plugin/etcd+kubernetes: Persist truncated state to client if CNAME lookup...

plugin/etcd+kubernetes: Persist truncated state to client if CNAME lookup response is truncated (#4715)

Persist the TC bit to client response for truncated CNAME lookups.
Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

plugin/backend_lookup.go

@@ -14,10 +14,10 @@ import (
 )
 
 // A returns A records from Backend or an error.
-func A(ctx context.Context, b ServiceBackend, zone string, state request.Request, previousRecords []dns.RR, opt Options) (records []dns.RR, err error) {
+func A(ctx context.Context, b ServiceBackend, zone string, state request.Request, previousRecords []dns.RR, opt Options) (records []dns.RR, truncated bool, err error) {
 	services, err := checkForApex(ctx, b, zone, state, opt)
 	if err != nil {
-		return nil, err
+		return nil, false, err
 	}
 
 	dup := make(map[string]struct{})
@@ -44,7 +44,7 @@ func A(ctx context.Context, b ServiceBackend, zone string, state request.Request
 			if dns.IsSubDomain(zone, dns.Fqdn(serv.Host)) {
 				state1 := state.NewWithQuestion(serv.Host, state.QType())
 				state1.Zone = zone
-				nextRecords, err := A(ctx, b, zone, state1, append(previousRecords, newRecord), opt)
+				nextRecords, tc, err := A(ctx, b, zone, state1, append(previousRecords, newRecord), opt)
 
 				if err == nil {
 					// Not only have we found something we should add the CNAME and the IP addresses.
@@ -53,6 +53,9 @@ func A(ctx context.Context, b ServiceBackend, zone string, state request.Request
 						records = append(records, nextRecords...)
 					}
 				}
+				if tc {
+					truncated = true
+				}
 				continue
 			}
 			// This means we can not complete the CNAME, try to look else where.
@@ -62,6 +65,9 @@ func A(ctx context.Context, b ServiceBackend, zone string, state request.Request
 			if e1 != nil {
 				continue
 			}
+			if m1.Truncated {
+				truncated = true
+			}
 			// Len(m1.Answer) > 0 here is well?
 			records = append(records, newRecord)
 			records = append(records, m1.Answer...)
@@ -77,14 +83,14 @@ func A(ctx context.Context, b ServiceBackend, zone string, state request.Request
 			// nada
 		}
 	}
-	return records, nil
+	return records, truncated, nil
 }
 
 // AAAA returns AAAA records from Backend or an error.
-func AAAA(ctx context.Context, b ServiceBackend, zone string, state request.Request, previousRecords []dns.RR, opt Options) (records []dns.RR, err error) {
+func AAAA(ctx context.Context, b ServiceBackend, zone string, state request.Request, previousRecords []dns.RR, opt Options) (records []dns.RR, truncated bool, err error) {
 	services, err := checkForApex(ctx, b, zone, state, opt)
 	if err != nil {
-		return nil, err
+		return nil, false, err
 	}
 
 	dup := make(map[string]struct{})
@@ -112,7 +118,7 @@ func AAAA(ctx context.Context, b ServiceBackend, zone string, state request.Requ
 			if dns.IsSubDomain(zone, dns.Fqdn(serv.Host)) {
 				state1 := state.NewWithQuestion(serv.Host, state.QType())
 				state1.Zone = zone
-				nextRecords, err := AAAA(ctx, b, zone, state1, append(previousRecords, newRecord), opt)
+				nextRecords, tc, err := AAAA(ctx, b, zone, state1, append(previousRecords, newRecord), opt)
 
 				if err == nil {
 					// Not only have we found something we should add the CNAME and the IP addresses.
@@ -121,6 +127,9 @@ func AAAA(ctx context.Context, b ServiceBackend, zone string, state request.Requ
 						records = append(records, nextRecords...)
 					}
 				}
+				if tc {
+					truncated = true
+				}
 				continue
 			}
 			// This means we can not complete the CNAME, try to look else where.
@@ -129,6 +138,9 @@ func AAAA(ctx context.Context, b ServiceBackend, zone string, state request.Requ
 			if e1 != nil {
 				continue
 			}
+			if m1.Truncated {
+				truncated = true
+			}
 			// Len(m1.Answer) > 0 here is well?
 			records = append(records, newRecord)
 			records = append(records, m1.Answer...)
@@ -145,7 +157,7 @@ func AAAA(ctx context.Context, b ServiceBackend, zone string, state request.Requ
 			}
 		}
 	}
-	return records, nil
+	return records, truncated, nil
 }
 
 // SRV returns SRV records from the Backend.
@@ -223,7 +235,7 @@ func SRV(ctx context.Context, b ServiceBackend, zone string, state request.Reque
 			// Internal name, we should have some info on them, either v4 or v6
 			// Clients expect a complete answer, because we are a recursor in their view.
 			state1 := state.NewWithQuestion(srv.Target, dns.TypeA)
-			addr, e1 := A(ctx, b, zone, state1, nil, opt)
+			addr, _, e1 := A(ctx, b, zone, state1, nil, opt)
 			if e1 == nil {
 				extra = append(extra, addr...)
 			}
@@ -289,7 +301,7 @@ func MX(ctx context.Context, b ServiceBackend, zone string, state request.Reques
 			}
 			// Internal name
 			state1 := state.NewWithQuestion(mx.Mx, dns.TypeA)
-			addr, e1 := A(ctx, b, zone, state1, nil, opt)
+			addr, _, e1 := A(ctx, b, zone, state1, nil, opt)
 			if e1 == nil {
 				extra = append(extra, addr...)
 			}
@@ -329,11 +341,11 @@ func CNAME(ctx context.Context, b ServiceBackend, zone string, state request.Req
 }
 
 // TXT returns TXT records from Backend or an error.
-func TXT(ctx context.Context, b ServiceBackend, zone string, state request.Request, previousRecords []dns.RR, opt Options) (records []dns.RR, err error) {
+func TXT(ctx context.Context, b ServiceBackend, zone string, state request.Request, previousRecords []dns.RR, opt Options) (records []dns.RR, truncated bool, err error) {
 
 	services, err := b.Services(ctx, state, true, opt)
 	if err != nil {
-		return nil, err
+		return nil, false, err
 	}
 
 	dup := make(map[string]struct{})
@@ -360,8 +372,10 @@ func TXT(ctx context.Context, b ServiceBackend, zone string, state request.Reque
 			if dns.IsSubDomain(zone, dns.Fqdn(serv.Host)) {
 				state1 := state.NewWithQuestion(serv.Host, state.QType())
 				state1.Zone = zone
-				nextRecords, err := TXT(ctx, b, zone, state1, append(previousRecords, newRecord), opt)
-
+				nextRecords, tc, err := TXT(ctx, b, zone, state1, append(previousRecords, newRecord), opt)
+				if tc {
+					truncated = true
+				}
 				if err == nil {
 					// Not only have we found something we should add the CNAME and the IP addresses.
 					if len(nextRecords) > 0 {
@@ -386,13 +400,13 @@ func TXT(ctx context.Context, b ServiceBackend, zone string, state request.Reque
 		case dns.TypeTXT:
 			if _, ok := dup[serv.Host]; !ok {
 				dup[serv.Host] = struct{}{}
-				return append(records, serv.NewTXT(state.QName())), nil
+				return append(records, serv.NewTXT(state.QName())), truncated, nil
 			}
 
 		}
 	}
 
-	return records, nil
+	return records, truncated, nil
 }
 
 // PTR returns the PTR records from the backend, only services that have a domain name as host are included.

plugin/etcd/handler.go

@@ -21,16 +21,17 @@ func (e *Etcd) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (
 
 	var (
 		records, extra []dns.RR
+		truncated      bool
 		err            error
 	)
 
 	switch state.QType() {
 	case dns.TypeA:
-		records, err = plugin.A(ctx, e, zone, state, nil, opt)
+		records, truncated, err = plugin.A(ctx, e, zone, state, nil, opt)
 	case dns.TypeAAAA:
-		records, err = plugin.AAAA(ctx, e, zone, state, nil, opt)
+		records, truncated, err = plugin.AAAA(ctx, e, zone, state, nil, opt)
 	case dns.TypeTXT:
-		records, err = plugin.TXT(ctx, e, zone, state, nil, opt)
+		records, truncated, err = plugin.TXT(ctx, e, zone, state, nil, opt)
 	case dns.TypeCNAME:
 		records, err = plugin.CNAME(ctx, e, zone, state, opt)
 	case dns.TypePTR:
@@ -49,7 +50,7 @@ func (e *Etcd) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (
 		fallthrough
 	default:
 		// Do a fake A lookup, so we can distinguish between NODATA and NXDOMAIN
-		_, err = plugin.A(ctx, e, zone, state, nil, opt)
+		_, _, err = plugin.A(ctx, e, zone, state, nil, opt)
 	}
 	if err != nil && e.IsNameError(err) {
 		if e.Fall.Through(state.Name()) {
@@ -68,6 +69,7 @@ func (e *Etcd) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (
 
 	m := new(dns.Msg)
 	m.SetReply(r)
+	m.Truncated = truncated
 	m.Authoritative = true
 	m.Answer = append(m.Answer, records...)
 	m.Extra = append(m.Extra, extra...)

plugin/kubernetes/handler.go

@@ -22,18 +22,19 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 	state.Zone = zone
 
 	var (
-		records []dns.RR
-		extra   []dns.RR
-		err     error
+		records   []dns.RR
+		extra     []dns.RR
+		truncated bool
+		err       error
 	)
 
 	switch state.QType() {
 	case dns.TypeA:
-		records, err = plugin.A(ctx, &k, zone, state, nil, plugin.Options{})
+		records, truncated, err = plugin.A(ctx, &k, zone, state, nil, plugin.Options{})
 	case dns.TypeAAAA:
-		records, err = plugin.AAAA(ctx, &k, zone, state, nil, plugin.Options{})
+		records, truncated, err = plugin.AAAA(ctx, &k, zone, state, nil, plugin.Options{})
 	case dns.TypeTXT:
-		records, err = plugin.TXT(ctx, &k, zone, state, nil, plugin.Options{})
+		records, truncated, err = plugin.TXT(ctx, &k, zone, state, nil, plugin.Options{})
 	case dns.TypeCNAME:
 		records, err = plugin.CNAME(ctx, &k, zone, state, plugin.Options{})
 	case dns.TypePTR:
@@ -58,7 +59,7 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 		// Do a fake A lookup, so we can distinguish between NODATA and NXDOMAIN
 		fake := state.NewWithQuestion(state.QName(), dns.TypeA)
 		fake.Zone = state.Zone
-		_, err = plugin.A(ctx, &k, zone, fake, nil, plugin.Options{})
+		_, _, err = plugin.A(ctx, &k, zone, fake, nil, plugin.Options{})
 	}
 
 	if k.IsNameError(err) {
@@ -81,6 +82,7 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 
 	m := new(dns.Msg)
 	m.SetReply(r)
+	m.Truncated = truncated
 	m.Authoritative = true
 	m.Answer = append(m.Answer, records...)
 	m.Extra = append(m.Extra, extra...)

plugin/kubernetes/kubernetes.go

@@ -15,7 +15,6 @@ import (
 	"github.com/coredns/coredns/plugin/kubernetes/object"
 	"github.com/coredns/coredns/plugin/pkg/dnsutil"
 	"github.com/coredns/coredns/plugin/pkg/fall"
-	"github.com/coredns/coredns/plugin/pkg/upstream"
 	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
@@ -35,7 +34,7 @@ import (
 type Kubernetes struct {
 	Next             plugin.Handler
 	Zones            []string
-	Upstream         *upstream.Upstream
+	Upstream         Upstreamer
 	APIServerList    []string
 	APICertAuth      string
 	APIClientCert    string
@@ -53,6 +52,11 @@ type Kubernetes struct {
 	autoPathSearch   []string // Local search path from /etc/resolv.conf. Needed for autopath.
 }
 
+// Upstreamer is used to resolve CNAME or other external targets
+type Upstreamer interface {
+	Lookup(ctx context.Context, state request.Request, name string, typ uint16) (*dns.Msg, error)
+}
+
 // New returns a initialized Kubernetes. It default interfaceAddrFunc to return 127.0.0.1. All other
 // values default to their zero value, primaryZoneIndex will thus point to the first zone.
 func New(zones []string) *Kubernetes {