AD::Cascade that supports X-Cascade

actionpack/lib/action_dispatch.rb

@@ -41,6 +41,7 @@ module ActionDispatch
 
   autoload_under 'middleware' do
     autoload :Callbacks
+    autoload :Cascade
     autoload :ParamsParser
     autoload :Rescue
     autoload :ShowExceptions

actionpack/lib/action_dispatch/middleware/cascade.rb

@@ -0,0 +1,29 @@
+module ActionDispatch
+  class Cascade
+    def self.new(*apps)
+      apps = apps.flatten
+
+      case apps.length
+      when 0
+        raise ArgumentError, "app is required"
+      when 1
+        apps.first
+      else
+        super(apps)
+      end
+    end
+
+    def initialize(apps)
+      @apps = apps
+    end
+
+    def call(env)
+      result = nil
+      @apps.each do |app|
+        result = app.call(env)
+        break unless result[1]["X-Cascade"] == "pass"
+      end
+      result
+    end
+  end
+end