Apply clang-format 18 to merge-conflict resolution code

The Phase 1 merge conflict resolutions introduced formatting that failed
the CI lint job (clang-format 18.1.3). Reformatted with the exact CI
version; no functional changes.

CMakeLists.txt

@@ -58,15 +58,18 @@ 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")
 
 # --- Main executables ---
-add_executable(server ${SERVER_SRCS} ${SHARED_SRCS})
+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)
 
-add_executable(client ${CLIENT_SRCS} ${SHARED_SRCS})
+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)
 
@@ -79,7 +82,7 @@ set(TEST_INCLUDES tests src/shared src/server src/client)
 
 # Monolithic test binary (backward compatible)
 file(GLOB TEST_SRCS "tests/test_*.c" "tests/runner.c")
-add_executable(tests ${TEST_SRCS} ${SHARED_SRCS} src/client/scanner.c src/client/client_cli.c)
+add_executable(tests ${TEST_SRCS} ${SHARED_SRCS} ${FILE_STORE_SRCS} ${SERVER_RECEIVER_SRCS} src/client/scanner.c src/client/client_cli.c src/client/client_validation.c src/client/usage.c)
 target_include_directories(tests PRIVATE ${TEST_INCLUDES})
 target_compile_definitions(tests PRIVATE FASTSYNC_TEST_BUILD)
 target_link_libraries(tests PRIVATE ${TEST_LIBS})
@@ -94,7 +97,7 @@ if(ENABLE_FUZZ)
   file(GLOB FUZZ_SRCS "tests/fuzz/*.c")
 	foreach(FUZZ_SRC ${FUZZ_SRCS})
 		get_filename_component(FUZZ_NAME ${FUZZ_SRC} NAME_WE)
-		add_executable(${FUZZ_NAME} ${FUZZ_SRC} ${SHARED_SRCS})
+    add_executable(${FUZZ_NAME} ${FUZZ_SRC} ${SHARED_SRCS} ${FILE_STORE_SRCS} ${SERVER_RECEIVER_SRCS})
 		target_include_directories(${FUZZ_NAME} PRIVATE ${TEST_INCLUDES})
 		target_compile_options(${FUZZ_NAME} PRIVATE -fsanitize=fuzzer,address,undefined -fno-omit-frame-pointer)
 		target_link_options(${FUZZ_NAME} PRIVATE -fsanitize=fuzzer,address,undefined)

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
@@ -66,8 +66,12 @@ replacement for every rsync feature or protocol mode.
 - Owner/group, ACL, xattr, hard-link, device, and special-file handling is
   incomplete or unavailable.
 - Sparse-file handling does not yet preserve all holes correctly.
-- `--partial`, `--partial-dir`, `--append`, and `--append-verify` are not yet
-  full rsync-style resumable transfers.
+- `--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.
 
@@ -79,10 +83,172 @@ partial, alternate, and planned behavior.
 
 ### Build
 
-Requirements: C11 compiler, CMake 3.22 or newer, xxHash, zstd, OpenSSL,
-pthreads, and an SSH client for SSH transport. The first CMake configure fetches
-xxHash from GitHub, so network access is required unless the dependency is
-already cached.
+### 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 |
+| `--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 |
+| `--max-depth <n>` | Maximum directory depth to recurse (0 = unlimited, default: 0) |
+| `--log-file <path>` | Write log messages to file instead of stderr |
+| `--source-dir <path>` | Source directory (overrides `FASTSYNC_SOURCE_DIR`) |
+| `--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`) |
+| `--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 |
+
+### Server
+
+| Argument | Description |
+|----------|-------------|
+| `--stdio` | Run in stdio mode (for SSH transport; single connection then exits) |
+| `-p <port>` | TCP listen port (default: 8080, range: 1–65535) |
+| `--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) |
+| `--destination-root <path>` | Authorized destination root (default: `.`) |
+| `--allow-delete` | Permit manifest deletion |
+| `--allow-unauthenticated` | Permit plaintext TCP clients |
+| `-v, --verbose` | Enable debug logging |
+| `--help` | Show help |
+
+## Environment Variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `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
+
+### 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
+
+## Security Features
+
+### Path Traversal Protection
+All received file paths are validated by `has_path_traversal()` before any disk operation. Any path containing `..` components is rejected with `STATUS_ERROR`, preventing directory escape attacks.
+
+### TLS Certificate Verification
+TLS requires `--ca` and performs mutual TLS verification (`SSL_VERIFY_PEER` with depth 4). Connections without certificate verification are rejected.
+
+### Connection Limits
+The server enforces a maximum of 100 concurrent connections (configurable via `max_connections` in `Server`). When the limit is reached, new connections are immediately rejected and closed.
+
+### Abort Handling
+If the client receives `SIGINT` (Ctrl+C) during a transfer, it sends `STATUS_ABORT` to the server. The server then cleans up temporary files and exits the child process, preventing incomplete files from remaining on disk.
+
+### Atomic Writes
+Received files are written to a temporary path (suffixed with `.tmp`) and then atomically renamed to the final filename via `rename()`. This prevents partial or corrupted files from appearing at the destination if the transfer is interrupted.
+
+## Build Requirements
+
+- C11 compiler
+- CMake >= 3.22
+- zstd library
+- OpenSSL (development headers and libraries)
+- pthreads
+- SSH client (for SSH transport mode only)
+
+### Installing Dependencies
+
+**Ubuntu/Debian:**
+```bash
+sudo apt install cmake build-essential libzstd-dev libssl-dev openssh-client
+```
+
+**Nix:**
+```bash
+nix-shell  # provides zstd, openssl, cmake, gcc
+```
+
+## Building
 
 ```bash
 cmake -B build -S .
@@ -105,6 +271,7 @@ working directory, so use a destination below that directory unless the
 remote server is otherwise configured with a matching authorized root.
 
 ```bash
+ssh user@host 'mkdir -p destination'
 ./build/client /path/to/source user@host:destination
 ```
 
@@ -124,8 +291,10 @@ Then run the client:
   --save-to-disk
 ```
 
-### TLS transfer
+Plain TCP requires the explicit `--allow-unauthenticated` server option. Use TLS for
+authenticated network connections.
 
+### TLS transfer
 ```bash
 ./build/server --destination-root /path/to --tls --cert server.pem --key server-key.pem -p 8443
 ./build/client --tls --cert client.pem --key client-key.pem --ca ca.pem \
@@ -140,32 +309,32 @@ These examples show the intended rsync-style workflow. Options marked as
 FastSync-native are optional performance or transport extensions.
 
 ```bash
-# Basic synchronization
+#Basic synchronization
 ./build/client /source/ /destination/
 
-# Archive-style synchronization (current FastSync archive behavior)
+#Archive - style synchronization(current FastSync archive behavior)
 ./build/client -a /source/ user@host:destination/
 
-# Preview a transfer without changing the destination
+#Preview a transfer without changing the destination
 ./build/client -n /source/ /destination/
 
-# Exclude temporary and object files
+#Exclude temporary and object files
 ./build/client --exclude '*.tmp' --exclude '*.o' \
   /source/ user@host:destination/
 
-# Remove destination entries not present in the source
+#Remove destination entries not present in the source
 ./build/client --delete /source/ user@host:destination/
 
-# Skip unchanged files using size and modification time
+#Skip unchanged files using size and modification time
 ./build/client --incremental /source/ user@host:destination/
 
-# Verify content when size and time are not sufficient
+#Verify content when size and time are not sufficient
 ./build/client --incremental --checksum /source/ user@host:destination/
 
-# Preserve supported mode and timestamp metadata
+#Preserve supported mode and timestamp metadata
 ./build/client -M /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/
 ```
@@ -180,6 +349,10 @@ features without changing the meaning of ordinary compatibility options.
 | `-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`. |
+| `--zl <n>` | Alias for `--compress-level`. |
+| `--skip-compress <list>` | Skip compression for comma-separated suffixes; incompatible with `-s`. |
+| `--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. |
@@ -200,6 +373,11 @@ 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.
 
+`--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.
+
 ## Client Options
 
 ### Selection and transfer
@@ -215,14 +393,16 @@ before FastSync can claim full rsync CLI compatibility.
 | `--include-from <file>` | Read include patterns from a file. |
 | `--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-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`. |
 | `--inplace` | Write directly to the destination instead of using a temporary file. |
 
 ### Metadata and links
@@ -230,7 +410,8 @@ before FastSync can claim full rsync CLI compatibility.
 | Option | Description |
 |---|---|
 | `-M`, `--preserve` | Preserve supported file metadata, currently mode and modification time. |
-| `-l`, `--links` | Request symlink preservation; link-target transfer remains incomplete. |
+| `-l`, `--links` | Request symlink preservation;
+link-target transfer remains incomplete. |
 | `--copy-links` | Copy symlink referents. |
 | `--safe-links` | Skip symlinks that point outside the transfer tree. |
 | `--copy-unsafe-links` | Copy unsafe symlink referents. |
@@ -273,7 +454,8 @@ before FastSync can claim full rsync CLI compatibility.
 | `--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. |
+| `--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. |
 | `-v`, `--verbose` | Enable debug logging. |
 | `--help` | Print server usage. |
@@ -302,11 +484,11 @@ before FastSync can claim full rsync CLI compatibility.
 
 ## Protocol and Security
 
-FastSync protocol version `2.2.0` is shared by the client and server. The
+FastSync protocol version `2.4.0` is shared by the client and server. The
 current protocol is sender-driven and includes configuration negotiation,
-incremental checks, checksums, manifests, keep-alives, abort handling, and
-FastSync-native delta messages. Client and server versions must currently
-match exactly.
+including the maximum allocation limit, incremental checks, checksums,
+manifests, keep-alives, abort handling, 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

RSYNC_COMPAT.md

@@ -6,11 +6,12 @@ This document maps rsync's full feature set to FastSync's current implementation
 
 | Status | Count | Description |
 |--------|-------|-------------|
-| ✅ Implemented | 34 | Feature works end-to-end |
-| 🔀 Alt Arg | 3 | Functionality exists but under different flag/semantics |
-| ⚠️ Partial | 1 | Flag parsed/stored but behavior incomplete |
-| ❌ Not Implemented | 98 | Flag not recognized or no behavior |
-| **Total** | **136** | |
+| ✅ Implemented | 35 | Feature works end-to-end |
+| 🔀 Alt Arg | 4 | Functionality exists but under different flag/semantics |
+| ⚠️ Partial | 5 | Flag parsed/stored but behavior incomplete |
+| 🔄 Compatibility No-op | 1 | Flag is accepted for CLI compatibility but has no effect |
+| ❌ Not Implemented | 95 | Flag not recognized or no behavior |
+| **Total** | **141** | |
 
 ---
 
@@ -20,12 +21,12 @@ This document maps rsync's full feature set to FastSync's current implementation
 |------|-------------------|-----------------|-------|
 | `-a`, `--archive` | Archive mode is -rlptgoD | 🔀 Alt Arg | Maps to -c -m -M (compression + multithread + metadata) |
 | `-v`, `--verbose` | Increase verbosity | ✅ Implemented | Sets `log_level=DEBUG` |
-| `-q`, `--quiet` | Suppress non-error messages | ❌ Not Implemented | Removed because it had no effect |
+| `-q`, `--quiet` | Suppress non-error messages | ✅ Implemented | Suppresses client output while preserving errors |
 | `--help` | Show help | ✅ Implemented | Prints usage and exits; `-h` is not accepted |
 | `-V`, `--version` | Print version | ✅ Implemented | |
-| `--info=FLAGS` | Fine-grained info verbosity | ❌ Not Implemented | Removed because it had no effect |
-| `--debug=FLAGS` | Fine-grained debug verbosity | ❌ Not Implemented | Removed because it had no effect |
-| `--stderr=MODE` | Change stderr output mode | ❌ Not Implemented | |
+| `--info=FLAGS` | Fine-grained info verbosity | ✅ Implemented | Supports `copy`, `misc`, `skip`, `stats`, `all`, and `none`; explicit flags override `--verbose`, and `none` suppresses info output; unsupported names are rejected |
+| `--debug=FLAGS` | Fine-grained debug verbosity | ✅ Implemented | `io`, `proto`, `pack`, and `util` are supported; `--debug=help` lists flags; other rsync categories are rejected |
+| `--stderr=MODE` | Change stderr output mode | ⚠️ Partial | `errors` (default) and `all` are supported; `client` is rejected because FastSync has no rsync message channel |
 | `--no-motd` | Suppress daemon MOTD | ❌ Not Implemented | |
 | `--exclude=PATTERN` | Exclude files matching pattern | ✅ Implemented | Glob matching in scanner |
 | `--include=PATTERN` | Include files matching pattern | ✅ Implemented | Glob matching in scanner |
@@ -36,14 +37,14 @@ This document maps rsync's full feature set to FastSync's current implementation
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
 | `--stats` | Give transfer stats | ✅ Implemented | Prints file/byte counts |
-| `-h`, `--human-readable` | Human-readable numbers | ❌ Not Implemented | Removed because it had no effect |
+| `-h`, `--human-readable` | Human-readable numbers | ✅ Implemented | Formats transfer byte sizes using binary units |
 | `-i`, `--itemize-changes` | Per-file change summary | ❌ Not Implemented | Removed because it had no effect |
 | `--progress` | Show progress | ✅ Implemented | Progress callback in sender |
-| `-P` | Same as --partial --progress | ❌ Not Implemented | |
+| `-P` | Same as --partial --progress | ⚠️ Partial | Parses and enables progress, but interrupted files are not retained for resumable transfers |
 | `--out-format=FORMAT` | Custom output format | ❌ Not Implemented | Removed because it had no effect |
 | `--log-file=FILE` | Log to file | ✅ Implemented | `log_file` config field |
 | `--log-file-format=FMT` | Log format | ❌ Not Implemented | |
-| `--8-bit-output` | Leave high-bit chars unescaped | ❌ Not Implemented | |
+| `--8-bit-output`, `-8` | Leave high-bit chars unescaped | ✅ Implemented | Applies to displayed paths and protocol debug output |
 | `--list-only` | List files instead of copying | ❌ Not Implemented | Removed because it had no effect |
 
 ## 3. File Selection
@@ -58,11 +59,11 @@ This document maps rsync's full feature set to FastSync's current implementation
 | `--max-size=SIZE` | Skip files larger than SIZE | ✅ Implemented | `max_size` in scanner |
 | `--min-size=SIZE` | Skip files smaller than SIZE | ✅ Implemented | `min_size` in scanner |
 | `-I`, `--ignore-times` | Don't skip files matching size+time | ❌ Not Implemented | |
-| `--size-only` | Skip based on size only | ❌ Not Implemented | |
-| `-@`, `--modify-window=NUM` | Mod-time comparison accuracy | ❌ Not Implemented | |
-| `--existing` | Skip creating new files on receiver | ❌ Not Implemented | |
+| `--size-only` | Skip based on size only | ✅ Implemented | With `--incremental`, ignores mtime |
+| `-@`, `--modify-window=NUM` | Mod-time comparison accuracy | ✅ Implemented | Whole-second tolerance with nanosecond-aware comparisons |
+| `--existing` | Skip creating new files on receiver | ✅ Implemented | Existing destination files continue through normal update handling |
 | `--ignore-existing` | Skip updating existing files | ❌ Not Implemented | |
-| `--remove-source-files` | Sender removes synced files | ❌ Not Implemented | |
+| `--remove-source-files` | Sender removes regular files after confirmed transfer | ✅ Implemented | |
 
 ## 4. Directory Options
 
@@ -71,7 +72,7 @@ This document maps rsync's full feature set to FastSync's current implementation
 | `-r`, `--recursive` | Recurse into directories | ✅ Implemented | Default behavior |
 | `-R`, `--relative` | Use relative path names | ❌ Not Implemented | Removed because it had no effect |
 | `--no-implied-dirs` | Don't send implied dirs with -R | ❌ Not Implemented | |
-| `-d`, `--dirs` | Transfer dirs without recursing | ❌ Not Implemented | |
+| `-d`, `--dirs`, `--old-dirs`, `--old-d` | Transfer dirs without recursing | ❌ Not Implemented | The aliases are recognized and rejected explicitly; they depend on the unimplemented `--dirs` behavior |
 | `--mkpath` | Create missing path components | ❌ Not Implemented | |
 
 ## 5. Transfer Modifications
@@ -101,7 +102,7 @@ This document maps rsync's full feature set to FastSync's current implementation
 |------|-------------------|-----------------|-------|
 | `--delete` | Delete extraneous files from dest | ✅ Implemented | `use_delete` config field |
 | `--delete-before` | Delete before transfer | ❌ Not Implemented | Removed because it had no effect |
-| `--delete-during` | Delete during transfer | ❌ Not Implemented | |
+| `--del`, `--delete-during` | Delete during transfer | ❌ Not Implemented | Both flags are recognized but rejected; delete timing is not implemented |
 | `--delete-delay` | Find deletions during, delete after | ❌ Not Implemented | |
 | `--delete-after` | Delete after transfer | ❌ Not Implemented | Removed because it had no effect |
 | `--delete-excluded` | Also delete excluded files | ❌ Not Implemented | Removed because it had no effect |
@@ -119,8 +120,8 @@ This document maps rsync's full feature set to FastSync's current implementation
 | `-o`, `--owner` | Preserve owner | ✅ Implemented | Part of -M |
 | `-g`, `--group` | Preserve group | ✅ Implemented | Part of -M |
 | `-t`, `--times` | Preserve modification times | ✅ Implemented | Part of -M |
-| `-E`, `--executability` | Preserve executability | ❌ Not Implemented | |
-| `--chmod=CHMOD` | Affect file permissions | ❌ Not Implemented | |
+| `-E`, `--executability` | Preserve executability | ✅ Implemented | Preserves executable permission bits (implies metadata preservation) |
+| `--chmod=CHMOD` | Affect file permissions | ✅ Implemented | Supports numeric and symbolic `ugo` `rwx` changes; retains receiver safety masking |
 | `-A`, `--acls` | Preserve ACLs | ❌ Not Implemented | Removed because it had no effect |
 | `-X`, `--xattrs` | Preserve extended attributes | ❌ Not Implemented | Removed because it had no effect |
 | `-H`, `--hard-links` | Preserve hard links | ❌ Not Implemented | Removed because it had no effect |
@@ -171,10 +172,10 @@ This document maps rsync's full feature set to FastSync's current implementation
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
 | `-z`, `--compress` | Compress file data | 🔀 Alt Arg | Always uses zstd (rsync supports multiple algorithms) |
-| `--compress-choice=STR` | Choose compression algorithm | ❌ Not Implemented | Removed because it had no effect; FastSync always uses zstd |
-| `--compress-level=NUM` | Set compression level | ✅ Implemented | 1-22, default 5 |
+| `--compress-choice=STR`, `--zc=STR` | Choose compression algorithm | ✅ Implemented | FastSync supports `zstd` and `none` |
+| `--compress-level=NUM`, `--zl=NUM` | Set compression level | ✅ Implemented | 1-22, default 5 |
 | `--compress-threads=NUM` | Set compression threads | ❌ Not Implemented | |
-| `--skip-compress=LIST` | Skip compress for suffixes | ❌ Not Implemented | Internal skip for hardcoded types; not user-configurable |
+| `--skip-compress=LIST` | Skip compress for suffixes | ✅ Implemented | Comma-separated, case-insensitive suffix list; empty list skips none; incompatible with FastSync chunk serialization (`-s`) |
 
 ## 13. Connectivity
 
@@ -211,7 +212,7 @@ This document maps rsync's full feature set to FastSync's current implementation
 | Max data/string/chunk sizes | Prevent OOM attacks | ✅ Implemented | Per-message limits |
 | Per-connection memory limit | 1GB per connection | ✅ Implemented | `MAX_CONNECTION_MEMORY` |
 | `--trust-sender` | Trust remote sender's file list | ❌ Not Implemented | |
-| `--old-args` | Disable modern arg protection | ❌ Not Implemented | |
+| `--old-args` | Disable modern arg protection | ✅ Implemented | SSH-only legacy mode; restores raw remote command construction and permits shell interpretation of the configured server path |
 | `--ignore-missing-args` | Ignore missing source args | ❌ Not Implemented | |
 | `--delete-missing-args` | Delete missing source args | ❌ Not Implemented | |
 
@@ -229,12 +230,12 @@ This document maps rsync's full feature set to FastSync's current implementation
 |------|-------------------|-----------------|-------|
 | `--stop-after=MINS` | Stop after N minutes | ❌ Not Implemented | |
 | `--stop-at=TIME` | Stop at specified time | ❌ Not Implemented | |
-| `--fsync` | Fsync every written file | ❌ Not Implemented | |
+| `--fsync` | Fsync every written file before publication | ✅ Implemented | |
 | `--protocol=NUM` | Force older protocol version | ❌ Not Implemented | |
 | `--iconv=CONVERT_SPEC` | Charset conversion | ❌ Not Implemented | |
 | `--checksum-seed=NUM` | Set checksum seed | ❌ Not Implemented | |
-| `-s`, `--secluded-args` | Use protocol to send args | ❌ Not Implemented | |
-| `--no-OPTION` | Turn off implied option | ❌ Not Implemented | |
+| `--secluded-args` | Use protocol to send args | 🔄 Compatibility No-op | Accepted for CLI compatibility; it does not change FastSync transport or protocol behavior. `-s` remains chunk serialization. |
+| `--no-OPTION` | Turn off implied option | ✅ Supported | Supported boolean FastSync options and archive-implied options; unsafe or value-taking options are rejected. |
 
 ---
 
@@ -247,13 +248,14 @@ Ranked by user demand, implementation complexity, and interoperability impact:
 | 1 | `--whole-file` / `-W` | Low | High — users expect opt-out of delta |
 | 2 | `--ignore-times` / `-I` | Low | Medium — useful for forcing re-transfer |
 | 3 | `--size-only` | Low | Medium — common migration scenario |
-| 4 | `--existing` / `--ignore-existing` | Low | Medium — common sync patterns |
-| 5 | `--remove-source-files` | Low | High — common for moves/backup |
-| 6 | `--delete-during` | Medium | High — performance improvement |
-| 7 | `--delay-updates` | Medium | High — atomic updates |
-| 8 | `--chmod` | Low | Medium — permission flexibility |
-| 9 | `--executability` / `-E` | Low | Low — simple flag |
-| 10 | `--skip-compress` | Low | Medium — performance tuning |
+| 4 | `--ignore-existing` | Low | Medium — common sync patterns |
+| 5 | `--existing` | Low | Medium — common sync patterns |
+| 6 | `--remove-source-files` | Low | High — common for moves/backup |
+| 7 | `--delete-during` | Medium | High — performance improvement |
+| 8 | `--delay-updates` | Medium | High — atomic updates |
+| 9 | `--chmod` | Low | Medium — permission flexibility |
+| 10 | `--executability` / `-E` | Low | Low — simple flag |
+| 11 | `--skip-compress` | Low | Medium — performance tuning |
 
 ---
 

src/client/client_send.h

@@ -7,6 +7,7 @@
 
 int send_chunk(Client* client, Chunk* chunk, Config* config);
 int send_files(Config* config);
-int send_files_multithreaded(Config* config);
+/* Takes ownership only when *config is set to NULL on return. */
+int send_files_multithreaded(Config** config);
 
 #endif

src/client/client_validation.c

@@ -0,0 +1,60 @@
+#include "client_validation.h"
+#include "log.h"
+#include "usage.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");
+    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)");
+    return false;
+  }
+  if (config->compression_threads > 0 && !config->use_compression) {
+    log_message(LOG_LEVEL_ERROR, "--compress-threads requires compression (-c or -z)");
+    return false;
+  }
+  if (config->transport == TRANSPORT_SSH && config->use_sendfile) {
+    log_message(LOG_LEVEL_ERROR, "-f/--sendfile is not supported with SSH transport");
+    return false;
+  }
+  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) {
+    log_message(LOG_LEVEL_ERROR,
+                "--skip-compress cannot be combined with -s (chunk serialization)");
+    return false;
+  }
+  if (config->use_delta && !config->whole_file && !config->use_incremental) {
+    log_message(LOG_LEVEL_ERROR, "--delta requires --incremental");
+    return false;
+  }
+  if (config->use_delta && !config->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;
+  }
+  if (config->append || config->append_verify) {
+    fprintf(
+        stderr,
+        "Error: --append and --append-verify are not supported yet; refusing to ignore option\n");
+    return false;
+  }
+  if (config->use_tls) {
+    if (!config->tls_cert || !config->tls_key || !config->tls_ca) {
+      log_message(LOG_LEVEL_ERROR, "--tls requires --cert, --key, and --ca");
+      return false;
+    }
+  }
+  return true;
+}

src/client/client_validation.h

@@ -0,0 +1,9 @@
+#ifndef CLIENT_VALIDATION_H
+#define CLIENT_VALIDATION_H
+
+#include "config.h"
+#include <stdbool.h>
+
+bool validate_config(const Config* config);
+
+#endif

src/client/scanner.c

@@ -1,3 +1,4 @@
+#include "log.h"
 #include "scanner.h"
 #include "array_list.h"
 #include "chunk.h"
@@ -52,13 +53,84 @@ static bool safe_relative_link(const char* source_root, const char* containing_d
   return safe;
 }
 
-DirectoryScanner* directory_scanner_create(const char* root_directory, 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,
-                                           bool follow_symlinks, bool copy_links, bool safe_links,
-                                           bool copy_unsafe_links, bool checksum) {
+typedef struct {
+  char* path;
+  struct stat stats;
+  bool is_directory;
+} ScannerEntry;
+
+/* Inspect symlinks, resolve the entry type, and apply file filters once for both scanners. */
+static int scanner_inspect_entry(const ScannerOptions* options, const char* source_root,
+                                 const char* containing_dir, const char* name,
+                                 ScannerEntry* entry) {
+  entry->path = path_cat(containing_dir, name);
+  if (!entry->path)
+    return -1;
+
+  struct stat link_stats;
+  if (lstat(entry->path, &link_stats) != 0) {
+    free(entry->path);
+    return 0;
+  }
+  bool is_symlink = S_ISLNK(link_stats.st_mode);
+  if (is_symlink && !options->follow_symlinks && !options->copy_links && !options->safe_links &&
+      !options->copy_unsafe_links)
+    goto skip;
+
+  if (is_symlink && options->safe_links) {
+    char link_target[4096];
+    ssize_t length = readlink(entry->path, link_target, sizeof(link_target) - 1);
+    if (length < 0)
+      goto skip;
+    link_target[length] = '\0';
+    if (link_target[0] == '/' || !safe_relative_link(source_root, containing_dir, link_target))
+      goto skip;
+  }
+
+  if (is_symlink && options->copy_unsafe_links && !options->copy_links) {
+    char link_target[4096];
+    ssize_t length = readlink(entry->path, link_target, sizeof(link_target) - 1);
+    if (length < 0)
+      goto skip;
+    link_target[length] = '\0';
+    if (link_target[0] != '/')
+      goto skip;
+  }
+
+  if (is_symlink && options->follow_symlinks && !options->copy_links)
+    entry->stats = link_stats;
+  else if (stat(entry->path, &entry->stats) != 0)
+    goto skip;
+
+  entry->is_directory = S_ISDIR(entry->stats.st_mode);
+  if (entry->is_directory)
+    return 1;
+  for (int i = 0; i < options->exclude_count; i++)
+    if (glob_match(options->exclude_patterns[i], name))
+      goto skip;
+  if (options->include_count > 0) {
+    bool included = false;
+    for (int i = 0; i < options->include_count; i++)
+      if (glob_match(options->include_patterns[i], name))
+        included = true;
+    if (!included)
+      goto skip;
+  }
+  if ((options->max_size > 0 && (unsigned long long)entry->stats.st_size > options->max_size) ||
+      (options->min_size > 0 && (unsigned long long)entry->stats.st_size < options->min_size))
+    goto skip;
+  return 1;
+
+skip:
+  free(entry->path);
+  entry->path = NULL;
+  return 0;
+}
+
+DirectoryScanner* directory_scanner_create_with_options(const char* root_directory,
+                                                        const ScannerOptions* options) {
+  if (!root_directory || !options)
+    return NULL;
   DirectoryScanner* scanner = calloc(1, sizeof(DirectoryScanner));
   if (scanner == NULL)
     return NULL;
@@ -69,21 +141,21 @@ DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_
   }
   scanner->current_dir = NULL;
   scanner->current_path = NULL;
-  scanner->use_metadata = use_metadata;
-  scanner->chunk_size = chunk_size > 0 ? chunk_size : DESIRED_CHUNK_SIZE;
-  scanner->exclude_patterns = exclude_patterns;
-  scanner->exclude_count = exclude_count;
-  scanner->include_patterns = include_patterns;
-  scanner->include_count = include_count;
-  scanner->max_size = max_size;
-  scanner->min_size = min_size;
-  scanner->max_depth = max_depth;
+  scanner->use_metadata = options->use_metadata;
+  scanner->chunk_size = options->chunk_size > 0 ? options->chunk_size : DESIRED_CHUNK_SIZE;
+  scanner->exclude_patterns = options->exclude_patterns;
+  scanner->exclude_count = options->exclude_count;
+  scanner->include_patterns = options->include_patterns;
+  scanner->include_count = options->include_count;
+  scanner->max_size = options->max_size;
+  scanner->min_size = options->min_size;
+  scanner->max_depth = options->max_depth;
   scanner->current_depth = 0;
-  scanner->follow_symlinks = follow_symlinks;
-  scanner->copy_links = copy_links;
-  scanner->safe_links = safe_links;
-  scanner->copy_unsafe_links = copy_unsafe_links;
-  scanner->checksum = checksum;
+  scanner->follow_symlinks = options->follow_symlinks;
+  scanner->copy_links = options->copy_links;
+  scanner->safe_links = options->safe_links;
+  scanner->copy_unsafe_links = options->copy_unsafe_links;
+  scanner->checksum = options->checksum;
   scanner->failed = false;
   DirEntry* root = dir_entry_create(root_directory, 0);
   if (!root) {
@@ -100,6 +172,20 @@ DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_
   return scanner;
 }
 
+DirectoryScanner* directory_scanner_create(const char* root_directory, 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,
+                                           bool follow_symlinks, bool copy_links, bool safe_links,
+                                           bool copy_unsafe_links, bool checksum) {
+  ScannerOptions options = {
+      use_metadata,    chunk_size, exclude_patterns, exclude_count,     include_patterns,
+      include_count,   max_size,   min_size,         max_depth,         0,
+      follow_symlinks, copy_links, safe_links,       copy_unsafe_links, checksum};
+  return directory_scanner_create_with_options(root_directory, &options);
+}
+
 void directory_scanner_destroy(DirectoryScanner* scanner) {
   if (scanner == NULL)
     return;
@@ -141,7 +227,7 @@ static int open_next_directory(DirectoryScanner* scanner) {
   free(de);
   scanner->current_dir = opendir(scanner->current_path);
   if (scanner->current_dir == NULL) {
-    perror("Could not open directory");
+    log_perror("Could not open directory");
     free(scanner->current_path);
     scanner->current_path = NULL;
     scanner->failed = true;
@@ -167,7 +253,7 @@ Chunk* directory_scanner_next(DirectoryScanner* scanner) {
         break;
     }
 
-    struct dirent* entry = readdir(scanner->current_dir);
+    const struct dirent* entry = readdir(scanner->current_dir);
     if (entry == NULL) {
       closedir(scanner->current_dir);
       scanner->current_dir = NULL;
@@ -179,67 +265,27 @@ Chunk* directory_scanner_next(DirectoryScanner* scanner) {
     if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
       continue;
 
-    char* cur_path = path_cat(scanner->current_path, entry->d_name);
-    if (!cur_path) {
+    ScannerOptions options = {scanner->use_metadata,     scanner->chunk_size,
+                              scanner->exclude_patterns, scanner->exclude_count,
+                              scanner->include_patterns, scanner->include_count,
+                              scanner->max_size,         scanner->min_size,
+                              scanner->max_depth,        0,
+                              scanner->follow_symlinks,  scanner->copy_links,
+                              scanner->safe_links,       scanner->copy_unsafe_links,
+                              scanner->checksum};
+    ScannerEntry inspected;
+    int inspection = scanner_inspect_entry(&options, scanner->current_path, scanner->current_path,
+                                           entry->d_name, &inspected);
+    if (inspection < 0) {
       scanner->failed = true;
       break;
     }
-    struct stat stats;
-    struct stat lstats;
-    bool is_symlink = false;
-    if (lstat(cur_path, &lstats) != 0) {
-      free(cur_path);
+    if (inspection == 0)
       continue;
-    }
-    is_symlink = S_ISLNK(lstats.st_mode);
+    char* cur_path = inspected.path;
+    struct stat stats = inspected.stats;
 
-    if (is_symlink && !scanner->follow_symlinks && !scanner->copy_links && !scanner->safe_links &&
-        !scanner->copy_unsafe_links) {
-      free(cur_path);
-      continue;
-    }
-
-    if (is_symlink && scanner->safe_links) {
-      char link_target[4096];
-      ssize_t len = readlink(cur_path, link_target, sizeof(link_target) - 1);
-      if (len < 0) {
-        free(cur_path);
-        continue;
-      }
-      link_target[len] = '\0';
-      if (link_target[0] == '/' ||
-          !safe_relative_link(scanner->current_path, scanner->current_path, link_target)) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    if (is_symlink && scanner->copy_unsafe_links && !scanner->copy_links) {
-      char link_target[4096];
-      ssize_t len = readlink(cur_path, link_target, sizeof(link_target) - 1);
-      if (len < 0) {
-        free(cur_path);
-        continue;
-      }
-      link_target[len] = '\0';
-      bool unsafe = (link_target[0] == '/');
-      if (!unsafe) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    bool use_lstat = is_symlink && scanner->follow_symlinks && !scanner->copy_links;
-    if (use_lstat) {
-      stats = lstats;
-    } else {
-      if (stat(cur_path, &stats) != 0) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    if (S_ISDIR(stats.st_mode)) {
+    if (inspected.is_directory) {
       int next_depth = scanner->current_depth + 1;
       if (scanner->max_depth <= 0 || next_depth < scanner->max_depth) {
         DirEntry* de = dir_entry_create(cur_path, next_depth);
@@ -254,38 +300,6 @@ Chunk* directory_scanner_next(DirectoryScanner* scanner) {
         free(cur_path);
         continue;
       }
-      bool excluded = false;
-      for (int i = 0; i < scanner->exclude_count; i++) {
-        if (glob_match(scanner->exclude_patterns[i], entry->d_name)) {
-          excluded = true;
-          break;
-        }
-      }
-      if (excluded) {
-        free(cur_path);
-        continue;
-      }
-
-      if (scanner->include_count > 0) {
-        bool included = false;
-        for (int i = 0; i < scanner->include_count; i++) {
-          if (glob_match(scanner->include_patterns[i], entry->d_name)) {
-            included = true;
-            break;
-          }
-        }
-        if (!included) {
-          free(cur_path);
-          continue;
-        }
-      }
-
-      if ((scanner->max_size > 0 && (unsigned long long)stats.st_size > scanner->max_size) ||
-          (scanner->min_size > 0 && (unsigned long long)stats.st_size < scanner->min_size)) {
-        free(cur_path);
-        continue;
-      }
-
       File* file = file_create(cur_path);
       if (file == NULL) {
         free(cur_path);
@@ -336,29 +350,17 @@ typedef struct {
   ParallelScanner* ps;
   char** dirs;
   int dir_count;
-  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;
-  bool follow_symlinks;
-  bool copy_links;
-  bool safe_links;
-  bool copy_unsafe_links;
-  bool checksum;
+  ScannerOptions options;
+  ProtocolSession* allocation_session;
 } ParallelWorkerArg;
 
 static int parallel_worker_thread(void* arg) {
   ParallelWorkerArg* wa = (ParallelWorkerArg*)arg;
+  ProtocolSession* allocation_session = wa->allocation_session;
+  if (allocation_session)
+    protocol_session_bind(allocation_session);
   for (int i = 0; i < wa->dir_count; i++) {
-    DirectoryScanner* ds = directory_scanner_create(
-        wa->dirs[i], wa->use_metadata, wa->chunk_size, wa->exclude_patterns, wa->exclude_count,
-        wa->include_patterns, wa->include_count, wa->max_size, wa->min_size, wa->max_depth,
-        wa->follow_symlinks, wa->copy_links, wa->safe_links, wa->copy_unsafe_links, wa->checksum);
+    DirectoryScanner* ds = directory_scanner_create_with_options(wa->dirs[i], &wa->options);
     if (!ds) {
       mtx_lock(&wa->ps->result_mutex);
       wa->ps->failed = true;
@@ -366,6 +368,8 @@ static int parallel_worker_thread(void* arg) {
       cnd_broadcast(&wa->ps->result_not_empty);
       cnd_broadcast(&wa->ps->result_not_full);
       mtx_unlock(&wa->ps->result_mutex);
+      for (int j = i; j < wa->dir_count; j++)
+        free(wa->dirs[j]);
       break;
     }
     Chunk* chunk;
@@ -398,24 +402,28 @@ static int parallel_worker_thread(void* arg) {
     cnd_signal(&ps->result_not_empty);
   }
   mtx_unlock(&ps->result_mutex);
+  if (allocation_session)
+    protocol_session_unbind();
   return thrd_success;
 }
 
-ParallelScanner* parallel_scanner_create(char* root_directory, 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 num_threads, bool follow_symlinks, bool copy_links,
-                                         bool safe_links, bool copy_unsafe_links, bool checksum) {
-  ParallelScanner* ps = calloc(1, sizeof(ParallelScanner));
-  if (!ps)
-    return NULL;
+static void parallel_scanner_creation_failed(ParallelScanner* ps) {
+  mtx_lock(&ps->result_mutex);
+  ps->failed = true;
+  atomic_store(&ps->cancelled, true);
+  ps->expected_threads = ps->created_threads;
+  if (ps->completed >= ps->expected_threads)
+    ps->done = true;
+  cnd_broadcast(&ps->result_not_empty);
+  cnd_broadcast(&ps->result_not_full);
+  mtx_unlock(&ps->result_mutex);
+}
+
+/* Initialize result queue and synchronization primitives. Returns true on success. */
+static bool parallel_scanner_init(ParallelScanner* ps) {
   ps->result_queue = queue_create(100, chunk_destroy);
-  if (!ps->result_queue) {
-    free(ps);
-    return NULL;
-  }
+  if (!ps->result_queue)
+    return false;
   atomic_init(&ps->cancelled, false);
   int init = 0;
   bool ok = true;
@@ -440,295 +448,247 @@ ParallelScanner* parallel_scanner_create(char* root_directory, bool use_metadata
     if (init >= 1)
       mtx_destroy(&ps->result_mutex);
     queue_destroy(ps->result_queue);
+    ps->result_queue = NULL;
+    return false;
+  }
+  return true;
+}
+
+/* Split files into chunks of roughly chunk_size bytes. Returns the first chunk (also stored
+ * chunks beyond the first are enqueued on `queue`). Nulls out consumed entries in `files`.
+ * Sets *failed on allocation/enqueue errors. */
+static Chunk* batch_files(ArrayList* files, unsigned long long chunk_size, Queue* queue,
+                          bool* failed) {
+  Chunk* first = NULL;
+  if (files->size <= 0)
+    return NULL;
+  ArrayList* batch = array_list_create(NULL);
+  if (!batch) {
+    *failed = true;
+    return NULL;
+  }
+  unsigned long long batch_size = 0;
+  for (int i = 0; i < files->size; i++) {
+    File* f = (File*)files->items[i];
+    if (!array_list_add(batch, f)) {
+      *failed = true;
+      break;
+    }
+    batch_size += f->data->size;
+    if (batch_size >= chunk_size || i == files->size - 1) {
+      void** items = array_list_to_array(batch);
+      if (!items) {
+        *failed = true;
+        array_list_delete(batch);
+        batch = NULL;
+        break;
+      }
+      Chunk* c = chunk_create((File**)items, batch->size);
+      free(items);
+      if (!c) {
+        *failed = true;
+        array_list_delete(batch);
+        batch = NULL;
+        break;
+      }
+      int batch_start = i - batch->size + 1;
+      for (int j = batch_start; j <= i; j++)
+        files->items[j] = NULL;
+      batch->item_destroyer = NULL;
+      array_list_delete(batch);
+      batch = NULL;
+      if (!first) {
+        first = c;
+      } else {
+        if (!queue_enqueue(queue, c)) {
+          chunk_destroy(c);
+          *failed = true;
+        }
+      }
+      if (i < files->size - 1) {
+        batch = array_list_create(NULL);
+        if (!batch) {
+          *failed = true;
+          break;
+        }
+        batch_size = 0;
+      }
+    }
+  }
+  if (batch) {
+    batch->item_destroyer = NULL;
+    array_list_delete(batch);
+  }
+  return first;
+}
+
+/* Scan one root-directory entry into either the subdirs or files list. */
+static void scan_root_entry(const ScannerOptions* options, const char* root_directory,
+                            const struct dirent* entry, ArrayList* root_files, ArrayList* subdirs,
+                            ParallelScanner* ps) {
+  ScannerEntry inspected;
+  int inspection =
+      scanner_inspect_entry(options, root_directory, root_directory, entry->d_name, &inspected);
+  if (inspection < 0) {
+    ps->failed = true;
+    return;
+  }
+  if (inspection == 0)
+    return;
+  char* cur_path = inspected.path;
+  struct stat st = inspected.stats;
+  if (inspected.is_directory) {
+    if (!array_list_add(subdirs, cur_path)) {
+      free(cur_path);
+      ps->failed = true;
+    }
+    return;
+  }
+  File* file = file_create(cur_path);
+  free(cur_path);
+  if (!file) {
+    ps->failed = true;
+    return;
+  }
+  file->data->size = st.st_size;
+  if (options->use_metadata)
+    file->metadata = file_metadata_create(&st);
+  if (options->use_metadata && !file->metadata) {
+    file_destroy(file);
+    ps->failed = true;
+    return;
+  }
+  if (!array_list_add(root_files, file)) {
+    file_destroy(file);
+    ps->failed = true;
+  }
+}
+
+/* Scan the root directory itself, collecting root files and subdirectories.
+ * Returns false if the root directory could not be opened. */
+static bool scan_root_directory(ParallelScanner* ps, const char* root_directory,
+                                const ScannerOptions* options, ArrayList* root_files,
+                                ArrayList* subdirs) {
+  DIR* dir = opendir(root_directory);
+  if (!dir) {
+    log_perror("Could not open root directory for parallel scan");
+    return false;
+  }
+  const struct dirent* entry;
+  while ((entry = readdir(dir)) != NULL) {
+    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
+      continue;
+    scan_root_entry(options, root_directory, entry, root_files, subdirs, ps);
+  }
+  closedir(dir);
+  return true;
+}
+
+/* Spawn worker threads, one per group of subdirectories. */
+static void spawn_parallel_workers(ParallelScanner* ps, ArrayList* subdirs,
+                                   const ScannerOptions* options, unsigned long long cs) {
+  if (subdirs->size <= 0)
+    return;
+  int n = options->num_threads > 0 ? options->num_threads : 4;
+  if (n > subdirs->size)
+    n = subdirs->size;
+
+  ps->num_threads = n;
+  ps->expected_threads = n;
+  ps->threads = calloc(n, sizeof(thrd_t));
+  if (!ps->threads) {
+    ps->num_threads = 0;
+    ps->expected_threads = 0;
+    ps->failed = true;
+    return;
+  }
+  int dirs_per_thread = subdirs->size / n;
+  int remainder = subdirs->size % n;
+  int start = 0;
+  ps->num_threads = 0;
+  for (int t = 0; t < n; t++) {
+    int count = dirs_per_thread + (t < remainder ? 1 : 0);
+    if (count == 0)
+      break;
+    ParallelWorkerArg* wa = calloc(1, sizeof(ParallelWorkerArg));
+    if (!wa) {
+      parallel_scanner_creation_failed(ps);
+      break;
+    }
+    wa->ps = ps;
+    wa->dirs = calloc(count, sizeof(char*));
+    if (!wa->dirs) {
+      free(wa);
+      parallel_scanner_creation_failed(ps);
+      break;
+    }
+    bool dup_ok = true;
+    for (int j = 0; j < count; j++) {
+      wa->dirs[j] = str_dup((char*)subdirs->items[start + j]);
+      if (!wa->dirs[j])
+        dup_ok = false;
+    }
+    if (!dup_ok) {
+      for (int j = 0; j < count; j++)
+        free(wa->dirs[j]);
+      free(wa->dirs);
+      free(wa);
+      parallel_scanner_creation_failed(ps);
+      break;
+    }
+    wa->dir_count = count;
+    wa->options = *options;
+    wa->options.chunk_size = cs;
+    wa->allocation_session = ps->allocation_session;
+    start += count;
+    if (thrd_create(&ps->threads[t], parallel_worker_thread, wa) != thrd_success) {
+      for (int j = 0; j < count; j++)
+        free(wa->dirs[j]);
+      free(wa->dirs);
+      free(wa);
+      parallel_scanner_creation_failed(ps);
+      break;
+    }
+    ps->num_threads++;
+    ps->created_threads++;
+  }
+}
+
+ParallelScanner* parallel_scanner_create_with_options(const char* root_directory,
+                                                      const ScannerOptions* options,
+                                                      ProtocolSession* allocation_session) {
+  if (!root_directory || !options)
+    return NULL;
+  ParallelScanner* ps = calloc(1, sizeof(ParallelScanner));
+  if (!ps)
+    return NULL;
+  if (!parallel_scanner_init(ps)) {
     free(ps);
     return NULL;
   }
-
-  DIR* dir = opendir(root_directory);
-  if (!dir) {
-    perror("Could not open root directory for parallel scan");
-    parallel_scanner_destroy(ps);
-    return NULL;
-  }
+  ps->allocation_session = allocation_session;
 
   ArrayList* root_files = array_list_create(file_destroy);
   ArrayList* subdirs = array_list_create(free);
   if (!root_files || !subdirs) {
     array_list_delete(root_files);
     array_list_delete(subdirs);
-    closedir(dir);
     parallel_scanner_destroy(ps);
     return NULL;
   }
-  struct dirent* entry;
-  while ((entry = readdir(dir)) != NULL) {
-    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
-      continue;
-    char* cur_path = path_cat(root_directory, entry->d_name);
-    if (!cur_path)
-      continue;
-    struct stat lstats;
-    if (lstat(cur_path, &lstats) != 0) {
-      free(cur_path);
-      continue;
-    }
-    bool is_symlink = S_ISLNK(lstats.st_mode);
 
-    // Skip symlinks unless the user explicitly enabled following/copying them.
-    if (is_symlink && !follow_symlinks && !copy_links && !safe_links && !copy_unsafe_links) {
-      free(cur_path);
-      continue;
-    }
-
-    // --safe-links: reject symlinks pointing outside the source tree.
-    if (is_symlink && safe_links) {
-      char link_target[4096];
-      ssize_t len = readlink(cur_path, link_target, sizeof(link_target) - 1);
-      if (len < 0) {
-        free(cur_path);
-        continue;
-      }
-      link_target[len] = 0;
-      if (link_target[0] == '/' ||
-          !safe_relative_link(root_directory, root_directory, link_target)) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    // --copy-unsafe-links (without --copy-links): only copy absolute symlinks.
-    if (is_symlink && copy_unsafe_links && !copy_links) {
-      char link_target[4096];
-      ssize_t len = readlink(cur_path, link_target, sizeof(link_target) - 1);
-      if (len < 0) {
-        free(cur_path);
-        continue;
-      }
-      link_target[len] = 0;
-      bool unsafe = (link_target[0] == '/');
-      if (!unsafe) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    // Determine whether to use lstat or stat results for the entry.
-    struct stat st;
-    bool use_lstat_res = is_symlink && follow_symlinks && !copy_links;
-    if (use_lstat_res) {
-      st = lstats;
-    } else {
-      if (stat(cur_path, &st) != 0) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    if (S_ISDIR(st.st_mode)) {
-      if (!array_list_add(subdirs, cur_path)) {
-        free(cur_path);
-        ps->failed = true;
-      }
-    } else {
-      bool excluded = false;
-      for (int i = 0; i < exclude_count; i++) {
-        if (glob_match(exclude_patterns[i], entry->d_name)) {
-          excluded = true;
-          break;
-        }
-      }
-      if (excluded) {
-        free(cur_path);
-        continue;
-      }
-      if (include_count > 0) {
-        bool included = false;
-        for (int i = 0; i < include_count; i++) {
-          if (glob_match(include_patterns[i], entry->d_name)) {
-            included = true;
-            break;
-          }
-        }
-        if (!included) {
-          free(cur_path);
-          continue;
-        }
-      }
-      if ((max_size > 0 && (unsigned long long)st.st_size > max_size) ||
-          (min_size > 0 && (unsigned long long)st.st_size < min_size)) {
-        free(cur_path);
-        continue;
-      }
-      File* file = file_create(cur_path);
-      free(cur_path);
-      if (!file) {
-        ps->failed = true;
-        continue;
-      }
-      file->data->size = st.st_size;
-      if (use_metadata)
-        file->metadata = file_metadata_create(&st);
-      if (use_metadata && !file->metadata) {
-        file_destroy(file);
-        ps->failed = true;
-        continue;
-      }
-      if (!array_list_add(root_files, file)) {
-        file_destroy(file);
-        ps->failed = true;
-      }
-    }
+  if (!scan_root_directory(ps, root_directory, options, root_files, subdirs)) {
+    array_list_delete(root_files);
+    array_list_delete(subdirs);
+    parallel_scanner_destroy(ps);
+    return NULL;
   }
-  closedir(dir);
 
-  unsigned long long cs = chunk_size > 0 ? chunk_size : DESIRED_CHUNK_SIZE;
-  if (root_files->size > 0) {
-    ArrayList* batch = array_list_create(NULL);
-    if (!batch) {
-      ps->failed = true;
-      array_list_delete(root_files);
-      array_list_delete(subdirs);
-      parallel_scanner_destroy(ps);
-      return NULL;
-    }
-    unsigned long long batch_size = 0;
-    Chunk* first = NULL;
-    for (int i = 0; i < root_files->size; i++) {
-      File* f = (File*)root_files->items[i];
-      if (!array_list_add(batch, f)) {
-        ps->failed = true;
-        break;
-      }
-      batch_size += f->data->size;
-      if (batch_size >= cs || i == root_files->size - 1) {
-        void** items = array_list_to_array(batch);
-        if (!items) {
-          ps->failed = true;
-          batch->item_destroyer = file_destroy;
-          array_list_delete(batch);
-          batch = NULL;
-          break;
-        }
-        Chunk* c = chunk_create((File**)items, batch->size);
-        free(items);
-        if (!c) {
-          ps->failed = true;
-          batch->item_destroyer = file_destroy;
-          array_list_delete(batch);
-          batch = NULL;
-          break;
-        }
-        batch->item_destroyer = NULL;
-        array_list_delete(batch);
-        batch = NULL;
-        if (!first) {
-          first = c;
-        } else {
-          if (!queue_enqueue(ps->result_queue, c)) {
-            chunk_destroy(c);
-            ps->failed = true;
-          }
-        }
-        if (i < root_files->size - 1) {
-          batch = array_list_create(NULL);
-          if (!batch) {
-            ps->failed = true;
-            break;
-          }
-          batch_size = 0;
-        }
-      }
-    }
-    if (batch) {
-      batch->item_destroyer = NULL;
-      array_list_delete(batch);
-    }
-    ps->initial_chunk = first;
-    root_files->item_destroyer = NULL;
-  }
+  unsigned long long cs = options->chunk_size > 0 ? options->chunk_size : DESIRED_CHUNK_SIZE;
+  ps->initial_chunk = batch_files(root_files, cs, ps->result_queue, &ps->failed);
   array_list_delete(root_files);
 
-  int n = num_threads > 0 ? num_threads : 4;
-  if (n > subdirs->size)
-    n = subdirs->size > 0 ? subdirs->size : 1;
-
-  if (subdirs->size > 0) {
-    ps->num_threads = n;
-    ps->expected_threads = n;
-    ps->threads = calloc(n, sizeof(thrd_t));
-    if (!ps->threads) {
-      array_list_delete(subdirs);
-      parallel_scanner_destroy(ps);
-      return NULL;
-    }
-    int dirs_per_thread = subdirs->size / n;
-    int remainder = subdirs->size % n;
-    int start = 0;
-    ps->num_threads = 0;
-    for (int t = 0; t < n; t++) {
-      int count = dirs_per_thread + (t < remainder ? 1 : 0);
-      if (count == 0)
-        break;
-      ParallelWorkerArg* wa = calloc(1, sizeof(ParallelWorkerArg));
-      if (!wa) {
-        ps->failed = true;
-        break;
-      }
-      wa->ps = ps;
-      wa->dirs = calloc(count, sizeof(char*));
-      if (!wa->dirs) {
-        free(wa);
-        ps->failed = true;
-        break;
-      }
-      bool dup_ok = true;
-      for (int j = 0; j < count; j++) {
-        wa->dirs[j] = str_dup((char*)subdirs->items[start + j]);
-        if (!wa->dirs[j])
-          dup_ok = false;
-      }
-      if (!dup_ok) {
-        for (int j = 0; j < count; j++)
-          free(wa->dirs[j]);
-        free(wa->dirs);
-        free(wa);
-        ps->failed = true;
-        break;
-      }
-      wa->dir_count = count;
-      wa->use_metadata = use_metadata;
-      wa->chunk_size = cs;
-      wa->exclude_patterns = exclude_patterns;
-      wa->exclude_count = exclude_count;
-      wa->include_patterns = include_patterns;
-      wa->include_count = include_count;
-      wa->max_size = max_size;
-      wa->min_size = min_size;
-      wa->max_depth = max_depth;
-      wa->follow_symlinks = follow_symlinks;
-      wa->copy_links = copy_links;
-      wa->safe_links = safe_links;
-      wa->copy_unsafe_links = copy_unsafe_links;
-      wa->checksum = checksum;
-      start += count;
-      if (thrd_create(&ps->threads[t], parallel_worker_thread, wa) != thrd_success) {
-        for (int j = 0; j < count; j++)
-          free(wa->dirs[j]);
-        free(wa->dirs);
-        free(wa);
-        ps->failed = true;
-        atomic_store(&ps->cancelled, true);
-        ps->expected_threads = ps->created_threads;
-        mtx_lock(&ps->result_mutex);
-        cnd_broadcast(&ps->result_not_empty);
-        cnd_broadcast(&ps->result_not_full);
-        mtx_unlock(&ps->result_mutex);
-        break;
-      }
-      ps->num_threads++;
-      ps->created_threads++;
-    }
-  }
+  spawn_parallel_workers(ps, subdirs, options, cs);
   array_list_delete(subdirs);
   return ps;
 }
@@ -741,6 +701,11 @@ Chunk* parallel_scanner_next(ParallelScanner* ps) {
   }
   if (ps->num_threads == 0) {
     mtx_lock(&ps->result_mutex);
+    if (!queue_is_empty(ps->result_queue)) {
+      Chunk* chunk = queue_dequeue(ps->result_queue);
+      mtx_unlock(&ps->result_mutex);
+      return chunk;
+    }
     ps->done = true;
     mtx_unlock(&ps->result_mutex);
     return NULL;

src/client/scanner.h

@@ -2,12 +2,31 @@
 #define SCANNER_H
 
 #include "chunk.h"
+#include "protocol.h"
 #include "queue.h"
 #include <dirent.h>
 #include <stdbool.h>
 #include <threads.h>
 #include <stdatomic.h>
 
+typedef struct {
+  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 num_threads;
+  bool follow_symlinks;
+  bool copy_links;
+  bool safe_links;
+  bool copy_unsafe_links;
+  bool checksum;
+} ScannerOptions;
+
 typedef struct {
   Queue* directories;
   DIR* current_dir;
@@ -44,6 +63,7 @@ typedef struct {
   atomic_bool cancelled;
   int completed;
   Chunk* initial_chunk;
+  ProtocolSession* allocation_session;
 } ParallelScanner;
 
 DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_metadata,
@@ -53,17 +73,15 @@ DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_
                                            unsigned long long min_size, int max_depth,
                                            bool follow_symlinks, bool copy_links, bool safe_links,
                                            bool copy_unsafe_links, bool checksum);
+DirectoryScanner* directory_scanner_create_with_options(const char* root_directory,
+                                                        const ScannerOptions* options);
 Chunk* directory_scanner_next(DirectoryScanner* scanner);
 bool directory_scanner_failed(const DirectoryScanner* scanner);
 void directory_scanner_destroy(DirectoryScanner* scanner);
 
-ParallelScanner* parallel_scanner_create(char* root_directory, 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 num_threads, bool follow_symlinks, bool copy_links,
-                                         bool safe_links, bool copy_unsafe_links, bool checksum);
+ParallelScanner* parallel_scanner_create_with_options(const char* root_directory,
+                                                      const ScannerOptions* options,
+                                                      ProtocolSession* allocation_session);
 Chunk* parallel_scanner_next(ParallelScanner* scanner);
 bool parallel_scanner_failed(const ParallelScanner* scanner);
 void parallel_scanner_destroy(ParallelScanner* scanner);

src/client/usage.c

@@ -1,8 +1,9 @@
-#include "stdio.h"
+#include "usage.h"
+#include <stdio.h>
 #include <delta.h>
 #include <chunk.h>
 
-static __attribute__((unused)) void print_usage() {
+void print_usage(void) {
   printf("Usage:\n");
   printf("  fastsync [options] <source> <destination>\n");
   printf("  fastsync [options] --source-dir <src> --dest-dir <dst>\n");
@@ -17,26 +18,51 @@ static __attribute__((unused)) void print_usage() {
   printf("  -z [level]          Alias for -c\n");
   printf("  -a, --archive       Archive mode (-c -m -M)\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("  --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("  --delete            Delete files on receiver not in source\n");
+  printf("  --ignore-existing  Skip files that already exist on receiver\n");
+  printf(
+      "  --dirs, --old-dirs, --old-d  Transfer directories without recursing (not implemented)\n");
+  printf("  --del               Alias for --delete-during (not implemented)\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("  --max-size <n>      Skip files larger than n bytes\n");
   printf("  --min-size <n>      Skip files smaller than n bytes\n");
+  printf("  --max-alloc <SIZE>  Maximum single allocation (default: 1G)\n");
   printf("  --incremental       Skip files unchanged since last transfer\n");
+  printf("  --size-only         Skip incremental files matching in size, ignoring mtime\n");
+  printf("  -I, --ignore-times  Transfer files even when size and mtime match\n");
+  printf("  -@, --modify-window <sec>  Modification time tolerance\n");
+  printf("  -u, --update        Skip files newer than the source on receiver\n");
+  printf("  --existing          Skip files not already present at destination\n");
+  printf("  --checksum-choice, --cc <alg>  Checksum algorithm (not supported yet; xxHash64 is "
+         "used)\n");
   printf("  --delta             Delta transfer for changed files (requires --incremental)\n");
+  printf("  -W, --whole-file    Transfer changed files without delta processing\n");
   printf("  --delta-block <n>   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("  --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("  -E, --executability Preserve executable permission bits\n");
+  printf("  --chmod <changes>   Modify transferred permissions (rsync syntax)\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");
@@ -55,19 +81,34 @@ static __attribute__((unused)) void print_usage() {
   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("  -h, --human-readable  Print byte sizes in human-readable form\n");
   printf("  --max-depth <n>     Maximum directory depth (0=unlimited)\n");
   printf("  --log-file <path>   Write log messages to file\n");
+  printf("  --stderr=MODE       Route logging to stderr: errors or all\n");
   printf("  --partial           Keep partial files on interrupted transfer\n");
   printf("  --partial-dir <dir> Directory for partial files\n");
   printf("  --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("  -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("  -S, --sparse        Handle sparse files efficiently\n");
   printf("  --inplace           Update files in-place (no temp+rename)\n");
+  printf("  --fsync             Fsync every written file before publication\n");
   printf("  --compress-level <n>    Compression level (default: 5)\n");
+  printf("  --zl <n>             Alias for --compress-level\n");
+  printf("  --skip-compress=LIST    Skip compression for comma-separated suffixes\n");
+  printf("  --compress-threads <n> Compression worker threads (requires zstd threaded support)\n");
+  printf("  --no-OPTION         Disable a supported boolean option\n");
   printf("  --help              Show this help\n");
   printf("  -V, --version       Show version\n");
 }
+
+void print_debug_usage(void) {
+  printf("Supported debug flags: IO,PROTO,PACK,UTIL,ALL,NONE\n");
+  printf("Flags may be comma-separated, for example: --debug=io,proto\n");
+  printf("Other rsync debug flags are unsupported and rejected.\n");
+}

src/client/usage.h

@@ -0,0 +1,7 @@
+#ifndef USAGE_H
+#define USAGE_H
+
+void print_usage(void);
+void print_debug_usage(void);
+
+#endif

src/server/receiver.c

@@ -0,0 +1,154 @@
+#include "receiver.h"
+
+#include "chunk.h"
+#include "log.h"
+#include "metadata.h"
+#include "protocol.h"
+#include "utils.h"
+#include <stdlib.h>
+#include <sys/stat.h>
+
+static bool receiver_process_chunk(Chunk* chunk, const ReceiverSink* sink) {
+  if (!chunk || !sink || !sink->store_file)
+    return false;
+  for (int i = 0; i < chunk->element_count; i++) {
+    File* file = chunk->items[i];
+    if (!file) {
+      chunk_destroy(chunk);
+      return false;
+    }
+    chunk->items[i] = NULL;
+    if (!sink->store_file(file, sink->context)) {
+      chunk_destroy(chunk);
+      return false;
+    }
+  }
+  chunk_destroy(chunk);
+  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);
+    if (!check_path)
+      return false;
+    unsigned long long check_size;
+    long long check_mtime;
+    long long check_mtime_nsec;
+    if (!receive_n_data(file_descriptor, &check_size, sizeof(check_size)) ||
+        !receive_n_data(file_descriptor, &check_mtime, sizeof(check_mtime)) ||
+        !receive_n_data(file_descriptor, &check_mtime_nsec, sizeof(check_mtime_nsec)) ||
+        check_mtime_nsec < 0 || check_mtime_nsec >= 1000000000LL) {
+      free(check_path);
+      send_status(file_descriptor, STATUS_ERROR);
+      return false;
+    }
+    if (!utils_valid_batch_path(check_path)) {
+      free(check_path);
+      send_status(file_descriptor, STATUS_ERROR);
+      return false;
+    }
+    if (check_size > MAX_RECEIVE_FILE_SIZE) {
+      free(check_path);
+      send_status(file_descriptor, STATUS_ERROR);
+      return false;
+    }
+    char* full_path = path_cat(config->receive_root_directory, check_path);
+    if (!full_path) {
+      free(check_path);
+      send_status(file_descriptor, STATUS_ERROR);
+      return false;
+    }
+    struct stat st;
+    bool has_old = file_stat_secure(full_path, &st);
+    long long old_mtime_nsec = 0;
+    if (has_old) {
+#ifdef __linux__
+      old_mtime_nsec = st.st_mtim.tv_nsec;
+#endif
+    }
+    bool match = !config->ignore_times && has_old && (unsigned long long)st.st_size == check_size &&
+                 metadata_mtime_matches(st.st_mtime, old_mtime_nsec, (time_t)check_mtime,
+                                        (long)check_mtime_nsec, config->modify_window);
+    bool sent = send_status(file_descriptor, match ? STATUS_OK : STATUS_NEXT);
+    free(full_path);
+    free(check_path);
+    if (!sent)
+      return false;
+  }
+  return true;
+}
+
+int receiver_process(Config* config, int file_descriptor, const ReceiverSink* sink) {
+  Status status;
+  if (!receive_status(file_descriptor, &status))
+    return -1;
+  while (status == STATUS_NEXT || status == STATUS_CHUNK || status == STATUS_CHECK ||
+         status == STATUS_KEEPALIVE || status == STATUS_ABORT || status == STATUS_CHECK_BATCH) {
+    if (status == STATUS_KEEPALIVE) {
+      if (!send_status(file_descriptor, STATUS_KEEPALIVE))
+        return -1;
+      goto next;
+    }
+    if (status == STATUS_ABORT) {
+      log_message(LOG_LEVEL_INFO, "Received abort from client, cleaning up");
+      return -1;
+    }
+    if (status == STATUS_CHECK) {
+      bool skipped;
+      File* file = receive_incremental_check(file_descriptor, config, &skipped);
+      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))
+        goto receive_error;
+    } else if (status == STATUS_CHECK_BATCH) {
+      if (!receiver_process_batch(config, file_descriptor))
+        return -1;
+      goto next;
+    } else {
+      File* file = file_receive(config, file_descriptor);
+      if (!file) {
+        log_message(LOG_LEVEL_ERROR, "Failed to receive file");
+        goto receive_error;
+      }
+      if (!sink->store_file(file, sink->context))
+        goto receive_error;
+    }
+  next:
+    if (!receive_status(file_descriptor, &status))
+      goto receive_error;
+  }
+  if (status == STATUS_MANIFEST && receive_manifest(file_descriptor, config, &status) != 0)
+    return -1;
+  if (status != STATUS_FINISHED) {
+    log_message(LOG_LEVEL_ERROR, "Did not receive FINISHED Status");
+    goto receive_error;
+  }
+  if (sink->send_success && !send_status(file_descriptor, STATUS_OK))
+    return -1;
+  return 0;
+
+receive_error:
+  if (sink->send_error)
+    send_status(file_descriptor, STATUS_ERROR);
+  return -1;
+}
+
+static bool receiver_save_file(File* file, void* context) {
+  Config* config = context;
+  bool success =
+      !config->save_to_disk || file_save_to_disk(config->receive_root_directory, file, config);
+  file_destroy(file);
+  return success;
+}
+
+int receiver_receive_files(Config* config, int file_descriptor) {
+  ReceiverSink sink = {receiver_save_file, config, true, true};
+  return receiver_process(config, file_descriptor, &sink);
+}

src/server/receiver.h

@@ -0,0 +1,19 @@
+#ifndef RECEIVER_H
+#define RECEIVER_H
+
+#include "config.h"
+#include "file.h"
+
+typedef bool (*ReceiverFileSink)(File* file, void* context);
+
+typedef struct {
+  ReceiverFileSink store_file;
+  void* context;
+  bool send_error;
+  bool send_success;
+} ReceiverSink;
+
+int receiver_process(Config* config, int file_descriptor, const ReceiverSink* sink);
+int receiver_receive_files(Config* config, int file_descriptor);
+
+#endif

src/server/server.c

@@ -1,54 +1,103 @@
-#include "array_list.h"
-#include "chunk.h"
 #include "config.h"
-#include "data.h"
+#include "chunk.h"
 #include "file.h"
 #include "log.h"
+#include "metadata.h"
 #include "multiprocessing.h"
-#include "protocol.h"
 #include "queue.h"
+#include "receiver.h"
 #include "transport_tcp.h"
 #include "transport_tls.h"
 #include "unistd.h"
 #include "utils.h"
+#include <fcntl.h>
+#include <limits.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <limits.h>
-#include <fcntl.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include <openssl/x509.h>
 
 static char* authorized_root;
 static int authorized_root_fd = -1;
 static bool allow_delete;
+static bool allow_unauthenticated;
+static const char* required_client_cn;
+
+static bool tls_client_identity_allowed(SSL* ssl) {
+  if (!ssl || !required_client_cn)
+    return false;
+  X509* certificate = SSL_get1_peer_certificate(ssl);
+  if (!certificate)
+    return false;
+  char common_name[256];
+  int length = X509_NAME_get_text_by_NID(X509_get_subject_name(certificate), NID_commonName,
+                                         common_name, sizeof(common_name));
+  size_t required_length = strlen(required_client_cn);
+  bool allowed = length >= 0 && (size_t)length == required_length &&
+                 required_length < sizeof(common_name) &&
+                 memcmp(common_name, required_client_cn, required_length) == 0;
+  X509_free(certificate);
+  return allowed;
+}
+
+static void release_authorization(void) {
+  file_set_authorized_root(-1, NULL);
+  utils_set_authorized_root_fd(-1);
+  if (authorized_root_fd >= 0)
+    close(authorized_root_fd);
+  authorized_root_fd = -1;
+  free(authorized_root);
+  authorized_root = NULL;
+}
 
 static bool path_is_within(const char* root, const char* path) {
   size_t n = strlen(root);
   return strncmp(root, path, n) == 0 && (path[n] == '\0' || path[n] == '/');
 }
 
-static bool valid_batch_path(const char* path) {
-  return path && path[0] != '\0' && path[0] != '/' && !has_path_traversal(path) &&
-         strchr(path, '\0') == path + strlen(path);
-}
-
 static bool __attribute__((unused)) configure_authorization(const char* root) {
   char resolved[PATH_MAX];
-  if (!root || !realpath(root, resolved))
+  if (!root) {
+    file_set_authorized_root(-1, NULL);
+    utils_set_authorized_root(-1, NULL);
     return false;
+  }
+  int root_fd = open(root, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+  if (root_fd < 0) {
+    file_set_authorized_root(-1, NULL);
+    utils_set_authorized_root(-1, NULL);
+    return false;
+  }
+  char fd_path[64];
+  int fd_path_length = snprintf(fd_path, sizeof(fd_path), "/proc/self/fd/%d", root_fd);
+  if (fd_path_length < 0 || (size_t)fd_path_length >= sizeof(fd_path) ||
+      !realpath(fd_path, resolved)) {
+    close(root_fd);
+    file_set_authorized_root(-1, NULL);
+    utils_set_authorized_root(-1, NULL);
+    return false;
+  }
   authorized_root = str_dup(resolved);
-  if (!authorized_root)
+  if (!authorized_root) {
+    close(root_fd);
+    file_set_authorized_root(-1, NULL);
+    utils_set_authorized_root(-1, NULL);
     return false;
-  authorized_root_fd = open(resolved, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
-  if (authorized_root_fd < 0) {
+  }
+  authorized_root_fd = root_fd;
+  if (!file_set_authorized_root(authorized_root_fd, authorized_root) ||
+      !utils_set_authorized_root(authorized_root_fd, authorized_root)) {
+    file_set_authorized_root(-1, NULL);
+    utils_set_authorized_root(-1, NULL);
+    close(authorized_root_fd);
+    authorized_root_fd = -1;
     free(authorized_root);
     authorized_root = NULL;
     return false;
   }
-  file_set_authorized_root(authorized_root_fd, authorized_root);
-  utils_set_authorized_root_fd(authorized_root_fd);
   return true;
 }
 
@@ -113,16 +162,36 @@ int receive_files(Config* config, int fd) {
           free(check_path);
           return -1;
         }
-        if (!valid_batch_path(check_path)) {
+        long long check_mtime_nsec;
+        if (!receive_n_data(fd, &check_mtime_nsec, sizeof(check_mtime_nsec)) ||
+            check_mtime_nsec < 0 || check_mtime_nsec >= 1000000000LL) {
+          free(check_path);
+          send_status(fd, STATUS_ERROR);
+          return -1;
+        }
+        if (!utils_valid_batch_path(check_path)) {
           free(check_path);
           send_status(fd, STATUS_ERROR);
           return -1;
         }
-        char* full_path = path_cat(config->receive_root_directory, check_path);
         struct stat st;
-        bool has_old = full_path && lstat(full_path, &st) == 0;
-        bool match = has_old && (unsigned long long)st.st_size == check_size &&
-                     (long long)st.st_mtime == check_mtime;
+        char* full_path = path_cat(config->receive_root_directory, check_path);
+        if (!full_path) {
+          free(check_path);
+          send_status(fd, STATUS_ERROR);
+          return -1;
+        }
+        bool has_old = full_path && file_stat_secure(full_path, &st);
+        long long old_mtime_nsec = 0;
+        if (has_old) {
+#ifdef __linux__
+          old_mtime_nsec = st.st_mtim.tv_nsec;
+#endif
+        }
+        bool match = !config->ignore_times && has_old &&
+                     (unsigned long long)st.st_size == check_size &&
+                     metadata_mtime_matches(st.st_mtime, old_mtime_nsec, (time_t)check_mtime,
+                                            (long)check_mtime_nsec, config->modify_window);
         bool sent = send_status(fd, match ? STATUS_OK : STATUS_NEXT);
         free(full_path);
         free(check_path);
@@ -153,8 +222,9 @@ int receive_files(Config* config, int fd) {
   }
 
   if (status == STATUS_MANIFEST) {
-    if (receive_manifest(fd, config, &status) != 0)
+    if (receive_manifest(fd, config, &status) != 0) {
       return -1;
+    }
   }
   if (status != STATUS_FINISHED) {
     log_message(LOG_LEVEL_ERROR, "Did not receive FINISHED Status");
@@ -167,39 +237,60 @@ int receive_files(Config* config, int fd) {
 
 void handler(int file_descriptor) {
   SSL* ssl = io_get_ssl();
+  ProtocolSession session;
+  protocol_session_init(&session, file_descriptor, file_descriptor);
+  protocol_session_set_ssl(&session, ssl);
+  protocol_session_bind(&session);
   Config* config = config_receive(file_descriptor);
   if (config == NULL) {
     log_message(LOG_LEVEL_ERROR, "Failed to receive config");
     close(file_descriptor);
+    protocol_session_unbind();
     return;
   }
+  protocol_set_8_bit_output(config->eight_bit_output);
   if (!authorized_root) {
     log_message(LOG_LEVEL_ERROR, "No server-side destination root configured");
     config_delete(config);
     close(file_descriptor);
+    protocol_session_unbind();
     return;
   }
-  char resolved_destination[PATH_MAX];
-  char* canonical_destination = realpath(config->receive_root_directory, NULL);
-  const char* destination =
-      canonical_destination ? canonical_destination : config->receive_root_directory;
-  if (has_path_traversal(destination) || !path_is_within(authorized_root, destination)) {
-    log_message(LOG_LEVEL_ERROR, "Rejected destination outside authorized root");
-    free(canonical_destination);
+  if (!allow_unauthenticated && ssl == NULL) {
+    log_message(LOG_LEVEL_ERROR, "Rejected unauthenticated plaintext connection");
+    config_delete(config);
+    close(file_descriptor);
+    protocol_session_unbind();
+    return;
+  }
+  if (ssl && required_client_cn && !tls_client_identity_allowed(ssl)) {
+    log_message(LOG_LEVEL_ERROR, "Rejected TLS client with unauthorized identity");
     config_delete(config);
     close(file_descriptor);
     return;
   }
-  if (canonical_destination)
-    snprintf(resolved_destination, sizeof(resolved_destination), "%s", canonical_destination);
-  else
-    snprintf(resolved_destination, sizeof(resolved_destination), "%s", destination);
-  free(canonical_destination);
-  free(config->receive_root_directory);
-  config->receive_root_directory = str_dup(resolved_destination);
+  char* destination = config->receive_root_directory;
+  char* joined_destination = NULL;
+  if (destination && destination[0] != '/')
+    joined_destination = path_cat(authorized_root, destination);
+  if (joined_destination)
+    destination = joined_destination;
+  if (!destination || has_path_traversal(destination) ||
+      !path_is_within(authorized_root, destination)) {
+    log_message(LOG_LEVEL_ERROR, "Rejected destination outside authorized root");
+    free(joined_destination);
+    config_delete(config);
+    close(file_descriptor);
+    return;
+  }
+  if (joined_destination) {
+    free(config->receive_root_directory);
+    config->receive_root_directory = joined_destination;
+  }
   if (!config->receive_root_directory) {
     config_delete(config);
     close(file_descriptor);
+    protocol_session_unbind();
     return;
   }
   config->use_delete = config->use_delete && allow_delete;
@@ -208,6 +299,7 @@ void handler(int file_descriptor) {
     if (q == NULL) {
       config_delete(config);
       close(file_descriptor);
+      protocol_session_unbind();
       return;
     }
     PipelineContextReceiver* context =
@@ -216,16 +308,19 @@ void handler(int file_descriptor) {
       queue_destroy(q);
       config_delete(config);
       close(file_descriptor);
+      protocol_session_unbind();
       return;
     }
+    protocol_session_set_max_alloc(&context->session, config->max_alloc);
+    atomic_store(&context->session.total_allocated_bytes,
+                 atomic_load(&session.total_allocated_bytes));
     thrd_t receiver, writer;
-    bool receiver_created = false;
+    bool receiver_created = thrd_create(&receiver, receive_thread, context) == thrd_success;
     bool writer_created = false;
-    receiver_created = (thrd_create(&receiver, receive_thread, context) == thrd_success);
     if (receiver_created)
-      writer_created = (thrd_create(&writer, write_thread, context) == thrd_success);
+      writer_created = thrd_create(&writer, write_thread, context) == thrd_success;
     if (!receiver_created || !writer_created) {
-      perror("Error creating Threads");
+      log_perror("Error creating Threads");
       if (receiver_created) {
         mtx_lock(&context->mutex);
         atomic_store(&context->cancelled, true);
@@ -240,22 +335,23 @@ void handler(int file_descriptor) {
       if (writer_created)
         thrd_join(writer, NULL);
       pipeline_context_receiver_destroy(context);
+      protocol_session_unbind();
       return;
     }
     int receiver_result;
     int writer_result;
     thrd_join(receiver, &receiver_result);
     thrd_join(writer, &writer_result);
-    if (receiver_result == thrd_success && writer_result == thrd_success)
-      send_status(file_descriptor, STATUS_OK);
-    else
-      send_status(file_descriptor, STATUS_ERROR);
+    send_status(file_descriptor, receiver_result == thrd_success && writer_result == thrd_success
+                                     ? STATUS_OK
+                                     : STATUS_ERROR);
     pipeline_context_receiver_destroy(context);
   } else {
-    if (receive_files(config, file_descriptor) != 0)
+    if (receiver_receive_files(config, file_descriptor) != 0)
       log_message(LOG_LEVEL_ERROR, "Transfer failed");
     config_delete(config);
   }
+  protocol_session_unbind();
   close(file_descriptor);
 }
 
@@ -264,16 +360,14 @@ static Server* g_server = NULL;
 
 static void cleanup(int sig) {
   (void)sig;
-  if (g_server) {
+  if (g_server)
     server_delete(&g_server);
-  }
   _exit(0);
 }
 
 static void print_server_usage(void) {
   printf("FastSync Server\n");
-  printf("Usage: fastsync-server [options]\n");
-  printf("\n");
+  printf("Usage: fastsync-server [options]\n\n");
   printf("Options:\n");
   printf("  --stdio             Run in stdio mode (SSH transport)\n");
   printf("  -p <port>           TCP port (default: 8080, range: 1-65535)\n");
@@ -281,17 +375,17 @@ static void print_server_usage(void) {
   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("  --client-cn <name>  Required TLS client certificate CN\n");
   printf("  --destination-root <path>  Authorized destination root (default: .)\n");
   printf("  --allow-delete      Permit manifest deletion\n");
+  printf("  --allow-unauthenticated  Allow plaintext/anonymous network clients\n");
   printf("  -v, --verbose       Enable debug logging\n");
   printf("  --help              Show this help\n");
 }
 
 int main(int argc, char* argv[]) {
   bool use_tls = false;
-  char* tls_cert = NULL;
-  char* tls_key = NULL;
-  char* tls_ca = NULL;
+  char *tls_cert = NULL, *tls_key = NULL, *tls_ca = NULL;
   int port = 8080;
   const char* destination_root = ".";
   bool stdio_mode = false;
@@ -305,6 +399,7 @@ int main(int argc, char* argv[]) {
       stdio_mode = true;
     } else if (strcmp(argv[i], "-v") == 0 || strcmp(argv[i], "--verbose") == 0) {
       set_log_level(LOG_LEVEL_DEBUG);
+      set_log_debug_flags(LOG_DEBUG_ALL);
     } else if (strcmp(argv[i], "--tls") == 0) {
       use_tls = true;
     } else if (strcmp(argv[i], "--cert") == 0 && i + 1 < argc) {
@@ -313,65 +408,78 @@ int main(int argc, char* argv[]) {
       tls_key = argv[++i];
     } else if (strcmp(argv[i], "--ca") == 0 && i + 1 < argc) {
       tls_ca = argv[++i];
+    } else if (strcmp(argv[i], "--client-cn") == 0 && i + 1 < argc) {
+      required_client_cn = argv[++i];
     } else if (strcmp(argv[i], "--destination-root") == 0 && i + 1 < argc) {
       destination_root = argv[++i];
     } else if (strcmp(argv[i], "--allow-delete") == 0) {
       allow_delete = true;
+    } else if (strcmp(argv[i], "--allow-unauthenticated") == 0) {
+      allow_unauthenticated = true;
     } else if (strcmp(argv[i], "-p") == 0 && i + 1 < argc) {
       char* end;
       long p = strtol(argv[++i], &end, 10);
       if (*end || p <= 0 || p > 65535) {
-        fprintf(stderr, "Error: invalid port '%s' (must be 1-65535)\n", argv[i]);
+        char* escaped = output_escape(argv[i], false);
+        fprintf(stderr, "Error: invalid port '%s' (must be 1-65535)\n",
+                escaped ? escaped : "<allocation failed>");
+        free(escaped);
         return 1;
       }
       port = (int)p;
     } else if (argv[i][0] == '-') {
-      fprintf(stderr, "Unknown option: %s\n", argv[i]);
+      char* escaped = output_escape(argv[i], false);
+      fprintf(stderr, "Unknown option: %s\n", escaped ? escaped : "<allocation failed>");
+      free(escaped);
       print_server_usage();
       return 1;
     }
   }
-
-  if (tls_ca && !use_tls) {
+  if (tls_ca && !use_tls)
     log_message(LOG_LEVEL_WARNING, "--ca has no effect without --tls");
-  }
-
   signal(SIGINT, cleanup);
   signal(SIGTERM, cleanup);
   if (!configure_authorization(destination_root)) {
-    fprintf(stderr, "Error: invalid destination root '%s'\n", destination_root);
+    char* escaped = output_escape(destination_root, false);
+    fprintf(stderr, "Error: invalid destination root '%s'\n",
+            escaped ? escaped : "<allocation failed>");
+    free(escaped);
     return 1;
   }
   if (stdio_mode) {
+    /* SSH authenticates the stdio transport outside of FastSync. */
+    allow_unauthenticated = true;
     io_set_fds(STDIN_FILENO, STDOUT_FILENO);
     handler(STDIN_FILENO);
-    file_set_authorized_root(-1, NULL);
-    utils_set_authorized_root_fd(-1);
-    close(authorized_root_fd);
-    free(authorized_root);
+    release_authorization();
     return 0;
   }
   g_server = server_create(port);
-  if (g_server == NULL) {
+  if (!g_server) {
     log_message(LOG_LEVEL_ERROR, "Failed to create server");
+    release_authorization();
     return 1;
   }
   if (use_tls) {
-    if (!tls_cert || !tls_key) {
-      fprintf(stderr, "Error: --tls requires --cert and --key\n");
+    if (!tls_cert || !tls_key || !tls_ca || !required_client_cn) {
+      fprintf(stderr, "Error: --tls requires --cert, --key, --ca, and --client-cn\n");
       server_delete(&g_server);
+      release_authorization();
       return 1;
     }
     tls_global_init();
     if (!server_create_tls(g_server, tls_cert, tls_key, tls_ca)) {
       log_message(LOG_LEVEL_ERROR, "Failed to set up TLS");
       server_delete(&g_server);
+      release_authorization();
       return 1;
     }
     server_listen_tls(g_server, handler);
   } else {
     server_listen(g_server, handler);
   }
+  server_delete(&g_server);
+  release_authorization();
   return 0;
 }
-#endif /* !FASTSYNC_SERVER_AS_LIB */
+#endif

src/shared/array_list.c

@@ -1,16 +1,18 @@
+#include "log.h"
 #include "array_list.h"
+#include "protocol.h"
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 ArrayList* array_list_create(void (*item_destroyer)(void* item)) {
-  ArrayList* list = (ArrayList*)malloc(sizeof(ArrayList));
+  ArrayList* list = (ArrayList*)protocol_alloc(sizeof(ArrayList));
   if (list == NULL) {
-    perror("ERROR: Could not allocate memory for array list struct");
+    log_perror("ERROR: Could not allocate memory for array list struct");
     return NULL;
   }
 
-  list->items = malloc(INITIAL_ARRAY_SIZE * sizeof(void*));
+  list->items = protocol_alloc(INITIAL_ARRAY_SIZE * sizeof(void*));
   if (list->items == NULL) {
     free(list);
     return NULL;
@@ -34,15 +36,15 @@ void array_list_delete(ArrayList* array_list) {
   free(array_list);
 }
 
-bool array_list_extend(ArrayList* array_list) {
+static bool array_list_extend(ArrayList* array_list) {
   if (array_list == NULL)
     return false;
   int new_capacity = array_list->capacity * 2;
   if (new_capacity == 0)
     new_capacity = INITIAL_ARRAY_SIZE;
-  void* new_items = realloc(array_list->items, new_capacity * sizeof(void*));
+  void* new_items = protocol_realloc(array_list->items, new_capacity * sizeof(void*));
   if (new_items == NULL) {
-    perror("ERROR: Could not reallocate memory for array list items");
+    log_perror("ERROR: Could not reallocate memory for array list items");
     return false;
   }
   array_list->items = new_items;
@@ -66,9 +68,9 @@ void** array_list_to_array(const ArrayList* array_list) {
   if (array_list == NULL) {
     return NULL;
   }
-  void** array = malloc(array_list->size * sizeof(void*));
+  void** array = protocol_alloc(array_list->size * sizeof(void*));
   if (array == NULL) {
-    perror("Could not malloc space for array from array list!");
+    log_perror("Could not malloc space for array from array list!");
     return NULL;
   }
   memcpy(array, array_list->items, array_list->size * sizeof(void*));

src/shared/array_list.h

@@ -14,7 +14,6 @@ typedef struct ArrayList {
 
 ArrayList* array_list_create(void (*item_destroyer)(void* item));
 void array_list_delete(ArrayList* array_list);
-bool array_list_extend(ArrayList* array_list);
 bool array_list_add(ArrayList* array_list, void* item);
 void** array_list_to_array(const ArrayList* array_list);
 

src/shared/chmod.c

@@ -0,0 +1,90 @@
+#include "chmod.h"
+#include <stddef.h>
+#include <string.h>
+
+static bool parse_clause(mode_t* mode, const char* begin, const char* end) {
+  const char* p = begin;
+  unsigned who = 0;
+  while (p < end && strchr("ugoa", *p)) {
+    if (*p == 'a')
+      who = 7;
+    else
+      who |= *p == 'u' ? 1U : (*p == 'g' ? 2U : 4U);
+    p++;
+  }
+  if (who == 0)
+    who = 7;
+  if (p == end || (*p != '+' && *p != '-' && *p != '='))
+    return false;
+  char operation = *p++;
+  mode_t bits = 0;
+  while (p < end) {
+    mode_t bit;
+    switch (*p++) {
+    case 'r':
+      bit = 4;
+      break;
+    case 'w':
+      bit = 2;
+      break;
+    case 'x':
+      bit = 1;
+      break;
+    default:
+      return false;
+    }
+    bits |= bit;
+  }
+  for (unsigned class_index = 0; class_index < 3; class_index++) {
+    unsigned class_bit = 1U << class_index;
+    if (!(who & class_bit))
+      continue;
+    mode_t shift = (mode_t)((2U - class_index) * 3U);
+    mode_t mask = (mode_t)(7U << shift);
+    mode_t class_bits = (mode_t)(bits << shift);
+    if (operation == '+')
+      *mode |= class_bits;
+    else if (operation == '-')
+      *mode &= ~class_bits;
+    else
+      *mode = (*mode & ~mask) | class_bits;
+  }
+  return true;
+}
+
+bool chmod_apply(mode_t mode, const char* spec, mode_t* result) {
+  if (!spec || !*spec || !result)
+    return false;
+  bool numeric = true;
+  size_t length = strlen(spec);
+  if (length > 4)
+    numeric = false;
+  for (size_t i = 0; i < length && numeric; i++)
+    numeric = spec[i] >= '0' && spec[i] <= '7';
+  if (numeric) {
+    if (length == 0 || length > 4)
+      return false;
+    mode_t parsed = 0;
+    for (size_t i = 0; i < length; i++)
+      parsed = (mode_t)((parsed << 3) | (spec[i] - '0'));
+    *result = parsed;
+    return true;
+  }
+
+  mode_t changed = mode;
+  const char* begin = spec;
+  while (*begin) {
+    const char* end = strchr(begin, ',');
+    if (!end)
+      end = begin + strlen(begin);
+    if (!parse_clause(&changed, begin, end))
+      return false;
+    if (*end == '\0')
+      break;
+    begin = end + 1;
+    if (!*begin)
+      return false;
+  }
+  *result = changed;
+  return true;
+}

src/shared/chmod.h

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

src/shared/chunk.c

@@ -1,4 +1,6 @@
 #include <stddef.h>
+#include <stdint.h>
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -11,21 +13,33 @@
 #include "log.h"
 #include "metadata.h"
 #include "protocol.h"
+#include "utils.h"
 
 /* Maximum individual file data size within a chunk (64 MB) */
 #define MAX_FILE_DATA_SIZE (64ULL * 1024 * 1024)
+#define MAX_FILES_PER_CHUNK 65536U
 
 Chunk* chunk_create(File** items, int element_count) {
-  Chunk* chunk = (Chunk*)malloc(sizeof(Chunk));
+  if (element_count < 0 || (element_count > 0 && items == NULL))
+    return NULL;
+  Chunk* chunk = (Chunk*)protocol_alloc(sizeof(Chunk));
   if (chunk == NULL) {
-    perror("ERROR: Could not allocate memory for chunk structure");
+    log_perror("ERROR: Could not allocate memory for chunk structure");
     return NULL;
   }
 
-  chunk->items = (File**)malloc(element_count * sizeof(File*));
-  if (chunk->items == NULL) {
-    free(chunk);
-    return NULL;
+  if (element_count == 0) {
+    chunk->items = NULL;
+  } else {
+    if ((size_t)element_count > SIZE_MAX / sizeof(File*)) {
+      free(chunk);
+      return NULL;
+    }
+    chunk->items = (File**)protocol_alloc((size_t)element_count * sizeof(File*));
+    if (chunk->items == NULL) {
+      free(chunk);
+      return NULL;
+    }
   }
 
   for (int i = 0; i < element_count; i++) {
@@ -50,15 +64,37 @@ void chunk_destroy(void* item) {
 }
 
 static unsigned long long per_file_serialize_size(File* file, bool use_metadata) {
-  return sizeof(size_t) + strlen(file->path) +
-         (use_metadata ? sizeof(int) + (file->metadata ? FILE_METADATA_WIRE_SIZE : 0) : 0) +
-         sizeof(size_t) + file->data->size;
+  unsigned long long size = sizeof(size_t);
+  size_t path_len = strlen(file->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)
+    return 0;
+  size += path_len;
+  if (metadata_size > ULLONG_MAX - size)
+    return 0;
+  size += metadata_size;
+  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;
 }
 
 Data* chunk_serialize(Chunk* chunk, bool use_metadata) {
+  if (!chunk || chunk->element_count < 0 || (chunk->element_count > 0 && chunk->items == NULL))
+    return NULL;
   unsigned long long data_size = 0;
   for (int i = 0; i < chunk->element_count; i++) {
-    data_size += per_file_serialize_size(chunk->items[i], use_metadata);
+    if (!chunk->items[i] || !chunk->items[i]->path || !chunk->items[i]->data ||
+        (chunk->items[i]->data->size > 0 && !chunk->items[i]->data->data) ||
+        chunk->items[i]->path[0] == '\0' || has_path_traversal(chunk->items[i]->path))
+      return NULL;
+    unsigned long long file_size = per_file_serialize_size(chunk->items[i], use_metadata);
+    if (file_size == 0 || file_size > ULLONG_MAX - data_size || data_size + file_size > SIZE_MAX)
+      return NULL;
+    data_size += file_size;
   }
   Data* data = data_create_empty(data_size);
   if (data == NULL) {
@@ -87,11 +123,20 @@ Data* chunk_serialize(Chunk* chunk, bool use_metadata) {
 }
 
 Chunk* chunk_deserialize(Data* data, bool use_metadata) {
+  if (!data || (!data->data && data->size != 0))
+    return NULL;
   ArrayList* files = array_list_create(file_destroy);
+  if (files == NULL)
+    return NULL;
   char* data_pointer = data->data;
   size_t remaining_size = data->size;
 
   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;
+    }
     if (remaining_size < sizeof(size_t)) {
       log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for path length");
       array_list_delete(files);
@@ -103,48 +148,77 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
     data_pointer += sizeof(size_t);
     remaining_size -= sizeof(size_t);
 
-    if (remaining_size < path_len) {
+    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;
     }
 
-    char* path = malloc(path_len + 1);
+    if (path_len == SIZE_MAX) {
+      array_list_delete(files);
+      return NULL;
+    }
+    char* path = protocol_alloc(path_len + 1);
     if (path == NULL) {
-      perror("Could not allocate memory for file path");
+      log_perror("Could not allocate memory for file path");
       array_list_delete(files);
       return NULL;
     }
     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;
+    }
     data_pointer += path_len;
     remaining_size -= path_len;
 
+    if (path_len == 0 || has_path_traversal(path)) {
+      free(path);
+      array_list_delete(files);
+      return NULL;
+    }
+
     File* file = file_create(path);
     free(path);
+    if (file == NULL) {
+      array_list_delete(files);
+      return NULL;
+    }
 
     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;
       }
       // Peek at present flag to determine total size needed before reading
       int present_flag;
       memcpy(&present_flag, data_pointer, sizeof(int));
-      if (present_flag && remaining_size < sizeof(int) + FILE_METADATA_WIRE_SIZE) {
+      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;
       }
       file->metadata = metadata_from_buf(&data_pointer);
       remaining_size -= sizeof(int);
-      if (file->metadata)
+      if (present_flag == 1) {
+        if (file->metadata == NULL) {
+          file_destroy(file);
+          array_list_delete(files);
+          return NULL;
+        }
         remaining_size -= FILE_METADATA_WIRE_SIZE;
+      }
     }
 
     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;
     }
@@ -156,6 +230,7 @@ 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;
     }
@@ -164,29 +239,50 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
     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;
     }
 
-    void* file_data = malloc(file_data_size);
+    size_t allocation_size = file_data_size > 0 ? file_data_size : 1;
+    void* file_data = protocol_alloc(allocation_size);
     if (file_data == NULL) {
-      perror("Could not allocate memory for file data");
+      log_perror("Could not allocate memory for file data");
+      file_destroy(file);
       array_list_delete(files);
       return NULL;
     }
     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;
+    }
     data_destroy(file->data);
-    file->data = data_create(file_data, file_data_size);
+    file->data = replacement;
     data_pointer += file_data_size;
     remaining_size -= file_data_size;
 
-    array_list_add(files, file);
+    if (!array_list_add(files, file)) {
+      file_destroy(file);
+      array_list_delete(files);
+      return NULL;
+    }
   }
 
   File** file_array = (File**)array_list_to_array(files);
+  if (files->size > 0 && file_array == NULL) {
+    array_list_delete(files);
+    return NULL;
+  }
   Chunk* chunk = chunk_create(file_array, files->size);
 
   free(file_array);
+  if (chunk == NULL) {
+    array_list_delete(files);
+    return NULL;
+  }
   files->item_destroyer = NULL;
   array_list_delete(files);
 
@@ -194,27 +290,32 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
 }
 
 Data* chunk_compress(Chunk* chunk, int compression_level, bool use_metadata) {
+  return chunk_compress_with_threads(chunk, compression_level, use_metadata, 0);
+}
+
+Data* chunk_compress_with_threads(Chunk* chunk, int compression_level, bool use_metadata,
+                                  int compression_threads) {
   log_message(LOG_LEVEL_DEBUG, "Starting to compress chunk");
   Data* serialized = chunk_serialize(chunk, use_metadata);
   if (serialized == NULL)
     return NULL;
-  Data* compressed = data_compress(serialized, compression_level);
+  Data* compressed = data_compress_with_threads(serialized, compression_level, compression_threads);
   data_destroy(serialized);
   if (compressed == NULL)
     return NULL;
-  log_message(LOG_LEVEL_DEBUG, "Chunk successfully compressed");
+  log_debug_message(LOG_DEBUG_PACK, "Chunk successfully compressed");
   return compressed;
 }
 
 Chunk* receive_chunk_data(int fd, const Config* config) {
-  Data* chunk_data = receive_data(fd);
+  Data* chunk_data = receive_data_limited(fd, MAX_CHUNK_SIZE);
   if (chunk_data == NULL) {
     log_message(LOG_LEVEL_ERROR, "Failed to receive chunk data");
     return NULL;
   }
   Data* data_to_process = chunk_data;
   if (config->use_compression) {
-    data_to_process = data_decompress(chunk_data);
+    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");

src/shared/chunk.h

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

src/shared/compression.c

@@ -1,31 +1,53 @@
 #include "compression.h"
 #include "data.h"
 #include "log.h"
+#include "protocol.h"
 #include <stdlib.h>
+#include <limits.h>
+#include <stdint.h>
 #include <string.h>
 #include <strings.h>
+#include <unistd.h>
 #include <zstd.h>
 
 #define INITIAL_DECOMPRESS_BUF_SIZE (1024 * 1024)
 #define MAX_DECOMPRESSED_SIZE (100ULL * 1024 * 1024) /* 100 MB hard ceiling */
 
-static const char* SKIP_COMPRESSION_EXTENSIONS[] = {".jpg", ".jpeg", ".png", ".gif", ".mp4", ".mkv",
-                                                    ".zip", ".gz",   ".xz",  ".zst", NULL};
+static char* SKIP_COMPRESSION_EXTENSIONS[] = {".jpg", ".jpeg", ".png", ".gif", ".mp4", ".mkv",
+                                              ".zip", ".gz",   ".xz",  ".zst", NULL};
 
 bool compression_should_skip(const char* path) {
+  return compression_should_skip_with_suffixes(path, NULL, -1);
+}
+
+bool compression_should_skip_with_suffixes(const char* path, char* const* suffixes, int count) {
   if (!path)
     return false;
   const char* dot = strrchr(path, '.');
   if (!dot)
     return false;
-  for (int i = 0; SKIP_COMPRESSION_EXTENSIONS[i]; i++) {
-    if (strcasecmp(dot, SKIP_COMPRESSION_EXTENSIONS[i]) == 0)
+  if (count < 0) {
+    suffixes = SKIP_COMPRESSION_EXTENSIONS;
+    count = 0;
+    while (SKIP_COMPRESSION_EXTENSIONS[count])
+      count++;
+  }
+  for (int i = 0; i < count; i++) {
+    if (strcasecmp(dot, suffixes[i]) == 0)
       return true;
   }
   return false;
 }
 
 Data* data_compress(Data* data_to_compress, int compression_level) {
+  return data_compress_with_threads(data_to_compress, compression_level, 0);
+}
+
+Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
+                                 int compression_threads) {
+  if (!data_to_compress || (!data_to_compress->data && data_to_compress->size != 0) ||
+      compression_threads < 0 || compression_threads > COMPRESSION_MAX_THREADS)
+    return NULL;
   log_message(LOG_LEVEL_DEBUG, "Starting to compress data");
   size_t dst_size = ZSTD_compressBound(data_to_compress->size);
   Data* compressed_data = data_create_empty(dst_size);
@@ -47,6 +69,30 @@ Data* data_compress(Data* data_to_compress, int compression_level) {
     return NULL;
   }
 
+  if (compression_threads > 0) {
+    long online_cpus = sysconf(_SC_NPROCESSORS_ONLN);
+    int available_threads = online_cpus > 0 && online_cpus < compression_threads
+                                ? (int)online_cpus
+                                : compression_threads;
+    zret = ZSTD_CCtx_setParameter(cctx, ZSTD_c_nbWorkers, available_threads);
+    if (ZSTD_isError(zret)) {
+      log_message(LOG_LEVEL_ERROR, "Failed to set compression threads: %s",
+                  ZSTD_getErrorName(zret));
+      ZSTD_freeCCtx(cctx);
+      data_destroy(compressed_data);
+      return NULL;
+    }
+    /* Streaming compression needs the source size before threaded mode can end a frame. */
+    zret = ZSTD_CCtx_setPledgedSrcSize(cctx, data_to_compress->size);
+    if (ZSTD_isError(zret)) {
+      log_message(LOG_LEVEL_ERROR, "Failed to set compression source size: %s",
+                  ZSTD_getErrorName(zret));
+      ZSTD_freeCCtx(cctx);
+      data_destroy(compressed_data);
+      return NULL;
+    }
+  }
+
   ZSTD_inBuffer input = {data_to_compress->data, data_to_compress->size, 0};
   ZSTD_outBuffer output = {compressed_data->data, dst_size, 0};
 
@@ -64,13 +110,16 @@ Data* data_compress(Data* data_to_compress, int compression_level) {
   compressed_data->size = output.pos;
   ZSTD_freeCCtx(cctx);
 
-  log_message(LOG_LEVEL_DEBUG, "Data succesfully compressed from %zu to %zu",
-              data_to_compress->size, compressed_data->size);
+  log_debug_message(LOG_DEBUG_UTIL, "Data succesfully compressed from %zu to %zu",
+                    data_to_compress->size, compressed_data->size);
   return compressed_data;
 }
 
-Data* data_decompress(Data* compressed_data) {
-  log_message(LOG_LEVEL_DEBUG, "Start to decompress 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;
+  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)) {
@@ -82,15 +131,16 @@ Data* data_decompress(Data* compressed_data) {
   // 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)
+      return NULL;
     dst_size = compressed_data->size * 3;
     if (dst_size < INITIAL_DECOMPRESS_BUF_SIZE)
       dst_size = INITIAL_DECOMPRESS_BUF_SIZE;
-    if (dst_size > MAX_DECOMPRESSED_SIZE)
-      dst_size = MAX_DECOMPRESSED_SIZE;
   }
-  if (dst_size > MAX_DECOMPRESSED_SIZE) {
-    log_message(LOG_LEVEL_ERROR, "Declared decompressed size exceeds %llu bytes",
-                (unsigned long long)MAX_DECOMPRESSED_SIZE);
+  unsigned long long hard_limit =
+      maximum_size < MAX_DECOMPRESSED_SIZE ? maximum_size : MAX_DECOMPRESSED_SIZE;
+  if (dst_size > hard_limit) {
+    log_message(LOG_LEVEL_ERROR, "Declared decompressed size exceeds %llu bytes", hard_limit);
     return NULL;
   }
 
@@ -101,6 +151,8 @@ Data* data_decompress(Data* compressed_data) {
   }
 
   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);
   if (!uncompressed_data) {
     log_message(LOG_LEVEL_ERROR, "Failed to allocate decompression buffer");
@@ -121,7 +173,7 @@ Data* data_decompress(Data* compressed_data) {
       return NULL;
     }
     if (ret > 0 && output.pos == output.size) {
-      if (buf_size >= MAX_DECOMPRESSED_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);
@@ -129,9 +181,9 @@ Data* data_decompress(Data* compressed_data) {
         return NULL;
       }
       buf_size *= 2;
-      if (buf_size > MAX_DECOMPRESSED_SIZE)
-        buf_size = MAX_DECOMPRESSED_SIZE;
-      void* new_data = realloc(uncompressed_data->data, buf_size);
+      if (buf_size > hard_limit)
+        buf_size = (size_t)hard_limit;
+      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);
@@ -147,6 +199,10 @@ Data* data_decompress(Data* compressed_data) {
   uncompressed_data->size = output.pos;
   ZSTD_freeDCtx(dctx);
 
-  log_message(LOG_LEVEL_DEBUG, "Decompressed data successfully");
+  log_debug_message(LOG_DEBUG_UTIL, "Decompressed data successfully");
   return uncompressed_data;
 }
+
+Data* data_decompress(Data* compressed_data) {
+  return data_decompress_limited(compressed_data, MAX_DECOMPRESSED_SIZE);
+}

src/shared/compression.h

@@ -4,8 +4,14 @@
 #include "data.h"
 #include <stdbool.h>
 
+#define COMPRESSION_MAX_THREADS 64
+
 Data* data_compress(Data* data_to_compress, int compression_level);
+Data* data_compress_with_threads(Data* data_to_compress, int compression_level,
+                                 int compression_threads);
 Data* data_decompress(Data* compressed_data);
+Data* data_decompress_limited(Data* compressed_data, size_t maximum_size);
 bool compression_should_skip(const char* path);
+bool compression_should_skip_with_suffixes(const char* path, char* const* suffixes, int count);
 
 #endif

src/shared/config.c

@@ -1,4 +1,5 @@
 #include "config.h"
+#include "chmod.h"
 #include "delta.h"
 #include "log.h"
 #include "protocol.h"
@@ -17,10 +18,14 @@ static void config_set_defaults(Config* config) {
   config->use_chunk_serialization = false;
   config->use_compression = false;
   config->use_metadata = false;
+  config->use_executability = false;
+  config->metadata_explicitly_disabled = false;
   config->show_progress = false;
   config->dry_run = false;
+  config->remove_source_files = false;
   config->use_delete = false;
   config->compression_level = 5;
+  config->compression_threads = 0;
   config->use_sendfile = false;
   config->chunk_size = DEFAULT_CHUNK_SIZE;
   config->ssh_port = 22;
@@ -33,8 +38,13 @@ static void config_set_defaults(Config* config) {
   config->include_count = 0;
   config->max_size = 0;
   config->min_size = 0;
+  config->max_alloc = DEFAULT_MAX_ALLOC;
   config->use_incremental = false;
+  config->ignore_times = false;
+  config->size_only = false;
   config->use_delta = false;
+  config->whole_file = false;
+  config->modify_window = 0;
   config->delta_block_size = DELTA_BLOCK_SIZE_DEFAULT;
   config->delta_max_file_size = DELTA_MAX_FILE_SIZE;
   config->use_tls = false;
@@ -68,8 +78,12 @@ static void config_set_defaults(Config* config) {
   config->debug_level = 0;
   config->list_only = false;
   config->human_readable = false;
+  config->eight_bit_output = false;
+  config->existing = false;
+  config->ignore_existing = false;
   config->update = false;
   config->inplace = false;
+  config->use_fsync = false;
   config->append = false;
   config->append_verify = false;
   config->delete_excluded = false;
@@ -82,6 +96,7 @@ static void config_set_defaults(Config* config) {
   config->relative = false;
   config->rsh_command = NULL;
   config->rsync_path = NULL;
+  config->old_args = false;
   config->temp_dir = NULL;
   config->compare_dest = NULL;
   config->copy_dest = NULL;
@@ -98,6 +113,55 @@ static void config_set_defaults(Config* config) {
   config->server_mode = false;
   config->checksum = false;
   config->compress_choice = NULL;
+  config->chmod_spec = NULL;
+  config->skip_compress_suffixes = NULL;
+  config->skip_compress_count = 0;
+  config->skip_compress_set = false;
+}
+
+static bool valid_wire_bool(int value) {
+  return value == 0 || value == 1;
+}
+
+static bool receive_wire_bool(int fd, bool* value) {
+  int wire_value;
+  if (!receive_int(fd, &wire_value) || !valid_wire_bool(wire_value))
+    return false;
+  *value = wire_value != 0;
+  return true;
+}
+
+static bool validate_received_config(const Config* config) {
+  return valid_wire_bool(config->save_to_disk) && valid_wire_bool(config->use_multithreading) &&
+         valid_wire_bool(config->use_chunk_serialization) &&
+         valid_wire_bool(config->use_compression) && valid_wire_bool(config->use_metadata) &&
+         valid_wire_bool(config->use_executability) && valid_wire_bool(config->use_sendfile) &&
+         valid_wire_bool(config->use_delete) && valid_wire_bool(config->use_incremental) &&
+         valid_wire_bool(config->size_only) && valid_wire_bool(config->ignore_times) &&
+         valid_wire_bool(config->use_delta) && valid_wire_bool(config->backup) &&
+         valid_wire_bool(config->follow_symlinks) && valid_wire_bool(config->copy_links) &&
+         valid_wire_bool(config->safe_links) && valid_wire_bool(config->copy_unsafe_links) &&
+         valid_wire_bool(config->preserve_hard_links) && valid_wire_bool(config->preserve_acls) &&
+         valid_wire_bool(config->preserve_xattrs) && valid_wire_bool(config->preserve_devices) &&
+         valid_wire_bool(config->preserve_sparse) && valid_wire_bool(config->ignore_existing) &&
+         valid_wire_bool(config->existing) && valid_wire_bool(config->update) &&
+         valid_wire_bool(config->inplace) && valid_wire_bool(config->append) &&
+         valid_wire_bool(config->use_fsync) && valid_wire_bool(config->append_verify) &&
+         valid_wire_bool(config->delete_excluded) && valid_wire_bool(config->delete_after) &&
+         valid_wire_bool(config->relative) && valid_wire_bool(config->prune_empty_dirs) &&
+         valid_wire_bool(config->partial) && valid_wire_bool(config->delete_before) &&
+         valid_wire_bool(config->checksum) && valid_wire_bool(config->eight_bit_output) &&
+         !(config->skip_compress_set && config->use_chunk_serialization) &&
+         (!config->use_compression ||
+          (config->compression_level >= 1 && config->compression_level <= 22)) &&
+         config->chunk_size > 0 && config->chunk_size <= MAX_CHUNK_SIZE &&
+         config->delta_block_size >= DELTA_BLOCK_SIZE_MIN &&
+         config->delta_block_size <= DELTA_BLOCK_SIZE_MAX &&
+         config->delta_max_file_size <= DELTA_MAX_FILE_SIZE && config->modify_window >= 0 &&
+         config->max_delete >= 0 && config->skip_compress_count >= 0 &&
+         config->skip_compress_count <= 10000 && config->max_alloc > 0 &&
+         (!config->chmod_spec || !*config->chmod_spec ||
+          chmod_apply(0, config->chmod_spec, &(mode_t){0}));
 }
 
 Config* config_create(void) {
@@ -108,7 +172,7 @@ Config* config_create(void) {
   return config;
 }
 
-bool is_remote_dest(const char* s) {
+bool config_is_remote_dest(const char* s) {
   if (s == NULL)
     return false;
   const char* colon = strchr(s, ':');
@@ -124,7 +188,7 @@ bool is_remote_dest(const char* s) {
 }
 
 void config_parse_ssh_dest(Config* config) {
-  if (!is_remote_dest(config->receive_root_directory))
+  if (!config_is_remote_dest(config->receive_root_directory))
     return;
   config->transport = TRANSPORT_SSH;
   config->ssh_destination = str_dup(config->receive_root_directory);
@@ -137,6 +201,10 @@ void config_parse_ssh_dest(Config* config) {
 void config_delete(Config* config) {
   if (config == NULL)
     return;
+  if (config->log_file) {
+    fclose(config->log_file);
+    config->log_file = NULL;
+  }
   free(config->version);
   free(config->send_directory);
   free(config->receive_root_directory);
@@ -167,108 +235,195 @@ void config_delete(Config* config) {
   free(config->bind_address);
   free(config->daemon_config);
   free(config->compress_choice);
+  free(config->chmod_spec);
+  if (config->skip_compress_suffixes) {
+    for (int i = 0; i < config->skip_compress_count; i++)
+      free(config->skip_compress_suffixes[i]);
+    free(config->skip_compress_suffixes);
+  }
   if (config->filters) {
     array_list_delete(config->filters);
   }
   free(config);
 }
 
-/* Wire format order (must match config_receive and be updated when PROTOCOL_VERSION bumps):
- * version, send_directory, receive_root_directory, save_to_disk, use_multithreading,
- * use_chunk_serialization, use_compression, use_metadata, compression_level, chunk_size,
- * use_sendfile, use_delete, use_incremental, use_delta, delta_block_size, delta_max_file_size,
- * backup, backup_dir, follow_symlinks, copy_links, safe_links, copy_unsafe_links,
- * preserve_hard_links, preserve_acls, preserve_xattrs, preserve_devices, preserve_sparse,
- * update, inplace, append, append_verify, delete_excluded, delete_after, max_delete, relative,
- * prune_empty_dirs, temp_dir, partial, partial_dir, suffix, delete_before, checksum,
- * compress_choice, status
- */
+/* Each helper is deliberately ordered to match the wire format. Keep the
+ * helper call order in config_send and config_receive unchanged when adding
+ * fields. */
+static bool send_core_fields(int fd, const Config* c) {
+  if (!send_str(fd, c->version) || !send_int(fd, c->eight_bit_output))
+    return false;
+  protocol_set_8_bit_output(c->eight_bit_output);
+  if (!send_n_data(fd, &c->max_alloc, sizeof(c->max_alloc)))
+    return false;
+  return send_str(fd, c->send_directory) && send_str(fd, c->receive_root_directory) &&
+         send_int(fd, c->save_to_disk) && send_int(fd, c->use_multithreading) &&
+         send_int(fd, c->use_chunk_serialization) && send_int(fd, c->use_compression) &&
+         send_int(fd, c->use_metadata) && send_int(fd, c->use_executability) &&
+         send_int(fd, c->compression_level) &&
+         send_n_data(fd, &c->chunk_size, sizeof(c->chunk_size)) && send_int(fd, c->use_sendfile);
+}
+
+static bool send_delta_fields(int fd, const Config* c) {
+  return send_int(fd, c->use_delete) && send_int(fd, c->use_incremental) &&
+         send_int(fd, c->size_only) && send_int(fd, c->ignore_times) &&
+         send_int(fd, c->use_delta && !c->whole_file) &&
+         send_n_data(fd, &c->delta_block_size, sizeof(c->delta_block_size)) &&
+         send_n_data(fd, &c->delta_max_file_size, sizeof(unsigned long long));
+}
+
+static bool send_file_options(int fd, const Config* c) {
+  return send_int(fd, c->backup) && send_str(fd, c->backup_dir ? c->backup_dir : "") &&
+         send_int(fd, c->follow_symlinks) && send_int(fd, c->copy_links) &&
+         send_int(fd, c->safe_links) && send_int(fd, c->copy_unsafe_links) &&
+         send_int(fd, c->preserve_hard_links) && send_int(fd, c->preserve_acls) &&
+         send_int(fd, c->preserve_xattrs) && send_int(fd, c->preserve_devices) &&
+         send_int(fd, c->preserve_sparse);
+}
+
+static bool send_selection_options(int fd, const Config* c) {
+  return send_int(fd, c->ignore_existing) && send_int(fd, c->existing) && send_int(fd, c->update) &&
+         send_int(fd, c->inplace) && send_int(fd, c->append) && send_int(fd, c->use_fsync) &&
+         send_int(fd, c->append_verify) && send_int(fd, c->delete_excluded) &&
+         send_int(fd, c->delete_after) && send_n_data(fd, &c->max_delete, sizeof(c->max_delete)) &&
+         send_int(fd, c->relative) && send_int(fd, c->prune_empty_dirs);
+}
+
+static bool send_skip_compress_options(int fd, const Config* c) {
+  if (!send_int(fd, c->skip_compress_set) || !send_int(fd, c->skip_compress_count))
+    return false;
+  for (int i = 0; i < c->skip_compress_count; i++) {
+    if (!send_str(fd, c->skip_compress_suffixes[i]))
+      return false;
+  }
+  return true;
+}
+
+static bool send_resume_options(int fd, const Config* c) {
+  return send_str(fd, c->temp_dir ? c->temp_dir : "") && send_int(fd, c->partial) &&
+         send_str(fd, c->partial_dir ? c->partial_dir : "") &&
+         send_str(fd, c->suffix ? c->suffix : "") && send_int(fd, c->delete_before) &&
+         send_int(fd, c->checksum) && send_int(fd, c->modify_window) &&
+         send_str(fd, c->compress_choice ? c->compress_choice : "") &&
+         send_str(fd, c->chmod_spec ? c->chmod_spec : "") && send_skip_compress_options(fd, c);
+}
+
+static bool receive_core_fields(int fd, Config* c) {
+  int value;
+  if (!receive_wire_bool(fd, &c->eight_bit_output))
+    return false;
+  protocol_set_8_bit_output(c->eight_bit_output);
+  if (!receive_n_data(fd, &c->max_alloc, sizeof(c->max_alloc)) || c->max_alloc == 0)
+    return false;
+  if (c->max_alloc > MAX_SERVER_ALLOC)
+    c->max_alloc = MAX_SERVER_ALLOC;
+  protocol_session_set_max_alloc(NULL, c->max_alloc);
+  c->send_directory = receive_str(fd);
+  c->receive_root_directory = receive_str(fd);
+  if (!c->send_directory || !c->receive_root_directory)
+    return false;
+  if (!receive_wire_bool(fd, &c->save_to_disk) || !receive_wire_bool(fd, &c->use_multithreading) ||
+      !receive_wire_bool(fd, &c->use_chunk_serialization) ||
+      !receive_wire_bool(fd, &c->use_compression) || !receive_wire_bool(fd, &c->use_metadata) ||
+      !receive_wire_bool(fd, &c->use_executability))
+    return false;
+  if (!receive_int(fd, &value))
+    return false;
+  c->compression_level = value;
+  if (!receive_n_data(fd, &c->chunk_size, sizeof(c->chunk_size)))
+    return false;
+  if (!receive_wire_bool(fd, &c->use_sendfile))
+    return false;
+  return true;
+}
+
+static bool receive_delta_fields(int fd, Config* c) {
+  if (!receive_wire_bool(fd, &c->use_delete))
+    return false;
+  if (!receive_wire_bool(fd, &c->use_incremental))
+    return false;
+  if (!receive_wire_bool(fd, &c->size_only))
+    return false;
+  if (!receive_wire_bool(fd, &c->ignore_times))
+    return false;
+  if (!receive_wire_bool(fd, &c->use_delta))
+    return false;
+  return receive_n_data(fd, &c->delta_block_size, sizeof(c->delta_block_size)) &&
+         receive_n_data(fd, &c->delta_max_file_size, sizeof(unsigned long long));
+}
+
+static bool receive_file_options(int fd, Config* c) {
+  if (!receive_wire_bool(fd, &c->backup))
+    return false;
+  c->backup_dir = receive_str(fd);
+  if (!c->backup_dir)
+    return false;
+  bool* flags[] = {&c->follow_symlinks,   &c->copy_links,          &c->safe_links,
+                   &c->copy_unsafe_links, &c->preserve_hard_links, &c->preserve_acls,
+                   &c->preserve_xattrs,   &c->preserve_devices,    &c->preserve_sparse};
+  for (size_t i = 0; i < sizeof(flags) / sizeof(flags[0]); i++) {
+    if (!receive_wire_bool(fd, flags[i]))
+      return false;
+  }
+  return true;
+}
+
+static bool receive_selection_options(int fd, Config* c) {
+  bool* flags[] = {&c->ignore_existing, &c->existing,        &c->update,
+                   &c->inplace,         &c->append,          &c->use_fsync,
+                   &c->append_verify,   &c->delete_excluded, &c->delete_after};
+  for (size_t i = 0; i < sizeof(flags) / sizeof(flags[0]); i++) {
+    if (!receive_wire_bool(fd, flags[i]))
+      return false;
+  }
+  if (!receive_n_data(fd, &c->max_delete, sizeof(c->max_delete)))
+    return false;
+  if (!receive_wire_bool(fd, &c->relative))
+    return false;
+  if (!receive_wire_bool(fd, &c->prune_empty_dirs))
+    return false;
+  return true;
+}
+
+static bool receive_resume_options(int fd, Config* c) {
+  c->temp_dir = receive_str(fd);
+  if (!c->temp_dir || !receive_wire_bool(fd, &c->partial))
+    return false;
+  c->partial_dir = receive_str(fd);
+  c->suffix = c->partial_dir ? receive_str(fd) : NULL;
+  if (!c->partial_dir || !c->suffix || !receive_wire_bool(fd, &c->delete_before))
+    return false;
+  if (!receive_wire_bool(fd, &c->checksum))
+    return false;
+  if (!receive_n_data(fd, &c->modify_window, sizeof(c->modify_window)))
+    return false;
+  c->compress_choice = receive_str(fd);
+  if (!c->compress_choice)
+    return false;
+  c->chmod_spec = receive_str(fd);
+  if (!c->chmod_spec || !receive_wire_bool(fd, &c->skip_compress_set) ||
+      !receive_int(fd, &c->skip_compress_count) || c->skip_compress_count < 0 ||
+      c->skip_compress_count > 10000)
+    return false;
+  if (c->skip_compress_count > 0) {
+    c->skip_compress_suffixes = calloc((size_t)c->skip_compress_count, sizeof(char*));
+    if (!c->skip_compress_suffixes)
+      return false;
+    for (int i = 0; i < c->skip_compress_count; i++) {
+      c->skip_compress_suffixes[i] = receive_str(fd);
+      if (!c->skip_compress_suffixes[i])
+        return false;
+    }
+  }
+  return true;
+}
+
 bool config_send(int file_descriptor, const Config* config) {
-  if (!send_str(file_descriptor, config->version))
-    return false;
-  if (!send_str(file_descriptor, config->send_directory))
-    return false;
-  if (!send_str(file_descriptor, config->receive_root_directory))
-    return false;
-  if (!send_int(file_descriptor, config->save_to_disk))
-    return false;
-  if (!send_int(file_descriptor, config->use_multithreading))
-    return false;
-  if (!send_int(file_descriptor, config->use_chunk_serialization))
-    return false;
-  if (!send_int(file_descriptor, config->use_compression))
-    return false;
-  if (!send_int(file_descriptor, config->use_metadata))
-    return false;
-  if (!send_int(file_descriptor, config->compression_level))
-    return false;
-  if (!send_n_data(file_descriptor, &config->chunk_size, sizeof(config->chunk_size)))
-    return false;
-  if (!send_int(file_descriptor, config->use_sendfile))
-    return false;
-  if (!send_int(file_descriptor, config->use_delete))
-    return false;
-  if (!send_int(file_descriptor, config->use_incremental))
-    return false;
-  if (!send_int(file_descriptor, config->use_delta))
-    return false;
-  if (!send_n_data(file_descriptor, &config->delta_block_size, sizeof(config->delta_block_size)))
-    return false;
-  if (!send_n_data(file_descriptor, &config->delta_max_file_size, sizeof(unsigned long long)))
-    return false;
-  if (!send_int(file_descriptor, config->backup))
-    return false;
-  if (!send_str(file_descriptor, config->backup_dir ? config->backup_dir : ""))
-    return false;
-  if (!send_int(file_descriptor, config->follow_symlinks))
-    return false;
-  if (!send_int(file_descriptor, config->copy_links))
-    return false;
-  if (!send_int(file_descriptor, config->safe_links))
-    return false;
-  if (!send_int(file_descriptor, config->copy_unsafe_links))
-    return false;
-  if (!send_int(file_descriptor, config->preserve_hard_links))
-    return false;
-  if (!send_int(file_descriptor, config->preserve_acls))
-    return false;
-  if (!send_int(file_descriptor, config->preserve_xattrs))
-    return false;
-  if (!send_int(file_descriptor, config->preserve_devices))
-    return false;
-  if (!send_int(file_descriptor, config->preserve_sparse))
-    return false;
-  if (!send_int(file_descriptor, config->update))
-    return false;
-  if (!send_int(file_descriptor, config->inplace))
-    return false;
-  if (!send_int(file_descriptor, config->append))
-    return false;
-  if (!send_int(file_descriptor, config->append_verify))
-    return false;
-  if (!send_int(file_descriptor, config->delete_excluded))
-    return false;
-  if (!send_int(file_descriptor, config->delete_after))
-    return false;
-  if (!send_n_data(file_descriptor, &config->max_delete, sizeof(config->max_delete)))
-    return false;
-  if (!send_int(file_descriptor, config->relative))
-    return false;
-  if (!send_int(file_descriptor, config->prune_empty_dirs))
-    return false;
-  if (!send_str(file_descriptor, config->temp_dir ? config->temp_dir : ""))
-    return false;
-  if (!send_int(file_descriptor, config->partial))
-    return false;
-  if (!send_str(file_descriptor, config->partial_dir ? config->partial_dir : ""))
-    return false;
-  if (!send_str(file_descriptor, config->suffix ? config->suffix : ""))
-    return false;
-  if (!send_int(file_descriptor, config->delete_before))
-    return false;
-  if (!send_int(file_descriptor, config->checksum))
-    return false;
-  if (!send_str(file_descriptor, config->compress_choice ? config->compress_choice : ""))
+  protocol_session_set_max_alloc(NULL, config->max_alloc);
+  if (!send_core_fields(file_descriptor, config) || !send_delta_fields(file_descriptor, config) ||
+      !send_file_options(file_descriptor, config) ||
+      !send_selection_options(file_descriptor, config) ||
+      !send_resume_options(file_descriptor, config))
     return false;
   Status status;
   if (!receive_status(file_descriptor, &status))
@@ -280,163 +435,39 @@ bool config_send(int file_descriptor, const Config* config) {
   return true;
 }
 
-/* Wire format order: see the comment above config_send. */
 Config* config_receive(int file_descriptor) {
-  Config* config = (Config*)malloc(sizeof(Config));
-  if (config == NULL)
+  Config* config = config_create();
+  if (!config)
     return NULL;
-  config_set_defaults(config);
   free(config->version);
   config->version = receive_str(file_descriptor);
-  if (!config->version) {
-    free(config->server_host);
-    free(config);
-    return NULL;
-  }
+  if (!config->version)
+    goto error;
   if (strcmp(config->version, PROTOCOL_VERSION) != 0) {
-    fprintf(stderr, "Protocol version mismatch: client=%s, server=%s\n", config->version,
-            PROTOCOL_VERSION);
-    free(config->version);
-    free(config->server_host);
-    free(config);
+    char* escaped_version = output_escape(config->version, false);
+    fprintf(stderr, "Protocol version mismatch: client=%s, server=%s\n",
+            escaped_version ? escaped_version : "<allocation failed>", PROTOCOL_VERSION);
+    free(escaped_version);
     send_status(file_descriptor, STATUS_ERROR);
-    return NULL;
+    goto error;
   }
-  config->send_directory = receive_str(file_descriptor);
-  if (!config->send_directory) {
-    free(config->version);
-    free(config->server_host);
-    free(config);
-    return NULL;
-  }
-  config->receive_root_directory = receive_str(file_descriptor);
-  if (!config->receive_root_directory) {
-    free(config->version);
-    free(config->send_directory);
-    free(config->server_host);
-    free(config);
-    return NULL;
-  }
-  int tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->save_to_disk = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->use_multithreading = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->use_chunk_serialization = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->use_compression = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->use_metadata = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->compression_level = tmp;
-  if (!receive_n_data(file_descriptor, &config->chunk_size, sizeof(config->chunk_size)))
-    goto error;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->use_sendfile = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->use_delete = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->use_incremental = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->use_delta = tmp;
-  if (!receive_n_data(file_descriptor, &config->delta_block_size, sizeof(config->delta_block_size)))
-    goto error;
-  if (!receive_n_data(file_descriptor, &config->delta_max_file_size, sizeof(unsigned long long)))
-    goto error;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->backup = tmp;
-  config->backup_dir = receive_str(file_descriptor);
-  if (config->backup_dir == NULL)
-    goto error;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->follow_symlinks = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->copy_links = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->safe_links = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->copy_unsafe_links = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->preserve_hard_links = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->preserve_acls = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->preserve_xattrs = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->preserve_devices = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->preserve_sparse = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->update = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->inplace = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->append = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->append_verify = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->delete_excluded = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->delete_after = tmp;
-  if (!receive_n_data(file_descriptor, &config->max_delete, sizeof(config->max_delete)))
-    goto error;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->relative = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->prune_empty_dirs = tmp;
-  config->temp_dir = receive_str(file_descriptor);
-  if (config->temp_dir == NULL)
-    goto error;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->partial = tmp;
-  config->partial_dir = receive_str(file_descriptor);
-  if (config->partial_dir == NULL)
-    goto error;
-  config->suffix = receive_str(file_descriptor);
-  if (config->suffix == NULL)
-    goto error;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->delete_before = tmp;
-  if (!receive_int(file_descriptor, &tmp))
-    goto error;
-  config->checksum = tmp;
-  config->compress_choice = receive_str(file_descriptor);
-  if (config->compress_choice == NULL)
+  if (!receive_core_fields(file_descriptor, config) ||
+      !receive_delta_fields(file_descriptor, config) ||
+      !receive_file_options(file_descriptor, config) ||
+      !receive_selection_options(file_descriptor, config) ||
+      !receive_resume_options(file_descriptor, config))
     goto error;
   if (config->compress_choice[0] != '\0' && strcmp(config->compress_choice, "zstd") != 0 &&
       strcmp(config->compress_choice, "none") != 0) {
-    fprintf(stderr, "Unsupported compression choice: %s\n", config->compress_choice);
+    char* escaped_choice = output_escape(config->compress_choice, config->eight_bit_output);
+    fprintf(stderr, "Unsupported compression choice: %s\n",
+            escaped_choice ? escaped_choice : "<allocation failed>");
+    free(escaped_choice);
+    send_status(file_descriptor, STATUS_ERROR);
+    goto error;
+  }
+  if (!validate_received_config(config)) {
+    fprintf(stderr, "Invalid configuration received from client\n");
     send_status(file_descriptor, STATUS_ERROR);
     goto error;
   }
@@ -445,15 +476,6 @@ Config* config_receive(int file_descriptor) {
   return config;
 
 error:
-  free(config->version);
-  free(config->send_directory);
-  free(config->receive_root_directory);
-  free(config->server_host);
-  free(config->backup_dir);
-  free(config->temp_dir);
-  free(config->partial_dir);
-  free(config->suffix);
-  free(config->compress_choice);
-  free(config);
+  config_delete(config);
   return NULL;
 }

src/shared/config.h

@@ -18,10 +18,14 @@ typedef struct Config {
   bool use_compression;
   bool use_sendfile;
   bool use_metadata;
+  bool use_executability;
+  bool metadata_explicitly_disabled;
   bool show_progress;
   bool dry_run;
+  bool remove_source_files;
   bool use_delete;
   int compression_level;
+  int compression_threads;
   unsigned long long chunk_size;
   int ssh_port;
   TransportType transport;
@@ -33,8 +37,13 @@ typedef struct Config {
   int include_count;
   unsigned long long max_size;
   unsigned long long min_size;
+  unsigned long long max_alloc;
   bool use_incremental;
+  bool ignore_times;
+  bool size_only;
   bool use_delta;
+  bool whole_file;
+  int modify_window;
   uint32_t delta_block_size;
   unsigned long long delta_max_file_size;
   bool use_tls;
@@ -74,10 +83,14 @@ typedef struct Config {
   int debug_level;
   bool list_only;
   bool human_readable;
+  bool eight_bit_output;
 
   // Issue #127: Transfer modes
+  bool existing;
+  bool ignore_existing;
   bool update;
   bool inplace;
+  bool use_fsync;
   bool append;
   bool append_verify;
 
@@ -96,6 +109,7 @@ typedef struct Config {
   // Issue #130: Remote shell/connection options
   char* rsh_command;
   char* rsync_path;
+  bool old_args;
   char* temp_dir;
   char* compare_dest;
   char* copy_dest;
@@ -126,16 +140,21 @@ typedef struct Config {
 
   // PR #184: Compression algorithm negotiation
   char* compress_choice;
+  char* chmod_spec;
+
+  char** skip_compress_suffixes;
+  int skip_compress_count;
+  bool skip_compress_set;
 } Config;
 
-#define PROTOCOL_VERSION "2.2.0"
+#define PROTOCOL_VERSION "2.4.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)
 
 Config* config_create(void);
 void config_delete(Config* config);
 bool config_send(int file_descriptor, const Config* config);
 Config* config_receive(int file_descriptor);
-bool is_remote_dest(const char* s);
+bool config_is_remote_dest(const char* s);
 void config_parse_ssh_dest(Config* config);
 
 #endif

src/shared/data.c

@@ -1,11 +1,12 @@
 #include "data.h"
 #include "log.h"
+#include "protocol.h"
 #include <stdlib.h>
 
 Data* data_create_empty(size_t data_size) {
   /* malloc(0) is UB; allocate at least 1 byte but preserve requested size */
   size_t alloc_size = data_size > 0 ? data_size : 1;
-  void* data = malloc(alloc_size);
+  void* data = protocol_alloc(alloc_size);
   if (data == NULL) {
     log_message(LOG_LEVEL_ERROR, "Could not allocate memory for empty data");
     return NULL;
@@ -14,18 +15,19 @@ Data* data_create_empty(size_t data_size) {
 }
 
 Data* data_create_reserve(size_t size) {
-  Data* d = malloc(sizeof(Data));
+  Data* d = protocol_alloc(sizeof(Data));
   if (d == NULL) {
     log_message(LOG_LEVEL_ERROR, "Could not allocate memory for data");
     return NULL;
   }
   d->data = NULL;
   d->size = size;
+  d->protocol_charge = 0;
   return d;
 }
 
 Data* data_create(void* data, size_t data_size) {
-  Data* new_data = malloc(sizeof(Data));
+  Data* new_data = protocol_alloc(sizeof(Data));
   if (new_data == NULL) {
     log_message(LOG_LEVEL_ERROR, "Could not allocate memory for data");
     free(data);
@@ -33,12 +35,15 @@ Data* data_create(void* data, size_t data_size) {
   }
   new_data->data = data;
   new_data->size = data_size;
+  new_data->protocol_charge = 0;
   return new_data;
 }
 
 void data_destroy(Data* data) {
   if (data == NULL)
     return;
+  if (data->protocol_charge != 0)
+    protocol_release_memory(data->protocol_charge);
   free(data->data);
   free(data);
 }

src/shared/data.h

@@ -6,11 +6,14 @@
 typedef struct {
   void* data;
   size_t size;
+  /* Non-zero only for a buffer charged to the protocol connection budget. */
+  size_t protocol_charge;
 } Data;
 
 Data* data_create_empty(size_t data_size);
 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);
 
 #endif

src/shared/delta.c

@@ -1,6 +1,8 @@
 #include "delta.h"
 #include "log.h"
+#include "protocol.h"
 #include <stdint.h>
+#include <limits.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -36,16 +38,24 @@ DeltaSignature* delta_signature_create(const void* old_file_data, uint64_t old_f
   if (old_file_data == NULL || old_file_size == 0 || block_size == 0)
     return NULL;
 
+  if (old_file_size > DELTA_MAX_FILE_SIZE || block_size > DELTA_BLOCK_SIZE_MAX ||
+      old_file_size > UINT32_MAX * (uint64_t)block_size)
+    return NULL;
+
   uint32_t block_count = (uint32_t)((old_file_size + block_size - 1) / block_size);
 
-  DeltaSignature* sig = malloc(sizeof(DeltaSignature));
+  DeltaSignature* sig = protocol_alloc(sizeof(DeltaSignature));
   if (!sig)
     return NULL;
 
   sig->file_size = old_file_size;
   sig->block_size = block_size;
   sig->block_count = block_count;
-  sig->blocks = malloc(block_count * sizeof(DeltaBlockSig));
+  if (block_count == 0) {
+    free(sig);
+    return NULL;
+  }
+  sig->blocks = protocol_alloc((size_t)block_count * sizeof(DeltaBlockSig));
   if (!sig->blocks) {
     free(sig);
     return NULL;
@@ -67,10 +77,13 @@ Data* delta_signature_serialize(const DeltaSignature* sig) {
   if (!sig)
     return NULL;
 
-  uint64_t total = sizeof(uint64_t) + sizeof(uint32_t) + sizeof(uint32_t) +
-                   (uint64_t)sig->block_count * (sizeof(uint32_t) + sizeof(uint32_t));
+  uint64_t block_bytes = (uint64_t)sig->block_count * (sizeof(uint32_t) + sizeof(uint32_t));
+  uint64_t total = sizeof(uint64_t) + sizeof(uint32_t) + sizeof(uint32_t) + block_bytes;
+  if (block_bytes > UINT64_MAX - (sizeof(uint64_t) + sizeof(uint32_t) + sizeof(uint32_t)) ||
+      total > SIZE_MAX)
+    return NULL;
 
-  uint8_t* buf = malloc((size_t)total);
+  uint8_t* buf = protocol_alloc((size_t)total);
   if (!buf)
     return NULL;
 
@@ -99,7 +112,7 @@ DeltaSignature* delta_signature_deserialize(const Data* data) {
   const uint8_t* buf = (const uint8_t*)data->data;
   size_t pos = 0;
 
-  DeltaSignature* sig = malloc(sizeof(DeltaSignature));
+  DeltaSignature* sig = protocol_alloc(sizeof(DeltaSignature));
   if (!sig)
     return NULL;
 
@@ -118,6 +131,13 @@ DeltaSignature* delta_signature_deserialize(const Data* data) {
     return NULL;
   }
 
+  if (sig->block_size == 0 || sig->block_size > DELTA_BLOCK_SIZE_MAX ||
+      sig->file_size > DELTA_MAX_FILE_SIZE || sig->file_size == 0 ||
+      (sig->file_size + sig->block_size - 1) / sig->block_size != sig->block_count) {
+    free(sig);
+    return NULL;
+  }
+
   uint64_t expected = sizeof(uint64_t) + sizeof(uint32_t) + sizeof(uint32_t) +
                       (uint64_t)sig->block_count * (sizeof(uint32_t) + sizeof(uint32_t));
   if (data->size < expected) {
@@ -130,7 +150,7 @@ DeltaSignature* delta_signature_deserialize(const Data* data) {
     free(sig);
     return NULL;
   }
-  sig->blocks = malloc((size_t)blocks_size);
+  sig->blocks = protocol_alloc((size_t)blocks_size);
   if (!sig->blocks) {
     free(sig);
     return NULL;
@@ -156,8 +176,10 @@ void delta_signature_destroy(DeltaSignature* sig) {
 static bool ensure_capacity(DeltaInstruction** instrs, uint32_t* capacity, uint32_t count) {
   if (count < *capacity)
     return true;
+  if (*capacity > MAX_DELTA_INSTRUCTIONS / 2)
+    return false;
   uint32_t new_cap = *capacity * 2;
-  DeltaInstruction* tmp = realloc(*instrs, new_cap * sizeof(DeltaInstruction));
+  DeltaInstruction* tmp = protocol_realloc(*instrs, (size_t)new_cap * sizeof(DeltaInstruction));
   if (!tmp)
     return false;
   *instrs = tmp;
@@ -169,10 +191,12 @@ static bool flush_literal(DeltaInstruction** instrs, uint32_t* capacity, uint32_
                           const uint8_t* data, uint64_t start, uint64_t end) {
   if (start >= end)
     return true;
+  if (end - start > UINT32_MAX || *count >= MAX_DELTA_INSTRUCTIONS)
+    return false;
   uint32_t lit_len = (uint32_t)(end - start);
   if (!ensure_capacity(instrs, capacity, *count))
     return false;
-  uint8_t* lit_data = malloc(lit_len);
+  uint8_t* lit_data = protocol_alloc(lit_len);
   if (!lit_data)
     return false;
   memcpy(lit_data, data + start, lit_len);
@@ -183,16 +207,26 @@ static bool flush_literal(DeltaInstruction** instrs, uint32_t* capacity, uint32_
   return true;
 }
 
+static void free_instructions(DeltaInstruction* instrs, uint32_t count) {
+  if (!instrs)
+    return;
+  for (uint32_t i = 0; i < count; i++)
+    if (instrs[i].type == DELTA_INSTR_LITERAL)
+      free(instrs[i].literal.data);
+  free(instrs);
+}
+
 Delta* delta_compute(const void* new_file_data, uint64_t new_file_size, const DeltaSignature* sig,
                      uint32_t block_size) {
-  if (!new_file_data || !sig || new_file_size == 0 || block_size == 0)
+  if (!new_file_data || !sig || !sig->blocks || new_file_size == 0 || block_size == 0 ||
+      block_size > DELTA_BLOCK_SIZE_MAX || sig->block_size != block_size)
     return NULL;
 
   const uint8_t* new_data = (const uint8_t*)new_file_data;
 
   uint32_t capacity = 64;
   uint32_t count = 0;
-  DeltaInstruction* instrs = malloc(capacity * sizeof(DeltaInstruction));
+  DeltaInstruction* instrs = protocol_alloc((size_t)capacity * sizeof(DeltaInstruction));
   if (!instrs)
     return NULL;
 
@@ -236,14 +270,14 @@ Delta* delta_compute(const void* new_file_data, uint64_t new_file_size, const De
         if (xxh == sig->blocks[j].xxhash) {
           if (has_literal) {
             if (!flush_literal(&instrs, &capacity, &count, new_data, literal_start, i)) {
-              free(instrs);
+              free_instructions(instrs, count);
               return NULL;
             }
             has_literal = false;
           }
 
           if (!ensure_capacity(&instrs, &capacity, count)) {
-            free(instrs);
+            free_instructions(instrs, count);
             return NULL;
           }
           instrs[count].type = DELTA_INSTR_BLOCK_MATCH;
@@ -271,18 +305,14 @@ Delta* delta_compute(const void* new_file_data, uint64_t new_file_size, const De
 
   if (has_literal) {
     if (!flush_literal(&instrs, &capacity, &count, new_data, literal_start, new_file_size)) {
-      free(instrs);
+      free_instructions(instrs, count);
       return NULL;
     }
   }
 
-  Delta* delta = malloc(sizeof(Delta));
+  Delta* delta = protocol_alloc(sizeof(Delta));
   if (!delta) {
-    for (uint32_t k = 0; k < count; k++) {
-      if (instrs[k].type == DELTA_INSTR_LITERAL)
-        free(instrs[k].literal.data);
-    }
-    free(instrs);
+    free_instructions(instrs, count);
     return NULL;
   }
 
@@ -292,11 +322,24 @@ Delta* delta_compute(const void* new_file_data, uint64_t new_file_size, const De
   delta->delta_size = 0;
 
   for (uint32_t k = 0; k < count; k++) {
+    if (delta->delta_size == UINT64_MAX) {
+      delta_destroy(delta);
+      return NULL;
+    }
     delta->delta_size += 1;
     if (instrs[k].type == DELTA_INSTR_BLOCK_MATCH) {
+      if (delta->delta_size > UINT64_MAX - sizeof(uint32_t) * 3) {
+        delta_destroy(delta);
+        return NULL;
+      }
       delta->delta_size += sizeof(uint32_t) * 3;
     } else {
-      delta->delta_size += sizeof(uint32_t) + instrs[k].literal.length;
+      uint64_t extra = sizeof(uint32_t) + instrs[k].literal.length;
+      if (delta->delta_size > UINT64_MAX - extra) {
+        delta_destroy(delta);
+        return NULL;
+      }
+      delta->delta_size += extra;
     }
   }
 
@@ -307,8 +350,13 @@ Data* delta_serialize(const Delta* delta) {
   if (!delta)
     return NULL;
 
-  uint64_t total = sizeof(uint64_t) + sizeof(uint32_t) + delta->delta_size;
-  uint8_t* buf = malloc((size_t)total);
+  if (delta->instruction_count > 0 && !delta->instructions)
+    return NULL;
+  uint64_t header_size = sizeof(uint64_t) + sizeof(uint32_t);
+  if (delta->delta_size > UINT64_MAX - header_size || header_size + delta->delta_size > SIZE_MAX)
+    return NULL;
+  uint64_t total = header_size + delta->delta_size;
+  uint8_t* buf = protocol_alloc((size_t)total);
   if (!buf)
     return NULL;
 
@@ -348,7 +396,7 @@ Delta* delta_deserialize(const Data* data) {
   const uint8_t* buf = (const uint8_t*)data->data;
   size_t pos = 0;
 
-  Delta* delta = malloc(sizeof(Delta));
+  Delta* delta = protocol_alloc(sizeof(Delta));
   if (!delta)
     return NULL;
 
@@ -365,8 +413,11 @@ Delta* delta_deserialize(const Data* data) {
     return NULL;
   }
 
-  delta->instructions = malloc(delta->instruction_count * sizeof(DeltaInstruction));
-  if (!delta->instructions) {
+  delta->instructions =
+      delta->instruction_count == 0
+          ? NULL
+          : protocol_alloc((size_t)delta->instruction_count * sizeof(DeltaInstruction));
+  if (delta->instruction_count > 0 && !delta->instructions) {
     free(delta);
     return NULL;
   }
@@ -375,11 +426,7 @@ Delta* delta_deserialize(const Data* data) {
 
   for (uint32_t i = 0; i < delta->instruction_count; i++) {
     if (pos >= data->size) {
-      for (uint32_t k = 0; k < i; k++) {
-        if (delta->instructions[k].type == DELTA_INSTR_LITERAL)
-          free(delta->instructions[k].literal.data);
-      }
-      free(delta->instructions);
+      free_instructions(delta->instructions, i);
       free(delta);
       return NULL;
     }
@@ -391,12 +438,8 @@ Delta* delta_deserialize(const Data* data) {
     delta->delta_size += 1;
 
     if (type == DELTA_OP_BLOCK_MATCH) {
-      if (pos + sizeof(uint32_t) * 3 > data->size) {
-        for (uint32_t k = 0; k < i; k++) {
-          if (delta->instructions[k].type == DELTA_INSTR_LITERAL)
-            free(delta->instructions[k].literal.data);
-        }
-        free(delta->instructions);
+      if (data->size - pos < sizeof(uint32_t) * 3) {
+        free_instructions(delta->instructions, i);
         free(delta);
         return NULL;
       }
@@ -409,12 +452,8 @@ Delta* delta_deserialize(const Data* data) {
       pos += sizeof(uint32_t);
       delta->delta_size += sizeof(uint32_t) * 3;
     } else if (type == DELTA_OP_LITERAL) {
-      if (pos + sizeof(uint32_t) > data->size) {
-        for (uint32_t k = 0; k < i; k++) {
-          if (delta->instructions[k].type == DELTA_INSTR_LITERAL)
-            free(delta->instructions[k].literal.data);
-        }
-        free(delta->instructions);
+      if (data->size - pos < sizeof(uint32_t)) {
+        free_instructions(delta->instructions, i);
         free(delta);
         return NULL;
       }
@@ -423,23 +462,15 @@ Delta* delta_deserialize(const Data* data) {
       pos += sizeof(uint32_t);
 
       uint32_t lit_len = delta->instructions[i].literal.length;
-      if (pos + lit_len > data->size) {
-        for (uint32_t k = 0; k < i; k++) {
-          if (delta->instructions[k].type == DELTA_INSTR_LITERAL)
-            free(delta->instructions[k].literal.data);
-        }
-        free(delta->instructions);
+      if (lit_len > data->size - pos) {
+        free_instructions(delta->instructions, i);
         free(delta);
         return NULL;
       }
-      delta->instructions[i].literal.data = malloc(lit_len);
+      delta->instructions[i].literal.data = protocol_alloc(lit_len ? lit_len : 1);
       if (!delta->instructions[i].literal.data) {
         log_message(LOG_LEVEL_ERROR, "Failed to allocate %u bytes for literal data", lit_len);
-        for (uint32_t k = 0; k < i; k++) {
-          if (delta->instructions[k].type == DELTA_INSTR_LITERAL)
-            free(delta->instructions[k].literal.data);
-        }
-        free(delta->instructions);
+        free_instructions(delta->instructions, i);
         free(delta);
         return NULL;
       }
@@ -447,11 +478,7 @@ Delta* delta_deserialize(const Data* data) {
       pos += lit_len;
       delta->delta_size += sizeof(uint32_t) + lit_len;
     } else {
-      for (uint32_t k = 0; k < i; k++) {
-        if (delta->instructions[k].type == DELTA_INSTR_LITERAL)
-          free(delta->instructions[k].literal.data);
-      }
-      free(delta->instructions);
+      free_instructions(delta->instructions, i);
       free(delta);
       return NULL;
     }
@@ -463,10 +490,11 @@ Delta* delta_deserialize(const Data* data) {
 void* delta_apply(const void* old_data, uint64_t old_size, const Delta* delta,
                   uint32_t block_size) {
   if (!old_data || !delta || (delta->new_file_size > 0 && delta->instructions == NULL) ||
-      (delta->instruction_count > 0 && block_size == 0))
+      (delta->instruction_count > 0 && block_size == 0) ||
+      delta->new_file_size > DELTA_MAX_FILE_SIZE || delta->new_file_size > SIZE_MAX)
     return NULL;
 
-  void* output = malloc((size_t)delta->new_file_size);
+  void* output = protocol_alloc(delta->new_file_size ? (size_t)delta->new_file_size : 1);
   if (!output)
     return NULL;
 
@@ -491,7 +519,7 @@ void* delta_apply(const void* old_data, uint64_t old_size, const Delta* delta,
       }
       memcpy(out + out_pos, old + src_offset, len);
       out_pos += len;
-    } else {
+    } else if (delta->instructions[i].type == DELTA_INSTR_LITERAL) {
       uint32_t len = delta->instructions[i].literal.length;
       if (out_pos > delta->new_file_size || (uint64_t)len > delta->new_file_size - out_pos) {
         free(output);
@@ -499,6 +527,9 @@ void* delta_apply(const void* old_data, uint64_t old_size, const Delta* delta,
       }
       memcpy(out + out_pos, delta->instructions[i].literal.data, len);
       out_pos += len;
+    } else {
+      free(output);
+      return NULL;
     }
   }
 
@@ -534,7 +565,7 @@ bool delta_should_attempt(uint64_t old_size, uint64_t new_size, uint64_t max_fil
 }
 
 bool delta_is_worthwhile(const Delta* delta, uint64_t new_file_size) {
-  if (!delta || delta->instruction_count == 0)
+  if (!delta || delta->instruction_count == 0 || new_file_size == 0)
     return false;
 
   bool has_match = false;

src/shared/file.h

@@ -1,45 +1,51 @@
 #ifndef FILE_H
 #define FILE_H
 
-#include "config.h"
-#include "data.h"
+#include "file_send.h"
+#include "file_receive.h"
+#include "file_types.h"
 #include <stdbool.h>
+#include <stdint.h>
 #include <sys/stat.h>
 
-typedef enum { FILE_TYPE_REGULAR, FILE_TYPE_SYMLINK, FILE_TYPE_DIR } FileType;
-
-typedef struct {
-  mode_t mode;
-  uid_t uid;
-  gid_t gid;
-  time_t mtime_sec;
-  long mtime_nsec;
-} FileMetadata;
-
-typedef struct {
-  char* path;
-  Data* data;
-  FileMetadata* metadata;
-  bool skip;
-} File;
+/* File/FileMetadata lifecycle, local disk helpers, and secure filesystem
+   primitives shared by the send/receive pipelines. */
 
 File* file_create(const char* path);
 void file_destroy(void* item);
 bool file_load_data(File* file);
 bool file_checksum(File* file, uint64_t* checksum);
-File* file_receive(const Config* config, int file_descriptor);
-bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
-                            int compression_level, bool send_path);
-bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int compression_level,
-                        bool send_path);
 size_t file_content_to_buffer(File* file);
 FileMetadata* file_metadata_create(const struct stat* stats);
 void file_metadata_destroy(void* metadata);
-bool to_disk(const char* path, const void* data, unsigned long long data_size, bool inplace,
-             bool sparse);
-bool file_save_to_disk(const char* root_directory, const File* file, const Config* config);
-void file_set_authorized_root(int fd, const char* canonical_path);
-File* receive_incremental_check(int fd, const Config* config, bool* skipped);
-int receive_manifest(int fd, const Config* config, int* next_status);
+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);
+
+/* Secure path/filesystem primitives (symlink-safe, O_NOFOLLOW, root-confined). */
+bool file_path_exists_secure(const char* path);
+bool file_stat_secure(const char* path, struct stat* st);
+bool file_destination_is_newer_secure(const char* path, const FileMetadata* metadata);
+int file_open_secure_parent(const char* path, char** leaf_out, bool create_dirs);
+bool file_ensure_directory_secure(const char* path);
+bool file_rename_secure(const char* old_path, const char* new_path);
+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);
+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);
+/* 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);
+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);
 
 #endif

src/shared/file_receive.c

@@ -0,0 +1,655 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <libgen.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "array_list.h"
+#include "chmod.h"
+#include "compression.h"
+#include "config.h"
+#include "data.h"
+#include "delta.h"
+#include "file.h"
+#include "log.h"
+#include "metadata.h"
+#include "protocol.h"
+#include "utils.h"
+
+#define MAX_SERVER_DELETE_COUNT 100000U
+#define MAX_FILE_DATA_SIZE MAX_RECEIVE_FILE_SIZE
+
+bool file_save_to_disk(const char* root_directory, const File* file, const Config* config) {
+  /* Backups are incompatible with ignore-existing: moving the entry first
+     would make a concurrent no-replace commit overwrite its old name. */
+  bool backup_enabled = config && config->backup && !config->ignore_existing;
+  bool inplace = config && config->inplace;
+  bool sparse = config && config->preserve_sparse;
+  bool preserve_executability = config && config->use_executability;
+  const char* backup_suffix = (config && config->suffix) ? config->suffix : "~";
+  const char* backup_dir = (config && config->backup_dir) ? config->backup_dir : NULL;
+  const char* partial_dir = (config && config->partial_dir) ? config->partial_dir : NULL;
+  char *confined_backup = NULL, *confined_partial = NULL, *disk_path = NULL;
+  char* destination_path = NULL;
+  char *backup_path = NULL, *parent_copy = NULL;
+
+  if (!file || !file->path || !file->data || (file->data->size != 0 && !file->data->data) ||
+      has_path_traversal(file->path) ||
+      (backup_enabled &&
+       (!backup_suffix || backup_suffix[0] == '\0' || strchr(backup_suffix, '/') != NULL ||
+        strcmp(backup_suffix, ".") == 0 || strcmp(backup_suffix, "..") == 0))) {
+    log_message(LOG_LEVEL_ERROR, "Invalid file or path received");
+    return false;
+  }
+
+  /* These options arrive from the client.  They are names below the server
+     root, never independent filesystem roots. */
+  if ((backup_dir && (backup_dir[0] == '/' || has_path_traversal(backup_dir))) ||
+      (partial_dir && (partial_dir[0] == '/' || has_path_traversal(partial_dir))))
+    return false;
+  if (backup_dir && !(confined_backup = path_cat(root_directory, backup_dir)))
+    return false;
+  if (partial_dir && !(confined_partial = path_cat(root_directory, partial_dir))) {
+    free(confined_backup);
+    return false;
+  }
+
+  const char* actual_root =
+      (partial_dir && config && config->partial) ? confined_partial : root_directory;
+  destination_path = path_cat(root_directory, file->path);
+  disk_path = path_cat(actual_root, file->path);
+  if (destination_path == NULL || disk_path == NULL) {
+    free(confined_backup);
+    free(confined_partial);
+    free(destination_path);
+    free(disk_path);
+    return false;
+  }
+
+  /* --existing checks the final destination, not a temporary partial path. */
+  if (config && config->existing && !file_path_exists_secure(destination_path)) {
+    free(confined_backup);
+    free(confined_partial);
+    free(destination_path);
+    free(disk_path);
+    return true;
+  }
+
+  /* --ignore-existing checks the final destination before partial files or
+     overwrite policies can modify it. */
+  if (config && config->ignore_existing) {
+    bool exists = file_path_exists_secure(destination_path);
+    if (exists) {
+      free(confined_backup);
+      free(confined_partial);
+      free(destination_path);
+      free(disk_path);
+      return true;
+    }
+  }
+  free(destination_path);
+  destination_path = NULL;
+
+  /* --update is receiver-side policy: never replace a newer destination.
+     The secure stat does not require read permission on the destination. */
+  if (config && config->update && file_destination_is_newer_secure(disk_path, file->metadata)) {
+    free(confined_backup);
+    free(confined_partial);
+    free(disk_path);
+    return true;
+  }
+
+  if (backup_enabled) {
+    struct stat backup_stat;
+    if (file_stat_secure(disk_path, &backup_stat)) {
+      if (backup_dir) {
+        backup_path = path_cat(confined_backup, file->path);
+      } else {
+        size_t path_len = strlen(disk_path);
+        size_t suffix_len = strlen(backup_suffix);
+        if (path_len > SIZE_MAX - suffix_len - 1)
+          goto fail;
+        backup_path = malloc(path_len + suffix_len + 1);
+        if (backup_path) {
+          memcpy(backup_path, disk_path, path_len);
+          memcpy(backup_path + path_len, backup_suffix, suffix_len + 1);
+        }
+      }
+      if (!backup_path)
+        goto fail;
+      parent_copy = str_dup(backup_path);
+      if (!parent_copy || !file_ensure_directory_secure(dirname(parent_copy)))
+        goto fail;
+      free(parent_copy);
+      parent_copy = NULL;
+      if (!file_rename_secure(disk_path, backup_path))
+        goto fail;
+      free(backup_path);
+      backup_path = NULL;
+    }
+  }
+
+  FileMetadata adjusted_metadata;
+  const FileMetadata* metadata = file->metadata;
+  if (metadata && config && config->chmod_spec && *config->chmod_spec) {
+    adjusted_metadata = *metadata;
+    if (!chmod_apply(adjusted_metadata.mode, config->chmod_spec, &adjusted_metadata.mode))
+      goto fail;
+    metadata = &adjusted_metadata;
+  }
+  bool ok = config && config->ignore_existing
+                ? file_to_disk_secure_no_replace(disk_path, file->data->data, file->data->size,
+                                                 sparse, metadata, preserve_executability)
+            : config && config->update
+                ? file_to_disk_secure_update(disk_path, file->data->data, file->data->size, inplace,
+                                             sparse, metadata, preserve_executability)
+                : file_to_disk_secure_with_fsync(disk_path, file->data->data, file->data->size,
+                                                 inplace, sparse, metadata, preserve_executability,
+                                                 config && config->use_fsync);
+  free(parent_copy);
+  free(backup_path);
+  free(confined_backup);
+  free(confined_partial);
+  free(destination_path);
+  free(disk_path);
+  return ok;
+
+fail:
+  free(parent_copy);
+  free(backup_path);
+  free(confined_backup);
+  free(confined_partial);
+  free(destination_path);
+  free(disk_path);
+  return false;
+}
+
+static File* receive_delta_file(int fd, const Config* config, const char* check_path,
+                                void* old_data, unsigned long long old_size, bool* failed) {
+  if (!old_data)
+    return NULL;
+
+  DeltaSignature* sig = delta_signature_create(old_data, old_size, config->delta_block_size);
+  if (!sig) {
+    free(old_data);
+    *failed = true;
+    return NULL;
+  }
+
+  Data* sig_data = delta_signature_serialize(sig);
+  if (!sig_data) {
+    delta_signature_destroy(sig);
+    free(old_data);
+    *failed = true;
+    return NULL;
+  }
+
+  bool sig_sent = send_status(fd, STATUS_DELTA_SIGNATURE) && send_data(fd, sig_data);
+  data_destroy(sig_data);
+
+  if (!sig_sent) {
+    delta_signature_destroy(sig);
+    free(old_data);
+    *failed = true;
+    return NULL;
+  }
+
+  Status resp;
+  if (!receive_status(fd, &resp)) {
+    delta_signature_destroy(sig);
+    free(old_data);
+    *failed = true;
+    return NULL;
+  }
+
+  if (resp == STATUS_DELTA_DATA) {
+    Data* delta_data = receive_data_limited(fd, MAX_RECEIVE_FILE_SIZE);
+    if (!delta_data) {
+      delta_signature_destroy(sig);
+      free(old_data);
+      *failed = true;
+      return NULL;
+    }
+
+    Data* raw_delta = delta_data;
+    if (config->use_compression &&
+        !compression_should_skip_with_suffixes(
+            check_path, config->skip_compress_suffixes,
+            config->skip_compress_set ? config->skip_compress_count : -1)) {
+      raw_delta = data_decompress_limited(delta_data, MAX_RECEIVE_FILE_SIZE);
+      data_destroy(delta_data);
+      if (!raw_delta) {
+        free(old_data);
+        delta_signature_destroy(sig);
+        *failed = true;
+        return NULL;
+      }
+    }
+
+    Delta* delta = delta_deserialize(raw_delta);
+    data_destroy(raw_delta);
+    if (!delta) {
+      free(old_data);
+      delta_signature_destroy(sig);
+      *failed = true;
+      return NULL;
+    }
+
+    uint64_t new_size = delta->new_file_size;
+    if (new_size > MAX_RECEIVE_FILE_SIZE || new_size > SIZE_MAX) {
+      delta_destroy(delta);
+      free(old_data);
+      delta_signature_destroy(sig);
+      send_status(fd, STATUS_ERROR);
+      return NULL;
+    }
+    void* new_data = delta_apply(old_data, old_size, delta, config->delta_block_size);
+    delta_destroy(delta);
+
+    if (!new_data) {
+      free(old_data);
+      delta_signature_destroy(sig);
+      *failed = true;
+      return NULL;
+    }
+
+    File* file = file_create(check_path);
+    if (!file) {
+      free(new_data);
+      free(old_data);
+      delta_signature_destroy(sig);
+      *failed = true;
+      return NULL;
+    }
+
+    if (config->use_metadata) {
+      int meta_ok = 1;
+      file->metadata = metadata_receive(fd, &meta_ok);
+      if (!meta_ok) {
+        file_destroy(file);
+        free(new_data);
+        free(old_data);
+        delta_signature_destroy(sig);
+        *failed = true;
+        return NULL;
+      }
+    }
+
+    Data* replacement = data_create(new_data, (size_t)new_size);
+    if (replacement == NULL) {
+      file_destroy(file);
+      free(old_data);
+      delta_signature_destroy(sig);
+      send_status(fd, STATUS_ERROR);
+      return NULL;
+    }
+    data_destroy(file->data);
+    file->data = replacement;
+
+    free(old_data);
+    delta_signature_destroy(sig);
+    return file;
+  }
+
+  if (resp == STATUS_NEXT) {
+    delta_signature_destroy(sig);
+    free(old_data);
+
+    File* file = file_create(check_path);
+    if (!file) {
+      *failed = true;
+      return NULL;
+    }
+
+    if (config->use_metadata) {
+      int meta_ok = 1;
+      file->metadata = metadata_receive(fd, &meta_ok);
+      if (!meta_ok) {
+        file_destroy(file);
+        *failed = true;
+        return NULL;
+      }
+    }
+
+    Data* file_data = receive_data_limited(fd, MAX_RECEIVE_FILE_SIZE);
+    if (file_data == NULL) {
+      file_destroy(file);
+      *failed = true;
+      return NULL;
+    }
+
+    if (config->use_compression &&
+        !compression_should_skip_with_suffixes(
+            file->path, config->skip_compress_suffixes,
+            config->skip_compress_set ? config->skip_compress_count : -1)) {
+      Data* uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_FILE_SIZE);
+      data_destroy(file_data);
+      if (uncompressed == NULL) {
+        file_destroy(file);
+        *failed = true;
+        return NULL;
+      }
+      if (uncompressed->size > MAX_FILE_DATA_SIZE) {
+        data_destroy(uncompressed);
+        file_destroy(file);
+        send_status(fd, STATUS_ERROR);
+        return NULL;
+      }
+      file_data = uncompressed;
+    }
+
+    data_destroy(file->data);
+    file->data = file_data;
+    return file;
+  }
+
+  delta_signature_destroy(sig);
+  free(old_data);
+  send_status(fd, STATUS_ERROR);
+  *failed = true;
+  return NULL;
+}
+
+File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
+  if (!config || !skipped) {
+    send_status(fd, STATUS_ERROR);
+    return NULL;
+  }
+  *skipped = false;
+  char* check_path = receive_str(fd);
+  if (check_path == NULL) {
+    return NULL;
+  }
+
+  unsigned long long check_size;
+  long long check_mtime;
+  long long check_mtime_nsec;
+  uint64_t check_checksum = 0;
+  if (!receive_n_data(fd, &check_size, sizeof(check_size)) ||
+      !receive_n_data(fd, &check_mtime, sizeof(check_mtime))) {
+    free(check_path);
+    return NULL;
+  }
+  if (!receive_n_data(fd, &check_mtime_nsec, sizeof(check_mtime_nsec)) || check_mtime_nsec < 0 ||
+      check_mtime_nsec >= 1000000000LL) {
+    free(check_path);
+    send_status(fd, STATUS_ERROR);
+    return NULL;
+  }
+  if (config->checksum && !receive_n_data(fd, &check_checksum, sizeof(check_checksum))) {
+    free(check_path);
+    return NULL;
+  }
+
+  if (check_size > MAX_RECEIVE_FILE_SIZE) {
+    free(check_path);
+    send_status(fd, STATUS_ERROR);
+    return NULL;
+  }
+
+  if (has_path_traversal(check_path)) {
+    char* escaped_path = output_escape(check_path, log_get_8_bit_output());
+    log_message(LOG_LEVEL_ERROR, "Path traversal detected: %s",
+                escaped_path ? escaped_path : "<allocation failed>");
+    free(escaped_path);
+    free(check_path);
+    return NULL;
+  }
+
+  char* full_path = path_cat(config->receive_root_directory, check_path);
+  if (!full_path) {
+    free(check_path);
+    send_status(fd, STATUS_ERROR);
+    return NULL;
+  }
+  struct stat st;
+  bool has_old_file = false;
+  int old_fd = -1;
+  char* leaf = NULL;
+  int parent_fd = file_open_secure_parent(full_path, &leaf, false);
+  if (parent_fd >= 0) {
+    old_fd = openat(parent_fd, leaf, O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
+    free(leaf);
+    close(parent_fd);
+    has_old_file = old_fd >= 0 && fstat(old_fd, &st) == 0 && S_ISREG(st.st_mode);
+  }
+  unsigned long long old_size = has_old_file ? (unsigned long long)st.st_size : 0;
+  void* old_data = NULL;
+  if (has_old_file && old_size > 0 && old_size <= MAX_RECEIVE_FILE_SIZE && old_size <= SIZE_MAX) {
+    old_data = protocol_alloc((size_t)old_size);
+    if (old_data) {
+      size_t got = 0;
+      while (got < (size_t)old_size) {
+        ssize_t n = read(old_fd, (char*)old_data + got, (size_t)old_size - got);
+        if (n <= 0) {
+          free(old_data);
+          old_data = NULL;
+          break;
+        }
+        got += (size_t)n;
+      }
+    }
+  }
+  if (old_fd >= 0) {
+    close(old_fd);
+  }
+
+  bool match =
+      !config->ignore_times && has_old_file && (unsigned long long)st.st_size == check_size;
+  if (match && config->checksum) {
+    uint64_t old_checksum = old_size == 0 ? delta_xxhash64("", 0) : 0;
+    if (old_data)
+      old_checksum = delta_xxhash64(old_data, (size_t)old_size);
+    match = (old_size == 0 || old_data) && old_checksum == check_checksum;
+    free(old_data);
+    old_data = NULL;
+  } else if (match && !config->size_only) {
+    long long old_mtime_nsec = 0;
+#ifdef __linux__
+    old_mtime_nsec = st.st_mtim.tv_nsec;
+#endif
+    match = metadata_mtime_matches(st.st_mtime, old_mtime_nsec, (time_t)check_mtime,
+                                   (long)check_mtime_nsec, config->modify_window);
+  }
+
+  if (match) {
+    free(old_data);
+    if (!send_status(fd, STATUS_OK)) {
+      free(full_path);
+      free(check_path);
+      return NULL;
+    }
+    free(full_path);
+    free(check_path);
+    *skipped = true;
+    return NULL;
+  }
+
+  bool try_delta = config->use_delta && !config->whole_file && has_old_file && old_data != NULL &&
+                   delta_should_attempt(old_size, check_size, config->delta_max_file_size);
+
+  if (try_delta) {
+    bool delta_failed = false;
+    File* delta_file =
+        receive_delta_file(fd, config, check_path, old_data, old_size, &delta_failed);
+    old_data = NULL; /* receive_delta_file consumes the snapshot on every path */
+    if (delta_file) {
+      free(full_path);
+      free(check_path);
+      return delta_file;
+    }
+    if (delta_failed) {
+      free(full_path);
+      free(check_path);
+      return NULL;
+    }
+    free(old_data);
+    old_data = NULL;
+    try_delta = false;
+  }
+
+  if (!try_delta) {
+    free(old_data);
+    old_data = NULL;
+    if (!send_status(fd, STATUS_NEXT)) {
+      free(full_path);
+      free(check_path);
+      return NULL;
+    }
+  }
+
+  File* file = file_create(check_path);
+  free(check_path);
+  free(full_path);
+  if (file == NULL) {
+    return NULL;
+  }
+
+  if (config->use_metadata) {
+    int meta_ok = 1;
+    file->metadata = metadata_receive(fd, &meta_ok);
+    if (!meta_ok) {
+      file_destroy(file);
+      return NULL;
+    }
+  }
+
+  Data* file_data = receive_data_limited(fd, MAX_RECEIVE_FILE_SIZE);
+  if (file_data == NULL) {
+    file_destroy(file);
+    return NULL;
+  }
+
+  if (config->use_compression &&
+      !compression_should_skip_with_suffixes(file->path, config->skip_compress_suffixes,
+                                             config->skip_compress_set ? config->skip_compress_count
+                                                                       : -1)) {
+    Data* uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_FILE_SIZE);
+    data_destroy(file_data);
+    if (uncompressed == NULL) {
+      file_destroy(file);
+      return NULL;
+    }
+    if (uncompressed->size > MAX_FILE_DATA_SIZE) {
+      data_destroy(uncompressed);
+      file_destroy(file);
+      send_status(fd, STATUS_ERROR);
+      return NULL;
+    }
+    file_data = uncompressed;
+  }
+
+  data_destroy(file->data);
+  file->data = file_data;
+  return file;
+}
+
+File* file_receive(const Config* config, int file_descriptor) {
+  char* path = receive_str(file_descriptor);
+  if (path == NULL)
+    return NULL;
+  if (path[0] == '\0' || has_path_traversal(path)) {
+    char* escaped_path = output_escape(path, log_get_8_bit_output());
+    log_message(LOG_LEVEL_ERROR, "Invalid received file path: %s",
+                escaped_path ? escaped_path : "<allocation failed>");
+    free(escaped_path);
+    free(path);
+    return NULL;
+  }
+  File* file = file_create(path);
+  free(path);
+  if (file == NULL)
+    return NULL;
+  if (config->use_metadata) {
+    int meta_ok = 1;
+    file->metadata = metadata_receive(file_descriptor, &meta_ok);
+    if (!meta_ok) {
+      file_destroy(file);
+      return NULL;
+    }
+  }
+  Data* file_data = receive_data_limited(file_descriptor, MAX_RECEIVE_FILE_SIZE);
+  if (file_data == NULL) {
+    file_destroy(file);
+    return NULL;
+  }
+  if (config->use_compression &&
+      !compression_should_skip_with_suffixes(file->path, config->skip_compress_suffixes,
+                                             config->skip_compress_set ? config->skip_compress_count
+                                                                       : -1)) {
+    Data* file_data_uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_FILE_SIZE);
+    data_destroy(file_data);
+    if (file_data_uncompressed == NULL) {
+      file_destroy(file);
+      return NULL;
+    }
+    if (file_data_uncompressed->size > MAX_FILE_DATA_SIZE) {
+      data_destroy(file_data_uncompressed);
+      file_destroy(file);
+      return NULL;
+    }
+    file_data = file_data_uncompressed;
+  }
+  data_destroy(file->data);
+  file->data = file_data;
+  return file;
+}
+
+int receive_manifest(int fd, const Config* config, int* next_status) {
+  if (!config) {
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
+  int received_status = STATUS_ERROR;
+  int* status_out = next_status ? next_status : &received_status;
+  int count;
+  if (!receive_int(fd, &count)) {
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
+  if (count < 0 || count > MAX_MANIFEST_ENTRIES) {
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
+  ArrayList* manifest = array_list_create(free);
+  if (!manifest) {
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
+  size_t manifest_bytes = 0;
+  for (int i = 0; i < count; i++) {
+    char* s = receive_str(fd);
+    size_t entry_size = s ? strlen(s) : 0;
+    if (!s || s[0] == '\0' || s[0] == '/' || has_path_traversal(s) ||
+        entry_size > MAX_MANIFEST_BYTES - manifest_bytes ||
+        (manifest_bytes += entry_size) > MAX_MANIFEST_BYTES || !array_list_add(manifest, s)) {
+      free(s);
+      array_list_delete(manifest);
+      send_status(fd, STATUS_ERROR);
+      return -1;
+    }
+  }
+  if (!receive_status(fd, status_out)) {
+    array_list_delete(manifest);
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
+  /* Deletion is a commit operation: never perform it until the sender has
+     completed the manifest frame successfully. */
+  if (*status_out != STATUS_FINISHED || !config->use_delete) {
+    array_list_delete(manifest);
+    if (*status_out != STATUS_FINISHED)
+      send_status(fd, STATUS_ERROR);
+    return *status_out == STATUS_FINISHED ? 0 : -1;
+  }
+  fprintf(stderr, "Deleting files not in manifest...\n");
+  bool deletion_ok =
+      delete_extras_limited(config->receive_root_directory, manifest, MAX_SERVER_DELETE_COUNT);
+  array_list_delete(manifest);
+  if (!deletion_ok)
+    send_status(fd, STATUS_ERROR);
+  return deletion_ok ? 0 : -1;
+}

src/shared/file_receive.h

@@ -0,0 +1,15 @@
+#ifndef FILE_RECEIVE_H
+#define FILE_RECEIVE_H
+
+#include "config.h"
+#include "file_types.h"
+#include <stdbool.h>
+
+/* Server-side file receive/save path. */
+
+File* file_receive(const Config* config, int file_descriptor);
+File* receive_incremental_check(int fd, const Config* config, bool* skipped);
+int receive_manifest(int fd, const Config* config, int* next_status);
+bool file_save_to_disk(const char* root_directory, const File* file, const Config* config);
+
+#endif

src/shared/file_send.c

@@ -0,0 +1,154 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <poll.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/sendfile.h>
+#include <sys/stat.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "compression.h"
+#include "data.h"
+#include "file.h"
+#include "log.h"
+#include "metadata.h"
+#include "protocol.h"
+
+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);
+}
+
+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) {
+  if (!file || !file->path || !file->data || (file->data->size != 0 && !file->data->data))
+    return false;
+  const Data* data_to_send = file->data;
+  Data* compressed_data = NULL;
+  if (compression_level > 0 &&
+      !compression_should_skip_with_suffixes(file->path, skip_suffixes, skip_count)) {
+    compressed_data =
+        data_compress_with_threads(file->data, compression_level, compression_threads);
+    if (compressed_data == NULL) {
+      log_message(LOG_LEVEL_ERROR, "Failed to compress file data");
+      return false;
+    }
+    data_to_send = compressed_data;
+  }
+  if (send_path && !send_str(file_descriptor, file->path)) {
+    data_destroy(compressed_data);
+    return false;
+  }
+  if (use_metadata && !metadata_send(file_descriptor, file->metadata)) {
+    data_destroy(compressed_data);
+    return false;
+  }
+  if (!send_data(file_descriptor, data_to_send)) {
+    data_destroy(compressed_data);
+    return false;
+  }
+  data_destroy(compressed_data);
+  return true;
+}
+
+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);
+}
+
+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) {
+  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);
+
+  if (send_path && !send_str(file_descriptor, file->path))
+    return false;
+  if (use_metadata && !metadata_send(file_descriptor, file->metadata))
+    return false;
+
+  int fd = open(file->path, O_RDONLY);
+  if (fd == -1) {
+    log_perror("Could not open file for sendfile");
+    return false;
+  }
+
+  unsigned long long file_size = file->data->size;
+  struct stat source_stat;
+  if (fstat(fd, &source_stat) != 0 || !S_ISREG(source_stat.st_mode) ||
+      (unsigned long long)source_stat.st_size < file_size) {
+    close(fd);
+    return false;
+  }
+  if (!send_n_data(file_descriptor, &file_size, sizeof(unsigned long long))) {
+    close(fd);
+    return false;
+  }
+
+  /* sendfile cannot encrypt TLS records.  Keep the framing identical but
+     route encrypted transfers through the deadline-aware IO layer. */
+  if (io_get_ssl() != NULL) {
+    unsigned char buffer[64 * 1024];
+    unsigned long long remaining = file_size;
+    bool ok = true;
+    while (remaining > 0) {
+      size_t want = remaining > sizeof(buffer) ? sizeof(buffer) : (size_t)remaining;
+      ssize_t got = read(fd, buffer, want);
+      if (got <= 0 || !send_n_data(file_descriptor, buffer, (size_t)got)) {
+        ok = false;
+        break;
+      }
+      remaining -= (unsigned long long)got;
+    }
+    close(fd);
+    return ok;
+  }
+
+  off_t offset = 0;
+  struct timespec deadline;
+  clock_gettime(CLOCK_MONOTONIC, &deadline);
+  deadline.tv_sec += 60;
+  while ((unsigned long long)offset < file_size) {
+    struct timespec now;
+    clock_gettime(CLOCK_MONOTONIC, &now);
+    long long remaining = (long long)(deadline.tv_sec - now.tv_sec) * 1000LL +
+                          (deadline.tv_nsec - now.tv_nsec) / 1000000LL;
+    if (remaining <= 0) {
+      close(fd);
+      return false;
+    }
+    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);
+      return false;
+    }
+    ssize_t sent = sendfile(file_descriptor, fd, &offset, file_size - offset);
+    if (sent == -1) {
+      if (errno == EAGAIN || errno == EINTR)
+        continue;
+      log_perror("sendfile failed");
+      close(fd);
+      return false;
+    }
+    if (sent == 0) {
+      close(fd);
+      return false;
+    }
+  }
+
+  close(fd);
+  return true;
+}

src/shared/file_send.h

@@ -0,0 +1,21 @@
+#ifndef FILE_SEND_H
+#define FILE_SEND_H
+
+#include "file_types.h"
+#include <stdbool.h>
+
+/* Client-side file send path. */
+
+bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
+                            int compression_level, bool send_path);
+bool file_send_single_calls_with_skip(File* file, int file_descriptor, bool use_metadata,
+                                      int compression_level, bool send_path,
+                                      char* const* skip_suffixes, int skip_count,
+                                      int compression_threads);
+bool 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);
+
+#endif

src/shared/file_store.c

@@ -0,0 +1,198 @@
+#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;
+  unsigned long long done = 0;
+  while (done < size) {
+    ssize_t n = write(fd, p + done, (size_t)(size - done));
+    if (n < 0 && errno == EINTR)
+      continue;
+    if (n <= 0)
+      return false;
+    done += (unsigned long long)n;
+  }
+  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)
+    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);
+      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;
+}

src/shared/file_store.h

@@ -0,0 +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);
+
+#endif

src/shared/file_types.h

@@ -0,0 +1,25 @@
+#ifndef FILE_TYPES_H
+#define FILE_TYPES_H
+
+#include "data.h"
+#include <stdbool.h>
+#include <sys/stat.h>
+
+typedef enum { FILE_TYPE_REGULAR, FILE_TYPE_SYMLINK, FILE_TYPE_DIR } FileType;
+
+typedef struct {
+  mode_t mode;
+  uid_t uid;
+  gid_t gid;
+  time_t mtime_sec;
+  long mtime_nsec;
+} FileMetadata;
+
+typedef struct {
+  char* path;
+  Data* data;
+  FileMetadata* metadata;
+  bool skip;
+} File;
+
+#endif

src/shared/log.c

@@ -1,20 +1,61 @@
 #include "log.h"
+#include <errno.h>
+#include <stdbool.h>
 #include <stdarg.h>
 #include <stdio.h>
+#include <string.h>
 #include <time.h>
 
 static const char* log_level_strings[] = {"DEBUG", "INFO", "WARN", "ERROR"};
 static LogLevel current_log_level = LOG_LEVEL_WARNING;
+static uint32_t current_debug_flags = 0;
+static uint32_t info_flags = 0;
+static bool info_flags_explicit = false;
 static FILE* log_fp = NULL;
+static _Thread_local bool eight_bit_output;
+static LogStderrMode stderr_mode = LOG_STDERR_ERRORS;
 
 void set_log_level(LogLevel level) {
   current_log_level = level;
 }
 
+void set_log_debug_flags(uint32_t flags) {
+  current_debug_flags = flags;
+}
+
+uint32_t get_log_debug_flags(void) {
+  return current_debug_flags;
+}
+
+void set_log_info_flags(uint32_t flags) {
+  info_flags = flags;
+  info_flags_explicit = true;
+}
+
+uint32_t get_log_info_flags(void) {
+  return info_flags;
+}
+
 void log_set_file(FILE* fp) {
   log_fp = fp;
 }
 
+void log_set_8_bit_output(bool enabled) {
+  eight_bit_output = enabled;
+}
+
+bool log_get_8_bit_output(void) {
+  return eight_bit_output;
+}
+
+void log_set_stderr_mode(LogStderrMode mode) {
+  stderr_mode = mode;
+}
+
+LogStderrMode log_get_stderr_mode(void) {
+  return stderr_mode;
+}
+
 static inline void write_message(FILE* dest_io, LogLevel log_level, struct tm t, const char* format,
                                  va_list args) {
   fprintf(dest_io, "%04d-%02d-%02d %02d:%02d:%02d [%s]: ", t.tm_year + 1900, t.tm_mon + 1,
@@ -35,7 +76,7 @@ void log_message(LogLevel log_level, const char* format, ...) {
     return;
 
   FILE* dest_io = stdout;
-  if (log_level == LOG_LEVEL_ERROR) {
+  if (stderr_mode == LOG_STDERR_ALL || log_level == LOG_LEVEL_ERROR) {
     dest_io = stderr;
   }
 
@@ -50,3 +91,50 @@ void log_message(LogLevel log_level, const char* format, ...) {
     va_end(args);
   }
 }
+
+void log_debug_message(LogDebugFlag flag, const char* format, ...) {
+  if (current_log_level > LOG_LEVEL_DEBUG || !(current_debug_flags & flag))
+    return;
+
+  time_t now = time(NULL);
+  struct tm t;
+  if (!localtime_r(&now, &t))
+    return;
+
+  va_list args;
+  va_start(args, format);
+  write_message(stdout, LOG_LEVEL_DEBUG, t, format, args);
+  va_end(args);
+
+  if (log_fp) {
+    va_start(args, format);
+    write_message(log_fp, LOG_LEVEL_DEBUG, t, format, args);
+    va_end(args);
+  }
+}
+
+void log_info_message(LogInfoFlag flag, const char* format, ...) {
+  if ((info_flags_explicit && (info_flags & flag) == 0) ||
+      (!info_flags_explicit && current_log_level > LOG_LEVEL_DEBUG))
+    return;
+
+  time_t now = time(NULL);
+  struct tm t;
+  if (!localtime_r(&now, &t))
+    return;
+
+  va_list args;
+  va_start(args, format);
+  write_message(stdout, LOG_LEVEL_INFO, t, format, args);
+  va_end(args);
+
+  if (log_fp) {
+    va_start(args, format);
+    write_message(log_fp, LOG_LEVEL_INFO, t, format, args);
+    va_end(args);
+  }
+}
+
+void log_perror(const char* context) {
+  log_message(LOG_LEVEL_ERROR, "%s: %s", context, strerror(errno));
+}

src/shared/log.h

@@ -2,11 +2,41 @@
 #define LOG_H
 
 #include <stdio.h>
+#include <stdbool.h>
+#include <stdint.h>
 
 typedef enum { LOG_LEVEL_DEBUG, LOG_LEVEL_INFO, LOG_LEVEL_WARNING, LOG_LEVEL_ERROR } LogLevel;
+typedef enum { LOG_STDERR_ERRORS, LOG_STDERR_ALL } LogStderrMode;
+
+typedef enum {
+  LOG_DEBUG_IO = 1u << 0,
+  LOG_DEBUG_PROTO = 1u << 1,
+  LOG_DEBUG_PACK = 1u << 2,
+  LOG_DEBUG_UTIL = 1u << 3,
+  LOG_DEBUG_ALL = (1u << 4) - 1,
+} LogDebugFlag;
+
+typedef enum {
+  LOG_INFO_COPY = 1u << 0,
+  LOG_INFO_MISC = 1u << 1,
+  LOG_INFO_SKIP = 1u << 2,
+  LOG_INFO_STATS = 1u << 3,
+  LOG_INFO_ALL = LOG_INFO_COPY | LOG_INFO_MISC | LOG_INFO_SKIP | LOG_INFO_STATS,
+} LogInfoFlag;
 
 void log_message(LogLevel log_level, const char* message, ...);
+void log_perror(const char* context);
 void set_log_level(LogLevel level);
+void set_log_debug_flags(uint32_t flags);
+uint32_t get_log_debug_flags(void);
+void log_debug_message(LogDebugFlag flag, const char* message, ...);
+void set_log_info_flags(uint32_t flags);
+uint32_t get_log_info_flags(void);
+void log_info_message(LogInfoFlag flag, const char* message, ...);
 void log_set_file(FILE* fp);
+void log_set_8_bit_output(bool enabled);
+bool log_get_8_bit_output(void);
+void log_set_stderr_mode(LogStderrMode mode);
+LogStderrMode log_get_stderr_mode(void);
 
 #endif

src/shared/metadata.c

@@ -2,6 +2,7 @@
 #include "file.h"
 #include "log.h"
 #include "protocol.h"
+#include "utils.h"
 #include <errno.h>
 #include <fcntl.h>
 #include <stdint.h>
@@ -24,6 +25,29 @@ typedef char static_assert_mode_t_fits[(sizeof(mode_t) <= sizeof(int32_t)) ? 1 :
 typedef char static_assert_uid_t_fits[(sizeof(uid_t) <= sizeof(int32_t)) ? 1 : -1];
 typedef char static_assert_gid_t_fits[(sizeof(gid_t) <= sizeof(int32_t)) ? 1 : -1];
 
+bool metadata_mtime_matches(time_t left_sec, long left_nsec, time_t right_sec, long right_nsec,
+                            int modify_window) {
+  int64_t left = (int64_t)left_sec;
+  int64_t right = (int64_t)right_sec;
+  int64_t seconds;
+  int64_t nanoseconds;
+
+  if (left > right || (left == right && left_nsec >= right_nsec)) {
+    seconds = left - right;
+    nanoseconds = (int64_t)left_nsec - (int64_t)right_nsec;
+  } else {
+    seconds = right - left;
+    nanoseconds = (int64_t)right_nsec - (int64_t)left_nsec;
+  }
+  if (nanoseconds < 0) {
+    seconds--;
+    nanoseconds += 1000000000LL;
+  }
+  if (modify_window == 0)
+    return left == right;
+  return seconds < modify_window || (seconds == modify_window && nanoseconds == 0);
+}
+
 void metadata_to_buf(char** buf, const FileMetadata* m) {
   int32_t present = (m != NULL) ? 1 : 0;
   memcpy(*buf, &present, sizeof(present));
@@ -51,9 +75,11 @@ FileMetadata* metadata_from_buf(char** buf) {
   int32_t present;
   memcpy(&present, *buf, sizeof(present));
   *buf += sizeof(present);
+  if (present != 0 && present != 1)
+    return NULL;
   if (!present)
     return NULL;
-  FileMetadata* m = malloc(sizeof(FileMetadata));
+  FileMetadata* m = protocol_alloc(sizeof(FileMetadata));
   if (m == NULL)
     return NULL;
   int32_t mode;
@@ -76,10 +102,15 @@ FileMetadata* metadata_from_buf(char** buf) {
   memcpy(&mtime_nsec, *buf, sizeof(mtime_nsec));
   *buf += sizeof(mtime_nsec);
   m->mtime_nsec = (long)mtime_nsec;
+  if (present != 1 || mtime_nsec < 0 || mtime_nsec >= 1000000000LL || mode < 0 || uid < 0 ||
+      gid < 0) {
+    free(m);
+    return NULL;
+  }
   return m;
 }
 
-bool metadata_send(int file_descriptor, FileMetadata* m) {
+bool metadata_send(int file_descriptor, const FileMetadata* m) {
   if (m == NULL) {
     int32_t zero = 0;
     return send_n_data(file_descriptor, &zero, sizeof(zero));
@@ -115,7 +146,7 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
       *ok = 0;
     return NULL;
   }
-  FileMetadata* m = malloc(sizeof(FileMetadata));
+  FileMetadata* m = protocol_alloc(sizeof(FileMetadata));
   if (m == NULL) {
     if (ok)
       *ok = 0;
@@ -172,11 +203,27 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
   return m;
 }
 
-void file_restore_metadata(const char* path, const FileMetadata* metadata) {
+static mode_t metadata_mode(const FileMetadata* metadata, mode_t current_mode,
+                            bool preserve_executability) {
+  const mode_t execute_bits = S_IXUSR | S_IXGRP | S_IXOTH;
+  if (preserve_executability)
+    return (current_mode & 0777 & ~execute_bits) | (metadata->mode & execute_bits);
+  return metadata->mode & 0777 & ~(S_IWGRP | S_IWOTH);
+}
+
+void file_restore_metadata(const char* path, const FileMetadata* metadata,
+                           bool preserve_executability) {
   if (metadata == NULL)
     return;
-  if (chmod(path, metadata->mode & 07777 & ~(S_ISUID | S_ISGID)) != 0)
-    log_message(LOG_LEVEL_WARNING, "Failed to chmod %s: %s", path, strerror(errno));
+  struct stat current;
+  mode_t current_mode = stat(path, &current) == 0 ? current.st_mode : 0;
+  mode_t safe_mode = metadata_mode(metadata, current_mode, preserve_executability);
+  if (chmod(path, safe_mode) != 0) {
+    char* escaped_path = output_escape(path, log_get_8_bit_output());
+    log_message(LOG_LEVEL_WARNING, "Failed to chmod %s: %s",
+                escaped_path ? escaped_path : "<allocation failed>", strerror(errno));
+    free(escaped_path);
+  }
   /* Never apply client-supplied ownership.  The descriptor API below is the
      receiver write path; retain this legacy API only for compatibility. */
   struct timespec times[2];
@@ -184,15 +231,23 @@ void file_restore_metadata(const char* path, const FileMetadata* metadata) {
   times[0].tv_nsec = UTIME_OMIT;
   times[1].tv_sec = metadata->mtime_sec;
   times[1].tv_nsec = metadata->mtime_nsec;
-  if (utimensat(AT_FDCWD, path, times, 0) != 0)
-    log_message(LOG_LEVEL_WARNING, "Failed to set timestamps on %s: %s", path, strerror(errno));
+  if (utimensat(AT_FDCWD, path, times, 0) != 0) {
+    char* escaped_path = output_escape(path, log_get_8_bit_output());
+    log_message(LOG_LEVEL_WARNING, "Failed to set timestamps on %s: %s",
+                escaped_path ? escaped_path : "<allocation failed>", strerror(errno));
+    free(escaped_path);
+  }
 }
 
-bool file_restore_metadata_fd(int fd, const FileMetadata* metadata) {
+bool file_restore_metadata_fd(int fd, const FileMetadata* metadata, bool preserve_executability) {
   if (fd < 0 || metadata == NULL)
     return metadata == NULL;
   bool ok = true;
-  if (fchmod(fd, metadata->mode & 07777 & ~(S_ISUID | S_ISGID)) != 0)
+  struct stat current;
+  if (fstat(fd, &current) != 0)
+    return false;
+  mode_t safe_mode = metadata_mode(metadata, current.st_mode, preserve_executability);
+  if (fchmod(fd, safe_mode) != 0)
     ok = false;
   /* Client uid/gid values are deliberately not authoritative. */
   struct timespec times[2] = {{.tv_sec = 0, .tv_nsec = UTIME_OMIT},

src/shared/metadata.h

@@ -5,6 +5,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <sys/stat.h>
+#include <time.h>
 
 /*
  * Wire format (introduced in protocol version 2.0.0):
@@ -27,9 +28,14 @@
 
 void metadata_to_buf(char** buf, const FileMetadata* m);
 FileMetadata* metadata_from_buf(char** buf);
-bool metadata_send(int file_descriptor, FileMetadata* m);
+bool metadata_send(int file_descriptor, const FileMetadata* m);
 FileMetadata* metadata_receive(int file_descriptor, int* ok);
-void file_restore_metadata(const char* path, const FileMetadata* metadata);
-bool file_restore_metadata_fd(int fd, const FileMetadata* metadata);
+void file_restore_metadata(const char* path, const FileMetadata* metadata,
+                           bool preserve_executability);
+bool file_restore_metadata_fd(int fd, const FileMetadata* metadata, bool preserve_executability);
+
+/* Compare timestamps using rsync's whole-second modification window. */
+bool metadata_mtime_matches(time_t left_sec, long left_nsec, time_t right_sec, long right_nsec,
+                            int modify_window);
 
 #endif

src/shared/multiprocessing.c

@@ -1,4 +1,5 @@
 #include "multiprocessing.h"
+#include "receiver.h"
 
 #include "array_list.h"
 #include "chunk.h"
@@ -14,10 +15,6 @@
 #include <string.h>
 #include <threads.h>
 
-static bool valid_batch_path(const char* path) {
-  return path && path[0] != '\0' && path[0] != '/' && !has_path_traversal(path);
-}
-
 PipelineContextSender* pipeline_context_sender_create(Config* config, Queue* queue_scanner,
                                                       Queue* queue_loader) {
   PipelineContextSender* context = malloc(sizeof(PipelineContextSender));
@@ -29,9 +26,14 @@ PipelineContextSender* pipeline_context_sender_create(Config* config, Queue* que
   context->scanner_done = false;
   context->loader_done = false;
   context->manifest = NULL;
+  context->remove_source_files = NULL;
+  context->total_files = 0;
   context->progress_bytes = 0;
+  context->total_bytes = 0;
   context->sender_done = false;
   atomic_init(&context->cancelled, false);
+  protocol_session_init(&context->allocation_session, -1, -1);
+  protocol_session_set_max_alloc(&context->allocation_session, config->max_alloc);
   int init = 0;
   if (mtx_init(&context->mutex_scanner, mtx_plain) != thrd_success)
     goto fail;
@@ -58,7 +60,7 @@ PipelineContextSender* pipeline_context_sender_create(Config* config, Queue* que
   return context;
 
 fail:
-  perror("Error initializing synchronization objects");
+  log_perror("Error initializing synchronization objects");
   if (init >= 6)
     cnd_destroy(&context->condition_not_empty_loader);
   if (init >= 5)
@@ -79,6 +81,8 @@ void pipeline_context_sender_destroy(PipelineContextSender* context) {
   if (context->manifest) {
     array_list_delete(context->manifest);
   }
+  if (context->remove_source_files)
+    array_list_delete(context->remove_source_files);
   config_delete(context->config);
   queue_destroy(context->queue_scanner);
   queue_destroy(context->queue_loader);
@@ -101,6 +105,8 @@ PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue*
   context->queue = queue;
   context->file_descriptor = file_descriptor;
   context->ssl = ssl;
+  protocol_session_init(&context->session, file_descriptor, file_descriptor);
+  protocol_session_set_ssl(&context->session, ssl);
   context->receiver_done = false;
   atomic_init(&context->cancelled, false);
   int init = 0;
@@ -117,7 +123,7 @@ PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue*
   return context;
 
 fail:
-  perror("Error initializing synchronization objects");
+  log_perror("Error initializing synchronization objects");
   if (init >= 3)
     cnd_destroy(&context->condition_not_empty);
   if (init >= 2)
@@ -137,24 +143,14 @@ void pipeline_context_receiver_destroy(PipelineContextReceiver* context) {
   free(context);
 }
 
-static bool receive_chunk_enqueue(int file_descriptor, PipelineContextReceiver* context) {
-  Chunk* chunk = receive_chunk_data(file_descriptor, context->config);
-  if (chunk == NULL)
-    return false;
-
-  for (int i = 0; i < chunk->element_count; i++) {
-    File* file = chunk->items[i];
-    chunk->items[i] = NULL;
-    if (!queue_enqueue_multithreaded_cancel(context->queue, file, &context->mutex,
-                                            &context->condition_not_empty,
-                                            &context->condition_not_full, &context->cancelled)) {
-      file_destroy(file);
-      chunk_destroy(chunk);
-      return false;
-    }
-  }
-  chunk_destroy(chunk);
-  return true;
+static bool receiver_enqueue_file(File* file, void* context_pointer) {
+  PipelineContextReceiver* context = context_pointer;
+  if (queue_enqueue_multithreaded_cancel(context->queue, file, &context->mutex,
+                                         &context->condition_not_empty,
+                                         &context->condition_not_full, &context->cancelled))
+    return true;
+  file_destroy(file);
+  return false;
 }
 
 static void receiver_thread_fail(PipelineContextReceiver* context) {
@@ -167,123 +163,44 @@ static void receiver_thread_fail(PipelineContextReceiver* context) {
 }
 
 int receive_thread(void* pipeline_context) {
-#define RECEIVE_THREAD_FAIL()                                                                      \
-  do {                                                                                             \
-    receiver_thread_fail(context);                                                                 \
-    return thrd_error;                                                                             \
-  } while (0)
   PipelineContextReceiver* context = (PipelineContextReceiver*)pipeline_context;
-  if (context->ssl)
-    io_set_ssl(context->ssl);
+  protocol_session_bind(&context->session);
   mtx_lock(&context->mutex);
   int file_descriptor = context->file_descriptor;
   const Config* config = context->config;
   mtx_unlock(&context->mutex);
 
-  Status status;
-  if (!receive_status(file_descriptor, &status))
-    RECEIVE_THREAD_FAIL();
-  while (status == STATUS_NEXT || status == STATUS_CHUNK || status == STATUS_CHECK ||
-         status == STATUS_KEEPALIVE || status == STATUS_ABORT || status == STATUS_CHECK_BATCH) {
-    if (status == STATUS_KEEPALIVE) {
-      if (!send_status(file_descriptor, STATUS_KEEPALIVE))
-        RECEIVE_THREAD_FAIL();
-      goto next;
-    }
-    if (status == STATUS_ABORT) {
-      log_message(LOG_LEVEL_INFO, "Received abort from client, cleaning up");
-      RECEIVE_THREAD_FAIL();
-    }
-    if (status == STATUS_CHECK) {
-      bool skipped;
-      File* file = receive_incremental_check(file_descriptor, config, &skipped);
-      if (!skipped) {
-        if (file == NULL)
-          RECEIVE_THREAD_FAIL();
-        if (!queue_enqueue_multithreaded_cancel(
-                context->queue, file, &context->mutex, &context->condition_not_empty,
-                &context->condition_not_full, &context->cancelled)) {
-          file_destroy(file);
-          RECEIVE_THREAD_FAIL();
-        }
-      }
-    } else if (status == STATUS_CHUNK) {
-      if (!receive_chunk_enqueue(file_descriptor, context))
-        RECEIVE_THREAD_FAIL();
-    } else if (status == STATUS_CHECK_BATCH) {
-      int count;
-      if (config->checksum || !receive_int(file_descriptor, &count) || count < 0 ||
-          count > MAX_MANIFEST_ENTRIES)
-        RECEIVE_THREAD_FAIL();
-      for (int i = 0; i < count; i++) {
-        char* check_path = receive_str(file_descriptor);
-        if (!check_path)
-          RECEIVE_THREAD_FAIL();
-        unsigned long long check_size;
-        long long check_mtime;
-        if (!receive_n_data(file_descriptor, &check_size, sizeof(check_size)) ||
-            !receive_n_data(file_descriptor, &check_mtime, sizeof(check_mtime))) {
-          free(check_path);
-          RECEIVE_THREAD_FAIL();
-        }
-        if (!valid_batch_path(check_path)) {
-          free(check_path);
-          if (!send_status(file_descriptor, STATUS_ERROR))
-            RECEIVE_THREAD_FAIL();
-          RECEIVE_THREAD_FAIL();
-        }
-        char* full_path = path_cat(config->receive_root_directory, check_path);
-        struct stat st;
-        bool has_old = full_path && lstat(full_path, &st) == 0;
-        bool match = has_old && (unsigned long long)st.st_size == check_size &&
-                     (long long)st.st_mtime == check_mtime;
-        if (!send_status(file_descriptor, match ? STATUS_OK : STATUS_NEXT))
-          RECEIVE_THREAD_FAIL();
-        free(full_path);
-        free(check_path);
-      }
-      goto next;
-    } else {
-      File* file = file_receive(config, file_descriptor);
-      if (file) {
-        if (!queue_enqueue_multithreaded_cancel(
-                context->queue, file, &context->mutex, &context->condition_not_empty,
-                &context->condition_not_full, &context->cancelled)) {
-          file_destroy(file);
-          receiver_thread_fail(context);
-          return thrd_error;
-        }
-      } else {
-        log_message(LOG_LEVEL_ERROR, "Failed to receive file");
-        RECEIVE_THREAD_FAIL();
-      }
-    }
-  next:
-    if (!receive_status(file_descriptor, &status))
-      RECEIVE_THREAD_FAIL();
+  ReceiverSink sink = {receiver_enqueue_file, context, false, false};
+  if (receiver_process((Config*)config, file_descriptor, &sink) != 0) {
+    receiver_thread_fail(context);
+    protocol_session_unbind();
+    return thrd_error;
   }
-  if (status == STATUS_MANIFEST) {
-    if (receive_manifest(file_descriptor, config, &status) != 0)
-      RECEIVE_THREAD_FAIL();
-  }
-  if (status != STATUS_FINISHED)
-    RECEIVE_THREAD_FAIL();
   mtx_lock(&context->mutex);
   context->receiver_done = true;
   cnd_signal(&context->condition_not_empty);
   mtx_unlock(&context->mutex);
-#undef RECEIVE_THREAD_FAIL
+  protocol_session_unbind();
   return thrd_success;
 }
 
 int write_thread(void* pipeline_context) {
   PipelineContextReceiver* context = (PipelineContextReceiver*)pipeline_context;
-  if (context->ssl)
-    io_set_ssl(context->ssl);
+  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 =
@@ -291,6 +208,7 @@ int write_thread(void* pipeline_context) {
                                     &context->condition_not_full, &context->receiver_done);
     if (file == NULL) {
       free(root_directory);
+      protocol_session_unbind();
       return thrd_success;
     }
     if (save_to_disk && !file_save_to_disk(root_directory, file, context->config)) {
@@ -302,6 +220,7 @@ int write_thread(void* pipeline_context) {
       cnd_broadcast(&context->condition_not_empty);
       mtx_unlock(&context->mutex);
       free(root_directory);
+      protocol_session_unbind();
       return thrd_error;
     }
     file_destroy(file);

src/shared/multiprocessing.h

@@ -24,10 +24,14 @@ typedef struct {
   cnd_t condition_not_empty_loader;
   bool loader_done;
   ArrayList* manifest;
+  ArrayList* remove_source_files;
   mtx_t mutex_progress;
+  int total_files;
   unsigned long long progress_bytes;
+  unsigned long long total_bytes;
   bool sender_done;
   atomic_bool cancelled;
+  ProtocolSession allocation_session;
 } PipelineContextSender;
 
 typedef struct PipelineContextReceiver {
@@ -35,6 +39,7 @@ typedef struct PipelineContextReceiver {
   Config* config;
   int file_descriptor;
   SSL* ssl;
+  ProtocolSession session;
   mtx_t mutex;
   cnd_t condition_not_full;
   cnd_t condition_not_empty;

src/shared/protocol.c

@@ -1,5 +1,6 @@
 #include "protocol.h"
 #include "log.h"
+#include "utils.h"
 #include <errno.h>
 #include <limits.h>
 #include <openssl/ssl.h>
@@ -13,75 +14,199 @@
 
 #define RECEIVE_TIMEOUT_SEC 60 /* 60 second per-message timeout */
 #define SEND_TIMEOUT_SEC 60
-#define MAX_CONNECTION_MEMORY (1024ULL * 1024 * 1024) /* 1 GB total per connection */
+#define MAX_CONNECTION_MEMORY (256ULL * 1024 * 1024) /* bounded cumulative receive budget */
 
 static __thread int io_read_fd = -1;
 static __thread int io_write_fd = -1;
 static __thread SSL* io_ssl;
+static __thread ProtocolSession* bound_session;
+static __thread ProtocolSession legacy_io_session = {
+    .read_fd = -1, .write_fd = -1, .max_alloc = DEFAULT_MAX_ALLOC};
 
 static unsigned long long io_bwlimit = 0;
-static long long bw_tokens = 0;
-static struct timespec bw_last_refill = {0, 0};
 static mtx_t bw_mutex;
 static once_flag bw_mutex_once = ONCE_FLAG_INIT;
 
-static __thread unsigned long long total_allocated_bytes = 0;
+static unsigned long long global_bwlimit(void);
 
+static bool protocol_reserve_memory(ProtocolSession* session, size_t charge) {
+  unsigned long long allocated = atomic_load(&session->total_allocated_bytes);
+  while (true) {
+    if (allocated > MAX_CONNECTION_MEMORY ||
+        (unsigned long long)charge > MAX_CONNECTION_MEMORY - allocated)
+      return false;
+    if (atomic_compare_exchange_weak(&session->total_allocated_bytes, &allocated,
+                                     allocated + (unsigned long long)charge))
+      return true;
+  }
+}
+
+static void protocol_release_memory_for_session(ProtocolSession* session, size_t charge) {
+  unsigned long long allocated = atomic_load(&session->total_allocated_bytes);
+  while (true) {
+    unsigned long long remaining = (unsigned long long)charge >= allocated ? 0 : allocated - charge;
+    if (atomic_compare_exchange_weak(&session->total_allocated_bytes, &allocated, remaining))
+      break;
+  }
+}
+
+void protocol_release_memory(size_t charge) {
+  ProtocolSession* session = bound_session ? bound_session : &legacy_io_session;
+  protocol_release_memory_for_session(session, charge);
+}
 void io_set_fds(int read_fd, int write_fd) {
+  bound_session = NULL;
   io_read_fd = read_fd;
   io_write_fd = write_fd;
   /* A descriptor switch starts a new transport; never reuse a TLS object
      belonging to a previous connection or test pipe. */
   io_ssl = NULL;
-  total_allocated_bytes = 0;
+  legacy_io_session.read_fd = read_fd;
+  legacy_io_session.write_fd = write_fd;
+  legacy_io_session.ssl = NULL;
+  legacy_io_session.eight_bit_output = false;
+  atomic_store(&legacy_io_session.total_allocated_bytes, 0);
+  legacy_io_session.max_alloc = DEFAULT_MAX_ALLOC;
+  protocol_session_set_bwlimit(&legacy_io_session, global_bwlimit());
+}
+
+void protocol_session_init(ProtocolSession* session, int read_fd, int write_fd) {
+  if (!session)
+    return;
+  memset(session, 0, sizeof(*session));
+  session->read_fd = read_fd;
+  session->write_fd = write_fd;
+  session->max_alloc = DEFAULT_MAX_ALLOC;
+  atomic_init(&session->total_allocated_bytes, 0);
+  protocol_session_set_bwlimit(session, global_bwlimit());
+}
+
+void protocol_session_set_max_alloc(ProtocolSession* session, unsigned long long max_alloc) {
+  if (!session)
+    session = bound_session ? bound_session : &legacy_io_session;
+  session->max_alloc = max_alloc;
+}
+
+static bool allocation_allowed(const ProtocolSession* session, size_t size) {
+  return (unsigned long long)size <= session->max_alloc;
+}
+
+static void* protocol_alloc_for_session(const ProtocolSession* session, size_t size) {
+  if (!allocation_allowed(session, size))
+    return NULL;
+  return malloc(size);
+}
+
+static void* protocol_realloc_for_session(const ProtocolSession* session, void* ptr, size_t size) {
+  if (!allocation_allowed(session, size))
+    return NULL;
+  return realloc(ptr, size);
+}
+
+void* protocol_alloc(size_t size) {
+  const ProtocolSession* session = bound_session ? bound_session : &legacy_io_session;
+  return protocol_alloc_for_session(session, size);
+}
+
+void* protocol_realloc(void* ptr, size_t size) {
+  const ProtocolSession* session = bound_session ? bound_session : &legacy_io_session;
+  return protocol_realloc_for_session(session, ptr, size);
+}
+
+void protocol_session_bind(ProtocolSession* session) {
+  bound_session = session;
+  log_set_8_bit_output(session && session->eight_bit_output);
+}
+
+void protocol_session_unbind(void) {
+  bound_session = NULL;
+}
+
+void protocol_session_set_ssl(ProtocolSession* session, SSL* ssl) {
+  if (session)
+    session->ssl = ssl;
 }
 
 static void bw_mutex_init(void) {
   mtx_init(&bw_mutex, mtx_plain);
 }
 
+static unsigned long long global_bwlimit(void) {
+  unsigned long long limit;
+  call_once(&bw_mutex_once, bw_mutex_init);
+  mtx_lock(&bw_mutex);
+  limit = io_bwlimit;
+  mtx_unlock(&bw_mutex);
+  return limit;
+}
+
 void io_set_bwlimit(unsigned long long bytes_per_sec) {
   call_once(&bw_mutex_once, bw_mutex_init);
   mtx_lock(&bw_mutex);
-  io_bwlimit = bytes_per_sec;
-  bw_tokens = (long long)io_bwlimit;
-  clock_gettime(CLOCK_MONOTONIC, &bw_last_refill);
+  io_bwlimit =
+      bytes_per_sec > (unsigned long long)LLONG_MAX ? (unsigned long long)LLONG_MAX : bytes_per_sec;
   mtx_unlock(&bw_mutex);
 }
 
-static void bw_throttle(size_t bytes_written) {
-  if (io_bwlimit == 0)
+void protocol_session_set_bwlimit(ProtocolSession* session, unsigned long long bytes_per_sec) {
+  if (!session)
+    return;
+  session->bwlimit =
+      bytes_per_sec > (unsigned long long)LLONG_MAX ? (unsigned long long)LLONG_MAX : bytes_per_sec;
+  session->bw_tokens = (long long)session->bwlimit;
+  struct timespec now;
+  clock_gettime(CLOCK_MONOTONIC, &now);
+  session->bw_last_refill_sec = now.tv_sec;
+  session->bw_last_refill_nsec = now.tv_nsec;
+}
+
+void protocol_session_set_8_bit_output(ProtocolSession* session, bool enabled) {
+  if (!session)
+    return;
+  session->eight_bit_output = enabled;
+  if (session == bound_session)
+    log_set_8_bit_output(enabled);
+}
+
+void protocol_set_8_bit_output(bool enabled) {
+  ProtocolSession* session = bound_session ? bound_session : &legacy_io_session;
+  protocol_session_set_8_bit_output(session, enabled);
+}
+
+static void bw_throttle_session(ProtocolSession* session, size_t bytes_written) {
+  if (session->bwlimit == 0)
     return;
-  call_once(&bw_mutex_once, bw_mutex_init);
-  mtx_lock(&bw_mutex);
 
   struct timespec now;
   clock_gettime(CLOCK_MONOTONIC, &now);
 
-  long long elapsed_ns =
-      (now.tv_sec - bw_last_refill.tv_sec) * 1000000000LL + (now.tv_nsec - bw_last_refill.tv_nsec);
-  bw_last_refill = now;
+  long long elapsed_ns = (now.tv_sec - session->bw_last_refill_sec) * 1000000000LL +
+                         (now.tv_nsec - session->bw_last_refill_nsec);
+  session->bw_last_refill_sec = now.tv_sec;
+  session->bw_last_refill_nsec = now.tv_nsec;
 
-  long long tokens_to_add = (long long)((double)io_bwlimit * elapsed_ns / 1000000000.0);
-  bw_tokens += tokens_to_add;
-  if (bw_tokens > (long long)io_bwlimit)
-    bw_tokens = (long long)io_bwlimit;
+  long long tokens_to_add = (long long)((double)session->bwlimit * elapsed_ns / 1000000000.0);
+  session->bw_tokens += tokens_to_add;
+  if (session->bw_tokens > (long long)session->bwlimit)
+    session->bw_tokens = (long long)session->bwlimit;
 
-  bw_tokens -= (long long)bytes_written;
+  session->bw_tokens -= bytes_written;
 
-  if (bw_tokens < 0) {
-    long long deficit_us = (long long)((double)(-bw_tokens) / io_bwlimit * 1000000.0);
+  if (session->bw_tokens < 0) {
+    long long deficit_us =
+        (long long)((double)(-session->bw_tokens) / session->bwlimit * 1000000.0);
     if (deficit_us >= 1000)
       poll(NULL, 0, (int)(deficit_us / 1000));
     else
       usleep((useconds_t)deficit_us);
-    bw_tokens = 0;
-    clock_gettime(CLOCK_MONOTONIC, &bw_last_refill);
+    session->bw_tokens = 0;
+    session->bw_last_refill_sec = now.tv_sec;
+    session->bw_last_refill_nsec = now.tv_nsec;
   }
-  mtx_unlock(&bw_mutex);
 }
 
 void io_set_ssl(SSL* ssl) {
+  bound_session = NULL;
   io_ssl = ssl;
 }
 
@@ -89,8 +214,31 @@ SSL* io_get_ssl(void) {
   return io_ssl;
 }
 
-static int io_fd(int dir_fd, int file_descriptor) {
-  return (dir_fd != -1) ? dir_fd : file_descriptor;
+static ProtocolSession* legacy_session(int read_fd, int write_fd) {
+  if (bound_session)
+    return bound_session;
+  int target_read_fd = io_read_fd != -1 ? io_read_fd : read_fd;
+  int target_write_fd = io_write_fd != -1 ? io_write_fd : write_fd;
+  if (legacy_io_session.read_fd != target_read_fd ||
+      legacy_io_session.write_fd != target_write_fd) {
+    legacy_io_session.read_fd = target_read_fd;
+    legacy_io_session.write_fd = target_write_fd;
+    atomic_store(&legacy_io_session.total_allocated_bytes, 0);
+    legacy_io_session.max_alloc = DEFAULT_MAX_ALLOC;
+    protocol_session_set_bwlimit(&legacy_io_session, global_bwlimit());
+  } else if (legacy_io_session.bwlimit != global_bwlimit()) {
+    protocol_session_set_bwlimit(&legacy_io_session, global_bwlimit());
+  }
+  legacy_io_session.ssl = io_ssl;
+  return &legacy_io_session;
+}
+
+bool send_n_data(int file_descriptor, const void* data, size_t data_size) {
+  return protocol_send_n_data(legacy_session(-1, file_descriptor), data, data_size);
+}
+
+bool receive_n_data(int file_descriptor, void* data, size_t data_size) {
+  return protocol_receive_n_data(legacy_session(file_descriptor, -1), data, data_size);
 }
 
 static int deadline_remaining_ms(const struct timespec* deadline) {
@@ -104,9 +252,13 @@ static int deadline_remaining_ms(const struct timespec* deadline) {
   return ms > INT_MAX ? INT_MAX : (int)ms;
 }
 
-bool send_n_data(int file_descriptor, const void* data, size_t data_size) {
-  log_message(LOG_LEVEL_DEBUG, "    Sending n Data: %zu", data_size);
-  int fd = io_fd(io_write_fd, file_descriptor);
+bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t data_size) {
+  if (!data && data_size != 0)
+    return false;
+  log_debug_message(LOG_DEBUG_IO, "    Sending n Data: %zu", data_size);
+  if (!session)
+    return false;
+  int fd = session->write_fd;
   struct timespec deadline;
   clock_gettime(CLOCK_MONOTONIC, &deadline);
   deadline.tv_sec += SEND_TIMEOUT_SEC;
@@ -114,7 +266,7 @@ bool send_n_data(int file_descriptor, const void* data, size_t data_size) {
   ssize_t total_bytes_send = 0;
   while ((size_t)total_bytes_send < data_size) {
     size_t chunk = data_size - total_bytes_send;
-    if (io_bwlimit > 0 && chunk > 65536)
+    if (session->bwlimit > 0 && chunk > 65536)
       chunk = 65536;
     struct pollfd pfd = {.fd = fd, .events = wait_events};
     int poll_result = poll(&pfd, 1, deadline_remaining_ms(&deadline));
@@ -127,13 +279,13 @@ bool send_n_data(int file_descriptor, const void* data, size_t data_size) {
     if (pfd.revents & (POLLERR | POLLNVAL))
       return false;
     ssize_t bytes_send;
-    if (io_ssl)
-      bytes_send = SSL_write(io_ssl, (const char*)data + total_bytes_send, chunk);
+    if (session->ssl)
+      bytes_send = SSL_write(session->ssl, (const char*)data + total_bytes_send, chunk);
     else
       bytes_send = write(fd, (const char*)data + total_bytes_send, chunk);
     if (bytes_send <= 0) {
-      if (io_ssl) {
-        int ssl_err = SSL_get_error(io_ssl, (int)bytes_send);
+      if (session->ssl) {
+        int ssl_err = SSL_get_error(session->ssl, (int)bytes_send);
         if (ssl_err == SSL_ERROR_WANT_WRITE || ssl_err == SSL_ERROR_WANT_READ) {
           wait_events = ssl_err == SSL_ERROR_WANT_WRITE ? POLLOUT : POLLIN;
           continue;
@@ -142,16 +294,20 @@ bool send_n_data(int file_descriptor, const void* data, size_t data_size) {
       log_message(LOG_LEVEL_ERROR, "Could not send data");
       return false;
     }
-    bw_throttle((size_t)bytes_send);
+    bw_throttle_session(session, (size_t)bytes_send);
     total_bytes_send += bytes_send;
+    if (session->ssl)
+      wait_events = POLLOUT;
   }
-  log_message(LOG_LEVEL_DEBUG, "    Send n Data: %zu", total_bytes_send);
+  log_debug_message(LOG_DEBUG_IO, "    Send n Data: %zu", total_bytes_send);
   return true;
 }
 
-bool receive_n_data(int file_descriptor, void* data, size_t data_size) {
-  log_message(LOG_LEVEL_DEBUG, "    Receiving n Data: %zu", data_size);
-  int fd = io_fd(io_read_fd, file_descriptor);
+bool protocol_receive_n_data(ProtocolSession* session, void* data, size_t data_size) {
+  log_debug_message(LOG_DEBUG_IO, "    Receiving n Data: %zu", data_size);
+  if (!session)
+    return false;
+  int fd = session->read_fd;
 
   struct timespec deadline;
   clock_gettime(CLOCK_MONOTONIC, &deadline);
@@ -160,31 +316,33 @@ bool receive_n_data(int file_descriptor, void* data, size_t data_size) {
   size_t total_bytes_received = 0;
   short wait_events = POLLIN;
   while (total_bytes_received < data_size) {
-    struct pollfd pfd = {.fd = fd, .events = wait_events};
-    int poll_result = poll(&pfd, 1, deadline_remaining_ms(&deadline));
-    if (poll_result == 0) {
-      log_message(LOG_LEVEL_ERROR, "Receive timeout after %ds", RECEIVE_TIMEOUT_SEC);
-      return false;
+    if (!session->ssl || SSL_pending(session->ssl) == 0) {
+      struct pollfd pfd = {.fd = fd, .events = wait_events};
+      int poll_result = poll(&pfd, 1, deadline_remaining_ms(&deadline));
+      if (poll_result == 0) {
+        log_message(LOG_LEVEL_ERROR, "Receive timeout after %ds", RECEIVE_TIMEOUT_SEC);
+        return false;
+      }
+      if (poll_result < 0) {
+        if (errno == EINTR)
+          continue;
+        return false;
+      }
+      /* POLLHUP may accompany the final readable bytes on pipes/sockets. */
+      if (pfd.revents & (POLLERR | POLLNVAL))
+        return false;
     }
-    if (poll_result < 0) {
-      if (errno == EINTR)
-        continue;
-      return false;
-    }
-    /* POLLHUP may accompany the final readable bytes on pipes/sockets. */
-    if (pfd.revents & (POLLERR | POLLNVAL))
-      return false;
 
     ssize_t bytes_received;
-    if (io_ssl)
-      bytes_received =
-          SSL_read(io_ssl, (char*)data + total_bytes_received, data_size - total_bytes_received);
+    if (session->ssl)
+      bytes_received = SSL_read(session->ssl, (char*)data + total_bytes_received,
+                                data_size - total_bytes_received);
     else
       bytes_received =
           read(fd, (char*)data + total_bytes_received, data_size - total_bytes_received);
     if (bytes_received <= 0) {
-      if (io_ssl) {
-        int ssl_err = SSL_get_error(io_ssl, (int)bytes_received);
+      if (session->ssl) {
+        int ssl_err = SSL_get_error(session->ssl, (int)bytes_received);
         if (ssl_err == SSL_ERROR_WANT_WRITE || ssl_err == SSL_ERROR_WANT_READ) {
           wait_events = ssl_err == SSL_ERROR_WANT_WRITE ? POLLOUT : POLLIN;
           continue;
@@ -196,9 +354,11 @@ bool receive_n_data(int file_descriptor, void* data, size_t data_size) {
         log_message(LOG_LEVEL_ERROR, "Could not receive bytes");
       return false;
     }
-    total_bytes_received += bytes_received;
+    total_bytes_received += (size_t)bytes_received;
+    if (session->ssl)
+      wait_events = POLLIN;
   }
-  log_message(LOG_LEVEL_DEBUG, "    Received n Data: %zu", total_bytes_received);
+  log_debug_message(LOG_DEBUG_IO, "    Received n Data: %zu", total_bytes_received);
   return true;
 }
 
@@ -231,108 +391,154 @@ static const char* status_to_string(Status status) {
   }
 }
 
-bool send_str(int file_descriptor, const char* data) {
+bool protocol_send_str(ProtocolSession* session, const char* data) {
   if (data == NULL)
     return false;
   size_t size = strlen(data);
-  if (!send_n_data(file_descriptor, &size, sizeof(size_t)))
+  if (!protocol_send_n_data(session, &size, sizeof(size_t)))
     return false;
-  if (!send_n_data(file_descriptor, data, size))
+  if (!protocol_send_n_data(session, data, size))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Send String: %s", data);
+  log_debug_message(LOG_DEBUG_PROTO, "Send String: %s", data);
   return true;
 }
 
-char* receive_str(int file_descriptor) {
+char* protocol_receive_str(ProtocolSession* session) {
   size_t size;
-  if (!receive_n_data(file_descriptor, &size, sizeof(size_t)))
+  if (!protocol_receive_n_data(session, &size, sizeof(size_t)))
     return NULL;
-  if (size > MAX_STRING_SIZE || size > SIZE_MAX - 1 ||
-      size + 1 > MAX_CONNECTION_MEMORY - total_allocated_bytes) {
+  if (size > MAX_STRING_SIZE || size > SIZE_MAX - 1) {
     log_message(LOG_LEVEL_ERROR, "String size %zu exceeds maximum %llu", size,
                 (unsigned long long)MAX_STRING_SIZE);
     return NULL;
   }
-  char* data = (char*)malloc(size + 1);
+  char* data = (char*)protocol_alloc_for_session(session, size + 1);
   if (data == NULL)
     return NULL;
-  if (!receive_n_data(file_descriptor, data, size)) {
+  if (!protocol_receive_n_data(session, data, size)) {
     free(data);
     return NULL;
   }
+  if (memchr(data, '\0', size) != NULL) {
+    free(data);
+    log_message(LOG_LEVEL_ERROR, "Received string contains an embedded NUL");
+    return NULL;
+  }
   data[size] = '\0';
-  total_allocated_bytes += size + 1;
-  log_message(LOG_LEVEL_DEBUG, "Received String: %s", data);
+  log_debug_message(LOG_DEBUG_PROTO, "Received String: %s", data);
   return data;
 }
 
-bool send_data(int file_descriptor, const Data* data) {
+bool protocol_send_data(ProtocolSession* session, const Data* data) {
+  if (!data || (!data->data && data->size != 0))
+    return false;
+  if (!session)
+    return false;
   unsigned long long data_size = data->size;
-  if (!send_n_data(file_descriptor, &data_size, sizeof(unsigned long long)))
+  if (!protocol_send_n_data(session, &data_size, sizeof(unsigned long long)))
     return false;
-  if (!send_n_data(file_descriptor, data->data, data_size))
+  if (!protocol_send_n_data(session, data->data, data_size))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Send %lld data", data_size);
+  log_debug_message(LOG_DEBUG_PROTO, "Send %lld data", data_size);
   return true;
 }
 
-Data* receive_data(int file_descriptor) {
-  unsigned long long size = 0;
-  if (!receive_n_data(file_descriptor, &size, sizeof(unsigned long long)))
+Data* protocol_receive_data_limited(ProtocolSession* session, unsigned long long maximum_size) {
+  if (!session)
     return NULL;
-  if (size > MAX_DATA_PAYLOAD_SIZE) {
+  unsigned long long size = 0;
+  if (!protocol_receive_n_data(session, &size, sizeof(unsigned long long)))
+    return NULL;
+  if (size > MAX_DATA_PAYLOAD_SIZE || size > maximum_size) {
     log_message(LOG_LEVEL_ERROR, "Data size %llu exceeds maximum %llu", size,
                 (unsigned long long)MAX_DATA_PAYLOAD_SIZE);
     return NULL;
   }
+  if (size > SIZE_MAX)
+    return NULL;
   size_t allocation_size = size == 0 ? 1 : (size_t)size;
-  if (allocation_size > MAX_CONNECTION_MEMORY - total_allocated_bytes) {
+  if (!protocol_reserve_memory(session, allocation_size)) {
     log_message(LOG_LEVEL_ERROR, "Per-connection memory limit exceeded (%llu + %llu > %llu)",
-                (unsigned long long)total_allocated_bytes, size,
+                (unsigned long long)atomic_load(&session->total_allocated_bytes), size,
                 (unsigned long long)MAX_CONNECTION_MEMORY);
     return NULL;
   }
-  void* data = malloc(allocation_size);
-  if (data == NULL)
-    return NULL;
-  if (!receive_n_data(file_descriptor, data, (size_t)size)) {
-    free(data);
+  void* data = protocol_alloc_for_session(session, allocation_size);
+  if (data == NULL) {
+    protocol_release_memory_for_session(session, allocation_size);
     return NULL;
   }
-  total_allocated_bytes += allocation_size;
-  log_message(LOG_LEVEL_DEBUG, "Received %lld data", size);
+  if (!protocol_receive_n_data(session, data, (size_t)size)) {
+    free(data);
+    protocol_release_memory_for_session(session, allocation_size);
+    return NULL;
+  }
+  log_debug_message(LOG_DEBUG_PROTO, "Received %lld data", size);
   Data* result = data_create(data, (size_t)size);
   if (!result) {
-    free(data);
-    total_allocated_bytes -= allocation_size;
+    protocol_release_memory_for_session(session, allocation_size);
+    return NULL;
   }
+  result->protocol_charge = allocation_size;
   return result;
 }
 
-bool send_int(int file_descriptor, int data) {
-  if (!send_n_data(file_descriptor, &data, sizeof(int)))
+Data* protocol_receive_data(ProtocolSession* session) {
+  return protocol_receive_data_limited(session, MAX_DATA_PAYLOAD_SIZE);
+}
+
+bool protocol_send_int(ProtocolSession* session, int data) {
+  if (!protocol_send_n_data(session, &data, sizeof(int)))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Send Int: %d", data);
+  log_debug_message(LOG_DEBUG_PROTO, "Send Int: %d", data);
   return true;
 }
 
-bool receive_int(int file_descriptor, int* data) {
-  if (!receive_n_data(file_descriptor, data, sizeof(int)))
+bool protocol_receive_int(ProtocolSession* session, int* data) {
+  if (!protocol_receive_n_data(session, data, sizeof(int)))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Received Int: %d", *data);
+  log_debug_message(LOG_DEBUG_PROTO, "Received Int: %d", *data);
   return true;
 }
 
-bool send_status(int file_descriptor, Status status) {
-  if (!send_n_data(file_descriptor, &status, sizeof(Status)))
+bool protocol_send_status(ProtocolSession* session, Status status) {
+  if (!protocol_send_n_data(session, &status, sizeof(Status)))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Send Status: %s", status_to_string(status));
+  log_debug_message(LOG_DEBUG_PROTO, "Send Status: %s", status_to_string(status));
   return true;
 }
 
-bool receive_status(int file_descriptor, Status* status) {
-  if (!receive_n_data(file_descriptor, status, sizeof(Status)))
+bool protocol_receive_status(ProtocolSession* session, Status* status) {
+  if (!protocol_receive_n_data(session, status, sizeof(Status)))
     return false;
-  log_message(LOG_LEVEL_DEBUG, "Received Status: %s", status_to_string(*status));
+  log_debug_message(LOG_DEBUG_PROTO, "Received Status: %s", status_to_string(*status));
   return true;
 }
+
+bool send_str(int fd, const char* data) {
+  return protocol_send_str(legacy_session(-1, fd), data);
+}
+char* receive_str(int fd) {
+  return protocol_receive_str(legacy_session(fd, -1));
+}
+bool send_data(int fd, const Data* data) {
+  return protocol_send_data(legacy_session(-1, fd), data);
+}
+Data* receive_data(int fd) {
+  return protocol_receive_data_limited(legacy_session(fd, -1), MAX_DATA_PAYLOAD_SIZE);
+}
+Data* receive_data_limited(int fd, unsigned long long maximum_size) {
+  return protocol_receive_data_limited(legacy_session(fd, -1), maximum_size);
+}
+bool send_int(int fd, int data) {
+  return protocol_send_int(legacy_session(-1, fd), data);
+}
+bool receive_int(int fd, int* data) {
+  return protocol_receive_int(legacy_session(fd, -1), data);
+}
+bool send_status(int fd, Status status) {
+  return protocol_send_status(legacy_session(-1, fd), status);
+}
+bool receive_status(int fd, Status* status) {
+  return protocol_receive_status(legacy_session(fd, -1), status);
+}

src/shared/protocol.h

@@ -4,21 +4,46 @@
 #include "data.h"
 #include <stdbool.h>
 #include <stddef.h>
+#include <stdatomic.h>
 
 /* Maximum allowed string size for receive_str (64 KB) */
 #define MAX_STRING_SIZE (64 * 1024)
 
 /* Maximum allowed data payload size for receive_data (100 MB) */
 #define MAX_DATA_PAYLOAD_SIZE (100ULL * 1024 * 1024)
+/* Maximum uncompressed file payload accepted by the receiver. */
+#define MAX_RECEIVE_FILE_SIZE (64ULL * 1024 * 1024)
 
 /* Maximum chunk size (64 MB) — prevents unbounded allocation from the wire */
 #define MAX_CHUNK_SIZE (64ULL * 1024 * 1024)
 #define MAX_MANIFEST_ENTRIES (1024 * 1024)
 /* Aggregate bytes retained by one received deletion manifest. */
 #define MAX_MANIFEST_BYTES (16ULL * 1024 * 1024)
+#define DEFAULT_MAX_ALLOC (1ULL * 1024 * 1024 * 1024)
+/* Server policy ceiling for a client-provided allocation limit. */
+#define MAX_SERVER_ALLOC (256ULL * 1024 * 1024)
 
 typedef struct ssl_st SSL;
 
+/*
+ * Explicit owner of protocol I/O.  A session does not own the descriptors or
+ * SSL object; it only describes the transport used by a transfer.  This makes
+ * it safe to pass the transport to a worker without relying on inherited
+ * thread-local state.
+ */
+typedef struct ProtocolSession {
+  int read_fd;
+  int write_fd;
+  SSL* ssl;
+  unsigned long long bwlimit;
+  long long bw_tokens;
+  long long bw_last_refill_sec;
+  long bw_last_refill_nsec;
+  atomic_ullong total_allocated_bytes;
+  bool eight_bit_output;
+  unsigned long long max_alloc;
+} ProtocolSession;
+
 typedef int Status;
 enum NET_STATUS {
   STATUS_OK,
@@ -39,6 +64,29 @@ void io_set_fds(int read_fd, int write_fd);
 void io_set_bwlimit(unsigned long long bytes_per_sec);
 void io_set_ssl(SSL* ssl);
 SSL* io_get_ssl(void);
+
+void protocol_session_init(ProtocolSession* session, int read_fd, int write_fd);
+/* Transitional bridge for helpers whose signatures still carry only an fd. */
+void protocol_session_bind(ProtocolSession* session);
+void protocol_session_unbind(void);
+void protocol_session_set_ssl(ProtocolSession* session, SSL* ssl);
+void protocol_session_set_bwlimit(ProtocolSession* session, unsigned long long bytes_per_sec);
+void protocol_session_set_max_alloc(ProtocolSession* session, unsigned long long max_alloc);
+void* protocol_alloc(size_t size);
+void* protocol_realloc(void* ptr, size_t size);
+void protocol_session_set_8_bit_output(ProtocolSession* session, bool enabled);
+void protocol_set_8_bit_output(bool enabled);
+bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t data_size);
+bool protocol_receive_n_data(ProtocolSession* session, void* data, size_t data_size);
+bool protocol_send_str(ProtocolSession* session, const char* data);
+char* protocol_receive_str(ProtocolSession* session);
+bool protocol_send_data(ProtocolSession* session, const Data* data);
+Data* protocol_receive_data(ProtocolSession* session);
+Data* protocol_receive_data_limited(ProtocolSession* session, unsigned long long maximum_size);
+bool protocol_send_int(ProtocolSession* session, int data);
+bool protocol_receive_int(ProtocolSession* session, int* data);
+bool protocol_send_status(ProtocolSession* session, Status status);
+bool protocol_receive_status(ProtocolSession* session, Status* status);
 bool send_n_data(int file_descriptor, const void* data, size_t data_size);
 bool receive_n_data(int file_descriptor, void* data, size_t data_size);
 
@@ -46,6 +94,7 @@ bool send_str(int file_descriptor, const char* data);
 char* receive_str(int file_descriptor);
 bool send_data(int file_descriptor, const Data* data);
 Data* receive_data(int file_descriptor);
+Data* receive_data_limited(int file_descriptor, unsigned long long maximum_size);
 bool send_int(int file_descriptor, int data);
 bool receive_int(int file_descriptor, int* data);
 bool send_status(int file_descriptor, Status status);

src/shared/queue.c

@@ -1,3 +1,4 @@
+#include "log.h"
 #include <stdbool.h>
 #include <limits.h>
 #include <stdio.h>
@@ -13,7 +14,7 @@ Queue* queue_create(int capacity, void (*destroyer)(void* item)) {
 
   Queue* queue = (Queue*)malloc(sizeof(Queue));
   if (queue == NULL) {
-    perror("ERROR: Could not allocate memory for queue structure");
+    log_perror("ERROR: Could not allocate memory for queue structure");
     return NULL;
   }
 
@@ -72,7 +73,7 @@ static bool queue_double_capacity(Queue* queue) {
     new_capacity = 100;
   void** new_items = malloc(new_capacity * sizeof(void*));
   if (new_items == NULL) {
-    perror("ERROR: Could not allocate memory for doubling capacity of queue.");
+    log_perror("ERROR: Could not allocate memory for doubling capacity of queue.");
     return false;
   }
   for (int i = 0; i < queue->size; i++)
@@ -127,7 +128,7 @@ bool queue_enqueue_multithreaded_cancel(Queue* queue, void* item, mtx_t* mutex,
 
 void* queue_dequeue(Queue* queue) {
   if (queue == NULL || queue_is_empty(queue)) {
-    perror("ERROR: Could not dequeue from null or empty queue.");
+    log_perror("ERROR: Could not dequeue from null or empty queue.");
     return NULL;
   }
 

src/shared/transport_ssh.c

@@ -1,7 +1,9 @@
+#include "log.h"
 #include "transport_ssh.h"
 #include "utils.h"
 #include <fcntl.h>
 #include <stdio.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
@@ -14,6 +16,12 @@ typedef struct {
   char* remote_path;
 } RemoteDest;
 
+static void ssh_child_setup_failed(int status_fd) {
+  ssize_t wret = write(status_fd, "x", 1);
+  (void)wret;
+  _exit(1);
+}
+
 static void remote_dest_destroy(RemoteDest* r) {
   free(r->user);
   free(r->host);
@@ -67,16 +75,63 @@ static int parse_remote_dest(const char* dest, RemoteDest* r) {
   return 0;
 }
 
-Client* client_connect_ssh(const char* destination, int port, const char* server_path) {
+char* ssh_build_remote_command(const char* server_path, bool old_args) {
+  const char* path = server_path ? server_path : "fastsync-server";
+  const char* suffix = " --stdio";
+  size_t path_len = strlen(path);
+  size_t suffix_len = strlen(suffix);
+
+  if (old_args) {
+    if (path_len > SIZE_MAX - suffix_len - 1)
+      return NULL;
+    char* command = malloc(path_len + suffix_len + 1);
+    if (!command)
+      return NULL;
+    memcpy(command, path, path_len);
+    memcpy(command + path_len, suffix, suffix_len + 1);
+    return command;
+  }
+
+  /* Quote the executable as one remote-shell word. This is the default safety boundary. */
+  size_t quote_count = 0;
+  for (const char* p = path; *p; p++)
+    if (*p == '\'')
+      quote_count++;
+  if (path_len > SIZE_MAX - suffix_len - 4 ||
+      quote_count > (SIZE_MAX - path_len - suffix_len - 4) / 4)
+    return NULL;
+  size_t command_len = path_len + quote_count * 4 + suffix_len + 4;
+  char* command = malloc(command_len + 1);
+  if (!command)
+    return NULL;
+  char* out = command;
+  *out++ = '\'';
+  for (const char* p = path; *p; p++) {
+    if (*p == '\'') {
+      memcpy(out, "'\\''", 4);
+      out += 4;
+    } else {
+      *out++ = *p;
+    }
+  }
+  *out++ = '\'';
+  memcpy(out, suffix, suffix_len + 1);
+  return command;
+}
+
+Client* client_connect_ssh(const char* destination, int port, const char* server_path,
+                           bool old_args) {
   RemoteDest r;
   if (parse_remote_dest(destination, &r) != 0) {
-    fprintf(stderr, "Invalid remote destination: %s\n", destination);
+    char* escaped = output_escape(destination, false);
+    fprintf(stderr, "Invalid remote destination: %s\n", escaped ? escaped : "<allocation failed>");
+    free(escaped);
     return NULL;
   }
 
   int sv[2];
   if (socketpair(AF_UNIX, SOCK_STREAM, 0, sv) < 0) {
-    perror("socketpair failed");
+    log_perror("socketpair failed");
     remote_dest_destroy(&r);
     return NULL;
   }
@@ -89,7 +144,7 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
 
   int exec_pipe[2];
   if (pipe(exec_pipe) < 0) {
-    perror("pipe failed");
+    log_perror("pipe failed");
     close(sv[0]);
     close(sv[1]);
     remote_dest_destroy(&r);
@@ -98,7 +153,7 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
 
   pid_t pid = fork();
   if (pid < 0) {
-    perror("fork failed");
+    log_perror("fork failed");
     close(sv[0]);
     close(sv[1]);
     close(exec_pipe[0]);
@@ -110,11 +165,12 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
   if (pid == 0) {
     close(sv[0]);
     close(exec_pipe[0]);
-    fcntl(exec_pipe[1], F_SETFD, FD_CLOEXEC);
-    if (sv[1] != STDIN_FILENO)
-      dup2(sv[1], STDIN_FILENO);
-    if (sv[1] != STDOUT_FILENO)
-      dup2(sv[1], STDOUT_FILENO);
+    if (fcntl(exec_pipe[1], F_SETFD, FD_CLOEXEC) < 0)
+      ssh_child_setup_failed(exec_pipe[1]);
+    if (sv[1] != STDIN_FILENO && dup2(sv[1], STDIN_FILENO) < 0)
+      ssh_child_setup_failed(exec_pipe[1]);
+    if (sv[1] != STDOUT_FILENO && dup2(sv[1], STDOUT_FILENO) < 0)
+      ssh_child_setup_failed(exec_pipe[1]);
     if (sv[1] > 1)
       close(sv[1]);
 
@@ -125,7 +181,7 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
       ssh_user_len = strlen(r.host) + 1;
     char* ssh_user = malloc(ssh_user_len);
     if (!ssh_user)
-      _exit(1);
+      ssh_child_setup_failed(exec_pipe[1]);
     if (r.user && r.user[0] != '\0')
       snprintf(ssh_user, ssh_user_len, "%s@%s", r.user, r.host);
     else
@@ -134,6 +190,9 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
     char* ssh_argv[16];
     int ac = 0;
     char port_str[16];
+    char* remote_command = ssh_build_remote_command(server_path, old_args);
+    if (!remote_command)
+      ssh_child_setup_failed(exec_pipe[1]);
     ssh_argv[ac++] = "ssh";
     ssh_argv[ac++] = "-o";
     ssh_argv[ac++] = "Compression=no";
@@ -147,14 +206,11 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
       ssh_argv[ac++] = port_str;
     }
     ssh_argv[ac++] = ssh_user;
-    ssh_argv[ac++] = (char*)(server_path ? server_path : "fastsync-server");
-    ssh_argv[ac++] = "--stdio";
+    ssh_argv[ac++] = remote_command;
     ssh_argv[ac] = NULL;
     execvp("ssh", ssh_argv);
-    perror("exec of ssh failed");
-    ssize_t wret = write(exec_pipe[1], "x", 1);
-    (void)wret;
-    _exit(1);
+    log_perror("exec of ssh failed");
+    ssh_child_setup_failed(exec_pipe[1]);
   }
 
   close(sv[1]);
@@ -164,12 +220,15 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
   ssize_t n = read(exec_pipe[0], &exec_status, 1);
   close(exec_pipe[0]);
 
-  if (n > 0) {
+  if (n != 0) {
     close(sv[0]);
     waitpid(pid, NULL, 0);
     remote_dest_destroy(&r);
+    const char* path = server_path ? server_path : "fastsync-server";
+    char* escaped = output_escape(path, false);
     fprintf(stderr, "Error: could not launch '%s --stdio' on remote\n",
-            server_path ? server_path : "fastsync-server");
+            escaped ? escaped : "<allocation failed>");
+    free(escaped);
     return NULL;
   }
 

src/shared/transport_ssh.h

@@ -3,6 +3,8 @@
 
 #include "transport_tcp.h"
 
-Client* client_connect_ssh(const char* destination, int port, const char* server_path);
+Client* client_connect_ssh(const char* destination, int port, const char* server_path,
+                           bool old_args);
+char* ssh_build_remote_command(const char* server_path, bool old_args);
 
 #endif

src/shared/transport_tcp.c

@@ -1,6 +1,7 @@
 #include "transport_tcp.h"
 #include "log.h"
 #include "protocol.h"
+#include "utils.h"
 #include <arpa/inet.h>
 #include <errno.h>
 #include <netdb.h>
@@ -30,20 +31,20 @@ static void sigchld_handler(int sig) {
 Server* server_create(int port) {
   Server* server = (Server*)malloc(sizeof(Server));
   if (server == NULL) {
-    perror("Could not allocate space for Server");
+    log_perror("Could not allocate space for Server");
     return NULL;
   }
 
   int file_descriptor = socket(AF_INET, SOCK_STREAM, 0);
   if (file_descriptor < 0) {
-    perror("Could not create Socket!");
+    log_perror("Could not create Socket!");
     free(server);
     return NULL;
   }
   server->file_descriptor = file_descriptor;
   int opt = 1;
   if (setsockopt(server->file_descriptor, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) {
-    perror("Error setting a socket option!");
+    log_perror("Error setting a socket option!");
     close(server->file_descriptor);
     free(server);
     return NULL;
@@ -59,7 +60,7 @@ Server* server_create(int port) {
 
   if (bind(server->file_descriptor, (struct sockaddr*)&server->address, server->address_length) <
       0) {
-    perror("Could not bind server");
+    log_perror("Could not bind server");
     close(server->file_descriptor);
     free(server);
     return NULL;
@@ -83,7 +84,7 @@ void server_delete(Server** server) {
 static void accept_loop(Server* server, void (*child_fn)(int, void*), void* child_ctx,
                         const char* log_fmt) {
   if (listen(server->file_descriptor, SOMAXCONN) < 0) {
-    perror("Could not listen on port!");
+    log_perror("Could not listen on port!");
     return;
   }
   signal(SIGCHLD, sigchld_handler);
@@ -92,7 +93,7 @@ static void accept_loop(Server* server, void (*child_fn)(int, void*), void* chil
     socklen_t client_len = sizeof(client_addr);
     int fd = accept(server->file_descriptor, (struct sockaddr*)&client_addr, &client_len);
     if (fd < 0) {
-      perror("Could not accept the connection");
+      log_perror("Could not accept the connection");
       continue;
     }
     tcp_apply_socket_timeout(fd);
@@ -151,6 +152,10 @@ int tcp_get_contimeout_sec(void) {
   return g_contimeout_sec;
 }
 
+int tcp_get_timeout_sec(void) {
+  return g_timeout_sec;
+}
+
 static void tcp_apply_socket_timeout(int fd) {
   struct timeval tv;
   tv.tv_sec = g_timeout_sec;
@@ -173,7 +178,7 @@ Client* client_create() {
   return client;
 }
 
-bool client_connect(Client* client, char* host, int port) {
+bool tcp_connect_socket(Client* client, char* host, int port) {
   struct addrinfo hints;
   struct addrinfo* result;
   memset(&hints, 0, sizeof(hints));
@@ -186,7 +191,10 @@ bool client_connect(Client* client, char* host, int port) {
 
   int err = getaddrinfo(host, port_str, &hints, &result);
   if (err != 0 || result == NULL) {
-    fprintf(stderr, "Could not resolve host: %s (%s)\n", host, gai_strerror(err));
+    char* escaped_host = output_escape(host, false);
+    fprintf(stderr, "Could not resolve host: %s (%s)\n",
+            escaped_host ? escaped_host : "<allocation failed>", gai_strerror(err));
+    free(escaped_host);
     return false;
   }
 
@@ -218,10 +226,16 @@ bool client_connect(Client* client, char* host, int port) {
   freeaddrinfo(result);
 
   if (!connected) {
-    perror("Could not connect to Server!");
+    log_perror("Could not connect to Server!");
     return false;
   }
 
+  return true;
+}
+
+bool client_connect(Client* client, char* host, int port) {
+  if (!tcp_connect_socket(client, host, port))
+    return false;
   tcp_apply_socket_timeout(client->file_descriptor);
   return true;
 }

src/shared/transport_tcp.h

@@ -30,9 +30,11 @@ void server_accept_loop(Server* server, void (*child_fn)(int, void*), void* chil
 void server_delete(Server** server);
 Client* client_create();
 bool client_connect(Client* client, char* host, int port);
+bool tcp_connect_socket(Client* client, char* host, int port);
 void client_disconnect(Client* client);
 void client_delete(Client* client);
 void tcp_set_timeouts(int timeout_sec, int contimeout_sec);
 int tcp_get_contimeout_sec(void);
+int tcp_get_timeout_sec(void);
 
 #endif

src/shared/transport_tls.c

@@ -2,8 +2,8 @@
 #include "log.h"
 #include "protocol.h"
 #include "transport_tcp.h"
+#include "utils.h"
 #include <arpa/inet.h>
-#include <netdb.h>
 #include <openssl/err.h>
 #include <openssl/ssl.h>
 #include <signal.h>
@@ -11,7 +11,9 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 #include <sys/wait.h>
+#include <time.h>
 #include <unistd.h>
 
 bool tls_global_init(void) {
@@ -34,6 +36,10 @@ static void log_ssl_errors(void) {
 
 static SSL_CTX* create_ssl_ctx(bool is_server, const char* cert, const char* key,
                                const char* ca_path) {
+  if (!is_server && !ca_path) {
+    log_message(LOG_LEVEL_ERROR, "TLS clients require a CA certificate path");
+    return NULL;
+  }
   const SSL_METHOD* method = is_server ? TLS_server_method() : TLS_client_method();
   SSL_CTX* ctx = SSL_CTX_new(method);
   if (!ctx) {
@@ -42,17 +48,37 @@ static SSL_CTX* create_ssl_ctx(bool is_server, const char* cert, const char* key
     return NULL;
   }
 
-  SSL_CTX_set_min_proto_version(ctx, TLS1_2_VERSION);
+  if (SSL_CTX_set_min_proto_version(ctx, TLS1_2_VERSION) != 1) {
+    SSL_CTX_free(ctx);
+    return NULL;
+  }
+  if (SSL_CTX_set_cipher_list(ctx, "HIGH:!aNULL:!eNULL:!MD5:!RC4:!3DES") != 1) {
+    SSL_CTX_free(ctx);
+    return NULL;
+  }
 
   if (cert && key) {
+    struct stat key_stat;
+    if (stat(key, &key_stat) != 0 || !S_ISREG(key_stat.st_mode) || key_stat.st_uid != geteuid() ||
+        (key_stat.st_mode & (S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH))) {
+      log_message(LOG_LEVEL_ERROR, "TLS private key must be owned by the current user and private");
+      SSL_CTX_free(ctx);
+      return NULL;
+    }
     if (SSL_CTX_use_certificate_file(ctx, cert, SSL_FILETYPE_PEM) <= 0) {
-      log_message(LOG_LEVEL_ERROR, "Failed to load certificate: %s", cert);
+      char* escaped = output_escape(cert, false);
+      log_message(LOG_LEVEL_ERROR, "Failed to load certificate: %s",
+                  escaped ? escaped : "<allocation failed>");
+      free(escaped);
       log_ssl_errors();
       SSL_CTX_free(ctx);
       return NULL;
     }
     if (SSL_CTX_use_PrivateKey_file(ctx, key, SSL_FILETYPE_PEM) <= 0) {
-      log_message(LOG_LEVEL_ERROR, "Failed to load private key: %s", key);
+      char* escaped = output_escape(key, false);
+      log_message(LOG_LEVEL_ERROR, "Failed to load private key: %s",
+                  escaped ? escaped : "<allocation failed>");
+      free(escaped);
       log_ssl_errors();
       SSL_CTX_free(ctx);
       return NULL;
@@ -66,7 +92,10 @@ static SSL_CTX* create_ssl_ctx(bool is_server, const char* cert, const char* key
 
   if (ca_path) {
     if (!SSL_CTX_load_verify_locations(ctx, ca_path, NULL)) {
-      log_message(LOG_LEVEL_ERROR, "Failed to load CA: %s", ca_path);
+      char* escaped = output_escape(ca_path, false);
+      log_message(LOG_LEVEL_ERROR, "Failed to load CA: %s",
+                  escaped ? escaped : "<allocation failed>");
+      free(escaped);
       log_ssl_errors();
       SSL_CTX_free(ctx);
       return NULL;
@@ -86,15 +115,22 @@ static SSL* wrap_fd_with_ssl(int fd, SSL_CTX* ctx, bool is_server, const char* h
     log_message(LOG_LEVEL_ERROR, "Failed to create SSL object");
     return NULL;
   }
-  SSL_set_fd(ssl, fd);
+  if (SSL_set_fd(ssl, fd) != 1) {
+    SSL_free(ssl);
+    return NULL;
+  }
 
   // Enable hostname verification for client connections when a hostname is provided.
   // Must be done before SSL_connect to take effect during the handshake.
   if (!is_server && hostname) {
-    SSL_set1_host(ssl, hostname);
+    if (SSL_set1_host(ssl, hostname) != 1) {
+      SSL_free(ssl);
+      return NULL;
+    }
   }
 
   // Retry SSL_accept/SSL_connect on WANT_READ/WANT_WRITE (non-blocking handshake)
+  time_t deadline = time(NULL) + (is_server ? tcp_get_timeout_sec() : tcp_get_contimeout_sec());
   int ret;
   do {
     if (is_server)
@@ -104,7 +140,8 @@ static SSL* wrap_fd_with_ssl(int fd, SSL_CTX* ctx, bool is_server, const char* h
 
     if (ret <= 0) {
       int ssl_err = SSL_get_error(ssl, ret);
-      if (ssl_err == SSL_ERROR_WANT_READ || ssl_err == SSL_ERROR_WANT_WRITE)
+      if ((ssl_err == SSL_ERROR_WANT_READ || ssl_err == SSL_ERROR_WANT_WRITE) &&
+          time(NULL) < deadline)
         continue;
       log_message(LOG_LEVEL_ERROR, "SSL %s failed", is_server ? "accept" : "connect");
       log_ssl_errors();
@@ -132,8 +169,10 @@ struct tls_child_ctx {
 static void tls_child_fn(int fd, void* arg) {
   struct tls_child_ctx* ctx = (struct tls_child_ctx*)arg;
   SSL* ssl = wrap_fd_with_ssl(fd, ctx->ssl_ctx, true, NULL);
-  if (!ssl)
+  if (!ssl) {
+    io_set_ssl(NULL);
     return;
+  }
   io_set_ssl(ssl);
   ctx->handler(fd);
   SSL_shutdown(ssl);
@@ -149,57 +188,19 @@ bool server_listen_tls(Server* server, void (*handler)(int file_descriptor)) {
 
 bool client_connect_tls(Client* client, char* host, int port, const char* cert_path,
                         const char* key_path, const char* ca_path) {
-  struct addrinfo hints;
-  struct addrinfo* result;
-  memset(&hints, 0, sizeof(hints));
-  hints.ai_family = AF_UNSPEC;
-  hints.ai_socktype = SOCK_STREAM;
-  hints.ai_protocol = IPPROTO_TCP;
-
-  char port_str[16];
-  snprintf(port_str, sizeof(port_str), "%d", port);
-
-  int err = getaddrinfo(host, port_str, &hints, &result);
-  if (err != 0 || result == NULL) {
-    fprintf(stderr, "Could not resolve host: %s (%s)\n", host, gai_strerror(err));
-    return false;
-  }
-
-  struct addrinfo* rp;
-  bool connected = false;
-  for (rp = result; rp != NULL; rp = rp->ai_next) {
+  if (!tcp_connect_socket(client, host, port)) {
     if (client->file_descriptor >= 0)
       close(client->file_descriptor);
-
-    client->file_descriptor = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
-    if (client->file_descriptor < 0)
-      continue;
-
-    struct timeval ct;
-    ct.tv_sec = tcp_get_contimeout_sec();
-    ct.tv_usec = 0;
-    setsockopt(client->file_descriptor, SOL_SOCKET, SO_RCVTIMEO, &ct, sizeof(ct));
-    setsockopt(client->file_descriptor, SOL_SOCKET, SO_SNDTIMEO, &ct, sizeof(ct));
-
-    memcpy(&client->address, rp->ai_addr, rp->ai_addrlen);
-    client->address_length = rp->ai_addrlen;
-
-    if (connect(client->file_descriptor, (struct sockaddr*)&client->address,
-                client->address_length) == 0) {
-      connected = true;
-      break;
-    }
-  }
-  freeaddrinfo(result);
-
-  if (!connected) {
-    perror("Could not connect to Server!");
+    client->file_descriptor = -1;
     return false;
   }
 
   SSL_CTX* ctx = create_ssl_ctx(false, cert_path, key_path, ca_path);
-  if (!ctx)
+  if (!ctx) {
+    close(client->file_descriptor);
+    client->file_descriptor = -1;
     return false;
+  }
   client->ssl_ctx = ctx;
 
   // Pass the server hostname for TLS hostname verification (SSL_set1_host
@@ -209,6 +210,8 @@ bool client_connect_tls(Client* client, char* host, int port, const char* cert_p
   if (!ssl) {
     SSL_CTX_free(ctx);
     client->ssl_ctx = NULL;
+    close(client->file_descriptor);
+    client->file_descriptor = -1;
     return false;
   }
 

src/shared/utils.c

@@ -1,68 +1,124 @@
 #include "utils.h"
 #include "array_list.h"
 #include "libgen.h"
+#include "log.h"
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stdint.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
 static int authorized_root_fd = -1;
+static char* authorized_root_path;
+
+bool utils_set_authorized_root(int fd, const char* canonical_path) {
+  char* path_copy = canonical_path ? str_dup(canonical_path) : NULL;
+  if (canonical_path && !path_copy) {
+    authorized_root_fd = -1;
+    free(authorized_root_path);
+    authorized_root_path = NULL;
+    return false;
+  }
+  authorized_root_fd = fd;
+  free(authorized_root_path);
+  authorized_root_path = path_copy;
+  return true;
+}
 
 void utils_set_authorized_root_fd(int fd) {
-  authorized_root_fd = fd;
+  (void)utils_set_authorized_root(fd, NULL);
+}
+
+static bool path_is_within_root(const char* root, const char* path) {
+  size_t root_len = strlen(root);
+  return strncmp(root, path, root_len) == 0 && (path[root_len] == '\0' || path[root_len] == '/');
+}
+
+static int open_authorized_destination(const char* dest_root) {
+  if (authorized_root_fd < 0 || !authorized_root_path || !dest_root ||
+      !path_is_within_root(authorized_root_path, dest_root))
+    return -1;
+
+  int dirfd = dup(authorized_root_fd);
+  if (dirfd < 0)
+    return -1;
+
+  const char* relative_path = dest_root + strlen(authorized_root_path);
+  while (*relative_path == '/')
+    relative_path++;
+  char* relative = str_dup(*relative_path ? relative_path : ".");
+  if (!relative) {
+    close(dirfd);
+    return -1;
+  }
+
+  char* saveptr = NULL;
+  char* component = strtok_r(relative, "/", &saveptr);
+  while (component) {
+    if (strcmp(component, "..") == 0) {
+      free(relative);
+      close(dirfd);
+      return -1;
+    }
+    if (strcmp(component, ".") == 0) {
+      component = strtok_r(NULL, "/", &saveptr);
+      continue;
+    }
+    int next = openat(dirfd, component, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+    if (next < 0) {
+      free(relative);
+      close(dirfd);
+      return -1;
+    }
+    close(dirfd);
+    dirfd = next;
+    component = strtok_r(NULL, "/", &saveptr);
+  }
+
+  free(relative);
+  return dirfd;
 }
 
 bool mkdir_r(const char* path) {
-  size_t path_len = strlen(path);
-  char* path_duplicate = malloc(path_len + 1);
-  if (!path_duplicate)
+  if (!path || *path == '\0')
     return false;
-  memcpy(path_duplicate, path, path_len + 1);
-  size_t capacity = path_len + 2;
-  char* path_current = (char*)malloc(capacity * sizeof(char));
-  if (!path_current) {
-    free(path_duplicate);
+  char* duplicate = str_dup(path);
+  if (!duplicate)
+    return false;
+  int dirfd = open(path[0] == '/' ? "/" : ".", O_RDONLY | O_DIRECTORY | O_CLOEXEC | O_NOFOLLOW);
+  if (dirfd < 0) {
+    free(duplicate);
     return false;
   }
-  char* path_current_position = path_current;
-  if (path[0] == '/') {
-    path_current[0] = '/';
-    path_current[1] = '\0';
-    path_current_position += 1;
-  } else {
-    path_current[0] = '\0';
-  }
-  const char* delimiter = "/";
-  char* saveptr;
-  const char* part = strtok_r(path_duplicate, delimiter, &saveptr);
   bool ok = true;
-  while (part != NULL) {
-    size_t part_len = strlen(part);
-    if ((size_t)(path_current_position - path_current) + part_len + 2 > capacity) {
+  char* saveptr = NULL;
+  char* component = strtok_r(duplicate, "/", &saveptr);
+  while (component) {
+    if (strcmp(component, "..") == 0) {
       ok = false;
       break;
     }
-    memcpy(path_current_position, part, part_len);
-    path_current_position += part_len;
-    path_current_position[0] = '/';
-    path_current_position[1] = '\0';
-    path_current_position++;
-    struct stat st;
-    if (stat(path_current, &st) != 0) {
-      if (mkdir(path_current, 0755) != 0) {
-        perror("Could not create directory");
+    if (strcmp(component, ".") != 0) {
+      int next = openat(dirfd, component, O_RDONLY | O_DIRECTORY | O_CLOEXEC | O_NOFOLLOW);
+      if (next < 0 && errno == ENOENT) {
+        if (mkdirat(dirfd, component, 0755) == 0 || errno == EEXIST)
+          next = openat(dirfd, component, O_RDONLY | O_DIRECTORY | O_CLOEXEC | O_NOFOLLOW);
+      }
+      if (next < 0) {
         ok = false;
         break;
       }
+      close(dirfd);
+      dirfd = next;
     }
-    part = strtok_r(NULL, delimiter, &saveptr);
+    component = strtok_r(NULL, "/", &saveptr);
   }
-  free(path_duplicate);
-  free(path_current);
+  close(dirfd);
+  free(duplicate);
   return ok;
 }
 
@@ -77,6 +133,32 @@ char* str_dup(const char* string) {
   return new_string;
 }
 
+char* output_escape(const char* string, bool eight_bit_output) {
+  if (!string)
+    return NULL;
+  size_t length = strlen(string);
+  if (length > (SIZE_MAX - 1) / 5)
+    return NULL;
+  char* escaped = malloc(length * 5 + 1);
+  if (!escaped)
+    return NULL;
+  size_t out = 0;
+  for (size_t i = 0; i < length; i++) {
+    unsigned char byte = (unsigned char)string[i];
+    if ((byte >= 32 && byte <= 126) || (eight_bit_output && byte >= 128)) {
+      escaped[out++] = (char)byte;
+    } else {
+      escaped[out++] = '\\';
+      escaped[out++] = '#';
+      escaped[out++] = (char)('0' + ((byte >> 6) & 7));
+      escaped[out++] = (char)('0' + ((byte >> 3) & 7));
+      escaped[out++] = (char)('0' + (byte & 7));
+    }
+  }
+  escaped[out] = '\0';
+  return escaped;
+}
+
 /* Match a glob pattern against a string. Supported wildcards:
  *   ?      matches any single character except '/'.
  *   *      matches any sequence of characters within one path component (no '/').
@@ -132,6 +214,25 @@ bool glob_match(const char* pattern, const char* str) {
   return *str == '\0';
 }
 
+bool format_human_bytes(unsigned long long bytes, char* buffer, size_t buffer_size) {
+  static const char* const units[] = {"B", "KB", "MB", "GB", "TB", "PB", "EB"};
+  double value = (double)bytes;
+  size_t unit = 0;
+  int written;
+
+  if (!buffer || buffer_size == 0)
+    return false;
+  while (value >= 1024.0 && unit < sizeof(units) / sizeof(units[0]) - 1) {
+    value /= 1024.0;
+    unit++;
+  }
+  if (unit == 0)
+    written = snprintf(buffer, buffer_size, "%llu %s", bytes, units[unit]);
+  else
+    written = snprintf(buffer, buffer_size, "%.1f %s", value, units[unit]);
+  return written >= 0 && (size_t)written < buffer_size;
+}
+
 static bool is_dir_in_manifest(const char* rel_path, ArrayList* manifest) {
   size_t len = strlen(rel_path);
   for (int i = 0; i < manifest->size; i++) {
@@ -143,7 +244,8 @@ static bool is_dir_in_manifest(const char* rel_path, ArrayList* manifest) {
   return false;
 }
 
-static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifest) {
+static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifest,
+                             size_t max_delete, size_t* deleted_count) {
   int scanfd = dup(dirfd);
   if (scanfd < 0)
     return false;
@@ -152,15 +254,20 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifes
     close(scanfd);
     return false;
   }
-  bool all_removed = true;
   bool operation_ok = true;
   const struct dirent* entry;
   while ((entry = readdir(dir)) != NULL) {
     if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
       continue;
     char* child_rel = path_cat((char*)rel_path, entry->d_name);
+    if (!child_rel) {
+      operation_ok = false;
+      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;
     }
@@ -173,14 +280,24 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifes
       int childfd = openat(dirfd, entry->d_name, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
       bool child_removed = false;
       if (childfd >= 0) {
-        child_removed = delete_extras_fd(childfd, child_rel, manifest);
+        child_removed = delete_extras_fd(childfd, child_rel, manifest, max_delete, deleted_count);
+        if (!child_removed)
+          operation_ok = false;
         close(childfd);
-      }
-      if (child_removed && !is_dir_in_manifest(child_rel, manifest) &&
-          unlinkat(dirfd, entry->d_name, AT_REMOVEDIR) != 0 && errno != ENOENT) {
+      } else if (errno != ENOENT) {
         operation_ok = false;
-      } else if (!child_removed) {
-        all_removed = false;
+      }
+      if (child_removed && !is_dir_in_manifest(child_rel, manifest)) {
+        if (*deleted_count >= max_delete) {
+          operation_ok = false;
+        } else {
+          if (unlinkat(dirfd, entry->d_name, AT_REMOVEDIR) != 0) {
+            if (errno != ENOENT)
+              operation_ok = false;
+          } else {
+            (*deleted_count)++;
+          }
+        }
       }
     } else {
       // Check if relative path is in manifest
@@ -192,38 +309,61 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifes
         }
       }
       if (!found) {
-        if (unlinkat(dirfd, entry->d_name, 0) != 0 && errno != ENOENT)
+        if (*deleted_count >= max_delete) {
           operation_ok = false;
-        fprintf(stderr, "  Deleted: %s\n", child_rel);
-      } else {
-        all_removed = false;
+          free(child_rel);
+          continue;
+        }
+        if (unlinkat(dirfd, entry->d_name, 0) != 0) {
+          if (errno != ENOENT)
+            operation_ok = false;
+        } else {
+          (*deleted_count)++;
+        }
+        char* escaped_path = output_escape(child_rel, log_get_8_bit_output());
+        fprintf(stderr, "  Deleted: %s\n", escaped_path ? escaped_path : "<allocation failed>");
+        free(escaped_path);
       }
     }
     free(child_rel);
   }
   closedir(dir);
-  (void)all_removed;
   return operation_ok;
 }
 
-bool delete_extras(const char* dest_root, ArrayList* manifest) {
-  int rootfd = authorized_root_fd >= 0
-                   ? dup(authorized_root_fd)
-                   : open(dest_root, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+bool delete_extras_limited(const char* dest_root, ArrayList* manifest, size_t max_delete) {
+  if (!manifest)
+    return false;
+  int rootfd;
+  if (authorized_root_fd >= 0) {
+    if (authorized_root_path)
+      rootfd = open_authorized_destination(dest_root);
+    else if (dest_root == NULL)
+      rootfd = dup(authorized_root_fd);
+    else
+      rootfd = -1;
+  } else {
+    rootfd = open(dest_root, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+  }
   if (rootfd < 0)
     return false;
-  bool ok = delete_extras_fd(rootfd, "", manifest);
+  size_t deleted_count = 0;
+  bool ok = delete_extras_fd(rootfd, "", manifest, max_delete, &deleted_count);
   if (close(rootfd) != 0)
     ok = false;
   return ok;
 }
 
+bool delete_extras(const char* dest_root, ArrayList* manifest) {
+  return delete_extras_limited(dest_root, manifest, SIZE_MAX);
+}
+
 bool has_path_traversal(const char* path) {
   if (!path)
-    return false;
+    return true;
   char* dup = str_dup(path);
   if (!dup)
-    return false;
+    return true;
   char* saveptr;
   const char* part = strtok_r(dup, "/", &saveptr);
   while (part) {
@@ -237,6 +377,10 @@ bool has_path_traversal(const char* path) {
   return false;
 }
 
+bool utils_valid_batch_path(const char* path) {
+  return path && path[0] != '\0' && path[0] != '/' && !has_path_traversal(path);
+}
+
 char* path_cat(const char* path1, const char* path2) {
   if (path1 == NULL || *path1 == '\0')
     return str_dup(path2);
@@ -251,6 +395,8 @@ char* path_cat(const char* path1, const char* path2) {
     offset = 1;
     path2_len -= 1;
   }
+  if (path1_len > SIZE_MAX - path2_len - 2)
+    return NULL;
   char* new_path = malloc(path1_len + path2_len + 2);
   if (new_path == NULL)
     return NULL;

src/shared/utils.h

@@ -2,14 +2,22 @@
 #define UTILS_H
 
 #include "array_list.h"
+#include <stddef.h>
 #include <stdbool.h>
 
 bool mkdir_r(const char* path);
 char* str_dup(const char* string);
+char* output_escape(const char* string, bool eight_bit_output);
 char* path_cat(const char* path1, const char* path2);
 bool glob_match(const char* pattern, const char* str);
 bool delete_extras(const char* dest_root, ArrayList* manifest);
+bool delete_extras_limited(const char* dest_root, ArrayList* manifest, size_t max_delete);
+bool utils_set_authorized_root(int fd, const char* canonical_path);
+/* The fd-only compatibility form is fail-closed for path-based operations;
+ * callers should use utils_set_authorized_root with the canonical identity. */
 void utils_set_authorized_root_fd(int fd);
 bool has_path_traversal(const char* path);
+bool utils_valid_batch_path(const char* path);
+bool format_human_bytes(unsigned long long bytes, char* buffer, size_t buffer_size);
 
 #endif

tests/integration/common.py

@@ -25,7 +25,9 @@ class ServerManager:
     def start(self, extra_args=None):
         self.stop()
         self._port = _find_free_port()
-        cmd = SERVER_CMD + ["-p", str(self._port)]
+        # Plain TCP is intentionally explicit in the server; integration tests
+        # exercise that opt-in mode rather than relying on the secure default.
+        cmd = SERVER_CMD + ["-p", str(self._port), "--allow-unauthenticated"]
         if extra_args:
             cmd += extra_args
         self._proc = subprocess.Popen(cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)

tests/integration/test_features.py

@@ -26,6 +26,12 @@ def setup_test_data():
 
 
 class TestDryRun:
+    def test_human_readable_dry_run(self):
+        result, dur = run_client(SOURCE_DIR, DEST_DIR, flags=["-h", "--dry-run"])
+        assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:100]}"
+        assert "Total:" in result.stdout
+        assert "KB" in result.stdout
+
     def test_dry_run(self):
         clean_dir(DEST_DIR)
         result, dur = run_client(
@@ -35,6 +41,118 @@ class TestDryRun:
         assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:100]}"
         assert "Dry run:" in result.stdout, f"No dry run output: {result.stdout[:200]}"
 
+    def test_quiet_suppresses_dry_run_output(self):
+        result, dur = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["-q", "-n", "--progress", "--stats"],
+        )
+        assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:100]}"
+        assert result.stdout == ""
+        assert result.stderr == ""
+
+    def test_quiet_preserves_errors(self):
+        result, dur = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["--quiet", "--server-port", "1"],
+        )
+        assert result.returncode != 0
+        assert result.stderr != ""
+
+    @pytest.mark.parametrize("flags", [["-q", "-v"], ["-v", "-q"]])
+    def test_quiet_successful_transfer_and_verbose_order(self, shared_server, flags):
+        clean_dir(DEST_DIR)
+        result, dur = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=flags,
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:100]}"
+        assert result.stdout == ""
+        assert result.stderr == ""
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        mismatches, missing = verify_transfer(SOURCE_DIR, received)
+        assert not missing, f"Missing: {missing}"
+        assert not mismatches, f"Mismatch: {mismatches}"
+
+
+class TestRemoveSourceFiles:
+    def test_removes_only_transferred_regular_files(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "remove_source")
+        dest = os.path.join(TEST_DATA_DIR, "remove_dest")
+        clean_dir(source)
+        clean_dir(dest)
+        with open(os.path.join(source, "one.txt"), "wb") as f:
+            f.write(b"one")
+        with open(os.path.join(source, "two.txt"), "wb") as f:
+            f.write(b"two")
+        os.makedirs(os.path.join(source, "directory"))
+        os.symlink("one.txt", os.path.join(source, "link.txt"))
+
+        result, _ = run_client(source, dest, flags=["--remove-source-files", "-m"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"Remove-source sync failed: {result.stderr[:200]}"
+        assert not os.path.exists(os.path.join(source, "one.txt"))
+        assert not os.path.exists(os.path.join(source, "two.txt"))
+        assert os.path.isdir(os.path.join(source, "directory"))
+        assert os.path.islink(os.path.join(source, "link.txt"))
+
+    def test_single_threaded_removes_transferred_file(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "remove_single_source")
+        dest = os.path.join(TEST_DATA_DIR, "remove_single_dest")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "file.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"single threaded")
+
+        result, _ = run_client(source, dest, flags=["--remove-source-files"],
+                               port=shared_server.port)
+        assert result.returncode == 0
+        assert not os.path.exists(source_file)
+
+    def test_dry_run_preserves_source_files(self):
+        source = os.path.join(TEST_DATA_DIR, "remove_dry_source")
+        dest = os.path.join(TEST_DATA_DIR, "remove_dry_dest")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "file.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"keep")
+
+        result, _ = run_client(source, dest, flags=["--remove-source-files", "--dry-run"])
+        assert result.returncode == 0
+        assert os.path.isfile(source_file)
+
+    def test_failed_connection_preserves_source_files(self):
+        source = os.path.join(TEST_DATA_DIR, "remove_failed_source")
+        dest = os.path.join(TEST_DATA_DIR, "remove_failed_dest")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "file.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"keep after failure")
+
+        result, _ = run_client(source, dest, flags=["--remove-source-files"], port=1)
+        assert result.returncode != 0
+        assert os.path.isfile(source_file)
+
+    def test_incremental_skip_preserves_source_file(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "remove_skipped_source")
+        dest = os.path.join(TEST_DATA_DIR, "remove_skipped_dest")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "file.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"keep after skip")
+
+        result, _ = run_client(source, dest, port=shared_server.port)
+        assert result.returncode == 0
+        result, _ = run_client(source, dest,
+                               flags=["--remove-source-files", "--incremental"],
+                               port=shared_server.port)
+        assert result.returncode == 0
+        assert os.path.isfile(source_file)
+
 
 class TestArchiveMode:
     def test_archive_mode(self, shared_server):
@@ -51,6 +169,136 @@ class TestArchiveMode:
         assert not missing, f"Missing: {missing}"
         assert not mismatches, f"Mismatch: {mismatches}"
 
+    def test_archive_implied_options_can_be_negated(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, dur = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["--archive", "--no-compress", "--no-m", "--no-preserve"],
+            port=shared_server.port,
+        )
+        if result.returncode != 0:
+            pytest.fail(f"Exit {result.returncode}: {(result.stderr or result.stdout)[:200]}")
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        mismatches, missing = verify_transfer(SOURCE_DIR, received)
+        assert not missing, f"Missing: {missing}"
+        assert not mismatches, f"Mismatch: {mismatches}"
+
+
+class TestExecutability:
+    def test_preserves_only_executable_bits(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "executability_source")
+        dest = os.path.join(TEST_DATA_DIR, "executability_dest")
+        clean_dir(source)
+        clean_dir(dest)
+        source_file = os.path.join(source, "tool.sh")
+        with open(source_file, "w") as f:
+            f.write("#!/bin/sh\necho test\n")
+        os.chmod(source_file, 0o751)
+
+        result, _ = run_client(source, dest, flags=["-E"], port=shared_server.port)
+        assert result.returncode == 0, f"Executability sync failed: {result.stderr[:200]}"
+        received_file = os.path.join(get_dest_received_dir(dest, source), "tool.sh")
+        received_mode = os.stat(received_file).st_mode
+        assert received_mode & 0o111 == 0o111
+        assert received_mode & 0o600 == 0o600
+        assert received_mode & 0o077 == 0o011
+
+
+class TestChmod:
+    def test_chmod_applies_to_transferred_files(self, shared_server):
+        clean_dir(DEST_DIR)
+        source_file = os.path.join(SOURCE_DIR, "small.txt")
+        os.chmod(source_file, 0o777)
+        result, dur = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["--chmod=u=rw,go=r"],
+            port=shared_server.port,
+        )
+        if result.returncode != 0:
+            pytest.fail(f"Exit {result.returncode}: {(result.stderr or result.stdout)[:200]}")
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        assert (os.stat(os.path.join(received, "small.txt")).st_mode & 0o777) == 0o644
+
+
+class TestCompressionChoice:
+    def test_zstd_choice_compresses(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["--zc", "zstd"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"zstd sync failed: {(result.stderr or result.stdout)[:200]}"
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        mismatches, missing = verify_transfer(SOURCE_DIR, received)
+        assert not missing, f"Missing: {missing}"
+        assert not mismatches, f"Mismatch: {mismatches}"
+
+    def test_none_choice_disables_compression(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-z", "--compress-choice", "none"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"none sync failed: {(result.stderr or result.stdout)[:200]}"
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        mismatches, missing = verify_transfer(SOURCE_DIR, received)
+        assert not missing, f"Missing: {missing}"
+        assert not mismatches, f"Mismatch: {mismatches}"
+
+
+class TestSkipCompress:
+    def test_skip_compress_case_insensitive(self, shared_server):
+        clean_dir(DEST_DIR)
+        with open(os.path.join(SOURCE_DIR, "skip-case.TXT"), "wb") as f:
+            f.write((b"skip compression case test\n" * 100))
+        result, _ = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["-c", "--skip-compress=.txt"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Skip-compress sync failed: {(result.stderr or result.stdout)[:200]}"
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        with open(os.path.join(received, "skip-case.TXT"), "rb") as f:
+            assert f.read() == b"skip compression case test\n" * 100
+
+    def test_skip_compress_empty_list(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["-c", "--skip-compress="],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Empty skip-compress sync failed: {(result.stderr or result.stdout)[:200]}"
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        mismatches, missing = verify_transfer(SOURCE_DIR, received)
+        assert not missing, f"Missing: {missing}"
+        assert not mismatches, f"Mismatch: {mismatches}"
+
+    def test_skip_compress_incremental_full_fallback(self, shared_server):
+        clean_dir(DEST_DIR)
+        path = os.path.join(SOURCE_DIR, "incremental-skip.TXT")
+        with open(path, "wb") as f:
+            f.write(b"original skipped content\n")
+        flags = ["-c", "-M", "--skip-compress=.txt"]
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=flags, port=shared_server.port)
+        assert result.returncode == 0, f"Initial sync failed: {(result.stderr or result.stdout)[:200]}"
+        with open(path, "wb") as f:
+            f.write(b"updated skipped content\n")
+        result, _ = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=flags + ["--incremental"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Incremental sync failed: {(result.stderr or result.stdout)[:200]}"
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        with open(os.path.join(received, "incremental-skip.TXT"), "rb") as f:
+            assert f.read() == b"updated skipped content\n"
+
+    def test_skip_compress_rejects_chunk_serialization(self, shared_server):
+        result, _ = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["-c", "-s", "--skip-compress=.txt"],
+            port=shared_server.port,
+        )
+        assert result.returncode != 0
+        assert "cannot be combined" in (result.stderr or result.stdout)
+
 
 class TestExclude:
     def test_exclude_single(self, shared_server):
@@ -213,6 +461,225 @@ class TestIncremental:
         with open(received_file, "rb") as f:
             assert f.read() == b"hello world\n"
 
+    def test_size_only_skips_same_size_with_different_mtime(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-M"], port=shared_server.port)
+        assert result.returncode == 0
+
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        received_file = os.path.join(received, "small.txt")
+        with open(received_file, "wb") as f:
+            f.write(b"different!!\n")
+        os.utime(received_file, (time.time() - 3600, time.time() - 3600))
+
+        result, _ = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["-M", "--incremental", "--size-only"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Size-only sync failed: {result.stderr[:200]}"
+        with open(received_file, "rb") as f:
+            assert f.read() == b"different!!\n"
+
+    def test_ignore_times_transfers_same_size_and_mtime(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-M"], port=shared_server.port)
+        assert result.returncode == 0
+
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        source_file = os.path.join(SOURCE_DIR, "small.txt")
+        received_file = os.path.join(received, "small.txt")
+        source_stat = os.stat(source_file)
+        with open(received_file, "wb") as f:
+            f.write(b"stale data!\n")
+        os.utime(received_file, (source_stat.st_atime, source_stat.st_mtime))
+
+        result, _ = run_client(SOURCE_DIR, DEST_DIR,
+                               flags=["-M", "--incremental", "--ignore-times"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"Ignore-times sync failed: {result.stderr[:200]}"
+        with open(received_file, "rb") as f:
+            assert f.read() == b"hello world\n"
+
+    def test_modify_window_allows_subsecond_mtime_difference(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-M"], port=shared_server.port)
+        assert result.returncode == 0
+
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        source_file = os.path.join(SOURCE_DIR, "small.txt")
+        received_file = os.path.join(received, "small.txt")
+        source_stat = os.stat(source_file)
+        with open(received_file, "wb") as f:
+            f.write(b"modified!!!\n")
+        os.utime(received_file, ns=(source_stat.st_atime_ns,
+                                    source_stat.st_mtime_ns - 1500000000))
+
+        result, _ = run_client(SOURCE_DIR, DEST_DIR,
+                               flags=["-M", "--incremental", "--modify-window=2"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"Modify-window sync failed: {result.stderr[:200]}"
+        with open(received_file, "rb") as f:
+            assert f.read() == b"modified!!!\n"
+
+    def test_whole_file_disables_delta_and_keeps_compression(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-M"], port=shared_server.port)
+        assert result.returncode == 0
+
+        source_file = os.path.join(SOURCE_DIR, "medium.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"whole-file replacement\n" * 5000)
+
+        result, _ = run_client(
+            SOURCE_DIR,
+            DEST_DIR,
+            flags=["-M", "--incremental", "--delta", "-W", "-c"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Whole-file sync failed: {(result.stderr or result.stdout)[:200]}"
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        mismatches, missing = verify_transfer(SOURCE_DIR, received)
+        assert not missing, f"Missing: {missing}"
+        assert not mismatches, f"Mismatch: {mismatches}"
+
+
+class TestUpdate:
+    def test_update_skips_older_destination_and_allows_equal_or_newer_source(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+        assert result.returncode == 0
+
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        source_file = os.path.join(SOURCE_DIR, "small.txt")
+        received_file = os.path.join(received, "small.txt")
+        source_stat = os.stat(source_file)
+
+        with open(received_file, "wb") as f:
+            f.write(b"newer destination\n")
+        os.utime(received_file, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns + 10_000_000_000))
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+        assert result.returncode == 0
+        with open(received_file, "rb") as f:
+            assert f.read() == b"newer destination\n"
+
+        os.utime(received_file, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns))
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+        assert result.returncode == 0
+        with open(received_file, "rb") as f:
+            assert f.read() == b"hello world\n"
+
+    def test_update_skips_unreadable_newer_destination(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+        assert result.returncode == 0
+
+        received_file = os.path.join(get_dest_received_dir(DEST_DIR, SOURCE_DIR), "small.txt")
+        source_stat = os.stat(os.path.join(SOURCE_DIR, "small.txt"))
+        with open(received_file, "wb") as f:
+            f.write(b"protected destination\n")
+        os.utime(received_file, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns + 10_000_000_000))
+        original_mode = os.stat(received_file).st_mode
+        try:
+            os.chmod(received_file, 0)
+            result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+            assert result.returncode == 0
+            os.chmod(received_file, original_mode)
+            with open(received_file, "rb") as f:
+                assert f.read() == b"protected destination\n"
+        finally:
+            os.chmod(received_file, original_mode)
+
+        with open(received_file, "wb") as f:
+            f.write(b"older destination\n")
+        os.utime(received_file, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns - 10_000_000_000))
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+        assert result.returncode == 0
+        with open(received_file, "rb") as f:
+            assert f.read() == b"hello world\n"
+
+
+class TestExisting:
+    def test_existing_updates_existing_and_skips_new(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-M"], port=shared_server.port)
+        assert result.returncode == 0, f"Initial sync failed: {(result.stderr or result.stdout)[:200]}"
+
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        source_file = os.path.join(SOURCE_DIR, "small.txt")
+        new_source_file = os.path.join(SOURCE_DIR, "new-existing-test.txt")
+        with open(source_file, "wb") as f:
+            f.write(b"updated existing content\n")
+        with open(new_source_file, "wb") as f:
+            f.write(b"this file must not be created\n")
+
+        try:
+            result, _ = run_client(SOURCE_DIR, DEST_DIR,
+                                   flags=["-M", "--existing"], port=shared_server.port)
+            assert result.returncode == 0, f"--existing sync failed: {(result.stderr or result.stdout)[:200]}"
+
+            with open(os.path.join(received, "small.txt"), "rb") as f:
+                assert f.read() == b"updated existing content\n"
+            assert not os.path.exists(os.path.join(received, "new-existing-test.txt"))
+        finally:
+            os.unlink(new_source_file)
+            with open(source_file, "wb") as f:
+                f.write(b"hello world\n")
+
+
+class TestIgnoreExisting:
+    def test_ignore_existing_preserves_existing_and_transfers_new(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, port=shared_server.port)
+        assert result.returncode == 0
+
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        existing_file = os.path.join(received, "small.txt")
+        with open(existing_file, "wb") as f:
+            f.write(b"destination content\n")
+        new_source = os.path.join(SOURCE_DIR, "new.txt")
+        try:
+            with open(new_source, "wb") as f:
+                f.write(b"new file\n")
+
+            result, _ = run_client(SOURCE_DIR, DEST_DIR,
+                                   flags=["--ignore-existing"], port=shared_server.port)
+            assert result.returncode == 0, f"Sync failed: {(result.stderr or result.stdout)[:200]}"
+            with open(existing_file, "rb") as f:
+                assert f.read() == b"destination content\n"
+            with open(os.path.join(received, "new.txt"), "rb") as f:
+                assert f.read() == b"new file\n"
+        finally:
+            if os.path.lexists(new_source):
+                os.unlink(new_source)
+
+
+class TestIgnoreExisting:
+    def test_ignore_existing_preserves_existing_and_transfers_new(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, port=shared_server.port)
+        assert result.returncode == 0
+
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        existing_file = os.path.join(received, "small.txt")
+        with open(existing_file, "wb") as f:
+            f.write(b"destination content\n")
+        new_source = os.path.join(SOURCE_DIR, "new.txt")
+        try:
+            with open(new_source, "wb") as f:
+                f.write(b"new file\n")
+
+            result, _ = run_client(SOURCE_DIR, DEST_DIR,
+                                   flags=["--ignore-existing"], port=shared_server.port)
+            assert result.returncode == 0, f"Sync failed: {(result.stderr or result.stdout)[:200]}"
+            with open(existing_file, "rb") as f:
+                assert f.read() == b"destination content\n"
+            with open(os.path.join(received, "new.txt"), "rb") as f:
+                assert f.read() == b"new file\n"
+        finally:
+            if os.path.lexists(new_source):
+                os.unlink(new_source)
+
 
 class TestDelete:
     def test_delete_removes_extra_files(self, shared_server):
@@ -263,6 +730,75 @@ class TestProgress:
         assert "Sent " in output and "MB" in output, "--progress produced no stable byte marker"
         assert "Done." in output, "--progress did not report completion"
 
+    def test_human_readable_stats(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, dur = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["-h", "--stats"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:100]}"
+        assert "Stats:" in result.stderr
+        assert "KB" in result.stderr
+
+    def test_human_readable_progress_multithreaded(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, dur = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["-m", "-h", "--progress"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Exit {result.returncode}: {result.stderr[:100]}"
+        output = result.stdout + result.stderr
+        assert "Sent " in output
+        assert "KB" in output
+        assert "Done." in output
+
+
+class TestInfo:
+    def test_info_copy_reports_transfers(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["--info=copy"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Info sync failed: {(result.stderr or result.stdout)[:200]}"
+        output = result.stdout + result.stderr
+        assert "[INFO]" in output and "Transferring" in output
+
+    def test_info_stats_reports_multithreaded_transfer(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["-m", "--info=stats"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Info stats sync failed: {(result.stderr or result.stdout)[:200]}"
+        output = result.stdout + result.stderr
+        assert "[INFO]" in output and "Transfer summary:" in output
+
+    def test_info_rejects_unknown_flag(self):
+        result, _ = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["--info=unknown"],
+        )
+        assert result.returncode != 0
+        assert "unsupported --info flag" in result.stderr
+
+    @pytest.mark.parametrize("flags", [
+        ["--info=none", "--verbose"],
+        ["--verbose", "--info=none"],
+    ])
+    def test_info_none_suppresses_verbose_info(self, shared_server, flags):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=flags, port=shared_server.port)
+        assert result.returncode == 0, f"Info sync failed: {(result.stderr or result.stdout)[:200]}"
+        output = result.stdout + result.stderr
+        assert "[INFO]" not in output
+        assert "Transferring" not in output
+        assert "Transfer summary:" not in output
+
 
 class TestBandwidthLimit:
     def test_bwlimit_runs(self, shared_server):

tests/integration/test_tcp.py

@@ -71,6 +71,11 @@ class TestTCPFlags:
         r = _run_tcp_test("Compression (-c)", shared_server.port, ["-c"])
         assert r["status"] == "Success", r["error"]
 
+    def test_compression_threads(self, shared_server):
+        r = _run_tcp_test("Compression threads (-c --compress-threads=2)", shared_server.port,
+                          ["-c", "--compress-threads=2"])
+        assert r["status"] == "Success", r["error"]
+
     def test_chunk_serialization(self, shared_server):
         r = _run_tcp_test("Chunk Serialization (-s)", shared_server.port, ["-s"])
         assert r["status"] == "Success", r["error"]

tests/integration/test_tls.py

@@ -102,6 +102,7 @@ class TestTLSBasic:
         with ServerManager() as server:
             server.start(extra_args=[
                 "--tls", "--cert", certs["server_cert"], "--key", certs["server_key"],
+                "--ca", certs["ca"], "--client-cn", "fastsync-client",
             ])
             result, dur = run_client(
                 SOURCE_DIR, DEST_DIR,
@@ -125,6 +126,7 @@ class TestTLSBasic:
         with ServerManager() as server:
             server.start(extra_args=[
                 "--tls", "--cert", certs["server_cert"], "--key", certs["server_key"],
+                "--ca", certs["ca"], "--client-cn", "fastsync-client",
             ])
             result, dur = run_client(
                 SOURCE_DIR, DEST_DIR,
@@ -149,6 +151,7 @@ class TestTLSBasic:
         with ServerManager() as server:
             server.start(extra_args=[
                 "--tls", "--cert", certs["server_cert"], "--key", certs["server_key"],
+                "--ca", certs["ca"], "--client-cn", "fastsync-client",
             ])
             result, dur = run_client(
                 SOURCE_DIR, DEST_DIR,

tests/test_array_list.c

@@ -17,6 +17,8 @@ void test_array_list() {
 
   // Test adding
   int* val1 = malloc(sizeof(int));
+  if (!val1)
+    return;
   *val1 = 42;
   array_list_add(list, val1);
   EXPECT_EQ_INT(list->size, 1);
@@ -26,6 +28,8 @@ void test_array_list() {
   // Initial capacity is 100. Let's add 105 elements.
   for (int i = 0; i < 105; i++) {
     int* val = malloc(sizeof(int));
+    if (!val)
+      return;
     *val = i;
     array_list_add(list, val);
   }

tests/test_chunk.c

@@ -11,7 +11,7 @@ static void test_file_operations() {
   char* test_content = "Hello, Chunk System!";
   unsigned long long test_len = strlen(test_content);
 
-  to_disk(test_path, test_content, test_len, false, false);
+  file_write_to_disk(test_path, test_content, test_len, false, false);
 
   File* f = file_create(test_path);
   EXPECT_NOT_NULL(f);
@@ -43,8 +43,8 @@ static void test_chunk_operations() {
   char* content2 = "chunk item number 2";
   unsigned long long len2 = strlen(content2);
 
-  to_disk(path1, content1, len1, false, false);
-  to_disk(path2, content2, len2, false, false);
+  file_write_to_disk(path1, content1, len1, false, false);
+  file_write_to_disk(path2, content2, len2, false, false);
 
   struct stat st1, st2;
   stat(path1, &st1);

tests/test_client_cli.c

@@ -1,7 +1,11 @@
 #include "test_client_cli.h"
+#include "client_validation.h"
+#include "chmod.h"
 #include "config.h"
+#include "log.h"
 #include "test_utils.h"
 #include "utils.h"
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
@@ -9,6 +13,74 @@
 /* Declaration of parse_args from client_cli.c */
 int parse_args(Config* config, int argc, char* argv[], int* positional_args, int* positional_count);
 
+static Config* valid_client_config() {
+  Config* cfg = config_create();
+  if (!cfg)
+    return NULL;
+  cfg->send_directory = str_dup("/src");
+  cfg->receive_root_directory = str_dup("/dst");
+  return cfg;
+}
+
+static void test_validate_config_required_paths() {
+  Config* cfg = config_create();
+  EXPECT_FALSE(validate_config(cfg));
+  cfg->send_directory = str_dup("/src");
+  EXPECT_FALSE(validate_config(cfg));
+  config_delete(cfg);
+}
+
+static void test_validate_config_incompatible_options() {
+  Config* cfg = valid_client_config();
+  cfg->use_sendfile = true;
+  cfg->use_compression = true;
+  EXPECT_FALSE(validate_config(cfg));
+  cfg->use_compression = false;
+  cfg->use_incremental = true;
+  cfg->use_chunk_serialization = true;
+  EXPECT_FALSE(validate_config(cfg));
+  cfg->use_incremental = false;
+  cfg->skip_compress_set = true;
+  EXPECT_FALSE(validate_config(cfg));
+  cfg->skip_compress_set = false;
+  cfg->compression_threads = 2;
+  EXPECT_FALSE(validate_config(cfg));
+  cfg->use_compression = true;
+  cfg->use_sendfile = false;
+  EXPECT_TRUE(validate_config(cfg));
+  config_delete(cfg);
+}
+
+static void test_validate_config_tls_requirements() {
+  Config* cfg = valid_client_config();
+  cfg->use_tls = true;
+  EXPECT_FALSE(validate_config(cfg));
+  cfg->tls_cert = str_dup("cert.pem");
+  EXPECT_FALSE(validate_config(cfg));
+  cfg->tls_key = str_dup("key.pem");
+  EXPECT_FALSE(validate_config(cfg));
+  cfg->tls_ca = str_dup("ca.pem");
+  EXPECT_TRUE(validate_config(cfg));
+  config_delete(cfg);
+}
+
+static void test_validate_config_delta_sendfile_constraints() {
+  Config* cfg = valid_client_config();
+  cfg->use_delta = true;
+  EXPECT_FALSE(validate_config(cfg));
+  cfg->use_incremental = true;
+  cfg->use_sendfile = true;
+  EXPECT_FALSE(validate_config(cfg));
+
+  /* Whole-file makes delta selection inactive, so these combinations are valid. */
+  cfg->whole_file = true;
+  EXPECT_TRUE(validate_config(cfg));
+
+  cfg->use_incremental = false;
+  EXPECT_TRUE(validate_config(cfg));
+  config_delete(cfg);
+}
+
 /* Test main() with --help flag (early return path, no server connection needed) */
 static void test_cli_help() {
   /* We can't easily call main() because it calls send_files which needs a server.
@@ -54,6 +126,27 @@ static void test_cli_dry_run() {
   config_delete(cfg);
 }
 
+static void test_cli_remove_source_files() {
+  Config* cfg = config_create();
+  EXPECT_NOT_NULL(cfg);
+  EXPECT_FALSE(cfg->remove_source_files);
+  cfg->remove_source_files = true;
+  EXPECT_TRUE(cfg->remove_source_files);
+  config_delete(cfg);
+}
+
+static void test_parse_args_remove_source_files() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--remove-source-files", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  int ret = parse_args(cfg, 4, argv, positional_args, &positional_count);
+  EXPECT_EQ_INT(ret, 0);
+  EXPECT_TRUE(cfg->remove_source_files);
+  config_delete(cfg);
+}
+
 /* Test that --delete sets use_delete */
 static void test_cli_delete_flag() {
   Config* cfg = config_create();
@@ -128,6 +221,80 @@ static void test_parse_args_valid_port() {
   config_delete(cfg);
 }
 
+/* Test parse_args with --size-only. */
+static void test_parse_args_size_only() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--size-only", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->size_only);
+  EXPECT_EQ_INT(positional_count, 2);
+
+  config_delete(cfg);
+}
+
+static void test_parse_args_ignore_existing() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--ignore-existing", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  int ret = parse_args(cfg, 4, argv, positional_args, &positional_count);
+  EXPECT_EQ_INT(ret, 0);
+  EXPECT_TRUE(cfg->ignore_existing);
+
+  config_delete(cfg);
+}
+
+static void test_parse_args_executability() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "-E", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->use_executability);
+  EXPECT_TRUE(cfg->use_metadata);
+
+  config_delete(cfg);
+}
+
+static void test_parse_args_chmod() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--chmod=u=rw,go=r", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_STR(cfg->chmod_spec, "u=rw,go=r");
+  EXPECT_TRUE(cfg->use_metadata);
+  mode_t result;
+  EXPECT_TRUE(chmod_apply(0777, cfg->chmod_spec, &result));
+  EXPECT_EQ_INT(result, 0644);
+  config_delete(cfg);
+}
+
+static void test_parse_args_numeric_chmod() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--chmod", "7777", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_STR(cfg->chmod_spec, "7777");
+  EXPECT_TRUE(cfg->use_metadata);
+  config_delete(cfg);
+}
+
+static void test_parse_args_rejects_invalid_chmod() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--chmod=a+X", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+  config_delete(cfg);
+}
+
 /* Test parse_args rejects port > 65535 */
 static void test_parse_args_invalid_port() {
   Config* cfg = config_create();
@@ -194,6 +361,178 @@ static void test_parse_args_valid_compression_level() {
   config_delete(cfg);
 }
 
+static void test_parse_args_debug_flags() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--debug=io,proto,pack,util", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_INT(cfg->debug_level, LOG_DEBUG_ALL);
+  EXPECT_EQ_INT(get_log_debug_flags(), LOG_DEBUG_ALL);
+  config_delete(cfg);
+}
+
+static void test_parse_args_debug_help() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--debug=help"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 2, argv, positional_args, &positional_count), 1);
+  config_delete(cfg);
+}
+
+static void test_parse_args_debug_flags_validation() {
+  static const char* const values[] = {"", "io,", ",io", "io,,proto", "acl", "tls", "unknown"};
+  for (size_t i = 0; i < sizeof(values) / sizeof(values[0]); i++) {
+    Config* cfg = config_create();
+    char option[64];
+    snprintf(option, sizeof(option), "--debug=%s", values[i]);
+    char* argv[] = {"fastsync", option, "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+}
+
+static void test_parse_args_modify_window() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--modify-window=3", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_INT(cfg->modify_window, 3);
+  config_delete(cfg);
+
+  cfg = config_create();
+  char* short_argv[] = {"fastsync", "-@", "7", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 5, short_argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_INT(cfg->modify_window, 7);
+  config_delete(cfg);
+
+  cfg = config_create();
+  char* attached_argv[] = {"fastsync", "-@11", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, attached_argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_INT(cfg->modify_window, 11);
+  config_delete(cfg);
+}
+
+static void test_parse_args_rejects_invalid_modify_window() {
+  const char* values[] = {"-1", "not-a-number", ""};
+  for (size_t i = 0; i < sizeof(values) / sizeof(values[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", "--modify-window", (char*)values[i], "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+    EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+}
+
+static void test_parse_args_max_alloc_sizes() {
+  const char* values[] = {"1", "4K", "2m", "3G", "1T", "1P", "1E", "512B"};
+  const unsigned long long expected[] = {1,
+                                         4ULL * 1024,
+                                         2ULL * 1024 * 1024,
+                                         3ULL * 1024 * 1024 * 1024,
+                                         1ULL * 1024 * 1024 * 1024 * 1024,
+                                         1ULL * 1024 * 1024 * 1024 * 1024 * 1024,
+                                         1ULL * 1024 * 1024 * 1024 * 1024 * 1024 * 1024,
+                                         512};
+  for (size_t i = 0; i < sizeof(values) / sizeof(values[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", "--max-alloc", (char*)values[i], "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+    EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), 0);
+    EXPECT_TRUE(cfg->max_alloc == expected[i]);
+    config_delete(cfg);
+  }
+
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--max-alloc=8M", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->max_alloc == 8ULL * 1024 * 1024);
+  config_delete(cfg);
+}
+
+static void test_parse_args_rejects_invalid_max_alloc() {
+  const char* values[] = {"0",  "-1",  "+1",  " 1",   "1 ",
+                          "1Z", "1K2", "1 K", "1\tK", "18446744073709551615K"};
+  for (size_t i = 0; i < sizeof(values) / sizeof(values[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", "--max-alloc", (char*)values[i], "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+    EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+}
+
+static void test_parse_args_skip_compress() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--skip-compress=.ZIP, .GZ", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->skip_compress_set);
+  EXPECT_EQ_INT(cfg->skip_compress_count, 2);
+  EXPECT_EQ_STR(cfg->skip_compress_suffixes[0], ".ZIP");
+  EXPECT_EQ_STR(cfg->skip_compress_suffixes[1], ".GZ");
+  config_delete(cfg);
+}
+
+static void test_parse_args_empty_skip_compress() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--skip-compress=", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->skip_compress_set);
+  EXPECT_EQ_INT(cfg->skip_compress_count, 0);
+  config_delete(cfg);
+}
+
+static void test_parse_args_compression_threads() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--compress-threads", "4", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_INT(cfg->compression_threads, 4);
+  config_delete(cfg);
+
+  cfg = config_create();
+  char* equals_argv[] = {"fastsync", "--compress-threads=3", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, equals_argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_INT(cfg->compression_threads, 3);
+  config_delete(cfg);
+
+  cfg = config_create();
+  char* invalid_argv[] = {"fastsync", "--compress-threads=0", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, invalid_argv, positional_args, &positional_count), -1);
+  config_delete(cfg);
+
+  cfg = config_create();
+  char* excessive_argv[] = {"fastsync", "--compress-threads=65", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, excessive_argv, positional_args, &positional_count), -1);
+  config_delete(cfg);
+}
+
 /* Test parse_args unknown option returns error */
 static void test_parse_args_unknown_option() {
   Config* cfg = config_create();
@@ -207,11 +546,53 @@ static void test_parse_args_unknown_option() {
   config_delete(cfg);
 }
 
+/* Directory aliases must report the unsupported directory-only behavior clearly. */
+static void test_parse_args_rejects_dirs_aliases() {
+  static const char* const options[] = {"--dirs", "--old-dirs", "--old-d"};
+
+  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", (char*)options[i], "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+    FILE* log_file = tmpfile();
+    char log_buffer[256] = {0};
+
+    EXPECT_NOT_NULL(log_file);
+    log_set_file(log_file);
+
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+    fflush(log_file);
+    rewind(log_file);
+    EXPECT_TRUE(fread(log_buffer, 1, sizeof(log_buffer) - 1, log_file) > 0);
+    EXPECT_TRUE(strstr(log_buffer, options[i]) != NULL);
+    EXPECT_TRUE(strstr(log_buffer, "directory-only transfer is not implemented") != NULL);
+    EXPECT_TRUE(strstr(log_buffer, "requires --dirs") == NULL);
+    log_set_file(NULL);
+    fclose(log_file);
+    config_delete(cfg);
+  }
+}
+
+/* --del is recognized as the rsync alias, but its timing mode is not implemented. */
+static void test_parse_args_delete_during_alias_unimplemented() {
+  static const char* const options[] = {"--del", "--delete-during"};
+
+  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", (char*)options[i], "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+    EXPECT_FALSE(cfg->use_delete);
+    config_delete(cfg);
+  }
+}
+
 /* Parsed-but-unimplemented options must fail instead of being silently accepted. */
 static void test_parse_args_rejects_unimplemented_options() {
-  static const char* const options[] = {"-q",
-                                        "--quiet",
-                                        "--silent",
+  static const char* const options[] = {"--silent",
                                         "--queue-size",
                                         "-H",
                                         "--hard-links",
@@ -224,13 +605,7 @@ static void test_parse_args_rejects_unimplemented_options() {
                                         "-i",
                                         "--itemize-changes",
                                         "--out-format",
-                                        "--info",
-                                        "--debug",
                                         "--list-only",
-                                        "-h",
-                                        "--human-readable",
-                                        "-u",
-                                        "--update",
                                         "--append",
                                         "--append-verify",
                                         "--delete-excluded",
@@ -256,8 +631,8 @@ static void test_parse_args_rejects_unimplemented_options() {
                                         "--ipv4",
                                         "--daemon",
                                         "--config",
-                                         "--server",
-                                         "--compress-choice"};
+                                        "--server",
+                                        "--checksum-choice"};
 
   for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
     Config* cfg = config_create();
@@ -270,6 +645,92 @@ static void test_parse_args_rejects_unimplemented_options() {
   }
 }
 
+/* Test both rsync-compatible quiet spellings and option ordering. */
+static void test_parse_args_quiet() {
+  static const char* const options[][2] = {
+      {"-q", "-v"}, {"-v", "-q"}, {"--quiet", "-v"}, {"-v", "--quiet"}};
+  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", (char*)options[i][0], (char*)options[i][1], "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), 0);
+    EXPECT_TRUE(cfg->quiet);
+    config_delete(cfg);
+  }
+}
+
+static void test_parse_args_human_readable() {
+  static const char* const options[] = {"-h", "--human-readable"};
+  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", (char*)options[i], "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+    EXPECT_TRUE(cfg->human_readable);
+    config_delete(cfg);
+  }
+}
+
+static void test_parse_args_update() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "-u", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->update);
+  EXPECT_TRUE(cfg->use_metadata);
+  EXPECT_EQ_INT(positional_count, 2);
+
+  config_delete(cfg);
+}
+
+static void test_parse_args_info_flags() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--info=copy,skip", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_INT(cfg->info_level, LOG_INFO_COPY | LOG_INFO_SKIP);
+  EXPECT_EQ_INT(get_log_info_flags(), LOG_INFO_COPY | LOG_INFO_SKIP);
+  config_delete(cfg);
+}
+
+static void test_parse_args_info_verbose_order() {
+  char* argv_info_first[] = {"fastsync", "--info=none", "--verbose", "/src", "/dst"};
+  char* argv_verbose_first[] = {"fastsync", "--verbose", "--info=none", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  Config* cfg = config_create();
+  EXPECT_EQ_INT(parse_args(cfg, 5, argv_info_first, positional_args, &positional_count), 0);
+  EXPECT_EQ_INT(cfg->info_level, 0);
+  EXPECT_EQ_INT(get_log_info_flags(), 0);
+  config_delete(cfg);
+
+  cfg = config_create();
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 5, argv_verbose_first, positional_args, &positional_count), 0);
+  EXPECT_EQ_INT(cfg->info_level, 0);
+  EXPECT_EQ_INT(get_log_info_flags(), 0);
+  config_delete(cfg);
+}
+
+static void test_parse_args_rejects_invalid_info_flag() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--info=copy,unknown", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+  config_delete(cfg);
+}
+
 /* Test parse_args with --archive flag */
 static void test_parse_args_archive() {
   Config* cfg = config_create();
@@ -286,21 +747,415 @@ static void test_parse_args_archive() {
   config_delete(cfg);
 }
 
+/* Negations must override archive's implied options in argument order. */
+static void test_parse_args_negations() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync",      "--archive",    "--no-compress", "--no-m",
+                  "--no-preserve", "--no-dry-run", "/src",          "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 8, argv, positional_args, &positional_count), 0);
+  EXPECT_FALSE(cfg->use_compression);
+  EXPECT_FALSE(cfg->use_multithreading);
+  EXPECT_FALSE(cfg->use_metadata);
+  EXPECT_FALSE(cfg->dry_run);
+  EXPECT_EQ_INT(positional_count, 2);
+  config_delete(cfg);
+}
+
+static void test_parse_args_negation_order() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--no-z", "-c", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->use_compression);
+  config_delete(cfg);
+}
+
+static void test_parse_args_no_preserve_blocks_implicit_metadata() {
+  static const char* const options[][3] = {
+      {"--incremental", "--no-preserve", "/src"},
+      {"--no-preserve", "--incremental", "/src"},
+      {"--delta", "--no-preserve", "/src"},
+      {"--no-preserve", "--delta", "/src"},
+  };
+
+  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", (char*)options[i][0], (char*)options[i][1], (char*)options[i][2],
+                    "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), 0);
+    EXPECT_FALSE(cfg->use_metadata);
+    EXPECT_TRUE(cfg->metadata_explicitly_disabled);
+    config_delete(cfg);
+  }
+}
+
+/* Checksum-choice spellings are recognized and rejected until algorithms are implemented. */
+static void test_parse_args_checksum_choice_aliases() {
+  static const char* const options[] = {"--checksum-choice", "--cc"};
+
+  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", (char*)options[i], "xxh64", "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+}
+
+static void test_parse_args_rejects_unsafe_negation() {
+  static const char* const options[] = {"--no-archive", "--no-timeout", "--no-unknown"};
+  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", (char*)options[i], "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+}
+
+/* Both checksum-choice spellings require a value. */
+static void test_parse_args_checksum_choice_requires_value() {
+  static const char* const options[] = {"--checksum-choice", "--cc"};
+
+  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
+    Config* cfg = config_create();
+    char* argv[] = {"fastsync", (char*)options[i]};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 2, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+}
+
+static void test_parse_args_old_args() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--old-args", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->old_args);
+  config_delete(cfg);
+}
+
+static void test_parse_args_fsync() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--fsync", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->use_fsync);
+  config_delete(cfg);
+}
+
+static void test_parse_args_existing() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--existing", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->existing);
+  config_delete(cfg);
+}
+
+static void test_parse_args_ignore_times() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "-I", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->ignore_times);
+  config_delete(cfg);
+
+  cfg = config_create();
+  char* long_argv[] = {"fastsync", "--ignore-times", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, long_argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->ignore_times);
+  config_delete(cfg);
+}
+
+/* --secluded-args is accepted for compatibility but has no effect. */
+static void test_parse_args_secluded_args() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--secluded-args", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_FALSE(cfg->use_chunk_serialization);
+  config_delete(cfg);
+}
+
+static void test_parse_args_short_s_remains_chunk_serialization() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "-s", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->use_chunk_serialization);
+  config_delete(cfg);
+}
+
+static void test_parse_args_8_bit_output() {
+  Config* cfg = config_create();
+  char* long_argv[] = {"fastsync", "--8-bit-output", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, long_argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->eight_bit_output);
+  config_delete(cfg);
+
+  cfg = config_create();
+  char* short_argv[] = {"fastsync", "-8", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, short_argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->eight_bit_output);
+  config_delete(cfg);
+}
+
+static void test_parse_args_stderr_modes() {
+  static const char* const modes[] = {"errors", "all", "e", "a"};
+  static const LogStderrMode expected[] = {LOG_STDERR_ERRORS, LOG_STDERR_ALL, LOG_STDERR_ERRORS,
+                                           LOG_STDERR_ALL};
+  for (size_t i = 0; i < sizeof(modes) / sizeof(modes[0]); i++) {
+    Config* cfg = config_create();
+    char option[32];
+    snprintf(option, sizeof(option), "--stderr=%s", modes[i]);
+    char* argv[] = {"fastsync", option, "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+    EXPECT_EQ_INT(log_get_stderr_mode(), expected[i]);
+    config_delete(cfg);
+  }
+  log_set_stderr_mode(LOG_STDERR_ERRORS);
+}
+
+static void test_parse_args_rejects_unsupported_stderr_modes() {
+  static const char* const modes[] = {"client", "c", "invalid"};
+  for (size_t i = 0; i < sizeof(modes) / sizeof(modes[0]); i++) {
+    Config* cfg = config_create();
+    char option[32];
+    snprintf(option, sizeof(option), "--stderr=%s", modes[i]);
+    char* argv[] = {"fastsync", option, "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+  log_set_stderr_mode(LOG_STDERR_ERRORS);
+}
+
+/* Test both whole-file spellings and its precedence over delta selection. */
+static void test_parse_args_whole_file() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--delta", "--incremental", "-W", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 6, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->whole_file);
+  EXPECT_TRUE(cfg->use_delta);
+
+  config_delete(cfg);
+  cfg = config_create();
+  char* long_argv[] = {"fastsync", "--whole-file", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, long_argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->whole_file);
+  config_delete(cfg);
+}
+
+/* Test rsync-compatible compression-choice and compression-level aliases. */
+static void test_parse_args_compression_aliases() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--zc", "zstd", "--zl", "10", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  int ret = parse_args(cfg, 7, argv, positional_args, &positional_count);
+  EXPECT_EQ_INT(ret, 0);
+  EXPECT_EQ_STR(cfg->compress_choice, "zstd");
+  EXPECT_EQ_INT(cfg->compression_level, 10);
+  EXPECT_TRUE(cfg->use_compression);
+  EXPECT_EQ_INT(positional_count, 2);
+
+  config_delete(cfg);
+}
+
+/* Test rsync-compatible -P parsing; resumable partial-file retention is not implied. */
+static void test_parse_args_partial_progress() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "-P", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  int ret = parse_args(cfg, 4, argv, positional_args, &positional_count);
+  EXPECT_EQ_INT(ret, 0);
+  EXPECT_TRUE(cfg->partial);
+  EXPECT_TRUE(cfg->show_progress);
+  EXPECT_EQ_INT(positional_count, 2);
+
+  config_delete(cfg);
+}
+
+static void test_parse_args_compression_equals_and_none() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "-z", "--zc=none", "--zl=7", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  int ret = parse_args(cfg, 6, argv, positional_args, &positional_count);
+  EXPECT_EQ_INT(ret, 0);
+  EXPECT_EQ_STR(cfg->compress_choice, "none");
+  EXPECT_EQ_INT(cfg->compression_level, 7);
+  EXPECT_FALSE(cfg->use_compression);
+  config_delete(cfg);
+}
+
+static void test_parse_args_compression_canonical_equals() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--compress-choice=zstd", "--compress-level=7", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_STR(cfg->compress_choice, "zstd");
+  EXPECT_EQ_INT(cfg->compression_level, 7);
+  EXPECT_TRUE(cfg->use_compression);
+  EXPECT_EQ_INT(positional_count, 2);
+
+  config_delete(cfg);
+}
+
+static void test_parse_args_compression_alias_equals() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--zc=zstd", "--zl=7", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_STR(cfg->compress_choice, "zstd");
+  EXPECT_EQ_INT(cfg->compression_level, 7);
+  EXPECT_TRUE(cfg->use_compression);
+  EXPECT_EQ_INT(positional_count, 2);
+
+  config_delete(cfg);
+}
+
+static void test_parse_args_rejects_invalid_compression_level_equals() {
+  static const char* const values[] = {"0", "23", "invalid"};
+
+  for (size_t i = 0; i < sizeof(values) / sizeof(values[0]); i++) {
+    Config* cfg = config_create();
+    char option[32];
+    snprintf(option, sizeof(option), "--compress-level=%s", values[i]);
+    char* argv[] = {"fastsync", option, "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+}
+
+static void test_parse_args_rejects_invalid_compression_choice() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--compress-choice=bogus", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+  config_delete(cfg);
+}
+
 void test_client_cli() {
+  test_validate_config_required_paths();
+  test_validate_config_incompatible_options();
+  test_validate_config_tls_requirements();
+  test_validate_config_delta_sendfile_constraints();
   test_cli_help();
   test_cli_archive_flags();
   test_cli_dry_run();
+  test_cli_remove_source_files();
+  test_parse_args_remove_source_files();
   test_cli_delete_flag();
   test_cli_exclude_patterns();
   test_parse_args_help();
   test_parse_args_version();
   test_parse_args_valid_port();
+  test_parse_args_size_only();
+  test_parse_args_ignore_existing();
+  test_parse_args_executability();
+  test_parse_args_chmod();
+  test_parse_args_numeric_chmod();
+  test_parse_args_rejects_invalid_chmod();
   test_parse_args_invalid_port();
   test_parse_args_non_numeric_port();
   test_parse_args_invalid_server_port();
   test_parse_args_invalid_compression_level();
   test_parse_args_valid_compression_level();
+  test_parse_args_debug_flags();
+  test_parse_args_debug_help();
+  test_parse_args_debug_flags_validation();
+  test_parse_args_modify_window();
+  test_parse_args_rejects_invalid_modify_window();
+  test_parse_args_skip_compress();
+  test_parse_args_empty_skip_compress();
+  test_parse_args_compression_threads();
+  test_parse_args_max_alloc_sizes();
+  test_parse_args_rejects_invalid_max_alloc();
   test_parse_args_unknown_option();
+  test_parse_args_rejects_dirs_aliases();
+  test_parse_args_delete_during_alias_unimplemented();
   test_parse_args_rejects_unimplemented_options();
+  test_parse_args_quiet();
+  test_parse_args_human_readable();
+  test_parse_args_update();
+  test_parse_args_info_flags();
+  test_parse_args_info_verbose_order();
+  test_parse_args_rejects_invalid_info_flag();
   test_parse_args_archive();
+  test_parse_args_negations();
+  test_parse_args_negation_order();
+  test_parse_args_no_preserve_blocks_implicit_metadata();
+  test_parse_args_rejects_unsafe_negation();
+  test_parse_args_old_args();
+  test_parse_args_fsync();
+  test_parse_args_existing();
+  test_parse_args_ignore_times();
+  test_parse_args_8_bit_output();
+  test_parse_args_stderr_modes();
+  test_parse_args_rejects_unsupported_stderr_modes();
+  test_parse_args_secluded_args();
+  test_parse_args_short_s_remains_chunk_serialization();
+  test_parse_args_whole_file();
+  test_parse_args_compression_aliases();
+  test_parse_args_compression_equals_and_none();
+  test_parse_args_compression_canonical_equals();
+  test_parse_args_compression_alias_equals();
+  test_parse_args_rejects_invalid_compression_level_equals();
+  test_parse_args_rejects_invalid_compression_choice();
+  test_parse_args_partial_progress();
+  test_parse_args_checksum_choice_aliases();
+  test_parse_args_checksum_choice_requires_value();
 }

tests/test_compression.c

@@ -13,6 +13,8 @@ static void test_data_compress_decompress_roundtrip() {
   size_t len = strlen(original);
 
   char* buf = malloc(len);
+  if (!buf)
+    return;
   memcpy(buf, original, len);
   Data* original_data = data_create(buf, len);
   EXPECT_NOT_NULL(original_data);
@@ -53,6 +55,31 @@ static void test_data_compress_decompress_large() {
   data_destroy(decompressed);
 }
 
+static void test_skip_compress_suffix_matching() {
+  char* suffixes[] = {".ZIP", ".GZ"};
+  EXPECT_TRUE(compression_should_skip_with_suffixes("archive.zip", suffixes, 2));
+  EXPECT_TRUE(compression_should_skip_with_suffixes("backup.TAR.GZ", suffixes, 2));
+  EXPECT_FALSE(compression_should_skip_with_suffixes("notes.txt", suffixes, 2));
+  EXPECT_FALSE(compression_should_skip_with_suffixes("archive.zip", suffixes, 0));
+}
+
+static void test_data_compress_with_threads_roundtrip() {
+  const size_t size = 8 * 1024 * 1024;
+  Data* input = data_create_empty(size);
+  EXPECT_NOT_NULL(input);
+  for (size_t i = 0; i < size; i++)
+    ((char*)input->data)[i] = (char)((i / 4096) % 7);
+  Data* compressed = data_compress_with_threads(input, 3, 2);
+  EXPECT_NOT_NULL(compressed);
+  Data* decompressed = data_decompress(compressed);
+  EXPECT_NOT_NULL(decompressed);
+  EXPECT_EQ_INT((int)decompressed->size, (int)size);
+  EXPECT_EQ_INT(memcmp(decompressed->data, input->data, size), 0);
+  data_destroy(input);
+  data_destroy(compressed);
+  data_destroy(decompressed);
+}
+
 static void test_chunk_compress_decompress_roundtrip() {
   char* path1 = "temp_comp_test_1.txt";
   char* content1 = "chunk compression test file 1";
@@ -62,8 +89,8 @@ static void test_chunk_compress_decompress_roundtrip() {
   char* content2 = "chunk compression test file 2 with more data";
   unsigned long long len2 = strlen(content2);
 
-  to_disk(path1, content1, len1, false, false);
-  to_disk(path2, content2, len2, false, false);
+  file_write_to_disk(path1, content1, len1, false, false);
+  file_write_to_disk(path2, content2, len2, false, false);
 
   struct stat st1, st2;
   EXPECT_EQ_INT(stat(path1, &st1), 0);
@@ -113,5 +140,7 @@ static void test_chunk_compress_decompress_roundtrip() {
 void test_compression() {
   test_data_compress_decompress_roundtrip();
   test_data_compress_decompress_large();
+  test_skip_compress_suffix_matching();
+  test_data_compress_with_threads_roundtrip();
   test_chunk_compress_decompress_roundtrip();
 }

tests/test_config.c

@@ -95,6 +95,7 @@ static void test_pipeline_sender_lifecycle() {
   EXPECT_EQ_INT(pcs->queue_loader->capacity, 15);
   EXPECT_FALSE(pcs->scanner_done);
   EXPECT_FALSE(pcs->loader_done);
+  EXPECT_EQ_INT((int)pcs->allocation_session.max_alloc, (int)cfg->max_alloc);
 
   pipeline_context_sender_destroy(pcs);
 }
@@ -121,11 +122,25 @@ static void test_config_send_receive() {
   send_cfg->receive_root_directory = str_dup("/send/dst");
   send_cfg->save_to_disk = true;
   send_cfg->use_multithreading = true;
-  send_cfg->use_chunk_serialization = true;
+  send_cfg->use_chunk_serialization = false;
   send_cfg->use_compression = true;
   send_cfg->use_metadata = true;
+  send_cfg->use_executability = true;
+  send_cfg->use_delta = true;
+  send_cfg->whole_file = true;
+  send_cfg->ignore_times = true;
+  send_cfg->size_only = true;
   send_cfg->compression_level = 5;
   send_cfg->chunk_size = 1024;
+  send_cfg->eight_bit_output = true;
+  send_cfg->modify_window = 4;
+  send_cfg->existing = true;
+  send_cfg->ignore_existing = true;
+  send_cfg->skip_compress_set = true;
+  send_cfg->skip_compress_count = 1;
+  send_cfg->skip_compress_suffixes = calloc(1, sizeof(char*));
+  send_cfg->skip_compress_suffixes[0] = str_dup(".zip");
+  send_cfg->max_alloc = MAX_SERVER_ALLOC + 1;
 
   /* Use socketpair for bidirectional communication */
   int p[2];
@@ -154,12 +169,33 @@ static void test_config_send_receive() {
         ok = false;
       if (!recv_cfg->use_multithreading)
         ok = false;
-      if (!recv_cfg->use_chunk_serialization)
+      if (recv_cfg->use_chunk_serialization)
         ok = false;
       if (recv_cfg->compression_level != 5)
         ok = false;
       if (recv_cfg->chunk_size != 1024)
         ok = false;
+      if (!recv_cfg->use_executability)
+        ok = false;
+      if (!recv_cfg->size_only)
+        ok = false;
+      if (!recv_cfg->ignore_times)
+        ok = false;
+      if (!recv_cfg->eight_bit_output)
+        ok = false;
+      if (recv_cfg->use_delta)
+        ok = false;
+      if (recv_cfg->modify_window != 4)
+        ok = false;
+      if (!recv_cfg->existing)
+        ok = false;
+      if (!recv_cfg->ignore_existing)
+        ok = false;
+      if (!recv_cfg->skip_compress_set || recv_cfg->skip_compress_count != 1 ||
+          strcmp(recv_cfg->skip_compress_suffixes[0], ".zip") != 0)
+        ok = false;
+      if (recv_cfg->max_alloc != MAX_SERVER_ALLOC)
+        ok = false;
     }
     config_delete(recv_cfg);
     close(p[0]);
@@ -185,11 +221,11 @@ static void test_config_send_receive() {
 }
 
 static void test_config_send_receive_version_mismatch() {
-  /* Create a config with a different protocol version */
+  /* A peer using the previous wire format must be rejected. */
   Config* cfg = config_create();
   EXPECT_NOT_NULL(cfg);
   free(cfg->version);
-  cfg->version = str_dup("0.0");
+  cfg->version = str_dup("2.3.0");
   cfg->send_directory = str_dup("/src");
   cfg->receive_root_directory = str_dup("/dst");
 
@@ -224,26 +260,48 @@ static void test_config_send_receive_version_mismatch() {
   }
 }
 
-static void test_is_remote_dest() {
+static void test_config_receive_truncated() {
+  int p[2];
+  EXPECT_EQ_INT(socketpair(AF_UNIX, SOCK_STREAM, 0, p), 0);
+  io_set_fds(p[0], p[0]);
+  io_set_bwlimit(0);
+
+  /* A valid prefix exercises cleanup after allocated wire strings and a
+   * partially received scalar field. */
+  EXPECT_TRUE(send_str(p[1], PROTOCOL_VERSION));
+  unsigned long long max_alloc = DEFAULT_MAX_ALLOC;
+  EXPECT_TRUE(send_n_data(p[1], &max_alloc, sizeof(max_alloc)));
+  EXPECT_TRUE(send_str(p[1], "/src"));
+  EXPECT_TRUE(send_str(p[1], "/dst"));
+  EXPECT_TRUE(send_int(p[1], 1));
+  shutdown(p[1], SHUT_WR);
+
+  const Config* cfg = config_receive(p[0]);
+  EXPECT_NULL(cfg);
+  close(p[0]);
+  close(p[1]);
+}
+
+static void test_config_is_remote_dest() {
   /* Valid SSH-style destinations */
-  EXPECT_TRUE(is_remote_dest("user@host:/path"));
-  EXPECT_TRUE(is_remote_dest("host:/path"));
-  EXPECT_TRUE(is_remote_dest("user@192.168.1.1:/remote/path"));
+  EXPECT_TRUE(config_is_remote_dest("user@host:/path"));
+  EXPECT_TRUE(config_is_remote_dest("host:/path"));
+  EXPECT_TRUE(config_is_remote_dest("user@192.168.1.1:/remote/path"));
 
   /* Invalid destinations */
-  EXPECT_FALSE(is_remote_dest(NULL));
-  EXPECT_FALSE(is_remote_dest(""));
-  EXPECT_FALSE(is_remote_dest(":"));
-  EXPECT_FALSE(is_remote_dest("/local/path"));
-  EXPECT_FALSE(is_remote_dest("relative/path"));
+  EXPECT_FALSE(config_is_remote_dest(NULL));
+  EXPECT_FALSE(config_is_remote_dest(""));
+  EXPECT_FALSE(config_is_remote_dest(":"));
+  EXPECT_FALSE(config_is_remote_dest("/local/path"));
+  EXPECT_FALSE(config_is_remote_dest("relative/path"));
   /* C:/windows/path is treated as remote (colon with no preceding slash) */
-  EXPECT_TRUE(is_remote_dest("C:/windows/path"));
+  EXPECT_TRUE(config_is_remote_dest("C:/windows/path"));
 
   /* Edge cases */
-  EXPECT_FALSE(is_remote_dest("noslash"));
-  EXPECT_FALSE(is_remote_dest("/"));
-  EXPECT_TRUE(is_remote_dest("host:"));
-  EXPECT_TRUE(is_remote_dest("user@host:"));
+  EXPECT_FALSE(config_is_remote_dest("noslash"));
+  EXPECT_FALSE(config_is_remote_dest("/"));
+  EXPECT_TRUE(config_is_remote_dest("host:"));
+  EXPECT_TRUE(config_is_remote_dest("user@host:"));
 }
 
 void test_config() {
@@ -256,6 +314,7 @@ void test_config() {
   if (!is_running_under_valgrind()) {
     test_config_send_receive();
     test_config_send_receive_version_mismatch();
+    test_config_receive_truncated();
   }
-  test_is_remote_dest();
+  test_config_is_remote_dest();
 }

tests/test_file.c

@@ -1,6 +1,7 @@
 #include "test_file.h"
 #include "file.h"
 #include "data.h"
+#include "config.h"
 #include "utils.h"
 #include "protocol.h"
 #include "test_utils.h"
@@ -34,7 +35,8 @@ static void test_file_destroy_normal() {
 
 static void test_file_load_data() {
   const char* content = "Hello Load Test";
-  EXPECT_TRUE(to_disk("test_file_load_data.txt", content, strlen(content), false, false));
+  EXPECT_TRUE(
+      file_write_to_disk("test_file_load_data.txt", content, strlen(content), false, false));
 
   struct stat st;
   EXPECT_EQ_INT(stat("test_file_load_data.txt", &st), 0);
@@ -87,15 +89,177 @@ static void test_file_save_to_disk() {
   rmdir("test_save_tmp");
 }
 
-static void test_to_disk_basic() {
-  const char* content = "Basic to_disk test";
-  EXPECT_TRUE(to_disk("test_to_disk_basic.txt", content, strlen(content), false, false));
+static void test_file_save_to_disk_with_fsync_config() {
+  File* f = file_create("saved_file_fsync.txt");
+  EXPECT_NOT_NULL(f);
+  const char* content = "Save to disk with fsync";
+  f->data->data = malloc(strlen(content));
+  EXPECT_NOT_NULL(f->data->data);
+  memcpy(f->data->data, content, strlen(content));
+  f->data->size = strlen(content);
+
+  Config* config = config_create();
+  EXPECT_NOT_NULL(config);
+  config->use_fsync = true;
+  EXPECT_TRUE(file_save_to_disk("test_save_fsync_tmp", f, config));
 
   struct stat st;
-  EXPECT_EQ_INT(stat("test_to_disk_basic.txt", &st), 0);
+  EXPECT_EQ_INT(stat("test_save_fsync_tmp/saved_file_fsync.txt", &st), 0);
   EXPECT_EQ_INT((int)st.st_size, (int)strlen(content));
 
-  FILE* fp = fopen("test_to_disk_basic.txt", "rb");
+  file_destroy(f);
+  config_delete(config);
+  unlink("test_save_fsync_tmp/saved_file_fsync.txt");
+  rmdir("test_save_fsync_tmp");
+}
+
+static void test_file_save_to_disk_existing() {
+  const char* root = "test_existing_tmp";
+  const char* existing_path = "test_existing_tmp/existing.txt";
+  const char* missing_path = "test_existing_tmp/missing.txt";
+  EXPECT_TRUE(file_write_to_disk(existing_path, "old", 3, false, false));
+
+  Config* cfg = config_create();
+  EXPECT_NOT_NULL(cfg);
+  cfg->existing = true;
+
+  File* existing = file_create("existing.txt");
+  EXPECT_NOT_NULL(existing);
+  existing->data->data = malloc(3);
+  EXPECT_NOT_NULL(existing->data->data);
+  memcpy(existing->data->data, "new", 3);
+  existing->data->size = 3;
+  EXPECT_TRUE(file_save_to_disk(root, existing, cfg));
+  file_destroy(existing);
+
+  File* missing = file_create("missing.txt");
+  EXPECT_NOT_NULL(missing);
+  missing->data->data = malloc(7);
+  EXPECT_NOT_NULL(missing->data->data);
+  memcpy(missing->data->data, "skipped", 7);
+  missing->data->size = 7;
+  EXPECT_TRUE(file_save_to_disk(root, missing, cfg));
+  file_destroy(missing);
+
+  FILE* fp = fopen(existing_path, "rb");
+  char content[4] = {0};
+  EXPECT_NOT_NULL(fp);
+  // cppcheck-suppress knownConditionTrueFalse
+  if (fp) {
+    EXPECT_EQ_INT((int)fread(content, 1, 3, fp), 3);
+    fclose(fp);
+  }
+  EXPECT_EQ_STR(content, "new");
+  EXPECT_EQ_INT(access(missing_path, F_OK), -1);
+
+  config_delete(cfg);
+  unlink(existing_path);
+  rmdir("test_existing_tmp");
+}
+
+static void test_file_save_to_disk_ignore_existing() {
+  const char* path = "test_ignore_existing_tmp/existing.txt";
+  EXPECT_TRUE(file_write_to_disk(path, "old", 3, false, false));
+
+  File* file = file_create("existing.txt");
+  EXPECT_NOT_NULL(file);
+  file->data->data = malloc(3);
+  EXPECT_NOT_NULL(file->data->data);
+  memcpy(file->data->data, "new", 3);
+  file->data->size = 3;
+
+  Config* config = config_create();
+  EXPECT_NOT_NULL(config);
+  config->ignore_existing = true;
+  EXPECT_TRUE(file_save_to_disk("test_ignore_existing_tmp", file, config));
+
+  FILE* stream = fopen(path, "rb");
+  char content[4] = {0};
+  EXPECT_NOT_NULL(stream);
+  // cppcheck-suppress knownConditionTrueFalse
+  if (stream) {
+    EXPECT_EQ_INT((int)fread(content, 1, 3, stream), 3);
+    fclose(stream);
+  }
+  EXPECT_EQ_STR(content, "old");
+
+  file_destroy(file);
+  config_delete(config);
+  unlink(path);
+  rmdir("test_ignore_existing_tmp");
+}
+
+static void test_file_save_to_disk_ignore_existing_entry_types() {
+  const char* root = "test_ignore_existing_entries_tmp";
+  const char* directory = "test_ignore_existing_entries_tmp/directory";
+  const char* link = "test_ignore_existing_entries_tmp/link";
+  const char* target = "test_ignore_existing_entries_tmp/target";
+  const char* backup = "test_ignore_existing_entries_tmp/backup.txt~";
+  const char* backup_file = "test_ignore_existing_entries_tmp/backup.txt";
+  Config* config = config_create();
+  File* file = file_create("unused");
+
+  unlink(link);
+  unlink(target);
+  unlink(backup);
+  unlink(backup_file);
+  rmdir(directory);
+  rmdir(root);
+  EXPECT_NOT_NULL(config);
+  EXPECT_NOT_NULL(file);
+  // cppcheck-suppress knownConditionTrueFalse
+  if (!config || !file)
+    return;
+  config->ignore_existing = true;
+  config->backup = true;
+  file->data->data = malloc(3);
+  EXPECT_NOT_NULL(file->data->data);
+  // cppcheck-suppress knownConditionTrueFalse
+  if (!file->data->data) {
+    file_destroy(file);
+    config_delete(config);
+    return;
+  }
+  memcpy(file->data->data, "new", 3);
+  file->data->size = 3;
+
+  EXPECT_EQ_INT(mkdir(root, 0755), 0);
+  EXPECT_EQ_INT(mkdir(directory, 0755), 0);
+  EXPECT_TRUE(file_write_to_disk(target, "old", 3, false, false));
+  EXPECT_EQ_INT(symlink("target", link), 0);
+  free(file->path);
+  file->path = str_dup("directory");
+  EXPECT_TRUE(file_save_to_disk(root, file, config));
+  free(file->path);
+  file->path = str_dup("link");
+  EXPECT_TRUE(file_save_to_disk(root, file, config));
+
+  free(file->path);
+  file->path = str_dup("backup.txt");
+  EXPECT_TRUE(file_write_to_disk(backup_file, "old", 3, false, false));
+  EXPECT_TRUE(file_save_to_disk(root, file, config));
+  EXPECT_TRUE(file_path_exists_secure(backup_file));
+  EXPECT_FALSE(file_path_exists_secure(backup));
+
+  file_destroy(file);
+  config_delete(config);
+  unlink(link);
+  unlink(target);
+  unlink(backup_file);
+  rmdir(directory);
+  rmdir(root);
+}
+
+static void test_file_write_to_disk_basic() {
+  const char* content = "Basic file_write_to_disk test";
+  EXPECT_TRUE(file_write_to_disk("test_file_write_to_disk_basic.txt", content, strlen(content),
+                                 false, false));
+
+  struct stat st;
+  EXPECT_EQ_INT(stat("test_file_write_to_disk_basic.txt", &st), 0);
+  EXPECT_EQ_INT((int)st.st_size, (int)strlen(content));
+
+  FILE* fp = fopen("test_file_write_to_disk_basic.txt", "rb");
   EXPECT_NOT_NULL(fp);
   char buf[100];
   size_t nread = fread(buf, 1, sizeof(buf), fp);
@@ -103,12 +267,24 @@ static void test_to_disk_basic() {
   EXPECT_EQ_INT((int)nread, (int)strlen(content));
   EXPECT_EQ_INT(memcmp(buf, content, strlen(content)), 0);
 
-  unlink("test_to_disk_basic.txt");
+  unlink("test_file_write_to_disk_basic.txt");
 }
 
-static void test_to_disk_creates_dirs() {
+static void test_file_write_to_disk_with_fsync() {
+  const char* path = "test_file_write_to_disk_fsync.txt";
+  const char* content = "fsync file content";
+  EXPECT_TRUE(file_to_disk_secure_with_fsync(path, content, strlen(content), false, false, NULL,
+                                             false, true));
+  struct stat st;
+  EXPECT_EQ_INT(stat(path, &st), 0);
+  EXPECT_EQ_INT((int)st.st_size, (int)strlen(content));
+  unlink(path);
+}
+
+static void test_file_write_to_disk_creates_dirs() {
   const char* content = "Nested dir test";
-  EXPECT_TRUE(to_disk("test_nested_tmp/nested/file.txt", content, strlen(content), false, false));
+  EXPECT_TRUE(file_write_to_disk("test_nested_tmp/nested/file.txt", content, strlen(content), false,
+                                 false));
 
   struct stat st;
   EXPECT_EQ_INT(stat("test_nested_tmp/nested/file.txt", &st), 0);
@@ -126,15 +302,15 @@ static void test_to_disk_creates_dirs() {
   rmdir("test_nested_tmp");
 }
 
-static void test_to_disk_does_not_follow_symlink() {
-  const char* outside = "test_to_disk_outside.txt";
-  const char* link = "test_to_disk_link.txt";
+static void test_file_write_to_disk_does_not_follow_symlink() {
+  const char* outside = "test_file_write_to_disk_outside.txt";
+  const char* link = "test_file_write_to_disk_link.txt";
   const char* content = "confined";
   unlink(outside);
   unlink(link);
-  EXPECT_TRUE(to_disk(outside, "outside", 7, false, false));
+  EXPECT_TRUE(file_write_to_disk(outside, "outside", 7, false, false));
   EXPECT_EQ_INT(symlink(outside, link), 0);
-  EXPECT_TRUE(to_disk(link, content, strlen(content), false, false));
+  EXPECT_TRUE(file_write_to_disk(link, content, strlen(content), false, false));
   FILE* fp = fopen(outside, "rb");
   char buf[16] = {0};
   EXPECT_NOT_NULL(fp);
@@ -151,7 +327,7 @@ static void test_to_disk_does_not_follow_symlink() {
 
 static void test_file_content_to_buffer() {
   const char* content = "Buffer content test";
-  EXPECT_TRUE(to_disk("test_buffer_file.txt", content, strlen(content), false, false));
+  EXPECT_TRUE(file_write_to_disk("test_buffer_file.txt", content, strlen(content), false, false));
 
   File* f = file_create("test_buffer_file.txt");
   EXPECT_NOT_NULL(f);
@@ -273,7 +449,7 @@ static void test_file_send_no_path() {
 }
 
 static void test_file_metadata_create() {
-  EXPECT_TRUE(to_disk("test_meta_file.txt", "metadata test", 13, false, false));
+  EXPECT_TRUE(file_write_to_disk("test_meta_file.txt", "metadata test", 13, false, false));
   struct stat st;
   EXPECT_EQ_INT(stat("test_meta_file.txt", &st), 0);
 
@@ -382,7 +558,7 @@ static void test_file_send_single_calls_metadata_and_path() {
   /* Create a real file on disk so we can have metadata */
   const char* content = "File with metadata";
   size_t len = strlen(content);
-  EXPECT_TRUE(to_disk("test_meta_send.txt", content, len, false, false));
+  EXPECT_TRUE(file_write_to_disk("test_meta_send.txt", content, len, false, false));
 
   struct stat st;
   EXPECT_EQ_INT(stat("test_meta_send.txt", &st), 0);
@@ -455,9 +631,14 @@ void test_file() {
   test_file_load_data();
   test_file_load_data_missing_file();
   test_file_save_to_disk();
-  test_to_disk_basic();
-  test_to_disk_creates_dirs();
-  test_to_disk_does_not_follow_symlink();
+  test_file_save_to_disk_with_fsync_config();
+  test_file_save_to_disk_existing();
+  test_file_save_to_disk_ignore_existing();
+  test_file_save_to_disk_ignore_existing_entry_types();
+  test_file_write_to_disk_basic();
+  test_file_write_to_disk_with_fsync();
+  test_file_write_to_disk_creates_dirs();
+  test_file_write_to_disk_does_not_follow_symlink();
   test_file_content_to_buffer();
   test_file_save_to_disk_path_traversal();
   test_file_save_to_disk_deep_traversal();

tests/test_file_sendfile.c

@@ -15,7 +15,7 @@
 static void test_sendfile_basic() {
   const char* content = "Hello from sendfile test!";
   size_t len = strlen(content);
-  EXPECT_TRUE(to_disk("test_sendfile_basic.txt", content, len, false, false));
+  EXPECT_TRUE(file_write_to_disk("test_sendfile_basic.txt", content, len, false, false));
 
   File* file = file_create("test_sendfile_basic.txt");
   EXPECT_NOT_NULL(file);
@@ -77,7 +77,7 @@ static void test_sendfile_basic() {
 static void test_sendfile_empty_file() {
   const char* content = "";
   size_t len = 0;
-  EXPECT_TRUE(to_disk("test_sendfile_empty.txt", content, len, false, false));
+  EXPECT_TRUE(file_write_to_disk("test_sendfile_empty.txt", content, len, false, false));
 
   File* file = file_create("test_sendfile_empty.txt");
   EXPECT_NOT_NULL(file);
@@ -156,7 +156,7 @@ static void test_sendfile_missing_file() {
 static void test_sendfile_compression_fallback() {
   const char* content = "Compression fallback content";
   size_t len = strlen(content);
-  EXPECT_TRUE(to_disk("test_sendfile_comp.txt", content, len, false, false));
+  EXPECT_TRUE(file_write_to_disk("test_sendfile_comp.txt", content, len, false, false));
 
   struct stat st;
   EXPECT_EQ_INT(stat("test_sendfile_comp.txt", &st), 0);
@@ -222,7 +222,7 @@ static void test_sendfile_compression_fallback() {
 static void test_sendfile_no_path() {
   const char* content = "No path sendfile test";
   size_t len = strlen(content);
-  EXPECT_TRUE(to_disk("test_sendfile_nopath.txt", content, len, false, false));
+  EXPECT_TRUE(file_write_to_disk("test_sendfile_nopath.txt", content, len, false, false));
 
   File* file = file_create("test_sendfile_nopath.txt");
   EXPECT_NOT_NULL(file);

tests/test_fuzz_smoke.c

@@ -101,7 +101,7 @@ static void test_fuzz_delta_deserialize() {
 /* Smoke test for metadata_from_buf fuzz target */
 static void test_fuzz_metadata_from_buf() {
   /* Create a real file to get metadata from */
-  EXPECT_TRUE(to_disk("fuzz_meta_test.txt", "metadata test", 13, false, false));
+  EXPECT_TRUE(file_write_to_disk("fuzz_meta_test.txt", "metadata test", 13, false, false));
 
   struct stat st;
   EXPECT_EQ_INT(stat("fuzz_meta_test.txt", &st), 0);

tests/test_log.c

@@ -1,6 +1,8 @@
 #include "test_log.h"
 #include "log.h"
 #include "test_utils.h"
+#include <string.h>
+#include <unistd.h>
 
 /* Test default log level: WARNING and ERROR should print, DEBUG and INFO should not.
  * We can't easily capture stderr in unit tests, so we verify the functions don't crash
@@ -90,6 +92,29 @@ static void test_log_filtering() {
   EXPECT_TRUE(true);
 }
 
+static void test_log_stderr_mode_all() {
+  int pipe_fds[2];
+  EXPECT_EQ_INT(pipe(pipe_fds), 0);
+  int saved_stderr = dup(STDERR_FILENO);
+  EXPECT_TRUE(saved_stderr >= 0);
+  EXPECT_TRUE(dup2(pipe_fds[1], STDERR_FILENO) >= 0);
+  close(pipe_fds[1]);
+
+  set_log_level(LOG_LEVEL_WARNING);
+  log_set_stderr_mode(LOG_STDERR_ALL);
+  log_message(LOG_LEVEL_WARNING, "warning routed to stderr");
+  fflush(stderr);
+
+  EXPECT_TRUE(dup2(saved_stderr, STDERR_FILENO) >= 0);
+  close(saved_stderr);
+  char output[128] = {0};
+  ssize_t length = read(pipe_fds[0], output, sizeof(output) - 1);
+  close(pipe_fds[0]);
+  EXPECT_TRUE(length > 0);
+  EXPECT_TRUE(strstr(output, "warning routed to stderr") != NULL);
+  log_set_stderr_mode(LOG_STDERR_ERRORS);
+}
+
 /* Test that log_message handles various format strings */
 static void test_log_message_formats() {
   set_log_level(LOG_LEVEL_DEBUG);
@@ -112,5 +137,6 @@ void test_log() {
   test_log_set_level_info();
   test_log_set_level_error();
   test_log_filtering();
+  test_log_stderr_mode_all();
   test_log_message_formats();
 }

tests/test_metadata.c

@@ -1,4 +1,5 @@
 #include "test_metadata.h"
+#include "chmod.h"
 #include "metadata.h"
 #include "protocol.h"
 #include "test_utils.h"
@@ -122,10 +123,22 @@ static void test_metadata_rejects_invalid_values() {
   close(p[1]);
 }
 
+static void test_metadata_mtime_window() {
+  EXPECT_TRUE(metadata_mtime_matches(100, 100000000, 101, 600000000, 2));
+  EXPECT_FALSE(metadata_mtime_matches(100, 100000000, 102, 600000000, 2));
+  EXPECT_TRUE(metadata_mtime_matches(100, 100000000, 102, 100000000, 2));
+  EXPECT_TRUE(metadata_mtime_matches(100, 900000000, 102, 100000000, 2));
+  EXPECT_FALSE(metadata_mtime_matches(100, 100000000, 102, 900000000, 2));
+  EXPECT_TRUE(metadata_mtime_matches(100, 900000000, 102, 900000000, 2));
+  EXPECT_FALSE(metadata_mtime_matches(100, 900000000, 101, 100000001, 0));
+  EXPECT_TRUE(metadata_mtime_matches(100, 100000000, 100, 100000001, 0));
+  EXPECT_TRUE(metadata_mtime_matches(100, 100000000, 100, 100000000, 0));
+}
+
 static void test_file_restore_metadata() {
   const char* path = "temp_meta_restore_test.txt";
   const char* content = "test content";
-  EXPECT_TRUE(to_disk(path, content, strlen(content), false, false));
+  EXPECT_TRUE(file_write_to_disk(path, content, strlen(content), false, false));
 
   FileMetadata m;
   m.mode = 0644;
@@ -134,7 +147,7 @@ static void test_file_restore_metadata() {
   m.mtime_sec = 1234567890;
   m.mtime_nsec = 0;
 
-  file_restore_metadata(path, &m);
+  file_restore_metadata(path, &m, false);
 
   struct stat st;
   EXPECT_EQ_INT(stat(path, &st), 0);
@@ -144,6 +157,56 @@ static void test_file_restore_metadata() {
   unlink(path);
 }
 
+static void test_file_restore_executability_only() {
+  const char* path = "temp_exec_restore_test.txt";
+  EXPECT_TRUE(file_write_to_disk(path, "x", 1, false, false));
+  EXPECT_EQ_INT(chmod(path, 0644), 0);
+
+  FileMetadata m = {
+      .mode = 0751, .uid = getuid(), .gid = getgid(), .mtime_sec = 0, .mtime_nsec = 0};
+  file_restore_metadata(path, &m, true);
+
+  struct stat st;
+  EXPECT_EQ_INT(stat(path, &st), 0);
+  EXPECT_EQ_INT(st.st_mode & 0777, 0755);
+  unlink(path);
+}
+
+static void test_directory_restore_executability_only() {
+  const char* path = "temp_exec_restore_test_dir";
+  EXPECT_EQ_INT(mkdir(path, 0700), 0);
+
+  FileMetadata m = {
+      .mode = 0755, .uid = getuid(), .gid = getgid(), .mtime_sec = 0, .mtime_nsec = 0};
+  file_restore_metadata(path, &m, true);
+
+  struct stat st;
+  EXPECT_EQ_INT(stat(path, &st), 0);
+  EXPECT_EQ_INT(st.st_mode & 0777, 0711);
+  rmdir(path);
+}
+
+static void test_chmod_changes() {
+  mode_t result;
+  EXPECT_TRUE(chmod_apply(0777, "u=rw,go=r", &result));
+  EXPECT_EQ_INT(result, 0644);
+  EXPECT_TRUE(chmod_apply(0644, "a+x", &result));
+  EXPECT_EQ_INT(result, 0755);
+  result = 0777;
+  EXPECT_TRUE(chmod_apply(0777, "0000", &result));
+  EXPECT_EQ_INT(result, 0000);
+  result = 0777;
+  EXPECT_TRUE(chmod_apply(0777, "7777", &result));
+  EXPECT_EQ_INT(result, 07777);
+  result = 0777;
+  EXPECT_TRUE(chmod_apply(0777, "755", &result));
+  EXPECT_EQ_INT(result, 0755);
+  EXPECT_FALSE(chmod_apply(0777, "888", &result));
+  EXPECT_FALSE(chmod_apply(0777, "10000", &result));
+  EXPECT_FALSE(chmod_apply(0777, "a+X", &result));
+  EXPECT_FALSE(chmod_apply(0777, "a+r,", &result));
+}
+
 void test_metadata() {
   test_metadata_to_from_buf_roundtrip();
   test_metadata_to_buf_null();
@@ -151,5 +214,9 @@ void test_metadata() {
   test_metadata_send_receive_roundtrip();
   test_metadata_send_null();
   test_metadata_rejects_invalid_values();
+  test_metadata_mtime_window();
   test_file_restore_metadata();
+  test_file_restore_executability_only();
+  test_directory_restore_executability_only();
+  test_chmod_changes();
 }

tests/test_property.c

@@ -14,6 +14,8 @@
 static Data* random_data(int min_size, int max_size) {
   int size = min_size + rand() % (max_size - min_size + 1);
   char* buf = malloc(size);
+  if (!buf)
+    return NULL;
   for (int i = 0; i < size; i++)
     buf[i] = (char)(rand() % 256);
   return data_create(buf, size);
@@ -81,10 +83,12 @@ static void test_property_chunk_roundtrip() {
 
     int content_len = 1 + rand() % 4096;
     char* content = malloc(content_len);
+    if (!content)
+      return;
     for (int i = 0; i < content_len; i++)
       content[i] = (char)(rand() % 256);
 
-    to_disk(path, content, content_len, false, false);
+    file_write_to_disk(path, content, content_len, false, false);
 
     struct stat st;
     stat(path, &st);

tests/test_protocol.c

@@ -3,6 +3,60 @@
 #include <limits.h>
 #include <string.h>
 #include <unistd.h>
+#include <threads.h>
+
+typedef struct {
+  ProtocolSession* session;
+  bool allocation_allowed;
+} AllocationWorkerArg;
+
+static int allocation_worker(void* arg) {
+  AllocationWorkerArg* worker = arg;
+  protocol_session_bind(worker->session);
+  void* allocation = protocol_alloc(8);
+  worker->allocation_allowed = allocation != NULL;
+  free(allocation);
+  protocol_session_unbind();
+  return thrd_success;
+}
+
+typedef struct {
+  ProtocolSession* session;
+  int read_fd;
+  bool released;
+} AccountingWorkerArg;
+
+typedef struct {
+  ProtocolSession* session;
+  atomic_int* ready;
+  atomic_bool* release;
+  bool received;
+} ConcurrentAccountingWorkerArg;
+
+static int accounting_worker(void* arg) {
+  AccountingWorkerArg* worker = arg;
+  protocol_session_bind(worker->session);
+  Data* data = protocol_receive_data_limited(worker->session, 8);
+  if (data) {
+    data_destroy(data);
+    worker->released = atomic_load(&worker->session->total_allocated_bytes) == 0;
+  }
+  protocol_session_unbind();
+  return data ? thrd_success : thrd_error;
+}
+
+static int concurrent_accounting_worker(void* arg) {
+  ConcurrentAccountingWorkerArg* worker = arg;
+  protocol_session_bind(worker->session);
+  Data* data = protocol_receive_data_limited(worker->session, 8);
+  worker->received = data != NULL;
+  atomic_fetch_add(worker->ready, 1);
+  while (!atomic_load(worker->release))
+    thrd_yield();
+  data_destroy(data);
+  protocol_session_unbind();
+  return thrd_success;
+}
 
 static void test_send_receive_n_data() {
   int p[2];
@@ -38,6 +92,23 @@ static void test_send_receive_n_data_zero() {
   close(p[1]);
 }
 
+static void test_explicit_session_context() {
+  int p[2];
+  EXPECT_EQ_INT(pipe(p), 0);
+  ProtocolSession session;
+  protocol_session_init(&session, p[0], p[1]);
+  protocol_session_set_bwlimit(&session, 0);
+
+  const char payload[] = "explicit context";
+  char received[sizeof(payload)] = {0};
+  EXPECT_TRUE(protocol_send_n_data(&session, payload, sizeof(payload)));
+  EXPECT_TRUE(protocol_receive_n_data(&session, received, sizeof(received)));
+  EXPECT_EQ_INT(memcmp(payload, received, sizeof(payload)), 0);
+
+  close(p[0]);
+  close(p[1]);
+}
+
 static void test_send_receive_str() {
   int p[2];
   EXPECT_EQ_INT(pipe(p), 0);
@@ -170,9 +241,181 @@ static void test_receive_str_truncated() {
   close(p[0]);
 }
 
+static void test_max_alloc_rejects_single_buffer() {
+  int p[2];
+  EXPECT_EQ_INT(pipe(p), 0);
+  ProtocolSession session;
+  protocol_session_init(&session, p[0], p[1]);
+  protocol_session_set_max_alloc(&session, 4);
+  protocol_session_bind(&session);
+  char payload[8] = {0};
+  EXPECT_TRUE(write(p[1], &(size_t){sizeof(payload)}, sizeof(size_t)) == sizeof(size_t));
+  EXPECT_NULL(protocol_receive_str(&session));
+  protocol_session_unbind();
+  close(p[0]);
+  close(p[1]);
+}
+
+static void test_explicit_session_max_alloc_cannot_be_bypassed() {
+  int p[2];
+  EXPECT_EQ_INT(pipe(p), 0);
+  ProtocolSession explicit_session;
+  ProtocolSession unrelated_session;
+  protocol_session_init(&explicit_session, p[0], p[1]);
+  protocol_session_init(&unrelated_session, p[0], p[1]);
+  protocol_session_set_max_alloc(&explicit_session, 4);
+  protocol_session_set_max_alloc(&unrelated_session, 64);
+  protocol_session_bind(&unrelated_session);
+
+  unsigned long long size = 8;
+  EXPECT_EQ_INT((int)write(p[1], &size, sizeof(size)), (int)sizeof(size));
+  EXPECT_EQ_INT((int)write(p[1], "12345678", 8), 8);
+  EXPECT_NULL(protocol_receive_data_limited(&explicit_session, 8));
+  EXPECT_EQ_INT((int)atomic_load(&explicit_session.total_allocated_bytes), 0);
+
+  protocol_session_unbind();
+  close(p[0]);
+  close(p[1]);
+}
+
+static void test_max_alloc_allows_configured_buffer() {
+  ProtocolSession session;
+  protocol_session_init(&session, -1, -1);
+  protocol_session_set_max_alloc(&session, 4);
+  protocol_session_bind(&session);
+  void* allowed = protocol_alloc(4);
+  const void* rejected = protocol_alloc(5);
+  EXPECT_NOT_NULL(allowed);
+  EXPECT_NULL(rejected);
+  free(allowed);
+  protocol_session_unbind();
+}
+
+static void test_max_alloc_is_bound_in_worker_threads() {
+  enum { WORKER_COUNT = 4 };
+  ProtocolSession sessions[WORKER_COUNT];
+  AllocationWorkerArg args[WORKER_COUNT] = {0};
+  thrd_t threads[WORKER_COUNT];
+  for (int i = 0; i < WORKER_COUNT; i++) {
+    protocol_session_init(&sessions[i], -1, -1);
+    protocol_session_set_max_alloc(&sessions[i], 4);
+    args[i].session = &sessions[i];
+    EXPECT_EQ_INT(thrd_create(&threads[i], allocation_worker, &args[i]), thrd_success);
+  }
+  for (int i = 0; i < WORKER_COUNT; i++) {
+    int result;
+    EXPECT_EQ_INT(thrd_join(threads[i], &result), thrd_success);
+    EXPECT_EQ_INT(result, thrd_success);
+    EXPECT_FALSE(args[i].allocation_allowed);
+  }
+}
+
+static void test_protocol_accounting_is_released_in_worker_threads() {
+  enum { WORKER_COUNT = 4 };
+  ProtocolSession sessions[WORKER_COUNT];
+  AccountingWorkerArg args[WORKER_COUNT] = {0};
+  thrd_t threads[WORKER_COUNT];
+  for (int i = 0; i < WORKER_COUNT; i++) {
+    int p[2];
+    EXPECT_EQ_INT(pipe(p), 0);
+    protocol_session_init(&sessions[i], p[0], p[1]);
+    protocol_session_set_max_alloc(&sessions[i], 64);
+    unsigned long long size = 8;
+    EXPECT_EQ_INT((int)write(p[1], &size, sizeof(size)), (int)sizeof(size));
+    EXPECT_EQ_INT((int)write(p[1], "12345678", 8), 8);
+    close(p[1]);
+    args[i].session = &sessions[i];
+    args[i].read_fd = p[0];
+    EXPECT_EQ_INT(thrd_create(&threads[i], accounting_worker, &args[i]), thrd_success);
+  }
+  for (int i = 0; i < WORKER_COUNT; i++) {
+    int result;
+    EXPECT_EQ_INT(thrd_join(threads[i], &result), thrd_success);
+    EXPECT_EQ_INT(result, thrd_success);
+    EXPECT_TRUE(args[i].released);
+    EXPECT_EQ_INT((int)atomic_load(&sessions[i].total_allocated_bytes), 0);
+    close(args[i].read_fd);
+  }
+}
+
+static void test_protocol_accounting_reservation_is_atomic() {
+  enum { WORKER_COUNT = 8 };
+  int p[2];
+  EXPECT_EQ_INT(pipe(p), 0);
+  ProtocolSession session;
+  protocol_session_init(&session, p[0], p[1]);
+  protocol_session_set_max_alloc(&session, 64);
+  const unsigned long long budget_before = MAX_SERVER_ALLOC - 8;
+  atomic_store(&session.total_allocated_bytes, budget_before);
+
+  for (int i = 0; i < WORKER_COUNT; i++) {
+    unsigned long long size = 8;
+    EXPECT_EQ_INT((int)write(p[1], &size, sizeof(size)), (int)sizeof(size));
+    EXPECT_EQ_INT((int)write(p[1], "12345678", 8), 8);
+  }
+  close(p[1]);
+
+  atomic_int ready;
+  atomic_bool release;
+  atomic_init(&ready, 0);
+  atomic_init(&release, false);
+  ConcurrentAccountingWorkerArg args[WORKER_COUNT] = {0};
+  thrd_t threads[WORKER_COUNT];
+  for (int i = 0; i < WORKER_COUNT; i++) {
+    args[i].session = &session;
+    args[i].ready = &ready;
+    args[i].release = &release;
+    EXPECT_EQ_INT(thrd_create(&threads[i], concurrent_accounting_worker, &args[i]), thrd_success);
+  }
+  while (atomic_load(&ready) != WORKER_COUNT)
+    thrd_yield();
+  bool budget_ok = atomic_load(&session.total_allocated_bytes) == budget_before + 8;
+  atomic_store(&release, true);
+  int received = 0;
+  for (int i = 0; i < WORKER_COUNT; i++) {
+    int result;
+    EXPECT_EQ_INT(thrd_join(threads[i], &result), thrd_success);
+    EXPECT_EQ_INT(result, thrd_success);
+    received += args[i].received ? 1 : 0;
+  }
+  EXPECT_EQ_INT(received, 1);
+  EXPECT_TRUE(budget_ok);
+  EXPECT_EQ_INT((int)atomic_load(&session.total_allocated_bytes), (int)budget_before);
+  close(p[0]);
+}
+
+static void test_protocol_string_accounting_is_transient() {
+  int p[2];
+  EXPECT_EQ_INT(pipe(p), 0);
+  ProtocolSession session;
+  protocol_session_init(&session, p[0], p[1]);
+  protocol_session_set_max_alloc(&session, 64);
+  EXPECT_TRUE(protocol_send_str(&session, "temporary"));
+  char* received = protocol_receive_str(&session);
+  EXPECT_NOT_NULL(received);
+  EXPECT_EQ_STR(received, "temporary");
+  EXPECT_EQ_INT((int)atomic_load(&session.total_allocated_bytes), 0);
+  free(received);
+  close(p[0]);
+  close(p[1]);
+}
+
+static void test_protocol_accounting_release_does_not_underflow() {
+  ProtocolSession session;
+  protocol_session_init(&session, -1, -1);
+  atomic_store(&session.total_allocated_bytes, 4);
+  protocol_session_bind(&session);
+  protocol_release_memory(8);
+  EXPECT_EQ_INT((int)atomic_load(&session.total_allocated_bytes), 0);
+  protocol_release_memory(1);
+  EXPECT_EQ_INT((int)atomic_load(&session.total_allocated_bytes), 0);
+  protocol_session_unbind();
+}
+
 void test_protocol() {
   test_send_receive_n_data();
   test_send_receive_n_data_zero();
+  test_explicit_session_context();
   test_send_receive_str();
   test_send_receive_str_normal();
   test_send_receive_data();
@@ -180,4 +423,12 @@ void test_protocol() {
   test_send_receive_status();
   test_receive_n_data_truncated();
   test_receive_str_truncated();
+  test_max_alloc_rejects_single_buffer();
+  test_explicit_session_max_alloc_cannot_be_bypassed();
+  test_max_alloc_allows_configured_buffer();
+  test_max_alloc_is_bound_in_worker_threads();
+  test_protocol_accounting_is_released_in_worker_threads();
+  test_protocol_accounting_reservation_is_atomic();
+  test_protocol_string_accounting_is_transient();
+  test_protocol_accounting_release_does_not_underflow();
 }

tests/test_queue.c

@@ -122,6 +122,8 @@ static void test_queue_destroyer() {
 
   for (int i = 0; i < 3; i++) {
     int* val = malloc(sizeof(int));
+    if (!val)
+      break;
     *val = i;
     queue_enqueue(q, val);
   }
@@ -181,6 +183,8 @@ static void test_queue_multithreaded() {
 
   for (int i = 1; i <= 100; i++) {
     int* val = malloc(sizeof(int));
+    if (!val)
+      break;
     *val = i;
     queue_enqueue_multithreaded(q, val, &mutex, &cnd_empty, &cnd_full);
   }

tests/test_robustness.c

@@ -13,7 +13,7 @@
 static void test_chunk_deserialize_truncated() {
   char* path = "test_rob_trunc.txt";
   char* content = "hello";
-  to_disk(path, content, strlen(content), false, false);
+  file_write_to_disk(path, content, strlen(content), false, false);
 
   struct stat st;
   stat(path, &st);
@@ -109,6 +109,20 @@ static void test_delta_deserialize_garbage() {
   data_destroy(d);
 }
 
+static void test_delta_deserialize_respects_max_alloc() {
+  unsigned char serialized[sizeof(uint64_t) + sizeof(uint32_t)] = {0};
+  Data data = {.data = serialized, .size = sizeof(serialized)};
+  ProtocolSession session;
+  protocol_session_init(&session, -1, -1);
+  protocol_session_set_max_alloc(&session, sizeof(Delta) - 1);
+  protocol_session_bind(&session);
+
+  const Delta* result = delta_deserialize(&data);
+  EXPECT_NULL(result);
+
+  protocol_session_unbind();
+}
+
 static void test_delta_signature_deserialize_truncated() {
   char old_data[4096];
   for (int i = 0; i < 4096; i++)
@@ -206,6 +220,7 @@ void test_robustness() {
   test_delta_deserialize_truncated();
   test_delta_deserialize_empty();
   test_delta_deserialize_garbage();
+  test_delta_deserialize_respects_max_alloc();
   test_delta_deserialize_truncated_instructions();
   test_delta_signature_deserialize_truncated();
   test_delta_apply_null();

tests/test_scanner.c

@@ -7,7 +7,7 @@
 #include <unistd.h>
 
 static void create_test_file(const char* path, const char* content) {
-  (void)to_disk(path, content, strlen(content), false, false);
+  (void)file_write_to_disk(path, content, strlen(content), false, false);
 }
 
 static void test_scanner_single_file() {
@@ -385,6 +385,35 @@ static void test_scanner_no_patterns() {
   rmdir(dir);
 }
 
+static void test_parallel_scanner_root_chunks_without_workers() {
+  const char* dir = "test_parallel_scan_root";
+  const char* file1 = "test_parallel_scan_root/a.txt";
+  const char* file2 = "test_parallel_scan_root/b.txt";
+
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
+  create_test_file(file1, "a");
+  create_test_file(file2, "b");
+
+  ScannerOptions options = {false, 1, NULL,  0,     NULL,  0,     0,    0,
+                            0,     0, false, false, false, false, false};
+  ParallelScanner* scanner = parallel_scanner_create_with_options(dir, &options, NULL);
+  EXPECT_NOT_NULL(scanner);
+
+  int total_files = 0;
+  Chunk* chunk;
+  while ((chunk = parallel_scanner_next(scanner)) != NULL) {
+    total_files += chunk->element_count;
+    chunk_destroy(chunk);
+  }
+  EXPECT_EQ_INT(total_files, 2);
+  EXPECT_FALSE(parallel_scanner_failed(scanner));
+
+  parallel_scanner_destroy(scanner);
+  unlink(file1);
+  unlink(file2);
+  rmdir(dir);
+}
+
 void test_scanner() {
   test_scanner_single_file();
   test_scanner_multiple_files();
@@ -399,4 +428,5 @@ void test_scanner() {
   test_scanner_size_range();
   test_scanner_mixed_patterns();
   test_scanner_no_patterns();
+  test_parallel_scanner_root_chunks_without_workers();
 }

tests/test_server.c

@@ -11,11 +11,7 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
-/* Include server.c but rename main to avoid conflict with test runner's main */
-#define main server_main_
-#define FASTSYNC_SERVER_AS_LIB
-#include "server.c"
-#undef main
+#include "receiver.h"
 
 /* Test receive_files with immediate FINISHED status */
 static void test_receive_files_finished() {
@@ -36,7 +32,7 @@ static void test_receive_files_finished() {
     /* Child: use p[0] for both read and write */
     close(p[1]);
     io_set_fds(p[0], p[0]);
-    int ret = receive_files(cfg, p[0]);
+    int ret = receiver_receive_files(cfg, p[0]);
     close(p[0]);
     config_delete(cfg);
     _exit(ret == 0 ? 0 : 1);
@@ -88,7 +84,7 @@ static void test_receive_files_single_file() {
     /* Child: use p[0] for both read and write */
     close(p[1]);
     io_set_fds(p[0], p[0]);
-    int ret = receive_files(cfg, p[0]);
+    int ret = receiver_receive_files(cfg, p[0]);
     close(p[0]);
     config_delete(cfg);
     _exit(ret == 0 ? 0 : 1);
@@ -149,7 +145,7 @@ static void test_receive_files_abort() {
   if (pid == 0) {
     close(p[1]);
     io_set_fds(p[0], p[0]);
-    int ret = receive_files(cfg, p[0]);
+    int ret = receiver_receive_files(cfg, p[0]);
     close(p[0]);
     config_delete(cfg);
     /* Should return -1 on abort */
@@ -186,11 +182,40 @@ static void test_receive_manifest_rejects_traversal() {
   config_delete(cfg);
 }
 
+static void test_receive_incremental_check_rejects_invalid_nanoseconds() {
+  Config* cfg = config_create();
+  EXPECT_NOT_NULL(cfg);
+  cfg->receive_root_directory = str_dup("/tmp/dst");
+
+  int p[2];
+  EXPECT_EQ_INT(socketpair(AF_UNIX, SOCK_STREAM, 0, p), 0);
+  io_set_fds(p[0], p[1]);
+  EXPECT_TRUE(send_str(p[1], "file.txt"));
+  unsigned long long size = 0;
+  long long mtime = 100;
+  long long mtime_nsec = 1000000000LL;
+  EXPECT_TRUE(send_n_data(p[1], &size, sizeof(size)));
+  EXPECT_TRUE(send_n_data(p[1], &mtime, sizeof(mtime)));
+  EXPECT_TRUE(send_n_data(p[1], &mtime_nsec, sizeof(mtime_nsec)));
+
+  bool skipped = false;
+  EXPECT_NULL(receive_incremental_check(p[0], cfg, &skipped));
+  Status status;
+  EXPECT_TRUE(receive_status(p[1], &status));
+  EXPECT_EQ_INT(status, STATUS_ERROR);
+  EXPECT_FALSE(skipped);
+
+  close(p[0]);
+  close(p[1]);
+  config_delete(cfg);
+}
+
 void test_server() {
   if (!is_running_under_valgrind()) {
     test_receive_files_finished();
     test_receive_files_single_file();
     test_receive_files_abort();
     test_receive_manifest_rejects_traversal();
+    test_receive_incremental_check_rejects_invalid_nanoseconds();
   }
 }

tests/test_shared_utils.c

@@ -1,10 +1,66 @@
 #include "test_shared_utils.h"
 #include "utils.h"
+#include "protocol.h"
 #include "test_utils.h"
 #include <stdlib.h>
 #include <string.h>
+#include <threads.h>
+
+typedef struct {
+  bool eight_bit_output;
+  const char* expected;
+  int failed;
+} EscapeThreadArgs;
+
+static int escape_thread(void* arg) {
+  EscapeThreadArgs* args = arg;
+  for (int i = 0; i < 1000; i++) {
+    char* escaped = output_escape("x\xc3\xa9\n", args->eight_bit_output);
+    if (!escaped || strcmp(escaped, args->expected) != 0)
+      args->failed = 1;
+    free(escaped);
+  }
+  return 0;
+}
 
 void test_shared_utils() {
+  char formatted[32];
+  EXPECT_TRUE(format_human_bytes(0, formatted, sizeof(formatted)));
+  EXPECT_EQ_STR(formatted, "0 B");
+  EXPECT_TRUE(format_human_bytes(1024, formatted, sizeof(formatted)));
+  EXPECT_EQ_STR(formatted, "1.0 KB");
+  EXPECT_TRUE(format_human_bytes(1536 * 1024, formatted, sizeof(formatted)));
+  EXPECT_EQ_STR(formatted, "1.5 MB");
+  EXPECT_FALSE(format_human_bytes(1024, formatted, 4));
+
+  char high_bit[] = {'a', (char)0xc3, (char)0xa9, '\n', '\0'};
+  char* escaped = output_escape(high_bit, false);
+  EXPECT_EQ_STR(escaped, "a\\#303\\#251\\#012");
+  free(escaped);
+  escaped = output_escape(high_bit, true);
+  EXPECT_EQ_STR(escaped, "a\xc3\xa9\\#012");
+  free(escaped);
+
+  ProtocolSession safe_session;
+  ProtocolSession eight_bit_session;
+  protocol_session_init(&safe_session, -1, -1);
+  protocol_session_init(&eight_bit_session, -1, -1);
+  protocol_session_set_8_bit_output(&safe_session, false);
+  protocol_session_set_8_bit_output(&eight_bit_session, true);
+  EXPECT_FALSE(safe_session.eight_bit_output);
+  EXPECT_TRUE(eight_bit_session.eight_bit_output);
+
+  EscapeThreadArgs safe_args = {false, "x\\#303\\#251\\#012", 0};
+  EscapeThreadArgs eight_bit_args = {true, "x\xc3\xa9\\#012", 0};
+  thrd_t safe_thread;
+  thrd_t eight_bit_thread;
+  EXPECT_EQ_INT(thrd_create(&safe_thread, escape_thread, &safe_args), thrd_success);
+  EXPECT_EQ_INT(thrd_create(&eight_bit_thread, escape_thread, &eight_bit_args), thrd_success);
+  EXPECT_EQ_INT(thrd_join(safe_thread, NULL), thrd_success);
+  EXPECT_EQ_INT(thrd_join(eight_bit_thread, NULL), thrd_success);
+  EXPECT_FALSE(safe_args.failed);
+  EXPECT_FALSE(eight_bit_args.failed);
+
   // Test str_dup
   const char* dup_null = str_dup(NULL);
   EXPECT_NULL(dup_null);

tests/test_stress.c

@@ -32,6 +32,8 @@ static int mpmc_producer_func(void* arg) {
   ProducerCtx* ctx = (ProducerCtx*)arg;
   for (int i = 1; i <= ITEMS_PER_PRODUCER; i++) {
     int* val = malloc(sizeof(int));
+    if (!val)
+      return thrd_error;
     *val = ctx->producer_id * ITEMS_PER_PRODUCER + i;
     queue_enqueue_multithreaded(ctx->q, val, ctx->mutex, ctx->cnd_empty, ctx->cnd_full);
   }
@@ -121,6 +123,8 @@ static int bp_producer_func(void* arg) {
   BackpressureCtx* ctx = (BackpressureCtx*)arg;
   for (int i = 0; i < 5; i++) {
     int* val = malloc(sizeof(int));
+    if (!val)
+      return thrd_error;
     *val = i + 1;
     queue_enqueue_multithreaded(ctx->q, val, ctx->mutex, ctx->cnd_empty, ctx->cnd_full);
     ctx->items_sent++;
@@ -194,6 +198,8 @@ static void test_queue_rapid_create_destroy() {
 
     for (int j = 0; j < 3; j++) {
       int* val = malloc(sizeof(int));
+      if (!val)
+        break;
       *val = j;
       queue_enqueue(q, val);
     }

tests/test_transport_ssh.c

@@ -4,34 +4,39 @@
 
 static void test_ssh_connect_invalid_dest_no_colon() {
   /* cppcheck-suppress constVariablePointer */
-  Client* client = client_connect_ssh("invalid-destination-no-colon", 22, NULL);
+  Client* client = client_connect_ssh("invalid-destination-no-colon", 22, NULL, false);
   EXPECT_NULL(client);
 }
 
 static void test_ssh_connect_invalid_dest_empty() {
   /* cppcheck-suppress constVariablePointer */
-  Client* client = client_connect_ssh("", 22, NULL);
+  Client* client = client_connect_ssh("", 22, NULL, false);
   EXPECT_NULL(client);
 }
 
-/* Test client_connect_ssh with malformed destination (just a colon).
- * parse_remote_dest succeeds, ssh is exec'd and fails, but the function
- * creates a Client that must be cleaned up. */
+/* A child that cannot exec ssh must not be returned as a successful client. */
 static void test_ssh_connect_malformed() {
-  Client* client = client_connect_ssh(":", 22, NULL);
-  /* ssh binary exists, so exec succeeds; the function returns a Client.
-   * We just verify it doesn't crash and clean up properly. */
-  if (client != NULL) {
-    client_disconnect(client);
-    client_delete(client);
+  const char* old_path = getenv("PATH");
+  char* saved_path = old_path ? strdup(old_path) : NULL;
+  setenv("PATH", "", 1);
+
+  /* cppcheck-suppress constVariablePointer */
+  Client* client = client_connect_ssh(":", 22, NULL, false);
+
+  if (saved_path) {
+    setenv("PATH", saved_path, 1);
+    free(saved_path);
+  } else {
+    unsetenv("PATH");
   }
-  EXPECT_TRUE(true);
+
+  EXPECT_NULL(client);
 }
 
 /* Test client_connect_ssh with valid format but unreachable host.
  * The function launches ssh which will fail to connect, returns a Client. */
 static void test_ssh_connect_unreachable() {
-  Client* client = client_connect_ssh("nonexistent.invalid:/remote/path", 22, NULL);
+  Client* client = client_connect_ssh("nonexistent.invalid:/remote/path", 22, NULL, false);
   if (client != NULL) {
     client_disconnect(client);
     client_delete(client);
@@ -39,9 +44,24 @@ static void test_ssh_connect_unreachable() {
   EXPECT_TRUE(true);
 }
 
+static void test_ssh_remote_command_argument_modes() {
+  char* command = ssh_build_remote_command("fast sync; touch /tmp/pwned", false);
+  EXPECT_EQ_STR(command, "'fast sync; touch /tmp/pwned' --stdio");
+  free(command);
+
+  command = ssh_build_remote_command("fast'sync", false);
+  EXPECT_EQ_STR(command, "'fast'\\''sync' --stdio");
+  free(command);
+
+  command = ssh_build_remote_command("fast sync; touch /tmp/pwned", true);
+  EXPECT_EQ_STR(command, "fast sync; touch /tmp/pwned --stdio");
+  free(command);
+}
+
 void test_transport_ssh() {
   test_ssh_connect_invalid_dest_no_colon();
   test_ssh_connect_invalid_dest_empty();
   test_ssh_connect_malformed();
   test_ssh_connect_unreachable();
+  test_ssh_remote_command_argument_modes();
 }