Bug: the report ID is only prepended on Windows. It should be prepended for macOS/linux as well.

[benma]

Hi

Here, the report ID is prepended, but only for Windows:

usb/hid_enabled.go

Lines 126 to 128 in 87927bb

	if runtime.GOOS == "windows" {
	report = append([]byte{0x00}, b...)
	} else {

The same issue exists in the hid repo, where I commented about the same issue in 2018: karalabe/hid#7 (comment)

Since the first byte after the report ID can legitimately be a zero byte (a USB packet that starts with a zero byte), this code is broken on linux/macOS, where one has to manually prepend that zero byte report ID. Without prepending the zero byte report ID for linux/macOS, the lower level library will strip the the first byte if it is zero (see below), corrupting the packet:

usb/hidapi/libusb/hid.c

Lines 1003 to 1007 in 87927bb

	if (report_number == 0x0) {
	data++;
	length--;
	skipped_report_id = 1;
	}

This is a hard issue to find, as it can be a rare event that a packet starts with a zero byte (after the report ID).

See e.g. this PR which implements this workaround: https://github.com/digitalbitbox/bitbox02-api-go/pull/73/files