"ACK missed" when an incoming call is canceled unanswered

[serfreeman1337]

When the other side cancels an incoming call before we answer it the session locks until it timeouts with an "ACK missed" message.

Example handler:

d.HandleFunc(func(d *diago.DialogServerSession) {
	d.Progress()
	d.Ringing()

	fmt.Println("--- Waiting for hangup")
	
	<-d.Context().Done() // This should unlock on CANCEL.
	
	fmt.Println("--- Call hangup")
})

[emiago]

Hi @serfreeman1337 . Thanks for reporting, and showing code.
So mainly message might be confusing, but actually due to TIMER_I I believe for UDP this will hang.
Missed ACK could be excluded in this case also.
very related to
emiago/sipgo#148

Now I would need to verify is this actually needed for Cancelation.