add exemplar support to the OTLP HTTP and gRPC exporters (#4900)

CHANGELOG.md

@@ -14,6 +14,8 @@ The next release will require at least [Go 1.21].
 ### Added
 
 - Support [Go 1.22]. (#4890)
+- Add exemplar support to `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc`. (#4900)
+- Add exemplar support to `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#4900)
 
 ## [1.23.1] 2024-02-07
 

exporters/otlp/otlpmetric/otlpmetricgrpc/internal/transform/metricdata.go

@@ -148,6 +148,7 @@ func DataPoints[N int64 | float64](dPts []metricdata.DataPoint[N]) []*mpb.Number
 			Attributes:        AttrIter(dPt.Attributes.Iter()),
 			StartTimeUnixNano: timeUnixNano(dPt.StartTime),
 			TimeUnixNano:      timeUnixNano(dPt.Time),
+			Exemplars:         Exemplars(dPt.Exemplars),
 		}
 		switch v := any(dPt.Value).(type) {
 		case int64:
@@ -193,6 +194,7 @@ func HistogramDataPoints[N int64 | float64](dPts []metricdata.HistogramDataPoint
 			Sum:               &sum,
 			BucketCounts:      dPt.BucketCounts,
 			ExplicitBounds:    dPt.Bounds,
+			Exemplars:         Exemplars(dPt.Exemplars),
 		}
 		if v, ok := dPt.Min.Value(); ok {
 			vF64 := float64(v)
@@ -236,6 +238,7 @@ func ExponentialHistogramDataPoints[N int64 | float64](dPts []metricdata.Exponen
 			Sum:               &sum,
 			Scale:             dPt.Scale,
 			ZeroCount:         dPt.ZeroCount,
+			Exemplars:         Exemplars(dPt.Exemplars),
 
 			Positive: ExponentialHistogramDataPointBuckets(dPt.PositiveBucket),
 			Negative: ExponentialHistogramDataPointBuckets(dPt.NegativeBucket),
@@ -290,3 +293,28 @@ func timeUnixNano(t time.Time) uint64 {
 	}
 	return uint64(t.UnixNano())
 }
+
+// Exemplars returns a slice of OTLP Exemplars generated from exemplars.
+func Exemplars[N int64 | float64](exemplars []metricdata.Exemplar[N]) []*mpb.Exemplar {
+	out := make([]*mpb.Exemplar, 0, len(exemplars))
+	for _, exemplar := range exemplars {
+		e := &mpb.Exemplar{
+			FilteredAttributes: KeyValues(exemplar.FilteredAttributes),
+			TimeUnixNano:       timeUnixNano(exemplar.Time),
+			SpanId:             exemplar.SpanID,
+			TraceId:            exemplar.TraceID,
+		}
+		switch v := any(exemplar.Value).(type) {
+		case int64:
+			e.Value = &mpb.Exemplar_AsInt{
+				AsInt: v,
+			}
+		case float64:
+			e.Value = &mpb.Exemplar_AsDouble{
+				AsDouble: v,
+			}
+		}
+		out = append(out, e)
+	}
+	return out
+}