what is the best way to do keep alive socket checking in .NET?

Question

I am looking for a way to do a keep alive check in .NET. The scenario is for both UDP and TCP.

Currently in TCP what I do is that one side connects and when there is no data to send it sends a keep alive every X seconds.

I want the other side to check for data, and if non was received in X seconds, to raise an event or so.

One way i tried to do was do a blocking receive and set the socket's RecieveTimeout to X seconds. But the problem was whenever the Timeout happened, the socket's Receive would throw an SocketExeception and the socket on this side would close, is this the correct behaviour ? why does the socket close/die after the timeout instead of just going on ?

A check if there is data and sleep isn't acceptable (since I might be lagging on receiving data while sleeping).

So what is the best way to go about this, and why is the method i described on the other side failing ?

Answer 1

If you literally mean "KeepAlive", try the following.

    public static void SetTcpKeepAlive(Socket socket, uint keepaliveTime, uint keepaliveInterval)
    {
        /* the native structure
        struct tcp_keepalive {
        ULONG onoff;
        ULONG keepalivetime;
        ULONG keepaliveinterval;
        };
        */

        // marshal the equivalent of the native structure into a byte array
        uint dummy = 0;
        byte[] inOptionValues = new byte[Marshal.SizeOf(dummy) * 3];
        BitConverter.GetBytes((uint)(keepaliveTime)).CopyTo(inOptionValues, 0);
        BitConverter.GetBytes((uint)keepaliveTime).CopyTo(inOptionValues, Marshal.SizeOf(dummy));
        BitConverter.GetBytes((uint)keepaliveInterval).CopyTo(inOptionValues, Marshal.SizeOf(dummy) * 2);

        // write SIO_VALS to Socket IOControl
        socket.IOControl(IOControlCode.KeepAliveValues, inOptionValues, null);
    }

Note the time units are in milliseconds.