3 files changed, 30 insertions, 2 deletions
diff --git a/railties/lib/rails/configuration.rb b/railties/lib/rails/configuration.rb
index c3e1120fa3..45e2e521ef 100644
--- a/railties/lib/rails/configuration.rb
+++ b/railties/lib/rails/configuration.rb
@@ -19,6 +19,7 @@ module Rails
         middleware.use('ActionDispatch::Cookies')
         middleware.use(lambda { ActionController::Base.session_store }, lambda { ActionController::Base.session_options })
         middleware.use('ActionDispatch::Flash', :if => lambda { ActionController::Base.session_store })
+        middleware.use(lambda { Rails::Rack::Metal.new(Rails.application.config.paths.app.metals.to_a, Rails.application.config.metals) })
         middleware.use('ActionDispatch::ParamsParser')
         middleware.use('::Rack::MethodOverride')
         middleware.use('::ActionDispatch::Head')
diff --git a/railties/lib/rails/rack.rb b/railties/lib/rails/rack.rb
index d487bd0542..36945a6b0f 100644
--- a/railties/lib/rails/rack.rb
+++ b/railties/lib/rails/rack.rb
@@ -1,7 +1,8 @@
 module Rails
   module Rack
-    autoload :Debugger, "rails/rack/debugger"
+    autoload :Debugger,  "rails/rack/debugger"
     autoload :LogTailer, "rails/rack/log_tailer"
-    autoload :Static, "rails/rack/static"
+    autoload :Metal,     "rails/rack/metal"
+    autoload :Static,    "rails/rack/static"
   end
 end
diff --git a/railties/lib/rails/rack/metal.rb b/railties/lib/rails/rack/metal.rb
new file mode 100644
index 0000000000..565f95d7c4
--- /dev/null
+++ b/railties/lib/rails/rack/metal.rb
@@ -0,0 +1,26 @@
+require 'action_dispatch'
+
+module Rails
+  module Rack
+    class Metal
+      def initialize(metal_roots, metals=nil)
+        load_list = metals || Dir["{#{metal_roots.join(",")}}/**/*.rb"]
+
+        @metals = load_list.map { |metal|
+          metal = File.basename(metal, '.rb')
+          require_dependency metal
+          metal.camelize.constantize
+        }.compact
+      end
+
+      def new(app)
+        ActionDispatch::Cascade.new(@metals, app)
+      end
+
+      def name
+        ActionDispatch::Cascade.name
+      end
+      alias_method :to_s, :name
+    end
+  end
+end