Detect if a request cannot be routed and return immediately

[jpwilliams]

If a request cannot be routed to a queue, it'd be nice to know as soon as possible.
We can use the mandatory message option to have the message returned if that's the case, meaning we can throw an error back to the user that no such endpoint exists.

This does, however, come with a performance hit; it may be pertinent to expose this functionality as an optional extra.

[jacktuck]

Where's the performance hit?

[jpwilliams]

RabbitMQ in the past has published benchmarks where publishing wit mandatory: true has severely impacted performance. There have been blogs/updates since which mention improvements to the speed, though it's my understanding that there's still a small performance hit when using that flag.