ActionController::Metal is the simplest possible controller, providing a valid Rack interface without the additional niceties provided by ActionController::Base.

A sample metal controller might look like this:

class HelloController < ActionController::Metal
  def index
    self.response_body = "Hello World!"
  end
end

And then to route requests to your metal controller, you would add something like this to config/routes.rb:

get 'hello', to: HelloController.action(:index)

The action method returns a valid Rack application for the Rails router to dispatch to.

Rendering Helpers

ActionController::Metal by default provides no utilities for rendering views, partials, or other responses aside from explicitly calling of response_body=, content_type=, and status=. To add the render helpers you're used to having in a normal controller, you can do the following:

class HelloController < ActionController::Metal
  include AbstractController::Rendering
  include ActionView::Layouts
  append_view_path "#{Rails.root}/app/views"

  def index
    render "hello/index"
  end
end

Redirection Helpers

To add redirection helpers to your metal controller, do the following:

class HelloController < ActionController::Metal
  include ActionController::Redirecting
  include Rails.application.routes.url_helpers

  def index
    redirect_to root_url
  end
end

Other Helpers

You can refer to the modules included in ActionController::Base to see other features you can bring into your metal controller.

Methods

Class Public methods

action(name)

Returns a Rack endpoint for the given action name.

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 234
    def self.action(name)
      app = lambda { |env|
        req = ActionDispatch::Request.new(env)
        res = make_response! req
        new.dispatch(name, req, res)
      }

      if middleware_stack.any?
        middleware_stack.build(name, app)
      else
        app
      end
    end
🔎 See on GitHub

controller_name()

Returns the last part of the controller's name, underscored, without the ending Controller. For instance, PostsController returns posts. Namespaces are left out, so Admin::PostsController returns posts as well.

Returns

  • string

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 128
    def self.controller_name
      @controller_name ||= (name.demodulize.delete_suffix("Controller").underscore unless anonymous?)
    end
🔎 See on GitHub

dispatch(name, req, res)

Direct dispatch to the controller. Instantiates the controller, then executes the action named name.

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 250
    def self.dispatch(name, req, res)
      if middleware_stack.any?
        middleware_stack.build(name) { |env| new.dispatch(name, req, res) }.call req.env
      else
        new.dispatch(name, req, res)
      end
    end
🔎 See on GitHub

make_response!(request)

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 132
    def self.make_response!(request)
      ActionDispatch::Response.new.tap do |res|
        res.request = request
      end
    end
🔎 See on GitHub

middleware()

Alias for middleware_stack.

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 229
    def self.middleware
      middleware_stack
    end
🔎 See on GitHub

new()

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 152
    def initialize
      @_request = nil
      @_response = nil
      @_routes = nil
      super
    end
🔎 See on GitHub

use(*args, &block)

Pushes the given Rack middleware and its arguments to the bottom of the middleware stack.

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 222
      def use(*args, &block)
        middleware_stack.use(*args, &block)
      end
🔎 See on GitHub

Instance Public methods

controller_name()

Delegates to the class' controller_name.

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 143
    def controller_name
      self.class.controller_name
    end
🔎 See on GitHub

params()

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 159
    def params
      @_params ||= request.parameters
    end
🔎 See on GitHub

params=(val)

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 163
    def params=(val)
      @_params = val
    end
🔎 See on GitHub

performed?()

Tests if render or redirect has already happened.

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 183
    def performed?
      response_body || response.committed?
    end
🔎 See on GitHub

reset_session()

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 208
    def reset_session
      @_request.reset_session
    end
🔎 See on GitHub

response_body=(body)

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 174
    def response_body=(body)
      body = [body] unless body.nil? || body.respond_to?(:each)
      response.reset_body!
      return unless body
      response.body = body
      super
    end
🔎 See on GitHub

url_for(string)

Basic url_for that can be overridden for more robust functionality.

📝 Source code 
# File actionpack/lib/action_controller/metal.rb, line 170
    def url_for(string)
      string
    end
🔎 See on GitHub