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

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

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

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

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.
        """
        self.locks = {}
        self.host = socket.gethostbyname()
        self.pid = os.getpid()
        self.conn = conn

    def __del__(self):
        """
        On essaye de détruire tous les verrous hébergés par
        l'objet mourant.
        """
        for item, value in self.locks:
            try:
                self.removelock(item, value)
            except:
                pass
        del self.conn

    def addlock(self, item, value):
        """
        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 = self.getlock(item, value)
            if host == self.host and pid == self.pid():
                raise LdapLockedByYou("La donnée %r=%r est lockée par vous-même." % (item, value))
            elif host == self.host:
                status = crans_utils.process_status(pid)
                if status:
                    raise LdapLockedByOther("La donnée %r=%r est lockée par quelqu'un d'autre ou un processus." % (item, value))
                else:
                    self.removelock(item, value)
            else:
                raise LdapLockedByOther("La donnée %r=%r est lockée par quelqu'un d'autre ou un processus." % (item, value))
        except ldap.NO_SUCH_OBJECT:
            pass
        except LockFormatError:
            self.removelock(item, value)

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

        try:
            self.conn.add_s(dn, modlist)
            self.locks[item] = value
        except ldap.ALREADY_EXISTS:
            status = crans_utils.process_status(pid)
            if status:
                raise LdapLockedByOther("La donnée %r=%r est lockée par quelqu'un d'autre ou un processus." % (item, value))
            else:
                self.removelock(item, value)
                try:
                    self.conn.add_s(dn, modlist)
                    self.locks[item] = value
                except:
                    raise StandardError("Quelque chose a planté durant la pose du lock %s=%s" % (item, value))

    def removelock(self, item, value):
        """
        Libère le lock "$item=$value,$LOCKS_DN".
        """
        print "Deleting %s=%s,%s\n" % (item, value, LOCKS_DN)
        if self.locks.get(item, "") == value:
            self.locks.pop(item)
            self.conn.delete_s("%s=%s,%s" % (item, value, LOCKS_DN))
        else:
            print "Lock %s=%s,%s does not exist on this session" % (item, value, LOCKS_DN)
    
    def getlock(self, item, value):
        """
        Trouve le lock item=value, et renvoie le contenu de lockinfo
        via un couple host, pid
        """

        result = self.conn.search_s('%s=%s,%s' % (item, value, LOCKS_DN), 0)
        try:
            return result[0][1]['lockid'][0].split('-')
        except:
            raise LockFormatError