Advertised UUIDs are erased on subsequent calls to CentralDelegateManager scanner callback

[adamincera]

• bleak version: 0.8.0
• Python version: 3.8.5
• Operating System: macOS 10.15.7
• BlueZ version (bluetoothctl -v) in case of Linux: N/A

Description

When calling BleakScanner.discover() on macOS, devices which advertise service UUIDs are returned with device.metadata["uuids"] empty. For each of these devices, multiple calls are made to CentralManagerDelegate.did_discover_peripheral(). Each call to this function calls the following function, callback(), defined inside BleakScannerCoreBluetooth.start():

     def callback(p, a, r):
            self._identifiers[p.identifier()] = a
            if self._callback:
                self._callback(p, a, r)

If callback() is called multiple times, self._identifiers[p.identifier()] will only contain the advertising data a passed in on the final call.

Proposed Solution

I was able to fix the issue for my use case by changing callback() to the following:

       def callback(p, a, r):
            if p.identifier() in self._identifiers:
                self._identifiers[p.identifier()] = {**a, **self._identifiers[p.identifier()]}
            else:
                self._identifiers[p.identifier()] = a
            if self._callback:
                self._callback(p, a, r)

This change merges the advertising data objects according to the method described in this stackoverflow post. However, I am not familiar enough with this library to know if this could cause other adverse effects. Please let me know if this solution makes sense, or how I should test it.

[dlech]

I think this makes sense.

The dictionary update could probably be simplified to this:

self._identifiers.setdefault(p.identifier(), {}).update(a)

To test it, you could log the individual a dictionaries to see that they are indeed different (not all have the same keys) and then log the combined result to make sure it keeps the old data and updates the new/changed data.