allow to flatten struct

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

proto.go

@@ -3,14 +3,18 @@ package proto
 
 import (
 	"io"
-	"io/ioutil"
 
 	"github.com/unistack-org/micro/v3/codec"
+	rutil "github.com/unistack-org/micro/v3/util/reflect"
 	"google.golang.org/protobuf/proto"
 )
 
 type protoCodec struct{}
 
+const (
+	flattenTag = "flatten"
+)
+
 func (c *protoCodec) Marshal(v interface{}) ([]byte, error) {
 	switch m := v.(type) {
 	case nil:
@@ -18,6 +22,11 @@ func (c *protoCodec) Marshal(v interface{}) ([]byte, error) {
 	case *codec.Frame:
 		return m.Data, nil
 	case proto.Message:
+		if nv, nerr := rutil.StructFieldByTag(v, codec.DefaultTagName, flattenTag); nerr == nil {
+			if nm, ok := nv.(proto.Message); ok {
+				return proto.Marshal(nm)
+			}
+		}
 		return proto.Marshal(m)
 	}
 	return nil, codec.ErrInvalidMessage
@@ -33,6 +42,11 @@ func (c *protoCodec) Unmarshal(d []byte, v interface{}) error {
 	case *codec.Frame:
 		m.Data = d
 	case proto.Message:
+		if nv, nerr := rutil.StructFieldByTag(v, codec.DefaultTagName, flattenTag); nerr == nil {
+			if nm, ok := nv.(proto.Message); ok {
+				return proto.Unmarshal(d, nm)
+			}
+		}
 		return proto.Unmarshal(d, m)
 	}
 	return codec.ErrInvalidMessage
@@ -42,12 +56,12 @@ func (c *protoCodec) ReadHeader(conn io.Reader, m *codec.Message, t codec.Messag
 	return nil
 }
 
-func (c *protoCodec) ReadBody(conn io.Reader, b interface{}) error {
-	switch m := b.(type) {
+func (c *protoCodec) ReadBody(conn io.Reader, v interface{}) error {
+	switch m := v.(type) {
 	case nil:
 		return nil
 	case *codec.Frame:
-		buf, err := ioutil.ReadAll(conn)
+		buf, err := io.ReadAll(conn)
 		if err != nil {
 			return err
 		} else if len(buf) == 0 {
@@ -56,28 +70,45 @@ func (c *protoCodec) ReadBody(conn io.Reader, b interface{}) error {
 		m.Data = buf
 		return nil
 	case proto.Message:
-		buf, err := ioutil.ReadAll(conn)
+		buf, err := io.ReadAll(conn)
 		if err != nil {
 			return err
 		} else if len(buf) == 0 {
 			return nil
 		}
+		if nv, nerr := rutil.StructFieldByTag(v, codec.DefaultTagName, flattenTag); nerr == nil {
+			if nm, ok := nv.(proto.Message); ok {
+				return proto.Unmarshal(buf, nm)
+			}
+		}
 		return proto.Unmarshal(buf, m)
 	}
 	return codec.ErrInvalidMessage
 }
 
-func (c *protoCodec) Write(conn io.Writer, m *codec.Message, b interface{}) error {
-	switch m := b.(type) {
+func (c *protoCodec) Write(conn io.Writer, m *codec.Message, v interface{}) error {
+	switch m := v.(type) {
 	case nil:
 		return nil
 	case *codec.Frame:
 		_, err := conn.Write(m.Data)
 		return err
 	case proto.Message:
-		buf, err := proto.Marshal(m)
+		var buf []byte
+		var err error
+
+		if nv, nerr := rutil.StructFieldByTag(v, codec.DefaultTagName, flattenTag); nerr == nil {
+			if nm, ok := nv.(proto.Message); ok {
+				buf, err = proto.Marshal(nm)
+			}
+		} else {
+			buf, err = proto.Marshal(m)
+		}
+
 		if err != nil {
 			return err
+		} else if len(buf) == 0 {
+			return codec.ErrInvalidMessage
 		}
 		_, err = conn.Write(buf)
 		return err