104 lines
3.7 KiB
Python
104 lines
3.7 KiB
Python
from __future__ import annotations
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import os
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import sys
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from contextlib import suppress
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from errno import EACCES
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from pathlib import Path
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from typing import cast
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from ._api import BaseFileLock
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from ._util import ensure_directory_exists, raise_on_not_writable_file
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if sys.platform == "win32": # pragma: win32 cover
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import ctypes
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import msvcrt
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from ctypes import wintypes
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# Windows API constants for reparse point detection
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FILE_ATTRIBUTE_REPARSE_POINT = 0x00000400
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INVALID_FILE_ATTRIBUTES = 0xFFFFFFFF
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# Load kernel32.dll
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_kernel32 = ctypes.WinDLL("kernel32", use_last_error=True)
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_kernel32.GetFileAttributesW.argtypes = [wintypes.LPCWSTR]
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_kernel32.GetFileAttributesW.restype = wintypes.DWORD
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def _is_reparse_point(path: str) -> bool:
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"""
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Check if a path is a reparse point (symlink, junction, etc.) on Windows.
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:param path: Path to check
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:return: True if path is a reparse point, False otherwise
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:raises OSError: If GetFileAttributesW fails for reasons other than file-not-found
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"""
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attrs = _kernel32.GetFileAttributesW(path)
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if attrs == INVALID_FILE_ATTRIBUTES:
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# File doesn't exist yet - that's fine, we'll create it
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err = ctypes.get_last_error()
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if err == 2: # noqa: PLR2004 # ERROR_FILE_NOT_FOUND
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return False
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if err == 3: # noqa: PLR2004 # ERROR_PATH_NOT_FOUND
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return False
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# Some other error - let caller handle it
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return False
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return bool(attrs & FILE_ATTRIBUTE_REPARSE_POINT)
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class WindowsFileLock(BaseFileLock):
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"""Uses the :func:`msvcrt.locking` function to hard lock the lock file on Windows systems."""
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def _acquire(self) -> None:
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raise_on_not_writable_file(self.lock_file)
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ensure_directory_exists(self.lock_file)
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# Security check: Refuse to open reparse points (symlinks, junctions)
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# This prevents TOCTOU symlink attacks (CVE-TBD)
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if _is_reparse_point(self.lock_file):
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msg = f"Lock file is a reparse point (symlink/junction): {self.lock_file}"
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raise OSError(msg)
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flags = (
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os.O_RDWR # open for read and write
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| os.O_CREAT # create file if not exists
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| os.O_TRUNC # truncate file if not empty
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)
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try:
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fd = os.open(self.lock_file, flags, self._context.mode)
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except OSError as exception:
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if exception.errno != EACCES: # has no access to this lock
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raise
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else:
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try:
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msvcrt.locking(fd, msvcrt.LK_NBLCK, 1)
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except OSError as exception:
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os.close(fd) # close file first
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if exception.errno != EACCES: # file is already locked
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raise
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else:
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self._context.lock_file_fd = fd
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def _release(self) -> None:
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fd = cast("int", self._context.lock_file_fd)
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self._context.lock_file_fd = None
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msvcrt.locking(fd, msvcrt.LK_UNLCK, 1)
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os.close(fd)
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with suppress(OSError): # Probably another instance of the application hat acquired the file lock.
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Path(self.lock_file).unlink()
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else: # pragma: win32 no cover
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class WindowsFileLock(BaseFileLock):
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"""Uses the :func:`msvcrt.locking` function to hard lock the lock file on Windows systems."""
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def _acquire(self) -> None:
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raise NotImplementedError
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def _release(self) -> None:
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raise NotImplementedError
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__all__ = [
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"WindowsFileLock",
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]
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