flight\Engine::_etag PHP Метод

    public function _etag($id, $type = 'strong')
    {
        $id = ($type === 'weak' ? 'W/' : '') . $id;
        $this->response()->header('ETag', $id);
        if (isset($_SERVER['HTTP_IF_NONE_MATCH']) && $_SERVER['HTTP_IF_NONE_MATCH'] === $id) {
            $this->halt(304);
        }
    }