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分享TCP Socket一端关闭之后不报异常，而是接受0字节。
我用.net 3.5, VS 2008 开发， TCP Socket通讯，递归调用接受信息。在实际项目中发现当 Socket一端关闭（调用Socket.Close())后，另外一端不是报出异常（我期望是如此），而是不断递归调用接受0字节。我整理了下代码，下面Demo能重现此问题。期望有人能给出解释。
服务器端代码
客户端代码
服务端端和客户端关闭Socket部分互换后（注释服务器端，开启客户端关闭），服务器端也能长生此同样现象。
服务器端代码
class TestServer
{
static void Main()
{
try
{
TCPServer tcpServer = (TCPServer)TCPServer.GetInstance();
tcpServer.ServerIP = "127.0.0.1";
tcpServer.ServerPort = 3721;
tcpServer.CreatListener();
Console.WriteLine(String.Format("Server is ready with {0}:{1}", tcpServer.ServerIP, tcpServer.ServerPort));
}
catch (Exception e)
{
Console.WriteLine("Exception: {0}", e);
}
Console.WriteLine("Press Enter to Exit"); Console.ReadLine();
}
}
public abstract class PacketTransferBase
{
public PacketTransferBase()
{
}
private int count = 0;
/// <summary>
/// 接收信息
/// </summary>
/// <param name="ar"></param>
protected void ReceiveMessage(IAsyncResult ar)
{
try
{
StateObject so = (StateObject)ar.AsyncState;
Socket socket = so.workSocket;
//方法参考：http://msdn.microsoft.com/zh-cn/library/system.net.sockets.socket.endreceive.aspx
var length = socket.EndReceive(ar);
byte[] actualData = new byte[length];
Array.Copy(so.buffer, 0, actualData, 0, length);
Console.WriteLine(string.Format("TCPServer.ReceiveMessage: buffer.{0} at Socket.{1}.{2} with buffer[0].{3},buffer[1].{4},buffer[2].{5}", length, socket.Handle, socket.Connected, so.buffer[0], so.buffer[1], so.buffer[2]));
bool continueReceive = true;
Console.WriteLine(Encoding.UTF8.GetString(actualData));
if (count == 0)
{
socket.Send(Encoding.UTF8.GetBytes("this is a back message from server!"));
count++;
}
socket.Close();
if (continueReceive && socket != null && socket.Connected)
{
socket.BeginReceive(so.buffer, 0, StateObject.BUFFER_SIZE, 0, new AsyncCallback(ReceiveMessage), so);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message + ex.StackTrace);
}
}
}
/// <summary>
/// TCP服务器端
/// </summary>
public class TCPServer : PacketTransferBase
{
public string ServerIP { get; set; }
public int ServerPort { get; set; }
private static TCPServer _TCPServer = new TCPServer();
Socket socketServer = null;
private TCPServer()
{
}
public static PacketTransferBase GetInstance()
{
return _TCPServer;
}
/// <summary>
/// 服务器端建立侦听
/// </summary>
public void CreatListener()
{
//创建一个新的Socket,这里我们使用最常用的基于TCP的Stream Socket（流式套接字）
socketServer = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
//将该socket绑定到主机上面的某个端口
//方法参考：http://msdn.microsoft.com/zh-cn/library/system.net.sockets.socket.bind.aspx
socketServer.Bind(new IPEndPoint(IPAddress.Parse(ServerIP), ServerPort));
//启动监听，并且设置一个最大的队列长度
//方法参考：http://msdn.microsoft.com/zh-cn/library/system.net.sockets.socket.listen(v=VS.100).aspx
socketServer.Listen(100);
//开始接受客户端连接请求
//方法参考：http://msdn.microsoft.com/zh-cn/library/system.net.sockets.socket.beginaccept.aspx
socketServer.BeginAccept(new AsyncCallback(ClientAccepted), socketServer);
}
/// <summary>
/// 接收客户端
/// </summary>
/// <param name="ar"></param>
public void ClientAccepted(IAsyncResult ar)
{
try
{
var socketServer = ar.AsyncState as Socket;
//这就是客户端的Socket实例，我们后续可以将其保存起来
var socketClient = socketServer.EndAccept(ar);
//接收客户端的消息(这个和在客户端实现的方式是一样的）
StateObject so = new StateObject();
so.workSocket = socketClient;
socketClient.BeginReceive(so.buffer, 0, StateObject.BUFFER_SIZE, 0, new AsyncCallback(ReceiveMessage), so);
//准备接受下一个客户端请求
socketServer.BeginAccept(new AsyncCallback(ClientAccepted), socketServer);
}
catch (Exception ex)
{
Console.WriteLine(ex.Message + ex.StackTrace);
}
}
}
public class StateObject
{
public Socket workSocket = null;
public EndPoint tempRemoteEP = null;
public const int BUFFER_SIZE = 1024;
public byte[] buffer = new byte[BUFFER_SIZE];
}
客户端代码
class TestClient
{
static void Main()
{
try
{
TCPClient tcpClient = (TCPClient)TCPClient.GetInstance();
tcpClient.ServerIP = "127.0.0.1";
tcpClient.ServerPort = 3721;
Socket socket = tcpClient.ConnectToServer();
socket.Send(Encoding.UTF8.GetBytes("this is a test message from client!"));
}
catch (Exception e)
{
Console.WriteLine("Exception: {0}", e);
}
Console.WriteLine("Press Enter to Exit"); Console.ReadLine();
}
}
public abstract class PacketTransferBase
{
public PacketTransferBase()
{
}
private int count = 0;
/// <summary>
/// 接收信息
/// </summary>
/// <param name="ar"></param>
protected void ReceiveMessage(IAsyncResult ar)
{
try
{
StateObject so = (StateObject)ar.AsyncState;
Socket socket = so.workSocket;
//方法参考：http://msdn.microsoft.com/zh-cn/library/system.net.sockets.socket.endreceive.aspx
var length = socket.EndReceive(ar);
byte[] actualData = new byte[length];
Array.Copy(so.buffer, 0, actualData, 0, length);
Console.WriteLine(string.Format("TCPServer.ReceiveMessage: buffer.{0} at Socket.{1}.{2} with buffer[0].{3},buffer[1].{4},buffer[2].{5}", length, socket.Handle, socket.Connected, so.buffer[0], so.buffer[1], so.buffer[2]));
bool continueReceive = true;
Console.WriteLine(Encoding.UTF8.GetString(actualData));
//把以下代码去掉注释，把服务器端socket.Close()注释，则服务器端产生一样效果。
//if (count == 0)
//{
// socket.Send(Encoding.UTF8.GetBytes("this is a second message from server!"));
// count++;
//}
//socket.Close();
if (continueReceive && socket != null && socket.Connected)
{
socket.BeginReceive(so.buffer, 0, StateObject.BUFFER_SIZE, 0, new AsyncCallback(ReceiveMessage), so);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message + ex.StackTrace);
}
}
}
public class StateObject
{
public Socket workSocket = null;
public EndPoint tempRemoteEP = null;
public const int BUFFER_SIZE = 1024;
public byte[] buffer = new byte[BUFFER_SIZE];
}
/// <summary>
/// TCP 客户端
/// </summary>
public class TCPClient : PacketTransferBase
{
public string ServerIP { get; set; }
public int ServerPort { get; set; }
private static TCPClient _TCPClient = new TCPClient();
private TCPClient()
{
}
public static PacketTransferBase GetInstance()
{
return _TCPClient;
}
public Socket ConnectToServer()
{
//创建一个Socket
Socket socketClient = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
//连接到指定服务器的指定端口
//方法参考：http://msdn.microsoft.com/zh-cn/library/system.net.sockets.socket.connect.aspx
socketClient.Connect(ServerIP, ServerPort);
StateObject so = new StateObject();
so.workSocket = socketClient;
socketClient.BeginReceive(so.buffer, 0, StateObject.BUFFER_SIZE, 0, new AsyncCallback(ReceiveMessage), so);
return socketClient;
}
}
服务端端和客户端关闭Socket部分互换后（注释服务器端，开启客户端关闭），服务器端也能长生此同样现象。
...全文
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zhongmeiqing 2013-09-17
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楼主，我也遇到了这个问题，客户端异常断开连接，服务端马上就不断的接受空消息。一直在循环。请问楼主解决了吗？
catchdream 2013-02-01
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是的，要进行处理。不过我查论坛，或者msdn都没发现此情形，难道大家都没碰到过这种情况。。。
wenbin 2013-01-31
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接收到0字节说明连接已经断开，不再阻塞
所以在处理接收数据时一定要处理这种情况
当收到0字节时，处理连接的关闭事宜
足球中国 2013-01-31
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这个和短连接长连接又没有关系。。。。
catchdream 2013-01-31
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我用的短连接，用完就关，耗费资源少。
catchdream 2013-01-31
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我是这么做的，发现这个情形就是在一种情况有一边忘记关了，就出现上面的情况。。很奇怪。没查到有用的文档。这个也不像是 Keep-Alive数据报啊。那个应该没这么频繁吧。。
strife013 2013-01-31
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结束时发个消息给另一端手动判断吧
空格键 2013-01-31
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顶，接分啊
足球中国 2013-01-31
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这可能算是一个BUG吧。理论上是应该阻塞的。
还有更多的问题。
codeproject有一个开源东东很多也碰到过原子锁会出现负的情况。
使用心跳包吧。
