How to check if a socket is connected/disconnected in C#?

Question

How can you check if a network socket (System.Net.Sockets.Socket) is still connected if the other host doesn\'t send you a packet when it disconnects (e.g. because it discon

Answer 1

public static class SocketExtensions
{
    private const int BytesPerLong = 4; // 32 / 8
    private const int BitsPerByte = 8;

    public static bool IsConnected(this Socket socket)
    {
        try
        {
            return !(socket.Poll(1000, SelectMode.SelectRead) && socket.Available == 0);
        }
        catch (SocketException)
        {
            return false;
        }
    }


    /// 

    /// Sets the keep-alive interval for the socket.
    /// 
    /// The socket.
    /// Time between two keep alive "pings".
    /// Time between two keep alive "pings" when first one fails.
    /// If the keep alive infos were succefully modified.
    public static bool SetKeepAlive(this Socket socket, ulong time, ulong interval)
    {
        try
        {
            // Array to hold input values.
            var input = new[]
            {
                (time == 0 || interval == 0) ? 0UL : 1UL, // on or off
                time,
                interval
            };

            // Pack input into byte struct.
            byte[] inValue = new byte[3 * BytesPerLong];
            for (int i = 0; i < input.Length; i++)
            {
                inValue[i * BytesPerLong + 3] = (byte)(input[i] >> ((BytesPerLong - 1) * BitsPerByte) & 0xff);
                inValue[i * BytesPerLong + 2] = (byte)(input[i] >> ((BytesPerLong - 2) * BitsPerByte) & 0xff);
                inValue[i * BytesPerLong + 1] = (byte)(input[i] >> ((BytesPerLong - 3) * BitsPerByte) & 0xff);
                inValue[i * BytesPerLong + 0] = (byte)(input[i] >> ((BytesPerLong - 4) * BitsPerByte) & 0xff);
            }

            // Create bytestruct for result (bytes pending on server socket).
            byte[] outValue = BitConverter.GetBytes(0);

            // Write SIO_VALS to Socket IOControl.
            socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
            socket.IOControl(IOControlCode.KeepAliveValues, inValue, outValue);
        }
        catch (SocketException)
        {
            return false;
        }

        return true;
    }
}

1. Copy the SocketExtensions class to your project
2. Call the SetKeepAlive on your socket - socket.SetKeepAlive(1000, 2);
3. Add a timer to check the IsConnected function