BLEDeviceConnection.kt

private val callback = object: BluetoothGattCallback() {
    ...
    
    override fun onCharacteristicChanged(
        gatt: BluetoothGatt?,
        characteristic: BluetoothGattCharacteristic
    ) {
        super.onCharacteristicChanged(gatt, characteristic)
        Log.v("bluetooth", characteristic.value.contentToString())
    }
}
    
@RequiresPermission(PERMISSION_BLUETOOTH_CONNECT)
fun startReceivingPasswordUpdates() {
    val service = gatt?.getService(CTF_SERVICE_UUID)
    val characteristic = service?.getCharacteristic(PASSWORD_CHARACTERISTIC_UUID)
    if (characteristic != null) {
        gatt?.setCharacteristicNotification(characteristic, true)

        val CLIENT_CONFIG_DESCRIPTOR = UUID.fromString("00002902-0000-1000-8000-00805f9b34fb")
        val desc = characteristic.getDescriptor(CLIENT_CONFIG_DESCRIPTOR)
        desc?.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE)
        gatt?.writeDescriptor(desc)
    }
}