Action Controller Metal

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

Attributes

[R] request

The ActionDispatch::Request instance for the current request.
[R] response

The ActionDispatch::Response instance for the current response.

Class Public methods

action(name)

Returns a Rack endpoint for the given action name.

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 290
    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
πŸ”Ž 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

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 130
    def self.controller_name
      @controller_name ||= (name.demodulize.delete_suffix("Controller").underscore unless anonymous?)
    end
πŸ”Ž See on GitHub

dispatch(name, req, res)

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

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 306
    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
πŸ”Ž See on GitHub

make_response!(request)

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 134
    def self.make_response!(request)
      ActionDispatch::Response.new.tap do |res|
        res.request = request
      end
    end
πŸ”Ž See on GitHub

middleware()

The middleware stack used by this controller.

By default uses a variation of ActionDispatch::MiddlewareStack which allows for the following syntax:

class PostsController < ApplicationController
  use AuthenticationMiddleware, except: [:index, :show]
end

Read more about [Rails middleware stack] (guides.rubyonrails.org/rails_on_rack.html#action-dispatcher-middleware-stack) in the guides.

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 285
    def self.middleware
      middleware_stack
    end
πŸ”Ž See on GitHub

new()

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 185
    def initialize
      @_request = nil
      @_response = nil
      @_response_body = nil
      @_routes = nil
      @_params = nil
      super
    end
πŸ”Ž See on GitHub

use(...)

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

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 268
      def use(...)
        middleware_stack.use(...)
      end
πŸ”Ž See on GitHub

Instance Public methods

controller_name()

Delegates to the class’s ::controller_name.

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 156
    def controller_name
      self.class.controller_name
    end
πŸ”Ž See on GitHub

headers

Delegates to ActionDispatch::Response#headers.

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 180
    delegate :headers, to: "@_response"
πŸ”Ž See on GitHub

params()

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 194
    def params
      @_params ||= request.parameters
    end
πŸ”Ž See on GitHub

params=(val)

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 198
    def params=(val)
      @_params = val
    end
πŸ”Ž See on GitHub

performed?()

Tests if render or redirect has already happened.

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 220
    def performed?
      response_body || response.committed?
    end
πŸ”Ž See on GitHub

reset_session()

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 259
    def reset_session
      @_request.reset_session
    end
πŸ”Ž See on GitHub

response=(response)

Assign the response and mark it as committed. No further processing will occur.

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 243
    def response=(response)
      set_response!(response)

      # Force `performed?` to return true:
      @_response_body = true
    end
πŸ”Ž See on GitHub

response_body=(body)

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 209
    def response_body=(body)
      if body
        body = [body] if body.is_a?(String)
        response.body = body
        super
      else
        response.reset_body!
      end
    end
πŸ”Ž See on GitHub

session

The ActionDispatch::Request::Session instance for the current request. See further details in the Active Controller Session guide.

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 176
    delegate :session, to: "@_request"
πŸ”Ž See on GitHub

url_for(string)

Basic url_for that can be overridden for more robust functionality.

πŸ“ Source code 
# File actionpack/lib/action_controller/metal.rb, line 205
    def url_for(string)
      string
    end
πŸ”Ž See on GitHub