What if server didn't receive fd_close

Question

I have a high performance client server system programmed from the scratch. i am still improving my system. the server using io overlapping to handle connections. the server correctly handles disconnections and resource deallocations. at the client side i used shutdown command with sd_receive to notify the server that the client has no data to receive after final send from the client. this works well. and server detects that as a graceful disconnection. rarely i have observed when the connection is very slow the server doesn't detect this. I feel that the shutdown partial closure doesn't reach the server. how can i handle this. this is important the server shouldn't contain this kind of connections if so the server can not be stopped. and i do not want to close all such connection by force.

Answer 1

at the client side i used shutdown command with sd_receive to notify the server that the client has no data to receive after final send from the client.

It doesn't do that.

this works well

It doesn't work at all. The shutdown command with SD_RECEIVE that you're using is completely pointless. A close, or a shutdown with SD_SEND or SD_BOTH, sends a FIN: shutdown with SD_RECEIVE does exactly nothing on the wire, and specifically it does not 'notify the server' of anything.

I feel that the shutdown partial closure doesn't reach the server.

It never reaches the server. Your code doesn't work the way you think it does. What reaches the server is the FIN, which in turn is the result of the close, not the shutdown SD_RECEIVE.

What you need here is a read timeout at the server end. As you're using select() or whatever is delivering you the events, you will have to implement the timeout manually yourself.