服务端从容器中获取 SocketIO 单例， 然后 emit 推送消息给客户端，如果获取客户端收到消息后返回的 ack？

如题，感谢。

比如业务上的一个控制器， 调用此控制器向特定的 客户端 发送消息

```php
class SendMessageController{
public function index(){
$socket = ApplicationContext::getContainer()->get(SocketIO::class);
$reply = $socket->to($client_id)->emit('some_event', '消息体')->reply(); // $reply is null ?
}
}

```

以上返回的 reply 为 null

Start with SendMessageController::index and the SocketIO instance obtained through ApplicationContext::getContainer(); trace the to($client_id)->emit('some_event', '消息体')->reply() chain and how client acknowledgements are handled. Done means establishing whether this server-side call can receive the client's ack and defining the expected non-null reply behavior.

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