Rewrite yaml loader (#13803)

* Ignore entire __pycache__ folder instead of individual *.pyc files

* Rewrite the yaml loader to match PyYAML

The old implementation would fail in weird ways with configs that were
incorrect in just the right way. The new implementation just does what
PyYAML would do, only diverging in case of duplicate keys.

* Clarify duplicate yaml key ValueError message

Co-authored-by: Nicolas Mowen <nickmowen213@gmail.com>

---------

Co-authored-by: Nicolas Mowen <nickmowen213@gmail.com>

frigate/util/builtin.py

@@ -89,32 +89,31 @@ def deep_merge(dct1: dict, dct2: dict, override=False, merge_lists=False) -> dic
     return merged
 
 
-def load_config_with_no_duplicates(raw_config) -> dict:
-    """Get config ensuring duplicate keys are not allowed."""
+class NoDuplicateKeysLoader(yaml.loader.SafeLoader):
+    """A yaml SafeLoader that disallows duplicate keys"""
 
-    # https://stackoverflow.com/a/71751051
-    # important to use SafeLoader here to avoid RCE
-    class PreserveDuplicatesLoader(yaml.loader.SafeLoader):
-        pass
+    def construct_mapping(self, node, deep=False):
+        mapping = super().construct_mapping(node, deep=deep)
 
-    def map_constructor(loader, node, deep=False):
-        keys = [loader.construct_object(node, deep=deep) for node, _ in node.value]
-        vals = [loader.construct_object(node, deep=deep) for _, node in node.value]
-        key_count = Counter(keys)
-        data = {}
-        for key, val in zip(keys, vals):
-            if key_count[key] > 1:
-                raise ValueError(
-                    f"Config input {key} is defined multiple times for the same field, this is not allowed."
+        if len(node.value) != len(mapping):
+            # There's a duplicate key somewhere. Find it.
+            duplicate_keys = [
+                key
+                for key, count in Counter(
+                    self.construct_object(key, deep=deep) for key, _ in node.value
                 )
-            else:
-                data[key] = val
-        return data
+                if count > 1
+            ]
 
-    PreserveDuplicatesLoader.add_constructor(
-        yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG, map_constructor
-    )
-    return yaml.load(raw_config, PreserveDuplicatesLoader)
+            # This might be possible if PyYAML's construct_mapping() changes the node
+            # afterwards for some reason? I don't see why, but better safe than sorry.
+            assert len(duplicate_keys) > 0
+
+            raise ValueError(
+                f"Config field duplicates are not allowed, the following fields are duplicated in the config: {', '.join(duplicate_keys)}"
+            )
+
+        return mapping
 
 
 def clean_camera_user_pass(line: str) -> str: