服务端和客户端都必须建立通信套接字,而且服务端应先进入监听状态,然后客户端套接字发出连接请求,服务端收到请求后,建立另一个套接字进行通信,原来负责监听的套接字仍进行监听。-server and the client must have a communications socket, but the server should first enter the state eavesdropping, and then sent the client socket connection requ