Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/kubernetes/autopath.go

@@ -0,0 +1,53 @@
+package kubernetes
+
+import (
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/request"
+
+	"k8s.io/client-go/1.5/pkg/api"
+)
+
+// 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 authoriative for and thus if we want autopath.
+	zone := plugin.Zones(k.Zones).Matches(state.Name())
+	if zone == "" {
+		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, "") // sentinal
+	return search
+}
+
+// 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)
+		if !ok {
+			return nil
+		}
+		return p
+	}
+	return nil
+}