code: def add_decrypt_chunk(
              self, final_path, internal_fdstart, offsets, symkey, iv,
              hmac_datafile):
          # type: (CryptoOffload, str, int, blobxfer.models.download.Offsets,
          #        bytes, bytes, str) -> None
          
          self._task_queue.put(
              (CryptoAction.Decrypt, final_path, internal_fdstart, offsets,
               symkey, iv, hmac_datafile)
          )
docs: Add a chunk to decrypt
          :param CryptoOffload self: this
          :param str final_path: final path
          :param int internal_fdstart: internal fd offset start
          :param blobxfer.models.download.Offsets offsets: offsets
          :param bytes symkey: symmetric key
          :param bytes iv: initialization vector
          :param str hmac_datafile: encrypted data file