faye-rails is a Ruby gem which handles embedding Faye's rack-based server into the rails stack and providing it with access to controllers and views based on bindings and observers.

Due to the limitations of most Rack-based web servers available Faye can only be run on Thin, however if you are using thin, then you can add as many Faye servers as you want to the Rails router like so:

App::Application.routes.draw do
  faye_server '/faye', :timeout => 25
end

You can also pass a block to faye_server which will be executed in the context of the Faye server, thus you can call any methods on Faye::RackAdapter from within the block:

App::Application.routes.draw do
  faye_server '/faye', :timeout => 25 do
    class MockExtension
      def incoming(message, callback)
        callback.call(message)
      end
    end
    add_extension(MockExtension)
  end
end

If you really want to, you can ask Faye to start it's own listening Thin server on an arbitrary port:

App::Application.routes.draw do
  faye_server '/faye', :timeout => 25 do
    listen(9292)
  end
end

You can also do some rudimentary routing using the map method:

App::Application.routes.draw do
  faye_server '/faye', :timeout => 25 do
    map '/widgets/**' => WidgetsController
map :default => :block
  end
end

You can find more details on the #map method in the rdoc

faye-rails includes a controller for handling the binding between model events and channels with it's own DSL for managing channel-based events.

class WidgetController < FayeRails::Controller
end

You can subscribe to changes in models using the controller's observer DSL:

class WidgetController < FayeRails::Controller
  observe Widget, :create do |new_widget|
    publish('/widgets', new_widget.attributes)
  end
end

See the rdoc for more information.

The controller DSL elegantly wraps channel-based aspects of the Faye API so that you can easily group code based on specific channels.

You can make use of Faye's monitoring API by adding calls to monitor within the channel block. You are able to monitor :subscribe, :unsubscribe and :publish events. Blocks are executed within the context of a FayeRails::Controller::Monitor instance which will give you access to #client_id, #channel and #data (#data only having a value on :publish events).

class WidgetController < FayeRails::Controller
  channel '/widgets' do
    monitor :subscribe do
      puts "Client #{client_id} subscribed to #{channel}."
    end
    monitor :unsubscribe do
      puts "Client #{client_id} unsubscribed from #{channel}."
    end
    monitor :publish do
      puts "Client #{client_id} published #{data.inspect} to #{channel}."
    end
  end
end

You can quickly and easily filter incoming and outgoing messages for your specific channel using the controller's filter API, which wraps Faye's extensions API in a concise and channel-specific way.

class WidgetController < FayeRails::Controller
  channel '/widgets' do
    filter :in do
      puts "Inbound message #{message}."
      pass
    end
  end
end

You can add filters for :in, :out and :any, which will allow you to filter messages entering the server, exiting the server or both. The block passed to the filter is executed in the context of a FayeRails::Filter::DSL instance, which gives you access to the #message method, which contains the entire message payload from the client (including meta information you wouldn't see other ways). You also have access to the #pass, #modify, #block and #drop methods which are sugar around Faye's callback system - which is accessible via the #callback method if you want to do it that way. Check out the FayeRails::Filter::DSL rdoc for more information. Please note that all filters must call callback.call either via the sugar methods or directly to ensure that requests are not lost (not to mention potential memory leaks).

You can easily subscribe to a channel using the 'subscribe' method inside your channel block, like so:

class WidgetController < FayeRails::Controller
  channel '/widgets' do
    subscribe do
  puts "Received on channel #{channel}: #{message.inspect}"
end
  end
end

Thanks to James Coglan for the excellent Faye Bayeux implementetation and great support for Faye users.