rack-canonical-header

Inserts a canonical url with a predefined host to prevent search engines from crawling domains like herokuapp.com

git clone git@github.com:renuo/rack-canonical-header.git
cd rack-canonical-header
bin/setup

Add this line to your application's Gemfile:

gem 'rack-canonical-header'

And then execute bundle install

Set the CANONICAL_HOST env variable to the desired host (i.e. set it to the domain of your website like CANONICAL_HOST=example.com)

The gem will inject a header of the format Link: <http[s]://CANONICAL_HOST[/path]>; rel=canonical as soon as the env is present. The path and the scheme will be replaced with what was requested on the original domain.

Note that the gem does no redirects. Therefore, your non-canonical urls will still work if you access them directly. However, search engines will not list them.

If you're using a framework which uses Rack (like Hanami) you have to require and insert the middleware Canonical::Middleware manually into the rack stack.

For example:

require 'rack/auth/basic'
require 'rack-canonical-header'

module Web
  class Application < Hanami::Application
    configure do
      middleware.use Canonical::Middleware
    end
  end
end