Simple publish-subscribe 

messaging system 

example based on  kanbanery.com

• memory  
  
• redis (let you scale Faye service)
  

• protocol for transporting asynchronous messages
  
  
• primarily over HTTP
  
  
• low latency between a server and web clients
  

• object-based implementation of Bayeux
  
  
• delegates execution of Bayeux operations to the Engine
  
  
  
• easy to swap out the backend implementation
  
  
• does not know anything about HTTP or other network transports

require File.expand_path('../config/environment',  __FILE__)

bayeux = Faye::RackAdapter.new(
    :mount => '/faye',
    :timeout => 25
)

# some code

run bayeux

# ...

bayeux.add_extension(PushOnlyServer.new)
bayeux.add_extension(ServerAuth.new)

bayeux.bind(:subscribe) do |client_id, channel|
  Rails.logger.info "#{client_id} subscribed #{channel}"
end

# ...

# ...
class FayeExtension
  def incoming(message, callback)
    # ...
    callback.call(message)
  end

  def outgoing(message, callback)
    # ...
    callback.call(message)
  end
end
# ...

class PushOnlyServer
  def incoming(msg, callback)
    unless msg['channel'] =~ /^\/meta\//
      password = msg['ext'] &&
                 msg['ext']['password']

      if password != AppConfig.faye.push_secret
        msg['error'] = '403::Password required'
      end
    end

    callback.call(msg)
  end
  # ...
end

class PushOnlyServer
  # ...
  
  def outgoing(message, callback)
    unless message['ext'].nil?
      message['ext'].delete('password')
    end

    callback.call(message)
  end
end

class LiveUpdate
  def self.send_to_faye(...)
    # ...
      message = {
        :channel => 'channel-name',
        :data => {
          :event => 'event-name',
          :faye_socket_id => 'id'
        },
        :ext => {
          :password => 'secret'
        }
      }
      uri = URI.parse(internal_url)
      Net::HTTP.post_form(uri,
               :message => message.to_json)
   # ...
  end
end

class ServerAuth
  def incoming(msg, callback)
    # ...
    # some code on the next slide
    # ...

    # Call the server back now we're done
    callback.call(msg)
  end
end

# ...

    # Let non-subscribe messages through
    
    unless msg['channel'] == '/meta/subscribe'
      return callback.call(msg)
    end
    
# ...

# ...

    if msg['ext'].nil?
      msg['error'] = 'Missing ext key'
    else
      user_id = msg['ext']['user_id']
      
      # check if user can subscribe the channel
      # ...
      # more code on the next slide
    end

# ...

# ...

user_id = message['ext']['user_id']
faye_token = message['ext']['faye_token']
project_id = message['ext']['project_id']

project = Project.get(project_id)
      
if project.present?
  # ... next slide
else
  message['error'] = "Project doesn't exist"
end

# ...

# check if user has access to project etc
user = User.get(user_id)

if user && user.valid_faye_token?(faye_token)
  client_id = message['fayeClientId']
  # ...

  $semaphore.synchronize do
    $user_activities[client_id] = some_id
  end
elsif user
  message['error'] = "Invalid faye token"
else
  message['error'] = "User doesn't exist"
end

# ...

# key: faye client id
# value: list of project memberships ids
$user_activities = {}

$semaphore = Mutex.new
$update_thread = Thread.new do
  loop do
    sleep 60
    $semaphore.synchronize do
      ids = $user_activities.values.uniq
      # ...
      Project.update_activities(ids)
    end
  end
end

# CoffeeScript

class K2.FayeConnection
  
  connectAndBindEvents: ->
    # ...
    url = 'http://localhost:8090/faye'
    @faye_client = new Faye.Client url,
      timeout: timeout

    # client-side extension (next slide)
    
  # ...

# ...

@faye_client.addExtension outgoing: (message, callback) ->
  
  message.ext = message.ext or {}
  
  message.ext.user_id = K2.faye.currentUserId
  message.ext.faye_token = K2.faye.fayeToken
  message.ext.project_id = K2.faye.projectId
  
  callback(message)
  
# ...

class K2.FayeConnection
  # ...  
    @faye_client.bind 'transport:up', ->
      # the client is online
      
      console.log "New socket ID: " + faye_connection.faye_client._0
      
      # stop interval refreshing kanban board
      faye_connection.polling.stop()
      faye_connection.polling.fullRefresh()

class K2.FayeConnection
  # ...  
    @faye_client.bind 'transport:down', ->
      # the client is offline
      
      # update data with interval
      # kanbanery stuff - not related to faye
      faye_connection.polling.start() 
      faye_connected = false

class K2.FayeConnection
  subscribeToChannelAndBindEvents: ->
    
    subscription = @faye_client.subscribe @fayeChannelName(), (msg) ->
      
      console.log "GOT MESSAGE", msg
      
      # current faye socket id
      id = faye_connection.faye_client._0
      
      # ignore message sent by client
      if msg.faye_socket_id != id
        faye_connection.store.refresh msg.event

# subscription has been set up
# and acknowledged by the server

subscription.callback ->
  console.log "SUBSCRIBED"
  faye_connection.polling.stop()

# error while creating subscription
subscription.errback (error) ->
  console.log(error.message)
  faye_connection.polling.start()