public function getRawHeaders()
    {
        $headers = 'HTTP/1.1 ' . $this->statusCode . ' ' . $this->reasonPhrase . "\r\n";
        $lines = $this->getHeaderLines();
        if (!empty($lines)) {
            $headers .= implode("\r\n", $lines) . "\r\n";
        }

        return $headers . "\r\n";
    }