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.

frigate/config.py

@@ -9,6 +9,7 @@ from pathlib import Path
 from typing import Any, Dict, List, Optional, Tuple, Union
 
 import numpy as np
+import yaml
 from pydantic import (
     BaseModel,
     ConfigDict,
@@ -41,11 +42,11 @@ from frigate.ffmpeg_presets import (
 )
 from frigate.plus import PlusApi
 from frigate.util.builtin import (
+    NoDuplicateKeysLoader,
     deep_merge,
     escape_special_characters,
     generate_color_palette,
     get_ffmpeg_arg_list,
-    load_config_with_no_duplicates,
 )
 from frigate.util.config import StreamInfoRetriever, get_relative_coordinates
 from frigate.util.image import create_mask
@@ -1764,7 +1765,7 @@ class FrigateConfig(FrigateBaseModel):
             raw_config = f.read()
 
         if config_file.endswith(YAML_EXT):
-            config = load_config_with_no_duplicates(raw_config)
+            config = yaml.load(raw_config, NoDuplicateKeysLoader)
         elif config_file.endswith(".json"):
             config = json.loads(raw_config)
 
@@ -1772,5 +1773,5 @@ class FrigateConfig(FrigateBaseModel):
 
     @classmethod
     def parse_raw(cls, raw_config):
-        config = load_config_with_no_duplicates(raw_config)
+        config = yaml.load(raw_config, NoDuplicateKeysLoader)
         return cls.model_validate(config)

frigate/test/test_config.py

@@ -4,13 +4,14 @@ import unittest
 from unittest.mock import patch
 
 import numpy as np
+import yaml
 from pydantic import ValidationError
 
 from frigate.config import BirdseyeModeEnum, FrigateConfig
 from frigate.const import MODEL_CACHE_DIR
 from frigate.detectors import DetectorTypeEnum
 from frigate.plus import PlusApi
-from frigate.util.builtin import deep_merge, load_config_with_no_duplicates
+from frigate.util.builtin import NoDuplicateKeysLoader, deep_merge
 
 
 class TestConfig(unittest.TestCase):
@@ -1537,7 +1538,7 @@ class TestConfig(unittest.TestCase):
         """
 
         self.assertRaises(
-            ValueError, lambda: load_config_with_no_duplicates(raw_config)
+            ValueError, lambda: yaml.load(raw_config, NoDuplicateKeysLoader)
         )
 
     def test_object_filter_ratios_work(self):

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(
+                "Key redefinitions are not allowed: " + ", ".join(duplicate_keys)
+            )
+
+        return mapping
 
 
 def clean_camera_user_pass(line: str) -> str: