RabbitMQ, RPC, and Correlation ID Matching

Question

I'm following one of the RabbitMQ RPC tutorials (https://www.rabbitmq.com/tutorials/tutorial-six-dotnet.html) and got a little confused around Correlation ID matching.

The tutorial states:

That's when the CorrelationId property is used. We're going to set it to a unique value for every request. Later, when we receive a message in the callback queue we'll look at this property, and based on that we'll be able to match a response with a request. If we see an unknown CorrelationId value, we may safely discard the message - it doesn't belong to our requests.

But why is it "safe" to discard the message after we've already consumed it from the queue? What about the client that is expecting that message? Shouldn't the message be re-queued to prevent loss?

Answer 1

Sounds resonable. But after a requeue it will not be quaranteed that the sender of the original message will receive it. Without more knowledge about the setup of exchanges, bindings and queues it is hard to tell if requeuing makes sense or not.

The above linked tutorial intentionally seems not to cover this complex problem. I think it would be out of scope for a tutorial that tells the reader how to technically use the RPC feature of RabbitMQ.