After reading “Beyond REST? Building Data Services with XMPP PubSub” and other articles about PubSub with XMPP, I decided it would be worth to test it. However, I didn’t find any complete step by step guide in how to test it with ejabberd as XMPP server and XMPP4R as XMPP client.

Below are the steps I followed to test a subscriber (user “sub”) waiting for items published to the node (”home/localhost/pub/updates”) for the publisher (user “pub”). Note you can add as many subscribers/publishers as you want.

  1. install ejabberd (XMPP server). I followed instructions of this article (spanish) or article (english) without any surprise.
  2. create two ejabberd users: “pub” (the publisher) and “sub” (the subscriber).

    sudo ejabberdctl register pub localhost pub
    sudo ejabberdctl register sub localhost sub

  3. install XMPP4R Ruby gem.
    sudo gem install xmpp4r
  4. create file nodecreator.rb. See code below.
    
    #! /usr/bin/ruby
    require "rubygems"
    require "xmpp4r"
    
    require "xmpp4r/pubsub"
    require "xmpp4r/pubsub/helper/servicehelper.rb"
    require "xmpp4r/pubsub/helper/nodebrowser.rb"
    require "xmpp4r/pubsub/helper/nodehelper.rb"
    
    include Jabber
    Jabber::debug = true
    
    service = 'pubsub.localhost'
    jid = 'pub@localhost/laptop'
    
    password = 'pub'
    client = Client.new(JID.new(jid))
    client.connect
    client.auth(password)
    
    client.send(Jabber::Presence.new.set_type(:available))
    pubsub = PubSub::ServiceHelper.new(client, service)
    pubsub.create_node('home/localhost/pub/')
    pubsub.create_node('home/localhost/pub/updates')
    
  5. create file publisher.rb. See code below.
  6. 
    #! /usr/bin/ruby
    require "rubygems"
    
    require "xmpp4r"
    require "xmpp4r/pubsub"
    require "xmpp4r/pubsub/helper/servicehelper.rb"
    require "xmpp4r/pubsub/helper/nodebrowser.rb"
    require "xmpp4r/pubsub/helper/nodehelper.rb"
    include Jabber
    Jabber::debug = true
    jid = 'pub@localhost/laptop'
    
    password = 'pub'
    service = 'pubsub.localhost'
    node = 'home/localhost/pub/updates'
    # connect XMPP client
    client = Client.new(JID.new(jid))
    # remove "127.0.0.1" if you are not using a local ejabberd
    client.connect("127.0.0.1")
    client.auth(password)
    client.send(Jabber::Presence.new.set_type(:available))
    # create item
    pubsub = PubSub::ServiceHelper.new(client, service)
    item = Jabber::PubSub::Item.new
    xml = REXML::Element.new("greeting")
    xml.text = 'hello world!'
    
    item.add(xml);
    # publish item
    pubsub.publish_item_to(node, item)
    
  7. create file subscriber.rb. See code below.
    
    #! /usr/bin/ruby
    require "rubygems"
    require "xmpp4r"
    require "xmpp4r/pubsub"
    require "xmpp4r/pubsub/helper/servicehelper.rb"
    
    require "xmpp4r/pubsub/helper/nodebrowser.rb"
    require "xmpp4r/pubsub/helper/nodehelper.rb"include Jabber
    #Jabber::debug = true
    jid = 'sub@localhost/laptop'
    password = 'sub'
    node = 'home/localhost/pub/updates'
    service = 'pubsub.localhost'
    
    # connect XMPP client
    client = Client.new(JID.new(jid))
    # remove "127.0.0.1" if you are not using a local ejabberd
    client.connect("127.0.0.1")
    client.auth(password)
    client.send(Jabber::Presence.new.set_type(:available))
    sleep(1)
    # subscribe to the node
    pubsub = PubSub::ServiceHelper.new(client, service)
    pubsub.subscribe_to(node)
    subscriptions = pubsub.get_subscriptions_from_all_nodes()
    puts "subscriptions: #{subscriptions}\n\n"
    puts "events:\n"
    
    # set callback for new events
    
    
    pubsub.add_event_callback do |event|
    begin
    event.payload.each do |e|
    puts e,"----\n"
    end
    rescue
    puts "Error : #{$!} \n #{event}"
    
    end
    # infinite loop
    loop do
    sleep 1
    end
    
  8. run nodecreator.rb. It creates the XMPP node “home/localhost/pub/updates”. It creates first the node “home/localhost/pub” and then the “home/localhost/pub/updates”. Seems quite obvious but I spent some hours after I got it.
  9. check the nodes have been created. I used the discovery service functionality of Psi client.psi_service_discovery
  10. run subscriber.rb file. The “sub” user subscribes to the node ‘updates’ and waits for items in the “updates” node. Be aware you should close any XMPP connection with users “pub” and “sub” in case you are using any XMPP client such as Pidgin, Psi,… otherwise it won’t work.
  11. run publisher.rb file. It will send a message “<greetings>hello world!”</greetings> to the subscriber. Run it as many times as you want.
  12. If everything goes well yo will see in the subscriber screen a message like this.
    
    subscriptions: <subscription node='home/localhost/pub/updates' jid='sub@localhost' subscription='subscribed' xmlns='http://jabber.org/protocol/pubsub'/>
    
    events:
    <items node='home/localhost/pub/updates'><item id='3376'><greeting>hello world!</greeting></item></items>
    ----
    

Good Luck!

For this test, I used the following versions:

  • Operating System: Ubuntu 8.04
  • Ruby: 1.8.6
  • XMPP4R: 0.4
  • ejabberd: 1.1.4
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I’ve just installed Apache 2.2 and WordPress 2.3.3 after looking into some alternatives, mainly ruby-based solutions:

Alternative web servers:

  • lighttpd + fastcgi (old recommended solution)
  • apache + mod_ruby (“class sharing issue”)
  • nginx + mongrel (seems the de facto RoR solution)
  • SCGI?

Ruby-based weblogging systems:

  • typo (complex?)
  • mephysto (seems the most appropiate)
  • radiant (more a CMS than a blogging system)

The decision was made because I’m really new in Ruby and RoR and I would like to start taking notes about my progress in this area