plugin/etcd: small refactor (#1749)

* plugin/etcd: small refactor

I think this function can be smaller.

* and make it compile

plugin/backend_lookup.go

@@ -14,7 +14,7 @@ import (
 
 // A returns A records from Backend or an error.
 func A(b ServiceBackend, zone string, state request.Request, previousRecords []dns.RR, opt Options) (records []dns.RR, err error) {
-	services, err := checkZoneForRecord(b, zone, state, opt)
+	services, err := checkForApex(b, zone, state, opt)
 	if err != nil {
 		return nil, err
 	}
@@ -78,7 +78,7 @@ func A(b ServiceBackend, zone string, state request.Request, previousRecords []d
 
 // AAAA returns AAAA records from Backend or an error.
 func AAAA(b ServiceBackend, zone string, state request.Request, previousRecords []dns.RR, opt Options) (records []dns.RR, err error) {
-	services, err := checkZoneForRecord(b, zone, state, opt)
+	services, err := checkForApex(b, zone, state, opt)
 	if err != nil {
 		return nil, err
 	}
@@ -403,37 +403,26 @@ func newAddress(s msg.Service, name string, ip net.IP, what uint16) dns.RR {
 	return &dns.AAAA{Hdr: hdr, AAAA: ip}
 }
 
-func checkZoneForRecord(b ServiceBackend, zone string, state request.Request, opt Options) ([]msg.Service, error) {
-	var services []msg.Service
-	var err error
-	// if the zone name itself is queried we fake the query to search for a special entry
-	// this is equivalent to the NS search code
-	if state.Name() == zone {
+// checkForApex checks the spcecial apex.dns directory for records that will be returned as A or AAAA.
+func checkForApex(b ServiceBackend, zone string, state request.Request, opt Options) ([]msg.Service, error) {
+	if state.Name() != zone {
+		return b.Services(state, false, opt)
+	}
+
+	// If the zone name itself is queried we fake the query to search for a special entry
+	// this is equivalent to the NS search code.
 	old := state.QName()
 	state.Clear()
 	state.Req.Question[0].Name = dnsutil.Join([]string{"apex.dns", zone})
 
-		services, err = b.Services(state, false, opt)
-		if err != nil {
-			// it might be possible, that "apex.dns.zone" does not exists
-			// we set back the query and try it once again to restore the backward compatibility behavior
+	services, err := b.Services(state, false, opt)
+	if err == nil {
 		state.Req.Question[0].Name = old
-			services, err = b.Services(state, false, opt)
-			// if it still errors, we return the error
-			if err != nil {
 		return services, err
 	}
-		}
 
 	state.Req.Question[0].Name = old
-	} else {
-		services, err = b.Services(state, false, opt)
-		if err != nil {
-			return services, err
-		}
-	}
-
-	return services, err
+	return b.Services(state, false, opt)
 }
 
 const hostmaster = "hostmaster"