l, err := net.Listen("tcp", "127.0.0.1:0") // any available address
	if err != nil {
		log.Fatalf("net.Listen tcp :0: %v", err)
	}
	return l, l.Addr().String()
}

func startServer() {
	Register(new(Arith))
	Register(new(Embed))
	RegisterName("net.rpc.Arith", new(Arith))
	Register(BuiltinTypes{})

	var l net.Listener
	l, serverAddr = listenTCP()