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/setup.go

@@ -62,6 +62,8 @@ func kubernetesParse(c *caddy.Controller) (*Kubernetes, error) {
 		Proxy:              proxy.Proxy{},
 	}
 
+	k8s.autoPathSearch = searchFromResolvConf()
+
 	for c.Next() {
 		if c.Val() == "kubernetes" {
 			zones := c.RemainingArgs()
@@ -202,6 +204,15 @@ func kubernetesParse(c *caddy.Controller) (*Kubernetes, error) {
 	return nil, errors.New("kubernetes setup called without keyword 'kubernetes' in Corefile")
 }
 
+func searchFromResolvConf() []string {
+	rc, err := dns.ClientConfigFromFile("/etc/resolv.conf")
+	if err != nil {
+		return nil
+	}
+	middleware.Zones(rc.Search).Normalize()
+	return rc.Search
+}
+
 const (
 	defaultResyncPeriod = 5 * time.Minute
 	defautNdots         = 0