----- Original Message -----
Sent: Thursday, June 07, 2001 6:59
AM
Subject: [Sip] Early experiments: proxy
server, tagged To and matching Transaction Id problems.
I'm using sip 1.2.1 to further my understanding of the
SIP protocol in a hands on way. That's the plan anyway. To get my
hands dirty I'm trying to build a non-forking proxy server but have come up
with a couple of problems and wonder if anyone can point me in the right
direction.
I've provided my own builder, feature, state and operator
classes, each of which derives from the corresponding one in base. All
the work is done in myOperator::process. The other bits just allow me to
call the necessary addXXX()
myOperator::process() munges the request URI and adds the
proxy server to the via list, then calls sendAsync to forward the request
on.
So far so good, so I tested this with a couple of vovida
UA's. The INVITE is routed through OK and both 180 RINGING and 200 come
back to the proxy server as far as SipTransceiver::receive(). Here's
where the problems start.
1) The UA has correctly added a To: tag as the via list is
>1. This means that the transaction IDs for request & response do
not match, so the UDP retransmission is not cancelled. A crude hack to
not compare tags solves this problem but is there a better way?
2) With the hacked transaction ID from 1, run the ProxyServer,
and break on receiving the 200 status in SipTransceiver::receive(). The
call to udpConnection->cancel(*requestId) results in a log
entry of "failed to cancel msg (id not found)" presumably because the msg was
successfully cancelled by the returning 180 - there's a log entry of
"cancelling request after <200 response". I think I'm happy with
that, my confusion is over the msgQueue - I don't seem to be entering the
block of code:
// xxx this is the fix for retrans
if
(msgQueue == 0) // etc
I don't understand the use of msgQueue here, but assume that I
need to post the response to the queue to give myOperator::process a shot at
it.
Where am I going wrong?
Any help gratefully received!
----------
Giles Chamberlin
