app/vmagent/remotewrite: follow-up after a27c2f3773

- Fix Prometheus-compatible naming after applying the relabeling if -usePromCompatibleNaming command-line flag is set.
  This should prevent from possible Prometheus-incompatible metric names and label names generated by the relabeling.
- Do not return anything from relabelCtx.appendExtraLabels() function, since it cannot change the number of time series
  passed to it. Append labels for the passed time series in-place.
- Remove promrelabel.FinalizeLabels() call after adding extra labels to time series, since this call has been already
  made at relabelCtx.applyRelabeling(). It is user's responsibility if he passes labels with double underscore prefixes
  to -remoteWrite.label.

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4247

app/vmagent/remotewrite/relabel.go

@@ -98,24 +98,15 @@ func (rctx *relabelCtx) applyRelabeling(tss []prompbmarshal.TimeSeries, pcs *pro
 		ts := &tss[i]
 		labelsLen := len(labels)
 		labels = append(labels, ts.Labels...)
-		if *usePromCompatibleNaming {
-			// Replace unsupported Prometheus chars in label names and metric names with underscores.
-			tmpLabels := labels[labelsLen:]
-			for j := range tmpLabels {
-				label := &tmpLabels[j]
-				if label.Name == "__name__" {
-					label.Value = promrelabel.SanitizeMetricName(label.Value)
-				} else {
-					label.Name = promrelabel.SanitizeLabelName(label.Name)
-				}
-			}
-		}
 		labels = pcs.Apply(labels, labelsLen)
 		labels = promrelabel.FinalizeLabels(labels[:labelsLen], labels[labelsLen:])
 		if len(labels) == labelsLen {
 			// Drop the current time series, since relabeling removed all the labels.
 			continue
 		}
+		if *usePromCompatibleNaming {
+			fixPromCompatibleNaming(labels[labelsLen:])
+		}
 		tssDst = append(tssDst, prompbmarshal.TimeSeries{
 			Labels:  labels[labelsLen:],
 			Samples: ts.Samples,
@@ -125,11 +116,10 @@ func (rctx *relabelCtx) applyRelabeling(tss []prompbmarshal.TimeSeries, pcs *pro
 	return tssDst
 }
 
-func (rctx *relabelCtx) appendExtraLabels(tss []prompbmarshal.TimeSeries, extraLabels []prompbmarshal.Label) []prompbmarshal.TimeSeries {
+func (rctx *relabelCtx) appendExtraLabels(tss []prompbmarshal.TimeSeries, extraLabels []prompbmarshal.Label) {
 	if len(extraLabels) == 0 {
-		return tss
+		return
 	}
-	tssDst := tss[:0]
 	labels := rctx.labels[:0]
 	for i := range tss {
 		ts := &tss[i]
@@ -147,14 +137,9 @@ func (rctx *relabelCtx) appendExtraLabels(tss []prompbmarshal.TimeSeries, extraL
 				labels = append(labels, extraLabel)
 			}
 		}
-		labels = promrelabel.FinalizeLabels(labels[:labelsLen], labels[labelsLen:])
+		ts.Labels = labels[labelsLen:]
-		tssDst = append(tssDst, prompbmarshal.TimeSeries{
-			Labels:  labels[labelsLen:],
-			Samples: ts.Samples,
-		})
 	}
 	rctx.labels = labels
-	return tssDst
 }
 
 type relabelCtx struct {
@@ -181,3 +166,15 @@ func putRelabelCtx(rctx *relabelCtx) {
 	rctx.labels = rctx.labels[:0]
 	relabelCtxPool.Put(rctx)
 }
+
+func fixPromCompatibleNaming(labels []prompbmarshal.Label) {
+	// Replace unsupported Prometheus chars in label names and metric names with underscores.
+	for i := range labels {
+		label := &labels[i]
+		if label.Name == "__name__" {
+			label.Value = promrelabel.SanitizeMetricName(label.Value)
+		} else {
+			label.Name = promrelabel.SanitizeLabelName(label.Name)
+		}
+	}
+}

app/vmagent/remotewrite/relabel_test.go

@@ -42,9 +42,9 @@ func TestAppendExtraLabels(t *testing.T) {
 	f := func(extraLabels []prompbmarshal.Label, sTss, sExpTss string) {
 		rctx := &relabelCtx{}
 		tss, expTss := parseSeries(sTss), parseSeries(sExpTss)
-		gotTss := rctx.appendExtraLabels(tss, extraLabels)
+		rctx.appendExtraLabels(tss, extraLabels)
-		if !reflect.DeepEqual(gotTss, expTss) {
+		if !reflect.DeepEqual(tss, expTss) {
-			t.Fatalf("expected to have: \n%v;\ngot: \n%v", expTss, gotTss)
+			t.Fatalf("expected to have: \n%v;\ngot: \n%v", expTss, tss)
 		}
 	}
 

app/vmagent/remotewrite/remotewrite.go

@@ -355,7 +355,7 @@ func Push(at *auth.Token, wr *prompbmarshal.WriteRequest) {
 	var rctx *relabelCtx
 	rcs := allRelabelConfigs.Load()
 	pcsGlobal := rcs.global
-	if pcsGlobal.Len() > 0 || len(labelsGlobal) > 0 {
+	if pcsGlobal.Len() > 0 {
 		rctx = getRelabelCtx()
 	}
 	tss := wr.Timeseries
@@ -722,7 +722,7 @@ func (rwctx *remoteWriteCtx) pushInternal(tss []prompbmarshal.TimeSeries) {
 	if len(labelsGlobal) > 0 {
 		rctx := getRelabelCtx()
 		defer putRelabelCtx(rctx)
-		tss = rctx.appendExtraLabels(tss, labelsGlobal)
+		rctx.appendExtraLabels(tss, labelsGlobal)
 	}
 
 	pss := rwctx.pss