Send span.kind to jaeger and overwrite grpc metadata instead of using append (#441)

Co-authored-by: Rahul Patel <rghetia@yahoo.com>

exporter/trace/jaeger/jaeger.go

@@ -159,6 +159,7 @@ func spanDataToThrift(data *export.SpanData) *gen.Span {
 
 	tags = append(tags, getInt64Tag("status.code", int64(data.Status)),
 		getStringTag("status.message", data.Status.String()),
+		getStringTag("span.kind", data.SpanKind.String()),
 	)
 
 	// Ensure that if Status.Code is not OK, that we set the "error" tag on the Jaeger span.

exporter/trace/jaeger/jaeger_test.go

@@ -158,6 +158,7 @@ func Test_spanDataToThrift(t *testing.T) {
 	doubleValue := 123.456
 	boolTrue := true
 	statusMessage := "Unknown"
+	spanKind := "client"
 
 	tests := []struct {
 		name string
@@ -191,7 +192,8 @@ func Test_spanDataToThrift(t *testing.T) {
 				MessageEvents: []export.Event{
 					{Name: eventNameValue, Attributes: []core.KeyValue{key.String("k1", keyValue)}, Time: now},
 				},
-				Status: codes.Unknown,
+				Status:   codes.Unknown,
+				SpanKind: apitrace.SpanKindClient,
 			},
 			want: &gen.Span{
 				TraceIdLow:    651345242494996240,
@@ -206,6 +208,7 @@ func Test_spanDataToThrift(t *testing.T) {
 					{Key: "error", VType: gen.TagType_BOOL, VBool: &boolTrue},
 					{Key: "status.code", VType: gen.TagType_LONG, VLong: &statusCodeValue},
 					{Key: "status.message", VType: gen.TagType_STRING, VStr: &statusMessage},
+					{Key: "span.kind", VType: gen.TagType_STRING, VStr: &spanKind},
 				},
 				References: []*gen.SpanRef{
 					{

plugin/grpctrace/grpctrace.go

@@ -16,7 +16,6 @@ package grpctrace
 
 import (
 	"context"
-	"strings"
 
 	"google.golang.org/grpc/metadata"
 
@@ -34,11 +33,14 @@ type metadataSupplier struct {
 
 func (s *metadataSupplier) Get(key string) string {
 	values := s.metadata.Get(key)
-	return strings.Join(values, ",")
+	if len(values) == 0 {
+		return ""
+	}
+	return values[0]
 }
 
 func (s *metadataSupplier) Set(key string, value string) {
-	s.metadata.Append(key, value)
+	s.metadata.Set(key, value)
 }
 
 // Inject injects correlation context and span context into the gRPC