do not log NOERROR in log plugin when response is not available (#4725)

Signed-off-by: Ondrej Benkovsky <ondrej.benkovsky@wandera.com>

plugin/pkg/replacer/replacer.go

@@ -86,7 +86,7 @@ func appendValue(b []byte, state request.Request, rr *dnstest.Recorder, label st
 		return strconv.AppendInt(b, int64(state.Size()), 10)
 	// Recorded replacements.
 	case "{rcode}":
-		if rr == nil {
+		if rr == nil || rr.Msg == nil {
 			return append(b, EmptyValue...)
 		}
 		if rcode := dns.RcodeToString[rr.Rcode]; rcode != "" {

plugin/pkg/replacer/replacer_test.go

@@ -393,3 +393,52 @@ func TestMetadataMalformed(t *testing.T) {
 		}
 	}
 }
+
+func TestNoResponseWasWritten(t *testing.T) {
+	w := dnstest.NewRecorder(&test.ResponseWriter{})
+	r := new(dns.Msg)
+	r.SetQuestion("example.org.", dns.TypeHINFO)
+	r.Id = 1053
+	r.AuthenticatedData = true
+	r.CheckingDisabled = true
+	state := request.Request{W: w, Req: r}
+
+	replacer := New()
+	ctx := context.TODO()
+
+	// This couples the test very tightly to the code, but so be it.
+	expect := map[string]string{
+		"{type}":                    "HINFO",
+		"{name}":                    "example.org.",
+		"{class}":                   "IN",
+		"{proto}":                   "udp",
+		"{size}":                    "29",
+		"{remote}":                  "10.240.0.1",
+		"{port}":                    "40212",
+		"{local}":                   "127.0.0.1",
+		headerReplacer + "id}":      "1053",
+		headerReplacer + "opcode}":  "0",
+		headerReplacer + "do}":      "false",
+		headerReplacer + "bufsize}": "512",
+		"{rcode}":                   "-",
+		"{rsize}":                   "0",
+		"{duration}":                "0",
+		headerReplacer + "rflags}":  "-",
+	}
+	if len(expect) != len(labels) {
+		t.Fatalf("Expect %d labels, got %d", len(expect), len(labels))
+	}
+
+	for lbl := range labels {
+		repl := replacer.Replace(ctx, state, w, lbl)
+		if lbl == "{duration}" {
+			if repl[len(repl)-1] != 's' {
+				t.Errorf("Expected seconds, got %q", repl)
+			}
+			continue
+		}
+		if repl != expect[lbl] {
+			t.Errorf("Expected value %q, got %q", expect[lbl], repl)
+		}
+	}
+}