实现用户与用户之间的文件传送，首先需要运行服务端，然后登录客户端，登录成功后选择要发送的好友，然后选择文件发送给该好友-To achieve the file transfer between users and users, you first need to run the server, and then log on to the client, the successful login to send friends, and then the file sent to the f