perf: downsized test data, increased SSH socket buffer, and made chunk size configurable

- Reduced test data from 50MB to 25MB (test.py)
- Increased SSH socketpair buffer to 1MB via setsockopt (transport_ssh.c)
- Made chunk size configurable: new Config field, --chunk-size CLI flag,
  sent over wire, and used in scanner instead of DESIRED_CHUNK_SIZE
- Fixed DESIRED_CHUNK_SIZE macro parentheses (chunk.h)

src/client/client_cli.c

@@ -26,6 +26,7 @@ static void print_usage(void) {
   printf("  -f                  Enable sendfile (TCP only, not with -c or -s)\n");
   printf("  -v, --verbose       Enable debug logging\n");
   printf("  -M, --preserve      Preserve file metadata\n");
+  printf("  --chunk-size <n>    Chunk size in bytes (default: %d)\n", DEFAULT_CHUNK_SIZE);
   printf("  --source-dir <path> Source directory\n");
   printf("  --dest-dir <path>   Destination directory\n");
   printf("  --save-to-disk      Write received files to disk\n");
@@ -46,7 +47,7 @@ int main(int argc, char *argv[]) {
   }
 
   Config *config = config_create(str_dup("1.0.0"), NULL, NULL,
-                                 save_to_disk, false, false, false, false, 5, false);
+                                 save_to_disk, false, false, false, false, 5, false, 0);
 
   int positional_args[2];
   int positional_count = 0;
@@ -93,6 +94,10 @@ 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], "--chunk-size") == 0 && i + 1 < argc) {
+      unsigned long long val = strtoull(argv[++i], NULL, 10);
+      if (val > 0)
+        config->chunk_size = val;
     } 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/client_send.c

@@ -82,7 +82,7 @@ static int scan_directory_multithreaded(void *pipeline_context) {
   PipelineContextSender *context = (PipelineContextSender *)pipeline_context;
   mtx_lock(&context->mutex_scanner);
   DirectoryScanner *scanner =
-      directory_scanner_create(context->config->send_directory, context->config->use_metadata);
+      directory_scanner_create(context->config->send_directory, context->config->use_metadata, context->config->chunk_size);
   mtx_unlock(&context->mutex_scanner);
 
   Chunk *current_chunk;
@@ -138,7 +138,7 @@ int send_files(Config *config) {
     client_connect(client, server_host, server_port);
   }
   config_send(client->file_descriptor, config);
-  DirectoryScanner *scanner = directory_scanner_create(config->send_directory, config->use_metadata);
+  DirectoryScanner *scanner = directory_scanner_create(config->send_directory, config->use_metadata, config->chunk_size);
   Chunk *current_chunk;
   while ((current_chunk = directory_scanner_next(scanner)) != NULL) {
     if (!config->use_sendfile) {

src/client/scanner.c

@@ -11,12 +11,13 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
-DirectoryScanner *directory_scanner_create(char *root_directory, bool use_metadata) {
+DirectoryScanner *directory_scanner_create(char *root_directory, bool use_metadata, unsigned long long chunk_size) {
   DirectoryScanner *scanner = malloc(sizeof(DirectoryScanner));
   scanner->directories = queue_create(100, free);
   scanner->current_dir = NULL;
   scanner->current_path = NULL;
   scanner->use_metadata = use_metadata;
+  scanner->chunk_size = chunk_size > 0 ? chunk_size : DESIRED_CHUNK_SIZE;
   queue_enqueue(scanner->directories, str_dup(root_directory));
   return scanner;
 }
@@ -99,7 +100,7 @@ Chunk *directory_scanner_next(DirectoryScanner *scanner) {
         file->metadata = file_metadata_create(&stats);
       array_list_add(chunk_data, file);
       chunk_data_size += file->data->size;
-      if (chunk_data_size > DESIRED_CHUNK_SIZE) {
+      if (chunk_data_size > scanner->chunk_size) {
         free(cur_path);
         return chunk_data_to_chunk(chunk_data);
       }

src/client/scanner.h

@@ -11,9 +11,10 @@ typedef struct {
   DIR *current_dir;
   char *current_path;
   bool use_metadata;
+  unsigned long long chunk_size;
 } DirectoryScanner;
 
-DirectoryScanner *directory_scanner_create(char *root_directory, bool use_metadata);
+DirectoryScanner *directory_scanner_create(char *root_directory, bool use_metadata, unsigned long long chunk_size);
 Chunk *directory_scanner_next(DirectoryScanner *scanner);
 void directory_scanner_destroy(DirectoryScanner *scanner);