apps: Redirect /apps -> zulipchat.com/apps, except on upstream itself.

This page describes software the user will get from upstream for
their own devices, independent of what's on the server they're
using.  So it should live in a place maintained together with
that other software, rather than be distributed and versioned
with the server.

The use of ZILENCER_ENABLED to tell the difference is rather a hack
but is currently how we do this in the small handful of similar
spots; see #5245.

Fixes #5234.

zerver/tests/test_home.py

@@ -395,6 +395,23 @@ class HomeTest(ZulipTestCase):
         path = urllib.parse.urlparse(result['Location']).path
         self.assertEqual(path, "/")
 
+    def test_apps_view(self):
+        # type: () -> None
+        result = self.client_get('/apps')
+        self.assertEqual(result.status_code, 301)
+        self.assertTrue(result['Location'].endswith('/apps/'))
+
+        with self.settings(ZILENCER_ENABLED=False):
+            result = self.client_get('/apps/')
+        self.assertEqual(result.status_code, 301)
+        self.assertTrue(result['Location'] == 'https://zulipchat.com/apps/')
+
+        with self.settings(ZILENCER_ENABLED=True):
+            result = self.client_get('/apps/')
+        self.assertEqual(result.status_code, 200)
+        html = result.content.decode('utf-8')
+        self.assertIn('Appsolutely', html)
+
     def test_generate_204(self):
         # type: () -> None
         email = self.example_email("hamlet")

zerver/views/home.py

@@ -265,6 +265,12 @@ def desktop_home(request):
     # type: (HttpRequest) -> HttpResponse
     return HttpResponseRedirect(reverse('zerver.views.home.home'))
 
+def apps_view(request):
+    # type: (HttpRequest) -> HttpResponse
+    if settings.ZILENCER_ENABLED:
+        return render(request, 'zerver/apps.html')
+    return HttpResponseRedirect('https://zulipchat.com/apps/', status=301)
+
 def is_buggy_ua(agent):
     # type: (str) -> bool
     """Discrimiate CSS served to clients based on User Agent

zproject/urls.py

@@ -141,7 +141,7 @@ i18n_urls = [
     url(r'^api/endpoints/$', zerver.views.integrations.api_endpoint_docs, name='zerver.views.integrations.api_endpoint_docs'),
     url(r'^integrations/$', IntegrationView.as_view()),
     url(r'^about/$', TemplateView.as_view(template_name='zerver/about.html')),
-    url(r'^apps/$', TemplateView.as_view(template_name='zerver/apps.html')),
+    url(r'^apps/$', zerver.views.home.apps_view, name='zerver.views.home.apps_view'),
 
     url(r'^robots\.txt$', RedirectView.as_view(url='/static/robots.txt', permanent=True)),