Implement new function NewConstMetricWithCreatedTimestamp

NewConstMetricWithCreatedTimestamp generates constant counters with created timestamp set. It returns errors if it receives other metric types.

Signed-off-by: Arthur Silva Sens <arthur.sens@coralogix.com>

prometheus/counter.go

@@ -172,8 +172,8 @@ func (c *counter) Write(out *dto.Metric) error {
 		exemplar = e.(*dto.Exemplar)
 	}
 	val := c.get()
-
-	return populateMetric(CounterValue, val, c.labelPairs, exemplar, out, c.createdTs)
+	ct := c.createdTs.AsTime()
+	return populateMetric(CounterValue, val, c.labelPairs, exemplar, out, &ct)
 }
 
 func (c *counter) updateExemplar(v float64, l Labels) {

prometheus/value.go

@@ -14,6 +14,7 @@
 package prometheus
 
 import (
+	"errors"
 	"fmt"
 	"sort"
 	"time"
@@ -110,7 +111,7 @@ func NewConstMetric(desc *Desc, valueType ValueType, value float64, labelValues
 	}
 
 	metric := &dto.Metric{}
-	if err := populateMetric(valueType, value, MakeLabelPairs(desc, labelValues), nil, metric, timestamppb.Now()); err != nil {
+	if err := populateMetric(valueType, value, MakeLabelPairs(desc, labelValues), nil, metric, nil); err != nil {
 		return nil, err
 	}
 
@@ -130,6 +131,43 @@ func MustNewConstMetric(desc *Desc, valueType ValueType, value float64, labelVal
 	return m
 }
 
+// NewConstMetricWithCreatedTimestamp does the same thing as NewConstMetric, but generates Counters
+// with created timestamp set and returns an error for other metric types.
+func NewConstMetricWithCreatedTimestamp(desc *Desc, valueType ValueType, value float64, ct time.Time, labelValues ...string) (Metric, error) {
+	if desc.err != nil {
+		return nil, desc.err
+	}
+	if err := validateLabelValues(labelValues, len(desc.variableLabels.names)); err != nil {
+		return nil, err
+	}
+	switch valueType {
+	case CounterValue:
+		break
+	default:
+		return nil, errors.New("Created timestamps are only supported for counters")
+	}
+
+	metric := &dto.Metric{}
+	if err := populateMetric(valueType, value, MakeLabelPairs(desc, labelValues), nil, metric, &ct); err != nil {
+		return nil, err
+	}
+
+	return &constMetric{
+		desc:   desc,
+		metric: metric,
+	}, nil
+}
+
+// MustNewConstMetricWithCreatedTimestamp is a version of NewConstMetricWithCreatedTimestamp that panics where
+// NewConstMetricWithCreatedTimestamp would have returned an error.
+func MustNewConstMetricWithCreatedTimestamp(desc *Desc, valueType ValueType, value float64, ct time.Time, labelValues ...string) Metric {
+	m, err := NewConstMetricWithCreatedTimestamp(desc, valueType, value, ct, labelValues...)
+	if err != nil {
+		panic(err)
+	}
+	return m
+}
+
 type constMetric struct {
 	desc   *Desc
 	metric *dto.Metric
@@ -153,12 +191,17 @@ func populateMetric(
 	labelPairs []*dto.LabelPair,
 	e *dto.Exemplar,
 	m *dto.Metric,
-	cTs *timestamppb.Timestamp,
+	createdTimestamp *time.Time,
 ) error {
+	var ct *timestamppb.Timestamp
+	if createdTimestamp != nil {
+		ct = timestamppb.New(*createdTimestamp)
+	}
+
 	m.Label = labelPairs
 	switch t {
 	case CounterValue:
-		m.Counter = &dto.Counter{Value: proto.Float64(v), Exemplar: e, CreatedTimestamp: cTs}
+		m.Counter = &dto.Counter{Value: proto.Float64(v), Exemplar: e, CreatedTimestamp: ct}
 	case GaugeValue:
 		m.Gauge = &dto.Gauge{Value: proto.Float64(v)}
 	case UntypedValue:

prometheus/value_test.go

@@ -16,6 +16,10 @@ package prometheus
 import (
 	"fmt"
 	"testing"
+	"time"
+
+	dto "github.com/prometheus/client_model/go"
+	"google.golang.org/protobuf/types/known/timestamppb"
 )
 
 func TestNewConstMetricInvalidLabelValues(t *testing.T) {
@@ -54,3 +58,55 @@ func TestNewConstMetricInvalidLabelValues(t *testing.T) {
 		}
 	}
 }
+
+func TestNewConstMetricWithCreatedTimestamp(t *testing.T) {
+	ct := time.Now()
+	testCases := []struct {
+		desc             string
+		metricType       ValueType
+		createdTimestamp time.Time
+		expecErr         bool
+		expectedCt       *timestamppb.Timestamp
+	}{
+		{
+			desc:             "gauge with CT",
+			metricType:       GaugeValue,
+			createdTimestamp: ct,
+			expecErr:         true,
+			expectedCt:       nil,
+		},
+		{
+			desc:             "counter with CT",
+			metricType:       CounterValue,
+			createdTimestamp: ct,
+			expecErr:         false,
+			expectedCt:       timestamppb.New(ct),
+		},
+	}
+
+	for _, test := range testCases {
+		metricDesc := NewDesc(
+			"sample_value",
+			"sample value",
+			nil,
+			nil,
+		)
+		m, err := NewConstMetricWithCreatedTimestamp(metricDesc, test.metricType, float64(1), test.createdTimestamp)
+
+		if test.expecErr && err == nil {
+			t.Errorf("Expected error is test %s, got no err", test.desc)
+		}
+
+		if !test.expecErr && err != nil {
+			t.Errorf("Didn't expect error in test %s, got %s", test.desc, err.Error())
+		}
+
+		if test.expectedCt != nil {
+			var metric dto.Metric
+			m.Write(&metric)
+			if metric.Counter.CreatedTimestamp.AsTime() != test.expectedCt.AsTime() {
+				t.Errorf("Expected timestamp %v, got %v", test.expectedCt, &metric.Counter.CreatedTimestamp)
+			}
+		}
+	}
+}