From 3972b9f7610de8d2f4133303a90ee9b10c778b51 Mon Sep 17 00:00:00 2001
From: David Ashpole <dashpole@google.com>
Date: Tue, 10 Oct 2023 19:03:49 +0000
Subject: [PATCH] Add WithExplicitBucketBoundaries Histogram option to the
 metric api

---
 CHANGELOG.md               |  1 +
 metric/instrument.go       | 21 +++++++++++++++++++++
 metric/syncfloat64.go      | 10 ++++++++--
 metric/syncfloat64_test.go |  6 ++++++
 metric/syncint64.go        | 10 ++++++++--
 metric/syncint64_test.go   |  6 ++++++
 6 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 94870c638d6a..7ffcd4212398 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Added
 
 - Add `go.opentelemetry.io/otel/bridge/opencensus.InstallTraceBridge`, which installs the OpenCensus trace bridge, and replaces `opencensus.NewTracer`. (#4567)
+- Add `go.opentelemetry.io/otel/metric.WithExplicitBucketBoundaries`, which allows defining default explicit bucket boundaries when creating histogram instruments. (#4603)
 
 ### Deprecated
 
diff --git a/metric/instrument.go b/metric/instrument.go
index cdca00058c68..fc3be5caa398 100644
--- a/metric/instrument.go
+++ b/metric/instrument.go
@@ -39,6 +39,12 @@ type InstrumentOption interface {
 	Float64ObservableGaugeOption
 }
 
+// HistogramOption applies options to histogram instruments.
+type HistogramOption interface {
+	Int64HistogramOption
+	Float64HistogramOption
+}
+
 type descOpt string
 
 func (o descOpt) applyFloat64Counter(c Float64CounterConfig) Float64CounterConfig {
@@ -171,6 +177,21 @@ func (o unitOpt) applyInt64ObservableGauge(c Int64ObservableGaugeConfig) Int64Ob
 // The unit u should be defined using the appropriate [UCUM](https://ucum.org) case-sensitive code.
 func WithUnit(u string) InstrumentOption { return unitOpt(u) }
 
+// WithExplicitBucketBoundaries sets the instrument explicit bucket boundaries.
+func WithExplicitBucketBoundaries(bounds []float64) HistogramOption { return bucketOpt(bounds) }
+
+type bucketOpt []float64
+
+func (o bucketOpt) applyFloat64Histogram(c Float64HistogramConfig) Float64HistogramConfig {
+	c.explicitBucketBoundaries = o
+	return c
+}
+
+func (o bucketOpt) applyInt64Histogram(c Int64HistogramConfig) Int64HistogramConfig {
+	c.explicitBucketBoundaries = o
+	return c
+}
+
 // AddOption applies options to an addition measurement. See
 // [MeasurementOption] for other options that can be used as an AddOption.
 type AddOption interface {
diff --git a/metric/syncfloat64.go b/metric/syncfloat64.go
index f0b063721d81..0a4825ae6a79 100644
--- a/metric/syncfloat64.go
+++ b/metric/syncfloat64.go
@@ -147,8 +147,9 @@ type Float64Histogram interface {
 // Float64HistogramConfig contains options for synchronous counter instruments
 // that record int64 values.
 type Float64HistogramConfig struct {
-	description string
-	unit        string
+	description              string
+	unit                     string
+	explicitBucketBoundaries []float64
 }
 
 // NewFloat64HistogramConfig returns a new [Float64HistogramConfig] with all
@@ -171,6 +172,11 @@ func (c Float64HistogramConfig) Unit() string {
 	return c.unit
 }
 
+// ExplicitBucketBoundaries returns the configured explicit bucket boundaries.
+func (c Float64HistogramConfig) ExplicitBucketBoundaries() []float64 {
+	return c.explicitBucketBoundaries
+}
+
 // Float64HistogramOption applies options to a [Float64HistogramConfig]. See
 // [InstrumentOption] for other options that can be used as a
 // Float64HistogramOption.
diff --git a/metric/syncfloat64_test.go b/metric/syncfloat64_test.go
index 7132680b1316..51cef235317e 100644
--- a/metric/syncfloat64_test.go
+++ b/metric/syncfloat64_test.go
@@ -51,3 +51,9 @@ type float64Config interface {
 	Description() string
 	Unit() string
 }
+
+func TestFloat64ExplicitBucketHistogramConfiguration(t *testing.T) {
+	bounds := []float64{0.1, 0.5, 1.0}
+	got := NewFloat64HistogramConfig(WithExplicitBucketBoundaries(bounds))
+	assert.Equal(t, bounds, got.ExplicitBucketBoundaries(), "boundaries")
+}
diff --git a/metric/syncint64.go b/metric/syncint64.go
index 6f508eb66d40..56667d32fc01 100644
--- a/metric/syncint64.go
+++ b/metric/syncint64.go
@@ -147,8 +147,9 @@ type Int64Histogram interface {
 // Int64HistogramConfig contains options for synchronous counter instruments
 // that record int64 values.
 type Int64HistogramConfig struct {
-	description string
-	unit        string
+	description              string
+	unit                     string
+	explicitBucketBoundaries []float64
 }
 
 // NewInt64HistogramConfig returns a new [Int64HistogramConfig] with all opts
@@ -171,6 +172,11 @@ func (c Int64HistogramConfig) Unit() string {
 	return c.unit
 }
 
+// ExplicitBucketBoundaries returns the configured explicit bucket boundaries.
+func (c Int64HistogramConfig) ExplicitBucketBoundaries() []float64 {
+	return c.explicitBucketBoundaries
+}
+
 // Int64HistogramOption applies options to a [Int64HistogramConfig]. See
 // [InstrumentOption] for other options that can be used as an
 // Int64HistogramOption.
diff --git a/metric/syncint64_test.go b/metric/syncint64_test.go
index 51c02f5e041a..dcc351075c46 100644
--- a/metric/syncint64_test.go
+++ b/metric/syncint64_test.go
@@ -51,3 +51,9 @@ type int64Config interface {
 	Description() string
 	Unit() string
 }
+
+func TestInt64ExplicitBucketHistogramConfiguration(t *testing.T) {
+	bounds := []float64{0.1, 0.5, 1.0}
+	got := NewInt64HistogramConfig(WithExplicitBucketBoundaries(bounds))
+	assert.Equal(t, bounds, got.ExplicitBucketBoundaries(), "boundaries")
+}