plugin/file: Use NXDOMAIN response if CNAME target is NXDOMAIN (#4303)

* pass through nxdomain results
Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* return srvfail and nodata results
Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* add test
Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* cover more response cases
Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

plugin/file/lookup.go

@@ -307,8 +307,9 @@ func (z *Zone) externalLookup(ctx context.Context, state request.Request, elem *
 	targetName := rrs[0].(*dns.CNAME).Target
 	elem, _ = z.Tree.Search(targetName)
 	if elem == nil {
-		rrs = append(rrs, z.doLookup(ctx, state, targetName, qtype)...)
-		return rrs, z.Apex.ns(do), nil, Success
+		lookupRRs, result := z.doLookup(ctx, state, targetName, qtype)
+		rrs = append(rrs, lookupRRs...)
+		return rrs, z.Apex.ns(do), nil, result
 	}
 
 	i := 0
@@ -326,8 +327,9 @@ Redo:
 		targetName := cname[0].(*dns.CNAME).Target
 		elem, _ = z.Tree.Search(targetName)
 		if elem == nil {
-			rrs = append(rrs, z.doLookup(ctx, state, targetName, qtype)...)
-			return rrs, z.Apex.ns(do), nil, Success
+			lookupRRs, result := z.doLookup(ctx, state, targetName, qtype)
+			rrs = append(rrs, lookupRRs...)
+			return rrs, z.Apex.ns(do), nil, result
 		}
 
 		i++
@@ -352,15 +354,24 @@ Redo:
 	return rrs, z.Apex.ns(do), nil, Success
 }
 
-func (z *Zone) doLookup(ctx context.Context, state request.Request, target string, qtype uint16) []dns.RR {
+func (z *Zone) doLookup(ctx context.Context, state request.Request, target string, qtype uint16) ([]dns.RR, Result) {
 	m, e := z.Upstream.Lookup(ctx, state, target, qtype)
 	if e != nil {
-		return nil
+		return nil, Success
 	}
 	if m == nil {
-		return nil
+		return nil, Success
+	}
+	if m.Rcode == dns.RcodeNameError {
+		return m.Answer, NameError
+	}
+	if m.Rcode == dns.RcodeServerFailure {
+		return m.Answer, ServerFailure
+	}
+	if m.Rcode == dns.RcodeSuccess && len(m.Answer) == 0 {
+		return m.Answer, NoData
 	}
-	return m.Answer
+	return m.Answer, Success
 }
 
 // additionalProcessing checks the current answer section and retrieves A or AAAA records

test/file_upstream_test.go

@@ -58,6 +58,113 @@ www 3600 IN CNAME www.example.net.
 	}
 }
 
+func TestFileUpstreamError(t *testing.T) {
+	cases := map[string]test.Case{
+		"nxdomain": {
+			Qname: "nxdomain.example.org.", Qtype: dns.TypeA,
+			Answer: []dns.RR{
+				test.CNAME("nxdomain.example.org.	3600	IN	CNAME	nxdomain.example.net"),
+			},
+			Rcode: dns.RcodeNameError,
+		},
+		"nxdomain-chain": {
+			Qname: "chain1.example.org.", Qtype: dns.TypeA,
+			Answer: []dns.RR{
+				test.CNAME("chain1.example.org.	3600	IN	CNAME	nxdomain.example.org"),
+				test.CNAME("nxdomain.example.org.	3600	IN	CNAME	nxdomain.example.net"),
+			},
+			Rcode: dns.RcodeNameError,
+		},
+		"srvfail": {
+			Qname: "srvfail.example.org.", Qtype: dns.TypeA,
+			Rcode: dns.RcodeServerFailure,
+		},
+		"srvfail-chain": {
+			Qname: "chain2.example.org.", Qtype: dns.TypeA,
+			Rcode: dns.RcodeServerFailure,
+		},
+		"nodata": {
+			Qname: "nodata.example.org.", Qtype: dns.TypeA,
+			Answer: []dns.RR{
+				test.CNAME("nodata.example.org.	3600	IN	CNAME	nodata.example.net"),
+			},
+			Rcode: dns.RcodeSuccess,
+		},
+		"nodata-chain": {
+			Qname: "chain3.example.org.", Qtype: dns.TypeA,
+			Answer: []dns.RR{
+				test.CNAME("chain3.example.org.	3600	IN	CNAME	nodata.example.org"),
+				test.CNAME("nodata.example.org.	3600	IN	CNAME	nodata.example.net"),
+			},
+			Rcode: dns.RcodeSuccess,
+		},
+	}
+	name, rm, err := test.TempFile(".", `$ORIGIN example.org.
+@	3600 IN	SOA   sns.dns.icann.org. noc.dns.icann.org. (
+        2017042745 ; serial
+        7200       ; refresh (2 hours)
+        3600       ; retry (1 hour)
+        1209600    ; expire (2 weeks)
+        3600       ; minimum (1 hour)
+)
+
+    3600 IN NS    a.iana-servers.net.
+    3600 IN NS    b.iana-servers.net.
+
+chain1   3600 IN CNAME nxdomain
+nxdomain 3600 IN CNAME nxdomain.example.net.
+chain2   3600 IN CNAME srvfail
+srvfail  3600 IN CNAME srvfail.example.net.
+chain3   3600 IN CNAME nodata
+nodata   3600 IN CNAME nodata.example.net.
+
+`)
+	if err != nil {
+		t.Fatalf("Failed to create zone: %s", err)
+	}
+	defer rm()
+
+	corefile := `.:0 {
+	template ANY A nxdomain.example.net. {
+		rcode NXDOMAIN
+	}
+	template ANY A srvfail.example.net. {
+		rcode SERVFAIL
+	}
+	template ANY A nodata.example.net. {
+	}
+	file ` + name + ` example.org
+}`
+
+	i, udp, _, err := CoreDNSServerAndPorts(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+	defer i.Stop()
+
+	for n, tc := range cases {
+		t.Run(n, func(t *testing.T) {
+			m := new(dns.Msg)
+			m.SetQuestion(tc.Qname, tc.Qtype)
+			m.SetEdns0(4096, true)
+
+			r, err := dns.Exchange(m, udp)
+			if err != nil {
+				t.Fatalf("Could not exchange msg: %s", err)
+			}
+			if r.Rcode != tc.Rcode {
+				t.Fatalf("expected rcode %v, got %v", tc.Rcode, r.Rcode)
+			}
+			if n := len(r.Answer); n != len(tc.Answer) {
+				t.Fatalf("Expected %v answers, got %v", len(tc.Answer), n)
+			}
+			if err := test.Section(tc, test.Answer, r.Answer); err != nil {
+				t.Error(err)
+			}
+		})
+	}
+}
+
 // TestFileUpstreamAdditional runs two CoreDNS servers that serve example.org and foo.example.org.
 // example.org contains a cname to foo.example.org; this should be resolved via upstream.Self.
 func TestFileUpstreamAdditional(t *testing.T) {

test/go-test-tmpfile565156097

+$ORIGIN example.org.
+@	3600 IN	SOA   sns.dns.icann.org. noc.dns.icann.org. (
+        2017042745 ; serial
+        7200       ; refresh (2 hours)
+        3600       ; retry (1 hour)
+        1209600    ; expire (2 weeks)
+        3600       ; minimum (1 hour)
+)
+
+    3600 IN NS    a.iana-servers.net.
+    3600 IN NS    b.iana-servers.net.
+
+chain1   3600 IN CNAME nxdomain
+nxdomain 3600 IN CNAME nxdomain.example.net.
+chain2   3600 IN CNAME srvfail
+srvfail  3600 IN CNAME srvfail.example.net.
+chain3   3600 IN CNAME nodata
+nodata   3600 IN CNAME nodata.example.net.
+