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fix: support exemplars with empty label sets in OpenMetrics 2.0 #965

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Merged
bwplotka merged 1 commit into from
Aug 24, 2026
+28 −3
Merged

fix: support exemplars with empty label sets in OpenMetrics 2.0 #965

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10 changes: 7 additions & 3 deletions expfmt/openmetrics_2_0_create.go
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Original file line number Diff line number Diff line change
Expand Up @@ -260,7 +260,7 @@ func writeOpenMetrics20Sample(w enhancedWriter, name string, metric *dto.Metric,
}
}

if exemplar != nil && len(exemplar.Label) > 0 && exemplar.Timestamp != nil {
if exemplar != nil && exemplar.Timestamp != nil {
n, err = writeExemplar20(w, exemplar)
written += n
if err != nil {
Expand All @@ -279,7 +279,7 @@ func writeOpenMetrics20Sample(w enhancedWriter, name string, metric *dto.Metric,
// writeExemplar20 writes the provided exemplar in OpenMetrics 2.0 format to w.
// In OpenMetrics 2.0, exemplars without a timestamp are dropped.
func writeExemplar20(w enhancedWriter, e *dto.Exemplar) (int, error) {
if e == nil || len(e.Label) == 0 || e.Timestamp == nil {
if e == nil || e.Timestamp == nil {
return 0, nil
}
if err := validateExemplar20(e); err != nil {
Expand All @@ -291,7 +291,11 @@ func writeExemplar20(w enhancedWriter, e *dto.Exemplar) (int, error) {
if err != nil {
return written, err
}
n, err = writeOpenMetricsNameAndLabelPairs(w, "", e.Label, "", 0)
if len(e.Label) == 0 {
n, err = w.WriteString("{}")
} else {
n, err = writeOpenMetricsNameAndLabelPairs(w, "", e.Label, "", 0)
}
written += n
if err != nil {
return written, err
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21 changes: 21 additions & 0 deletions expfmt/openmetrics_2_0_create_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -161,6 +161,27 @@ node_memory_active_bytes 1.2345e+09 1234567890
},
out: `# TYPE http_requests_total counter
http_requests_total 1027 1234567891 st@1234567890 # {trace_id="1234"} 1 1234567890.5
`,
},
{
name: "CounterWithExemplarWithoutLabels",
in: &dto.MetricFamily{
Name: proto.String("http_requests_total"),
Type: dto.MetricType_COUNTER.Enum(),
Metric: []*dto.Metric{
{
Counter: &dto.Counter{
Value: proto.Float64(1027),
Exemplar: &dto.Exemplar{
Value: proto.Float64(1),
Timestamp: &timestamppb.Timestamp{Seconds: 1234567890, Nanos: 500000000},
},
},
},
},
},
out: `# TYPE http_requests_total counter
http_requests_total 1027 # {} 1 1234567890.5
`,
},
{
Expand Down
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