Extension of Metadata Transparent Transmission

// MetaHandler reads or writes metadata through certain protocol.
// The protocol will be a thrift.TProtocol usually.
type MetaHandler interface {
	WriteMeta(ctx context.Context, msg Message) (context.Context, error)
	ReadMeta(ctx context.Context, msg Message) (context.Context, error)
}

package transmeta

var	ClientTTHeaderHandler remote.MetaHandler = &clientTTHeaderHandler{}

// clientTTHeaderHandler implement remote.MetaHandler
type clientTTHeaderHandler struct{}

// WriteMeta of clientTTHeaderHandler writes headers of TTHeader protocol to transport
func (ch *clientTTHeaderHandler) WriteMeta(ctx context.Context, msg remote.Message) (context.Context, error) {
	ri := msg.RPCInfo()
	transInfo := msg.TransInfo()

	hd := map[uint16]string{
		transmeta.FromService:    ri.From().ServiceName(),
		transmeta.FromIDC:        ri.From().DefaultTag(consts.IDC, ""),
		transmeta.FromMethod:     ri.From().Method(),
		transmeta.ToService:      ri.To().ServiceName(),
		transmeta.ToMethod:       ri.To().Method(),
		transmeta.MsgType:        strconv.Itoa(int(msg.MessageType())),
	}
	transInfo.PutTransIntInfo(hd)

	if metainfo.HasMetaInfo(ctx) {
		hd := make(map[string]string)
		metainfo.SaveMetaInfoToMap(ctx, hd)
		transInfo.PutTransStrInfo(hd)
	}
	return ctx, nil
}

// ReadMeta of clientTTHeaderHandler reads headers of TTHeader protocol from transport
func (ch *clientTTHeaderHandler) ReadMeta(ctx context.Context, msg remote.Message) (context.Context, error) {
	ri := msg.RPCInfo()
	remote := remoteinfo.AsRemoteInfo(ri.To())
	if remote == nil {
		return ctx, nil
	}

	transInfo := msg.TransInfo()
	strInfo := transInfo.TransStrInfo()
	ad := strInfo[transmeta.HeaderTransRemoteAddr]
	if len(ad) > 0 {
		// when proxy case to get the actual remote address
		_ = remote.SetRemoteAddr(utils.NewNetAddr("tcp", ad))
	}
	return ctx, nil
}