Use GSeekable to pick out attachments

This is an alternative to loading the entire MMS payload blob and
picking out the attachments from main memory.
Signed-off-by: Kyle Evans <kvans32@gmail.com>

mm-sms.c

@@ -758,8 +758,8 @@ pur_mmsd_receive_message (GVariant *message_t)
 
   GFile *container = NULL;
   GFile *savepath;
-  char *contents;
-  gsize length, written = 0;
+  GFileInputStream *mms;
+  GSeekable *seek;
   gchar *tag;
   g_autoptr(GError)  error = NULL;
 
@@ -772,12 +772,8 @@ pur_mmsd_receive_message (GVariant *message_t)
     if (!container) {
       container = g_file_new_for_path (containerpath);
 
-      g_file_load_contents (container,
-                            NULL,
-                            &contents,
-                            &length,
-                            NULL,
-                            &error);
+      mms = g_file_read (container, NULL, NULL);
+      seek = G_SEEKABLE (mms);
 
       const gchar *home = g_get_home_dir ();
       tag = g_strconcat (date, sender, NULL);
@@ -816,12 +812,15 @@ pur_mmsd_receive_message (GVariant *message_t)
       break;
     }
 
-    if (!g_output_stream_write_all (G_OUTPUT_STREAM(out),
-                                    contents + data,
-                                    size,
-                                    &written,
-                                    NULL,
-                                    &error)) {
+    g_seekable_seek (seek, data, G_SEEK_SET, NULL, &error);
+
+    GBytes *chunk =
+    g_input_stream_read_bytes (G_INPUT_STREAM(mms), size, NULL, &error);
+
+    if (!g_output_stream_write_bytes (G_OUTPUT_STREAM(out),
+                                      chunk,
+                                      NULL,
+                                      &error)) {
       g_warning ("attachment not saved!");
 
       g_warning ("%s", error->message);
@@ -840,7 +839,6 @@ pur_mmsd_receive_message (GVariant *message_t)
     g_free (uri);
   }
 
-  g_free(contents);
   g_object_unref(container);
 }