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We have discovered the cause of the problem I described, but we
still do not understand why.<br>
<br>
After a SIP request arrives we make some changes to the
P-Preferred/Asserted-Identity headers after our own validation. To
allow these changes to be visible later (e.g. in $hdr() variables)
we call msg_apply_changes(). It seems that calling this function
causes the transaction matching to fail for subsequent messages
(e.g. ACK and CANCEL).<br>
<br>
<b>Non-Working Example:</b><tt><br>
append_hf("My-Header: yes\r\n");<br>
msg_apply_changes();<br>
if (is_present_hf("My-Header"))<br>
{<br>
# log("Found my header") - this gets run<br>
}<br>
t_relay();</tt><br>
If the destination responds with a 4XX then the ACK does not match
and the 4XX is retransmitted.<br>
If a CANCEL is sent, then it does not match and is not relayed.<br>
<br>
<b>Working Example:</b><tt><br>
append_hf("My-Header: yes\r\n");<br>
if (is_present_hf("My-Header"))<br>
{<br>
# log("Found my header") - this does not get run<br>
}<br>
t_relay();</tt><br>
In this example, the header is not found, but the transaction
matching works properly<br>
<br>
Is this something to do with re-parsing the request? And is it a bug
to be investigated?<br>
<br>
Regards,<br>
Hugh<br>
<br>
On 04/10/2011 15:15, Hugh Waite wrote:
<blockquote cite="mid:4E8B151F.2000305@crocodile-rcs.com"
type="cite">We are seeing an issue with ACKs to failure responses.
<br>
<br>
Our config is set up to forward an INVITE to another destination.
It replies with a 407 Auth Required. Kamailio sends an ACK to the
destination and relays the 407 back to the source. The source
sends an ACK, but this always fails the transaction match, so
kamailio keeps retransmitting the 407 (when using UDP)
<br>
<br>
UA KAM UA
<br>
<br>
-- INVITE --> -- INVITE -->
<br>
<-- 407 --
<br>
-- ACK -->
<br>
<-- 407 --
<br>
-- ACK -->
<br>
...
<br>
<-- 407 -- (retrans)
<br>
-- ACK -->
<br>
<br>
I wondered if it was the same issue as the stateless reply
(Flyspray #154), but this happens when we do a t_relay.
<br>
<br>
Basically, when t_check_trans() is called for the ACK, it does not
terminate the script. I have worked my way into the
t_check_trans() code and found that it does not find a matching
transaction; matching_3261() in t_lookup.c returns 0 because there
are no entries in that hash bucket.
<br>
<br>
Does anyone understand why this may be happening?
<br>
<br>
Regards,
<br>
Hugh
<br>
<br>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
--
Hugh Waite
Senior Design Engineer
Crocodile RCS Ltd.</pre>
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