docs: def _getsize_from_header(self, header):
          """
          Return the size from header
  
          Args:
              header (dict): Object header.
  
          Returns:
              int: Size in bytes.
          """
          # By default, assumes that information are in a standard HTTP header
          for key in self._SIZE_KEYS:
              try:
                  return int(header.pop(key))
              except KeyError:
                  continue
          else:
              raise UnsupportedOperation('getsize')