C# UDP 现有连接被远程主机强行关闭

Question

我正在为一个游戏创建一个服务器，该服务器使用异步方法通过 UDP 处理多个客户端，并且专门致力于干净的断开连接逻辑。当客户端硬崩溃时(他们的程序在没有适当的断开连接逻辑的情况下关闭)服务器上的 readCallback 抛出 SocketException

An existing connection was forcibly closed by the remote host

这是有道理的，但是当下次在 read 的循环中触发读取时，尽管在回调中处理了异常，它还是崩溃了。

    private void connectedState()
    {
        while (connected)
        {
            //reset the trigger to non-signaled
            readDone.Reset();

            read(socket);

            //block on reading data
            readDone.WaitOne();
        }
    }


    private void read(Socket sock)
    {
        // Creates an IpEndPoint to capture the identity of the sending host.
        IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
        EndPoint senderRemote = sender;

        // Create the state object.
        StateObject state = new StateObject();
        state.workSocket = sock;

        //crashes after an exception is caught within the callback
        sock.BeginReceiveFrom(state.buffer, 0, StateObject.MESSAGE_SIZE, SocketFlags.None, ref senderRemote, new AsyncCallback(readCallback), state);
    }


    private void readCallback(IAsyncResult ar)
    {
        StateObject state = (StateObject)ar.AsyncState;
        Socket sock = state.workSocket;

        EndPoint senderRemote = new IPEndPoint(IPAddress.Any, 0);

        try
        {
            // Read data from the client socket. 
            int bytesRead = sock.EndReceiveFrom(ar, ref senderRemote);

            if (bytesRead <= 0)
            {
                //handle disconnect logic
            }
            else
            {
                //handle the message received
            }
        }
        catch (SocketException se)
        {
            Console.WriteLine(se.ToString());
        }

        // Signal the read thread to continue
        readDone.Set();
    }

抛出了两个异常，我相信其中一个被捕获了:

---

抛出异常:System.dll 中的“System.Net.Sockets.SocketException” System.Net.Sockets.SocketException (0x80004005): 现有连接被远程主机强行关闭 在 System.Net.Sockets.Socket.EndReceiveFrom(IAsyncResult asyncResult，EndPoint＆endPoint) 在 CardCatacombs.Utilities.Networking.UDPNetworkConnection.readCallback(IAsyncResult ar) 在 C:\Users\kayas\Desktop\Practicum\Source\CardCatacombs\CardCatacombs\Utilities\Networking\UDPNetworkConnection.cs:line 424

抛出异常:System.dll 中的“System.Net.Sockets.SocketException” System.Net.Sockets.SocketException (0x80004005): 现有连接被远程主机强行关闭 在 System.Net.Sockets.Socket.DoBeginReceiveFrom(Byte[] 缓冲区，Int32 偏移量，Int32 大小，SocketFlags socketFlags，EndPoint endPointSnapshot，SocketAddress socketAddress，OverlappedAsyncResult asyncResult)

---

我希望能够干净地处理客户端崩溃并继续运行，因为还有其他客户端连接到服务器。

Answer 1

来自 this forum thread ，似乎UDP套接字也在接收ICMP消息并在接收时抛出异常。如果端口不再监听(在硬崩溃之后)，ICMP 消息会导致“强制关闭”异常。

如果不需要，可以在创建 UdpClient 时使用以下代码禁用此异常，如上文所述:

public const int SIO_UDP_CONNRESET = -1744830452;
var client = new UdpClient(endpoint);
client.Client.IOControl(
    (IOControlCode)SIO_UDP_CONNRESET, 
    new byte[] { 0, 0, 0, 0 }, 
    null
);

对于dotnet core用户，由于这个“Socket.IOControl”是Windows特有的控制代码，不支持其他平台，我们会得到以下异常:

Unhandled exception. System.PlatformNotSupportedException: Socket.IOControl handles Windows-specific control codes and is not supported on this platform.

为了更好的兼容性，我们应该检查当前的平台:

using System.Runtime.InterosServices;

if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
{
   //...
}