platform_utils_win32.py

# Copyright (C) 2016 The Android Open Source Project
#
# 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.

from ctypes import addressof
from ctypes import byref
from ctypes import c_buffer
from ctypes import c_ubyte
from ctypes import FormatError
from ctypes import get_last_error
from ctypes import Structure
from ctypes import Union
from ctypes import WinDLL
from ctypes import WinError
from ctypes.wintypes import BOOL
from ctypes.wintypes import BOOLEAN
from ctypes.wintypes import DWORD
from ctypes.wintypes import HANDLE
from ctypes.wintypes import LPCWSTR
from ctypes.wintypes import LPDWORD
from ctypes.wintypes import LPVOID
from ctypes.wintypes import ULONG
from ctypes.wintypes import USHORT
from ctypes.wintypes import WCHAR
import errno


kernel32 = WinDLL("kernel32", use_last_error=True)

UCHAR = c_ubyte

# Win32 error codes
ERROR_SUCCESS = 0
ERROR_NOT_SUPPORTED = 50
ERROR_PRIVILEGE_NOT_HELD = 1314

# Win32 API entry points
CreateSymbolicLinkW = kernel32.CreateSymbolicLinkW
CreateSymbolicLinkW.restype = BOOLEAN
CreateSymbolicLinkW.argtypes = (
    LPCWSTR,  # lpSymlinkFileName In
    LPCWSTR,  # lpTargetFileName In
    DWORD,  # dwFlags In
)

# Symbolic link creation flags
SYMBOLIC_LINK_FLAG_FILE = 0x00
SYMBOLIC_LINK_FLAG_DIRECTORY = 0x01
# symlink support for CreateSymbolicLink() starting with Windows 10 (1703,
# v10.0.14972)
SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE = 0x02

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
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
)

# Device I/O control flags and options
FSCTL_GET_REPARSE_POINT = 0x000900A8
IO_REPARSE_TAG_MOUNT_POINT = 0xA0000003
IO_REPARSE_TAG_SYMLINK = 0xA000000C
MAXIMUM_REPARSE_DATA_BUFFER_SIZE = 0x4000


class GENERIC_REPARSE_BUFFER(Structure):
    _fields_ = (("DataBuffer", UCHAR * 1),)


class SYMBOLIC_LINK_REPARSE_BUFFER(Structure):
    _fields_ = (
        ("SubstituteNameOffset", USHORT),
        ("SubstituteNameLength", USHORT),
        ("PrintNameOffset", USHORT),
        ("PrintNameLength", USHORT),
        ("Flags", ULONG),
        ("PathBuffer", WCHAR * 1),
    )

    @property
    def PrintName(self):
        arrayt = WCHAR * (self.PrintNameLength // 2)
        offset = type(self).PathBuffer.offset + self.PrintNameOffset
        return arrayt.from_address(addressof(self) + offset).value


class MOUNT_POINT_REPARSE_BUFFER(Structure):
    _fields_ = (
        ("SubstituteNameOffset", USHORT),
        ("SubstituteNameLength", USHORT),
        ("PrintNameOffset", USHORT),
        ("PrintNameLength", USHORT),
        ("PathBuffer", WCHAR * 1),
    )

    @property
    def PrintName(self):
        arrayt = WCHAR * (self.PrintNameLength // 2)
        offset = type(self).PathBuffer.offset + self.PrintNameOffset
        return arrayt.from_address(addressof(self) + offset).value


class REPARSE_DATA_BUFFER(Structure):
    class REPARSE_BUFFER(Union):
        _fields_ = (
            ("SymbolicLinkReparseBuffer", SYMBOLIC_LINK_REPARSE_BUFFER),
            ("MountPointReparseBuffer", MOUNT_POINT_REPARSE_BUFFER),
            ("GenericReparseBuffer", GENERIC_REPARSE_BUFFER),
        )

    _fields_ = (
        ("ReparseTag", ULONG),
        ("ReparseDataLength", USHORT),
        ("Reserved", USHORT),
        ("ReparseBuffer", REPARSE_BUFFER),
    )
    _anonymous_ = ("ReparseBuffer",)


def create_filesymlink(source, link_name):
    """Creates a Windows file symbolic link source pointing to link_name."""
    _create_symlink(source, link_name, SYMBOLIC_LINK_FLAG_FILE)


def create_dirsymlink(source, link_name):
    """Creates a Windows directory symbolic link source pointing to link_name."""  # noqa: E501
    _create_symlink(source, link_name, SYMBOLIC_LINK_FLAG_DIRECTORY)


def _create_symlink(source, link_name, dwFlags):
    if not CreateSymbolicLinkW(
        link_name,
        source,
        dwFlags | SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE,
    ):
        # See https://github.com/golang/go/pull/24307/files#diff-b87bc12e4da2497308f9ef746086e4f0  # noqa: E501
        # "the unprivileged create flag is unsupported below Windows 10 (1703,
        # v10.0.14972). retry without it."
        if not CreateSymbolicLinkW(link_name, source, dwFlags):
            code = get_last_error()
            error_desc = FormatError(code).strip()
            if code == ERROR_PRIVILEGE_NOT_HELD:
                raise OSError(errno.EPERM, error_desc, link_name)
            _raise_winerror(code, f'Error creating symbolic link "{link_name}"')


def islink(path):
    result = GetFileAttributesW(path)
    if result == INVALID_FILE_ATTRIBUTES:
        return False
    return bool(result & FILE_ATTRIBUTE_REPARSE_POINT)


def readlink(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:
        _raise_winerror(
            get_last_error(), f'Error opening symbolic link "{path}"'
        )
    target_buffer = 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),
        byref(n_bytes_returned),
        None,
    )
    CloseHandle(reparse_point_handle)
    if not io_result:
        _raise_winerror(
            get_last_error(), f'Error reading symbolic link "{path}"'
        )
    rdb = REPARSE_DATA_BUFFER.from_buffer(target_buffer)
    if rdb.ReparseTag == IO_REPARSE_TAG_SYMLINK:
        return rdb.SymbolicLinkReparseBuffer.PrintName
    elif rdb.ReparseTag == IO_REPARSE_TAG_MOUNT_POINT:
        return rdb.MountPointReparseBuffer.PrintName
    # Unsupported reparse point type.
    _raise_winerror(
        ERROR_NOT_SUPPORTED, f'Error reading symbolic link "{path}"'
    )


def _raise_winerror(code, error_desc):
    win_error_desc = FormatError(code).strip()
    error_desc = f"{error_desc}: {win_error_desc}"
    raise WinError(code, error_desc)