class FileUploadToURLExternal extends \JoliCode\Slack\Api\Runtime\Client\BaseEndpoint implements \JoliCode\Slack\Api\Runtime\Client\Endpoint
{
    use \JoliCode\Slack\Api\Runtime\Client\EndpointTrait;

    private $uri;

    public function __construct(string $uri, array $queryParameters = [], array $headerParameters = [])
    {
        $this->uri = $uri;

        $this->queryParameters = $queryParameters;
        $this->headerParameters = $headerParameters;
    }

    public function getMethod(): string
    {
        return 'POST';
    }

    public function getUri(): string
    {
        return $this->uri;
    }

    public function getBody(\Symfony\Component\Serializer\SerializerInterface $serializer, $streamFactory = null): array
    {
        return $this->getMultipartBody($streamFactory);
    }

    public function getExtraHeaders(): array
    {
        return ['Accept' => ['application/json']];
    }

    public function getAuthenticationScopes(): array
    {
        return ['slackAuth'];
    }

    protected function getQueryOptionsResolver(): \Symfony\Component\OptionsResolver\OptionsResolver
    {
        $optionsResolver = parent::getQueryOptionsResolver();
        $optionsResolver->setDefined(['filename', 'content', 'file']);
        $optionsResolver->setRequired([]);
        $optionsResolver->setDefaults([]);
        $optionsResolver->addAllowedTypes('filename', ['string']);
        $optionsResolver->addAllowedTypes('file', ['string', 'resource', '\Psr\Http\Message\StreamInterface']);
        $optionsResolver->addAllowedTypes('content', ['string']);

        return $optionsResolver;
    }

    protected function getHeadersOptionsResolver(): \Symfony\Component\OptionsResolver\OptionsResolver
    {
        $optionsResolver = parent::getHeadersOptionsResolver();
        // todo

        return $optionsResolver;
    }

    protected function transformResponseBody(\Psr\Http\Message\ResponseInterface $response, \Symfony\Component\Serializer\SerializerInterface $serializer, ?string $contentType = null)
    {
        $status = $response->getStatusCode();
        $body = (string) $response->getBody();
        if (200 === $status) {
            return $serializer->deserialize($body, 'JoliCode\Slack\CustomRoutes\Model\FilesUploadToURLExternalPostResponse200', 'json');
        }

        return $serializer->deserialize($body, 'JoliCode\Slack\CustomRoutes\Model\FilesUploadToURLExternalPostResponseDefault', 'json');
    }
}

public function testCompleteUploadExternal(): void
    {
        /* Step 1: Get the upload url */
        $client = $this->createClient();

        $filename = 'test-image.png';

        /** @var FilesGetUploadURLExternalGetResponse200 $response */
        $response = $client->filesGetUploadURLExternal([
            'filename' => $filename,
            'length' => filesize(__DIR__ . '/resources/test-image.png'),
        ]);

        $this->assertTrue($response->getOk());

        $this->assertNotEmpty($response->getUploadUrl());
        $this->assertNotEmpty($response->getFileId());

        // Save values for confirming upload
        $fileId = $response->getFileId();
        $uploadUrl = $response->getUploadUrl();

        /* Step 2: Send file to slack with post method */

        /** @var FilesUploadToURLExternalPostResponse200 $response */
        $response = $client->FileUploadToURLExternal($uploadUrl, [
            'filename' => $filename,
            'content' => file_get_contents(__DIR__ . '/resources/test-image.png'), // , 'r'),
        ]);

//        /** @var FilesUploadToURLExternalPostResponse200 $response */
//        $response = $client->FileUploadToURLExternal($uploadUrl, [
//            'filename' => $filename,
//            'content' => fopen(__DIR__ . '/resources/test-image.png', 'r'),
//        ]);

        $this->assertTrue($response->getOk());

        /* Step 3: confirm upload */
        $filesArr = [
            [
                'id' => $fileId,
                'title' => $filename,
            ],
        ];

        $response = $client->filesCompleteUploadExternal([
            'channel_id' => $_SERVER['SLACK_TEST_CHANNEL'],
            'files' => json_encode($filesArr),
        ]);

        $this->assertTrue($response->getOk());

        $expected = [
            'id' => $fileId,
            'title' => $filename,
        ];

        $this->assertSame($expected, $response['files']);
    }