Add MarshalJSON for core.Value (#281)

- fix #280, where stdout export will not print Attributes value from
  MessageEvents.
- add unit test for it.

api/core/key.go

@@ -17,6 +17,7 @@ package core
 //go:generate stringer -type=ValueType
 
 import (
+	"encoding/json"
 	"fmt"
 	"strconv"
 	"unsafe"
@@ -325,3 +326,14 @@ func (v *Value) Emit() string {
 		return "unknown"
 	}
 }
+
+// MarshalJSON returns the JSON encoding of the Value.
+func (v *Value) MarshalJSON() ([]byte, error) {
+	var jsonVal struct {
+		Type  string
+		Value interface{}
+	}
+	jsonVal.Type = v.Type().String()
+	jsonVal.Value = v.AsInterface()
+	return json.Marshal(jsonVal)
+}

exporter/trace/stdout/stdout.go

@@ -19,12 +19,7 @@ import (
 	"encoding/json"
 	"io"
 	"os"
-	"time"
 
-	"google.golang.org/grpc/codes"
-
-	"go.opentelemetry.io/otel/api/core"
-	apitrace "go.opentelemetry.io/otel/api/trace"
 	"go.opentelemetry.io/otel/sdk/export"
 )
 
@@ -48,72 +43,15 @@ func NewExporter(o Options) (*Exporter, error) {
 	}, nil
 }
 
-type jsonValue struct {
-	Type  string
-	Value interface{}
-}
-
-type jsonKeyValue struct {
-	Key   core.Key
-	Value jsonValue
-}
-
-type jsonSpanData struct {
-	SpanContext              core.SpanContext
-	ParentSpanID             core.SpanID
-	SpanKind                 apitrace.SpanKind
-	Name                     string
-	StartTime                time.Time
-	EndTime                  time.Time
-	Attributes               []jsonKeyValue
-	MessageEvents            []export.Event
-	Links                    []apitrace.Link
-	Status                   codes.Code
-	HasRemoteParent          bool
-	DroppedAttributeCount    int
-	DroppedMessageEventCount int
-	DroppedLinkCount         int
-	ChildSpanCount           int
-}
-
-func marshalSpanData(data *export.SpanData, pretty bool) ([]byte, error) {
-	jsd := jsonSpanData{
-		SpanContext:              data.SpanContext,
-		ParentSpanID:             data.ParentSpanID,
-		SpanKind:                 data.SpanKind,
-		Name:                     data.Name,
-		StartTime:                data.StartTime,
-		EndTime:                  data.EndTime,
-		Attributes:               toJSONAttributes(data.Attributes),
-		MessageEvents:            data.MessageEvents,
-		Links:                    data.Links,
-		Status:                   data.Status,
-		HasRemoteParent:          data.HasRemoteParent,
-		DroppedAttributeCount:    data.DroppedAttributeCount,
-		DroppedMessageEventCount: data.DroppedMessageEventCount,
-		DroppedLinkCount:         data.DroppedLinkCount,
-		ChildSpanCount:           data.ChildSpanCount,
-	}
-
-	if pretty {
-		return json.MarshalIndent(jsd, "", "\t")
-	}
-	return json.Marshal(jsd)
-}
-
-func toJSONAttributes(attributes []core.KeyValue) []jsonKeyValue {
-	jsonAttrs := make([]jsonKeyValue, len(attributes))
-	for i := 0; i < len(attributes); i++ {
-		jsonAttrs[i].Key = attributes[i].Key
-		jsonAttrs[i].Value.Type = attributes[i].Value.Type().String()
-		jsonAttrs[i].Value.Value = attributes[i].Value.AsInterface()
-	}
-	return jsonAttrs
-}
-
 // ExportSpan writes a SpanData in json format to stdout.
 func (e *Exporter) ExportSpan(ctx context.Context, data *export.SpanData) {
-	jsonSpan, err := marshalSpanData(data, e.pretty)
+	var jsonSpan []byte
+	var err error
+	if e.pretty {
+		jsonSpan, err = json.MarshalIndent(data, "", "\t")
+	} else {
+		jsonSpan, err = json.Marshal(data)
+	}
 	if err != nil {
 		// ignore writer failures for now
 		_, _ = e.outputWriter.Write([]byte("Error converting spanData to json: " + err.Error()))

exporter/trace/stdout/stdout_test.go

@@ -58,6 +58,10 @@ func TestExporter_ExportSpan(t *testing.T) {
 			key.String("key", keyValue),
 			key.Float64("double", doubleValue),
 		},
+		MessageEvents: []export.Event{
+			{Message: "foo", Attributes: []core.KeyValue{key.String("key", keyValue)}, Time: now},
+			{Message: "bar", Attributes: []core.KeyValue{key.Float64("double", doubleValue)}, Time: now},
+		},
 		SpanKind: trace.SpanKindInternal,
 		Status:   codes.Unknown,
 	}
@@ -84,7 +88,28 @@ func TestExporter_ExportSpan(t *testing.T) {
 		`"Value":{"Type":"FLOAT64","Value":123.456}` +
 		`}` +
 		`],` +
-		`"MessageEvents":null,` +
+		`"MessageEvents":[` +
+		`{` +
+		`"Message":"foo",` +
+		`"Attributes":[` +
+		`{` +
+		`"Key":"key",` +
+		`"Value":{"Type":"STRING","Value":"value"}` +
+		`}` +
+		`],` +
+		`"Time":` + string(expectedSerializedNow) +
+		`},` +
+		`{` +
+		`"Message":"bar",` +
+		`"Attributes":[` +
+		`{` +
+		`"Key":"double",` +
+		`"Value":{"Type":"FLOAT64","Value":123.456}` +
+		`}` +
+		`],` +
+		`"Time":` + string(expectedSerializedNow) +
+		`}` +
+		`],` +
 		`"Links":null,` +
 		`"Status":2,` +
 		`"HasRemoteParent":false,` +