Enable differentiation of different devices on a single USB serial port adapter

[jessebraham]

This issue was migrated from GitLab. The original issue can be found here:
https://gitlab.com/susurrus/serialport-rs/-/issues/81

It would be handy if it were possible to differentiate the different ports in a composite USB Serial adapter in some cross platform way, presumably by adding a field to the UsbPortInfo struct. I've attached an lsusb -v output for such a device. There seem to be two possible fields that would make this possible. Either the iInterface field (on line 45 and 115) which I believe is generally a human readable string or the bMasterInterface attribute in the CDCACM union (on line 55 and 125) which is a number.

The second method seems to be used to differentiate them by linux as seen below, but iInterface is available through udev.

aled@dufous-/dev: ls -l /dev/serial/by-id/
total 0
lrwxrwxrwx 1 root root 13 Jul 14 19:26 usb-Black_Sphere_Technologies_Black_Magic_Probe_DDD5ACC2-if00 -> ../../ttyACM0
lrwxrwxrwx 1 root root 13 Jul 14 19:26 usb-Black_Sphere_Technologies_Black_Magic_Probe_DDD5ACC2-if02 -> ../../ttyACM1

It looks like the library actually already queries the if number on Windows, although it is not exposed to the user. Funnily enough the example in the comment is exactly my use case, funny how life does that.

example.txt

If anything I said in regards to anything USB doesn't make any sense, I apologize in advance, USB is still kind of a blackbox to me. I can probably work on a pull request on the posix side of things, but I don't own a Windows box so I have no real way of testing windows stuff