fix codec.Frame in case of flatten struct tag

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

codec_test.go

@@ -3,8 +3,40 @@ package json
 import (
 	"bytes"
 	"testing"
+
+	"github.com/unistack-org/micro/v3/codec"
 )
 
+func TestFrame(t *testing.T) {
+	s := &codec.Frame{Data: []byte("test")}
+
+	buf, err := NewCodec().Marshal(s)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(buf, []byte(`test`)) {
+		t.Fatalf("bytes not equal %s != %s", buf, `test`)
+	}
+}
+
+func TestFrameFlatten(t *testing.T) {
+	s := &struct {
+		One  string
+		Name *codec.Frame `json:"name" codec:"flatten"`
+	}{
+		One:  "xx",
+		Name: &codec.Frame{Data: []byte("test")},
+	}
+
+	buf, err := NewCodec().Marshal(s)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(buf, []byte(`test`)) {
+		t.Fatalf("bytes not equal %s != %s", buf, `test`)
+	}
+}
+
 func TestStructByTag(t *testing.T) {
 	type Str struct {
 		Name []string `json:"name" codec:"flatten"`

json.go

@@ -43,10 +43,6 @@ func (c *jsonCodec) Marshal(v interface{}, opts ...codec.Option) ([]byte, error)
 		return nil, nil
 	}
 
-	if m, ok := v.(*codec.Frame); ok {
-		return m.Data, nil
-	}
-
 	options := c.opts
 	for _, o := range opts {
 		o(&options)
@@ -56,6 +52,10 @@ func (c *jsonCodec) Marshal(v interface{}, opts ...codec.Option) ([]byte, error)
 		v = nv
 	}
 
+	if m, ok := v.(*codec.Frame); ok {
+		return m.Data, nil
+	}
+
 	marshalOptions := DefaultMarshalOptions
 	if options.Context != nil {
 		if f, ok := options.Context.Value(marshalOptionsKey{}).(JsonMarshalOptions); ok {
@@ -80,11 +80,6 @@ func (c *jsonCodec) Unmarshal(b []byte, v interface{}, opts ...codec.Option) err
 		return nil
 	}
 
-	if m, ok := v.(*codec.Frame); ok {
-		m.Data = b
-		return nil
-	}
-
 	options := c.opts
 	for _, o := range opts {
 		o(&options)
@@ -94,6 +89,11 @@ func (c *jsonCodec) Unmarshal(b []byte, v interface{}, opts ...codec.Option) err
 		v = nv
 	}
 
+	if m, ok := v.(*codec.Frame); ok {
+		m.Data = b
+		return nil
+	}
+
 	unmarshalOptions := DefaultUnmarshalOptions
 	if options.Context != nil {
 		if f, ok := options.Context.Value(unmarshalOptionsKey{}).(JsonUnmarshalOptions); ok {