1 files changed, 29 insertions, 5 deletions
diff --git a/actionpack/lib/action_controller/middleware_stack.rb b/actionpack/lib/action_controller/middleware_stack.rb
index a6597a6fec..74f28565c0 100644
--- a/actionpack/lib/action_controller/middleware_stack.rb
+++ b/actionpack/lib/action_controller/middleware_stack.rb
@@ -1,19 +1,39 @@
 module ActionController
   class MiddlewareStack < Array
     class Middleware
-      attr_reader :klass, :args, :block
+      attr_reader :args, :block
 
       def initialize(klass, *args, &block)
-        if klass.is_a?(Class)
-          @klass = klass
+        @klass = klass
+
+        options = args.extract_options!
+        if options.has_key?(:if)
+          @conditional = options.delete(:if)
         else
-          @klass = klass.to_s.constantize
+          @conditional = true
         end
+        args << options unless options.empty?
 
         @args = args
         @block = block
       end
 
+      def klass
+        if @klass.is_a?(Class)
+          @klass
+        else
+          @klass.to_s.constantize
+        end
+      end
+
+      def active?
+        if @conditional.respond_to?(:call)
+          @conditional.call
+        else
+          @conditional
+        end
+      end
+
       def ==(middleware)
         case middleware
         when Middleware
@@ -50,8 +70,12 @@ module ActionController
       push(middleware)
     end
 
+    def active
+      find_all { |middleware| middleware.active? }
+    end
+
     def build(app)
-      reverse.inject(app) { |a, e| e.build(a) }
+      active.reverse.inject(app) { |a, e| e.build(a) }
     end
   end
 end