Getting Rails respond_with to recognize a custom media type

Posted on 23 Aug 2012 by Eric Oestrich

I am writing a sample hypermedia API in Rails, here, and recently came across some trouble trying to get Rails to recognize "application/hal+json" as a JSON format.

I ended up having to override respond_with to make it understand the HAL format. Not exactly what I hoped for, but it works.

config/initializers/mime_types.rb
Mime::Type.register "application/hal+json", :hal

ActionDispatch::ParamsParser::DEFAULT_PARSERS[Mime::Type.lookup('application/hal+json')] = 
  lambda do |body|
    JSON.parse(body)
  end
app/controllers/application_controller.rb<
class ApplicationController < ActionController::Base
  ...

  private
  def respond_with(resource, options = {})
    super(resource, options) do |format|
      format.hal do
        render options.merge(:json => resource)
      end
    end
  end
end
app/controllers/home_controller.rb
HomeController < ApplicationController
  respond_to :hal

  ...
end

This method doesn't give the benefit of auto status codes based on the HTTP verb. I did however get a monkey patch to work:

config/initializers/monkey_patching.rb
module ActionController
  class Responder
    def to_hal
      @format = :json
      api_behavior(nil)
    end
  end
end

The overload of respond_with is now no longer necessary, but we're accessing a protected method.

Resources:

  1. http://stackoverflow.com/questions/8700332/rails-3-and-json-default-renderer-but-custom-mime-type
  2. http://http://api.rubyonrails.org/classes/Mime/Type.html
  3. https://github.com/oestrich/hypermedia_rails/commit/1fc2d721aa80c384867d7d374baf3eada6e166e6
  4. http://api.rubyonrails.org/classes/ActionController/Responder.html
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