[OpenSIPS-Users] interaction between fix_nated_contact(), topology_hiding() and serial forking

Jeff Pyle jeff at ugnd.org
Wed Oct 28 00:31:27 EST 2020


This is on OpenSIPS 2.4.8.  Early in the script:

        if (nat_uac_test("34")) {               # 2, 32

Later in the script I run topology_hiding("CD"), and then t_relay() an
inbound initial INVITE upstream to another system that returns a 302 with
Contacts.  I handle that in a failure_route[] by serializing the branches
and relaying to them one at a time.  I don't have to go around this
t_relay() -> failure_route[] loop much because the first Contact usually
handles the request.

The problem I notice is that the updated Contact from fix_nated_contact()
early in the script is lost after I do the initial t_relay() to the
redirector to get the 302.  To work around that, I've modified the script
above to not fix_nated_contact() there, but do it in the branch_route[]
relaying to the first Contact from the 302 and then only if NAT_FLAG is
set.  That seems to be fine in most cases.

I one case from one phone system where OpenSIPS complains:
  ERROR:nathelper:fix_nated_contact_f: SCRIPT BUG - second attempt to
change URI Contact

This happens when I run fix_nated_contact() in the branch_route[] for the
first and only time.  I can't duplicate it with my own traffic in the lab
and it's maddening; it only happens with this one system that's not mine to
play with.  I've captured the messaging and don't see anything different in
the INVITEs coming into OpenSIPS, just some cosmetic stuff like one system
includes :5060 on the From domain and one doesn't.  Nothing that should
affect OpenSIPS' behavior in any of this.  It'll be very difficult to get a
full OpenSIPS debug in this case because it's on a production system but
there's got to be *something*.  Anyway...

So, it appears I have some strange interaction between fix_nated_contact(),
topology_hiding() and serial forking.  I mention topology_hiding() because
it's the only thing I can think of in my scenario that would update the
Contact outside of fix_nated_contact().

I'm stumped.  Any thoughts?

- Jeff
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