module ActionControllerExtensions
  def self.included(base)
    base::Dispatcher.send :include, DispatcherExtensions
  end

  module DispatcherExtensions
    def self.included(base)
      base.send :before_dispatch, :set_session_domain
    end

    def set_session_domain
      domain = @env['HTTP_HOST'].gsub(/:\d+$/, '').gsub(/^[^.]*/, '')
      puts "DOMAIN: #{domain}"
      @env['rack.session.options'].update :domain => domain
    end
  end
end

ActionController.send :include, ActionControllerExtensions

I tried to do a similar thing by hacking Rails session code so that the session domain could be specified with a Proc in the controller. It worked for sending cookies, but I was having trouble reconstituting them.

For developing on localhost with subdomains, I also ran into the invalid authenticity token problems, which we just worked around by creating an alias in /etc/hosts and accessing the site from there, with the session domain configured appropriately of course.

One important fact (explained in the linked “localhost & cookies” post above) is that this won’t work for localhost – in fact, if you try, your session won’t be saved at all, and you’ll have InvalidAuthenticityToken problems if you use authenticity checking.

Also, I think it’s always better to extend classes rather than reopen them – so, with those two things in mind, here’s a slight refactor (works fine in Rails 2.1):

module ActionControllerExtensions
  def self.included(base)
    base::Dispatcher.send :include, DispatcherExtensions
  end

  module DispatcherExtensions
    def self.included(base)
      base.send :before_dispatch, :set_session_domain
    end

    def set_session_domain
      ApplicationController.session_options.update :session_domain => "#{@request.host.gsub(/^[^.]*/, '')}" unless request.host.match /\.localhost$/
    end
  end
end

ActionController.send :include, ActionControllerExtensions

require 'activesupport'
require 'dispatcher'
module ActionController
  class Dispatcher
    def set_session_domain
      ActionController::Base.session_options[:session_domain] = "#{@request.domain}"
    end
    before_dispatch :set_session_domain
  end
end

not sure why

I think that maintaining several language version of any application is quite a lot work. There are several plugins of this type but since I haven’t tried any other of them (except GetText) I can’t tell if they are much better or worse.