Report unserializable data in websocket (#34072)

* Report unserializable data in websocket

* Fix tests

* log types too

homeassistant/util/json.py

@@ -4,8 +4,9 @@ import json
 import logging
 import os
 import tempfile
-from typing import Any, Dict, List, Optional, Type, Union
+from typing import Any, Callable, Dict, List, Optional, Type, Union
 
+from homeassistant.core import Event, State
 from homeassistant.exceptions import HomeAssistantError
 
 _LOGGER = logging.getLogger(__name__)
@@ -56,7 +57,7 @@ def save_json(
         json_data = json.dumps(data, sort_keys=True, indent=4, cls=encoder)
     except TypeError:
         # pylint: disable=no-member
-        msg = f"Failed to serialize to JSON: {filename}. Bad data found at {', '.join(find_paths_unserializable_data(data))}"
+        msg = f"Failed to serialize to JSON: {filename}. Bad data at {format_unserializable_data(find_paths_unserializable_data(data))}"
         _LOGGER.error(msg)
         raise SerializationError(msg)
 
@@ -85,30 +86,48 @@ def save_json(
                 _LOGGER.error("JSON replacement cleanup failed: %s", err)
 
 
-def find_paths_unserializable_data(bad_data: Any) -> List[str]:
+def format_unserializable_data(data: Dict[str, Any]) -> str:
+    """Format output of find_paths in a friendly way.
+
+    Format is comma separated: <path>=<value>(<type>)
+    """
+    return ", ".join(f"{path}={value}({type(value)}" for path, value in data.items())
+
+
+def find_paths_unserializable_data(
+    bad_data: Any, *, dump: Callable[[Any], str] = json.dumps
+) -> Dict[str, Any]:
     """Find the paths to unserializable data.
 
     This method is slow! Only use for error handling.
     """
     to_process = deque([(bad_data, "$")])
-    invalid = []
+    invalid = {}
 
     while to_process:
         obj, obj_path = to_process.popleft()
 
         try:
-            json.dumps(obj)
+            dump(obj)
             continue
-        except TypeError:
+        except (ValueError, TypeError):
             pass
 
+        # We convert states and events to dict so we can find bad data inside it
+        if isinstance(obj, State):
+            obj_path += f"(state: {obj.entity_id})"
+            obj = obj.as_dict()
+        elif isinstance(obj, Event):
+            obj_path += f"(event: {obj.event_type})"
+            obj = obj.as_dict()
+
         if isinstance(obj, dict):
             for key, value in obj.items():
                 try:
                     # Is key valid?
-                    json.dumps({key: None})
+                    dump({key: None})
                 except TypeError:
-                    invalid.append(f"{obj_path}<key: {key}>")
+                    invalid[f"{obj_path}<key: {key}>"] = key
                 else:
                     # Process value
                     to_process.append((value, f"{obj_path}.{key}"))
@@ -116,6 +135,6 @@ def find_paths_unserializable_data(bad_data: Any) -> List[str]:
             for idx, value in enumerate(obj):
                 to_process.append((value, f"{obj_path}[{idx}]"))
         else:
-            invalid.append(obj_path)
+            invalid[obj_path] = obj
 
     return invalid