lib/core: add ostree_checksum_file_at API

This is like `ostree_checksum_file` but fd-relative. This will be used
by https://github.com/ostreedev/ostree/pull/1258.

AFAICT, we actually didn't have any tests that check the `checksum` CLI.
Add a basic one here to test the old code as well as the new code.

Closes: #1263
Approved by: cgwalters

src/ostree/ot-builtin-checksum.c

@@ -32,7 +32,10 @@
  * man page (man/ostree-checksum.xml) when changing the option list.
  */
 
+static gboolean opt_ignore_xattrs;
+
 static GOptionEntry options[] = {
+  { "ignore-xattrs", 0, 0, G_OPTION_ARG_NONE, &opt_ignore_xattrs, "Don't include xattrs in checksum", NULL },
   { NULL }
 };
 
@@ -49,12 +52,14 @@ on_checksum_received (GObject    *obj,
 {
   AsyncChecksumData *data = user_data;
 
-  g_autofree guchar *csum = NULL;
-  data->success = ostree_checksum_file_async_finish ((GFile*)obj, result, &csum, data->error);
+  g_autofree guchar *csum_bytes = NULL;
+  data->success =
+    ostree_checksum_file_async_finish ((GFile*)obj, result, &csum_bytes, data->error);
   if (data->success)
     {
-      g_autofree char *checksum = ostree_checksum_from_bytes (csum);
-      g_print ("%s\n", checksum);
+      char csum[OSTREE_SHA256_STRING_LEN+1];
+      ostree_checksum_inplace_from_bytes (csum_bytes, csum);
+      g_print ("%s\n", csum);
     }
 
   g_main_loop_quit (data->loop);
@@ -73,15 +78,28 @@ ostree_builtin_checksum (int argc, char **argv, GCancellable *cancellable, GErro
     return glnx_throw (error, "A filename must be given");
   const char *path = argv[1];
 
-  g_autoptr(GFile) f = g_file_new_for_path (path);
-  g_autoptr(GMainLoop) loop = g_main_loop_new (NULL, FALSE);
+  /* for test coverage, use the async API if no flags are needed */
+  if (!opt_ignore_xattrs)
+    {
+      g_autoptr(GFile) f = g_file_new_for_path (path);
+      g_autoptr(GMainLoop) loop = g_main_loop_new (NULL, FALSE);
 
-  AsyncChecksumData data = { 0, };
+      AsyncChecksumData data = { 0, };
 
-  data.loop = loop;
-  data.error = error;
-  ostree_checksum_file_async (f, OSTREE_OBJECT_TYPE_FILE, G_PRIORITY_DEFAULT, cancellable,
-                              on_checksum_received, &data);
-  g_main_loop_run (data.loop);
-  return data.success;
+      data.loop = loop;
+      data.error = error;
+      ostree_checksum_file_async (f, OSTREE_OBJECT_TYPE_FILE, G_PRIORITY_DEFAULT,
+                                  cancellable, on_checksum_received, &data);
+      g_main_loop_run (data.loop);
+      return data.success;
+    }
+
+  g_autofree char *checksum = NULL;
+  if (!ostree_checksum_file_at (AT_FDCWD, path, NULL, OSTREE_OBJECT_TYPE_FILE,
+                                OSTREE_CHECKSUM_FLAGS_IGNORE_XATTRS, &checksum,
+                                cancellable, error))
+    return FALSE;
+
+  g_print ("%s\n", checksum);
+  return TRUE;
 }