AMQP creating subscribing to queues dynamically

Question

I am trying to build a simple chat application using AMQP, Websockets and Ruby. I understand that this may not be the best use-case to understand AMQP but I would like to understand where i am going wrong.

The following is my amqp-server code

require 'rubygems'
require 'amqp'
require 'mongo'
require 'em-websocket'
require 'json'

class MessageParser
  # message format => "room:harry_potter, nickname:siddharth, room:members"
  def self.parse(message)
    parsed_message = JSON.parse(message)

    response = {}
    if parsed_message['status'] == 'status'
      response[:status] = 'STATUS'
      response[:username] = parsed_message['username']
      response[:roomname] = parsed_message['roomname']
    elsif parsed_message['status'] == 'message'
      response[:status]   = 'MESSAGE'
      response[:message]  = parsed_message['message']
      response[:roomname] = parsed_message['roomname'].split().join('_')
    end

    response
  end
end

class MongoManager
  def self.establish_connection(database)
    @db ||= Mongo::Connection.new('localhost', 27017).db(database)
    @db.collection('rooms')

    @db
  end  
end


@sockets = []
EventMachine.run do
  connection = AMQP.connect(:host => '127.0.0.1')
  channel = AMQP::Channel.new(connection)

  puts "Connected to AMQP broker. #{AMQP::VERSION} "

  mongo = MongoManager.establish_connection("trackertalk_development")

  EventMachine::WebSocket.start(:host => '127.0.0.1', :port => 8080) do |ws|
    socket_detail = {:socket => ws}
    ws.onopen do 
      @sockets << socket_detail

    end

    ws.onmessage do |message|

      status  = MessageParser.parse(message)         
      exchange = channel.fanout(status[:roomname].split().join('_'))   

      if status[:status] == 'STATUS'               
         queue = channel.queue(status[:username], :durable => true)

        unless queue.subscribed? 
         puts "--------- SUBSCRIBED --------------"
         queue.bind(exchange).subscribe do |payload|
            puts "PAYLOAD :  #{payload}"
            ws.send(payload)
          end 
        else
          puts "----ALREADY SUBSCRIBED"
        end                  

        # only after 0.8.0rc14
        #queue = channel.queue(status[:username], :durable => true)      
        #AMQP::Consumer.new(channel, queue)        

      elsif status[:status] == 'MESSAGE'
        puts "********************* Message- published ******************************"
        exchange.publish(status[:message)  
      end                  
    end

    ws.onclose do 
      @sockets.delete ws
    end
  end    
end

I use the status to indicate whether the incoming message is a message for ongoing chat or for a status message requiring me to handle chores like subscribing to the queue.

The problem i face is that when I send a message like socket.send(JSON.stringify({status:'message', message:'test', roomname:'Harry Potter'}))

The exchange.publish' is called but it still doesn't get pushed via thews.send` to the browser.

Is there something fundamentally wrong with my understanding of EventMachine and AMQP?

Here is the pastie for the same code http://pastie.org/private/xosgb8tw1w5vuroa4w7a

My code seems to work as desired when i remove the durable => true from queue = channel.queue(status[:username], :durable => true)

The following is a snippet of my Rails view which identifies the user's username and the roomname and sends it as part of message via Websockets.

Though the code seems to work when i remove the durable => true I fail to understand why that affects the message being delivered. Please Ignore the mongo part of as it does not play any part yet.

I would also like to know if my approach to AMQP and its usage is correct



  
    <%= @room.name %>

AMQP creating subscribing to queues dynamically

2 Answers