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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, klass = ActionDispatch::Request)

Returns a Rack endpoint for the given action name.

# File actionpack/lib/action_controller/metal.rb, line 229
def self.action(name, klass = ActionDispatch::Request)
  if middleware_stack.any?
    middleware_stack.build(name) do |env|
      new.dispatch(name, klass.new(env))
    end
  else
    lambda { |env| new.dispatch(name, klass.new(env)) }
  end
end
call(env)

Makes the controller a Rack endpoint that runs the action in the given env's action_dispatch.request.path_parameters key.

# File actionpack/lib/action_controller/metal.rb, line 223
def self.call(env)
  req = ActionDispatch::Request.new env
  action(req.path_parameters[:action]).call(env)
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

# File actionpack/lib/action_controller/metal.rb, line 113
def self.controller_name
  @controller_name ||= name.demodulize.sub(/Controller$/, '').underscore
end
middleware()

Alias for middleware_stack.

# File actionpack/lib/action_controller/metal.rb, line 217
def self.middleware
  middleware_stack
end
new()
# File actionpack/lib/action_controller/metal.rb, line 131
def initialize
  @_headers = {"Content-Type" => "text/html"}
  @_status = 200
  @_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.

# File actionpack/lib/action_controller/metal.rb, line 212
def self.use(*args, &block)
  middleware_stack.use(*args, &block)
end
Instance Public methods
_status_code()
# File actionpack/lib/action_controller/metal.rb, line 239
def _status_code
  @_status
end
content_type()
# File actionpack/lib/action_controller/metal.rb, line 156
def content_type
  headers["Content-Type"]
end
content_type=(type)

Basic implementations for #content_type=, location=, and headers are provided to reduce the dependency on the RackDelegation module in Renderer and Redirector.

# File actionpack/lib/action_controller/metal.rb, line 152
def content_type=(type)
  headers["Content-Type"] = type.to_s
end
controller_name()

Delegates to the class' controller_name

# File actionpack/lib/action_controller/metal.rb, line 118
def controller_name
  self.class.controller_name
end
env()
# File actionpack/lib/action_controller/metal.rb, line 103
def env
  @_env ||= {}
end
location()
# File actionpack/lib/action_controller/metal.rb, line 160
def location
  headers["Location"]
end
location=(url)
# File actionpack/lib/action_controller/metal.rb, line 164
def location=(url)
  headers["Location"] = url
end
params()
# File actionpack/lib/action_controller/metal.rb, line 140
def params
  @_params ||= request.parameters
end
params=(val)
# File actionpack/lib/action_controller/metal.rb, line 144
def params=(val)
  @_params = val
end
performed?()
# File actionpack/lib/action_controller/metal.rb, line 186
def performed?
  response_body || (response && response.committed?)
end
response_body=(body)
# File actionpack/lib/action_controller/metal.rb, line 181
def response_body=(body)
  body = [body] unless body.nil? || body.respond_to?(:each)
  super
end
status()
# File actionpack/lib/action_controller/metal.rb, line 173
def status
  @_status
end
status=(status)
# File actionpack/lib/action_controller/metal.rb, line 177
def status=(status)
  @_status = Rack::Utils.status_code(status)
end
url_for(string)

basic #url_for that can be overridden for more robust functionality

# File actionpack/lib/action_controller/metal.rb, line 169
def url_for(string)
  string
end