WSAPoll() question

[gvanem]

Hello.

I find that on Windows-10 (22H2, build 19045) and with -DMG_ENABLE_POLL=1, there are some
mg_error(c, "socket error"); caused by if (fds[n].revents & POLLERR) { here:

mongoose/mongoose.c

Lines 9188 to 9193 in 5f1f4a0

	for (struct mg_connection *c = mgr->conns; c != NULL; c = c->next) {
	if (skip_iotest(c)) {
	// Socket not valid, ignore
	} else {
	if (fds[n].revents & POLLERR) {
	mg_error(c, "socket error");

Modifying the code to:

      if (fds[n].revents & POLLERR) {
        DWORD err;
        int   len = sizeof(err);
        getsockopt(FD(c), SOL_SOCKET, SO_ERROR, (char*)&err, &len);
        mg_error(c, "socket error: %lu", err);

I see only socket error: 0. And it doesn't seems to be any error with the connections.
This blog claims WSAPoll() is buggy, but that was back in 2012. And Microsoft writes:
As of Windows 10 version 2004, when a TCP socket fails to connect, (POLLHUP | POLLERR | POLLWRNORM) is indicated.

But which error is this really? Somebody is port-scanning my server?

[scaprile]

Moved to issue