class Capybara::Server::Middleware

def call(env)
  if env['PATH_INFO'] == '/__identify__'
    [200, {}, [@app.object_id.to_s]]
  else
    request_uri = env['REQUEST_URI']
    @counter.increment(request_uri)
    begin
      @extended_app.call(env)
    rescue *@server_errors => e
      @error ||= e
      raise e
    ensure
      @counter.decrement(request_uri)
    end
  end
end