Source code for model_permissions.backends

"""
django-model-permissions - simple object permissions for django.

Copyright (C) 2018 Mathias Stelzer

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
"""
from django.conf import settings
from django.contrib.auth.backends import (
    ModelBackend as DjangoModelBackend,
    AllowAllUsersModelBackend as DjangoAllowAllUsersModelBackend,
    RemoteUserBackend as DjangoRemoteUserBackend,
    AllowAllUsersRemoteUserBackend as DjangoAllowAllUsersRemoteUserBackend,
)
from django.utils.module_loading import import_string


# mixins

class BaseObjectBackendMixin(object):
    """Base class for object permission backends."""

    def get_permission_function(self, obj):
        """
        Get the function to list the given objects permissions.

        This checks the given object for a ``get_permissions`` method and,
        if it doesn't exist, the ``MODEL_PERMISSIONS`` setting to find the
        objects :ref:`manual-permission-function`.

        :param obj: The model instance to get the function for.
        :type  obj: :class:`django.db.models.Model`
        :return: The function to list the objects permissions.
        :rtype: :class:`callable`
        """
        get_permissions = getattr(obj, 'get_permissions', None)
        if get_permissions is not None:
            return self.model_permission_wrapper

        model_permissions = getattr(settings, 'MODEL_PERMISSIONS', {})
        f = model_permissions.get(obj._meta.label, None)
        if f is None:
            return

        if callable(f):
            return f

        # assume string
        return import_string(f)

    def model_permission_wrapper(self, user_obj, obj):
        """Object permission wrapper for the `get_permissions` model method."""
        return obj.get_permissions(user_obj)

    def get_object_permissions(self, user_obj, obj=None):
        """
        Get object permissions for the given user and object.

        Exit early and return an empty set if:

        * no object is given
        * the user is

           * inactive
           * anonymous
           * a superuser

        * no permission function can be found

        :param user_obj: User instance.
        :type  user_obj: :class:`django.contrib.auth.models.AbstractUser`
        :param obj: Model instance.
        :type  obj: :class:`django.db.models.Model`
        :return: Set of permissions.
        :rtype: :class:`set`
        """
        if obj is None:
            return set()

        get_permissions = self.get_permission_function(obj)
        if get_permissions is None:
            return set()

        perm_cache_name = '_{}_{}_perm_cache'.format(obj._meta.label, obj.pk)
        if not hasattr(user_obj, perm_cache_name):
            perms = get_permissions(user_obj, obj)
            if perms is None:
                perms = set()
            setattr(user_obj, perm_cache_name, perms)
        return getattr(user_obj, perm_cache_name)


class ObjectModelBackendMixin(BaseObjectBackendMixin):
    """Mixin for dual permission authentication backends."""

    def get_all_permissions(self, user_obj, obj=None):
        """Get all permissions for the given user and object."""
        perms = super().get_all_permissions(user_obj)
        perms.update(self.get_object_permissions(user_obj, obj=obj))
        return perms


class ObjectBackendMixin(BaseObjectBackendMixin):
    """Mixin for object-only permission authentication backends."""

    def get_all_permissions(self, user_obj, obj=None):
        """Get all permissions for the given user and object."""
        return self.get_object_permissions(user_obj, obj=obj)


# backends

class ObjectBackend(ObjectBackendMixin, DjangoModelBackend):
    """An authentication backend with object permissions only."""

    pass


class ObjectModelBackend(ObjectModelBackendMixin, DjangoModelBackend):
    """An authentication backend with default and object permissions."""

    pass


class AllowAllUsersObjectBackend(ObjectBackendMixin, DjangoAllowAllUsersModelBackend):
    """Django's `AllowAllUsersModelBackend` with object permissions only."""

    pass


class AllowAllUsersObjectModelBackend(ObjectModelBackendMixin, DjangoAllowAllUsersModelBackend):
    """Django's `AllowAllUsersModelBackend` with dual permissions."""

    pass


class RemoteUserObjectBackend(ObjectBackendMixin, DjangoRemoteUserBackend):
    """Django's `RemoteUserBackend` with object permissions only."""

    pass


class RemoteUserBackend(ObjectModelBackendMixin, DjangoRemoteUserBackend):
    """Django's `RemoteUserBackend` with dual permissions."""

    pass


class AllowAllUsersRemoteUserObjectBackend(ObjectBackendMixin, DjangoAllowAllUsersRemoteUserBackend):
    """Django's `AllowAllUsersRemoteUserBackend` with object permissions only."""

    pass


class AllowAllUsersRemoteUserBackend(ObjectModelBackendMixin, DjangoAllowAllUsersRemoteUserBackend):
    """Django's `AllowAllUsersRemoteUserBackend` with dual permissions."""

    pass