strict_preconditions: new config option / handling

radicale/app/__init__.py

@@ -75,6 +75,7 @@ class Application(ApplicationPartDelete, ApplicationPartHead,
     _extra_headers: Mapping[str, str]
     _permit_delete_collection: bool
     _permit_overwrite_collection: bool
+    _strict_preconditions: bool
 
     def __init__(self, configuration: config.Configuration) -> None:
         """Initialize Application.
@@ -116,6 +117,8 @@ class Application(ApplicationPartDelete, ApplicationPartHead,
         self._extra_headers = dict()
         for key in self.configuration.options("headers"):
             self._extra_headers[key] = configuration.get("headers", key)
+        self._strict_preconditions = configuration.get("storage", "strict_preconditions")
+        logger.info("strict preconditions check: %s", self._strict_preconditions)
 
     def _scrub_headers(self, environ: types.WSGIEnviron) -> types.WSGIEnviron:
         """Mask passwords and cookies."""

radicale/app/put.py

@@ -207,6 +207,9 @@ class ApplicationPartPut(ApplicationBase):
                 return httputils.NOT_ALLOWED
 
             etag = environ.get("HTTP_IF_MATCH", "")
+            if item and not etag and self._strict_preconditions:
+                logger.warning("Precondition failed for %r: existing item, no If-Match header, strict mode enabled", path)
+                return httputils.PRECONDITION_FAILED
             if not item and etag:
                 # Etag asked but no item found: item has been removed
                 logger.warning("Precondition failed on PUT request for %r (HTTP_IF_MATCH: %s, item not existing)", path, etag)