MINI Sh3ll

# Copyright (C) 2011 Canonical
#
# Authors:
#  Michael Vogt
#
# 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; version 3.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
# details.
#
# You should have received a copy of the GNU General Public License along with
# this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

from __future__ import print_function

import apt
from apt.cache import FetchFailedException
import apt_pkg
import difflib
import fnmatch
import glob
import hashlib
import logging
import lsb_release
import os
import re
import shutil
import stat
import subprocess
import tarfile
import tempfile
import time

from io import BytesIO, open

if "APT_CLONE_DEBUG_RESOLVER" in os.environ:
    apt_pkg.config.set("Debug::pkgProblemResolver", "1")
    apt_pkg.config.set("Debug::pkgDepCache::AutoInstall", "1")

class LowLevelCommands(object):
    """ calls to the lowlevel operations to install debs
        or repack a deb
    """
    dpkg_repack = "/usr/bin/dpkg-repack"

    def install_debs(self, debfiles, targetdir):
        if not debfiles:
            return True
        install_cmd = ["dpkg", "-i"]
        if targetdir != "/":
            install_cmd.insert(0, "chroot")
            install_cmd.insert(1, targetdir)
        ret = subprocess.call(install_cmd + debfiles)
        return (ret == 0)

    def repack_deb(self, pkgname, targetdir):
        """ dpkg-repack pkgname into targetdir """
        if not os.path.exists(self.dpkg_repack):
            raise IOError("no '%s' found" % self.dpkg_repack)
        repack_cmd = [self.dpkg_repack]
        if not os.getuid() == 0:
            if not os.path.exists("/usr/bin/fakeroot"):
                return
            repack_cmd = ["fakeroot", "-u"] + repack_cmd
        ret = subprocess.call(repack_cmd + [pkgname], cwd=targetdir)
        return (ret == 0)

    def debootstrap(self, targetdir, distro=None):
        if distro is None:
            distro = lsb_release.get_distro_information()['CODENAME']
        ret = subprocess.call(["debootstrap", distro, targetdir])
        return (ret == 0)

    def merge_keys(self, fromkeyfile, intokeyfile):
        ret = subprocess.call(['apt-key', '--keyring', intokeyfile,
                               'add', fromkeyfile])
        return (ret == 0)

    def bind_mount(self, olddir, newdir):
        ret = subprocess.call(["mount", "--bind", olddir, newdir])
        return (ret == 0)

    def bind_umount(self, binddir):
        ret = subprocess.call(["umount", binddir])
        return (ret == 0)


class AptClone(object):
    """ clone the package selection/installation of a existing system
        using the information that apt provides

        If dpkg-repack is installed, it will be used to generate debs
        for the obsolete ones.
    """
    CLONE_FILENAME = "apt-clone-state-%s.tar.gz" % os.uname()[1]

    TARPREFIX = "./"

    def __init__(self, fetch_progress=None, install_progress=None,
                 cache_cls=None):
        self.not_downloadable = set()
        self.version_mismatch = set()
        self.commands = LowLevelCommands()
        # fetch
        if fetch_progress:
            self.fetch_progress = fetch_progress
        else:
            self.fetch_progress =  apt.progress.text.AcquireProgress()
        # install
        if install_progress:
            self.install_progress = install_progress
        else:
            self.install_progress = apt.progress.base.InstallProgress()
        # FIXME: SIIIIILLLLLLLYYYYYYYYY use mock.patch instead to patch
        #        the apt.Cache() to a mock
        # cache class (e.g. apt.Cache)
        if cache_cls:
            self._cache_cls = cache_cls
        else:
            self._cache_cls = apt.Cache

    # save
    def save_state(self, sourcedir, target,
                   with_dpkg_repack=False, with_dpkg_status=False,
                   scrub_sources=False, extra_files=None):
        """ save the current system state (installed pacakges, enabled
            repositories ...) into the apt-state.tar.gz file in targetdir
        """
        if os.path.isdir(target):
            target = os.path.join(target, self.CLONE_FILENAME)
        else:
            if not target.endswith(".tar.gz"):
                target += ".apt-clone.tar.gz"

        if sourcedir != '/':
            apt_pkg.init_config()
            apt_pkg.config.set("Dir", sourcedir)
            apt_pkg.config.set("Dir::State::status",
                               os.path.join(sourcedir, 'var/lib/dpkg/status'))
            apt_pkg.init_system()

        with tarfile.open(name=target, mode="w:gz") as tar:
            self._write_uname(tar)
            self._write_state_installed_pkgs(sourcedir, tar)
            self._write_state_auto_installed(tar)
            self._write_state_sources_list(tar, scrub_sources)
            self._write_state_apt_preferences(tar)
            self._write_state_apt_keyring(tar)
            self._write_state_extra_files(extra_files, tar)
            if with_dpkg_status:
                self._write_state_dpkg_status(tar)
            if with_dpkg_repack:
                self._dpkg_repack(tar)

    def _get_host_info_dict(self):
        # not really uname
        host_info = { 'hostname'   : os.uname()[1],
                       'kernel'     : os.uname()[2],
                       'uname_arch' : os.uname()[4],
                       'arch'       : apt_pkg.config.find("APT::Architecture")
                     }
        return host_info

    def _write_uname(self, tar):
        host_info = self._get_host_info_dict()
        # save it
        f = tempfile.NamedTemporaryFile(mode='w')
        info = "\n".join(["%s: %s" % (key, value)
                          for (key, value) in host_info.items()])
        f.write(info+"\n")
        f.flush()
        tar.add(f.name, arcname="./var/lib/apt-clone/uname")

    def _write_state_extra_files(self, extra_files, tar):
        if extra_files is None:
            return
        for p in extra_files:
            for f in glob.glob(p):
                tar.add(f, arcname="./extra-files"+f)
                
    def _write_state_installed_pkgs(self, sourcedir, tar):
        cache = self._cache_cls(rootdir=sourcedir)
        s = ""
        foreign = ""
        distro_id = lsb_release.get_distro_information()['ID']
        for pkg in cache:
            if pkg.is_installed:
                # a version identifies the pacakge
                s += "%s %s %s\n" % (
                    pkg.name, pkg.installed.version, int(pkg.is_auto_installed))
                if not pkg.candidate or not pkg.candidate.downloadable:
                    self.not_downloadable.add(pkg.name)
                elif not (pkg.installed.downloadable and
                          pkg.candidate.downloadable):
                    self.version_mismatch.add(pkg.name)
                for o in pkg.installed.origins:
                    if o.archive == "now" and o.origin == "":
                        continue
                    if o.origin != distro_id:
                        foreign += "%s %s %s\n" % (
                            pkg.name, pkg.installed.version,
                            o.origin if o.origin != "" else "unknown")
                    break
        # store the installed.pkgs
        tarinfo = tarfile.TarInfo("./var/lib/apt-clone/installed.pkgs")
        s = s.encode('utf-8')
        tarinfo.size = len(s)
        tarinfo.mtime = time.time()
        tar.addfile(tarinfo, BytesIO(s))
        # store the foreign packages
        tarinfo = tarfile.TarInfo("./var/lib/apt-clone/foreign.pkgs")
        foreign = foreign.encode('utf-8')
        tarinfo.size = len(foreign)
        tarinfo.mtime = time.time()
        tar.addfile(tarinfo, BytesIO(foreign))

    def _write_state_dpkg_status(self, tar):
        # store dpkg-status, this is not strictly needed as installed.pkgs
        # should contain all we need, but we still keep it for debugging
        # reasons
        dpkg_status = apt_pkg.config.find_file("dir::state::status")
        tar.add(dpkg_status, arcname="./var/lib/apt-clone/dpkg-status")

    def _write_state_auto_installed(self, tar):
        extended_states = apt_pkg.config.find_file(
            "Dir::State::extended_states")
        if os.path.exists(extended_states):
            tar.add(extended_states, "./var/lib/apt-clone/extended_states")

    def _write_state_apt_preferences(self, tar):
        f = apt_pkg.config.find_file("Dir::Etc::preferences")
        if os.path.exists(f):
            tar.add(f, arcname="./etc/apt/preferences")
        p = apt_pkg.config.find_dir("Dir::Etc::preferencesparts",
                                    "/etc/apt/preferences.d")
        if os.path.exists(p):
            tar.add(p, arcname="./etc/apt/preferences.d")

    def _write_state_apt_keyring(self, tar):
        f = apt_pkg.config.find_file("Dir::Etc::trusted")
        if os.path.exists(f):
            tar.add(f, arcname="./etc/apt/trusted.gpg")
        p = apt_pkg.config.find_dir("Dir::Etc::trustedparts",
                                    "/etc/apt/trusted.gpg.d")
        if os.path.exists(p):
            tar.add(p, arcname="./etc/apt/trusted.gpg.d")

    def _write_state_sources_list(self, tar, scrub=False):
        sources_list = apt_pkg.config.find_file("Dir::Etc::sourcelist")
        self._add_file_to_tar_with_password_check(tar, sources_list, scrub,
            "./etc/apt/sources.list")
        source_parts = apt_pkg.config.find_dir("Dir::Etc::sourceparts")
        if os.path.exists(source_parts):
            tar.add(source_parts, arcname="./etc/apt/sources.list.d",
                    recursive=False)
            for source in os.listdir(source_parts):
                if source.startswith('.'):
                    continue
                if not source.endswith('.list'):
                    continue
                sources_file_name = '%s/%s' % (source_parts, source)
                if os.path.isdir(sources_file_name):
                    continue
                self._add_file_to_tar_with_password_check(tar,
                    sources_file_name, scrub,
                    "./etc/apt/sources.list.d/"+source)

    def _add_file_to_tar_with_password_check(self, tar, sources, scrub, arcname):
        if scrub:
            with tempfile.NamedTemporaryFile(mode='wb') as source_copy, open(sources, 'rb') as f:
                for line in f.readlines():
                    # compat with both py2/py3
                    if type(line) is bytes:
                        line = line.decode("UTF-8")
                    if re.search('/[^/@:]*:[^/@:]*@', line):
                        line = re.sub('/[^/@:]*:[^/@:]*@',
                            '/USERNAME:PASSWORD@', line)
                    # tempfile.NamedTemporaryFile cannot easily be made to
                    # open in Unicode mode in Python 2.  We can remove this
                    # once ubuntu-release-upgrader is run under Python 3
                    # (i.e. after Ubuntu 14.04).
                    source_copy.write(line.encode("utf-8"))
                    source_copy.flush()
                tar.add(source_copy.name, arcname=arcname)
        else:
            tar.add(sources, arcname=arcname)

    def _write_modified_files_from_etc(self, tar):
        #etcdir = os.path.join(apt_pkg.config.get("Dir"), "etc")
        pass

    def _dpkg_repack(self, tar):
        tdir = tempfile.mkdtemp()
        for pkgname in self.not_downloadable:
            self.commands.repack_deb(pkgname, tdir)
        tar.add(tdir, arcname="./var/lib/apt-clone/debs")
        shutil.rmtree(tdir)
        #print(tdir)

    # detect prefix
    def _detect_tarprefix(self, tar):
        #print(tar.getnames())
        if tar.getnames()[-1].startswith("./"):
            self.TARPREFIX = "./"
        else:
            self.TARPREFIX = ""

    # info
    def _get_info_distro(self, statefile):
        with tarfile.open(statefile) as tar:
            self._detect_tarprefix(tar)
            # guess distro infos
            f = tar.extractfile(self.TARPREFIX+"etc/apt/sources.list")
            for line in f.readlines():
                line = line.decode("utf-8")
                if line.startswith("#") or line.strip() == "":
                    continue
                l = line.split()
                if len(l) > 2 and not l[2].endswith("/"):
                    return l[2]
        return None

    def _get_clone_info_dict(self, statefile):
        distro = self._get_info_distro(statefile) or "unknown"
        # nr installed
        with tarfile.open(statefile) as tar:
            f = tar.extractfile(
                self.TARPREFIX + "var/lib/apt-clone/installed.pkgs")
            installed = autoinstalled = 0
            meta = []
            for line in f.readlines():
                line = line.decode("utf-8")
                (name, version, auto) = line.strip().split()
                installed += 1
                if int(auto):
                    autoinstalled += 1
                # FIXME: this is a bad way to figure out about the
                # meta-packages
                if name.endswith("-desktop"):
                    meta.append(name)
            # date
            m = tar.getmember(
                self.TARPREFIX + "var/lib/apt-clone/installed.pkgs")
            date = m.mtime
            # check hostname (if found)
            hostname = "unknown"
            arch = "unknown"
            if self.TARPREFIX+"var/lib/apt-clone/uname" in tar.getnames():
                info = tar.extractfile(
                    self.TARPREFIX + "var/lib/apt-clone/uname").read()
                section = apt_pkg.TagSection(info)
                hostname = section.get("hostname", "unknown")
                arch = section.get("arch", "unknown")
            return { 'hostname' : hostname,
                     'distro' : distro,
                     'meta' : ", ".join(meta),
                     'installed' : installed,
                     'autoinstalled' : autoinstalled,
                     'date' : time.ctime(date),
                     'arch' : arch,
                   }

    def info(self, statefile):
        return "Hostname: %(hostname)s\n"\
               "Arch: %(arch)s\n"\
               "Distro: %(distro)s\n"\
               "Meta: %(meta)s\n"\
               "Installed: %(installed)s pkgs (%(autoinstalled)s automatic)\n"\
               "Date: %(date)s\n" % self._get_clone_info_dict(statefile)

    # show-diff
    def _get_file_diff_against_clone(self, statefile, system_file, targetdir):
        with tarfile.open(statefile) as tar:
            self._detect_tarprefix(tar)
            clone_file = tar.extractfile(self.TARPREFIX+system_file[1:])
            clone_file_lines = []
            # FIXME: is there a better way for this? something to tell
            #        tarfile that really its all utf8?
            for line in clone_file.readlines():
                clone_file_lines.append(line.decode("utf-8"))
        system_file = targetdir+system_file
        if os.path.exists(system_file):
            with open(system_file) as fp:
                system_file_lines = fp.readlines()
        else:
            system_file_lines = []
        gen = difflib.unified_diff(
            system_file_lines, clone_file_lines,
            fromfile="current-system%s" % system_file, tofile=system_file)
        diff = []
        for line in gen:
            diff.append(line)
        return diff

    def show_diff(self, statefile, targetdir="/"):
        if targetdir != "/":
            apt_pkg.config.set("DPkg::Chroot-Directory", targetdir)

        # show info/uname diff
        print("Clone info differences: ")
        host_info = self._get_host_info_dict()
        clone_info = self._get_clone_info_dict(statefile)
        for key in host_info:
            if host_info.get(key, None) != clone_info.get(key, None):
                print(" '%s': clone='%s' system='%s'" % (
                        key, clone_info.get(key, None),
                        host_info.get(key, None)))
        print("")

        # show sources.list{,.d} diff
        sources_list_system = "/etc/apt/sources.list"
        diff = self._get_file_diff_against_clone(
            statefile, sources_list_system, targetdir)
        if diff:
            print("".join(diff))

        # FIXME: do sources.list.d diff too
        # FIXME: do apt-keyring diff
        #self._restore_package_selection(statefile, targetdir, protect_installed)
        # create new cache in the rootdir
        cache = self._cache_cls(rootdir=targetdir)
        with tarfile.open(statefile) as tar:
            f = tar.extractfile(
                self.TARPREFIX + "var/lib/apt-clone/installed.pkgs")
            # get the data
            installed_in_clone = {}
            for line in f.readlines():
                line = line.strip().decode('utf-8')
                if line.startswith("#") or line == "":
                    continue
                (name, version, auto) = line.split()
                installed_in_clone[name] = (version, auto)
        installed_on_system = {}
        for pkg in cache:
            if not pkg.installed:
                continue
            installed_on_system[pkg.name] = (
                pkg.installed.version, str(pkg.is_auto_installed))

        only_on_system = set(installed_on_system.keys()) - set(installed_in_clone.keys())
        if only_on_system:
            print("Installed on the system but not in the clone-file:")
            print(" ".join(sorted(only_on_system)))
            print("\n")

        only_in_clone =  set(installed_in_clone.keys()) - set(installed_on_system.keys())
        if only_in_clone:
            print("Installed in the clone-file but not in the system:")
            print(" ".join(sorted(only_in_clone)))
            print("\n")

        # show version differences
        pkgversion_differences = set()
        for pkgname in sorted(installed_in_clone):
            if not pkgname in installed_on_system:
                continue
            clone_file_pkgversion, clone_is_auto = installed_in_clone[pkgname]
            system_pkgversion, sys_is_auto = installed_on_system[pkgname]
            if clone_file_pkgversion != system_pkgversion:
                pkgversion_differences.add(
                    (pkgname, clone_file_pkgversion, system_pkgversion))
        if pkgversion_differences:
            print("Version differences: ")
            print("Pkgname <clone-file-version> <system-version>")
            for pkgname, clone_ver, system_ver in pkgversion_differences:
                print(" %s  <%s>   <%s>" % (pkgname, clone_ver, system_ver))


    # restore
    def restore_state(self, statefile, targetdir="/", exclude_pkgs=None,
                      new_distro=None, protect_installed=False, mirror=None):
        """ take a statefile produced via (like apt-state.tar.gz)
            save_state() and restore the packages/repositories
            into targetdir (that is usually "/")
        """

        if targetdir != "/":
            apt_pkg.config.set("DPkg::Chroot-Directory", targetdir)
            self.commands.bind_mount("/proc", os.path.join(targetdir, "proc"))
            self.commands.bind_mount("/sys", os.path.join(targetdir, "sys"))

        # detect prefix
        with tarfile.open(statefile) as tar:
            self._detect_tarprefix(tar)

        if not os.path.exists(targetdir):
            print("Dir '%s' does not exist, need to bootstrap first" % targetdir)
            distro = self._get_info_distro(statefile)
            self.commands.debootstrap(targetdir, distro)

        self._restore_sources_list(statefile, targetdir, mirror=mirror)
        self._restore_apt_keyring(statefile, targetdir)
        if new_distro:
            self._rewrite_sources_list(targetdir, new_distro)
        self._restore_package_selection(statefile, targetdir, protect_installed, exclude_pkgs)
        # FIXME: this needs to check if there are conflicts, e.g. via
        #        gdebi
        self._restore_not_downloadable_debs(statefile, targetdir)
        # restore after package to avoid e.g. conffile prompts
        self._restore_extra_files(statefile, targetdir)

        # and umount again
        if targetdir != "/":
            self.commands.bind_umount(os.path.join(targetdir, "proc"))
            self.commands.bind_umount(os.path.join(targetdir, "sys"))

    # simulate restore and return list of missing pkgs
    def simulate_restore_state(self, statefile, exclude_pkgs, new_distro=None):
        # create tmp target (with host system dpkg-status) to simulate in
        target = tempfile.mkdtemp()
        dpkg_status = apt_pkg.config.find_file("dir::state::status")
        if not os.path.exists(target+os.path.dirname(dpkg_status)):
            os.makedirs(target+os.path.dirname(dpkg_status))
        shutil.copy(dpkg_status, target+dpkg_status)
        # restore sources.list and update cache in tmp target
        self._restore_sources_list(statefile, target)
        # optionally rewrite on new distro
        if new_distro:
            self._rewrite_sources_list(target, new_distro)
        cache = self._cache_cls(rootdir=target)
        try:
            cache.update(apt.progress.base.AcquireProgress())
        except FetchFailedException:
            # This cannot be resolved here, but it should not be interpreted as
            # a fatal error.
            pass
        cache.open()
        # try to replay cache and see thats missing
        missing = self._restore_package_selection_in_cache(statefile, cache, exclude_pkgs=exclude_pkgs)
        shutil.rmtree(target)
        return missing

    def _restore_sources_list(self, statefile, targetdir, mirror=None):
        with tarfile.open(statefile) as tar:
            existing = os.path.join(targetdir, "etc", "apt", "sources.list")
            if os.path.exists(existing):
                shutil.copy(existing, '%s.apt-clone' % existing)
            tar.extract(self.TARPREFIX+"etc/apt/sources.list", targetdir)
            td_sources = os.path.join(targetdir, "etc", "apt", "sources.list")
            os.chmod(td_sources, stat.S_IRUSR | stat.S_IWUSR | stat.S_IRGRP |
                     stat.S_IROTH)
            if mirror:
                from aptsources.sourceslist import SourcesList
                apt_pkg.config.set("Dir::Etc::sourcelist", td_sources)
                sources = SourcesList()
                for entry in sources.list[:]:
                    if entry.uri != mirror:
                       entry.uri = mirror
                sources.save()
            try:
                tar.extract(self.TARPREFIX+"etc/apt/sources.list.d", targetdir)
            except KeyError:
                pass

    def _restore_apt_keyring(self, statefile, targetdir):
        existing = os.path.join(targetdir, "etc", "apt", "trusted.gpg")
        backup = '%s.apt-clone' % existing
        if os.path.exists(existing):
            shutil.copy(existing, backup)
        with tarfile.open(statefile) as tar:
            try:
                tar.extract(self.TARPREFIX+"etc/apt/trusted.gpg", targetdir)
            except KeyError:
                pass
            try:
                tar.extract(self.TARPREFIX+"etc/apt/trusted.gpg.d", targetdir)
            except KeyError:
                pass
            if os.path.exists(backup):
                self.commands.merge_keys(backup, existing)
                os.remove(backup)

    def _restore_package_selection_in_cache(self, statefile, cache, protect_installed=False, exclude_pkgs=None):
        # deal with excludes
        if exclude_pkgs is None:
            exclude_pkgs = []
        exclude_pkgs = set(exclude_pkgs)
        # reinstall packages
        missing = set()
        pkgs = set()
        # procted installed pkgs
        resolver = apt_pkg.ProblemResolver(cache._depcache)
        if protect_installed:
            for pkg in cache:
                if pkg.is_installed:
                    resolver.protect(pkg._pkg)
        # get the installed.pkgs data
        with tarfile.open(statefile) as tar:
            f = tar.extractfile(
                self.TARPREFIX + "var/lib/apt-clone/installed.pkgs")
            # the actiongroup will help libapt to speed up the following loop
            with cache.actiongroup():
                for line in f.readlines():
                    line = line.strip().decode('utf-8')
                    if line.startswith("#") or line == "":
                        continue
                    (name, version, auto) = line.split()
                    # tiny helper
                    def is_excluded(name, exclude_pkgs):
                        for excl in exclude_pkgs:
                            if fnmatch.fnmatch(name, excl):
                                return True
                    if is_excluded(name, exclude_pkgs):
                        continue
                    pkgs.add(name)
                    auto_installed = int(auto)
                    from_user = not auto_installed
                    if name in cache:
                        try:
                            # special mode, most useful for release-upgrades
                            if protect_installed:
                                cache[name].mark_install(from_user=from_user, auto_fix=False)
                                if cache.broken_count > 0:
                                    resolver.resolve()
                                    if not cache[name].marked_install:
                                        raise SystemError("pkg %s not marked upgrade" % name)
                            else:
                                # normal mode, this assume the system is consistent
                                cache[name].mark_install(from_user=from_user)
                        except SystemError as e:
                            logging.warning("can't add %s (%s)" % (name, e))
                            missing.add(name)
                        # ensure the auto install info is
                        cache[name].mark_auto(auto_installed)
        # check what is broken and try to fix
        if cache.broken_count > 0:
            resolver.resolve()
        # now go over and see what is missing
        for pkg in pkgs:
            if not pkg in cache:
                missing.add(pkg)
                continue
            if not (cache[pkg].is_installed or cache[pkg].marked_install):
                missing.add(pkg)
        return missing

    def _restore_package_selection(self, statefile, targetdir, protect_installed, exclude_pkgs):
        # create new cache
        cache = self._cache_cls(rootdir=targetdir)
        # python-apt Cache(rootdir=) will mangle dir::bin, fix that
        apt.apt_pkg.config.set("Dir::Bin", "/")
        apt.apt_pkg.config.set("Dir::Bin::dpkg", "/usr/bin/dpkg")
        try:
            cache.update(self.fetch_progress)
        except FetchFailedException:
            # This cannot be resolved here, but it should not be interpreted as
            # a fatal error.
            pass
        cache.open()
        self._restore_package_selection_in_cache(statefile, cache, protect_installed, exclude_pkgs)
        # do it
        cache.commit(self.fetch_progress, self.install_progress)

    def _restore_extra_files(self, statefile, targetdir):
        with tarfile.open(statefile) as tar:
            for m in tar.getmembers():
                prefix = self.TARPREFIX+"extra-files/"
                if m.name.startswith(prefix):
                    # strip prefix on extract
                    m.name = m.name[len(prefix):]
                    tar.extract(m, targetdir)

    def _restore_not_downloadable_debs(self, statefile, targetdir):
        with tarfile.open(statefile) as tar:
            try:
                debsdir = [ tarinfo for tarinfo in tar.getmembers() if tarinfo.name.startswith(self.TARPREFIX+"var/lib/apt-clone/debs/")]
                tar.extractall(targetdir,debsdir)
            except KeyError:
                return
        debs = []
        path = os.path.join(targetdir, "./var/lib/apt-clone/debs")
        for deb in glob.glob(os.path.join(path, "*.deb")):
            debpath = os.path.join(path, deb)
            debs.append(debpath)
        self.commands.install_debs(debs, targetdir)

    def _rewrite_sources_list(self, targetdir, new_distro):
        from aptsources.sourceslist import SourcesList, SourceEntry
        apt_pkg.config.set(
            "Dir::Etc::sourcelist",
            os.path.abspath(os.path.join(targetdir, "etc", "apt", "sources.list")))
        apt_pkg.config.set(
            "Dir::Etc::sourceparts",
            os.path.abspath(os.path.join(targetdir, "etc", "apt", "sources.list.d")))
        sources = SourcesList()

        for entry in sources.list[:]:
            if entry.invalid or entry.disabled:
                continue
            replacement = ''
            for pocket in ('updates', 'security', 'backports'):
                if entry.dist.endswith('-%s' % pocket):
                    replacement = '%s-%s' % (new_distro, pocket)
                    break
            if replacement:
                entry.dist = replacement
            else:
                entry.dist = new_distro

        existing = os.path.join(targetdir, "etc", "apt",
                                "sources.list.apt-clone")
        sourcelist = apt_pkg.config.find_file("Dir::Etc::sourcelist")
        if os.path.exists(existing):
            with open(existing, 'r') as fp:
                for line in fp:
                    src = SourceEntry(line, sourcelist)
                    if (src.invalid or src.disabled) or src not in sources:
                        sources.list.append(src)
            os.remove(existing)

        for entry in sources.list:
            if entry.uri.startswith('cdrom:'):
                # Make sure CD entries come first.
                sources.list.remove(entry)
                sources.list.insert(0, entry)
                entry.disabled = True
        sources.save()

    def _find_unowned_in_etc(self, sourcedir=""):
        if sourcedir:
            etcdir = os.path.join(sourcedir, "etc")
        else:
            etcdir = "/etc"
        # get all the files that dpkg "owns"
        owned = set()
        dpkg_basedir = os.path.dirname(apt_pkg.config.get("Dir::State::status"))
        for f in glob.glob(os.path.join(dpkg_basedir, "info", "*.list")):
            with open(f, encoding="utf-8") as fp:
                for line in fp:
                    if line.startswith("/etc/"):
                        owned.add(line.strip())
        # now go over etc
        unowned = set()
        for dirpath, dirnames, filenames in os.walk(etcdir):
            for name in filenames:
                fullname = os.path.join(dirpath[len(sourcedir):], name)
                if not fullname in owned:
                    unowned.add(fullname)
        return unowned

    def _find_modified_conffiles(self, sourcedir="/"):
        dpkg_status = sourcedir+apt_pkg.config.find("Dir::State::status")
        modified = set()
        # iterate dpkg-status file
        with open(dpkg_status) as fp:
            tag = apt_pkg.TagFile(fp)
            for entry in tag:
                if "conffiles" in entry:
                    for line in entry["conffiles"].split("\n"):
                        obsolete = None
                        if len(line.split()) == 3:
                            name, md5sum, obsolete = line.split()
                        else:
                            name, md5sum = line.split()
                        # update
                        path = sourcedir+name
                        md5sum = md5sum.strip()
                        # ignore oboslete conffiles
                        if obsolete == "obsolete":
                            continue
                        # user removed conffile
                        if not os.path.exists(path):
                            logging.debug("conffile %s removed" % path)
                            modified.add(path)
                            continue
                        # check content
                        md5 = hashlib.md5()
                        with open(path, 'rb') as fp:
                            md5.update(fp.read())
                        if md5.hexdigest() != md5sum:
                            logging.debug("conffile %s (%s != %s)" % (
                                    path, md5.hexdigest(), md5sum))
                            modified.add(path)
        return modified

    def _dump_debconf_database(self, sourcedir):
        print("not implemented yet")
        # debconf-copydb configdb newdb --config=Name:newdb --config=Driver:File --config=Filename:/tmp/lala.db
        #
        # debconf-copydb newdb configdb --config=Name:newdb --config=Driver:File --config=Filename:/tmp/lala.db
        #
        # dump to text with:
        #  debconf-copydb configdb pipe --config=Name:pipe
        #                 --config=Driver:Pipe --config=InFd:none
        #
        # restore from text with:
        #   ssh remotehost debconf-copydb pipe configdb --config=Name:pipe --config=Driver:Pipe