GuzzleHttp\Psr7\MultipartStream::addElement PHP Метод

    private function addElement(AppendStream $stream, array $element)
    {
        foreach (['contents', 'name'] as $key) {
            if (!array_key_exists($key, $element)) {
                throw new \InvalidArgumentException("A '{$key}' key is required");
            }
        }
        $element['contents'] = stream_for($element['contents']);
        if (empty($element['filename'])) {
            $uri = $element['contents']->getMetadata('uri');
            if (substr($uri, 0, 6) !== 'php://') {
                $element['filename'] = $uri;
            }
        }
        list($body, $headers) = $this->createElement($element['name'], $element['contents'], isset($element['filename']) ? $element['filename'] : null, isset($element['headers']) ? $element['headers'] : []);
        $stream->addStream(stream_for($this->getHeaders($headers)));
        $stream->addStream($body);
        $stream->addStream(stream_for("\r\n"));
    }