Introduce Rails Metal

  # app/metal/poller.rb
  class Poller < Rails::Rack::Metal
    def call(env)
      if env["PATH_INFO"] =~ /^\/poller/
        [200, {"Content-Type" => "application/json"}, Message.recent.to_json]
      else
        super
      end
    end
  end

* There is a generator to help you get started
    `script/generate metal poller`

* Also, metal bits can be ran standalone with rackup
    `rackup app/metal/poller.rb`

railties/lib/initializer.rb

@@ -155,6 +155,8 @@ def process
       initialize_framework_settings
       initialize_framework_views
 
+      initialize_metal
+
       add_support_load_paths
 
       load_gems
@@ -533,6 +535,12 @@ def initialize_i18n
       end
     end
 
+    def initialize_metal
+      Dir["#{configuration.root_path}/app/metal/*.rb"].each do |file|
+        configuration.middleware.use(File.basename(file, '.rb').camelize)
+      end
+    end
+
     # Initializes framework-specific settings for each of the loaded frameworks
     # (Configuration#frameworks). The available settings map to the accessors
     # on each of the corresponding Base classes.
@@ -915,6 +923,7 @@ def default_load_paths
         # Followed by the standard includes.
         paths.concat %w(
           app
+          app/metal
           app/models
           app/controllers
           app/helpers
@@ -933,6 +942,7 @@ def default_load_once_paths
 
       def default_eager_load_paths
         %w(
+          app/metal
           app/models
           app/controllers
           app/helpers

railties/lib/rails/rack.rb

@@ -2,6 +2,7 @@ module Rails
   module Rack
     autoload :Debugger, "rails/rack/debugger"
     autoload :Logger, "rails/rack/logger"
+    autoload :Metal, "rails/rack/metal"
     autoload :Static, "rails/rack/static"
   end
 end

railties/lib/rails/rack/metal.rb

+module Rails
+  module Rack
+    class Metal
+      NotFound = lambda { |env|
+        [404, {"Content-Type" => "text/html"}, "Not Found"]
+      }
+
+      def self.call(env)
+        new(NotFound).call(env)
+      end
+
+      def initialize(app)
+        @app = app
+      end
+
+      def call(env)
+        @app.call(env)
+      end
+    end
+  end
+end

railties/lib/rails_generator/generators/components/metal/USAGE

+Description:
+    Cast some metal!
+
+Examples:
+    `./script/generate metal poller`
+
+        This will create:
+            Metal: app/metal/poller.rb

railties/lib/rails_generator/generators/components/metal/metal_generator.rb

+class MetalGenerator < Rails::Generator::NamedBase
+  def manifest
+    record do |m|
+      m.directory 'app/metal'
+      m.template 'metal.rb', File.join('app/metal', "#{file_name}.rb")
+    end
+  end
+end

railties/lib/rails_generator/generators/components/metal/templates/metal.rb

+# Allow the metal piece to run in isolation
+require(File.dirname(__FILE__) + "/../../config/environment") unless defined?(Rails)
+
+class <%= class_name %> < Rails::Rack::Metal
+  def call(env)
+    if env["PATH_INFO"] =~ /^\/<%= file_name %>/
+      [200, {"Content-Type" => "text/html"}, "Hello, World!"]
+    else
+      super
+    end
+  end
+end