Fix homekit handling of 0 light brightness and fan speed (#29962)

* Fix homekit handling of 0 light brightness and fan speed

* Update homekit tests for new initial brightness/speed value

homeassistant/components/homekit/type_fans.py

@@ -88,8 +88,11 @@ class Fan(HomeAccessory):
             )
 
         if CHAR_ROTATION_SPEED in chars:
+            # Initial value is set to 100 because 0 is a special value (off). 100 is
+            # an arbitrary non-zero value. It is updated immediately by update_state
+            # to set to the correct initial value.
             self.char_speed = serv_fan.configure_char(
-                CHAR_ROTATION_SPEED, value=0, setter_callback=self.set_speed
+                CHAR_ROTATION_SPEED, value=100, setter_callback=self.set_speed
             )
 
         if CHAR_SWING_MODE in chars:
@@ -156,7 +159,22 @@ class Fan(HomeAccessory):
             speed = new_state.attributes.get(ATTR_SPEED)
             hk_speed_value = self.speed_mapping.speed_to_homekit(speed)
             if hk_speed_value is not None and self.char_speed.value != hk_speed_value:
-                self.char_speed.set_value(hk_speed_value)
+                # If the homeassistant component reports its speed as the first entry
+                # in its speed list but is not off, the hk_speed_value is 0. But 0
+                # is a special value in homekit. When you turn on a homekit accessory
+                # it will try to restore the last rotation speed state which will be
+                # the last value saved by char_speed.set_value. But if it is set to
+                # 0, HomeKit will update the rotation speed to 100 as it thinks 0 is
+                # off.
+                #
+                # Therefore, if the hk_speed_value is 0 and the device is still on,
+                # the rotation speed is mapped to 1 otherwise the update is ignored
+                # in order to avoid this incorrect behavior.
+                if hk_speed_value == 0:
+                    if state == STATE_ON:
+                        self.char_speed.set_value(1)
+                else:
+                    self.char_speed.set_value(hk_speed_value)
 
         # Handle Oscillating
         if self.char_swing is not None:

homeassistant/components/homekit/type_lights.py

@@ -82,8 +82,11 @@ class Light(HomeAccessory):
         )
 
         if CHAR_BRIGHTNESS in self.chars:
+            # Initial value is set to 100 because 0 is a special value (off). 100 is
+            # an arbitrary non-zero value. It is updated immediately by update_state
+            # to set to the correct initial value.
             self.char_brightness = serv_light.configure_char(
-                CHAR_BRIGHTNESS, value=0, setter_callback=self.set_brightness
+                CHAR_BRIGHTNESS, value=100, setter_callback=self.set_brightness
             )
         if CHAR_COLOR_TEMPERATURE in self.chars:
             min_mireds = self.hass.states.get(self.entity_id).attributes.get(
@@ -183,7 +186,21 @@ class Light(HomeAccessory):
             if not self._flag[CHAR_BRIGHTNESS] and isinstance(brightness, int):
                 brightness = round(brightness / 255 * 100, 0)
                 if self.char_brightness.value != brightness:
-                    self.char_brightness.set_value(brightness)
+                    # The homeassistant component might report its brightness as 0 but is
+                    # not off. But 0 is a special value in homekit. When you turn on a
+                    # homekit accessory it will try to restore the last brightness state
+                    # which will be the last value saved by char_brightness.set_value.
+                    # But if it is set to 0, HomeKit will update the brightness to 100 as
+                    # it thinks 0 is off.
+                    #
+                    # Therefore, if the the brighness is 0 and the device is still on,
+                    # the brightness is mapped to 1 otherwise the update is ignored in
+                    # order to avoid this incorrect behavior.
+                    if brightness == 0:
+                        if state == STATE_ON:
+                            self.char_brightness.set_value(1)
+                    else:
+                        self.char_brightness.set_value(brightness)
             self._flag[CHAR_BRIGHTNESS] = False
 
         # Handle color temperature

tests/components/homekit/test_type_fans.py

@@ -197,7 +197,10 @@ async def test_fan_speed(hass, hk_driver, cls, events):
     )
     await hass.async_block_till_done()
     acc = cls.fan(hass, hk_driver, "Fan", entity_id, 2, None)
-    assert acc.char_speed.value == 0
+
+    # Initial value can be anything but 0. If it is 0, it might cause HomeKit to set the
+    # speed to 100 when turning on a fan on a freshly booted up server.
+    assert acc.char_speed.value != 0
 
     await hass.async_add_job(acc.run)
     assert (

tests/components/homekit/test_type_lights.py

@@ -101,7 +101,9 @@ async def test_light_brightness(hass, hk_driver, cls, events):
     await hass.async_block_till_done()
     acc = cls.light(hass, hk_driver, "Light", entity_id, 2, None)
 
-    assert acc.char_brightness.value == 0
+    # Initial value can be anything but 0. If it is 0, it might cause HomeKit to set the
+    # brightness to 100 when turning on a light on a freshly booted up server.
+    assert acc.char_brightness.value != 0
 
     await hass.async_add_job(acc.run)
     await hass.async_block_till_done()