Set state of entity with invalid state to unknown (#99452)

* Set state of entity with invalid state to unknown

* Add test

* Apply suggestions from code review

Co-authored-by: Robert Resch <robert@resch.dev>

* Update test_entity.py

---------

Co-authored-by: Robert Resch <robert@resch.dev>

homeassistant/helpers/entity.py

@@ -35,7 +35,11 @@ from homeassistant.const import (
     EntityCategory,
 )
 from homeassistant.core import CALLBACK_TYPE, Context, HomeAssistant, callback
-from homeassistant.exceptions import HomeAssistantError, NoEntitySpecifiedError
+from homeassistant.exceptions import (
+    HomeAssistantError,
+    InvalidStateError,
+    NoEntitySpecifiedError,
+)
 from homeassistant.loader import bind_hass
 from homeassistant.util import dt as dt_util, ensure_unique_string, slugify
 
@@ -848,7 +852,15 @@ class Entity(ABC):
             self._context = None
             self._context_set = None
 
-        hass.states.async_set(entity_id, state, attr, self.force_update, self._context)
+        try:
+            hass.states.async_set(
+                entity_id, state, attr, self.force_update, self._context
+            )
+        except InvalidStateError:
+            _LOGGER.exception("Failed to set state, fall back to %s", STATE_UNKNOWN)
+            hass.states.async_set(
+                entity_id, STATE_UNKNOWN, {}, self.force_update, self._context
+            )
 
     def schedule_update_ha_state(self, force_refresh: bool = False) -> None:
         """Schedule an update ha state change task.

tests/helpers/test_entity.py

@@ -3,6 +3,7 @@ import asyncio
 from collections.abc import Iterable
 import dataclasses
 from datetime import timedelta
+import logging
 import threading
 from typing import Any
 from unittest.mock import MagicMock, PropertyMock, patch
@@ -1477,3 +1478,30 @@ async def test_warn_no_platform(
     caplog.clear()
     ent.async_write_ha_state()
     assert error_message not in caplog.text
+
+
+async def test_invalid_state(
+    hass: HomeAssistant, caplog: pytest.LogCaptureFixture
+) -> None:
+    """Test the entity helper catches InvalidState and sets state to unknown."""
+    ent = entity.Entity()
+    ent.entity_id = "test.test"
+    ent.hass = hass
+
+    ent._attr_state = "x" * 255
+    ent.async_write_ha_state()
+    assert hass.states.get("test.test").state == "x" * 255
+
+    caplog.clear()
+    ent._attr_state = "x" * 256
+    ent.async_write_ha_state()
+    assert hass.states.get("test.test").state == STATE_UNKNOWN
+    assert (
+        "homeassistant.helpers.entity",
+        logging.ERROR,
+        f"Failed to set state, fall back to {STATE_UNKNOWN}",
+    ) in caplog.record_tuples
+
+    ent._attr_state = "x" * 255
+    ent.async_write_ha_state()
+    assert hass.states.get("test.test").state == "x" * 255