Rack::Affiliates is a rack middleware that extracts information about the referrals came from an affiliated site. Specifically, it looks up for specific parameter (ref by default) in the request. If found, it persists affiliate tag, referring url and time in a cookie for later use.

Affiliate links tracking is very common task if you want to promote your online business. This middleware helps you to do that.

1. You associate an affiliate tag (for eg. ABC123) with your partner.
2. The affiliate promotes your business at http://partner.org by linking to your site with like http://yoursite.org?ref=ABC123.
3. A user clicks through the link and lands on your site.
4. Rack::Affiliates middleware finds ref parameter in the request, extracts affiliate tag and saves it in a cookie
5. User signs up (now or later) and you mark it as a referral from your partner
6. PROFIT!

Works with Rails version > 2 (including Rails 5).

Include the gem in your Gemfile:

gem 'rack-affiliates'

or install it:

gem install rack-affiliates

Add the middleware to your application stack:

# Rails 3+ App - in config/application.rb
class Application < Rails::Application
  ...
  config.middleware.use Rack::Affiliates
  ...
end

# Rails 2 App - in config/environment.rb
Rails::Initializer.run do |config|
  ...
  config.middleware.use "Rack::Affiliates"
  ...
end

Now you can check any request to see who came to your site via an affiliated link and use this information in your application. Affiliate tag is saved in the cookie and will come into play if user returns to your site later.

class ExampleController < ApplicationController
  def index
    str = if request.env['affiliate.tag'] && affiliate = User.find_by_affiliate_tag(request.env['affiliate.tag'])
      "Halo, referral! You've been referred here by #{affiliate.name} from #{request.env['affiliate.from']} @ #{Time.at(env['affiliate.time'])}"
    else
      "We're glad you found us on your own!"
    end
    
    render :text => str
  end
end

You can customize parameter name by providing :param option (default is ref). By default cookie is set for 30 days, you can extend time to live with :ttl option (default is 30 days).

#Rails 3+ in config/application.rb
class Application < Rails::Application
  ...
  config.middleware.use Rack::Affiliates, {:param => 'aff_id', :ttl => 3.months}
  ...
end

The :domain option allows to customize cookie domain.

#Rails 3+ in config/application.rb
class Application < Rails::Application
  ...
  config.middleware.use Rack::Affiliates, :domain => '.example.org'
  ...
end

The :path option allows to hardcode the cookie path allowing you to record affiliate links at any URL on your site.

#Rails 3+ in config/application.rb
class Application < Rails::Application
  ...
  config.middleware.use Rack::Affiliates, { :path => '/' }
  ...
end

Middleware will set cookie on .example.org so it's accessible on www.example.org, app.example.org etc.

The :overwrite option allows to set whether to overwrite the existing affiliate tag previously stored in cookies. By default it is set to true.

If you want to capture more attributes from the query string whenever it comes from an affiliate you can define those with the extra_params value.

#Rails 3+ in config/application.rb
class Application < Rails::Application
  ...
  config.middleware.use Rack::Affiliates, { :extra_params => [:great_query_parameter] }
  ...
end

These will be availble through env['affiliate.extras'] as a hash with the same keys.

Thanks goes to Rack::Referrals (https://github.com/deviantech/rack-referrals) for the inspiration.