[asterisk-dev] Local channel variable propagation: expired hack or a bug?

[Kirill Katsnelson]

On 170103 2114, Richard Mudgett wrote:
> On Tue, Jan 3, 2017 at 9:38 PM, Kirill Katsnelson <kkm at smartaction.com>
> wrote:
>
>> With Asterisk 1.8 we were relying on the behavior of Originate with Local
>> channels as mentioned in https://issues.asterisk.org/ji
>> ra/browse/ASTERISK-17239. This no longer works in Asterisk 13.
>>
> You were definitely depending upon an implementation detail and some luck
> on when the optimization would happen.  Asterisk versions before v12 used
> masquerades to implement local channel optimizations.  The channel
> executing dialplan before the wait turns into a different channel after the
> wait because of the masquerade.  The wait simply made the local channel
> optimization more likely to happen during the wait because the optimization
> could happen any time during the exchange of media frames.  Asterisk v12+
> no longer optimizes local channels this way.  Instead it moves a channel
> from one bridge to another.  (See discussion on
> https://issues.asterisk.org/jira/browse/ASTERISK-26681)

Richard, thanks for the explanation and notes. I pretty much suspected 
that I was relying on undefined behavior.

I am thinking of using the IMPORT() function to get channel variables 
from the second "half" of the Local channel. That works, but I have to 
rely on knowing the naming scheme of the channels: drop the last 
character, which is the '1' after the ';', and then add a '2').

   P = "${CHANNEL(name):0:-1}2";  // Local/Sample at test-local-00000007;2
   Q = "${IMPORT(${P},QUUX)}";

But this also a bit hackish. Is this naming scheme not going to change 
so I can rely on it? Can you maybe think of a more 
canonical/kosher/reliable approach?

  -kkm