[sr-dev] ACKs to failure responses do not match transactions
Henning Westerholt
hw at kamailio.org
Wed Oct 5 16:45:40 CEST 2011
On Wednesday 05 October 2011, Hugh Waite wrote:
> We have discovered the cause of the problem I described, but we still do
> not understand why.
Hello Hugh,
> 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).
>
> Non-Working Example:
> append_hf("My-Header: yes\r\n");
> msg_apply_changes();
> if (is_present_hf("My-Header"))
> {
> # log("Found my header") - this gets run
> }
> t_relay();
> If the destination responds with a 4XX then the ACK does not match and the
> 4XX is retransmitted. If a CANCEL is sent, then it does not match and is
> not relayed.
>
> Working Example:
> append_hf("My-Header: yes\r\n");
> if (is_present_hf("My-Header"))
> {
> # log("Found my header") - this does not get run
> }
> t_relay();
> In this example, the header is not found, but the transaction matching
> works properly
>
> Is this something to do with re-parsing the request? And is it a bug to be
> investigated?
It is documentated that msg_apply_changes() is a bit risky function.. But i'm
not aware of this side effects so far. It could be a design limitation (then
it needs to be properly documented) or just a bug. Can you please open a bug
report on the tracker about this?
Best regards,
Henning
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