plugin/file: respond correctly to IXFR message (#3177)

* plugin/file: respond correctly to IXFR message

Respond with a sing SOA record to an IXFR request if the SOA serials
match.

The added test fails on the current code with:

~~~
=== RUN   TestIxfrResponse
--- FAIL: TestIxfrResponse (0.00s)
    secondary_test.go:122: Expected answer section with single RR
FAIL
exit status 1
~~~

And obviously passes with the new code. This should cut down on the
weird number of zone transfers that I was seeing. At some point IXFR
support might be cool.

Fixes: #3176

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

* reuse code

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

* Sligtht tweaks

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

1 files changed, 46 insertions, 0 deletions

diff --git a/test/secondary_test.go b/test/secondary_test.go
index 1aef05d29..1d65dfb2a 100644
--- a/test/secondary_test.go
+++ b/test/secondary_test.go
@@ -83,3 +83,49 @@ func TestSecondaryZoneTransfer(t *testing.T) {
 		t.Fatalf("Expected answer section")
 	}
 }
+
+func TestIxfrResponse(t *testing.T) {
+	// ixfr query with current soa should return single packet with that soa (no transfer needed).
+	name, rm, err := test.TempFile(".", exampleOrg)
+	if err != nil {
+		t.Fatalf("Failed to create zone: %s", err)
+	}
+	defer rm()
+
+	corefile := `example.org:0 {
+       file ` + name + ` {
+	       transfer to *
+       }
+}
+`
+
+	i, udp, _, err := CoreDNSServerAndPorts(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+	defer i.Stop()
+
+	m := new(dns.Msg)
+	m.SetQuestion("example.org.", dns.TypeIXFR)
+	m.Ns = []dns.RR{test.SOA("example.org. IN SOA sns.dns.icann.org. noc.dns.icann.org. 2015082541 7200 3600 1209600 3600")} // copied from exampleOrg
+
+	var r *dns.Msg
+	// This is now async; we need to wait for it to be transferred.
+	for i := 0; i < 10; i++ {
+		r, _ = dns.Exchange(m, udp)
+		if len(r.Answer) != 0 {
+			break
+		}
+		time.Sleep(100 * time.Microsecond)
+	}
+	if len(r.Answer) != 1 {
+		t.Fatalf("Expected answer section with single RR")
+	}
+	soa, ok := r.Answer[0].(*dns.SOA)
+	if !ok {
+		t.Fatalf("Expected answer section with SOA RR")
+	}
+	if soa.Serial != 2015082541 {
+		t.Fatalf("Serial should be %d, got %d", 2015082541, soa.Serial)
+	}
+}