protected function uploadChunk($uri, $data)
    {
        $response = $this->client->request(
            'POST',
            $uri,
            [
                'headers' => [
                    'Content-Length' => strlen($data),
                    'Content-Type'   => 'application/octet-stream',
                ],
                'body' => $data,
            ]
        );

        return (string) $response->getBody();
    }