这个问题在TX 面试的时候问过我。 不过当时demo并没有注意这个问题， 还好面试官换问题了。。
一： 正常关闭：
如果客户端是主动申请close ， 会发送一串byte数 为0的数据到服务器，服务器就会收到count个数为0，则表示正常关闭。此时服务器正常操作close
（这里有个问题是，即便客户端自己正常发送空数据进来，服务器也不会收到0数据，所以当服务器收到0的时候就代表客户端请求正常关闭）。
二：异常关闭：
如果客户端强制点了X ，则代表未经过（退出游戏）正常关闭操作，当服务器捕获异常（远程主机强制关闭），则停止这个socket连接
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Net.Sockets; using System.Net; namespace TcpServer { class Program { static byte[] dataBuffer = new byte[1024]; static void Main(string[] args) { StartServerAsync(); Console.ReadKey(); } static void StartServerAsync() { Socket socketServer = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); IPAddress iPAddress = IPAddress.Parse("192.168.200.1"); IPEndPoint iPEndPoint = new IPEndPoint(iPAddress, 88); socketServer.Bind(iPEndPoint); socketServer.Listen(10); //Socket clientSocket = socketServer.Accept(); 下面支持多个客户端，改为异步， 之前c++服务器用的epoll这里似乎不需要关注 socketServer.BeginAccept(AcceptCallBack, socketServer); } static void AcceptCallBack(IAsyncResult ar) { Socket socketServer = ar.AsyncState as Socket; Socket socketClient = socketServer.EndAccept(ar); string msg = "Hello"; socketClient.Send(System.Text.Encoding.UTF8.GetBytes(msg)); socketClient.BeginReceive(dataBuffer, 0, 1024, SocketFlags.None, ReceiveCallBack, socketClient); socketServer.BeginAccept(AcceptCallBack, socketServer); } static void ReceiveCallBack(IAsyncResult ar) { // ar.AsyncState 可以获得之前传递的object Socket socketClient=null ; try { socketClient = ar.AsyncState as Socket; int count = socketClient.EndReceive(ar); if (count == 0) { //即便是空数据也不会是0，客户端不会发送空数据， 只有在结束时才有0的可能性 socketClient.Close(); return; } string msgReceive = Encoding.UTF8.GetString(dataBuffer, 0, count); Console.WriteLine(msgReceive); socketClient.BeginReceive(dataBuffer, 0, 1024, SocketFlags.None, ReceiveCallBack, socketClient); } catch (Exception e) { Console.WriteLine(e); if (socketClient != null) { socketClient.Close(); } } } void StartServerSync() { Socket socketServer = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); IPAddress iPAddress = IPAddress.Parse("192.168.200.1"); IPEndPoint iPEndPoint = new IPEndPoint(iPAddress, 88); socketServer.Bind(iPEndPoint); socketServer.Listen(10); Socket clientSocket = socketServer.Accept(); string msg = "Hello"; clientSocket.Send(System.Text.Encoding.UTF8.GetBytes(msg)); byte[] databuffer = new byte[1024]; int count = clientSocket.Receive(databuffer); string megReceive = System.Text.Encoding.UTF8.GetString(databuffer, 0, count); Console.Write(databuffer); clientSocket.Close(); socketServer.Close(); } } }