Declare passive

[steviebiddles]

• Update declarer interface with new passive methods
• Add DeclareQueuePassive
• Add DeclareExchangePassive
• Add tests for new methods

Allow users to test for the existence of a queue.

[kron4eg]

@steviebiddles I would rather not change existing interface. But instead added new functions in func Declare* family (DeclareQueuePassive). And type assert inside them if passed in Declarer interface is implementing those *Passive methods.

[kron4eg]

It needs to not break existing interfaces

[kron4eg]

@steviebiddles BTW, are you aware of this streadway/amqp#242 ?
Calling Declare passive methods will cause channel close in case if there is no target they checked for on broker.

[steviebiddles]

Thanks for the update. I was not aware of that but if that is the way the protocol works it should be ok to make the changes.

[kron4eg]

@steviebiddles yeah, just don't change exiting interface as I've pointed out previously.

[steviebiddles]

I am new to Go and I have been trying to implement the *Passive methods without making changes to the existing interface. I created a new interface DeclarerPassive and i'm trying the type assert inside the new methods that implement the new interface.

//...
return func(c Declarer) error {
		cp, found := c.(DeclarerPassive)
		if !found {
			return errors.New("Type not found.")
		}
//...

When I debug and step over I see that c and cp are the type I expect but found is always false.

Is this the change you recommended?

[kron4eg]

@steviebiddles you need to design your DeclarerPassive interface with two methods https://godoc.org/github.com/streadway/amqp#Channel.ExchangeDeclarePassive and https://godoc.org/github.com/streadway/amqp#Channel.QueueDeclarePassive
(just method signatures)
You see found == false because you run those in tests. In production program https://godoc.org/github.com/streadway/amqp#Channel will be passed inside as Declarer and thus it will satisfy your DeclarerPassive.

[steviebiddles]

I added the interface and refactored the passive methods. The tests are passing without any changes to them.

[steviebiddles]

Are these changes what you expected?