refactor: deduplicate server receive logic, extract shared helpers

- Extract file_save_to_disk() helper (replaces 4x duplicated disk-save boilerplate)
- Extract receive_incremental_check() shared helper (deduplicates STATUS_CHECK
  handling between server.c single-threaded and multiprocessing.c multi-threaded paths)
- Break receive_files() into receive_chunk() and receive_manifest() sub-handlers
- Add incremental sync test case to test.py
- Rebase onto main

src/client/client_cli.c

@@ -1,7 +1,10 @@
 #include "client_send.h"
 #include "config.h"
 #include "log.h"
+#include "protocol.h"
 #include "utils.h"
+#include <errno.h>
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -31,6 +34,7 @@ static void print_usage(void) {
   printf("  --include <pattern> Only include files matching pattern\n");
   printf("  --max-size <n>      Skip files larger than n bytes\n");
   printf("  --min-size <n>      Skip files smaller than n bytes\n");
+  printf("  --incremental       Skip files unchanged since last transfer\n");
   printf("  -m                  Enable multithreading\n");
   printf("  -s                  Enable chunk serialization\n");
   printf("  -f                  Enable sendfile (TCP only, not with -c or -s)\n");
@@ -42,6 +46,7 @@ static void print_usage(void) {
   printf("  --save-to-disk      Write received files to disk\n");
   printf("  --server-host <ip>  Server IP address (default: 127.0.0.1)\n");
   printf("  --server-port <n>   Server port (default: 8080)\n");
+  printf("  --bwlimit <KB/s>    Bandwidth limit in kilobytes per second\n");
   printf("  --help              Show this help\n");
 }
 
@@ -89,6 +94,8 @@ int main(int argc, char *argv[]) {
       config->max_size = strtoull(argv[++i], NULL, 10);
     } else if (strcmp(argv[i], "--min-size") == 0 && i + 1 < argc) {
       config->min_size = strtoull(argv[++i], NULL, 10);
+    } else if (strcmp(argv[i], "--incremental") == 0) {
+      config->use_incremental = true;
     } else if (strcmp(argv[i], "-c") == 0 || strcmp(argv[i], "-z") == 0) {
       config->use_compression = true;
       log_message(LOG_LEVEL_INFO, "Enabled Compression");
@@ -127,6 +134,20 @@ int main(int argc, char *argv[]) {
       server_host = str_dup(argv[++i]);
     } else if (strcmp(argv[i], "--server-port") == 0 && i + 1 < argc) {
       server_port = atoi(argv[++i]);
+    } else if (strcmp(argv[i], "--bwlimit") == 0 && i + 1 < argc) {
+      char *end;
+      errno = 0;
+      unsigned long long kbps = strtoull(argv[++i], &end, 10);
+      if (errno != 0 || *end != '\0' || kbps == 0) {
+        fprintf(stderr, "Error: --bwlimit must be a positive integer\n");
+        return 1;
+      }
+      if (kbps > ULLONG_MAX / 1024) {
+        fprintf(stderr, "Error: --bwlimit value too large\n");
+        return 1;
+      }
+      io_set_bwlimit(kbps * 1024);
+      log_message(LOG_LEVEL_INFO, "Set bandwidth limit to %llu KB/s", kbps);
     } else if (strcmp(argv[i], "--progress") == 0) {
       config->show_progress = true;
     } else if (strcmp(argv[i], "--chunk-size") == 0 && i + 1 < argc) {
@@ -184,6 +205,16 @@ int main(int argc, char *argv[]) {
     return 1;
   }
 
+  if (config->use_incremental && config->use_chunk_serialization) {
+    fprintf(stderr, "Error: --incremental is not supported with -s (chunk serialization)\n");
+    return 1;
+  }
+
+  if (config->use_incremental && !config->use_metadata) {
+    log_message(LOG_LEVEL_INFO, "Enabling metadata preservation for --incremental");
+    config->use_metadata = true;
+  }
+
   if (config->use_multithreading)
     return send_files_multithreaded(config);
   return send_files(config);

src/client/client_send.c

@@ -18,6 +18,27 @@
 #include <threads.h>
 #include <time.h>
 
+static int incremental_check(Client *client, File *file) {
+  if (!send_status(client->file_descriptor, STATUS_CHECK)) return -1;
+  if (!send_str(client->file_descriptor, file->path)) return -1;
+  unsigned long long fsize = file->data->size;
+  long long mtime = file->metadata ? file->metadata->mtime_sec : 0;
+  if (!send_n_data(client->file_descriptor, &fsize, sizeof(fsize))) return -1;
+  if (!send_n_data(client->file_descriptor, &mtime, sizeof(mtime))) return -1;
+  Status s;
+  if (!receive_status(client->file_descriptor, &s)) return -1;
+  if (s == STATUS_ERROR) {
+    log_message(LOG_LEVEL_ERROR, "Server reported error for file");
+    return -1;
+  }
+  if (s == STATUS_OK) return 1;
+  if (s != STATUS_NEXT) {
+    log_message(LOG_LEVEL_ERROR, "Unexpected server status");
+    return -1;
+  }
+  return 0;
+}
+
 int send_chunk(Client *client, Chunk *chunk, Config *config) {
   if (config->use_chunk_serialization) {
     if (!send_status(client->file_descriptor, STATUS_CHUNK)) return -1;
@@ -32,12 +53,29 @@ int send_chunk(Client *client, Chunk *chunk, Config *config) {
     data_destroy(data);
   } else if (config->use_sendfile && !config->use_compression) {
     for (int i = 0; i < chunk->element_count; i++) {
+      if (config->use_incremental) {
+        int rc = incremental_check(client, chunk->items[i]);
+        if (rc < 0) return -1;
+        if (rc > 0) continue;
+        if (!file_send_sendfile_no_path(chunk->items[i], client->file_descriptor, config->use_metadata))
+          return -1;
+      } else {
         if (!send_status(client->file_descriptor, STATUS_NEXT)) return -1;
         if (!file_send_sendfile(chunk->items[i], client->file_descriptor, config->use_metadata))
           return -1;
       }
+    }
   } else {
     for (int i = 0; i < chunk->element_count; i++) {
+      if (config->use_incremental) {
+        int rc = incremental_check(client, chunk->items[i]);
+        if (rc < 0) return -1;
+        if (rc > 0) continue;
+        if (!file_send_single_calls_no_path(chunk->items[i], client->file_descriptor,
+                                       config->use_metadata,
+                                       config->use_compression ? config->compression_level : 0))
+          return -1;
+      } else {
         if (!send_status(client->file_descriptor, STATUS_NEXT)) return -1;
         if (!file_send_single_calls(chunk->items[i], client->file_descriptor,
                                config->use_metadata,
@@ -45,6 +83,7 @@ int send_chunk(Client *client, Chunk *chunk, Config *config) {
           return -1;
       }
     }
+  }
   return 0;
 }
 

src/server/server.c

@@ -5,7 +5,6 @@
 #include "data.h"
 #include "file.h"
 #include "log.h"
-#include "metadata.h"
 #include "multiprocessing.h"
 #include "protocol.h"
 #include "queue.h"
@@ -17,15 +16,10 @@
 #include <stdlib.h>
 #include <string.h>
 
-int receive_files(Config *config, int file_descriptor) {
+static int receive_chunk(int fd, Config *config) {
-  Status status;
+  Data *chunk_data = receive_data(fd);
-  if (!receive_status(file_descriptor, &status)) return -1;
-  while (status == STATUS_NEXT || status == STATUS_CHUNK) {
-    if (status == STATUS_CHUNK) {
-      Data *chunk_data = receive_data(file_descriptor);
   if (chunk_data == NULL) {
     log_message(LOG_LEVEL_ERROR, "Failed to receive chunk data");
-        send_status(file_descriptor, STATUS_ERROR);
     return -1;
   }
   Data *data_to_process = chunk_data;
@@ -34,7 +28,6 @@ int receive_files(Config *config, int file_descriptor) {
     data_destroy(chunk_data);
     if (data_to_process == NULL) {
       log_message(LOG_LEVEL_ERROR, "Failed to decompress chunk");
-          send_status(file_descriptor, STATUS_ERROR);
       return -1;
     }
   }
@@ -42,64 +35,79 @@ int receive_files(Config *config, int file_descriptor) {
   data_destroy(data_to_process);
   if (chunk == NULL) {
     log_message(LOG_LEVEL_ERROR, "Failed to deserialize chunk, skipping");
-        send_status(file_descriptor, STATUS_ERROR);
     return -1;
   }
 
   for (int i = 0; i < chunk->element_count; i++) {
-        if (config->save_to_disk) {
+    if (config->save_to_disk)
-          char *disk_path = path_cat(config->receive_root_directory, chunk->items[i]->path);
+      file_save_to_disk(config->receive_root_directory, chunk->items[i]);
-          if (disk_path) {
-            to_disk(disk_path, chunk->items[i]->data->data, chunk->items[i]->data->size);
-            file_restore_metadata(disk_path, chunk->items[i]->metadata);
-            free(disk_path);
-          }
-        }
   }
   chunk_destroy(chunk);
-    } else {
+  return 0;
-      File *file = file_receive(config, file_descriptor);
+}
-      if (file == NULL) {
+
-        log_message(LOG_LEVEL_ERROR, "Failed to receive file");
+static int receive_manifest(int fd, Config *config, Status *next_status) {
-        send_status(file_descriptor, STATUS_ERROR);
-        return -1;
-      }
-      if (config->save_to_disk) {
-        char *disk_path = path_cat(config->receive_root_directory, file->path);
-        if (disk_path) {
-          to_disk(disk_path, file->data->data, file->data->size);
-          file_restore_metadata(disk_path, file->metadata);
-          free(disk_path);
-        }
-      }
-      file_destroy(file);
-    }
-    if (!receive_status(file_descriptor, &status)) {
-      send_status(file_descriptor, STATUS_ERROR);
-      return -1;
-    }
-  }
-  if (status == STATUS_MANIFEST) {
   int count;
-    if (!receive_int(file_descriptor, &count)) return -1;
+  if (!receive_int(fd, &count)) return -1;
   ArrayList *manifest = array_list_create(free);
   if (manifest) {
     for (int i = 0; i < count; i++) {
-        char *s = receive_str(file_descriptor);
+      char *s = receive_str(fd);
       if (s) array_list_add(manifest, s);
     }
     fprintf(stderr, "Deleting files not in manifest...\n");
     delete_extras(config->receive_root_directory, manifest);
     array_list_delete(manifest);
   }
-    if (!receive_status(file_descriptor, &status)) return -1;
+  if (!receive_status(fd, next_status)) return -1;
+  return 0;
+}
+
+int receive_files(Config *config, int fd) {
+  Status status;
+  if (!receive_status(fd, &status)) return -1;
+
+  while (status == STATUS_NEXT || status == STATUS_CHUNK || status == STATUS_CHECK) {
+    if (status == STATUS_CHECK) {
+      bool skipped;
+      File *file = receive_incremental_check(fd, config, &skipped);
+      if (skipped) goto next;
+      if (file == NULL && !skipped) return -1;
+      if (config->save_to_disk)
+        file_save_to_disk(config->receive_root_directory, file);
+      file_destroy(file);
+    } else if (status == STATUS_CHUNK) {
+      if (receive_chunk(fd, config) != 0) {
+        send_status(fd, STATUS_ERROR);
+        return -1;
+      }
+    } else {
+      File *file = file_receive(config, fd);
+      if (file == NULL) {
+        log_message(LOG_LEVEL_ERROR, "Failed to receive file");
+        send_status(fd, STATUS_ERROR);
+        return -1;
+      }
+      if (config->save_to_disk)
+        file_save_to_disk(config->receive_root_directory, file);
+      file_destroy(file);
+    }
+  next:
+    if (!receive_status(fd, &status)) {
+      send_status(fd, STATUS_ERROR);
+      return -1;
+    }
+  }
+
+  if (status == STATUS_MANIFEST) {
+    if (receive_manifest(fd, config, &status) != 0) return -1;
   }
   if (status != STATUS_FINISHED) {
     log_message(LOG_LEVEL_ERROR, "Did not receive FINISHED Status");
-    send_status(file_descriptor, STATUS_ERROR);
+    send_status(fd, STATUS_ERROR);
     return -1;
   }
-  send_status(file_descriptor, STATUS_OK);
+  send_status(fd, STATUS_OK);
   return 0;
 }
 

src/shared/config.c

@@ -38,6 +38,7 @@ Config *config_create(char *version, char *send_directory,
   config->include_count = 0;
   config->max_size = 0;
   config->min_size = 0;
+  config->use_incremental = false;
   return config;
 }
 
@@ -89,6 +90,7 @@ bool config_send(int file_descriptor, Config *config) {
   if (!send_int(file_descriptor, (int)config->chunk_size)) return false;
   if (!send_int(file_descriptor, config->use_sendfile)) return false;
   if (!send_int(file_descriptor, config->use_delete)) return false;
+  if (!send_int(file_descriptor, config->use_incremental)) return false;
   Status status;
   if (!receive_status(file_descriptor, &status)) return false;
   if (status != STATUS_OK) {
@@ -134,6 +136,8 @@ Config *config_receive(int file_descriptor) {
   config->use_sendfile = tmp;
   if (!receive_int(file_descriptor, &tmp)) goto error;
   config->use_delete = tmp;
+  if (!receive_int(file_descriptor, &tmp)) goto error;
+  config->use_incremental = tmp;
   config->show_progress = false;
   config->dry_run = false;
   config->ssh_port = 22;

src/shared/config.h

@@ -32,9 +32,10 @@ typedef struct Config {
   int include_count;
   unsigned long long max_size;
   unsigned long long min_size;
+  bool use_incremental;
 } Config;
 
-#define PROTOCOL_VERSION "1.0.0"
+#define PROTOCOL_VERSION "1.1.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)
 
 Config *config_create(char *version, char *send_directory,

src/shared/file.c

@@ -96,26 +96,156 @@ bool file_load_data(File *file) {
   return true;
 }
 
-bool file_send_single_calls(File *file, int file_descriptor, bool use_metadata, int compression_level) {
+bool file_send_single_calls_no_path(File *file, int file_descriptor, bool use_metadata, int compression_level) {
+  Data *data_to_send = file->data;
+  Data *compressed_data = NULL;
   if (compression_level > 0) {
-    Data *compressed_data = data_compress(file->data, compression_level);
+    compressed_data = data_compress(file->data, compression_level);
     if (compressed_data == NULL) {
       log_message(LOG_LEVEL_ERROR, "Failed to compress file data");
       return false;
     }
-    data_destroy(file->data);
+    data_to_send = compressed_data;
-    if (compressed_data == NULL) {
-      log_message(LOG_LEVEL_ERROR, "Compression failed in file_send_single_calls");
-      exit(EXIT_FAILURE);
   }
-    file->data = compressed_data;
+  if (use_metadata && !metadata_send(file_descriptor, file->metadata)) {
+    data_destroy(compressed_data);
+    return false;
   }
-  if (!send_str(file_descriptor, file->path)) return false;
+  if (!send_data(file_descriptor, data_to_send)) {
-  if (use_metadata && !metadata_send(file_descriptor, file->metadata)) return false;
+    data_destroy(compressed_data);
-  if (!send_data(file_descriptor, file->data)) return false;
+    return false;
+  }
+  data_destroy(compressed_data);
   return true;
 }
 
+bool file_send_sendfile_no_path(File *file, int file_descriptor, bool use_metadata) {
+  if (use_metadata && !metadata_send(file_descriptor, file->metadata)) return false;
+
+  int fd = open(file->path, O_RDONLY);
+  if (fd == -1) {
+    perror("Could not open file for sendfile");
+    return false;
+  }
+
+  unsigned long long file_size = file->data->size;
+  if (!send_n_data(file_descriptor, &file_size, sizeof(unsigned long long))) {
+    close(fd);
+    return false;
+  }
+
+  off_t offset = 0;
+  while (offset < file_size) {
+    ssize_t sent = sendfile(file_descriptor, fd, &offset, file_size - offset);
+    if (sent == -1) {
+      perror("sendfile failed");
+      close(fd);
+      return false;
+    }
+  }
+
+  close(fd);
+  return true;
+}
+
+bool file_send_single_calls(File *file, int file_descriptor, bool use_metadata, int compression_level) {
+  Data *data_to_send = file->data;
+  Data *compressed_data = NULL;
+  if (compression_level > 0) {
+    compressed_data = data_compress(file->data, compression_level);
+    if (compressed_data == NULL) {
+      log_message(LOG_LEVEL_ERROR, "Failed to compress file data");
+      return false;
+    }
+    data_to_send = compressed_data;
+  }
+  if (!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;
+  }
+  data_destroy(compressed_data);
+  return true;
+}
+
+bool file_save_to_disk(const char *root_directory, File *file) {
+  char *disk_path = path_cat((char *)root_directory, file->path);
+  if (disk_path == NULL) return false;
+  bool ok = to_disk(disk_path, file->data->data, file->data->size);
+  if (ok) file_restore_metadata(disk_path, file->metadata);
+  free(disk_path);
+  return ok;
+}
+
+File *receive_incremental_check(int fd, Config *config, bool *skipped) {
+  *skipped = false;
+  char *check_path = receive_str(fd);
+  if (check_path == NULL) { send_status(fd, STATUS_ERROR); return NULL; }
+
+  unsigned long long check_size;
+  long long check_mtime;
+  if (!receive_n_data(fd, &check_size, sizeof(check_size)) ||
+      !receive_n_data(fd, &check_mtime, sizeof(check_mtime))) {
+    free(check_path);
+    send_status(fd, STATUS_ERROR);
+    return NULL;
+  }
+
+  char *full_path = path_cat(config->receive_root_directory, check_path);
+  struct stat st;
+  bool match = false;
+  if (full_path && stat(full_path, &st) == 0 &&
+      (unsigned long long)st.st_size == check_size &&
+      (long long)st.st_mtime == check_mtime) {
+    match = true;
+  }
+  free(full_path);
+
+  if (match) {
+    if (!send_status(fd, STATUS_OK)) { free(check_path); return NULL; }
+    free(check_path);
+    *skipped = true;
+    return NULL;
+  }
+
+  if (!send_status(fd, STATUS_NEXT)) { free(check_path); return NULL; }
+
+  File *file = file_create(check_path);
+  free(check_path);
+  if (file == NULL) { send_status(fd, STATUS_ERROR); 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); return NULL; }
+  }
+
+  Data *file_data = receive_data(fd);
+  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;
+}
+
 bool to_disk(const char *path, const void *data, unsigned long long data_size) {
   char *directory = str_dup(path);
   char *dir_to_free = directory;
@@ -178,7 +308,9 @@ File *file_receive(Config *config, int file_descriptor) {
   free(path);
   if (file == NULL) return NULL;
   if (config->use_metadata) {
-    file->metadata = metadata_receive(file_descriptor);
+    int meta_ok = 1;
+    file->metadata = metadata_receive(file_descriptor, &meta_ok);
+    if (!meta_ok) { file_destroy(file); return NULL; }
   }
   Data *file_data = receive_data(file_descriptor);
   if (file_data == NULL) {

src/shared/file.h

@@ -25,10 +25,14 @@ void file_destroy(void *item);
 bool file_load_data(File *file);
 File *file_receive(Config *config, int file_descriptor);
 bool file_send_single_calls(File *file, int file_descriptor, bool use_metadata, int compression_level);
+bool file_send_single_calls_no_path(File *file, int file_descriptor, bool use_metadata, int compression_level);
 bool file_send_sendfile(File *file, int file_descriptor, bool use_metadata);
+bool file_send_sendfile_no_path(File *file, int file_descriptor, bool use_metadata);
 size_t file_content_to_buffer(File *file);
 FileMetadata *file_metadata_create(struct stat *stats);
 void file_metadata_destroy(void *metadata);
 bool to_disk(const char *path, const void *data, unsigned long long data_size);
+bool file_save_to_disk(const char *root_directory, File *file);
+File *receive_incremental_check(int fd, Config *config, bool *skipped);
 
 #endif

src/shared/metadata.c

@@ -50,22 +50,28 @@ bool metadata_send(int file_descriptor, FileMetadata *m) {
          send_n_data(file_descriptor, &m->mtime_nsec, sizeof(long));
 }
 
-FileMetadata *metadata_receive(int file_descriptor) {
+FileMetadata *metadata_receive(int file_descriptor, int *ok) {
   int present;
-  if (!receive_n_data(file_descriptor, &present, sizeof(int)))
+  if (!receive_n_data(file_descriptor, &present, sizeof(int))) {
+    if (ok) *ok = 0;
     return NULL;
-  if (!present)
+  }
+  if (!present) {
+    if (ok) *ok = 1;
     return NULL;
+  }
   FileMetadata *m = malloc(sizeof(FileMetadata));
-  if (m == NULL) return NULL;
+  if (m == NULL) { if (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))) {
     free(m);
+    if (ok) *ok = 0;
     return NULL;
   }
+  if (ok) *ok = 1;
   return m;
 }
 

src/shared/metadata.h

@@ -10,7 +10,7 @@
 void metadata_to_buf(char **buf, FileMetadata *m);
 FileMetadata *metadata_from_buf(char **buf);
 bool metadata_send(int file_descriptor, FileMetadata *m);
-FileMetadata *metadata_receive(int file_descriptor);
+FileMetadata *metadata_receive(int file_descriptor, int *ok);
 void file_restore_metadata(const char *path, FileMetadata *metadata);
 
 #endif

src/shared/multiprocessing.c

@@ -6,7 +6,6 @@
 #include "data.h"
 #include "file.h"
 #include "log.h"
-#include "metadata.h"
 #include "protocol.h"
 #include "queue.h"
 #include "utils.h"
@@ -126,8 +125,17 @@ int receive_thread(void *pipeline_context) {
 
   Status status;
   if (!receive_status(file_descriptor, &status)) return thrd_error;
-  while (status == STATUS_NEXT || status == STATUS_CHUNK) {
+  while (status == STATUS_NEXT || status == STATUS_CHUNK || status == STATUS_CHECK) {
-    if (status == STATUS_CHUNK) {
+    if (status == STATUS_CHECK) {
+      bool skipped;
+      File *file = receive_incremental_check(file_descriptor, config, &skipped);
+      if (!skipped) {
+        if (file == NULL) return thrd_error;
+        queue_enqueue_multithreaded(context->queue, file, &context->mutex,
+                                    &context->condition_not_empty,
+                                    &context->condition_not_full);
+      }
+    } else if (status == STATUS_CHUNK) {
       receive_chunk_enqueue(file_descriptor, context);
     } else {
       File *file = file_receive(config, file_descriptor);
@@ -182,14 +190,8 @@ int write_thread(void *pipeline_context) {
       free(root_directory);
       return thrd_success;
     }
-    if (save_to_disk) {
+    if (save_to_disk)
-      char *disk_path = path_cat(root_directory, file->path);
+      file_save_to_disk(root_directory, file);
-      if (disk_path) {
-        to_disk(disk_path, file->data->data, file->data->size);
-        file_restore_metadata(disk_path, file->metadata);
-        free(disk_path);
-      }
-    }
     file_destroy(file);
   }
 }

src/shared/protocol.c

@@ -1,18 +1,59 @@
 #include "protocol.h"
 #include "log.h"
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 #include <unistd.h>
 
 static __thread int io_read_fd = -1;
 static __thread int io_write_fd = -1;
 
+static unsigned long long io_bwlimit = 0;
+static long long bw_tokens = 0;
+static struct timespec bw_last_refill = {0, 0};
+
 void io_set_fds(int read_fd, int write_fd) {
   io_read_fd = read_fd;
   io_write_fd = write_fd;
 }
 
+void io_set_bwlimit(unsigned long long bytes_per_sec) {
+  io_bwlimit = bytes_per_sec;
+  bw_tokens = (long long)io_bwlimit;
+  clock_gettime(CLOCK_MONOTONIC, &bw_last_refill);
+}
+
+static void bw_throttle(size_t bytes_written) {
+  if (io_bwlimit == 0) return;
+
+  struct timespec now;
+  clock_gettime(CLOCK_MONOTONIC, &now);
+
+  long long elapsed_ns = (now.tv_sec - bw_last_refill.tv_sec) * 1000000000LL +
+                         (now.tv_nsec - bw_last_refill.tv_nsec);
+  bw_last_refill = now;
+
+  long long tokens_to_add = (long long)((double)io_bwlimit * elapsed_ns / 1000000000.0);
+  bw_tokens += tokens_to_add;
+  if (bw_tokens > (long long)io_bwlimit)
+    bw_tokens = (long long)io_bwlimit;
+
+  bw_tokens -= (long long)bytes_written;
+
+  if (bw_tokens < 0) {
+    long long deficit_ns = (long long)((double)(-bw_tokens) / io_bwlimit * 1000000000.0);
+    struct timespec sleep_time, remaining;
+    sleep_time.tv_sec = deficit_ns / 1000000000LL;
+    sleep_time.tv_nsec = deficit_ns % 1000000000LL;
+    while (nanosleep(&sleep_time, &remaining) < 0 && errno == EINTR)
+      sleep_time = remaining;
+    bw_tokens = 0;
+    clock_gettime(CLOCK_MONOTONIC, &bw_last_refill);
+  }
+}
+
 static int io_fd(int dir_fd, int file_descriptor) {
   return (dir_fd != -1) ? dir_fd : file_descriptor;
 }
@@ -22,12 +63,16 @@ bool send_n_data(int file_descriptor, void *data, size_t data_size) {
   int fd = io_fd(io_write_fd, file_descriptor);
   ssize_t total_bytes_send = 0;
   while (total_bytes_send < data_size) {
+    size_t chunk = data_size - total_bytes_send;
+    if (io_bwlimit > 0 && chunk > 65536)
+      chunk = 65536;
     ssize_t bytes_send =
-        write(fd, (char *)data + total_bytes_send, data_size - total_bytes_send);
+        write(fd, (char *)data + total_bytes_send, chunk);
     if (bytes_send <= 0) {
       log_message(LOG_LEVEL_ERROR, "Could not send data");
       return false;
     }
+    bw_throttle((size_t)bytes_send);
     total_bytes_send += bytes_send;
   }
   log_message(LOG_LEVEL_DEBUG, "    Send n Data: %zu", total_bytes_send);
@@ -66,6 +111,8 @@ static const char *status_to_string(Status status) {
     return "NEXT";
   case STATUS_CHUNK:
     return "CHUNK";
+  case STATUS_CHECK:
+    return "CHECK";
   default:
     return "UNKNOWN";
   }

src/shared/protocol.h

@@ -6,9 +6,10 @@
 #include <stddef.h>
 
 typedef int Status;
-enum NET_STATUS { STATUS_OK, STATUS_ERROR, STATUS_FINISHED, STATUS_NEXT, STATUS_CHUNK, STATUS_MANIFEST };
+enum NET_STATUS { STATUS_OK, STATUS_ERROR, STATUS_FINISHED, STATUS_NEXT, STATUS_CHUNK, STATUS_MANIFEST, STATUS_CHECK };
 
 void io_set_fds(int read_fd, int write_fd);
+void io_set_bwlimit(unsigned long long bytes_per_sec);
 bool send_n_data(int file_descriptor, void *data, size_t data_size);
 bool receive_n_data(int file_descriptor, void *data, size_t data_size);
 

test.py

@@ -383,6 +383,33 @@ def run_profile(profile_name, source_dir, dest_dir):
         except Exception as e:
             results.append({"name": "Progress (--progress)", "suite": profile_name, "status": "Error", "time": "N/A", "error": str(e)})
 
+        # Incremental sync (--incremental) — first sync, then second sync should skip all
+        print(f"\n  --- Incremental (--incremental) ---")
+        try:
+            flags = BASE_CLIENT_FLAGS + ["-M"]
+            srv = subprocess.Popen(SERVER_CMD, stdout=subprocess.DEVNULL, stderr=None)
+            time.sleep(0.5)
+            first_cmd = client_prefix + BASE_CLIENT_CMD + ["--source-dir", source_dir, "--dest-dir", dest_dir] + flags
+            r1 = subprocess.run(first_cmd, text=True, capture_output=True)
+            wait_proc(srv)
+            if r1.returncode != 0:
+                raise RuntimeError(f"First sync failed: {r1.stderr[:100]}")
+            srv2 = subprocess.Popen(SERVER_CMD, stdout=subprocess.DEVNULL, stderr=None)
+            time.sleep(0.5)
+            second_cmd = client_prefix + BASE_CLIENT_CMD + ["--source-dir", source_dir, "--dest-dir", dest_dir] + flags + ["--incremental"]
+            start = time.monotonic()
+            r2 = subprocess.run(second_cmd, text=True, capture_output=True, timeout=30)
+            duration = time.monotonic() - start
+            wait_proc(srv2)
+            r = {"name": "Incremental (--incremental)", "suite": profile_name,
+                 "status": "Success" if r2.returncode == 0 else "Failed",
+                 "time": f"{duration:.4f}s" if r2.returncode == 0 else "N/A",
+                 "error": "" if r2.returncode == 0 else f"Exit {r2.returncode}: {(r2.stderr or r2.stdout)[:60]}"}
+            results.append(r)
+        except Exception as e:
+            results.append({"name": "Incremental (--incremental)", "suite": profile_name,
+                            "status": "Error", "time": "N/A", "error": str(e)})
+
         # Chunk size (--chunk-size 5242880)
         feature_flags = BASE_CLIENT_FLAGS + ["--chunk-size", "5242880"]
         cmd = client_prefix + BASE_CLIENT_CMD + ["--source-dir", source_dir, "--dest-dir", dest_dir] + feature_flags