Autobahn pubsub, queues and topics?

Question

The Autobahn documentation is a bit unclear on which/how clients receive messages once they are published. Out of the box it seems that a message is broadcast to all subscribers of a topic - they all get it. But is there any way to distribute a message to a single client? Something in the lines of a queue where multiple publishers add messages to a queue and messages are distributed to "free" subscribers, round robin style? Guess it can also be referred to as the Simple Pirate pattern.

Answer 1

As noted normally publish goes to all subscribers.

If you want to publish and direct to a specific subscriber(s), then you direct with the eligible parameter. Here is the WAMP doc:

http://autobahn.ws/python/reference/autobahn.wamp.html?highlight=eligible#autobahn.wamp.message.Publish

class autobahn.wamp.message.Publish(request, topic, args=None, kwargs=None, acknowledge=None, excludeMe=None, exclude=None, eligible=None, discloseMe=None)

In your case you would need to provide the list of eligible session ids eg eligible = ( 1,2,3, )

I don't have a v2 example, but, judging by the source, I'd guess something like:

self.publish(u'com.myapp.topic1',  eligible = [100, 200, 300] )

In v1 I used this technique to publish to a subset of the subscribers. In v2, I am using the subscription topic itself to limit who receives the message. So, I might create com.pub.m1, com.pub.m2, com.pub.m3, etc instead of com.pub, and my clients subscribe to the topic which dictates what they will receive.