platform_utils.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
import os
import platform
import shutil
import stat


def isWindows():
    """Returns True when running with the native port of Python for Windows,
    False when running on any other platform (including the Cygwin port of
    Python).
    """
    # Note: The cygwin port of Python returns "CYGWIN_NT_xxx"
    return platform.system() == "Windows"


def symlink(source, link_name):
    """Creates a symbolic link pointing to source named link_name.

    Note: On Windows, source must exist on disk, as the implementation needs
    to know whether to create a "File" or a "Directory" symbolic link.
    """
    if isWindows():
        import platform_utils_win32

        source = _validate_winpath(source)
        link_name = _validate_winpath(link_name)
        target = os.path.join(os.path.dirname(link_name), source)
        if isdir(target):
            platform_utils_win32.create_dirsymlink(
                _makelongpath(source), link_name
            )
        else:
            platform_utils_win32.create_filesymlink(
                _makelongpath(source), link_name
            )
    else:
        return os.symlink(source, link_name)


def _validate_winpath(path):
    path = os.path.normpath(path)
    if _winpath_is_valid(path):
        return path
    raise ValueError(
        f'Path "{path}" must be a relative path or an absolute '
        "path starting with a drive letter"
    )


def _winpath_is_valid(path):
    """Windows only: returns True if path is relative (e.g. ".\\foo") or is
    absolute including a drive letter (e.g. "c:\\foo"). Returns False if path
    is ambiguous (e.g. "x:foo" or "\\foo").
    """
    assert isWindows()
    path = os.path.normpath(path)
    drive, tail = os.path.splitdrive(path)
    if tail:
        if not drive:
            return tail[0] != os.sep  # "\\foo" is invalid
        else:
            return tail[0] == os.sep  # "x:foo" is invalid
    else:
        return not drive  # "x:" is invalid


def _makelongpath(path):
    """Return the input path normalized to support the Windows long path syntax
    ("\\\\?\\" prefix) if needed, i.e. if the input path is longer than the
    MAX_PATH limit.
    """
    if isWindows():
        # Note: MAX_PATH is 260, but, for directories, the maximum value is
        # actually 246.
        if len(path) < 246:
            return path
        if path.startswith("\\\\?\\"):
            return path
        if not os.path.isabs(path):
            return path
        # Append prefix and ensure unicode so that the special longpath syntax
        # is supported by underlying Win32 API calls
        return "\\\\?\\" + os.path.normpath(path)
    else:
        return path


def rmtree(path, ignore_errors=False):
    """shutil.rmtree(path) wrapper with support for long paths on Windows.

    Availability: Unix, Windows.
    """
    onerror = None
    if isWindows():
        path = _makelongpath(path)
        onerror = handle_rmtree_error
    shutil.rmtree(path, ignore_errors=ignore_errors, onerror=onerror)


def handle_rmtree_error(function, path, excinfo):
    # Allow deleting read-only files.
    os.chmod(path, stat.S_IWRITE)
    function(path)


def rename(src, dst):
    """os.rename(src, dst) wrapper with support for long paths on Windows.

    Availability: Unix, Windows.
    """
    if isWindows():
        # On Windows, rename fails if destination exists, see
        # https://docs.python.org/2/library/os.html#os.rename
        try:
            os.rename(_makelongpath(src), _makelongpath(dst))
        except OSError as e:
            if e.errno == errno.EEXIST:
                os.remove(_makelongpath(dst))
                os.rename(_makelongpath(src), _makelongpath(dst))
            else:
                raise
    else:
        shutil.move(src, dst)


def remove(path, missing_ok=False):
    """Remove (delete) the file path. This is a replacement for os.remove that
    allows deleting read-only files on Windows, with support for long paths and
    for deleting directory symbolic links.

    Availability: Unix, Windows.
    """
    longpath = _makelongpath(path) if isWindows() else path
    try:
        os.remove(longpath)
    except OSError as e:
        if e.errno == errno.EACCES:
            os.chmod(longpath, stat.S_IWRITE)
            # Directory symbolic links must be deleted with 'rmdir'.
            if islink(longpath) and isdir(longpath):
                os.rmdir(longpath)
            else:
                os.remove(longpath)
        elif missing_ok and e.errno == errno.ENOENT:
            pass
        else:
            raise


def walk(top, topdown=True, onerror=None, followlinks=False):
    """os.walk(path) wrapper with support for long paths on Windows.

    Availability: Windows, Unix.
    """
    if isWindows():
        return _walk_windows_impl(top, topdown, onerror, followlinks)
    else:
        return os.walk(top, topdown, onerror, followlinks)


def _walk_windows_impl(top, topdown, onerror, followlinks):
    try:
        names = listdir(top)
    except Exception as err:
        if onerror is not None:
            onerror(err)
        return

    dirs, nondirs = [], []
    for name in names:
        if isdir(os.path.join(top, name)):
            dirs.append(name)
        else:
            nondirs.append(name)

    if topdown:
        yield top, dirs, nondirs
    for name in dirs:
        new_path = os.path.join(top, name)
        if followlinks or not islink(new_path):
            yield from _walk_windows_impl(
                new_path, topdown, onerror, followlinks
            )
    if not topdown:
        yield top, dirs, nondirs


def listdir(path):
    """os.listdir(path) wrapper with support for long paths on Windows.

    Availability: Windows, Unix.
    """
    return os.listdir(_makelongpath(path))


def rmdir(path):
    """os.rmdir(path) wrapper with support for long paths on Windows.

    Availability: Windows, Unix.
    """
    os.rmdir(_makelongpath(path))


def isdir(path):
    """os.path.isdir(path) wrapper with support for long paths on Windows.

    Availability: Windows, Unix.
    """
    return os.path.isdir(_makelongpath(path))


def islink(path):
    """os.path.islink(path) wrapper with support for long paths on Windows.

    Availability: Windows, Unix.
    """
    if isWindows():
        import platform_utils_win32

        return platform_utils_win32.islink(_makelongpath(path))
    else:
        return os.path.islink(path)


def readlink(path):
    """Return a string representing the path to which the symbolic link
    points. The result may be either an absolute or relative pathname;
    if it is relative, it may be converted to an absolute pathname using
    os.path.join(os.path.dirname(path), result).

    Availability: Windows, Unix.
    """
    if isWindows():
        import platform_utils_win32

        return platform_utils_win32.readlink(_makelongpath(path))
    else:
        return os.readlink(path)


def realpath(path):
    """Return the canonical path of the specified filename, eliminating
    any symbolic links encountered in the path.

    Availability: Windows, Unix.
    """
    if isWindows():
        current_path = os.path.abspath(path)
        path_tail = []
        for c in range(0, 100):  # Avoid cycles
            if islink(current_path):
                target = readlink(current_path)
                current_path = os.path.join(
                    os.path.dirname(current_path), target
                )
            else:
                basename = os.path.basename(current_path)
                if basename == "":
                    path_tail.append(current_path)
                    break
                path_tail.append(basename)
                current_path = os.path.dirname(current_path)
        path_tail.reverse()
        result = os.path.normpath(os.path.join(*path_tail))
        return result
    else:
        return os.path.realpath(path)