Support custom response formats (example for messagepack)

Support custom response formats (example for MessagePack)

We are experimenting with MessagePack, a high-performance schemaless binary encoding as an optional additional response format to our JSON APIs. Some of the responses we send are quite large, and MessagePack is about 50% faster than the ruby json libraries at encoding them.

Fortunately, adding MessagePack responses to our acts_as_api-based web service was easy.

First, you must tell acts_as_api that it should accept an additional api format. You can do this as follows:

ActsAsApi::Config.accepted_api_formats << :mpac

Then, you must add MessagePack as a rails renderer. This will do the trick:

ActionController::Renderers.add :mpac do |object, options|
  self.content_type ||= 'application/messagepack'
  self.response_body = MessagePack.pack(object)
end

Finally, because MessagePack doesn't come with the ability to serialize a TimeWithZone, you need to monkey patch it in:

module ActiveSupport
  class TimeWithZone
   def to_msgpack(out='')
     self.to_s.to_msgpack(out)
   end
  end
end

I put all three of these in config/initializers/messagepack.rb and it did the trick.

Author: bennytheshap