Merge remote-tracking branch 'origin/release-2-3' into 487-internal-content

core/fields.py

+# DEPRECATED CODE - DO NOT USE!
+
 from django import forms
 from features.gestalten import models as entities_models
 import functools
@@ -81,7 +83,7 @@ class EmailGestalt(Email):
     has_data = True
 
     def get_data(self, form_data):
-        return entities_models.Gestalt.get_or_create(form_data)
+        return entities_models.Gestalt.objects.get_or_create_by_email(form_data)
 
 
 email_gestalt = functools.partial(fieldclass_factory, EmailGestalt)
@@ -108,7 +110,7 @@ class CurrentGestalt(Field):
         if self.view.request.user.is_authenticated:
             return self.view.request.user.gestalt
         elif not self.null:
-            return entities_models.Gestalt.get_or_create(form_data)
+            return entities_models.Gestalt.objects.get_or_create_by_email(form_data)
         else:
             return None
 

core/migrations/0002_auto_20180607_1128.py

+# Generated by Django 2.0.5 on 2018-06-07 09:28
+
+import core.models
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='permissiontoken',
+            name='secret_key',
+            field=models.CharField(default=core.models.generate_token, max_length=15, unique=True),
+        ),
+    ]

core/models.py

@@ -91,8 +91,8 @@ class PermissionToken(models.Model):
     authenticated user is really allowed to access the given resource.
     """
     gestalt = models.ForeignKey('gestalten.Gestalt', on_delete=models.CASCADE)
-    # FIXME: secret_key should be unique
-    secret_key = models.CharField(max_length=PERMISSION_TOKEN_LENGTH, default=generate_token)
+    secret_key = models.CharField(
+            max_length=PERMISSION_TOKEN_LENGTH, default=generate_token, unique=True)
     time_created = models.DateTimeField(auto_now_add=True)
     # Every feature (e.g. the calendar) defines its own unique string describing its permission
     # token (e.g. "calendar-read").

debian/control

@@ -10,8 +10,8 @@ Package: stadtgestalten
 Architecture: all
 # python3-requests: for django-allauth
 # python3-six: for django-mailbox
-Depends: python3-pil, python3-requests, python3-six, ${misc:Depends},
- ${python3:Depends}, moreutils, python3-xapian
+Depends: python3-html2text, python3-pil, python3-requests, python3-six,
+ python3-xapian ${misc:Depends}, ${python3:Depends}, moreutils
 Recommends: ghostscript, python3-psycopg2, uwsgi, uwsgi-plugin-python3,
  uwsgi-plugin-router-access, ${misc:Recommends}
 Suggests: sqlite3, postgresql-client-common

debian/stadtgestalten.cron.d

-# optional:
-#    MAILTO=admin@example.org
-
 # process incoming mails
+# The LMTP daemon (since grouprise 2.3) is supposed to handle incoming mail in the future.
+# This requires changes of the SMTP server setup. We will start with single recipient groups, until
+# all traffic is handled by LMTP.
 */3 * * * * root        chronic sh -c 'stadtctl getmail 2>&1 | grep -vE "^(INFO:|WARNING:django_mailbox.models:.*content-transfer-encoding)"'
 
 # calculate scores for groups and users

features/content/models.py

@@ -14,7 +14,8 @@ class Content(core.models.Model):
 
     # FIXME: remove when django bug #28988 is fixed
     poll = models.OneToOneField(
-            'polls.WorkaroundPoll', null=True, blank=True, related_name='content')
+            'polls.WorkaroundPoll', null=True, blank=True, related_name='content',
+            on_delete=models.CASCADE)
 
     title = models.CharField(max_length=255)
     image = models.ForeignKey('images.Image', blank=True, null=True, on_delete=models.SET_NULL)

features/content/templates/content/contributed.txt

@@ -5,5 +5,5 @@ Beitrag mit Kommentaren online lesen und kommentieren:
 
 -- 
 {% if contribution %}Du erhältst diese Benachrichtigung, weil Du den Beitrag {{ object.container.subject }} kommentiert hast.
-{% url 'content-permalink' object.container.associations.first.pk as path %}{{ path|full_url }}#{% ref contribution %}{% elif subscription and membership %}Du erhältst diese Benachrichtigung, weil Du Mitglied der Gruppe {{ membership.group }} bist und die Gruppe abonniert hast.
-{{ subscription.subscribed_to.get_absolute_url|full_url }}{% endif %}
+{% url 'content-permalink' object.container.associations.first.pk as path %}{{ path|full_url }}#{% ref contribution %}{% elif subscription and membership %}Du erhältst diese Benachrichtigung, weil Du Mitglied der Gruppe '{{ membership.group }}' bist und die Gruppe abonniert hast. Zum Verlassen der Gruppe folge bitte diesem Verweis:
+{% if membership.member.can_login %}{% url 'resign' membership.group.pk as resign_url %}{% else %}{% url 'resign-request' membership.group.pk as resign_url %}{% endif %}{{ resign_url|full_url }}{% endif %}

features/content/templates/content/created.txt

 {% block content %}{% endblock %}
 {% block footer %}{% if subscription %}
 -- 
-Du erhältst diese Benachrichtigung, weil Du {% if membership %}Mitglied der Gruppe {{ membership.group }} bist und die Gruppe{% else %}die Gruppe {{ subscription.subscribed_to }}{% endif %} abonniert hast.
-{{ subscription.subscribed_to.get_absolute_url|full_url }}{% endif %}{% endblock %}
+Du erhältst diese Benachrichtigung, weil Du {% if membership %}Mitglied der Gruppe '{{ membership.group }}' bist und die Gruppe{% else %}die Gruppe '{{ subscription.subscribed_to }}'{% endif %} abonniert hast. Zum {% if membership %}Verlassen der Gruppe{% else %}Abbestellen der Benachrichtigungen{% endif %} folge bitte diesem Verweis:
+{% if membership %}{% if membership.member.can_login %}{% url 'resign' membership.group.pk as resign_url %}{% else %}{% url 'resign-request' membership.group.pk as resign_url %}{% endif %}{{ resign_url|full_url }}{% else %}{% if subscription.subscriber.can_login %}{% url 'group-unsubscribe' subscription.subscribed_to.pk as unsub_url %}{% else %}{% url 'group-unsubscribe-request' subscription.subscribed_to.pk as unsub_url %}{% endif %}{{ unsub_url|full_url }}{% endif %}{% endif %}{% endblock %}

features/contributions/migrations/0011_auto_20180529_1026.py

+# Generated by Django 2.0.5 on 2018-05-29 08:26
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('contributions', '0010_auto_20180123_1057'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='contribution',
+            name='attached_to',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='attachments', to='contributions.Contribution'),
+        ),
+    ]

features/contributions/signals.py

-import logging
-
-import django.conf
 import django.db.models.signals
-import django_mailbox.signals
-from django.conf import settings
-from django.db.models.functions import Lower
 from django.dispatch import receiver
 
-import core.models
-from features.associations import models as associations
-from features.content.models import Content
-from features.conversations import models as conversations
-from features.files import models as files
-from features.gestalten import models as gestalten
-from features.groups import models as groups
-from . import models, notifications
+from . import notifications
 
-logger = logging.getLogger(__name__)
 
 post_create = django.dispatch.Signal(providing_args=['instance'])
 
@@ -24,137 +10,3 @@ post_create = django.dispatch.Signal(providing_args=['instance'])
 @receiver(post_create)
 def contribution_created(sender, instance, **kwargs):
     notifications.ContributionCreated.send_all(instance)
-
-
-def get_sender(message):
-
-    try:
-        gestalt = gestalten.Gestalt.objects.annotate(email=Lower('user__email')).get(
-                email=message.from_address[0].lower())
-    except gestalten.Gestalt.DoesNotExist:
-        try:
-            gestalt = gestalten.Gestalt.objects.annotate(
-                    email=Lower('user__emailaddress__email')).get(
-                            email=message.from_address[0].lower())
-        except gestalten.Gestalt.DoesNotExist:
-            gestalt = None
-    return gestalt
-
-
-def is_autoresponse(msg):
-    email = msg.get_email_object()
-
-    # RFC 3834 (https://tools.ietf.org/html/rfc3834#section-5)
-    if email.get('Auto-Submitted') == 'no':
-        return False
-    elif email.get('Auto-Submitted'):
-        return True
-
-    # non-standard fields (https://tools.ietf.org/html/rfc3834#section-3.1.8)
-    if email.get('Precedence') == 'bulk':
-        return True
-    if email.get('X-AUTORESPONDER'):
-        return True
-
-    return False
-
-
-@receiver(django_mailbox.signals.message_received)
-def process_incoming_message(sender, message, **args):
-    token_beg = len(django.conf.settings.DEFAULT_REPLY_TO_EMAIL.split('{')[0])
-    token_end = len(django.conf.settings.DEFAULT_REPLY_TO_EMAIL.rsplit('}')[1])
-    DOMAIN = django.conf.settings.DEFAULT_REPLY_TO_EMAIL.split('@')[1]
-
-    def create_contribution(container, gestalt, message, in_reply_to=None):
-        text = message.text.strip()
-        if text == '':
-            text = message.html
-        t = models.Text.objects.create(text=text)
-        contribution = models.Contribution.objects.create(
-                author=gestalt,
-                container=container,
-                in_reply_to=in_reply_to,
-                contribution=t)
-        files.File.objects.create_from_message(message, attached_to=contribution)
-        return contribution
-
-    def process_reply(address):
-        token = address[token_beg:-token_end]
-        try:
-            in_reply_to_text = models.Contribution.objects.get_by_message_id(
-                    message.get_email_object().get('In-Reply-To'))
-        except models.Contribution.DoesNotExist:
-            in_reply_to_text = None
-        key = core.models.PermissionToken.objects.get(secret_key=token)
-        sender = get_sender(message)
-        if key.gestalt != sender:
-            raise django.core.exceptions.PermissionDenied(
-                    'Du darfst diese Benachrichtigung nicht unter dieser E-Mail-Adresse '
-                    'beantworten. Du hast folgende Möglichkeiten:\n'
-                    '* Melde Dich auf der Website an und beantworte die Nachricht dort.\n'
-                    '* Antworte unter der E-Mail-Adresse, an die die Benachrichtigung '
-                    'gesendet wurde.\n'
-                    '* Füge die E-Mail-Adresse, unter der Du antworten möchtest, Deinem '
-                    'Benutzerkonto hinzu.')
-        if type(key.target) == Content:
-            container = key.target
-        else:
-            container = key.target.container
-        contribution = create_contribution(
-                container, key.gestalt, message, in_reply_to=in_reply_to_text)
-        post_create.send(sender=None, instance=contribution)
-
-    def process_initial(address):
-        local, domain = address.split('@')
-        if domain != DOMAIN:
-            raise ValueError('Domain does not match.')
-        gestalt = get_sender(message)
-        group = groups.Group.objects.get(slug=local)
-        if gestalt and gestalt.user.has_perm(
-                'conversations.create_group_conversation_by_email', group):
-            conversation = conversations.Conversation.objects.create(subject=message.subject)
-            contribution = create_contribution(conversation, gestalt, message)
-            associations.Association.objects.create(
-                    entity_type=group.content_type, entity_id=group.id,
-                    container_type=conversation.content_type, container_id=conversation.id)
-            post_create.send(sender=None, instance=contribution)
-        else:
-            raise django.core.exceptions.PermissionDenied(
-                    'Du darfst mit dieser Gruppe kein Gespräch per E-Mail beginnen. Bitte '
-                    'verwende die Schaltfläche auf der Webseite.')
-
-    def process_message(address):
-        try:
-            process_reply(address)
-        except core.models.PermissionToken.DoesNotExist:
-            if address == settings.STADTGESTALTEN_BOT_EMAIL:
-                for to_address in message.to_addresses:
-                    process_initial(to_address)
-            else:
-                process_initial(address)
-
-    # FIXME: use X-Stadtgestalten-to header (mailbox without domain)
-    delivered_to = message.get_email_object()['Delivered-To']
-    if not delivered_to:
-        logger.error('Could not process message {}: no Delivered-To header'.format(message.id))
-        return
-    for address in [delivered_to]:
-        address = address.lstrip('<')
-        address = address.rstrip('>')
-        if not is_autoresponse(message):
-            try:
-                process_message(address)
-            except ValueError as e:
-                logger.error('Could not process receiver {} in message {}. {}'.format(
-                    address, message.id, e))
-            except (groups.Group.DoesNotExist, django.core.exceptions.PermissionDenied) as e:
-                logger.warning('Could not process receiver {} in message {}. {}'.format(
-                    address, message.id, e))
-                django.core.mail.send_mail(
-                        'Re: {}'.format(message.subject).replace('\n', ' ').replace('\r', ''),
-                        'Konnte die Nachricht nicht verarbeiten. {}'.format(e),
-                        from_email=django.conf.settings.DEFAULT_FROM_EMAIL,
-                        recipient_list=[message.from_header],
-                        fail_silently=True)
-        else:
-            logger.warning('Ignored message {} as autoresponse'.format(message.id))

features/contributions/tests.py

 import django
-from django.core import mail
 from django.urls import reverse
-from django_mailbox import models as mailbox_models, signals as mailbox_signals
 
 import features.articles.tests
-from core import tests
-from features.associations import models as associations
-from features.gestalten import tests as gestalten
-from features.memberships import test_mixins as memberships
 from . import models
 
 
@@ -23,70 +17,6 @@ class ContributionMixin(features.articles.tests.ArticleMixin):
         self.contribution = self.create_contribution()
 
 
-class ContentReplyByEmail(
-        memberships.AuthenticatedMemberMixin, tests.Test):
-    def test_content_reply_by_email(self):
-        # create article
-        self.client.post(
-                reverse('create-group-article', args=(self.group.slug,)),
-                {'title': 'Test', 'text': 'Test'})
-        a = self.assertExists(associations.Association, content__title='Test')
-        self.assertNotificationSent()
-        # generate reply message
-        reply_to = mail.outbox[0].extra_headers['Reply-To']
-        msg = mailbox_models.Message(
-                from_header=self.gestalt.user.email,
-                body='Delivered-To: {}\n\nText B'.format(reply_to))
-        # send signal like getmail would
-        mailbox_signals.message_received.send(self, message=msg)
-        self.assertExists(
-                models.Contribution, content=a.content.get(),
-                text__text='Text B')
-
-
-class ConversationInitiateByEmail(memberships.MemberMixin, tests.Test):
-    def test_conversation_initiate_by_email(self):
-        # generate initial message
-        msg = mailbox_models.Message(
-                from_header=self.gestalt.user.email,
-                body='Delivered-To: {}@localhost\n\nText A'.format(self.group.slug))
-        # send signal like getmail would
-        mailbox_signals.message_received.send(self, message=msg)
-        self.assertExists(
-                models.Contribution, conversation__associations__group=self.group,
-                text__text='Text A')
-
-    def test_conversation_initiate_by_email_failing(self):
-        # generate initial message
-        msg = mailbox_models.Message(
-                from_header=self.gestalt.user.email,
-                body='Delivered-To: not-existing@localhost\n\nText A')
-        # send signal like getmail would
-        mailbox_signals.message_received.send(self, message=msg)
-        self.assertEqual(len(mail.outbox), 1)
-
-
-class ConversationReplyByEmail(
-        gestalten.AuthenticatedMixin, gestalten.OtherGestaltMixin, tests.Test):
-    def test_texts_reply_by_email(self):
-        # send message to other_gestalt via web interface
-        self.client.post(
-                self.get_url('create-gestalt-conversation', self.other_gestalt.pk),
-                {'subject': 'Subject A', 'text': 'Text A'})
-        text_a = self.assertExists(models.Contribution, conversation__subject='Subject A')
-        self.assertNotificationSent()
-        # generate reply message
-        reply_to = mail.outbox[0].extra_headers['Reply-To']
-        msg = mailbox_models.Message(
-                from_header=self.other_gestalt.user.email,
-                body='Delivered-To: {}\n\nText B'.format(reply_to))
-        # send signal like getmail would
-        mailbox_signals.message_received.send(self, message=msg)
-        self.assertExists(
-                models.Contribution, conversation=text_a.conversation.get(),
-                text__text='Text B')
-
-
 class Delete(ContributionMixin, django.test.TestCase):
     def test_delete_contribution(self):
         delete_url = reverse(

features/conversations/forms.py

@@ -51,7 +51,7 @@ class Create(forms.ModelForm):
         self.contribution.contribution = contributions_models.Text.objects.create(
                 text=self.cleaned_data['text'])
         if 'author' in self.cleaned_data:
-            self.contribution.author = gestalten.Gestalt.get_or_create(
+            self.contribution.author = gestalten.Gestalt.objects.get_or_create_by_email(
                     self.cleaned_data['author'])
         self.contribution.save()
 

features/conversations/templates/conversations/contributed.txt

@@ -6,6 +6,6 @@ Nachricht online lesen und beantworten:
 {% if contribution %}
 Du erhältst diese Benachrichtigung, weil Du Dich an dem Gespräch {{ object.container.subject }} beteiligt hast.
 {% url 'conversation' object.container.associations.first.pk as path %}{{ path|full_url }}#{% ref contribution %}
-{% elif subscription %}
-Du erhältst diese Benachrichtigung weil Du {% if membership %}Mitglied der Gruppe {{ membership.group }} bist und die Gruppe{% else %}die Gruppe {{ subscription.subscribed_to }}{% endif %} abonniert hast.
-{{ subscription.subscribed_to.get_absolute_url|full_url }}{% endif %}
+{% elif subscription and membership %}
+Du erhältst diese Benachrichtigung weil Du Mitglied der Gruppe '{{ membership.group }}' bist und die Gruppe abonniert hast. Zum Verlassen der Gruppe folge bitte diesem Verweis:
+{% if membership.member.can_login %}{% url 'resign' membership.group.pk as resign_url %}{% else %}{% url 'resign-request' membership.group.pk as resign_url %}{% endif %}{{ resign_url|full_url }}{% endif %}

features/conversations/templates/conversations/create.html

@@ -28,6 +28,13 @@
     <form method="post">
         {% csrf_token %}
         {% if form.author %}
+            <div class="disclaimer content-block">
+                <p>
+                Deine E-Mail-Adresse wird zusammen mit Deiner Nachricht dauerhaft gespeichert. Du erhältst Benachrichtungen für Antworten auf Deine Nachricht.
+                </p>
+                <p>Um die E-Mail-Adresse später zu löschen, <a href="{% url 'account_signup' %}">leg ein Benutzerkonto unter der E-Mail-Adresse an</a> und lösche es anschließend oder <a href="{% url 'create-group-conversation' about_group.pk %}">schreib uns eine Nachricht</a>.
+                </p>
+            </div>
             {% field form.author %}
         {% endif %}
         {% field form.subject %}

features/events/views.py

@@ -107,29 +107,64 @@ class BaseCalendarFeed(ICalFeed):
                 return authenticated_gestalt.user
         return None
 
+    # the following methods describe ICAL properties
+    # See http://django-ical.readthedocs.io/en/latest/usage.html#property-reference-and-extensions
+    def product_id(self):
+        return 'stadtgestalten'
+
+    def timezone(self):
+        return django.utils.timezone.get_default_timezone_name()
+
     def items(self):
         return self.get_queryset().order_by('-content__time')
 
+    def item_class(self, item):
+        if item.content.first().associations.first().public:
+            return 'PUBLIC'
+        else:
+            return 'PRIVATE'
+
     def item_title(self, item):
         return item.content.first().title
 
     def item_description(self, item):
-        return item.content.first().subject
+        return item.content.first().versions.last().text
 
     def item_location(self, item):
         return item.content.first().place
 
     def item_start_datetime(self, item):
-        return item.content.first().time
+        tz = django.utils.timezone.get_default_timezone()
+        return item.content.first().time.astimezone(tz)
+
+    def item_end_datetime(self, item):
+        tz = django.utils.timezone.get_default_timezone()
+        return item.content.first().until_time.astimezone(tz)
 
 
 class GroupCalendarFeed(BaseCalendarFeed, features.groups.views.Mixin):
 
+    def title(self):
+        site_name = sites_models.Site.objects.get_current().name
+        group = self.get_group()
+        if group is None:
+            return None
+        else:
+            return '{} ({})'.format(group.name, site_name)
+
     def items(self):
         filter_dict = {'group': self.get_group(),
                        'public': (self.kwargs['domain'] == "public")}
         return super().items().filter(**filter_dict)
 
+    def item_guid(self, item):
+        domain = sites_models.Site.objects.get_current().domain
+        group = self.get_group()
+        if group is None:
+            return None
+        else:
+            return '{}.{}@{}'.format(group.name, item.id, domain)
+
     def get_calendar_owner(self):
         return self.get_group()
 

features/files/models.py

-from os import path
-import re
+import io
+import os
+import tempfile
+from typing import List
 
 import django
 from django.db import models
+import django.core.files
+from features.imports.signals import ParsedMailAttachment
 from imagekit.models import ImageSpecField
 from imagekit.processors import ResizeToFit, Transpose
 
@@ -10,15 +14,44 @@ import core
 from features.contributions import models as contributions
 
 
-EXCLUDE_RE = r'Content-Type: application/pgp-signature'
+IGNORE_CONTENT_TYPES = {'application/pgp-signature'}
+
+
+def get_unique_storage_filename(name_template: str, base_dir: str,
+                                default_prefix: str='attachment-') -> str:
+    """ determine a suitable name for a file to be stored in a directory
+
+    The file may not overwrite an existing file and it should keep its original extension.
+    """
+    temp_kwargs = {'dir': base_dir, 'prefix': default_prefix, 'delete': False}
+    if name_template:
+        basename, extension = os.path.splitext(os.path.basename(name_template))
+        if extension:
+            temp_kwargs['suffix'] = '.' + extension
+        if basename:
+            temp_kwargs['prefix'] = basename + '-'
+    storage_file = tempfile.NamedTemporaryFile(**temp_kwargs)
+    storage_file.close()
+    return storage_file.name
 
 
 class FileManager(models.Manager):
-    def create_from_message(self, message, attached_to):
-        for attachment in message.attachments.all():
-            if re.search(EXCLUDE_RE, attachment.headers):
+    def create_from_message_attachments(self, attachments: List[ParsedMailAttachment],
+                                        attached_to):
+        for attachment in attachments:
+            if attachment.content_type in IGNORE_CONTENT_TYPES:
                 continue
-            f = self.create(file=attachment.document, filename=attachment.get_filename())
+
+            if attachment.data is not None:
+                # create the file and reference it
+                filename = get_unique_storage_filename(attachment.filename,
+                                                       File.file.field.storage.base_location)
+                f = self.create()
+                f.file.save(os.path.basename(filename),
+                            django.core.files.File(io.BytesIO(attachment.data)))
+            else:
+                file_source = attachment.model_obj
+                f = self.create(file=file_source, filename=attachment.filename)
             contributions.Contribution.objects.create(
                     container_id=attached_to.container_id,
                     container_type=attached_to.container_type,
@@ -54,7 +87,7 @@ class File(core.models.Model):
 
     @property
     def display_name(self):
-        return self.filename or path.basename(self.file.name)
+        return self.filename or os.path.basename(self.file.name)
 
     def __str__(self):
         return self.display_name
@@ -63,13 +96,13 @@ class File(core.models.Model):
         return self.file.url
 
     def is_image(self):
-        root, ext = path.splitext(self.file.name.lower())
+        root, ext = os.path.splitext(self.file.name.lower())
         return ext in ('.svg', '.apng', '.png', '.gif', '.jpg', '.jpeg')
 
     def is_video(self):
-        root, ext = path.splitext(self.file.name.lower())
+        root, ext = os.path.splitext(self.file.name.lower())
         return ext in ('.mp4', '.ogg', '.webm')
 
     def is_audio(self):
-        root, ext = path.splitext(self.file.name.lower())
+        root, ext = os.path.splitext(self.file.name.lower())
         return ext in ('.opus', '.ogg', '.aac', '.mp3', '.flac', '.m4a')

features/files/tests.py

+import contextlib
 import os
 import shutil
+import unittest
+import tempfile
 
 import django
 import django_mailbox
 
-import core
+import core.tests
 from features.associations import models as associations
+from features.files.models import get_unique_storage_filename
 from features.images import tests as images
 from features.memberships import test_mixins as memberships
 
@@ -93,6 +97,42 @@ class Gestalt(images.ImageMixin, memberships.AuthenticatedMemberMixin, core.test
         self.assertOk(url=self.get_group_file_url())
 
 
+class FilenameGenerator(unittest.TestCase):
+
+    def setUp(self):
+        self._base_dir = tempfile.mkdtemp()
+        # Manage a set of created filenames.  Otherwise the 'tearDown' method preempts the context
+        # cleanup and thus fails to remove the temporary directory.
+        self._filenames = set()
+        super().setUp()
+
+    def tearDown(self):
+        for filename in self._filenames:
+            os.unlink(filename)
+        os.rmdir(self._base_dir)
+
+    @contextlib.contextmanager
+    def get_unique_filename(self, name_template, default_prefix=None):
+        filename = get_unique_storage_filename(name_template, self._base_dir,
+                                               default_prefix=default_prefix)
+        self._filenames.add(filename)