sdk/metric/metricdata: Add MarshalJSON for Extrema (#4827)

* json marshal for Extrema type, makefile typo fix

* MarshalText implementation, cleanup

* update changelog

* changelog fix

* Update CHANGELOG.md

* MarshalText behavior update on invalid Extrema

* Fix Marshal outputs json text representation of nil

* Updated mockData to include example with Min and Max values.

* null value test, changelog fix

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
Co-authored-by: Aaron Clawson <3766680+MadVikingGod@users.noreply.github.com>

CHANGELOG.md

@@ -18,6 +18,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Fix `ContainerID` resource detection on systemd when cgroup path has a colon. (#4449)
 - Fix `go.opentelemetry.io/otel/sdk/metric` to cache instruments to avoid leaking memory when the same instrument is created multiple times. (#4820)
+- Fix 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`. (#4827)
 
 ## [1.23.0-rc.1] 2024-01-18
 

exporters/stdout/stdoutmetric/example_test.go

@@ -77,6 +77,27 @@ var (
 							},
 						},
 					},
+					{
+						Name:        "requests.size",
+						Description: "Size of received requests",
+						Unit:        "kb",
+						Data: metricdata.Histogram[int64]{
+							Temporality: metricdata.DeltaTemporality,
+							DataPoints: []metricdata.HistogramDataPoint[int64]{
+								{
+									Attributes:   attribute.NewSet(attribute.String("server", "central")),
+									StartTime:    now,
+									Time:         now.Add(1 * time.Second),
+									Count:        10,
+									Bounds:       []float64{1, 5, 10},
+									BucketCounts: []uint64{1, 3, 6, 0},
+									Sum:          128,
+									Min:          metricdata.NewExtrema[int64](3),
+									Max:          metricdata.NewExtrema[int64](30),
+								},
+							},
+						},
+					},
 					{
 						Name:        "latency",
 						Description: "Time spend processing received requests",
@@ -228,6 +249,44 @@ func Example() {
 	//           }
 	//         },
 	//         {
+	//           "Name": "requests.size",
+	//           "Description": "Size of received requests",
+	//           "Unit": "kb",
+	//           "Data": {
+	//             "DataPoints": [
+	//               {
+	//                 "Attributes": [
+	//                   {
+	//                     "Key": "server",
+	//                     "Value": {
+	//                       "Type": "STRING",
+	//                       "Value": "central"
+	//                     }
+	//                   }
+	//                 ],
+	//                 "StartTime": "0001-01-01T00:00:00Z",
+	//                 "Time": "0001-01-01T00:00:00Z",
+	//                 "Count": 10,
+	//                 "Bounds": [
+	//                   1,
+	//                   5,
+	//                   10
+	//                 ],
+	//                 "BucketCounts": [
+	//                   1,
+	//                   3,
+	//                   6,
+	//                   0
+	//                 ],
+	//                 "Min": 3,
+	//                 "Max": 30,
+	//                 "Sum": 128
+	//               }
+	//             ],
+	//             "Temporality": "DeltaTemporality"
+	//           }
+	//         },
+	//         {
 	//           "Name": "latency",
 	//           "Description": "Time spend processing received requests",
 	//           "Unit": "ms",
@@ -257,8 +316,8 @@ 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 @@ type Extrema[N int64 | float64] struct {
 	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 +1013,24 @@ 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, "null", &metricdata.Extrema[int64]{})
+
+	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)
+}