ * freshly allocated buffer.  This is pure CPU/malloc work and must happen
+ * OUTSIDE the log mutex: the mutex only guards the log_fp pointer, so a
+ * stalled stderr/stdout pipe cannot block every logging thread.  Returns NULL
+ * on allocation/formatting failure. */
+static char* format_log_line(LogLevel log_level, const 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,
-          t.tm_mday, t.tm_hour, t.tm_min, t.tm_sec, log_level_strings[log_level]);
+  char prefix[64];
+  int prefix_len = snprintf(
+      prefix, sizeof(prefix), "%04d-%02d-%02d %02d:%02d:%02d [%s]: ", t->tm_year + 1900,
+      t->tm_mon + 1, t->tm_mday, t->tm_hour, t->tm_min, t->tm_sec, log_level_strings[log_level]);
+  if (prefix_len < 0 || prefix_len >= (int)sizeof(prefix))
+    return NULL;
+  va_list copy;
+  va_copy(copy, args);
+  int body_len = vsnprintf(NULL, 0, format, copy);
+  va_end(copy);
+  if (body_len < 0)
+    return NULL;
+  size_t total = (size_t)prefix_len + (size_t)body_len;
+  char* line = malloc(total + 2); /* body bytes + '\n' + NUL */
+  if (!line)
+    return NULL;
+  memcpy(line, prefix, (size_t)prefix_len);
+  vsnprintf(line + prefix_len, (size_t)body_len + 1, format, args);
+  line[total] = '\n';
+  line[total + 1] = '\0';
+  return line;
+}
 
-  vfprintf(dest_io, format, args);
-  fprintf(dest_io, "\n");
+/* Write an already-formatted line to the console and, if configured, the log
+ * file.  Only the log_fp pointer is read under the mutex (so log_set_file /
+ * config_delete cannot free it while it is in use); the single console fputs
+ * runs unlocked but is internally atomic per stdio stream. */
+static void emit_log_line(FILE* console, const char* line) {
+  fputs(line, console);
+  call_once(&log_mutex_once, log_mutex_init);
+  mtx_lock(&log_mutex);
+  FILE* file = log_fp;
+  if (file)
+    fputs(line, file);
+  mtx_unlock(&log_mutex);
 }
 
 void log_message(LogLevel log_level, const char* format, ...) {
@@ -82,14 +138,12 @@ void log_message(LogLevel log_level, const char* format, ...) {
 
   va_list args;
   va_start(args, format);
-  write_message(dest_io, log_level, t, format, args);
+  char* line = format_log_line(log_level, &t, format, args);
   va_end(args);
-
-  if (log_fp) {
-    va_start(args, format);
-    write_message(log_fp, log_level, t, format, args);
-    va_end(args);
-  }
+  if (!line)
+    return;
+  emit_log_line(dest_io, line);
+  free(line);
 }
 
 void log_debug_message(LogDebugFlag flag, const char* format, ...) {
@@ -103,14 +157,12 @@ void log_debug_message(LogDebugFlag flag, const char* format, ...) {
 
   va_list args;
   va_start(args, format);
-  write_message(stdout, LOG_LEVEL_DEBUG, t, format, args);
+  char* line = format_log_line(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);
-  }
+  if (!line)
+    return;
+  emit_log_line(stdout, line);
+  free(line);
 }
 
 void log_info_message(LogInfoFlag flag, const char* format, ...) {
@@ -125,14 +177,12 @@ void log_info_message(LogInfoFlag flag, const char* format, ...) {
 
   va_list args;
   va_start(args, format);
-  write_message(stdout, LOG_LEVEL_INFO, t, format, args);
+  char* line = format_log_line(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);
-  }
+  if (!line)
+    return;
+  emit_log_line(stdout, line);
+  free(line);
 }
 
 void log_perror(const char* context) {

src/shared/log.h

@@ -29,6 +29,10 @@ 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);