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Filename : sysrestore.py
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# Authors: Mark McLoughlin <markmc@redhat.com>
#
# Copyright (C) 2007  Red Hat
# see file 'COPYING' for use and warranty information
#
# 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 3 of the License, or
# (at your option) any later version.
#
# 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, see <http://www.gnu.org/licenses/>.
#

#
# This module provides a very simple API which allows
# ipa-xxx-install --uninstall to restore certain
# parts of the system configuration to the way it was
# before ipa-server-install was first run

from __future__ import absolute_import

import logging
import os
import os.path
import shutil
import random

from hashlib import sha256

import six
# pylint: disable=import-error
if six.PY3:
    # The SafeConfigParser class has been renamed to ConfigParser in Py3
    from configparser import ConfigParser as SafeConfigParser
else:
    from ConfigParser import SafeConfigParser
# pylint: enable=import-error

from ipaplatform.tasks import tasks
from ipaplatform.paths import paths

if six.PY3:
    unicode = str

logger = logging.getLogger(__name__)

SYSRESTORE_PATH = paths.TMP
SYSRESTORE_INDEXFILE = "sysrestore.index"
SYSRESTORE_STATEFILE = "sysrestore.state"


class FileStore:
    """Class for handling backup and restore of files"""

    def __init__(self, path=SYSRESTORE_PATH, index_file=SYSRESTORE_INDEXFILE):
        """Create a _StoreFiles object, that uses @path as the
        base directory.

        The file @path/sysrestore.index is used to store information
        about the original location of the saved files.
        """
        self._path = path
        self._index = os.path.join(self._path, index_file)

        self.random = random.Random()

        self.files = {}
        self._load()

    def _load(self):
        """Load the file list from the index file. @files will
        be an empty dictionary if the file doesn't exist.
        """

        logger.debug("Loading Index file from '%s'", self._index)

        self.files = {}

        p = SafeConfigParser(interpolation=None)
        p.optionxform = str
        p.read(self._index)

        for section in p.sections():
            if section == "files":
                for (key, value) in p.items(section):
                    self.files[key] = value

    def save(self):
        """Save the file list to @_index. If @files is an empty
        dict, then @_index should be removed.
        """
        logger.debug("Saving Index File to '%s'", self._index)

        if len(self.files) == 0:
            logger.debug("  -> no files, removing file")
            if os.path.exists(self._index):
                os.remove(self._index)
            return

        p = SafeConfigParser(interpolation=None)
        p.optionxform = str

        p.add_section('files')
        for (key, value) in self.files.items():
            p.set('files', key, str(value))

        with open(self._index, "w") as f:
            p.write(f)

    def backup_file(self, path):
        """Create a copy of the file at @path - as long as an exact copy
        does not already exist - which will be restored to its
        original location by restore_files().
        """
        logger.debug("Backing up system configuration file '%s'", path)

        if not os.path.isabs(path):
            raise ValueError("Absolute path required")

        if not os.path.isfile(path):
            logger.debug("  -> Not backing up - '%s' doesn't exist", path)
            return

        _reldir, backupfile = os.path.split(path)

        with open(path, 'rb') as f:
            cont_hash = sha256(f.read()).hexdigest()

        filename = "{hexhash}-{bcppath}".format(hexhash=cont_hash,
                                                bcppath=backupfile)

        backup_path = os.path.join(self._path, filename)
        if os.path.exists(backup_path):
            logger.debug("  -> Not backing up - already have a copy of '%s'",
                         path)
            return

        shutil.copy2(path, backup_path)

        stat = os.stat(path)

        template = '{stat.st_mode},{stat.st_uid},{stat.st_gid},{path}'
        self.files[filename] = template.format(stat=stat, path=path)
        self.save()

    def has_file(self, path):
        """Checks whether file at @path was added to the file store

        Returns #True if the file exists in the file store, #False otherwise
        """
        result = False
        for _key, value in self.files.items():
            _mode, _uid, _gid, filepath = value.split(',', 3)
            if (filepath == path):
                result = True
                break
        return result

    def restore_file(self, path, new_path=None):
        """Restore the copy of a file at @path to its original
        location and delete the copy.

        Takes optional parameter @new_path which specifies the
        location where the file is to be restored.

        Returns #True if the file was restored, #False if there
        was no backup file to restore
        """

        if new_path is None:
            logger.debug("Restoring system configuration file '%s'",
                         path)
        else:
            logger.debug("Restoring system configuration file '%s' to '%s'",
                         path, new_path)

        if not os.path.isabs(path):
            raise ValueError("Absolute path required")
        if new_path is not None and not os.path.isabs(new_path):
            raise ValueError("Absolute new path required")

        mode = None
        uid = None
        gid = None
        filename = None

        for (key, value) in self.files.items():
            (mode,uid,gid,filepath) = value.split(',', 3)
            if (filepath == path):
                filename = key
                break

        if not filename:
            raise ValueError("No such file name in the index")

        backup_path = os.path.join(self._path, filename)
        if not os.path.exists(backup_path):
            logger.debug("  -> Not restoring - '%s' doesn't exist",
                         backup_path)
            return False

        if new_path is not None:
            path = new_path

        shutil.copy(backup_path, path)  # SELinux needs copy
        os.remove(backup_path)

        os.chown(path, int(uid), int(gid))
        os.chmod(path, int(mode))

        tasks.restore_context(path)

        del self.files[filename]
        self.save()

        return True

    def restore_all_files(self):
        """Restore the files in the inbdex to their original
        location and delete the copy.

        Returns #True if the file was restored, #False if there
        was no backup file to restore
        """

        if len(self.files) == 0:
            return False

        for (filename, value) in self.files.items():

            (mode,uid,gid,path) = value.split(',', 3)

            backup_path = os.path.join(self._path, filename)
            if not os.path.exists(backup_path):
                logger.debug("  -> Not restoring - '%s' doesn't exist",
                             backup_path)
                continue

            shutil.copy(backup_path, path)  # SELinux needs copy
            os.remove(backup_path)

            os.chown(path, int(uid), int(gid))
            os.chmod(path, int(mode))

            tasks.restore_context(path)

        # force file to be deleted
        self.files = {}
        self.save()

        return True

    def has_files(self):
        """Return True or False if there are any files in the index

        Can be used to determine if a program is configured.
        """

        return len(self.files) > 0

    def untrack_file(self, path):
        """Remove file at path @path from list of backed up files.

        Does not remove any files from the filesystem.

        Returns #True if the file was untracked, #False if there
        was no backup file to restore
        """

        logger.debug("Untracking system configuration file '%s'", path)

        if not os.path.isabs(path):
            raise ValueError("Absolute path required")

        filename = None

        for (key, value) in self.files.items():
            _mode, _uid, _gid, filepath = value.split(',', 3)
            if (filepath == path):
                filename = key
                break

        if not filename:
            raise ValueError("No such file name in the index")

        backup_path = os.path.join(self._path, filename)
        if not os.path.exists(backup_path):
            logger.debug("  -> Not restoring - '%s' doesn't exist",
                         backup_path)
            return False

        try:
            os.unlink(backup_path)
        except Exception as e:
            logger.error('Error removing %s: %s', backup_path, str(e))

        del self.files[filename]
        self.save()

        return True


class StateFile:
    """A metadata file for recording system state which can
    be backed up and later restored.
    StateFile gets reloaded every time to prevent loss of information
    recorded by child processes. But we do not solve concurrency
    because there is no need for it right now.
    The format is something like:

    [httpd]
    running=True
    enabled=False
    """

    def __init__(self, path=SYSRESTORE_PATH, state_file=SYSRESTORE_STATEFILE):
        """Create a StateFile object, loading from @path.

        The dictionary @modules, a member of the returned object,
        is where the state can be modified. @modules is indexed
        using a module name to return another dictionary containing
        key/value pairs with the saved state of that module.

        The keys in these latter dictionaries are arbitrary strings
        and the values may either be strings or booleans.
        """
        self._path = os.path.join(path, state_file)

        self.modules = {}

        self._load()

    def _load(self):
        """Load the modules from the file @_path. @modules will
        be an empty dictionary if the file doesn't exist.
        """
        logger.debug("Loading StateFile from '%s'", self._path)

        self.modules = {}

        p = SafeConfigParser(interpolation=None)
        p.optionxform = str
        p.read(self._path)

        for module in p.sections():
            self.modules[module] = {}
            for (key, value) in p.items(module):
                if value == str(True):
                    value = True
                elif value == str(False):
                    value = False
                self.modules[module][key] = value

    def save(self):
        """Save the modules to @_path. If @modules is an empty
        dict, then @_path should be removed.
        """
        logger.debug("Saving StateFile to '%s'", self._path)

        for module in list(self.modules):
            if len(self.modules[module]) == 0:
                del self.modules[module]

        if len(self.modules) == 0:
            logger.debug("  -> no modules, removing file")
            if os.path.exists(self._path):
                os.remove(self._path)
            return

        p = SafeConfigParser(interpolation=None)
        p.optionxform = str

        for module, vals in self.modules.items():
            p.add_section(module)
            for (key, value) in vals.items():
                p.set(module, key, str(value))

        with open(self._path, "w") as f:
            p.write(f)

    def backup_state(self, module, key, value):
        """Backup an item of system state from @module, identified
        by the string @key and with the value @value. @value may be
        a string or boolean.
        """
        if not isinstance(value, (str, bool, unicode)):
            raise ValueError("Only strings, booleans or unicode strings "
                             "are supported")

        self._load()

        if module not in self.modules:
            self.modules[module] = {}

        if key not in self.modules:
            self.modules[module][key] = value

        self.save()

    def get_state(self, module, key):
        """Return the value of an item of system state from @module,
        identified by the string @key.

        If the item doesn't exist, #None will be returned, otherwise
        the original string or boolean value is returned.
        """
        self._load()

        if module not in self.modules:
            return None

        return self.modules[module].get(key, None)

    def delete_state(self, module, key):
        """Delete system state from @module, identified by the string
        @key.

        If the item doesn't exist, no change is done.
        """
        self._load()

        try:
            del self.modules[module][key]
        except KeyError:
            pass
        else:
            self.save()

    def restore_state(self, module, key):
        """Return the value of an item of system state from @module,
        identified by the string @key, and remove it from the backed
        up system state.

        If the item doesn't exist, #None will be returned, otherwise
        the original string or boolean value is returned.
        """

        value = self.get_state(module, key)

        if value is not None:
            self.delete_state(module, key)

        return value

    def has_state(self, module):
        """Return True or False if there is any state stored for @module.

        Can be used to determine if a service is configured.
        """

        return module in self.modules