posixemulation.py
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# -*- coding: utf-8 -*-
r"""
werkzeug.posixemulation
~~~~~~~~~~~~~~~~~~~~~~~
Provides a POSIX emulation for some features that are relevant to
web applications. The main purpose is to simplify support for
systems such as Windows NT that are not 100% POSIX compatible.
Currently this only implements a :func:`rename` function that
follows POSIX semantics. Eg: if the target file already exists it
will be replaced without asking.
This module was introduced in 0.6.1 and is not a public interface.
It might become one in later versions of Werkzeug.
:copyright: 2007 Pallets
:license: BSD-3-Clause
"""
import errno
import os
import random
import sys
import time
from ._compat import to_unicode
from .filesystem import get_filesystem_encoding
can_rename_open_file = False
if os.name == "nt":
try:
import ctypes
_MOVEFILE_REPLACE_EXISTING = 0x1
_MOVEFILE_WRITE_THROUGH = 0x8
_MoveFileEx = ctypes.windll.kernel32.MoveFileExW
def _rename(src, dst):
src = to_unicode(src, get_filesystem_encoding())
dst = to_unicode(dst, get_filesystem_encoding())
if _rename_atomic(src, dst):
return True
retry = 0
rv = False
while not rv and retry < 100:
rv = _MoveFileEx(
src, dst, _MOVEFILE_REPLACE_EXISTING | _MOVEFILE_WRITE_THROUGH
)
if not rv:
time.sleep(0.001)
retry += 1
return rv
# new in Vista and Windows Server 2008
_CreateTransaction = ctypes.windll.ktmw32.CreateTransaction
_CommitTransaction = ctypes.windll.ktmw32.CommitTransaction
_MoveFileTransacted = ctypes.windll.kernel32.MoveFileTransactedW
_CloseHandle = ctypes.windll.kernel32.CloseHandle
can_rename_open_file = True
def _rename_atomic(src, dst):
ta = _CreateTransaction(None, 0, 0, 0, 0, 1000, "Werkzeug rename")
if ta == -1:
return False
try:
retry = 0
rv = False
while not rv and retry < 100:
rv = _MoveFileTransacted(
src,
dst,
None,
None,
_MOVEFILE_REPLACE_EXISTING | _MOVEFILE_WRITE_THROUGH,
ta,
)
if rv:
rv = _CommitTransaction(ta)
break
else:
time.sleep(0.001)
retry += 1
return rv
finally:
_CloseHandle(ta)
except Exception:
def _rename(src, dst):
return False
def _rename_atomic(src, dst):
return False
def rename(src, dst):
# Try atomic or pseudo-atomic rename
if _rename(src, dst):
return
# Fall back to "move away and replace"
try:
os.rename(src, dst)
except OSError as e:
if e.errno != errno.EEXIST:
raise
old = "%s-%08x" % (dst, random.randint(0, sys.maxsize))
os.rename(dst, old)
os.rename(src, dst)
try:
os.unlink(old)
except Exception:
pass
else:
rename = os.rename
can_rename_open_file = True