can oslo_messaging support basic.return

[JiaJunsu]

Consider a scenario like this: A want to send a message to B, when the message reach at the broker, B hasn't create the queue to receive message. I found the broker just drop the message and "basic.publish" sucessed.

The amqp protocol has defined “basic.return” to address such cases. Can oslo_messaging support this?

[Ken Giusti (kgiusti)]

This is an interesting idea, however the kombu library (which oslo.messaging uses to interface with rabbitmq) does not currently support basic.return. The 'immediate' and 'mandatory' flags are not implemented:

See: https://github.com/celery/kombu/blob/master/kombu/messaging.py#L129

I did try to set those flags on publish - just to see what happens:

File "oslo_messaging/_drivers/impl_rabbit.py", line 807, in ensure
    ret, channel = autoretry_method()
  File "/home/kgiusti/work/openstack/oslo.messaging/.tox/py27/lib/python2.7/site-packages/kombu/connection.py", line 494, in _ensured
    return fun(*args, **kwargs)
  File "/home/kgiusti/work/openstack/oslo.messaging/.tox/py27/lib/python2.7/site-packages/kombu/connection.py", line 570, in __call__
    return fun(*args, channel=channels[0], **kwargs), channels[0]
  File "oslo_messaging/_drivers/impl_rabbit.py", line 795, in execute_method
    self._set_current_channel(channel)
  File "oslo_messaging/_drivers/impl_rabbit.py", line 852, in _set_current_channel
    on_return=my_bad)
  File "/home/kgiusti/work/openstack/oslo.messaging/.tox/py27/lib/python2.7/site-packages/kombu/messaging.py", line 77, in __init__
    self.revive(self._channel)
  File "/home/kgiusti/work/openstack/oslo.messaging/.tox/py27/lib/python2.7/site-packages/kombu/messaging.py", line 232, in revive
    self._channel.events['basic_return'].add(self.on_return)
AttributeError: 'Channel' object has no attribute 'events'

So yeah - it isn't supported.

If the kombu project did decide to provide this we could try using it in oslo.messaging, but for now we can't.

[Gabriele Santomaggio (gsantomaggio)]

Kombu actually supports the mandatory flag.

@kgiusti the error you see in your tests is [1] ( I fixed it, now the tests work)

Mandatory flag can't be used on "memory" transport in kombu since "memory" transport does not follow AMQP protocol, see [2]

btw we are working on "mandatory" flag implementation, see [3],[4] and [5]

-
Gabriele Santomaggio
Cloud Developer @SUSE

1- https://github.com/celery/kombu/pull/1053
2- https://github.com/celery/kombu/issues/1050
3- https://blueprints.launchpad.net/oslo.messaging/+spec/transport-options
4- https://review.opendev.org/#/c/666241/
5- https://review.opendev.org/#/c/660373/

[Gabriele Santomaggio (gsantomaggio)]

Please see also the blueprint: [1]

1-https://blueprints.launchpad.net/oslo.messaging/+spec/transport-options