DM-46936: Fix cache exception when unexpected files present

doc/changes/DM-46936.bugfix.md

@@ -0,0 +1 @@
+Fix a bug where DatastoreCacheManager would raise  ValueError('badly formed hexadecimal UUID string') if files with unexpected names are present in the cache directory when trying to load a file from the cache.

python/lsst/daf/butler/datastore/cache_manager.py

@@ -129,7 +129,10 @@ def _parse_cache_name(cached_location: str) -> tuple[uuid.UUID, str | None, str
     ext = "." + root_ext.pop(0) if root_ext else None
 
     parts = root.split("_")
-    id_ = uuid.UUID(parts.pop(0))
+    try:
+        id_ = uuid.UUID(parts.pop(0))
+    except ValueError as e:
+        raise InvalidCacheFilenameError(f"Invalid or missing ID in cache file name: {cached_location}") from e
     component = parts.pop(0) if parts else None
     return id_, component, ext
 
@@ -894,9 +897,14 @@ def scan_cache(self) -> None:
             if file.relative_to(self._temp_exempt_directory) is not None:
                 continue
 
-            path_in_cache = self._register_cache_entry(file, can_exist=True)
-            if path_in_cache:
-                found.add(path_in_cache)
+            try:
+                path_in_cache = self._register_cache_entry(file, can_exist=True)
+                if path_in_cache:
+                    found.add(path_in_cache)
+            except InvalidCacheFilenameError:
+                # Skip files that are in the cache directory, but were not
+                # created by us.
+                pass
 
         # Find any files that were recorded in the cache but are no longer
         # on disk. (something else cleared them out?)
@@ -1194,3 +1202,9 @@ def known_to_cache(self, ref: DatasetRef, extension: str | None = None) -> bool:
 
     def __str__(self) -> str:
         return f"{type(self).__name__}()"
+
+
+class InvalidCacheFilenameError(Exception):
+    """Raised when attempting to register a file in the cache with a name in
+    the incorrect format.
+    """

tests/test_datastore.py

@@ -1744,6 +1744,26 @@ def testExplicitCacheDir(self) -> None:
         # Test that the cache directory is not marked temporary
         self.assertFalse(cache_manager.cache_directory.isTemporary)
 
+    def testUnexpectedFilesInCacheDir(self) -> None:
+        """Test for regression of a bug where extraneous files in a cache
+        directory would cause all cache lookups to raise an exception.
+        """
+        config_str = f"""
+cached:
+  root: '{self.root}'
+  cacheable:
+    metric0: true
+        """
+
+        for filename in ["unexpected.txt", "unexpected", "un_expected", "un_expected.txt"]:
+            unexpected_file = os.path.join(self.root, filename)
+            with open(unexpected_file, "w") as fh:
+                fh.write("test")
+
+        cache_manager = self._make_cache_manager(config_str)
+        cache_manager.scan_cache()
+        self.assertCache(cache_manager)
+
     def assertCache(self, cache_manager: DatastoreCacheManager) -> None:
         self.assertTrue(cache_manager.should_be_cached(self.refs[0]))
         self.assertFalse(cache_manager.should_be_cached(self.refs[1]))