feat: add rsync-compatible size-only option

src/client/client_cli.c

@@ -139,6 +139,7 @@ static const OptionEntry OPTION_TABLE[] = {
     {"--dry-run", "-n", OPT_FLAG, offsetof(Config, dry_run)},
     {"--delete", NULL, OPT_FLAG, offsetof(Config, use_delete)},
     {"--incremental", NULL, OPT_FLAG, offsetof(Config, use_incremental)},
+    {"--size-only", NULL, OPT_FLAG, offsetof(Config, size_only)},
     {"--delta", NULL, OPT_FLAG, offsetof(Config, use_delta)},
     {"--save-to-disk", NULL, OPT_FLAG, offsetof(Config, save_to_disk)},
     {"--progress", NULL, OPT_FLAG, offsetof(Config, show_progress)},

src/client/usage.c

@@ -28,6 +28,7 @@ void print_usage(void) {
   printf("  --max-size <n>      Skip files larger than n bytes\n");
   printf("  --min-size <n>      Skip files smaller than n bytes\n");
   printf("  --incremental       Skip files unchanged since last transfer\n");
+  printf("  --size-only         Skip incremental files matching in size, ignoring mtime\n");
   printf("  --delta             Delta transfer for changed files (requires --incremental)\n");
   printf("  --delta-block <n>   Delta block size in bytes (default: %d)\n",
          DELTA_BLOCK_SIZE_DEFAULT);

src/server/receiver.c

@@ -61,7 +61,7 @@ static bool receiver_process_batch(Config* config, int file_descriptor) {
     struct stat st;
     bool has_old = file_stat_secure(full_path, &st);
     bool match = has_old && (unsigned long long)st.st_size == check_size &&
-                 (long long)st.st_mtime == check_mtime;
+                 (config->size_only || (long long)st.st_mtime == check_mtime);
     bool sent = send_status(file_descriptor, match ? STATUS_OK : STATUS_NEXT);
     free(full_path);
     free(check_path);

src/server/server.c

@@ -175,7 +175,7 @@ int receive_files(Config* config, int fd) {
         }
         bool has_old = full_path && file_stat_secure(full_path, &st);
         bool match = has_old && (unsigned long long)st.st_size == check_size &&
-                     (long long)st.st_mtime == check_mtime;
+                     (config->size_only || (long long)st.st_mtime == check_mtime);
         bool sent = send_status(fd, match ? STATUS_OK : STATUS_NEXT);
         free(full_path);
         free(check_path);

src/shared/config.c

@@ -34,6 +34,7 @@ static void config_set_defaults(Config* config) {
   config->max_size = 0;
   config->min_size = 0;
   config->use_incremental = false;
+  config->size_only = false;
   config->use_delta = false;
   config->delta_block_size = DELTA_BLOCK_SIZE_DEFAULT;
   config->delta_max_file_size = DELTA_MAX_FILE_SIZE;
@@ -117,10 +118,10 @@ static bool validate_received_config(const Config* config) {
          valid_wire_bool(config->use_chunk_serialization) &&
          valid_wire_bool(config->use_compression) && valid_wire_bool(config->use_metadata) &&
          valid_wire_bool(config->use_sendfile) && valid_wire_bool(config->use_delete) &&
-         valid_wire_bool(config->use_incremental) && valid_wire_bool(config->use_delta) &&
-         valid_wire_bool(config->backup) && valid_wire_bool(config->follow_symlinks) &&
-         valid_wire_bool(config->copy_links) && valid_wire_bool(config->safe_links) &&
-         valid_wire_bool(config->copy_unsafe_links) &&
+         valid_wire_bool(config->use_incremental) && valid_wire_bool(config->size_only) &&
+         valid_wire_bool(config->use_delta) && valid_wire_bool(config->backup) &&
+         valid_wire_bool(config->follow_symlinks) && valid_wire_bool(config->copy_links) &&
+         valid_wire_bool(config->safe_links) && valid_wire_bool(config->copy_unsafe_links) &&
          valid_wire_bool(config->preserve_hard_links) && valid_wire_bool(config->preserve_acls) &&
          valid_wire_bool(config->preserve_xattrs) && valid_wire_bool(config->preserve_devices) &&
          valid_wire_bool(config->preserve_sparse) && valid_wire_bool(config->update) &&
@@ -228,7 +229,7 @@ static bool send_core_fields(int fd, const Config* c) {
 
 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_int(fd, c->size_only) && 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));
 }
@@ -281,6 +282,8 @@ static bool receive_delta_fields(int fd, Config* c) {
     return false;
   if (!receive_wire_bool(fd, &c->use_incremental))
     return false;
+  if (!receive_wire_bool(fd, &c->size_only))
+    return false;
   if (!receive_wire_bool(fd, &c->use_delta))
     return false;
   return receive_n_data(fd, &c->delta_block_size, sizeof(c->delta_block_size)) &&

src/shared/config.h

@@ -34,6 +34,7 @@ typedef struct Config {
   unsigned long long max_size;
   unsigned long long min_size;
   bool use_incremental;
+  bool size_only;
   bool use_delta;
   uint32_t delta_block_size;
   unsigned long long delta_max_file_size;

src/shared/file_receive.c

@@ -383,7 +383,7 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
     match = (old_size == 0 || old_data) && old_checksum == check_checksum;
     free(old_data);
     old_data = NULL;
-  } else if (match) {
+  } else if (match && !config->size_only) {
     match = (long long)st.st_mtime == check_mtime;
   }