From a69a315dbdc6c4558a469c5da10bb58da20c4d0e Mon Sep 17 00:00:00 2001
From: Sebastian Zagrodzki <sebek@zagrodzki.net>
Date: Sat, 29 Apr 2017 00:50:38 +0200
Subject: [PATCH] Verify that interface and alternate numbers are 0-based
 indices, we rely on this assumption in the config.

---
 usb/libusb.go | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/usb/libusb.go b/usb/libusb.go
index 9b9dbb6..a9503ae 100644
--- a/usb/libusb.go
+++ b/usb/libusb.go
@@ -228,7 +228,7 @@ func (libusbImpl) getDeviceDesc(d *libusbDevice) (*Descriptor, error) {
 			Cap:  int(cfg.bNumInterfaces),
 		}
 		c.Interfaces = make([]InterfaceInfo, 0, len(ifaces))
-		for _, iface := range ifaces {
+		for ifNum, iface := range ifaces {
 			if iface.num_altsetting == 0 {
 				continue
 			}
@@ -240,7 +240,7 @@ func (libusbImpl) getDeviceDesc(d *libusbDevice) (*Descriptor, error) {
 				Cap:  int(iface.num_altsetting),
 			}
 			descs := make([]InterfaceSetting, 0, len(alts))
-			for _, alt := range alts {
+			for altNum, alt := range alts {
 				i := InterfaceSetting{
 					Number:    int(alt.bInterfaceNumber),
 					Alternate: int(alt.bAlternateSetting),
@@ -248,6 +248,12 @@ func (libusbImpl) getDeviceDesc(d *libusbDevice) (*Descriptor, error) {
 					SubClass:  Class(alt.bInterfaceSubClass),
 					Protocol:  Protocol(alt.bInterfaceProtocol),
 				}
+				if ifNum != i.Number {
+					return nil, fmt.Errorf("config %d interface at index %d has number %d, USB standard states they should be identical", c.Config, ifNum, i.Number)
+				}
+				if altNum != i.Alternate {
+					return nil, fmt.Errorf("config %d interface %d alternate settings at index %d has number %d, USB standard states they should be identical", c.Config, i.Number, altNum, i.Alternate)
+				}
 				var ends []C.struct_libusb_endpoint_descriptor
 				*(*reflect.SliceHeader)(unsafe.Pointer(&ends)) = reflect.SliceHeader{
 					Data: uintptr(unsafe.Pointer(alt.endpoint)),