net: dns: Resolve localhost name

Allow user to query localhost name and get a localhost address
127.0.0.1 or ::1 back. This is only enabled if loopback driver
is used as the use case does not make much sense otherwise.

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

subsys/net/lib/dns/resolve.c

@@ -1827,6 +1827,48 @@ int dns_resolve_name_internal(struct dns_resolve_context *ctx,
 	ARG_UNUSED(use_cache);
 #endif /* CONFIG_DNS_RESOLVER_CACHE */
 
+	/* If we get a query to localhost, then short circuit early */
+	if ((IS_ENABLED(CONFIG_NET_LOOPBACK) || IS_ENABLED(CONFIG_NET_TEST)) &&
+	    strcmp(query, "localhost") == 0) {
+		struct dns_addrinfo info = { 0 };
+
+		if (type == DNS_QUERY_TYPE_A) {
+			if (!IS_ENABLED(CONFIG_NET_IPV4)) {
+				return -EAFNOSUPPORT;
+			}
+
+			struct in_addr addr4 = INADDR_LOOPBACK_INIT;
+
+			memcpy(&net_sin(&info.ai_addr)->sin_addr, &addr4,
+			       sizeof(struct in_addr));
+
+			info.ai_family = AF_INET;
+			info.ai_addr.sa_family = AF_INET;
+			info.ai_addrlen = sizeof(struct sockaddr_in);
+
+		} else if (type == DNS_QUERY_TYPE_AAAA) {
+			if (!IS_ENABLED(CONFIG_NET_IPV6)) {
+				return -EAFNOSUPPORT;
+			}
+
+			struct in6_addr addr6 = IN6ADDR_LOOPBACK_INIT;
+
+			memcpy(&net_sin6(&info.ai_addr)->sin6_addr, &addr6,
+			       sizeof(struct in6_addr));
+
+			info.ai_family = AF_INET6;
+			info.ai_addr.sa_family = AF_INET6;
+			info.ai_addrlen = sizeof(struct sockaddr_in6);
+		} else {
+			return -EINVAL;
+		}
+
+		cb(DNS_EAI_INPROGRESS, &info, user_data);
+		cb(DNS_EAI_ALLDONE, NULL, user_data);
+
+		return 0;
+	}
+
 	if (IS_ENABLED(CONFIG_NET_HOSTNAME_ENABLE)) {
 		const char *hostname = net_hostname_get();
 		struct dns_addrinfo info = { 0 };