Fix handling undecoded mqtt sensor payloads

homeassistant/components/mqtt/sensor.py

@@ -237,28 +237,32 @@ def _update_state(self, msg: ReceiveMessage) -> None:
             payload = msg.payload
         if payload is PayloadSentinel.DEFAULT:
             return
-        new_value = str(payload)
+        if not isinstance(payload, str):
+            _LOGGER.warning(
+                "Invalid undecoded state message '%s' received from '%s'",
+                payload,
+                msg.topic,
+            )
+            return
         if self._numeric_state_expected:
-            if new_value == "":
+            if payload == "":
                 _LOGGER.debug("Ignore empty state from '%s'", msg.topic)
-            elif new_value == PAYLOAD_NONE:
+            elif payload == PAYLOAD_NONE:
                 self._attr_native_value = None
             else:
-                self._attr_native_value = new_value
+                self._attr_native_value = payload
             return
         if self.device_class in {
             None,
             SensorDeviceClass.ENUM,
-        } and not check_state_too_long(_LOGGER, new_value, self.entity_id, msg):
-            self._attr_native_value = new_value
+        } and not check_state_too_long(_LOGGER, payload, self.entity_id, msg):
+            self._attr_native_value = payload
             return
         try:
-            if (payload_datetime := dt_util.parse_datetime(new_value)) is None:
+            if (payload_datetime := dt_util.parse_datetime(payload)) is None:
                 raise ValueError
         except ValueError:
-            _LOGGER.warning(
-                "Invalid state message '%s' from '%s'", msg.payload, msg.topic
-            )
+            _LOGGER.warning("Invalid state message '%s' from '%s'", payload, msg.topic)
             self._attr_native_value = None
             return
         if self.device_class == SensorDeviceClass.DATE:

tests/components/mqtt/test_sensor.py

@@ -110,6 +110,42 @@ async def test_setting_sensor_value_via_mqtt_message(
     assert state.attributes.get("unit_of_measurement") == "fav unit"
 
 
+@pytest.mark.parametrize(
+    "hass_config",
+    [
+        {
+            mqtt.DOMAIN: {
+                sensor.DOMAIN: {
+                    "name": "test",
+                    "state_topic": "test-topic",
+                    "unit_of_measurement": "%",
+                    "device_class": "battery",
+                    "encoding": "",
+                }
+            }
+        }
+    ],
+)
+async def test_handling_undecoded_sensor_value(
+    hass: HomeAssistant,
+    mqtt_mock_entry: MqttMockHAClientGenerator,
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """Test the setting of the value via MQTT."""
+    await mqtt_mock_entry()
+
+    state = hass.states.get("sensor.test")
+    assert state.state == STATE_UNKNOWN
+
+    async_fire_mqtt_message(hass, "test-topic", b"88")
+    state = hass.states.get("sensor.test")
+    assert state.state == STATE_UNKNOWN
+    assert (
+        "Invalid undecoded state message 'b'88'' received from 'test-topic'"
+        in caplog.text
+    )
+
+
 @pytest.mark.parametrize(
     "hass_config",
     [