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#!/usr/bin/python
# Copyright 2019 The Cobalt Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Provides functions for symlinking on Windows."""
import ctypes
from ctypes import wintypes
import os
DWORD = wintypes.DWORD
LPCWSTR = wintypes.LPCWSTR
HANDLE = wintypes.HANDLE
LPVOID = wintypes.LPVOID
BOOL = wintypes.BOOL
USHORT = wintypes.USHORT
ULONG = wintypes.ULONG
WCHAR = wintypes.WCHAR
kernel32 = ctypes.windll.kernel32
LPDWORD = ctypes.POINTER(DWORD)
UCHAR = ctypes.c_ubyte
GetFileAttributesW = kernel32.GetFileAttributesW
GetFileAttributesW.restype = DWORD
GetFileAttributesW.argtypes = (LPCWSTR,) # lpFileName In
INVALID_FILE_ATTRIBUTES = 0xFFFFFFFF
FILE_ATTRIBUTE_REPARSE_POINT = 0x00400
CreateFileW = kernel32.CreateFileW
CreateFileW.restype = HANDLE
CreateFileW.argtypes = (
LPCWSTR, # lpFileName In
DWORD, # dwDesiredAccess In
DWORD, # dwShareMode In
LPVOID, # lpSecurityAttributes In_opt
DWORD, # dwCreationDisposition In
DWORD, # dwFlagsAndAttributes In
HANDLE) # hTemplateFile In_opt
CloseHandle = kernel32.CloseHandle
CloseHandle.restype = BOOL
CloseHandle.argtypes = (HANDLE,) # hObject In
INVALID_HANDLE_VALUE = HANDLE(-1).value # pylint:disable=invalid-name
OPEN_EXISTING = 3
FILE_FLAG_BACKUP_SEMANTICS = 0x02000000
FILE_FLAG_OPEN_REPARSE_POINT = 0x00200000
DeviceIoControl = kernel32.DeviceIoControl
DeviceIoControl.restype = BOOL
DeviceIoControl.argtypes = (
HANDLE, # hDevice In
DWORD, # dwIoControlCode In
LPVOID, # lpInBuffer In_opt
DWORD, # nInBufferSize In
LPVOID, # lpOutBuffer Out_opt
DWORD, # nOutBufferSize In
LPDWORD, # lpBytesReturned Out_opt
LPVOID) # lpOverlapped Inout_opt
FSCTL_GET_REPARSE_POINT = 0x000900A8
IO_REPARSE_TAG_MOUNT_POINT = 0xA0000003
IO_REPARSE_TAG_SYMLINK = 0xA000000C
MAXIMUM_REPARSE_DATA_BUFFER_SIZE = 0x4000
SYMBOLIC_LINK_FLAG_DIRECTORY = 0x1
# Developer Mode must be enabled in order to use the following flag.
SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE = 0x2
SYMLINK_FLAG_RELATIVE = 0x1
class GenericReparseBuffer(ctypes.Structure):
"""Win32 api data structure."""
_fields_ = (('DataBuffer', UCHAR * 1),)
class SymbolicLinkReparseBuffer(ctypes.Structure):
"""Win32 api data structure."""
_fields_ = (('SubstituteNameOffset', USHORT),
('SubstituteNameLength', USHORT), ('PrintNameOffset', USHORT),
('PrintNameLength', USHORT), ('Flags', ULONG), ('PathBuffer',
WCHAR * 1))
@property
def print_name(self):
arrayt = WCHAR * (self.PrintNameLength // 2)
offset = type(self).PathBuffer.offset + self.PrintNameOffset
return arrayt.from_address(ctypes.addressof(self) + offset).value
@property
def substitute_name(self):
arrayt = WCHAR * (self.SubstituteNameLength // 2)
offset = type(self).PathBuffer.offset + self.SubstituteNameOffset
return arrayt.from_address(ctypes.addressof(self) + offset).value
@property
def is_relative_path(self):
return bool(self.Flags & SYMLINK_FLAG_RELATIVE)
class MountPointReparseBuffer(ctypes.Structure):
"""Win32 api data structure."""
_fields_ = (('SubstituteNameOffset', USHORT),
('SubstituteNameLength', USHORT), ('PrintNameOffset', USHORT),
('PrintNameLength', USHORT), ('PathBuffer', WCHAR * 1))
@property
def print_name(self):
arrayt = WCHAR * (self.PrintNameLength // 2)
offset = type(self).PathBuffer.offset + self.PrintNameOffset
return arrayt.from_address(ctypes.addressof(self) + offset).value
@property
def substitute_name(self):
arrayt = WCHAR * (self.SubstituteNameLength // 2)
offset = type(self).PathBuffer.offset + self.SubstituteNameOffset
return arrayt.from_address(ctypes.addressof(self) + offset).value
class ReparseDataBuffer(ctypes.Structure):
"""Win32 api data structure."""
class ReparseBuffer(ctypes.Union):
"""Win32 api data structure."""
_fields_ = (('SymbolicLinkReparseBuffer', SymbolicLinkReparseBuffer),
('MountPointReparseBuffer', MountPointReparseBuffer),
('GenericReparseBuffer', GenericReparseBuffer))
_fields_ = (('ReparseTag', ULONG), ('ReparseDataLength', USHORT),
('Reserved', USHORT), ('ReparseBuffer', ReparseBuffer))
_anonymous_ = ('ReparseBuffer',)
def _ToUnicode(s):
try:
return s.decode('utf-8')
except AttributeError:
return s
_kdll = None
def _GetKernel32Dll():
global _kdll
if _kdll:
return _kdll
_kdll = ctypes.windll.LoadLibrary('kernel32.dll')
return _kdll
def FastCreateReparseLink(from_folder, link_folder):
"""Creates a reparse link.
Args:
from_folder: The folder that the link will point to.
link_folder: The path of the link to be created.
Returns:
None
Raises:
OSError: if link cannot be created
"""
from_folder = _ToUnicode(from_folder)
link_folder = _ToUnicode(link_folder)
par_dir = os.path.dirname(link_folder)
if not os.path.isdir(par_dir):
os.makedirs(par_dir)
kdll = _GetKernel32Dll()
# Only supported from Windows 10 Insiders build 14972
flags = SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE | \
SYMBOLIC_LINK_FLAG_DIRECTORY
ok = kdll.CreateSymbolicLinkW(link_folder, from_folder, flags)
if not ok or not FastIsReparseLink(link_folder):
raise OSError('Could not create sym link ' + link_folder + ' to ' +
from_folder)
def FastIsReparseLink(path):
path = _ToUnicode(path)
result = GetFileAttributesW(path)
if result == INVALID_FILE_ATTRIBUTES:
return False
return bool(result & FILE_ATTRIBUTE_REPARSE_POINT)
def FastReadReparseLink(path):
"""See api docstring, above."""
path = _ToUnicode(path)
reparse_point_handle = CreateFileW(
path, 0, 0, None, OPEN_EXISTING,
FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS, None)
if reparse_point_handle == INVALID_HANDLE_VALUE:
return None
# Remove false positive below.
# pylint: disable=deprecated-method
target_buffer = ctypes.c_buffer(MAXIMUM_REPARSE_DATA_BUFFER_SIZE)
n_bytes_returned = DWORD()
io_result = DeviceIoControl(reparse_point_handle, FSCTL_GET_REPARSE_POINT,
None, 0, target_buffer, len(target_buffer),
ctypes.byref(n_bytes_returned), None)
CloseHandle(reparse_point_handle)
if not io_result:
return None
rdb = ReparseDataBuffer.from_buffer(target_buffer)
if rdb.ReparseTag == IO_REPARSE_TAG_SYMLINK:
return rdb.SymbolicLinkReparseBuffer.print_name
elif rdb.ReparseTag == IO_REPARSE_TAG_MOUNT_POINT:
return rdb.MountPointReparseBuffer.print_name
return None