[OpenSIPS-Users] rtpengine_answer() is silently ignored on request route handling the initial INVITE when acting as an UAS - what am I missing?

[Pavel Sindelka]

Hello Andrea,

which particular aspect are you interested in?

The behavior can be demonstrated using just this simple route:

|route {|
|    if (is_method("INVITE") && !has_totag()) {|
|        t_newtran();|
|        rtpengine_use_set(1);|
|        rtpengine_offer( , , $var(sdp-offer), $rb(application/sdp));|
||
||
||#       ... forward the SDP offer as modified by rtpengine using 
another protocol||
||
||
||#       ... receive the SDP answer from the other protocol and store 
it into ||||$var(orig-sdp-answer) ||
||
||
||#### rtpengine_answer("to-tag=$sig_local_totag", , 
$var(new-sdp-answer), $var(orig-sdp-answer));||
||rtpengine_offer("force-answer to-tag=$sig_local_totag", , 
$var(new-sdp-answer), $var(orig-sdp-answer));||
||||
||        $var(contact) = "<sip:" + $socket_in(ip) + ":" + 
$socket_in(port) + ">";
         append_to_reply("Contact: $var(contact)\r\n");
         append_to_reply("Content-Type: application/sdp\r\n");||
||t_reply_with_body(200, "OK", $var(new-sdp-answer));
         exit;||
||    }||
||
||
||    #### handle other methods & reINVITEs ####||
||}||

I am currently trying to understand why, upon receiving the 
|answer| command, |rtpengine| changes the port it has indicated in its 
modified SDP offer and chooses another one for actually forwarding the 
media received from the calling party, but that's off-topic here.

Pavel


Dne 09.03.2026 v 13:00 users-request at lists.opensips.org napsal(a):
> Date: Sun, 8 Mar 2026 08:14:09 -0500
> From: Andrea Sannucci<andrea at andreasannucci.eu>
> To: OpenSIPS users mailling list<users at lists.opensips.org>, Pavel
> 	Sindelka<sindelka.p at gmail.com>
> Subject: Re: [OpenSIPS-Users] rtpengine_answer() is silently ignored
> 	on request route handling the initial INVITE when acting as an UAS -
> 	what am I missing?
> Message-ID:<77f081b4-e3c6-48ea-b9be-7bb4611b6fe5 at andreasannucci.eu>
> Content-Type: text/plain; charset="utf-8"; Format="flowed"
>
> Hello,
>
> can you show your configuration?
>
> Regards
>
> -----
> Andrea Sannucci - @AS
>
> El 8/03/2026 a las 8:01 a. m., Pavel Sindelka escribió:
>> Hello,
>>
>> https://opensips.org/docs/modules/3.6.x/rtpengine.html#func_rtpengine_answer 
>> doesn't mention any restrictions on use of this function, but in
>> reality opensips does not send anything to rtpengine if
>> |rtpengine_answer()| is called on a request route handling the INVITE.
>> Nothing in the log, no UDP exchange on the rtpengine control port,
>> regardless whether |rtpengine_offer()| is called earlier on that route
>> or not. If it is, the information exchange with rtpengine related to
>> |rtpengine_offer()| can be seen both in the log and on the rtpengine
>> control port.
>>
>> The intended overall workflow is to call |rtpengine_offer()|, handle
>> the mangled SDP offer internally and generate the SDP answer, and get
>> it "mangled back" using |rtpengine_answer()| before using it as the
>> body of a locally generated 200 response to the INVITE. Could it be
>> that as of now, |rtpengine_manage()| not only "combines the
>> functionality ... based on message type and method ..." but the three
>> individual methods have actually become just aliases of
>> |rtpengine_manage()| for backward compatibility? Or is the actual
>> execution of |rtpengine_answer()| suppressed thanks to some
>> undocumented plausibility check?
>>
>> Is there any way to enforce execution of |rtpengine_answer()| on a
>> request route handling the INVITE?
>>
>> Thank you for advice.
>>
>> Pavel
>>
>>
>> _______________________________________________
>> Users mailing list
>> Users at lists.opensips.org
>> http://lists.opensips.org/cgi-bin/mailman/listinfo/users
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