Synnefo

        self.fblocker = FileBlocker(**params)

        self.hashlen = self.fblocker.hashlen

    def block_hash(self, data):

        """Hash a block of data"""

           and a data 'patch' applied at offset. Return:

           (the hash of the new block, if the block already existed)

        """

        r_hash = None

        r_existed = True

        (f_hash, f_existed) = self.fblocker.block_delta(blkhash, offset, data)