This is why I decided to read “Programming Erlang”. I’ve nearly read half of the book and my expectations has been really exceeded:

• smooth pace of the book goes from basic knowledge to the hardest part (sequential programming -> advanced sequential programming -> concurrent programming -> distributed programming -> programming multicore CPUs).
• clear and easy to understand examples.
• some complete examples such as an IRC Lite implementation gives you the concepts in action.
• interesting concepts: functional programming, concurrency, distributed programming, fault-tolerant programs.

As missing parts (not sure if they are cover at the end of the book), I found out the following:

• a bit of history of Erlang. Why erlang?
• Comparison between Erlang and other concurrency oriented languages such as Scala, Clojure, Stackless Python, …

To sum up, really a MUST READ if you are curious about other programming languages apart from Java, Python or Ruby.

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.

#! /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)

6. 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
   

7. 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.
8. check the nodes have been created. I used the discovery service functionality of Psi client.
9. 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.
10. run publisher.rb file. It will send a message “<greetings>hello world!”</greetings> to the subscriber. Run it as many times as you want.
11. 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

• text editor: vim 7.1
• web browser: Firefox 3.0.3 (webdeveloper, firebug, firecookie, YSlow, vimperator, del.icio.us)
• IM client: pidgin 2.4.1
• java editor: eclipse 3.3.2
• web server: apache2 2.2.8 (php5, “mod_ruby”)
• gnome-do (quicksilver for gnome)
• glipper (similar to klipper)
• network protocol analyzer: wireshark
• virtual machine: VirtualBox 1.5.6_OSE with Windows XP.
• oracle client: SQLDeveloper

There is still a list of issues pending to fix:

• battery life. I followed the tips (powertop, cpufrequtils,  …) of this article although not sure anot the improvement.
• screen resolution. 1200×800 maximum resolution. I installed fglrx driver through envy but does not improve the resolution (1680*1050 seems the maximum, see this article).
• CD/DVD writer. brasero nor cdrecord command tool worked.
• video codecs. AVI files are reproduced very slowly.
• email client with Exchange support. Evolution does not manage properly meeting requests.
• glipper. It crashes in every start up.
• rubygems. Rubygems from repository does not work properly. You have to install it manually.

“The de-facto Ruby (and Rails) deployment system seems to change rapidly (remember Apache+FastCGI, then lighttpd+FastCGI, then Apache+Mongrel, then Nginx+Mongrel…?) and while Passenger may or may not be a de-facto standard in a few years’ time, it’s certainly becoming the standard for now, so jump on board!”

Really quick the install and set up in Ubuntu.

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

1. download gizmo deb package from here
2. mv ~/.asoundrc.asoundconf ~/.asoundrc.asoundconf.bak
3. sudo mv /etc/asound.conf /etc/asound.conf.bak
4. mv .asoundrc .asoundrc.bak
5. sudo /etc/init.d/alsa-utils restart
6. sudo dpkg -i ~/Desktop/gizmo-project_3.0.1.68_i386.deb

Now it’s up and running but no friend with gizmo to call!