Improve error logging on invalid MQTT entity state (#118006)

* Improve error logging on invalid MQTT entity state

* Explain not hanlding TpeError and ValueError

* Move length check closer to source

* use _LOGGER.exception

homeassistant/components/mqtt/util.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import asyncio
 from functools import lru_cache
+import logging
 import os
 from pathlib import Path
 import tempfile
@@ -12,7 +13,7 @@ from typing import Any
 import voluptuous as vol
 
 from homeassistant.config_entries import ConfigEntry, ConfigEntryState
-from homeassistant.const import Platform
+from homeassistant.const import MAX_LENGTH_STATE_STATE, STATE_UNKNOWN, Platform
 from homeassistant.core import HomeAssistant
 from homeassistant.helpers import config_validation as cv, template
 from homeassistant.helpers.typing import ConfigType
@@ -31,7 +32,7 @@ from .const import (
     DEFAULT_RETAIN,
     DOMAIN,
 )
-from .models import DATA_MQTT, DATA_MQTT_AVAILABLE
+from .models import DATA_MQTT, DATA_MQTT_AVAILABLE, ReceiveMessage
 
 AVAILABILITY_TIMEOUT = 30.0
 
@@ -261,6 +262,28 @@ async def async_create_certificate_temp_files(
     await hass.async_add_executor_job(_create_temp_dir_and_files)
 
 
+def check_state_too_long(
+    logger: logging.Logger, proposed_state: str, entity_id: str, msg: ReceiveMessage
+) -> bool:
+    """Check if the processed state is too long and log warning."""
+    if (state_length := len(proposed_state)) > MAX_LENGTH_STATE_STATE:
+        logger.warning(
+            "Cannot update state for entity %s after processing "
+            "payload on topic %s. The requested state (%s) exceeds "
+            "the maximum allowed length (%s). Fall back to "
+            "%s, failed state: %s",
+            entity_id,
+            msg.topic,
+            state_length,
+            MAX_LENGTH_STATE_STATE,
+            STATE_UNKNOWN,
+            proposed_state[:8192],
+        )
+        return True
+
+    return False
+
+
 def get_file_path(option: str, default: str | None = None) -> str | None:
     """Get file path of a certificate file."""
     temp_dir = Path(tempfile.gettempdir()) / TEMP_DIR_NAME