@classmethod
def block_size(cls, header_chunk):
    """Return the total block size in chunks, given the header chunks"""
    if cls.header_type(header_chunk) == 'file':
        return cls.header_size(header_chunk)
    elif cls.header_type(header_chunk) == 'data':
        return cls.data_block_size(header_chunk)
    raise ValueError('Cannot determine size of unknown block type')
