docs: clarify rsync compatibility roadmap

fix: link receiver into fuzz targets
fix: satisfy cppcheck const analysis
2026-08-15 12:49:07 +02:00 · 2026-08-15 12:34:19 +02:00 · 2026-08-15 12:30:52 +02:00 · 2026-08-15 12:27:18 +02:00 · 2026-08-15 11:52:05 +02:00
32 changed files with 1321 additions and 1192 deletions
@@ -8,30 +8,34 @@ set(CMAKE_C_STANDARD_REQUIRED ON)

 add_compile_options(-Wall -g -O3)

+# --- Sanitizer option ---
 set(SANITIZER "none" CACHE STRING "Sanitizer to enable (address, thread, undefined, none)")
 set_property(CACHE SANITIZER PROPERTY STRINGS address thread undefined none)
+
 if(SANITIZER STREQUAL "address")
-  add_compile_options(-fsanitize=address -fno-omit-frame-pointer -g)
-  add_link_options(-fsanitize=address)
+	add_compile_options(-fsanitize=address -fno-omit-frame-pointer -g)
+	add_link_options(-fsanitize=address)
 elseif(SANITIZER STREQUAL "thread")
-  add_compile_options(-fsanitize=thread -fno-omit-frame-pointer -g)
-  add_link_options(-fsanitize=thread)
+	add_compile_options(-fsanitize=thread -fno-omit-frame-pointer -g)
+	add_link_options(-fsanitize=thread)
 elseif(SANITIZER STREQUAL "undefined")
-  add_compile_options(-fsanitize=undefined -fno-omit-frame-pointer -g)
-  add_link_options(-fsanitize=undefined)
+	add_compile_options(-fsanitize=undefined -fno-omit-frame-pointer -g)
+	add_link_options(-fsanitize=undefined)
 elseif(NOT SANITIZER STREQUAL "none")
-  message(FATAL_ERROR "Unknown sanitizer: ${SANITIZER}. Supported values: address, thread, undefined, none")
+	message(FATAL_ERROR "Unknown sanitizer: ${SANITIZER}. Supported values: address, thread, undefined, none")
 endif()

+# --- Strict warnings option ---
 option(STRICT_WARNINGS "Enable strict warnings (Wextra, Wpedantic, Werror)" OFF)
 if(STRICT_WARNINGS)
-  add_compile_options(-Wextra -Wpedantic -Werror)
+	add_compile_options(-Wextra -Wpedantic -Werror)
 endif()

+# --- Coverage option ---
 option(ENABLE_COVERAGE "Enable gcov coverage" OFF)
 if(ENABLE_COVERAGE)
-  add_compile_options(--coverage -fprofile-arcs -ftest-coverage -O0 -g)
-  add_link_options(--coverage)
+	add_compile_options(--coverage -fprofile-arcs -ftest-coverage -O0 -g)
+	add_link_options(--coverage)
 endif()

 include(FetchContent)
@@ -45,102 +49,58 @@ FetchContent_MakeAvailable(xxhash)

 set(THREADS_PREFER_PTHREAD_FLAG ON)
 find_package(Threads REQUIRED)
+
 find_library(ZSTD_LIBRARY zstd)
 if(NOT ZSTD_LIBRARY)
-  message(FATAL_ERROR "zstd library not found. Ensure it is in your nix-shell!")
+	message(FATAL_ERROR "zstd library not found. Ensure it is in your nix-shell!")
 endif()
+
 find_package(OpenSSL REQUIRED)

-set(SHARED_SRCS
-  src/shared/array_list.c
-  src/shared/chunk.c
-  src/shared/compression.c
-  src/shared/config.c
-  src/shared/data.c
-  src/shared/delta.c
-  src/shared/file.c
-  src/shared/log.c
-  src/shared/metadata.c
-  src/shared/multiprocessing.c
-  src/shared/protocol.c
-  src/shared/queue.c
-  src/shared/transport_ssh.c
-  src/shared/transport_tcp.c
-  src/shared/transport_tls.c
-  src/shared/utils.c
-)
-set(SERVER_SRCS src/server/server.c)
-set(CLIENT_SRCS
-  src/client/client_cli.c
-  src/client/client_send.c
-  src/client/scanner.c
-  src/client/usage.c
-)
+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")

-function(configure_fastsync_target target)
-  target_include_directories(${target} PRIVATE src/shared src/server src/client)
-  target_link_libraries(${target} PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
-endfunction()
+# --- Main executables ---
+add_executable(server ${SERVER_SRCS} ${SHARED_SRCS} ${FILE_STORE_SRCS})
+target_include_directories(server PRIVATE src/shared src/server src/client)
+target_link_libraries(server PRIVATE Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)

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

+# --- Testing ---
 enable_testing()
-set(TEST_SRCS
-  tests/runner.c
-  tests/test_array_list.c
-  tests/test_chunk.c
-  tests/test_client_cli.c
-  tests/test_compression.c
-  tests/test_config.c
-  tests/test_data.c
-  tests/test_delta.c
-  tests/test_file.c
-  tests/test_file_sendfile.c
-  tests/test_fuzz_smoke.c
-  tests/test_glob.c
-  tests/test_log.c
-  tests/test_metadata.c
-  tests/test_multiprocessing.c
-  tests/test_property.c
-  tests/test_protocol.c
-  tests/test_queue.c
-  tests/test_robustness.c
-  tests/test_scanner.c
-  tests/test_server.c
-  tests/test_shared_utils.c
-  tests/test_stress.c
-  tests/test_transport_ssh.c
-  tests/test_transport_tcp.c
-  tests/test_transport_tls.c
-)
-add_executable(tests ${TEST_SRCS} ${SHARED_SRCS} src/client/scanner.c src/client/client_cli.c)
-configure_fastsync_target(tests)
-target_include_directories(tests PRIVATE tests)
+
+# Common test libraries
+set(TEST_LIBS Threads::Threads ${ZSTD_LIBRARY} OpenSSL::SSL OpenSSL::Crypto xxhash)
+set(TEST_INCLUDES tests src/shared src/server src/client)
+
+# 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)
+target_include_directories(tests PRIVATE ${TEST_INCLUDES})
 target_compile_definitions(tests PRIVATE FASTSYNC_TEST_BUILD)
+target_link_libraries(tests PRIVATE ${TEST_LIBS})
 add_test(NAME unit_all COMMAND tests)

+# --- Fuzz targets (requires clang) ---
 option(ENABLE_FUZZ "Build fuzz targets (requires clang)" OFF)
 if(ENABLE_FUZZ)
  if(NOT CMAKE_C_COMPILER_ID MATCHES "Clang")
    message(FATAL_ERROR "ENABLE_FUZZ requires Clang (compiler is ${CMAKE_C_COMPILER_ID})")
  endif()
-  set(FUZZ_SRCS
-    tests/fuzz/fuzz_chunk_deserialize.c
-    tests/fuzz/fuzz_compress_decompress.c
-    tests/fuzz/fuzz_delta_deserialize.c
-    tests/fuzz/fuzz_delta_signature_deserialize.c
-    tests/fuzz/fuzz_glob_match.c
-    tests/fuzz/fuzz_metadata_from_buf.c
-  )
-  foreach(FUZZ_SRC ${FUZZ_SRCS})
-    get_filename_component(FUZZ_NAME ${FUZZ_SRC} NAME_WE)
-    add_executable(${FUZZ_NAME} ${FUZZ_SRC} ${SHARED_SRCS})
-    configure_fastsync_target(${FUZZ_NAME})
-    target_include_directories(${FUZZ_NAME} PRIVATE tests)
-    target_compile_options(${FUZZ_NAME} PRIVATE -fsanitize=fuzzer,address,undefined -fno-omit-frame-pointer)
-    target_link_options(${FUZZ_NAME} PRIVATE -fsanitize=fuzzer,address,undefined)
-  endforeach()
+  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} ${SERVER_RECEIVER_SRCS})
+		target_include_directories(${FUZZ_NAME} PRIVATE ${TEST_INCLUDES})
+		target_compile_options(${FUZZ_NAME} PRIVATE -fsanitize=fuzzer,address,undefined -fno-omit-frame-pointer)
+		target_link_options(${FUZZ_NAME} PRIVATE -fsanitize=fuzzer,address,undefined)
+		target_link_libraries(${FUZZ_NAME} PRIVATE ${TEST_LIBS})
+	endforeach()
 endif()
@@ -45,7 +45,7 @@ replacement for every rsync feature or protocol mode.

 - Recursive directory scanning.
 - Rsync-style source and destination arguments.
- SSH transport using `user@host:destination` paths below the remote authorized root.
+- SSH transport using `user@host:/path` destinations.
 - TCP client/server transfers.
 - Dry runs, excludes, includes, size filters, backups, statistics, and
  bandwidth limiting.
@@ -79,10 +79,8 @@ partial, alternate, and planned behavior.

 ### Build

-Requirements: C11 compiler, CMake 3.22 or newer, xxHash, zstd, OpenSSL,
-pthreads, and an SSH client for SSH transport. The first CMake configure fetches
-xxHash from GitHub, so network access is required unless the dependency is
-already cached.
+Requirements: C11 compiler, CMake 3.22 or newer, zstd, OpenSSL, pthreads,
+and an SSH client for SSH transport.

 ```bash
 cmake -B build -S .
@@ -100,12 +98,10 @@ cmake --build build -j$(nproc)
 ### SSH transfer

 The remote host must have `fastsync-server` available in `PATH`, or use
-`--fastsync-server-path`. SSH starts `fastsync-server --stdio` in its remote
-working directory, so use a destination below that directory unless the
-remote server is otherwise configured with a matching authorized root.
+`--fastsync-server-path`.

 ```bash
-./build/client /path/to/source user@host:destination
+./build/client /path/to/source user@host:/path/to/destination
 ```

 ### TCP transfer
@@ -113,7 +109,7 @@ remote server is otherwise configured with a matching authorized root.
 Start the FastSync server:

 ```bash
-./build/server --destination-root /path/to -p 8080
+./build/server -p 8080
 ```

 Then run the client:
@@ -127,7 +123,7 @@ Then run the client:
 ### TLS transfer

 ```bash
-./build/server --destination-root /path/to --tls --cert server.pem --key server-key.pem -p 8443
+./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 \
@@ -144,30 +140,30 @@ FastSync-native are optional performance or transport extensions.
 ./build/client /source/ /destination/

 # Archive-style synchronization (current FastSync archive behavior)
-./build/client -a /source/ user@host:destination/
+./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/
+  /source/ user@host:/destination/

 # Remove destination entries not present in the source
-./build/client --delete /source/ user@host:destination/
+./build/client --delete /source/ user@host:/destination/

 # Skip unchanged files using size and modification time
-./build/client --incremental /source/ user@host:destination/
+./build/client --incremental /source/ user@host:/destination/

 # Verify content when size and time are not sufficient
-./build/client --incremental --checksum /source/ user@host:destination/
+./build/client --incremental --checksum /source/ user@host:/destination/

 # Preserve supported mode and timestamp metadata
-./build/client -M /source/ user@host:destination/
+./build/client -M /source/ user@host:/destination/

 # Keep backups of overwritten destination files
-./build/client --backup --backup-dir backups \
-  /source/ user@host:destination/
+./build/client --backup --backup-dir /backups \
+  /source/ user@host:/destination/
 ```

 ## FastSync Extensions
@@ -221,8 +217,8 @@ before FastSync can claim full rsync CLI compatibility.
 | `--backup` | Back up overwritten files. |
 | `--backup-dir <dir>` | Store backups under a separate directory. |
 | `--suffix <suffix>` | Set the backup filename suffix. |
-| `--partial` | Select partial-transfer handling. With `--partial-dir`, completed files are written there; resumable transfers are not implemented. |
-| `--partial-dir <dir>` | Set a relative partial-transfer directory below the server destination root; use with `--partial`. |
+| `--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
@@ -273,7 +269,6 @@ before FastSync can claim full rsync CLI compatibility.
 | `--cert <path>` | TLS certificate file. |
 | `--key <path>` | TLS private key file. |
 | `--ca <path>` | CA file for peer verification. |
-| `--destination-root <path>` | Confine received files to this server-side root; defaults to the current directory. |
 | `--allow-delete` | Permit client delete manifests. Deletion is refused by default. |
 | `-v`, `--verbose` | Enable debug logging. |
 | `--help` | Print server usage. |
@@ -152,14 +152,14 @@ This document maps rsync's full feature set to FastSync's current implementation

 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `-S`, `--sparse` | Sparse block handling | ⚠️ Partial | Flag is accepted, but full hole preservation is not implemented |
+| `-S`, `--sparse` | Sparse block handling | ✅ Implemented | `preserve_sparse` config field |
 | `--preallocate` | Allocate dest files before writing | ❌ Not Implemented | |

 ## 11. Checksum & Comparison

 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `--checksum` | Skip based on checksum | ✅ Implemented | With `--incremental`, compares xxHash64 content checksums; `-c` remains compression |
+| `--checksum` | Skip based on checksum | ❌ Not Implemented | Removed because it had no effect; `-c` means compression |
 | `--checksum-choice=STR` | Choose checksum algorithm | ❌ Not Implemented | xxHash used internally |
 | `--compare-dest=DIR` | Compare dest files relative to DIR | ❌ Not Implemented | Removed because it had no effect |
 | `--copy-dest=DIR` | Include copies of unchanged files | ❌ Not Implemented | Removed because it had no effect |
@@ -1,10 +1,12 @@
 #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>
@@ -12,7 +14,6 @@
 #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. */
@@ -360,55 +361,6 @@ 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) {
-      fprintf(stderr, "Error: --tls requires --cert and --key\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) {
@@ -28,6 +28,87 @@
 /* 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);
@@ -43,12 +124,10 @@ 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(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);
+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);
  if (!scanner)
    return -1;
  Chunk* chunk;
@@ -291,49 +370,22 @@ int send_chunk(Client* client, Chunk* chunk, Config* config) {

 static int send_chunks_multithreaded(void* pipeline_context) {
  PipelineContextSender* context = (PipelineContextSender*)pipeline_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;
-    }
-  } 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;
-    }
+  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);
+    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);
  if (!config_send(client->file_descriptor, context->config)) {
-    client_disconnect(client);
-    client_delete(client);
-    mtx_lock(&context->mutex_progress);
-    context->sender_done = true;
-    mtx_unlock(&context->mutex_progress);
+    disconnect_transfer_client(client);
+    mark_sender_done(context);
+    protocol_session_unbind();
    return thrd_error;
  }

@@ -346,35 +398,26 @@ static int send_chunks_multithreaded(void* pipeline_context) {
        if (send_delete_manifest(client->file_descriptor, context->manifest) != 0)
          goto send_fail;
      }
-      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);
+      bool ok = finalize_transfer(client);
+      disconnect_transfer_client(client);
+      mark_sender_done(context);
+      protocol_session_unbind();
      return ok ? thrd_success : thrd_error;

    send_fail:
      pipeline_cancel(context);
-      client_disconnect(client);
-      client_delete(client);
-      mtx_lock(&context->mutex_progress);
-      context->sender_done = true;
-      mtx_unlock(&context->mutex_progress);
+      disconnect_transfer_client(client);
+      mark_sender_done(context);
+      protocol_session_unbind();
      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);
-      client_disconnect(client);
-      client_delete(client);
-      mtx_lock(&context->mutex_progress);
-      context->sender_done = true;
-      mtx_unlock(&context->mutex_progress);
+      disconnect_transfer_client(client);
+      mark_sender_done(context);
+      protocol_session_unbind();
      return thrd_error;
    }
    if (context->config->show_progress) {
@@ -393,13 +436,9 @@ static int send_chunks_multithreaded(void* pipeline_context) {

 static int scan_directory_multithreaded(void* pipeline_context) {
  PipelineContextSender* context = (PipelineContextSender*)pipeline_context;
-  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);
+  ScannerOptions options = scanner_options_from_config(context->config, 4);
+  ParallelScanner* scanner =
+      parallel_scanner_create_with_options(context->config->send_directory, &options);

  Chunk* current_chunk;
  if (scanner == NULL) {
@@ -410,28 +449,14 @@ 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);
-      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);
-          pipeline_cancel(context);
-          chunk_destroy(current_chunk);
-          parallel_scanner_destroy(scanner);
-          return thrd_error;
-        }
-      }
+      bool manifest_ok = add_chunk_to_manifest(context->manifest, current_chunk);
      mtx_unlock(&context->mutex_scanner);
+      if (!manifest_ok) {
+        pipeline_cancel(context);
+        chunk_destroy(current_chunk);
+        parallel_scanner_destroy(scanner);
+        return thrd_error;
+      }
    }
    if (!queue_enqueue_multithreaded_cancel(
            context->queue_scanner, current_chunk, &context->mutex_scanner,
@@ -540,61 +565,37 @@ int send_files(Config* config) {
  if (config->dry_run)
    return send_dry_run_manifest(config);

-  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;
-    }
-    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)) {
-    client_disconnect(client);
-    client_delete(client);
+  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" : "");
    return 1;
  }
-  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);
+  ProtocolSession session;
+  protocol_session_init(&session, client->file_descriptor, client->file_descriptor);
+  protocol_session_set_ssl(&session, (SSL*)client->ssl);
+  protocol_session_bind(&session);
+  if (!config_send(client->file_descriptor, config)) {
+    disconnect_transfer_client(client);
+    protocol_session_unbind();
+    return 1;
+  }
+  ScannerOptions scanner_options = scanner_options_from_config(config, 0);
+  DirectoryScanner* scanner =
+      directory_scanner_create_with_options(config->send_directory, &scanner_options);
  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 = config->use_delete ? array_list_create(free) : NULL;
+  ArrayList* manifest = create_transfer_manifest(config);
  if (!scanner || (config->use_delete && !manifest)) {
    if (scanner)
      directory_scanner_destroy(scanner);
    if (manifest)
      array_list_delete(manifest);
-    client_disconnect(client);
-    client_delete(client);
+    disconnect_transfer_client(client);
+    protocol_session_unbind();
    return 1;
  }
  while ((current_chunk = directory_scanner_next(scanner)) != NULL) {
@@ -602,30 +603,10 @@ 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 (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);
-          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 (!add_chunk_to_manifest(manifest, current_chunk)) {
+      chunk_destroy(current_chunk);
+      goto send_fail;
    }
    if (!config->use_sendfile) {
      for (int i = 0; i < current_chunk->element_count; i++) {
@@ -669,10 +650,7 @@ int send_files(Config* config) {
    array_list_delete(manifest);
    manifest = NULL;
  }
-  if (!send_status(client->file_descriptor, STATUS_FINISHED))
-    goto send_fail;
-  Status s;
-  int ok = receive_status(client->file_descriptor, &s) && s == STATUS_OK;
+  bool ok = finalize_transfer(client);
  double elapsed_total = difftime(time(NULL), start);
  if (config->show_progress) {
    double rate = elapsed_total > 0 ? total_bytes / (1048576.0 * elapsed_total) : 0;
@@ -684,16 +662,16 @@ int send_files(Config* config) {
            rate);
  }
  directory_scanner_destroy(scanner);
-  client_disconnect(client);
-  client_delete(client);
+  disconnect_transfer_client(client);
+  protocol_session_unbind();
  return ok ? 0 : 1;

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

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

  thrd_t scanner, loader, sender;
  bool scanner_created = false;
@@ -0,0 +1,50 @@
+#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;
+}
@@ -0,0 +1,9 @@
+#ifndef CLIENT_VALIDATION_H
+#define CLIENT_VALIDATION_H
+
+#include "config.h"
+#include <stdbool.h>
+
+bool validate_config(const Config* config);
+
+#endif
@@ -52,13 +52,84 @@ static bool safe_relative_link(const char* source_root, const char* containing_d
  return safe;
 }

-DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_metadata,
-                                           unsigned long long chunk_size, char** exclude_patterns,
-                                           int exclude_count, char** include_patterns,
-                                           int include_count, unsigned long long max_size,
-                                           unsigned long long min_size, int max_depth,
-                                           bool follow_symlinks, bool copy_links, bool safe_links,
-                                           bool copy_unsafe_links, bool checksum) {
+typedef struct {
+  char* path;
+  struct stat stats;
+  bool is_directory;
+} ScannerEntry;
+
+/* Inspect symlinks, resolve the entry type, and apply file filters once for both scanners. */
+static int scanner_inspect_entry(const ScannerOptions* options, const char* source_root,
+                                 const char* containing_dir, const char* name,
+                                 ScannerEntry* entry) {
+  entry->path = path_cat(containing_dir, name);
+  if (!entry->path)
+    return -1;
+
+  struct stat link_stats;
+  if (lstat(entry->path, &link_stats) != 0) {
+    free(entry->path);
+    return 0;
+  }
+  bool is_symlink = S_ISLNK(link_stats.st_mode);
+  if (is_symlink && !options->follow_symlinks && !options->copy_links && !options->safe_links &&
+      !options->copy_unsafe_links)
+    goto skip;
+
+  if (is_symlink && options->safe_links) {
+    char link_target[4096];
+    ssize_t length = readlink(entry->path, link_target, sizeof(link_target) - 1);
+    if (length < 0)
+      goto skip;
+    link_target[length] = '\0';
+    if (link_target[0] == '/' || !safe_relative_link(source_root, containing_dir, link_target))
+      goto skip;
+  }
+
+  if (is_symlink && options->copy_unsafe_links && !options->copy_links) {
+    char link_target[4096];
+    ssize_t length = readlink(entry->path, link_target, sizeof(link_target) - 1);
+    if (length < 0)
+      goto skip;
+    link_target[length] = '\0';
+    if (link_target[0] != '/')
+      goto skip;
+  }
+
+  if (is_symlink && options->follow_symlinks && !options->copy_links)
+    entry->stats = link_stats;
+  else if (stat(entry->path, &entry->stats) != 0)
+    goto skip;
+
+  entry->is_directory = S_ISDIR(entry->stats.st_mode);
+  if (entry->is_directory)
+    return 1;
+  for (int i = 0; i < options->exclude_count; i++)
+    if (glob_match(options->exclude_patterns[i], name))
+      goto skip;
+  if (options->include_count > 0) {
+    bool included = false;
+    for (int i = 0; i < options->include_count; i++)
+      if (glob_match(options->include_patterns[i], name))
+        included = true;
+    if (!included)
+      goto skip;
+  }
+  if ((options->max_size > 0 && (unsigned long long)entry->stats.st_size > options->max_size) ||
+      (options->min_size > 0 && (unsigned long long)entry->stats.st_size < options->min_size))
+    goto skip;
+  return 1;
+
+skip:
+  free(entry->path);
+  entry->path = NULL;
+  return 0;
+}
+
+DirectoryScanner* directory_scanner_create_with_options(const char* root_directory,
+                                                        const ScannerOptions* options) {
+  if (!root_directory || !options)
+    return NULL;
  DirectoryScanner* scanner = calloc(1, sizeof(DirectoryScanner));
  if (scanner == NULL)
    return NULL;
@@ -69,21 +140,21 @@ DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_
  }
  scanner->current_dir = NULL;
  scanner->current_path = NULL;
-  scanner->use_metadata = use_metadata;
-  scanner->chunk_size = chunk_size > 0 ? chunk_size : DESIRED_CHUNK_SIZE;
-  scanner->exclude_patterns = exclude_patterns;
-  scanner->exclude_count = exclude_count;
-  scanner->include_patterns = include_patterns;
-  scanner->include_count = include_count;
-  scanner->max_size = max_size;
-  scanner->min_size = min_size;
-  scanner->max_depth = max_depth;
+  scanner->use_metadata = options->use_metadata;
+  scanner->chunk_size = options->chunk_size > 0 ? options->chunk_size : DESIRED_CHUNK_SIZE;
+  scanner->exclude_patterns = options->exclude_patterns;
+  scanner->exclude_count = options->exclude_count;
+  scanner->include_patterns = options->include_patterns;
+  scanner->include_count = options->include_count;
+  scanner->max_size = options->max_size;
+  scanner->min_size = options->min_size;
+  scanner->max_depth = options->max_depth;
  scanner->current_depth = 0;
-  scanner->follow_symlinks = follow_symlinks;
-  scanner->copy_links = copy_links;
-  scanner->safe_links = safe_links;
-  scanner->copy_unsafe_links = copy_unsafe_links;
-  scanner->checksum = checksum;
+  scanner->follow_symlinks = options->follow_symlinks;
+  scanner->copy_links = options->copy_links;
+  scanner->safe_links = options->safe_links;
+  scanner->copy_unsafe_links = options->copy_unsafe_links;
+  scanner->checksum = options->checksum;
  scanner->failed = false;
  DirEntry* root = dir_entry_create(root_directory, 0);
  if (!root) {
@@ -100,6 +171,20 @@ DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_
  return scanner;
 }

+DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_metadata,
+                                           unsigned long long chunk_size, char** exclude_patterns,
+                                           int exclude_count, char** include_patterns,
+                                           int include_count, unsigned long long max_size,
+                                           unsigned long long min_size, int max_depth,
+                                           bool follow_symlinks, bool copy_links, bool safe_links,
+                                           bool copy_unsafe_links, bool checksum) {
+  ScannerOptions options = {
+      use_metadata,    chunk_size, exclude_patterns, exclude_count,     include_patterns,
+      include_count,   max_size,   min_size,         max_depth,         0,
+      follow_symlinks, copy_links, safe_links,       copy_unsafe_links, checksum};
+  return directory_scanner_create_with_options(root_directory, &options);
+}
+
 void directory_scanner_destroy(DirectoryScanner* scanner) {
  if (scanner == NULL)
    return;
@@ -167,7 +252,7 @@ Chunk* directory_scanner_next(DirectoryScanner* scanner) {
        break;
    }

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

-    char* cur_path = path_cat(scanner->current_path, entry->d_name);
-    if (!cur_path) {
+    ScannerOptions options = {scanner->use_metadata,     scanner->chunk_size,
+                              scanner->exclude_patterns, scanner->exclude_count,
+                              scanner->include_patterns, scanner->include_count,
+                              scanner->max_size,         scanner->min_size,
+                              scanner->max_depth,        0,
+                              scanner->follow_symlinks,  scanner->copy_links,
+                              scanner->safe_links,       scanner->copy_unsafe_links,
+                              scanner->checksum};
+    ScannerEntry inspected;
+    int inspection = scanner_inspect_entry(&options, scanner->current_path, scanner->current_path,
+                                           entry->d_name, &inspected);
+    if (inspection < 0) {
      scanner->failed = true;
      break;
    }
-    struct stat stats;
-    struct stat lstats;
-    bool is_symlink = false;
-    if (lstat(cur_path, &lstats) != 0) {
-      free(cur_path);
+    if (inspection == 0)
      continue;
-    }
-    is_symlink = S_ISLNK(lstats.st_mode);
+    char* cur_path = inspected.path;
+    struct stat stats = inspected.stats;

-    if (is_symlink && !scanner->follow_symlinks && !scanner->copy_links && !scanner->safe_links &&
-        !scanner->copy_unsafe_links) {
-      free(cur_path);
-      continue;
-    }
-
-    if (is_symlink && scanner->safe_links) {
-      char link_target[4096];
-      ssize_t len = readlink(cur_path, link_target, sizeof(link_target) - 1);
-      if (len < 0) {
-        free(cur_path);
-        continue;
-      }
-      link_target[len] = '\0';
-      if (link_target[0] == '/' ||
-          !safe_relative_link(scanner->current_path, scanner->current_path, link_target)) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    if (is_symlink && scanner->copy_unsafe_links && !scanner->copy_links) {
-      char link_target[4096];
-      ssize_t len = readlink(cur_path, link_target, sizeof(link_target) - 1);
-      if (len < 0) {
-        free(cur_path);
-        continue;
-      }
-      link_target[len] = '\0';
-      bool unsafe = (link_target[0] == '/');
-      if (!unsafe) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    bool use_lstat = is_symlink && scanner->follow_symlinks && !scanner->copy_links;
-    if (use_lstat) {
-      stats = lstats;
-    } else {
-      if (stat(cur_path, &stats) != 0) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    if (S_ISDIR(stats.st_mode)) {
+    if (inspected.is_directory) {
      int next_depth = scanner->current_depth + 1;
      if (scanner->max_depth <= 0 || next_depth < scanner->max_depth) {
        DirEntry* de = dir_entry_create(cur_path, next_depth);
@@ -254,38 +299,6 @@ Chunk* directory_scanner_next(DirectoryScanner* scanner) {
        free(cur_path);
        continue;
      }
-      bool excluded = false;
-      for (int i = 0; i < scanner->exclude_count; i++) {
-        if (glob_match(scanner->exclude_patterns[i], entry->d_name)) {
-          excluded = true;
-          break;
-        }
-      }
-      if (excluded) {
-        free(cur_path);
-        continue;
-      }
-
-      if (scanner->include_count > 0) {
-        bool included = false;
-        for (int i = 0; i < scanner->include_count; i++) {
-          if (glob_match(scanner->include_patterns[i], entry->d_name)) {
-            included = true;
-            break;
-          }
-        }
-        if (!included) {
-          free(cur_path);
-          continue;
-        }
-      }
-
-      if ((scanner->max_size > 0 && (unsigned long long)stats.st_size > scanner->max_size) ||
-          (scanner->min_size > 0 && (unsigned long long)stats.st_size < scanner->min_size)) {
-        free(cur_path);
-        continue;
-      }
-
      File* file = file_create(cur_path);
      if (file == NULL) {
        free(cur_path);
@@ -336,29 +349,13 @@ typedef struct {
  ParallelScanner* ps;
  char** dirs;
  int dir_count;
-  bool use_metadata;
-  unsigned long long chunk_size;
-  char** exclude_patterns;
-  int exclude_count;
-  char** include_patterns;
-  int include_count;
-  unsigned long long max_size;
-  unsigned long long min_size;
-  int max_depth;
-  bool follow_symlinks;
-  bool copy_links;
-  bool safe_links;
-  bool copy_unsafe_links;
-  bool checksum;
+  ScannerOptions options;
 } 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(
-        wa->dirs[i], wa->use_metadata, wa->chunk_size, wa->exclude_patterns, wa->exclude_count,
-        wa->include_patterns, wa->include_count, wa->max_size, wa->min_size, wa->max_depth,
-        wa->follow_symlinks, wa->copy_links, wa->safe_links, wa->copy_unsafe_links, wa->checksum);
+    DirectoryScanner* ds = directory_scanner_create_with_options(wa->dirs[i], &wa->options);
    if (!ds) {
      mtx_lock(&wa->ps->result_mutex);
      wa->ps->failed = true;
@@ -401,13 +398,10 @@ static int parallel_worker_thread(void* arg) {
  return thrd_success;
 }

-ParallelScanner* parallel_scanner_create(char* root_directory, bool use_metadata,
-                                         unsigned long long chunk_size, char** exclude_patterns,
-                                         int exclude_count, char** include_patterns,
-                                         int include_count, unsigned long long max_size,
-                                         unsigned long long min_size, int max_depth,
-                                         int num_threads, bool follow_symlinks, bool copy_links,
-                                         bool safe_links, bool copy_unsafe_links, bool checksum) {
+ParallelScanner* parallel_scanner_create_with_options(const char* root_directory,
+                                                      const ScannerOptions* options) {
+  if (!root_directory || !options)
+    return NULL;
  ParallelScanner* ps = calloc(1, sizeof(ParallelScanner));
  if (!ps)
    return NULL;
@@ -460,105 +454,27 @@ ParallelScanner* parallel_scanner_create(char* root_directory, bool use_metadata
    parallel_scanner_destroy(ps);
    return NULL;
  }
-  struct dirent* entry;
+  const struct dirent* entry;
  while ((entry = readdir(dir)) != NULL) {
    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
      continue;
-    char* cur_path = path_cat(root_directory, entry->d_name);
-    if (!cur_path)
-      continue;
-    struct stat lstats;
-    if (lstat(cur_path, &lstats) != 0) {
-      free(cur_path);
+    ScannerEntry inspected;
+    int inspection =
+        scanner_inspect_entry(options, root_directory, root_directory, entry->d_name, &inspected);
+    if (inspection < 0) {
+      ps->failed = true;
      continue;
    }
-    bool is_symlink = S_ISLNK(lstats.st_mode);
-
-    // Skip symlinks unless the user explicitly enabled following/copying them.
-    if (is_symlink && !follow_symlinks && !copy_links && !safe_links && !copy_unsafe_links) {
-      free(cur_path);
+    if (inspection == 0)
      continue;
-    }
-
-    // --safe-links: reject symlinks pointing outside the source tree.
-    if (is_symlink && safe_links) {
-      char link_target[4096];
-      ssize_t len = readlink(cur_path, link_target, sizeof(link_target) - 1);
-      if (len < 0) {
-        free(cur_path);
-        continue;
-      }
-      link_target[len] = 0;
-      if (link_target[0] == '/' ||
-          !safe_relative_link(root_directory, root_directory, link_target)) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    // --copy-unsafe-links (without --copy-links): only copy absolute symlinks.
-    if (is_symlink && copy_unsafe_links && !copy_links) {
-      char link_target[4096];
-      ssize_t len = readlink(cur_path, link_target, sizeof(link_target) - 1);
-      if (len < 0) {
-        free(cur_path);
-        continue;
-      }
-      link_target[len] = 0;
-      bool unsafe = (link_target[0] == '/');
-      if (!unsafe) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    // Determine whether to use lstat or stat results for the entry.
-    struct stat st;
-    bool use_lstat_res = is_symlink && follow_symlinks && !copy_links;
-    if (use_lstat_res) {
-      st = lstats;
-    } else {
-      if (stat(cur_path, &st) != 0) {
-        free(cur_path);
-        continue;
-      }
-    }
-
-    if (S_ISDIR(st.st_mode)) {
+    char* cur_path = inspected.path;
+    struct stat st = inspected.stats;
+    if (inspected.is_directory) {
      if (!array_list_add(subdirs, cur_path)) {
        free(cur_path);
        ps->failed = true;
      }
    } 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) {
@@ -566,9 +482,9 @@ ParallelScanner* parallel_scanner_create(char* root_directory, bool use_metadata
        continue;
      }
      file->data->size = st.st_size;
-      if (use_metadata)
+      if (options->use_metadata)
        file->metadata = file_metadata_create(&st);
-      if (use_metadata && !file->metadata) {
+      if (options->use_metadata && !file->metadata) {
        file_destroy(file);
        ps->failed = true;
        continue;
@@ -581,7 +497,7 @@ ParallelScanner* parallel_scanner_create(char* root_directory, bool use_metadata
  }
  closedir(dir);

-  unsigned long long cs = chunk_size > 0 ? chunk_size : DESIRED_CHUNK_SIZE;
+  unsigned long long cs = options->chunk_size > 0 ? options->chunk_size : DESIRED_CHUNK_SIZE;
  if (root_files->size > 0) {
    ArrayList* batch = array_list_create(NULL);
    if (!batch) {
@@ -648,7 +564,7 @@ ParallelScanner* parallel_scanner_create(char* root_directory, bool use_metadata
  }
  array_list_delete(root_files);

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

@@ -696,20 +612,8 @@ ParallelScanner* parallel_scanner_create(char* root_directory, bool use_metadata
        break;
      }
      wa->dir_count = count;
-      wa->use_metadata = use_metadata;
-      wa->chunk_size = cs;
-      wa->exclude_patterns = exclude_patterns;
-      wa->exclude_count = exclude_count;
-      wa->include_patterns = include_patterns;
-      wa->include_count = include_count;
-      wa->max_size = max_size;
-      wa->min_size = min_size;
-      wa->max_depth = max_depth;
-      wa->follow_symlinks = follow_symlinks;
-      wa->copy_links = copy_links;
-      wa->safe_links = safe_links;
-      wa->copy_unsafe_links = copy_unsafe_links;
-      wa->checksum = checksum;
+      wa->options = *options;
+      wa->options.chunk_size = cs;
      start += count;
      if (thrd_create(&ps->threads[t], parallel_worker_thread, wa) != thrd_success) {
        for (int j = 0; j < count; j++)
@@ -733,6 +637,20 @@ ParallelScanner* parallel_scanner_create(char* root_directory, bool use_metadata
  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;
@@ -8,6 +8,24 @@
 #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;
@@ -53,17 +71,21 @@ DirectoryScanner* directory_scanner_create(const char* root_directory, bool use_
                                           unsigned long long min_size, int max_depth,
                                           bool follow_symlinks, bool copy_links, bool safe_links,
                                           bool copy_unsafe_links, bool checksum);
+DirectoryScanner* directory_scanner_create_with_options(const char* root_directory,
+                                                        const ScannerOptions* options);
 Chunk* directory_scanner_next(DirectoryScanner* scanner);
 bool directory_scanner_failed(const DirectoryScanner* scanner);
 void directory_scanner_destroy(DirectoryScanner* scanner);

-ParallelScanner* parallel_scanner_create(char* root_directory, bool use_metadata,
+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);
+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);
@@ -1,8 +1,9 @@
-#include "stdio.h"
+#include "usage.h"
+#include <stdio.h>
 #include <delta.h>
 #include <chunk.h>

-static __attribute__((unused)) void print_usage() {
+void print_usage(void) {
  printf("Usage:\n");
  printf("  fastsync [options] <source> <destination>\n");
  printf("  fastsync [options] --source-dir <src> --dest-dir <dst>\n");
@@ -0,0 +1,6 @@
+#ifndef USAGE_H
+#define USAGE_H
+
+void print_usage(void);
+
+#endif
@@ -0,0 +1,126 @@
+#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);
+}
@@ -0,0 +1,19 @@
+#ifndef RECEIVER_H
+#define RECEIVER_H
+
+#include "config.h"
+#include "file.h"
+
+typedef bool (*ReceiverFileSink)(File* file, void* context);
+
+typedef struct {
+  ReceiverFileSink store_file;
+  void* context;
+  bool send_error;
+  bool send_success;
+} ReceiverSink;
+
+int receiver_process(Config* config, int file_descriptor, const ReceiverSink* sink);
+int receiver_receive_files(Config* config, int file_descriptor);
+
+#endif
@@ -2,20 +2,19 @@
 #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>

 static char* authorized_root;
 static int authorized_root_fd = -1;
@@ -26,14 +25,6 @@ static bool path_is_within(const char* root, const char* path) {
  return strncmp(root, path, n) == 0 && (path[n] == '\0' || path[n] == '/');
 }

-static bool save_received_file(File* file, void* context) {
-  Config* config = context;
-  if (config->save_to_disk && !file_save_to_disk(config->receive_root_directory, file, config))
-    return false;
-  file_destroy(file);
-  return true;
-}
-
 static bool __attribute__((unused)) configure_authorization(const char* root) {
  char resolved[PATH_MAX];
  if (!root || !realpath(root, resolved))
@@ -52,22 +43,24 @@ static bool __attribute__((unused)) configure_authorization(const char* root) {
  return true;
 }

-int receive_files(Config* config, int fd) {
-  return receive_files_common(config, fd, save_received_file, config, true);
-}
-
 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;
  }
  char resolved_destination[PATH_MAX];
@@ -79,6 +72,7 @@ void handler(int file_descriptor) {
    free(canonical_destination);
    config_delete(config);
    close(file_descriptor);
+    protocol_session_unbind();
    return;
  }
  if (canonical_destination)
@@ -91,6 +85,7 @@ 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;
@@ -99,6 +94,7 @@ void handler(int file_descriptor) {
    if (q == NULL) {
      config_delete(config);
      close(file_descriptor);
+      protocol_session_unbind();
      return;
    }
    PipelineContextReceiver* context =
@@ -107,14 +103,14 @@ 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 = false;
+    bool receiver_created = thrd_create(&receiver, receive_thread, context) == thrd_success;
    bool writer_created = false;
-    receiver_created = (thrd_create(&receiver, receive_thread, context) == thrd_success);
    if (receiver_created)
-      writer_created = (thrd_create(&writer, write_thread, context) == thrd_success);
+      writer_created = thrd_create(&writer, write_thread, context) == thrd_success;
    if (!receiver_created || !writer_created) {
      perror("Error creating Threads");
      if (receiver_created) {
@@ -131,22 +127,23 @@ void handler(int file_descriptor) {
      if (writer_created)
        thrd_join(writer, NULL);
      pipeline_context_receiver_destroy(context);
+      protocol_session_unbind();
      return;
    }
    int receiver_result;
    int writer_result;
    thrd_join(receiver, &receiver_result);
    thrd_join(writer, &writer_result);
-    if (receiver_result == thrd_success && writer_result == thrd_success)
-      send_status(file_descriptor, STATUS_OK);
-    else
-      send_status(file_descriptor, STATUS_ERROR);
+    send_status(file_descriptor, receiver_result == thrd_success && writer_result == thrd_success
+                                     ? STATUS_OK
+                                     : STATUS_ERROR);
    pipeline_context_receiver_destroy(context);
  } else {
-    if (receive_files(config, file_descriptor) != 0)
+    if (receiver_receive_files(config, file_descriptor) != 0)
      log_message(LOG_LEVEL_ERROR, "Transfer failed");
    config_delete(config);
  }
+  protocol_session_unbind();
  close(file_descriptor);
 }

@@ -155,16 +152,14 @@ static Server* g_server = NULL;

 static void cleanup(int sig) {
  (void)sig;
-  if (g_server) {
+  if (g_server)
    server_delete(&g_server);
-  }
  _exit(0);
 }

 static void print_server_usage(void) {
  printf("FastSync Server\n");
-  printf("Usage: fastsync-server [options]\n");
-  printf("\n");
+  printf("Usage: fastsync-server [options]\n\n");
  printf("Options:\n");
  printf("  --stdio             Run in stdio mode (SSH transport)\n");
  printf("  -p <port>           TCP port (default: 8080, range: 1-65535)\n");
@@ -180,9 +175,7 @@ static void print_server_usage(void) {

 int main(int argc, char* argv[]) {
  bool use_tls = false;
-  char* tls_cert = NULL;
-  char* tls_key = NULL;
-  char* tls_ca = NULL;
+  char *tls_cert = NULL, *tls_key = NULL, *tls_ca = NULL;
  int port = 8080;
  const char* destination_root = ".";
  bool stdio_mode = false;
@@ -222,11 +215,8 @@ 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)) {
@@ -243,7 +233,7 @@ int main(int argc, char* argv[]) {
    return 0;
  }
  g_server = server_create(port);
-  if (g_server == NULL) {
+  if (!g_server) {
    log_message(LOG_LEVEL_ERROR, "Failed to create server");
    return 1;
  }
@@ -265,4 +255,4 @@ int main(int argc, char* argv[]) {
  }
  return 0;
 }
-#endif /* !FASTSYNC_SERVER_AS_LIB */
+#endif
@@ -173,39 +173,158 @@ void config_delete(Config* config) {
  free(config);
 }

-static bool config_send_string(int file_descriptor, const char* value, bool optional) {
-  return send_str(file_descriptor, value ? value : (optional ? "" : NULL));
+/* 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);
 }

-#define CONFIG_SEND_VERSION(field)                                                                 \
-  do {                                                                                             \
-    if (!config_send_string(file_descriptor, config->field, false))                                \
-      return false;                                                                                \
-  } while (0);
-#define CONFIG_SEND_STRING(field)                                                                  \
-  do {                                                                                             \
-    if (!config_send_string(file_descriptor, config->field, false))                                \
-      return false;                                                                                \
-  } while (0);
-#define CONFIG_SEND_OPTIONAL_STRING(field)                                                         \
-  do {                                                                                             \
-    if (!config_send_string(file_descriptor, config->field, true))                                 \
-      return false;                                                                                \
-  } while (0);
-#define CONFIG_SEND_INTEGER(field)                                                                 \
-  do {                                                                                             \
-    if (!send_int(file_descriptor, config->field))                                                 \
-      return false;                                                                                \
-  } while (0);
-#define CONFIG_SEND_DATA(field)                                                                    \
-  do {                                                                                             \
-    if (!send_n_data(file_descriptor, &config->field, sizeof(config->field)))                      \
-      return false;                                                                                \
-  } while (0);
+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;
+}

 bool config_send(int file_descriptor, const Config* config) {
-  CONFIG_WIRE_FIELDS(CONFIG_SEND_VERSION, CONFIG_SEND_STRING, CONFIG_SEND_OPTIONAL_STRING,
-                     CONFIG_SEND_INTEGER, CONFIG_SEND_DATA)
+  if (!send_core_fields(file_descriptor, config) || !send_delta_fields(file_descriptor, config) ||
+      !send_file_options(file_descriptor, config) ||
+      !send_selection_options(file_descriptor, config) ||
+      !send_resume_options(file_descriptor, config))
+    return false;
  Status status;
  if (!receive_status(file_descriptor, &status))
    return false;
@@ -216,60 +335,26 @@ bool config_send(int file_descriptor, const Config* config) {
  return true;
 }

-#undef CONFIG_SEND_VERSION
-#undef CONFIG_SEND_STRING
-#undef CONFIG_SEND_OPTIONAL_STRING
-#undef CONFIG_SEND_INTEGER
-#undef CONFIG_SEND_DATA
-
-static bool config_receive_string(int file_descriptor, char** destination) {
-  char* value = receive_str(file_descriptor);
-  if (!value)
-    return false;
-  *destination = value;
-  return true;
-}
-
-#define CONFIG_RECEIVE_VERSION(field)                                                              \
-  do {                                                                                             \
-    free(config->field);                                                                           \
-    config->field = receive_str(file_descriptor);                                                  \
-    if (!config->field)                                                                            \
-      goto error;                                                                                  \
-    if (strcmp(config->field, PROTOCOL_VERSION) != 0) {                                            \
-      fprintf(stderr, "Protocol version mismatch: client=%s, server=%s\n", config->field,          \
-              PROTOCOL_VERSION);                                                                   \
-      config_delete(config);                                                                       \
-      send_status(file_descriptor, STATUS_ERROR);                                                  \
-      return NULL;                                                                                 \
-    }                                                                                              \
-  } while (0);
-#define CONFIG_RECEIVE_STRING(field)                                                               \
-  do {                                                                                             \
-    if (!config_receive_string(file_descriptor, &config->field))                                   \
-      goto error;                                                                                  \
-  } while (0);
-#define CONFIG_RECEIVE_OPTIONAL_STRING(field) CONFIG_RECEIVE_STRING(field)
-#define CONFIG_RECEIVE_INTEGER(field)                                                              \
-  do {                                                                                             \
-    if (!receive_int(file_descriptor, &tmp))                                                       \
-      goto error;                                                                                  \
-    config->field = tmp;                                                                           \
-  } while (0);
-#define CONFIG_RECEIVE_DATA(field)                                                                 \
-  do {                                                                                             \
-    if (!receive_n_data(file_descriptor, &config->field, sizeof(config->field)))                   \
-      goto error;                                                                                  \
-  } while (0);
-
 Config* config_receive(int file_descriptor) {
-  Config* config = (Config*)malloc(sizeof(Config));
-  if (config == NULL)
+  Config* config = config_create();
+  if (!config)
    return NULL;
-  config_set_defaults(config);
-  int tmp;
-  CONFIG_WIRE_FIELDS(CONFIG_RECEIVE_VERSION, CONFIG_RECEIVE_STRING, CONFIG_RECEIVE_OPTIONAL_STRING,
-                     CONFIG_RECEIVE_INTEGER, CONFIG_RECEIVE_DATA)
+  free(config->version);
+  config->version = receive_str(file_descriptor);
+  if (!config->version)
+    goto error;
+  if (strcmp(config->version, PROTOCOL_VERSION) != 0) {
+    fprintf(stderr, "Protocol version mismatch: client=%s, server=%s\n", config->version,
+            PROTOCOL_VERSION);
+    send_status(file_descriptor, STATUS_ERROR);
+    goto error;
+  }
+  if (!receive_core_fields(file_descriptor, config) ||
+      !receive_delta_fields(file_descriptor, config) ||
+      !receive_file_options(file_descriptor, config) ||
+      !receive_selection_options(file_descriptor, config) ||
+      !receive_resume_options(file_descriptor, config))
+    goto error;
  if (config->compress_choice[0] != '\0' && strcmp(config->compress_choice, "zstd") != 0 &&
      strcmp(config->compress_choice, "none") != 0) {
    fprintf(stderr, "Unsupported compression choice: %s\n", config->compress_choice);
@@ -284,9 +369,3 @@ error:
  config_delete(config);
  return NULL;
 }
-
-#undef CONFIG_RECEIVE_VERSION
-#undef CONFIG_RECEIVE_STRING
-#undef CONFIG_RECEIVE_OPTIONAL_STRING
-#undef CONFIG_RECEIVE_INTEGER
-#undef CONFIG_RECEIVE_DATA
@@ -128,53 +128,6 @@ typedef struct Config {
  char* compress_choice;
 } Config;

-/* Keep the on-wire field order in one place. The first three strings require
- * values when sent; optional strings are encoded as empty strings when NULL. */
-#define CONFIG_WIRE_FIELDS(VERSION, STRING, OPTIONAL_STRING, INTEGER, DATA)                        \
-  VERSION(version)                                                                                 \
-  STRING(send_directory)                                                                           \
-  STRING(receive_root_directory)                                                                   \
-  INTEGER(save_to_disk)                                                                            \
-  INTEGER(use_multithreading)                                                                      \
-  INTEGER(use_chunk_serialization)                                                                 \
-  INTEGER(use_compression)                                                                         \
-  INTEGER(use_metadata)                                                                            \
-  INTEGER(compression_level)                                                                       \
-  DATA(chunk_size)                                                                                 \
-  INTEGER(use_sendfile)                                                                            \
-  INTEGER(use_delete)                                                                              \
-  INTEGER(use_incremental)                                                                         \
-  INTEGER(use_delta)                                                                               \
-  DATA(delta_block_size)                                                                           \
-  DATA(delta_max_file_size)                                                                        \
-  INTEGER(backup)                                                                                  \
-  OPTIONAL_STRING(backup_dir)                                                                      \
-  INTEGER(follow_symlinks)                                                                         \
-  INTEGER(copy_links)                                                                              \
-  INTEGER(safe_links)                                                                              \
-  INTEGER(copy_unsafe_links)                                                                       \
-  INTEGER(preserve_hard_links)                                                                     \
-  INTEGER(preserve_acls)                                                                           \
-  INTEGER(preserve_xattrs)                                                                         \
-  INTEGER(preserve_devices)                                                                        \
-  INTEGER(preserve_sparse)                                                                         \
-  INTEGER(update)                                                                                  \
-  INTEGER(inplace)                                                                                 \
-  INTEGER(append)                                                                                  \
-  INTEGER(append_verify)                                                                           \
-  INTEGER(delete_excluded)                                                                         \
-  INTEGER(delete_after)                                                                            \
-  DATA(max_delete)                                                                                 \
-  INTEGER(relative)                                                                                \
-  INTEGER(prune_empty_dirs)                                                                        \
-  OPTIONAL_STRING(temp_dir)                                                                        \
-  INTEGER(partial)                                                                                 \
-  OPTIONAL_STRING(partial_dir)                                                                     \
-  OPTIONAL_STRING(suffix)                                                                          \
-  INTEGER(delete_before)                                                                           \
-  INTEGER(checksum)                                                                                \
-  OPTIONAL_STRING(compress_choice)
-
 #define PROTOCOL_VERSION "2.2.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)

@@ -19,6 +19,7 @@
 #include "config.h"
 #include "data.h"
 #include "file.h"
+#include "file_store.h"
 #include "metadata.h"
 #include "protocol.h"
 #include "utils.h"
@@ -153,17 +154,8 @@ 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);
-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) {
-  authorized_root_fd = fd;
-  free(authorized_root_path);
-  authorized_root_path = canonical_path ? str_dup(canonical_path) : NULL;
+  file_store_set_authorized_root(fd, canonical_path);
 }

 static bool path_is_within_root(const char* root, const char* path) {
@@ -280,7 +272,7 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
          mkdir_r(bdir);
          free(backup_dir_path);
        }
-        if (!rename_secure(disk_path, backup_path)) {
+        if (!file_store_rename_secure(disk_path, backup_path)) {
          free(backup_path);
          free(resolved_root);
          free(confined_backup);
@@ -335,8 +327,8 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
  free(resolved_dir);
  free(resolved_root);

-  bool ok = to_disk_secure(disk_path, file->data->data, file->data->size, inplace, sparse,
-                           file->metadata);
+  bool ok = file_store_write_secure(disk_path, file->data->data, file->data->size, inplace, sparse,
+                                    file->metadata);
  free(confined_backup);
  free(confined_partial);
  free(disk_path);
@@ -532,7 +524,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
  int old_fd = -1;
  if (full_path) {
    char* leaf = NULL;
-    int parent_fd = open_secure_parent(full_path, &leaf);
+    int parent_fd = file_store_open_secure_parent(full_path, &leaf);
    if (parent_fd >= 0) {
      old_fd = openat(parent_fd, leaf, O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
      free(leaf);
@@ -651,243 +643,11 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
  return file;
 }

-static int 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_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 (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);
-  int new_parent = 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;
-}
-
-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);
-  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 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;
+  return file_store_write_secure(path, data, data_size, inplace, sparse, NULL);
 }

 bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int compression_level,
@@ -0,0 +1,159 @@
+#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;
+}
@@ -0,0 +1,13 @@
+#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
@@ -1,4 +1,5 @@
 #include "multiprocessing.h"
+#include "receiver.h"

 #include "array_list.h"
 #include "chunk.h"
@@ -13,106 +14,6 @@
 #include <stdlib.h>
 #include <string.h>
 #include <threads.h>
-#include <sys/stat.h>
-
-static bool valid_batch_path(const char* path) {
-  return path && path[0] != '\0' && path[0] != '/' && !has_path_traversal(path);
-}
-
-static bool handle_batch_checks(int file_descriptor, const Config* config) {
-  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;
-    bool received = receive_n_data(file_descriptor, &check_size, sizeof(check_size)) &&
-                    receive_n_data(file_descriptor, &check_mtime, sizeof(check_mtime));
-    if (!received || !valid_batch_path(check_path)) {
-      free(check_path);
-      if (received)
-        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 receive_files_common(const Config* config, int file_descriptor, ReceivedFileHandler handler,
-                         void* context, bool send_completion_status) {
-  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;
-    } else if (status == STATUS_ABORT) {
-      log_message(LOG_LEVEL_INFO, "Received abort from client, cleaning up");
-      return -1;
-    } else if (status == STATUS_CHECK_BATCH) {
-      if (!handle_batch_checks(file_descriptor, config))
-        return -1;
-    } else {
-      if (status == STATUS_CHUNK) {
-        Chunk* chunk = receive_chunk_data(file_descriptor, config);
-        if (!chunk)
-          return -1;
-        for (int i = 0; i < chunk->element_count; i++) {
-          File* file = chunk->items[i];
-          chunk->items[i] = NULL;
-          if (!handler(file, context)) {
-            file_destroy(file);
-            chunk_destroy(chunk);
-            return -1;
-          }
-        }
-        chunk_destroy(chunk);
-      } else {
-        bool skipped = false;
-        File* file = status == STATUS_CHECK
-                         ? receive_incremental_check(file_descriptor, config, &skipped)
-                         : file_receive(config, file_descriptor);
-        if (!skipped) {
-          if (!file || !handler(file, context)) {
-            file_destroy(file);
-            if (status == STATUS_NEXT)
-              log_message(LOG_LEVEL_ERROR, "Failed to receive file");
-            return -1;
-          }
-        }
-      }
-    }
-    if (!receive_status(file_descriptor, &status))
-      return -1;
-  }
-  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");
-    if (send_completion_status)
-      send_status(file_descriptor, STATUS_ERROR);
-    return -1;
-  }
-  if (send_completion_status && !send_status(file_descriptor, STATUS_OK))
-    return -1;
-  return 0;
-}

 PipelineContextSender* pipeline_context_sender_create(Config* config, Queue* queue_scanner,
                                                      Queue* queue_loader) {
@@ -197,6 +98,8 @@ PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue*
  context->queue = queue;
  context->file_descriptor = file_descriptor;
  context->ssl = ssl;
+  protocol_session_init(&context->session, file_descriptor, file_descriptor);
+  protocol_session_set_ssl(&context->session, ssl);
  context->receiver_done = false;
  atomic_init(&context->cancelled, false);
  int init = 0;
@@ -233,37 +136,49 @@ void pipeline_context_receiver_destroy(PipelineContextReceiver* context) {
  free(context);
 }

-static bool enqueue_received_file(File* file, void* context) {
-  PipelineContextReceiver* receiver = context;
-  return queue_enqueue_multithreaded_cancel(receiver->queue, file, &receiver->mutex,
-                                            &receiver->condition_not_empty,
-                                            &receiver->condition_not_full, &receiver->cancelled);
+static bool receiver_enqueue_file(File* file, void* context_pointer) {
+  PipelineContextReceiver* context = context_pointer;
+  if (queue_enqueue_multithreaded_cancel(context->queue, file, &context->mutex,
+                                         &context->condition_not_empty,
+                                         &context->condition_not_full, &context->cancelled))
+    return true;
+  file_destroy(file);
+  return false;
+}
+
+static void receiver_thread_fail(PipelineContextReceiver* context) {
+  mtx_lock(&context->mutex);
+  atomic_store(&context->cancelled, true);
+  context->receiver_done = true;
+  cnd_broadcast(&context->condition_not_empty);
+  cnd_broadcast(&context->condition_not_full);
+  mtx_unlock(&context->mutex);
 }

 int receive_thread(void* pipeline_context) {
  PipelineContextReceiver* context = (PipelineContextReceiver*)pipeline_context;
-  if (context->ssl)
-    io_set_ssl(context->ssl);
+  protocol_session_bind(&context->session);
  mtx_lock(&context->mutex);
  int file_descriptor = context->file_descriptor;
  const Config* config = context->config;
  mtx_unlock(&context->mutex);

-  int result = receive_files_common(config, file_descriptor, enqueue_received_file, context, false);
+  ReceiverSink sink = {receiver_enqueue_file, context, false, false};
+  if (receiver_process((Config*)config, file_descriptor, &sink) != 0) {
+    receiver_thread_fail(context);
+    protocol_session_unbind();
+    return thrd_error;
+  }
  mtx_lock(&context->mutex);
-  if (result != 0)
-    atomic_store(&context->cancelled, true);
  context->receiver_done = true;
  cnd_signal(&context->condition_not_empty);
-  cnd_broadcast(&context->condition_not_full);
  mtx_unlock(&context->mutex);
-  return result == 0 ? thrd_success : thrd_error;
+  protocol_session_unbind();
+  return thrd_success;
 }

 int write_thread(void* pipeline_context) {
  PipelineContextReceiver* context = (PipelineContextReceiver*)pipeline_context;
-  if (context->ssl)
-    io_set_ssl(context->ssl);
  mtx_lock(&context->mutex);
  bool save_to_disk = context->config->save_to_disk;
  char* root_directory = str_dup(context->config->receive_root_directory);
@@ -35,6 +35,7 @@ typedef struct PipelineContextReceiver {
  Config* config;
  int file_descriptor;
  SSL* ssl;
+  ProtocolSession session;
  mtx_t mutex;
  cnd_t condition_not_full;
  cnd_t condition_not_empty;
@@ -42,11 +43,6 @@ typedef struct PipelineContextReceiver {
  atomic_bool cancelled;
 } PipelineContextReceiver;

-typedef bool (*ReceivedFileHandler)(File* file, void* context);
-
-int receive_files_common(const Config* config, int file_descriptor, ReceivedFileHandler handler,
-                         void* context, bool send_completion_status);
-
 PipelineContextSender* pipeline_context_sender_create(Config* config, Queue* queue_scanner,
                                                      Queue* queue_loader);
 void pipeline_context_sender_destroy(PipelineContextSender* context);
@@ -18,6 +18,7 @@
 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;
@@ -28,6 +29,7 @@ static once_flag bw_mutex_once = ONCE_FLAG_INIT;
 static __thread unsigned long long total_allocated_bytes = 0;

 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
@@ -36,6 +38,29 @@ 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);
 }
@@ -49,39 +74,51 @@ void io_set_bwlimit(unsigned long long bytes_per_sec) {
  mtx_unlock(&bw_mutex);
 }

-static void bw_throttle(size_t bytes_written) {
-  if (io_bwlimit == 0)
+void protocol_session_set_bwlimit(ProtocolSession* session, unsigned long long bytes_per_sec) {
+  if (!session)
+    return;
+  session->bwlimit = bytes_per_sec;
+  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)
    return;
-  call_once(&bw_mutex_once, bw_mutex_init);
-  mtx_lock(&bw_mutex);

  struct timespec now;
  clock_gettime(CLOCK_MONOTONIC, &now);

-  long long elapsed_ns =
-      (now.tv_sec - bw_last_refill.tv_sec) * 1000000000LL + (now.tv_nsec - bw_last_refill.tv_nsec);
-  bw_last_refill = now;
+  long long elapsed_ns = (now.tv_sec - session->bw_last_refill_sec) * 1000000000LL +
+                         (now.tv_nsec - session->bw_last_refill_nsec);
+  session->bw_last_refill_sec = now.tv_sec;
+  session->bw_last_refill_nsec = now.tv_nsec;

-  long long tokens_to_add = (long long)((double)io_bwlimit * elapsed_ns / 1000000000.0);
-  bw_tokens += tokens_to_add;
-  if (bw_tokens > (long long)io_bwlimit)
-    bw_tokens = (long long)io_bwlimit;
+  long long tokens_to_add = (long long)((double)session->bwlimit * elapsed_ns / 1000000000.0);
+  session->bw_tokens += tokens_to_add;
+  if (session->bw_tokens > (long long)session->bwlimit)
+    session->bw_tokens = (long long)session->bwlimit;

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

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

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

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

-static int io_fd(int dir_fd, int file_descriptor) {
-  return (dir_fd != -1) ? dir_fd : file_descriptor;
+static ProtocolSession* legacy_session(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 deadline_remaining_ms(const struct timespec* deadline) {
@@ -104,9 +165,11 @@ static int deadline_remaining_ms(const struct timespec* deadline) {
  return ms > INT_MAX ? INT_MAX : (int)ms;
 }

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

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

  struct timespec deadline;
  clock_gettime(CLOCK_MONOTONIC, &deadline);
@@ -176,15 +241,15 @@ bool receive_n_data(int file_descriptor, void* data, size_t data_size) {
      return false;

    ssize_t bytes_received;
-    if (io_ssl)
-      bytes_received =
-          SSL_read(io_ssl, (char*)data + total_bytes_received, data_size - total_bytes_received);
+    if (session->ssl)
+      bytes_received = SSL_read(session->ssl, (char*)data + total_bytes_received,
+                                data_size - total_bytes_received);
    else
      bytes_received =
          read(fd, (char*)data + total_bytes_received, data_size - total_bytes_received);
    if (bytes_received <= 0) {
-      if (io_ssl) {
-        int ssl_err = SSL_get_error(io_ssl, (int)bytes_received);
+      if (session->ssl) {
+        int ssl_err = SSL_get_error(session->ssl, (int)bytes_received);
        if (ssl_err == SSL_ERROR_WANT_WRITE || ssl_err == SSL_ERROR_WANT_READ) {
          wait_events = ssl_err == SSL_ERROR_WANT_WRITE ? POLLOUT : POLLIN;
          continue;
@@ -231,24 +296,24 @@ static const char* status_to_string(Status status) {
  }
 }

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

-char* receive_str(int file_descriptor) {
+char* protocol_receive_str(ProtocolSession* session) {
  size_t size;
-  if (!receive_n_data(file_descriptor, &size, sizeof(size_t)))
+  if (!protocol_receive_n_data(session, &size, sizeof(size_t)))
    return NULL;
  if (size > MAX_STRING_SIZE || size > SIZE_MAX - 1 ||
-      size + 1 > MAX_CONNECTION_MEMORY - total_allocated_bytes) {
+      size + 1 > MAX_CONNECTION_MEMORY - session->total_allocated_bytes) {
    log_message(LOG_LEVEL_ERROR, "String size %zu exceeds maximum %llu", size,
                (unsigned long long)MAX_STRING_SIZE);
    return NULL;
@@ -256,29 +321,29 @@ char* receive_str(int file_descriptor) {
  char* data = (char*)malloc(size + 1);
  if (data == NULL)
    return NULL;
-  if (!receive_n_data(file_descriptor, data, size)) {
+  if (!protocol_receive_n_data(session, data, size)) {
    free(data);
    return NULL;
  }
  data[size] = '\0';
-  total_allocated_bytes += size + 1;
+  session->total_allocated_bytes += size + 1;
  log_message(LOG_LEVEL_DEBUG, "Received String: %s", data);
  return data;
 }

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

-Data* receive_data(int file_descriptor) {
+Data* protocol_receive_data(ProtocolSession* session) {
  unsigned long long size = 0;
-  if (!receive_n_data(file_descriptor, &size, sizeof(unsigned long long)))
+  if (!protocol_receive_n_data(session, &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,
@@ -286,53 +351,86 @@ Data* receive_data(int file_descriptor) {
    return NULL;
  }
  size_t allocation_size = size == 0 ? 1 : (size_t)size;
-  if (allocation_size > MAX_CONNECTION_MEMORY - total_allocated_bytes) {
+  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)total_allocated_bytes, size,
+                (unsigned long long)session->total_allocated_bytes, size,
                (unsigned long long)MAX_CONNECTION_MEMORY);
    return NULL;
  }
  void* data = malloc(allocation_size);
  if (data == NULL)
    return NULL;
-  if (!receive_n_data(file_descriptor, data, (size_t)size)) {
+  if (!protocol_receive_n_data(session, data, (size_t)size)) {
    free(data);
    return NULL;
  }
-  total_allocated_bytes += allocation_size;
+  session->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);
-    total_allocated_bytes -= allocation_size;
+    session->total_allocated_bytes -= allocation_size;
  }
  return result;
 }

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

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

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

-bool receive_status(int file_descriptor, Status* status) {
-  if (!receive_n_data(file_descriptor, status, sizeof(Status)))
+bool protocol_receive_status(ProtocolSession* session, Status* status) {
+  if (!protocol_receive_n_data(session, status, sizeof(Status)))
    return false;
  log_message(LOG_LEVEL_DEBUG, "Received Status: %s", status_to_string(*status));
  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);
+}
@@ -19,6 +19,23 @@

 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,
@@ -39,6 +56,23 @@ 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, const char* host, int port) {
+bool tcp_connect_socket(Client* client, char* host, int port) {
  struct addrinfo hints;
  struct addrinfo* result;
  memset(&hints, 0, sizeof(hints));
@@ -222,12 +222,14 @@ bool tcp_connect_socket(Client* client, const char* host, int port) {
    return false;
  }

-  tcp_apply_socket_timeout(client->file_descriptor);
  return true;
 }

 bool client_connect(Client* client, char* host, int port) {
-  return tcp_connect_socket(client, host, port);
+  if (!tcp_connect_socket(client, host, port))
+    return false;
+  tcp_apply_socket_timeout(client->file_descriptor);
+  return true;
 }

 void client_disconnect(Client* client) {
@@ -29,8 +29,8 @@ void server_accept_loop(Server* server, void (*child_fn)(int, void*), void* chil
                        const char* log_fmt);
 void server_delete(Server** server);
 Client* client_create();
-bool tcp_connect_socket(Client* client, const char* host, int port);
 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);
@@ -2,14 +2,13 @@
 #include "log.h"
 #include "protocol.h"
 #include "transport_tcp.h"
+#include <arpa/inet.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/wait.h>
 #include <unistd.h>

 bool tls_global_init(void) {
@@ -237,6 +237,10 @@ bool has_path_traversal(const char* path) {
  return false;
 }

+bool utils_valid_batch_path(const char* path) {
+  return path && path[0] != '\0' && path[0] != '/' && !has_path_traversal(path);
+}
+
 char* path_cat(const char* path1, const char* path2) {
  if (path1 == NULL || *path1 == '\0')
    return str_dup(path2);
@@ -11,5 +11,6 @@ bool glob_match(const char* pattern, const char* str);
 bool delete_extras(const char* dest_root, ArrayList* manifest);
 void utils_set_authorized_root_fd(int fd);
 bool has_path_traversal(const char* path);
+bool utils_valid_batch_path(const char* path);

 #endif
@@ -1,4 +1,5 @@
 #include "test_client_cli.h"
+#include "client_validation.h"
 #include "config.h"
 #include "test_utils.h"
 #include "utils.h"
@@ -9,6 +10,56 @@
 /* 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.
@@ -256,8 +307,8 @@ static void test_parse_args_rejects_unimplemented_options() {
                                        "--ipv4",
                                        "--daemon",
                                        "--config",
-                                         "--server",
-                                         "--compress-choice"};
+                                        "--server",
+                                        "--compress-choice"};

  for (size_t i = 0; i < sizeof(options) / sizeof(options[0]); i++) {
    Config* cfg = config_create();
@@ -287,6 +338,10 @@ 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();
@@ -224,6 +224,26 @@ 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"));
@@ -256,6 +276,7 @@ void test_config() {
  if (!is_running_under_valgrind()) {
    test_config_send_receive();
    test_config_send_receive_version_mismatch();
+    test_config_receive_truncated();
  }
  test_is_remote_dest();
 }
@@ -38,6 +38,23 @@ static void test_send_receive_n_data_zero() {
  close(p[1]);
 }

+static void test_explicit_session_context() {
+  int p[2];
+  EXPECT_EQ_INT(pipe(p), 0);
+  ProtocolSession session;
+  protocol_session_init(&session, p[0], p[1]);
+  protocol_session_set_bwlimit(&session, 0);
+
+  const char payload[] = "explicit context";
+  char received[sizeof(payload)] = {0};
+  EXPECT_TRUE(protocol_send_n_data(&session, payload, sizeof(payload)));
+  EXPECT_TRUE(protocol_receive_n_data(&session, received, sizeof(received)));
+  EXPECT_EQ_INT(memcmp(payload, received, sizeof(payload)), 0);
+
+  close(p[0]);
+  close(p[1]);
+}
+
 static void test_send_receive_str() {
  int p[2];
  EXPECT_EQ_INT(pipe(p), 0);
@@ -173,6 +190,7 @@ 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();
@@ -11,11 +11,7 @@
 #include <sys/wait.h>
 #include <unistd.h>

-/* Include server.c but rename main to avoid conflict with test runner's main */
-#define main server_main_
-#define FASTSYNC_SERVER_AS_LIB
-#include "server.c"
-#undef main
+#include "receiver.h"

 /* Test receive_files with immediate FINISHED status */
 static void test_receive_files_finished() {
@@ -36,7 +32,7 @@ static void test_receive_files_finished() {
    /* Child: use p[0] for both read and write */
    close(p[1]);
    io_set_fds(p[0], p[0]);
-    int ret = receive_files(cfg, p[0]);
+    int ret = receiver_receive_files(cfg, p[0]);
    close(p[0]);
    config_delete(cfg);
    _exit(ret == 0 ? 0 : 1);
@@ -88,7 +84,7 @@ static void test_receive_files_single_file() {
    /* Child: use p[0] for both read and write */
    close(p[1]);
    io_set_fds(p[0], p[0]);
-    int ret = receive_files(cfg, p[0]);
+    int ret = receiver_receive_files(cfg, p[0]);
    close(p[0]);
    config_delete(cfg);
    _exit(ret == 0 ? 0 : 1);
@@ -149,7 +145,7 @@ static void test_receive_files_abort() {
  if (pid == 0) {
    close(p[1]);
    io_set_fds(p[0], p[0]);
-    int ret = receive_files(cfg, p[0]);
+    int ret = receiver_receive_files(cfg, p[0]);
    close(p[0]);
    config_delete(cfg);
    /* Should return -1 on abort */
Author	SHA1	Message	Date
TapTap	c220dc0739	docs: clarify rsync compatibility roadmap CI / lint (pull_request) Successful in 30s 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 17s Details CI / coverage (pull_request) Successful in 32s Details CI / build-and-test (pull_request) Successful in 1m15s Details CI / valgrind (pull_request) Successful in 34s Details	2026-08-15 12:49:07 +02:00
TapTap	298976aefb	fix: link receiver into fuzz targets CI / lint (pull_request) Successful in 29s Details CI / sanitizers (address) (pull_request) Successful in 37s Details CI / sanitizers (undefined) (pull_request) Successful in 36s Details CI / fuzz-build (pull_request) Successful in 16s 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 33s Details	2026-08-15 12:34:19 +02:00
TapTap	3b7f97853c	fix: satisfy cppcheck const analysis CI / lint (pull_request) Successful in 31s Details CI / sanitizers (address) (pull_request) Successful in 38s Details CI / sanitizers (undefined) (pull_request) Successful in 37s Details CI / fuzz-build (pull_request) Failing after 14s Details CI / coverage (pull_request) Successful in 32s Details CI / build-and-test (pull_request) Successful in 1m15s Details CI / valgrind (pull_request) Successful in 33s Details	2026-08-15 12:30:52 +02:00
TapTap	8cca891b9a	refactor: split transfer and protocol responsibilities CI / lint (pull_request) Failing after 30s Details CI / build-and-test (pull_request) Has been skipped Details CI / sanitizers (address) (pull_request) Has been skipped Details CI / sanitizers (undefined) (pull_request) Has been skipped Details CI / fuzz-build (pull_request) Has been skipped Details CI / coverage (pull_request) Has been skipped Details CI / valgrind (pull_request) Has been skipped Details	2026-08-15 12:27:18 +02:00
TapTap	786e686563	fix: satisfy clang-format in CLI test 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 14s Details CI / coverage (pull_request) Successful in 31s Details CI / build-and-test (pull_request) Successful in 1m16s Details CI / valgrind (pull_request) Successful in 33s Details	2026-08-15 11:52:05 +02:00