class Capybara::Server::Middleware

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

def initialize(app, server_errors)
  @app = app
  @counter = Counter.new
  @server_errors = server_errors
end

def pending_requests?
  @counter.value > 0
end