Update histogram helpers api (#44978)

### What does this PR do?

Add assertion on input data and allow helpers to produce blank sketches - for use in DataDog/dd-go#212091

### Motivation

### Describe how you validated your changes

### Additional Notes


Co-authored-by: ibraheem.aboulnaga <ibraheem.aboulnaga@datadoghq.com>

Author: IbraheemA

pkg/opentelemetry-mapping-go/otlp/metrics/histograms.go

@@ -6,6 +6,7 @@
 package metrics
 
 import (
+	"errors"
 	"fmt"
 	"math"
 	"time"
@@ -56,17 +57,25 @@ func getBounds(explicitBounds pcommon.Float64Slice, idx int) (lowerBound float64
 }
 
 // CreateDDSketchFromHistogramOfDuration creates a DDSketch from regular histogram data point
-func CreateDDSketchFromHistogramOfDuration(dp pmetric.HistogramDataPoint, unit string) (*ddsketch.DDSketch, error) {
+func CreateDDSketchFromHistogramOfDuration(dp *pmetric.HistogramDataPoint, unit string) (*ddsketch.DDSketch, error) {
 	relativeAccuracy := 0.01 // 1% relative accuracy
 	maxNumBins := 2048
 	newSketch, err := ddsketch.LogCollapsingLowestDenseDDSketch(relativeAccuracy, maxNumBins)
 	if err != nil {
 		return nil, err
 	}
 
+	if dp == nil {
+		return newSketch, nil
+	}
+
 	bucketCounts := dp.BucketCounts()
 	explicitBounds := dp.ExplicitBounds()
 
+	if bucketCounts.Len() != explicitBounds.Len()+1 {
+		return nil, errors.New("bucket counts length does not match explicit bounds length")
+	}
+
 	// Get scaling factor to convert unit to nanoseconds
 	scaleToNanos := getTimeUnitScaleToNanos(unit)
 
@@ -161,13 +170,13 @@ func toStoreFromExponentialBucketsWithUnitScale(b pmetric.ExponentialHistogramDa
 }
 
 // CreateDDSketchFromExponentialHistogramOfDuration creates a DDSketch from exponential histogram data point
-func CreateDDSketchFromExponentialHistogramOfDuration(p pmetric.ExponentialHistogramDataPoint, unit string) (*ddsketch.DDSketch, error) {
+func CreateDDSketchFromExponentialHistogramOfDuration(p *pmetric.ExponentialHistogramDataPoint, scale int32, unit string) (*ddsketch.DDSketch, error) {
 	// Create the DDSketch stores
 	scaleToNanos := getTimeUnitScaleToNanos(unit)
 
 	// Create the DDSketch mapping that corresponds to the ExponentialHistogram settings
 	gammaWithOnePercentAccuracy := 1.01 / 0.99
-	gamma := math.Pow(2, math.Pow(2, float64(-p.Scale())))
+	gamma := math.Pow(2, math.Pow(2, float64(-scale)))
 	gamma = math.Min(gamma, gammaWithOnePercentAccuracy)
 	indexOffset := math.Log(scaleToNanos)
 	mapping, err := mapping.NewLogarithmicMappingWithGamma(gamma, indexOffset)
@@ -176,9 +185,16 @@ func CreateDDSketchFromExponentialHistogramOfDuration(p pmetric.ExponentialHisto
 	}
 
 	// Calculate the base for the exponential histogram
-	base := math.Pow(2, math.Pow(2, float64(-p.Scale())))
-	positiveStore := toStoreFromExponentialBucketsWithUnitScale(p.Positive(), mapping, base, scaleToNanos)
-	negativeStore := toStoreFromExponentialBucketsWithUnitScale(p.Negative(), mapping, base, scaleToNanos)
+	base := math.Pow(2, math.Pow(2, float64(-scale)))
+	var positiveStore store.Store
+	var negativeStore store.Store
+	if p != nil {
+		positiveStore = toStoreFromExponentialBucketsWithUnitScale(p.Positive(), mapping, base, scaleToNanos)
+		negativeStore = toStoreFromExponentialBucketsWithUnitScale(p.Negative(), mapping, base, scaleToNanos)
+	} else {
+		positiveStore = store.NewDenseStore()
+		negativeStore = store.NewDenseStore()
+	}
 
 	// Create DDSketch with the above mapping and stores
 	sketch := ddsketch.NewDDSketch(mapping, positiveStore, negativeStore)

pkg/opentelemetry-mapping-go/otlp/metrics/histograms_test.go

@@ -471,7 +471,7 @@ func TestCreateDDSketchFromHistogramOfDuration(t *testing.T) {
 			}
 
 			// Test the function
-			sketch, err := CreateDDSketchFromHistogramOfDuration(dp, tt.unit)
+			sketch, err := CreateDDSketchFromHistogramOfDuration(&dp, tt.unit)
 			if tt.hasError {
 				assert.Error(t, err)
 				return
@@ -596,7 +596,7 @@ func TestCreateDDSketchFromExponentialHistogramOfDuration(t *testing.T) {
 			}
 
 			// Test the function
-			sketch, err := CreateDDSketchFromExponentialHistogramOfDuration(dp, tt.unit)
+			sketch, err := CreateDDSketchFromExponentialHistogramOfDuration(&dp, tt.scale, tt.unit)
 			if tt.hasError {
 				assert.Error(t, err)
 				return

releasenotes/notes/update-histogram-helpers-api-c6b4d67248b89943.yaml

@@ -0,0 +1,11 @@
+# Each section from every release note are combined when the
+# CHANGELOG.rst is rendered. So the text needs to be worded so that
+# it does not depend on any information only available in another
+# section. This may mean repeating some details, but each section
+# must be readable independently of the other.
+#
+# Each section note must be formatted as reStructuredText.
+---
+enhancements:
+  - |
+    Update the histogram helpers API in the `pkg/opentelemetry-mapping-go/otlp/metrics` package. The API now accepts accept pointers to the OTLP data points, and returns blank DDSketches when the pointer is nil.