From 8521fdea0e4cff0cb1e41c2ca62c3e9960b60c9d Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Fri, 10 Oct 2014 16:31:09 +0100
Subject: [PATCH] Reply with array of addresses for delegated query

---
 server/mdns_server.go | 16 ++++++++++------
 server/server.go      | 13 ++++++++++---
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/server/mdns_server.go b/server/mdns_server.go
index b9ccd6ba..d289b642 100644
--- a/server/mdns_server.go
+++ b/server/mdns_server.go
@@ -24,14 +24,18 @@ func NewMDNSServer(zone *ZoneDb) (*MDNSServer, error) {
 	return retval, nil
 }
 
-func makeDNSReply(r *dns.Msg, name string, addr net.IP) *dns.Msg {
+func makeDNSReply(r *dns.Msg, name string, addrs []net.IP) *dns.Msg {
 	m := new(dns.Msg)
 	m.SetReply(r)
 	m.RecursionAvailable = true
-	hdr := dns.RR_Header{Name: name, Rrtype: dns.TypeA,
-		Class: dns.ClassINET, Ttl: 3600}
-	a := &dns.A{hdr, addr}
-	m.Answer = append(m.Answer, a)
+	m.Answer = make([]dns.RR, len(addrs))
+	for i, addr := range addrs {
+		if ip4 := addr.To4(); ip4 != nil {
+			hdr := dns.RR_Header{Name: name, Rrtype: dns.TypeA,
+				Class: dns.ClassINET, Ttl: 3600}
+			m.Answer[i] = &dns.A{hdr, addr}
+		}
+	}
 	return m
 }
 
@@ -56,7 +60,7 @@ func (s *MDNSServer) Start(ifi *net.Interface) error {
 			q := r.Question[0]
 			ip, err := s.zone.MatchLocal(q.Name)
 			if err == nil {
-				m := makeDNSReply(r, q.Name, ip)
+				m := makeDNSReply(r, q.Name, []net.IP{ip})
 				s.SendResponse(m)
 			} else if s.addrIsLocal(w.RemoteAddr()) {
 				// ignore this - it's our own query received via multicast
diff --git a/server/server.go b/server/server.go
index 36adf65c..9a67701f 100644
--- a/server/server.go
+++ b/server/server.go
@@ -52,7 +52,7 @@ func queryHandler(zone Zone, mdnsClient *MDNSClient) dns.HandlerFunc {
 		q := r.Question[0]
 		ip, err := zone.MatchLocal(q.Name)
 		if err == nil {
-			m := makeDNSReply(r, q.Name, ip)
+			m := makeDNSReply(r, q.Name, []net.IP{ip})
 			w.WriteMsg(m)
 		} else {
 			log.Printf("Failed lookup for %s; sending mDNS query", q.Name)
@@ -62,7 +62,7 @@ func queryHandler(zone Zone, mdnsClient *MDNSClient) dns.HandlerFunc {
 				// Loop terminates when channel is closed by MDNSClient on timeout
 				for resp := range channel {
 					log.Printf("Got address response %s to query %s addr %s", resp.Name, q.Name, resp.Addr)
-					m := makeDNSReply(r, resp.Name, resp.Addr)
+					m := makeDNSReply(r, resp.Name, []net.IP{resp.Addr})
 					w.WriteMsg(m)
 				}
 			}()
@@ -77,7 +77,14 @@ func notUsHandler() dns.HandlerFunc {
 		q := r.Question[0]
 		addrs, err := net.LookupIP(q.Name)
 		if err == nil {
-			m := makeDNSReply(r, q.Name, addrs[0])
+			// Filter out ipv6 addresses
+			filtered := make([]net.IP, 0)
+			for _, addr := range addrs {
+				if ip4 := addr.To4(); ip4 != nil {
+					filtered = append(filtered, ip4)
+				}
+			}
+			m := makeDNSReply(r, q.Name, filtered)
 			w.WriteMsg(m)
 		} else {
 			m := makeDNSFailResponse(r)