[SR-Users] Fix missing Via with t_reply()

[Daniel-Constantin Mierla]

Hello,


On 14.08.17 14:30, Mikko Lehto wrote:
> 2016-03-18 Daniel-Constantin Mierla <miconda at gmail.com> wrote:
>
>> My guess that the sbc_5 is so poor implemented that it takes the Via
>> from last request, which is CANCEL, but CANCEL is a hop-by-hop request
>> in this case. If my guess is confirmed, the implementation of sbc_5 is
>> really far away from RFC3261, something that I haven't probably seen
>> since 2002/3.
>>
>> To test, you can try to use forward() for CANCEL instead of t_relay().
>> But you need to know where to send it -- same address as for INVITE --
>> you can hardcode some values in config for sake of simplicity to test. A
>> proper workaround can be built using htable module to store where the
>> invite was sent, using call-id as a key.
> Hi Grant, Daniel
>
> I accidentally found this 2016 thread and wanted to share my different solution.
>
> I ran into similar issue: 487 reply from SIP phone UA came with
> insufficient Via headers after CANCEL.
> In fact situation looked exactly like described above:
> Via stack for reply to INVITE seem to be taken incorrectly from CANCEL.
> I did not observe any errors from Kamailio, but Asterisk chan_sip
> (original INVITE sender) spits:
> ---
> parse_via: received request without a Via header
> handle_incoming: Dropping this SIP message with Call-ID 'abc', it's incomplete
> ---
>
>
> My quick solution was to reply locally with t_reply() when
> branch with missing second via was winning:
> ---
>  ...usrloc lookup()...
> +t_on_branch_failure("TOUSER");
>  t_on_failure("FAILURE_TOUSER");
>  route(RELAY);
>
> +event_route[tm:branch-failure:TOUSER]
> +{
> +    # Save branch ruid if broken Via detected
> +    # If this branch wins, Via will be "fixed" with local reply
> +    if ( $T_rpl($sel(via[2])) == $null ) $avp(secondviamissing) = $T(ruid);
> +}
> +
>  failure_route[FAILURE_TOUSER]
>  {
> +    if ( $avp(secondviamissing) != $null && $avp(secondviamissing) == $T(ruid) )
> +    {
> +        # Some UAs (VP530P 23.70.74.5) seem to copy Via stack from CANCEL
> +        # Lets "add" missing Via by creating internal reply
> +        append_to_reply("X-log: viafix\r\n");
> +        t_reply("$T(reply_code)", "$T_reply_reason");
> +        exit;
> +    }
>  }
> ---
>
> That seems to do the trick, at least in simple non-branching case.
>
> What do you think?
> (other than using single $avp(secondviamissing) for whole transaction...) 
>
Could be a workaround, indeed.

But I guess you can do it directly in the failure_route, without
event_route, testing if the reply has a second via there and using
t_reply() if not.

Cheers,
Daniel

-- 
Daniel-Constantin Mierla
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