Fix empty log body printed by stdoutlog exporter

CHANGELOG.md

@@ -13,6 +13,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Add `RecordFactory` in `go.opentelemetry.io/otel/log/logtest` to facilitate testing the bridge implementations. (#5263)
 - Add `RecordFactory` in `go.opentelemetry.io/otel/sdk/log/logtest` to facilitate testing the exporter and processor implementations. (#5258)
 - Add example for `go.opentelemetry.io/otel/exporters/stdout/stdoutlog`. (#5242)
+- Add `MarshalJSON` method for `go.opentelemetry.io/otel/log.Value` to support JSON serialization. (#5311)
 
 ### Changed
 
@@ -24,6 +25,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - The `go.opentelemetry.io/otel/exporters/stdout/stdoutlog` exporter won't print `AttributeValueLengthLimit` and `AttributeCountLimit` fields now, instead it prints the `DroppedAttributes` field. (#5272)
 - Improved performance in the `Stringer` implementation of `go.opentelemetry.io/otel/baggage.Member` by reducing the number of allocations. (#5286)
 
+### Fixed
+
+- Fix the empty output of `go.opentelemetry.io/otel/log.Value` in `go.opentelemetry.io/otel/exporters/stdout/stdoutlog`. (#5311)
+
 ## [1.26.0/0.48.0/0.2.0-alpha] 2024-04-24
 
 ### Added

exporters/stdout/stdoutlog/exporter_test.go

@@ -183,7 +183,7 @@ func getJSON(now *time.Time) string {
 		timestamps = "\"Timestamp\":" + string(serializedNow) + ",\"ObservedTimestamp\":" + string(serializedNow) + ","
 	}
 
-	return "{" + timestamps + "\"Severity\":9,\"SeverityText\":\"INFO\",\"Body\":{},\"Attributes\":[{\"Key\":\"key\",\"Value\":{}},{\"Key\":\"key2\",\"Value\":{}},{\"Key\":\"key3\",\"Value\":{}},{\"Key\":\"key4\",\"Value\":{}},{\"Key\":\"key5\",\"Value\":{}},{\"Key\":\"bool\",\"Value\":{}}],\"TraceID\":\"0102030405060708090a0b0c0d0e0f10\",\"SpanID\":\"0102030405060708\",\"TraceFlags\":\"01\",\"Resource\":[{\"Key\":\"foo\",\"Value\":{\"Type\":\"STRING\",\"Value\":\"bar\"}}],\"Scope\":{\"Name\":\"name\",\"Version\":\"version\",\"SchemaURL\":\"https://example.com/custom-schema\"},\"DroppedAttributes\":10}\n"
+	return "{" + timestamps + "\"Severity\":9,\"SeverityText\":\"INFO\",\"Body\":{\"Type\":\"String\",\"Value\":\"test\"},\"Attributes\":[{\"Key\":\"key\",\"Value\":{\"Type\":\"String\",\"Value\":\"value\"}},{\"Key\":\"key2\",\"Value\":{\"Type\":\"String\",\"Value\":\"value\"}},{\"Key\":\"key3\",\"Value\":{\"Type\":\"String\",\"Value\":\"value\"}},{\"Key\":\"key4\",\"Value\":{\"Type\":\"String\",\"Value\":\"value\"}},{\"Key\":\"key5\",\"Value\":{\"Type\":\"String\",\"Value\":\"value\"}},{\"Key\":\"bool\",\"Value\":{\"Type\":\"Bool\",\"Value\":true}}],\"TraceID\":\"0102030405060708090a0b0c0d0e0f10\",\"SpanID\":\"0102030405060708\",\"TraceFlags\":\"01\",\"Resource\":[{\"Key\":\"foo\",\"Value\":{\"Type\":\"STRING\",\"Value\":\"bar\"}}],\"Scope\":{\"Name\":\"name\",\"Version\":\"version\",\"SchemaURL\":\"https://example.com/custom-schema\"},\"DroppedAttributes\":10}\n"
 }
 
 func getJSONs(now *time.Time) string {
@@ -200,31 +200,52 @@ func getPrettyJSON(now *time.Time) string {
 	return `{` + timestamps + `
 	"Severity": 9,
 	"SeverityText": "INFO",
-	"Body": {},
+	"Body": {
+		"Type": "String",
+		"Value": "test"
+	},
 	"Attributes": [
 		{
 			"Key": "key",
-			"Value": {}
+			"Value": {
+				"Type": "String",
+				"Value": "value"
+			}
 		},
 		{
 			"Key": "key2",
-			"Value": {}
+			"Value": {
+				"Type": "String",
+				"Value": "value"
+			}
 		},
 		{
 			"Key": "key3",
-			"Value": {}
+			"Value": {
+				"Type": "String",
+				"Value": "value"
+			}
 		},
 		{
 			"Key": "key4",
-			"Value": {}
+			"Value": {
+				"Type": "String",
+				"Value": "value"
+			}
 		},
 		{
 			"Key": "key5",
-			"Value": {}
+			"Value": {
+				"Type": "String",
+				"Value": "value"
+			}
 		},
 		{
 			"Key": "bool",
-			"Value": {}
+			"Value": {
+				"Type": "Bool",
+				"Value": true
+			}
 		}
 	],
 	"TraceID": "0102030405060708090a0b0c0d0e0f10",

log/keyvalue.go

@@ -7,6 +7,7 @@
 
 import (
 	"bytes"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"math"
@@ -300,6 +301,38 @@
 	}
 }
 
+// MarshalJSON implements a custom marshal function to encode Value.
+func (v Value) MarshalJSON() ([]byte, error) {
+	var jsonVal struct {
+		Type  string
+		Value interface{}
+	}
+	jsonVal.Type = v.Kind().String()
+
+	switch v.Kind() {
+	case KindString:
+		jsonVal.Value = v.asString()
+	case KindInt64:
+		jsonVal.Value = v.asInt64()
+	case KindFloat64:
+		jsonVal.Value = v.asFloat64()
+	case KindBool:
+		jsonVal.Value = v.asBool()
+	case KindBytes:
+		jsonVal.Value = v.asBytes()
+	case KindMap:
+		jsonVal.Value = v.asMap()
+	case KindSlice:
+		jsonVal.Value = v.asSlice()
+	case KindEmpty:
+		jsonVal.Value = nil
+	default:
+		return nil, errKind
+	}
+
+	return json.Marshal(jsonVal)
+}
+
 // A KeyValue is a key-value pair used to represent a log attribute (a
 // superset of [go.opentelemetry.io/otel/attribute.KeyValue]) and map item.
 type KeyValue struct {

log/keyvalue_test.go

@@ -8,6 +8,7 @@
 package log_test
 
 import (
+	"encoding/json"
 	"testing"
 
 	"github.com/go-logr/logr"
@@ -377,3 +378,84 @@ func TestAllocationLimits(t *testing.T) {
 	// Convince the linter these values are used.
 	_, _, _, _, _, _, _ = i, f, b, by, s, slice, m
 }
+
+func TestValueMarshalJSON(t *testing.T) {
+	testCases := []struct {
+		value log.Value
+		want  string
+	}{
+		{
+			value: log.Empty("test").Value,
+			want:  `{"Type":"Empty","Value":null}`,
+		},
+		{
+			value: log.BoolValue(true),
+			want:  `{"Type":"Bool","Value":true}`,
+		},
+		{
+			value: log.Float64Value(3.14),
+			want:  `{"Type":"Float64","Value":3.14}`,
+		},
+		{
+			value: log.Int64Value(42),
+			want:  `{"Type":"Int64","Value":42}`,
+		},
+		{
+			value: log.StringValue("hello"),
+			want:  `{"Type":"String","Value":"hello"}`,
+		},
+		{
+			value: log.BytesValue([]byte{1, 2, 3}),
+			// The base64 encoding of []byte{1, 2, 3} is "AQID".
+			want: `{"Type":"Bytes","Value":"AQID"}`,
+		},
+		{
+			value: log.SliceValue(
+				log.Empty("empty").Value,
+				log.BoolValue(true),
+				log.Float64Value(2.2),
+				log.IntValue(3),
+				log.StringValue("4"),
+				log.BytesValue([]byte{5}),
+				log.SliceValue(
+					log.IntValue(6),
+					log.MapValue(
+						log.Int("seven", 7),
+					),
+				),
+				log.MapValue(
+					log.Int("nine", 9),
+				),
+			),
+			want: `{"Type":"Slice","Value":[{"Type":"Empty","Value":null},{"Type":"Bool","Value":true},{"Type":"Float64","Value":2.2},{"Type":"Int64","Value":3},{"Type":"String","Value":"4"},{"Type":"Bytes","Value":"BQ=="},{"Type":"Slice","Value":[{"Type":"Int64","Value":6},{"Type":"Map","Value":[{"Key":"seven","Value":{"Type":"Int64","Value":7}}]}]},{"Type":"Map","Value":[{"Key":"nine","Value":{"Type":"Int64","Value":9}}]}]}`,
+		},
+		{
+			value: log.MapValue(
+				log.Empty("empty"),
+				log.Bool("one", true),
+				log.Float64("two", 2.2),
+				log.Int("three", 3),
+				log.String("four", "4"),
+				log.Bytes("five", []byte{5}),
+				log.Slice("six",
+					log.IntValue(6),
+					log.MapValue(
+						log.Int("seven", 7),
+					),
+				),
+				log.Map("eight",
+					log.Int("nine", 9),
+				),
+			),
+			want: `{"Type":"Map","Value":[{"Key":"empty","Value":{"Type":"Empty","Value":null}},{"Key":"one","Value":{"Type":"Bool","Value":true}},{"Key":"two","Value":{"Type":"Float64","Value":2.2}},{"Key":"three","Value":{"Type":"Int64","Value":3}},{"Key":"four","Value":{"Type":"String","Value":"4"}},{"Key":"five","Value":{"Type":"Bytes","Value":"BQ=="}},{"Key":"six","Value":{"Type":"Slice","Value":[{"Type":"Int64","Value":6},{"Type":"Map","Value":[{"Key":"seven","Value":{"Type":"Int64","Value":7}}]}]}},{"Key":"eight","Value":{"Type":"Map","Value":[{"Key":"nine","Value":{"Type":"Int64","Value":9}}]}}]}`,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.value.String(), func(t *testing.T) {
+			got, err := json.Marshal(tc.value)
+			require.NoError(t, err)
+			assert.JSONEq(t, tc.want, string(got))
+		})
+	}
+}