Rack-based Session Stores on Rails

Rails edge is now using Rack-based session stores. That means you can access the same session on any Rack applications. Read about it on the Rails blog.

Nothing changes though on how you use sessions on Rails. On your Rails app, you’ll have something like

session[:user] = some_user_id

Let’s see how we can access the same session on a Rack application. You can read about Rack here.

Rack handles session using Rack::Session::Cookie. Create a file config.ru

use Rack::Session::Cookie, :key => '_railssession_session', :domain => 'railssession.labs.admoolabs.com'
run Proc.new {|env| [200, {"Content-Type" => "text/html"}, "Rack session 'user' has a value of #{env['rack.session'][:user] || 'nil'}."]}

The key should be the same key that you used on config/environment.rb on your Rails app.

Check out the demo. Set session[:user] on the Rails app, then view the session on the Rack app.

Capistrano

Capistrano is used for “automating tasks via SSH on remote servers, like software installation, application deployment, configuration management, ad hoc server monitoring, and more.” It is written in ruby and is commonly used to deploy Rails applications. Capistrano can be used to deploy applications written on any language. It runs commands on remote servers via SSH so it’s not specific to any language.

I will show you how to use capistrano for deploying a Rails application. The goal is to deploy an application by running one command – “cap deploy”. This should update your code from Subversion, and restart your server.

I assume that you have a rails setup on your server. I use the nginx web server, mongrels and mongrel_cluster.

To install capistrano

gem install capistrano

To start using capistrano on your Rails application,

cd RAILS_ROOT
capify .

You should see two files – Capfile and config/deploy.rb. Capistrano looks for Capfile when you run any capistrano commands. The default Capfile loads config/deploy.rb. deploy.rb contains the settings for your application.

We will deploy the Rails app “Hello Labs”. This can be found on our repository. Let’s edit deploy.rb.

Set the user and runner that will run the commands on your server.

set :user, "crigor"
set :runner, "crigor"

Set the application name

set :application, "hellolabs"

Set the scm and repository

set :scm, :subversion
set :repository, "http://labs.svn.admoolabs.com/hellolabs/trunk"

The default :scm is actually :subversion but I like to put it anyway.

Set the directory on the target server where you will deploy the application.

set :deploy_to, "/var/www/#{application}"

application is “hellolabs” which you set earlier. The deploy_to directory, which I’ll call DEPLOY_ROOT, is /var/www/hellolabs. You should create this directory on the target server. On Ubuntu, I set the group to www-data so mongrel has access to it.

Set the servers.

role :app, 'hello.labs.admoolabs.com'
role :web, 'hello.labs.admoolabs.com'
role :db, 'hello.labs.admoolabs.com', :primary => true

You can also use the IP address instead of the domain.

If nginx, mongrel, and mysql are all on the same server, put the same domain or IP address.

Now we will run our first capistrano task. Make sure /var/www/hellolabs exists on your server. On the RAILS_ROOT, run

cap deploy:setup

This will create the releases directory and shared directory under the hellolabs directory on the remote server. If you get a permission error, make sure the user you specified has access to /var/www/hellolabs.

Capistrano will ask for you server password. If you don’t want to enter your password every time you run a capistrano task, you can add

set :password, "mypassword"

Check if we have met the dependencies.

cap deploy:check

The output, if deploy:check is successful, looks like this.

Before we deploy the app, we define the deploy:restart task. By default capistrano runs /var/www/hellolabs/current/script/process/reaper. I use mongrel and mongrel_cluster so let’s add

namespace :deploy do
  desc "Restart the mongrels"
  task :restart do
    run "mongrel_rails cluster::restart -C #{shared_path}/config/mongrel_cluster.yml"
  end
end

Create the /var/www/hellolabs/shared/config directory and add mongrel_cluster.yml. We also need to add database.yml. I don’t commit database.yml in my repository since it contains the database password.

We have to symlink mongrel_cluster.yml and database.yml every time we deploy.

after "deploy:update_code", "deploy:symlink_configs"
namespace :deploy do
  desc "Symlink the config files."
  task :symlink_configs do
    run "ln -nfs #{shared_path}/config/database.yml #{latest_release}/config/database.yml"
    run "ln -nfs #{shared_path}/config/mongrel_cluster.yml #{latest_release}/config/mongrel_cluster.yml"
  end
end

We’re now ready to deploy our application.

cap deploy

If you see something similar to this, your app has been deployed.

The releases directory will contain directories with the timestamp as the name like 20081017125102 and 20081017132929. These directories will contain the rails application.

Below, you can see that current is a symlink to 20081017132929. /var/www/hellolabs/current is your RAILS_ROOT.

cap_directory_structure.jpg

Check the URL of your app. http://hello.labs.admoolabs.com

If you need a username and password to checkout your repostory, add

set :scm_username, "username"
set :scm_password, "password"

To get the list of capistrano tasks available, run cap -T.

For more information, check the capistrano website.

Here is the complete deploy.rb

set :user, "crigor"
set :runner, "crigor"

set :application, "hellolabs"
set :scm, :subversion
set :repository, "http://labs.svn.admoolabs.com/hellolabs/trunk"
set :deploy_to, "/var/www/#{application}"

role :app, 'hello.labs.admoolabs.com'
role :web, 'hello.labs.admoolabs.com'
role :db, 'hello.labs.admoolabs.com', :primary => true

after "deploy:update_code", "deploy:symlink_configs"
namespace :deploy do
  desc "Symlink the config files."
  task :symlink_configs do
    run "ln -nfs #{shared_path}/config/database.yml #{latest_release}/config/database.yml"
    run "ln -nfs #{shared_path}/config/mongrel_cluster.yml #{latest_release}/config/mongrel_cluster.yml"
  end

  desc "Restart the mongrels"
  task :restart do
    run "mongrel_rails cluster::restart -C #{shared_path}/config/mongrel_cluster.yml"
  end
end

Scraping bot

I just recently found the joys of scraping. Yes, the “technique” is a bit underhanded, but it sure is fun. I guess as long as you don’t profit off of it, it’s ok(and it doesn’t affect the site you’re scraping). If you scraped a site just to present it in a different design(like scrape all the news off CNN and then make a site called BNN or something and then charged users with a smaller fee), then yeah, that’s just plain dirty.

I scrape for fun and that’s it. Anyways, there I was, scraping movie schedules off the only movie schedule site that I know of( clickthecity.com ) and suddenly, I had an idea. What if I just made an RSS feed for a movie house that I liked? It would be just so cool since clickthecity(or CTC) doesn’t have an RSS feed. So I started researching about makign RSS feed, and while doing so, Topher brought about the idea of making a bot. He showed me how jabberbot and from there I went on and played around with it.

To make the scraper, I used the Rubyful-soup plugin for Ruby on Rails(along with Mechanize). Using it was easy, and the main problem actually was how to traverse the atrocious table layout of clickthecity. Once I got over that hurdle though, getting the info I wanted was easy. And what did I need? I only just needed the date of the showtimes(so I’ll know if it was the latest update), the location of the cinemas(the mall the cinemas were located), the cinema name(or number), the movies being shown on each movie house,  and the show times of each. These were saved into a database I made(I had a bit of a trouble in putting them in, especially since there were movie houses that had two different movies being shown the same day)

Next was the bot itself. Like I said, I used jabberbot, which was also a handy plugin for Ruby on Rails. The syntax was easy, and this was the easiest part. I made a new google account just for the bot and now it is up. I still have yet to make it work on yahoo messenger(Topher tried it and it didn’t work, but I haven’t tried it for myself yet) so I’ll just have to settle with Gtalk.

The flow of the program is simple: scrape the data from clickthecity.com and then save it to the database(done using a rake task I made). I have yet to automate these tasks, along with the connection of the bot(I still have to manually start it using another rake task). Anyways, after manually callign the rake tasks for scraping the site and starting the bot, movieschedule-bot is ready to go.

So far, I only added a select few movie houses that me and my friends usually go to. You can actually add movieschedules (yes, google mail) to your gtalk/gmail contact list and start using it(don’t worry about down times. that just means I am currently updating/restarting it – try again after five minutes if it doesn’t work) Don’t try to spam it though as right now it is running from my local machine. I have yet to upload it to my free Heroku account and make it run the bot forever.

So there you have it. A scraper bot. There are a LOT of other uses for this, like a thesaurus bot, wikipedia bot, imdb bot or something but that’s for another discussion. As you can see, bots can be useful too! Right now, movieschedules is looking for more friends. Be kind to it!

To start using  movieschedules, just add it to your Google contact list then type “help” and send it. It will return you a list of commands that are currently available. Have fun!

Railsconf 2008

I will be at Railsconf 2008 at Portland. I still haven’t finalized the sessions I’m attending but I’m sure it will be great.


RailsConf 2008

Alphabar on Rails

I am working on this little project right now using Ruby on Rails and I ran into some trouble with the alphabar plugin. First, alphabar uses the with_scope method which, since Rails 2.0 I believe, has been protected, giving me some errors since I froze my Rails version. I was able to overcome this obstacle by using the send method instead. Just change the last part of the find method of the plugin from:

model.with_scope({:find => {:conditions => conditions}})
{model.find :all}

to:

model.send(:with_scope, {:find => {:conditions => conditions}})
{model.find :all}

After I finally got that to work the plugin was very useful, although the alphabar was limited to letters and blank which is useful if you don’t need numbers. To accomodate numbers just add this to the alphabar helper:

('0'..'9').to_a.each do |i|
slots << i
end

Theoretically it should work for any character but I haven’t tried it yet.

So there you have it. Hoepfully somebody having trouble with this plugin will find this post useful.

Run from Capistrano

You can run shell commands from capistrano using the run method. For example, to create a symlink from the shared directory to the current directory, you’ll write

run "ln -nfs #{deploy_to}/shared/config/database.yml #{release_path}/config/database.yml"

run can also take a block like this

run "rsync /path/to/file host:/path/to/file" do |channel, stream, text|
  logger.info "[#{stream}] #{text}"
  output = case text
  when /\bpassword.*:/i
    "#{password}\n"
  when %r{\(yes/no\)}
    "yes\n"
  end
  channel.send_data(output) if output
end

When you run a command it might ask for your password. To handle this in capistrano, use send_data to send a response.

Check lib/capistrano/recipes/deploy/scm/subversion.rb on the capistrano gem to see how capistrano handles subversion commands.

RailsConf 2007 Keynote Videos

The keynote videos from RailsConf 2007 are now available online. Get them here.

DHH’s presentation is available here. DHH made a live demo showing REST and made a mistake. He said he wanted to show how easy it is to debug in Rails. I say the same thing when something goes wrong in my live demos. :)

nl2br in RoR

I recently found out that line breaks are not recognized when displaying a large block of text on the view (e.g. a post body). In PHP this was handled by the nl2br method but I had no luck finding a similar function in RoR. So I did what any sane person would do, create one myself. I placed this method in our model to format a particular field but it seems a better choice to put it in a helper.

def nl2br(text)

return text.gsub(/\n/, ‘<br/>’)

end

And there you have it, your very own nl2br method. Either you just found something really useful or I just wasted 2 minutes of your time. If anyone has a better solution or if I missed a function for this let us know by dropping a comment.

Small But Terrible

I’m pretty sure most of us have been in a situation where we have been trying to fix a bug for hours and finally seeing that there had just been some tiny typo or maybe even a commented line of code. I’ve been through a lot of those experiences before, especially when I was still learning to code, and most of the time, I just breathe out a huge sigh of relied or just plainly laugh at myself.

Reminiscing about those ‘good old days’ could be fun too. Here’s some of those ‘what the hell/oh come on/I knew it was just a simple mistake!’ scenarios that I have experienced or just know of:

These are just some of the mistakes that we can encounter while coding and minimizing the chances of these happening can help in coding a lot faster and having more time dealing with bugs that matter.

January 2008 PhRUG Meet-up

A PhRUG meet-up was held on Jan 16, 2008 at Ateneo de Manila University sponsored by Admoo Labs. 30 people attended the event. I gave a presentation on ‘Website Development with Ruby on Rails’. Greg Moreno talked about RSpec.You can download a copy of my presentation here. Pictures are here.

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