private function parseResponse($rawResponse, $headerSize)
    {
        foreach (self::$CONNECTION_ESTABLISHED_HEADERS as $established_header) {
            if (stripos($rawResponse, $established_header) !== false) {
                $rawResponse = str_ireplace($established_header, '', $rawResponse);
                // Older cURL versions did not account for proxy headers in the
                // header size
                if (!$this->needsCurlProxyFix()) {
                    $headerSize -= strlen($established_header);
                }
                break;
            }
        }

        $responseBody = substr($rawResponse, $headerSize);

        return $responseBody;
    }