context_processor: Cache whether user is admin (Closes: #781)

plinth/context_processors.py

@@ -43,5 +43,5 @@ def common(request):
         'submenu': cfg.main_menu.active_item(request),
         'active_menu_urls': active_menu_urls,
         'box_name': _(cfg.box_name),
-        'user_is_admin': is_user_admin(request.user)
+        'user_is_admin': is_user_admin(request, True)
     }

plinth/middleware.py

@@ -102,5 +102,5 @@ class AdminRequiredMiddleware(object):
            hasattr(view_func, 'IS_NON_ADMIN'):
             return
 
-        if not is_user_admin(request.user):
+        if not is_user_admin(request):
             raise PermissionDenied

plinth/modules/users/forms.py

@@ -171,7 +171,7 @@ class UserUpdateForm(ValidNewUsernameCheckMixin, forms.ModelForm):
 
         super(UserUpdateForm, self).__init__(*args, **kwargs)
 
-        if not is_user_admin(request.user):
+        if not is_user_admin(request):
             self.fields['is_active'].widget = forms.HiddenInput()
             self.fields['groups'].disabled = True
 

plinth/modules/users/views.py

@@ -85,7 +85,7 @@ class UserUpdate(ContextMixin, SuccessMessageMixin, UpdateView):
     def dispatch(self, request, *args, **kwargs):
         """Handle a request and return a HTTP response."""
         if self.request.user.get_username() != self.kwargs['slug'] \
-           and not is_user_admin(self.request.user):
+           and not is_user_admin(self.request):
             raise PermissionDenied
 
         return super().dispatch(request, *args, **kwargs)
@@ -156,7 +156,7 @@ class UserChangePassword(ContextMixin, SuccessMessageMixin, FormView):
     def dispatch(self, request, *args, **kwargs):
         """Handle a request and return a HTTP response."""
         if self.request.user.get_username() != self.kwargs['slug'] \
-           and not is_user_admin(self.request.user):
+           and not is_user_admin(self.request):
             raise PermissionDenied
 
         return super().dispatch(request, *args, **kwargs)

plinth/utils.py

@@ -52,6 +52,14 @@ def non_admin_view(func):
     return func
 
 
-def is_user_admin(user):
+def is_user_admin(request, cached=False):
     """Return whether user is an administrator."""
-    return user.groups.filter(name='admin').exists()
+    if not request.user.is_authenticated():
+        return False
+
+    if 'cache_user_is_admin' in request.session and cached:
+        return request.session['cache_user_is_admin']
+
+    user_is_admin = request.user.groups.filter(name='admin').exists()
+    request.session['cache_user_is_admin'] = user_is_admin
+    return user_is_admin