k8s/autopath: Add CNAMES (#771)

* Add unit tests & cnames

* more progress

* fix

* next mw dependent unit tests

* add tests for OnNXDOMAIN

* Add AAAA and ndots unit tests; fix request.NewWithQuestion

* Correct default value in README

* add CNAMEs to readme

* review

* fix autopath examples

* fix and test CNAME response order

1 files changed, 33 insertions, 18 deletions

diff --git a/middleware/kubernetes/handler.go b/middleware/kubernetes/handler.go
index f1a247923..a5916ccf7 100644
--- a/middleware/kubernetes/handler.go
+++ b/middleware/kubernetes/handler.go
@@ -6,7 +6,6 @@ import (
 
 	"github.com/coredns/coredns/middleware"
 	"github.com/coredns/coredns/middleware/pkg/dnsutil"
-	"github.com/coredns/coredns/middleware/rewrite"
 	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
@@ -23,7 +22,6 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 	m := new(dns.Msg)
 	m.SetReply(r)
 	m.Authoritative, m.RecursionAvailable, m.Compress = true, true, true
-
 	// Check that query matches one of the zones served by this middleware,
 	// otherwise delegate to the next in the pipeline.
 	zone := middleware.Zones(k.Zones).Matches(state.Name())
@@ -40,10 +38,10 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 		// Set the zone to this specific request.
 		zone = state.Name()
 	}
-
 	records, extra, _, err := k.routeRequest(zone, state)
 
-	if k.AutoPath.Enabled && k.IsNameError(err) {
+	// Check for Autopath search eligibility
+	if k.AutoPath.Enabled && k.IsNameError(err) && (state.QType() == dns.TypeA || state.QType() == dns.TypeAAAA) {
 		p := k.findPodWithIP(state.IP())
 		for p != nil {
 			name, path, ok := splitSearch(zone, state.QName(), p.Namespace)
@@ -53,38 +51,50 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 			if (dns.CountLabel(name) - 1) < k.AutoPath.NDots {
 				break
 			}
-			// Search "svc.cluster.local" and "cluster.local"
+			origQName := state.QName()
+			// Search "svc.cluster.local." and "cluster.local."
 			for i := 0; i < 2; i++ {
 				path = strings.Join(dns.SplitDomainName(path)[1:], ".")
-				state = state.NewWithQuestion(strings.Join([]string{name, path}, "."), state.QType())
-				records, extra, _, err = k.routeRequest(zone, state)
+				newstate := state.NewWithQuestion(strings.Join([]string{name, path}, "."), state.QType())
+				records, extra, _, err = k.routeRequest(zone, newstate)
 				if !k.IsNameError(err) {
+					records = append(records, nil)
+					copy(records[1:], records)
+					records[0] = newCNAME(origQName, records[0].Header().Name, records[0].Header().Ttl)
 					break
 				}
 			}
 			if !k.IsNameError(err) {
 				break
 			}
-			// Fallthrough with the host search path (if set)
-			wr := rewrite.NewResponseReverter(w, r)
+			// Try host search path (if set) in the next middleware
+			apw := NewAutoPathWriter(w, r)
 			for _, hostsearch := range k.AutoPath.HostSearchPath {
-				r = state.NewWithQuestion(strings.Join([]string{name, hostsearch}, "."), state.QType()).Req
-				rcode, nextErr := middleware.NextOrFailure(k.Name(), k.Next, ctx, wr, r)
-				if rcode == dns.RcodeSuccess {
+				newstate := state.NewWithQuestion(strings.Join([]string{name, hostsearch}, "."), state.QType())
+				rcode, nextErr := middleware.NextOrFailure(k.Name(), k.Next, ctx, apw, newstate.Req)
+				if apw.Sent {
 					return rcode, nextErr
 				}
 			}
 			// Search . in this middleware
-			state = state.NewWithQuestion(strings.Join([]string{name, "."}, ""), state.QType())
-			records, extra, _, err = k.routeRequest(zone, state)
+			newstate := state.NewWithQuestion(strings.Join([]string{name, "."}, ""), state.QType())
+			records, extra, _, err = k.routeRequest(zone, newstate)
 			if !k.IsNameError(err) {
+				records = append(records, nil)
+				copy(records[1:], records)
+				records[0] = newCNAME(origQName, records[0].Header().Name, records[0].Header().Ttl)
 				break
 			}
 			// Search . in the next middleware
-			r = state.Req
-			rcode, nextErr := middleware.NextOrFailure(k.Name(), k.Next, ctx, wr, r)
-			if rcode == dns.RcodeNameError {
-				rcode = k.AutoPath.OnNXDOMAIN
+			apw.Rcode = k.AutoPath.OnNXDOMAIN
+			newstate = state.NewWithQuestion(strings.Join([]string{name, "."}, ""), state.QType())
+			r = newstate.Req
+			rcode, nextErr := middleware.NextOrFailure(k.Name(), k.Next, ctx, apw, r)
+			if !apw.Sent && nextErr == nil {
+				r = dnsutil.Dedup(r)
+				state.SizeAndDo(r)
+				r, _ = state.Scrub(r)
+				apw.ForceWriteMsg(r)
 			}
 			return rcode, nextErr
 		}
@@ -115,6 +125,11 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 	return dns.RcodeSuccess, nil
 }
 
+func newCNAME(name string, target string, ttl uint32) *dns.CNAME {
+	// TODO factor this out and put in dnsutil
+	return &dns.CNAME{Hdr: dns.RR_Header{Name: name, Rrtype: dns.TypeCNAME, Class: dns.ClassINET, Ttl: ttl}, Target: dns.Fqdn(target)}
+}
+
 func (k *Kubernetes) routeRequest(zone string, state request.Request) (records []dns.RR, extra []dns.RR, debug []dns.RR, err error) {
 	switch state.Type() {
 	case "A":