disconnected_callback called with the backend object instead of BleakClient

[deymo]

• bleak version: v0.19.5
• Python version: 3.10.9
• Operating System: Debian
• BlueZ version (bluetoothctl -v) in case of Linux: 5.66

Description

When creating a BleakClient we can pass a callback to the disconnected_callback parameter to be called when the device disconnects. The type for this parameter is Optional[Callable[[BleakClient], None]] and the documentation for this parameter says "The callable must take one argument, which will be this client object." so I'm assuming the expected parameter is a BleakClient object.

However, the parameter is just forwarded to the backend, where at least in bluez, winrt and corebluetooth it is called with:

  if self._disconnected_callback is not None:
     self._disconnected_callback(self)

where self is the backend type.

In general this is not much of a difference since most methods and properties in BleakClient are just forwarded to the self._backend but in the case of start_notify the backend and BleakClient are different:.

BleakClient.start_notify takes a callback with two arguments (Callable[[BleakGATTCharacteristic, bytearray], Union[None, Awaitable[None]]) but it wraps with a functools.partial or equivalent asyncio thing so that the backend gets a callback with only one argument (the bytearray). Also, the first argument (the characteristic) is converted to a BleakGATTCharacteristic if not already, so passing a string to cli.start_notify gets an error since the backend assumes it was already converted to the backend's type.

What I Did

The example to reproduce this requires to disconnect and reconnect the device. Start the example until you see some "on_notification" messages, then get the device out of range until you see the "on_disconnect" and then back in range so the reconnect triggers.

import asyncio, bleak, sys

CHAR_UUID = 'some uuid' # Use a characteristic that sends periodic notifications

def on_notification(cli, data):
    print('on_notification', type(cli), data)

async def on_disconnect_async(cli):
    await cli.connect()
    await cli.start_notify(CHAR_UUID, on_notification)

def on_disconnect(cli):
    print('on_disconnect', type(cli))
    asyncio.get_event_loop().call_soon(asyncio.ensure_future, on_disconnect_async(cli))

async def main():
    cli = bleak.BleakClient(sys.argv[1], disconnected_callback=on_disconnect)
    await cli.connect()
    await cli.start_notify(CHAR_UUID, on_notification)
    print('connected')
    while True:
        await asyncio.sleep(1)

if __name__ == '__main__':
    asyncio.run(main())

The output is roughly:

connected
on_notification <class 'bleak.backends.bluezdbus.characteristic.BleakGATTCharacteristicBlueZDBus'> bytearray(b'.....')
....
on_disconnect <class 'bleak.backends.bluezdbus.client.BleakClientBlueZDBus'>

followed by this exception:

  File ".../test.py", line 10, in on_disconnect_async
    await cli.start_notify(CHAR_UUID, on_notification)
  File ".../bleak/backends/bluezdbus/client.py", line 873, in start_notify
    self._notification_callbacks[characteristic.path] = callback
AttributeError: 'str' object has no attribute 'path'