12 files changed, 541 insertions, 12 deletions

diff --git a/src/mailman/docs/NEWS.rst b/src/mailman/docs/NEWS.rst
index 3c175d0ed..a81bff574 100644
--- a/src/mailman/docs/NEWS.rst
+++ b/src/mailman/docs/NEWS.rst
@@ -38,6 +38,10 @@ Architecture
 
 REST
 ----
+ * Preferences for addresses, users, and members can be accessed, changed, and
+   deleted through the REST interface.  Hierarchical, combined preferences for
+   members, and system preferences can be read through the REST interface.
+   (LP: #821438)
  * The IMailingList attribute ``host_name`` has been renamed to ``mail_host``
    for consistency.  This changes the REST API for mailing list
    resources. (LP: #787599)
diff --git a/src/mailman/interfaces/mailinglist.py b/src/mailman/interfaces/mailinglist.py
index 9ae779409..c08e257c1 100644
--- a/src/mailman/interfaces/mailinglist.py
+++ b/src/mailman/interfaces/mailinglist.py
@@ -32,6 +32,8 @@ __all__ = [
 from flufl.enum import Enum
 from zope.interface import Interface, Attribute
 
+from mailman.interfaces.member import MemberRole
+
 
 
 class Personalization(Enum):
@@ -232,7 +234,7 @@ class IMailingList(Interface):
         :rtype: Roster
         """
 
-    def subscribe(subscriber, role):
+    def subscribe(subscriber, role=MemberRole.member):
         """Subscribe the given address or user to the mailing list.
 
         :param subscriber: The address or user to subscribe to the mailing
diff --git a/src/mailman/interfaces/member.py b/src/mailman/interfaces/member.py
index 0a8a5cfd5..5073b3059 100644
--- a/src/mailman/interfaces/member.py
+++ b/src/mailman/interfaces/member.py
@@ -184,7 +184,7 @@ class IMember(Interface):
     receive_list_copy = Attribute(
         """Should an explicit recipient receive a list copy?
 
-        Unlike going through the preferences, this attribute return the
+        Unlike going through `preferences`, this attribute returns the
         preference value based on the following lookup order:
 
         1. The member
@@ -196,7 +196,7 @@ class IMember(Interface):
     receive_own_postings = Attribute(
         """Should the poster get a list copy of their own messages?
 
-        Unlike going through the preferences, this attribute return the
+        Unlike going through `preferences`, this attribute returns the
         preference value based on the following lookup order:
 
         1. The member
@@ -208,7 +208,7 @@ class IMember(Interface):
     delivery_mode = Attribute(
         """The preferred delivery mode.
 
-        Unlike going through the preferences, this attribute return the
+        Unlike going through `preferences`, this attribute returns the
         preference value based on the following lookup order:
 
         1. The member
@@ -220,7 +220,7 @@ class IMember(Interface):
     delivery_status = Attribute(
         """The delivery status.
 
-        Unlike going through the preferences, this attribute return the
+        Unlike going through `preferences`, this attribute returns the
         preference value based on the following lookup order:
 
         1. The member
diff --git a/src/mailman/rest/addresses.py b/src/mailman/rest/addresses.py
index a97043e9c..5d479d9cb 100644
--- a/src/mailman/rest/addresses.py
+++ b/src/mailman/rest/addresses.py
@@ -33,6 +33,7 @@ from zope.component import getUtility
 
 from mailman.rest.helpers import CollectionMixin, etag, path_to
 from mailman.rest.members import MemberCollection
+from mailman.rest.preferences import Preferences
 from mailman.interfaces.usermanager import IUserManager
 
 
@@ -102,6 +103,18 @@ class AnAddress(_AddressBase):
             return http.not_found()
         return AddressMemberships(self._address)
 
+    @resource.child()
+    def preferences(self, request, segments):
+        """/addresses/<email>/preferences"""
+        if len(segments) != 0:
+            return http.bad_request()
+        if self._address is None:
+            return http.not_found()
+        child = Preferences(
+            self._address.preferences,
+            'addresses/{0}'.format(self._address.email))
+        return child, []
+
 
 
 class UserAddresses(_AddressBase):
diff --git a/src/mailman/rest/docs/preferences.rst b/src/mailman/rest/docs/preferences.rst
new file mode 100644
index 000000000..e82fd6001
--- /dev/null
+++ b/src/mailman/rest/docs/preferences.rst
@@ -0,0 +1,233 @@
+===========
+Preferences
+===========
+
+Addresses have preferences.
+::
+
+    >>> from mailman.interfaces.usermanager import IUserManager
+    >>> from zope.component import getUtility
+    >>> user_manager = getUtility(IUserManager)
+
+    >>> anne = user_manager.create_address('anne@example.com')
+    >>> transaction.commit()
+
+Although to start with, an address has no preferences.
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/anne@example.com'
+    ...           '/preferences')
+    http_etag: "..."
+    self_link: http://localhost:9001/3.0/addresses/anne@example.com/preferences
+
+Once the address is given some preferences, they are available through the
+REST API.
+
+    >>> anne.preferences.acknowledge_posts = True
+    >>> transaction.commit()
+    >>> dump_json('http://localhost:9001/3.0/addresses/anne@example.com'
+    ...           '/preferences')
+    acknowledge_posts: True
+    http_etag: "..."
+    self_link: http://localhost:9001/3.0/addresses/anne@example.com/preferences
+
+Similarly, users have their own set of preferences, which also start out empty.
+::
+
+    >>> bart = user_manager.create_user('bart@example.com')
+    >>> transaction.commit()
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/bart@example.com'
+    ...           '/preferences')
+    http_etag: "..."
+    self_link: http://localhost:9001/3.0/addresses/bart@example.com/preferences
+
+Setting a preference on the user's address does not set them on the user.
+::
+
+    >>> list(bart.addresses)[0].preferences.acknowledge_posts = True
+    >>> transaction.commit()
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/bart@example.com'
+    ...           '/preferences')
+    acknowledge_posts: True
+    http_etag: "..."
+    self_link: http://localhost:9001/3.0/addresses/bart@example.com/preferences
+
+    >>> dump_json('http://localhost:9001/3.0/users/1/preferences')
+    http_etag: "..."
+    self_link: http://localhost:9001/3.0/users/1/preferences
+
+Users have their own set of preferences.
+
+    >>> bart.preferences.receive_own_postings = False
+    >>> transaction.commit()
+    >>> dump_json('http://localhost:9001/3.0/users/1/preferences')
+    http_etag: "..."
+    receive_own_postings: False
+    self_link: http://localhost:9001/3.0/users/1/preferences
+
+Similarly, members have their own separate set of preferences, and just like
+the above, setting a preference on the member's address or user does not set
+the preference on the member.
+::
+
+    >>> from mailman.interfaces.member import MemberRole
+    >>> mlist = create_list('test@example.com')
+    >>> bart_member = mlist.subscribe(list(bart.addresses)[0])
+    >>> bart_member.preferences.receive_list_copy = False
+    >>> transaction.commit()
+    >>> dump_json('http://localhost:9001/3.0/members/1/preferences')
+    http_etag: "..."
+    receive_list_copy: False
+    self_link: http://localhost:9001/3.0/members/1/preferences
+
+
+Changing preferences
+====================
+
+Preferences for the address, user, or member can be changed through the API.
+You can change all the preferences for a particular object by using an HTTP
+PUT operation.
+::
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/bart@example.com'
+    ...           '/preferences', {
+    ...           'acknowledge_posts': True,
+    ...           'delivery_mode': 'plaintext_digests',
+    ...           'delivery_status': 'by_user',
+    ...           'preferred_language': 'ja',
+    ...           'receive_list_copy': True,
+    ...           'receive_own_postings': False,
+    ...           }, method='PUT')
+    content-length: 0
+    date: ...
+    server: ...
+    status: 204
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/bart@example.com'
+    ...           '/preferences')
+    acknowledge_posts: True
+    delivery_mode: plaintext_digests
+    delivery_status: by_user
+    http_etag: "..."
+    preferred_language: ja
+    receive_list_copy: True
+    receive_own_postings: False
+    self_link: http://localhost:9001/3.0/addresses/bart@example.com/preferences
+
+You can also update just a few of the attributes using PATCH.
+::
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/bart@example.com'
+    ...           '/preferences', {
+    ...           'delivery_mode': 'plaintext_digests',
+    ...           'receive_list_copy': False,
+    ...           }, method='PATCH')
+    content-length: 0
+    date: ...
+    server: ...
+    status: 204
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/bart@example.com'
+    ...           '/preferences')
+    acknowledge_posts: True
+    delivery_mode: plaintext_digests
+    delivery_status: by_user
+    http_etag: "..."
+    preferred_language: ja
+    receive_list_copy: False
+    receive_own_postings: False
+    self_link: http://localhost:9001/3.0/addresses/bart@example.com/preferences
+
+
+Deleting preferences
+====================
+
+Preferences for any of the levels, member, user, or address, can be entirely
+deleted.
+::
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/anne@example.com'
+    ...           '/preferences', {
+    ...           'preferred_language': 'ja',
+    ...           }, method='PATCH')
+    content-length: 0
+    date: ...
+    server: ...
+    status: 204
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/anne@example.com'
+    ...           '/preferences')
+    acknowledge_posts: True
+    http_etag: "5219245d1eea98bc107032013af20ef91bfb5c51"
+    preferred_language: ja
+    self_link: http://localhost:9001/3.0/addresses/anne@example.com/preferences
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/anne@example.com'
+    ...           '/preferences', method='DELETE')
+    content-length: 0
+    date: ...
+    server: ...
+    status: 204
+
+    >>> dump_json('http://localhost:9001/3.0/addresses/anne@example.com'
+    ...           '/preferences')
+    http_etag: "..."
+    self_link: http://localhost:9001/3.0/addresses/anne@example.com/preferences
+
+
+Combined member preferences
+===========================
+
+The member resource provides a way to access the set of preference in effect
+for a specific subscription.  This stacks the preferences, so that a value is
+always available.  The preference value is looked up first on the member,
+falling back to the address, then user, then system preference.
+
+Preferences accessed through this interface are always read only.
+
+    >>> dump_json('http://localhost:9001/3.0/members/1/all/preferences')
+    acknowledge_posts: True
+    delivery_mode: plaintext_digests
+    delivery_status: by_user
+    http_etag: "..."
+    preferred_language: ja
+    receive_list_copy: False
+    receive_own_postings: False
+    self_link: http://localhost:9001/3.0/members/1/all/preferences
+
+These preferences cannot be changed.
+
+    >>> dump_json('http://localhost:9001/3.0/members/1/all/preferences', {
+    ...           'delivery_status': 'enabled',
+    ...           }, method='PATCH')
+    Traceback (most recent call last):
+    ...
+    HTTPError: HTTP Error 405: 405 Method Not Allowed
+
+
+System preferences
+==================
+
+The Mailman system itself has a default set of preference.  All preference
+lookups fall back to these values, which are read-only.
+
+    >>> dump_json('http://localhost:9001/3.0/system/preferences')
+    acknowledge_posts: False
+    delivery_mode: regular
+    delivery_status: enabled
+    hide_address: True
+    http_etag: "..."
+    preferred_language: en
+    receive_list_copy: True
+    receive_own_postings: True
+    self_link: http://localhost:9001/3.0/system/preferences
+
+These preferences cannot be changed.
+
+    >>> dump_json('http://localhost:9001/3.0/system/preferences', {
+    ...           'delivery_status': 'enabled',
+    ...           }, method='PATCH')
+    Traceback (most recent call last):
+    ...
+    HTTPError: HTTP Error 405: 405 Method Not Allowed
diff --git a/src/mailman/rest/members.py b/src/mailman/rest/members.py
index f15a2204a..bf739ed32 100644
--- a/src/mailman/rest/members.py
+++ b/src/mailman/rest/members.py
@@ -44,6 +44,7 @@ from mailman.interfaces.user import UnverifiedAddressError
 from mailman.interfaces.usermanager import IUserManager
 from mailman.rest.helpers import (
     CollectionMixin, PATCH, etag, no_content, path_to)
+from mailman.rest.preferences import Preferences, ReadOnlyPreferences
 from mailman.rest.validator import (
     Validator, enum_validator, subscriber_validator)
 
@@ -115,6 +116,30 @@ class AMember(_MemberBase):
             return http.not_found()
         return http.ok([], self._resource_as_json(self._member))
 
+    @resource.child()
+    def preferences(self, request, segments):
+        """/members/<id>/preferences"""
+        if len(segments) != 0:
+            return http.bad_request()
+        if self._member is None:
+            return http.not_found()
+        child = Preferences(
+            self._member.preferences,
+            'members/{0}'.format(self._member.member_id.int))
+        return child, []
+
+    @resource.child()
+    def all(self, request, segments):
+        """/members/<id>/all/preferences"""
+        if len(segments) == 0:
+            return http.not_found()
+        if self._member is None:
+            return http.not_found()
+        child = ReadOnlyPreferences(
+            self._member,
+            'members/{0}/all'.format(self._member.member_id.int))
+        return child, []
+
     @resource.DELETE()
     def delete(self, request):
         """Delete the member (i.e. unsubscribe)."""
diff --git a/src/mailman/rest/preferences.py b/src/mailman/rest/preferences.py
new file mode 100644
index 000000000..d231d1055
--- /dev/null
+++ b/src/mailman/rest/preferences.py
@@ -0,0 +1,119 @@
+# Copyright (C) 2011 by the Free Software Foundation, Inc.
+#
+# This file is part of GNU Mailman.
+#
+# GNU Mailman 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.
+#
+# GNU Mailman 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
+# GNU Mailman.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Preferences."""
+
+from __future__ import absolute_import, unicode_literals
+
+__metaclass__ = type
+__all__ = [
+    'ReadOnlyPreferences',
+    'Preferences',
+    ]
+
+
+from lazr.config import as_boolean
+from restish import http, resource
+
+from mailman.interfaces.member import DeliveryMode, DeliveryStatus
+from mailman.rest.helpers import PATCH, etag, no_content, path_to
+from mailman.rest.validator import (
+    Validator, enum_validator, language_validator)
+
+
+PREFERENCES = (
+    'acknowledge_posts',
+    'delivery_mode',
+    'delivery_status',
+    'hide_address',
+    'preferred_language',
+    'receive_list_copy',
+    'receive_own_postings',
+    )
+
+
+
+class ReadOnlyPreferences(resource.Resource):
+    """.../<object>/preferences"""
+
+    def __init__(self, parent, base_url):
+        self._parent = parent
+        self._base_url = base_url
+
+    @resource.GET()
+    def preferences(self, segments):
+        resource = dict()
+        for attr in PREFERENCES:
+            # Handle this one specially.
+            if attr == 'preferred_language':
+                continue
+            value = getattr(self._parent, attr, None)
+            if value is not None:
+                resource[attr] = value
+        # Add the preferred language, if it's not missing.
+        preferred_language = self._parent.preferred_language
+        if preferred_language is not None:
+            resource['preferred_language'] = preferred_language.code
+        # Add the self link.
+        resource['self_link'] = path_to(
+            '{0}/preferences'.format(self._base_url))
+        return http.ok([], etag(resource))
+    
+
+
+class Preferences(ReadOnlyPreferences):
+    """Preferences which can be changed."""
+
+    def patch_put(self, request, is_optional):
+        if self._parent is None:
+            return http.not_found()
+        kws = dict(
+            acknowledge_posts=as_boolean,
+            delivery_mode=enum_validator(DeliveryMode),
+            delivery_status=enum_validator(DeliveryStatus),
+            preferred_language=language_validator,
+            receive_list_copy=as_boolean,
+            receive_own_postings=as_boolean,
+            )
+        if is_optional:
+            # For a PUT, all attributes are optional.
+            kws['_optional'] = kws.keys()
+        try:
+            values = Validator(**kws)(request)
+        except ValueError as error:
+            return http.bad_request([], str(error))
+        for key, value in values.items():
+            setattr(self._parent, key, value)
+        return no_content()
+
+    @PATCH()
+    def patch_preferences(self, request):
+        """Patch the preferences."""
+        return self.patch_put(request, is_optional=True)
+
+    @resource.PUT()
+    def put_preferences(self, request):
+        """Change all preferences."""
+        return self.patch_put(request, is_optional=False)
+
+    @resource.DELETE()
+    def delete_preferences(self, request):
+        """Delete all preferences."""
+        for attr in PREFERENCES:
+            if hasattr(self._parent, attr):
+                setattr(self._parent, attr, None)
+        return no_content()
diff --git a/src/mailman/rest/root.py b/src/mailman/rest/root.py
index dc9717de4..9ba6ad20d 100644
--- a/src/mailman/rest/root.py
+++ b/src/mailman/rest/root.py
@@ -29,12 +29,14 @@ from base64 import b64decode
 from restish import guard, http, resource
 
 from mailman.config import config
+from mailman.core.constants import system_preferences
 from mailman.core.system import system
 from mailman.rest.addresses import AllAddresses, AnAddress
 from mailman.rest.domains import ADomain, AllDomains
 from mailman.rest.helpers import etag, path_to
 from mailman.rest.lists import AList, AllLists
 from mailman.rest.members import AMember, AllMembers, FindMembers
+from mailman.rest.preferences import ReadOnlyPreferences
 from mailman.rest.users import AUser, AllUsers
 
 
@@ -73,11 +75,18 @@ class TopLevel(resource.Resource):
     @resource.child()
     def system(self, request, segments):
         """/<api>/system"""
-        resource = dict(
-            mailman_version=system.mailman_version,
-            python_version=system.python_version,
-            self_link=path_to('system'),
-            )
+        if len(segments) == 0:
+            resource = dict(
+                mailman_version=system.mailman_version,
+                python_version=system.python_version,
+                self_link=path_to('system'),
+                )
+        elif len(segments) > 1:
+            return http.bad_request()
+        elif segments[0] == 'preferences':
+            return ReadOnlyPreferences(system_preferences, 'system'), []
+        else:
+            return http.bad_request()
         return http.ok([], etag(resource))
 
     @resource.child()
diff --git a/src/mailman/rest/tests/test_membership.py b/src/mailman/rest/tests/test_membership.py
index 2d2351fca..ea3357506 100644
--- a/src/mailman/rest/tests/test_membership.py
+++ b/src/mailman/rest/tests/test_membership.py
@@ -229,6 +229,17 @@ class TestMembership(unittest.TestCase):
         else:
             raise AssertionError('Expected HTTPError')
 
+    def test_member_all_without_preferences(self):
+        # /members/<id>/all should return a 404 when it isn't trailed by
+        # `preferences`
+        try:
+            # For Python 2.6
+            call_api('http://localhost:9001/3.0/members/1/all')
+        except HTTPError as exc:
+            self.assertEqual(exc.code, 404)
+        else:
+            raise AssertionError('Expected HTTPError')
+
 
 
 def test_suite():
diff --git a/src/mailman/rest/tests/test_root.py b/src/mailman/rest/tests/test_root.py
new file mode 100644
index 000000000..856767947
--- /dev/null
+++ b/src/mailman/rest/tests/test_root.py
@@ -0,0 +1,93 @@
+# Copyright (C) 2011 by the Free Software Foundation, Inc.
+#
+# This file is part of GNU Mailman.
+#
+# GNU Mailman 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.
+#
+# GNU Mailman 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
+# GNU Mailman.  If not, see <http://www.gnu.org/licenses/>.
+
+"""REST root object tests."""
+
+from __future__ import absolute_import, unicode_literals
+
+__metaclass__ = type
+__all__ = [
+    'test_suite',
+    ]
+
+
+import unittest
+
+from urllib2 import HTTPError
+
+from mailman.testing.helpers import call_api
+from mailman.testing.layers import RESTLayer
+
+
+
+class TestSystem(unittest.TestCase):
+    layer = RESTLayer
+
+    def test_system_url_too_long(self):
+        # /system/foo/bar is not allowed.
+        try:
+            # For Python 2.6.
+            call_api('http://localhost:9001/3.0/system/foo/bar')
+        except HTTPError as exc:
+            self.assertEqual(exc.code, 400)
+        else:
+            raise AssertionError('Expected HTTPError')
+
+    def test_system_url_not_preferences(self):
+        # /system/foo where `foo` is not `preferences`.
+        try:
+            # For Python 2.6.
+            call_api('http://localhost:9001/3.0/system/foo')
+        except HTTPError as exc:
+            self.assertEqual(exc.code, 400)
+        else:
+            raise AssertionError('Expected HTTPError')
+
+    def test_system_preferences_are_read_only(self):
+        # /system/preferences are read-only.
+        try:
+            # For Python 2.6.
+            call_api('http://localhost:9001/3.0/system/preferences', {
+                     'acknowledge_posts': True,
+                     }, method='PATCH')
+        except HTTPError as exc:
+            self.assertEqual(exc.code, 405)
+        else:
+            raise AssertionError('Expected HTTPError')
+        # /system/preferences are read-only.
+        try:
+            # For Python 2.6.
+            call_api('http://localhost:9001/3.0/system/preferences', {
+                'acknowledge_posts': False,
+                'delivery_mode': 'regular',
+                'delivery_status': 'enabled',
+                'hide_address': True,
+                'preferred_language': 'en',
+                'receive_list_copy': True,
+                'receive_own_postings': True,
+                }, method='PUT')
+        except HTTPError as exc:
+            self.assertEqual(exc.code, 405)
+        else:
+            raise AssertionError('Expected HTTPError')
+
+
+
+def test_suite():
+    suite = unittest.TestSuite()
+    suite.addTest(unittest.makeSuite(TestSystem))
+    return suite
diff --git a/src/mailman/rest/users.py b/src/mailman/rest/users.py
index 3fdf5d7e8..857d29471 100644
--- a/src/mailman/rest/users.py
+++ b/src/mailman/rest/users.py
@@ -34,6 +34,7 @@ from mailman.interfaces.address import ExistingAddressError
 from mailman.interfaces.usermanager import IUserManager
 from mailman.rest.addresses import UserAddresses
 from mailman.rest.helpers import CollectionMixin, etag, no_content, path_to
+from mailman.rest.preferences import Preferences
 from mailman.rest.validator import Validator
 from mailman.utilities.passwords import (
     encrypt_password, make_user_friendly_password)
@@ -152,3 +153,15 @@ class AUser(_UserBase):
             return http.not_found()
         getUtility(IUserManager).delete_user(self._user)
         return no_content()
+
+    @resource.child()
+    def preferences(self, request, segments):
+        """/addresses/<email>/preferences"""
+        if len(segments) != 0:
+            return http.bad_request()
+        if self._user is None:
+            return http.not_found()
+        child = Preferences(
+            self._user.preferences,
+            'users/{0}'.format(self._user.user_id.int))
+        return child, []
diff --git a/src/mailman/rest/validator.py b/src/mailman/rest/validator.py
index cf32ca838..60d8a22d6 100644
--- a/src/mailman/rest/validator.py
+++ b/src/mailman/rest/validator.py
@@ -23,11 +23,15 @@ __metaclass__ = type
 __all__ = [
     'Validator',
     'enum_validator',
+    'language_validator',
     'subscriber_validator',
     ]
 
 
 from uuid import UUID
+from zope.component import getUtility
+
+from mailman.interfaces.languages import ILanguageManager
 
 
 COMMASPACE = ', '
@@ -46,8 +50,6 @@ class enum_validator:
         return self._enum_class[enum_value]
 
 
-
-    
 def subscriber_validator(subscriber):
     """Convert an email-or-int to an email-or-UUID."""
     try:
@@ -56,6 +58,11 @@ def subscriber_validator(subscriber):
         return subscriber
 
 
+def language_validator(code):
+    """Convert a language code to a Language object."""
+    return getUtility(ILanguageManager)[code]
+
+
 
 class Validator:
     """A validator of parameter input."""