Add range check for temperature and humidity

Adds a check to guard against physically impossible reported values. Temperatures below absolute zero, or humidity outside 0-100 %, likely are the result of an invalid received packet and should be disregarded (disregard entire packet, other data probably also wrong).

Author: henryk

src/thermopro_ble/parser.py

@@ -11,6 +11,7 @@
 import logging
 from math import tanh
 from struct import Struct
+from typing import Union
 
 from bluetooth_data_tools import short_address
 from bluetooth_sensor_state_data import BluetoothData
@@ -29,6 +30,9 @@
 UNPACK_TEMP_HUMID = Struct("<hB").unpack
 UNPACK_SPIKE_TEMP = Struct("<BHHH").unpack
 
+ABSOLUTE_MIN_HUMIDITY__PERCENTAGE = 0
+ABSOLUTE_MAX_HUMIDITY__PERCENTAGE = 100
+ABSOLUTE_MIN_TEMPERATURE__CELCIUS = -273.15
 
 # TP96x battery values appear to be a voltage reading, probably in millivolts.
 # This means that calculating battery life from it is a non-linear function.
@@ -41,6 +45,15 @@ def tp96_battery(voltage: int) -> float:
     clamped = max(0, min(raw, 100))
     return round(clamped, 2)
 
+def is_temp_hum_invalid(temperature: Union[int, float], humidity: Union[int, float]) -> bool:
+    """Returns true if the measured values are outside the physically possible range."""
+    # Note: This will not catch implausibly high temperature values, but a clear
+    # upper temperature cutoff is not easy to define
+    if temperature < ABSOLUTE_MIN_TEMPERATURE__CELCIUS:
+        return True
+    if not (ABSOLUTE_MIN_HUMIDITY__PERCENTAGE <= humidity <= ABSOLUTE_MAX_HUMIDITY__PERCENTAGE):
+        return True
+    return False
 
 class ThermoProBluetoothDeviceData(BluetoothData):
     """Date update for ThermoPro Bluetooth devices."""
@@ -91,6 +104,11 @@ def _start_update(self, service_info: BluetoothServiceInfo) -> None:
             internal_temp = internal_temp - 30
             ambient_temp = ambient_temp - 30
             battery_percent = tp96_battery(battery_voltage)
+
+            if is_temp_hum_invalid(internal_temp, 0) or is_temp_hum_invalid(ambient_temp, 0):
+                # Invalid packet, probably corrupted
+                return
+            
             self.update_predefined_sensor(
                 SensorLibrary.TEMPERATURE__CELSIUS,
                 internal_temp,
@@ -110,16 +128,21 @@ def _start_update(self, service_info: BluetoothServiceInfo) -> None:
                 key=f"battery_probe_{probe_one_indexed}",
                 name=f"Probe {probe_one_indexed} Battery",
             )
-            return
-
-        # TP357S seems to be in 6, TP397 and TP393 in 4
-        battery_byte = data[6] if len(data) == 7 else data[4]
-        if battery_byte in BATTERY_VALUE_TO_LEVEL:
-            self.update_predefined_sensor(
-                SensorLibrary.BATTERY__PERCENTAGE,
-                BATTERY_VALUE_TO_LEVEL[battery_byte],
-            )
-
-        (temp, humi) = UNPACK_TEMP_HUMID(data[1:4])
-        self.update_predefined_sensor(SensorLibrary.TEMPERATURE__CELSIUS, temp / 10)
-        self.update_predefined_sensor(SensorLibrary.HUMIDITY__PERCENTAGE, humi)
+        else:
+           # TP357S seems to be in 6, TP397 and TP393 in 4
+            battery_byte = data[6] if len(data) == 7 else data[4]
+            (temp_deci, humi) = UNPACK_TEMP_HUMID(data[1:4])
+            temp = temp_deci / 10
+
+            if is_temp_hum_invalid(temp, humi):
+                # Invalid data, probably corrupted
+                return
+            
+            if battery_byte in BATTERY_VALUE_TO_LEVEL:
+                self.update_predefined_sensor(
+                    SensorLibrary.BATTERY__PERCENTAGE,
+                    BATTERY_VALUE_TO_LEVEL[battery_byte],
+                )
+    
+            self.update_predefined_sensor(SensorLibrary.TEMPERATURE__CELSIUS, temp)
+            self.update_predefined_sensor(SensorLibrary.HUMIDITY__PERCENTAGE, humi)