Use the fallback for reverse lookups too

I considered a couple of different factorings, that is

 * Implementing the fallback as a Lookup
 * Having a server struct that held the resolv.conf and methods for
   handling queries

but ultimately, this is simple and works.

nameserver/server.go

@@ -51,6 +51,7 @@ func queryHandler(lookups []Lookup) dns.HandlerFunc {
 }
 
 func rdnsHandler(lookups []Lookup) dns.HandlerFunc {
+	fallback := notUsHandler()
 	return func(w dns.ResponseWriter, r *dns.Msg) {
 		q := r.Question[0]
 		Debug.Printf("Reverse query: %+v", q)
@@ -62,13 +63,12 @@ func rdnsHandler(lookups []Lookup) dns.HandlerFunc {
 					return
 				}
 			}
-			Info.Printf("[dns msgid %d] No results for type %s query %s",
-				r.MsgHdr.Id, dns.TypeToString[q.Qtype], q.Name)
+			fallback(w, r)
+			return
 		} else {
 			Warning.Printf("[dns msgid %d] Unexpected reverse query type %s: %+v",
 				r.MsgHdr.Id, dns.TypeToString[q.Qtype], q)
 		}
-		w.WriteMsg(makeDNSFailResponse(r))
 	}
 }
 
@@ -80,7 +80,7 @@ func notUsHandler() dns.HandlerFunc {
 	checkFatal(err)
 	return func(w dns.ResponseWriter, r *dns.Msg) {
 		q := r.Question[0]
-		Debug.Printf("[dns msgid %d] Non-local query: %+v", r.MsgHdr.Id, q)
+		Debug.Printf("[dns msgid %d] Fallback query: %+v", r.MsgHdr.Id, q)
 		for _, server := range config.Servers {
 			reply, err := dns.Exchange(r, fmt.Sprintf("%s:%s", server, config.Port))
 			if err != nil {

nameserver/server_test.go

@@ -78,5 +78,14 @@ func TestDNSServer(t *testing.T) {
 		t.Fatal("Number of answers > 0")
 	}
 
-	// Not testing MDNS functionality of server here (yet)
+	m.SetQuestion("8.8.8.8.in-addr.arpa.", dns.TypePTR)
+	r, _, err = c.Exchange(m, dnsAddr)
+	wt.AssertNoErr(t, err)
+	wt.AssertStatus(t, r.Rcode, dns.RcodeSuccess, "DNS success response code")
+	if !(len(r.Answer) > 0) {
+		t.Fatal("Number of answers > 0")
+	}
+
+	// Not testing MDNS functionality of server here (yet), since it
+	// needs two servers, each listening on its own address
 }