[PATCH] Windows: add convertInterfaceIndexToLUID syscall

[kayrus <kay.diam@gmail.com>]

This change can be used to easily get an access to any interface by name, e.g.

iface, err := net.InterfaceByName(name)
if err ! nil {
	return err
}

luid, err := winipcfg.LUIDFromIndex(uint32(iface.Index))
if err != nil {
	return err
}
---
 tunnel/winipcfg/luid.go              | 11 +++++++++++
 tunnel/winipcfg/winipcfg.go          |  1 +
 tunnel/winipcfg/zwinipcfg_windows.go |  9 +++++++++
 3 files changed, 21 insertions(+)

diff --git a/tunnel/winipcfg/luid.go b/tunnel/winipcfg/luid.go
index efdf1ba4..02ba65b4 100644
--- a/tunnel/winipcfg/luid.go
+++ b/tunnel/winipcfg/luid.go
@@ -63,6 +63,17 @@ func LUIDFromGUID(guid *windows.GUID) (LUID, error) {
 	return luid, nil
 }
 
+// LUIDFromIndex function converts a local index for a network interface to the locally unique identifier (LUID) for the interface.
+// https://docs.microsoft.com/en-us/windows/desktop/api/netioapi/nf-netioapi-convertinterfaceindextoluid
+func LUIDFromIndex(index uint32) (LUID, error) {
+	var luid LUID
+	err := convertInterfaceIndexToLUID(index, &luid)
+	if err != nil {
+		return 0, err
+	}
+	return luid, nil
+}
+
 // IPAddress method returns MibUnicastIPAddressRow struct that matches to provided 'ip' argument. Corresponds to GetUnicastIpAddressEntry
 // (https://docs.microsoft.com/en-us/windows/desktop/api/netioapi/nf-netioapi-getunicastipaddressentry)
 func (luid LUID) IPAddress(ip net.IP) (*MibUnicastIPAddressRow, error) {
diff --git a/tunnel/winipcfg/winipcfg.go b/tunnel/winipcfg/winipcfg.go
index 54040a1c..dd09d3a0 100644
--- a/tunnel/winipcfg/winipcfg.go
+++ b/tunnel/winipcfg/winipcfg.go
@@ -30,6 +30,7 @@ import (
 //sys	getIfTable2Ex(level MibIfEntryLevel, table **mibIfTable2) (ret error) = iphlpapi.GetIfTable2Ex
 //sys	convertInterfaceLUIDToGUID(interfaceLUID *LUID, interfaceGUID *windows.GUID) (ret error) = iphlpapi.ConvertInterfaceLuidToGuid
 //sys	convertInterfaceGUIDToLUID(interfaceGUID *windows.GUID, interfaceLUID *LUID) (ret error) = iphlpapi.ConvertInterfaceGuidToLuid
+//sys	convertInterfaceIndexToLUID(interfaceIndex uint32, interfaceLUID *LUID) (ret error) = iphlpapi.ConvertInterfaceIndexToLuid
 
 // GetAdaptersAddresses function retrieves the addresses associated with the adapters on the local computer.
 // https://docs.microsoft.com/en-us/windows/desktop/api/iphlpapi/nf-iphlpapi-getadaptersaddresses
diff --git a/tunnel/winipcfg/zwinipcfg_windows.go b/tunnel/winipcfg/zwinipcfg_windows.go
index c4bf3b00..ac89fec1 100644
--- a/tunnel/winipcfg/zwinipcfg_windows.go
+++ b/tunnel/winipcfg/zwinipcfg_windows.go
@@ -42,6 +42,7 @@ var (
 
 	procCancelMibChangeNotify2          = modiphlpapi.NewProc("CancelMibChangeNotify2")
 	procConvertInterfaceGuidToLuid      = modiphlpapi.NewProc("ConvertInterfaceGuidToLuid")
+	procConvertInterfaceIndexToLuid     = modiphlpapi.NewProc("ConvertInterfaceIndexToLuid")
 	procConvertInterfaceLuidToGuid      = modiphlpapi.NewProc("ConvertInterfaceLuidToGuid")
 	procCreateAnycastIpAddressEntry     = modiphlpapi.NewProc("CreateAnycastIpAddressEntry")
 	procCreateIpForwardEntry2           = modiphlpapi.NewProc("CreateIpForwardEntry2")
@@ -88,6 +89,14 @@ func convertInterfaceGUIDToLUID(interfaceGUID *windows.GUID, interfaceLUID *LUID
 	return
 }
 
+func convertInterfaceIndexToLUID(interfaceIndex uint32, interfaceLUID *LUID) (ret error) {
+	r0, _, _ := syscall.Syscall(procConvertInterfaceIndexToLuid.Addr(), 2, uintptr(interfaceIndex), uintptr(unsafe.Pointer(interfaceLUID)), 0)
+	if r0 != 0 {
+		ret = syscall.Errno(r0)
+	}
+	return
+}
+
 func convertInterfaceLUIDToGUID(interfaceLUID *LUID, interfaceGUID *windows.GUID) (ret error) {
 	r0, _, _ := syscall.Syscall(procConvertInterfaceLuidToGuid.Addr(), 2, uintptr(unsafe.Pointer(interfaceLUID)), uintptr(unsafe.Pointer(interfaceGUID)), 0)
 	if r0 != 0 {
-- 
2.25.1