tar_file.py

"""
Tar file support
"""

#*****************************************************************************
#       Copyright (C) 2016 Volker Braun <[email protected]>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#                  http://www.gnu.org/licenses/
#*****************************************************************************

from __future__ import print_function

import os
import copy
import tarfile
import stat
import subprocess
import time

from io import BytesIO

from sage_bootstrap.uncompress.filter_os_files import filter_os_files


class SageBaseTarFile(tarfile.TarFile):
    """
    Same as tarfile.TarFile, but applies a reasonable umask (0022) to the
    permissions of all extracted files and directories, and fixes
    the encoding of file names in the tarball to be 'utf-8' instead of
    depending on locale settings.

    Previously this applied the user's current umask per the default behavior
    of the ``tar`` utility, but this did not provide sufficiently reliable
    behavior in all cases, such as when the user's umask is not strict enough.

    This also sets the modified timestamps on all extracted files to the same
    time (the current time), not the timestamps stored in the tarball. This
    is meant to work around https://bugs.python.org/issue32773

    See https://github.com/sagemath/sage/issues/20218#comment:16 and
    https://github.com/sagemath/sage/issues/24567 for more background.
    """

    umask = 0o022

    def __init__(self, *args, **kwargs):

        kwargs['encoding'] = 'utf-8'

        # Unfortunately the only way to get the current umask is to set it
        # and then restore it
        super(SageBaseTarFile, self).__init__(*args, **kwargs)

        # Extracted files will have this timestamp
        self._extracted_mtime = time.time()

    @property
    def names(self):
        """
        List of filenames in the archive.

        Filters out names of OS-related files that shouldn't be in the
        archive (.DS_Store, etc.)
        """

        return filter_os_files(self.getnames())

    def chmod(self, tarinfo, targetpath):
        """Apply ``self.umask`` instead of the permissions in the TarInfo."""
        tarinfo = copy.copy(tarinfo)
        tarinfo.mode &= ~self.umask
        tarinfo.mode |= stat.S_IWUSR
        tarinfo.mode &= ~(stat.S_ISUID | stat.S_ISGID)
        return super(SageBaseTarFile, self).chmod(tarinfo, targetpath)

    def utime(self, tarinfo, targetpath):
        """Override to keep the extraction time as the file's timestamp."""
        tarinfo.mtime = self._extracted_mtime
        return super(SageBaseTarFile, self).utime(tarinfo, targetpath)

    def extractall(self, path='.', members=None, **kwargs):
        """
        Same as tarfile.TarFile.extractall but allows filenames for
        the members argument (like zipfile.ZipFile).

        .. note::
            The additional ``**kwargs`` are for Python 2/3 compatibility, since
            different versions of this method accept additional arguments.
        """
        if members:
            name_to_member = dict([member.name, member] for member in self.getmembers())
            members = [m if isinstance(m, tarfile.TarInfo)
                       else name_to_member[m]
                       for m in members]
        return super(SageBaseTarFile, self).extractall(path=path,
                                                       members=members,
                                                       **kwargs)

    def extractbytes(self, member):
        """
        Return the contents of the specified archive member as bytes.

        If the member does not exist, returns None.
        """

        if member in self.getnames():
            reader = self.extractfile(member)
            return reader.read()

    def _extract_member(self, tarinfo, targetpath, **kwargs):
        """
        Override to ensure that our custom umask is applied over the entire
        directory tree, even for directories that are not explicitly listed in
        the tarball.

        .. note::
            The additional ``**kwargs`` are for Python 2/3 compatibility, since
            different versions of this method accept additional arguments.
        """
        old_umask = os.umask(self.umask)
        try:
            super(SageBaseTarFile, self)._extract_member(tarinfo, targetpath,
                                                         **kwargs)
        finally:
            os.umask(old_umask)


class SageTarFile(SageBaseTarFile):
    """
    A wrapper around SageBaseTarFile such that SageTarFile(filename) is
    essentially equivalent to TarFile.open(filename) which is more
    flexible than the basic TarFile.__init__
    """
    def __new__(cls, filename):
        return SageBaseTarFile.open(filename)

    @staticmethod
    def can_read(filename):
        """
        Given an archive filename, returns True if this class can read and
        process the archive format of that file.
        """
        return tarfile.is_tarfile(filename)


class SageTarXZFile(SageBaseTarFile):
    """
    A ``.tar.xz`` file which is uncompressed in memory.
    """
    def __new__(cls, filename):
        # Read uncompressed data through a pipe
        proc = subprocess.Popen(["xz", "-d", "-c", filename], stdout=subprocess.PIPE)
        data, _ = proc.communicate()
        return SageBaseTarFile(mode="r", fileobj=BytesIO(data))

    @staticmethod
    def can_read(filename):
        """
        Given an archive filename, returns True if this class can read and
        process the archive format of that file.
        """
        devnull = open(os.devnull, 'w')
        try:
            subprocess.check_call(["xz", "-l", filename], stdout=devnull, stderr=devnull)
        except Exception:
            return False
        return True