Has Face is a neat little gem that uses the face.com API to ensure that an image contains a persons face. It’s very simple to use and can be easily integrated into an existing rails application.

To get started add the has_face gem to your Gemfile and run a bundle install

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Run the generator to copy over an initializer:

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The initializer should look something like this:

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Now we’ll need to make a face.com developer account. You can signup for a free account over at face.com. Once you have signed up, place your API key and API secret in the initializer config.

The last option in the initializer (skip_validation_on_error) will change the behavior of has_face when an error occurs. If set to true, when an error occurs a warning will be logged to the logfile with detailed information about the failure and face validation will be skipped. This can be useful if you want your application to function if the API service is not reachable. If the value is false then an exception will be raised when an API call fails, this will allow you to manually handle the exception yourself, please check the documentation for details on the errors raised.

Once the initializer settings are setup then we can add face validation to a model. In the example below I’m using carrierwave to attach the image to the model but other image attachment gems should also work fine (anything that correctly responds to `path` should be OK).

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That’s it, that’s all we need to have a functioning face validator. There are a few other options that I haven’t covered here in this short guide, please consult the readme for more detailed information.

It doesn’t handle character encodings though so I went about adding that. With the handy rchardet gem and IConv, detecting the character encoding of the incoming string and converting it to UTF-8 was pretty simple. I’ve created a pull request for the gem that will hopefully be accepted.

The essential code is below, and revolves mainly around the detection and conversion. Using //TRANSLIT causes IConv to try and convert the incoming character code to something that exists in the UTF8 character set, and then //IGNORE will ignore any characters that don’t exist in the UTF8 character set. Chaining //TRANSLIT and then //IGNORE will make IConv try a conversion first and then ignore anything it cannot convert.

I used this gem after the above changes to convert about 400,000 records of text data with ASCII, windows-1252, IBM866 and other character encodings from an old SQLite installation to a new postgres database without any issues.

Sending push notifications directly from a Rails application can be slow and we probably don’t want to have the user waiting until the notification is sent, instead apn_sender can be setup to run a worker which is constantly connected to the apple push notification service. When there are new notifications to send, the notifications are queued up and sent through the always open connection that is maintained by the worker.

apn_sender uses redis as a message queue to keep track of the notifications waiting to be sent, you’ll need to install it before using the gem.

To add apn_sender in your Rails 3 application, just add the gem to your Gemfile. We’re going to need the daemons gem too so we’ll include that as well.

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Now we can create our daemon which we will be using for sending push notifications, this can be placed anywhere, I’ve put mine in script/apn_sender. Make sure to add execute permission to the file after creating so we can run it.

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Before the daemon can start running we’ll need to put our iOS push certificate into the application. Instructions for generating the certificates are available at the Apple Developer site. The certificates need to be placed inside of /config/certs and should be named apn_development.pem or apn_production.pem for production.

Once the certificates are in their correct locations, we can start up the daemon. The daemon does not know about the Rails environment so we need to specify this when starting it up. The daemon supports start, stop and restart commands. There is a verbose flag available to output more information (which can be helpful when debugging).

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Our application is now set up to send push notifications, this can now easily be performed by adding a new notification to the queue. The notify method on the APN class will take a push notification token and then our parameters, we can specify the alert message to show the user, whether or not we want sound as well as the number to display on the badge icon. Anything else we pass to notify will be sent as metadata in the push notification. Here’s an example of creating a notification.

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The worker should pick up the notification within a few seconds and send it off. The apn_sender has many other features that I haven’t covered, you can view the full documentation over at https://github.com/kdonovan/apn_sender.

After checking out the project the change was pretty simple but it highlighted an issue that I’ve seen in plenty of code where caching is done too broadly. In this case the cacheing (or memoization) was performed without taking into account the variable that was sent to establish the connection in the first place. The offending method looked like this :

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This was set on the class and as such @connection would never be created after the first call, whether the token was reset or not. I just changed it so that the connection is cached for each @token the system uses. For us it’s a small number or users, but in a larger context of course you’d need to implement some invalidation protocols to stop the following code from (slowly) swallowing the world :

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NoToken is just a class inheriting from StandardError that I chucked in there, the only thing that makes the gem now work properly come afterwards. I setup a hash and then store a new connection for each new incoming token, the connection is keyed by the token in the @connections hash. All pretty simple.

I’ve created a pull request that will hopefully be accepted soon, I think it fixes an unexpected problem with the gem.

To list the methods and procs registered with a particular callback, append _callback_chain to the callback name that you wish to list and send that to your class from the Rails console.

This used to work in Rails 2.3.x and I’d used it a few times before, however trying to use it in Rails 3 gave me problems :


HourEntry.before_save_callback_chain
NoMethodError: undefined method `before_save_callback_chain' for #


After some digging around ActiveRecord then ActiveModel and ActiveSupport I figured I could just access the _#{type}_callbacks method and then reject and select these arrays to get what was required. This is what I came up with to get the before_save callbacks that I was interested in.


HourEntry._save_callbacks.select { |callback| callback.kind.eql?(:before) }


This returns me the array of callback objects that are chained before I call save on the HourEntry model. If I want to check for a particular proc being in that chain then I can do :


HourEntry._save_callbacks.select { |callback| callback.kind.eql?(:after) }.collect(&:filter).include?(:archive_if_no_users)


It’s not optimal chaining a number of enumerable methods but I think it seems pretty readable.

I am hoping that the callback_chain methods return at some point (though I only used them sparingly) but more than that I’m hoping someone might be able to set me straight on how I’m going about getting around the callback chains on ActiveRecord and ActiveModel.

ree-1.8.7-2011.02 :132 > Story.joins(:hour_entries).this_week
NoMethodError: undefined method `this_week' for #

The problem was that the .this_week call was being sent to Story rather than to HourEntry. Here’s where Darcy chimed in with the scoped.merge call. It went a little something like this :

Story.scoped.merge HourEntry.this_week

This successfully merged the scope defined by Story with the scope defined by the HourEntry.this_week call and I get all the stories that have HourEntry objects that are returned by the .this_week scope.

The final stage for this call was :

Story.scoped.merge HourEntry.worked_on_by(user).this_week

This then returns all the stories you’ve worked on this week. Add a bit of grouping/distinct and it’s done and done. The additional nice part about this is composing these scopes will allow me to do a lot more in the future, very quickly.

Doing something like :

    Model.reflect_on_all_associations

Will give you all the associations for that model, it’s pretty dirty though and so an easy way to tidy it up is :

    Model.reflect_on_all_associations.collect{ |association|
        association.name.to_s.classify
    }

So, as usual with Rails it was easy as pie, I just am putting this here for future use :)

Edit : Thanks to Darcy for tidying up my previous mess :P

Gemsets and the Gemset Hierarchy

Whilst Bundler solves most of the problems related to isolating gems for me personally, on most projects I develop for there are things that make rvm’s implementation of gemsets (especially when used along with bundler) invaluable to me as a ruby developer.

Isolating Gems

A major strength of RVM is the ability to isolate gems at the system level. This keeps them safely partitioned from any other gems unrelated to my project. The way bundler isolates gems is for the most part at run time – It changes the way rubygems works to solve it’s problem and either installs all gems to a user specified path or to your gem directory.

If you are using the usr specified path option, you must to remember that your custom rubygems bin directory is not contained in your PATH. This means that you must either manually add it to the PATH, or your need to manually prefix each command with bundle exec, or alternatively you can generate the binaries into your applications bin directory and each command with ./bin/

If you take the opposite approach and install your gems into your gem home, you then need to be aware of the fact that each next install will overwrite any previous binaries – the canonical example being Rails 2 and Rails 3. The way that rubygems generates binaries lets you run gem-binary-name _version_ something to call the binary loaded from a specified gem version. Unfortunately, in Rails 3, the rails binary was moved from the rails gem into the railties gem which just so happens to break this feature of rubygems. You can try this for yourself on a new rvm gemset, install rails 2.3.8 and rails 3.0.0 and then try rails _2.3.8_ -v. If you are using the simple solution of installing to gem home, even though you are using bundler it will still overwrite the binary.

One common suggestion is to just create a wrapper binary manually (e.g. rails2) or always prefix your commands with bundle exec. In contrast RVM’s isolation works by explicitly setting rubygems home and path to directories isolated under RVM. RVM takes this even further using gemsets (think subdirectories) to handle more fine grain isolation. For example, I personally use 1 gemset per application, thus avoiding the issues described above as for each application I will have only a single version of rails installed. Even better, switching is shell-local and only persists for a single shell instance. This means that I can have two different applications with two completely different versions of Rails running at the same time in different terminal sessions without issue.

As an added bonus, because RVM isolates at the rubygems system level (using environment variables), your application doesn’t actually need to know or care about conflicts from gems that the application does not use.

Combining RVM and Bundler yields a great deal of flexibility and consisency. This affords you the ‘best of both worlds’, system level isolation with the ability to install gems from git repositories, and in application gem loading based on application environment.

For more information RVM’s gemsets, check out the Gemset’s section on the rvm site. For more information on Bundler, check out Bundler’s documentation.

Gemset Hierarchy

The second feature I use often is the global gemset. Each ruby interpreter installation comes with two gemsets out of the box – the default (blank) gemset (e.g. ree-1.8.7-2010.02) and the global gemset (e.g. ree-1.8.7-2010.02@global). When you use any gemset, rvm not only sets the gem home to a uniq directory for the given gemset (ensuring gems are installed in the correct place) but it also sets GEM_PATH.

Much like PATH, GEM_PATH is a colon separated list of directories that rubygems uses to look up gems when requiring them. By installing a gem to the global gemset for any ruby, e.g. ree-1.8.7-2010.02@global, it will automatically be made available (including it’s binaries) inside both the default gemset and any user-defined gemsets. E.g.,

• ree-1.8.7-2010.02
• ree-1.8.7-2010.02@bighelpmob
• ree-1.8.7-2010.02@tedxperth

Will all have access to gems installed in ree-1.8.7-2010.02@global.

This comes in super handy for things like awesome_print, wirble, bundler, git-up, homesick – Namely, gems you want available in every environment.

Unfortunately, bundler currently does not support multiple items in BUNDLE_PATH. We have hope it will be added in the future but for now gems you want shared between apps using bundler, you’ll get some duplication.

Default Global Gemset Contents

As an added bonus along side the global gemsets, rvm provides a way to declare a file which tells it what gems to install initially. To do this, it uses a ruby string-based directory hierarchy (see the link below) to look for a global.gems file that rvm then imports – For example, my ~/.rvm/gemsets/global.gems (that is imported into the global gemset of all ruby interpreter installs) contains the following simple list:

rake
rdoc
awesome_print
bundler
git-up
ghost
homesick
wirble

For more information on this feature, be sure to read the Automatic Gemset Initialization page on the RVM site.

Set operations

If you are writing gems, one of the most important things you can do as a Ruby developer these days is to ensure they work on all of the major implementations. At the moment, for most gem developers you should generally be testing your code against:

• REE / 1.8.7
• 1.9.2
• Rubinius
• Jruby

And optionally, MagLev and MacRuby. RVM provides tools making it simple to run code and commands against multiple rubies. This includes but is not limited to running Rake tasks and tests / specs. The idea being to make it as frictionless as possible to test your gem against all of the above interpreters. As an example, you can run:

rvm rake test

Which will run rake test against all of your installed ruby interpreters (using default gemset for each). You may need to do some manual setup (e.g. installing test gem dependencies) but rvm tries to make it all as simple as possible and more importantly, heavily integrated into your normal work flow whilst staying out of the way.

Along side rake, rvm also provides wrappers for many common binaries (e.g. ruby, spec and the like) plus the --json and --yaml flags which make it simple to get a summarised view of the program results. Using rvm exec, you can even perform set operations against any arbitrary command.

There is a whole lot more set operations can do and I suggest anyone using or considering using rvm read the set’s section on the rvm site. Go forth and have sets!

Tools for easing dependency-related pains

One of the most commonly encountered problems (since for most people, the ruby interpreter you’d normally use is distributed as a binary install) are related to external dependencies – Namely, things like readline, iconv and openssl.

In an attempt to make life easier (and in particular, work around common problems like a neutered libedit instead of readline on OSX), rvm provides the rvm package set of commands that make it easy to install sandboxed versions of these in the ~/.rvm/usr directory.

As an example, to work around the libedit vs. readline issue on OSX, you can build your ruby against readline 6.0 by running:

rvm package install readline
rvm install <ruby> --with-readline-dir=$HOME/.rvm/usr

And, as an added bonus, to automatically patch older versions of ree and 1.8.7 to respond to Control-C immediately (for example, in irb) instead of when you press enter, you can replace the rvm install command above with:

rvm install <ruby> --with-readline-dir=$HOME/.rvm/usr --patch readline-fix

Simple Ruby Upgrades

Say, for example, a new version of 1.9.2 comes out in the next few weeks and you want to automatically update your rubies to match it correctly. As of approximately rvm 1.0.0, we added an rvm upgrade command that automatically handles doing the following:

• Installing the new ruby
• Moving across gemsets
• Updating wrapper scripts and aliases

The only thing you typically have to update are references in your .rvmrc’s and your passenger configuration. But, with a little forethought (e.g. creating an alias using rvm alias create), it’s entirely possible to make it so the entire upgrade is automatic.

I have personally used this feature to move from the 1.9.2 release candidate to the final patchlevel 0 release – I used rvm upgrade to simplify the process of updating each time it was bumped.

This is currently undocumented on the rvm site but documentation will be added – for the moment, in your rvm install, run rvm help upgrade and/or rvm upgrade help.

Location Matters

One of the underlying decisions related to rvm’s architecture is where it installs your rubies – In most cases, rvm will install your rubies into ~/.rvm/rubies and gems into ~/.rvm/gems. This means that you should almost never have to use sudo for commands (there are a few exceptions, most notably passenger which relies on root permission in order to bind to port 80).

This approach is simple on the scale of things but also brings a lot of freedom – for one, it means you are free to experiment with a Ruby / RVM setup, wiping it away when you’re done with a simple rm -rf ~/.rvm && mv .rvm-original .rvm.

.rvmrc files

All of this is fine and dandy, but when you still have to manually switch ruby interpreters and rubies each time you do something, it can become mildly annoying rather fast. For this exact reason RVM offers project-specific .rvmrc files – If you haven’t encountered them before, project .rvmrc’s are files that are automatically sourced into the current shell when you change (cd) into a directory containing one. These files can contain anything that is valid shell script (and to prevent RVM automatically running code you don’t want, it defaults to asking you to trust it the first time it is run) making things like project bootstrapping and configuration simple and mostly automatic after a quick setup in the project root directory:

rvm --rvmrc --create <ruby>@<gemset>

In my own projects, I use these to automatically install the Ruby if not present, create and use a project-specific gemset and then do the minimum possible required to bootstrap the new environment – in most cases, this is simply a matter of installing a few gems (e.g. for me, I install bundler via rvm gemset import).

In some cases, I even automatically run bundle install (with 1.0, if you have the gems already installed, this is very fast) hence the first time I cd into a project it essentially bootstraps the entire environment for me automatically.

Ultimately, this approach means that the Ruby interpreter and gemset switching are completely transparent to me – No matter which project I’m using, ruby and irb are available and point to the correct executable for the current project I am in. When integrated with some code I wrote for ruby summer of code, it’s even possible to have passenger automatically use this .rvmrc file to automatically change your application’s gemset at run time.

For more information on .rvmrc files, check out the rvmrc page and the Project Workflow page on the rvm site. See RVM’s passenger integration page page for more details on gemsets with passenger.

Conclusion

I hope that you have found at least one new or useful thing about RVM. RVM has been invaluable to me as a developer on multiple open source projects over the last several months. It makes it simple for me to do things that are otherwise harder or less flexible and generally stays out of my way.

Specjour has been a bit of a turn-key miracle worker with our RSpec suite, however lately we’ve started to require some custom database setup that we do in a seeds.rb file as well as some custom bundler install parameters as most of our devs don’t have MySQL installed. Both of our needs were being nicely stomped on by Specjour so I thought it was time to look elsewhere.

I took a trip down Hydra lane and while getting to the point of having a working, local, dual runner system was a piece of cake, getting something working remotely via SSH took me hours of pain. Debugging the remote SSH workers was a nightmare and I spent a couple of hours running through code before deciding it was probably better to update our existing solution rather than tooling up a brand new one.

Back to the Specjour code. Specjour includes a rails directory inside which is an init.rb which Rails will run at initialisation (it’s part of what Rails does) but the Specjour initialiser will always just run the default database setup task no matter what initialiser you’ve got setup. We had a specjour initialiser that runs if ENV['PREPARE_DB'] was populated, which it is by Specjour, the problem was that the Specjour initialiser ran in the Rails after_initialization hook and therefore stomped all over our database setup.

The first step was just to have our initialiser write to another ENV element and then to have the Specjour after_initialize handler respect this. This isn’t too hard to implement as the after_initialize handler is just a block that is attached and so inside of this block you just need to check that ENV element. In my case I created a new ENV['DB_PREPPED'] element when my database setup had completed and then when the after_initialize block runs it checks for ENV['DB_PREPPED'] and will do nothing if that’s been set to true.

Easy. I now had Specjour respecting our database setup task.

The next step was to try and test this outside of a Rails application, not only that but to test the operation of a block (anonymous function?). To do this I setup a stub on a mock Rails class and let it capture the after_initialize block and then I ran a number of specs against this block.

module Specjour
  module DbScrub
  end
end

DO_NOT_REQUIRE = true

describe "Rails Initialiser" do
  before :all do
    ENV['PREPARE_DB'] = "true"

    stub(Specjour::DbScrub).scrub

    class Rails
      class << self; attr_accessor :configuration; end
      class << self; attr_accessor :test_block; end
    end

    config = Object.new
    stub(config).after_initialize { |args|
      object = Object.new
      Rails.test_block = args
      object
    }
    Rails.configuration = config

    require 'rails/init'
  end

... tests ...

This code essentially mocks up Rails.configuration and then stubs the after_initialize method. This stub then places the block that after_initialize yields to into Rails.test_block. When I require 'rails/init' it sequentially processes the file (as with all Ruby) and the stub will capture the block. After this is a bunch of tests I run an whether the Specjour::DbScrub.scrub method is called or not, so it’s nothing special.

I felt like at this stage I had fairly well tested the main aspects of the database setup.

The next issue was with how bundler was being handled. We have a situation where we would like to install sometimes without some gems. Some of the gems we use and have written use applications we’d rather not maintain in development and get tested in our staging and production environments. We generally will run a bundle install in development without the production or metrics groups so I wanted to have the ability to pass through a custom bundler command. That’s pretty easy now with my gem. Inside .specjour/bundler.yml there is a command property. I think this is more complex than what’s required, but I can foresee us needing a number of custom rake tasks and shell scripts so this bundler.yml should have probably started life as a settings/commands/something_generic.yml

To test this part of my changes was pretty simple. I basically just stubbed the system calls to bundler to give certain return values and checked to make sure the correct program flow happened.

describe ".bundle_install" do
    let :manager do
      stub.instance_of(Specjour::Manager).project_path { "/tmp" }

      stub(Dir).chdir(anything) { |args|
        args.last.call # This yields to the block for Dir.chdir()
      }

      manager = Specjour::Manager.new
      stub(manager).project_path { "blah" }
      mock(manager).system('bundle lock')

      manager
    end

    it "should perform a bundle lock" do
      stub(manager).system('bundle check > /dev/null') { true }

      manager.bundle_install
    end

    it "should check if there are gems required" do
      mock(manager).system('bundle check > /dev/null') { true }

      manager.bundle_install
    end

    context "when gems are required" do
      before :each do
        # Not a before :all as it needs to hook into the let hook above

        stub(manager).system('bundle check > /dev/null') { false }
      end

      context "and there is a bundler YAML file" do
        before :each do
          config_file = ".specjour/bundler.yml"

          mock(File).exists?(config_file) { true }
          mock(File).read(config_file) { "" }
          mock(YAML).load(anything) {
            { 'command' => "do it" }
          }
        end

        it "should get the bundle command from the YAML file" do
          mock(manager).system('do it > /dev/null')
          manager.bundle_install
        end
      end

      context "and there is no bundler YAML file" do
        before :each do
          mock(File).exists?(".specjour/bundler.yml") { false }
        end

        it "should perform a bundle install" do
          mock(manager).system('bundle install > /dev/null')
          manager.bundle_install
        end
      end
    end
  end

You can see that I stubbed our the Dir.chdir block to just yield directly to the call, otherwise it’ll throw an exception. Then I stubbed and mocked out the Kernel.system calls as necessary. Kernel methods are generally included into Ruby objects so you don’t stub Kernel, you stub the object that has the Kernel methods. Most of the testing is pretty basic, but I’d be keen to hear if I’m doing anything incorrectly!

This was my first major venture into adding functionality to a public project and it was good fun. I think it made me do a little better work than I might normally, it’s a great motivation to potentially have peers look at how you do things.

After bundling it all up and testing it here with over a dozen developers and even more machines I’m pretty happy with how it functions. I’ve made a pull request back to the original gem creator and hopefully he’ll like what I’ve done. In the meantime if you want to check it out then my Specjour is available on Git Hub.

i7 iMac – Quad Core Hyperthreading

real 11m14.131s
user 0m0.776s
sys 0m0.348s

Acer – E5200 Dual Core E5200

real 35m56.658s
user 0m0.870s
sys 0m2.500s

It seems like the little Acer box offers slightly better value for money in this case. I’d like to see how we’d do with some virtualisation sitting on top this, but I think the included memory will be quite limiting in this regard. I wonder whether the processor resources are actually being fully utilised.