Zend\Diactoros\CallbackStream::getMetadata PHP Method

    public function getMetadata($key = null)
    {
        $metadata = ['eof' => $this->eof(), 'stream_type' => 'callback', 'seekable' => false];
        if (null === $key) {
            return $metadata;
        }
        if (!array_key_exists($key, $metadata)) {
            return null;
        }
        return $metadata[$key];
    }