public static function upload_returns() {
        return new external_single_structure(
             array(
                 'contextid' => new external_value(PARAM_INT, ''),
                 'component' => new external_value(PARAM_COMPONENT, ''),
                 'filearea'  => new external_value(PARAM_AREA, ''),
                 'itemid'   => new external_value(PARAM_INT, ''),
                 'filepath' => new external_value(PARAM_TEXT, ''),
                 'filename' => new external_value(PARAM_FILE, ''),
                 'url'      => new external_value(PARAM_TEXT, ''),
             )
        );
    }