URLs that stay the same when a file is replaced. Fixes #478

docs/installation.rst

@@ -110,6 +110,34 @@ secure downloads
 
 See :ref:`secure_downloads` section.
 
+Canonical URLs
+..............
+
+You can configure your project to generate canonical URLs for your public files. Just include django-filer's
+URLConf in your project's ``urls.py``::
+
+    urlpatterns = [
+        ...
+        url(r'^filer/', include('filer.urls')),
+        ...
+    ]
+
+Contrary to the file's actual URL, the canonical URL does not change if you upload a new version of the file.
+Thus, you can safely share the canonical URL. As long as the file exists, people will be redirected to its
+latest version.
+
+The canonical URL is displayed in the "advanced" panel on the file's admin page. It has the form::
+
+    /filer/canonical/1442488644/12/
+
+The "filer" part of the URL is configured in the project's URLconf as described above. The "canonical" part can be
+changed with the setting ``FILER_CANONICAL_URL``, which defaults to ``'canonical/'``. Example::
+
+    # settings.py
+
+    FILER_CANONICAL_URL = 'sharing/'
+
+
 debugging and logging
 .....................
 

docs/settings.rst

@@ -143,4 +143,13 @@ Defaults to ``False``
 Defines the dotted path to a custom Image model; please include the model name.
 Example: 'my.app.models.CustomImage'
 
-Defaults to ``False``
+Defaults to ``False``
+
+
+``FILER_CANONICAL_URL``
+-----------------------
+
+Defines the path element common to all canonical file URLs.
+
+Defaults to ``'canonical/'``
+

filer/admin/fileadmin.py

@@ -23,7 +23,7 @@ class FileAdmin(PrimitivePermissionAwareModelAdmin):
     list_per_page = 10
     search_fields = ['name', 'original_filename', 'sha1', 'description']
     raw_id_fields = ('owner',)
-    readonly_fields = ('sha1',)
+    readonly_fields = ('sha1', 'display_canonical')
 
     # save_as hack, because without save_as it is impossible to hide the
     # save_and_add_another if save_as is False. To show only save_and_continue
@@ -45,7 +45,7 @@ def build_fieldsets(cls, extra_main_fields=(), extra_advanced_fields=(), extra_f
                 'fields': ('name', 'owner', 'description',) + extra_main_fields,
             }),
             (_('Advanced'), {
-                'fields': ('file', 'sha1',) + extra_advanced_fields,
+                'fields': ('file', 'sha1', 'display_canonical') + extra_advanced_fields,
                 'classes': ('collapse',),
                 }),
             ) + extra_fieldsets
@@ -141,4 +141,13 @@ def get_model_perms(self, request):
             'delete': False,
         }
 
+    def display_canonical(self, instance):
+        canonical = instance.canonical_url
+        if canonical:
+            return '<a href="%s">%s</a>' % (canonical, canonical)
+        else:
+            return '-'
+    display_canonical.allow_tags = True
+    display_canonical.short_description = _('canonical URL')
+
 FileAdmin.fieldsets = FileAdmin.build_fieldsets()

filer/models/filemodels.py

@@ -240,6 +240,19 @@ def url(self):
             r = ''
         return r
 
+    @property
+    def canonical_url(self):
+        url = ''
+        if self.file and self.is_public:
+            try:
+                url = urlresolvers.reverse('canonical', kwargs={
+                    'uploaded_at': self.uploaded_at.strftime('%s'),
+                    'file_id': self.id
+                })
+            except urlresolvers.NoReverseMatch:
+                pass  # No canonical url, return empty string
+        return url
+
     @property
     def path(self):
         try:

filer/settings.py

@@ -219,3 +219,6 @@ def update_server_settings(settings, defaults, s, t):
 FILER_PRIVATEMEDIA_THUMBNAIL_SERVER = load_object(FILER_SERVERS['private']['thumbnails']['ENGINE'])(**FILER_SERVERS['private']['thumbnails']['OPTIONS'])
 
 FILER_DUMP_PAYLOAD = getattr(settings, 'FILER_DUMP_PAYLOAD', False)  # Whether the filer shall dump the files payload
+
+FILER_CANONICAL_URL = getattr(settings, 'FILER_CANONICAL_URL', 'canonical/')
+

filer/test_utils/templates/404.html

@@ -0,0 +1 @@
+404

filer/test_utils/urls.py

@@ -10,4 +10,5 @@
         {'document_root': settings.MEDIA_ROOT, 'show_indexes': True}),
     url(r'^admin/', include(admin.site.urls)),
     url(r'^', include('filer.server.urls')),
+    url(r'^filer/', include('filer.urls')),
 )

filer/tests/models.py

@@ -223,3 +223,47 @@ def test_custom_model(self):
 
             reloaded = Image.objects.get(pk=image.pk)
             self.assertEqual(reloaded.author, image.author)
+
+    def test_canonical_url(self):
+        """
+        Check that a public file's canonical url redirects to the file's current version
+        """
+        image = self.create_filer_image()
+        image.save()
+        # Private file
+        image.is_public = False
+        image.save()
+        canonical = image.canonical_url
+        self.assertEqual(self.client.get(canonical).status_code, 404)
+        # First public version
+        image.is_public = True
+        image.save()
+        canonical = image.canonical_url
+        file_url_1 = image.file.url
+        self.assertRedirects(self.client.get(canonical), file_url_1)
+        # Second public version
+        img_2 = create_image()
+        image_name_2 = 'test_file_2.jpg'
+        filename_2 = os.path.join(settings.FILE_UPLOAD_TEMP_DIR, image_name_2)
+        img_2.save(filename_2, 'JPEG')
+        file_2 = DjangoFile(open(filename_2, 'rb'), name=image_name_2)
+        image.file = file_2
+        image.save()
+        file_url_2 = image.file.url
+        self.assertNotEqual(file_url_1, file_url_2)
+        self.assertRedirects(self.client.get(canonical), file_url_2)
+        # No file
+        image.file = None
+        image.save()
+        self.assertEqual(self.client.get(canonical).status_code, 404)
+        # Teardown
+        image.file = file_2
+        image.save()
+        os.remove(filename_2)
+
+    def test_canonical_url_settings(self):
+        image = self.create_filer_image()
+        image.save()
+        canonical = image.canonical_url
+        self.assertTrue(canonical.startswith('/filer/test-path/'))
+

filer/urls.py

@@ -0,0 +1,13 @@
+#-*- coding: utf-8 -*-
+from django.conf.urls import url
+
+from filer import settings as filer_settings
+from filer import views
+
+urlpatterns = [
+    url(
+        filer_settings.FILER_CANONICAL_URL + r'(?P<uploaded_at>[0-9]+)/(?P<file_id>[0-9]+)/$',
+        views.canonical,
+        name='canonical'
+    ),
+]

filer/views.py

@@ -5,11 +5,11 @@
 from django.contrib.admin import widgets
 from django.contrib.auth.decorators import login_required
 from django.core.exceptions import PermissionDenied
-from django.http import HttpResponseRedirect
-from django.shortcuts import render
+from django.http import HttpResponseRedirect, Http404
+from django.shortcuts import render, redirect, get_object_or_404
 from django.utils.translation import ugettext_lazy as _
 
-from .models import Folder, Image, Clipboard, tools, FolderRoot
+from .models import Folder, File, Image, Clipboard, tools, FolderRoot
 from . import settings as filer_settings
 
 
@@ -57,6 +57,16 @@ def _userperms(item, request):
     return r
 
 
+def canonical(request, uploaded_at, file_id):
+    """
+    Redirect to the current url of a public file
+    """
+    filer_file = get_object_or_404(File, pk=file_id, is_public=True)
+    if uploaded_at != filer_file.uploaded_at.strftime('%s') or not filer_file.file:
+        raise Http404('No %s matches the given query.' % File._meta.object_name)
+    return redirect(filer_file.url)
+
+
 @login_required
 def edit_folder(request, folder_id):
     # TODO: implement edit_folder view

test_settings.py

@@ -4,6 +4,8 @@
 
 gettext = lambda s: s
 
+BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+
 HELPER_SETTINGS = {
     'NOSE_ARGS': [
         '-s',
@@ -50,7 +52,9 @@
         'easy_thumbnails.processors.filters',
     ),
     'FILE_UPLOAD_TEMP_DIR': mkdtemp(),
-    'FILER_IMAGE_MODEL': False
+    'FILER_IMAGE_MODEL': False,
+    'TEMPLATE_DIRS': (os.path.join(BASE_DIR, 'django-filer', 'filer', 'test_utils', 'templates'),),
+    'FILER_CANONICAL_URL': 'test-path/',
 
 }
 if os.environ.get('CUSTOM_IMAGE', False):