Discard tags with empty fields

Labels with empty key or value are not allowed by the remote write spec, so if any seen tag contains them then they are not mapped to the related label.

Author: codebien

pkg/remotewrite/prometheus.go

@@ -21,8 +21,11 @@ func MapTagSet(t *metrics.TagSet) []*prompb.Label {
 labels := make([]*prompb.Label, 0, n.Len())
 for !n.IsRoot() {
 prev, key, value := n.Data()
-labels = append(labels, &prompb.Label{Name: key, Value: value})
 n = prev
+if key == "" || value == "" {
+continue
+}
+labels = append(labels, &prompb.Label{Name: key, Value: value})
 }
 return labels
 }

pkg/remotewrite/prometheus_test.go

@@ -17,12 +17,19 @@ func TestMapSeries(t *testing.T) {
 t.Parallel()
 
 r := metrics.NewRegistry()
+tags := r.RootTagSet().
+With("tagk1", "tagv1").With("b1", "v1").
+// labels with empty key or value are not allowed
+// so they will be not added as labels
+With("tagEmptyValue", "").
+With("", "tagEmptyKey")
+
 series := metrics.TimeSeries{
 Metric: &metrics.Metric{
 Name: "test",
 Type: metrics.Counter,
 },
-Tags: r.RootTagSet().With("tagk1", "tagv1").With("b1", "v1"),
+Tags: tags,
 }
 
 lbls := MapSeries(series, "")