add plugin code from coredns/plugin/kubernetes

Author: WangXiangUSTC

Diff for: autopath.go

@@ -0,0 +1,62 @@
+package kubernetes
+
+import (
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/kubernetes/object"
+	"github.com/coredns/coredns/request"
+)
+
+// AutoPath implements the AutoPathFunc call from the autopath plugin.
+// 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 authoritative for and thus if we want autopath.
+	zone := plugin.Zones(k.Zones).Matches(state.Name())
+	if zone == "" {
+		return nil
+	}
+
+	// cluster.local {
+	//    autopath @kubernetes
+	//    kubernetes {
+	//        pods verified #
+	//    }
+	// }
+	// if pods != verified will cause panic and return SERVFAIL, expect worked as normal without autopath function
+	if !k.opts.initPodCache {
+		return nil
+	}
+
+	ip := state.IP()
+
+	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, "") // sentinel
+	return search
+}
+
+// podWithIP return the api.Pod for source IP. It returns nil if nothing can be found.
+func (k *Kubernetes) podWithIP(ip string) *object.Pod {
+	if k.podMode != podModeVerified {
+		return nil
+	}
+	ps := k.APIConn.PodIndex(ip)
+	if len(ps) == 0 {
+		return nil
+	}
+	return ps[0]
+}