[asterisk-bugs] [JIRA] (ASTERISK-29909) Add support for withdrawing a call

[Kfir Itzhak (JIRA)]

Kfir Itzhak created ASTERISK-29909:
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             Summary: Add support for withdrawing a call
                 Key: ASTERISK-29909
                 URL: https://issues.asterisk.org/jira/browse/ASTERISK-29909
             Project: Asterisk
          Issue Type: Improvement
      Security Level: None
          Components: Applications/app_queue
    Affects Versions: 19.1.0, 18.9.0, 16.23.0
         Environment: All
            Reporter: Kfir Itzhak


Hi,

We use app_queue extensively and it works well.
But often, managers would like to retrieve a call, to dispatch it to a specific agent. 
This requires to have a way to withdraw a call from the queue, in a clean manner. Such functionality didn't exist, and for years we used the Redirect() AMI command, however it caused a lot of grief.

With the Redirect() command, these happened often:
1) An already answered call (by an agent) was redirected.
2) A call that is no longer in the queue (e.g. exceeded max wait time), was redirected.
3) It is possible to send more than one Redirect() request, and all of them will be processed, leading to multiple redirects.
These happen due to timing issues. We check that the call is really in the queue first and not answered, but by the time the Redirect() command is sent, it is possible that the call is already answered, or is no longer in the queue.

Therefore, i developed a more native, generic solution for withdrawing a call from the queue.
The new AMI command "QueueWithdrawCaller" works by signaling the caller's channel to exit the queue whenever it can. This is a best effort request (it may happen and it may not), this keeps it fairly simple and bug-free, while being suitable for 95% of the cases.
Due to the best effort design, if the caller is listening to an announcement or is in a breakout menu, it will wait until these are over.
Because this is likely to be used for retrieving a caller from a queue and dispatching to a specific agent, an optional parameter exists, that later can be retrieved using the QUEUE_WITHDRAW_INFO dialplan variable. In our system, we store the target extension number in this field, and later read it in the dialplan and dispatch the caller to that extension.
For the queue log, A WITHDRAW verb was added.
For AMI, QueueCallerAbandon is generated as usual, but QueueCallerAbandon lacks information why a call was abandoned from a queue, but this will be resolved in a separate issue that adds a Reason field to this AMI event. I am creating a separate issue & pull request for it, to prevent conflicts.



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