def serialize(buff)
      serialized_data = ''
      @data.each_pair do |key, value|
        data_str = key + '=' + value
        serialized_data = serialized_data + [data_str.length, data_str].pack('Va*')
      end
      total_byte = serialized_data.length
      return buff.write([total_byte, serialized_data].pack('Va*'))
    end
def serialize(buff)
      serialized_data = ''
      @data.each_pair do |key, value|
        data_str = key + '=' + value
        serialized_data = serialized_data + [data_str.length, data_str].pack('Va*')
      end
      total_byte = serialized_data.length
      return buff.write([total_byte, serialized_data].pack('Va*'))
    end
serialize the data into header.
 return the byte of the serialized data.
 @param [IO] buff where to write data
 @return [Integer] byte of serialized data