Customizable error response handling (custom nacks)

[erithmetic]

Code related to #165

By default a nack is always sent on an exception.

Allows configuring custom handlers similar to the way logging is configured:

class Requeue
  def handle(delivery_info, properties, broker, e)
    if e.is_a?(Net::HTTPRetriableError) && !delivery_info.redelivered
      broker.requeue delivery_info.delivery_tag
      true
    else
      # Pass and let default nack handler nack the message
      false
    end
  end
end

Hutch::Config.set :error_acknowledgements, [
  Requeue.new
]

[michaelklishin]

Why not simply have a non-empty default for error_acknowledgements?

[michaelklishin]

Answering my own question: because :error_acknowldgements is not a list, it's a chain of responsibility. Why so? Because double-acking would result in a channel exception and make underlying channel useless.

[michaelklishin]

The overall idea is sound. However, I find the way you fall back to the default a bit odd. Once that is addressed, I think we can move forward with this. Thank you!

[michaelklishin]

Since the interface here is a single function, it makes more sense to use call so that functions (blocks, procs, etc) can be used as well.

[michaelklishin]

Scratch the above. It would lead to inconsistency with error handlers, which use handle and it is way too late to change that.

[michaelklishin]

@dkastner merged with some minor tweaks. Thank you!

[erithmetic]

Thanks for taking a look!