first pass at the action warden, currently just reproducing basic rack functionality

lib/vagrant/action/builder.rb

@@ -112,34 +112,11 @@ module Vagrant
       def to_app(env)
         # Prepend the error halt task so errneous environments are halted
         # before the chain even begins.
-        items = stack.dup.unshift([Env::ErrorHalt, [], nil])
+        middleware = stack.dup.push([Env::ErrorHalt, [], nil])
 
         # Convert each middleware into a lambda which takes the next
         # middleware.
-        items = items.collect do |item|
-          klass, args, block = item
-
-          lambda do |app|
-            if klass.is_a?(Class)
-              # A middleware klass which is to be instantiated with the
-              # app, env, and any arguments given
-              klass.new(app, env, *args, &block)
-            elsif klass.respond_to?(:call)
-              # Make it a lambda which calls the item then forwards
-              # up the chain
-              lambda do |e|
-                klass.call(e)
-                app.call(e)
-              end
-            else
-              raise "Invalid middleware: #{item.inspect}"
-            end
-          end
-        end
-
-        # Append the final step and convert into flattened call chain.
-        items << lambda { |env| }
-        items[0...-1].reverse.inject(items.last) { |a,e| e.call(a) }
+        Vagrant::Action::Warden.new(middleware, env)
       end
 
       # Runs the builder stack with the given environment.

lib/vagrant/action/warden.rb

@@ -0,0 +1,36 @@
+module Vagrant
+  class Action
+    class Warden
+      attr_accessor :actions
+
+      def initialize(middleware, env)
+        @stack = []
+        @actions = middleware.map { |m| finalize_middleware(m, env) }.reverse
+      end
+
+      def call(env)
+        return if @actions.empty?
+        @stack.push(@actions.pop).last.call(env)
+      end
+
+      def finalize_middleware(middleware, env)
+        klass, args, block = middleware
+
+        if klass.is_a?(Class)
+          # A middleware klass which is to be instantiated with the
+          # app, env, and any arguments given
+          klass.new(self, env, *args, &block)
+        elsif klass.respond_to?(:call)
+          # Make it a lambda which calls the item then forwards
+          # up the chain
+          lambda do |e|
+            klass.call(e)
+            self.call(e)
+          end
+        else
+          raise "Invalid middleware: #{middleware.inspect}"
+        end
+      end
+    end
+  end
+end

test/vagrant/action/builder_test.rb

@@ -166,7 +166,7 @@ class ActionBuilderTest < Test::Unit::TestCase
         middleware.stubs(:is_a?).with(Class).returns(true)
         middleware.expects(:new).with(anything, env).returns(result)
         @instance.use middleware
-        result = @instance.to_app(env)
+        result = @instance.to_app(env).actions.first
         assert result.kind_of?(Vagrant::Action::Env::ErrorHalt)
       end