django1/django/utils/_os.py

import os
import stat
import sys
import tempfile
from os.path import join, normcase, normpath, abspath, isabs, sep, dirname

from django.core.exceptions import SuspiciousFileOperation
from django.utils.encoding import force_text
from django.utils import six

try:
    WindowsError = WindowsError
except NameError:
    class WindowsError(Exception):
        pass

if six.PY2:
    fs_encoding = sys.getfilesystemencoding() or sys.getdefaultencoding()


# Under Python 2, define our own abspath function that can handle joining
# unicode paths to a current working directory that has non-ASCII characters
# in it.  This isn't necessary on Windows since the Windows version of abspath
# handles this correctly. It also handles drive letters differently than the
# pure Python implementation, so it's best not to replace it.
if six.PY3 or os.name == 'nt':
    abspathu = abspath
else:
    def abspathu(path):
        """
        Version of os.path.abspath that uses the unicode representation
        of the current working directory, thus avoiding a UnicodeDecodeError
        in join when the cwd has non-ASCII characters.
        """
        if not isabs(path):
            path = join(os.getcwdu(), path)
        return normpath(path)


def upath(path):
    """
    Always return a unicode path.
    """
    if six.PY2 and not isinstance(path, six.text_type):
        return path.decode(fs_encoding)
    return path


def npath(path):
    """
    Always return a native path, that is unicode on Python 3 and bytestring on
    Python 2.
    """
    if six.PY2 and not isinstance(path, bytes):
        return path.encode(fs_encoding)
    return path


def safe_join(base, *paths):
    """
    Joins one or more path components to the base path component intelligently.
    Returns a normalized, absolute version of the final path.

    The final path must be located inside of the base path component (otherwise
    a ValueError is raised).
    """
    base = force_text(base)
    paths = [force_text(p) for p in paths]
    final_path = abspathu(join(base, *paths))
    base_path = abspathu(base)
    # Ensure final_path starts with base_path (using normcase to ensure we
    # don't false-negative on case insensitive operating systems like Windows),
    # further, one of the following conditions must be true:
    #  a) The next character is the path separator (to prevent conditions like
    #     safe_join("/dir", "/../d"))
    #  b) The final path must be the same as the base path.
    #  c) The base path must be the most root path (meaning either "/" or "C:\\")
    if (not normcase(final_path).startswith(normcase(base_path + sep)) and
            normcase(final_path) != normcase(base_path) and
            dirname(normcase(base_path)) != normcase(base_path)):
        raise SuspiciousFileOperation(
            'The joined path ({}) is located outside of the base path '
            'component ({})'.format(final_path, base_path))
    return final_path


def rmtree_errorhandler(func, path, exc_info):
    """
    On Windows, some files are read-only (e.g. in in .svn dirs), so when
    rmtree() tries to remove them, an exception is thrown.
    We catch that here, remove the read-only attribute, and hopefully
    continue without problems.
    """
    exctype, value = exc_info[:2]
    # looking for a windows error
    if exctype is not WindowsError or 'Access is denied' not in str(value):
        raise
    # file type should currently be read only
    if ((os.stat(path).st_mode & stat.S_IREAD) != stat.S_IREAD):
        raise
    # convert to read/write
    os.chmod(path, stat.S_IWRITE)
    # use the original function to repeat the operation
    func(path)


def symlinks_supported():
    """
    A function to check if creating symlinks are supported in the
    host platform and/or if they are allowed to be created (e.g.
    on Windows it requires admin permissions).
    """
    tmpdir = tempfile.mkdtemp()
    original_path = os.path.join(tmpdir, 'original')
    symlink_path = os.path.join(tmpdir, 'symlink')
    os.makedirs(original_path)
    try:
        os.symlink(original_path, symlink_path)
        supported = True
    except (OSError, NotImplementedError, AttributeError):
        supported = False
    else:
        os.remove(symlink_path)
    finally:
        os.rmdir(original_path)
        os.rmdir(tmpdir)
        return supported