plugin/kubernetes: correctly set NODATA for ns (#1229)

* plugin/kubernetes: Add GetNamespaceByName

A bare or wildcard query for just the namespace should return NODATA,
not NXDOMAIN, otherwise we deny the entirety of the names under the
namespace.

Add test to check for this in pod verified mode.

* Review

More comments and move namespace code to namespace.go

plugin/kubernetes/kubernetes.go

@@ -304,7 +304,14 @@ func (k *Kubernetes) findPods(r recordRequest, zone string) (pods []msg.Service,
 	podname := r.service
 	zonePath := msg.Path(zone, "coredns")
 	ip := ""
+
 	err = errNoItems
+	if wildcard(podname) && !wildcard(namespace) {
+		// If namespace exist, err should be nil, so that we return nodata instead of NXDOMAIN
+		if k.namespace(namespace) {
+			err = nil
+		}
+	}
 
 	if strings.Count(podname, "-") == 3 && !strings.Contains(podname, "--") {
 		ip = strings.Replace(podname, "-", ".", -1)
@@ -336,7 +343,14 @@ func (k *Kubernetes) findPods(r recordRequest, zone string) (pods []msg.Service,
 // findServices returns the services matching r from the cache.
 func (k *Kubernetes) findServices(r recordRequest, zone string) (services []msg.Service, err error) {
 	zonePath := msg.Path(zone, "coredns")
-	err = errNoItems // Set to errNoItems to signal really nothing found, gets reset when name is matched.
+
+	err = errNoItems
+	if wildcard(r.service) && !wildcard(r.namespace) {
+		// If namespace exist, err should be nil, so that we return nodata instead of NXDOMAIN
+		if k.namespace(namespace) {
+			err = nil
+		}
+	}
 
 	var (
 		endpointsListFunc func() []*api.Endpoints
@@ -449,15 +463,6 @@ func wildcard(s string) bool {
 	return s == "*" || s == "any"
 }
 
-// namespaceExposed returns true when the namespace is exposed.
-func (k *Kubernetes) namespaceExposed(namespace string) bool {
-	_, ok := k.Namespaces[namespace]
-	if len(k.Namespaces) > 0 && !ok {
-		return false
-	}
-	return true
-}
-
 const (
 	// Svc is the DNS schema for kubernetes services
 	Svc = "svc"