Coverage for /pythoncovmergedfiles/medio/medio/usr/local/lib/python3.11/site-packages/google_crc32c/_checksum.py: 36%

1# Copyright 2020 Google LLC 

2# 

3# Licensed under the Apache License, Version 2.0 (the "License"); 

4# you may not use this file except in compliance with the License. 

5# You may obtain a copy of the License at 

6# 

7# https://www.apache.org/licenses/LICENSE-2.0 

8# 

9# Unless required by applicable law or agreed to in writing, software 

10# distributed under the License is distributed on an "AS IS" BASIS, 

11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 

12# See the License for the specific language governing permissions and 

13# limitations under the License. 

14 

15import struct 

16 

17 

18class CommonChecksum(object): 

19 """Hashlib-alike helper for CRC32C operations. 

20 

21 This class should not be used directly and requires an update implementation. 

22 

23 Args: 

24 initial_value (Optional[bytes]): the initial chunk of data from 

25 which the CRC32C checksum is computed. Defaults to b''. 

26 """ 

27 

28 __slots__ = () 

29 

30 def __init__(self, initial_value=b""): 

31 self._crc = 0 

32 if initial_value != b"": 

33 self.update(initial_value) 

34 

35 def update(self, data): 

36 """Update the checksum with a new chunk of data. 

37 

38 Args: 

39 chunk (Optional[bytes]): a chunk of data used to extend 

40 the CRC32C checksum. 

41 """ 

42 raise NotImplementedError 

43 

44 def digest(self): 

45 """Big-endian order, per RFC 4960. 

46 

47 See: https://cloud.google.com/storage/docs/json_api/v1/objects#crc32c 

48 

49 Returns: 

50 bytes: An eight-byte digest string. 

51 """ 

52 return struct.pack(">L", self._crc) 

53 

54 def hexdigest(self): 

55 """Like :meth:`digest` except returns as a bytestring of double length. 

56 

57 Returns 

58 bytes: A sixteen byte digest string, contaiing only hex digits. 

59 """ 

60 return "{:08x}".format(self._crc).encode("ascii") 

61 

62 def copy(self): 

63 """Create another checksum with the same CRC32C value. 

64 

65 Returns: 

66 Checksum: the new instance. 

67 """ 

68 clone = self.__class__() 

69 clone._crc = self._crc 

70 return clone 

71 

72 def consume(self, stream, chunksize): 

73 """Consume chunks from a stream, extending our CRC32 checksum. 

74 

75 Args: 

76 stream (BinaryIO): the stream to consume. 

77 chunksize (int): the size of the read to perform 

78 

79 Returns: 

80 Generator[bytes, None, None]: Iterable of the chunks read from the 

81 stream. 

82 """ 

83 while True: 

84 chunk = stream.read(chunksize) 

85 if not chunk: 

86 break 

87 self.update(chunk) 

88 yield chunk