How to check if client disconnected abruptly

Question

I have this online chat code using socket and TCPListener, but when the client simply disconnects abruptly or loses connection, it is not removed from the ArrayList so-called clients.

public void ServiceClient()
    {
        Socket client = clientsocket;
        bool keepalive = true;

        while (keepalive)
        {
            Byte[] buffer = new Byte[1024];
            client.Receive(buffer);
            string clientcommand = System.Text.Encoding.UTF8.GetString(buffer);

            string[] tokens = clientcommand.Split(new Char[] { '|' });
            Console.WriteLine(clientcommand);

            if (tokens[0] == "CONN")
            {
                for (int n = 0; n < clients.Count; n++)
                {
                    Client cl = (Client)clients[n];
                    SendToClient(cl, "JOIN|" + tokens[1]);
                }
                EndPoint ep = client.RemoteEndPoint;
                //string add = ep.ToString();
                Client c = new Client(tokens[1], ep, clientservice, client);
                clients.Add(c);
                string message = "LIST|" + GetChatterList() + "\r\n";
                SendToClient(c, message);
                this.Invoke(new Action(() => lbClients.Items.Add(c.Name)));

                //txtLogs.AppendText("-> SISTEMA: ", Color.Red);
                //txtLogs.AppendText(DateTime.Now.ToString("HH:mm:ss") + "h - " + "Entrou no chat: " + c.Name, Color.White);
                //txtLogs.AppendText("\r\n");
            }
            else if (tokens[0] == "CHAT")
            {
                for (int n = 0; n < clients.Count; n++)
                {
                    Client cl = (Client)clients[n];
                    this.Invoke(new Action(() => SendToClient(cl, clientcommand)));
                    str = clientcommand;
                    var charsToRemove = new string[] { "CHAT|" };
                    foreach (var c in charsToRemove)
                    {
                        str = str.Replace(c, string.Empty);
                    }
                }
                //txtLogs.AppendText("-> CHAT: ", Color.DodgerBlue);
                //txtLogs.AppendText(str, Color.White);
            }
            if (tokens[0] == "PRIV")
            {
                string destclient = tokens[3];
                for (int n = 0; n < clients.Count; n++)
                {
                    Client cl = (Client)clients[n];

                    if (cl.Name.CompareTo(tokens[3]) == 0)
                    {
                        SendToClient(cl, clientcommand);
                        var str = clientcommand;
                        var charsToRemove = new string[] { "PRIV|", "|", tokens[3] };
                        foreach (var c in charsToRemove)
                        {
                            str = str.Replace(c, string.Empty);
                        }
                        txtLogs.AppendText("-> PRIVADO: ", Color.Gold);
                        txtLogs.AppendText("Para: ", Color.LimeGreen);
                        txtLogs.AppendText(tokens[3], Color.White);
                        txtLogs.AppendText(" De: ", Color.LimeGreen);
                        txtLogs.AppendText(str, Color.White);
                        txtLogs.AppendText("\r\n");
                    }
                    if (cl.Name.CompareTo(tokens[1]) == 0)
                    {
                        SendToClient(cl, clientcommand);
                        var str = clientcommand;
                        var charsToRemove = new string[] { "PRIV|", "|", tokens[1] };
                        foreach (var c in charsToRemove)
                        {
                            str = str.Replace(c, string.Empty);
                        }
                        txtLogs.AppendText("-> PRIVADO: ", Color.Gold);
                        txtLogs.AppendText("Para: ", Color.LimeGreen);
                        txtLogs.AppendText(tokens[1], Color.White);
                        txtLogs.AppendText(" De: ", Color.LimeGreen);
                        txtLogs.AppendText(str, Color.White);
                        txtLogs.AppendText("\r\n");
                    }
                }
            }
            else if (tokens[0] == "GONE")
            {
                int remove = 0;
                bool found = false;
                int c = clients.Count;
                for (int n = 0; n < c; n++)
                {
                    Client cl = (Client)clients[n];
                    SendToClient(cl, clientcommand);
                    if (cl.Name.CompareTo(tokens[1]) == 0)
                    {
                        remove = n;
                        found = true;
                        this.Invoke(new Action(() => lbClients.Items.Remove(cl.Name)));

                        txtLogs.AppendText("-> SISTEMA: ", Color.Red);
                        txtLogs.AppendText(DateTime.Now.ToString("HH:mm:ss") + "h - " + "Saiu no chat: " + cl.Name, Color.White);
                        txtLogs.AppendText("\r\n");
                    }
                }
                if (found)
                    clients.RemoveAt(remove);
                client.Close();
                keepalive = false;
            }
            /*else
            {
                int remove = 0;
                bool found = false;
                int c = clients.Count;
                for (int n = 0; n < c; n++)
                {
                    Client cl = (Client)clients[n];
                    SendToClient(cl, clientcommand);
                    if (cl.Name.CompareTo(tokens[1]) == 0)
                    {
                        remove = n;
                        found = true;
                        lbClients.Items.Remove(cl);
                        //lbClients.Items.Remove(cl.Name + " : " + cl.Host.ToString());
                    }
                }
                if (found)
                    this.Invoke(new Action(() => clients.RemoveAt(remove)));
                client.Close();
                keepalive = false;
            }*/
        }
    }

With this, how to know if the customer is no longer operating and how to remove it from the ArrayList and of ListBox?

Answer 1

One way to do this control is for the client to keep sending messages to the server for a predetermined time.

For example, even if the client has no message to send to the server, every 5 seconds it should send a message "I am here".

The server must control the reception times for each client. If the server does not receive a message from a client for 7 seconds (every 5 seconds the client must send a message, and another 2 seconds of tolerance) then the server removes the client from its client list.

I don’t work with C# but second this MSDN page when you set up Receivetimeout in socket you need to treat exceptions.

In this link of MSDN I put there is an example of handling exceptions, I am putting here:

// Displays sending with a connected socket
// using the overload that takes a buffer and socket flags.
public static int SendReceiveTest2(Socket server)
{
    byte[] msg = Encoding.UTF8.GetBytes("This is a test");
    byte[] bytes = new byte[256];
    try  // <------------------- VEJA ISTO
    {
        // Blocks until send returns.
        int byteCount = server.Send(msg, SocketFlags.None);
        Console.WriteLine("Sent {0} bytes.", byteCount);

        // Get reply from the server.
        byteCount = server.Receive(bytes, SocketFlags.None);
        if (byteCount > 0)
            Console.WriteLine(Encoding.UTF8.GetString(bytes));
    }
    catch (SocketException e) // <------------- VEJA ISTO
    {
        Console.WriteLine("{0} Error code: {1}.", e.Message, e.ErrorCode);
        return (e.ErrorCode);
    }
    return 0;
}