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/reverse.go

@@ -0,0 +1,55 @@
+package kubernetes
+
+import (
+	"strings"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/etcd/msg"
+	"github.com/coredns/coredns/plugin/pkg/dnsutil"
+	"github.com/coredns/coredns/request"
+)
+
+// Reverse implements the ServiceBackend interface.
+func (k *Kubernetes) Reverse(state request.Request, exact bool, opt plugin.Options) ([]msg.Service, error) {
+
+	ip := dnsutil.ExtractAddressFromReverse(state.Name())
+	if ip == "" {
+		return nil, nil
+	}
+
+	records := k.serviceRecordForIP(ip, state.Name())
+	return records, nil
+}
+
+// serviceRecordForIP gets a service record with a cluster ip matching the ip argument
+// If a service cluster ip does not match, it checks all endpoints
+func (k *Kubernetes) serviceRecordForIP(ip, name string) []msg.Service {
+	// First check services with cluster ips
+	svcList := k.APIConn.ServiceList()
+
+	for _, service := range svcList {
+		if (len(k.Namespaces) > 0) && !k.namespaceExposed(service.Namespace) {
+			continue
+		}
+		if service.Spec.ClusterIP == ip {
+			domain := strings.Join([]string{service.Name, service.Namespace, Svc, k.primaryZone()}, ".")
+			return []msg.Service{{Host: domain}}
+		}
+	}
+	// If no cluster ips match, search endpoints
+	epList := k.APIConn.EndpointsList()
+	for _, ep := range epList.Items {
+		if (len(k.Namespaces) > 0) && !k.namespaceExposed(ep.ObjectMeta.Namespace) {
+			continue
+		}
+		for _, eps := range ep.Subsets {
+			for _, addr := range eps.Addresses {
+				if addr.IP == ip {
+					domain := strings.Join([]string{endpointHostname(addr), ep.ObjectMeta.Name, ep.ObjectMeta.Namespace, Svc, k.primaryZone()}, ".")
+					return []msg.Service{{Host: domain}}
+				}
+			}
+		}
+	}
+	return nil
+}