Capturing exceptions raised in EventListener callbacks

README.md

@@ -52,7 +52,7 @@ events, such as when a client subscribe to a channel.
 
 ```ruby
   # A chat listener will by default listen to events
-  # sent to channel whose name begins with '/chat'
+  # sent to any channel whose name begins with '/chat'
   class ChatListener < Alondra::EventListener
 
     # If you want to listen to other channels than the default ones
@@ -67,9 +67,12 @@ events, such as when a client subscribe to a channel.
     # This will be fire any time a client subscribe to
     # any of the observed channels
     on :subscribed, :to => :member do
-      @user = resource
 
-      # You can push notifications from listeners
+      # If you use Cookie Based Session Store,
+      # you can access the rails session from the listener
+      @user = User.find(session[:user_id])
+
+      # Push notifications from listener
       push '/users/user', :to => channel_name
     end
   end
@@ -118,7 +121,7 @@ In the client you can listen to these events using the javacript API:
 
 ```
 
-This technique is also especially useful if you use something like Backbone.js
+This technique is especially useful if you use something like Backbone.js
 to render your app frontend.
 
 

lib/alondra/event_listener.rb

@@ -64,7 +64,13 @@ def receive(event)
 
       matching_callbacks = self.class.callbacks.find_all { |c| c.matches?(event) }
       matching_callbacks.each do |callback|
-        self.instance_exec(event, &callback.proc)
+        begin
+          self.instance_exec(event, &callback.proc)
+        rescue Exception => ex
+          Rails.logger.error 'Error while processing event listener callback'
+          Rails.logger.error ex.message
+          Rails.logger.error ex.stacktrace if ex.respond_to? :stacktrace
+        end
       end
     end
   end

test/models/event_listener_test.rb

@@ -61,6 +61,10 @@ def self.custom_events
       ChatListener.custom_events << event
     end
 
+    on :boom do |event|
+      event.boom!
+    end
+
   end
 
 
@@ -195,5 +199,15 @@ class OverwrittenDefaultPatternsListener < EventListener
 
       assert_equal ChatListener.custom_events.last, event
     end
+
+    test 'capture exceptions launched in event listener' do
+      boom = BogusEvent.new :event => :boom, :resource => Chat.new, :channel => '/chats/'
+      EventRouter.new.process(boom)
+
+      event = Event.new :event => :custom, :resource => Chat.new, :channel => '/chats/'
+      EventRouter.new.process(event)
+
+      assert_equal ChatListener.custom_events.last, event
+    end
   end
 end

test/support/mocks/bogus_event.rb

@@ -3,7 +3,12 @@ module Alondra
   class BogusException < StandardError; end
 
   class BogusEvent < Event
+
     def to_json
+      boom!
+    end
+
+    def boom!
       raise BogusException.new("Ha ha ha, I'm evil!")
     end
   end