Installing Ubuntu Pangolin on Beagle Bone

Just a quick note if you’re like me and you want to put Ubuntu on your Beagle Bone. The Beagle Bone is a sweet little palm-sized motherboard/processor guy that’s nice for little hardware projects. It comes with the Angstrom operating system loaded onto the SD card. This operating system was fine for initial development but I ran into an issue where I couldn’t leave a server to run and log out. If I checked back the server was always dead no matter what I did to detach it (maybe it was just pegging itself and restarting). So I wanted to see if Ubuntu would handle any better.

Anyways, I kept trying to just flash an image from the official Ubuntu page onto an SD card and boot it, but it wasn’t working. Then I saw that there is a script that does all the work for you mentioned on this page:

http://elinux.org/BeagleBoardUbuntu#Canonical.2FUbuntu_Images

Works like a charm, and Ubuntu does seem to be more stable than Angstrom on the Beagle Bone. Thanks to the author of the script, Robert C. Nelson.

Rails and Ext non-Ajax Signup Form with Password Confirmation

This is, uh, a technical post.

Probably there are others who want to do the same somewhat senseless thing: use Ext to do form validation while keeping a boring non-Ajax post-and-response. The bottom line is that Ext favors doing it the Ajax way, and the Ajax way isn’t that hard to set up with Rails (just handle the form submission as normal but return JSON or XML to signal success or failure). But if you’re like me and working on a deadline, there can be a cognitive burden to switching to Ajax posting that you might want to avoid. Paradoxically, you might find yourself wasting a lot of time trying to figure out how to do it the “old-fashioned” way. Well, here’s one working standard-submission Signup Form, with fancy validations and all the kinks worked out.

Here’s the top half of the file users/new.html.erb, which is nearly the same as the code generated by restful-authentication:

<% @user.password = @user.password_confirmation = nil %>
<%= error_messages_for :user %>
<div id="no-js-form">
    <% form_for :user, :url => users_path, :html => {:id => "signup-form"} do |f| -%>
    <p>
        <label for="login">
            Real Name
        </label>
        <br/>
        <%= f.text_field :name, :id => "signup_name_field" %>
    </p>
    <p>
        <label for="login">
            User Name
        </label>
        <br/>
        <%= f.text_field :login, :id => "signup_login_field" %>
    </p>
    <p>
        <label for="email">
            Email
        </label>
        <br/>
        <%= f.text_field :email, :id => "signup_email_field" %>
    </p>
    <p>
        <label for="password">
            Password
        </label>
        <br/>
        <%= f.password_field :password, :id => "signup_password_field" %>
    </p>
    <p>
        <label for="password_confirmation">
            Confirm Password
        </label>
        <br/>
        <%= f.password_field :password_confirmation, :id => "signup_password_confirmation_field" %>
    </p>
    <p>
        <label for="password_confirmation">
            Role
        </label>
        <br/>
        <%= f.select :role, [["consumer","consumer"],["vendor","vendor"]], :id => "signup_role_field" %>
    </p>
    <p>
        <%= submit_tag 'Sign up', :id => "signup_submit_button" %>
    </p>
    <% end -%>
</div>
<div id="js-form-panel">
</div>

The only differences are a div wrapping the form (“no-js-form”) and the “js-form-panel” at the end. You’re going to laugh at me, but this form is buzzword-friendly; it’s unobtrusive in an ugly way. If javascript is turned on, the form will work, and the following will fail:

<script type="text/javascript">
    /* 
     Thanks to:
     http://www.extjswithrails.com/2008_03_01_archive.html for standardSubmit tip (hard to find!)
     http://extjs.com/forum/showthread.php?t=23068 for password confirmation
     Anyone else I stole semantics from
     */
    // Look, I'm copying over the authenticity token to send in the JS-generated form. LOL!
    var authenticity_token = document['forms'][0]['authenticity_token'].value;
 
    Ext.onReady(function(){
        $('no-js-form').hide();
 
        var myForm;
 
        function submitHandler(){
            form = myForm.getForm();
            form_as_dom = form.getEl().dom;
            form_as_dom.action = form.url;
            form_as_dom.submit();
        }
        myForm = new Ext.form.FormPanel({
            monitorValid: true,
            standardSubmit: true,
            url: "/users",
            applyTo: "js-form-panel",
            title: "Signup as a New User",
            width: 310,
            autoHeight: true,
            items: [new Ext.form.TextField({
                allowBlank: false,
                msgTarget: 'side',
                name: "user[name]",
                id: 'js_signup_name_field',
                fieldLabel: "Real Name"
            }), new Ext.form.TextField({
                allowBlank: false,
                vtype: 'alphanum',
                msgTarget: 'side',
                name: "user[login]",
                id: 'js_signup_login_field',
                fieldLabel: "Username"
            }), new Ext.form.TextField({
                allowBlank: false,
                vtype: 'email',
                msgTarget: 'side',
                name: "user[email]",
                id: 'js_signup_email_field',
                fieldLabel: "Email"
            }), new Ext.form.TextField({
                allowBlank: false,
                inputType: 'password',
                vType: 'password',
                msgTarget: 'side',
                name: "user[password]",
                id: 'js_signup_password_field',
                fieldLabel: "Password"
            }), new Ext.form.TextField({
                fieldLabel: "Password Confirm:",
                allowBlank: false,
                inputType: 'password',
                name: "user[password_confirmation]",
                initialPasswordField: 'signup_password_field',
                vType: 'password',
                msgTarget: 'side',
                id: 'js_signup_password_confirmation_field',
                fieldLabel: "Confirm Password",
                validator: function(value){
                    return (value == document.getElementById("js_signup_password_field").value) 
|| "Your passwords do not match";
                }
            }), new Ext.form.Hidden({
                name: "authenticity_token",
                value: authenticity_token
            }), new Ext.form.Hidden({
                name: "user[role]",
                value: "consumer"
            }), ],
            buttons: [{
                handler: submitHandler,
                text: "Signup",
                formBind: true
            }]
        });
 
    });
 
</script>

The noteworthy steps are: first, I hide the ‘no-js-form’, then I copy the authenticity_token that gets generated by a rails form to put in the js-generated form. Then, standardSubmit : true is the config option that makes a FormPanel not submit as an XmlHttpRequest. The funny code in the submitHandler is getting the underlying form object and calling submit on it, but as I write this it doesn’t make sense why both would be necessary. Finally, formbind : true causes the submit button to be deactivated while there are failing validations, and there’s some handy code for making sure that the password_confirmation matches password (totally lifted from somewhere else, see above).

Setup for Alexandria Development: Part II

(…after too much grief today installing Mephisto and mucking with Apache virtualhosts; I’ll get Part I back from the ether eventually) Update: Done. Update: This is a post moved over from the short-lived Mephisto blog, and ported back in time.

First of all, the alexandria binary is just a ruby script that does a require ‘alexandria’ and runs Alexandria.main.

Alexandria.main is a method on the Alexandria ‘module’ that is used throughout the code (modules are ‘namespaces’ to avoid naming conflicts). This method is found in lib/alexandria.rb:

As you should be able to see, this method isn’t doing anything but setting up some global variables (like $DEBUG) and logging, and doing something weird with http_proxy. The real line is Alexandria::UI.main. That’s in lib/alexandria/ui.rb:

module Pango
  def self.ellipsizable?
    @ellipsizable ||= Pango.constants.include?('ELLIPSIZE_END')
  end
end
 
module Alexandria
  module UI
    def self.main
      Gnome::Program.new('alexandria', VERSION).app_datadir =
        Config::MAIN_DATA_DIR
      Icons.init
      MainApp.new
      Gtk.main
    end
  end
end

Gtk.main is the main loop of a gtk program. You set up your windows and widgets before running it, and it makes them all spin until you exit. So, after Icons.init runs (guess what that does), MainApp.new does all the work from now on.

The Pango code above this is interesting for seeing some Ruby syntax and features. Pango is a text-rendering and layout library inside gtk. The code is adding an elipsizable? “question” method (return true/false) to the Pango module. self.elipsizable? means that it’s defining a class method, a method on a class that doesn’t depend on instance data. ||= is a way of saying, “set the variable to this unless it’s already been set to something else (ie, it’s not nil)”.

Unfortunately, MainApp.new is in the massive MainApp class at lib/alexandria/ui/main_app.rb. This class does a lot (too much). The main thing it does is handle all the callbacks from the main window and its widgets. Let’s just take a look at the top:

 
module Alexandria
  module UI
    class MainApp < GladeBase
      attr_accessor :main_app, :actiongroup, :appbar
      include Logging
      include GetText
      GetText.bindtextdomain(Alexandria::TEXTDOMAIN, nil, nil, "UTF-8")
 
      module Columns
        COVER_LIST, COVER_ICON, TITLE, TITLE_REDUCED, AUTHORS,
        ISBN, PUBLISHER, PUBLISH_DATE, EDITION, RATING, IDENT,
        NOTES, REDD, OWN, WANT, TAGS = (0..16).to_a
      end
 
      # The maximum number of rating stars displayed.
      MAX_RATING_STARS = 5
 
      def initialize
        super("main_app.glade")
        @prefs = Preferences.instance
        load_libraries
        initialize_ui
        on_books_selection_changed
        restore_preferences
      end
    #... snip
    end
    # ... snip
  end
end

A couple points here. MainApp inherits from GladeBase. The attr_accessor is a declaration that makes the @main_app, @actiongroup and @appbar instance variables publicly readable and settable. super(“main_app.glade”) calls the initialize method on GladeBase with the glade file that contains the definitions for all the widgets Alexandria uses. The names of the methods tell you about what they do (good!). Because these methods need to know about what the user’s preferences are, @prefs has been made available before they are called.

To understand what MainApp is doing, it seems like we need to understand what GladeBase is.

module Alexandria
  module UI
    class GladeBase
      def initialize(filename)
        file = File.join(Alexandria::Config::DATA_DIR, 'glade', filename)
        glade = GladeXML.new(file, nil, Alexandria::TEXTDOMAIN) { |handler| method(handler) }
        glade.widget_names.each do |name|
          begin
            instance_variable_set("@#{name}".intern, glade[name])
          rescue
          end
        end
      end
    end
  end
end

So GladeBase is using GladeXML to get the widgets out of the xml file and load them into memory. It then iterates through them, *adding them to MainApp (instance_variable_set is doing the work). So if there’s a widget called @main_menu, MainApp will get this variable to work with. These widgets work exactly as though they had been created “by hand”.

If you’ve been following, take a look at load_libraries and see if the code there makes sense. Here’s a short snippet:

      def load_libraries
        completion_models = CompletionModels.instance
        if @libraries
          @libraries.all_regular_libraries.each do |library|
            if library.is_a?(Library)
              library.delete_observer(self)
              completion_models.remove_source(library)
            end
          end
          @libraries.reload
        else
          #On start
 
          @libraries = Libraries.instance
          @libraries.reload
# ...

This is where things start to get confusing. load_libraries is also being used to reload libraries, so first it checks to see if @library has been defined already (refactoring opportunity). In the normal case, Libraries gets called by by invoking Libraries.instance. To understand this, you have to know that Libraries uses a factory class method to make sure that Libraries only gets created once (making the Libraries instance a “singleton”).

At the bottom of load_libraries is some interesting code:

# ...
        @libraries.all_regular_libraries.each do |library|
          library.add_observer(self)
          completion_models.add_source(library)
        end
# ...

This is telling each library in @libraries (the Libraries singleton) to add self as an “observer”. What does this mean? It means that class Library is “observable”. To see what that means you have to look at Library. First let’s look at Libraries, in lib/alexandria/library.rb:

  class Libraries
    attr_reader :all_libraries, :ruined_books
 
    include Observable
    include Singleton
 
# ... snip
 
    #######
    private
    #######
 
    def initialize
      @all_libraries = []
    end
 
    def notify(action, library)
      changed
      notify_observers(self, action, library)
    end
  end
end

Libraries is including the Observable and Singleton modules to give it special methods (in Python these are called “mixins”). Singleton gave it the instance method. Observable is giving it the notify_observers method. What this method does is “call up” all the observers of this instance by calling their update methods.

Libraries has many Librarys (it’s a little weird to give a class a plural name). Each library is an observer of Libraries. Library is also Observable:

 
  class Library < Array
    include Logging
# ...
    include Observable

As we saw above, MainApp adds itself as an observer to each library. If you look on MainApp you’ll see that it has an update method:

def update(*ary)
# ...
  end

*ary means that it accepts an array as its argument. This method gets called from many places in Library, like this:

        source_library.notify_observers(source_library,
                                        BOOK_REMOVED,
                                        book)

That’s all for now. To learn more about Observers read this.

Setup for Alexandria Development: Part I

This is the first in a series of brain-dumps of my knowledge about Alexandria and related development issues. Be warned, the approach I will take in these posts will be to discuss boring and perhaps obvious details as they occur to me. You are advised to skim.

Getting the code

First things first, you should be able to checkout a copy of Alexandria from subversion. You can find instructions here, but unless you want to pull down the entire tree this is the actual URL you want:

svn co svn+ssh://method@rubyforge.org/var/svn/alexandria/trunk/alexandria

Btw, this is worth looking at if you want to play around with code without committing to a central repository.

Initial setup

Let’s look at the directory structure of the checked out copy (called the working directory).

(alexandria root)
alexandria.desktop.in (Used to add Alexandria to the Gnome menu)
Rakefile                         (The `rake` command looks for this)
/spec                            (Specs go in here)
alexandria.xcodeproj        (MacOS XCode project file)
/data                            (Configuration files go here)
/lib                               (Alexandria code libraries are here)
tasks.rb                        (Rakefile uses this file)
/bin                              (Actual system-wide alexandria command goes here)
/debian                         (Contains templates needed to create debs)
/tests                           (For old 'test/unit' tests)
/doc                             (Docs go here)
/po                               (Language files go here)
/schemas                       (Used in gconf, configuration file like Windows registry)

You will need to get a copy of rubygems. For some reason, the Ubuntu packaged rubygem never seems to actually work, so you should just compile and install rubygems from here. On Ubuntu or Debian, you should run sudo apt-get install build-essential ruby1.8-dev because some gems will need to build “extensions”. You can use either your distro’s rake or install rake from gem. You install gems with:

sudo gem install (package)

You should install rake, rspec, rcov and zentest (autotest):

sudo gem install rake rspec rcov zentest

To work on the website you will also need staticmatic.

Rake and Testing

In the root of your working directory you should now be able to type rake -T and you will see a long list of rake “tasks” defined in the Rakefile and tasks.rb. The most important tasks for development purposes are sudo rake install to install to your system (it installs in /usr/lib/ so be careful) and rake spec, for running the test suite.

Rspec is super cool, but you’ll have to study the tutorials to learn how to use it. A great way to learn Ruby and Rspec at the same time is to ‘spec out’ basic Ruby types! For example, if you’re unsure about how an array method works, you can do this:

describe Array do
   it "should sort strings alphabetically" do
      ["b", "a", "c"].sort.first.should == "a"
   end
end

Just don’t get confused by the pattern of writing specs to cover code that’s already been written. The basic idea behind Behavior-Driven Development is that you write tests that show how your code will behave before writing the code. The only way to really learn how to do this is to force yourself to write some code this way.

Because BDD is supposed to happen before you write code, Alexandria has very poor test “coverage” at the moment, and its not easy to add specs to the code the way it is now. Still, it’s good practice to try and understand the behavior of a method on a class and write a spec for it. Take a look at the files in specs/alexandria for examples.

When a project has good test coverage it’s possible to work according to a very fast “red-to-green” development cycle. Autotest is a tool that will run ‘rake spec’ every time you change a file that’s being monitored. This is great because, again if the test suite is good, you can know the second you break the code! It’s even better if you use desktop notifications with Autotest. This is the version I use with Ubuntu Gutsy. One note: the file he links to is only good for Gentoo, you want this one.

That’s all for now. I’ll do another one tomorrow.