Report which data causes JSON serialization error (#31901)

homeassistant/util/json.py

@@ -1,4 +1,5 @@
 """JSON utility functions."""
+from collections import deque
 import json
 import logging
 import os
@@ -51,10 +52,17 @@ def save_json(
 
     Returns True on success.
     """
+    try:
+        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))}"
+        _LOGGER.error(msg)
+        raise SerializationError(msg)
+
     tmp_filename = ""
     tmp_path = os.path.split(filename)[0]
     try:
-        json_data = json.dumps(data, sort_keys=True, indent=4, cls=encoder)
         # Modern versions of Python tempfile create this file with mode 0o600
         with tempfile.NamedTemporaryFile(
             mode="w", encoding="utf-8", dir=tmp_path, delete=False
@@ -64,9 +72,6 @@ def save_json(
         if not private:
             os.chmod(tmp_filename, 0o644)
         os.replace(tmp_filename, filename)
-    except TypeError as error:
-        _LOGGER.exception("Failed to serialize to JSON: %s", filename)
-        raise SerializationError(error)
     except OSError as error:
         _LOGGER.exception("Saving JSON file failed: %s", filename)
         raise WriteError(error)
@@ -78,3 +83,39 @@ def save_json(
                 # If we are cleaning up then something else went wrong, so
                 # we should suppress likely follow-on errors in the cleanup
                 _LOGGER.error("JSON replacement cleanup failed: %s", err)
+
+
+def find_paths_unserializable_data(bad_data: Union[List, Dict]) -> List[str]:
+    """Find the paths to unserializable data.
+
+    This method is slow! Only use for error handling.
+    """
+    to_process = deque([(bad_data, "$")])
+    invalid = []
+
+    while to_process:
+        obj, obj_path = to_process.popleft()
+
+        try:
+            json.dumps(obj)
+            valid = True
+        except TypeError:
+            valid = False
+
+        if isinstance(obj, dict):
+            for key, value in obj.items():
+                try:
+                    # Is key valid?
+                    json.dumps({key: None})
+                except TypeError:
+                    invalid.append(f"{obj_path}<key: {key}>")
+                else:
+                    # Process value
+                    to_process.append((value, f"{obj_path}.{key}"))
+        elif isinstance(obj, list):
+            for idx, value in enumerate(obj):
+                to_process.append((value, f"{obj_path}[{idx}]"))
+        elif not valid:  # type: ignore
+            invalid.append(obj_path)
+
+    return invalid

tests/util/test_json.py

@@ -9,13 +9,16 @@ from unittest.mock import Mock
 import pytest
 
 from homeassistant.exceptions import HomeAssistantError
-from homeassistant.util.json import SerializationError, load_json, save_json
+from homeassistant.util.json import (
+    SerializationError,
+    find_paths_unserializable_data,
+    load_json,
+    save_json,
+)
 
 # Test data that can be saved as JSON
 TEST_JSON_A = {"a": 1, "B": "two"}
 TEST_JSON_B = {"a": "one", "B": 2}
-# Test data that can not be saved as JSON (keys must be strings)
-TEST_BAD_OBJECT = {("A",): 1}
 # Test data that can not be loaded as JSON
 TEST_BAD_SERIALIED = "THIS IS NOT JSON\n"
 TMP_DIR = None
@@ -71,9 +74,12 @@ def test_overwrite_and_reload():
 
 def test_save_bad_data():
     """Test error from trying to save unserialisable data."""
-    fname = _path_for("test4")
-    with pytest.raises(SerializationError):
-        save_json(fname, TEST_BAD_OBJECT)
+    with pytest.raises(SerializationError) as excinfo:
+        save_json("test4", {"hello": set()})
+
+    assert "Failed to serialize to JSON: test4. Bad data found at $.hello" in str(
+        excinfo.value
+    )
 
 
 def test_load_bad_data():
@@ -99,3 +105,20 @@ def test_custom_encoder():
     save_json(fname, Mock(), encoder=MockJSONEncoder)
     data = load_json(fname)
     assert data == "9"
+
+
+def test_find_unserializable_data():
+    """Find unserializeable data."""
+    assert find_paths_unserializable_data(1) == []
+    assert find_paths_unserializable_data([1, 2]) == []
+    assert find_paths_unserializable_data({"something": "yo"}) == []
+
+    assert find_paths_unserializable_data({"something": set()}) == ["$.something"]
+    assert find_paths_unserializable_data({"something": [1, set()]}) == [
+        "$.something[1]"
+    ]
+    assert find_paths_unserializable_data([1, {"bla": set(), "blub": set()}]) == [
+        "$[1].bla",
+        "$[1].blub",
+    ]
+    assert find_paths_unserializable_data({("A",): 1}) == ["$<key: ('A',)>"]