ActionController::Metal can be a middleware

actionpack/lib/action_controller/metal.rb

@@ -47,7 +47,7 @@ def controller_path
     # and response object available. You might wish to control the
     # environment and response manually for performance reasons.
 
-    attr_internal :status, :headers, :content_type
+    attr_internal :status, :headers, :content_type, :app, :response
 
     def initialize(*)
       @_headers = {}
@@ -75,7 +75,34 @@ def call(name, env)
 
     # :api: private
     def to_a
-      [status, headers, response_body]
+      response ? response.to_a : [status, headers, response_body]
+    end
+
+    class ActionEndpoint
+      def initialize(controller, action)
+        @controller, @action = controller, action
+      end
+
+      def call(env)
+        controller = @controller.new.call(@action, env)
+      end
+    end
+
+    class ActionMiddleware
+      def initialize(controller, action)
+        @controller, @action = controller, action
+      end
+
+      def call(env)
+        controller = @controller.new
+        controller.app = @app
+        controller.call(@action, env)
+      end
+
+      def new(app)
+        @app = app
+        self
+      end
     end
 
     # Return a rack endpoint for the given action. Memoize the endpoint, so
@@ -89,9 +116,12 @@ def to_a
     # Proc:: A rack application
     def self.action(name)
       @actions ||= {}
-      @actions[name.to_s] ||= proc do |env|
-        new.call(name, env)
-      end
+      @actions[name.to_s] ||= ActionEndpoint.new(self, name)
+    end
+
+    def self.middleware(name)
+      @middlewares ||= {}
+      @middlewares[name.to_s] ||= ActionMiddleware.new(self, name)
     end
   end
 end

actionpack/lib/action_controller/metal/rack_convenience.rb

@@ -5,7 +5,7 @@ module RackConvenience
     included do
       delegate :headers, :status=, :location=, :content_type=,
                :status, :location, :content_type, :to => "@_response"
-      attr_internal :request, :response
+      attr_internal :request
     end
 
     def call(name, env)
@@ -19,12 +19,6 @@ def params
       @_params ||= @_request.parameters
     end
 
-    # :api: private
-    def to_a
-      @_response.prepare!
-      @_response.to_a
-    end
-
     def response_body=(body)
       response.body = body if response
       super

actionpack/lib/action_dispatch/http/response.rb

@@ -161,13 +161,16 @@ def assign_default_content_type_and_charset!
       headers[CONTENT_TYPE] = type
     end
 
-    def prepare!
+    def to_a
       assign_default_content_type_and_charset!
       handle_conditional_get!
       self["Set-Cookie"] = @cookie.join("\n")
       self["ETag"]       = @etag if @etag
+      super
     end
 
+    alias prepare! to_a
+
     def each(&callback)
       if @body.respond_to?(:call)
         @writer = lambda { |x| callback.call(x) }

actionpack/test/new_base/metal_test.rb

@@ -0,0 +1,45 @@
+require File.join(File.expand_path(File.dirname(__FILE__)), "test_helper")
+
+module MetalTest
+  class MetalMiddleware < ActionController::Metal
+    def index
+      if env["PATH_INFO"] =~ /authed/
+        self.response = app.call(env)
+      else
+        self.response_body = "Not authed!"
+        self.status = 401
+      end
+    end
+  end
+
+  class Endpoint
+    def call(env)
+      [200, {}, "Hello World"]
+    end
+  end
+
+  class TestMiddleware < ActiveSupport::TestCase
+    def setup
+      @app = Rack::Builder.new do
+        use MetalMiddleware.middleware(:index)
+        run Endpoint.new
+      end.to_app
+    end
+
+    test "it can call the next app by using @app" do
+      env = Rack::MockRequest.env_for("/authed")
+      response = @app.call(env)
+
+      assert_equal "Hello World", response[2]
+    end
+
+    test "it can return a response using the normal AC::Metal techniques" do
+      env = Rack::MockRequest.env_for("/")
+      response = @app.call(env)
+
+      assert_equal "Not authed!", response[2]
+      assert_equal 401, response[0]
+    end
+  end
+end
+