use metadata.Metadata (#8)

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

tracer/context.go

@@ -29,8 +29,8 @@ func FromContext(ctx context.Context) (traceID string, parentSpanID string, isFo
 
 // NewContext saves the trace and span ids in the context
 func NewContext(ctx context.Context, traceID, parentSpanID string) context.Context {
-	return metadata.MergeContext(ctx, map[string]string{
-		traceIDKey: traceID,
-		spanIDKey:  parentSpanID,
-	}, true)
+	md := metadata.New(2)
+	md.Set(traceIDKey, traceID)
+	md.Set(spanIDKey, parentSpanID)
+	return metadata.MergeContext(ctx, md, true)
 }

tracer/trace.go

@@ -4,6 +4,8 @@ package tracer
 import (
 	"context"
 	"time"
+
+	"github.com/unistack-org/micro/v3/metadata"
 )
 
 var (
@@ -46,7 +48,7 @@ type Span struct {
 	// Duration in nano seconds
 	Duration time.Duration
 	// associated data
-	Metadata map[string]string
+	Metadata metadata.Metadata
 	// Type
 	Type SpanType
 }