How to check whether socket connection is alive ?

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Hi,

I am developing a client server application on windows.
I am using winsock api.

Is ther any function by which i can check the status of the socket connection.

flow of my program is like.

1 ) Establish a connection to the server
2 ) Do something with the socket
3 ) Keep idle
4 ) Send something to the server.

While sending any data to server in 4th step, is ther any way for me to check whether the connection is still alive ?

Posted 3-Oct-12 0:55am

PrafullaVedante

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michaelmel 3-Oct-12 20:10pm

Generally, in your 4th step, if the connection is not alive, your send() will return an error. Generally, your connection can remain active indefinitely, even if idle.

PrafullaVedante 4-Oct-12 2:16am

ammm ... is ther any way if i just want to check the status of the connection.

If i use return code of send , i will need to send something each time to check connection's aliveness.. :(

michaelmel 4-Oct-12 20:26pm

If you opened socket with a keep-alive option, TCP will automatically send a heartbeat message to monitor the connection and close it if it is not alive. From memory, keep-alive is default option with Winsock and most UNIX/Linux implementations.

The other option which I use a fair bit is to send my own hearbeat packet into connection (both ways). This also has the advantage that intermediate devices such as routers don't try to be too smart and drop the connection as inactive - as it always has some (small) traffic.

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michaelmel · Answer 1 · 2012-10-04T14:34:00

Ok, I will just sum it all up and add one more option:

1) Generally, in your 4th step, if the connection is not alive, your send() will return an error. (Note: your connection can remain active indefinitely, even if you send no traffic into it).

2) If you've opened the socket with a keep-alive option, TCP will automatically send a heartbeat message to monitor the connection and close it if it is not alive. From memory, keep-alive is a default option with Winsock and most UNIX/Linux implementations.

3) The other option which I use a fair bit is to send my own hearbeat packet into connection (both ways). This also has the advantage that intermediate devices such as routers don't try to be too smart and drop the connection as inactive - as it always has some (small) traffic.

4) And finally, to check for connection being alive, you can use recv with MSG_PEEK option, something like:

char data;
recv(socket,&data,1, MSG_PEEK);//read one byte

but make sure you are in non-blocking mode. (Note - using PEEK makes sure that the received data is not de-queued and can be read/processed by proper receive routine). This is the method used by Ulimiate TCP/IP.