[sr-dev] ACKs to failure responses do not match transactions

[Hugh Waite]

I have found the problem.

When msg_apply_changes() copies the sip_msg structure, it copies 
msg_flags which includes FL_HASH_INDEX indicating that the hash_index is 
valid (which is now zero).

I have attached a patch which updates the msg_apply_changes() function 
to copy the hash_index as it is in the original msg. This will be valid 
if the flag is set, and therefore avoid unecessary hash calculation.

Hugh

On 05/10/2011 15:25, Hugh Waite wrote:
> We have discovered the cause of the problem I described, but we still 
> do not understand why.
>
> 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?
>
> Regards,
> Hugh
>
> On 04/10/2011 15:15, Hugh Waite wrote:
>> We are seeing an issue with ACKs to failure responses.
>>
>> 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)
>>
>> UA            KAM              UA
>>
>>  -- INVITE -->   -- INVITE -->
>> <--   407  --
>>                  --   ACK  -->
>> <--   407  --
>>  --   ACK  -->
>>  ...
>> <--   407  -- (retrans)
>>  --   ACK  -->
>>
>> I wondered if it was the same issue as the stateless reply (Flyspray 
>> #154), but this happens when we do a t_relay.
>>
>> 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.
>>
>> Does anyone understand why this may be happening?
>>
>> Regards,
>> Hugh
>>
>
> -- 
> --
> Hugh Waite
> Senior Design Engineer
> Crocodile RCS Ltd.
> _______________________________________________
> sr-dev mailing list
> sr-dev at lists.sip-router.org
> http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-dev

-- 
--
Hugh Waite
Senior Design Engineer
Crocodile RCS Ltd.

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