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.

import errno

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

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, 'Error creating symbolic link "{}"'.format(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(), 'Error opening symbolic link "{}"'.format(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(), 'Error reading symbolic link "{}"'.format(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, 'Error reading symbolic link "{}"'.format(path)
    )


def _raise_winerror(code, error_desc):
    win_error_desc = FormatError(code).strip()
    error_desc = "{0}: {1}".format(error_desc, win_error_desc)
    raise WinError(code, error_desc)