Question

I write a comunication program with c/s mode in C# ,server and client program on different computer. Today after client progarm connected to server progarm ,then I pulled out cable from network adapter (after this , client and server program didn’t do anything), stranger thing happened. I found out socket of server program still keep connected status. and I use command “netstat -a -n” to retrieve network information ,and get information like following :

TCP 192.168.1.2:3645 192.168.1.3:1863 ESTABLISHED

192.168.1.2 (Server IP Address)
192.168.1.3 (Client IP Address)

Do anyone know the reason ? how to solve this problem .
I wanna how server program can receive the event and close the socket when network cable of client computer has been pulled out.

Please give me some advices or solutions.

Thanks

Answer 1

I think it can be solved by using TCP keepalive.
refrencehttp://tldp.org/HOWTO/TCP-Keepalive-HOWTO/overview.html

after connecting , set socket keepalive property . msdn say this switch default status is off , if set keepalive to on , socket will check the network status automaticly , and first check time is 2 hours after last operation on socket. but the time can be adjsut to short . then after first check , socket will servral times. if connection is down or died,
socket will throw exception .

C# Source:

    uint dummy = 0;
    byte[] inOptionValues = new byte[Marshal.SizeOf(dummy) * 3];
    //set keepalive on
    BitConverter.GetBytes((uint)1).CopyTo(inOptionValues, 0); 
    //interval time between last operation on socket and first checking. example:5000ms=5s
    BitConverter.GetBytes((uint)5000).CopyTo(inOptionValues, Marshal.SizeOf(dummy));
    //after first checking, socket will check serval times by 1000ms.
    BitConverter.GetBytes((uint)1000).CopyTo(inOptionValues, Marshal.SizeOf(dummy) * 2);

    Socket socket = __Client.Client;
    socket.IOControl(IOControlCode.KeepAliveValues, inOptionValues, null);

I have checked. It’s running ok.