建立一个基于UDP的二人网络聊天的程序，要有登陆功能，登陆成功后可实现客户端和服务器端信息的互发，否则不能进入聊天。-A UDP-based chat program for two, there must log function, the landing can be achieved after the success of the client and server send each other information, or can not access the chat.