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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
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Class Public methods

action(name)

Returns a Rack endpoint for the given action name.

Source: show | on GitHub 

# 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

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: show | on GitHub 

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

dispatch(name, req, res)

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

Source: show | on GitHub 

# 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

make_response!(request)

Source: show | on GitHub 

# 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

middleware()

Alias for middleware_stack.

Source: show | on GitHub 

# File actionpack/lib/action_controller/metal.rb, line 229
def self.middleware
  middleware_stack
end

new()

Source: show | on GitHub 

# File actionpack/lib/action_controller/metal.rb, line 152
def initialize
  @_request = nil
  @_response = nil
  @_routes = nil
  super
end

use(*args, &block)

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

Source: show | on GitHub 

# File actionpack/lib/action_controller/metal.rb, line 222
def use(*args, &block)
  middleware_stack.use(*args, &block)
end

Instance Public methods

controller_name()

Delegates to the class' controller_name.

Source: show | on GitHub 

# File actionpack/lib/action_controller/metal.rb, line 143
def controller_name
  self.class.controller_name
end

params()

Source: show | on GitHub 

# File actionpack/lib/action_controller/metal.rb, line 159
def params
  @_params ||= request.parameters
end

params=(val)

Source: show | on GitHub 

# File actionpack/lib/action_controller/metal.rb, line 163
def params=(val)
  @_params = val
end

performed?()

Tests if render or redirect has already happened.

Source: show | on GitHub 

# File actionpack/lib/action_controller/metal.rb, line 183
def performed?
  response_body || response.committed?
end

reset_session()

Source: show | on GitHub 

# File actionpack/lib/action_controller/metal.rb, line 208
def reset_session
  @_request.reset_session
end

response_body=(body)

Source: show | on GitHub 

# 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

url_for(string)

Basic url_for that can be overridden for more robust functionality.

Source: show | on GitHub 

# File actionpack/lib/action_controller/metal.rb, line 170
def url_for(string)
  string
end