fix: features and enhancements — issues #70, #36, #34, #33, #32, #57, #40, #37

src/client/client_cli.c

@@ -55,8 +55,8 @@ 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("  --help              Show this help\n");
-  printf("  -V, --version       Show version and exit\n");
 }
 
 int main(int argc, char* argv[]) {
@@ -81,9 +81,6 @@ 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;
@@ -203,6 +200,8 @@ 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], "-v") == 0 || strcmp(argv[i], "--verbose") == 0) {
       set_log_level(LOG_LEVEL_DEBUG);
     } else if (argv[i][0] == '-') {

src/client/scanner.c

@@ -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;
@@ -24,12 +35,62 @@ 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;
+  scanner->follow_symlinks = follow_symlinks;
   queue_enqueue(scanner->directories, str_dup(root_directory));
   return scanner;
 }
@@ -42,6 +103,12 @@ 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 +171,76 @@ 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);
+      }
+      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++) {

src/client/scanner.h

@@ -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 +26,11 @@ 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);
 

src/server/server.c

@@ -11,11 +11,47 @@
 #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;
+  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 +65,7 @@ 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 +75,7 @@ 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 +86,7 @@ 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);
     }
@@ -135,7 +171,6 @@ 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[]) {
@@ -150,9 +185,6 @@ 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);

src/shared/compression.c

@@ -1,7 +1,8 @@
 #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)
@@ -66,8 +67,16 @@ 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");

src/shared/config.c

@@ -14,8 +14,6 @@ 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;
@@ -47,6 +45,8 @@ 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;
@@ -129,6 +129,26 @@ 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;
@@ -223,6 +243,70 @@ 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;
+
+  // Receive exclude patterns
+  int ec;
+  if (!receive_int(file_descriptor, &ec))
+    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;
+  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))

src/shared/config.h

@@ -40,9 +40,11 @@ typedef struct Config {
   char* tls_cert;
   char* tls_key;
   char* tls_ca;
+  bool follow_symlinks;
+  bool partial;
 } Config;
 
-#define PROTOCOL_VERSION "2.0.0"
+#define PROTOCOL_VERSION "1.3.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)
 
 Config* config_create(char* version, char* send_directory, char* receive_directory,

src/shared/data.c

@@ -3,7 +3,9 @@
 #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;

src/shared/data.h

@@ -1,7 +1,7 @@
 #ifndef DATA_H
 #define DATA_H
 
-#include <stdlib.h>
+#include "stdlib.h"
 
 typedef struct {
   void* data;

src/shared/file.c

@@ -1,5 +1,4 @@
 #include <dirent.h>
-#include <errno.h>
 #include <fcntl.h>
 #include <libgen.h>
 #include <stddef.h>
@@ -21,6 +20,9 @@
 #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) {
@@ -35,7 +37,7 @@ File* file_create(const char* path) {
     return NULL;
   }
 
-  memcpy(file->path, path, path_len + 1);
+  strcpy(file->path, path);
   file->data = data_create_reserve(0);
   if (file->data == NULL) {
     free(file->path);
@@ -43,6 +45,8 @@ File* file_create(const char* path) {
     return NULL;
   }
   file->metadata = NULL;
+  file->type = FILE_TYPE_REGULAR;
+  file->link_target = NULL;
   return file;
 }
 
@@ -56,6 +60,8 @@ void file_destroy(void* item) {
   file->metadata = NULL;
   free(file->path);
   file->path = NULL;
+  free(file->link_target);
+  file->link_target = NULL;
   free(file);
 }
 
@@ -84,6 +90,14 @@ 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) {
@@ -99,10 +113,69 @@ bool file_load_data(File* file) {
   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[STREAM_CHUNK_SIZE];
+  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");
+      }
+      fclose(fp);
+      return false;
+    }
+    if (!send_n_data(file_descriptor, buf, nread)) {
+      fclose(fp);
+      return false;
+    }
+    remaining -= (unsigned long long)nread;
+  }
+  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) {
@@ -111,14 +184,6 @@ 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;
-  }
   if (!send_data(file_descriptor, data_to_send)) {
     data_destroy(compressed_data);
     return false;
@@ -128,6 +193,18 @@ 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) {
+    char* disk_path = path_cat((char*)root_directory, file->path);
+    if (disk_path == NULL)
+      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;
@@ -331,6 +408,18 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
   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) {
+      sprintf(partial_path, "%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;
 
@@ -386,6 +475,26 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
     }
   }
 
+  // Read file type indicator
+  int file_type;
+  if (!receive_int(fd, &file_type)) {
+    file_destroy(file);
+    send_status(fd, STATUS_ERROR);
+    return NULL;
+  }
+  file->type = (FileType)file_type;
+
+  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_data(fd);
   if (file_data == NULL) {
     file_destroy(file);
@@ -447,13 +556,14 @@ 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);
@@ -463,6 +573,11 @@ bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int
   if (use_metadata && !metadata_send(file_descriptor, file->metadata))
     return false;
 
+  // Send file type indicator
+  int ft = (int)file->type;
+  if (!send_int(file_descriptor, ft))
+    return false;
+
   int fd = open(file->path, O_RDONLY);
   if (fd == -1) {
     perror("Could not open file for sendfile");
@@ -505,6 +620,30 @@ 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);
@@ -519,6 +658,7 @@ File* file_receive(const Config* config, int file_descriptor) {
     }
     file_data = file_data_uncompressed;
   }
+
   data_destroy(file->data);
   file->data = file_data;
   return file;

src/shared/file.h

@@ -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);

src/shared/log.c

@@ -14,8 +14,7 @@ void log_message(LogLevel log_level, char* format, ...) {
   if (log_level < current_log_level)
     return;
   time_t now = time(NULL);
-  struct tm result_buf;
-  const struct tm* t = localtime_r(&now, &result_buf);
+  const struct tm* t = localtime(&now);
 
   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]);

src/shared/metadata.c

@@ -4,103 +4,67 @@
 #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) {
-  int32_t present = (m != NULL) ? 1 : 0;
-  memcpy(*buf, &present, sizeof(present));
-  *buf += sizeof(present);
+  int present = (m != NULL) ? 1 : 0;
+  memcpy(*buf, &present, sizeof(int));
+  *buf += sizeof(int);
   if (m == NULL)
     return;
-  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);
+  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);
 }
 
 FileMetadata* metadata_from_buf(char** buf) {
-  int32_t present;
-  memcpy(&present, *buf, sizeof(present));
-  *buf += sizeof(present);
+  int present;
+  memcpy(&present, *buf, sizeof(int));
+  *buf += sizeof(int);
   if (!present)
     return NULL;
   FileMetadata* m = malloc(sizeof(FileMetadata));
-  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;
+  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);
   return m;
 }
 
 bool metadata_send(int file_descriptor, FileMetadata* m) {
   if (m == NULL) {
-    int32_t zero = 0;
-    return send_n_data(file_descriptor, &zero, sizeof(zero));
+    int zero = 0;
+    return send_n_data(file_descriptor, &zero, sizeof(int));
   }
-  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));
+  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));
 }
 
 FileMetadata* metadata_receive(int file_descriptor, int* ok) {
-  int32_t present;
-  if (!receive_n_data(file_descriptor, &present, sizeof(present))) {
+  int present;
+  if (!receive_n_data(file_descriptor, &present, sizeof(int))) {
     if (ok)
       *ok = 0;
     return NULL;
@@ -116,46 +80,16 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
       *ok = 0;
     return NULL;
   }
-  int32_t mode;
-  if (!receive_n_data(file_descriptor, &mode, sizeof(mode))) {
+  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))) {
     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;

src/shared/metadata.h

@@ -3,24 +3,10 @@
 
 #include "file.h"
 #include <stdbool.h>
-#include <stdint.h>
 #include <sys/stat.h>
 
-/*
- * 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.
- */
-
-#define FILE_METADATA_WIRE_SIZE (sizeof(int32_t) * 3 + sizeof(int64_t) * 2)
+#define FILE_METADATA_WIRE_SIZE                                                                    \
+  (sizeof(mode_t) + sizeof(uid_t) + sizeof(gid_t) + sizeof(time_t) + sizeof(long))
 
 void metadata_to_buf(char** buf, const FileMetadata* m);
 FileMetadata* metadata_from_buf(char** buf);

src/shared/protocol.c

@@ -138,6 +138,10 @@ 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 +155,11 @@ 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;

src/shared/protocol.h

@@ -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;

src/shared/transport_ssh.c

@@ -124,7 +124,10 @@ Client* client_connect_ssh(const char* destination, int port) {
     else
       snprintf(ssh_user, sizeof(ssh_user), "%s", r.host);
 
-    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 +138,24 @@ 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) {
+        free(ssh_argv);
+        _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) {
+      free(ssh_argv);
+      _exit(1);
+    }
     ssh_argv[ac++] = ssh_user;
     ssh_argv[ac++] = "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;
@@ -174,7 +186,7 @@ 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;

src/shared/transport_tcp.c

@@ -2,29 +2,64 @@
 #include "log.h"
 #include "protocol.h"
 #include <arpa/inet.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);
+  if (fd < 0) {
+    fd = socket(AF_INET, SOCK_STREAM, 0);
+  }
+  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;
   int opt = 1;
   if (setsockopt(server->file_descriptor, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) {
     perror("Error setting a socket option!");
@@ -33,19 +68,64 @@ 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;
+  // Determine address family from the actual socket
+  struct sockaddr_storage* addr = &server->address;
+  socklen_t addr_len = sizeof(*addr);
+  if (getsockname(fd, (struct sockaddr*)addr, &addr_len) == 0) {
+    // Use the family of the socket we actually created
+  }
+
+  struct sockaddr_in* addr4 = (struct sockaddr_in*)addr;
+  struct sockaddr_in6* addr6 = (struct sockaddr_in6*)addr;
+
+  if (addr->ss_family == AF_INET6) {
+    addr6->sin6_family = AF_INET6;
+    addr6->sin6_addr = in6addr_any;
+    addr6->sin6_port = htons(port);
+    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);
+    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 (addr->ss_family == 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;
 }
@@ -70,13 +150,14 @@ static void accept_loop(Server* server, void (*child_fn)(int, void*), void* chil
   }
   signal(SIGCHLD, SIG_IGN);
   while (1) {
-    struct sockaddr_in client_addr;
+    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) {
       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 +179,11 @@ 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 +191,23 @@ 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 +215,52 @@ 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
+  memcpy(&client->address, rp->ai_addr, rp->ai_addrlen);
+  client->address_length = rp->ai_addrlen;
+  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 +271,10 @@ 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);

src/shared/transport_tcp.h

@@ -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;
@@ -30,5 +32,6 @@ 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

src/shared/transport_tls.c

@@ -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)

src/shared/utils.c

@@ -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) {
@@ -49,12 +59,11 @@ 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);
-  memcpy(new_string, string, strlen(string) + 1);
+  strcpy(new_string, string);
   return new_string;
 }
 

tests/test_data.c

@@ -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();

tests/test_file.c

@@ -217,6 +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, (int)FILE_TYPE_REGULAR);
     Data* received = receive_data(p[0]);
     close(p[0]);
 
@@ -271,7 +275,7 @@ void test_file() {
   test_to_disk_basic();
   test_to_disk_creates_dirs();
   test_file_content_to_buffer();
-  if (!is_running_under_valgrind()) {
+  if (!getenv("FASTSYNC_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

tests/test_protocol.c

@@ -169,6 +169,23 @@ 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)));
+
+  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();
@@ -179,4 +196,5 @@ void test_protocol() {
   test_send_receive_status();
   test_receive_n_data_truncated();
   test_receive_str_truncated();
+  test_receive_str_oversized();
 }

tests/test_utils.h

@@ -2,24 +2,9 @@
 #define TEST_UTILS_H
 
 #include <stdio.h>
-#include <stdlib.h>
 #include <string.h>
 #include <stdbool.h>
 
-// Detect if running under valgrind by checking /proc/self/maps for vgpreload.
-// This is used to skip fork-based tests that are incompatible with valgrind
-// (the instrumented parent runs too slowly, causing pipe timeouts).
-static inline bool is_running_under_valgrind(void) {
-  FILE* f = fopen("/proc/self/maps", "r");
-  if (!f)
-    return false;
-  char buf[4096];
-  size_t n = fread(buf, 1, sizeof(buf) - 1, f);
-  fclose(f);
-  buf[n] = '\0';
-  return strstr(buf, "vgpreload") != NULL;
-}
-
 // Global test suite status
 extern int tests_run;
 extern int tests_failed;