code: func NewServerCodec(conn io.ReadWriteCloser) rpc.ServerCodec {
  	return &serverCodec{
  		dec:     json.NewDecoder(conn),
  		enc:     json.NewEncoder(conn),
  		c:       conn,
  		pending: make(map[uint64]*json.RawMessage),
  	}
  }
docs: // NewServerCodec returns a new rpc.ServerCodec using JSON-RPC on conn.