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

[Ovidiu Sas]

Take a look at the port-latching option for the port change.

-ovidiu

On Mon, Mar 9, 2026 at 3:25 PM Pavel Sindelka <sindelka.p at gmail.com> wrote:
>
> 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
>
>
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