#! /usr/bin/env python
# -*- coding: ISO-8859-15 -*-

# CUPSPyKota accounting backend
#
# PyKota - Print Quotas for CUPS and LPRng
#
# (c) 2003, 2004, 2005, 2006 Jerome Alet <alet@librelogiciel.com>
# 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.
#
# 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.
#
# $Id$
#
#

import sys
import os
import fcntl
import time
import errno
import tempfile
import popen2
import cStringIO
import shlex
import signal
import md5
import fnmatch
import pwd
import socket
import smtplib
from email.MIMEText import MIMEText
from email.Header import Header

from mx import DateTime

from pykota.tool import PyKotaTool, PyKotaToolError, crashed
from pykota.accounter import openAccounter
# TODO : remove the three lines below and the code which handles
# TODO : them in a future release.
from pykota.ipp import IPPRequest as oldIPPRequest
from pykota.ipp import IPPError as oldIPPError

try :
    from pkipplib import pkipplib
except ImportError :        
    haspkipplib = False
else :    
    haspkipplib = True
    
class FakeObject :        
    """Fake object."""
    def __init__(self, name) :
        """Fake init."""
        self.Name = name
        
class FakePrinter(FakeObject) :        
    """Fake printer instance."""
    pass
    
class FakeUser(FakeObject) :    
    """Fake user instance."""
    def __init__(self, name) :
        """Fake init."""
        self.Email = name
        FakeObject.__init__(self, name)
    
class CUPSBackend(PyKotaTool) :
    """Base class for tools with no database access."""
    def __init__(self) :
        """Initializes the CUPS backend wrapper."""
        PyKotaTool.__init__(self)
        signal.signal(signal.SIGTERM, signal.SIG_IGN)
        signal.signal(signal.SIGPIPE, signal.SIG_IGN)
        self.MyName = "PyKota"
        self.myname = "cupspykota"
        self.pid = os.getpid()
        self.DataFile = None
        
    def deferredInit(self) :    
        """Deferred initialization."""
        PyKotaTool.deferredInit(self)
        self.gotSigTerm = 0
        self.disableSigInt()
        self.installSigTermHandler()
        
    def sigtermHandler(self, signum, frame) :
        """Sets an attribute whenever SIGTERM is received."""
        self.gotSigTerm = 1
        self.printInfo(_("SIGTERM received, job %s cancelled.") % self.JobId)
        os.environ["PYKOTASTATUS"] = "CANCELLED"
        
    def deinstallSigTermHandler(self) :           
        """Deinstalls the SIGTERM handler."""
        self.logdebug("Deinstalling SIGTERM handler...")
        signal.signal(signal.SIGTERM, signal.SIG_IGN)
        self.logdebug("SIGTERM handler deinstalled.")
        
    def installSigTermHandler(self) :           
        """Installs the SIGTERM handler."""
        self.logdebug("Installing SIGTERM handler...")
        signal.signal(signal.SIGTERM, self.sigtermHandler)
        self.logdebug("SIGTERM handler installed.")
        
    def disableSigInt(self) :    
        """Disables the SIGINT signal (which raises KeyboardInterrupt)."""
        self.logdebug("Disabling SIGINT...")
        self.oldSigIntHandler = signal.signal(signal.SIGINT, signal.SIG_IGN)
        self.logdebug("SIGINT disabled.")
        
    def enableSigInt(self) :    
        """Enables the SIGINT signal (which raises KeyboardInterrupt)."""
        self.logdebug("Enabling SIGINT...")
        signal.signal(signal.SIGINT, self.oldSigIntHandler)
        self.logdebug("SIGINT enabled.")
        
    def waitForLock(self) :    
        """Waits until we can acquire the lock file."""
        self.logdebug("Waiting for lock...")
        stillrunning = True
        try :
            while 1 :
                self.lockfile = open(self.lockfilename, "a+")
                fcntl.lockf(self.lockfile, fcntl.LOCK_EX) # Will wait until lock available
                self.lockfile.seek(0, 0)      
                try : 
                    oldpid = int(self.lockfile.readlines()[-1].strip())
                except :    
                    stillrunning = False
                else :    
                    try :
                        os.kill(oldpid, 0)
                    except OSError :    
                        stillrunning = False
                if not stillrunning :        
                    self.lockfile.truncate(0)
                    self.lockfile.seek(0, 0)
                    self.lockfile.write("%s\n" % self.pid)
                    self.lockfile.flush()
                    break
                else :    
                    self.lockfile.close()
                    time.sleep(0.1)
        except IOError :            
            self.logdebug("I/O Error while waiting for lock.")
        else :
            self.logdebug("Lock acquired.")
                    
    def discoverOtherBackends(self) :    
        """Discovers the other CUPS backends.
        
           Executes each existing backend in turn in device enumeration mode.
           Returns the list of available backends.
        """
        # Unfortunately this method can't output any debug information
        # to stdout or stderr, else CUPS considers that the device is
        # not available.
        available = []
        (directory, myname) = os.path.split(sys.argv[0])
        if not directory :
            directory = "./"
        tmpdir = tempfile.gettempdir()
        lockfilename = os.path.join(tmpdir, "%s..LCK" % myname)
        if os.path.exists(lockfilename) :
            lockfile = open(lockfilename, "r")
            pid = int(lockfile.read())
            lockfile.close()
            try :
                # see if the pid contained in the lock file is still running
                os.kill(pid, 0)
            except OSError, err :
                if err.errno != errno.EPERM :
                    # process doesn't exist anymore
                    os.remove(lockfilename)
            
        if not os.path.exists(lockfilename) :
            lockfile = open(lockfilename, "w")
            lockfile.write("%i" % self.pid)
            lockfile.close()
            allbackends = [ os.path.join(directory, b) \
                                for b in os.listdir(directory) \
                                    if os.access(os.path.join(directory, b), os.X_OK) \
                                        and (b != myname)] 
            for backend in allbackends :                            
                answer = os.popen(backend, "r")
                try :
                    devices = [line.strip() for line in answer.readlines()]
                except :    
                    devices = []
                status = answer.close()
                if status is None :
                    for d in devices :
                        # each line is of the form : 
                        # 'xxxx xxxx "xxxx xxx" "xxxx xxx"'
                        # so we have to decompose it carefully
                        fdevice = cStringIO.StringIO(d)
                        tokenizer = shlex.shlex(fdevice)
                        tokenizer.wordchars = tokenizer.wordchars + \
                                                        r".:,?!~/\_$*-+={}[]()#"
                        arguments = []
                        while 1 :
                            token = tokenizer.get_token()
                            if token :
                                arguments.append(token)
                            else :
                                break
                        fdevice.close()
                        try :
                            (devicetype, device, name, fullname) = arguments
                        except ValueError :    
                            pass    # ignore this 'bizarre' device
                        else :    
                            if name.startswith('"') and name.endswith('"') :
                                name = name[1:-1]
                            if fullname.startswith('"') and fullname.endswith('"') :
                                fullname = fullname[1:-1]
                            available.append('%s %s:%s "%s+%s" "%s managed %s"' \
                                                 % (devicetype, self.myname, \
                                                    device, self.MyName, \
                                                    name, self.MyName, \
                                                    fullname))
            os.remove(lockfilename)
        available.append('direct %s:// "%s+Nothing" "%s managed Virtual Printer"' \
                             % (self.myname, self.MyName, self.MyName))
        return available
                        
    def initBackendParameters(self) :    
        """Initializes the backend's attributes."""
        # check that the DEVICE_URI environment variable's value is 
        # prefixed with self.myname otherwise don't touch it.
        # If this is the case, we have to remove the prefix from 
        # the environment before launching the real backend 
        self.logdebug("Initializing backend...")
        
        self.PrinterName = os.environ.get("PRINTER", "")
        directories = [ self.config.getPrinterDirectory(self.PrinterName),
                        "/tmp",
                        "/var/tmp" ]
        self.Directory = None
        for direc in directories :
            if os.access(direc, os.O_RDWR) :
                self.Directory = direc
                break
            else :
                self.printInfo("Insufficient permissions to access to temporary directory %s" % direc, "warn")
                
        self.Action = "ALLOW"   # job allowed by default
        self.Reason = None
        self.JobId = sys.argv[1].strip()
        # use CUPS' user when printing test pages from CUPS' web interface
        self.UserName = sys.argv[2].strip() or self.originalUserName or pwd.getpwuid(os.geteuid())[0]
        self.Title = sys.argv[3].strip()
        self.Copies = int(sys.argv[4].strip())
        self.Options = sys.argv[5].strip()
        if len(sys.argv) == 7 :
            self.InputFile = sys.argv[6] # read job's datas from file
        else :    
            self.InputFile = None        # read job's datas from stdin
        self.DataFile = os.path.join(self.Directory, "%s-%s-%s-%s" % \
                   (self.myname, self.PrinterName, self.UserName, self.JobId))
        
        muststartwith = "%s:" % self.myname
        device_uri = os.environ.get("DEVICE_URI", "")
        if device_uri.startswith(muststartwith) :
            fulldevice_uri = device_uri[:]
            device_uri = fulldevice_uri[len(muststartwith):]
            for i in range(2) :
                if device_uri.startswith("/") :  
                    device_uri = device_uri[1:]
        try :
            (backend, destination) = device_uri.split(":", 1) 
        except ValueError :    
            if not device_uri :
                self.logdebug("Not attached to an existing print queue.")
                backend = ""
                printerhostname = ""
            else :    
                raise PyKotaToolError, "Invalid DEVICE_URI : %s\n" % device_uri
        else :        
            while destination.startswith("/") :
                destination = destination[1:]
            checkauth = destination.split("@", 1)    
            if len(checkauth) == 2 :
                destination = checkauth[1]
            printerhostname = destination.split("/")[0].split(":")[0]
            
        self.PrinterHostName = printerhostname    
        self.RealBackend = backend
        self.DeviceURI = device_uri
        
        connerror = False
        if haspkipplib :
            self.ControlFile = "NotUsedAnymore"
            self.logdebug("Querying CUPS server...")
            cupsserver = pkipplib.CUPS() # TODO : username and password and/or encryption
            answer = cupsserver.getJobAttributes(self.JobId)
            if answer is None :
                self.printInfo(_("Network error while querying the CUPS server : %s") \
                                          % cupsserver.lastErrorMessage, "error")
                connerror = True                        
            else :    
                self.logdebug("CUPS server answered without error.")
                try :
                    john = answer.job["job-originating-host-name"]
                except KeyError :    
                    try :
                        john = answer.operation["job-originating-host-name"]
                    except KeyError :    
                        john = (None, None)
                try :        
                    jbing = answer.job["job-billing"]
                except KeyError :    
                    jbing = (None, None)
                    
        if connerror or not haspkipplib :        
            (ippfilename, ippmessage) = self.parseIPPRequestFile()
            self.ControlFile = ippfilename
            john = ippmessage.operation_attributes.get("job-originating-host-name", \
                   ippmessage.job_attributes.get("job-originating-host-name", \
                   (None, None)))
            jbing = ippmessage.job_attributes.get("job-billing", (None, None))
                
        if type(john) == type([]) : 
            john = john[-1]
        (chtype, self.ClientHost) = john 
        if type(jbing) == type([]) : 
            jbing = jbing[-1]
        (jbtype, self.JobBillingCode) = jbing
        
        baselockfilename = self.DeviceURI.replace("/", ".")
        baselockfilename = baselockfilename.replace(":", ".")
        baselockfilename = baselockfilename.replace("?", ".")
        baselockfilename = baselockfilename.replace("&", ".")
        baselockfilename = baselockfilename.replace("@", ".")
        self.lockfilename = os.path.join(self.Directory, "%s-%s..LCK" % (self.myname, baselockfilename))
        
        self.logdebug("Backend : %s" % self.RealBackend)
        self.logdebug("DeviceURI : %s" % self.DeviceURI)
        self.logdebug("Printername : %s" % self.PrinterName)
        self.logdebug("Username : %s" % self.UserName)
        self.logdebug("JobId : %s" % self.JobId)
        self.logdebug("Title : %s" % self.Title)
        self.logdebug("Filename : %s" % self.InputFile)
        self.logdebug("Copies : %s" % self.Copies)
        self.logdebug("Options : %s" % self.Options)
        self.logdebug("Directory : %s" % self.Directory) 
        self.logdebug("DataFile : %s" % self.DataFile)
        self.logdebug("ControlFile : %s" % self.ControlFile)
        self.logdebug("JobBillingCode : %s" % self.JobBillingCode)
        self.logdebug("JobOriginatingHostName : %s" % self.ClientHost)
        
        # fakes some entries to allow for external mailto
        # before real entries are extracted from the database.
        self.User = FakeUser(self.UserName)
        self.Printer = FakePrinter(self.PrinterName)
        
        self.enableSigInt()
        self.logdebug("Backend initialized.")
        
    def overwriteJobAttributes(self) :
        """Overwrites some of the job's attributes if needed."""
        self.logdebug("Sanitizing job's attributes...")
        # First overwrite the job ticket
        self.overwriteJobTicket()
        
        # do we want to strip out the Samba/Winbind domain name ?
        separator = self.config.getWinbindSeparator()
        if separator is not None :
            self.UserName = self.UserName.split(separator)[-1]
            
        # do we want to lowercase usernames ?    
        if self.config.getUserNameToLower() :
            self.UserName = self.UserName.lower()
            
        # do we want to strip some prefix off of titles ?    
        stripprefix = self.config.getStripTitle(self.PrinterName)
        if stripprefix :
            if fnmatch.fnmatch(self.Title[:len(stripprefix)], stripprefix) :
                self.logdebug("Prefix [%s] removed from job's title [%s]." \
                                      % (stripprefix, self.Title))
                self.Title = self.Title[len(stripprefix):]
                
        self.logdebug("Username : %s" % self.UserName)
        self.logdebug("BillingCode : %s" % self.JobBillingCode)
        self.logdebug("Title : %s" % self.Title)
        self.logdebug("Job's attributes sanitizing done.")
                
    def didUserConfirm(self) :
        """Asks for user confirmation through an external script.
        
           returns False if the end user wants to cancel the job, else True.
        """
        self.logdebug("Checking if we have to ask for user's confirmation...")
        answer = None                         
        confirmationcommand = self.config.getAskConfirmation(self.PrinterName)
        if confirmationcommand :
            self.logdebug("Launching subprocess [%s] to ask for user confirmation." \
                                     % confirmationcommand)
            inputfile = os.popen(confirmationcommand, "r")
            try :
                for answer in inputfile.xreadlines() :
                    answer = answer.strip().upper()
                    if answer == "CANCEL" :
                        break
            except IOError, msg :            
                self.logdebug("IOError while reading subprocess' output : %s" % msg)
            inputfile.close()    
            self.logdebug("User's confirmation received : %s" % (((answer == "CANCEL") and "CANCEL") or "CONTINUE"))
        else :    
            self.logdebug("No need to ask for user's confirmation, job processing will continue.")
        return (answer != "CANCEL")    
        
    def overwriteJobTicket(self) :    
        """Should we overwrite the job's ticket (username and billingcode) ?"""
        self.logdebug("Checking if we need to overwrite the job ticket...")
        jobticketcommand = self.config.getOverwriteJobTicket(self.PrinterName)
        if jobticketcommand :
            username = billingcode = action = None
            self.logdebug("Launching subprocess [%s] to overwrite the job ticket." \
                                     % jobticketcommand)
            self.regainPriv()                         
            inputfile = os.popen(jobticketcommand, "r")
            try :
                for line in inputfile.xreadlines() :
                    line = line.strip()
                    if line in ("DENY", "AUTH=NO", "AUTH=IMPOSSIBLE") :
                        self.logdebug("Seen %s command." % line)
                        action = "DENY"
                    elif line == "CANCEL" :
                        self.logdebug("Seen CANCEL command.")
                        action = "CANCEL"
                    elif line.startswith("USERNAME=") :    
                        username = line.split("=", 1)[1].strip()
                        self.logdebug("Seen new username [%s]" % username)
                    elif line.startswith("BILLINGCODE=") :    
                        billingcode = line.split("=", 1)[1].strip()
                        self.logdebug("Seen new billing code [%s]" % billingcode)
            except IOError, msg :            
                self.logdebug("IOError while reading subprocess' output : %s" % msg)
            inputfile.close()    
            self.dropPriv()
            
            # now overwrite the job's ticket if new data was supplied
            if action == "DENY" :
                self.Action = action
                self.Reason = _("You are not allowed to print at this time.")
            elif action == "CANCEL" :
                self.Action = action
                self.Reason = _("Print job cancelled.")
                os.environ["PYKOTASTATUS"] = "CANCELLED"
            else :
                # don't overwrite anything unless job authorized
                # to continue to the physical printer.
                if username and username.strip() :
                    self.UserName = username
                if billingcode is not None :
                    self.JobBillingCode = billingcode 
        self.logdebug("Job ticket overwriting done.")
            
    def saveDatasAndCheckSum(self) :
        """Saves the input datas into a static file."""
        self.logdebug("Duplicating data stream into %s" % self.DataFile)
        mustclose = 0
        outfile = open(self.DataFile, "wb")    
        if self.InputFile is not None :
            self.regainPriv()
            infile = open(self.InputFile, "rb")
            mustclose = 1
        else :    
            infile = sys.stdin
        CHUNK = 64*1024         # read 64 Kb at a time
        dummy = 0
        sizeread = 0
        checksum = md5.new()
        while 1 :
            data = infile.read(CHUNK) 
            if not data :
                break
            sizeread += len(data)    
            outfile.write(data)
            checksum.update(data)    
            if not (dummy % 32) : # Only display every 2 Mb
                self.logdebug("%s bytes saved..." % sizeread)
            dummy += 1    
        if mustclose :    
            infile.close()
            self.dropPriv()
            
        outfile.close()
        self.JobSizeBytes = sizeread    
        self.JobMD5Sum = checksum.hexdigest()
        
        self.logdebug("JobSizeBytes : %s" % self.JobSizeBytes)
        self.logdebug("JobMD5Sum : %s" % self.JobMD5Sum)
        self.logdebug("Data stream duplicated into %s" % self.DataFile)
            
    def clean(self) :
        """Cleans up the place."""
        self.logdebug("Cleaning up...")
        self.regainPriv()
        self.deinstallSigTermHandler()
        if not self.config.getPrinterKeepFiles(self.PrinterName) :
            self.logdebug("Work file %s will be deleted." % self.DataFile)
            try :
                if os.path.exists(self.DataFile) :
                    os.remove(self.DataFile)
            except OSError, msg :
                self.logdebug("Problem while deleting work file %s : %s" % (self.DataFile, msg))
            else :
                self.logdebug("Work file %s has been deleted." % self.DataFile)
        else :    
            self.logdebug("Work file %s will be kept." % self.DataFile)
        PyKotaTool.clean(self)    
        self.logdebug("Removing lock...")
        try :
            fcntl.flock(self.lockfile, fcntl.LOCK_UN)
            self.lockfile.close()
            # NB : we don't remove the lock file, since it might already be opened by another process.
        except :    
            pass
        else :    
            self.logdebug("Lock removed.")
        self.logdebug("Clean.")
            
    def precomputeJobSize(self) :    
        """Computes the job size with a software method."""
        self.logdebug("Precomputing job's size...")
        self.preaccounter.beginJob(None)
        self.preaccounter.endJob(None)
        self.softwareJobSize = self.preaccounter.getJobSize(None)
        self.logdebug("Precomputed job's size is %s pages." % self.softwareJobSize)
        
    def precomputeJobPrice(self) :    
        """Precomputes the job price with a software method."""
        self.logdebug("Precomputing job's price...")
        self.softwareJobPrice = self.UserPQuota.computeJobPrice(self.softwareJobSize)
        self.logdebug("Precomputed job's price is %.3f credits." \
                                   % self.softwareJobPrice)
        
    def getCupsConfigDirectives(self, directives=[]) :
        """Retrieves some CUPS directives from its configuration file.
        
           Returns a mapping with lowercased directives as keys and 
           their setting as values.
        """
        self.logdebug("Parsing CUPS' configuration file...")
        dirvalues = {} 
        cupsroot = os.environ.get("CUPS_SERVERROOT", "/etc/cups")
        cupsdconf = os.path.join(cupsroot, "cupsd.conf")
        try :
            conffile = open(cupsdconf, "r")
        except IOError :    
            raise PyKotaToolError, "Unable to open %s" % cupsdconf
        else :    
            for line in conffile.readlines() :
                linecopy = line.strip().lower()
                for di in [d.lower() for d in directives] :
                    if linecopy.startswith("%s " % di) :
                        try :
                            val = line.split()[1]
                        except :    
                            pass # ignore errors, we take the last value in any case.
                        else :    
                            dirvalues[di] = val
            conffile.close()            
        self.logdebug("CUPS' configuration file parsed successfully.")
        return dirvalues       
            
    def parseIPPRequestFile(self) :        
        """Parses the IPP message file and returns a tuple (filename, parsedvalue)."""
        self.logdebug("Parsing IPP request file...")
        
        class DummyClass :
            """Class used to avoid errors."""
            operation_attributes = {}
            job_attributes = {}
            
        ippmessage = DummyClass() # in case the code below fails
        
        self.regainPriv()
        cupsdconf = self.getCupsConfigDirectives(["RequestRoot"])
        requestroot = cupsdconf.get("requestroot", "/var/spool/cups")
        if (len(self.JobId) < 5) and self.JobId.isdigit() :
            ippmessagefile = "c%05i" % int(self.JobId)
        else :    
            ippmessagefile = "c%s" % self.JobId
        ippmessagefile = os.path.join(requestroot, ippmessagefile)
        try :
            ippdatafile = open(ippmessagefile)
        except :    
            self.logdebug("Unable to open IPP request file %s" % ippmessagefile)
        else :    
            self.logdebug("Parsing of IPP request file %s begins." % ippmessagefile)
            try :
                ippmessage = oldIPPRequest(ippdatafile.read())
                ippmessage.parse()
            except oldIPPError, msg :    
                self.printInfo("Error while parsing %s : %s" \
                                      % (ippmessagefile, msg), "warn")
            else :    
                self.logdebug("Parsing of IPP request file %s ends." \
                                       % ippmessagefile)
            ippdatafile.close()
        self.dropPriv()
        self.logdebug("IPP request file parsed successfully.")
        return (ippmessagefile, ippmessage)
                
    def exportJobInfo(self) :    
        """Exports the actual job's attributes to the environment."""
        self.logdebug("Exporting job information to the environment...")
        os.environ["DEVICE_URI"] = self.DeviceURI       # WARNING !
        os.environ["PYKOTAPRINTERNAME"] = self.PrinterName
        os.environ["PYKOTADIRECTORY"] = self.Directory
        os.environ["PYKOTADATAFILE"] = self.DataFile
        os.environ["PYKOTAJOBSIZEBYTES"] = str(self.JobSizeBytes)
        os.environ["PYKOTAMD5SUM"] = self.JobMD5Sum
        os.environ["PYKOTAJOBORIGINATINGHOSTNAME"] = self.ClientHost or ""
        os.environ["PYKOTAJOBID"] = self.JobId
        os.environ["PYKOTAUSERNAME"] = self.UserName
        os.environ["PYKOTATITLE"] = self.Title
        os.environ["PYKOTACOPIES"] = str(self.Copies)
        os.environ["PYKOTAOPTIONS"] = self.Options
        os.environ["PYKOTAFILENAME"] = self.InputFile or ""
        os.environ["PYKOTAJOBBILLING"] = self.JobBillingCode or ""
        os.environ["PYKOTACONTROLFILE"] = self.ControlFile
        os.environ["PYKOTAPRINTERHOSTNAME"] = self.PrinterHostName
        os.environ["PYKOTAPRECOMPUTEDJOBSIZE"] = str(self.softwareJobSize)
        self.logdebug("Environment updated.")
        
    def exportUserInfo(self) :
        """Exports user information to the environment."""
        self.logdebug("Exporting user information to the environment...")
        os.environ["PYKOTAOVERCHARGE"] = str(self.User.OverCharge)
        os.environ["PYKOTALIMITBY"] = str(self.User.LimitBy)
        os.environ["PYKOTABALANCE"] = str(self.User.AccountBalance or 0.0)
        os.environ["PYKOTALIFETIMEPAID"] = str(self.User.LifeTimePaid or 0.0)
        os.environ["PYKOTAUSERDESCRIPTION"] = str(self.User.Description or "")
        
        os.environ["PYKOTAPAGECOUNTER"] = str(self.UserPQuota.PageCounter or 0)
        os.environ["PYKOTALIFEPAGECOUNTER"] = str(self.UserPQuota.LifePageCounter or 0)
        os.environ["PYKOTASOFTLIMIT"] = str(self.UserPQuota.SoftLimit)
        os.environ["PYKOTAHARDLIMIT"] = str(self.UserPQuota.HardLimit)
        os.environ["PYKOTADATELIMIT"] = str(self.UserPQuota.DateLimit)
        os.environ["PYKOTAWARNCOUNT"] = str(self.UserPQuota.WarnCount)
        
        # TODO : move this elsewhere once software accounting is done only once.
        os.environ["PYKOTAPRECOMPUTEDJOBPRICE"] = str(self.softwareJobPrice)
        
        self.logdebug("Environment updated.")
        
    def exportPrinterInfo(self) :
        """Exports printer information to the environment."""
        self.logdebug("Exporting printer information to the environment...")
        # exports the list of printers groups the current
        # printer is a member of
        os.environ["PYKOTAPGROUPS"] = ",".join([p.Name for p in self.storage.getParentPrinters(self.Printer)])
        os.environ["PYKOTAPRINTERDESCRIPTION"] = str(self.Printer.Description or "")
        os.environ["PYKOTAPRINTERMAXJOBSIZE"] = str(self.Printer.MaxJobSize or _("Unlimited"))
        os.environ["PYKOTAPRINTERPASSTHROUGHMODE"] = (self.Printer.PassThrough and _("ON")) or _("OFF")
        os.environ["PYKOTAPRICEPERPAGE"] = str(self.Printer.PricePerPage or 0)
        os.environ["PYKOTAPRICEPERJOB"] = str(self.Printer.PricePerJob or 0)
        self.logdebug("Environment updated.")
        
    def exportPhaseInfo(self, phase) :
        """Exports phase information to the environment."""
        self.logdebug("Exporting phase information [%s] to the environment..." % phase)
        os.environ["PYKOTAPHASE"] = phase
        self.logdebug("Environment updated.")
        
    def exportJobSizeAndPrice(self) :
        """Exports job's size and price information to the environment."""
        self.logdebug("Exporting job's size and price information to the environment...")
        os.environ["PYKOTAJOBSIZE"] = str(self.JobSize)
        os.environ["PYKOTAJOBPRICE"] = str(self.JobPrice)
        self.logdebug("Environment updated.")
        
    def exportReason(self) :
        """Exports the job's action status and optional reason."""
        self.logdebug("Exporting job's action status...")
        os.environ["PYKOTAACTION"] = str(self.Action)
        if self.Reason :
            os.environ["PYKOTAREASON"] = str(self.Reason)
        self.logdebug("Environment updated.")
        
    def acceptJob(self) :        
        """Returns the appropriate exit code to tell CUPS all is OK."""
        return 0
            
    def removeJob(self) :            
        """Returns the appropriate exit code to let CUPS think all is OK.
        
           Returning 0 (success) prevents CUPS from stopping the print queue.
        """   
        return 0
        
    def launchPreHook(self) :
        """Allows plugging of an external hook before the job gets printed."""
        prehook = self.config.getPreHook(self.PrinterName)
        if prehook :
            self.logdebug("Executing pre-hook [%s]..." % prehook)
            retcode = os.system(prehook)
            self.logdebug("pre-hook exited with status %s." % retcode)
        
    def launchPostHook(self) :
        """Allows plugging of an external hook after the job gets printed and/or denied."""
        posthook = self.config.getPostHook(self.PrinterName)
        if posthook :
            self.logdebug("Executing post-hook [%s]..." % posthook)
            retcode = os.system(posthook)
            self.logdebug("post-hook exited with status %s." % retcode)
            
    def improveMessage(self, message) :        
        """Improves a message by adding more informations in it if possible."""
        try :
            return "%s@%s(%s) => %s" % (self.UserName, \
                                        self.PrinterName, \
                                        self.JobId, \
                                        message)
        except :                                               
            return message
        
    def logdebug(self, message) :        
        """Improves the debug message before outputting it."""
        PyKotaTool.logdebug(self, self.improveMessage(message))
        
    def printInfo(self, message, level="info") :        
        """Improves the informational message before outputting it."""
        self.logger.log_message(self.improveMessage(message), level)
    
    def startingBanner(self, withaccounting) :
        """Retrieves a starting banner for current printer and returns its content."""
        self.logdebug("Retrieving starting banner...")
        self.printBanner(self.config.getStartingBanner(self.PrinterName), withaccounting)
        self.logdebug("Starting banner retrieved.")
    
    def endingBanner(self, withaccounting) :
        """Retrieves an ending banner for current printer and returns its content."""
        self.logdebug("Retrieving ending banner...")
        self.printBanner(self.config.getEndingBanner(self.PrinterName), withaccounting)
        self.logdebug("Ending banner retrieved.")
        
    def printBanner(self, bannerfileorcommand, withaccounting) :
        """Reads a banner or generates one through an external command.
        
           Returns the banner's content in a format which MUST be accepted
           by the printer.
        """
        self.logdebug("Printing banner...")
        if bannerfileorcommand :
            if os.access(bannerfileorcommand, os.X_OK) or \
                  not os.path.isfile(bannerfileorcommand) :
                self.logdebug("Launching %s to generate a banner." % bannerfileorcommand)
                child = popen2.Popen3(bannerfileorcommand, capturestderr=1)
                self.runOriginalBackend(child.fromchild, isBanner=1)
                child.tochild.close()
                child.childerr.close()
                child.fromchild.close()
                status = child.wait()
                if os.WIFEXITED(status) :
                    status = os.WEXITSTATUS(status)
                self.printInfo(_("Banner generator %s exit code is %s") \
                                         % (bannerfileorcommand, str(status)))
                if withaccounting :
                    if self.accounter.isSoftware :
                        self.BannerSize += 1 # TODO : fix this by passing the banner's content through software accounting
            else :
                self.logdebug("Using %s as the banner." % bannerfileorcommand)
                try :
                    fh = open(bannerfileorcommand, 'rb')
                except IOError, msg :    
                    self.printInfo("Impossible to open %s : %s" \
                                       % (bannerfileorcommand, msg), "error")
                else :    
                    self.runOriginalBackend(fh, isBanner=1)
                    fh.close()
                    if withaccounting :
                        if self.accounter.isSoftware :
                            self.BannerSize += 1 # TODO : fix this by passing the banner's content through software accounting
        self.logdebug("Banner printed...")
                
    def handleBanner(self, bannertype, withaccounting) :
        """Handles the banner with or without accounting."""
        if withaccounting :
            acc = "with"
        else :    
            acc = "without"
        self.logdebug("Handling %s banner %s accounting..." % (bannertype, acc))
        if (self.Action == 'DENY') and \
           (self.UserPQuota.WarnCount >= \
                            self.config.getMaxDenyBanners(self.PrinterName)) :
            self.printInfo(_("Banner won't be printed : maximum number of deny banners reached."), \
                             "warn")
        else :
            if self.Action == 'DENY' :
                self.logdebug("Incrementing the number of deny banners for user %s on printer %s" \
                                  % (self.UserName, self.PrinterName))
                self.UserPQuota.incDenyBannerCounter() # increments the warning counter
                self.exportUserInfo()
            getattr(self, "%sBanner" % bannertype)(withaccounting)
        self.logdebug("%s banner done." % bannertype.title())
        
    def sanitizeJobSize(self) :    
        """Sanitizes the job's size if needed."""
        # TODO : there's a difficult to see bug here when banner accounting is activated and hardware accounting is used.
        self.logdebug("Sanitizing job's size...")
        if self.softwareJobSize and (self.JobSize != self.softwareJobSize) :
            self.printInfo(_("Beware : computed job size (%s) != precomputed job size (%s)") % \
                                       (self.JobSize, self.softwareJobSize), \
                           "error")
            (limit, replacement) = self.config.getTrustJobSize(self.PrinterName)
            if limit is None :
                self.printInfo(_("The job size will be trusted anyway according to the 'trustjobsize' directive"), "warn")
            else :
                if self.JobSize <= limit :
                    self.printInfo(_("The job size will be trusted because it is inferior to the 'trustjobsize' directive's limit %s") % limit, "warn")
                else :
                    self.printInfo(_("The job size will be modified according to the 'trustjobsize' directive : %s") % replacement, "warn")
                    if replacement == "PRECOMPUTED" :
                        self.JobSize = self.softwareJobSize
                    else :    
                        self.JobSize = replacement
        self.logdebug("Job's size sanitized.")
                        
    def getPrinterUserAndUserPQuota(self) :        
        """Returns a tuple (policy, printer, user, and user print quota) on this printer.
        
           "OK" is returned in the policy if both printer, user and user print quota
           exist in the Quota Storage.
           Otherwise, the policy as defined for this printer in pykota.conf is returned.
           
           If policy was set to "EXTERNAL" and one of printer, user, or user print quota
           doesn't exist in the Quota Storage, then an external command is launched, as
           defined in the external policy for this printer in pykota.conf
           This external command can do anything, like automatically adding printers
           or users, for example, and finally extracting printer, user and user print
           quota from the Quota Storage is tried a second time.
           
           "EXTERNALERROR" is returned in case policy was "EXTERNAL" and an error status
           was returned by the external command.
        """
        self.logdebug("Retrieving printer, user, and user print quota entry from database...")
        for passnumber in range(1, 3) :
            printer = self.storage.getPrinter(self.PrinterName)
            user = self.storage.getUser(self.UserName)
            userpquota = self.storage.getUserPQuota(user, printer)
            if printer.Exists and user.Exists and userpquota.Exists :
                policy = "OK"
                break
            (policy, args) = self.config.getPrinterPolicy(self.PrinterName)
            if policy == "EXTERNAL" :    
                commandline = self.formatCommandLine(args, user, printer)
                if not printer.Exists :
                    self.printInfo(_("Printer %s not registered in the PyKota system, applying external policy (%s) for printer %s") % (self.PrinterName, commandline, self.PrinterName))
                if not user.Exists :
                    self.printInfo(_("User %s not registered in the PyKota system, applying external policy (%s) for printer %s") % (self.UserName, commandline, self.PrinterName))
                if not userpquota.Exists :
                    self.printInfo(_("User %s doesn't have quota on printer %s in the PyKota system, applying external policy (%s) for printer %s") % (self.UserName, self.PrinterName, commandline, self.PrinterName))
                if os.system(commandline) :
                    self.printInfo(_("External policy %s for printer %s produced an error. Job rejected. Please check PyKota's configuration files.") % (commandline, self.PrinterName), "error")
                    policy = "EXTERNALERROR"
                    break
            else :        
                if not printer.Exists :
                    self.printInfo(_("Printer %s not registered in the PyKota system, applying default policy (%s)") % (self.PrinterName, policy))
                if not user.Exists :
                    self.printInfo(_("User %s not registered in the PyKota system, applying default policy (%s) for printer %s") % (self.UserName, policy, self.PrinterName))
                if not userpquota.Exists :
                    self.printInfo(_("User %s doesn't have quota on printer %s in the PyKota system, applying default policy (%s)") % (self.UserName, self.PrinterName, policy))
                break
                
        if policy == "EXTERNAL" :    
            if not printer.Exists :
                self.printInfo(_("Printer %s still not registered in the PyKota system, job will be rejected") % self.PrinterName)
            if not user.Exists :
                self.printInfo(_("User %s still not registered in the PyKota system, job will be rejected on printer %s") % (self.UserName, self.PrinterName))
            if not userpquota.Exists :
                self.printInfo(_("User %s still doesn't have quota on printer %s in the PyKota system, job will be rejected") % (self.UserName, self.PrinterName))
        self.Policy = policy         
        self.Printer = printer
        self.User = user
        self.UserPQuota = userpquota
        self.logdebug("Retrieval of printer, user and user print quota entry done.")
        
    def getBillingCode(self) :    
        """Extracts the billing code from the database.
         
           An optional script is launched to notify the user when
           the billing code is unknown and PyKota was configured to
           deny printing in this case.
        """
        self.logdebug("Retrieving billing code information from the database...")
        self.BillingCode = None
        if self.JobBillingCode :
            self.BillingCode = self.storage.getBillingCode(self.JobBillingCode)
            if self.BillingCode.Exists :
                self.logdebug("Billing code [%s] found in database." % self.JobBillingCode)
            else :
                msg = "Unknown billing code [%s] : " % self.JobBillingCode
                (newaction, script) = self.config.getUnknownBillingCode(self.PrinterName)
                if newaction == "CREATE" :
                    self.logdebug(msg + "will be created.")
                    self.storage.addBillingCode(self.BillingCode)
                    self.BillingCode = self.storage.getBillingCode(self.JobBillingCode)
                    if self.BillingCode.Exists :
                        self.logdebug(msg + "has been created.")
                    else :    
                        self.printInfo(msg + "couldn't be created.", "error")
                else :    
                    self.logdebug(msg + "job will be denied.")
                    self.Action = newaction
                    if script is not None : 
                        self.logdebug(msg + "launching subprocess [%s] to notify user." % script)
                        os.system(script)
        self.logdebug("Retrieval of billing code information done.")
        
    def checkIfDupe(self) :    
        """Checks if the job is a duplicate, and handles the situation."""
        self.logdebug("Checking if the job is a duplicate...")
        denyduplicates = self.config.getDenyDuplicates(self.PrinterName)
        if not denyduplicates :
            self.logdebug("We don't care about duplicate jobs after all.")
        else :
            if self.Printer.LastJob.Exists \
                    and (self.Printer.LastJob.UserName == self.UserName) \
                    and (self.Printer.LastJob.JobMD5Sum == self.JobMD5Sum) :
                now = DateTime.now()
                try :
                    previous = DateTime.ISO.ParseDateTime(str(self.Printer.LastJob.JobDate)).localtime()
                except :
                    previous = now
                difference = (now - previous).seconds
                duplicatesdelay = self.config.getDuplicatesDelay(self.PrinterName)
                self.logdebug("Difference with previous job : %.2f seconds. Duplicates delay : %.2f seconds." % (difference, duplicatesdelay))
                if difference > duplicatesdelay :
                    self.logdebug("Duplicate job allowed because previous one is more than %.2f seconds old." % duplicatesdelay)
                else :
                    # TODO : use the current user's last job instead of  
                    # TODO : the current printer's last job. This would be
                    # TODO : better but requires an additional database query
                    # TODO : with SQL, and is much more complex with the 
                    # TODO : actual LDAP schema. Maybe this is not very
                    # TODO : important, because usually duplicate jobs are sucessive.
                    msg = _("Job is a dupe")
                    if denyduplicates == 1 :
                        self.printInfo("%s : %s." % (msg, _("Printing is denied by configuration")), "warn")
                        self.Action = "DENY"
                        self.Reason = _("Duplicate print jobs are not allowed on printer %s.") % self.PrinterName
                    else :    
                        self.logdebug("Launching subprocess [%s] to see if duplicate jobs should be allowed or not." % denyduplicates)
                        fanswer = os.popen(denyduplicates, "r")
                        self.Action = fanswer.read().strip().upper()
                        fanswer.close()
                        if self.Action == "DENY" :     
                            self.printInfo("%s : %s." % (msg, _("Subprocess denied printing of a dupe")), "warn")
                            self.Reason = _("Duplicate print jobs are not allowed on printer %s at this time.") % self.PrinterName
                        else :    
                            self.printInfo("%s : %s." % (msg, _("Subprocess allowed printing of a dupe")), "warn")
            else :            
                self.logdebug("Job doesn't seem to be a duplicate.")
        self.logdebug("Checking if the job is a duplicate done.")
        
    def tellUser(self) :
        """Sends a message to an user."""
        self.logdebug("Sending some feedback to user %s..." % self.UserName)  
        if not self.Reason :
            self.logdebug("No feedback to send to user %s." % self.UserName)
        else :    
            (mailto, arguments) = self.config.getMailTo(self.PrinterName)
            if mailto == "EXTERNAL" :
                # TODO : clean this again
                self.regainPriv()
                self.externalMailTo(arguments, self.Action, self.User, self.Printer, self.Reason)
                self.dropPriv()
            else :    
                # TODO : clean this again
                admin = self.config.getAdmin(self.PrinterName)
                adminmail = self.config.getAdminMail(self.PrinterName)
                usermail = self.User.Email or self.User.Name
                if "@" not in usermail :
                    usermail = "%s@%s" % (usermail, self.maildomain or self.smtpserver)
                destination = []
                if mailto in ("BOTH", "ADMIN") :
                    destination.append(adminmail)
                if mailto in ("BOTH", "USER") :    
                    destination.append(usermail)
                    
                fullmessage = self.Reason + (_("\n\nYour system administrator :\n\n\t%s - <%s>\n") % (admin, adminmail))
                try :    
                    server = smtplib.SMTP(self.smtpserver)
                except socket.error, msg :    
                    self.printInfo(_("Impossible to connect to SMTP server : %s") % msg, "error")
                else :
                    try :
                        msg = MIMEText(fullmessage, _charset=self.charset)
                        msg["Subject"] = str(Header(_("Print Quota"), charset=self.charset))
                        msg["From"] = adminmail
                        if mailto in ("BOTH", "USER") :
                            msg["To"] = usermail
                            if mailto == "BOTH" :
                                msg["Cc"] = adminmail
                        else :    
                            msg["To"] = adminmail
                        server.sendmail(adminmail, destination, msg.as_string())
                    except smtplib.SMTPException, answer :    
                        try :
                            for (k, v) in answer.recipients.items() :
                                self.printInfo(_("Impossible to send mail to %s, error %s : %s") % (k, v[0], v[1]), "error")
                        except AttributeError :
                            self.printInfo(_("Problem when sending mail : %s") % str(answer), "error")
                    server.quit()
            self.logdebug("Feedback sent to user %s." % self.UserName)
                
    def mainWork(self) :    
        """Main work is done here."""
        if not self.JobSizeBytes :
            # if no data to pass to real backend, probably a filter
            # higher in the chain failed because of a misconfiguration.
            # we deny the job in this case (nothing to print anyway)
            self.Reason = _("Job contains no data. Printing is denied.")
            self.printInfo(self.Reason, "error")
            self.tellUser()
            return self.removeJob()
            
        self.getPrinterUserAndUserPQuota()
        if self.Policy == "EXTERNALERROR" :
            # Policy was 'EXTERNAL' and the external command returned an error code
            self.Reason = _("Error in external policy script. Printing is denied.")
            self.printInfo(self.Reason, "error")
            self.tellUser()
            return self.removeJob()
        elif self.Policy == "EXTERNAL" :
            # Policy was 'EXTERNAL' and the external command wasn't able
            # to add either the printer, user or user print quota
            self.Reason = _("Still no print quota entry for user %s on printer %s after external policy. Printing is denied.") % (self.UserName, self.PrinterName)
            self.printInfo(self.Reason, "warn")
            self.tellUser()
            return self.removeJob()
        elif self.Policy == "DENY" :    
            # Either printer, user or user print quota doesn't exist,
            # and the job should be rejected.
            self.Reason = _("Printing is denied by printer policy.")
            self.printInfo(self.Reason, "warn")
            self.tellUser()
            return self.removeJob()
        elif self.Policy == "ALLOW" :
            # ALLOW means : Either printer, user or user print quota doesn't exist,
            #               but the job should be allowed anyway.
            self.Reason = _("Job allowed by printer policy. No accounting will be done.")
            self.printInfo(self.Reason, "warn")
            self.tellUser()
            return self.printJobDatas()
        elif self.Policy == "OK" :
            # OK means : Both printer, user and user print quota exist, job should
            #            be allowed if current user is allowed to print on this printer
            return self.doWork()
        else :    
            self.Reason = _("Invalid policy %s for printer %s") % (self.Policy, self.PrinterName)
            self.printInfo(self.Reason, "error")
            self.tellUser()
            return self.removeJob()
    
    def doWork(self) :    
        """The accounting work is done here."""
        self.precomputeJobPrice()
        self.exportUserInfo()
        self.exportPrinterInfo()
        self.exportPhaseInfo("BEFORE")
        
        if self.Action not in ("DENY", "CANCEL") : 
            if not self.didUserConfirm() :
                self.Action = "CANCEL"
                self.Reason = _("Print job cancelled.")
                os.environ["PYKOTASTATUS"] = "CANCELLED"
                
        if self.Action not in ("DENY", "CANCEL") : 
            if self.Printer.MaxJobSize and (self.softwareJobSize > self.Printer.MaxJobSize) :
                # This printer was set to refuse jobs this large.
                self.printInfo(_("Precomputed job size (%s pages) too large for printer %s.") % (self.softwareJobSize, self.PrinterName), "warn")
                self.Action = "DENY"
                # here we don't put the precomputed job size in the message
                # because in case of error the user could complain :-)
                self.Reason = _("You are not allowed to print so many pages on printer %s at this time.") % self.PrinterName
            
        if self.Action not in ("DENY", "CANCEL") :
            if self.User.LimitBy == "noprint" :
                self.printInfo(_("User %s is not allowed to print at this time.") % self.UserName, "warn")
                self.Action = "DENY"
                self.Reason = _("Your account settings forbid you to print at this time.")
                
        if self.Action not in ("DENY", "CANCEL") :
            # If printing is still allowed at this time, we
            # need to extract the billing code information from the database.
            # No need to do this if the job is denied, this way we
            # save some database queries.
            self.getBillingCode()
            
        if self.Action not in ("DENY", "CANCEL") :
            # If printing is still allowed at this time, we
            # need to check if the job is a dupe or not, and what to do then.
            # No need to do this if the job is denied, this way we
            # save some database queries.
            self.checkIfDupe()
                    
        if self.Action not in ("DENY", "CANCEL") :
            # If printing is still allowed at this time, we
            # need to check the user's print quota on the current printer.
            # No need to do this if the job is denied, this way we
            # save some database queries.
            if self.User.LimitBy in ('noquota', 'nochange') :
                self.logdebug("User %s is allowed to print with no limit, no need to check quota." % self.UserName)
            elif self.Printer.PassThrough :    
                self.logdebug("Printer %s is in PassThrough mode, no need to check quota." % self.PrinterName)
            else :
                self.logdebug("Checking user %s print quota entry on printer %s" \
                                    % (self.UserName, self.PrinterName))
                self.Action = self.checkUserPQuota(self.UserPQuota)
                if self.Action.startswith("POLICY_") :
                    self.Action = self.Action[7:]
                if self.Action == "DENY" :
                    self.printInfo(_("Print Quota exceeded for user %s on printer %s") % (self.UserName, self.PrinterName))
                    self.Reason = self.config.getHardWarn(self.PrinterName)
                elif self.Action == "WARN" :    
                    self.printInfo(_("Print Quota low for user %s on printer %s") % (self.UserName, self.PrinterName))
                    if self.User.LimitBy and (self.User.LimitBy.lower() == "balance") : 
                        self.Reason = self.config.getPoorWarn()
                    else :     
                        self.Reason = self.config.getSoftWarn(self.PrinterName)
            
        # exports some new environment variables
        self.exportReason()
        
        # now tell the user if he needs to know something
        self.tellUser()
        
        # launches the pre hook
        self.launchPreHook()
        
        # handle starting banner pages without accounting
        self.BannerSize = 0
        accountbanner = self.config.getAccountBanner(self.PrinterName)
        if accountbanner in ["ENDING", "NONE"] :
            self.handleBanner("starting", 0)
        
        if self.Action == "DENY" :
            self.printInfo(_("Job denied, no accounting will be done."))
        elif self.Action == "CANCEL" :    
            self.printInfo(_("Job cancelled, no accounting will be done."))
        else :
            self.printInfo(_("Job accounting begins."))
            self.deinstallSigTermHandler()
            self.accounter.beginJob(self.Printer)
            self.installSigTermHandler()
        
        # handle starting banner pages with accounting
        if accountbanner in ["STARTING", "BOTH"] :
            if not self.gotSigTerm :
                self.handleBanner("starting", 1)
        
        # pass the job's data to the real backend    
        if (not self.gotSigTerm) and (self.Action in ["ALLOW", "WARN"]) :
            retcode = self.printJobDatas()
        else :        
            retcode = self.removeJob()
        
        # indicate phase change
        self.exportPhaseInfo("AFTER")
        
        # handle ending banner pages with accounting
        if accountbanner in ["ENDING", "BOTH"] :
            if not self.gotSigTerm :
                self.handleBanner("ending", 1)
        
        # stops accounting
        if self.Action == "DENY" :
            self.printInfo(_("Job denied, no accounting has been done."))
        elif self.Action == "CANCEL" :    
            self.printInfo(_("Job cancelled, no accounting has been done."))
        else :
            self.deinstallSigTermHandler()
            self.accounter.endJob(self.Printer)
            self.installSigTermHandler()
            self.printInfo(_("Job accounting ends."))
        
        # Do all these database changes within a single transaction    
        # NB : we don't enclose ALL the changes within a single transaction
        # because while waiting for the printer to answer its internal page
        # counter, we would open the door to accounting problems for other
        # jobs launched by the same user at the same time on other printers.
        # All the code below doesn't take much time, so it's fine.
        self.storage.beginTransaction()
        try :
            onbackenderror = self.config.getPrinterOnBackendError(self.PrinterName)
            if retcode :
                # NB : We don't send any feedback to the end user. Only the admin
                # has to know that the real CUPS backend failed.
                self.Action = "PROBLEM"
                self.exportReason()
                if "NOCHARGE" in onbackenderror :
                    self.JobSize = 0
                    self.printInfo(_("Job size forced to 0 because the real CUPS backend failed. No accounting will be done."), "warn")
                else :    
                    self.printInfo(_("The real CUPS backend failed, but the job will be accounted for anyway."), "warn")
                    
            # retrieve the job size    
            if self.Action == "DENY" :
                self.JobSize = 0
                self.printInfo(_("Job size forced to 0 because printing is denied."))
            elif self.Action == "CANCEL" :     
                self.JobSize = 0
                self.printInfo(_("Job size forced to 0 because printing was cancelled."))
            else :    
                self.UserPQuota.resetDenyBannerCounter()
                if (self.Action != "PROBLEM") or ("CHARGE" in onbackenderror) : 
                    self.JobSize = self.accounter.getJobSize(self.Printer)
                    self.sanitizeJobSize()
                    self.JobSize += self.BannerSize
            self.printInfo(_("Job size : %i") % self.JobSize)
            
            if ((self.Action == "PROBLEM") and ("NOCHARGE" in onbackenderror)) or \
                (self.Action in ("DENY", "CANCEL")) :
                self.JobPrice = 0.0
            elif (self.User.LimitBy == "nochange") or self.Printer.PassThrough :
                # no need to update the quota for the current user on this printer
                self.printInfo(_("User %s's quota on printer %s won't be modified") % (self.UserName, self.PrinterName))
                self.JobPrice = 0.0
            else :
                # update the quota for the current user on this printer 
                self.printInfo(_("Updating user %s's quota on printer %s") % (self.UserName, self.PrinterName))
                self.JobPrice = self.UserPQuota.increasePagesUsage(self.JobSize)
            
            # adds the current job to history    
            self.Printer.addJobToHistory(self.JobId, self.User, self.accounter.getLastPageCounter(), \
                                    self.Action, self.JobSize, self.JobPrice, self.InputFile, \
                                    self.Title, self.Copies, self.Options, self.ClientHost, \
                                    self.JobSizeBytes, self.JobMD5Sum, None, self.JobBillingCode, \
                                    self.softwareJobSize, self.softwareJobPrice)
            self.printInfo(_("Job added to history."))
            
            if hasattr(self, "BillingCode") and self.BillingCode and self.BillingCode.Exists :
                if (self.Action in ("ALLOW", "WARN")) or \
                   ((self.Action == "PROBLEM") and ("CHARGE" in onbackenderror)) :
                    self.BillingCode.consume(self.JobSize, self.JobPrice)
                    self.printInfo(_("Billing code %s was updated.") % self.BillingCode.BillingCode)
        except :    
            self.storage.rollbackTransaction()
            raise
        else :    
            self.storage.commitTransaction()
            
        # exports some new environment variables
        self.exportJobSizeAndPrice()
        
        # then re-export user information with new values
        self.exportUserInfo()
        
        # handle ending banner pages without accounting
        if accountbanner in ["STARTING", "NONE"] :
            self.handleBanner("ending", 0)
                    
        self.launchPostHook()
            
        return retcode    
               
    def printJobDatas(self) :           
        """Sends the job's datas to the real backend."""
        self.logdebug("Sending job's datas to real backend...")
        
        delay = 0
        number = 1
        for onb in self.config.getPrinterOnBackendError(self.PrinterName) :
            if onb.startswith("RETRY:") :
                try :
                    (number, delay) = [int(p) for p in onb[6:].split(":", 2)]
                    if (number < 0) or (delay < 0) :
                        raise ValueError
                except ValueError :    
                    self.printInfo(_("Incorrect value for the 'onbackenderror' directive in section [%s]") % self.PrinterName, "error")
                    delay = 0
                    number = 1
                else :    
                    break
        loopcnt = 1 
        while True :            
            if self.InputFile is None :
                infile = open(self.DataFile, "rb")
            else :    
                infile = None
            retcode = self.runOriginalBackend(infile)
            if self.InputFile is None :
                infile.close()
            if not retcode :
                break
            else :
                if (not number) or (loopcnt < number) :
                    self.logdebug(_("The real backend produced an error, we will try again in %s seconds.") % delay)
                    time.sleep(delay)
                    loopcnt += 1
                else :    
                    break
            
        self.logdebug("Job's datas sent to real backend.")
        return retcode
        
    def runOriginalBackend(self, filehandle=None, isBanner=0) :
        """Launches the original backend."""
        originalbackend = os.path.join(os.path.split(sys.argv[0])[0], self.RealBackend)
        if not isBanner :
            arguments = [os.environ["DEVICE_URI"]] + sys.argv[1:]
        else :    
            # For banners, we absolutely WANT
            # to remove any filename from the command line !
            self.logdebug("It looks like we try to print a banner.")
            arguments = [os.environ["DEVICE_URI"]] + sys.argv[1:6]
        arguments[2] = self.UserName # in case it was overwritten by external script
        # TODO : do something about job-billing option, in case it was overwritten as well...
        # TODO : do something about the job title : if we are printing a banner and the backend
        # TODO : uses the job's title to name an output file (cups-pdf:// for example), we're stuck !
        
        self.logdebug("Starting original backend %s with args %s" % (originalbackend, " ".join(['"%s"' % a for a in arguments])))
        self.regainPriv()    
        pid = os.fork()
        self.logdebug("Forked !")
        if pid == 0 :
            if filehandle is not None :
                self.logdebug("Redirecting file handle to real backend's stdin")
                os.dup2(filehandle.fileno(), 0)
            try :
                self.logdebug("Calling execve...")
                os.execve(originalbackend, arguments, os.environ)
            except OSError, msg :
                self.logdebug("execve() failed: %s" % msg)
            self.logdebug("We shouldn't be there !!!")    
            os._exit(-1)
        self.dropPriv()    
        
        self.logdebug("Waiting for original backend to exit...")    
        killed = 0
        status = -1
        while status == -1 :
            try :
                status = os.waitpid(pid, 0)[1]
            except OSError, (err, msg) :
                if (err == 4) and self.gotSigTerm :
                    os.kill(pid, signal.SIGTERM)
                    killed = 1
                    
        if os.WIFEXITED(status) :
            status = os.WEXITSTATUS(status)
            message = "CUPS backend %s returned %d." % \
                            (originalbackend, status)
            if status :
                level = "error"
                self.Reason = message
            else :    
                level = "info"
            self.printInfo(message, level)
            return status
        elif not killed :
            self.Reason = "CUPS backend %s died abnormally." % originalbackend
            self.printInfo(self.Reason, "error")
            return -1
        else :
            self.Reason = "CUPS backend %s was killed." % originalbackend
            self.printInfo(self.Reason, "warn")
            return 1
        
if __name__ == "__main__" :    
    # This is a CUPS backend, we should act and die like a CUPS backend
    wrapper = CUPSBackend()
    if len(sys.argv) == 1 :
        print "\n".join(wrapper.discoverOtherBackends())
        sys.exit(0)                
    elif len(sys.argv) not in (6, 7) :    
        sys.stderr.write("ERROR: %s job-id user title copies options [file]\n"\
                              % sys.argv[0])
        sys.exit(1)
    else :    
        try :
            wrapper.deferredInit()
            wrapper.initBackendParameters()
            wrapper.waitForLock()
            if os.environ.get("PYKOTASTATUS") == "CANCELLED" :
                raise KeyboardInterrupt
            wrapper.saveDatasAndCheckSum()
            wrapper.preaccounter = openAccounter(wrapper, ispreaccounter=1)
            wrapper.accounter = openAccounter(wrapper)
            wrapper.precomputeJobSize()
            wrapper.exportJobInfo() # exports a first time to give hints to external scripts 
            wrapper.overwriteJobAttributes()
            wrapper.exportJobInfo() # re-exports in case it was overwritten
            retcode = wrapper.mainWork()
        except KeyboardInterrupt :    
            wrapper.printInfo(_("Job %s interrupted by the administrator !") % wrapper.JobId, "warn")
            retcode = 0
        except SystemExit, err :    
            retcode = err.code
        except :    
            try :
                wrapper.crashed("cupspykota backend failed")
            except :    
                crashed("cupspykota backend failed")
            retcode = 1
        wrapper.clean()
        sys.exit(retcode)