private function parseResponseHeaders($raw_response_headers)
    {
        $response_header_array = explode("\r\n\r\n", $raw_response_headers);
        $response_header  = '';
        for ($i = count($response_header_array) - 1; $i >= 0; $i--) {
            if (stripos($response_header_array[$i], 'HTTP/') === 0) {
                $response_header = $response_header_array[$i];
                break;
            }
        }

        $response_headers = new CaseInsensitiveArray();
        list($first_line, $headers) = $this->parseHeaders($response_header);
        $response_headers['Status-Line'] = $first_line;
        foreach ($headers as $key => $value) {
            $response_headers[$key] = $value;
        }
        return $response_headers;
    }