public static function joinAsUser($args)
 {
     $uid = self::preDispatch();
     $fileId = intval(@$args['file_id']);
     $file = new File($fileId);
     if ($file->getPermissions() & \OCP\PERMISSION_UPDATE) {
         self::join($uid, $file);
     } else {
         \OCP\JSON::success(array('permissions' => $file->getPermissions(), 'id' => $fileId));
     }
     exit;
 }