From 279c2ba796370b06e319902796d40237a4725e39 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emanuel=20Sch=C3=BCtze?= <emanuel@intevation.de>
Date: Wed, 8 Nov 2017 10:34:47 +0100
Subject: [PATCH] Adds elements to restricted data cache only if cache already
 exists (hotfix for #3427).

Prevents corrupt cache if restricted data cache is cleared while runtime.
---
 openslides/utils/autoupdate.py |  4 ++--
 openslides/utils/cache.py      | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/openslides/utils/autoupdate.py b/openslides/utils/autoupdate.py
index 4def9179a..c804f4f7d 100644
--- a/openslides/utils/autoupdate.py
+++ b/openslides/utils/autoupdate.py
@@ -99,7 +99,7 @@ def ws_add_site(message: Any) -> None:
 
                 output.append(formatted_data)
                 # Cache restricted data for user
-                restricted_data_cache.add_element(
+                restricted_data_cache.update_element(
                     user_id,
                     collection.collection_string,
                     data['id'],
@@ -293,7 +293,7 @@ def send_data(message: ChannelMessageFormat) -> None:
         for collection_element in collection_elements:
             formatted_data = collection_element.as_autoupdate_for_user(user)
             if formatted_data['action'] == 'changed':
-                restricted_data_cache.add_element(
+                restricted_data_cache.update_element(
                     user_id or 0,
                     collection_element.collection_string,
                     collection_element.id,
diff --git a/openslides/utils/cache.py b/openslides/utils/cache.py
index b9f6ae6eb..1cb16d31f 100644
--- a/openslides/utils/cache.py
+++ b/openslides/utils/cache.py
@@ -363,6 +363,17 @@ class RestrictedDataCache:
 
     base_cache_key = 'restricted_user_cache'
 
+    def update_element(self, user_id: int, collection_string: str, id: int, data: object) -> None:
+        """
+        Adds on element to the cache only if the cache exists for the user.
+
+        Note: This method is not atomic. So in very rare cases it is possible
+        that the restricted date cache can become corrupt. The best solution would be to
+        use a lua script instead. See also #3427.
+        """
+        if self.exists_for_user(user_id):
+            self.add_element(user_id, collection_string, id, data)
+
     def add_element(self, user_id: int, collection_string: str, id: int, data: object) -> None:
         """
         Adds one element to the cache. If the cache does not exists for the user,
@@ -413,6 +424,9 @@ class DummyRestrictedDataCache:
     Dummy RestrictedDataCache that does nothing.
     """
 
+    def update_element(self, user_id: int, collection_string: str, id: int, data: object) -> None:
+        pass
+
     def add_element(self, user_id: int, collection_string: str, id: int, data: object) -> None:
         pass