Improve the mingw getaddrinfo stub to handle more use cases

Allow the node parameter to be null, which is used for getting
the default bind address.

Also allow the hints parameter to be null, to improve standard
conformance of the stub implementation a little.

Signed-off-by: Martin Storsjo <martin@martin.st>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -1039,19 +1039,22 @@ static int WSAAPI getaddrinfo_stub(const char *node, const char *service,
 				   const struct addrinfo *hints,
 				   struct addrinfo **res)
 {
-	struct hostent *h = gethostbyname(node);
+	struct hostent *h = NULL;
 	struct addrinfo *ai;
 	struct sockaddr_in *sin;
 
-	if (!h)
-		return WSAGetLastError();
+	if (node) {
+		h = gethostbyname(node);
+		if (!h)
+			return WSAGetLastError();
+	}
 
 	ai = xmalloc(sizeof(struct addrinfo));
 	*res = ai;
 	ai->ai_flags = 0;
 	ai->ai_family = AF_INET;
-	ai->ai_socktype = hints->ai_socktype;
-	switch (hints->ai_socktype) {
+	ai->ai_socktype = hints ? hints->ai_socktype : 0;
+	switch (ai->ai_socktype) {
 	case SOCK_STREAM:
 		ai->ai_protocol = IPPROTO_TCP;
 		break;
@@ -1063,14 +1066,25 @@ static int WSAAPI getaddrinfo_stub(const char *node, const char *service,
 		break;
 	}
 	ai->ai_addrlen = sizeof(struct sockaddr_in);
-	ai->ai_canonname = strdup(h->h_name);
+	if (hints && (hints->ai_flags & AI_CANONNAME))
+		ai->ai_canonname = h ? strdup(h->h_name) : NULL;
+	else
+		ai->ai_canonname = NULL;
 
 	sin = xmalloc(ai->ai_addrlen);
 	memset(sin, 0, ai->ai_addrlen);
 	sin->sin_family = AF_INET;
+	/* Note: getaddrinfo is supposed to allow service to be a string,
+	 * which should be looked up using getservbyname. This is
+	 * currently not implemented */
 	if (service)
 		sin->sin_port = htons(atoi(service));
-	sin->sin_addr = *(struct in_addr *)h->h_addr;
+	if (h)
+		sin->sin_addr = *(struct in_addr *)h->h_addr;
+	else if (hints && (hints->ai_flags & AI_PASSIVE))
+		sin->sin_addr.s_addr = INADDR_ANY;
+	else
+		sin->sin_addr.s_addr = INADDR_LOOPBACK;
 	ai->ai_addr = (struct sockaddr *)sin;
 	ai->ai_next = 0;
 	return 0;