Merge 8566af1 into f9dee5b

README.md

@@ -719,6 +719,17 @@ Whatever::Application.config.middleware.use ExceptionNotification::Rack,
 
 You can make use of both the environment and the exception inside the lambda to decide wether to avoid or not sending the notification.
 
+## Rack X-Cascade Header
+
+Some rack apps (Rails in particular) utilize the "X-Cascade" header to pass the request-handling responsibility to the next middleware in the stack.
+
+Rails' routing middleware uses this strategy, rather than raising an exception, to handle routing errors (e.g. 404s); to be notified whenever a 404 occurs, set this option to "false."
+
+### :ignore_cascade_pass
+
+*Boolean, default: true*
+
+Set to false to trigger notifications when another rack middleware sets the "X-Cascade" header to "pass."
 
 ## Background Notifications
 

lib/exception_notification/rack.rb

@@ -1,5 +1,7 @@
 module ExceptionNotification
   class Rack
+    class CascadePassException < Exception; end
+
     def initialize(app, options = {})
       @app = app
 
@@ -19,18 +21,30 @@ def initialize(app, options = {})
         end
       end
 
+      @ignore_cascade_pass = options.delete(:ignore_cascade_pass) { true }
+
       options.each do |notifier_name, options|
         ExceptionNotifier.register_exception_notifier(notifier_name, options)
       end
     end
 
     def call(env)
-      @app.call(env)
+      _, headers, _ = response = @app.call(env)
+
+      if !@ignore_cascade_pass && headers['X-Cascade'] == 'pass'
+        msg = "This exception means that the preceding Rack middleware set the 'X-Cascade' header to 'pass' -- in " <<
+          "Rails, this often means that the route was not found (404 error)."
+        raise CascadePassException, msg
+      end
+
+      response
     rescue Exception => exception
       if ExceptionNotifier.notify_exception(exception, :env => env)
         env['exception_notifier.delivered'] = true
       end
-      raise exception
+
+      raise exception unless exception.is_a?(CascadePassException)
+      response
     end
 
     private

test/exception_notification/rack_test.rb

@@ -0,0 +1,20 @@
+require 'test_helper'
+
+class RackTest < ActiveSupport::TestCase
+
+  setup do
+    @pass_app = Object.new
+    @pass_app.stubs(:call).returns([nil, { 'X-Cascade' => 'pass' }, nil])
+  end
+
+  test "should ignore \"X-Cascade\" header by default" do
+    ExceptionNotifier.expects(:notify_exception).never
+    ExceptionNotification::Rack.new(@pass_app).call({})
+  end
+
+  test "should notify on \"X-Cascade\" = \"pass\" if ignore_cascade_pass option is false" do
+    ExceptionNotifier.expects(:notify_exception).once
+    ExceptionNotification::Rack.new(@pass_app, :ignore_cascade_pass => false).call({})
+  end
+
+end