No SERVFAIL and no forwarding multicast names (#86)

* Return NXDOMAIN instead of SERVFAIL

* Actually reorder template and return noerror

Author: mdegat01

Dockerfile

@@ -17,6 +17,8 @@ RUN \
     && git clone --depth 1 -b v${COREDNS_VERSION} https://github.com/coredns/coredns \
     && cp -rf plugins/* coredns/plugin/ \
     && cd coredns \
+    && sed -i "/^template:template/d" plugin.cfg \
+    && sed -i "/^hosts:.*/a template:template" plugin.cfg \
     && sed -i "/^forward:.*/i fallback:fallback" plugin.cfg \
     && sed -i "/^hosts:.*/a mdns:mdns" plugin.cfg \
     && sed -i "/route53:route53/d" plugin.cfg \

plugins/mdns/mdns.go

@@ -69,6 +69,7 @@ func (m MDNS) AddARecord(msg *dns.Msg, state *request.Request, name string, addr
 }
 
 func (m MDNS) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	// If systemd-resolved isn't available, plugin can't do anything. Pass to the next one.
 	if m.Resolver == nil {
 		return plugin.NextOrFailure(m.Name(), m.Next, ctx, w, r)
 	}
@@ -99,14 +100,16 @@ func (m MDNS) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (i
 		// There may be uncommon errors though so not swallowing it while debugging
 		log.Debug(err)
 
-	} else if m.AddARecord(msg, &state, hostName, addresses) {
+	} else {
+		m.AddARecord(msg, &state, hostName, addresses)
 		log.Debug(msg)
-		w.WriteMsg(msg)
-		return dns.RcodeSuccess, nil
 	}
 
-	log.Debugf("No records found for '%s', forwarding to next plugin.", state.QName())
-	return plugin.NextOrFailure(m.Name(), m.Next, ctx, w, r)
+	// Plugin only processes A and AAAA type multicast queries (.local or single name)
+	// Whether an answer was found or not this is end of the line, do not forward to external resolvers
+	// Always return NOERROR since we are not authoritative for this domain
+	w.WriteMsg(msg)
+	return dns.RcodeSuccess, nil
 }
 
 func GetPrimaryInterface(ctx context.Context, resolver *resolve1.Manager) int32 {

rootfs/usr/share/tempio/corefile

@@ -11,6 +11,9 @@
     template ANY AAAA local.hass.io hassio {
         rcode NOERROR
     }
+    template ANY A local.hass.io hassio {
+        rcode NXDOMAIN
+    }
     mdns
     forward . {{ join " " .servers }} {{ if len .locals | eq 0 }}dns://127.0.0.11{{ else }}{{ join " " .locals }}{{ end }} {
         except local.hass.io