public function getStreamAsync(string $buffer = ''): \Generator
    {
        list($clazz, $extra) = $this->nextStreams[$this->key--];
        $obj = new $clazz();
        if ($obj instanceof ProxyStreamInterface) {
            $obj->setExtra($extra);
        }
        yield $obj->connect($this, $buffer);

        return $obj;
    }