Fix query for SOA record for delegated zone (#3875)

Addresses a bug in the file plugin where SOA queries to zone delegations are
inappropriately returned the SOA for the delegating zone, and not a downward
referral to the delegated zone.

Here is an example of what I believe the expected downward referral in response
to a SOA query for a delegated zone should be (note that no SOA record is
returned):

~~~
; <<>> DiG 9.11.3-1ubuntu1.5-Ubuntu <<>> @k.root-servers.net. miek.nl. SOA
; (2 servers found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 58381
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 3, ADDITIONAL: 7
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;miek.nl.                       IN      SOA

;; AUTHORITY SECTION:
nl.                     172800  IN      NS      ns1.dns.nl.
nl.                     172800  IN      NS      ns2.dns.nl.
nl.                     172800  IN      NS      ns3.dns.nl.

;; ADDITIONAL SECTION:
ns1.dns.nl.             172800  IN      A       194.0.28.53
ns2.dns.nl.             172800  IN      A       194.146.106.42
ns3.dns.nl.             172800  IN      A       194.0.25.24
ns1.dns.nl.             172800  IN      AAAA    2001:678:2c:0:194:0:28:53
ns2.dns.nl.             172800  IN      AAAA    2001:67c:1010:10::53
ns3.dns.nl.             172800  IN      AAAA    2001:678:20::24
~~~

See #3852 for the original fix.

Modified clouddns/route53 and removed the faulty tests there.

Signed-off-by: Miek Gieben <miek@miek.nl>

4 files changed, 36 insertions, 35 deletions

diff --git a/plugin/clouddns/clouddns_test.go b/plugin/clouddns/clouddns_test.go
index dafd65bba..7d9db85f3 100644
--- a/plugin/clouddns/clouddns_test.go
+++ b/plugin/clouddns/clouddns_test.go
@@ -10,7 +10,7 @@ import (
 	"github.com/coredns/coredns/plugin/pkg/fall"
 	"github.com/coredns/coredns/plugin/pkg/upstream"
 	"github.com/coredns/coredns/plugin/test"
-	crequest "github.com/coredns/coredns/request"
+	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
 	gcp "google.golang.org/api/dns/v1"
@@ -138,7 +138,7 @@ func TestCloudDNS(t *testing.T) {
 	r.Fall = fall.Zero
 	r.Fall.SetZonesFromArgs([]string{"gov."})
 	r.Next = test.HandlerFunc(func(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
-		state := crequest.Request{W: w, Req: r}
+		state := request.Request{W: w, Req: r}
 		qname := state.Name()
 		m := new(dns.Msg)
 		rcode := dns.RcodeServerFailure
@@ -211,30 +211,24 @@ func TestCloudDNS(t *testing.T) {
 		// 5. Explicit SOA query for example.org.
 		{
 			qname: "example.org",
-			qtype: dns.TypeSOA,
-			wantAnswer: []string{"org.	300	IN	SOA	ns-cloud-e1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 300 259200 300"},
-		},
-		// 6. Explicit SOA query for example.org.
-		{
-			qname: "example.org",
 			qtype: dns.TypeNS,
 			wantNS: []string{"org.	300	IN	SOA	ns-cloud-c1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 300 259200 300"},
 		},
-		// 7. AAAA query for split-example.org must return NODATA.
+		// 6. AAAA query for split-example.org must return NODATA.
 		{
 			qname:       "split-example.gov",
 			qtype:       dns.TypeAAAA,
 			wantRetCode: dns.RcodeSuccess,
 			wantNS: []string{"org.	300	IN	SOA	ns-cloud-c1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 300 259200 300"},
 		},
-		// 8. Zone not configured.
+		// 7. Zone not configured.
 		{
 			qname:        "badexample.com",
 			qtype:        dns.TypeA,
 			wantRetCode:  dns.RcodeServerFailure,
 			wantMsgRCode: dns.RcodeServerFailure,
 		},
-		// 9. No record found. Return SOA record.
+		// 8. No record found. Return SOA record.
 		{
 			qname:        "bad.org",
 			qtype:        dns.TypeA,
@@ -242,25 +236,25 @@ func TestCloudDNS(t *testing.T) {
 			wantMsgRCode: dns.RcodeNameError,
 			wantNS: []string{"org.	300	IN	SOA	ns-cloud-c1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 300 259200 300"},
 		},
-		// 10. No record found. Fallthrough.
+		// 9. No record found. Fallthrough.
 		{
 			qname: "example.gov",
 			qtype: dns.TypeA,
 			wantAnswer: []string{"example.gov.	300	IN	A	2.4.6.8"},
 		},
-		// 11. other-zone.example.org is stored in a different hosted zone. success
+		// 10. other-zone.example.org is stored in a different hosted zone. success
 		{
 			qname: "other-example.org",
 			qtype: dns.TypeA,
 			wantAnswer: []string{"other-example.org.	300	IN	A	3.5.7.9"},
 		},
-		// 12. split-example.org only has A record. Expect NODATA.
+		// 11. split-example.org only has A record. Expect NODATA.
 		{
 			qname: "split-example.org",
 			qtype: dns.TypeAAAA,
 			wantNS: []string{"org.	300	IN	SOA	ns-cloud-e1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 300 259200 300"},
 		},
-		// 13. *.www.example.org is a wildcard CNAME to www.example.org.
+		// 12. *.www.example.org is a wildcard CNAME to www.example.org.
 		{
 			qname: "a.www.example.org",
 			qtype: dns.TypeA,
diff --git a/plugin/file/delegation_test.go b/plugin/file/delegation_test.go
index a317b827b..a6da6215c 100644
--- a/plugin/file/delegation_test.go
+++ b/plugin/file/delegation_test.go
@@ -57,6 +57,17 @@ var delegationTestCases = []test.Case{
 		},
 	},
 	{
+		Qname: "foo.delegated.miek.nl.", Qtype: dns.TypeSOA,
+		Ns: []dns.RR{
+			test.NS("delegated.miek.nl.	1800	IN	NS	a.delegated.miek.nl."),
+			test.NS("delegated.miek.nl.	1800	IN	NS	ns-ext.nlnetlabs.nl."),
+		},
+		Extra: []dns.RR{
+			test.A("a.delegated.miek.nl. 1800 IN A 139.162.196.78"),
+			test.AAAA("a.delegated.miek.nl. 1800 IN AAAA 2a01:7e00::f03c:91ff:fef1:6735"),
+		},
+	},
+	{
 		Qname: "miek.nl.", Qtype: dns.TypeSOA,
 		Answer: []dns.RR{
 			test.SOA("miek.nl.	1800	IN	SOA	linode.atoom.net. miek.miek.nl. 1282630057 14400 3600 604800 14400"),
diff --git a/plugin/file/lookup.go b/plugin/file/lookup.go
index 3d8d899df..28da3d4d0 100644
--- a/plugin/file/lookup.go
+++ b/plugin/file/lookup.go
@@ -44,13 +44,15 @@ func (z *Zone) Lookup(ctx context.Context, state request.Request, qname string)
 		return nil, nil, nil, ServerFailure
 	}
 
-	if qtype == dns.TypeSOA {
-		return ap.soa(do), ap.ns(do), nil, Success
-	}
-	if qtype == dns.TypeNS && qname == z.origin {
-		nsrrs := ap.ns(do)
-		glue := tr.Glue(nsrrs, do) // technically this isn't glue
-		return nsrrs, nil, glue, Success
+	if qname == z.origin {
+		switch qtype {
+		case dns.TypeSOA:
+			return ap.soa(do), ap.ns(do), nil, Success
+		case dns.TypeNS:
+			nsrrs := ap.ns(do)
+			glue := tr.Glue(nsrrs, do) // technically this isn't glue
+			return nsrrs, nil, glue, Success
+		}
 	}
 
 	var (
diff --git a/plugin/route53/route53_test.go b/plugin/route53/route53_test.go
index aa5c82b9c..4b3fe1ebe 100644
--- a/plugin/route53/route53_test.go
+++ b/plugin/route53/route53_test.go
@@ -167,30 +167,24 @@ func TestRoute53(t *testing.T) {
 		// 5. Explicit SOA query for example.org.
 		{
 			qname: "example.org",
-			qtype: dns.TypeSOA,
-			wantAnswer: []string{"org.	300	IN	SOA	ns-15.awsdns-00.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400"},
-		},
-		// 6. Explicit SOA query for example.org.
-		{
-			qname: "example.org",
 			qtype: dns.TypeNS,
 			wantNS: []string{"org.	300	IN	SOA	ns-1536.awsdns-00.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400"},
 		},
-		// 7. AAAA query for split-example.org must return NODATA.
+		// 6. AAAA query for split-example.org must return NODATA.
 		{
 			qname:       "split-example.gov",
 			qtype:       dns.TypeAAAA,
 			wantRetCode: dns.RcodeSuccess,
 			wantNS: []string{"org.	300	IN	SOA	ns-1536.awsdns-00.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400"},
 		},
-		// 8. Zone not configured.
+		// 7. Zone not configured.
 		{
 			qname:        "badexample.com",
 			qtype:        dns.TypeA,
 			wantRetCode:  dns.RcodeServerFailure,
 			wantMsgRCode: dns.RcodeServerFailure,
 		},
-		// 9. No record found. Return SOA record.
+		// 8. No record found. Return SOA record.
 		{
 			qname:        "bad.org",
 			qtype:        dns.TypeA,
@@ -198,25 +192,25 @@ func TestRoute53(t *testing.T) {
 			wantMsgRCode: dns.RcodeNameError,
 			wantNS: []string{"org.	300	IN	SOA	ns-1536.awsdns-00.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400"},
 		},
-		// 10. No record found. Fallthrough.
+		// 9. No record found. Fallthrough.
 		{
 			qname: "example.gov",
 			qtype: dns.TypeA,
 			wantAnswer: []string{"example.gov.	300	IN	A	2.4.6.8"},
 		},
-		// 11. other-zone.example.org is stored in a different hosted zone. success
+		// 10. other-zone.example.org is stored in a different hosted zone. success
 		{
 			qname: "other-example.org",
 			qtype: dns.TypeA,
 			wantAnswer: []string{"other-example.org.	300	IN	A	3.5.7.9"},
 		},
-		// 12. split-example.org only has A record. Expect NODATA.
+		// 11. split-example.org only has A record. Expect NODATA.
 		{
 			qname: "split-example.org",
 			qtype: dns.TypeAAAA,
 			wantNS: []string{"org.	300	IN	SOA	ns-15.awsdns-00.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400"},
 		},
-		// 13. *.www.example.org is a wildcard CNAME to www.example.org.
+		// 12. *.www.example.org is a wildcard CNAME to www.example.org.
 		{
 			qname: "a.www.example.org",
 			qtype: dns.TypeA,