[SR-Users] Hop by hop CANCEL, wrong to header

[Vitaliy Aleksandrov]

Hi all,

I have a question about CANCEL message processing.

My call sceraio:
When an INVITE request comes I need to rewrite a domain part of the 
several headers(to, from, contact, SDP ip) according to the outgoing 
interface.
I can do it before t_relay(), but when destination user has more then 
one locations and they are reachable through different interfaces all 
forked INVITEs will have the same domain.
To avoid that problem i have tried to move rewriting part(subst from the 
textops module) to the branch_route.

Unfortunately that solution didn't helped me, because "To" header of the 
outgoing CANCEL messages is wrong (unchanged. as it was at the moment 
when transaction was created by the t_relay() ).
As i understood from the documentation and mailing list kamailio builds 
CANCEL based on outgoing INVITE.

I did a small research and found that Kamailio really takes outgoing 
INVITE from each branch (invite_transaction_cell -> 
uac[b_id].request.buffer) and builds CANCEL (build_local_reparse() from 
tm/t_msgbuilder.c) based on it.
But kamailio does an exception for the To header which is described below:
***cancel_branch* function (from t_cancel.c) calls 
*build_local_reparse*() and fills one of the parameters with a pointer 
to unmodified To header.
*    build_local_reparse*() uses received To header to construct 
outgoing CANCEL.

I have changed:
     cancel = build_local_reparse(t, branch, &len, CANCEL, CANCEL_LEN, 
&t->to, reason);
to:
     cancel = build_local_reparse(t, branch, &len, CANCEL, CANCEL_LEN, 
NULL, reason);
and it works for me now.

It looks like if E2E_CANCEL_HOP_BY_HOP *e2e_cancel()* (t_fwd.c) will 
call *e2e_cancel_branch()* which works as i want instead of 
*cancel_branch()*, but it is just my assumption.

Why does kamailio generate CANCEL requests in such a way ? Did i miss 
something from the RFC3261 or kamailio documentation ?

Thanks in advance for any help !


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