Reading Geek Night

An open community event for techy-types is getting underway in Reading.  These events are for people to get together in an informal setting, share knowledge and have a couple of beers!

The first of these monthly events is happening next Tuesday on the 10th November.  Add http://readinggeeknight.com/ to your bookmarks and check it out regularly for updates.  You can also follow @rdggeek on twitter or the #rdggeek hashtag.

Talks lined up for the first event are:

Who do you think you are? Ben NunneyThe internet is everywhere, and all of us in the tech community are connected in some way, shape or form. But how powerful is your digital identity, and what does it actu- ally matter to you? The talk will be a brief look at what your digital identity is, was, and can be – who are you, in the eyes of the internet? Does your boss really care what you had for lunch?

A practical introduction to Ruby on Rails Chris TingleyThis live code demonstration will take you from your first line of Ruby code, through some fundamental features of Rails with pit stops in MVC, CRUD, REST, automated testing and meta-programming, crossing the finish line with a functional web app! Hold on to your hats, all this WILL happen in 15 minutes.

What Is Windows Azure? Dom GreenWhat is Windows Azure? How will cloud computing change how we develop applications, manage our IT infrastructure, or even set up an online business? This whirl-wind talk will introduce Windows Azure, Microsoftʼs cloud computing platform.

Coding for kids Jim Anning – Coding is not routinely taught in UK schools until 6th form level. How can we encourage a new generation of kids to code? A quick introduction to MIT’s Scratch programming environment.

Installing modporter for Rails on Ubuntu Hardy Heron

It’s not an uncommon scenario for Apache to not play nicely with Rails when dealing with multipart forms and large uploaded files. There are a few solutions out there, but the best we have seen is modporter from the guys at ActionRails.

So, you’ll need a few things to beef up Apache; if you haven’t got them already:

sudo apt-get install libapache2-mod-apreq2
sudo apt-get install libapreq2-dev
sudo apt-get install apache2-threaded-dev

Now fetch the latest ModPorter from github from here. Once you have downloaded and unpacked this, edit the Rakefile and change the apxs variable to apxs2, then type:

cd modporter-directory
rake

And, you’ll probably want the modporter plugin for Rails to give you a nice consistent interface for uploaded files rather than differentiate String IOs and UploadedFile objects.

If you have git:

script/plugin install git://github.com/actionrails/modporter-plugin.git

Otherwise, download the tar from here, unpack and stick in your vendor/plugins directory.

Now configure Apache to use load some additional modules, edit your apache.conf file to include (your path to modules may be different):

LoadModule apreq_module modules/mod_apreq2.so
LoadModule porter_module modules/mod_porter.so

Tracking down a stolen laptop

This is a bit off-topic, but worthwhile sharing.

I recently, rather unfortunately had my laptop stolen and now I have a replacement; I remember hearing about software that could use the built in iSight to take photos of the thieves and mail them back to me.

After looking on the net and finding some rather good, but pay-ware applications, I came across the Prey Project offering an open source free alternative. I went about installing the software and after checking that it worked went about tweaking it to work with how I have my laptop set up.

I use file vault (thank God it was switched on the laptop that was stolen) and have a password on wake so my personal files are secure. However, even with crontab running Prey once a minute, I figured that if the thief couldn’t log into my laptop, it was a bit pointless. So I have used two tactics that will hopefully result in my getting some pictures if the unfortunate were to happen again:

  1. Enable logging in of the Guest account. This means if the thief reboots the laptop (to try and log in as a different user rather than get the password screen from wake), they can log into a sandboxed account with Prey happily snapshotting away.
  2. Put Prey in the crontab that runs for the login screens:

in /private/etc/crontab (this may not exist):

*/1 * * * * cd /usr/share/prey; ./prey.sh

Of course, there are no guarantees, but it’s better than nothing.

10,000 Hits!

Just a quick note to say we have just reached 10,000 hits to the Workbooks Technical Blog. Thanks for reading!

./java: No such file or directory (on Linux)

… and when you look, it exists, it has the correct permissions and everything. Do a long-listing and it’s readable and executable by everyone, and all the directories up the tree also are.  It just doesn’t start!  I spent a while looking for this and didn’t find it on google so hopefully this helps someone.

The clues:

$ file java
java: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for GNU/Linux 2.2.5, dynamically linked (uses shared libs), stripped


$ uname -a

reports a 64-bit OS.

The problem is you’re running a 64-bit OS with insufficient 32-bit shared library support to run a 32-bit binary.

The solution:

$ sudo aptitude install ia32-libs

(Courtesy of http://www.debian-administration.org/articles/534)


PS: Yes, I know I could get a 64-bit java interpreter….

Posted in Uncategorized. Tags: , . 1 Comment »

Ruby is beautiful – longest word length

Sometimes it makes me smile how things can be implemented in such a simple and beautiful way in Ruby.

We needed a method to return the length of the longest word in a string. So we opened up the String class and gave it a new toy to play with:

class String
  # Returns the length of the longest word in the string
  def longest_word_length
    words = self.split(' ')
    words.any? ? words.max{ |a,b| a.length <=> b.length }.length : 0
  end
end

Of course, an RSpec example will keep our testing Yang intact!

describe String do
  it "can determine the longest word in a string" do
    "".longest_word_length.should eql(0)
    "hello".longest_word_length.should eql(5)
    "this is the longest word".longest_word_length.should eql(7)
    "two words".longest_word_length.should eql(5)
    "same size".longest_word_length.should eql(4)
  end
end

Are there any little methods you have written that make you smile at their simplicity?

Comparison <=> operator on string attributes of ActiveRecord objects

Here’s a little gotcha for you which caught me out by surprise, obvious when you think about it, but irritating if you miss it: the ruby String comparison operator does case-sensitive comparisons.

# Good:
['C', 'b', 'A', 'D'].sort #=> ['A', 'b', 'C', 'D']

# Bad (what <=> gives you out the box):
['C', 'b', 'A', 'D'].sort #=> ['A', 'C', 'D', 'b']

For a nice efficient implementation of a AR model comparitor use the String#casecmp method for a case-insensitive comparison:

class MyObject
  def <=>(other)
    self.my_attribute.casecmp(other.my_attribute)
  end
end

Overriding fundamental ActiveRecord methods (like destroy) whilst preserving callbacks

OK, so you’ve decided that it’s a good idea for you to override one of the fundamental methods on one of your ActiveRecord models. But in doing so, you have discovered that all of a sudden your callbacks have stopped working.

The reason for this is when your class is loaded, ActiveRecord::Callbacks have already hooked in the callback methods around the relevant methods using alias_method_chain meaning that the once named destroy method is now called destroy_without_callbacks.

So, to actually override the destroy method, use the following code:

def destroy_without_callbacks
  unless new_record?
    # do your code here
  end
  freeze
end

Note that the implementations will differ for other methods e.g. create, so you should check the ActiveRecord base class to see what should be in there.

Does your rabbit tell you about your build?

A rabbit is for life…

A French company called Violet sells a number of “Things” – internet-enabled devices that interact with you and/or your environment.  (Actually you can buy them from lots of resellers).  They include mirrors, stamps, lamps and strangely rabbits!  The first generation rabbit was called Nabaztag (Nabaztag is Armenian for “rabbit”), whilst the second  generation is called a Nabaztag:tag, and amongst other enhancements, has been blessed with the ability to “sniff” RFID tags and play MP3 files.  You can identify a Nabaztag:tag by it’s belly-button microphone which enables the rabbit to hear a small number of single word commands, e.g. “weather” and respond, e.g. by telling you what the weather will be.  Wikipedia can tell you more about Nabatztags.

I recently got a Nabaztag:tag.  He (or is it a she?) comes in clean pure white, although Violet also sells coloured replacement ears, and many people customise their rabbit’s look.  Of course, the geek in me didn’t care too much about style and rather wanted to fiddle with how it works and get it to do different things…

Cruisecontrol.rb is for peace of mind…

As was alluded to in a previous blog post, we use CruiseControl.rb to do continuous integration of our code.  Within ten minutes of checking some code into Subversion (yes we use that too), our CruiseControl.rb server will automatically

  • check the updated code out
  • update the application’s database using Rails migrations
  • start the application
  • run our unit tests, our integration tests and our performance tests
  • do some profiling of our code
  • shut down the application again
  • build our documentation
  • and finally trawl through our code picking out the TODOs and FIXMEs etc.

This is great, but how do we know whether it worked or not?  Well, we use CCMenu which sits on our menu bars and quietly shows a coloured blob giving the current state of the build.  Some of us integrate it with Growl to actively tell us whether it succeeded or failed when the build completes.  But that wasn’t enough for me!

Tell me, tell me now!

Yep, I had to integrate CruiseControl.rb and my rabbit.  Unfortunately, CruiseControl’s documentation on writing plugins is a little sparse (I couldn’t find any truly complete documentation), and Violet’s documentation isn’t ideal either (and they keep moving it although there is some general consensus between them all).

So, I’ve tried to simplify it for you.  First I wrote a CruiseControl.rb plugin using the sparse documentation and got it working, but it didn’t do much because I’d only learnt about a couple of hooks.  Thinking that there must be more, I trawled the CruiseControl.rb source code to discover all the possible hooks… and there were lots more!  So I added methods for all of the possible CruiseControlRB hooks to my plugin.

Finally, I used that complete template plugin to integrate with my rabbit.  And here’s the code:

#!/usr/bin/ruby

require 'net/http'
require 'uri'

class NabaztagNotifier

  # Configure your Nabaztag's details here.
  NABAZTAG_SERIAL_NUMBER = 'xxxxxxxxxxxx'
  NABAZTAG_TOKEN = 'yyyyyyyyyy'

  COLOURS = {
    :black    => "0,0,0",
    :red      => "255,0,0",
    :green    => "0,255,0",
    :blue     => "0,0,255",
    :magenta  => "255,0,255",
    :cyan     => "0,255,255",
    :yellow   => "255,255,0",
    :white    => "255,255,255",
  }

  def initialize(project)
#    puts "initialize"
  end

  def no_new_revisions_detected
#    puts "no_new_revisions_detected"
  end

  def new_revisions_detected(revisions)
#    puts "new_revisions_detected"
  end

  def sleeping
#    puts "sleeping"
  end

  def build_requested
#    puts "build_requested"
  end

  def configuration_modified
#    puts "configuration_modified"
  end

  def build_initiated
#    puts "build_initiated"
  end

  def build_started(build)
#    puts "build_started"
    rabbit(:colour => :yellow, :message => "Build started for #{committer(build)}", :status => :building)
  end

  def build_finished(build)
#    puts "build_finished"
    if build.successful?
      rabbit(:colour => :green, :message => "Build fixed by #{committer(build)}", :status => :success)
    elsif build.failed?
      rabbit(:colour => :red, :message => "Build broken by #{committer(build)}", :status => :failure)
    elsif build.incomplete?
      rabbit(:colour => :yellow, :message => "Build incomplete", :status => :incomplete)
    else
      rabbit(:colour => :yellow, :message => "Build status unknown", :status => :unknown)
    end
  end

  def build_loop_failed(error)
#    puts "Build loop failed: #{error.class}: #{error.message}"
    rabbit(:colour => :red, :message => "Build failed with an error", :status => :failure)
  end

  def build_broken(build, previous_build)
#    puts "build_broken"
#    rabbit(:colour => :red, :message => "Build broken by #{committer(build)}", :status => :failure)
  end

  def build_fixed(build, previous_build)
#    puts "build_fixed"
#    rabbit(:colour => :green, :message => "Build fixed by #{committer(build)}", :status => :success)
  end

  private

  #
  def committer(build)
    match = build.changeset.match(/ committed by (\w+) /)
    if match.nil?
      return "unknown"
    elsif match[1].length > 1
      return "#{match[1][0,1].upcase} #{match[1][1..-1].capitalize}"
    else
      return match[1]
    end
  end

  def rabbit(options)
    url = "http://api.nabaztag.com/vl/FR/api.jsp?sn=#{NABAZTAG_SERIAL_NUMBER}&token=#{NABAZTAG_TOKEN}"

    # Quarter second tempo
    url += "&chor=4"

    # Ears up => success
    # Ears down => failure
    # Ears askew => unknown
    if options.has_key?(:status)
      angle = case options[:status]
        when :success
          [0, 0]
        when :failure
          [180, 180]
        else
          [90, 90]
        end
      angle.each_index do |ear|
        url += ",0,motor,#{ear},#{angle[ear]},0,#{ear}"
      end
    end

    # Colour:
    #   Symbol => named colour
    #   String => "R,G,B"  (0-255 in each value)
    if options.has_key?(:colour)
      colour = case options[:colour]
      when nil
        COLOURS[:blue]
      when Symbol
        COLOURS[options[:colour]]
      when String
        options[:colour]
      else
        COLOURS[:white]
      end

      (0..12).each do |n|
        url += ",#{n    },led,#{n % 4 + 1},#{colour}"
        url += ",#{n + 1},led,#{n % 4 + 1},#{COLOURS[:black]}"
      end
      url += ",14,led,1,#{colour},14,led,2,#{colour},14,led,3,#{colour}"
    end

    # Message
    url += "&tts=#{URI.escape(options[:message])}&ttlive=10" if options[:message]

    puts "Sending Nabaztag: #{url}"
    $stdout.flush
    Net::HTTP.get_print URI.parse(url)
  end

  public

  def test
    puts "testing"
    rabbit(:colour => :blue, :message => "Boo", :status => :abc)
    build_started(nil)
  end

end

# Uncomment the following line to test:
# NabaztagNotifier.new(nil).test

Project.plugin :nabaztag_notifier

As it stands, it is a drop in CruiseControl.rb/Nabaztag:tag plugin that announces the start of a build and who started it, and the completion of a build and who broke it or fixed it.  However, it is ripe for extension to make it do what you need – make the rabbit more chatty, or rip out the Nabaztag bits and reuse it as the starting place for a standard CruiseControl.rb plugin.

Installing it

There are 3 steps to installing the Nabaztag:tag CruiseControl.rb plugin.

  1. Installing the plugin depends somewhat on your CruiseControl.rb version.  So far we’ve used two different versions:
    • in the first you had to put the above file in builder_plugins/installed directory in CruiseControl.rb, making sure that the file has the right owner and permissions.
    • in our current CruiseControl.rb version, you need to put it in the builder_plugins directory, again making sure that the file has the right owner and permissions.
  2. Then, you’ll need to edit the first few lines to set the
        NABAZTAG_SERIAL_NUMBER = 'xxxxxxxxxxxx'
        NABAZTAG_TOKEN = 'yyyyyyyyyy'

    You can get the serial number from your rabbit – follow the Violet instructions for registering. Once you have registered with Violet and opened your violet.net account, then you can configure your rabbit to join the “Violet ecosystem”, i.e. generate the token.  Now you have the serial number and the token, update the appropriate lines in the plugin.

  3. Finally, simply restart CruiseControl.rb to pick up the plugin.

To test that it is working, start a build – if you start one from CruiseControl.rb’s web interface, the rabbit should announce “Build started for unknown” whilst flashing yellow LEDs and cocking his ears forward expectantly.  Later, hopefully your build will succeed and the rabbit will announce “Build fixed by unknown”, flash green LEDs and perk his ears up, but if it fails then the rabbit will announce “Build broken by unknown”, flash red LEDs and put his ears down flat.

How to tweak it to suit you

Out of the box, the plugin will announce the start and completion of the builds, along with the Subversion committer of the latest checkin.  To help the rabbit pronounce our usernames, the plugin splits the first character off the username, e.g. “jsmith” becomes “J Smith”.  This is done in the private committer() method – modify it to suit the pronunciation of your Subversion usernames, or even to cope with a different source code control system.

By default, the plugin uses the very boring, but universal colours of green meaning good, red meaning bad and yellow meaning warning.  Hence, the rabbit flashes yellow when announcing the start of a build, red if the build fails and green if it succeeds.  You can modify the COLOURS constant in the script to define more colours, and then refer to them in calls to the rabbit() method.  The colours are defined as red/green/blue combinations between 0 and 255.

As I just alluded to, the private rabbit() method does the hard work of putting together a message and a choreography (what Violet calls a sequence of ear movements and LED flashes).  So, this is the method you would modify if you want to change the rabbit’s behaviour.  The Violet documentation (or wherever it is today) isn’t particularly clear, but hopefully is a bit easier to follow with this example.  One thing you could do is to use the voice API parameter to use something other than the default voice.

Finally, as I mentioned earlier, the plugin includes methods for all the hooks I could find in CruiseControl.rb.  You could use any of them to make your rabbit more chatty, or to integrate CruiseControl.rb with other services such as sending emails, writing to logs, etc.

Good luck; have fun.

Avoid minification with IE conditional javascript

In order to save bandwidth, merging and minification of CSS and JS; assets is really useful.  However be wary of including any code in that which uses IE conditional javascript.  Something I did not realise existed until digging into this issue, despite many years of conditionally dealing with different browsers!  For those not in the know, in IE /*@cc_on!@*/ will “evaluate” to ! thereby making var isIE = !false; which is true, of course.  Any other browsers will ignore the comment and set var isIE = false.

Helpful until that code is run through a minification which strips all comments and is not aware of such things!

Annoyingly, code from a 3rd party that is part of our application was being minified in production mode and uses this technique to identity if a browser is IE or not.  Which gave very spurious results when testing IE…  The solution for us, rather than hacking the 3rd party code was to use a direct include of the file into the pages that require it, and to use ?v=x.x.x after the filename in the source to ensure we can still force reloads in clients after we make changes to it (probably just an upgrade) in future.  This was something the merging and minification process kindly gave us for free.  In this case I made the number match the version of the 3rd party source we are using for consistency.  This is a pain in that it requires changes to templates and it not automatic, but modifications to the included file in this case are likely to be rare, and is the easiest option allowing the rest of our assets to still be merged and minified.