Thread: Non-blocking connect()?

Every time I call connect() on a host that isn't alive it takes like 30 seconds to complete... I want to minimize this time by specifying my own "timeout", so say... I want a timeout of 5 seconds, if connect() cannot find the host in 5 seconds then the function returns. I'm looking on MSDN and all I can see it say is this:

Code:

With a nonblocking socket, the connection attempt cannot be completed immediately. In this case, connect will return 
SOCKET_ERROR, and WSAGetLastError will return WSAEWOULDBLOCK. In this case, there are three possible scenarios:

* Use the select function to determine the completion of the connection request by checking to see if the socket is writeable.

But the only problem is that MSDN doesn't mention HOW to make the socket or connect() nonblocking.

So I'm just wondering how I can do this, I'm going to be using a function Check_Host() and I'm guessing I'll need a non-blocking connect(), then a call to select() with a timeout specified of 5 seconds or whatever I choose, and if select() errors after that 5 seconds the host is assumed not alive.

Only problem is I have no idea how to do the whole non-blocking thing Thanks.

Originally Posted by bithub

Your assumption is pretty much correct. Just call select() on the nonblocking socket to see if it is writable. If select() times out, then the socket still hasn't connected after your timeout time. You can then call closesocket() on that socket and assume that the connection failed. Keep in mind that on some slow hosts, it is entirely possible that a connection attempt could take longer than 5 seconds.

Thanks for the reply. Ok well that's good to know, only problem now is I'm still uncertain how I'm supposed to put my socket in nonblocking state

Originally Posted by pobri19

But the only problem is that MSDN doesn't mention HOW to make the socket or connect() nonblocking.

Originally Posted by bithub

Code:

fcntl(sockfd, F_SETFL, O_NONBLOCK);

Is that not a linux thing? I don't see fcntl() mentioned on MSDN. When I google for it, the examples say include "fcntl.h", the compiler seems to acknowledge the file is there (because it doesn't say file not found) but it still says

Code:

'fcntl': identifier not found
'F_SETFL' : undeclared identifier
'O_NONBLOCK' : undeclared identifier

When I try and compile if my program calls fcntl().

Originally Posted by bithub

Sorry, forgot you were using Windows. Use ioctlsocket() instead of fcntl().

Thanks

Hmm this is my attempt but it doesn't appear to be working :/ Says that the host is down even if it isn't.

Code:

int Host_Alive(arguments * args) {
	args->serv.sin_addr.S_un.S_addr = inet_addr(args->sz_address);
	args->serv.sin_family = AF_INET;
	args->serv.sin_port = htons(args->port);

	args->sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
 
	unsigned long iMode = 0;
	ioctlsocket(args->sockfd, FIONBIO, &iMode); // put socket in non-blocking state
 
	fd_set socket_set;
	timeval timer;
 
	socket_set.fd_array[0] = args->sockfd;
	socket_set.fd_count = 1;
 
	timer.tv_sec = args->timeout;
 
	int ret = select(0, &socket_set, &socket_set, &socket_set, &timer);
 
	if (!ret || ret == SOCKET_ERROR) {
		printf("[!] Host %s:%d not alive!\n", args->sz_address, args->port);
		free(args);
		closesocket(args->sockfd);
		return 0;
	}
 
	else
		printf("[!] Host up!\n");
 
	free(args);
	closesocket(args->sockfd);
 
	return 1;
}

How about printing out what ret is, so you know why it's giving the error.


Quzah.