From 953a577ba29a553c22a08aefe0e1ecec7a4189d0 Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Thu, 2 Oct 2014 18:06:16 +0100
Subject: [PATCH] Add multicast

---
 dns/main.go | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/dns/main.go b/dns/main.go
index 2de4225b..f9182274 100644
--- a/dns/main.go
+++ b/dns/main.go
@@ -19,7 +19,26 @@ func makeDNSReply(r *dns.Msg, name string, addr net.IP) *dns.Msg {
 	return m
 }
 
+var mdnsClient *weavedns.MDNSClient
+
+func handleMDNS(w dns.ResponseWriter, r *dns.Msg) {
+	// Here we have to handle both requests incoming, responses to queries
+	// we sent out, and responses to queries that other nodes sent
+	// And we also get to see our own queries!
+	if len(r.Answer) > 0 {
+		mdnsClient.HandleResponse(r)
+	} else if len(r.Question) > 0 {
+		q := r.Question[0]
+		ip, err := zone.MatchLocal(q.Name)
+		if err == nil {
+			m := makeDNSReply(r, q.Name, net.ParseIP(ip))
+			mdnsClient.SendResponse(m)
+		}
+	}
+}
+
 func handleLocal(w dns.ResponseWriter, r *dns.Msg) {
+	log.Printf("Received message:", r)
 	q := r.Question[0]
 	ip, err := zone.MatchLocal(q.Name)
 	if err == nil {
@@ -27,6 +46,17 @@ func handleLocal(w dns.ResponseWriter, r *dns.Msg) {
 		w.WriteMsg(m)
 	} else {
 		log.Printf("Failed lookup for %s", q.Name)
+		// We don't know the answer; see if someone else does
+		channel := make(chan *weavedns.ResponseA, 4)
+		go func() {
+			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)
+				w.WriteMsg(m)
+			}
+			// FIXME: need to add a time-out either here or in mdnsClient
+		}()
+		mdnsClient.SendQuery(q.Name, dns.TypeA, channel)
 	}
 	return
 }
@@ -35,5 +65,20 @@ func main() {
 	LocalServeMux := dns.NewServeMux()
 	LocalServeMux.HandleFunc("local", handleLocal)
 	go weavedns.ListenHttp(zone)
+
+	MDNSServeMux := dns.NewServeMux()
+	MDNSServeMux.HandleFunc("local", handleMDNS)
+
+	conn, err := weavedns.LinkLocalMulticastListener()
+	if err != nil {
+		log.Fatal(err)
+	}
+	mdnsClient, err = weavedns.NewMDNSClient()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	go dns.ActivateAndServe(nil, conn, MDNSServeMux)
+
 	dns.ListenAndServe(":5300", "udp", LocalServeMux)
 }