网络适​​配器关闭时检测客户端断开连接

Question

我无法检测客户端与主机的断开连接。 目前我的代码是这样的：

Task.Run(() => {
 // Create server
 Socket server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp) {
  ReceiveTimeout = -1,
 };

 server.Bind(new IPEndPoint(IPAddress.Any, port));
 server.Listen(-1);

 // Start listening
 while (true) {
  Socket socket = server.Accept();

  new Thread(() => {
   try {
    Process(socket);
   } catch (Exception ex) {
    Trace.WriteLine("Socket connection processing error: " + ex.Message);
   }
  }).Start();
 }
});

// Host client process
void Process(Socket socket) {
  byte[] response;
  int received;
  var ip = IPAddress.Parse(((IPEndPoint) socket.RemoteEndPoint).Address.ToString());
  Events.OnNodeConnected(ip);

  while (true) {
   // Rceive data
   response = new byte[socket.ReceiveBufferSize];
   received = socket.Receive(response);

   // Check connection
   if (!socket.IsConnected()) {
    socket.Close();
    Events.OnNodeDisconnected(ip);
    return;
   }

   try {
    // Decode recieved data
    List < byte > respBytesList = new List < byte > (response);

和IsConnected()扩展：

public static class SocketExtensions {
 public static bool IsConnected(this Socket socket) {
  try {
   return !(socket.Poll(1, SelectMode.SelectRead) && socket.Available == 0);
  } catch (SocketException) {
   return false;
  }
 }
}

关闭应用程序时有效，但关闭网卡时无效。 我正在 VirtualBox 上运行的 Debian 虚拟机上对此进行测试。 在这种情况下，有没有办法检测断开连接？

Answer 1

关闭应用程序时有效，但关闭网卡时无效。

关掉网卡其实不是断网。 如果再次打开网卡，现有连接可以继续（假设接口仍然具有相同的 IP 地址） - 这在暂停笔记本电脑并稍后恢复时很常见。

对于 TCP，真正的断开连接只是显式断开连接（FIN 被发送），它在显式关闭套接字时完成，或者在应用程序退出或应用程序崩溃时由操作系统内核隐式完成。

相反，您要求的不是显式断开连接，而是检测当前是否无法访问对等方，例如线路（临时）断开连接或系统崩溃时。 这可以通过在应用程序级别或 TCP 级别使用某种心跳来完成。 后者称为 TCP 保持活动，通过发送空 TCP 数据包并检查是否发回 ACK 来工作。 有关如何使用它的示例，请参见此处。

Answer 2

我有类似的问题，当我想知道我的网络接口是否已知时

我正在使用这段代码来检查不同的网络接口：

文件 NetworkMonitor.cs

using System.Collections;
using System.Diagnostics;
using System.Timers;

namespace NetWork.Plus
{
    /// <summary>
    /// The NetworkMonitor class monitors network speed for each network adapter on the computer,
    /// using classes for Performance counter in .NET library.
    /// </summary>
    public class NetworkMonitor
    {
        private Timer timer;                        // The timer event executes every second to refresh the values in adapters.
        private ArrayList adapters;                 // The list of adapters on the computer.
        private ArrayList monitoredAdapters;        // The list of currently monitored adapters.

        public NetworkMonitor()
        {
            this.adapters   =   new ArrayList();
            this.monitoredAdapters  =   new ArrayList();
            EnumerateNetworkAdapters();

            timer   =   new Timer(1000);
            timer.Elapsed   +=  new ElapsedEventHandler(timer_Elapsed);
        }

        /// <summary>
        /// Enumerates network adapters installed on the computer.
        /// </summary>
        private void EnumerateNetworkAdapters()
        {
            PerformanceCounterCategory category =   new PerformanceCounterCategory("Network Interface");

            foreach (string name in category.GetInstanceNames())
            {
                // This one exists on every computer.
                if (name == "MS TCP Loopback interface")
                    continue;
                // Create an instance of NetworkAdapter class, and create performance counters for it.
                NetworkAdapter adapter  =   new NetworkAdapter(name);
                adapter.dlCounter   =   new PerformanceCounter("Network Interface", "Bytes Received/sec", name);
                adapter.ulCounter   =   new PerformanceCounter("Network Interface", "Bytes Sent/sec", name);
                this.adapters.Add(adapter);         // Add it to ArrayList adapter
            }
        }

        private void timer_Elapsed(object sender, ElapsedEventArgs e)
        {
            foreach (NetworkAdapter adapter in this.monitoredAdapters)
                adapter.refresh();
        }

        /// <summary>
        /// Get instances of NetworkAdapter for installed adapters on this computer.
        /// </summary>
        public NetworkAdapter[] Adapters
        {
            get
            {
                return (NetworkAdapter[])this.adapters.ToArray(typeof(NetworkAdapter));
            }
        }

        // Enable the timer and add all adapters to the monitoredAdapters list, unless the adapters list is empty.
        public void StartMonitoring()
        {
            if (this.adapters.Count > 0)
            {
                foreach(NetworkAdapter adapter in this.adapters)
                    if (!this.monitoredAdapters.Contains(adapter))
                    {
                        this.monitoredAdapters.Add(adapter);
                        adapter.init();
                    }

                timer.Enabled   =   true;
            }
        }

        // Enable the timer, and add the specified adapter to the monitoredAdapters list
        public void StartMonitoring(NetworkAdapter adapter)
        {
            if (!this.monitoredAdapters.Contains(adapter))
            {
                this.monitoredAdapters.Add(adapter);
                adapter.init();
            }
            timer.Enabled   =   true;
        }

        // Disable the timer, and clear the monitoredAdapters list.
        public void StopMonitoring()
        {
            this.monitoredAdapters.Clear();
            timer.Enabled   =   false;
        }

        // Remove the specified adapter from the monitoredAdapters list, and disable the timer if the monitoredAdapters list is empty.
        public void StopMonitoring(NetworkAdapter adapter)
        {
            if (this.monitoredAdapters.Contains(adapter))
                this.monitoredAdapters.Remove(adapter); 
            if(this.monitoredAdapters.Count == 0)
                timer.Enabled   =   false;
        }
    }
}



file NetworkAdapter.cs

using System.Diagnostics;

namespace NetWork.Plus
{
    /// <summary>
    /// Represents a network adapter installed on the machine.
    /// Properties of this class can be used to obtain current network speed.
    /// </summary>
    public class NetworkAdapter
    {
        /// <summary>
        /// Instances of this class are supposed to be created only in an NetworkMonitor.
        /// </summary>
        internal NetworkAdapter(string name)
        {
            this.name   =   name;
        }

        private long dlSpeed, ulSpeed;              // Download\Upload speed in bytes per second.
        private long dlValue, ulValue;              // Download\Upload counter value in bytes.
        private long dlValueOld, ulValueOld;        // Download\Upload counter value one second earlier, in bytes.

        internal string name;                               // The name of the adapter.
        internal PerformanceCounter dlCounter, ulCounter;   // Performance counters to monitor download and upload speed.

        /// <summary>
        /// Preparations for monitoring.
        /// </summary>
        internal void init()
        {
            // Since dlValueOld and ulValueOld are used in method refresh() to calculate network speed, they must have be initialized.
            this.dlValueOld =   this.dlCounter.NextSample().RawValue;
            this.ulValueOld =   this.ulCounter.NextSample().RawValue;
        }

        /// <summary>
        /// Obtain new sample from performance counters, and refresh the values saved in dlSpeed, ulSpeed, etc.
        /// This method is supposed to be called only in NetworkMonitor, one time every second.
        /// </summary>
        internal void refresh()
        {
            this.dlValue    =   this.dlCounter.NextSample().RawValue;
            this.ulValue    =   this.ulCounter.NextSample().RawValue;

            // Calculates download and upload speed.
            this.dlSpeed    =   this.dlValue - this.dlValueOld;
            this.ulSpeed    =   this.ulValue - this.ulValueOld;

            this.dlValueOld =   this.dlValue;
            this.ulValueOld =   this.ulValue;
        }

        /// <summary>
        /// Overrides method to return the name of the adapter.
        /// </summary>
        /// <returns>The name of the adapter.</returns>
        public override string ToString()
        {
            return this.name;
        }

        /// <summary>
        /// The name of the network adapter.
        /// </summary>
        public string Name
        {
            get
            {
                return this.name;
            }
        }
        /// <summary>
        /// Current download speed in bytes per second.
        /// </summary>
        public long DownloadSpeed
        {
            get
            {
                return this.dlSpeed;
            }
        }
        /// <summary>
        /// Current upload speed in bytes per second.
        /// </summary>
        public long UploadSpeed
        {
            get
            {
                return this.ulSpeed;
            }
        }
        /// <summary>
        /// Current download speed in kbytes per second.
        /// </summary>
        public double DownloadSpeedKbps
        {
            get
            {
                return this.dlSpeed/1024.0;
            }
        }
        /// <summary>
        /// Current upload speed in kbytes per second.
        /// </summary>
        public double UploadSpeedKbps
        {
            get
            {
                return this.ulSpeed/1024.0;
            }
        }
    }
}

您可以像这样使用这些文件，例如：

    private NetworkAdapter[] adapters;
    private NetworkMonitor monitor;   

您捕获网络设备列表，因此您可以检查您的首选网络设备是已知还是未知

    monitor =   new NetworkMonitor();
    this.adapters   =   monitor.Adapters;

如果你愿意，你可以测量下载和/或上传的速度。

遵循框架的版本，您必须在 exe.config 文件中包含这段代码:(以避免错误 -> InvalidOperation : Instance 'XXX' does not exist in the specified Category）

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.net>
    <settings>
      <performanceCounters enabled="true" />
    </settings>
  </system.net>
</configuration>