Fix USB interface on macOS

[parasyte]

When the usbportinfo-interface feature is enabled on macOS, the UsbPortInfo::interface is always None. A careful reading of https://developer.apple.com/library/archive/documentation/DeviceDrivers/Conceptual/USBBook/USBOverview/USBOverview.html#//apple_ref/doc/uid/TP40002644-BBIDGCHB indicates that device matching or interface matching needs to be considered on a per-application basis. This PR switches the class to IOUSBHostInterface when the feature is enabled, allowing the interface number to be returned.

I am not familiar with macOS, but this seems like a fair compromise without changing the serialport APIs to make a distinction between searching for devices and searching for interfaces.

[sirhcel]

Thank you for spotting this @parasyte and for preparing this PR!

The IOUSBHostDevice class does not provide interface information but at a first glance does the IOUSBHostInterface class provide everything for UsbPortInfo. Since the feature gate usbportinfo-interface is scheduled to disappear with the next major release and the field UsbPortInfo::interfaceto become generally available.

After weighing this for while: Shouldn't looking up the information from IOUSBHostInterface instead from IOUSBHostDevice be the default?

[parasyte]

So, again I need to be transparent that I don’t know Mac APIs. But my interpretation of the docs suggests that the Device and Interface classes should be used when you want either device or interface information. And that is going to be an application’s concern, not the library’s.

So, while it does appear, at least empirically, that the Interface class gives you everything you want… I’m not sure I would rely on that. They are different things for a reason. I suspect some devices might be capable of exposing information differently about itself (e.g. through the Device class) and about all of its interfaces (Interface class).

All in all, I’m in favor of just using the Interface class to simplify things. It can always be changed later if it breaks anything, right?

[sirhcel]

So, again I need to be transparent that I don’t know Mac APIs. But my interpretation of the docs suggests that the Device and Interface classes should be used when you want either device or interface information. And that is going to be an application’s concern, not the library’s.

My knowledge of the macOS APIs is limited. But as USB serial device are - to the extend of my understanding - are always accessed through the endpoints specified by an USB interface, looking up things from the perspective of an USB interface seems the right thing to do to me here.

So, while it does appear, at least empirically, that the Interface class gives you everything you want… I’m not sure I would rely on that. They are different things for a reason. I suspect some devices might be capable of exposing information differently about itself (e.g. through the Device class) and about all of its interfaces (Interface class).

This might be the case but as all information we are currently interested in is (also) provided through IOUSBHostInterface, this looks good for me to go.

All in all, I’m in favor of just using the Interface class to simplify things. It can always be changed later if it breaks anything, right?

Great! As we are not changing/breaking the public API here, we are fine to roll out a patch release if things don't work out as expected.