111 lines
3.9 KiB
Python
111 lines
3.9 KiB
Python
# coding=utf-8
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# Copyright 2019-present, the HuggingFace Inc. team.
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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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# http://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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"""Git LFS related utilities"""
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import io
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import os
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from contextlib import AbstractContextManager
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from typing import BinaryIO
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class SliceFileObj(AbstractContextManager):
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"""
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Utility context manager to read a *slice* of a seekable file-like object as a seekable, file-like object.
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This is NOT thread safe
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Inspired by stackoverflow.com/a/29838711/593036
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Credits to @julien-c
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Args:
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fileobj (`BinaryIO`):
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A file-like object to slice. MUST implement `tell()` and `seek()` (and `read()` of course).
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`fileobj` will be reset to its original position when exiting the context manager.
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seek_from (`int`):
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The start of the slice (offset from position 0 in bytes).
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read_limit (`int`):
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The maximum number of bytes to read from the slice.
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Attributes:
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previous_position (`int`):
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The previous position
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Examples:
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Reading 200 bytes with an offset of 128 bytes from a file (ie bytes 128 to 327):
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```python
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>>> with open("path/to/file", "rb") as file:
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... with SliceFileObj(file, seek_from=128, read_limit=200) as fslice:
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... fslice.read(...)
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```
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Reading a file in chunks of 512 bytes
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```python
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>>> import os
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>>> chunk_size = 512
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>>> file_size = os.getsize("path/to/file")
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>>> with open("path/to/file", "rb") as file:
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... for chunk_idx in range(ceil(file_size / chunk_size)):
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... with SliceFileObj(file, seek_from=chunk_idx * chunk_size, read_limit=chunk_size) as fslice:
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... chunk = fslice.read(...)
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```
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"""
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def __init__(self, fileobj: BinaryIO, seek_from: int, read_limit: int):
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self.fileobj = fileobj
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self.seek_from = seek_from
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self.read_limit = read_limit
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def __enter__(self):
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self._previous_position = self.fileobj.tell()
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end_of_stream = self.fileobj.seek(0, os.SEEK_END)
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self._len = min(self.read_limit, end_of_stream - self.seek_from)
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# ^^ The actual number of bytes that can be read from the slice
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self.fileobj.seek(self.seek_from, io.SEEK_SET)
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return self
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def __exit__(self, exc_type, exc_value, traceback):
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self.fileobj.seek(self._previous_position, io.SEEK_SET)
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def read(self, n: int = -1):
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pos = self.tell()
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if pos >= self._len:
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return b""
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remaining_amount = self._len - pos
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data = self.fileobj.read(remaining_amount if n < 0 else min(n, remaining_amount))
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return data
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def tell(self) -> int:
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return self.fileobj.tell() - self.seek_from
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def seek(self, offset: int, whence: int = os.SEEK_SET) -> int:
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start = self.seek_from
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end = start + self._len
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if whence in (os.SEEK_SET, os.SEEK_END):
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offset = start + offset if whence == os.SEEK_SET else end + offset
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offset = max(start, min(offset, end))
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whence = os.SEEK_SET
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elif whence == os.SEEK_CUR:
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cur_pos = self.fileobj.tell()
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offset = max(start - cur_pos, min(offset, end - cur_pos))
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else:
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raise ValueError(f"whence value {whence} is not supported")
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return self.fileobj.seek(offset, whence) - self.seek_from
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def __iter__(self):
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yield self.read(n=4 * 1024 * 1024)
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