[OpenSIPS-Users] B2B bye method handling

[Ross]

(I'm new to opensips, so bare with me if I'm off track).

I setup a very simple configuration using b2bua for a quick top hiding 
setup/proxy, and it works correctly, except for handling BYE messages 
coming from the upstream connection. Note, db_mode is set to 0 for both 
b2b_logic + entities.

setup: source client (aka invite initiator) -> os/b2b -> upstream

Quick Issue description:

Call sessions is established, and works fine, and when the client 
disconnects (initiates the bye message), the call disconnects cleanly 
with all parties as expected. (this is good/normal)

But when the server side disconnects first (sends the initial bye 
message), opensips improperly handles the bye message by believing it to 
be from the client side. Therefore doesn't properly send the 
corresponding responses to the remote parties.

In more detail:

Delving into the code, and looking at some packet sniffs/debugs, I've 
come to the idea that the b2b code (notably starting dlg.c:706) doesn't 
take into account that the new BYE message will have the To/From Fields 
reversed when from the server as it's not technically a response. 
Because of this, the b2b_parse_key on 708 fails as it's only looking at 
the "to" field tag for it's index key.

Then the request falls through and is then incorrectly parsed as a 
client sourced packet, as that lookup uses a different index key 
(callid), which is correct for the session.

I've tested this using metaswitch and asterisk in both the client and 
server positions and they both return the same data (to/from), but would 
like anyone else's thoughts on this.  Apologies, while I can read code, 
I'm not a proper programmer to make a real patch.

Thanks,
   Ross.