[exporter/debug] output buckets for exponential histograms (#14656)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
the `writeexponentialhistogramdatapoints` function in the debug
exporter’s normal verbosity mode previously had todo placeholder and did
not print any bucket data. this change implements the missing bucket
display.

each bucket is now printed as `leX=Y`, where `X` is the computed upper
bound and `Y` is the bucket count. for positive buckets, the upper bound
is calculated as `exp((index+1) * factor)`, and for negative buckets as
`-exp(index * factor)`, where `factor = math.Ldexp(math.Ln2, -scale)`.
negative buckets are listed from most-negative to least-negative, and
the zero bucket is printed as `zero=N` when its count is non-zero.
<!-- Issue number if applicable -->
#### Link to tracking issue
Fixes #10463

<!--Describe what testing was performed and which tests were added.-->
#### Testing

<!--Describe the documentation added.-->
#### Documentation
No documentation changes required.
<!--Please delete paragraphs that you did not use before submitting.-->

---------

Signed-off-by: arpit529srivastava <arpitsrivastava529@gmail.com>

Author: Arpit529Srivastava

.chloggen/debug-exporter-exponential-histogram-buckets.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. receiver/otlp)
+component: exporter/debug
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Output bucket counts for exponential histogram data points in normal verbosity.
+
+# One or more tracking issues or pull requests related to the change
+issues: [10463]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

exporter/debugexporter/internal/normal/metrics.go

@@ -6,6 +6,7 @@ package normal // import "go.opentelemetry.io/collector/exporter/debugexporter/i
 import (
 	"bytes"
 	"fmt"
+	"math"
 	"strconv"
 	"strings"
 
@@ -115,21 +116,39 @@ func writeExponentialHistogramDataPoints(metric pmetric.Metric) (lines []string)
 		dataPoint := metric.ExponentialHistogram().DataPoints().At(i)
 		dataPointAttributes := writeAttributes(dataPoint.Attributes())
 
-		var value string
-		value = fmt.Sprintf("count=%d", dataPoint.Count())
+		var value strings.Builder
+		fmt.Fprintf(&value, "count=%d", dataPoint.Count())
 		if dataPoint.HasSum() {
-			value += fmt.Sprintf(" sum=%v", dataPoint.Sum())
+			fmt.Fprintf(&value, " sum=%v", dataPoint.Sum())
 		}
 		if dataPoint.HasMin() {
-			value += fmt.Sprintf(" min=%v", dataPoint.Min())
+			fmt.Fprintf(&value, " min=%v", dataPoint.Min())
 		}
 		if dataPoint.HasMax() {
-			value += fmt.Sprintf(" max=%v", dataPoint.Max())
+			fmt.Fprintf(&value, " max=%v", dataPoint.Max())
 		}
 
-		// TODO display buckets
+		factor := math.Ldexp(math.Ln2, -int(dataPoint.Scale()))
 
-		dataPointLine := fmt.Sprintf("%s{%s} %s\n", metric.Name(), strings.Join(dataPointAttributes, ","), value)
+		negB := dataPoint.Negative()
+		for j := negB.BucketCounts().Len() - 1; j >= 0; j-- {
+			index := float64(negB.Offset()) + float64(j)
+			upperBound := -math.Exp(index * factor)
+			fmt.Fprintf(&value, " le%v=%d", upperBound, negB.BucketCounts().At(j))
+		}
+
+		if dataPoint.ZeroCount() != 0 {
+			fmt.Fprintf(&value, " zero=%d", dataPoint.ZeroCount())
+		}
+
+		posB := dataPoint.Positive()
+		for j := 0; j < posB.BucketCounts().Len(); j++ {
+			index := float64(posB.Offset()) + float64(j)
+			upperBound := math.Exp((index + 1) * factor)
+			fmt.Fprintf(&value, " le%v=%d", upperBound, posB.BucketCounts().At(j))
+		}
+
+		dataPointLine := fmt.Sprintf("%s{%s} %s\n", metric.Name(), strings.Join(dataPointAttributes, ","), value.String())
 		lines = append(lines, dataPointLine)
 	}
 	return lines

exporter/debugexporter/internal/normal/metrics_test.go

@@ -4,6 +4,8 @@
 package normal
 
 import (
+	"fmt"
+	"math"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -107,7 +109,7 @@ http.server.request.duration{http.response.status_code=200,http.request.method=G
 `,
 		},
 		{
-			name: "exponential histogram",
+			name: "exponential histogram without buckets",
 			input: func() pmetric.Metrics {
 				metrics := pmetric.NewMetrics()
 				metric := metrics.ResourceMetrics().AppendEmpty().ScopeMetrics().AppendEmpty().Metrics().AppendEmpty()
@@ -126,6 +128,57 @@ ScopeMetrics #0
 http.server.request.duration{http.response.status_code=200,http.request.method=GET} count=1340 sum=99.573 min=0.017 max=8.13
 `,
 		},
+		{
+			name: "exponential histogram with buckets",
+			input: func() pmetric.Metrics {
+				metrics := pmetric.NewMetrics()
+				metric := metrics.ResourceMetrics().AppendEmpty().ScopeMetrics().AppendEmpty().Metrics().AppendEmpty()
+				metric.SetName("http.server.request.duration")
+				dataPoint := metric.SetEmptyExponentialHistogram().DataPoints().AppendEmpty()
+				dataPoint.Attributes().PutInt("http.response.status_code", 200)
+				dataPoint.Attributes().PutStr("http.request.method", "GET")
+				dataPoint.SetCount(1340)
+				dataPoint.SetSum(99.573)
+				dataPoint.SetMin(0.017)
+				dataPoint.SetMax(8.13)
+				dataPoint.SetScale(3)
+				dataPoint.SetZeroCount(3)
+				dataPoint.Negative().SetOffset(-2)
+				dataPoint.Negative().BucketCounts().FromRaw([]uint64{10, 20})
+				dataPoint.Positive().SetOffset(1)
+				dataPoint.Positive().BucketCounts().FromRaw([]uint64{40, 50, 60})
+				return metrics
+			}(),
+			expected: func() string {
+				f := math.Ldexp(math.Ln2, -3)
+				return fmt.Sprintf("ResourceMetrics #0\nScopeMetrics #0\n"+
+					"http.server.request.duration{http.response.status_code=200,http.request.method=GET}"+
+					" count=1340 sum=99.573 min=0.017 max=8.13"+
+					" le%v=20 le%v=10 zero=3 le%v=40 le%v=50 le%v=60\n",
+					-math.Exp(-1*f), -math.Exp(-2*f),
+					math.Exp(2*f), math.Exp(3*f), math.Exp(4*f))
+			}(),
+		},
+		{
+			name: "exponential histogram with positive buckets only",
+			input: func() pmetric.Metrics {
+				metrics := pmetric.NewMetrics()
+				metric := metrics.ResourceMetrics().AppendEmpty().ScopeMetrics().AppendEmpty().Metrics().AppendEmpty()
+				metric.SetName("latency")
+				dataPoint := metric.SetEmptyExponentialHistogram().DataPoints().AppendEmpty()
+				dataPoint.SetCount(2)
+				dataPoint.SetScale(1)
+				dataPoint.Positive().SetOffset(1)
+				dataPoint.Positive().BucketCounts().FromRaw([]uint64{1, 1})
+				return metrics
+			}(),
+			expected: func() string {
+				f := math.Ldexp(math.Ln2, -1)
+				return fmt.Sprintf("ResourceMetrics #0\nScopeMetrics #0\n"+
+					"latency{} count=2 le%v=1 le%v=1\n",
+					math.Exp(2*f), math.Exp(3*f))
+			}(),
+		},
 		{
 			name: "summary",
 			input: func() pmetric.Metrics {