[asterisk-bugs] [JIRA] (ASTERISK-28766) PJSIP blind transfer not completed after using Proceeding()

[lvl (JIRA)]

lvl created ASTERISK-28766:
------------------------------

             Summary: PJSIP blind transfer not completed after using Proceeding()
                 Key: ASTERISK-28766
                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-28766
             Project: Asterisk
          Issue Type: Bug
      Security Level: None
          Components: Channels/chan_pjsip
    Affects Versions: 16.8.0
            Reporter: lvl


If you perform a blind transfer (REFER), transfer the call to an extension that uses {{Proceeding()}} then remains in the dialplan and does **not** dial out, the transferer will not be notified of the transfer success.

To clarify. A transfer to the following extensions will finish properly:

{code}
s,1,Proceeding()
s,2,Dial(PJSIP/bla)
{code}

{code}
s,1,Playback(bla)
{code}

While the following extension will fail:

{code}
s,1,Proceeding()
s,2,Playback(bla)
{code}

Why is this? Transfer status is handled by refer_progress_framehook in https://github.com/asterisk/asterisk/blob/master/res/res_pjsip_refer.c#L218

Apparently, if the target extension executes a {{Dial()}}, this generates a control frame of the AST_CONTROL_ANSWER type which will trigger {{refer_progress_notify}} with a status 200. This will signal to the transferer that the transfer is accepted and their phone can disconnect.

However, if the call remains in the dialplan no such control frame is generated, even if you explicitly {{Answer()}}. In this case, the transfer status is normally detected by the passing of a AST_FRAME_VOICE. But that code only triggers if {{progress->subclass}} is null, e.g. once any control frame has been detected, a subsequent voice frame can no longer trigger transfer completion.

This code was introduced in https://github.com/asterisk/asterisk/commit/77002bc377f19ea11e60732c486b6ef371688773 and subtly changed in https://github.com/asterisk/asterisk/commit/344cdab3a71d8f8b3517e7efe6864165142b14ca. My best guess is that the intention was to prevent duplicate progress messages from being generated when a voice frame was detected after a control frame had already triggered the appropriate notify.

But this premise is false, as the passing of e.g. a AST_CONTROL_PROCEEDING frame (triggering a 100) should not prevent a AST_FRAME_VOICE frame from later triggering a 200.



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