plugin/kubernetes: PTR/A reverse query corner cases (#1551)

* better handle non PTR rev zone qrys

* vice versa

* tests

* comment typo

* much cleaner

plugin/kubernetes/kubernetes.go

@@ -274,6 +274,10 @@ func (k *Kubernetes) Records(state request.Request, exact bool) ([]msg.Service,
 		return nil, e
 	}
 
+	if dnsutil.IsReverse(state.Name()) {
+		return nil, errNoItems
+	}
+
 	if !wildcard(r.namespace) && !k.namespaceExposed(r.namespace) {
 		return nil, errNsNotExposed
 	}

plugin/kubernetes/reverse.go

@@ -14,7 +14,8 @@ func (k *Kubernetes) Reverse(state request.Request, exact bool, opt plugin.Optio
 
 	ip := dnsutil.ExtractAddressFromReverse(state.Name())
 	if ip == "" {
-		return nil, nil
+		_, e := k.Records(state, exact)
+		return nil, e
 	}
 
 	records := k.serviceRecordForIP(ip, state.Name())

plugin/kubernetes/reverse_test.go

@@ -18,12 +18,35 @@ func (APIConnReverseTest) HasSynced() bool                 { return true }
 func (APIConnReverseTest) Run()                            { return }
 func (APIConnReverseTest) Stop() error                     { return nil }
 func (APIConnReverseTest) PodIndex(string) []*api.Pod      { return nil }
-func (APIConnReverseTest) SvcIndex(string) []*api.Service  { return nil }
 func (APIConnReverseTest) EpIndex(string) []*api.Endpoints { return nil }
 func (APIConnReverseTest) EndpointsList() []*api.Endpoints { return nil }
 func (APIConnReverseTest) ServiceList() []*api.Service     { return nil }
 func (APIConnReverseTest) Modified() int64                 { return 0 }
 
+func (APIConnReverseTest) SvcIndex(svc string) []*api.Service {
+	if svc != "svc1.testns" {
+		return nil
+	}
+	svcs := []*api.Service{
+		{
+			ObjectMeta: meta.ObjectMeta{
+				Name:      "svc1",
+				Namespace: "testns",
+			},
+			Spec: api.ServiceSpec{
+				ClusterIP: "192.168.1.100",
+				Ports: []api.ServicePort{{
+					Name:     "http",
+					Protocol: "tcp",
+					Port:     80,
+				}},
+			},
+		},
+	}
+	return svcs
+
+}
+
 func (APIConnReverseTest) SvcIndexReverse(ip string) []*api.Service {
 	if ip != "192.168.1.100" {
 		return nil
@@ -162,11 +185,32 @@ func TestReverse(t *testing.T) {
 		},
 		{
 			Qname: "example.org.cluster.local.", Qtype: dns.TypePTR,
+			Rcode: dns.RcodeNameError,
+			Ns: []dns.RR{
+				test.SOA("cluster.local.       300     IN      SOA     ns.dns.cluster.local. hostmaster.cluster.local. 1502989566 7200 1800 86400 60"),
+			},
+		},
+		{
+			Qname: "svc1.testns.svc.cluster.local.", Qtype: dns.TypePTR,
 			Rcode: dns.RcodeSuccess,
 			Ns: []dns.RR{
 				test.SOA("cluster.local.       300     IN      SOA     ns.dns.cluster.local. hostmaster.cluster.local. 1502989566 7200 1800 86400 60"),
 			},
 		},
+		{
+			Qname: "svc1.testns.svc.0.10.in-addr.arpa.", Qtype: dns.TypeA,
+			Rcode: dns.RcodeNameError,
+			Ns: []dns.RR{
+				test.SOA("0.10.in-addr.arpa.       300     IN      SOA     ns.dns.0.10.in-addr.arpa. hostmaster.0.10.in-addr.arpa. 1502989566 7200 1800 86400 60"),
+			},
+		},
+		{
+			Qname: "100.0.0.10.cluster.local.", Qtype: dns.TypePTR,
+			Rcode: dns.RcodeNameError,
+			Ns: []dns.RR{
+				test.SOA("cluster.local.       300     IN      SOA     ns.dns.cluster.local. hostmaster.cluster.local. 1502989566 7200 1800 86400 60"),
+			},
+		},
 	}
 
 	ctx := context.TODO()

plugin/pkg/dnsutil/reverse.go

@@ -29,6 +29,11 @@ func ExtractAddressFromReverse(reverseName string) string {
 	return f(strings.Split(search, "."))
 }
 
+// IsReverse returns true if name is in a reverse zone
+func IsReverse(name string) bool {
+	return strings.HasSuffix(name, v4arpaSuffix) || strings.HasSuffix(name, v6arpaSuffix)
+}
+
 func reverse(slice []string) string {
 	for i := 0; i < len(slice)/2; i++ {
 		j := len(slice) - i - 1