.. -*- coding: utf-8 -*-

.. _TutosPhotoWebSiteSecurity:

Security, testing and migration
-------------------------------

This part will cover various topics:

* configuring security
* migrating existing instance
* writing some unit tests

Here is the ``read`` security model I want:

* folders, files, images and comments should have one of the following visibility:

  - ``public``, everyone can see it
  - ``authenticated``, only authenticated users can see it
  - ``restricted``, only a subset of authenticated users can see it

* managers (e.g. me) can see everything
* only authenticated users can see people
* everyone can see classifier entities, such as tag

Also:

* unless explicitly specified, the visibility of an image should be the same as
its parent folder
* the visibility of a comment should be the same as the commented entity
* If there is no parent entity, the default visibility is ``authenticated``.

Regarding write security, that's much easier:

* anonymous can't write anything
* authenticated users can only add comment
* managers will add the remaining stuff

Now, let's implement that!

Proper security in CubicWeb is done **at the schema level**, so you don't have to
bother with it in views: users will only see what they can see automatically.

.. _adv_tuto_security:

Step 1: configuring security into the schema
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In the schema, you can grant access according to:

* groups
* to some RQL expressions: users get access if the expression returns some results

To implement the read security defined earlier, groups are not enough, we'll
need some RQL expression. Here is the idea:

* add a `visibility` attribute on `Folder`, `File` and `Comment`, which may be one of
  the value explained above
* add a `may_be_read_by` relation from `Folder`, `File` and `Comment` to `users`,
  which will define who can see the entity
* security propagation will be done in hooks

.. Note::

   What makes `visibility` an attribute and not a relation is that its object
   is a primitive type, here `String`.

   Other builtin primitives are String, Int, BigInt, Float, Decimal, Boolean,
   Date, Datetime, Time, Interval, Byte and Password and for more information
   read :ref:`EntityType`

So the first thing to do is to modify my cube's :file:`schema.py` to define those
relations:

.. sourcecode:: python

    from yams.constraints import StaticVocabularyConstraint


    class visibility(RelationDefinition):
        subject = ('Folder', 'File', 'Comment')
        object = 'String'
        constraints = [StaticVocabularyConstraint(('public', 'authenticated',
                                                   'restricted', 'parent'))]
        default = 'parent'
        cardinality = '11'  # required


    class may_be_read_by(RelationDefinition):
        __permissions__ = {
            'read': ('managers', 'users'),
            'add': ('managers',),
            'delete': ('managers',),
        }

        subject = ('Folder', 'File', 'Comment',)
        object = 'CWUser'

We can note the following points:

* we've added a new `visibility` attribute to `Folder`, `File`, `Image` and `Comment`
  using a `RelationDefinition`

* `cardinality = '11'` means this attribute is required. This is usually hidden
  under the `required` argument given to the `String` constructor, but we can
  rely on this here (same thing for StaticVocabularyConstraint, which is usually
  hidden by the `vocabulary` argument)

* the `parent` possible value will be used for visibility propagation

* think to secure the `may_be_read_by` permissions, else any user can add/delete it
  by default, which somewhat breaks our security model...

Now, we should be able to define security rules in the schema, based on these new
attribute and relation. Here is the code to add to :file:`schema.py`:

.. sourcecode:: python

    from cubicweb.schema import ERQLExpression

    VISIBILITY_PERMISSIONS = {
        'read':   ('managers',
                   ERQLExpression('X visibility "public"'),
                   ERQLExpression('X may_be_read_by U')),
        'add':    ('managers',),
        'update': ('managers', 'owners',),
        'delete': ('managers', 'owners'),
    }
    AUTH_ONLY_PERMISSIONS = {
            'read':   ('managers', 'users'),
            'add':    ('managers',),
            'update': ('managers', 'owners',),
            'delete': ('managers', 'owners'),
    }
    CLASSIFIERS_PERMISSIONS = {
            'read':   ('managers', 'users', 'guests'),
            'add':    ('managers',),
            'update': ('managers', 'owners',),
            'delete': ('managers', 'owners'),
    }

    from cubicweb_folder.schema import Folder
    from cubicweb_file.schema import File
    from cubicweb_comment.schema import Comment
    from cubicweb_person.schema import Person
    from cubicweb_tag.schema import Tag

    Folder.__permissions__ = VISIBILITY_PERMISSIONS
    File.__permissions__ = VISIBILITY_PERMISSIONS
    Comment.__permissions__ = VISIBILITY_PERMISSIONS.copy()
    Comment.__permissions__['add'] = ('managers', 'users',)
    Person.__permissions__ = AUTH_ONLY_PERMISSIONS
    Tag.__permissions__ = CLASSIFIERS_PERMISSIONS

What's important in there:

* `VISIBILITY_PERMISSIONS` provides read access to managers group, if
  `visibility` attribute's value is 'public', or if user (designed by the 'U'
  variable in the expression) is linked to the entity (the 'X' variable) through
  the `may_be_read_by` permission

* we modify permissions of the entity types we use by importing them and
  modifying their `__permissions__` attribute

* notice the `.copy()`: we only want to modify 'add' permission for `Comment`,
  not for all entity types using `VISIBILITY_PERMISSIONS`!

* the remaining part of the security model is done using regular groups:

  - `users` is the group to which all authenticated users will belong
  - `guests` is the group of anonymous users


.. _adv_tuto_security_propagation:

Step 2: security propagation in hooks
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To fullfill the requirements defined earlier, we have to implement:

  Also, unless explicity specified, visibility of an image should be the same as
  its parent folder, as well as visibility of a comment should be the same as the
  commented entity.

This kind of `active` rule will be done using CubicWeb's hook
system. Hooks are triggered on database events such as addition of a new
entity or relation.

The tricky part of the requirement is in *unless explicitly specified*, notably
because when the entity is added, we don't know yet its 'parent'
entity (e.g. Folder of an File, File commented by a Comment). To handle such things,
CubicWeb provides `Operation`, which allow to schedule things to do at commit time.

In our case we will:

* on entity creation, schedule an operation that will set default visibility

* when a `parent` relation is added, propagate parent's visibility unless the
  child already has a visibility set

Here is the code in cube's :file:`hooks.py`:

.. sourcecode:: python

    from cubicweb.predicates import is_instance
    from cubicweb.server import hook


    class SetVisibilityOp(hook.DataOperationMixIn, hook.Operation):

        def precommit_event(self):
            for eid in self.get_data():
                entity = self.cnx.entity_from_eid(eid)

                if entity.visibility == 'parent':
                    entity.cw_set(visibility=u'authenticated')


    class SetVisibilityHook(hook.Hook):
        __regid__ = 'sytweb.setvisibility'
        __select__ = hook.Hook.__select__ & is_instance('Folder', 'File', 'Comment')
        events = ('after_add_entity',)

        def __call__(self):
            SetVisibilityOp.get_instance(self._cw).add_data(self.entity.eid)


    class SetParentVisibilityHook(hook.Hook):
        __regid__ = 'sytweb.setparentvisibility'
        __select__ = hook.Hook.__select__ & hook.match_rtype('filed_under', 'comments')
        events = ('after_add_relation',)

        def __call__(self):
            parent = self._cw.entity_from_eid(self.eidto)
            child = self._cw.entity_from_eid(self.eidfrom)

            if child.visibility == 'parent':
                child.cw_set(visibility=parent.visibility)

Notice:

* hooks are application objects, hence have selectors that should match entity or
  relation types to which the hook applies. To match a relation type, we use the
  hook specific `match_rtype` selector.

* usage of `DataOperationMixIn`: instead of adding an operation for each added entity,
  `DataOperationMixIn` allows to create a single one and to store entity's eids to be
  processed in the transaction data. This is a good pratice to avoid heavy
  operations manipulation cost when creating a lot of entities in the same
  transaction.

* the `precommit_event` method of the operation will be called at transaction's
  commit time.

* in a hook, `self._cw` is the repository session, not a web request as usually
  in views

* according to hook's event, you have access to different attributes on the hook
  instance. Here:

  - `self.entity` is the newly added entity on 'after_add_entity' events

  - `self.eidfrom` / `self.eidto` are the eid of the subject / object entity on
    'after_add_relation' events (you may also get the relation type using
    `self.rtype`)

The `parent` visibility value is used to tell "propagate using parent security"
because we want that attribute to be required, so we can't use `None` value else
we'll get an error before we get any chance to propagate...

Now, we also want to propagate the `may_be_read_by` relation. Fortunately,
CubicWeb provides some base hook classes for such things, so we only have to add
the following code to :file:`hooks.py`:

.. sourcecode:: python

    # relations where the "parent" entity is the subject
    S_RELS = set()
    # relations where the "parent" entity is the object
    O_RELS = set(('filed_under', 'comments',))


    class AddEntitySecurityPropagationHook(hook.PropagateRelationHook):
        """propagate permissions when new entity are added"""
        __regid__ = 'sytweb.addentity_security_propagation'
        __select__ = (hook.PropagateRelationHook.__select__
                      & hook.match_rtype_sets(S_RELS, O_RELS))
        main_rtype = 'may_be_read_by'
        subject_relations = S_RELS
        object_relations = O_RELS


    class AddPermissionSecurityPropagationHook(hook.PropagateRelationAddHook):
        """propagate permissions when new entity are added"""
        __regid__ = 'sytweb.addperm_security_propagation'
        __select__ = (hook.PropagateRelationAddHook.__select__
                      & hook.match_rtype('may_be_read_by',))
        subject_relations = S_RELS
        object_relations = O_RELS


    class DelPermissionSecurityPropagationHook(hook.PropagateRelationDelHook):
        __regid__ = 'sytweb.delperm_security_propagation'
        __select__ = (hook.PropagateRelationDelHook.__select__
                      & hook.match_rtype('may_be_read_by',))
        subject_relations = S_RELS
        object_relations = O_RELS

* the `AddEntitySecurityPropagationHook` will propagate the relation
  when `filed_under` or `comments` relations are added

  - the `S_RELS` and `O_RELS` set as well as the `match_rtype_sets` selector are
    used here so that if my cube is used by another one, it'll be able to
    configure security propagation by simply adding relation to one of the two
    sets.

* the two others will propagate permissions changes on parent entities to
  children entities


.. _adv_tuto_tesing_security:

Step 3: testing our security
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Security is tricky. Writing some tests for it is a very good idea. You should
even write them first, as Test Driven Development recommends!

Here is a small test case that will check the basis of our security
model, in :file:`test/test_sytweb.py`:

.. sourcecode:: python

    from cubicweb.devtools import testlib
    from cubicweb import Binary


    class SecurityTC(testlib.CubicWebTC):

        def test_visibility_propagation(self):
            with self.admin_access.repo_cnx() as cnx:
                # create a user for later security checks
                toto = self.create_user(cnx, 'toto')

                cnx.commit()

                # init some data using the default manager connection
                folder = cnx.create_entity('Folder',
                                           name=u'restricted',
                                           visibility=u'restricted')
                photo1 = cnx.create_entity('File',
                                           data_name=u'photo1.jpg',
                                           data=Binary(b'xxx'),
                                           filed_under=folder)

                cnx.commit()

                # visibility propagation
                self.assertEquals(photo1.visibility, 'restricted')

                # unless explicitly specified
                photo2 = cnx.create_entity('File',
                                           data_name=u'photo2.jpg',
                                           data=Binary(b'xxx'),
                                           visibility=u'public',
                                           filed_under=folder)

                cnx.commit()

                self.assertEquals(photo2.visibility, 'public')

            with self.new_access('toto').repo_cnx() as cnx:
                # test security
                self.assertEqual(1, len(cnx.execute('File X'))) # only the public one
                self.assertEqual(0, len(cnx.execute('Folder X'))) # restricted...

            with self.admin_access.repo_cnx() as cnx:
                # may_be_read_by propagation
                folder = cnx.entity_from_eid(folder.eid)
                folder.cw_set(may_be_read_by=toto)

                cnx.commit()

            with self.new_access('toto').repo_cnx() as cnx:
                photo1 = cnx.entity_from_eid(photo1.eid)

                self.failUnless(photo1.may_be_read_by)

                # test security with permissions
                self.assertEquals(2, len(cnx.execute('File X'))) # now toto has access to photo2
                self.assertEquals(1, len(cnx.execute('Folder X'))) # and to restricted folder


    if __name__ == '__main__':
        from unittest import main
        main()

It's not complete, but shows most things you'll want to do in tests: adding some
content, creating users and connecting as them in the test, etc...

To run it type:

.. sourcecode:: bash

    $ python3 test/test_sytweb.py
    ======================================================================
    -> creating tables [====================]
    -> inserting default user and default groups.
    -> storing the schema in the database [====================]
    -> database for instance data initialized.
    .
    ----------------------------------------------------------------------
    Ran 1 test in 22.547s

    OK


The first execution is taking time, since it creates a sqlite database for the
test instance. The second one will be much quicker:

.. sourcecode:: bash

    $ python3 test/test_sytweb.py
    ======================================================================
    .
    ----------------------------------------------------------------------
    Ran 1 test in 2.662s

    OK

If you do some changes in your schema, you'll have to force regeneration of that
database. You do that by removing the tmpdb files before running the test: ::

    $ rm data/database/tmpdb*


.. _adv_tuto_migration_script:

Step 4: writing the migration script and migrating the instance
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Prior to those changes, I created an instance, fed it with some data, so I
don't want to create a new one, but to migrate the existing one. Let's see how to
do that.

Migration commands should be put in the cube's :file:`migration` directory, in a
file named :file:`<X.Y.Z>_Any.py` ('Any' being there mostly for historical
reasons and '<X.Y.Z>' being the version number of the cube we are going to release.)

Here I'll create a :file:`migration/0.2.0_Any.py` file containing the following
instructions:

.. sourcecode:: python

  add_relation_type('may_be_read_by')
  add_relation_type('visibility')
  sync_schema_props_perms()

Then I update the version number in the cube's :file:`__pkginfo__.py` to 0.2.0. And
that's it! Those instructions will:

* update the instance's schema by adding our two new relations and update the
  underlying database tables accordingly (the first two instructions)

* update schema's permissions definition (the last instruction)


To migrate my instance I simply type::

   cubicweb-ctl upgrade sytweb_instance

You'll then be asked some questions to do the migration step by step. You should say
YES when it asks if a backup of your database should be done, so you can get back
to initial state if anything goes wrong...