External event distribution.

[Juris Breicis]

Hi everyone,

First off - many thanks and all of my appreciation for wonderful job you are doing with this project.

We have been actively using WAMP (Autobahn|Python and Autobahn|JS) for over a year now, in production and are truly amazed by the quality of 

library you are providing.

Now as we grow our service, we have come across a challenge, I wanted to ask your quick opinion on:

Our backend system would generate a fairly large event stream; these events have to be distributed to a very dynamic set of clients;

By very dynamic - I mean - something which can not be handled via suffixed subscription addresses. like com.myapp.something.1, com.myapp.something.2, etc.

By design these events are such that don't want clients to dismiss them as not important; what I want is to do is - "event delivery authorization":

On each and every event: go through the subscriber list, and perform external validation if this user is entitled to receive this specific event or not.

Is there a standardized way how I can register such validator with crossbar.io , or I have to hack on a router code to achieve this?

Thanks in advance,

Juris

[Tobias Oberstein]

Hi Juris,

thanks for the nice words! Encouraging;) Can you talk a little about what you do or about your system/app? Curious ..

Crossbar.io has a feature called "dynamic authorization": http://crossbar.io/docs/Authorization/#dynamic-authorization

With this, you setup a WAMP component as a dynamic authorizer that will get called by Crossbar.io whenever _other_ session want to run an action (call, register, subscribe, publish) on an URI. The authorizer can allow or deny the specific action.

However, when a publish action on some URI is allowed, all subscribers get the event. A subscribe is also an action of course.

Hope this helps,
/Tobias

[Juris Breicis]

Hi, Tobias,

Here is a brief introduction to what we are doing:

https://www.youtube.com/watch?v=aOAHePJT7vE

What we are trying to achieve now (without spilling too much beans on the topic), is to inform our PBX users of relevant call events.

Now - the *relevant* is a key word here - as the parameters for determining which is *relevant* for me a user are dynamic and that decision is made on the backend.

I know I could always have event URIs: blah.blah.blah.{orgnizationID}.{userID}.specific_event and then use that for user based routing; but from a perspective of cleaner and easier maintained 

frontend and backend code, I was thinking of "plugable postprocessor" prior to distributing the event; allow me to explain:

API would allow me to register pre-delivery processor to a crossbar, stating URI to pre-process, and a registered rpc method for pre-processing.

For the sake of example:

Event URI: com.service.events.new_conversation

Event pre-processor:  com.service.preprocess.new_conversation

Now - whenever crossbar.io were to dispatch com.service.events.new_conversation to a subscribed client, it would first call the com.service.preprocess.new_conversation on each and every meesage-client combo it would be about to send with two parameters: 1) event contents and  2) subscribed user

Then our pre-processor would either: a) return the same event data or modify it if needed (say - removing certain keys from event data),  or b) raise and exception if this event should not be distributed to the specific user.

Perhaps something to think about for crossbar.io 2.0 ? :)

/Juris

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[Juris Breicis]

Hi everyone, 

As it turns out - I have been a lazy doc reader. Colleague pointed me towards http://crossbar.io/docs/Subscriber-Black-and-Whitelisting/ blacklisting and whitlisting subscribers when publishing event, which would achieve excatly what we wanted. Crisis averted. Nothing to see here, people. Move along. And sorry for jumping the gun!

[Alexander Gödde]

Hi Juris!

Not a problem - Crossbar.io is powerful but also complex. Glad you found something that fits for you!

Regards,

Alex

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