Re: [PATCH] ipv6 rework in udp_establish_listener

Pascal Terjan, le Wed 17 Aug 2005 14:36:37 +0200, a écrit :
> (talking only for my patch, not the other ipv6 patches that I did not
> yet really read but I think it uses getaddrinfo so will be more tricky 
> to have working...)

No, it's _much_ easier to make working than using AF_INET6 & co by
hand. getaddrinfo gives you every information you need: address family,
protocol, address, ... You just need a HAVE_GETADDRINFO, and then you
can use a loop like:

int sock;
struct addrinfo hints, *res, *cur;
memset(&hints,0,sizeof(hints));
hints.ai_flags = AI_PASSIVE;
hints.ai_family = PF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
if (getaddrinfo(NULL, listen_port, &hints, &res) != 0) {
	/* handle error */
} else {
	for (cur = res; cur; cur = cur->ai_next) {
		if ((sock = socket(cur->ai_family, cur->ai_socktype, cur->ai_protocol)) <0) {
			if (errno != EAFNOSUPPORT) {
				/* warn about error */
			}
			continue;
		}
		if (bind(sock, cur->ai_addr, cur->ai_addrlen)) {
			/* warn about error */
			close(sock);
			continue;
		}
		if (listen(sock, 1)) {
			/* warn about error */
			close(sock);
			continue;
		}
		/* did it */
		break;
	}
	freeaddrinfo(res);
	if (cur)
		return sock;
	else {
		/* print error: failed to find a way to establish server
		 */
		 return -1;
	}
}

This will correctly look through all adress families and protocols that
can provide a "passive" "stream" service, and establish a listening
socket for the first that succeeds (when both libc _and_ kernel support
ipv6).

No #ifdef foo6 or #ifdef HAVE_GETNAMEINFO... Just #ifdef
HAVE_GETADDRINFO, and you've got fully IPv4 _and_ IPv6 working code.

Note that this loop is just about the same for establishing a
connection. And it will correctly try the different IPs that could be
associated with a dns name, in case the first ones don't work.

This really _is_ the preferred way to implement things nowadays.

Regards,
Samuel