Blocking accept in socketpair implementation may cause permanent hang after system resume from sleep

[syou121]

Description:
On Windows platform, mosquitto may permanently hang when the system resumes from sleep state. After analysis, this issue occurs in the net__socketpair implementation.

Details:
In the current implementation, while the connect socket is set to non-blocking mode, the accept remains blocking
During system resume from sleep, when the network stack might not be fully initialized, the non-blocking connect may return EINPROGRESS or EWOULDBLOCK
The code proceeds to the blocking accept call, but since the connection might never complete, the accept call may block indefinitely

Affected Versions:
2.0.18 and later version

My Reproduce Experience:
After I wake up my Windows system, sometimes my program call "ondisconnect" callback. Then my program called "mosquitto_new" function and stuck in "net__socketpair function in lib/net_mosq.c" forever.

Related Code:

		if(net__socket_nonblock(&spR)){
			COMPAT_CLOSE(listensock);
			continue;
		}
		if(connect(spR, (struct sockaddr *)&ss, ss_len) < 0){
#ifdef WIN32
			errno = WSAGetLastError();
#endif
			**if(errno != EINPROGRESS && errno != COMPAT_EWOULDBLOCK)**{
				COMPAT_CLOSE(spR);
				COMPAT_CLOSE(listensock);
				continue;
			}
		}
		**spW = accept(listensock, NULL, 0);**

[syou121]

Or maybe I use wrong method to reconnect... But I wonder if it is a question.

[syou121]

I found my firewall caused the problem, because it banned "localhost" when waking up computer. But the blocking problem of MQTT still happens.