1 files changed, 76 insertions, 0 deletions
diff --git a/actionpack/lib/action_dispatch/middleware/reloader.rb b/actionpack/lib/action_dispatch/middleware/reloader.rb
new file mode 100644
index 0000000000..29289a76b4
--- /dev/null
+++ b/actionpack/lib/action_dispatch/middleware/reloader.rb
@@ -0,0 +1,76 @@
+module ActionDispatch
+  # ActionDispatch::Reloader provides prepare and cleanup callbacks,
+  # intended to assist with code reloading during development.
+  #
+  # Prepare callbacks are run before each request, and cleanup callbacks
+  # after each request. In this respect they are analogs of ActionDispatch::Callback's
+  # before and after callbacks. However, cleanup callbacks are not called until the
+  # request is fully complete -- that is, after #close has been called on
+  # the response body. This is important for streaming responses such as the
+  # following:
+  #
+  #     self.response_body = lambda { |response, output|
+  #       # code here which refers to application models
+  #     }
+  #
+  # Cleanup callbacks will not be called until after the response_body lambda
+  # is evaluated, ensuring that it can refer to application models and other
+  # classes before they are unloaded.
+  #
+  # By default, ActionDispatch::Reloader is included in the middleware stack
+  # only in the development environment; specifically, when config.cache_classes
+  # is false. Callbacks may be registered even when it is not included in the
+  # middleware stack, but are executed only when +ActionDispatch::Reloader.prepare!+
+  # or +ActionDispatch::Reloader.cleanup!+ are called manually.
+  #
+  class Reloader
+    include ActiveSupport::Callbacks
+
+    define_callbacks :prepare, :scope => :name
+    define_callbacks :cleanup, :scope => :name
+
+    # Add a prepare callback. Prepare callbacks are run before each request, prior
+    # to ActionDispatch::Callback's before callbacks.
+    def self.to_prepare(*args, &block)
+      set_callback(:prepare, *args, &block)
+    end
+
+    # Add a cleanup callback. Cleanup callbacks are run after each request is
+    # complete (after #close is called on the response body).
+    def self.to_cleanup(*args, &block)
+      set_callback(:cleanup, *args, &block)
+    end
+
+    # Execute all prepare callbacks.
+    def self.prepare!
+      new(nil).run_callbacks :prepare
+    end
+
+    # Execute all cleanup callbacks.
+    def self.cleanup!
+      new(nil).run_callbacks :cleanup
+    end
+
+    def initialize(app)
+      @app = app
+    end
+
+    module CleanupOnClose
+      def close
+        super if defined?(super)
+      ensure
+        ActionDispatch::Reloader.cleanup!
+      end
+    end
+
+    def call(env)
+      run_callbacks :prepare
+      response = @app.call(env)
+      response[2].extend(CleanupOnClose)
+      response
+    rescue Exception
+      run_callbacks :cleanup
+      raise
+    end
+  end
+end