简单的ftp服务器端和客户端，两个程序同时运行，在客户端可以使用pwd、cd、quit、help、get、put、dir等命令进行操作，实现下载、上传文件等操作。-A simple ftp server-side and client-side, the two programs are running at the same time, the client can use the pwd, cd, quit, help, get, put, dir and other commands to download, upload files, and so.