getBodyAndExtraHeaders example

$this->client = $client ?? HttpClient::create();

        parent::__construct([], $history, $cookieJar);
    }

    /** * @param Request $request */
    protected function doRequest(object $request): Response
    {
        $headers = $this->getHeaders($request);
        [$body, $extraHeaders] = $this->getBodyAndExtraHeaders($request, $headers);

        $response = $this->client->request($request->getMethod(), $request->getUri(), [
            'headers' => array_merge($headers, $extraHeaders),
            'body' => $body,
            'max_redirects' => 0,
        ]);

        return new Response($response->getContent(false), $response->getStatusCode(), $response->getHeaders(false));
    }

    /** * @return array [$body, $headers] */