middleware/kubernetes: put reverse function in own file (#863)

Move reverse function and (some) test code to reverse*.go

middleware/kubernetes/reverse.go

@@ -0,0 +1,32 @@
+package kubernetes
+
+import (
+	"net"
+
+	"github.com/coredns/coredns/middleware"
+	"github.com/coredns/coredns/middleware/etcd/msg"
+	"github.com/coredns/coredns/middleware/pkg/dnsutil"
+	"github.com/coredns/coredns/request"
+)
+
+// Reverse implements the ServiceBackend interface.
+func (k *Kubernetes) Reverse(state request.Request, exact bool, opt middleware.Options) ([]msg.Service, []msg.Service, error) {
+
+	ip := dnsutil.ExtractAddressFromReverse(state.Name())
+	if ip == "" {
+		return nil, nil, nil
+	}
+
+	records := k.getServiceRecordForIP(ip, state.Name())
+	return records, nil, nil
+}
+
+func (k *Kubernetes) isRequestInReverseRange(name string) bool {
+	ip := dnsutil.ExtractAddressFromReverse(name)
+	for _, c := range k.ReverseCidrs {
+		if c.Contains(net.ParseIP(ip)) {
+			return true
+		}
+	}
+	return false
+}