refactor: merge File/FileReceive, add optional metadata transfer with -M flag

- Remove FileReceive struct; use File everywhere with nullable FileMetadata*
- Remove struct stat from File; file size lives in Data->size (data_create_reserve)
- Add FileMetadata struct (mode, uid, gid, mtime) sent conditionally over wire
- Add -M / --preserve flag to client
- Restore permissions, ownership, timestamps on disk write
- Wire format uses per-file present flag for metadata (zero overhead when off)

src/client/client.c

@@ -49,7 +49,7 @@ 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);
+      directory_scanner_create(context->config->send_directory, context->config->use_metadata);
   mtx_unlock(&context->mutex_scanner);
 
   Chunk *current_chunk;
@@ -127,7 +127,7 @@ int send_files(Config *config) {
   int port = env_port ? atoi(env_port) : 8080;
   client_connect(client, (char *)ip, port);
   config_send(client->file_descriptor, config);
-  DirectoryScanner *scanner = directory_scanner_create(config->send_directory);
+  DirectoryScanner *scanner = directory_scanner_create(config->send_directory, config->use_metadata);
   Chunk *current_chunk;
   while ((current_chunk = directory_scanner_next(scanner)) != NULL) {
     for (int i = 0; i < current_chunk->element_count; i++)
@@ -192,7 +192,7 @@ int main(int argc, char *argv[]) {
   }
 
   Config *config = config_create(str_dup("1.0.0"), source_dir, dest_dir,
-                                 save_to_disk, false, false, false, 5, 20);
+                                 save_to_disk, false, false, false, false, 5, 20);
   for (int i = 1; i < argc; i++) {
     if (strcmp(argv[i], "-c") == 0) {
       config->use_compression = true;
@@ -215,6 +215,9 @@ int main(int argc, char *argv[]) {
       config->receive_root_directory = str_dup(argv[++i]);
     } else if (strcmp(argv[i], "--save-to-disk") == 0) {
       config->save_to_disk = true;
+    } else if (strcmp(argv[i], "-M") == 0 || strcmp(argv[i], "--preserve") == 0) {
+      config->use_metadata = true;
+      log_message(LOG_LEVEL_INFO, "Enabled metadata preservation");
     } else {
       handle_arg(argv[i], "-m", &config->use_multithreading,
                  "Enabled Multithreading");

src/client/scanner.c

@@ -1,6 +1,7 @@
 #include "scanner.h"
 #include "array_list.h"
 #include "chunk.h"
+#include "file.h"
 #include "queue.h"
 #include "utils.h"
 #include <dirent.h>
@@ -10,11 +11,12 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
-DirectoryScanner *directory_scanner_create(char *root_directory) {
+DirectoryScanner *directory_scanner_create(char *root_directory, bool use_metadata) {
   DirectoryScanner *scanner = malloc(sizeof(DirectoryScanner));
   scanner->directories = queue_create(100, free);
   scanner->current_dir = NULL;
   scanner->current_path = NULL;
+  scanner->use_metadata = use_metadata;
   queue_enqueue(scanner->directories, str_dup(root_directory));
   return scanner;
 }
@@ -91,9 +93,12 @@ Chunk *directory_scanner_next(DirectoryScanner *scanner) {
     if (!S_ISREG(stats.st_mode)) {
       queue_enqueue(scanner->directories, (void *)cur_path);
     } else {
-      File *file = file_create(cur_path, &stats);
+      File *file = file_create(cur_path);
+      file->data->size = stats.st_size;
+      if (scanner->use_metadata)
+        file->metadata = file_metadata_create(&stats);
       array_list_add(chunk_data, file);
-      chunk_data_size += file->stats.st_size;
+      chunk_data_size += file->data->size;
       if (chunk_data_size > DESIRED_CHUNK_SIZE)
         return chunk_data_to_chunk(chunk_data);
       free(cur_path);

src/client/scanner.h

@@ -4,14 +4,16 @@
 #include "chunk.h"
 #include "queue.h"
 #include <dirent.h>
+#include <stdbool.h>
 
 typedef struct {
   Queue *directories;
   DIR *current_dir;
   char *current_path;
+  bool use_metadata;
 } DirectoryScanner;
 
-DirectoryScanner *directory_scanner_create(char *root_directory);
+DirectoryScanner *directory_scanner_create(char *root_directory, bool use_metadata);
 Chunk *directory_scanner_next(DirectoryScanner *scanner);
 void directory_scanner_destroy(DirectoryScanner *scanner);