feat: add --fastsync-server-path flag to configure remote server binary path

Merge pull request 'Merge remaining 4 PRs: memory safety, refactoring, test coverage, integration cleanup' (#93 ) from merge-all into main
Reviewed-on: #93
2026-07-21 18:13:17 +02:00 · 2026-07-21 16:08:38 +02:00 · 2026-07-21 15:52:41 +02:00 · 2026-07-21 15:46:38 +02:00 · 2026-07-21 15:11:22 +02:00 · 2026-07-21 15:04:41 +02:00
35 changed files with 1149 additions and 232 deletions
@@ -55,7 +55,11 @@ static void print_usage(void) {
  printf("  --cert <path>       TLS certificate file (PEM)\n");
  printf("  --key <path>        TLS private key file (PEM)\n");
  printf("  --ca <path>         TLS CA certificate file (PEM)\n");
+  printf("  --partial           Keep partial files on interrupted transfer\n");
+  printf("  --fastsync-server-path <path>\n");
+  printf("                      Path to fastsync-server on remote (default: fastsync-server)\n");
  printf("  --help              Show this help\n");
+  printf("  -V, --version       Show version and exit\n");
 }

 int main(int argc, char* argv[]) {
@@ -68,10 +72,14 @@ int main(int argc, char* argv[]) {
    save_to_disk = true;
  }

-  Config* config = config_create(str_dup(PROTOCOL_VERSION), NULL, NULL, save_to_disk, false, false,
-                                 false, false, 5, false, 0);
  int exit_code = 0;
  bool config_owned_by_pipeline = false;
+  Config* config = config_create(str_dup(PROTOCOL_VERSION), NULL, NULL, save_to_disk, false, false,
+                                 false, false, 5, false, 0);
+  if (config == NULL) {
+    exit_code = 1;
+    goto cleanup;
+  }

  int positional_args[2];
  int positional_count = 0;
@@ -80,6 +88,9 @@ int main(int argc, char* argv[]) {
    if (strcmp(argv[i], "--help") == 0) {
      print_usage();
      goto cleanup;
+    } else if (strcmp(argv[i], "-V") == 0 || strcmp(argv[i], "--version") == 0) {
+      printf("fastsync version %s\n", PROTOCOL_VERSION);
+      goto cleanup;
    } else if (strcmp(argv[i], "-a") == 0 || strcmp(argv[i], "--archive") == 0) {
      config->use_compression = true;
      config->use_multithreading = true;
@@ -88,7 +99,14 @@ int main(int argc, char* argv[]) {
    } else if (strcmp(argv[i], "-n") == 0 || strcmp(argv[i], "--dry-run") == 0) {
      config->dry_run = true;
    } else if (strcmp(argv[i], "-p") == 0 && i + 1 < argc) {
-      config->ssh_port = atoi(argv[++i]);
+      char* end;
+      long p = strtol(argv[++i], &end, 10);
+      if (*end != '\0' || p <= 0 || p > 65535) {
+        fprintf(stderr, "Error: invalid SSH port '%s' (must be 1-65535)\n", argv[i]);
+        exit_code = 1;
+        goto cleanup;
+      }
+      config->ssh_port = (int)p;
    } else if (strcmp(argv[i], "--delete") == 0) {
      config->use_delete = true;
    } else if (strcmp(argv[i], "--exclude") == 0 && i + 1 < argc) {
@@ -165,7 +183,14 @@ int main(int argc, char* argv[]) {
      free(config->server_host);
      config->server_host = str_dup(argv[++i]);
    } else if (strcmp(argv[i], "--server-port") == 0 && i + 1 < argc) {
-      config->server_port = atoi(argv[++i]);
+      char* end;
+      long p = strtol(argv[++i], &end, 10);
+      if (*end != '\0' || p <= 0 || p > 65535) {
+        fprintf(stderr, "Error: invalid server port '%s' (must be 1-65535)\n", argv[i]);
+        exit_code = 1;
+        goto cleanup;
+      }
+      config->server_port = (int)p;
    } else if (strcmp(argv[i], "--bwlimit") == 0 && i + 1 < argc) {
      char* end;
      errno = 0;
@@ -199,6 +224,11 @@ int main(int argc, char* argv[]) {
    } else if (strcmp(argv[i], "--ca") == 0 && i + 1 < argc) {
      free(config->tls_ca);
      config->tls_ca = str_dup(argv[++i]);
+    } else if (strcmp(argv[i], "--partial") == 0) {
+      config->partial = true;
+    } else if (strcmp(argv[i], "--fastsync-server-path") == 0 && i + 1 < argc) {
+      free(config->fastsync_server_path);
+      config->fastsync_server_path = str_dup(argv[++i]);
    } else if (strcmp(argv[i], "-v") == 0 || strcmp(argv[i], "--verbose") == 0) {
      set_log_level(LOG_LEVEL_DEBUG);
    } else if (argv[i][0] == '-') {
@@ -228,7 +228,8 @@ static int send_chunks_multithreaded(void* pipeline_context) {
      fprintf(stderr, "Error: -f/--sendfile is not supported with SSH transport\n");
      return 1;
    }
-    client = client_connect_ssh(context->config->ssh_destination, context->config->ssh_port);
+    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,
@@ -385,7 +386,8 @@ int send_files(Config* config) {
      fprintf(stderr, "Error: -f/--sendfile is not supported with SSH transport\n");
      return 1;
    }
-    client = client_connect_ssh(config->ssh_destination, config->ssh_port);
+    client =
+        client_connect_ssh(config->ssh_destination, config->ssh_port, config->fastsync_server_path);
    if (!client)
      return 1;
  } else if (config->use_tls) {
@@ -16,6 +16,17 @@ DirectoryScanner* directory_scanner_create(char* root_directory, bool use_metada
                                           int exclude_count, char** include_patterns,
                                           int include_count, unsigned long long max_size,
                                           unsigned long long min_size) {
+  return directory_scanner_create_full(root_directory, use_metadata, chunk_size, exclude_patterns,
+                                       exclude_count, include_patterns, include_count, max_size,
+                                       min_size, true);
+}
+
+DirectoryScanner* directory_scanner_create_full(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, bool follow_symlinks) {
  DirectoryScanner* scanner = malloc(sizeof(DirectoryScanner));
  if (scanner == NULL)
    return NULL;
@@ -24,13 +35,75 @@ DirectoryScanner* directory_scanner_create(char* root_directory, bool use_metada
  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;
+  /* Deep-copy exclude patterns */
+  if (exclude_count > 0 && exclude_patterns != NULL) {
+    scanner->exclude_patterns = malloc((size_t)exclude_count * sizeof(char*));
+    if (scanner->exclude_patterns == NULL) {
+      queue_destroy(scanner->directories);
+      free(scanner);
+      return NULL;
+    }
+    for (int i = 0; i < exclude_count; i++) {
+      scanner->exclude_patterns[i] = str_dup(exclude_patterns[i]);
+      if (scanner->exclude_patterns[i] == NULL) {
+        for (int j = 0; j < i; j++)
+          free(scanner->exclude_patterns[j]);
+        free(scanner->exclude_patterns);
+        queue_destroy(scanner->directories);
+        free(scanner);
+        return NULL;
+      }
+    }
+  } else {
+    scanner->exclude_patterns = NULL;
+  }
  scanner->exclude_count = exclude_count;
-  scanner->include_patterns = include_patterns;
+
+  /* Deep-copy include patterns */
+  if (include_count > 0 && include_patterns != NULL) {
+    scanner->include_patterns = malloc((size_t)include_count * sizeof(char*));
+    if (scanner->include_patterns == NULL) {
+      for (int i = 0; i < exclude_count; i++)
+        free(scanner->exclude_patterns[i]);
+      free(scanner->exclude_patterns);
+      queue_destroy(scanner->directories);
+      free(scanner);
+      return NULL;
+    }
+    for (int i = 0; i < include_count; i++) {
+      scanner->include_patterns[i] = str_dup(include_patterns[i]);
+      if (scanner->include_patterns[i] == NULL) {
+        for (int j = 0; j < i; j++)
+          free(scanner->include_patterns[j]);
+        free(scanner->include_patterns);
+        for (int j = 0; j < exclude_count; j++)
+          free(scanner->exclude_patterns[j]);
+        free(scanner->exclude_patterns);
+        queue_destroy(scanner->directories);
+        free(scanner);
+        return NULL;
+      }
+    }
+  } else {
+    scanner->include_patterns = NULL;
+  }
  scanner->include_count = include_count;
  scanner->max_size = max_size;
  scanner->min_size = min_size;
-  queue_enqueue(scanner->directories, str_dup(root_directory));
+  scanner->follow_symlinks = follow_symlinks;
+  char* root_copy = str_dup(root_directory);
+  if (root_copy == NULL) {
+    for (int i = 0; i < scanner->include_count; i++)
+      free(scanner->include_patterns[i]);
+    free(scanner->include_patterns);
+    for (int i = 0; i < scanner->exclude_count; i++)
+      free(scanner->exclude_patterns[i]);
+    free(scanner->exclude_patterns);
+    queue_destroy(scanner->directories);
+    free(scanner);
+    return NULL;
+  }
+  queue_enqueue(scanner->directories, root_copy);
  return scanner;
 }

@@ -42,6 +115,12 @@ void directory_scanner_destroy(DirectoryScanner* scanner) {
    scanner->current_dir = NULL;
  }
  free(scanner->current_path);
+  for (int i = 0; i < scanner->exclude_count; i++)
+    free(scanner->exclude_patterns[i]);
+  free(scanner->exclude_patterns);
+  for (int i = 0; i < scanner->include_count; i++)
+    free(scanner->include_patterns[i]);
+  free(scanner->include_patterns);
  queue_destroy(scanner->directories);
  free(scanner);
 }
@@ -104,13 +183,81 @@ Chunk* directory_scanner_next(DirectoryScanner* scanner) {

    char* cur_path = path_cat(scanner->current_path, entry->d_name);
    struct stat stats;
-    if (stat(cur_path, &stats) != 0) {
+    // Use lstat to detect symlinks
+    if (lstat(cur_path, &stats) != 0) {
      free(cur_path);
      continue;
    }

+    // If follow_symlinks is enabled and this is a symlink, resolve it
+    if (scanner->follow_symlinks && S_ISLNK(stats.st_mode)) {
+      struct stat target_stats;
+      if (stat(cur_path, &target_stats) != 0) {
+        // Broken symlink, skip
+        free(cur_path);
+        continue;
+      }
+      stats = target_stats;
+    }
+
    if (S_ISDIR(stats.st_mode)) {
      queue_enqueue(scanner->directories, (void*)cur_path);
+    } else if (S_ISLNK(stats.st_mode)) {
+      // Handle symlink (not following)
+      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;
+        }
+      }
+
+      File* file = file_create(cur_path);
+      if (file == NULL) {
+        free(cur_path);
+        continue;
+      }
+      file->type = FILE_TYPE_SYMLINK;
+      // Read link target
+      char link_buf[4096];
+      ssize_t link_len = readlink(cur_path, link_buf, sizeof(link_buf) - 1);
+      if (link_len >= 0) {
+        link_buf[link_len] = '\0';
+        file->link_target = str_dup(link_buf);
+        if (file->link_target == NULL) {
+          file_destroy(file);
+          free(cur_path);
+          continue;
+        }
+      }
+      file->data->size = 0;
+      if (scanner->use_metadata)
+        file->metadata = file_metadata_create(&stats);
+      array_list_add(chunk_data, file);
+      chunk_data_size += 1; // small size for symlinks
+      if (chunk_data_size > scanner->chunk_size) {
+        free(cur_path);
+        return chunk_data_to_chunk(chunk_data);
+      }
+      free(cur_path);
    } else {
      bool excluded = false;
      for (int i = 0; i < scanner->exclude_count; i++) {
@@ -18,6 +18,7 @@ typedef struct {
  int include_count;
  unsigned long long max_size;
  unsigned long long min_size;
+  bool follow_symlinks;
 } DirectoryScanner;

 DirectoryScanner* directory_scanner_create(char* root_directory, bool use_metadata,
@@ -25,6 +26,12 @@ DirectoryScanner* directory_scanner_create(char* root_directory, bool use_metada
                                           int exclude_count, char** include_patterns,
                                           int include_count, unsigned long long max_size,
                                           unsigned long long min_size);
+DirectoryScanner* directory_scanner_create_full(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, bool follow_symlinks);
 Chunk* directory_scanner_next(DirectoryScanner* scanner);
 void directory_scanner_destroy(DirectoryScanner* scanner);

@@ -11,11 +11,49 @@
 #include "transport_tls.h"
 #include "unistd.h"
 #include "utils.h"
+#include <libgen.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

+// Check if a file path should be excluded based on config patterns
+static bool is_excluded(const char* path, const Config* config) {
+  // Extract filename from path
+  char* path_dup = str_dup(path);
+  if (!path_dup)
+    return false;
+  /* basename(3) may return a pointer into path_dup or a static buffer;
+   * either way we free path_dup, not fname. */
+  char* fname = basename(path_dup);
+
+  // Check exclude patterns
+  for (int i = 0; i < config->exclude_count; i++) {
+    if (glob_match(config->exclude_patterns[i], fname)) {
+      free(path_dup);
+      return true;
+    }
+  }
+
+  // Check include patterns (if any, file must match at least one)
+  if (config->include_count > 0) {
+    bool included = false;
+    for (int i = 0; i < config->include_count; i++) {
+      if (glob_match(config->include_patterns[i], fname)) {
+        included = true;
+        break;
+      }
+    }
+    if (!included) {
+      free(path_dup);
+      return true;
+    }
+  }
+
+  free(path_dup);
+  return false;
+}
+
 int receive_files(Config* config, int fd) {
  Status status;
  if (!receive_status(fd, &status))
@@ -29,7 +67,7 @@ int receive_files(Config* config, int fd) {
        goto next;
      if (file == NULL && !skipped)
        return -1;
-      if (config->save_to_disk)
+      if (config->save_to_disk && !is_excluded(file->path, config))
        file_save_to_disk(config->receive_root_directory, file);
      file_destroy(file);
    } else if (status == STATUS_CHUNK) {
@@ -39,7 +77,7 @@ int receive_files(Config* config, int fd) {
        return -1;
      }
      for (int i = 0; i < chunk->element_count; i++) {
-        if (config->save_to_disk)
+        if (config->save_to_disk && !is_excluded(chunk->items[i]->path, config))
          file_save_to_disk(config->receive_root_directory, chunk->items[i]);
      }
      chunk_destroy(chunk);
@@ -50,7 +88,7 @@ int receive_files(Config* config, int fd) {
        send_status(fd, STATUS_ERROR);
        return -1;
      }
-      if (config->save_to_disk)
+      if (config->save_to_disk && !is_excluded(file->path, config))
        file_save_to_disk(config->receive_root_directory, file);
      file_destroy(file);
    }
@@ -113,13 +151,12 @@ void handler(int file_descriptor) {
 }

 static Server* g_server = NULL;
+static volatile sig_atomic_t g_server_cleanup_requested = 0;

 static void cleanup(int sig) {
  (void)sig;
-  if (g_server) {
-    server_delete(&g_server);
-  }
-  _exit(0);
+  server_request_shutdown();
+  g_server_cleanup_requested = 1;
 }

 static void print_server_usage(void) {
@@ -135,6 +172,7 @@ static void print_server_usage(void) {
  printf("  --ca <path>         TLS CA certificate file (PEM)\n");
  printf("  -v, --verbose       Enable debug logging\n");
  printf("  --help              Show this help\n");
+  printf("  -V, --version       Show version and exit\n");
 }

 int main(int argc, char* argv[]) {
@@ -149,6 +187,9 @@ int main(int argc, char* argv[]) {
    if (strcmp(argv[i], "--help") == 0) {
      print_server_usage();
      return 0;
+    } else if (strcmp(argv[i], "-V") == 0 || strcmp(argv[i], "--version") == 0) {
+      printf("fastsync-server version %s\n", PROTOCOL_VERSION);
+      return 0;
    } else if (strcmp(argv[i], "--stdio") == 0) {
      io_set_fds(STDIN_FILENO, STDOUT_FILENO);
      handler(STDIN_FILENO);
@@ -205,5 +246,10 @@ int main(int argc, char* argv[]) {
  } else {
    server_listen(g_server, handler);
  }
+
+  /* Graceful shutdown: delete the server */
+  if (g_server_cleanup_requested)
+    log_message(LOG_LEVEL_INFO, "Shutdown requested, cleaning up");
+  server_delete(&g_server);
  return 0;
 }
@@ -1,13 +1,26 @@
 #include "compression.h"
 #include "data.h"
 #include "log.h"
-#include "stdlib.h"
+#include <stdint.h>
+#include <stdlib.h>
 #include "zstd.h"

 #define INITIAL_DECOMPRESS_BUF_SIZE (1024 * 1024)

 Data* data_compress(Data* data_to_compress, int compression_level) {
  log_message(LOG_LEVEL_DEBUG, "Starting to compress data");
+
+  /* Clamp compression level to valid zstd range [1, 22] */
+  if (compression_level < 1) {
+    log_message(LOG_LEVEL_WARNING, "compression_level %d out of range [1,22], using 1",
+                compression_level);
+    compression_level = 1;
+  } else if (compression_level > 22) {
+    log_message(LOG_LEVEL_WARNING, "compression_level %d out of range [1,22], using 22",
+                compression_level);
+    compression_level = 22;
+  }
+
  size_t dst_size = ZSTD_compressBound(data_to_compress->size);
  Data* compressed_data = data_create_empty(dst_size);
  if (compressed_data == NULL)
@@ -66,8 +79,16 @@ Data* data_decompress(Data* compressed_data) {
    return NULL;
  }

-  size_t buf_size =
-      (!ZSTD_isError(dst_size) && dst_size > 0) ? (size_t)dst_size : INITIAL_DECOMPRESS_BUF_SIZE;
+  size_t buf_size = INITIAL_DECOMPRESS_BUF_SIZE;
+  if (!ZSTD_isError(dst_size) && dst_size > 0) {
+    if (dst_size > SIZE_MAX) {
+      log_message(LOG_LEVEL_ERROR,
+                  "Decompressed size %llu exceeds addressable memory, using fallback buffer",
+                  dst_size);
+    } else {
+      buf_size = (size_t)dst_size;
+    }
+  }
  Data* uncompressed_data = data_create_empty(buf_size);
  if (!uncompressed_data) {
    log_message(LOG_LEVEL_ERROR, "Failed to allocate decompression buffer");
@@ -4,6 +4,7 @@
 #include "protocol.h"
 #include "utils.h"
 #include <stdbool.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -14,6 +15,8 @@ Config* config_create(char* version, char* send_directory, char* receive_directo
                      bool use_sendfile, unsigned long long chunk_size) {

  Config* config = malloc(sizeof(Config));
+  if (config == NULL)
+    return NULL;
  config->version = version;
  config->send_directory = send_directory;
  config->receive_root_directory = receive_directory;
@@ -31,6 +34,7 @@ Config* config_create(char* version, char* send_directory, char* receive_directo
  config->ssh_port = 22;
  config->transport = TRANSPORT_TCP;
  config->ssh_destination = NULL;
+  config->fastsync_server_path = NULL;
  config->exclude_patterns = NULL;
  config->exclude_count = 0;
  config->include_patterns = NULL;
@@ -45,6 +49,8 @@ Config* config_create(char* version, char* send_directory, char* receive_directo
  config->tls_cert = NULL;
  config->tls_key = NULL;
  config->tls_ca = NULL;
+  config->follow_symlinks = false;
+  config->partial = false;
  config->server_host = str_dup("127.0.0.1");
  config->server_port = 8080;
  return config;
@@ -77,10 +83,13 @@ void config_parse_ssh_dest(Config* config) {
 }

 void config_delete(Config* config) {
+  if (config == NULL)
+    return;
  free(config->version);
  free(config->send_directory);
  free(config->receive_root_directory);
  free(config->ssh_destination);
+  free(config->fastsync_server_path);
  for (int i = 0; i < config->exclude_count; i++)
    free(config->exclude_patterns[i]);
  free(config->exclude_patterns);
@@ -127,6 +136,26 @@ bool config_send(int file_descriptor, const Config* config) {
    return false;
  if (!send_n_data(file_descriptor, &config->delta_max_file_size, sizeof(unsigned long long)))
    return false;
+  if (!send_int(file_descriptor, config->exclude_count))
+    return false;
+  for (int i = 0; i < config->exclude_count; i++) {
+    if (!send_str(file_descriptor, config->exclude_patterns[i]))
+      return false;
+  }
+  if (!send_int(file_descriptor, config->include_count))
+    return false;
+  for (int i = 0; i < config->include_count; i++) {
+    if (!send_str(file_descriptor, config->include_patterns[i]))
+      return false;
+  }
+  if (!send_n_data(file_descriptor, &config->max_size, sizeof(config->max_size)))
+    return false;
+  if (!send_n_data(file_descriptor, &config->min_size, sizeof(config->min_size)))
+    return false;
+  if (!send_int(file_descriptor, config->follow_symlinks))
+    return false;
+  if (!send_int(file_descriptor, config->partial))
+    return false;
  Status status;
  if (!receive_status(file_descriptor, &status))
    return false;
@@ -211,6 +240,7 @@ Config* config_receive(int file_descriptor) {
  config->ssh_port = 22;
  config->transport = TRANSPORT_TCP;
  config->ssh_destination = NULL;
+  config->fastsync_server_path = NULL;
  config->exclude_patterns = NULL;
  config->exclude_count = 0;
  config->include_patterns = NULL;
@@ -221,6 +251,82 @@ Config* config_receive(int file_descriptor) {
  config->tls_cert = NULL;
  config->tls_key = NULL;
  config->tls_ca = NULL;
+  config->follow_symlinks = false;
+  config->partial = false;
+
+#define MAX_PATTERN_COUNT 10000
+
+  // Receive exclude patterns
+  int ec;
+  if (!receive_int(file_descriptor, &ec))
+    goto error;
+  if (ec > MAX_PATTERN_COUNT) {
+    log_message(LOG_LEVEL_ERROR, "Exclude pattern count %d exceeds maximum %d", ec,
+                MAX_PATTERN_COUNT);
+    goto error;
+  }
+  config->exclude_count = ec;
+  if (ec > 0) {
+    config->exclude_patterns = malloc((size_t)ec * sizeof(char*));
+    if (!config->exclude_patterns) {
+      config->exclude_count = 0;
+      goto error;
+    }
+    for (int i = 0; i < ec; i++) {
+      config->exclude_patterns[i] = receive_str(file_descriptor);
+      if (!config->exclude_patterns[i]) {
+        for (int j = 0; j < i; j++)
+          free(config->exclude_patterns[j]);
+        free(config->exclude_patterns);
+        config->exclude_patterns = NULL;
+        config->exclude_count = 0;
+        goto error;
+      }
+    }
+  }
+
+  // Receive include patterns
+  int ic;
+  if (!receive_int(file_descriptor, &ic))
+    goto error;
+  if (ic > MAX_PATTERN_COUNT) {
+    log_message(LOG_LEVEL_ERROR, "Include pattern count %d exceeds maximum %d", ic,
+                MAX_PATTERN_COUNT);
+    goto error;
+  }
+  config->include_count = ic;
+  if (ic > 0) {
+    config->include_patterns = malloc((size_t)ic * sizeof(char*));
+    if (!config->include_patterns) {
+      config->include_count = 0;
+      goto error;
+    }
+    for (int i = 0; i < ic; i++) {
+      config->include_patterns[i] = receive_str(file_descriptor);
+      if (!config->include_patterns[i]) {
+        for (int j = 0; j < i; j++)
+          free(config->include_patterns[j]);
+        free(config->include_patterns);
+        config->include_patterns = NULL;
+        config->include_count = 0;
+        goto error;
+      }
+    }
+  }
+
+  if (!receive_n_data(file_descriptor, &config->max_size, sizeof(config->max_size)))
+    goto error;
+  if (!receive_n_data(file_descriptor, &config->min_size, sizeof(config->min_size)))
+    goto error;
+  int tmp_follow;
+  if (!receive_int(file_descriptor, &tmp_follow))
+    goto error;
+  config->follow_symlinks = tmp_follow;
+  int tmp_partial;
+  if (!receive_int(file_descriptor, &tmp_partial))
+    goto error;
+  config->partial = tmp_partial;
+
  config->server_host = str_dup("127.0.0.1");
  config->server_port = 8080;
  if (!send_status(file_descriptor, STATUS_OK))
@@ -231,6 +337,16 @@ error:
  free(config->version);
  free(config->send_directory);
  free(config->receive_root_directory);
+  for (int i = 0; i < config->exclude_count; i++)
+    free(config->exclude_patterns[i]);
+  free(config->exclude_patterns);
+  for (int i = 0; i < config->include_count; i++)
+    free(config->include_patterns[i]);
+  free(config->include_patterns);
+  free(config->tls_cert);
+  free(config->tls_key);
+  free(config->tls_ca);
+  free(config->ssh_destination);
  free(config->server_host);
  free(config);
  return NULL;
@@ -24,6 +24,7 @@ typedef struct Config {
  int ssh_port;
  TransportType transport;
  char* ssh_destination;
+  char* fastsync_server_path;
  char** exclude_patterns;
  int exclude_count;
  char** include_patterns;
@@ -40,9 +41,11 @@ typedef struct Config {
  char* tls_cert;
  char* tls_key;
  char* tls_ca;
+  bool follow_symlinks;
+  bool partial;
 } Config;

-#define PROTOCOL_VERSION "1.4.0"
+#define PROTOCOL_VERSION "2.0.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)

 Config* config_create(char* version, char* send_directory, char* receive_directory,
@@ -1,9 +1,11 @@
 #include "data.h"
 #include "log.h"
-#include "stdlib.h"
+#include <stdlib.h>

 Data* data_create_empty(size_t data_size) {
-  void* data = malloc(data_size);
+  /* malloc(0) is UB; allocate at least 1 byte but preserve requested size */
+  size_t alloc_size = data_size > 0 ? data_size : 1;
+  void* data = malloc(alloc_size);
  if (data == NULL) {
    log_message(LOG_LEVEL_ERROR, "Could not allocate memory for empty data");
    return NULL;
@@ -1,7 +1,7 @@
 #ifndef DATA_H
 #define DATA_H

-#include "stdlib.h"
+#include <stdlib.h>

 typedef struct {
  void* data;
@@ -1,7 +1,9 @@
 #include <dirent.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <libgen.h>
 #include <stddef.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -20,6 +22,9 @@
 #include "protocol.h"
 #include "utils.h"

+#define STREAM_THRESHOLD (64ULL * 1024 * 1024) /* 64 MB */
+#define STREAM_CHUNK_SIZE (1ULL * 1024 * 1024) /* 1 MB */
+
 File* file_create(const char* path) {
  File* file = (File*)malloc(sizeof(File));
  if (file == NULL) {
@@ -34,7 +39,7 @@ File* file_create(const char* path) {
    return NULL;
  }

-  strcpy(file->path, path);
+  memcpy(file->path, path, path_len + 1);
  file->data = data_create_reserve(0);
  if (file->data == NULL) {
    free(file->path);
@@ -42,6 +47,8 @@ File* file_create(const char* path) {
    return NULL;
  }
  file->metadata = NULL;
+  file->type = FILE_TYPE_REGULAR;
+  file->link_target = NULL;
  return file;
 }

@@ -55,6 +62,8 @@ void file_destroy(void* item) {
  file->metadata = NULL;
  free(file->path);
  file->path = NULL;
+  free(file->link_target);
+  file->link_target = NULL;
  free(file);
 }

@@ -83,6 +92,14 @@ void file_metadata_destroy(void* metadata) {
 bool file_load_data(File* file) {
  if (file == NULL)
    return false;
+  // Symlinks have no data to load
+  if (file->type == FILE_TYPE_SYMLINK)
+    return true;
+  // For streaming files, just record the size, don't load into memory
+  if (file->data->size > STREAM_THRESHOLD) {
+    // Don't allocate; streaming will read directly from disk
+    return true;
+  }
  if (file->data->data == NULL) {
    file->data->data = malloc(file->data->size);
    if (file->data->data == NULL) {
@@ -93,15 +110,86 @@ bool file_load_data(File* file) {
  size_t bytes_read = file_content_to_buffer(file);
  if (bytes_read != file->data->size) {
    log_message(LOG_LEVEL_ERROR, "Did not read expected amount of bytes from file");
+    free(file->data->data);
+    file->data->data = NULL;
+    file->data->size = 0;
    return false;
  }
  return true;
 }

+// Stream file content in chunks without loading entire file into RAM
+static bool file_send_streaming(File* file, int file_descriptor) {
+  unsigned long long total_size = file->data->size;
+  // Send total size prefix (same wire format as send_data)
+  if (!send_n_data(file_descriptor, &total_size, sizeof(total_size)))
+    return false;
+
+  FILE* fp = fopen(file->path, "rb");
+  if (!fp) {
+    perror("Could not open file for streaming");
+    return false;
+  }
+
+  char* buf = malloc(STREAM_CHUNK_SIZE);
+  if (!buf) {
+    fclose(fp);
+    return false;
+  }
+  unsigned long long remaining = total_size;
+  while (remaining > 0) {
+    size_t to_read = (size_t)((remaining < STREAM_CHUNK_SIZE) ? remaining : STREAM_CHUNK_SIZE);
+    size_t nread = fread(buf, 1, to_read, fp);
+    if (nread != to_read) {
+      if (ferror(fp)) {
+        perror("Read error during streaming");
+      }
+      send_status(file_descriptor, STATUS_ERROR);
+      free(buf);
+      fclose(fp);
+      return false;
+    }
+    if (!send_n_data(file_descriptor, buf, nread)) {
+      send_status(file_descriptor, STATUS_ERROR);
+      free(buf);
+      fclose(fp);
+      return false;
+    }
+    remaining -= (unsigned long long)nread;
+  }
+  free(buf);
+  fclose(fp);
+  return true;
+}
+
 bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
                            int compression_level, bool send_path) {
+  if (send_path && !send_str(file_descriptor, file->path))
+    return false;
+  if (use_metadata && !metadata_send(file_descriptor, file->metadata))
+    return false;
+
+  // Send file type indicator so receiver can distinguish regular from symlink
+  int ft = (int)file->type;
+  if (!send_int(file_descriptor, ft))
+    return false;
+
+  if (file->type == FILE_TYPE_SYMLINK) {
+    // Send link target, then zero-length data
+    if (!send_str(file_descriptor, file->link_target ? file->link_target : ""))
+      return false;
+    Data empty = {NULL, 0};
+    return send_data(file_descriptor, &empty);
+  }
+
  const Data* data_to_send = file->data;
  Data* compressed_data = NULL;
+
+  // Streaming mode: for large files without compression, stream from disk
+  if (file->data->size > STREAM_THRESHOLD && compression_level == 0) {
+    return file_send_streaming(file, file_descriptor);
+  }
+
  if (compression_level > 0) {
    compressed_data = data_compress(file->data, compression_level);
    if (compressed_data == NULL) {
@@ -110,19 +198,6 @@ bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
    }
    data_to_send = compressed_data;
  }
-  if (send_path && !send_str(file_descriptor, file->path)) {
-    data_destroy(compressed_data);
-    return false;
-  }
-  if (use_metadata && !metadata_send(file_descriptor, file->metadata)) {
-    data_destroy(compressed_data);
-    return false;
-  }
-  int ft = 0; // FILE_TYPE_REGULAR
-  if (!send_int(file_descriptor, ft)) {
-    data_destroy(compressed_data);
-    return false;
-  }
  if (!send_data(file_descriptor, data_to_send)) {
    data_destroy(compressed_data);
    return false;
@@ -132,9 +207,37 @@ bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
 }

 bool file_save_to_disk(const char* root_directory, File* file) {
+  if (file->type == FILE_TYPE_SYMLINK && file->link_target) {
+    // Validate link_target — reject absolute paths or traversal
+    if (file->link_target[0] == '/' || strstr(file->link_target, "..") != NULL) {
+      log_message(LOG_LEVEL_ERROR, "Path traversal blocked in symlink target: %s",
+                  file->link_target);
+      return false;
+    }
    char* disk_path = path_cat((char*)root_directory, file->path);
    if (disk_path == NULL)
      return false;
+    if (strstr(disk_path, "..") != NULL) {
+      log_message(LOG_LEVEL_ERROR, "Path traversal blocked: %s", disk_path);
+      free(disk_path);
+      return false;
+    }
+    unlink(disk_path);
+    bool ok = (symlink(file->link_target, disk_path) == 0);
+    if (ok && file->metadata)
+      file_restore_metadata(disk_path, file->metadata);
+    free(disk_path);
+    return ok;
+  }
+
+  char* disk_path = path_cat((char*)root_directory, file->path);
+  if (disk_path == NULL)
+    return false;
+  if (strstr(disk_path, "..") != NULL) {
+    log_message(LOG_LEVEL_ERROR, "Path traversal blocked: %s", disk_path);
+    free(disk_path);
+    return false;
+  }
  bool ok = to_disk(disk_path, file->data->data, file->data->size);
  if (ok)
    file_restore_metadata(disk_path, file->metadata);
@@ -160,6 +263,43 @@ static void* old_data_from_path(const char* full_path, unsigned long long old_si
  return data;
 }

+/**
+ * Helper: receive data from wire, optionally decompress, and store in file.
+ * On success, returns the received Data* (caller owns it). On failure, returns NULL.
+ * If `file_data` is received via receive_data(fd), this function handles decompression
+ * when config->use_compression is set.
+ */
+static Data* receive_and_decompress(int fd, const Config* config) {
+  Data* file_data = receive_data(fd);
+  if (file_data == NULL)
+    return NULL;
+  if (config->use_compression) {
+    Data* uncompressed = data_decompress(file_data);
+    data_destroy(file_data);
+    if (uncompressed == NULL)
+      return NULL;
+    file_data = uncompressed;
+  }
+  return file_data;
+}
+
+/**
+ * Helper: receive metadata from wire and assign to file.
+ * Returns true on success (metadata may be NULL if absent), false on I/O error.
+ */
+static bool receive_and_assign_metadata(int fd, const Config* config, File* file) {
+  if (!config->use_metadata)
+    return true;
+  int meta_ok = 1;
+  file->metadata = metadata_receive(fd, &meta_ok);
+  if (!meta_ok) {
+    file_destroy(file);
+    send_status(fd, STATUS_ERROR);
+    return false;
+  }
+  return true;
+}
+
 static File* receive_delta_file(int fd, const Config* config, const char* check_path,
                                void* old_data, unsigned long long old_size) {
  if (!old_data) {
@@ -279,34 +419,16 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
      return NULL;
    }

-    if (config->use_metadata) {
-      int meta_ok = 1;
-      file->metadata = metadata_receive(fd, &meta_ok);
-      if (!meta_ok) {
-        file_destroy(file);
-        send_status(fd, STATUS_ERROR);
+    if (!receive_and_assign_metadata(fd, config, file))
      return NULL;
-      }
-    }

-    Data* file_data = receive_data(fd);
+    Data* file_data = receive_and_decompress(fd, config);
    if (file_data == NULL) {
      file_destroy(file);
      send_status(fd, STATUS_ERROR);
      return NULL;
    }

-    if (config->use_compression) {
-      Data* uncompressed = data_decompress(file_data);
-      data_destroy(file_data);
-      if (uncompressed == NULL) {
-        file_destroy(file);
-        send_status(fd, STATUS_ERROR);
-        return NULL;
-      }
-      file_data = uncompressed;
-    }
-
    data_destroy(file->data);
    file->data = file_data;
    return file;
@@ -335,10 +457,29 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
  }

  char* full_path = path_cat(config->receive_root_directory, check_path);
+  if (full_path && strstr(full_path, "..") != NULL) {
+    log_message(LOG_LEVEL_ERROR, "Path traversal blocked: %s", full_path);
+    free(full_path);
+    free(check_path);
+    send_status(fd, STATUS_ERROR);
+    return NULL;
+  }
  struct stat st;
  bool has_old_file = (full_path && stat(full_path, &st) == 0);
  unsigned long long old_size = has_old_file ? (unsigned long long)st.st_size : 0;

+  // Check for partial file if enabled
+  if (config->partial && !has_old_file && full_path) {
+    char* partial_path = malloc(strlen(full_path) + 20);
+    if (partial_path) {
+      snprintf(partial_path, strlen(full_path) + 20, "%s.fastsync-partial", full_path);
+      has_old_file = (stat(partial_path, &st) == 0);
+      if (has_old_file)
+        old_size = (unsigned long long)st.st_size;
+      free(partial_path);
+    }
+  }
+
  bool match = has_old_file && (unsigned long long)st.st_size == check_size &&
               (long long)st.st_mtime == check_mtime;

@@ -384,15 +525,8 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
    return NULL;
  }

-  if (config->use_metadata) {
-    int meta_ok = 1;
-    file->metadata = metadata_receive(fd, &meta_ok);
-    if (!meta_ok) {
-      file_destroy(file);
-      send_status(fd, STATUS_ERROR);
+  if (!receive_and_assign_metadata(fd, config, file))
    return NULL;
-    }
-  }

  int file_type;
  if (!receive_int(fd, &file_type)) {
@@ -400,25 +534,26 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
    send_status(fd, STATUS_ERROR);
    return NULL;
  }
+  file->type = (FileType)file_type;

-  Data* file_data = receive_data(fd);
+  if (file->type == FILE_TYPE_SYMLINK) {
+    char* link_target = receive_str(fd);
+    if (link_target) {
+      file->link_target = link_target;
+    }
+    Data* empty_data = receive_data(fd);
+    if (empty_data)
+      data_destroy(empty_data);
+    return file;
+  }
+
+  Data* file_data = receive_and_decompress(fd, config);
  if (file_data == NULL) {
    file_destroy(file);
    send_status(fd, STATUS_ERROR);
    return NULL;
  }

-  if (config->use_compression) {
-    Data* uncompressed = data_decompress(file_data);
-    data_destroy(file_data);
-    if (uncompressed == NULL) {
-      file_destroy(file);
-      send_status(fd, STATUS_ERROR);
-      return NULL;
-    }
-    file_data = uncompressed;
-  }
-
  data_destroy(file->data);
  file->data = file_data;
  return file;
@@ -462,13 +597,14 @@ done:

 bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int compression_level,
                        bool send_path) {
+  // Handle symlinks
+  if (file->type == FILE_TYPE_SYMLINK) {
+    return file_send_single_calls(file, file_descriptor, use_metadata, compression_level,
+                                  send_path);
+  }
+
  // sendfile is incompatible with compression (kernel zero-copy).
  // If compression is requested, fall back to the regular send path.
-  // NOTE: This is a safety net only — callers must ensure compression_level == 0
-  // before calling file_send_sendfile. The fallback to file_send_single_calls
-  // preserves the send_path contract, but callers should not rely on it for
-  // correctness (the --sendfile flag is validated to be mutually exclusive with
-  // -c/--compress at the CLI layer).
  if (compression_level > 0)
    return file_send_single_calls(file, file_descriptor, use_metadata, compression_level,
                                  send_path);
@@ -478,7 +614,7 @@ bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int
  if (use_metadata && !metadata_send(file_descriptor, file->metadata))
    return false;

-  int ft = 0; // FILE_TYPE_REGULAR
+  int ft = (int)file->type;
  if (!send_int(file_descriptor, ft))
    return false;

@@ -496,8 +632,13 @@ bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int

  off_t offset = 0;
  while ((unsigned long long)offset < file_size) {
-    ssize_t sent = sendfile(file_descriptor, fd, &offset, file_size - offset);
+    size_t send_count = (size_t)(file_size - (unsigned long long)offset);
+    if ((unsigned long long)send_count != file_size - (unsigned long long)offset)
+      send_count = SIZE_MAX;
+    ssize_t sent = sendfile(file_descriptor, fd, &offset, send_count);
    if (sent == -1) {
+      if (errno == EINTR)
+        continue;
      perror("sendfile failed");
      close(fd);
      return false;
@@ -524,11 +665,30 @@ File* file_receive(const Config* config, int file_descriptor) {
      return NULL;
    }
  }
+
+  // Receive file type indicator
  int file_type;
  if (!receive_int(file_descriptor, &file_type)) {
    file_destroy(file);
    return NULL;
  }
+  file->type = (FileType)file_type;
+
+  if (file->type == FILE_TYPE_SYMLINK) {
+    char* link_target = receive_str(file_descriptor);
+    if (link_target == NULL) {
+      file_destroy(file);
+      return NULL;
+    }
+    file->link_target = link_target;
+    // Receive and discard zero-length data
+    Data* empty_data = receive_data(file_descriptor);
+    if (empty_data)
+      data_destroy(empty_data);
+    return file;
+  }
+
+  // Regular file - receive data
  Data* file_data = receive_data(file_descriptor);
  if (file_data == NULL) {
    file_destroy(file);
@@ -543,6 +703,7 @@ File* file_receive(const Config* config, int file_descriptor) {
    }
    file_data = file_data_uncompressed;
  }
+
  data_destroy(file->data);
  file->data = file_data;
  return file;
@@ -6,6 +6,8 @@
 #include <stdbool.h>
 #include <sys/stat.h>

+typedef enum { FILE_TYPE_REGULAR, FILE_TYPE_SYMLINK, FILE_TYPE_DIR } FileType;
+
 typedef struct {
  mode_t mode;
  uid_t uid;
@@ -18,6 +20,8 @@ typedef struct {
  char* path;
  Data* data;
  FileMetadata* metadata;
+  FileType type;
+  char* link_target;
 } File;

 File* file_create(const char* path);
@@ -10,11 +10,14 @@ void set_log_level(LogLevel level) {
  current_log_level = level;
 }

-void log_message(LogLevel log_level, char* format, ...) {
+void log_message(LogLevel log_level, const char* format, ...) {
  if (log_level < current_log_level)
    return;
  time_t now = time(NULL);
-  const struct tm* t = localtime(&now);
+  struct tm result_buf;
+  const struct tm* t = localtime_r(&now, &result_buf);
+  if (t == NULL)
+    return;

  fprintf(stderr, "%04d-%02d-%02d %02d:%02d:%02d [%s]: ", t->tm_year + 1900, t->tm_mon + 1,
          t->tm_mday, t->tm_hour, t->tm_min, t->tm_sec, log_level_strings[log_level]);
@@ -3,7 +3,7 @@

 typedef enum { LOG_LEVEL_DEBUG, LOG_LEVEL_INFO, LOG_LEVEL_WARNING, LOG_LEVEL_ERROR } LogLevel;

-void log_message(LogLevel log_level, char* message, ...);
+void log_message(LogLevel log_level, const char* message, ...);
 void set_log_level(LogLevel level);

 #endif
@@ -4,67 +4,103 @@
 #include "protocol.h"
 #include <errno.h>
 #include <fcntl.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <time.h>
 #include <unistd.h>

+/*
+ * Wire format serialization (protocol version 2.0.0+):
+ * All metadata fields are serialized as fixed-width integers (int32_t / int64_t)
+ * to ensure cross-platform binary compatiblity.  See metadata.h for the
+ * exact wire layout.
+ *
+ * Compile-time assertions verify that the native platform types fit within
+ * the chosen fixed-width representations.
+ */
+typedef char static_assert_mode_t_fits[(sizeof(mode_t) <= sizeof(int32_t)) ? 1 : -1];
+typedef char static_assert_uid_t_fits[(sizeof(uid_t) <= sizeof(int32_t)) ? 1 : -1];
+typedef char static_assert_gid_t_fits[(sizeof(gid_t) <= sizeof(int32_t)) ? 1 : -1];
+
 void metadata_to_buf(char** buf, const FileMetadata* m) {
-  int present = (m != NULL) ? 1 : 0;
-  memcpy(*buf, &present, sizeof(int));
-  *buf += sizeof(int);
+  int32_t present = (m != NULL) ? 1 : 0;
+  memcpy(*buf, &present, sizeof(present));
+  *buf += sizeof(present);
  if (m == NULL)
    return;
-  memcpy(*buf, &m->mode, sizeof(mode_t));
-  *buf += sizeof(mode_t);
-  memcpy(*buf, &m->uid, sizeof(uid_t));
-  *buf += sizeof(uid_t);
-  memcpy(*buf, &m->gid, sizeof(gid_t));
-  *buf += sizeof(gid_t);
-  memcpy(*buf, &m->mtime_sec, sizeof(time_t));
-  *buf += sizeof(time_t);
-  memcpy(*buf, &m->mtime_nsec, sizeof(long));
-  *buf += sizeof(long);
+  int32_t mode = (int32_t)m->mode;
+  memcpy(*buf, &mode, sizeof(mode));
+  *buf += sizeof(mode);
+  int32_t uid = (int32_t)m->uid;
+  memcpy(*buf, &uid, sizeof(uid));
+  *buf += sizeof(uid);
+  int32_t gid = (int32_t)m->gid;
+  memcpy(*buf, &gid, sizeof(gid));
+  *buf += sizeof(gid);
+  int64_t mtime_sec = (int64_t)m->mtime_sec;
+  memcpy(*buf, &mtime_sec, sizeof(mtime_sec));
+  *buf += sizeof(mtime_sec);
+  int64_t mtime_nsec = (int64_t)m->mtime_nsec;
+  memcpy(*buf, &mtime_nsec, sizeof(mtime_nsec));
+  *buf += sizeof(mtime_nsec);
 }

 FileMetadata* metadata_from_buf(char** buf) {
-  int present;
-  memcpy(&present, *buf, sizeof(int));
-  *buf += sizeof(int);
+  int32_t present;
+  memcpy(&present, *buf, sizeof(present));
+  *buf += sizeof(present);
  if (!present)
    return NULL;
  FileMetadata* m = malloc(sizeof(FileMetadata));
-  memcpy(&m->mode, *buf, sizeof(mode_t));
-  *buf += sizeof(mode_t);
-  memcpy(&m->uid, *buf, sizeof(uid_t));
-  *buf += sizeof(uid_t);
-  memcpy(&m->gid, *buf, sizeof(gid_t));
-  *buf += sizeof(gid_t);
-  memcpy(&m->mtime_sec, *buf, sizeof(time_t));
-  *buf += sizeof(time_t);
-  memcpy(&m->mtime_nsec, *buf, sizeof(long));
-  *buf += sizeof(long);
+  if (m == NULL)
+    return NULL;
+  int32_t mode;
+  memcpy(&mode, *buf, sizeof(mode));
+  *buf += sizeof(mode);
+  m->mode = (mode_t)mode;
+  int32_t uid;
+  memcpy(&uid, *buf, sizeof(uid));
+  *buf += sizeof(uid);
+  m->uid = (uid_t)uid;
+  int32_t gid;
+  memcpy(&gid, *buf, sizeof(gid));
+  *buf += sizeof(gid);
+  m->gid = (gid_t)gid;
+  int64_t mtime_sec;
+  memcpy(&mtime_sec, *buf, sizeof(mtime_sec));
+  *buf += sizeof(mtime_sec);
+  m->mtime_sec = (time_t)mtime_sec;
+  int64_t mtime_nsec;
+  memcpy(&mtime_nsec, *buf, sizeof(mtime_nsec));
+  *buf += sizeof(mtime_nsec);
+  m->mtime_nsec = (long)mtime_nsec;
  return m;
 }

 bool metadata_send(int file_descriptor, FileMetadata* m) {
  if (m == NULL) {
-    int zero = 0;
-    return send_n_data(file_descriptor, &zero, sizeof(int));
+    int32_t zero = 0;
+    return send_n_data(file_descriptor, &zero, sizeof(zero));
  }
-  int present = 1;
-  return send_n_data(file_descriptor, &present, sizeof(int)) &&
-         send_n_data(file_descriptor, &m->mode, sizeof(mode_t)) &&
-         send_n_data(file_descriptor, &m->uid, sizeof(uid_t)) &&
-         send_n_data(file_descriptor, &m->gid, sizeof(gid_t)) &&
-         send_n_data(file_descriptor, &m->mtime_sec, sizeof(time_t)) &&
-         send_n_data(file_descriptor, &m->mtime_nsec, sizeof(long));
+  int32_t present = 1;
+  int32_t mode = (int32_t)m->mode;
+  int32_t uid = (int32_t)m->uid;
+  int32_t gid = (int32_t)m->gid;
+  int64_t mtime_sec = (int64_t)m->mtime_sec;
+  int64_t mtime_nsec = (int64_t)m->mtime_nsec;
+  return send_n_data(file_descriptor, &present, sizeof(present)) &&
+         send_n_data(file_descriptor, &mode, sizeof(mode)) &&
+         send_n_data(file_descriptor, &uid, sizeof(uid)) &&
+         send_n_data(file_descriptor, &gid, sizeof(gid)) &&
+         send_n_data(file_descriptor, &mtime_sec, sizeof(mtime_sec)) &&
+         send_n_data(file_descriptor, &mtime_nsec, sizeof(mtime_nsec));
 }

 FileMetadata* metadata_receive(int file_descriptor, int* ok) {
-  int present;
-  if (!receive_n_data(file_descriptor, &present, sizeof(int))) {
+  int32_t present;
+  if (!receive_n_data(file_descriptor, &present, sizeof(present))) {
    if (ok)
      *ok = 0;
    return NULL;
@@ -80,16 +116,46 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
      *ok = 0;
    return NULL;
  }
-  if (!receive_n_data(file_descriptor, &m->mode, sizeof(mode_t)) ||
-      !receive_n_data(file_descriptor, &m->uid, sizeof(uid_t)) ||
-      !receive_n_data(file_descriptor, &m->gid, sizeof(gid_t)) ||
-      !receive_n_data(file_descriptor, &m->mtime_sec, sizeof(time_t)) ||
-      !receive_n_data(file_descriptor, &m->mtime_nsec, sizeof(long))) {
+  int32_t mode;
+  if (!receive_n_data(file_descriptor, &mode, sizeof(mode))) {
    free(m);
    if (ok)
      *ok = 0;
    return NULL;
  }
+  m->mode = (mode_t)mode;
+  int32_t uid;
+  if (!receive_n_data(file_descriptor, &uid, sizeof(uid))) {
+    free(m);
+    if (ok)
+      *ok = 0;
+    return NULL;
+  }
+  m->uid = (uid_t)uid;
+  int32_t gid;
+  if (!receive_n_data(file_descriptor, &gid, sizeof(gid))) {
+    free(m);
+    if (ok)
+      *ok = 0;
+    return NULL;
+  }
+  m->gid = (gid_t)gid;
+  int64_t mtime_sec;
+  if (!receive_n_data(file_descriptor, &mtime_sec, sizeof(mtime_sec))) {
+    free(m);
+    if (ok)
+      *ok = 0;
+    return NULL;
+  }
+  m->mtime_sec = (time_t)mtime_sec;
+  int64_t mtime_nsec;
+  if (!receive_n_data(file_descriptor, &mtime_nsec, sizeof(mtime_nsec))) {
+    free(m);
+    if (ok)
+      *ok = 0;
+    return NULL;
+  }
+  m->mtime_nsec = (long)mtime_nsec;
  if (ok)
    *ok = 1;
  return m;
@@ -98,7 +164,7 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
 void file_restore_metadata(const char* path, FileMetadata* metadata) {
  if (metadata == NULL)
    return;
-  if (chmod(path, metadata->mode & 07777) != 0)
+  if (chmod(path, metadata->mode & 07777 & ~(S_ISUID | S_ISGID)) != 0)
    log_message(LOG_LEVEL_WARNING, "Failed to chmod %s: %s", path, strerror(errno));
  if (chown(path, metadata->uid, metadata->gid) != 0)
    log_message(LOG_LEVEL_WARNING, "Failed to chown %s: %s", path, strerror(errno));
@@ -3,10 +3,27 @@

 #include "file.h"
 #include <stdbool.h>
+#include <stdint.h>
 #include <sys/stat.h>

-#define FILE_METADATA_WIRE_SIZE                                                                    \
-  (sizeof(mode_t) + sizeof(uid_t) + sizeof(gid_t) + sizeof(time_t) + sizeof(long))
+/*
+ * Wire format (introduced in protocol version 2.0.0):
+ *   int32_t present
+ *   int32_t mode    (was mode_t, platform-dependent)
+ *   int32_t uid     (was uid_t,  platform-dependent)
+ *   int32_t gid     (was gid_t,  platform-dependent)
+ *   int64_t mtime_sec (was time_t, platform-dependent)
+ *   int64_t mtime_nsec (was long,  platform-dependent)
+ *
+ * Prior to 2.0.0 the wire format used the raw platform-dependent types,
+ * which broke compatiblity across different systems.  All fields are now
+ * serialized as fixed-width integers.
+ */
+
+/* Size of metadata fields on wire, excluding the int32_t `present` field that
+ * is always sent first. The total wire size for present metadata is
+ * sizeof(int32_t) + FILE_METADATA_WIRE_SIZE (32 bytes on most platforms). */
+#define FILE_METADATA_WIRE_SIZE (sizeof(int32_t) * 3 + sizeof(int64_t) * 2)

 void metadata_to_buf(char** buf, const FileMetadata* m);
 FileMetadata* metadata_from_buf(char** buf);
@@ -79,6 +79,11 @@ bool send_n_data(int file_descriptor, const void* data, size_t data_size) {
    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 (ssl_err == SSL_ERROR_WANT_WRITE || ssl_err == SSL_ERROR_WANT_READ)
+          continue;
+      }
      log_message(LOG_LEVEL_ERROR, "Could not send data");
      return false;
    }
@@ -102,6 +107,11 @@ bool receive_n_data(int file_descriptor, void* data, size_t data_size) {
      bytes_received =
          read(fd, (char*)data + total_bytes_received, data_size - total_bytes_received);
    if (bytes_received <= 0) {
+      if (io_ssl && bytes_received < 0) {
+        int ssl_err = SSL_get_error(io_ssl, (int)bytes_received);
+        if (ssl_err == SSL_ERROR_WANT_READ || ssl_err == SSL_ERROR_WANT_WRITE)
+          continue;
+      }
      if (bytes_received == 0)
        log_message(LOG_LEVEL_ERROR, "Connection closed while receiving data");
      else
@@ -138,6 +148,10 @@ static const char* status_to_string(Status status) {
 }

 bool send_str(int file_descriptor, const char* data) {
+  if (data == NULL) {
+    log_message(LOG_LEVEL_ERROR, "send_str called with NULL data");
+    return false;
+  }
  size_t size = strlen(data);
  if (!send_n_data(file_descriptor, &size, sizeof(size_t)))
    return false;
@@ -151,6 +165,11 @@ char* receive_str(int file_descriptor) {
  size_t size;
  if (!receive_n_data(file_descriptor, &size, sizeof(size_t)))
    return NULL;
+  if (size > MAX_STRING_SIZE) {
+    log_message(LOG_LEVEL_ERROR, "receive_str: size %zu exceeds maximum %zu", size,
+                (size_t)MAX_STRING_SIZE);
+    return NULL;
+  }
  char* data = (char*)malloc(size + 1);
  if (data == NULL)
    return NULL;
@@ -169,14 +188,20 @@ bool send_data(int file_descriptor, const Data* data) {
    return false;
  if (!send_n_data(file_descriptor, data->data, data_size))
    return false;
-  log_message(LOG_LEVEL_DEBUG, "Send %lld data", data_size);
+  log_message(LOG_LEVEL_DEBUG, "Send %llu data", data_size);
  return true;
 }

+#define MAX_DATA_SIZE (1024ULL * 1024 * 1024)
+
 Data* receive_data(int file_descriptor) {
  unsigned long long size = 0;
  if (!receive_n_data(file_descriptor, &size, sizeof(unsigned long long)))
    return NULL;
+  if ((size_t)size != size || size > MAX_DATA_SIZE) {
+    log_message(LOG_LEVEL_ERROR, "receive_data size %llu exceeds limits", size);
+    return NULL;
+  }
  void* data = malloc((size_t)size);
  if (data == NULL)
    return NULL;
@@ -184,7 +209,7 @@ Data* receive_data(int file_descriptor) {
    free(data);
    return NULL;
  }
-  log_message(LOG_LEVEL_DEBUG, "Received %lld data", size);
+  log_message(LOG_LEVEL_DEBUG, "Received %llu data", size);
  return data_create(data, (size_t)size);
 }

@@ -5,6 +5,9 @@
 #include <stdbool.h>
 #include <stddef.h>

+/* Maximum allowed string size for receive_str (10 MB) */
+#define MAX_STRING_SIZE (10 * 1024 * 1024)
+
 typedef struct ssl_st SSL;

 typedef int Status;
@@ -67,7 +67,7 @@ static int parse_remote_dest(const char* dest, RemoteDest* r) {
  return 0;
 }

-Client* client_connect_ssh(const char* destination, int port) {
+Client* client_connect_ssh(const char* destination, int port, const char* server_path) {
  RemoteDest r;
  if (parse_remote_dest(destination, &r) != 0) {
    fprintf(stderr, "Invalid remote destination: %s\n", destination);
@@ -119,12 +119,18 @@ Client* client_connect_ssh(const char* destination, int port) {
      close(sv[1]);

    char ssh_user[512];
+    int needed;
    if (r.user && r.user[0] != '\0')
-      snprintf(ssh_user, sizeof(ssh_user), "%s@%s", r.user, r.host);
+      needed = snprintf(ssh_user, sizeof(ssh_user), "%s@%s", r.user, r.host);
    else
-      snprintf(ssh_user, sizeof(ssh_user), "%s", r.host);
+      needed = snprintf(ssh_user, sizeof(ssh_user), "%s", r.host);
+    if ((size_t)needed >= sizeof(ssh_user))
+      fprintf(stderr, "Warning: ssh_user string truncated\n");

-    char* ssh_argv[16];
+    size_t ssh_argv_max = 32;
+    char** ssh_argv = calloc(ssh_argv_max, sizeof(char*));
+    if (ssh_argv == NULL)
+      _exit(1);
    int ac = 0;
    char port_str[16];
    ssh_argv[ac++] = "ssh";
@@ -135,15 +141,22 @@ Client* client_connect_ssh(const char* destination, int port) {
    ssh_argv[ac++] = "-o";
    ssh_argv[ac++] = "ControlPath=~/.cache/fastsync-%r@%h:%p";
    if (port > 0 && port != 22) {
+      if ((size_t)ac + 2 >= ssh_argv_max) {
+        _exit(1);
+      }
      ssh_argv[ac++] = "-p";
      snprintf(port_str, sizeof(port_str), "%d", port);
      ssh_argv[ac++] = port_str;
    }
+    if ((size_t)ac + 3 >= ssh_argv_max) {
+      _exit(1);
+    }
    ssh_argv[ac++] = ssh_user;
-    ssh_argv[ac++] = "fastsync-server";
+    ssh_argv[ac++] = (char*)(server_path ? server_path : "fastsync-server");
    ssh_argv[ac++] = "--stdio";
    ssh_argv[ac] = NULL;
    execvp("ssh", ssh_argv);
+    free(ssh_argv);
    perror("exec of ssh failed");
    ssize_t wret = write(exec_pipe[1], "x", 1);
    (void)wret;
@@ -161,7 +174,8 @@ Client* client_connect_ssh(const char* destination, int port) {
    close(sv[0]);
    waitpid(pid, NULL, 0);
    remote_dest_destroy(&r);
-    fprintf(stderr, "Error: could not launch 'fastsync-server --stdio' on remote\n");
+    fprintf(stderr, "Error: could not launch '%s --stdio' on remote\n",
+            server_path ? server_path : "fastsync-server");
    return NULL;
  }

@@ -174,7 +188,7 @@ Client* client_connect_ssh(const char* destination, int port) {
    return NULL;
  }
  client->file_descriptor = sv[0];
-  client->address.sin_family = AF_UNIX;
+  client->address.ss_family = AF_UNIX;
  client->address_length = 0;
  client->ssh_child_pid = pid;
  client->ssl = NULL;
@@ -3,6 +3,6 @@

 #include "transport_tcp.h"

-Client* client_connect_ssh(const char* destination, int port);
+Client* client_connect_ssh(const char* destination, int port, const char* server_path);

 #endif
@@ -2,29 +2,68 @@
 #include "log.h"
 #include "protocol.h"
 #include <arpa/inet.h>
+#include <errno.h>
+#include <netdb.h>
 #include <openssl/ssl.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
+#include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>

+bool set_socket_timeouts(int fd) {
+  struct timeval tv;
+  tv.tv_sec = 30;
+  tv.tv_usec = 0;
+
+  int keepalive = 1;
+  if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &keepalive, sizeof(keepalive)) < 0) {
+    perror("Could not set SO_KEEPALIVE");
+    return false;
+  }
+  if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)) < 0) {
+    perror("Could not set SO_RCVTIMEO");
+    return false;
+  }
+  if (setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv)) < 0) {
+    perror("Could not set SO_SNDTIMEO");
+    return false;
+  }
+  return true;
+}
+
 Server* server_create(int port) {
  Server* server = (Server*)malloc(sizeof(Server));
  if (server == NULL) {
    perror("Could not allocate space for Server");
    return NULL;
  }
+  memset(&server->address, 0, sizeof(server->address));

-  int file_descriptor = socket(AF_INET, SOCK_STREAM, 0);
-  if (file_descriptor < 0) {
+  // Try IPv6 first, fall back to IPv4
+  int fd = socket(AF_INET6, SOCK_STREAM, 0);
+  sa_family_t domain = AF_INET6;
+  if (fd < 0) {
+    fd = socket(AF_INET, SOCK_STREAM, 0);
+    domain = AF_INET;
+  }
+  if (fd < 0) {
    perror("Could not create Socket!");
    free(server);
    return NULL;
  }
-  server->file_descriptor = file_descriptor;
+
+  if (!set_socket_timeouts(fd)) {
+    close(fd);
+    free(server);
+    return NULL;
+  }
+
+  server->file_descriptor = fd;
+  server->ssl_ctx = NULL;
  int opt = 1;
  if (setsockopt(server->file_descriptor, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) {
    perror("Error setting a socket option!");
@@ -33,19 +72,61 @@ Server* server_create(int port) {
    return NULL;
  }

-  server->address.sin_family = AF_INET;
-  server->address.sin_addr.s_addr = INADDR_ANY;
-  server->address.sin_port = htons(port);
-  server->address_length = sizeof(server->address);
-  server->ssl_ctx = NULL;
+  // Use the domain from the socket we actually created
+  struct sockaddr_storage* addr = &server->address;
+  struct sockaddr_in* addr4 = (struct sockaddr_in*)addr;
+  struct sockaddr_in6* addr6 = (struct sockaddr_in6*)addr;
+
+  if (domain == AF_INET6) {
+    addr6->sin6_family = AF_INET6;
+    addr6->sin6_addr = in6addr_any;
+    addr6->sin6_port = htons(port);
+    addr->ss_family = AF_INET6;
+    server->address_length = sizeof(struct sockaddr_in6);
+  } else {
+    addr4->sin_family = AF_INET;
+    addr4->sin_addr.s_addr = INADDR_ANY;
+    addr4->sin_port = htons(port);
+    addr->ss_family = AF_INET;
+    server->address_length = sizeof(struct sockaddr_in);
+  }

  if (bind(server->file_descriptor, (struct sockaddr*)&server->address, server->address_length) <
      0) {
+    // If IPv6 bind failed (maybe no IPv6), try IPv4
+    if (domain == AF_INET6) {
+      close(fd);
+      fd = socket(AF_INET, SOCK_STREAM, 0);
+      if (fd < 0) {
+        perror("Could not create IPv4 Socket!");
+        free(server);
+        return NULL;
+      }
+      if (!set_socket_timeouts(fd)) {
+        close(fd);
+        free(server);
+        return NULL;
+      }
+      server->file_descriptor = fd;
+      setsockopt(server->file_descriptor, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
+      memset(addr, 0, sizeof(*addr));
+      addr4->sin_family = AF_INET;
+      addr4->sin_addr.s_addr = INADDR_ANY;
+      addr4->sin_port = htons(port);
+      server->address_length = sizeof(struct sockaddr_in);
+      if (bind(server->file_descriptor, (struct sockaddr*)addr, server->address_length) < 0) {
        perror("Could not bind server");
        close(server->file_descriptor);
        free(server);
        return NULL;
      }
+    } else {
+      perror("Could not bind server");
+      close(server->file_descriptor);
+      free(server);
+      return NULL;
+    }
+  }

  return server;
 }
@@ -62,6 +143,15 @@ void server_delete(Server** server) {
  *server = NULL;
 }

+/* Flag set by server_request_shutdown() to request graceful shutdown
+   of the accept loop. Accessed only from transport_tcp.c so it won't
+   cause linker errors when this file is compiled into client/test targets. */
+static volatile sig_atomic_t g_tcp_cleanup_requested = 0;
+
+void server_request_shutdown(void) {
+  g_tcp_cleanup_requested = 1;
+}
+
 static void accept_loop(Server* server, void (*child_fn)(int, void*), void* child_ctx,
                        const char* log_fmt) {
  if (listen(server->file_descriptor, SOMAXCONN) < 0) {
@@ -69,14 +159,20 @@ static void accept_loop(Server* server, void (*child_fn)(int, void*), void* chil
    return;
  }
  signal(SIGCHLD, SIG_IGN);
-  while (1) {
-    struct sockaddr_in client_addr;
+  while (!g_tcp_cleanup_requested) {
+    struct sockaddr_storage client_addr;
    socklen_t client_len = sizeof(client_addr);
    int fd = accept(server->file_descriptor, (struct sockaddr*)&client_addr, &client_len);
    if (fd < 0) {
+      if (errno == EINTR) {
+        if (g_tcp_cleanup_requested)
+          break;
+        continue;
+      }
      perror("Could not accept the connection");
      continue;
    }
+    set_socket_timeouts(fd);
    log_message(LOG_LEVEL_INFO, "%s", log_fmt);
    pid_t pid = fork();
    if (pid == 0) {
@@ -98,7 +194,11 @@ static void plain_child_fn(int fd, void* ctx) {
 }

 bool server_listen(Server* server, void (*handler)(int file_descriptor)) {
-  log_message(LOG_LEVEL_INFO, "Start Listening on Port: %d", ntohs(server->address.sin_port));
+  struct sockaddr_in* addr4 = (struct sockaddr_in*)&server->address;
+  int port = (server->address.ss_family == AF_INET6)
+                 ? ntohs(((struct sockaddr_in6*)&server->address)->sin6_port)
+                 : ntohs(addr4->sin_port);
+  log_message(LOG_LEVEL_INFO, "Start Listening on Port: %d", port);
  struct plain_ctx ctx = {handler};
  accept_loop(server, plain_child_fn, &ctx, "Received Connection");
  return true;
@@ -106,25 +206,23 @@ bool server_listen(Server* server, void (*handler)(int file_descriptor)) {

 void server_accept_loop(Server* server, void (*child_fn)(int, void*), void* child_ctx,
                        const char* log_fmt) {
-  log_message(LOG_LEVEL_INFO, "Start TLS Listening on Port: %d", ntohs(server->address.sin_port));
+  struct sockaddr_in* addr4 = (struct sockaddr_in*)&server->address;
+  int port = (server->address.ss_family == AF_INET6)
+                 ? ntohs(((struct sockaddr_in6*)&server->address)->sin6_port)
+                 : ntohs(addr4->sin_port);
+  log_message(LOG_LEVEL_INFO, "Start TLS Listening on Port: %d", port);
  accept_loop(server, child_fn, child_ctx, log_fmt);
 }

 Client* client_create() {
-  int file_descriptor = socket(AF_INET, SOCK_STREAM, 0);
-  if (file_descriptor < 0) {
-    perror("Could not create Socket!");
-    return NULL;
-  }
-
  Client* client = (Client*)malloc(sizeof(Client));
  if (client == NULL) {
-    close(file_descriptor);
    return NULL;
  }
-  client->file_descriptor = file_descriptor;
-  client->address.sin_family = AF_INET;
+  memset(&client->address, 0, sizeof(client->address));
+  client->address.ss_family = AF_UNSPEC;
  client->address_length = sizeof(client->address);
+  client->file_descriptor = -1;
  client->ssh_child_pid = -1;
  client->ssl = NULL;
  client->ssl_ctx = NULL;
@@ -132,18 +230,55 @@ Client* client_create() {
 }

 bool client_connect(Client* client, char* host, int port) {
-  client->address.sin_port = htons(port);
+  struct addrinfo hints, *res, *rp;
+  memset(&hints, 0, sizeof(hints));
+  hints.ai_family = AF_UNSPEC;
+  hints.ai_socktype = SOCK_STREAM;

-  if (inet_pton(AF_INET, host, &client->address.sin_addr) <= 0) {
-    perror("Could not convert host address!");
+  char port_str[16];
+  snprintf(port_str, sizeof(port_str), "%d", port);
+
+  int gai_err = getaddrinfo(host, port_str, &hints, &res);
+  if (gai_err != 0) {
+    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(gai_err));
    return false;
  }

-  if (connect(client->file_descriptor, (struct sockaddr*)&client->address, client->address_length) <
-      0) {
+  // Try IPv6 first, then IPv4
+  int fd = -1;
+  for (rp = res; rp != NULL; rp = rp->ai_next) {
+    fd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
+    if (fd < 0)
+      continue;
+    if (!set_socket_timeouts(fd)) {
+      close(fd);
+      fd = -1;
+      continue;
+    }
+    if (connect(fd, rp->ai_addr, rp->ai_addrlen) == 0)
+      break;
+    close(fd);
+    fd = -1;
+  }
+
+  if (fd < 0) {
    perror("Could not connect to Server!");
+    freeaddrinfo(res);
    return false;
  }
+
+  // Save the connected address
+  socklen_t addr_len = rp->ai_addrlen;
+  if (addr_len > sizeof(client->address))
+    addr_len = sizeof(client->address);
+  memcpy(&client->address, rp->ai_addr, addr_len);
+  client->address_length = addr_len;
+  freeaddrinfo(res);
+
+  // Close old fd if any and set new one
+  if (client->file_descriptor >= 0)
+    close(client->file_descriptor);
+  client->file_descriptor = fd;
  return true;
 }

@@ -154,7 +289,10 @@ void client_disconnect(Client* client) {
    client->ssl = NULL;
    io_set_ssl(NULL);
  }
+  if (client->file_descriptor >= 0) {
    close(client->file_descriptor);
+    client->file_descriptor = -1;
+  }
  if (client->ssh_child_pid > 0) {
    int status;
    waitpid(client->ssh_child_pid, &status, 0);
@@ -165,6 +303,7 @@ void client_disconnect(Client* client) {
 void client_delete(Client* client) {
  if (client == NULL)
    return;
+  client_disconnect(client);
  if (client->ssl_ctx) {
    SSL_CTX_free(client->ssl_ctx);
    client->ssl_ctx = NULL;
@@ -1,19 +1,21 @@
 #ifndef TRANSPORT_TCP_H
 #define TRANSPORT_TCP_H

+#include <netdb.h>
 #include <netinet/in.h>
 #include <stdbool.h>
+#include <sys/socket.h>
 #include <sys/types.h>

 typedef struct Server {
-  struct sockaddr_in address;
+  struct sockaddr_storage address;
  unsigned int address_length;
  int file_descriptor;
  void* ssl_ctx;
 } Server;

 typedef struct Client {
-  struct sockaddr_in address;
+  struct sockaddr_storage address;
  unsigned int address_length;
  int file_descriptor;
  pid_t ssh_child_pid;
@@ -26,9 +28,11 @@ bool server_listen(Server* server, void (*handler)(int file_descriptor));
 void server_accept_loop(Server* server, void (*child_fn)(int, void*), void* child_ctx,
                        const char* log_fmt);
 void server_delete(Server** server);
+void server_request_shutdown(void);
 Client* client_create();
 bool client_connect(Client* client, char* host, int port);
 void client_disconnect(Client* client);
 void client_delete(Client* client);
+bool set_socket_timeouts(int fd);

 #endif
@@ -5,6 +5,8 @@
 #include <arpa/inet.h>
 #include <openssl/err.h>
 #include <openssl/ssl.h>
+#include <openssl/x509.h>
+#include <openssl/x509v3.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -72,6 +74,12 @@ static SSL_CTX* create_ssl_ctx(bool is_server, const char* cert, const char* key
    }
    SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER, NULL);
    SSL_CTX_set_verify_depth(ctx, 4);
+  } else {
+    if (!is_server) {
+      log_message(LOG_LEVEL_WARNING,
+                  "No CA path provided — TLS server certificate will not be verified");
+    }
+    SSL_CTX_set_verify(ctx, SSL_VERIFY_NONE, NULL);
  }

  return ctx;
@@ -84,6 +92,7 @@ static SSL* wrap_fd_with_ssl(int fd, SSL_CTX* ctx, bool is_server) {
    return NULL;
  }
  SSL_set_fd(ssl, fd);
+
  int ret;
  if (is_server)
    ret = SSL_accept(ssl);
@@ -96,6 +105,17 @@ static SSL* wrap_fd_with_ssl(int fd, SSL_CTX* ctx, bool is_server) {
    SSL_free(ssl);
    return NULL;
  }
+
+  // In client mode, check verification result if peer verification was requested
+  if (!is_server) {
+    long verify_result = SSL_get_verify_result(ssl);
+    if (verify_result != X509_V_OK) {
+      log_message(LOG_LEVEL_ERROR, "TLS certificate verification failed: %ld", verify_result);
+      SSL_free(ssl);
+      return NULL;
+    }
+  }
+
  return ssl;
 }

@@ -133,16 +153,9 @@ bool server_listen_tls(Server* server, void (*handler)(int file_descriptor)) {

 bool client_connect_tls(Client* client, char* host, int port, const char* cert_path,
                        const char* key_path, const char* ca_path) {
-  client->address.sin_port = htons(port);
-  if (inet_pton(AF_INET, host, &client->address.sin_addr) <= 0) {
-    perror("Could not convert host address!");
+  // Use the common TCP connection logic (with IPv6 support)
+  if (!client_connect(client, host, port))
    return false;
-  }
-  if (connect(client->file_descriptor, (struct sockaddr*)&client->address, client->address_length) <
-      0) {
-    perror("Could not connect to Server!");
-    return false;
-  }

  SSL_CTX* ctx = create_ssl_ctx(false, cert_path, key_path, ca_path);
  if (!ctx)
@@ -155,6 +168,14 @@ bool client_connect_tls(Client* client, char* host, int port, const char* cert_p
    client->ssl_ctx = NULL;
    return false;
  }
+
+  // Set SNI and enable hostname verification
+  SSL_set_tlsext_host_name(ssl, host);
+  X509_VERIFY_PARAM* param = SSL_get0_param(ssl);
+  if (param) {
+    X509_VERIFY_PARAM_set1_host(param, host, 0);
+  }
+
  client->ssl = ssl;
  io_set_ssl(ssl);
  return true;
@@ -10,19 +10,23 @@
 #include <unistd.h>

 bool mkdir_r(const char* path) {
-  char* path_duplicate = malloc(strlen(path) + 1);
+  size_t path_len = strlen(path);
+  char* path_duplicate = malloc(path_len + 1);
  if (!path_duplicate)
    return false;
-  strcpy(path_duplicate, path);
-  char* path_current = (char*)malloc((strlen(path) + 2) * sizeof(char));
+  memcpy(path_duplicate, path, path_len + 1);
+  /* Buffer for building subpaths: path_len + 1 for leading '/' + 1 for null */
+  size_t buf_size = path_len + 2;
+  char* path_current = (char*)malloc(buf_size);
  if (!path_current) {
    free(path_duplicate);
    return false;
  }
-  char* path_current_position = path_current;
+  size_t pos = 0;
  if (path[0] == '/') {
-    strcpy(path_current, "/");
-    path_current_position += 1;
+    path_current[0] = '/';
+    path_current[1] = '\0';
+    pos = 1;
  } else {
    path_current[0] = '\0';
  }
@@ -31,10 +35,16 @@ bool mkdir_r(const char* path) {
  const char* part = strtok_r(path_duplicate, delimiter, &saveptr);
  bool ok = true;
  while (part != NULL) {
-    strcpy(path_current_position, part);
-    path_current_position += strlen(part) * sizeof(char);
-    strcpy(path_current_position, "/");
-    path_current_position += sizeof(char);
+    size_t part_len = strlen(part);
+    if (pos + part_len + 1 >= buf_size) {
+      ok = false;
+      break;
+    }
+    memcpy(path_current + pos, part, part_len);
+    pos += part_len;
+    path_current[pos] = '/';
+    pos++;
+    path_current[pos] = '\0';
    struct stat st;
    if (stat(path_current, &st) != 0) {
      if (mkdir(path_current, 0755) != 0) {
@@ -49,18 +59,34 @@ bool mkdir_r(const char* path) {
  free(path_current);
  return ok;
 }
-
 char* str_dup(const char* string) {
  if (string == NULL)
    return NULL;
  char* new_string = (char*)malloc(strlen(string) + 1);
-  strcpy(new_string, string);
+  memcpy(new_string, string, strlen(string) + 1);
  return new_string;
 }

 bool glob_match(const char* pattern, const char* str) {
  while (*pattern) {
    if (*pattern == '*') {
+      /* Check for double-star (globstar) pattern */
+      if (*(pattern + 1) == '*') {
+        pattern += 2;
+        /* Trailing double-star matches everything */
+        if (*pattern == '\0')
+          return true;
+        /* double-star slash: match at any depth */
+        if (*pattern == '/')
+          pattern++;
+        while (*str) {
+          if (glob_match(pattern, str))
+            return true;
+          str++;
+        }
+        return glob_match(pattern, str);
+      }
+      /* Single * — does not cross / boundaries */
      pattern++;
      while (*str && *str != '/') {
        if (glob_match(pattern, str))
@@ -74,8 +100,17 @@ bool glob_match(const char* pattern, const char* str) {
      pattern++;
      str++;
    } else {
-      if (*pattern != *str)
+      if (*pattern != *str) {
+        /* If pattern has a '/' followed by '**', allow zero path components */
+        if (*pattern == '/' && *(pattern + 1) == '*' && *(pattern + 2) == '*') {
+          /* Skip over slash-double-star and try to match rest against current str */
+          const char* rest = pattern + 3;
+          if (*rest == '/')
+            rest++;
+          return glob_match(rest, str);
+        }
        return false;
+      }
      pattern++;
      str++;
    }
@@ -99,7 +134,7 @@ static void delete_extras_walk(const char* abs_path, const char* rel_path, Array
  if (!dir)
    return;
  bool all_removed = true;
-  struct dirent* entry;
+  const struct dirent* entry;
  while ((entry = readdir(dir)) != NULL) {
    if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
      continue;
@@ -149,18 +184,17 @@ void delete_extras(const char* dest_root, ArrayList* manifest) {
  delete_extras_walk(dest_root, "", manifest);
 }

-char* path_cat(const char* path1, char* path2) {
+char* path_cat(const char* path1, const char* path2) {
  if (path1 == NULL || *path1 == '\0')
    return str_dup(path2);
  if (path2 == NULL || *path2 == '\0')
    return str_dup(path1);
  int path1_len = strlen(path1);
  int path2_len = strlen(path2);
-  char* path2_pointer = path2;
  if (path1[path1_len - 1] == '/')
    path1_len -= 1;
  if (path2[0] == '/') {
-    path2_pointer += 1;
+    path2++;
    path2_len -= 1;
  }
  char* new_path = malloc(path1_len + path2_len + 2);
@@ -168,7 +202,7 @@ char* path_cat(const char* path1, char* path2) {
    return NULL;
  memcpy(new_path, path1, path1_len);
  new_path[path1_len] = '/';
-  memcpy(new_path + path1_len + 1, path2_pointer, path2_len);
+  memcpy(new_path + path1_len + 1, path2, path2_len);
  new_path[path1_len + path2_len + 1] = '\0';
  return new_path;
 }
@@ -6,7 +6,7 @@

 bool mkdir_r(const char* path);
 char* str_dup(const char* string);
-char* path_cat(const char* path1, char* path2);
+char* path_cat(const char* path1, const char* path2);
 bool glob_match(const char* pattern, const char* str);
 void delete_extras(const char* dest_root, ArrayList* manifest);

@@ -23,6 +23,14 @@ static void test_data_create_empty() {
  data_destroy(d);
 }

+static void test_data_create_empty_zero() {
+  Data* d = data_create_empty(0);
+  EXPECT_NOT_NULL(d);
+  EXPECT_NOT_NULL(d->data);
+  EXPECT_EQ_INT((int)d->size, 0);
+  data_destroy(d);
+}
+
 static void test_data_create_reserve() {
  Data* d = data_create_reserve(1024);
  EXPECT_NOT_NULL(d);
@@ -44,6 +52,7 @@ static void test_data_destroy_normal() {
 void test_data() {
  test_data_create();
  test_data_create_empty();
+  test_data_create_empty_zero();
  test_data_create_reserve();
  test_data_destroy_null();
  test_data_destroy_normal();
@@ -217,9 +217,10 @@ static void test_file_send_no_path() {
  pid_t pid = fork();
  if (pid == 0) {
    close(p[1]);
+    // Read file type indicator
    int file_type;
    EXPECT_TRUE(receive_int(p[0], &file_type));
-    EXPECT_EQ_INT(file_type, 0); /* FILE_TYPE_REGULAR */
+    EXPECT_EQ_INT(file_type, (int)FILE_TYPE_REGULAR);
    Data* received = receive_data(p[0]);
    close(p[0]);

@@ -224,11 +224,10 @@ static void test_sendfile_no_path() {
  pid_t pid = fork();
  if (pid == 0) {
    close(p[1]);
-    /* When send_path is false, the sender sends file_type + raw data (size + bytes).
-     * Read file_type first with assertion, then receive data. */
+    /* When send_path is false, the sender still sends file_type + data */
    int file_type;
    EXPECT_TRUE(receive_int(p[0], &file_type));
-    EXPECT_EQ_INT(file_type, 0); /* FILE_TYPE_REGULAR */
+    EXPECT_EQ_INT(file_type, (int)FILE_TYPE_REGULAR);
    Data* received = receive_data(p[0]);
    close(p[0]);

@@ -259,11 +258,16 @@ static void test_sendfile_no_path() {
 }

 void test_file_sendfile() {
-  test_sendfile_missing_file(); // no fork, always runs
-  if (!getenv("FASTSYNC_UNDER_VALGRIND")) {
+  if (!is_running_under_valgrind()) {
+    // Fork tests are skipped under valgrind because the parent process runs
+    // orders of magnitude slower than the child (parent is instrumented, child
+    // is not), which causes pipe-based protocol handshake timeouts. The parent
+    // process itself has zero valgrind errors -- the failures are all in the
+    // forked children where inherited allocations are reported as leaks.
    test_sendfile_basic();
    test_sendfile_empty_file();
    test_sendfile_compression_fallback();
    test_sendfile_no_path();
  }
+  test_sendfile_missing_file(); // no fork, safe under valgrind
 }
@@ -49,6 +49,33 @@ static void test_glob_question_star() {
  EXPECT_TRUE(glob_match("?*.txt", "a.txt"));
 }

+static void test_glob_doublestar_match_all() {
+  EXPECT_TRUE(glob_match("**", "anything"));
+  EXPECT_TRUE(glob_match("**", "path/to/file"));
+}
+
+static void test_glob_doublestar_prefix() {
+  EXPECT_TRUE(glob_match("**/foo", "foo"));
+  EXPECT_TRUE(glob_match("**/foo", "bar/foo"));
+  EXPECT_TRUE(glob_match("**/foo", "a/b/c/foo"));
+  EXPECT_FALSE(glob_match("**/foo", "foobar"));
+  EXPECT_FALSE(glob_match("**/foo", "bar/foobar"));
+}
+
+static void test_glob_doublestar_suffix() {
+  EXPECT_TRUE(glob_match("foo/**", "foo"));
+  EXPECT_TRUE(glob_match("foo/**", "foo/bar"));
+  EXPECT_TRUE(glob_match("foo/**", "foo/bar/baz"));
+  EXPECT_FALSE(glob_match("foo/**", "foobar"));
+}
+
+static void test_glob_doublestar_mid() {
+  EXPECT_TRUE(glob_match("a/**/b", "a/b"));
+  EXPECT_TRUE(glob_match("a/**/b", "a/x/b"));
+  EXPECT_TRUE(glob_match("a/**/b", "a/x/y/z/b"));
+  EXPECT_FALSE(glob_match("a/**/b", "a/x/bad"));
+}
+
 void test_glob() {
  test_glob_exact_match();
  test_glob_question_mark();
@@ -60,4 +87,8 @@ void test_glob() {
  test_glob_slash_not_matched();
  test_glob_complex();
  test_glob_question_star();
+  test_glob_doublestar_match_all();
+  test_glob_doublestar_prefix();
+  test_glob_doublestar_suffix();
+  test_glob_doublestar_mid();
 }
@@ -173,6 +173,23 @@ static void test_receive_str_truncated() {
  close(p[0]);
 }

+static void test_receive_str_oversized() {
+  int p[2];
+  EXPECT_EQ_INT(pipe(p), 0);
+  io_set_fds(p[0], p[1]);
+  io_set_bwlimit(0);
+
+  /* Send a size exceeding MAX_STRING_SIZE */
+  size_t huge = MAX_STRING_SIZE + 1;
+  EXPECT_TRUE(send_n_data(0, &huge, sizeof(size_t)));
+
+  const char* received = receive_str(0);
+  EXPECT_NULL(received);
+
+  close(p[0]);
+  close(p[1]);
+}
+
 void test_protocol() {
  test_send_receive_n_data();
  test_send_receive_n_data_zero();
@@ -183,4 +200,5 @@ void test_protocol() {
  test_send_receive_status();
  test_receive_n_data_truncated();
  test_receive_str_truncated();
+  test_receive_str_oversized();
 }
@@ -154,8 +154,6 @@ static void test_scanner_exclude_pattern() {
 }

 static void test_scanner_exclude_subdirectory() {
-  /* Exclude patterns match filenames only (via entry->d_name).
-   * Files inside subdirectories are also matched by filename. */
  const char* root = "test_scan_excl_sub";
  const char* sub = "test_scan_excl_sub/sub";
  const char* root_txt = "test_scan_excl_sub/root.txt";
@@ -169,7 +167,6 @@ static void test_scanner_exclude_subdirectory() {
  create_test_file(sub_txt, content);
  create_test_file(sub_tmp, content);

-  /* Exclude *.tmp — should exclude sub/temp.tmp but keep root.txt and sub/data.txt */
  char* exclude[] = {"*.tmp"};
  DirectoryScanner* scanner =
      directory_scanner_create((char*)root, false, 0, exclude, 1, NULL, 0, 0, 0);
@@ -180,7 +177,6 @@ static void test_scanner_exclude_subdirectory() {
  while ((chunk = directory_scanner_next(scanner)) != NULL) {
    total += chunk->element_count;
    for (int i = 0; i < chunk->element_count; i++) {
-      /* No path should end in .tmp */
      size_t len = strlen(chunk->items[i]->path);
      EXPECT_TRUE(len < 4 || strcmp(chunk->items[i]->path + len - 4, ".tmp") != 0);
    }
@@ -197,10 +193,6 @@ static void test_scanner_exclude_subdirectory() {
 }

 static void test_scanner_include_and_exclude() {
-  /* In the scanner, exclude is checked first and takes precedence.
-   * Include patterns act as an additional filter: if include_count > 0,
-   * the file must match one of the include patterns (after not being excluded).
-   * This test uses non-overlapping exclude and include patterns. */
  const char* dir = "test_scan_inc_exc";
  const char* f_txt = "test_scan_inc_exc/a.txt";
  const char* f_log = "test_scan_inc_exc/b.log";
@@ -212,7 +204,6 @@ static void test_scanner_include_and_exclude() {
  create_test_file(f_log, content);
  create_test_file(f_bak, content);

-  /* Exclude *.bak. Include *.txt and *.log. */
  char* exclude[] = {"*.bak"};
  char* include[] = {"*.txt", "*.log"};
  DirectoryScanner* scanner =
@@ -230,7 +221,6 @@ static void test_scanner_include_and_exclude() {
    if (strstr(chunk->items[i]->path, "b.log"))
      found_log = 1;
  }
-  /* a.txt included by *.txt, b.log included by *.log, c.bak excluded by *.bak */
  EXPECT_TRUE(found_txt);
  EXPECT_TRUE(found_log);

@@ -9,14 +9,14 @@
 static void test_ssh_connect_invalid_dest() {
  /* Missing colon — parse_remote_dest should fail and return NULL */
  /* cppcheck-suppress constVariablePointer */
-  Client* client = client_connect_ssh("invalid-destination-no-colon", 22);
+  Client* client = client_connect_ssh("invalid-destination-no-colon", 22, NULL);
  EXPECT_NULL(client);
 }

 /* Test client_connect_ssh with empty destination */
 static void test_ssh_connect_empty_dest() {
  /* cppcheck-suppress constVariablePointer */
-  Client* client = client_connect_ssh("", 22);
+  Client* client = client_connect_ssh("", 22, NULL);
  EXPECT_NULL(client);
 }

@@ -24,7 +24,7 @@ static void test_ssh_connect_empty_dest() {
 * parse_remote_dest succeeds, ssh is exec'd and fails, but the function
 * creates a Client that must be cleaned up. */
 static void test_ssh_connect_malformed() {
-  Client* client = client_connect_ssh(":", 22);
+  Client* client = client_connect_ssh(":", 22, NULL);
  /* ssh binary exists, so exec succeeds; the function returns a Client.
   * We just verify it doesn't crash and clean up properly. */
  if (client != NULL) {
@@ -37,7 +37,7 @@ static void test_ssh_connect_malformed() {
 /* Test client_connect_ssh with valid format but unreachable host.
 * The function launches ssh which will fail to connect, returns a Client. */
 static void test_ssh_connect_unreachable() {
-  Client* client = client_connect_ssh("nonexistent.invalid:/remote/path", 22);
+  Client* client = client_connect_ssh("nonexistent.invalid:/remote/path", 22, NULL);
  if (client != NULL) {
    client_disconnect(client);
    client_delete(client);
@@ -8,8 +8,8 @@
 static void test_client_create_delete() {
  Client* client = client_create();
  EXPECT_NOT_NULL(client);
-  EXPECT_TRUE(client->file_descriptor >= 0);
-  EXPECT_EQ_INT(client->address.sin_family, AF_INET);
+  EXPECT_EQ_INT(client->file_descriptor, -1);
+  EXPECT_EQ_INT(client->address.ss_family, AF_UNSPEC);
  EXPECT_EQ_INT(client->ssh_child_pid, -1);
  EXPECT_NULL(client->ssl);
  EXPECT_NULL(client->ssl_ctx);
@@ -30,7 +30,7 @@ static void test_server_create_delete() {
  Server* server = server_create(0);
  EXPECT_NOT_NULL(server);
  EXPECT_TRUE(server->file_descriptor >= 0);
-  EXPECT_EQ_INT(server->address.sin_family, AF_INET);
+  EXPECT_TRUE(server->address.ss_family == AF_INET || server->address.ss_family == AF_INET6);
  EXPECT_NULL(server->ssl_ctx);

  /* Clean up */
@@ -57,9 +57,8 @@ static void test_client_create_multiple() {
  Client* c2 = client_create();
  EXPECT_NOT_NULL(c1);
  EXPECT_NOT_NULL(c2);
-  EXPECT_TRUE(c1->file_descriptor >= 0);
-  EXPECT_TRUE(c2->file_descriptor >= 0);
-  EXPECT_TRUE(c1->file_descriptor != c2->file_descriptor);
+  EXPECT_EQ_INT(c1->file_descriptor, -1);
+  EXPECT_EQ_INT(c2->file_descriptor, -1);

  client_delete(c1);
  client_delete(c2);