huffman_decode decodes the bitstring provided as parameters. :param int i: the bitstring to decode :param int ibl: the bitlength of i :return: str: the string decoded from the bitstring :raises: AssertionError, InvalidEncodingException
(cls, i, ibl)
| 1043 | |
| 1044 | @classmethod |
| 1045 | def huffman_decode(cls, i, ibl): |
| 1046 | # type: (int, int) -> str |
| 1047 | """ huffman_decode decodes the bitstring provided as parameters. |
| 1048 | |
| 1049 | :param int i: the bitstring to decode |
| 1050 | :param int ibl: the bitlength of i |
| 1051 | :return: str: the string decoded from the bitstring |
| 1052 | :raises: AssertionError, InvalidEncodingException |
| 1053 | """ |
| 1054 | assert i >= 0 |
| 1055 | assert ibl >= 0 |
| 1056 | |
| 1057 | if isinstance(cls.static_huffman_tree, type(None)): |
| 1058 | cls.huffman_compute_decode_tree() |
| 1059 | assert not isinstance(cls.static_huffman_tree, type(None)) |
| 1060 | |
| 1061 | s = [] |
| 1062 | j = 0 |
| 1063 | interrupted = False |
| 1064 | cur = cls.static_huffman_tree |
| 1065 | cur_sym = 0 |
| 1066 | cur_sym_bl = 0 |
| 1067 | while j < ibl: |
| 1068 | b = (i >> (ibl - j - 1)) & 1 |
| 1069 | cur_sym = (cur_sym << 1) + b |
| 1070 | cur_sym_bl += 1 |
| 1071 | elmt = cur[b] |
| 1072 | |
| 1073 | if isinstance(elmt, HuffmanNode): |
| 1074 | interrupted = True |
| 1075 | cur = elmt |
| 1076 | if isinstance(cur, type(None)): |
| 1077 | raise AssertionError() |
| 1078 | elif isinstance(elmt, EOS): |
| 1079 | raise InvalidEncodingException('Huffman decoder met the full EOS symbol') # noqa: E501 |
| 1080 | elif isinstance(elmt, bytes): |
| 1081 | interrupted = False |
| 1082 | s.append(elmt) |
| 1083 | cur = cls.static_huffman_tree |
| 1084 | cur_sym = 0 |
| 1085 | cur_sym_bl = 0 |
| 1086 | else: |
| 1087 | raise InvalidEncodingException('Should never happen, so incidentally it will') # noqa: E501 |
| 1088 | j += 1 |
| 1089 | |
| 1090 | if interrupted: |
| 1091 | # Interrupted values true if the bitstring ends in the middle of a |
| 1092 | # symbol; this symbol must be, according to RFC7541 par5.2 the MSB |
| 1093 | # of the EOS symbol |
| 1094 | if cur_sym_bl > 7: |
| 1095 | raise InvalidEncodingException('Huffman decoder is detecting padding longer than 7 bits') # noqa: E501 |
| 1096 | eos_symbol = cls.static_huffman_code[-1] |
| 1097 | eos_msb = eos_symbol[0] >> (eos_symbol[1] - cur_sym_bl) |
| 1098 | if eos_msb != cur_sym: |
| 1099 | raise InvalidEncodingException('Huffman decoder is detecting unexpected padding format') # noqa: E501 |
| 1100 | return b''.join(s) |
| 1101 | |
| 1102 | @classmethod |
no test coverage detected