fix: harden remaining review findings

fix: address remaining PR review findings
fix: address delegated review findings
2026-08-15 13:44:31 +02:00 · 2026-08-15 13:24:13 +02:00 · 2026-08-15 13:13:57 +02:00 · 2026-08-15 12:49:30 +02:00 · 2026-08-15 12:34:41 +02:00 · 2026-08-15 11:55:41 +02:00
36 changed files with 2054 additions and 1610 deletions
@@ -58,18 +58,15 @@ endif()
 find_package(OpenSSL REQUIRED)

 file(GLOB SHARED_SRCS "src/shared/*.c")
-set(FILE_STORE_SRCS 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} ${FILE_STORE_SRCS})
+add_executable(server ${SERVER_SRCS} ${SHARED_SRCS})
 target_include_directories(server PRIVATE src/shared src/server src/client)
 target_link_libraries(server PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)

-add_executable(client ${CLIENT_SRCS} ${SHARED_SRCS} ${FILE_STORE_SRCS} ${SERVER_RECEIVER_SRCS})
+add_executable(client ${CLIENT_SRCS} ${SHARED_SRCS})
 target_include_directories(client PRIVATE src/shared src/server src/client)
 target_link_libraries(client PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)

@@ -82,7 +79,7 @@ set(TEST_INCLUDES tests src/shared src/server src/client)

 # Monolithic test binary (backward compatible)
 file(GLOB TEST_SRCS "tests/test_*.c" "tests/runner.c")
-add_executable(tests ${TEST_SRCS} ${SHARED_SRCS} ${FILE_STORE_SRCS} ${SERVER_RECEIVER_SRCS} src/client/scanner.c src/client/client_cli.c src/client/client_validation.c src/client/usage.c)
+add_executable(tests ${TEST_SRCS} ${SHARED_SRCS} src/client/scanner.c src/client/client_cli.c)
 target_include_directories(tests PRIVATE ${TEST_INCLUDES})
 target_compile_definitions(tests PRIVATE FASTSYNC_TEST_BUILD)
 target_link_libraries(tests PRIVATE ${TEST_LIBS})
@@ -97,7 +94,7 @@ 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} ${FILE_STORE_SRCS} ${SERVER_RECEIVER_SRCS})
+		add_executable(${FUZZ_NAME} ${FUZZ_SRC} ${SHARED_SRCS})
 		target_include_directories(${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)
@@ -1,377 +1,370 @@
 # FastSync

-FastSync is a high-performance file synchronization tool designed to become a
-drop-in replacement for common `rsync` workflows. It keeps the familiar
-source/destination model and rsync-style options while adding optional
-multithreading, streaming zstd compression, chunking, zero-copy TCP transfers,
-and native TCP/TLS transports.
+A high-performance file synchronization system with SSH and TCP transport, TLS encryption, streaming zstd compression, multithreaded transfer, incremental sync, metadata preservation, and rsync-compatible CLI flags.

-The compatibility target is straightforward:
+## Technical Overview

- Existing rsync commands should keep the same meaning.
- FastSync-only performance options should be additive and optional.
- A normal compatibility-mode transfer should prioritize rsync filesystem
-  semantics over maximum throughput.
+1. **Dual transport**: custom TCP client-server or SSH subprocess (rsync-style `user@host:/path`)
+2. **TLS encryption**: OpenSSL-based TLS 1.2+ for encrypted TCP connections with optional CA verification
+3. **Chunked file transfer**: files grouped into configurable-size chunks (default ~10 MB)
+4. **Streaming zstd compression** (levels 1–22) using `ZSTD_compressStream2`
+5. **Multithreading**: producer-consumer pipeline with thread-safe queues (scanner → loader → sender)
+6. **Incremental sync**: skip files unchanged since last transfer (compares size + mtime)
+7. **Batch incremental**: send incremental checks in batched groups for reduced round-trips
+8. **Metadata preservation**: file mode and mtime are restored when enabled; ownership and atime are intentionally not restored
+9. **`sendfile()` zero-copy** on TCP (~2× faster on loopback)
+10. **SSH ControlMaster** for connection reuse across repeated invocations
+11. **Bandwidth limiting**: token-bucket throttling (`--bwlimit`)
+12. **`--delete`**: receiver removes files not present in sender manifest
+13. **`--exclude` / `--include`**: glob-pattern filename filtering
+14. **Path traversal protection**: `..` sequences in file paths are rejected automatically
+15. **Connection limits**: server enforces maximum concurrent connections (default 100)
+16. **Keep-alive**: periodic `STATUS_KEEPALIVE` messages detect stalled connections
+17. **Abort handling**: `SIGINT` sends `STATUS_ABORT` for clean server-side teardown
+18. **Atomic writes**: received files are written to a temporary name then atomically renamed
+19. **Backup mode**: `--backup` preserves overwritten files with optional `--backup-dir`
+20. **Log file**: `--log-file` redirects log output to a file instead of stderr
+21. **Transfer statistics**: `--stats` prints summary of transferred bytes, files, and timing

-FastSync currently speaks its own protocol to `fastsync-server`. SSH mode
-starts that server remotely; it does not yet interoperate with an unmodified
-rsync client or rsync daemon. See [Compatibility Status](#compatibility-status)
-for the current boundary.
+## System Architecture

-## Why FastSync
+### Client
+- Recursively scans source directories (BFS), supports exclude and include patterns
+- Groups files into chunks (configurable size)
+- Streaming zstd compression with configurable level
+- Chunk serialization (compact binary format) or per-file transfer
+- Incremental transfer: sends file metadata to server, skips unchanged files
+- Batch incremental: groups incremental checks to minimize round-trips
+- Manifests all sent paths when `--delete` is active
+- Sends via TCP `sendfile()` or SSH pipe
+- Optional progress display with throughput
+- Bandwidth limiting via token-bucket algorithm
+- Configurable I/O and connection timeouts (`--timeout`, `--contimeout`)
+- Backup overwritten files (`--backup`) with optional directory (`--backup-dir`)
+- Transfer statistics summary (`--stats`)
+- Maximum directory depth control (`--max-depth`)
+- Log file output (`--log-file`)
+- Exclude patterns from file (`--exclude-from`)

-FastSync uses a producer-consumer transfer pipeline and can combine several
-optimizations for large or high-latency transfers:
+### Server
+- TCP mode: listens on configurable port (default 8080); SSH mode: runs via `--stdio`
+- TLS mode: wraps TCP connections with OpenSSL with optional CA verification
+- Receives and reassembles files
+- Decompresses (streaming zstd), deserializes, restores metadata
+- Handles incremental checks: compares size + mtime against destination files
+- Handles batch incremental checks for reduced round-trips
+- Processes `STATUS_MANIFEST` for `--delete`: walks destination tree, removes extras
+- Per-connection concurrency via `fork()` with configurable connection limit (default 100)
+- Thread pool for parallel processing
+- Atomic writes: files written to `.tmp` path then atomically renamed on success
+- Abort handling: cleanly shuts down on `STATUS_ABORT` from client
+- Path traversal protection: rejects file paths containing `..`

- Multithreaded scanning, loading, and sending.
- Streaming zstd compression with levels 1 through 22.
- Configurable file chunking and compact chunk serialization.
- `sendfile()` zero-copy transfers over TCP.
- Batched incremental checks to reduce round trips.
- Optional block-level delta transfer for FastSync peers.
- Bandwidth limiting, progress reporting, statistics, and backups.
- TCP, SSH, and TLS transports.
- Atomic temporary-file writes by default.
+## Protocol Details

-These optimizations are disabled or selected independently. Users can start
-with rsync-style commands and add FastSync options when they are useful.
+### Status Codes
+| Code | Meaning |
+|------|---------|
+| `STATUS_OK` | Operation successful |
+| `STATUS_ERROR` | Error occurred |
+| `STATUS_FINISHED` | Transfer complete |
+| `STATUS_NEXT` | Ready for next file (per-file mode) |
+| `STATUS_CHUNK` | Following data is a serialized chunk |
+| `STATUS_MANIFEST` | Following data is a file manifest (for `--delete`) |
+| `STATUS_CHECK` | Incremental check: client sends file path + size + mtime and, when negotiated, checksum; server responds with OK (skip) or NEXT (send) |
+| `STATUS_CHECK_BATCH` | Batch incremental check: multiple file checks sent in one message |
+| `STATUS_KEEPALIVE` | Keep-alive heartbeat to detect stalled connections |
+| `STATUS_ABORT` | Abort signal: client interrupts, server cleans up and exits |
+| `STATUS_DELTA_SIGNATURE` | Delta sync: following data is a file signature (rsync-style rolling hash) |
+| `STATUS_DELTA_DATA` | Delta sync: following data is a delta patch for a file |

-## Compatibility Status
+### Wire Format — Metadata

-FastSync is currently an rsync-compatible CLI in progress, not a complete
-replacement for every rsync feature or protocol mode.
+When `use_metadata` is enabled (`-M`), each file entry carries a 4-byte `present` flag followed by five fields (`mode`, `uid`, `gid`, `mtime_sec`, `mtime_nsec`). When disabled globally, no metadata bytes are sent — zero wire overhead.

-### Working today
-
- Recursive directory scanning.
- Rsync-style source and destination arguments.
- SSH transport using `user@host:/path` destinations.
- TCP client/server transfers.
- Dry runs, excludes, includes, size filters, backups, statistics, and
-  bandwidth limiting.
- Incremental size/mtime checks and optional xxHash64 content checks.
- FastSync-native delta transfer for changed files.
- Optional mode and timestamp preservation.
- Delete manifests with server-side delete authorization.
- Temporary-file writes with atomic rename by default.
- Path traversal checks and destination-root confinement.
-
-### Not yet equivalent to rsync
-
- The FastSync wire protocol is not the rsync wire protocol.
- SSH mode requires `fastsync-server` on the remote host.
- Archive mode does not yet provide all of rsync's `-rlptgoD` behavior.
- Symlink transfer is incomplete; link targets are not yet recreated in all
-  modes.
- Owner/group, ACL, xattr, hard-link, device, and special-file handling is
-  incomplete or unavailable.
- Sparse-file handling does not yet preserve all holes correctly.
- `--partial`, `--partial-dir`, `--append`, and `--append-verify` are not yet
-  full rsync-style resumable transfers.
- Several rsync short options currently have FastSync-specific meanings. Do
-  not assume every short option is interchangeable yet.
-
-The detailed flag matrix is maintained in
-[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md). It distinguishes implemented,
-partial, alternate, and planned behavior.
-
-## Quick Start
-
-### Build
-
-Requirements: C11 compiler, CMake 3.22 or newer, zstd, OpenSSL, pthreads,
-and an SSH client for SSH transport.
-
-```bash
-cmake -B build -S .
-cmake --build build -j$(nproc)
+### Transfer Flow
+```
+Config → (STATUS_NEXT | STATUS_CHUNK | STATUS_CHECK | STATUS_CHECK_BATCH)* → [STATUS_MANIFEST] → STATUS_FINISHED → STATUS_OK
 ```

-With Nix:
+Keep-alive (`STATUS_KEEPALIVE`) may be sent at any point during the transfer. The receiver resets its inactivity timer on receipt. If no data arrives within the receive timeout, the connection is aborted.

-```bash
-nix-shell
-cmake -B build -S .
-cmake --build build -j$(nproc)
-```
+Abort (`STATUS_ABORT`) may be sent at any point. On receipt the server cleans up temporary files and exits the child process.

-### SSH transfer
+### Protocol Version

-The remote host must have `fastsync-server` available in `PATH`, or use
-`--fastsync-server-path`.
+`2.2.0` — server and client must match. This version adds a 64-bit XXH64 checksum to checksum-enabled `STATUS_CHECK` messages and validates the negotiated compression choice (`zstd` or `none`). Older clients and servers must not be mixed with this version; mismatch results in `STATUS_ERROR`.

-```bash
-./build/client /path/to/source user@host:/path/to/destination
-```
+Config negotiation is sender-driven: the client serializes transfer options and the server applies them while receiving and writing files. `--checksum` compares size and content checksum instead of timestamps. `--compress-choice zstd` enables zstd; `none` disables it. Unsupported choices are rejected during config exchange.

-### TCP transfer
-
-Start the FastSync server:
-
-```bash
-./build/server -p 8080
-```
-
-Then run the client:
-
-```bash
-./build/client --server-host 127.0.0.1 --server-port 8080 \
-  --source-dir /path/to/source --dest-dir /path/to/destination \
-  --save-to-disk
-```
-
-### TLS transfer
-
-```bash
-./build/server --tls --cert server.pem --key server-key.pem -p 8443
-./build/client --tls --cert client.pem --key client-key.pem --ca ca.pem \
-  --server-host example.com --server-port 8443 \
-  --source-dir /path/to/source --dest-dir /path/to/destination \
-  --save-to-disk
-```
-
-## Common Workflows
-
-These examples show the intended rsync-style workflow. Options marked as
-FastSync-native are optional performance or transport extensions.
-
-```bash
-# Basic synchronization
-./build/client /source/ /destination/
-
-# Archive-style synchronization (current FastSync archive behavior)
-./build/client -a /source/ user@host:/destination/
-
-# Preview a transfer without changing the destination
-./build/client -n /source/ /destination/
-
-# Exclude temporary and object files
-./build/client --exclude '*.tmp' --exclude '*.o' \
-  /source/ user@host:/destination/
-
-# Remove destination entries not present in the source
-./build/client --delete /source/ user@host:/destination/
-
-# Skip unchanged files using size and modification time
-./build/client --incremental /source/ user@host:/destination/
-
-# Verify content when size and time are not sufficient
-./build/client --incremental --checksum /source/ user@host:/destination/
-
-# Preserve supported mode and timestamp metadata
-./build/client -M /source/ user@host:/destination/
-
-# Keep backups of overwritten destination files
-./build/client --backup --backup-dir /backups \
-  /source/ user@host:/destination/
-```
-
-## FastSync Extensions
-
-FastSync-native options are intended to add performance or operational
-features without changing the meaning of ordinary compatibility options.
-
-| Option | Purpose |
-|---|---|
-| `-m` | Enable the multithreaded scanner/loader/sender pipeline. |
-| `-c [level]`, `-z [level]` | Enable streaming zstd compression, levels 1-22. |
-| `--compress-level <n>` | Set the zstd compression level. |
-| `--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. |
-| `--delta` | Use FastSync-native block delta transfer. Requires `--incremental`. |
-| `--delta-block <bytes>` | Set the FastSync delta block size. |
-| `--delta-max <bytes>` | Limit files eligible for FastSync delta transfer. |
-| `--server-host <host>` | Select the TCP server host. |
-| `--server-port <port>` | Select the TCP server port. |
-| `--tls` | Enable TLS for TCP transport. |
-| `--bwlimit <KB/s>` | Apply token-bucket bandwidth limiting. |
-| `--progress` | Show transfer progress and throughput. |
-| `--stats` | Print transfer statistics. |
-| `--timeout <seconds>` | Set I/O timeout. |
-| `--contimeout <seconds>` | Set connection timeout. |
-
-Current short-option conflicts are tracked as compatibility work. In
-particular, FastSync currently uses `-p` for SSH port, `-s` for chunk
-serialization, and `-S` for sparse handling. These meanings must be reconciled
-before FastSync can claim full rsync CLI compatibility.
-
-## Client Options
-
-### Selection and transfer
-
-| Option | Description |
-|---|---|
-| `-a`, `--archive` | Enable current archive preset. Full rsync archive semantics are planned. |
-| `-n`, `--dry-run` | Scan and report without writing files. |
-| `--delete` | Request removal of destination entries absent from the source. The server must allow deletion. |
-| `--exclude <pattern>` | Exclude matching paths. Repeatable. |
-| `--include <pattern>` | Include matching paths. Repeatable. |
-| `--exclude-from <file>` | Read exclude patterns from a file. |
-| `--include-from <file>` | Read include patterns from a file. |
-| `--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` | Keep received data under the configured partial location. Full resume semantics are planned. |
-| `--partial-dir <dir>` | Set the partial transfer directory. |
-| `--inplace` | Write directly to the destination instead of using a temporary file. |
-
-### Metadata and links
-
-| Option | Description |
-|---|---|
-| `-M`, `--preserve` | Preserve supported file metadata, currently mode and modification time. |
-| `-l`, `--links` | Request symlink preservation; link-target transfer remains incomplete. |
-| `--copy-links` | Copy symlink referents. |
-| `--safe-links` | Skip symlinks that point outside the transfer tree. |
-| `--copy-unsafe-links` | Copy unsafe symlink referents. |
-| `-S`, `--sparse` | Request sparse-file handling; full hole preservation is planned. |
-
-### Output and logging
-
-| Option | Description |
-|---|---|
-| `-v`, `--verbose` | Enable debug logging. |
-| `--progress` | Show live transfer progress. |
-| `--stats` | Print transfer statistics. |
-| `--log-file <path>` | Write log output to a file. |
-| `-V`, `--version` | Print the FastSync protocol version. |
-| `--help` | Print command usage. |
-
-### Paths and transport
-
-| Option | Description |
-|---|---|
-| `-p <port>` | SSH port in the current CLI. This conflicts with rsync's `-p` permissions option and is planned for correction. |
-| `--fastsync-server-path <path>` | Remote FastSync server path for SSH mode. |
-| `--source-dir <path>` | Set the source directory explicitly. |
-| `--dest-dir <path>` | Set the destination directory explicitly. |
-| `--save-to-disk` | Enable server-side disk persistence. |
-| `--server-host <host>` | TCP server address. |
-| `--server-port <port>` | TCP server port. |
-| `--tls` | Enable TLS. Requires `--cert` and `--key`. |
-| `--cert <path>` | TLS certificate file. |
-| `--key <path>` | TLS private key file. |
-| `--ca <path>` | CA file for peer verification. |
-
-## Server Options
-
-| Option | Description |
-|---|---|
-| `--stdio` | Serve one SSH connection over standard input/output. |
-| `-p <port>` | TCP listen port. |
-| `--tls` | Enable TLS. |
-| `--cert <path>` | TLS certificate file. |
-| `--key <path>` | TLS private key file. |
-| `--ca <path>` | CA file for peer verification. |
-| `--allow-delete` | Permit client delete manifests. Deletion is refused by default. |
-| `-v`, `--verbose` | Enable debug logging. |
-| `--help` | Print server usage. |
-
-## Architecture
+## Command-Line Arguments

 ### Client

- Recursively scans the source tree with include, exclude, size, and depth
-  filters.
- Sends individual files or serialized chunks.
- Performs incremental checks and optional content checksums.
- Uses a multithreaded producer-consumer pipeline when requested.
- Sends over TCP, TLS-wrapped TCP, or an SSH subprocess.
- Supports progress, statistics, backups, timeouts, and bandwidth limiting.
+| Argument | Description |
+|----------|-------------|
+| Positional | `<source> <dest>` — automatic SSH detection if dest contains `:` |
+| `-c [level]` | Compression with optional level (1–22, default 5) |
+| `-z [level]` | Alias for `-c` |
+| `-a, --archive` | Archive mode: enables `-c -m -M` (no `-s`) |
+| `-m` | Multithreading mode |
+| `-s` | Chunk serialization (batch all files per chunk) |
+| `-f, --sendfile` | Sendfile zero-copy. Incompatible with `-c` / `-s`. TCP only. |
+| `-M, --preserve` | Preserve supported file metadata (mode and mtime; ownership and atime are unsupported) |
+| `-n, --dry-run` | Scan and print what would be transferred |
+| `-p <port>` | SSH port (default: 22) |
+| `-v, --verbose` | Enable debug logging |
+| `--progress` | Show real-time transfer speed |
+| `--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 |
+| `--incremental` | Skip files unchanged since last transfer (size + mtime). Auto-enables `--preserve`. Incompatible with `-s`. |
+| `--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) |
+| `--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

- Runs as a TCP listener or one-shot SSH `--stdio` server.
- Receives and reassembles files and decompresses streaming zstd data.
- Applies supported metadata and writes files through a confined destination
-  root.
- Uses temporary files and atomic rename by default.
- Handles delete manifests only when explicitly authorized.
- Enforces connection, message-size, and path-safety limits.
+| 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 |

-## Protocol and Security
+## Environment Variables

-FastSync protocol version `2.2.0` 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.
+| 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 |

-TLS provides encrypted TCP transport. Supplying `--ca` enables certificate
-verification; without it, traffic is encrypted but peer identity is not
-verified. Use certificate verification for deployments where authentication
-matters. The default TCP transport is not encrypted.
+## Implementation Details

-The receiver protects its destination root with path validation, `openat()`
-directory traversal, `O_NOFOLLOW`, temporary files, and atomic renames. Delete
-operations require the server's explicit `--allow-delete` policy.
+### 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

-## Compatibility Roadmap
+### 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

-The project will reach the drop-in replacement goal in stages:
+## Security Features

-1. Correct rsync option meanings, including short options, combined options,
-   and `--option=value` syntax.
-2. Add differential tests that compare FastSync and rsync contents, metadata,
-   links, deletes, filters, dry runs, and exit codes.
-3. Make `-a` implement the expected recursive, links, permissions, times,
-   owner/group, and supported special-file behavior.
-4. Complete symlink, sparse-file, metadata, delete-policy, and resumable-write
-   semantics.
-5. Add rsync remote-shell and daemon protocol interoperability.
-6. Keep FastSync performance options as negotiated, optional extensions.
+### 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.

-The exhaustive implementation matrix and compatibility notes are in
-[`RSYNC_COMPAT.md`](RSYNC_COMPAT.md).
+### 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 . && cmake --build build -j$(nproc)
+```
+
+## Running
+
+### Server (TCP mode)
+```bash
+./build/server --allow-unauthenticated
+```
+
+### Server with TLS
+```bash
+./build/server --tls --cert server.pem --key server-key.pem --ca ca.pem --client-cn fastsync-client
+```
+
+### Server via SSH
+Place the `fastsync-server` binary in the remote `$PATH`. The client runs `ssh user@host fastsync-server --stdio` automatically when an SSH-style destination is given.
+
+### Client — SSH (rsync-style)
+```bash
+./build/client /path/to/send user@host:/path/to/receive
+```
+
+### Client — TCP
+```bash
+./build/client --source-dir /path/to/send --dest-dir /path/to/receive --save-to-disk
+```
+
+Plain TCP requires the explicit `--allow-unauthenticated` server option. Use TLS for
+authenticated network connections.
+
+### Client — TCP with TLS
+```bash
+./build/client --tls --cert client.pem --key client-key.pem --ca ca.pem \
+  --source-dir /path/to/send --dest-dir /path/to/receive --save-to-disk
+```
+
+### Common Options
+```bash
+# Archive mode (compression + multithreading + metadata)
+./build/client -a /path/to/send user@host:/path
+
+# Dry run
+./build/client -n /path/to/send /path/to/receive
+
+# With progress and custom chunk size
+./build/client --progress --chunk-size 2097152 /src user@host:/dst
+
+# Exclude temporary files + delete extras on receiver
+./build/client --exclude "*.tmp" --exclude "*.o" --delete /src user@host:/dst
+
+# Incremental sync (skip unchanged files)
+./build/client --incremental /src user@host:/dst
+
+# Bandwidth limit to 1 MB/s
+./build/client --bwlimit 1024 /src user@host:/dst
+
+# With timeouts and stats
+./build/client --timeout 60 --contimeout 15 --stats /src user@host:/dst
+
+# Backup overwritten files to a directory
+./build/client --backup --backup-dir /backups /src user@host:/dst
+
+# Exclude patterns from file, limit depth
+./build/client --exclude-from ignore.txt --max-depth 3 /src user@host:/dst
+
+# Log to file
+./build/client --log-file /tmp/fastsync.log /src user@host:/dst
+
+# All features
+./build/client -a --progress --chunk-size 5242880 --exclude "*.log" --delete /src /dst
+```

 ## Testing

-Run the unit test binary:
-
 ```bash
+# Unit tests (18 suites — array_list, chunk, compression, config, data, delta, file, glob,
+#                      metadata, property, protocol, queue, robustness, scanner,
+#                      shared_utils, stress, transport_tcp, transport_ssh, transport_tls)
 ./build/tests
+
+# Integration + benchmark suite
+python3 test.py
 ```

-Run the Python integration suite:
+The benchmark prints throughput metrics, best configuration, and speedup vs rsync.

-```bash
-python3 -m pytest tests/
-```
+## Performance Considerations

-For stricter local validation:
+1. Chunk size (~10 MB default) balances memory and transfer efficiency
+2. Compression level trades CPU for bandwidth
+3. `sendfile()` bypasses userspace — ~2× faster on localhost for large files
+4. Multithreading scales with core count and uses memory-based pipeline sizing
+5. Metadata transfer adds negligible overhead (~24 bytes per file when enabled)
+6. SSH socketpair buffer set to 1 MB for improved pipe throughput
+7. SSH ControlMaster reuses connections across repeated invocations
+8. Incremental sync eliminates redundant transfers entirely
+9. Batch incremental reduces round-trips by grouping multiple checks into one message
+10. Bandwidth limiting uses token-bucket with nanosleep for accurate throttling
+11. Atomic writes add a single `rename()` per file — negligible overhead
+12. Path traversal check is O(n) in path length with negligible cost

-```bash
-cmake -B build-strict -S . -DSTRICT_WARNINGS=ON
-cmake --build build-strict -j$(nproc)
-cmake -B build-asan -S . -DSANITIZER=address
-cmake --build build-asan -j$(nproc)
-```
+## Benchmark Results

-The benchmark tool compares FastSync configurations with rsync under
-controlled local and network conditions:
+25 MB of mixed file sizes over `localhost` with disk I/O throttled (reads ≤ 15 MB/s, writes ≤ 10 MB/s) and network emulation via `tc netem`. Each test was run 3×; the median is reported below.

-```bash
-python3 benchmark/bench.py --help
-```
+### LAN (1000 Mbit, 20 ms ±1 ms, 0.1% loss)

-Benchmark results measure transfer performance only. They do not establish
-rsync protocol or filesystem-semantic compatibility.
+| Configuration | Time | vs rsync (archive) | vs rsync (compress) |
+|---|---|---|---|
+| **Best: `-m -c`** | **0.20 s** | **11.2× faster** | **3.6× faster** |
+| Compression (`-c`) | 0.31 s | 7.3× faster | 2.3× faster |
+| Standard | 1.27 s | 1.8× faster | — |
+| rsync (archive) | 2.27 s | — | — |
+| rsync (archive + compress) | 0.72 s | — | — |

-## Performance Guidance
+### WAN (100 Mbit, 50 ms ±10 ms, 1% loss)

- Use `-m` for workloads with many files or enough CPU parallelism.
- Use `-c` or `-z` when network bandwidth is more constrained than CPU.
- Tune `--chunk-size` for file sizes, memory limits, and network latency.
- Use `-f` for large uncompressed TCP transfers where zero-copy I/O helps.
- Use `--incremental` to avoid retransmitting unchanged files.
- Use `--delta` for changed files when both endpoints are FastSync peers.
- Use `--bwlimit` when sharing a link with other traffic.
+| Configuration | Time | vs rsync (archive) | vs rsync (compress) |
+|---|---|---|---|
+| **Best: `-m -c`** | **0.39 s** | **44.8× faster** | **3.8× faster** |
+| Compression (`-c`) | 0.64 s | 27.3× faster | 2.3× faster |
+| Standard | 7.12 s | 2.4× faster | — |
+| rsync (archive) | 17.44 s | — | — |
+| rsync (archive + compress) | 1.47 s | — | — |

-Always validate the compatibility behavior required by a deployment before
-replacing an existing rsync job.
+Compression reduces the data on the wire enough that the transfer becomes latency-bound rather than bandwidth-bound. On WAN, the best configuration runs 10.8× faster than the theoretical limit for uncompressed data, since zstd shrinks the 25 MB payload to a fraction of its original size over the wire.
@@ -1,12 +1,10 @@
 #include "client_send.h"
-#include "client_validation.h"
 #include "config.h"
 #include "delta.h"
 #include "log.h"
 #include "protocol.h"
 #include "transport_tcp.h"
 #include "transport_tls.h"
-#include "usage.h"
 #include "utils.h"
 #include <errno.h>
 #include <limits.h>
@@ -14,6 +12,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include "usage.c"

 #ifndef FASTSYNC_TEST_BUILD
 /* Parse environment variables for source/destination directories and save-to-disk flag. */
@@ -361,6 +360,55 @@ int parse_args(Config* config, int argc, char* argv[], int* positional_args,
  return 0;
 }

+#ifndef FASTSYNC_TEST_BUILD
+/* Validate config after parsing. Returns true if valid. */
+static bool validate_config(const Config* config) {
+  if (!config->send_directory || !config->receive_root_directory) {
+    fprintf(stderr, "Error: source and destination directories are required\n");
+    print_usage();
+    return false;
+  }
+  if (config->use_sendfile && (config->use_chunk_serialization || config->use_compression)) {
+    fprintf(stderr, "Error: -f/--sendfile cannot be combined with -c (compression) or -s (chunk "
+                    "serialization)\n");
+    return false;
+  }
+  if (config->transport == TRANSPORT_SSH && config->use_sendfile) {
+    fprintf(stderr, "Error: -f/--sendfile is not supported with SSH transport\n");
+    return false;
+  }
+  if (config->use_incremental && config->use_chunk_serialization) {
+    fprintf(stderr, "Error: --incremental is not supported with -s (chunk serialization)\n");
+    return false;
+  }
+  if (config->use_delta && !config->use_incremental) {
+    fprintf(stderr, "Error: --delta requires --incremental\n");
+    return false;
+  }
+  if (config->use_delta && config->use_chunk_serialization) {
+    fprintf(stderr, "Error: --delta cannot be combined with -s (chunk serialization)\n");
+    return false;
+  }
+  if (config->use_delta && config->use_sendfile) {
+    fprintf(stderr, "Error: --delta cannot be combined with -f (sendfile)\n");
+    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) {
+      fprintf(stderr, "Error: --tls requires --cert, --key, and --ca\n");
+      return false;
+    }
+  }
+  return true;
+}
+#endif /* FASTSYNC_TEST_BUILD */
+
 static int read_patterns_from_file(const char* filepath, char*** patterns, int* count) {
  FILE* fp = fopen(filepath, "r");
  if (!fp) {
@@ -28,87 +28,6 @@
 /* Forward declaration for progress-reporting thread used in multithreaded send. */
 static int progress_thread_fn(void* arg);

-static ScannerOptions scanner_options_from_config(const Config* config, int num_threads) {
-  ScannerOptions options = {
-      config->use_metadata,  config->chunk_size,        config->exclude_patterns,
-      config->exclude_count, config->include_patterns,  config->include_count,
-      config->max_size,      config->min_size,          config->max_depth,
-      num_threads,           config->follow_symlinks,   config->copy_links,
-      config->safe_links,    config->copy_unsafe_links, config->checksum};
-  return options;
-}
-
-/* Select the configured transport for both transfer execution paths. */
-static Client* connect_transfer_client(const Config* config) {
-  if (config->transport == TRANSPORT_SSH) {
-    if (config->use_sendfile) {
-      fprintf(stderr, "Error: -f/--sendfile is not supported with SSH transport\n");
-      return NULL;
-    }
-    return client_connect_ssh(config->ssh_destination, config->ssh_port,
-                              config->fastsync_server_path);
-  }
-
-  Client* client = client_create();
-  if (!client)
-    return NULL;
-  bool connected;
-  if (config->use_tls) {
-    connected = client_connect_tls(client, config->server_host, config->server_port,
-                                   config->tls_cert, config->tls_key, config->tls_ca);
-  } else {
-    connected = client_connect(client, config->server_host, config->server_port);
-  }
-  if (!connected) {
-    client_delete(client);
-    return NULL;
-  }
-  return client;
-}
-
-static void disconnect_transfer_client(Client* client) {
-  if (!client)
-    return;
-  client_disconnect(client);
-  client_delete(client);
-}
-
-static ArrayList* create_transfer_manifest(const Config* config) {
-  return config->use_delete ? array_list_create(free) : NULL;
-}
-
-static bool add_chunk_to_manifest(ArrayList* manifest, const Chunk* chunk) {
-  if (!manifest)
-    return true;
-  for (int i = 0; i < chunk->element_count; i++) {
-    const char* path = chunk->items[i]->path;
-    if (*path == '/')
-      path++;
-    char* entry = str_dup(path);
-    if (!entry) {
-      log_message(LOG_LEVEL_ERROR, "Failed to allocate manifest entry");
-      return false;
-    }
-    if (!array_list_add(manifest, entry)) {
-      free(entry);
-      return false;
-    }
-  }
-  return true;
-}
-
-static bool finalize_transfer(Client* client) {
-  Status status;
-  return send_status(client->file_descriptor, STATUS_FINISHED) &&
-         receive_status(client->file_descriptor, &status) && status == STATUS_OK;
-}
-
-static void mark_sender_done(PipelineContextSender* context) {
-  mtx_lock(&context->mutex_progress);
-  context->sender_done = true;
-  mtx_unlock(&context->mutex_progress);
-}
-
 static void pipeline_cancel(PipelineContextSender* context) {
  mtx_lock(&context->mutex_scanner);
  mtx_lock(&context->mutex_loader);
@@ -124,10 +43,12 @@ static void pipeline_cancel(PipelineContextSender* context) {
 }

 /* Print dry-run manifest showing files that would be transferred. Returns 0 on success. */
-static int send_dry_run_manifest(const Config* config) {
-  ScannerOptions options = scanner_options_from_config(config, 0);
-  DirectoryScanner* scanner =
-      directory_scanner_create_with_options(config->send_directory, &options);
+static int send_dry_run_manifest(Config* config) {
+  DirectoryScanner* scanner = directory_scanner_create(
+      config->send_directory, config->use_metadata, config->chunk_size, config->exclude_patterns,
+      config->exclude_count, config->include_patterns, config->include_count, config->max_size,
+      config->min_size, config->max_depth, config->follow_symlinks, config->copy_links,
+      config->safe_links, config->copy_unsafe_links, config->checksum);
  if (!scanner)
    return -1;
  Chunk* chunk;
@@ -370,22 +291,49 @@ int send_chunk(Client* client, Chunk* chunk, Config* config) {

 static int send_chunks_multithreaded(void* pipeline_context) {
  PipelineContextSender* context = (PipelineContextSender*)pipeline_context;
-  Client* client = connect_transfer_client(context->config);
-  if (!client) {
-    if (context->config->transport == TRANSPORT_TCP)
-      fprintf(stderr, "Error: could not connect to server%s\n",
-              context->config->use_tls ? " via TLS" : "");
-    mark_sender_done(context);
+  Client* client;
+  if (context->config->transport == TRANSPORT_SSH) {
+    if (context->config->use_sendfile) {
+      fprintf(stderr, "Error: -f/--sendfile is not supported with SSH transport\n");
+      mtx_lock(&context->mutex_progress);
+      context->sender_done = true;
+      mtx_unlock(&context->mutex_progress);
+      return 1;
+    }
+    client = client_connect_ssh(context->config->ssh_destination, context->config->ssh_port,
+                                context->config->fastsync_server_path);
+  } else if (context->config->use_tls) {
+    client = client_create();
+    if (!client || !client_connect_tls(client, context->config->server_host,
+                                       context->config->server_port, context->config->tls_cert,
+                                       context->config->tls_key, context->config->tls_ca)) {
+      if (client)
+        client_delete(client);
+      fprintf(stderr, "Error: could not connect to server via TLS\n");
+      mtx_lock(&context->mutex_progress);
+      context->sender_done = true;
+      mtx_unlock(&context->mutex_progress);
      return thrd_error;
    }
-  ProtocolSession session;
-  protocol_session_init(&session, client->file_descriptor, client->file_descriptor);
-  protocol_session_set_ssl(&session, (SSL*)client->ssl);
-  protocol_session_bind(&session);
+  } else {
+    client = client_create();
+    if (!client ||
+        !client_connect(client, context->config->server_host, context->config->server_port)) {
+      if (client)
+        client_delete(client);
+      fprintf(stderr, "Error: could not connect to server\n");
+      mtx_lock(&context->mutex_progress);
+      context->sender_done = true;
+      mtx_unlock(&context->mutex_progress);
+      return thrd_error;
+    }
+  }
  if (!config_send(client->file_descriptor, context->config)) {
-    disconnect_transfer_client(client);
-    mark_sender_done(context);
-    protocol_session_unbind();
+    client_disconnect(client);
+    client_delete(client);
+    mtx_lock(&context->mutex_progress);
+    context->sender_done = true;
+    mtx_unlock(&context->mutex_progress);
    return thrd_error;
  }

@@ -398,26 +346,35 @@ static int send_chunks_multithreaded(void* pipeline_context) {
        if (send_delete_manifest(client->file_descriptor, context->manifest) != 0)
          goto send_fail;
      }
-      bool ok = finalize_transfer(client);
-      disconnect_transfer_client(client);
-      mark_sender_done(context);
-      protocol_session_unbind();
+      if (!send_status(client->file_descriptor, STATUS_FINISHED))
+        goto send_fail;
+      Status s;
+      int ok = receive_status(client->file_descriptor, &s) && s == STATUS_OK;
+      client_disconnect(client);
+      client_delete(client);
+      mtx_lock(&context->mutex_progress);
+      context->sender_done = true;
+      mtx_unlock(&context->mutex_progress);
      return ok ? thrd_success : thrd_error;

    send_fail:
      pipeline_cancel(context);
-      disconnect_transfer_client(client);
-      mark_sender_done(context);
-      protocol_session_unbind();
+      client_disconnect(client);
+      client_delete(client);
+      mtx_lock(&context->mutex_progress);
+      context->sender_done = true;
+      mtx_unlock(&context->mutex_progress);
      return thrd_error;
    }
    if (send_chunk(client, current_chunk, context->config) != 0) {
      fprintf(stderr, "Error: unexpected error while sending chunk\n");
      chunk_destroy(current_chunk);
      pipeline_cancel(context);
-      disconnect_transfer_client(client);
-      mark_sender_done(context);
-      protocol_session_unbind();
+      client_disconnect(client);
+      client_delete(client);
+      mtx_lock(&context->mutex_progress);
+      context->sender_done = true;
+      mtx_unlock(&context->mutex_progress);
      return thrd_error;
    }
    if (context->config->show_progress) {
@@ -436,9 +393,13 @@ static int send_chunks_multithreaded(void* pipeline_context) {

 static int scan_directory_multithreaded(void* pipeline_context) {
  PipelineContextSender* context = (PipelineContextSender*)pipeline_context;
-  ScannerOptions options = scanner_options_from_config(context->config, 4);
-  ParallelScanner* scanner =
-      parallel_scanner_create_with_options(context->config->send_directory, &options);
+  ParallelScanner* scanner = parallel_scanner_create(
+      context->config->send_directory, context->config->use_metadata, context->config->chunk_size,
+      context->config->exclude_patterns, context->config->exclude_count,
+      context->config->include_patterns, context->config->include_count, context->config->max_size,
+      context->config->min_size, context->config->max_depth, 4, context->config->follow_symlinks,
+      context->config->copy_links, context->config->safe_links, context->config->copy_unsafe_links,
+      context->config->checksum);

  Chunk* current_chunk;
  if (scanner == NULL) {
@@ -449,15 +410,29 @@ static int scan_directory_multithreaded(void* pipeline_context) {
  while ((current_chunk = parallel_scanner_next(scanner)) != NULL) {
    if (context->config->use_delete) {
      mtx_lock(&context->mutex_scanner);
-      bool manifest_ok = add_chunk_to_manifest(context->manifest, current_chunk);
+      for (int i = 0; i < current_chunk->element_count; i++) {
+        const char* p = current_chunk->items[i]->path;
+        if (*p == '/')
+          p++;
+        char* manifest_entry = str_dup(p);
+        if (!manifest_entry) {
+          log_message(LOG_LEVEL_ERROR, "Failed to allocate manifest entry");
+          mtx_unlock(&context->mutex_scanner);
+          pipeline_cancel(context);
+          parallel_scanner_destroy(scanner);
+          return thrd_error;
+        }
+        if (!array_list_add(context->manifest, manifest_entry)) {
+          free(manifest_entry);
          mtx_unlock(&context->mutex_scanner);
-      if (!manifest_ok) {
          pipeline_cancel(context);
          chunk_destroy(current_chunk);
          parallel_scanner_destroy(scanner);
          return thrd_error;
        }
      }
+      mtx_unlock(&context->mutex_scanner);
+    }
    if (!queue_enqueue_multithreaded_cancel(
            context->queue_scanner, current_chunk, &context->mutex_scanner,
            &context->condition_not_empty_scanner, &context->condition_not_full_scanner,
@@ -565,37 +540,61 @@ int send_files(Config* config) {
  if (config->dry_run)
    return send_dry_run_manifest(config);

-  Client* client = connect_transfer_client(config);
-  if (!client) {
-    if (config->transport == TRANSPORT_TCP)
-      fprintf(stderr, "Error: could not connect to server%s\n", config->use_tls ? " via TLS" : "");
+  Client* client;
+  if (config->transport == TRANSPORT_SSH) {
+    if (config->use_sendfile) {
+      fprintf(stderr, "Error: -f/--sendfile is not supported with SSH transport\n");
      return 1;
    }
-  ProtocolSession session;
-  protocol_session_init(&session, client->file_descriptor, client->file_descriptor);
-  protocol_session_set_ssl(&session, (SSL*)client->ssl);
-  protocol_session_bind(&session);
+    client =
+        client_connect_ssh(config->ssh_destination, config->ssh_port, config->fastsync_server_path);
+    if (!client)
+      return 1;
+  } else if (config->use_tls) {
+    client = client_create();
+    if (!client || !client_connect_tls(client, config->server_host, config->server_port,
+                                       config->tls_cert, config->tls_key, config->tls_ca)) {
+      if (client) {
+        client_disconnect(client);
+        client_delete(client);
+      }
+      fprintf(stderr, "Error: could not connect to server via TLS\n");
+      return 1;
+    }
+  } else {
+    client = client_create();
+    if (!client || !client_connect(client, config->server_host, config->server_port)) {
+      if (client) {
+        client_disconnect(client);
+        client_delete(client);
+      }
+      fprintf(stderr, "Error: could not connect to server\n");
+      return 1;
+    }
+  }
  if (!config_send(client->file_descriptor, config)) {
-    disconnect_transfer_client(client);
-    protocol_session_unbind();
+    client_disconnect(client);
+    client_delete(client);
    return 1;
  }
-  ScannerOptions scanner_options = scanner_options_from_config(config, 0);
-  DirectoryScanner* scanner =
-      directory_scanner_create_with_options(config->send_directory, &scanner_options);
+  DirectoryScanner* scanner = directory_scanner_create(
+      config->send_directory, config->use_metadata, config->chunk_size, config->exclude_patterns,
+      config->exclude_count, config->include_patterns, config->include_count, config->max_size,
+      config->min_size, config->max_depth, config->follow_symlinks, config->copy_links,
+      config->safe_links, config->copy_unsafe_links, config->checksum);
  Chunk* current_chunk;
  unsigned long long total_bytes = 0;
  int total_files = 0;
  time_t last_progress = 0;
  time_t start = time(NULL);
-  ArrayList* manifest = create_transfer_manifest(config);
+  ArrayList* manifest = config->use_delete ? array_list_create(free) : NULL;
  if (!scanner || (config->use_delete && !manifest)) {
    if (scanner)
      directory_scanner_destroy(scanner);
    if (manifest)
      array_list_delete(manifest);
-    disconnect_transfer_client(client);
-    protocol_session_unbind();
+    client_disconnect(client);
+    client_delete(client);
    return 1;
  }
  while ((current_chunk = directory_scanner_next(scanner)) != NULL) {
@@ -603,10 +602,30 @@ int send_files(Config* config) {
    for (int i = 0; i < current_chunk->element_count; i++) {
      chunk_bytes += current_chunk->items[i]->data->size;
      total_files++;
-    }
-    if (!add_chunk_to_manifest(manifest, current_chunk)) {
+      if (manifest) {
+        const char* p = current_chunk->items[i]->path;
+        if (*p == '/')
+          p++;
+        char* manifest_entry = str_dup(p);
+        if (!manifest_entry) {
+          log_message(LOG_LEVEL_ERROR, "Failed to allocate manifest entry");
          chunk_destroy(current_chunk);
-      goto send_fail;
+          array_list_delete(manifest);
+          directory_scanner_destroy(scanner);
+          client_disconnect(client);
+          client_delete(client);
+          return 1;
+        }
+        if (!array_list_add(manifest, manifest_entry)) {
+          free(manifest_entry);
+          chunk_destroy(current_chunk);
+          array_list_delete(manifest);
+          directory_scanner_destroy(scanner);
+          client_disconnect(client);
+          client_delete(client);
+          return 1;
+        }
+      }
    }
    if (!config->use_sendfile) {
      for (int i = 0; i < current_chunk->element_count; i++) {
@@ -650,7 +669,10 @@ int send_files(Config* config) {
    array_list_delete(manifest);
    manifest = NULL;
  }
-  bool ok = finalize_transfer(client);
+  if (!send_status(client->file_descriptor, STATUS_FINISHED))
+    goto send_fail;
+  Status s;
+  int ok = receive_status(client->file_descriptor, &s) && s == STATUS_OK;
  double elapsed_total = difftime(time(NULL), start);
  if (config->show_progress) {
    double rate = elapsed_total > 0 ? total_bytes / (1048576.0 * elapsed_total) : 0;
@@ -662,16 +684,16 @@ int send_files(Config* config) {
            rate);
  }
  directory_scanner_destroy(scanner);
-  disconnect_transfer_client(client);
-  protocol_session_unbind();
+  client_disconnect(client);
+  client_delete(client);
  return ok ? 0 : 1;

 send_fail:
  if (manifest)
    array_list_delete(manifest);
  directory_scanner_destroy(scanner);
-  disconnect_transfer_client(client);
-  protocol_session_unbind();
+  client_disconnect(client);
+  client_delete(client);
  return 1;
 }

@@ -707,7 +729,7 @@ int send_files_multithreaded(Config* config) {
    return 1;
  }
  if (config->use_delete)
-    context->manifest = create_transfer_manifest(config);
+    context->manifest = array_list_create(free);

  thrd_t scanner, loader, sender;
  bool scanner_created = false;
@@ -1,50 +0,0 @@
-#include "client_validation.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) {
-    fprintf(stderr, "Error: source and destination directories are required\n");
-    print_usage();
-    return false;
-  }
-  if (config->use_sendfile && (config->use_chunk_serialization || config->use_compression)) {
-    fprintf(stderr, "Error: -f/--sendfile cannot be combined with -c (compression) or -s (chunk "
-                    "serialization)\n");
-    return false;
-  }
-  if (config->transport == TRANSPORT_SSH && config->use_sendfile) {
-    fprintf(stderr, "Error: -f/--sendfile is not supported with SSH transport\n");
-    return false;
-  }
-  if (config->use_incremental && config->use_chunk_serialization) {
-    fprintf(stderr, "Error: --incremental is not supported with -s (chunk serialization)\n");
-    return false;
-  }
-  if (config->use_delta && !config->use_incremental) {
-    fprintf(stderr, "Error: --delta requires --incremental\n");
-    return false;
-  }
-  if (config->use_delta && config->use_chunk_serialization) {
-    fprintf(stderr, "Error: --delta cannot be combined with -s (chunk serialization)\n");
-    return false;
-  }
-  if (config->use_delta && config->use_sendfile) {
-    fprintf(stderr, "Error: --delta cannot be combined with -f (sendfile)\n");
-    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) {
-      fprintf(stderr, "Error: --tls requires --cert and --key\n");
-      return false;
-    }
-  }
-  return true;
-}
@@ -1,9 +0,0 @@
-#ifndef CLIENT_VALIDATION_H
-#define CLIENT_VALIDATION_H
-
-#include "config.h"
-#include <stdbool.h>
-
-bool validate_config(const Config* config);
-
-#endif
@@ -52,84 +52,13 @@ static bool safe_relative_link(const char* source_root, const char* containing_d
  return safe;
 }

-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* 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) {
  DirectoryScanner* scanner = calloc(1, sizeof(DirectoryScanner));
  if (scanner == NULL)
    return NULL;
@@ -140,21 +69,21 @@ DirectoryScanner* directory_scanner_create_with_options(const char* root_directo
  }
  scanner->current_dir = NULL;
  scanner->current_path = NULL;
-  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->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->current_depth = 0;
-  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->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->failed = false;
  DirEntry* root = dir_entry_create(root_directory, 0);
  if (!root) {
@@ -171,20 +100,6 @@ DirectoryScanner* directory_scanner_create_with_options(const char* root_directo
  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;
@@ -252,7 +167,7 @@ Chunk* directory_scanner_next(DirectoryScanner* scanner) {
        break;
    }

-    const struct dirent* entry = readdir(scanner->current_dir);
+    struct dirent* entry = readdir(scanner->current_dir);
    if (entry == NULL) {
      closedir(scanner->current_dir);
      scanner->current_dir = NULL;
@@ -264,27 +179,67 @@ Chunk* directory_scanner_next(DirectoryScanner* scanner) {
    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
      continue;

-    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) {
+    char* cur_path = path_cat(scanner->current_path, entry->d_name);
+    if (!cur_path) {
      scanner->failed = true;
      break;
    }
-    if (inspection == 0)
+    struct stat stats;
+    struct stat lstats;
+    bool is_symlink = false;
+    if (lstat(cur_path, &lstats) != 0) {
+      free(cur_path);
      continue;
-    char* cur_path = inspected.path;
-    struct stat stats = inspected.stats;
+    }
+    is_symlink = S_ISLNK(lstats.st_mode);

-    if (inspected.is_directory) {
+    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)) {
      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);
@@ -299,6 +254,38 @@ 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);
@@ -349,13 +336,29 @@ typedef struct {
  ParallelScanner* ps;
  char** dirs;
  int dir_count;
-  ScannerOptions options;
+  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;
 } ParallelWorkerArg;

 static int parallel_worker_thread(void* arg) {
  ParallelWorkerArg* wa = (ParallelWorkerArg*)arg;
  for (int i = 0; i < wa->dir_count; i++) {
-    DirectoryScanner* ds = directory_scanner_create_with_options(wa->dirs[i], &wa->options);
+    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);
    if (!ds) {
      mtx_lock(&wa->ps->result_mutex);
      wa->ps->failed = true;
@@ -398,10 +401,13 @@ static int parallel_worker_thread(void* arg) {
  return thrd_success;
 }

-ParallelScanner* parallel_scanner_create_with_options(const char* root_directory,
-                                                      const ScannerOptions* options) {
-  if (!root_directory || !options)
-    return NULL;
+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;
@@ -454,27 +460,105 @@ ParallelScanner* parallel_scanner_create_with_options(const char* root_directory
    parallel_scanner_destroy(ps);
    return NULL;
  }
-  const struct dirent* entry;
+  struct dirent* entry;
  while ((entry = readdir(dir)) != NULL) {
    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
      continue;
-    ScannerEntry inspected;
-    int inspection =
-        scanner_inspect_entry(options, root_directory, root_directory, entry->d_name, &inspected);
-    if (inspection < 0) {
-      ps->failed = true;
+    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;
    }
-    if (inspection == 0)
+    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;
-    char* cur_path = inspected.path;
-    struct stat st = inspected.stats;
-    if (inspected.is_directory) {
+    }
+
+    // --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) {
@@ -482,9 +566,9 @@ ParallelScanner* parallel_scanner_create_with_options(const char* root_directory
        continue;
      }
      file->data->size = st.st_size;
-      if (options->use_metadata)
+      if (use_metadata)
        file->metadata = file_metadata_create(&st);
-      if (options->use_metadata && !file->metadata) {
+      if (use_metadata && !file->metadata) {
        file_destroy(file);
        ps->failed = true;
        continue;
@@ -497,7 +581,7 @@ ParallelScanner* parallel_scanner_create_with_options(const char* root_directory
  }
  closedir(dir);

-  unsigned long long cs = options->chunk_size > 0 ? options->chunk_size : DESIRED_CHUNK_SIZE;
+  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) {
@@ -564,7 +648,7 @@ ParallelScanner* parallel_scanner_create_with_options(const char* root_directory
  }
  array_list_delete(root_files);

-  int n = options->num_threads > 0 ? options->num_threads : 4;
+  int n = num_threads > 0 ? num_threads : 4;
  if (n > subdirs->size)
    n = subdirs->size > 0 ? subdirs->size : 1;

@@ -612,8 +696,20 @@ ParallelScanner* parallel_scanner_create_with_options(const char* root_directory
        break;
      }
      wa->dir_count = count;
-      wa->options = *options;
-      wa->options.chunk_size = cs;
+      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++)
@@ -637,20 +733,6 @@ ParallelScanner* parallel_scanner_create_with_options(const char* root_directory
  return ps;
 }

-ParallelScanner* parallel_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,
-                                         int num_threads, 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,        num_threads,       follow_symlinks,  copy_links,
-                            safe_links,       copy_unsafe_links, checksum};
-  return parallel_scanner_create_with_options(root_directory, &options);
-}
-
 Chunk* parallel_scanner_next(ParallelScanner* ps) {
  if (ps->initial_chunk) {
    Chunk* c = ps->initial_chunk;
@@ -8,24 +8,6 @@
 #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;
@@ -71,21 +53,17 @@ 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(const char* root_directory, bool use_metadata,
+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);
 Chunk* parallel_scanner_next(ParallelScanner* scanner);
 bool parallel_scanner_failed(const ParallelScanner* scanner);
 void parallel_scanner_destroy(ParallelScanner* scanner);
@@ -1,9 +1,8 @@
-#include "usage.h"
-#include <stdio.h>
+#include "stdio.h"
 #include <delta.h>
 #include <chunk.h>

-void print_usage(void) {
+static __attribute__((unused)) void print_usage() {
  printf("Usage:\n");
  printf("  fastsync [options] <source> <destination>\n");
  printf("  fastsync [options] --source-dir <src> --dest-dir <dst>\n");
@@ -1,6 +0,0 @@
-#ifndef USAGE_H
-#define USAGE_H
-
-void print_usage(void);
-
-#endif
@@ -1,126 +0,0 @@
-#include "receiver.h"
-
-#include "chunk.h"
-#include "log.h"
-#include "protocol.h"
-#include "utils.h"
-#include <stdlib.h>
-#include <sys/stat.h>
-
-static bool receiver_process_chunk(Chunk* chunk, const ReceiverSink* sink) {
-  for (int i = 0; i < chunk->element_count; i++) {
-    File* file = chunk->items[i];
-    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;
-    if (!receive_n_data(file_descriptor, &check_size, sizeof(check_size)) ||
-        !receive_n_data(file_descriptor, &check_mtime, sizeof(check_mtime))) {
-      free(check_path);
-      return false;
-    }
-    if (!utils_valid_batch_path(check_path)) {
-      free(check_path);
-      send_status(file_descriptor, STATUS_ERROR);
-      return false;
-    }
-    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;
-    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);
-}
@@ -1,19 +0,0 @@
-#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
@@ -1,30 +1,57 @@
+#include "array_list.h"
+#include "chunk.h"
 #include "config.h"
+#include "data.h"
 #include "file.h"
 #include "log.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));
+  bool allowed = length >= 0 && (size_t)length < sizeof(common_name) &&
+                 strcmp(common_name, required_client_cn) == 0;
+  X509_free(certificate);
+  return allowed;
+}

 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))
@@ -39,28 +66,147 @@ static bool __attribute__((unused)) configure_authorization(const char* root) {
    return false;
  }
  file_set_authorized_root(authorized_root_fd, authorized_root);
-  utils_set_authorized_root_fd(authorized_root_fd);
+  utils_set_authorized_root(authorized_root_fd, authorized_root);
  return true;
 }

+int receive_files(Config* config, int fd) {
+  Status status;
+  if (!receive_status(fd, &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) {
+      send_status(fd, STATUS_KEEPALIVE);
+      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(fd, config, &skipped);
+      if (skipped)
+        goto next;
+      if (file == NULL && !skipped)
+        return -1;
+      if (config->save_to_disk &&
+          !file_save_to_disk(config->receive_root_directory, file, config)) {
+        file_destroy(file);
+        send_status(fd, STATUS_ERROR);
+        return -1;
+      }
+      file_destroy(file);
+    } else if (status == STATUS_CHUNK) {
+      Chunk* chunk = receive_chunk_data(fd, config);
+      if (chunk == NULL) {
+        send_status(fd, STATUS_ERROR);
+        return -1;
+      }
+      for (int i = 0; i < chunk->element_count; i++) {
+        if (config->save_to_disk &&
+            !file_save_to_disk(config->receive_root_directory, chunk->items[i], config)) {
+          chunk_destroy(chunk);
+          send_status(fd, STATUS_ERROR);
+          return -1;
+        }
+      }
+      chunk_destroy(chunk);
+    } else if (status == STATUS_CHECK_BATCH) {
+      int count;
+      /* Batch framing has no checksum field yet; never silently downgrade a
+         checksum-enabled transfer into mtime-only matching. */
+      if (config->checksum || !receive_int(fd, &count) || count < 0 || count > MAX_MANIFEST_ENTRIES)
+        return -1;
+      for (int i = 0; i < count; i++) {
+        char* check_path = receive_str(fd);
+        if (!check_path)
+          return -1;
+        unsigned long long check_size;
+        long long check_mtime;
+        if (!receive_n_data(fd, &check_size, sizeof(check_size)) ||
+            !receive_n_data(fd, &check_mtime, sizeof(check_mtime))) {
+          free(check_path);
+          return -1;
+        }
+        if (!valid_batch_path(check_path)) {
+          free(check_path);
+          send_status(fd, STATUS_ERROR);
+          return -1;
+        }
+        struct stat st;
+        char* full_path = path_cat(config->receive_root_directory, check_path);
+        bool has_old = full_path && file_stat_secure(full_path, &st);
+        bool match = has_old && (unsigned long long)st.st_size == check_size &&
+                     (long long)st.st_mtime == check_mtime;
+        bool sent = send_status(fd, match ? STATUS_OK : STATUS_NEXT);
+        free(full_path);
+        free(check_path);
+        if (!sent)
+          return -1;
+      }
+      goto next;
+    } else {
+      File* file = file_receive(config, fd);
+      if (file == NULL) {
+        log_message(LOG_LEVEL_ERROR, "Failed to receive file");
+        send_status(fd, STATUS_ERROR);
+        return -1;
+      }
+      if (config->save_to_disk &&
+          !file_save_to_disk(config->receive_root_directory, file, config)) {
+        file_destroy(file);
+        send_status(fd, STATUS_ERROR);
+        return -1;
+      }
+      file_destroy(file);
+    }
+  next:
+    if (!receive_status(fd, &status)) {
+      send_status(fd, STATUS_ERROR);
+      return -1;
+    }
+  }
+
+  if (status == STATUS_MANIFEST) {
+    if (receive_manifest(fd, config, &status) != 0)
+      return -1;
+  }
+  if (status != STATUS_FINISHED) {
+    log_message(LOG_LEVEL_ERROR, "Did not receive FINISHED Status");
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
+  send_status(fd, STATUS_OK);
+  return 0;
+}
+
 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;
  }
  if (!authorized_root) {
    log_message(LOG_LEVEL_ERROR, "No server-side destination root configured");
    config_delete(config);
    close(file_descriptor);
-    protocol_session_unbind();
+    return;
+  }
+  if (!allow_unauthenticated && ssl == NULL) {
+    log_message(LOG_LEVEL_ERROR, "Rejected unauthenticated plaintext connection");
+    config_delete(config);
+    close(file_descriptor);
+    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;
  }
  char resolved_destination[PATH_MAX];
@@ -72,7 +218,6 @@ void handler(int file_descriptor) {
    free(canonical_destination);
    config_delete(config);
    close(file_descriptor);
-    protocol_session_unbind();
    return;
  }
  if (canonical_destination)
@@ -85,7 +230,6 @@ void handler(int file_descriptor) {
  if (!config->receive_root_directory) {
    config_delete(config);
    close(file_descriptor);
-    protocol_session_unbind();
    return;
  }
  config->use_delete = config->use_delete && allow_delete;
@@ -94,7 +238,6 @@ void handler(int file_descriptor) {
    if (q == NULL) {
      config_delete(config);
      close(file_descriptor);
-      protocol_session_unbind();
      return;
    }
    PipelineContextReceiver* context =
@@ -103,14 +246,14 @@ void handler(int file_descriptor) {
      queue_destroy(q);
      config_delete(config);
      close(file_descriptor);
-      protocol_session_unbind();
      return;
    }
    thrd_t receiver, writer;
-    bool receiver_created = thrd_create(&receiver, receive_thread, context) == thrd_success;
+    bool receiver_created = false;
    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");
      if (receiver_created) {
@@ -127,23 +270,22 @@ 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);
-    send_status(file_descriptor, receiver_result == thrd_success && writer_result == thrd_success
-                                     ? STATUS_OK
-                                     : STATUS_ERROR);
+    if (receiver_result == thrd_success && writer_result == thrd_success)
+      send_status(file_descriptor, STATUS_OK);
+    else
+      send_status(file_descriptor, STATUS_ERROR);
    pipeline_context_receiver_destroy(context);
  } else {
-    if (receiver_receive_files(config, file_descriptor) != 0)
+    if (receive_files(config, file_descriptor) != 0)
      log_message(LOG_LEVEL_ERROR, "Transfer failed");
    config_delete(config);
  }
-  protocol_session_unbind();
  close(file_descriptor);
 }

@@ -152,14 +294,16 @@ 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\n");
+  printf("Usage: fastsync-server [options]\n");
+  printf("\n");
  printf("Options:\n");
  printf("  --stdio             Run in stdio mode (SSH transport)\n");
  printf("  -p <port>           TCP port (default: 8080, range: 1-65535)\n");
@@ -167,15 +311,19 @@ 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, *tls_key = NULL, *tls_ca = NULL;
+  char* tls_cert = NULL;
+  char* tls_key = NULL;
+  char* tls_ca = NULL;
  int port = 8080;
  const char* destination_root = ".";
  bool stdio_mode = false;
@@ -197,10 +345,14 @@ 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);
@@ -215,8 +367,11 @@ int main(int argc, char* argv[]) {
      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)) {
@@ -224,22 +379,24 @@ int main(int argc, char* argv[]) {
    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);
+    utils_set_authorized_root(-1, NULL);
    close(authorized_root_fd);
    free(authorized_root);
    return 0;
  }
  g_server = server_create(port);
-  if (!g_server) {
+  if (g_server == NULL) {
    log_message(LOG_LEVEL_ERROR, "Failed to create server");
    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);
      return 1;
    }
@@ -255,4 +412,4 @@ int main(int argc, char* argv[]) {
  }
  return 0;
 }
-#endif
+#endif /* !FASTSYNC_SERVER_AS_LIB */
@@ -1,4 +1,6 @@
 #include <stddef.h>
+#include <stdint.h>
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -14,19 +16,30 @@

 /* 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) {
+  if (element_count < 0 || (element_count > 0 && items == NULL))
+    return NULL;
  Chunk* chunk = (Chunk*)malloc(sizeof(Chunk));
  if (chunk == NULL) {
    perror("ERROR: Could not allocate memory for chunk structure");
    return NULL;
  }

-  chunk->items = (File**)malloc(element_count * sizeof(File*));
+  if (element_count == 0) {
+    chunk->items = NULL;
+  } else {
+    if ((size_t)element_count > SIZE_MAX / sizeof(File*)) {
+      free(chunk);
+      return NULL;
+    }
+    chunk->items = (File**)malloc((size_t)element_count * sizeof(File*));
    if (chunk->items == NULL) {
      free(chunk);
      return NULL;
    }
+  }

  for (int i = 0; i < element_count; i++) {
    chunk->items[i] = items[i];
@@ -50,15 +63,31 @@ 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) {
  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);
+    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) {
@@ -88,10 +117,17 @@ Data* chunk_serialize(Chunk* chunk, bool use_metadata) {

 Chunk* chunk_deserialize(Data* data, bool use_metadata) {
  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);
@@ -109,6 +145,10 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
      return NULL;
    }

+    if (path_len == SIZE_MAX) {
+      array_list_delete(files);
+      return NULL;
+    }
    char* path = malloc(path_len + 1);
    if (path == NULL) {
      perror("Could not allocate memory for file path");
@@ -117,34 +157,53 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
    }
    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;

    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 +215,7 @@ 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 +224,47 @@ 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 = malloc(allocation_size);
    if (file_data == NULL) {
      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)
    files->item_destroyer = NULL;
  array_list_delete(files);

@@ -100,6 +100,35 @@ static void config_set_defaults(Config* config) {
  config->compress_choice = NULL;
 }

+static bool valid_wire_bool(int value) {
+  return value == 0 || value == 1;
+}
+
+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_sendfile) && valid_wire_bool(config->use_delete) &&
+         valid_wire_bool(config->use_incremental) && 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->update) &&
+         valid_wire_bool(config->inplace) && valid_wire_bool(config->append) &&
+         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) &&
+         (!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->max_delete >= 0;
+}
+
 Config* config_create(void) {
  Config* config = malloc(sizeof(Config));
  if (!config)
@@ -173,157 +202,102 @@ void config_delete(Config* config) {
  free(config);
 }

-/* 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) {
-  return send_str(fd, c->version) && 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->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->use_delta) &&
-         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->update) && send_int(fd, c->inplace) && send_int(fd, c->append) &&
-         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_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_str(fd, c->compress_choice ? c->compress_choice : "");
-}
-
-static bool receive_core_fields(int fd, Config* c) {
-  int value;
-  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_int(fd, &value))
-    return false;
-  c->save_to_disk = value;
-  if (!receive_int(fd, &value))
-    return false;
-  c->use_multithreading = value;
-  if (!receive_int(fd, &value))
-    return false;
-  c->use_chunk_serialization = value;
-  if (!receive_int(fd, &value))
-    return false;
-  c->use_compression = value;
-  if (!receive_int(fd, &value))
-    return false;
-  c->use_metadata = value;
-  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_int(fd, &value))
-    return false;
-  c->use_sendfile = value;
-  return true;
-}
-
-static bool receive_delta_fields(int fd, Config* c) {
-  int value;
-  if (!receive_int(fd, &value))
-    return false;
-  c->use_delete = value;
-  if (!receive_int(fd, &value))
-    return false;
-  c->use_incremental = value;
-  if (!receive_int(fd, &value))
-    return false;
-  c->use_delta = value;
-  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) {
-  int value;
-  if (!receive_int(fd, &value))
-    return false;
-  c->backup = value;
-  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_int(fd, &value))
-      return false;
-    *flags[i] = value;
-  }
-  return true;
-}
-
-static bool receive_selection_options(int fd, Config* c) {
-  int value;
-  bool* flags[] = {&c->update,        &c->inplace,         &c->append,
-                   &c->append_verify, &c->delete_excluded, &c->delete_after};
-  for (size_t i = 0; i < sizeof(flags) / sizeof(flags[0]); i++) {
-    if (!receive_int(fd, &value))
-      return false;
-    *flags[i] = value;
-  }
-  if (!receive_n_data(fd, &c->max_delete, sizeof(c->max_delete)))
-    return false;
-  if (!receive_int(fd, &value))
-    return false;
-  c->relative = value;
-  if (!receive_int(fd, &value))
-    return false;
-  c->prune_empty_dirs = value;
-  return true;
-}
-
-static bool receive_resume_options(int fd, Config* c) {
-  int value;
-  c->temp_dir = receive_str(fd);
-  if (!c->temp_dir || !receive_int(fd, &value))
-    return false;
-  c->partial = value;
-  c->partial_dir = receive_str(fd);
-  c->suffix = c->partial_dir ? receive_str(fd) : NULL;
-  if (!c->partial_dir || !c->suffix || !receive_int(fd, &value))
-    return false;
-  c->delete_before = value;
-  if (!receive_int(fd, &value))
-    return false;
-  c->checksum = value;
-  c->compress_choice = receive_str(fd);
-  return c->compress_choice != NULL;
-}
-
+/* 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
+ */
 bool config_send(int file_descriptor, const Config* config) {
-  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))
+  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 : ""))
    return false;
  Status status;
  if (!receive_status(file_descriptor, &status))
@@ -335,25 +309,175 @@ 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_create();
-  if (!config)
+  Config* config = (Config*)malloc(sizeof(Config));
+  if (config == NULL)
    return NULL;
+  config_set_defaults(config);
  free(config->version);
  config->version = receive_str(file_descriptor);
-  if (!config->version)
-    goto error;
+  if (!config->version) {
+    free(config->server_host);
+    free(config);
+    return NULL;
+  }
  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);
    send_status(file_descriptor, STATUS_ERROR);
-    goto error;
+    return 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))
+  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;
+  if (!valid_wire_bool(tmp))
+    goto error;
+  config->save_to_disk = tmp;
+  if (!receive_int(file_descriptor, &tmp))
+    goto error;
+  if (!valid_wire_bool(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;
+  if (!valid_wire_bool(tmp))
+    goto error;
+  config->use_compression = tmp;
+  if (!receive_int(file_descriptor, &tmp))
+    goto error;
+  if (!valid_wire_bool(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;
+  if (!valid_wire_bool(tmp))
+    goto error;
+  config->use_sendfile = tmp;
+  if (!receive_int(file_descriptor, &tmp))
+    goto error;
+  if (!valid_wire_bool(tmp))
+    goto error;
+  config->use_delete = tmp;
+  if (!receive_int(file_descriptor, &tmp))
+    goto error;
+  if (!valid_wire_bool(tmp))
+    goto error;
+  config->use_incremental = tmp;
+  if (!receive_int(file_descriptor, &tmp))
+    goto error;
+  if (!valid_wire_bool(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)
    goto error;
  if (config->compress_choice[0] != '\0' && strcmp(config->compress_choice, "zstd") != 0 &&
      strcmp(config->compress_choice, "none") != 0) {
@@ -361,11 +485,25 @@ Config* config_receive(int file_descriptor) {
    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;
+  }
  if (!send_status(file_descriptor, STATUS_OK))
    goto error;
  return config;

 error:
-  config_delete(config);
+  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);
  return NULL;
 }
@@ -36,6 +36,9 @@ 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 || 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));
@@ -118,6 +121,13 @@ 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) {
@@ -463,7 +473,8 @@ 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);
@@ -19,11 +19,13 @@
 #include "config.h"
 #include "data.h"
 #include "file.h"
-#include "file_store.h"
 #include "metadata.h"
 #include "protocol.h"
 #include "utils.h"

+#define MAX_SERVER_DELETE_COUNT 100000U
+#define MAX_FILE_DATA_SIZE (64ULL * 1024 * 1024)
+
 bool file_checksum(File* file, uint64_t* checksum) {
  if (!file || !checksum || !file->data)
    return false;
@@ -154,8 +156,38 @@ bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
  return true;
 }

+static bool to_disk_secure(const char* path, const void* data, unsigned long long data_size,
+                           bool inplace, bool sparse, const FileMetadata* metadata);
+static int open_secure_parent(const char* path, char** leaf_out, bool create_dirs);
+
+bool file_path_exists_secure(const char* path) {
+  struct stat st;
+  return file_stat_secure(path, &st);
+}
+
+bool file_stat_secure(const char* path, struct stat* st) {
+  if (!path || !st)
+    return false;
+  char* leaf = NULL;
+  int parent_fd = open_secure_parent(path, &leaf, false);
+  if (parent_fd < 0)
+    return false;
+  int fd = openat(parent_fd, leaf, O_RDONLY | O_NONBLOCK | O_CLOEXEC | O_NOFOLLOW);
+  bool exists = fd >= 0 && fstat(fd, st) == 0 && S_ISREG(st->st_mode);
+  if (fd >= 0)
+    close(fd);
+  close(parent_fd);
+  free(leaf);
+  return exists;
+}
+static bool rename_secure(const char* old_path, const char* new_path);
+static int authorized_root_fd = -1;
+static char* authorized_root_path;
+
 void file_set_authorized_root(int fd, const char* canonical_path) {
-  file_store_set_authorized_root(fd, canonical_path);
+  authorized_root_fd = fd;
+  free(authorized_root_path);
+  authorized_root_path = canonical_path ? str_dup(canonical_path) : NULL;
 }

 static bool path_is_within_root(const char* root, const char* path) {
@@ -272,7 +304,7 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
          mkdir_r(bdir);
          free(backup_dir_path);
        }
-        if (!file_store_rename_secure(disk_path, backup_path)) {
+        if (!rename_secure(disk_path, backup_path)) {
          free(backup_path);
          free(resolved_root);
          free(confined_backup);
@@ -327,7 +359,7 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
  free(resolved_dir);
  free(resolved_root);

-  bool ok = file_store_write_secure(disk_path, file->data->data, file->data->size, inplace, sparse,
+  bool ok = to_disk_secure(disk_path, file->data->data, file->data->size, inplace, sparse,
                           file->metadata);
  free(confined_backup);
  free(confined_partial);
@@ -432,8 +464,16 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
      }
    }

+    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 = data_create(new_data, (size_t)new_size);
+    file->data = replacement;

    free(old_data);
    delta_signature_destroy(sig);
@@ -475,6 +515,12 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
        send_status(fd, STATUS_ERROR);
        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;
    }

@@ -485,6 +531,7 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_

  delta_signature_destroy(sig);
  free(old_data);
+  send_status(fd, STATUS_ERROR);
  return NULL;
 }

@@ -524,7 +571,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
  int old_fd = -1;
  if (full_path) {
    char* leaf = NULL;
-    int parent_fd = file_store_open_secure_parent(full_path, &leaf);
+    int parent_fd = 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);
@@ -534,7 +581,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
  }
  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) {
+  if (has_old_file && old_size > 0 && old_size <= DELTA_MAX_FILE_SIZE && old_size <= SIZE_MAX) {
    old_data = malloc((size_t)old_size);
    if (old_data) {
      size_t got = 0;
@@ -635,6 +682,12 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
      send_status(fd, STATUS_ERROR);
      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;
  }

@@ -643,11 +696,243 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
  return file;
 }

+static int open_secure_parent(const char* path, char** leaf_out, bool create_dirs) {
+  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 && authorized_root_path && path[0] == '/' &&
+      path_is_within_root(authorized_root_path, path)) {
+    fd = dup(authorized_root_fd);
+    size_t root_len = strlen(authorized_root_path);
+    char* relative = str_dup(path + root_len);
+    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 && strcmp(component, "..") != 0) {
+      int next = openat(fd, component, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+      if (create_dirs && next < 0 && errno == ENOENT && mkdirat(fd, component, 0755) == 0)
+        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;
+}
+
+static bool rename_secure(const char* old_path, const char* new_path) {
+  char *old_leaf = NULL, *new_leaf = NULL;
+  int old_parent = open_secure_parent(old_path, &old_leaf, true);
+  int new_parent = open_secure_parent(new_path, &new_leaf, true);
+  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;
+}
+
+static bool to_disk_secure(const char* path, const void* data, unsigned long long data_size,
+                           bool inplace, bool sparse, const FileMetadata* metadata) {
+  char* leaf = NULL;
+  int dirfd = open_secure_parent(path, &leaf, true);
+  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);
+    }
+  } else {
+    char tmp[NAME_MAX];
+    for (unsigned int i = 0; i < 100 && !ok; ++i) {
+      snprintf(tmp, sizeof(tmp), ".%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);
+      if (close(fd) != 0)
+        ok = false;
+      fd = -1;
+      if (ok && renameat(dirfd, tmp, dirfd, leaf) != 0)
+        ok = false;
+      if (!ok)
+        unlinkat(dirfd, tmp, 0);
+    }
+  }
+  if (fd >= 0)
+    close(fd);
+  close(dirfd);
+  free(leaf);
+  return ok;
+}
+
 bool to_disk(const char* path, const void* data, unsigned long long data_size, bool inplace,
             bool sparse) {
  if (!path || (!data && data_size != 0) || has_path_traversal(path))
    return false;
-  return file_store_write_secure(path, data, data_size, inplace, sparse, NULL);
+  return to_disk_secure(path, data, data_size, inplace, sparse, NULL);
+  /* Kept below only as historical context; all writes use descriptor-relative operations. */
+  char* tmp_path = NULL;
+  char* directory = NULL;
+
+  char* path_dup = str_dup(path);
+  if (!path_dup)
+    return false;
+  const char* dir_result = dirname(path_dup);
+  directory = str_dup(dir_result);
+  free(path_dup);
+  if (!directory)
+    return false;
+
+  bool ok = true;
+  if (!mkdir_r(directory))
+    goto done;
+
+  if (inplace) {
+    FILE* file_pointer = fopen(path, "wb");
+    if (file_pointer == NULL) {
+      perror("Could not open file for inplace write");
+      ok = false;
+      goto done;
+    }
+    if (sparse && data_size > 0) {
+      if (fseek(file_pointer, data_size - 1, SEEK_SET) != 0) {
+        perror("Failed to seek for sparse file");
+        fclose(file_pointer);
+        ok = false;
+        goto done;
+      }
+      if (fwrite("", 1, 1, file_pointer) != 1) {
+        perror("Failed to write sparse file");
+        fclose(file_pointer);
+        ok = false;
+        goto done;
+      }
+      rewind(file_pointer);
+    }
+    if (data_size > 0 && fwrite(data, 1, data_size, file_pointer) != data_size) {
+      perror("Failed to write all data to file");
+      fclose(file_pointer);
+      ok = false;
+      goto done;
+    }
+    fclose(file_pointer);
+    free(directory);
+    return true;
+  }
+
+  size_t path_len = strlen(path);
+  tmp_path = malloc(path_len + 5);
+  if (!tmp_path) {
+    ok = false;
+    goto done;
+  }
+  memcpy(tmp_path, path, path_len);
+  memcpy(tmp_path + path_len, ".tmp", 5);
+
+  FILE* file_pointer = fopen(tmp_path, "wb");
+  if (file_pointer == NULL) {
+    perror("Could not open temporary file");
+    ok = false;
+    goto done;
+  }
+  if (sparse && data_size > 0) {
+    if (fseek(file_pointer, data_size - 1, SEEK_SET) != 0) {
+      perror("Failed to seek for sparse file");
+      fclose(file_pointer);
+      ok = false;
+      goto done;
+    }
+    if (fwrite("", 1, 1, file_pointer) != 1) {
+      perror("Failed to write sparse file");
+      fclose(file_pointer);
+      ok = false;
+      goto done;
+    }
+    rewind(file_pointer);
+  }
+  if (fwrite(data, 1, data_size, file_pointer) != data_size) {
+    perror("Failed to write all data to temporary file");
+    fclose(file_pointer);
+    unlink(tmp_path);
+    ok = false;
+    goto done;
+  }
+  fclose(file_pointer);
+
+  if (rename(tmp_path, path) != 0) {
+    perror("Failed to atomically rename temporary file");
+    unlink(tmp_path);
+    ok = false;
+    goto done;
+  }
+
+done:
+  free(tmp_path);
+  free(directory);
+  return ok;
 }

 bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int compression_level,
@@ -771,6 +1056,11 @@ File* file_receive(const Config* config, int file_descriptor) {
      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);
@@ -828,7 +1118,8 @@ int receive_manifest(int fd, const Config* config, int* next_status) {
    return *status_out == STATUS_FINISHED ? 0 : -1;
  }
  fprintf(stderr, "Deleting files not in manifest...\n");
-  bool deletion_ok = delete_extras(config->receive_root_directory, manifest);
+  bool deletion_ok =
+      delete_extras_limited(config->receive_root_directory, manifest, MAX_SERVER_DELETE_COUNT);
  array_list_delete(manifest);
  return deletion_ok ? 0 : -1;
 }
@@ -40,6 +40,8 @@ bool to_disk(const char* path, const void* data, unsigned long long data_size, b
 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);
+bool file_path_exists_secure(const char* path);
+bool file_stat_secure(const char* path, struct stat* st);
 int receive_manifest(int fd, const Config* config, int* next_status);

 #endif
@@ -1,159 +0,0 @@
-#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] == '/');
-}
-
-void file_store_set_authorized_root(int fd, const char* canonical_path) {
-  authorized_root_fd = fd;
-  free(authorized_root_path);
-  authorized_root_path = canonical_path ? str_dup(canonical_path) : NULL;
-}
-
-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 && authorized_root_path && path[0] == '/' &&
-      path_is_within_root(authorized_root_path, path)) {
-    fd = dup(authorized_root_fd);
-    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 && strcmp(component, "..") != 0) {
-      int next = openat(fd, component, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
-      if (next < 0 && errno == ENOENT && mkdirat(fd, component, 0755) == 0)
-        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) {
-  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);
-    }
-  } else {
-    char tmp[NAME_MAX];
-    for (unsigned int i = 0; i < 100 && !ok; ++i) {
-      snprintf(tmp, sizeof(tmp), ".%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);
-      if (close(fd) != 0)
-        ok = false;
-      fd = -1;
-      if (ok && renameat(dirfd, tmp, dirfd, leaf) != 0)
-        ok = false;
-      if (!ok)
-        unlinkat(dirfd, tmp, 0);
-    }
-  }
-  if (fd >= 0)
-    close(fd);
-  close(dirfd);
-  free(leaf);
-  return ok;
-}
@@ -1,13 +0,0 @@
-#ifndef FILE_STORE_H
-#define FILE_STORE_H
-
-#include "file.h"
-#include <stdbool.h>
-
-void 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);
-
-#endif
@@ -76,6 +76,11 @@ 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;
 }

@@ -175,7 +180,8 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
 void file_restore_metadata(const char* path, const FileMetadata* metadata) {
  if (metadata == NULL)
    return;
-  if (chmod(path, metadata->mode & 07777 & ~(S_ISUID | S_ISGID)) != 0)
+  mode_t safe_mode = metadata->mode & 0777 & ~(S_IWGRP | S_IWOTH);
+  if (chmod(path, safe_mode) != 0)
    log_message(LOG_LEVEL_WARNING, "Failed to chmod %s: %s", path, strerror(errno));
  /* Never apply client-supplied ownership.  The descriptor API below is the
     receiver write path; retain this legacy API only for compatibility. */
@@ -192,7 +198,8 @@ bool file_restore_metadata_fd(int fd, const FileMetadata* metadata) {
  if (fd < 0 || metadata == NULL)
    return metadata == NULL;
  bool ok = true;
-  if (fchmod(fd, metadata->mode & 07777 & ~(S_ISUID | S_ISGID)) != 0)
+  mode_t safe_mode = metadata->mode & 0777 & ~(S_IWGRP | S_IWOTH);
+  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},
@@ -1,5 +1,4 @@
 #include "multiprocessing.h"
-#include "receiver.h"

 #include "array_list.h"
 #include "chunk.h"
@@ -15,6 +14,10 @@
 #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));
@@ -98,8 +101,6 @@ 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;
@@ -136,14 +137,24 @@ void pipeline_context_receiver_destroy(PipelineContextReceiver* context) {
  free(context);
 }

-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);
+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 void receiver_thread_fail(PipelineContextReceiver* context) {
@@ -156,29 +167,119 @@ 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;
-  protocol_session_bind(&context->session);
+  if (context->ssl)
+    io_set_ssl(context->ssl);
  mtx_lock(&context->mutex);
  int file_descriptor = context->file_descriptor;
  const Config* config = context->config;
  mtx_unlock(&context->mutex);

-  ReceiverSink sink = {receiver_enqueue_file, context, false, false};
-  if (receiver_process((Config*)config, file_descriptor, &sink) != 0) {
+  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 && file_stat_secure(full_path, &st);
+        bool match = has_old && (unsigned long long)st.st_size == check_size &&
+                     (long long)st.st_mtime == check_mtime && S_ISREG(st.st_mode);
+        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);
-    protocol_session_unbind();
          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();
+  }
+  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);
-  protocol_session_unbind();
+#undef RECEIVE_THREAD_FAIL
  return thrd_success;
 }

 int write_thread(void* pipeline_context) {
  PipelineContextReceiver* context = (PipelineContextReceiver*)pipeline_context;
+  if (context->ssl)
+    io_set_ssl(context->ssl);
  mtx_lock(&context->mutex);
  bool save_to_disk = context->config->save_to_disk;
  char* root_directory = str_dup(context->config->receive_root_directory);
@@ -35,7 +35,6 @@ 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;
@@ -13,12 +13,11 @@

 #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 unsigned long long io_bwlimit = 0;
 static long long bw_tokens = 0;
@@ -26,10 +25,9 @@ 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 __thread unsigned long long total_allocated_bytes;

 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
@@ -38,29 +36,6 @@ void io_set_fds(int read_fd, int write_fd) {
  total_allocated_bytes = 0;
 }

-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;
-  if (io_bwlimit)
-    protocol_session_set_bwlimit(session, io_bwlimit);
-}
-
-void protocol_session_bind(ProtocolSession* session) {
-  bound_session = session;
-}
-
-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);
 }
@@ -74,51 +49,39 @@ void io_set_bwlimit(unsigned long long bytes_per_sec) {
  mtx_unlock(&bw_mutex);
 }

-void protocol_session_set_bwlimit(ProtocolSession* session, unsigned long long bytes_per_sec) {
-  if (!session)
-    return;
-  session->bwlimit = bytes_per_sec;
-  session->bw_tokens = (long long)bytes_per_sec;
-  struct timespec now;
-  clock_gettime(CLOCK_MONOTONIC, &now);
-  session->bw_last_refill_sec = now.tv_sec;
-  session->bw_last_refill_nsec = now.tv_nsec;
-}
-
-static void bw_throttle_session(ProtocolSession* session, size_t bytes_written) {
-  if (session->bwlimit == 0)
+static void bw_throttle(size_t bytes_written) {
+  if (io_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 - 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 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 tokens_to_add = (long long)((double)session->bwlimit * elapsed_ns / 1000000000.0);
-  session->bw_tokens += tokens_to_add;
-  if (session->bw_tokens > (long long)session->bwlimit)
-    session->bw_tokens = (long long)session->bwlimit;
+  long long 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;

-  session->bw_tokens -= bytes_written;
+  bw_tokens -= (long long)bytes_written;

-  if (session->bw_tokens < 0) {
-    long long deficit_us =
-        (long long)((double)(-session->bw_tokens) / session->bwlimit * 1000000.0);
+  if (bw_tokens < 0) {
+    long long deficit_us = (long long)((double)(-bw_tokens) / io_bwlimit * 1000000.0);
    if (deficit_us >= 1000)
      poll(NULL, 0, (int)(deficit_us / 1000));
    else
      usleep((useconds_t)deficit_us);
-    session->bw_tokens = 0;
-    session->bw_last_refill_sec = now.tv_sec;
-    session->bw_last_refill_nsec = now.tv_nsec;
+    bw_tokens = 0;
+    clock_gettime(CLOCK_MONOTONIC, &bw_last_refill);
  }
+  mtx_unlock(&bw_mutex);
 }

 void io_set_ssl(SSL* ssl) {
-  bound_session = NULL;
  io_ssl = ssl;
 }

@@ -126,32 +89,8 @@ SSL* io_get_ssl(void) {
  return io_ssl;
 }

-static ProtocolSession* legacy_session(void) {
-  static __thread ProtocolSession session;
-  if (bound_session)
-    return bound_session;
-  session.read_fd = io_read_fd;
-  session.write_fd = io_write_fd;
-  session.ssl = io_ssl;
-  session.bwlimit = io_bwlimit;
-  session.bw_tokens = (unsigned long long)(bw_tokens < 0 ? 0 : bw_tokens);
-  session.bw_last_refill_sec = bw_last_refill.tv_sec;
-  session.bw_last_refill_nsec = bw_last_refill.tv_nsec;
-  return &session;
-}
-
-bool send_n_data(int file_descriptor, const void* data, size_t data_size) {
-  ProtocolSession* session = legacy_session();
-  if (session->write_fd == -1)
-    session->write_fd = file_descriptor;
-  return protocol_send_n_data(session, data, data_size);
-}
-
-bool receive_n_data(int file_descriptor, void* data, size_t data_size) {
-  ProtocolSession* session = legacy_session();
-  if (session->read_fd == -1)
-    session->read_fd = file_descriptor;
-  return protocol_receive_n_data(session, data, data_size);
+static int io_fd(int dir_fd, int file_descriptor) {
+  return (dir_fd != -1) ? dir_fd : file_descriptor;
 }

 static int deadline_remaining_ms(const struct timespec* deadline) {
@@ -165,11 +104,9 @@ static int deadline_remaining_ms(const struct timespec* deadline) {
  return ms > INT_MAX ? INT_MAX : (int)ms;
 }

-bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t data_size) {
+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);
-  if (!session)
-    return false;
-  int fd = session->write_fd;
+  int fd = io_fd(io_write_fd, file_descriptor);
  struct timespec deadline;
  clock_gettime(CLOCK_MONOTONIC, &deadline);
  deadline.tv_sec += SEND_TIMEOUT_SEC;
@@ -177,7 +114,7 @@ bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t dat
  ssize_t total_bytes_send = 0;
  while ((size_t)total_bytes_send < data_size) {
    size_t chunk = data_size - total_bytes_send;
-    if (session->bwlimit > 0 && chunk > 65536)
+    if (io_bwlimit > 0 && chunk > 65536)
      chunk = 65536;
    struct pollfd pfd = {.fd = fd, .events = wait_events};
    int poll_result = poll(&pfd, 1, deadline_remaining_ms(&deadline));
@@ -190,13 +127,13 @@ bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t dat
    if (pfd.revents & (POLLERR | POLLNVAL))
      return false;
    ssize_t bytes_send;
-    if (session->ssl)
-      bytes_send = SSL_write(session->ssl, (const char*)data + total_bytes_send, chunk);
+    if (io_ssl)
+      bytes_send = SSL_write(io_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 (session->ssl) {
-        int ssl_err = SSL_get_error(session->ssl, (int)bytes_send);
+      if (io_ssl) {
+        int ssl_err = SSL_get_error(io_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;
@@ -205,18 +142,16 @@ bool protocol_send_n_data(ProtocolSession* session, const void* data, size_t dat
      log_message(LOG_LEVEL_ERROR, "Could not send data");
      return false;
    }
-    bw_throttle_session(session, (size_t)bytes_send);
+    bw_throttle((size_t)bytes_send);
    total_bytes_send += bytes_send;
  }
  log_message(LOG_LEVEL_DEBUG, "    Send n Data: %zu", total_bytes_send);
  return true;
 }

-bool protocol_receive_n_data(ProtocolSession* session, void* data, size_t data_size) {
+bool receive_n_data(int file_descriptor, void* data, size_t data_size) {
  log_message(LOG_LEVEL_DEBUG, "    Receiving n Data: %zu", data_size);
-  if (!session)
-    return false;
-  int fd = session->read_fd;
+  int fd = io_fd(io_read_fd, file_descriptor);

  struct timespec deadline;
  clock_gettime(CLOCK_MONOTONIC, &deadline);
@@ -241,15 +176,15 @@ bool protocol_receive_n_data(ProtocolSession* session, void* data, size_t data_s
      return false;

    ssize_t bytes_received;
-    if (session->ssl)
-      bytes_received = SSL_read(session->ssl, (char*)data + total_bytes_received,
-                                data_size - total_bytes_received);
+    if (io_ssl)
+      bytes_received =
+          SSL_read(io_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 (session->ssl) {
-        int ssl_err = SSL_get_error(session->ssl, (int)bytes_received);
+      if (io_ssl) {
+        int ssl_err = SSL_get_error(io_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;
@@ -296,24 +231,24 @@ static const char* status_to_string(Status status) {
  }
 }

-bool protocol_send_str(ProtocolSession* session, const char* data) {
+bool send_str(int file_descriptor, const char* data) {
  if (data == NULL)
    return false;
  size_t size = strlen(data);
-  if (!protocol_send_n_data(session, &size, sizeof(size_t)))
+  if (!send_n_data(file_descriptor, &size, sizeof(size_t)))
    return false;
-  if (!protocol_send_n_data(session, data, size))
+  if (!send_n_data(file_descriptor, data, size))
    return false;
  log_message(LOG_LEVEL_DEBUG, "Send String: %s", data);
  return true;
 }

-char* protocol_receive_str(ProtocolSession* session) {
+char* receive_str(int file_descriptor) {
  size_t size;
-  if (!protocol_receive_n_data(session, &size, sizeof(size_t)))
+  if (!receive_n_data(file_descriptor, &size, sizeof(size_t)))
    return NULL;
  if (size > MAX_STRING_SIZE || size > SIZE_MAX - 1 ||
-      size + 1 > MAX_CONNECTION_MEMORY - session->total_allocated_bytes) {
+      size + 1 > MAX_CONNECTION_MEMORY - total_allocated_bytes) {
    log_message(LOG_LEVEL_ERROR, "String size %zu exceeds maximum %llu", size,
                (unsigned long long)MAX_STRING_SIZE);
    return NULL;
@@ -321,29 +256,34 @@ char* protocol_receive_str(ProtocolSession* session) {
  char* data = (char*)malloc(size + 1);
  if (data == NULL)
    return NULL;
-  if (!protocol_receive_n_data(session, data, size)) {
+  if (!receive_n_data(file_descriptor, 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';
-  session->total_allocated_bytes += size + 1;
+  total_allocated_bytes += size + 1;
  log_message(LOG_LEVEL_DEBUG, "Received String: %s", data);
  return data;
 }

-bool protocol_send_data(ProtocolSession* session, const Data* data) {
+bool send_data(int file_descriptor, const Data* data) {
  unsigned long long data_size = data->size;
-  if (!protocol_send_n_data(session, &data_size, sizeof(unsigned long long)))
+  if (!send_n_data(file_descriptor, &data_size, sizeof(unsigned long long)))
    return false;
-  if (!protocol_send_n_data(session, data->data, data_size))
+  if (!send_n_data(file_descriptor, data->data, data_size))
    return false;
  log_message(LOG_LEVEL_DEBUG, "Send %lld data", data_size);
  return true;
 }

-Data* protocol_receive_data(ProtocolSession* session) {
+Data* receive_data(int file_descriptor) {
  unsigned long long size = 0;
-  if (!protocol_receive_n_data(session, &size, sizeof(unsigned long long)))
+  if (!receive_n_data(file_descriptor, &size, sizeof(unsigned long long)))
    return NULL;
  if (size > MAX_DATA_PAYLOAD_SIZE) {
    log_message(LOG_LEVEL_ERROR, "Data size %llu exceeds maximum %llu", size,
@@ -351,86 +291,51 @@ Data* protocol_receive_data(ProtocolSession* session) {
    return NULL;
  }
  size_t allocation_size = size == 0 ? 1 : (size_t)size;
-  if (allocation_size > MAX_CONNECTION_MEMORY - session->total_allocated_bytes) {
-    log_message(LOG_LEVEL_ERROR, "Per-connection memory limit exceeded (%llu + %llu > %llu)",
-                (unsigned long long)session->total_allocated_bytes, size,
-                (unsigned long long)MAX_CONNECTION_MEMORY);
+  if (allocation_size > MAX_CONNECTION_MEMORY - total_allocated_bytes) {
+    log_message(LOG_LEVEL_ERROR, "Per-connection memory limit exceeded");
    return NULL;
  }
  void* data = malloc(allocation_size);
  if (data == NULL)
    return NULL;
-  if (!protocol_receive_n_data(session, data, (size_t)size)) {
+  if (!receive_n_data(file_descriptor, data, (size_t)size)) {
    free(data);
    return NULL;
  }
-  session->total_allocated_bytes += allocation_size;
+  total_allocated_bytes += allocation_size;
  log_message(LOG_LEVEL_DEBUG, "Received %lld data", size);
  Data* result = data_create(data, (size_t)size);
  if (!result) {
    free(data);
-    session->total_allocated_bytes -= allocation_size;
+    total_allocated_bytes -= allocation_size;
  }
  return result;
 }

-bool protocol_send_int(ProtocolSession* session, int data) {
-  if (!protocol_send_n_data(session, &data, sizeof(int)))
+bool send_int(int file_descriptor, int data) {
+  if (!send_n_data(file_descriptor, &data, sizeof(int)))
    return false;
  log_message(LOG_LEVEL_DEBUG, "Send Int: %d", data);
  return true;
 }

-bool protocol_receive_int(ProtocolSession* session, int* data) {
-  if (!protocol_receive_n_data(session, data, sizeof(int)))
+bool receive_int(int file_descriptor, int* data) {
+  if (!receive_n_data(file_descriptor, data, sizeof(int)))
    return false;
  log_message(LOG_LEVEL_DEBUG, "Received Int: %d", *data);
  return true;
 }

-bool protocol_send_status(ProtocolSession* session, Status status) {
-  if (!protocol_send_n_data(session, &status, sizeof(Status)))
+bool send_status(int file_descriptor, Status status) {
+  if (!send_n_data(file_descriptor, &status, sizeof(Status)))
    return false;
  log_message(LOG_LEVEL_DEBUG, "Send Status: %s", status_to_string(status));
  return true;
 }

-bool protocol_receive_status(ProtocolSession* session, Status* status) {
-  if (!protocol_receive_n_data(session, status, sizeof(Status)))
+bool receive_status(int file_descriptor, Status* status) {
+  if (!receive_n_data(file_descriptor, status, sizeof(Status)))
    return false;
  log_message(LOG_LEVEL_DEBUG, "Received Status: %s", status_to_string(*status));
  return true;
 }
-
-bool send_str(int fd, const char* data) {
-  (void)fd;
-  return protocol_send_str(legacy_session(), data);
-}
-char* receive_str(int fd) {
-  (void)fd;
-  return protocol_receive_str(legacy_session());
-}
-bool send_data(int fd, const Data* data) {
-  (void)fd;
-  return protocol_send_data(legacy_session(), data);
-}
-Data* receive_data(int fd) {
-  (void)fd;
-  return protocol_receive_data(legacy_session());
-}
-bool send_int(int fd, int data) {
-  (void)fd;
-  return protocol_send_int(legacy_session(), data);
-}
-bool receive_int(int fd, int* data) {
-  (void)fd;
-  return protocol_receive_int(legacy_session(), data);
-}
-bool send_status(int fd, Status status) {
-  (void)fd;
-  return protocol_send_status(legacy_session(), status);
-}
-bool receive_status(int fd, Status* status) {
-  (void)fd;
-  return protocol_receive_status(legacy_session(), status);
-}
@@ -19,23 +19,6 @@

 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;
-  unsigned long long total_allocated_bytes;
-} ProtocolSession;
-
 typedef int Status;
 enum NET_STATUS {
  STATUS_OK,
@@ -56,23 +39,6 @@ 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);
-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);
-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);

@@ -173,7 +173,7 @@ Client* client_create() {
  return client;
 }

-bool tcp_connect_socket(Client* client, char* host, int port) {
+bool client_connect(Client* client, char* host, int port) {
  struct addrinfo hints;
  struct addrinfo* result;
  memset(&hints, 0, sizeof(hints));
@@ -222,12 +222,6 @@ bool tcp_connect_socket(Client* client, char* host, int port) {
    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;
 }
@@ -30,7 +30,6 @@ 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);
@@ -3,12 +3,16 @@
 #include "protocol.h"
 #include "transport_tcp.h"
 #include <arpa/inet.h>
+#include <netdb.h>
 #include <openssl/err.h>
 #include <openssl/ssl.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
 #include <unistd.h>

 bool tls_global_init(void) {
@@ -31,6 +35,10 @@ 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) {
@@ -39,9 +47,23 @@ 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);
      log_ssl_errors();
@@ -88,7 +110,10 @@ static SSL* wrap_fd_with_ssl(int fd, SSL_CTX* ctx, bool is_server, const char* h
  // 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)
@@ -146,8 +171,53 @@ 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) {
-  if (!tcp_connect_socket(client, host, port))
+  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 (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!");
+    return false;
+  }

  SSL_CTX* ctx = create_ssl_ctx(false, cert_path, key_path, ca_path);
  if (!ctx)
@@ -7,13 +7,67 @@
 #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;
+
+void utils_set_authorized_root(int fd, const char* canonical_path) {
+  authorized_root_fd = fd;
+  free(authorized_root_path);
+  authorized_root_path = canonical_path ? str_dup(canonical_path) : NULL;
+}

 void utils_set_authorized_root_fd(int fd) {
-  authorized_root_fd = fd;
+  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 || strcmp(component, "..") == 0) {
+      free(relative);
+      close(dirfd);
+      return -1;
+    }
+    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) {
@@ -143,7 +197,8 @@ 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;
@@ -173,12 +228,17 @@ 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);
        close(childfd);
      }
-      if (child_removed && !is_dir_in_manifest(child_rel, manifest) &&
-          unlinkat(dirfd, entry->d_name, AT_REMOVEDIR) != 0 && errno != ENOENT) {
+      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 && errno != ENOENT) {
+          operation_ok = false;
+        } else {
+          (*deleted_count)++;
+        }
      } else if (!child_removed) {
        all_removed = false;
      }
@@ -192,8 +252,15 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifes
        }
      }
      if (!found) {
+        if (*deleted_count >= max_delete) {
+          operation_ok = false;
+          free(child_rel);
+          continue;
+        }
        if (unlinkat(dirfd, entry->d_name, 0) != 0 && errno != ENOENT)
          operation_ok = false;
+        else
+          (*deleted_count)++;
        fprintf(stderr, "  Deleted: %s\n", child_rel);
      } else {
        all_removed = false;
@@ -206,18 +273,27 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, ArrayList* manifes
  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) {
+  int rootfd;
+  if (authorized_root_fd >= 0) {
+    rootfd =
+        authorized_root_path ? open_authorized_destination(dest_root) : dup(authorized_root_fd);
+  } 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;
@@ -237,10 +313,6 @@ 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);
@@ -2,6 +2,7 @@
 #define UTILS_H

 #include "array_list.h"
+#include <stddef.h>
 #include <stdbool.h>

 bool mkdir_r(const char* path);
@@ -9,8 +10,9 @@ char* str_dup(const char* string);
 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);
+void utils_set_authorized_root(int fd, const char* canonical_path);
 void utils_set_authorized_root_fd(int fd);
 bool has_path_traversal(const char* path);
-bool utils_valid_batch_path(const char* path);

 #endif
@@ -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)
@@ -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,
@@ -1,5 +1,4 @@
 #include "test_client_cli.h"
-#include "client_validation.h"
 #include "config.h"
 #include "test_utils.h"
 #include "utils.h"
@@ -10,56 +9,6 @@
 /* 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));
-  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_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));
-  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.
@@ -338,10 +287,6 @@ static void test_parse_args_archive() {
 }

 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();
@@ -224,26 +224,6 @@ static void test_config_send_receive_version_mismatch() {
  }
 }

-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));
-  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_is_remote_dest() {
  /* Valid SSH-style destinations */
  EXPECT_TRUE(is_remote_dest("user@host:/path"));
@@ -276,7 +256,6 @@ 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();
 }
@@ -38,23 +38,6 @@ 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);
@@ -190,7 +173,6 @@ static void test_receive_str_truncated() {
 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();
@@ -11,7 +11,11 @@
 #include <sys/wait.h>
 #include <unistd.h>

-#include "receiver.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

 /* Test receive_files with immediate FINISHED status */
 static void test_receive_files_finished() {
@@ -32,7 +36,7 @@ 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 = receiver_receive_files(cfg, p[0]);
+    int ret = receive_files(cfg, p[0]);
    close(p[0]);
    config_delete(cfg);
    _exit(ret == 0 ? 0 : 1);
@@ -84,7 +88,7 @@ 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 = receiver_receive_files(cfg, p[0]);
+    int ret = receive_files(cfg, p[0]);
    close(p[0]);
    config_delete(cfg);
    _exit(ret == 0 ? 0 : 1);
@@ -145,7 +149,7 @@ static void test_receive_files_abort() {
  if (pid == 0) {
    close(p[1]);
    io_set_fds(p[0], p[0]);
-    int ret = receiver_receive_files(cfg, p[0]);
+    int ret = receive_files(cfg, p[0]);
    close(p[0]);
    config_delete(cfg);
    /* Should return -1 on abort */
Author	SHA1	Message	Date
TapTap	78876b110e	fix: harden remaining review findings CI / lint (pull_request) Successful in 34s Details CI / sanitizers (address) (pull_request) Successful in 37s Details CI / sanitizers (undefined) (pull_request) Successful in 37s Details CI / fuzz-build (pull_request) Successful in 15s Details CI / coverage (pull_request) Successful in 33s Details CI / build-and-test (pull_request) Successful in 1m16s Details CI / valgrind (pull_request) Successful in 33s Details	2026-08-15 13:44:31 +02:00
TapTap	daf662cc2d	fix: address remaining PR review findings CI / lint (pull_request) Successful in 33s Details CI / sanitizers (address) (pull_request) Successful in 36s Details CI / sanitizers (undefined) (pull_request) Successful in 36s Details CI / fuzz-build (pull_request) Successful in 14s Details CI / coverage (pull_request) Successful in 31s Details CI / build-and-test (pull_request) Successful in 1m15s Details CI / valgrind (pull_request) Successful in 33s Details	2026-08-15 13:24:13 +02:00
TapTap	298bfe0d0f	fix: address delegated review findings CI / lint (pull_request) Successful in 33s Details CI / sanitizers (address) (pull_request) Successful in 35s Details CI / sanitizers (undefined) (pull_request) Successful in 36s Details CI / fuzz-build (pull_request) Successful in 14s Details CI / build-and-test (pull_request) Successful in 1m14s Details CI / coverage (pull_request) Successful in 30s Details CI / valgrind (pull_request) Successful in 33s Details	2026-08-15 13:13:57 +02:00
TapTap	6f8847899c	fix: validate remaining wire booleans CI / lint (pull_request) Successful in 34s Details CI / sanitizers (address) (pull_request) Successful in 35s Details CI / fuzz-build (pull_request) Successful in 14s Details CI / sanitizers (undefined) (pull_request) Successful in 35s Details CI / build-and-test (pull_request) Successful in 1m14s Details CI / coverage (pull_request) Successful in 31s Details CI / valgrind (pull_request) Successful in 33s Details	2026-08-15 12:49:30 +02:00
TapTap	ff189aeef2	fix: harden network security boundaries CI / lint (pull_request) Successful in 33s Details CI / sanitizers (address) (pull_request) Successful in 37s Details CI / sanitizers (undefined) (pull_request) Successful in 37s Details CI / fuzz-build (pull_request) Successful in 13s Details CI / coverage (pull_request) Successful in 32s Details CI / build-and-test (pull_request) Successful in 1m16s Details CI / valgrind (pull_request) Successful in 32s Details	2026-08-15 12:34:41 +02:00
TapTap	41b624db5a	Merge pull request 'fix: satisfy clang-format in CLI test' (#211 ) from fix/dev-ci-clang-format into dev CI / lint (push) Successful in 34s Details CI / sanitizers (address) (push) Successful in 37s Details CI / sanitizers (undefined) (push) Successful in 37s Details CI / fuzz-build (push) Successful in 14s Details CI / coverage (push) Successful in 31s Details CI / build-and-test (push) Successful in 1m16s Details CI / valgrind (push) Successful in 34s Details Reviewed-on: #211	2026-08-15 11:55:41 +02:00