sdk/metric/metricdata: Add MarshalJSON for Extrema

CHANGELOG.md

@@ -12,6 +12,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Add `WithEndpointURL` option to the `exporters/otlp/otlpmetric/otlpmetricgrpc`, `exporters/otlp/otlpmetric/otlpmetrichttp`, `exporters/otlp/otlptrace/otlptracegrpc` and `exporters/otlp/otlptrace/otlptracehttp` packages. (#4808)
 
+### Fixed
+
+- Fixed missing Mix and Max values for `go.opentelemetry.io/otel/exporters/stdout/stdoutmetric` by introducing `MarshalText` and `MarshalJSON` for type `Extrema` in `go.opentelemetry.io/sdk/metric/metricdata`. (#4826)
+
 ## [1.23.0-rc.1] 2024-01-18
 
 This is a release candidate for the v1.23.0 release.

exporters/stdout/stdoutmetric/example_test.go

@@ -257,8 +257,8 @@ func Example() {
 	//                   6,
 	//                   0
 	//                 ],
-	//                 "Min": {},
-	//                 "Max": {},
+	//                 "Min": null,
+	//                 "Max": null,
 	//                 "Sum": 57
 	//               }
 	//             ],

sdk/metric/metricdata/data.go

@@ -15,6 +15,7 @@
 package metricdata // import "go.opentelemetry.io/otel/sdk/metric/metricdata"
 
 import (
+	"encoding/json"
 	"time"
 
 	"go.opentelemetry.io/otel/attribute"
@@ -211,6 +212,19 @@
 	valid bool
 }
 
+// MarshalText converts the Extrema value to text.
+func (e Extrema[N]) MarshalText() ([]byte, error) {
+	if !e.valid {
+		return json.Marshal(nil)
+	}
+	return json.Marshal(e.value)
+}
+
+// MarshalJSON converts the Extrema value to JSON number.
+func (e *Extrema[N]) MarshalJSON() ([]byte, error) {
+	return e.MarshalText()
+}
+
 // NewExtrema returns an Extrema set to v.
 func NewExtrema[N int64 | float64](v N) Extrema[N] {
 	return Extrema[N]{value: v, valid: true}

sdk/metric/metricdata/metricdatatest/assertion_test.go

@@ -15,6 +15,7 @@
 package metricdatatest // import "go.opentelemetry.io/otel/sdk/metric/metricdata/metricdatatest"
 
 import (
+	"encoding/json"
 	"testing"
 	"time"
 
@@ -164,6 +165,8 @@ var (
 	minFloat64C              = metricdata.NewExtrema(-1.)
 	minInt64C                = metricdata.NewExtrema[int64](-1)
 
+	minFloat64D = metricdata.NewExtrema(-9.999999)
+
 	histogramDataPointInt64A = metricdata.HistogramDataPoint[int64]{
 		Attributes:   attrA,
 		StartTime:    startA,
@@ -1010,3 +1013,22 @@ func TestAssertAttributesFail(t *testing.T) {
 	}
 	assert.False(t, AssertHasAttributes(fakeT, sum, attribute.Bool("A", true)))
 }
+
+func AssertMarshal[N int64 | float64](t *testing.T, expected string, i *metricdata.Extrema[N]) {
+	t.Helper()
+
+	b, err := json.Marshal(i)
+	assert.NoError(t, err)
+	assert.Equal(t, expected, string(b))
+}
+
+func TestAssertMarshal(t *testing.T) {
+	AssertMarshal(t, "-1", &minFloat64A)
+	AssertMarshal(t, "3", &minFloat64B)
+	AssertMarshal(t, "-9.999999", &minFloat64D)
+	AssertMarshal(t, "99", &maxFloat64B)
+
+	AssertMarshal(t, "-1", &minInt64A)
+	AssertMarshal(t, "3", &minInt64B)
+	AssertMarshal(t, "99", &maxInt64B)
+}