A very thin abstract class for fast rails responses

ExampleProfileController

class ExampleProfileController < MetalController
  # assuming a route something like:
  # /profile/:user_id.json
  def show
    prof = Profile.find params['user_id']
    if prof
      respond_with prof
    else
      response_error 'not_found', "User id of #{params['user_id']} has not been found."
    end
  end
end

MetalController

class MetalController < ActionController::Metal
  abstract!

  include ActionController::ParamsWrapper

  def response_error(message, reason = nil, status = 400)
    args = {error: message, reason: reason}
    respond_with args, 'error', status
  end

  # This has the opinion that the params['format'] will tell you the
  # contnent type and that you can use Rails standard conversion for 
  # those and that this is a successful response, that you want to compress.
  # Each of these could be overridden by the appropriate argument.
  # (sure we could do the rails standard extract_options approach, but this
  # is supposed to be bare bones)
  #
  # The reason for compression is because in my usage this is called by a 
  # CDN caching service and it doesn't make sense for all data to be 
  # compressed so Apache/Nginx plugins for this don't make sense.
  #
  # There is treatment for JSONP if the request is a .js request, you
  # should probably remove that unless you know you want it.
  #
  # NOTE: If you pass a type then your data must already be in the
  # final format.
  #
  # NOTE: If you really don't want this thing compressed you need to
  # set the self.headers['Content-Encoding'] before respond_with
  def respond_with(data, js_callback = nil, status = 200, type = nil)
    if status >= 200 and status < 300 and !Rails.env.development?
      self.headers['ETag'] ||= %Q{"#{Digest::MD5.hexdigest(body)}"}
      self.headers['Cache-control'] ||= "max-age=18000"
    end
    self.headers['Date'] ||= Time.now.httpdate
    self.headers['Vary'] ||= 'Accept-Encoding'    

    
    unless type
      format = param['format']
      if format.eql?('js')
        body = data.to_json
        type = Mime::JS
        callback = js_callback || params['jsonp']
        body = %Q{#{params['jsonp'](#{data.to_json});}
      elsif format.eql?('xml')
        type = Mime::XML
        body = data.to_xml
      else
        body = data.to_json
        type = Mime::JSON
      end
    end

    self.content_type = type

    if self.headers['Content-Encoding']
      self.response_body = body
    else
      self.headers['Content-Encoding'] = 'gzip'
      self.response_body = ActiveSupport::Gzip.compress(body)
    end
  end
end