app/vmselect/prometheus: do not return time series with empty list of datapoints from /api/v1/query_range

This matches Prometheus behaviour.

This should fix https://github.com/jacksontj/promxy/issues/329

app/vmselect/prometheus/prometheus.go

@@ -797,14 +797,15 @@ func queryRangeHandler(w http.ResponseWriter, query string, start, end, step int
 
 	// Remove NaN values as Prometheus does.
 	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/153
-	removeNaNValuesInplace(result)
+	result = removeEmptyValuesAndTimeseries(result)
 
 	w.Header().Set("Content-Type", "application/json")
 	WriteQueryRangeResponse(w, result)
 	return nil
 }
 
-func removeNaNValuesInplace(tss []netstorage.Result) {
+func removeEmptyValuesAndTimeseries(tss []netstorage.Result) []netstorage.Result {
+	dst := tss[:0]
 	for i := range tss {
 		ts := &tss[i]
 		hasNaNs := false
@@ -816,6 +817,9 @@ func removeNaNValuesInplace(tss []netstorage.Result) {
 		}
 		if !hasNaNs {
 			// Fast path: nothing to remove.
+			if len(ts.Values) > 0 {
+				dst = append(dst, *ts)
+			}
 			continue
 		}
 
@@ -832,7 +836,11 @@ func removeNaNValuesInplace(tss []netstorage.Result) {
 		}
 		ts.Values = dstValues
 		ts.Timestamps = dstTimestamps
+		if len(ts.Values) > 0 {
+			dst = append(dst, *ts)
+		}
 	}
+	return dst
 }
 
 var queryRangeDuration = metrics.NewSummary(`vm_request_duration_seconds{path="/api/v1/query_range"}`)

app/vmselect/prometheus/prometheus_test.go

@@ -11,10 +11,10 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/netstorage"
 )
 
-func TestRemoveNaNValuesInplace(t *testing.T) {
+func TestRemoveEmptyValuesAndTimeseries(t *testing.T) {
 	f := func(tss []netstorage.Result, tssExpected []netstorage.Result) {
 		t.Helper()
-		removeNaNValuesInplace(tss)
+		tss = removeEmptyValuesAndTimeseries(tss)
 		if !reflect.DeepEqual(tss, tssExpected) {
 			t.Fatalf("unexpected result; got %v; want %v", tss, tssExpected)
 		}
@@ -30,6 +30,14 @@ func TestRemoveNaNValuesInplace(t *testing.T) {
 			Timestamps: []int64{100, 200, 300, 400},
 			Values:     []float64{nan, nan, 3, nan},
 		},
+		{
+			Timestamps: []int64{1, 2},
+			Values:     []float64{nan, nan},
+		},
+		{
+			Timestamps: nil,
+			Values:     nil,
+		},
 	}, []netstorage.Result{
 		{
 			Timestamps: []int64{100, 200, 300},