Rails middleware: redirect www.example.com to example.com (root domain), taken from http://blog.dynamic50.com/2011/02/22/redirect-all-requests-for-www-to-root-domain-with-heroku/

application.rb

config.autoload_paths += %W( #{ config.root }/lib/middleware )

production.rb

config.middleware.use "WwwMiddleware"

www_middleware.rb

# lib/middlewares/middleware.rb
class WwwMiddleware
  def initialize(app)
    @app = app
  end

  def call(env)
    request = Rack::Request.new(env)
    if request.host.starts_with?("www.")
      [301, {"Location" => request.url.sub("//www.", "//")}, self]
    else
      @app.call(env)
    end
  end

  def each(&block)
  end
end

You can use [] as the last response value

      [301, {"Location" => request.url.sub("//www.", "//")}, []]