Issue 388 (#389)

* add extra test

* middleware/auto: fix crash when calling empty handler

Don't call the next middleware, we should be auth. for this zone
getitng into this path we should respond with ServFail.

Fixes #388

test/auto_test.go

@@ -79,6 +79,44 @@ func TestAuto(t *testing.T) {
 	}
 }
 
+func TestAutoNonExistentZone(t *testing.T) {
+	tmpdir, err := ioutil.TempDir(os.TempDir(), "coredns")
+	if err != nil {
+		t.Fatal(err)
+	}
+	log.SetOutput(ioutil.Discard)
+
+	corefile := `.:0 {
+		auto {
+			directory ` + tmpdir + ` (.*) {1} 1
+		}
+		errors stdout
+	}
+`
+
+	i, err := CoreDNSServer(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+
+	udp, _ := CoreDNSServerPorts(i, 0)
+	if udp == "" {
+		t.Fatalf("Could not get UDP listening port")
+	}
+	defer i.Stop()
+
+	p := proxy.New([]string{udp})
+	state := request.Request{W: &test.ResponseWriter{}, Req: new(dns.Msg)}
+
+	resp, err := p.Lookup(state, "example.org.", dns.TypeA)
+	if err != nil {
+		t.Fatal("Expected to receive reply, but didn't")
+	}
+	if resp.Rcode != dns.RcodeServerFailure {
+		t.Fatalf("Expected reply to be a SERVFAIL, got %d", resp.Rcode)
+	}
+}
+
 const zoneContent = `; testzone
 @	IN	SOA	sns.dns.icann.org. noc.dns.icann.org. 2016082534 7200 3600 1209600 3600
 		NS	a.iana-servers.net.