[BUG] rtpengine_delete() with via-branch deletes entire call (missing from-tag in NG delete)

[baevga]

Hello OpenSIPS team!

OpenSIPS version you are running

version: opensips 3.6.6 (x86_64/linux)
flags: STATS: On, DISABLE_NAGLE, USE_MCAST, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, HP_MALLOC, F_PARALLEL_MALLOC, DBG_MALLOC, FAST_LOCK-FUTEX-ADAPTIVE_WAIT
ADAPTIVE_WAIT_LOOPS=1024, MAX_RECV_BUFFER_SIZE 262144, MAX_LISTEN 16, MAX_URI_SIZE 1024, BUF_SIZE 65535
poll method support: poll, epoll, sigio_rt, select.
git revision: 26c0c4e33
main.c compiled on  with gcc 11

Describe the bug
When using rtpengine_delete() with a per-branch via-branch-param (parallel forking), rtpengine tears down the entire call instead of only that branch.

NG delete from OpenSIPS includes call-id and via-branch, but no from-tag. On the rtpengine side that results in full call deletion.
Passing from-tag=... in the delete flags string does not appear in the NG dump either.

To Reproduce

1. Parallel fork INVITE to 2+ destinations.
2. On each branch offer, use a unique via-branch, e.g. rtpengine_offer("... via-branch-param=...")
3. One branch answers; another fails.
4. On the failed branch: rtpengine_delete("via-branch-param=...")
5. Check rtpengine NG dump for delete and the following log line.

Expected behavior
Only the media session for that via-branch is removed; the answered branch keeps audio.

NG delete should allow rtpengine to select the branch (in practice that means the delete must identify the branch correctly — in our traces, selective delete worked only when from-tag was present together with the matching via-branch).

Relevant System Logs
Broken (OpenSIPS rtpengine_delete() with only via-branch-param, no from-tag in NG message):

Dump for 'delete': { "call-id": "...", "via-branch": "z9hG4bK-....2", "received-from": [...], "command": "delete" }
Deleting entire call

Working workaround (same call, from-tag passed via blind rtpp_flags + matching via-branch):

rtpengine_delete("rtpp_flags=from-tag=" + $ft + " via-branch-param=" + $var(via_base) + "." + $T_branch_idx);

rtpengine log:

Dump for 'delete' from 10.1.1.5:44443: {
  "rtpp_flags": "from-tag=f7779212",
  "call-id": "lp1pYPWvMylt9qO7hYDpAA..",
  "via-branch": "z9hG4bK-524287-1---6280f370d54b3440.2",
  "received-from": [ "IP4", "10.1.1.55" ],
  "command": "delete"
}
Deleting call branch '' (via-branch 'z9hG4bK-524287-1---6280f370d54b3440.2')
Destroying monologue '' (z9hG4bK-524287-1---6280f370d54b3440.2)

Note: rtpp_flags is not documented in the OpenSIPS rtpengine module README; it works because OpenSIPS forwards unknown keys to rtpengine, and rtpengine parses from-tag from rtpp_flags. Passing from-tag=... directly in the flags string did not put from-tag in the NG dump on delete.

OS/environment information

• Operating System: Ubuntu 22.04.5 LTS (jammy)
• OpenSIPS installation: manual

Additional context
Possibly related to commit adfb884 on 3.6 (rtp_relay: do not enforce from_tag for delete command, cherry-pick of 12ed692) — that change looks like it may stop adding from-tag for OP_DELETE, but we are not sure this is the root cause.

OpenSIPS docs describe via-branch for creating one media session per branch and stopping only that session on delete.

[razvancrainea]

So I understand you are manually using the rtpengine_delete() function, and even if you force a from-tag, it is still not pushed? do note that you should not use rtpp_flags=from-tag=, but just "from-tag=" + $ft.
This was an intentional change that was addressing leaked branches due to missing events - but to be honest, I've never checked on the manual behavior, so I believe this report is valid. I will see what can be done to fix.
In the meantime, can you test just setting the from-tag, as intructed above?

[baevga]

Hello @razvancrainea!

Yes, when I pass it directly as "from-tag=" + $ft, it gets cut from the NG command.
I just ran a fresh test:

$var(from_tag) = "from-tag=" + $ft + " ";
$var(rtpengine_flags) =  $var(from_tag) + $var(rtp_via);

And here are some logs from OpenSIPS and RTPEngine

# OpenSIPS
[RTPE_DELETE] RTPengine delete flags=[from-tag=b6353c1d via-branch-param=z9hG4bK-524287-1---eafb01502ee14d13.1 ]

# RTPEngine
Dump for 'delete' from 10.1.1.5:45397: { "call-id": "4Ud5SjpLaKVo7s2nRe_UMA..", "via-branch": "z9hG4bK-524287-1---eafb01502ee14d13.1", "received-from": [ "IP4", "101.1.25" ], "command": "delete" }

Please have a look at this.