说明：  本程序是一个用C#编写的文件传输程序，分服务端和客户端。 服务端首先监听端口，等待客户端的连接请求，一旦连接成功，即把可供客户端下载的文件名称发给客户端，客户端接受到文件名称后，选择要下载的文件，并发给服务器。服务器根据客户端发送的文件名，选择指定的文件读取文件流，并把文件流内容赋值给网络流发送到客
(This procedure is to use C# to prepare a file transfer program, sub-client and client services. First of all, monitor server ports, waiting for client connection requests, once the connection, that is for the client to download the file name sent to client, client termination by the file name, choose to download the file and sent to the server. Server in accordance with the client to send the file name, select the specified file stream to read the document and the contents of the document flow to the network flow assignment is sent to the customer)