Added WithAggregationSelector to prometheus (#3341)

* Added WithAggregationSelector to prometheus

* Update CHANGELOG.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Address PR comments

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -11,6 +11,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Added
 
 - Prometheus exporter will register with a prometheus registerer on creation, there are options to control this. (#3239)
+- Added the `WithAggregationSelector` option to the `go.opentelemetry.io/otel/exporters/prometheus` package to change the `AggregationSelector` used. (#3341)
 
 ### Changed
 

exporters/prometheus/confg_test.go

@@ -19,22 +19,28 @@ import (
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/metric/aggregation"
+	"go.opentelemetry.io/otel/sdk/metric/view"
 )
 
 func TestNewConfig(t *testing.T) {
 	registry := prometheus.NewRegistry()
 
+	aggregationSelector := func(view.InstrumentKind) aggregation.Aggregation { return nil }
+
 	testCases := []struct {
-		name           string
-		options        []Option
-		wantRegisterer prometheus.Registerer
+		name            string
+		options         []Option
+		wantRegisterer  prometheus.Registerer
+		wantAggregation metric.AggregationSelector
 	}{
 		{
 			name:           "Default",
 			options:        nil,
 			wantRegisterer: prometheus.DefaultRegisterer,
 		},
-
 		{
 			name: "WithRegisterer",
 			options: []Option{
@@ -42,6 +48,23 @@ func TestNewConfig(t *testing.T) {
 			},
 			wantRegisterer: registry,
 		},
+		{
+			name: "WithAggregationSelector",
+			options: []Option{
+				WithAggregationSelector(aggregationSelector),
+			},
+			wantRegisterer:  prometheus.DefaultRegisterer,
+			wantAggregation: aggregationSelector,
+		},
+		{
+			name: "With Multiple Options",
+			options: []Option{
+				WithRegisterer(registry),
+				WithAggregationSelector(aggregationSelector),
+			},
+			wantRegisterer:  registry,
+			wantAggregation: aggregationSelector,
+		},
 		{
 			name: "nil options do nothing",
 			options: []Option{
@@ -58,3 +81,31 @@ func TestNewConfig(t *testing.T) {
 		})
 	}
 }
+
+func TestConfigManualReaderOptions(t *testing.T) {
+	aggregationSelector := func(view.InstrumentKind) aggregation.Aggregation { return nil }
+
+	testCases := []struct {
+		name            string
+		config          config
+		wantOptionCount int
+	}{
+		{
+			name:            "Default",
+			config:          config{},
+			wantOptionCount: 0,
+		},
+
+		{
+			name:            "WithAggregationSelector",
+			config:          config{aggregation: aggregationSelector},
+			wantOptionCount: 1,
+		},
+	}
+	for _, tt := range testCases {
+		t.Run(tt.name, func(t *testing.T) {
+			opts := tt.config.manualReaderOptions()
+			assert.Len(t, opts, tt.wantOptionCount)
+		})
+	}
+}

exporters/prometheus/config.go

@@ -16,11 +16,14 @@ package prometheus // import "go.opentelemetry.io/otel/exporters/prometheus"
 
 import (
 	"github.com/prometheus/client_golang/prometheus"
+
+	"go.opentelemetry.io/otel/sdk/metric"
 )
 
 // config contains options for the exporter.
 type config struct {
-	registerer prometheus.Registerer
+	registerer  prometheus.Registerer
+	aggregation metric.AggregationSelector
 }
 
 // newConfig creates a validated config configured with options.
@@ -37,6 +40,14 @@ func newConfig(opts ...Option) config {
 	return cfg
 }
 
+func (cfg config) manualReaderOptions() []metric.ManualReaderOption {
+	opts := []metric.ManualReaderOption{}
+	if cfg.aggregation != nil {
+		opts = append(opts, metric.WithAggregationSelector(cfg.aggregation))
+	}
+	return opts
+}
+
 // Option sets exporter option values.
 type Option interface {
 	apply(config) config
@@ -57,3 +68,13 @@ func WithRegisterer(reg prometheus.Registerer) Option {
 		return cfg
 	})
 }
+
+// WithAggregationSelector configure the Aggregation Selector the exporter will
+// use. If no AggregationSelector is provided the DefaultAggregationSelector is
+// used.
+func WithAggregationSelector(agg metric.AggregationSelector) Option {
+	return optionFunc(func(cfg config) config {
+		cfg.aggregation = agg
+		return cfg
+	})
+}

exporters/prometheus/exporter.go

@@ -50,7 +50,7 @@ func New(opts ...Option) (*Exporter, error) {
 	// this assumes that the default temporality selector will always return cumulative.
 	// we only support cumulative temporality, so building our own reader enforces this.
 	// TODO (#3244): Enable some way to configure the reader, but not change temporality.
-	reader := metric.NewManualReader()
+	reader := metric.NewManualReader(cfg.manualReaderOptions()...)
 
 	collector := &collector{
 		reader: reader,