feat: add skip-compress option

RSYNC_COMPAT.md

@@ -174,7 +174,7 @@ This document maps rsync's full feature set to FastSync's current implementation
 | `--compress-choice=STR` | Choose compression algorithm | ❌ Not Implemented | Removed because it had no effect; FastSync always uses zstd |
 | `--compress-level=NUM` | Set compression level | ✅ Implemented | 1-22, default 5 |
 | `--compress-threads=NUM` | Set compression threads | ❌ Not Implemented | |
-| `--skip-compress=LIST` | Skip compress for suffixes | ❌ Not Implemented | Internal skip for hardcoded types; not user-configurable |
+| `--skip-compress=LIST` | Skip compress for suffixes | ✅ Implemented | Comma-separated, case-insensitive suffix list; empty list skips none |
 
 ## 13. Connectivity
 

src/client/client_cli.c

@@ -119,6 +119,29 @@ static int config_add_pattern(char*** patterns, int* count, const char* value,
   return 0;
 }
 
+static int parse_skip_compress(Config* config, const char* value) {
+  char* list = str_dup(value);
+  if (!list)
+    return -1;
+  config->skip_compress_set = true;
+  for (char* token = strtok(list, ","); token; token = strtok(NULL, ",")) {
+    while (*token == ' ' || *token == '\t')
+      token++;
+    size_t len = strlen(token);
+    while (len > 0 && (token[len - 1] == ' ' || token[len - 1] == '\t'))
+      token[--len] = '\0';
+    if (len == 0)
+      continue;
+    if (config_add_pattern(&config->skip_compress_suffixes, &config->skip_compress_count, token,
+                           "--skip-compress") != 0) {
+      free(list);
+      return -1;
+    }
+  }
+  free(list);
+  return 0;
+}
+
 typedef enum {
   OPT_FLAG,
   OPT_STRING,
@@ -361,6 +384,12 @@ int parse_args(Config* config, int argc, char* argv[], int* positional_args,
         log_message(LOG_LEVEL_ERROR, "--compress-level must be between 1 and 22");
         return -1;
       }
+    } else if (strncmp(argv[i], "--skip-compress=", 16) == 0) {
+      if (parse_skip_compress(config, argv[i] + 16) != 0)
+        return -1;
+    } else if (opt_is(argv[i], "--skip-compress", NULL) && i + 1 < argc) {
+      if (parse_skip_compress(config, argv[++i]) != 0)
+        return -1;
     } else if (argv[i][0] == '-') {
       fprintf(stderr, "Unknown option: %s\n", argv[i]);
       print_usage();

src/client/client_send.c

@@ -234,7 +234,9 @@ static int send_delta(Client* client, File* file, DeltaSignature* sig, Config* c
     return send_status(client->file_descriptor, STATUS_NEXT) ? 1 : -1;
 
   Data* to_send = delta_data;
-  if (config->use_compression) {
+  int skip_count = config->skip_compress_set ? config->skip_compress_count : -1;
+  if (config->use_compression && !compression_should_skip_with_suffixes(
+                                     file->path, config->skip_compress_suffixes, skip_count)) {
     to_send = data_compress(delta_data, config->compression_level);
     data_destroy(delta_data);
     if (!to_send)
@@ -251,20 +253,23 @@ static int send_delta(Client* client, File* file, DeltaSignature* sig, Config* c
   return ok ? 0 : -1;
 }
 
-typedef bool (*file_send_fn)(File*, int, bool, int, bool);
-
 // Send a single file directly (non-incremental path).
-static bool send_file_direct(File* file, int fd, bool use_metadata, int compression_level) {
+static bool send_file_direct(File* file, int fd, bool use_metadata, int compression_level,
+                             const Config* config) {
   if (!send_status(fd, STATUS_NEXT))
     return false;
-  return file_send_single_calls(file, fd, use_metadata, compression_level, true);
+  int skip_count = config->skip_compress_set ? config->skip_compress_count : -1;
+  return file_send_single_calls_with_skip(file, fd, use_metadata, compression_level, true,
+                                          config->skip_compress_suffixes, skip_count);
 }
 
 // Send a single file directly via sendfile (non-incremental path).
-static bool send_file_direct_sendfile(File* file, int fd, bool use_metadata) {
+static bool send_file_direct_sendfile(File* file, int fd, bool use_metadata, const Config* config) {
   if (!send_status(fd, STATUS_NEXT))
     return false;
-  return file_send_sendfile(file, fd, use_metadata, 0, true);
+  int skip_count = config->skip_compress_set ? config->skip_compress_count : -1;
+  return file_send_sendfile_with_skip(file, fd, use_metadata, 0, true,
+                                      config->skip_compress_suffixes, skip_count);
 }
 
 // Process one file in a chunk: either via incremental check or direct send.
@@ -275,10 +280,12 @@ static int send_single_file(Client* client, File* file, Config* config, bool use
 
   if (!use_incremental) {
     if (use_sendfile) {
-      return send_file_direct_sendfile(file, client->file_descriptor, config->use_metadata) ? 0
+      return send_file_direct_sendfile(file, client->file_descriptor, config->use_metadata, config)
+                 ? 0
                  : -1;
     }
-    return send_file_direct(file, client->file_descriptor, config->use_metadata, compression_level)
+    return send_file_direct(file, client->file_descriptor, config->use_metadata, compression_level,
+                            config)
                ? 0
                : -1;
   }
@@ -304,13 +311,14 @@ static int send_single_file(Client* client, File* file, Config* config, bool use
         return -1;
     }
     // Fall through: send full file via sendfile (pass 0 for compression_level)
-    if (!file_send_sendfile(file, client->file_descriptor, config->use_metadata, 0, false))
+    int skip_count = config->skip_compress_set ? config->skip_compress_count : -1;
+    if (!file_send_sendfile_with_skip(file, client->file_descriptor, config->use_metadata, 0, false,
+                                      config->skip_compress_suffixes, skip_count))
       return -1;
     return 0;
   }
 
   // Incremental path with single_calls (supports compression and delta)
-  file_send_fn send_fn = (file_send_fn)file_send_single_calls;
   DeltaSignature* sig = NULL;
   int rc = incremental_check(client, file, config, &sig);
   if (rc < 0) {
@@ -338,7 +346,10 @@ static int send_single_file(Client* client, File* file, Config* config, bool use
         return -1;
     }
   }
-  if (!send_fn(file, client->file_descriptor, config->use_metadata, compression_level, false))
+  int skip_count = config->skip_compress_set ? config->skip_compress_count : -1;
+  if (!file_send_single_calls_with_skip(file, client->file_descriptor, config->use_metadata,
+                                        compression_level, false, config->skip_compress_suffixes,
+                                        skip_count))
     return -1;
   return 0;
 }

src/client/usage.c

@@ -69,6 +69,7 @@ void print_usage(void) {
   printf("  -S, --sparse        Handle sparse files efficiently\n");
   printf("  --inplace           Update files in-place (no temp+rename)\n");
   printf("  --compress-level <n>    Compression level (default: 5)\n");
+  printf("  --skip-compress=LIST    Skip compression for comma-separated suffixes\n");
   printf("  --help              Show this help\n");
   printf("  -V, --version       Show version\n");
 }

src/shared/compression.c

@@ -11,17 +11,27 @@
 #define INITIAL_DECOMPRESS_BUF_SIZE (1024 * 1024)
 #define MAX_DECOMPRESSED_SIZE (100ULL * 1024 * 1024) /* 100 MB hard ceiling */
 
-static const char* SKIP_COMPRESSION_EXTENSIONS[] = {".jpg", ".jpeg", ".png", ".gif", ".mp4", ".mkv",
+static char* SKIP_COMPRESSION_EXTENSIONS[] = {".jpg", ".jpeg", ".png", ".gif", ".mp4", ".mkv",
                                               ".zip", ".gz",   ".xz",  ".zst", NULL};
 
 bool compression_should_skip(const char* path) {
+  return compression_should_skip_with_suffixes(path, NULL, -1);
+}
+
+bool compression_should_skip_with_suffixes(const char* path, char* const* suffixes, int count) {
   if (!path)
     return false;
   const char* dot = strrchr(path, '.');
   if (!dot)
     return false;
-  for (int i = 0; SKIP_COMPRESSION_EXTENSIONS[i]; i++) {
-    if (strcasecmp(dot, SKIP_COMPRESSION_EXTENSIONS[i]) == 0)
+  if (count < 0) {
+    suffixes = SKIP_COMPRESSION_EXTENSIONS;
+    count = 0;
+    while (SKIP_COMPRESSION_EXTENSIONS[count])
+      count++;
+  }
+  for (int i = 0; i < count; i++) {
+    if (strcasecmp(dot, suffixes[i]) == 0)
       return true;
   }
   return false;

src/shared/compression.h

@@ -8,5 +8,6 @@ Data* data_compress(Data* data_to_compress, int compression_level);
 Data* data_decompress(Data* compressed_data);
 Data* data_decompress_limited(Data* compressed_data, size_t maximum_size);
 bool compression_should_skip(const char* path);
+bool compression_should_skip_with_suffixes(const char* path, char* const* suffixes, int count);
 
 #endif

src/shared/config.c

@@ -98,6 +98,9 @@ static void config_set_defaults(Config* config) {
   config->server_mode = false;
   config->checksum = false;
   config->compress_choice = NULL;
+  config->skip_compress_suffixes = NULL;
+  config->skip_compress_count = 0;
+  config->skip_compress_set = false;
 }
 
 static bool valid_wire_bool(int value) {
@@ -134,7 +137,8 @@ static bool validate_received_config(const Config* config) {
          config->chunk_size > 0 && config->chunk_size <= MAX_CHUNK_SIZE &&
          config->delta_block_size >= DELTA_BLOCK_SIZE_MIN &&
          config->delta_block_size <= DELTA_BLOCK_SIZE_MAX &&
-         config->delta_max_file_size <= DELTA_MAX_FILE_SIZE && config->max_delete >= 0;
+         config->delta_max_file_size <= DELTA_MAX_FILE_SIZE && config->max_delete >= 0 &&
+         config->skip_compress_count >= 0 && config->skip_compress_count <= 10000;
 }
 
 Config* config_create(void) {
@@ -208,6 +212,9 @@ void config_delete(Config* config) {
   free(config->bind_address);
   free(config->daemon_config);
   free(config->compress_choice);
+  for (int i = 0; i < config->skip_compress_count; i++)
+    free(config->skip_compress_suffixes[i]);
+  free(config->skip_compress_suffixes);
   if (config->filters) {
     array_list_delete(config->filters);
   }
@@ -249,11 +256,22 @@ static bool send_selection_options(int fd, const Config* c) {
          send_int(fd, c->relative) && send_int(fd, c->prune_empty_dirs);
 }
 
+static bool send_skip_compress_options(int fd, const Config* c) {
+  if (!send_int(fd, c->skip_compress_set) || !send_int(fd, c->skip_compress_count))
+    return false;
+  for (int i = 0; i < c->skip_compress_count; i++) {
+    if (!send_str(fd, c->skip_compress_suffixes[i]))
+      return false;
+  }
+  return true;
+}
+
 static bool send_resume_options(int fd, const Config* c) {
   return send_str(fd, c->temp_dir ? c->temp_dir : "") && send_int(fd, c->partial) &&
          send_str(fd, c->partial_dir ? c->partial_dir : "") &&
          send_str(fd, c->suffix ? c->suffix : "") && send_int(fd, c->delete_before) &&
-         send_int(fd, c->checksum) && send_str(fd, c->compress_choice ? c->compress_choice : "");
+         send_int(fd, c->checksum) && send_str(fd, c->compress_choice ? c->compress_choice : "") &&
+         send_skip_compress_options(fd, c);
 }
 
 static bool receive_core_fields(int fd, Config* c) {
@@ -330,7 +348,21 @@ static bool receive_resume_options(int fd, Config* c) {
   if (!receive_wire_bool(fd, &c->checksum))
     return false;
   c->compress_choice = receive_str(fd);
-  return c->compress_choice != NULL;
+  if (!c->compress_choice || !receive_wire_bool(fd, &c->skip_compress_set) ||
+      !receive_int(fd, &c->skip_compress_count) || c->skip_compress_count < 0 ||
+      c->skip_compress_count > 10000)
+    return false;
+  if (c->skip_compress_count > 0) {
+    c->skip_compress_suffixes = calloc((size_t)c->skip_compress_count, sizeof(char*));
+    if (!c->skip_compress_suffixes)
+      return false;
+    for (int i = 0; i < c->skip_compress_count; i++) {
+      c->skip_compress_suffixes[i] = receive_str(fd);
+      if (!c->skip_compress_suffixes[i])
+        return false;
+    }
+  }
+  return true;
 }
 
 bool config_send(int file_descriptor, const Config* config) {

src/shared/config.h

@@ -126,6 +126,10 @@ typedef struct Config {
 
   // PR #184: Compression algorithm negotiation
   char* compress_choice;
+
+  char** skip_compress_suffixes;
+  int skip_compress_count;
+  bool skip_compress_set;
 } Config;
 
 #define PROTOCOL_VERSION "2.2.0"

src/shared/file_receive.c

@@ -169,7 +169,10 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
     }
 
     Data* raw_delta = delta_data;
-    if (config->use_compression) {
+    if (config->use_compression &&
+        !compression_should_skip_with_suffixes(
+            check_path, config->skip_compress_suffixes,
+            config->skip_compress_set ? config->skip_compress_count : -1)) {
       raw_delta = data_decompress_limited(delta_data, MAX_RECEIVE_FILE_SIZE);
       data_destroy(delta_data);
       if (!raw_delta) {
@@ -272,7 +275,10 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
       return NULL;
     }
 
-    if (config->use_compression) {
+    if (config->use_compression &&
+        !compression_should_skip_with_suffixes(
+            file->path, config->skip_compress_suffixes,
+            config->skip_compress_set ? config->skip_compress_count : -1)) {
       Data* uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_FILE_SIZE);
       data_destroy(file_data);
       if (uncompressed == NULL) {
@@ -500,7 +506,10 @@ File* file_receive(const Config* config, int file_descriptor) {
     file_destroy(file);
     return NULL;
   }
-  if (config->use_compression && !compression_should_skip(file->path)) {
+  if (config->use_compression &&
+      !compression_should_skip_with_suffixes(file->path, config->skip_compress_suffixes,
+                                             config->skip_compress_set ? config->skip_compress_count
+                                                                       : -1)) {
     Data* file_data_uncompressed = data_decompress_limited(file_data, MAX_RECEIVE_FILE_SIZE);
     data_destroy(file_data);
     if (file_data_uncompressed == NULL) {

src/shared/file_send.c

@@ -19,11 +19,19 @@
 
 bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
                             int compression_level, bool send_path) {
+  return file_send_single_calls_with_skip(file, file_descriptor, use_metadata, compression_level,
+                                          send_path, NULL, -1);
+}
+
+bool file_send_single_calls_with_skip(File* file, int file_descriptor, bool use_metadata,
+                                      int compression_level, bool send_path,
+                                      char* const* skip_suffixes, int skip_count) {
   if (!file || !file->path || !file->data || (file->data->size != 0 && !file->data->data))
     return false;
   const Data* data_to_send = file->data;
   Data* compressed_data = NULL;
-  if (compression_level > 0 && !compression_should_skip(file->path)) {
+  if (compression_level > 0 &&
+      !compression_should_skip_with_suffixes(file->path, skip_suffixes, skip_count)) {
     compressed_data = data_compress(file->data, compression_level);
     if (compressed_data == NULL) {
       log_message(LOG_LEVEL_ERROR, "Failed to compress file data");
@@ -49,11 +57,18 @@ bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
 
 bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int compression_level,
                         bool send_path) {
+  return file_send_sendfile_with_skip(file, file_descriptor, use_metadata, compression_level,
+                                      send_path, NULL, -1);
+}
+
+bool file_send_sendfile_with_skip(File* file, int file_descriptor, bool use_metadata,
+                                  int compression_level, bool send_path, char* const* skip_suffixes,
+                                  int skip_count) {
   if (!file || !file->path || !file->data)
     return false;
   if (compression_level > 0)
-    return file_send_single_calls(file, file_descriptor, use_metadata, compression_level,
-                                  send_path);
+    return file_send_single_calls_with_skip(file, file_descriptor, use_metadata, compression_level,
+                                            send_path, skip_suffixes, skip_count);
 
   if (send_path && !send_str(file_descriptor, file->path))
     return false;

src/shared/file_send.h

@@ -8,7 +8,13 @@
 
 bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
                             int compression_level, bool send_path);
+bool file_send_single_calls_with_skip(File* file, int file_descriptor, bool use_metadata,
+                                      int compression_level, bool send_path,
+                                      char* const* skip_suffixes, int skip_count);
 bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int compression_level,
                         bool send_path);
+bool file_send_sendfile_with_skip(File* file, int file_descriptor, bool use_metadata,
+                                  int compression_level, bool send_path, char* const* skip_suffixes,
+                                  int skip_count);
 
 #endif

tests/integration/test_features.py

@@ -52,6 +52,35 @@ class TestArchiveMode:
         assert not mismatches, f"Mismatch: {mismatches}"
 
 
+class TestSkipCompress:
+    def test_skip_compress_case_insensitive(self, shared_server):
+        clean_dir(DEST_DIR)
+        with open(os.path.join(SOURCE_DIR, "skip-case.TXT"), "wb") as f:
+            f.write((b"skip compression case test\n" * 100))
+        result, _ = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["-c", "--skip-compress=.txt"],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Skip-compress sync failed: {(result.stderr or result.stdout)[:200]}"
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        with open(os.path.join(received, "skip-case.TXT"), "rb") as f:
+            assert f.read() == b"skip compression case test\n" * 100
+
+    def test_skip_compress_empty_list(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(
+            SOURCE_DIR, DEST_DIR,
+            flags=["-c", "--skip-compress="],
+            port=shared_server.port,
+        )
+        assert result.returncode == 0, f"Empty skip-compress sync failed: {(result.stderr or result.stdout)[:200]}"
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        mismatches, missing = verify_transfer(SOURCE_DIR, received)
+        assert not missing, f"Missing: {missing}"
+        assert not mismatches, f"Mismatch: {mismatches}"
+
+
 class TestExclude:
     def test_exclude_single(self, shared_server):
         clean_dir(DEST_DIR)

tests/test_client_cli.c

@@ -247,6 +247,32 @@ static void test_parse_args_valid_compression_level() {
   config_delete(cfg);
 }
 
+static void test_parse_args_skip_compress() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--skip-compress=.ZIP, .GZ", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->skip_compress_set);
+  EXPECT_EQ_INT(cfg->skip_compress_count, 2);
+  EXPECT_EQ_STR(cfg->skip_compress_suffixes[0], ".ZIP");
+  EXPECT_EQ_STR(cfg->skip_compress_suffixes[1], ".GZ");
+  config_delete(cfg);
+}
+
+static void test_parse_args_empty_skip_compress() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--skip-compress=", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->skip_compress_set);
+  EXPECT_EQ_INT(cfg->skip_compress_count, 0);
+  config_delete(cfg);
+}
+
 /* Test parse_args unknown option returns error */
 static void test_parse_args_unknown_option() {
   Config* cfg = config_create();
@@ -357,6 +383,8 @@ void test_client_cli() {
   test_parse_args_invalid_server_port();
   test_parse_args_invalid_compression_level();
   test_parse_args_valid_compression_level();
+  test_parse_args_skip_compress();
+  test_parse_args_empty_skip_compress();
   test_parse_args_unknown_option();
   test_parse_args_rejects_unimplemented_options();
   test_parse_args_archive();

tests/test_compression.c

@@ -55,6 +55,14 @@ static void test_data_compress_decompress_large() {
   data_destroy(decompressed);
 }
 
+static void test_skip_compress_suffix_matching() {
+  char* suffixes[] = {".ZIP", ".GZ"};
+  EXPECT_TRUE(compression_should_skip_with_suffixes("archive.zip", suffixes, 2));
+  EXPECT_TRUE(compression_should_skip_with_suffixes("backup.TAR.GZ", suffixes, 2));
+  EXPECT_FALSE(compression_should_skip_with_suffixes("notes.txt", suffixes, 2));
+  EXPECT_FALSE(compression_should_skip_with_suffixes("archive.zip", suffixes, 0));
+}
+
 static void test_chunk_compress_decompress_roundtrip() {
   char* path1 = "temp_comp_test_1.txt";
   char* content1 = "chunk compression test file 1";
@@ -115,5 +123,6 @@ static void test_chunk_compress_decompress_roundtrip() {
 void test_compression() {
   test_data_compress_decompress_roundtrip();
   test_data_compress_decompress_large();
+  test_skip_compress_suffix_matching();
   test_chunk_compress_decompress_roundtrip();
 }