public function setCacheHeader()
    {
        if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
            $this->setStatus(304);
            exit;
        }

        $this->setHeader('Expires', gmdate('D, d M Y H:i:s', time() + 365 * 24 * 60 * 60) . ' GMT');
        $this->setHeader('Last-Modified', gmdate('D, d M Y H:i:s') . ' GMT');
        $this->setHeader('Cache-Control', 'immutable');
    }