hook: gracefully ignore non functional hooks and fall back to none

In case a hook fails to load for some reason, fall back to the default
hook "none" and treat errors as warnings in the log.

This will gracefully ignore typos in hook names without crashing the
server, and it will also allow configuration of "rabbitmq" where i.e.
"pika" is missing.

Closes: #1490
Signed-off-by: Henning Schild <henning@hennsch.de>

radicale/hook/__init__.py

@@ -3,14 +3,23 @@ from enum import Enum
 from typing import Sequence
 
 from radicale import pathutils, utils
+from radicale.log import logger
 
 INTERNAL_TYPES: Sequence[str] = ("none", "rabbitmq")
 
 
 def load(configuration):
     """Load the storage module chosen in configuration."""
-    return utils.load_plugin(
-        INTERNAL_TYPES, "hook", "Hook", BaseHook, configuration)
+    try:
+        return utils.load_plugin(
+            INTERNAL_TYPES, "hook", "Hook", BaseHook, configuration)
+    except Exception as e:
+        logger.warn(e)
+        logger.warn("Hook \"%s\" failed to load, falling back to \"none\"." % configuration.get("hook", "type"))
+        configuration = configuration.copy()
+        configuration.update({"hook": {"type": "none"}}, "hook", privileged=True)
+        return utils.load_plugin(
+            INTERNAL_TYPES, "hook", "Hook", BaseHook, configuration)
 
 
 class BaseHook: