Feature request: expose nusb `DeviceInfo` without opening the device

[f-io]

nusb exposes DeviceInfo, which is currently not available in node-usb-rs: https://docs.rs/nusb/latest/nusb/struct.DeviceInfo.html

It gives device info (vendor, product, class, serial, interfaces) without opening the device first.
Useful for filtering for a specific device, or telling identical devices apart without having to open each one.

[thegecko]

This information should all be exposed on the WebUSB device without opening it, see the tests:

https://github.com/node-usb/node-usb-rs/blob/main/test/webusb.coffee#L52
https://github.com/node-usb/node-usb-rs/blob/main/test/webusb.coffee#L99

You should be able to list all devices and filter for what you need or create your own WebUSB instance with a DevicesFound function.

LMK if this doesn't support your needs

[f-io]

Ah yeah, you're right, it's all there without opening. My bad. I was iterating over device.configurations (the array), and the interfaces on those don't get populated without opening, instead of just device.configuration which has them ...

[f-io]

I have to come back to this ticket, serialNumber still opens the device.

Reading serialNumber (same for manufacturerName and productName) opens the device. For any device the process has no udev access to, the getter throws instead of returning a value:

const { usb } = require('usb')
for (const d of await usb.getDevices()) {
  try { console.log(d.vendorId.toString(16), d.serialNumber) }
  catch (e) { console.log(d.vendorId.toString(16), 'threw:', e.message) }
}

46d  threw: open error: permission denied (errno 13)
1a40 threw: open error: permission denied (errno 13)
5e3  threw: open error: permission denied (errno 13)
301a 202309130000001          <- has a udev rule

The values are already available without access. sysfs has them for every device that carries one, and nusb exposes them on DeviceInfo:

/sys/bus/usb/devices/1-1/serial -> 39181FDXXXXXXX

vendorId, productId, deviceClass, bus, address and ports are plain fields and work fine, so the three string fields look like the only ones taking the detour through an opened device. Caching them from DeviceInfo at construction would fix it.

This also makes the throw escape into an uncaughtException when the getter is used inside a hotplug listener, since the dispatcher has no error path.

[thegecko]

I'm unable to test this right now, but this should be working as you describe.

The three string values are checked on DeviceInfo before opening, see: https://github.com/node-usb/node-usb-rs/blob/main/src/webusb_device.rs#L386

[f-io]

The DeviceInfo check works, the fallback is the problem. A device without a serial will end up in _open().
Expected is null, the type says string | null, and a device without a serial has none.

[thegecko]

Ok, trouble is these strings aren't always available on DeviceInfo (I'm looking at you, Windows), and I can't see how to tell the difference between:

• An empty string entry on DeviceInfo (your case) which is None
• The system needs the user to open the device to retrieve the value, which also appears as None

@kevinmehall is there a way in nusb to tell the difference here? I want to avoid:

• adding code specific to Windows (assuming thats the only culprit not allowing string access without opening)
• always opening the device if any of these strings are missing

[kevinmehall]

Yeah, I've been thinking that API needs more detail than just Option. On Windows we can tell if the descriptor exists even if not cached but that's not currently exposed.

[thegecko]

I assume this can easily be determined by the existence of the the stringID in the descriptor?

[kevinmehall]

Yes, on Windows we parse the device and configuration descriptor and can see if the string descriptor indexes are non-zero. On Linux and macOS we just read everything from sysfs / IOKit registry. The tricky one in Android, where you can't read serial number at all without the same permission prompt as opening the device.