Use signed values for the AICS gain setting fields

bumble/profiles/aics.py

@@ -59,8 +59,8 @@
 # Constants
 # -----------------------------------------------------------------------------
 CHANGE_COUNTER_MAX_VALUE = 0xFF
-GAIN_SETTINGS_MIN_VALUE = 0
-GAIN_SETTINGS_MAX_VALUE = 255
+GAIN_SETTINGS_MIN_VALUE = -128
+GAIN_SETTINGS_MAX_VALUE = 127
 
 
 class ErrorCode(utils.OpenIntEnum):
@@ -131,13 +131,13 @@ class AudioInputState:
     attribute: Attribute | None = None
 
     def __bytes__(self) -> bytes:
-        return bytes(
-            [self.gain_settings, self.mute, self.gain_mode, self.change_counter]
+        return struct.pack(
+            "bBBB", self.gain_settings, self.mute, self.gain_mode, self.change_counter
         )
 
     @classmethod
     def from_bytes(cls, data: bytes):
-        gain_settings, mute, gain_mode, change_counter = struct.unpack("BBBB", data)
+        gain_settings, mute, gain_mode, change_counter = struct.unpack("bBBB", data)
         return cls(gain_settings, mute, gain_mode, change_counter)
 
     def update_gain_settings_unit(self, gain_settings_unit: int) -> None:
@@ -172,19 +172,18 @@ class GainSettingsProperties:
     @classmethod
     def from_bytes(cls, data: bytes):
         (gain_settings_unit, gain_settings_minimum, gain_settings_maximum) = (
-            struct.unpack('BBB', data)
+            struct.unpack('Bbb', data)
         )
         return GainSettingsProperties(
             gain_settings_unit, gain_settings_minimum, gain_settings_maximum
         )
 
     def __bytes__(self) -> bytes:
-        return bytes(
-            [
-                self.gain_settings_unit,
-                self.gain_settings_minimum,
-                self.gain_settings_maximum,
-            ]
+        return struct.pack(
+            'Bbb',
+            self.gain_settings_unit,
+            self.gain_settings_minimum,
+            self.gain_settings_maximum,
         )
 
 
@@ -201,7 +200,7 @@ async def on_write(self, connection: Connection, value: bytes) -> None:
         opcode = AudioInputControlPointOpCode(value[0])
 
         if opcode == AudioInputControlPointOpCode.SET_GAIN_SETTING:
-            gain_settings_operand = value[2]
+            gain_settings_operand = struct.unpack_from('b', value, 2)[0]
             await self._set_gain_settings(connection, gain_settings_operand)
         elif opcode == AudioInputControlPointOpCode.UNMUTE:
             await self._unmute(connection)

tests/profiles/aics_test.py

@@ -82,7 +82,7 @@ async def test_init_service(aics_client: AICSServiceProxy):
     assert (
         await aics_client.gain_settings_properties.read_value()
         == GainSettingsProperties(
-            gain_settings_unit=1, gain_settings_minimum=0, gain_settings_maximum=255
+            gain_settings_unit=1, gain_settings_minimum=-128, gain_settings_maximum=127
         )
     )
     assert await aics_client.audio_input_status.read_value() == (
@@ -179,6 +179,29 @@ async def test_set_gain_setting_when_gain_mode_MANUAL(aics_client: AICSServicePr
     )
 
 
+@pytest.mark.asyncio
+async def test_set_negative_gain_setting(aics_client: AICSServiceProxy):
+    aics_service.audio_input_state.gain_mode = GainMode.MANUAL
+    change_counter = 0
+    gain_settings = -10
+    await aics_client.audio_input_control_point.write_value(
+        bytes(
+            [
+                AudioInputControlPointOpCode.SET_GAIN_SETTING,
+                change_counter,
+                gain_settings & 0xFF,
+            ]
+        )
+    )
+
+    assert await aics_client.audio_input_state.read_value() == AudioInputState(
+        gain_settings=gain_settings,
+        mute=Mute.NOT_MUTED,
+        gain_mode=GainMode.MANUAL,
+        change_counter=change_counter,
+    )
+
+
 @pytest.mark.asyncio
 async def test_set_gain_setting_when_gain_mode_MANUAL_ONLY(
     aics_client: AICSServiceProxy,