private function getDefaultAdapter()
    {
        if (extension_loaded('curl')) {
            $this->parallelAdapter = new MultiAdapter($this->messageFactory);
            $this->adapter = function_exists('curl_reset')
                ? new CurlAdapter($this->messageFactory)
                : $this->parallelAdapter;
            if (ini_get('allow_url_fopen')) {
                $this->adapter = new StreamingProxyAdapter(
                    $this->adapter,
                    new StreamAdapter($this->messageFactory)
                );
            }
        } elseif (ini_get('allow_url_fopen')) {
            $this->adapter = new StreamAdapter($this->messageFactory);
        } else {
            throw new \RuntimeException('Guzzle requires cURL, the '
                . 'allow_url_fopen ini setting, or a custom HTTP adapter.');
        }
    }