public function getMaxAge($default = false)
    {
        $cacheControl = isset($this->response['header']['Cache-Control'])
            ? $this->response['header']['Cache-Control']
            : null;

        $maxAge = null;
        if ($cacheControl) {
            // max-age=2592000
            $part = explode('=', $cacheControl);
            $maxAge = ($part[0] == "max-age")
                ? (int) $part[1]
                : null;
        }

        if ($maxAge) {
            return $maxAge;
        }

        $expire = isset($this->response['header']['Expires'])
            ? strtotime($this->response['header']['Expires'])
            : null;

        return $expire ? $expire : $default;
    }