Modify topic before publishing

Hi,

We have some legacy devices that send to a topic that should be changed.

I tried to implement the modification of the message with a plugin that uses the server.OnMsgArrived hook, but it seems that I can modify the payload but not the topic.

here is the code:

func (t *Topicrw) OnMsgArrivedWrapper(pre server.OnMsgArrived) server.OnMsgArrived {
	return func(ctx context.Context, client server.Client, req *server.MsgArrivedRequest) error {
		fmt.Println("Msg arrived")
		req.Publish.TopicName = []byte("/another/topic")
		req.Message.Payload = []byte("my other payload")
		req.Message.Topic = "/changed/topic"
		return nil
	}
}

Following the code described in this issue https://github.com/DrmagicE/gmqtt/issues/24. I tried to republish the message with this code:

func (t *Topicrw) OnMsgArrivedWrapper(pre server.OnMsgArrived) server.OnMsgArrived {
	return func(ctx context.Context, client server.Client, req *server.MsgArrivedRequest) error {
		fmt.Println("Msg arrived")
		req.Publish.TopicName = []byte("/another/topic")
		req.Message.Payload = []byte("my other payload")
		req.Message.Topic = "/changed/topic"
		m := req.Message
		m.Topic = "/my/other/topic"
		m.Payload = []byte("lets change the payload")
		t.s.Publisher().Publish(m)
		req.Drop()
		return nil
	}
}

With the code above, a new message is published to another topic and the incoming message is supressed.

Is this code the right way to go?

Thank you very much!!!