C＃现有的连接被远程主机强行关闭：套接字编程

Question

我正在使用套接字。这是我的代码（对问题的描述更进一步）：

客户端：

    public void ReadCallback(IAsyncResult ar)
    {
        int fileNameLen = 1;
        String content = String.Empty;
        StateObject state = (StateObject)ar.AsyncState;
        Socket handler = state.workSocket;

        int bytesRead = handler.EndReceive(ar);
        if (bytesRead > 0)
        {

            if (flag == 0)
            {

                fileNameLen = BitConverter.ToInt32(state.buffer, 0);
                string fileName = Encoding.UTF8.GetString(state.buffer, 4, fileNameLen);
                receivedPath = mypath + @"XML\";
                if (!Directory.Exists(receivedPath))
                {
                    Directory.CreateDirectory(receivedPath);
                }
                receivedPath = receivedPath + fileName;
                flag++;

            }
            if (flag >= 1)
            {

                BinaryWriter writer = new BinaryWriter(File.Open(receivedPath, FileMode.Append));
                if (flag == 1)
                {
                    writer.Write(state.buffer, 4 + fileNameLen, bytesRead - (4 + fileNameLen));
                    flag++;
                }
                else
                    writer.Write(state.buffer, 0, bytesRead);
                writer.Close();
                handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
                new AsyncCallback(ReadCallback), state);
            }

        }
        else
        {
            //   Invoke(new MyDelegate(LabelWriter));
        }
    }

我在这条线上出现错误： int bytesRead = handler.EndReceive(ar);

如何避免此错误？： An existing connection was forcibly closed by the remote host

服务器端：

        public void ReadCallback(IAsyncResult ar)
        {
            try
            {

                int fileNameLen = 1;
                String content = String.Empty;
                StateObject state = (StateObject)ar.AsyncState;
                Socket handler = state.workSocket;
                string[] str = new string[2];
                str = handler.RemoteEndPoint.ToString().Split(':');
                IP = str[0].ToString();
                int bytesRead = handler.EndReceive(ar);

                if (bytesRead > 0)
                {
                    if (flag == 0)
                    {
                        fileNameLen = BitConverter.ToInt32(state.buffer, 0);
                        string fileName = Encoding.UTF8.GetString(state.buffer, 4, fileNameLen);
                        string[] getIP = new string[3];
                        getIP = fileName.Split('_');
                        #region Send Files in HandHeld
                        #region GetLoginFile
                        if (getIP[1].ToString().Equals("GetLoginFile"))
                        {
                            string getDirectory = @"Send_Hand_Held_Files\" + DateTime.Today.ToString("dd-MM-yyyy") + "\\" + getIP[0].ToString() + "\\XML";
                            string strmyFile = getDirectory + "\\Login.xml";
                            char[] delimiter = splitter.ToCharArray();
                            split = strmyFile.Split(delimiter);
                            int limit = split.Length;
                            fName = split[limit - 1].ToString();

                            byte[] LoginfileName = Encoding.UTF8.GetBytes(fName); //file name

                            byte[] fileData = File.ReadAllBytes(strmyFile);

                            byte[] LoginfileNameLen = BitConverter.GetBytes(LoginfileName.Length); //lenght of file name
                            clientData = new byte[4 + LoginfileName.Length + fileData.Length];

                            LoginfileNameLen.CopyTo(clientData, 0);
                            LoginfileName.CopyTo(clientData, 4);
                            fileData.CopyTo(clientData, 4 + LoginfileName.Length);

                            handler.BeginSend(clientData, 0, clientData.Length, 0, new AsyncCallback(SendCallBack), handler);
                            //handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
                            //new AsyncCallback(ReadCallback), state);
                            return;
                        }
 }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);

            }
            //SendData(IP);
        }

     private static void SendCallBack(IAsyncResult ar)
        {
            try
            {
                // Retrieve the socket from the state object.
                Socket client = (Socket)ar.AsyncState;

                // Complete sending the data to the remote device.
               // int bytesSent = client.EndSend(ar);
                //Console.WriteLine("Sent {0} bytes to server.", bytesSent);

                // Signal that all bytes have been sent.
                allDone.Set();

            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }
        }

Answer 1

您正在从中获得例外handler.EndReceive()。可以肯定的是，目前尚不清楚为什么会收到提到的特定异常，但是在投入生产时，此代码将在每次出现网络通信问题（常见）时抛出异常。

因此，EndReceive()无论如何，您可能应该尝试/抓住该呼叫。考虑一下一旦连接失败或服务器死机或其他原因，您的代码将需要做什么。

然后，您可以开始诊断特定问题。您尚未指定的一件重要事情：您是仅偶尔收到此错误，还是始终可复制地收到此错误？如果是前者，则可能只是正常的Internet连接波动。您的软件必须能够处理这些问题。如果是后者，那么我认为这听起来像是服务器上的问题。当您调用时BeginReceive()，系统将开始等待服务器中的某些内容。如果该“某事”是它接收到的数据，EndReceive()则将成功，但是，如果该“某事”是服务器已关闭该连接，则您的回调仍将被调用，然后EndReceive()将引发相关的SocketException。这是设计使然，因为几乎没有其他方法可以与您的代码进行通信，表明服务器已关闭连接。

编辑：看起来您的服务器代码需要相同的错误处理：EndReceive()如果客户端关闭连接，则对它的调用同样容易引发异常。（我知道您可以尝试/抓住整个大问题，但是它会输出一个MessageBox ...在服务器上无法正常工作，除非您希望有人一直坐在那里单击所有OK按钮。 ..）