subdomain_to_path_info.rb

class SubdomainToPathInfo # man I'm bad with names
  
  def initialize(app)
    @app = app
  end
  
  def call(env)
    @app.call(filter(env))
  end
  
  def filter(env)
    if env['SERVER_NAME'] =~ /(.*)\.domain\.com/
      env['PATH_INFO'] = "#{$1}#{env['PATH_INFO']}"
    end
    env
  end
  
end