plugin/file: fix local CNAME lookup (#1866)

* plugin/file: fix local CNAME lookup

Issue #1864 explains it will, when we serve the child zone as well we
should just recursive into ourself (upstream self). Thus relax the
IsSubDomain check in file/lookup.go and just query (even if the query
will hit a remote server).

I've looped over all other plugins that do something similar (CNAME
resolving) and they didn't do the IsSubDomain check; therefor I've
removed it from *file* as well.

Added test in file_upstream_test that shows this failed before but now
results in a reply.

Fixes #1864

* self does not need to be exported

* Fix test

We don't know if we had a valid reply. Check this.

1 files changed, 60 insertions, 2 deletions

diff --git a/test/file_upstream_test.go b/test/file_upstream_test.go
index dc4cbc45f..36f2bbc56 100644
--- a/test/file_upstream_test.go
+++ b/test/file_upstream_test.go
@@ -6,8 +6,6 @@ import (
 	"github.com/miekg/dns"
 )
 
-// TODO(miek): this test needs to be fleshed out.
-
 func TestFileUpstream(t *testing.T) {
 	name, rm, err := TempFile(".", `$ORIGIN example.org.
 @	3600 IN	SOA sns.dns.icann.org. noc.dns.icann.org. (
@@ -59,3 +57,63 @@ www 3600 IN CNAME   www.example.net.
 		t.Errorf("Failed to get address for CNAME, expected 10.0.0.1 got %s", x)
 	}
 }
+
+// TestFileUpstreamAdditional runs two CoreDNS servers that serve example.org and foo.example.org.
+// example.org contains a cname to foo.example.org; this should be resolved via upstream.Self.
+func TestFileUpstreamAdditional(t *testing.T) {
+	name, rm, err := TempFile(".", `$ORIGIN example.org.
+@	3600 IN	SOA sns.dns.icann.org. noc.dns.icann.org. 2017042745 7200 3600 1209600 3600
+
+	3600 IN NS b.iana-servers.net.
+
+www 3600 IN CNAME   www.foo
+`)
+	if err != nil {
+		t.Fatalf("Failed to create zone: %s", err)
+	}
+	defer rm()
+
+	name2, rm2, err2 := TempFile(".", `$ORIGIN foo.example.org.
+@	3600 IN	SOA sns.dns.icann.org. noc.dns.icann.org. 2017042745 7200 3600 1209600 3600
+
+	3600 IN NS b.iana-servers.net.
+
+www 3600 IN A   127.0.0.53
+`)
+	if err2 != nil {
+		t.Fatalf("Failed to create zone: %s", err2)
+	}
+	defer rm2()
+
+	corefile := `.:0 {
+	file ` + name + ` example.org {
+	       upstream
+	}
+	file ` + name2 + ` foo.example.org {
+	       upstream
+	}
+}
+`
+	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("www.example.org.", dns.TypeA)
+
+	r, err := dns.Exchange(m, udp)
+	if err != nil {
+		t.Fatalf("Could not exchange msg: %s", err)
+	}
+	if r.Rcode == dns.RcodeServerFailure {
+		t.Fatalf("Rcode should not be dns.RcodeServerFailure")
+	}
+	if x := len(r.Answer); x != 2 {
+		t.Errorf("Expected 2 RR in reply, got %d", x)
+	}
+	if x := r.Answer[1].(*dns.A).A.String(); x != "127.0.0.53" {
+		t.Errorf("Failed to get address for CNAME, expected 127.0.0.53, got %s", x)
+	}
+}