SetToken in SetResponse

[arigon]

Hi

I'm using SetResponse for responses to confirmable requests. Is it somehow possible to set the Token in SetResponse?
SetResponse is using the pool.Message which has SetToken available. So it should be easily possible to add SetToken into SetResponse but it would be a breaking change.

Alex

[jkralik]

Hi. The token is driven by go-coap. But what you can do is that you don't send a response via SetResponse but via WriteMessage where you can put your token. Something similar as is in

go-coap/examples/observe/server/main.go

Line 78 in 231b8cd

err := sendResponse(w.Client(), r.Token, subded, -1)

[arigon]

I tried, but WriteMessage has no ACK.

[jkralik]

ACK is sent via in separate message. So you just send a CON message.

[arigon]

Can you please give an example?

[jkralik]

eg:

func sendResponse(cc mux.Client, token []byte) error {
       m := message.Message{
		Code:    codes.Content,
		Token:   token,
		Context: cc.Context(),
		Body:    bytes.NewReader([]byte("data")),
	}
	var opts message.Options
	var buf []byte
	opts, n, err := opts.SetContentFormat(buf, message.TextPlain)
	if err == message.ErrTooSmall {
		buf = append(buf, make([]byte, n)...)
		opts, n, err = opts.SetContentFormat(buf, message.TextPlain)
	}
	if err != nil {
		return fmt.Errorf("cannot set content format to response: %w", err)
	}
	m.Options = opts
	return cc.WriteMessage(&m)
}


mux.HandlerFunc(func(w mux.ResponseWriter, r *mux.Message) {
  // we send response in another goroutine - so the peer gets separate message
  go func() {
    time.Sleep(time.Second*10) // do something
    err := sendResponse(w.Client(), r.Token)
    if err != nil {
      log.Printf("Error on transmitter: %v", err)
    }
  }()
})

[arigon]

But where is the ACK?

[jkralik]

It is handled by go-coap via separate message. Dňa ut 28. 9. 2021, 21:08 Alex ***@***.***> napísal(a):

…

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[arigon]

Well it doesn't. I tried it these days (I used the WriteMessage from the example) and the client (a sensor) isn't receiving the ACK. It only works with SetResponse.

[jkralik]

In v3 you can edit response message as you need it.

go-coap/net/responsewriter/responseWriter.go

Line 65 in b890196

func (r *ResponseWriter[C]) Message() *pool.Message {

Feel free to reopen the issue.