[LEDE-DEV] [PATCH mdns] Fix sending replies to PTR questions

[Rafał Miłecki]

From: Rafał Miłecki <rafal at milecki.pl>

When we receive PTR question it includes hostname (instance), e.g.:
mdnsd: parse_question (391): Q -> PTR lede._http._tcp.local

First of all we should check if it matches hostname we use before trying
to reply. Secondly service_reply expects service with domain appended
(without hostname/instance) so we need to strip received string out of
hostname before passing it.

Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
---
 dns.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/dns.c b/dns.c
index 91434f2..dac6f2c 100644
--- a/dns.c
+++ b/dns.c
@@ -367,9 +367,19 @@ parse_question(struct interface *iface, char *name, struct dns_question *q)
 		break;
 
 	case TYPE_PTR:
-		if (!strcmp(name, sdudp))
+		if (!strcmp(name, sdudp)) {
 			service_announce_services(iface, announce_ttl);
-		service_reply(iface, name, announce_ttl);
+		} else {
+			/* First dot separates instance name from the rest */
+			char *dot = strchr(name, '.');
+			/* Length of queried instance */
+			size_t len = dot ? dot - name : 0;
+
+			/* Make sure it's query for the instance name we use */
+			if (len && len == strlen(mdns_hostname) &&
+			    !strncmp(name, mdns_hostname, len))
+				service_reply(iface, dot + 1, announce_ttl);
+		}
 		break;
 
 	case TYPE_AAAA:
-- 
2.11.0