I need to perform some operations only after the time a TCP connection is fully closed, that's to say - all the data segments, as well as the finishing routine (FIN-ACK or RST) have been performed and done, and no packets will be sent on the wires.
Since closesocket() is not synchronous and could return before a full close of the connection and socket, I've used the SO_LINGER option to get the moment of closing.
According to the instructions in the MSDN for closesocket, and to the fact that my socket is non-blocking (and thus asynchronous), I wrote this code:
int ret;
/* config 2 secs of linger */
struct linger lng = {1, 2};
setsockopt(s, SOL_SOCKET, SO_LINGER, (const char*)&lng, sizeof(lng));
/* graceful close of TCP (FIN-ACK for both sides) */
shutdown(s, SD_BOTH);
/* linger routine for asynchronous sockets according to msdn */
do {
ret = closesocket(s);
} while (ret == SOCKET_ERROR && WSAGetLastError() == WSAEWOULDBLOCK);
/* my code to be run immediately after all the traffic */
printf("code to run after closing");
However, the closesocket call returns zero (success; instead of getting into the loop) and I see in Wireshark that my final printing is called before all the packets were sent, so - it looks like the linger isn't working.
By the way, the functions I used to open and connect the asynchronous socket were socket(), WSAIoctl() and its lpfnConnectEx() callback.
What's the reason that the lingered closesocket return before a full finish of the TCP connection? Is there a solution?
