protected function establishTunnel()
    {
        $donor   = new self;
        $connect = new HTTP_Request2(
            $this->request->getUrl(), HTTP_Request2::METHOD_CONNECT,
            array_merge($this->request->getConfig(), array('adapter' => $donor))
        );
        $response = $connect->send();
        // Need any successful (2XX) response
        if (200 > $response->getStatus() || 300 <= $response->getStatus()) {
            throw new HTTP_Request2_ConnectionException(
                'Failed to connect via HTTPS proxy. Proxy response: ' .
                $response->getStatus() . ' ' . $response->getReasonPhrase()
            );
        }
        $this->socket = $donor->socket;
        $this->socket->enableCrypto();
    }