plugin/dns64: preserve A fallback response codes (#8619)

* plugin/dns64: preserve fallback response codes

Signed-off-by: xinjun.jiang <xinjun.jiang@daocloud.io>

* plugin/dns64: mark written fallback replies as handled

Signed-off-by: xinjun.jiang <xinjun.jiang@daocloud.io>

---------

Signed-off-by: xinjun.jiang <xinjun.jiang@daocloud.io>

plugin/dns64/dns64.go

@@ -63,7 +63,7 @@ func (d *DNS64) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 
 	RequestsTranslatedCount.WithLabelValues(metrics.WithServer(ctx)).Inc()
 	w.WriteMsg(msg)
-	return msg.Rcode, nil
+	return dns.RcodeSuccess, nil
 }
 
 // Name implements the Handler interface.
@@ -134,6 +134,7 @@ func (d *DNS64) DoDNS64(ctx context.Context, w dns.ResponseWriter, r *dns.Msg, o
 func (d *DNS64) Synthesize(origReq, origResponse, resp *dns.Msg) *dns.Msg {
 	ret := dns.Msg{}
 	ret.SetReply(origReq)
+	ret.Rcode = resp.Rcode
 
 	// persist truncated state of AAAA response
 	ret.Truncated = resp.Truncated

plugin/dns64/dns64_test.go

@@ -581,3 +581,42 @@ func TestDNS64NilUpstreamResponse(t *testing.T) {
 		t.Error("Expected error when upstream returns nil response, got nil")
 	}
 }
+
+func TestDNS64FallbackError(t *testing.T) {
+	_, prefix, _ := net.ParseCIDR("64:ff9b::/96")
+	for _, rcode := range []int{dns.RcodeSuccess, dns.RcodeServerFailure, dns.RcodeRefused, dns.RcodeFormatError, dns.RcodeNameError, dns.RcodeNotImplemented} {
+		t.Run(dns.RcodeToString[rcode], func(t *testing.T) {
+			req := new(dns.Msg)
+			req.SetQuestion("example.com.", dns.TypeAAAA)
+			initial := new(dns.Msg)
+			initial.SetReply(req)
+			fallback := new(dns.Msg)
+			fallback.SetRcode(req, rcode)
+			fallback.Id++
+			fallback.Question[0].Qtype = dns.TypeA
+			fallback.Ns = []dns.RR{test.SOA("example.com. 60 IN SOA ns.example.com. hostmaster.example.com. 1 1 1 1 1")}
+			d := DNS64{
+				Next:     &fakeHandler{t, initial},
+				Prefix:   prefix,
+				Upstream: &fakeUpstream{t, req.Question[0].Name, fallback},
+			}
+			rec := dnstest.NewRecorder(&test.ResponseWriter{RemoteIP: "::1"})
+			got, err := d.ServeDNS(t.Context(), rec, req)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got != dns.RcodeSuccess {
+				t.Errorf("written fallback %s returned handler code %s, want NOERROR", dns.RcodeToString[rcode], dns.RcodeToString[got])
+			}
+			if rec.Msg.Rcode != rcode {
+				t.Errorf("fallback %s returned response code %s", dns.RcodeToString[rcode], dns.RcodeToString[rec.Msg.Rcode])
+			}
+			if rec.Msg.Id != req.Id || !reflect.DeepEqual(rec.Msg.Question, req.Question) {
+				t.Errorf("response did not preserve the original AAAA query: %s", rec.Msg)
+			}
+			if !reflect.DeepEqual(rec.Msg.Ns, fallback.Ns) {
+				t.Errorf("response did not preserve fallback authority records: %s", rec.Msg)
+			}
+		})
+	}
+}

test/dns64_test.go

@@ -0,0 +1,86 @@
+package test
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+func TestDNS64FallbackError(t *testing.T) {
+	for _, rcode := range []int{dns.RcodeSuccess, dns.RcodeServerFailure, dns.RcodeRefused, dns.RcodeFormatError, dns.RcodeNameError, dns.RcodeNotImplemented} {
+		t.Run(dns.RcodeToString[rcode], func(t *testing.T) {
+			corefile := fmt.Sprintf(`.:0 {
+				bind 127.0.0.1
+				dns64 {
+					allow_ipv4
+				}
+				template IN AAAA example.org {
+					rcode NOERROR
+				}
+				template IN A example.org {
+					rcode %s
+				}
+				template IN TXT example.org {
+					answer "{{ .Name }} 60 IN TXT \"connection reused\""
+				}
+			}`, dns.RcodeToString[rcode])
+			i, udp, tcp, err := CoreDNSServerAndPorts(corefile)
+			if err != nil {
+				t.Fatal(err)
+			}
+			t.Cleanup(func() { CoreDNSServerStop(i) })
+
+			for _, transport := range []struct {
+				net  string
+				addr string
+			}{{"udp", udp}, {"tcp", tcp}} {
+				t.Run(transport.net, func(t *testing.T) {
+					client := &dns.Client{Net: transport.net}
+					conn, err := client.Dial(transport.addr)
+					if err != nil {
+						t.Fatal(err)
+					}
+					defer conn.Close()
+
+					for attempt := range 3 {
+						for _, tc := range []struct {
+							qtype uint16
+							id    uint16
+							code  int
+						}{
+							{dns.TypeAAAA, uint16(101 + attempt), rcode},
+							{dns.TypeTXT, uint16(202 + attempt), dns.RcodeSuccess},
+						} {
+							query := new(dns.Msg)
+							query.SetQuestion("example.org.", tc.qtype)
+							query.Id = tc.id
+							if err := conn.SetDeadline(time.Now().Add(2 * time.Second)); err != nil {
+								t.Fatal(err)
+							}
+							if err := conn.WriteMsg(query); err != nil {
+								t.Fatal(err)
+							}
+							response, err := conn.ReadMsg()
+							if err != nil {
+								t.Fatal(err)
+							}
+							if response.Id != query.Id || len(response.Question) != 1 || response.Question[0] != query.Question[0] {
+								t.Fatalf("query ID %d (%s) received an unexpected reply: %s", query.Id, dns.TypeToString[tc.qtype], response)
+							}
+							if response.Rcode != tc.code {
+								t.Errorf("query %s returned %s, want %s", dns.TypeToString[tc.qtype], dns.RcodeToString[response.Rcode], dns.RcodeToString[tc.code])
+							}
+							if tc.qtype == dns.TypeTXT {
+								if len(response.Answer) != 1 || response.Answer[0].String() != "example.org.\t60\tIN\tTXT\t\"connection reused\"" {
+									t.Errorf("connection reuse did not return the TXT answer: %s", response)
+								}
+							}
+						}
+					}
+				})
+			}
+		})
+	}
+}