87 lines
2.6 KiB
Python
87 lines
2.6 KiB
Python
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# Copyright 2020 Google LLC
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# https://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import struct
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class CommonChecksum(object):
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"""Hashlib-alike helper for CRC32C operations.
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This class should not be used directly and requires an update implementation.
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Args:
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initial_value (Optional[bytes]): the initial chunk of data from
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which the CRC32C checksum is computed. Defaults to b''.
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"""
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def __init__(self, initial_value=b""):
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self._crc = 0
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if initial_value != b"":
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self.update(initial_value)
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def update(self, data):
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"""Update the checksum with a new chunk of data.
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Args:
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chunk (Optional[bytes]): a chunk of data used to extend
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the CRC32C checksum.
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"""
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raise NotImplemented()
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def digest(self):
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"""Big-endian order, per RFC 4960.
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See: https://cloud.google.com/storage/docs/json_api/v1/objects#crc32c
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Returns:
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bytes: An eight-byte digest string.
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"""
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return struct.pack(">L", self._crc)
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def hexdigest(self):
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"""Like :meth:`digest` except returns as a bytestring of double length.
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Returns
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bytes: A sixteen byte digest string, contaiing only hex digits.
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"""
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return "{:08x}".format(self._crc).encode("ascii")
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def copy(self):
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"""Create another checksum with the same CRC32C value.
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Returns:
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Checksum: the new instance.
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"""
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clone = self.__class__()
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clone._crc = self._crc
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return clone
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def consume(self, stream, chunksize):
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"""Consume chunks from a stream, extending our CRC32 checksum.
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Args:
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stream (BinaryIO): the stream to consume.
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chunksize (int): the size of the read to perform
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Returns:
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Generator[bytes, None, None]: Iterable of the chunks read from the
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stream.
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"""
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while True:
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chunk = stream.read(chunksize)
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if not chunk:
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break
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self.update(chunk)
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yield chunk
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