[rabbitmq-discuss] Message validation plugin

[Simon MacMullen]

On 04/12/2013 16:53, Dmitry Andrianov wrote:
> Hi, guys.
> If we need to create a Ravvit plugin doing some custom message
> validation (like rejecting a message if particular header is missing or
> another header is present) - what would be the best starting point?
> Which existing plugin should we be looking at?

An exchange decorator could do that as long as "rejecting the message" 
could take the form of closing the channel with an error.

A decorator gets attached to all exchanges, whereas an exchange tpye 
plugin obviously only applies to exchanges of a certain type.

The only exchange decorator at the moment is

http://hg.rabbitmq.com/rabbitmq-federation/file/85a819bbc3cc/src/rabbit_federation_exchange.erl

although note that its route/2 callback doesn't get invoked as it 
returns noroute from active_for/1.

You could do this with an exchange type also, delegating to the "actual" 
exchnage type you want and refusing to route if whatever validation fails.

> Also, while we are there - is it possible (and is it ok) to do things
> like creation of an exchange and setting up exchange-to-exchange binding
> in auth backend plugin? If it is not - what would be the best approach
> to perform couple of these actions each time new client connects?

It's not awful; it's not what it's designed for but it would work. You 
could write a plugin which subscribes to the rabbit_event handler, like 
the mgmt db does, but that's async.

Cheers, Simon

> Many thanks!
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