Is there a minimum BlueZ requirement for bless ?

[EasyRiderr]

Hi 👋🏼
I'm using bless on an old RPi0 2W, thus, by default, the BlueZ version is:

$ bluetoothctl --version
bluetoothctl: 5.50

When using the bless package from the current master version (4eef666), if the user enables notifications on a characteristic, the AcquireNotify method assumes that the mtu attributes exist in BlueZ options.

🚨 This is not the case with BlueZ 5.50... As you can see on the logs below:

asyncio[12332] ERROR Exception in callback MessageBus._make_method_handler.<locals>.handler.<locals>.done(<Task finishe...yError('mtu')>) at /home/user/.local/share/hatch/env/virtual/project/DptxPHBL/project/lib/python3.12/site-packages/dbus_next/aio/message_bus.py:349
handle: <Handle MessageBus._make_method_handler.<locals>.handler.<locals>.done(<Task finishe...yError('mtu')>) at /home/user/.local/share/hatch/env/virtual/project/DptxPHBL/project/lib/python3.12/site-packages/dbus_next/aio/message_bus.py:349>
Traceback (most recent call last):
  File "/opt/python-3.12/lib/python3.12/asyncio/events.py", line 88, in _run
    self._context.run(self._callback, *self._args)
  File "/home/user/.local/share/hatch/env/virtual/project/DptxPHBL/project/lib/python3.12/site-packages/dbus_next/aio/message_bus.py", line 351, in done
    result = fut.result()
             ^^^^^^^^^^^^
  File "/home/user/.local/share/hatch/env/virtual/project/DptxPHBL/project/lib/python3.12/site-packages/bless/backends/bluezdbus/dbus/characteristic.py", line 172, in AcquireNotify
    mtu: int = options["mtu"].value
               ~~~~~~~^^^^^^^
KeyError: 'mtu'

Does bless have minimum requirements regarding the BlueZ version? In this case, it would be beneficial to highlight it in the README or documentation.
Or, do you want to keep compatibility across all BlueZ versions? In this case, what would be a gentle manner of handling this corner case?

[kevincar]

Thank you, @EasyRiderr, for bringing up, yet again, another great point.

There is no listed BlueZ minimum version because I haven't yet really tested what the minimum supported version ought to be. On one hand, I think it could be feasible to support older versions and simply list warnings that functionality will be limited. On the other hand, doing this could make the backend code more complex by checking everything against a large number of different versions, which, unless there is a clean and straightforward way to do that, maintaining that sounds like a headache.

All of my linux-based testing has been on BlueZ version 5.64 I believe. Reading the MTU seems to have been added in version 5.51. Perhaps this can be the limit set as of now, but you are correct, that a BlueZ minimum requirement is not currently documented—though it ought to be.

[EasyRiderr]

Thanks for your reply !
Maybe we could automate the testing on several BlueZ version, but document a minimum BlueZ version sounds much more straightforward and easy.

[kevincar]

I agree. I think for now, I'll document that 5.51 may be the minimum. I'll look into adding this.