[Serusers] ACK processing (was: [Serdev] loose_route behaviour, detecting single?Route with myself)

[Martin Hoffmann]

Nils Ohlmeier wrote:
> On Thursday 12 July 2007 12:54:58 Martin Hoffmann wrote:
> >
> > Techically, there is no such thing. There is only ACKs to 2xx and
> > non-2xx responses. The former are always in-dialog requests, since the
> > 2xx creates the dialog should it not yet exists. The latter is a matter
> > of the transaction layer which doesn't know of dialogs.
> 
> You call them non-2xx ACKs, I called them out-of-dialog ACKs (because the 
> typical scenario for them is the acknowledgment of the 40[17] for the INVITE, 
> and there is no dialog yet). But we are speaking about the same here.

Finally figured that from your reply to Klaus.
 
> > In practice, an ACK to a non-2xx response always needs to be eaten by
> > tm. This t_relay() does. Any ACK to a 2xx response needs to be routed
> > like any other in-dialog request to the endpoint (save for some
> > elaborate processing such as authentication). Which means, my code
> > snipped does indeed lack a loose_route() before t_relay().
> 
> Ok, what is the loose_route suppose to do in this case?
> A 2xx ACK would be "routed" according to the Route headers by loose_route(), 
> and relayed by t_relay() then.

Meaning, it gets the treatment it deserves.

> And what about the pre-loaded non-2xx ACKs?
> I would treat them exactly the same way like the 2xx ACK. loose_route() will 
> consum the Route header and t_relay() then forwards it to the RURI (which 
> should be your proxy).

Now you made me read tm sources again. What actually happens inside tm
when you call t_relay() is that t_lookup_request() matches the
transaction the ACK belongs to, t_newtran() releases that transaction,
and t_relay_to() stops the script.

Thus, the call the loose_route() doesn't hurt, in the non-2xx case it
effectively is a no-op.

> But as I explained in my other reply 
> to Klaus it is quite tricky to distinguish a non-2xx ACK with pre-loaded 
> Route, from a 2xx ACK with just one Route header. Then the only difference is 
> the RURI.

There is another one: For the former you have a transaction, for the
latter you don't. tm happily exploits this difference. No need to worry
in your config.

Regards,
Martin