feat: add rsync-compatible fsync

RSYNC_COMPAT.md

@@ -229,7 +229,7 @@ This document maps rsync's full feature set to FastSync's current implementation
 |------|-------------------|-----------------|-------|
 | `--stop-after=MINS` | Stop after N minutes | ❌ Not Implemented | |
 | `--stop-at=TIME` | Stop at specified time | ❌ Not Implemented | |
-| `--fsync` | Fsync every written file | ❌ Not Implemented | |
+| `--fsync` | Fsync every written file before publication | ✅ Implemented | |
 | `--protocol=NUM` | Force older protocol version | ❌ Not Implemented | |
 | `--iconv=CONVERT_SPEC` | Charset conversion | ❌ Not Implemented | |
 | `--checksum-seed=NUM` | Set checksum seed | ❌ Not Implemented | |

src/client/client_cli.c

@@ -152,6 +152,7 @@ static const OptionEntry OPTION_TABLE[] = {
     {"--copy-unsafe-links", NULL, OPT_FLAG, offsetof(Config, copy_unsafe_links)},
     {"--sparse", "-S", OPT_FLAG, offsetof(Config, preserve_sparse)},
     {"--inplace", NULL, OPT_FLAG, offsetof(Config, inplace)},
+    {"--fsync", NULL, OPT_FLAG, offsetof(Config, use_fsync)},
     {"--checksum", NULL, OPT_FLAG, offsetof(Config, checksum)},
 
     {"--source-dir", NULL, OPT_STRING, offsetof(Config, send_directory)},

src/client/usage.c

@@ -68,6 +68,7 @@ void print_usage(void) {
   printf("  --copy-unsafe-links  Only transform unsafe symlinks into referent files\n");
   printf("  -S, --sparse        Handle sparse files efficiently\n");
   printf("  --inplace           Update files in-place (no temp+rename)\n");
+  printf("  --fsync             Fsync every written file before publication\n");
   printf("  --compress-level <n>    Compression level (default: 5)\n");
   printf("  --help              Show this help\n");
   printf("  -V, --version       Show version\n");

src/shared/config.c

@@ -70,6 +70,7 @@ static void config_set_defaults(Config* config) {
   config->human_readable = false;
   config->update = false;
   config->inplace = false;
+  config->use_fsync = false;
   config->append = false;
   config->append_verify = false;
   config->delete_excluded = false;
@@ -125,10 +126,11 @@ static bool validate_received_config(const Config* config) {
          valid_wire_bool(config->preserve_xattrs) && valid_wire_bool(config->preserve_devices) &&
          valid_wire_bool(config->preserve_sparse) && valid_wire_bool(config->update) &&
          valid_wire_bool(config->inplace) && valid_wire_bool(config->append) &&
-         valid_wire_bool(config->append_verify) && valid_wire_bool(config->delete_excluded) &&
+         valid_wire_bool(config->use_fsync) && valid_wire_bool(config->append_verify) &&
-         valid_wire_bool(config->delete_after) && valid_wire_bool(config->relative) &&
+         valid_wire_bool(config->delete_excluded) && valid_wire_bool(config->delete_after) &&
-         valid_wire_bool(config->prune_empty_dirs) && valid_wire_bool(config->partial) &&
+         valid_wire_bool(config->relative) && valid_wire_bool(config->prune_empty_dirs) &&
-         valid_wire_bool(config->delete_before) && valid_wire_bool(config->checksum) &&
+         valid_wire_bool(config->partial) && valid_wire_bool(config->delete_before) &&
+         valid_wire_bool(config->checksum) &&
          (!config->use_compression ||
           (config->compression_level >= 1 && config->compression_level <= 22)) &&
          config->chunk_size > 0 && config->chunk_size <= MAX_CHUNK_SIZE &&
@@ -244,9 +246,10 @@ static bool send_file_options(int fd, const Config* c) {
 
 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->use_fsync) && send_int(fd, c->append_verify) &&
-         send_int(fd, c->delete_after) && send_n_data(fd, &c->max_delete, sizeof(c->max_delete)) &&
+         send_int(fd, c->delete_excluded) && send_int(fd, c->delete_after) &&
-         send_int(fd, c->relative) && send_int(fd, c->prune_empty_dirs);
+         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) {
@@ -304,7 +307,7 @@ static bool receive_file_options(int fd, Config* c) {
 }
 
 static bool receive_selection_options(int fd, Config* c) {
-  bool* flags[] = {&c->update,        &c->inplace,         &c->append,
+  bool* flags[] = {&c->update,        &c->inplace,         &c->append,      &c->use_fsync,
                    &c->append_verify, &c->delete_excluded, &c->delete_after};
   for (size_t i = 0; i < sizeof(flags) / sizeof(flags[0]); i++) {
     if (!receive_wire_bool(fd, flags[i]))

src/shared/config.h

@@ -78,6 +78,7 @@ typedef struct Config {
   // Issue #127: Transfer modes
   bool update;
   bool inplace;
+  bool use_fsync;
   bool append;
   bool append_verify;
 
@@ -128,7 +129,7 @@ typedef struct Config {
   char* compress_choice;
 } Config;
 
-#define PROTOCOL_VERSION "2.2.0"
+#define PROTOCOL_VERSION "2.3.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)
 
 Config* config_create(void);

src/shared/file.c

@@ -302,8 +302,9 @@ bool file_rename_secure(const char* old_path, const char* new_path) {
   return ok;
 }
 
-bool file_to_disk_secure(const char* path, const void* data, unsigned long long data_size,
+bool file_to_disk_secure_with_fsync(const char* path, const void* data,
-                         bool inplace, bool sparse, const FileMetadata* metadata) {
+                                    unsigned long long data_size, bool inplace, bool sparse,
+                                    const FileMetadata* metadata, bool use_fsync) {
   char* leaf = NULL;
   int dirfd = file_open_secure_parent(path, &leaf, true);
   if (dirfd < 0)
@@ -317,6 +318,8 @@ bool file_to_disk_secure(const char* path, const void* data, unsigned long long
         ok = write_all(fd, data, data_size);
       if (ok && metadata)
         ok = file_restore_metadata_fd(fd, metadata);
+      if (ok && use_fsync)
+        ok = fsync(fd) == 0;
     }
   } else {
     char tmp[NAME_MAX];
@@ -331,6 +334,8 @@ bool file_to_disk_secure(const char* path, const void* data, unsigned long long
         ok = write_all(fd, data, data_size);
       if (ok && metadata)
         ok = file_restore_metadata_fd(fd, metadata);
+      if (ok && use_fsync)
+        ok = fsync(fd) == 0;
       if (close(fd) != 0)
         ok = false;
       fd = -1;
@@ -347,6 +352,11 @@ bool file_to_disk_secure(const char* path, const void* data, unsigned long long
   return ok;
 }
 
+bool file_to_disk_secure(const char* path, const void* data, unsigned long long data_size,
+                         bool inplace, bool sparse, const FileMetadata* metadata) {
+  return file_to_disk_secure_with_fsync(path, data, data_size, inplace, sparse, metadata, false);
+}
+
 bool file_write_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))

src/shared/file.h

@@ -32,5 +32,8 @@ bool file_ensure_directory_secure(const char* path);
 bool file_rename_secure(const char* old_path, const char* new_path);
 bool file_to_disk_secure(const char* path, const void* data, unsigned long long data_size,
                          bool inplace, bool sparse, const FileMetadata* metadata);
+bool file_to_disk_secure_with_fsync(const char* path, const void* data,
+                                    unsigned long long data_size, bool inplace, bool sparse,
+                                    const FileMetadata* metadata, bool use_fsync);
 
 #endif

src/shared/file_receive.c

@@ -103,8 +103,8 @@ bool file_save_to_disk(const char* root_directory, const File* file, const Confi
     }
   }
 
-  bool ok = file_to_disk_secure(disk_path, file->data->data, file->data->size, inplace, sparse,
+  bool ok = file_to_disk_secure_with_fsync(disk_path, file->data->data, file->data->size, inplace,
-                                file->metadata);
+                                           sparse, file->metadata, config && config->use_fsync);
   free(parent_copy);
   free(backup_path);
   free(confined_backup);

tests/test_client_cli.c

@@ -339,6 +339,17 @@ static void test_parse_args_archive() {
   config_delete(cfg);
 }
 
+static void test_parse_args_fsync() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--fsync", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->use_fsync);
+  config_delete(cfg);
+}
+
 void test_client_cli() {
   test_validate_config_required_paths();
   test_validate_config_incompatible_options();
@@ -360,4 +371,5 @@ void test_client_cli() {
   test_parse_args_unknown_option();
   test_parse_args_rejects_unimplemented_options();
   test_parse_args_archive();
+  test_parse_args_fsync();
 }

tests/test_config.c

@@ -124,6 +124,7 @@ static void test_config_send_receive() {
   send_cfg->use_chunk_serialization = true;
   send_cfg->use_compression = true;
   send_cfg->use_metadata = true;
+  send_cfg->use_fsync = true;
   send_cfg->compression_level = 5;
   send_cfg->chunk_size = 1024;
 
@@ -160,6 +161,8 @@ static void test_config_send_receive() {
         ok = false;
       if (recv_cfg->chunk_size != 1024)
         ok = false;
+      if (!recv_cfg->use_fsync)
+        ok = false;
     }
     config_delete(recv_cfg);
     close(p[0]);

tests/test_file.c

@@ -108,6 +108,17 @@ static void test_file_write_to_disk_basic() {
   unlink("test_file_write_to_disk_basic.txt");
 }
 
+static void test_file_write_to_disk_with_fsync() {
+  const char* path = "test_file_write_to_disk_fsync.txt";
+  const char* content = "fsync file content";
+  EXPECT_TRUE(
+      file_to_disk_secure_with_fsync(path, content, strlen(content), false, false, NULL, true));
+  struct stat st;
+  EXPECT_EQ_INT(stat(path, &st), 0);
+  EXPECT_EQ_INT((int)st.st_size, (int)strlen(content));
+  unlink(path);
+}
+
 static void test_file_write_to_disk_creates_dirs() {
   const char* content = "Nested dir test";
   EXPECT_TRUE(file_write_to_disk("test_nested_tmp/nested/file.txt", content, strlen(content), false,
@@ -459,6 +470,7 @@ void test_file() {
   test_file_load_data_missing_file();
   test_file_save_to_disk();
   test_file_write_to_disk_basic();
+  test_file_write_to_disk_with_fsync();
   test_file_write_to_disk_creates_dirs();
   test_file_write_to_disk_does_not_follow_symlink();
   test_file_content_to_buffer();