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/shared/file.c

@@ -11,15 +11,13 @@
 #include "log.h"
 #include "socket.h"
 
-File *file_create(const char *path, struct stat *stats) {
+File *file_create(const char *path) {
   File *file = (File *)malloc(sizeof(File));
   if (file == NULL) {
     perror("FATAL ERROR: Could not allocate memory for file struct");
     exit(EXIT_FAILURE);
   }
 
-  file->stats = *stats;
-
   int path_len = strlen(path);
   file->path = (char *)malloc(path_len + 1);
   if (file->path == NULL) {
@@ -29,7 +27,8 @@ File *file_create(const char *path, struct stat *stats) {
   }
 
   strcpy(file->path, path);
-  file->data = NULL;
+  file->data = data_create_reserve(0);
+  file->metadata = NULL;
   return file;
 }
 
@@ -39,15 +38,40 @@ void file_destroy(void *item) {
   File *file = (File *)item;
   data_destroy(file->data);
   file->data = NULL;
+  file_metadata_destroy(file->metadata);
+  file->metadata = NULL;
   free(file->path);
   file->path = NULL;
   free(file);
 }
 
+FileMetadata *file_metadata_create(struct stat *stats) {
+  FileMetadata *m = malloc(sizeof(FileMetadata));
+  if (m == NULL) {
+    perror("FATAL ERROR: Could not allocate memory for file metadata");
+    exit(EXIT_FAILURE);
+  }
+  m->mode = stats->st_mode;
+  m->uid = stats->st_uid;
+  m->gid = stats->st_gid;
+  m->mtime_sec = stats->st_mtime;
+#ifdef __linux__
+  m->mtime_nsec = stats->st_mtim.tv_nsec;
+#else
+  m->mtime_nsec = 0;
+#endif
+  return m;
+}
+
+void file_metadata_destroy(void *metadata) {
+  free(metadata);
+}
+
 void file_load_data(File *file) {
   if (file == NULL)
     return;
-  file->data = data_create_empty(file->stats.st_size);
+  if (file->data->data == NULL)
+    file->data->data = malloc(file->data->size);
   printf("%ld is file big", file->data->size);
   size_t bytes_read = file_content_to_buffer(file);
   if (bytes_read != file->data->size) {
@@ -62,8 +86,38 @@ void file_print(void *item) {
   printf("%s\n", ((File *)item)->path);
 }
 
+static void metadata_send(int file_descriptor, FileMetadata *m) {
+  if (m == NULL) {
+    int zero = 0;
+    send_n_data(file_descriptor, &zero, sizeof(int));
+    return;
+  }
+  int present = 1;
+  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 *file_receive_metadata(int file_descriptor) {
+  int present;
+  receive_n_data(file_descriptor, &present, sizeof(int));
+  if (!present)
+    return NULL;
+  FileMetadata *m = malloc(sizeof(FileMetadata));
+  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));
+  return m;
+}
+
 void file_send_single_calls(File *file, int file_descriptor) {
   send_str(file_descriptor, file->path);
+  metadata_send(file_descriptor, file->metadata);
   printf("Sending File: %ld", file->data->size);
   send_data(file_descriptor, file->data->data, file->data->size);
 }
@@ -75,29 +129,11 @@ size_t file_content_to_buffer(File *file) {
     return 0;
   }
   size_t bytes_read =
-      fread(file->data->data, 1, file->stats.st_size, file_pointer);
-  if (bytes_read != (size_t)file->stats.st_size) {
+      fread(file->data->data, 1, file->data->size, file_pointer);
+  if (bytes_read != (size_t)file->data->size) {
     perror("Read to many or to less bytes from File!");
     return 0;
   }
   fclose(file_pointer);
   return bytes_read;
 }
-
-FileReceive *file_receive_create(char *path, Data *data) {
-  FileReceive *file = malloc(sizeof(FileReceive));
-  file->path = path;
-  file->data = data;
-  return file;
-}
-
-void file_receive_destroy(void *file_receive) {
-  if (file_receive == NULL)
-    return;
-  FileReceive *file = (FileReceive *)file_receive;
-  data_destroy(file->data);
-  free(file->path);
-  free(file);
-}
-
-