prometheusexporter: add exemplar support

exporter/prometheusexporter/collector.go

@@ -176,6 +176,7 @@ func (c *collector) convertDoubleHistogram(metric pdata.Metric) (prometheus.Metr
 
 	indicesMap := make(map[float64]int)
 	buckets := make([]float64, 0, len(ip.BucketCounts()))
+
 	for index, bucket := range ip.ExplicitBounds() {
 		if _, added := indicesMap[bucket]; !added {
 			indicesMap[bucket] = index
@@ -197,11 +198,36 @@ func (c *collector) convertDoubleHistogram(metric pdata.Metric) (prometheus.Metr
 		points[bucket] = cumCount
 	}
 
+	arrLen := ip.Exemplars().Len()
+	exemplars := make([]prometheus.Exemplar, arrLen)
+	for i := 0; i < arrLen; i++ {
+		e := ip.Exemplars().At(i)
+
+		labels := make(prometheus.Labels, e.FilteredAttributes().Len())
+		e.FilteredAttributes().Range(func(k string, v pdata.Value) bool {
+			labels[k] = v.AsString()
+			return true
+		})
+
+		exemplars[i] = prometheus.Exemplar{
+			Value:     e.DoubleVal(),
+			Labels:    labels,
+			Timestamp: e.Timestamp().AsTime(),
+		}
+	}
+
 	m, err := prometheus.NewConstHistogram(desc, ip.Count(), ip.Sum(), points, attributes...)
 	if err != nil {
 		return nil, err
 	}
 
+	if arrLen > 0 {
+		m, err = prometheus.NewMetricWithExemplars(m, exemplars...)
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	if c.sendTimestamps {
 		return prometheus.NewMetricWithTimestamp(ip.Timestamp().AsTime(), m), nil
 	}

exporter/prometheusexporter/collector_test.go

@@ -87,6 +87,83 @@ func TestConvertInvalidMetric(t *testing.T) {
 	}
 }
 
+func TestConvertDoubleHistogramExemplar(t *testing.T) {
+	// initialize empty histogram
+	metric := pdata.NewMetric()
+	metric.SetDataType(pdata.MetricDataTypeHistogram)
+	metric.SetName("test_metric")
+	metric.SetDescription("this is test metric")
+	metric.SetUnit("T")
+
+	// initialize empty datapoint
+	hd := metric.Histogram().DataPoints().AppendEmpty()
+
+	bounds := []float64{5, 25, 90}
+	hd.SetExplicitBounds(bounds)
+	bc := []uint64{2, 35, 70}
+	hd.SetBucketCounts(bc)
+
+	exemplarTs, _ := time.Parse("unix", "Mon Jan _2 15:04:05 MST 2006")
+	exemplars := []prometheus.Exemplar{
+		{
+			Timestamp: exemplarTs,
+			Value:     3,
+			Labels:    prometheus.Labels{"test_label_0": "label_value_0"},
+		},
+		{
+			Timestamp: exemplarTs,
+			Value:     50,
+			Labels:    prometheus.Labels{"test_label_1": "label_value_1"},
+		},
+		{
+			Timestamp: exemplarTs,
+			Value:     78,
+			Labels:    prometheus.Labels{"test_label_2": "label_value_2"},
+		},
+	}
+
+	// add each exemplar value to the metric
+	for _, e := range exemplars {
+		pde := hd.Exemplars().AppendEmpty()
+		pde.SetDoubleVal(e.Value)
+		for k, v := range e.Labels {
+			pde.FilteredAttributes().InsertString(k, v)
+		}
+		pde.SetTimestamp(pdata.NewTimestampFromTime(e.Timestamp))
+	}
+
+	c := collector{
+		accumulator: &mockAccumulator{
+			[]pdata.Metric{metric},
+		},
+		logger: zap.NewNop(),
+	}
+
+	pbMetric, _ := c.convertDoubleHistogram(metric)
+	m := io_prometheus_client.Metric{}
+	pbMetric.Write(&m)
+
+	buckets := m.GetHistogram().GetBucket()
+
+	require.Equal(t, 3, len(buckets))
+
+	require.Equal(t, 3.0, buckets[0].GetExemplar().GetValue())
+	require.Equal(t, int32(128654848), buckets[0].GetExemplar().GetTimestamp().GetNanos())
+	require.Equal(t, 1, len(buckets[0].GetExemplar().GetLabel()))
+	require.Equal(t, "test_label_0", buckets[0].GetExemplar().GetLabel()[0].GetName())
+	require.Equal(t, "label_value_0", buckets[0].GetExemplar().GetLabel()[0].GetValue())
+
+	require.Equal(t, 0.0, buckets[1].GetExemplar().GetValue())
+	require.Equal(t, int32(0), buckets[1].GetExemplar().GetTimestamp().GetNanos())
+	require.Equal(t, 0, len(buckets[1].GetExemplar().GetLabel()))
+
+	require.Equal(t, 78.0, buckets[2].GetExemplar().GetValue())
+	require.Equal(t, int32(128654848), buckets[2].GetExemplar().GetTimestamp().GetNanos())
+	require.Equal(t, 1, len(buckets[2].GetExemplar().GetLabel()))
+	require.Equal(t, "test_label_2", buckets[2].GetExemplar().GetLabel()[0].GetName())
+	require.Equal(t, "label_value_2", buckets[2].GetExemplar().GetLabel()[0].GetValue())
+}
+
 // errorCheckCore keeps track of logged errors
 type errorCheckCore struct {
 	errorMessages []string

exporter/prometheusexporter/config.go

@@ -46,6 +46,9 @@ type Config struct {
 	// ResourceToTelemetrySettings defines configuration for converting resource attributes to metric labels.
 	ResourceToTelemetrySettings resourcetotelemetry.Settings `mapstructure:"resource_to_telemetry_conversion"`
 
+	// EnableOpenMetrics enables the use of the OpenMetrics encoding option for the prometheus exporter.
+	EnableOpenMetrics bool `mapstructure:"enable_open_metrics"`
+
 	// skipSanitizeLabel if enabled, labels that start with _ are not sanitized
 	skipSanitizeLabel bool
 }

exporter/prometheusexporter/factory.go

@@ -46,6 +46,7 @@ func createDefaultConfig() config.Exporter {
 		ConstLabels:       map[string]string{},
 		SendTimestamps:    false,
 		MetricExpiration:  time.Minute * 5,
+		EnableOpenMetrics: false,
 		skipSanitizeLabel: featuregate.IsEnabled(dropSanitizationGate.ID),
 	}
 }

exporter/prometheusexporter/go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/open-telemetry/opentelemetry-collector-contrib/internal/coreinternal v0.47.0
 	github.com/open-telemetry/opentelemetry-collector-contrib/pkg/resourcetotelemetry v0.47.0
 	github.com/open-telemetry/opentelemetry-collector-contrib/receiver/prometheusreceiver v0.47.0
-	github.com/prometheus/client_golang v1.12.1
+	github.com/prometheus/client_golang v1.12.2-0.20220318110013-3bc8f2c651ff
 	github.com/prometheus/client_model v0.2.0
 	github.com/prometheus/prometheus v1.8.2-0.20220117154355-4855a0c067e2
 	github.com/stretchr/testify v1.7.0