'Returns an json-compatible input shard spec for remaining inputs.'

def to_json(self):

    new_pos = self._blob_reader.tell()
    if self._has_iterated:
        new_pos -= 1
    return {self.BLOB_KEY_PARAM: self._blob_key, self.INITIAL_POSITION_PARAM: new_pos, self.END_POSITION_PARAM: self._end_position}
