models.py

# -*- mode: python; coding: utf-8 -*-
# Re2o est un logiciel d'administration développé initiallement au rezometz. Il
# se veut agnostique au réseau considéré, de manière à être installable en
# quelques clics.
#
# Copyright © 2016-2018  Gabriel Détraz
# Copyright © 2017  Goulven Kermarec
# Copyright © 2017  Augustin Lemesle
# Copyright © 2018  Charlie Jacomme
#
# 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.
"""machines.models
The models definitions for the Machines app
"""

from __future__ import unicode_literals

import base64
import hashlib
import re
from datetime import timedelta
from ipaddress import IPv6Address
from itertools import chain

from django.core.validators import MaxValueValidator, MinValueValidator
from django.db import models
from django.db.models import Q
from django.db.models.signals import post_save, post_delete
from django.dispatch import receiver
from django.forms import ValidationError
from django.utils import timezone
from django.utils.functional import cached_property
from django.utils.translation import ugettext_lazy as _
from macaddress.fields import MACAddressField, default_dialect
from netaddr import mac_bare, EUI, IPSet, IPRange, IPNetwork, IPAddress

import preferences.models
import users.models
from re2o.field_permissions import FieldPermissionModelMixin
from re2o.mixins import AclMixin, RevMixin


class Machine(RevMixin, FieldPermissionModelMixin, models.Model):
    """ Class définissant une machine, object parent user, objets fils
    interfaces"""
    user = models.ForeignKey('users.User', on_delete=models.CASCADE)
    name = models.CharField(
        max_length=255,
        help_text=_("Optional"),
        blank=True,
        null=True
    )
    active = models.BooleanField(default=True)

    class Meta:
        permissions = (
            ("view_machine", _("Can view a machine object")),
            ("change_machine_user",
             _("Can change the user of a machine")),
        )
        verbose_name = _("machine")
        verbose_name_plural = _("machines")

    @classmethod
    def get_instance(cls, machineid, *_args, **_kwargs):
        """Get the Machine instance with machineid.
        :param userid: The id
        :return: The user
        """
        return cls.objects.get(pk=machineid)

    def linked_objects(self):
        """Return linked objects : machine and domain.
        Usefull in history display"""
        return chain(
            self.interface_set.all(),
            Domain.objects.filter(
                interface_parent__in=self.interface_set.all()
            )
        )

    @staticmethod
    def can_change_user(user_request, *_args, **_kwargs):
        """Checks if an user is allowed to change the user who owns a
        Machine.

        Args:
            user_request: The user requesting to change owner.

        Returns:
            A tuple with a boolean stating if edition is allowed and an
            explanation message.
        """
        return (user_request.has_perm('machines.change_machine_user'),
                _("You don't have the right to change the machine's user."))

    @staticmethod
    def can_view_all(user_request, *_args, **_kwargs):
        """Vérifie qu'on peut bien afficher l'ensemble des machines,
        droit particulier correspondant
        :param user_request: instance user qui fait l'edition
        :return: True ou False avec la raison de l'échec le cas échéant"""
        if not user_request.has_perm('machines.view_machine'):
            return False, _("You don't have the right to view all the"
                            " machines.")
        return True, None

    @staticmethod
    def can_create(user_request, userid, *_args, **_kwargs):
        """Vérifie qu'un user qui fait la requète peut bien créer la machine
        et n'a pas atteint son quota, et crée bien une machine à lui
        :param user_request: Utilisateur qui fait la requête
        :param userid: id de l'user dont on va créer une machine
        :return: soit True, soit False avec la raison de l'échec"""
        try:
            user = users.models.User.objects.get(pk=userid)
        except users.models.User.DoesNotExist:
            return False, _("Nonexistent user.")
        max_lambdauser_interfaces = (preferences.models.OptionalMachine
            .get_cached_value(
            'max_lambdauser_interfaces'
        ))
        if not user_request.has_perm('machines.add_machine'):
            if not (preferences.models.OptionalMachine
                    .get_cached_value('create_machine')):
                return False, (_("You don't have the right to add a machine."))
            if user != user_request:
                return False, (_("You don't have the right to add a machine"
                                 " to another user."))
            if user.user_interfaces().count() >= max_lambdauser_interfaces:
                return False, (_("You reached the maximum number of interfaces"
                                 " that you are allowed to create yourself"
                                 " (%s)." % max_lambdauser_interfaces))
        return True, None

    def can_edit(self, user_request, *args, **kwargs):
        """Vérifie qu'on peut bien éditer cette instance particulière (soit
        machine de soi, soit droit particulier
        :param self: instance machine à éditer
        :param user_request: instance user qui fait l'edition
        :return: True ou False avec la raison le cas échéant"""
        if self.user != user_request:
            if (not user_request.has_perm('machines.change_interface') or
                    not self.user.can_edit(
                        self.user,
                        user_request,
                        *args,
                        **kwargs
                    )[0]):
                return False, (_("You don't have the right to edit a machine"
                                 " of another user."))
        return True, None

    def can_delete(self, user_request, *args, **kwargs):
        """Vérifie qu'on peut bien supprimer cette instance particulière (soit
        machine de soi, soit droit particulier
        :param self: instance machine à supprimer
        :param user_request: instance user qui fait l'edition
        :return: True ou False avec la raison de l'échec le cas échéant"""
        if self.user != user_request:
            if (not user_request.has_perm('machines.change_interface') or
                    not self.user.can_edit(
                        self.user,
                        user_request,
                        *args,
                        **kwargs
                    )[0]):
                return False, _("You don't have the right to delete a machine"
                                " of another user.")
        return True, None

    def can_view(self, user_request, *_args, **_kwargs):
        """Vérifie qu'on peut bien voir cette instance particulière (soit
        machine de soi, soit droit particulier
        :param self: instance machine à éditer
        :param user_request: instance user qui fait l'edition
        :return: True ou False avec la raison de l'échec le cas échéant"""
        if (not user_request.has_perm('machines.view_machine') and
                self.user != user_request):
            return False, _("You don't have the right to view other machines"
                            " than yours.")
        return True, None

    @cached_property
    def short_name(self):
        """Par defaut, renvoie le nom de la première interface
        de cette machine"""
        interfaces_set = self.interface_set.first()
        if interfaces_set:
            return str(interfaces_set.domain.name)
        else:
            return "None"

    @cached_property
    def complete_name(self):
        """Par defaut, renvoie le nom de la première interface
        de cette machine"""
        return str(self.interface_set.first())

    @cached_property
    def all_short_names(self):
        """Renvoie de manière unique, le nom des interfaces de cette
        machine"""
        return Domain.objects.filter(
            interface_parent__machine=self
        ).values_list('name', flat=True).distinct()

    @cached_property
    def get_name(self):
        """Return a name : user provided name or first interface name"""
        return self.name or self.short_name

    @cached_property
    def all_complete_names(self):
        """Renvoie tous les tls complets de la machine"""
        return [str(domain) for domain in Domain.objects.filter(
            Q(cname__interface_parent__machine=self) | Q(interface_parent__machine=self)
        )]

    def __init__(self, *args, **kwargs):
        super(Machine, self).__init__(*args, **kwargs)
        self.field_permissions = {
            'user': self.can_change_user,
        }

    def __str__(self):
        return str(self.user) + ' - ' + str(self.id) + ' - ' + str(self.name)


class MachineType(RevMixin, AclMixin, models.Model):
    """ Type de machine, relié à un type d'ip, affecté aux interfaces"""
    type = models.CharField(max_length=255)
    ip_type = models.ForeignKey(
        'IpType',
        on_delete=models.PROTECT,
        blank=True,
        null=True
    )

    class Meta:
        permissions = (
            ("view_machinetype", _("Can view a machine type object")),
            ("use_all_machinetype", _("Can use all machine types")),
        )
        verbose_name = _("machine type")
        verbose_name_plural = _("machine types")

    def all_interfaces(self):
        """ Renvoie toutes les interfaces (cartes réseaux) de type
        machinetype"""
        return Interface.objects.filter(type=self)

    @staticmethod
    def can_use_all(user_request, *_args, **_kwargs):
        """Check if an user can use every MachineType.

        Args:
            user_request: The user requesting edition.
        Returns:
            A tuple with a boolean stating if user can acces and an explanation
            message is acces is not allowed.
        """
        if not user_request.has_perm('machines.use_all_machinetype'):
            return False, (_("You don't have the right to use all machine"
                             " types."))
        return True, None

    def __str__(self):
        return self.type


class IpType(RevMixin, AclMixin, models.Model):
    """ Type d'ip, définissant un range d'ip, affecté aux machine types"""
    type = models.CharField(max_length=255)
    extension = models.ForeignKey('Extension', on_delete=models.PROTECT)
    need_infra = models.BooleanField(default=False)
    domaine_ip_start = models.GenericIPAddressField(protocol='IPv4')
    domaine_ip_stop = models.GenericIPAddressField(protocol='IPv4')
    domaine_ip_network = models.GenericIPAddressField(
        protocol='IPv4',
        null=True,
        blank=True,
        help_text=_("Network containing the domain's IPv4 range (optional)")
    )
    domaine_ip_netmask = models.IntegerField(
        default=24,
        validators=[
            MaxValueValidator(31),
            MinValueValidator(8)
        ],
        help_text=_("Netmask for the domain's IPv4 range")
    )
    reverse_v4 = models.BooleanField(
        default=False,
        help_text=_("Enable reverse DNS for IPv4"),
    )
    prefix_v6 = models.GenericIPAddressField(
        protocol='IPv6',
        null=True,
        blank=True
    )
    prefix_v6_length = models.IntegerField(
        default=64,
        validators=[
            MaxValueValidator(128),
            MinValueValidator(0)
        ]
    )
    reverse_v6 = models.BooleanField(
        default=False,
        help_text=_("Enable reverse DNS for IPv6"),
    )
    vlan = models.ForeignKey(
        'Vlan',
        on_delete=models.PROTECT,
        blank=True,
        null=True
    )
    ouverture_ports = models.ForeignKey(
        'OuverturePortList',
        blank=True,
        null=True
    )

    class Meta:
        permissions = (
            ("view_iptype", _("Can view an IP type object")),
            ("use_all_iptype", _("Can use all IP types")),
        )
        verbose_name = _("IP type")
        verbose_name_plural = "IP types"

    @cached_property
    def ip_range(self):
        """ Renvoie un objet IPRange à partir de l'objet IpType"""
        return IPRange(self.domaine_ip_start, end=self.domaine_ip_stop)

    @cached_property
    def ip_set(self):
        """ Renvoie une IPSet à partir de l'iptype"""
        return IPSet(self.ip_range)

    @cached_property
    def ip_set_as_str(self):
        """ Renvoie une liste des ip en string"""
        return [str(x) for x in self.ip_set]

    @cached_property
    def ip_set_cidrs_as_str(self):
        """Renvoie la liste des cidrs du range en str"""
        return [str(ip_range) for ip_range in self.ip_set.iter_cidrs()]

    @cached_property
    def ip_set_full_info(self):
        """Iter sur les range cidr, et renvoie network, broacast , etc"""
        return [
            {
                'network': str(ip_set.network),
                'netmask': str(ip_set.netmask),
                'netmask_cidr': str(ip_set.prefixlen),
                'broadcast': str(ip_set.broadcast),
                'vlan': str(self.vlan),
                'vlan_id': self.vlan.vlan_id
            } for ip_set in self.ip_set.iter_cidrs()
        ]

    @cached_property
    def ip6_set_full_info(self):
        if self.prefix_v6:
            return {
                'network': str(self.prefix_v6),
                'netmask': 'ffff:ffff:ffff:ffff::',
                'netmask_cidr': str(self.prefix_v6_length),
                'vlan': str(self.vlan),
                'vlan_id': self.vlan.vlan_id
            }
        else:
            return None

    @cached_property
    def ip_network(self):
        """Renvoie le network parent du range start-stop, si spécifié
        Différent de ip_set_cidrs ou iP_set, car lui est supérieur ou égal"""
        if self.domaine_ip_network:
            return IPNetwork(str(self.domaine_ip_network) + '/' + str(self.domaine_ip_netmask))
        return None

    @cached_property
    def ip_net_full_info(self):
        """Renvoie les infos du network contenant du range"""
        return {
            'network': str(self.ip_network.network),
            'netmask': str(self.ip_network.netmask),
            'broadcast': str(self.ip_network.broadcast),
            'netmask_cidr': str(self.ip_network.prefixlen),
        }

    @cached_property
    def complete_prefixv6(self):
        """Return the complete prefix v6 as cidr"""
        return str(self.prefix_v6) + "/" + str(self.prefix_v6_length)

    def ip_objects(self):
        """ Renvoie tous les objets ipv4 relié à ce type"""
        return IpList.objects.filter(ip_type=self)

    def free_ip(self):
        """ Renvoie toutes les ip libres associées au type donné (self)"""
        return IpList.objects.filter(
            interface__isnull=True
        ).filter(ip_type=self)

    def gen_ip_range(self):
        """ Cree les IpList associées au type self. Parcours pédestrement et
        crée les ip une par une. Si elles existent déjà, met à jour le type
        associé à l'ip"""
        # Creation du range d'ip dans les objets iplist
        ip_obj = [IpList(ip_type=self, ipv4=str(ip)) for ip in self.ip_range]
        listes_ip = IpList.objects.filter(
            ipv4__in=[str(ip) for ip in self.ip_range]
        )
        # Si il n'y a pas d'ip, on les crée
        if not listes_ip:
            IpList.objects.bulk_create(ip_obj)
        # Sinon on update l'ip_type
        else:
            listes_ip.update(ip_type=self)
        return

    def del_ip_range(self):
        """ Methode dépréciée, IpList est en mode cascade et supprimé
        automatiquement"""
        if Interface.objects.filter(ipv4__in=self.ip_objects()):
            raise ValidationError(_("One or several IP addresses from the"
                                    " range are affected, impossible to delete"
                                    " the range."))
        for ip in self.ip_objects():
            ip.delete()

    def check_replace_prefixv6(self):
        """Remplace les prefixv6 des interfaces liées à ce type d'ip"""
        if not self.prefix_v6:
            return
        else:
            for ipv6 in Ipv6List.objects.filter(
                    interface__in=Interface.objects.filter(
                        type__in=MachineType.objects.filter(ip_type=self)
                    )
            ):
                ipv6.check_and_replace_prefix(prefix=self.prefix_v6)

    def get_associated_ptr_records(self):
        from re2o.utils import all_active_assigned_interfaces
        if self.reverse_v4:
            return (all_active_assigned_interfaces()
                    .filter(type__ip_type=self)
                    .filter(ipv4__isnull=False))
        else:
            return None

    def get_associated_ptr_v6_records(self):
        from re2o.utils import all_active_interfaces
        if self.reverse_v6:
            return (all_active_interfaces(full=True)
                    .filter(type__ip_type=self))
        else:
            return None

    def clean(self):
        """ Nettoyage. Vérifie :
        - Que ip_stop est après ip_start
        - Qu'on ne crée pas plus gros qu'un /16
        - Que le range crée ne recoupe pas un range existant
        - Formate l'ipv6 donnée en /64"""
        if IPAddress(self.domaine_ip_start) > IPAddress(self.domaine_ip_stop):
            raise ValidationError(_("Range end must be after range start..."))
        # On ne crée pas plus grand qu'un /16
        if self.ip_range.size > 65536:
            raise ValidationError(_("The range is too large, you can't create"
                                    " a larger one than a /16."))
        # On check que les / ne se recoupent pas
        for element in IpType.objects.all().exclude(pk=self.pk):
            if not self.ip_set.isdisjoint(element.ip_set):
                raise ValidationError(_("The specified range is not disjoint"
                                        " from existing ranges."))
        # On formate le prefix v6
        if self.prefix_v6:
            self.prefix_v6 = str(IPNetwork(self.prefix_v6 + '/64').network)
        # On vérifie qu'un domaine network/netmask contiens bien le domaine ip start-stop
        if self.domaine_ip_network:
            if not self.domaine_ip_start in self.ip_network or not self.domaine_ip_stop in self.ip_network:
                raise ValidationError(_("If you specify a domain network or"
                                        " netmask, it must contain the"
                                        " domain's IP range."))
        return

    def save(self, *args, **kwargs):
        self.clean()
        super(IpType, self).save(*args, **kwargs)

    @staticmethod
    def can_use_all(user_request, *_args, **_kwargs):
        """Superdroit qui permet d'utiliser toutes les extensions sans
        restrictions
        :param user_request: instance user qui fait l'edition
        :return: True ou False avec la raison de l'échec le cas échéant"""
        return user_request.has_perm('machines.use_all_iptype'), None

    def __str__(self):
        return self.type


class Vlan(RevMixin, AclMixin, models.Model):
    """ Un vlan : vlan_id et nom
    On limite le vlan id entre 0 et 4096, comme défini par la norme"""
    vlan_id = models.PositiveIntegerField(validators=[MaxValueValidator(4095)])
    name = models.CharField(max_length=256)
    comment = models.CharField(max_length=256, blank=True)
    #Réglages supplémentaires
    arp_protect = models.BooleanField(default=False)
    dhcp_snooping = models.BooleanField(default=False)
    dhcpv6_snooping = models.BooleanField(default=False)
    igmp = models.BooleanField(
        default=False,
        help_text="Gestion multicast v4"
    )
    mld = models.BooleanField(
        default=False,
        help_text="Gestion multicast v6"
    )

    class Meta:
        permissions = (
            ("view_vlan", _("Can view a VLAN object")),
        )
        verbose_name = _("VLAN")
        verbose_name_plural = _("VLANs")

    def __str__(self):
        return self.name


class Nas(RevMixin, AclMixin, models.Model):
    """ Les nas. Associé à un machine_type.
    Permet aussi de régler le port_access_mode (802.1X ou mac-address) pour
    le radius. Champ autocapture de la mac à true ou false"""
    default_mode = '802.1X'
    AUTH = (
        ('802.1X', '802.1X'),
        ('Mac-address', 'Mac-address'),
    )

    name = models.CharField(max_length=255, unique=True)
    nas_type = models.ForeignKey(
        'MachineType',
        on_delete=models.PROTECT,
        related_name='nas_type'
    )
    machine_type = models.ForeignKey(
        'MachineType',
        on_delete=models.PROTECT,
        related_name='machinetype_on_nas'
    )
    port_access_mode = models.CharField(
        choices=AUTH,
        default=default_mode,
        max_length=32
    )
    autocapture_mac = models.BooleanField(default=False)

    class Meta:
        permissions = (
            ("view_nas", _("Can view a NAS device object")),
        )
        verbose_name = _("NAS device")
        verbose_name_plural = _("NAS devices")

    def __str__(self):
        return self.name


class SOA(RevMixin, AclMixin, models.Model):
    """
    Un enregistrement SOA associé à une extension
    Les valeurs par défault viennent des recommandations RIPE :
    https://www.ripe.net/publications/docs/ripe-203
    """
    name = models.CharField(max_length=255)
    mail = models.EmailField(
        help_text=_("Contact email address for the zone")
    )
    refresh = models.PositiveIntegerField(
        default=86400,  # 24 hours
        help_text=_("Seconds before the secondary DNS have to ask the primary"
                    " DNS serial to detect a modification")
    )
    retry = models.PositiveIntegerField(
        default=7200,  # 2 hours
        help_text=_("Seconds before the secondary DNS ask the serial again in"
                    " case of a primary DNS timeout")
    )
    expire = models.PositiveIntegerField(
        default=3600000,  # 1000 hours
        help_text=_("Seconds before the secondary DNS stop answering requests"
                    " in case of primary DNS timeout")
    )
    ttl = models.PositiveIntegerField(
        default=172800,  # 2 days
        help_text=_("Time to Live")
    )

    class Meta:
        permissions = (
            ("view_soa", _("Can view an SOA record object")),
        )
        verbose_name = _("SOA record")
        verbose_name_plural = _("SOA records")

    def __str__(self):
        return str(self.name)

    @cached_property
    def dns_soa_param(self):
        """
        Renvoie la partie de l'enregistrement SOA correspondant aux champs :
            <refresh>   ; refresh
            <retry>     ; retry
            <expire>    ; expire
            <ttl>       ; TTL
        """
        return (
            '    {refresh}; refresh\n'
            '    {retry}; retry\n'
            '    {expire}; expire\n'
            '    {ttl}; TTL'
        ).format(
            refresh=str(self.refresh).ljust(12),
            retry=str(self.retry).ljust(12),
            expire=str(self.expire).ljust(12),
            ttl=str(self.ttl).ljust(12)
        )

    @cached_property
    def dns_soa_mail(self):
        """ Renvoie le mail dans l'enregistrement SOA """
        mail_fields = str(self.mail).split('@')
        return mail_fields[0].replace('.', '\\.') + '.' + mail_fields[1] + '.'

    @classmethod
    def new_default_soa(cls):
        """ Fonction pour créer un SOA par défaut, utile pour les nouvelles
        extensions .
        /!\ Ne jamais supprimer ou renommer cette fonction car elle est
        utilisée dans les migrations de la BDD. """
        return cls.objects.get_or_create(
            name=_("SOA to edit"),
            mail="postmaser@example.com"
        )[0].pk


class Extension(RevMixin, AclMixin, models.Model):
    """ Extension dns type example.org. Précise si tout le monde peut
    l'utiliser, associé à un origin (ip d'origine)"""
    name = models.CharField(
        max_length=255,
        unique=True,
        help_text=_("Zone name, must begin with a dot (.example.org)")
    )
    need_infra = models.BooleanField(default=False)
    origin = models.ForeignKey(
        'IpList',
        on_delete=models.PROTECT,
        blank=True,
        null=True,
        help_text=_("A record associated with the zone")
    )
    origin_v6 = models.GenericIPAddressField(
        protocol='IPv6',
        null=True,
        blank=True,
        help_text=_("AAAA record associated with the zone")
    )
    soa = models.ForeignKey(
        'SOA',
        on_delete=models.CASCADE
    )
    dnssec = models.BooleanField(
        default=False,
        help_text=_("Should the zone be signed with DNSSEC")
    )

    class Meta:
        permissions = (
            ("view_extension", _("Can view an extension object")),
            ("use_all_extension", _("Can use all extensions")),
        )
        verbose_name = _("DNS extension")
        verbose_name_plural = _("DNS extensions")

    @cached_property
    def dns_entry(self):
        """ Une entrée DNS A et AAAA sur origin (zone self)"""
        entry = ""
        if self.origin:
            entry += "@               IN  A       " + str(self.origin)
        if self.origin_v6:
            if entry:
                entry += "\n"
            entry += "@               IN  AAAA    " + str(self.origin_v6)
        return entry

    def get_associated_sshfp_records(self):
        from re2o.utils import all_active_assigned_interfaces
        return (all_active_assigned_interfaces()
                .filter(type__ip_type__extension=self)
                .filter(machine__id__in=SshFp.objects.values('machine')))

    def get_associated_a_records(self):
        from re2o.utils import all_active_assigned_interfaces
        return (all_active_assigned_interfaces()
                .filter(type__ip_type__extension=self)
                .filter(ipv4__isnull=False))

    def get_associated_aaaa_records(self):
        from re2o.utils import all_active_interfaces
        return (all_active_interfaces(full=True)
                .filter(type__ip_type__extension=self))

    def get_associated_cname_records(self):
        from re2o.utils import all_active_assigned_interfaces
        return (Domain.objects
                .filter(extension=self)
                .filter(cname__interface_parent__in=all_active_assigned_interfaces())
                .prefetch_related('cname'))

    def get_associated_dname_records(self):
        return (DName.objects.filter(alias=self))

    @staticmethod
    def can_use_all(user_request, *_args, **_kwargs):
        """Superdroit qui permet d'utiliser toutes les extensions sans
        restrictions
        :param user_request: instance user qui fait l'edition
        :return: True ou False avec la raison de l'échec le cas échéant"""
        return user_request.has_perm('machines.use_all_extension'), None

    def __str__(self):
        return self.name

    def clean(self, *args, **kwargs):
        if self.name and self.name[0] != '.':
            raise ValidationError(_("An extension must begin with a dot."))
        super(Extension, self).clean(*args, **kwargs)


class Mx(RevMixin, AclMixin, models.Model):
    """ Entrées des MX. Enregistre la zone (extension) associée et la
    priorité
    Todo : pouvoir associer un MX à une interface """
    zone = models.ForeignKey('Extension', on_delete=models.PROTECT)
    priority = models.PositiveIntegerField()
    name = models.ForeignKey('Domain', on_delete=models.PROTECT)

    class Meta:
        permissions = (
            ("view_mx", _("Can view an MX record object")),
        )
        verbose_name = _("MX record")
        verbose_name_plural = _("MX records")

    @cached_property
    def dns_entry(self):
        """Renvoie l'entrée DNS complète pour un MX à mettre dans les
        fichiers de zones"""
        return "@               IN  MX  {prior} {name}".format(
            prior=str(self.priority).ljust(3),
            name=str(self.name)
        )

    def __str__(self):
        return str(self.zone) + ' ' + str(self.priority) + ' ' + str(self.name)


class Ns(RevMixin, AclMixin, models.Model):
    """Liste des enregistrements name servers par zone considéérée"""
    zone = models.ForeignKey('Extension', on_delete=models.PROTECT)
    ns = models.ForeignKey('Domain', on_delete=models.PROTECT)

    class Meta:
        permissions = (
            ("view_ns", _("Can view an NS record object")),
        )
        verbose_name = _("NS record")
        verbose_name_plural = _("NS records")

    @cached_property
    def dns_entry(self):
        """Renvoie un enregistrement NS complet pour les filezones"""
        return "@               IN  NS      " + str(self.ns)

    def __str__(self):
        return str(self.zone) + ' ' + str(self.ns)


class Txt(RevMixin, AclMixin, models.Model):
    """ Un enregistrement TXT associé à une extension"""
    zone = models.ForeignKey('Extension', on_delete=models.PROTECT)
    field1 = models.CharField(max_length=255)
    field2 = models.TextField(max_length=2047)

    class Meta:
        permissions = (
            ("view_txt", _("Can view a TXT record object")),
        )
        verbose_name = _("TXT record")
        verbose_name_plural = _("TXT records")

    def __str__(self):
        return str(self.zone) + " : " + str(self.field1) + " " + \
               str(self.field2)

    @cached_property
    def dns_entry(self):
        """Renvoie l'enregistrement TXT complet pour le fichier de zone"""
        return str(self.field1).ljust(15) + " IN  TXT     " + str(self.field2)


class DName(RevMixin, AclMixin, models.Model):
    """A DNAME entry for the DNS."""
    zone = models.ForeignKey('Extension', on_delete=models.PROTECT)
    alias = models.CharField(max_length=255)

    class Meta:
        permissions = (
            ("view_dname", _("Can view a DNAME record object")),
        )
        verbose_name = _("DNAME record")
        verbose_name_plural = _("DNAME records")

    def __str__(self):
        return str(self.zone) + " : " + str(self.alias)

    @cached_property
    def dns_entry(self):
        """Returns the DNAME record for the DNS zone file."""
        return str(self.alias).ljust(15) + " IN  DNAME   " + str(self.zone)


class Srv(RevMixin, AclMixin, models.Model):
    """ A SRV record """
    TCP = 'TCP'
    UDP = 'UDP'

    service = models.CharField(max_length=31)
    protocole = models.CharField(
        max_length=3,
        choices=(
            (TCP, 'TCP'),
            (UDP, 'UDP'),
        ),
        default=TCP,
    )
    extension = models.ForeignKey('Extension', on_delete=models.PROTECT)
    ttl = models.PositiveIntegerField(
        default=172800,  # 2 days
        help_text=_("Time to Live")
    )
    priority = models.PositiveIntegerField(
        default=0,
        validators=[MaxValueValidator(65535)],
        help_text=_("Priority of the target server (positive integer value,"
                    " the lower it is, the more the server will be used if"
                    " available)")
    )
    weight = models.PositiveIntegerField(
        default=0,
        validators=[MaxValueValidator(65535)],
        help_text=_("Relative weight for records with the same priority"
                    " (integer value between 0 and 65535)")
    )
    port = models.PositiveIntegerField(
        validators=[MaxValueValidator(65535)],
        help_text=_("TCP/UDP port")
    )
    target = models.ForeignKey(
        'Domain',
        on_delete=models.PROTECT,
        help_text=_("Target server")
    )

    class Meta:
        permissions = (
            ("view_srv", _("Can view an SRV record object")),
        )
        verbose_name = _("SRV record")
        verbose_name_plural = _("SRV records")

    def __str__(self):
        return str(self.service) + ' ' + str(self.protocole) + ' ' + \
               str(self.extension) + ' ' + str(self.priority) + \
               ' ' + str(self.weight) + str(self.port) + str(self.target)

    @cached_property
    def dns_entry(self):
        """Renvoie l'enregistrement SRV complet pour le fichier de zone"""
        return str(self.service) + '._' + str(self.protocole).lower() + \
               str(self.extension) + '. ' + str(self.ttl) + ' IN SRV ' + \
               str(self.priority) + ' ' + str(self.weight) + ' ' + \
               str(self.port) + ' ' + str(self.target) + '.'