1 files changed, 31 insertions, 0 deletions
diff --git a/railties/lib/rails/rack/cascade.rb b/railties/lib/rails/rack/cascade.rb
new file mode 100644
index 0000000000..d5af7fc77e
--- /dev/null
+++ b/railties/lib/rails/rack/cascade.rb
@@ -0,0 +1,31 @@
+require 'active_support/ordered_hash'
+
+module Rails
+  module Rack
+    # Try a request on several apps; return the first non-404 response.
+    class Cascade
+      attr_reader :apps
+
+      def initialize(apps)
+        @apps = ActiveSupport::OrderedHash.new
+        apps.each { |app| add app }
+      end
+
+      def call(env)
+        @apps.keys.each do |app|
+          result = app.call(env)
+          return result unless result[0].to_i == 404
+        end
+        Metal::NotFoundResponse
+      end
+
+      def add(app)
+        @apps[app] = true
+      end
+
+      def include?(app)
+        @apps.include?(app)
+      end
+    end
+  end
+end