middleware/authpath: Fix return from k8s mw (#871)

* middleware/authpath: Fix return from k8s mw

Return the correct search path from the kubernetes' AutoPath function.
Based on preliminary discussion in #870

* PodWithIP can be private

Fix and add docs to functions.

* CR: remove the error from AutoPathFunc

middleware/kubernetes/autopath.go

@@ -1,32 +1,46 @@
 package kubernetes
 
 import (
-	"fmt"
-
+	"github.com/coredns/coredns/middleware"
 	"github.com/coredns/coredns/request"
 
 	"k8s.io/client-go/1.5/pkg/api"
 )
 
-func (k *Kubernetes) AutoPath(state request.Request) ([]string, error) {
-	ip := state.IP()
-
-	pod := k.PodWithIP(ip)
-	if pod == nil {
-		return nil, fmt.Errorf("kubernets: no pod found for %s", ip)
+// AutoPath implements the AutoPathFunc call from the autopath middleware.
+// It returns a per-query search path or nil indicating no searchpathing should happen.
+func (k *Kubernetes) AutoPath(state request.Request) []string {
+	// Check if the query falls in a zone we are actually authoriative for and thus if we want autopath.
+	zone := middleware.Zones(k.Zones).Matches(state.Name())
+	if zone == "" {
+		return nil
 	}
 
-	// something something namespace
-	namespace := pod.Namespace
+	ip := state.IP()
 
-	search := []string{namespace} // TODO: way more
+	pod := k.podWithIP(ip)
+	if pod == nil {
+		return nil
+	}
 
+	search := make([]string, 3)
+	if zone == "." {
+		search[0] = pod.Namespace + ".svc."
+		search[1] = "svc."
+		search[2] = "."
+	} else {
+		search[0] = pod.Namespace + ".svc." + zone
+		search[1] = "svc." + zone
+		search[2] = zone
+	}
+
+	search = append(search, k.autoPathSearch...)
 	search = append(search, "") // sentinal
-	return search, nil
+	return search
 }
 
-// PodWithIP return the api.Pod for source IP ip. It return nil if nothing can be found.
-func (k *Kubernetes) PodWithIP(ip string) (p *api.Pod) {
+// podWithIP return the api.Pod for source IP ip. It returns nil if nothing can be found.
+func (k *Kubernetes) podWithIP(ip string) (p *api.Pod) {
 	objList := k.APIConn.PodIndex(ip)
 	for _, o := range objList {
 		p, ok := o.(*api.Pod)