lc_ldap/ldap_locks.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# LDAP_LOCKS.PY-- Locks for lc_ldap
#
## Copyright (C) 2013 Cr@ns <roots@crans.org>
# Authors:
#    * Antoine Durand-Gasselin <adg@crans.org>         
#    * Pierre-Elliott Bécue <becue@crans.org>
#
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
# * Redistributions of source code must retain the above copyright
#   notice, this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above copyright
#   notice, this list of conditions and the following disclaimer in the
#   documentation and/or other materials provided with the distribution.
# * Neither the name of the Cr@ns nor the names of its contributors may
#   be used to endorse or promote products derived from this software
#   without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT
# HOLDER> BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
# LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
# NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

import ldap
import os
import exceptions
import socket
import crans_utils
import collections
import time

class LockError(exceptions.StandardError):
    """
    Erreur standard de lock
    """
    pass

class LdapLockedByYou(LockError):
    """
    Classe d'erreur pour les locks par le process courant
    """
    pass

class LdapLockedByMySelf(LockError):
    """
    Classe d'erreur pour les locks par l'idlock courant
    """
    pass

class LdapLockedByOther(LockError):
    """
    Erreur car le lock est occupé par un autre process.
    """
    pass

class LockFormatError(LockError):
    """
    L'objet lock qu'on a récupéré n'est pas tel qu'on le voudrait
    """
    pass

class LockNotFound(LockError):
    """Le lock n'a pas été trouvé"""

LOCKS_DN = 'ou=lock,dc=crans,dc=org'

class LdapLockHolder:
    """
    Système de gestion des locks pour une instance de lc_ldap.
    """
    def __init__(self, conn):
        """
        On crée la connexion, et on crée un dico vide.
        """
        # On crée un Id => (item => set())
        self.locks = collections.defaultdict(lambda:collections.defaultdict(set))
        self.host = socket.gethostname()
        self.pid = os.getpid()
        self.conn = conn
        self.timeout = 600.0

    def newid(self):
        id = 'id_%s' % time.time()
        if id in self.locks:
            return self.newid()
        else:
            return id

    def purge(self, Id, purgeAll=False):
        """
        On essaye de détruire tous les verrous hébergés par
        l'objet.
        """
        if not purgeAll:
            for item, values in self.locks[Id].items():
                for value in values.copy():
                    self.removelock(item, value, Id)
        else:
            for Id in self.locks:
                self.purge(Id)

    def __del__(self):
        """
        En cas de destruction du lockholder
        """
        self.purge(purgeAll=True)

    def addlock(self, item, value, Id='default'):
        """
        Applique un verrou sur "$item=$value,$LOCKS_DN",
        si le précédent verrou était géré par la session
        courante de lc_ldap, on prévient l'utilisateur
        de la session, pour qu'il puisse éventuellement
        libérer le lock.

        Sinon, on ne peut pas override le lock, et on laisse
        tomber.
        """
        try:
            host, pid, begin = self.getlock(item, value)
            time_left = self.timeout - (time.time() - begin)
            if time_left <= 0:
                self.removelock(item, value, Id, True)
            elif Id!='default' and str(value) in self.locks[Id][item]:
                raise LdapLockedByMySelf("La donnée %r=%r est lockée par vous-même pour encore %ds." % (item, value, time_left))
            elif host == self.host and pid == self.pid:
                raise LdapLockedByYou("La donnée %r=%r est lockée par vous-même pour encore %ds." % (item, value, time_left))
            elif host == self.host:
                status = crans_utils.process_status(pid)
                if status:
                    raise LdapLockedByOther("La donnée %r=%r est lockée par un processus actif pour encore %ds." % (item, value, time_left))
                else:
                    self.removelock(item, value, Id, True)
            else:
                raise LdapLockedByOther("La donnée %r=%r est lockée depuis une autre machine pour encore %ds." % (item, value, time_left))
        except LockNotFound:
            pass

        dn = "%s=%s,%s" % (item, value, LOCKS_DN)
        lockid = "%s-%s-%s" % (self.host, self.pid, time.time())
        lockv = "lc_ldap_201308"
        modlist = ldap.modlist.addModlist({'objectClass' : 'lock',
                                           'lockid' : lockid,
                                           'lockv' : lockv,
                                           item : value})

        try:
            self.conn.add_s(dn, modlist)
            self.locks[Id][item].add(str(value))
        except ldap.ALREADY_EXISTS:
            # Quelqu'un à eu le lock avant nous, on réessaye
            # S'il a été libéré, banzai, sinon, ça lèvera une exception
            return self.addlock(item, value, Id)

    def removelock(self, item, value, Id='default', force=False):
        """
        Libère le lock "$item=$value,$LOCKS_DN".
        """
        try:
            if force or str(value) in self.locks[Id][item]:
                self.conn.delete_s("%s=%s,%s" % (item, value, LOCKS_DN))
        except ldap.NO_SUCH_OBJECT:
            pass
        finally:
            try:
                self.locks[Id][item].remove(value)
            except KeyError:
                pass
            if not self.locks[Id][item]:
                self.locks[Id].pop(item)
    
    def getlock(self, item, value):
        """
        Trouve le lock item=value, et renvoie le contenu de lockinfo
        via un triplet host, pid, begin
        """

        try:
            result = self.conn.search_s('%s=%s,%s' % (item, value, LOCKS_DN), 0)
            host, pid, begin = result[0][1]['lockid'][0].split('-')
            return host, int(pid), float(begin)
        except ldap.NO_SUCH_OBJECT:
            raise LockNotFound()
        except ValueError as e:
            self.removelock(item, value, Id, force=True)
            raise LockNotFound()