public function setDefaultUserAgent()
    {
        $user_agent = 'PHP-Curl-Class/' . self::VERSION . ' (+https://github.com/php-curl-class/php-curl-class)';
        $user_agent .= ' PHP/' . PHP_VERSION;
        $curl_version = curl_version();
        $user_agent .= ' curl/' . $curl_version['version'];
        $this->setUserAgent($user_agent);
    }