boundif: introduce API for socket binding

device/boundif_windows.go

@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2017-2019 WireGuard LLC. All Rights Reserved.
+ */
+
+package device
+
+import (
+	"encoding/binary"
+	"golang.org/x/sys/windows"
+	"unsafe"
+)
+
+const (
+	sockoptIP_UNICAST_IF   = 31
+	sockoptIPV6_UNICAST_IF = 31
+)
+
+func (device *Device) BindSocketToInterface4(interfaceIndex uint32) error {
+	/* MSDN says for IPv4 this needs to be in net byte order, so that it's like an IP address with leading zeros. */
+	bytes := make([]byte, 4)
+	binary.BigEndian.PutUint32(bytes, interfaceIndex)
+	interfaceIndex = *(*uint32)(unsafe.Pointer(&bytes[0]))
+
+	sysconn, err := device.net.bind.(*nativeBind).ipv4.SyscallConn()
+	if err != nil {
+		return err
+	}
+	err2 := sysconn.Control(func(fd uintptr) {
+		err = windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IP, sockoptIP_UNICAST_IF, int(interfaceIndex))
+	})
+	if err2 != nil {
+		return err2
+	}
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func (device *Device) BindSocketToInterface6(interfaceIndex uint32) error {
+	sysconn, err := device.net.bind.(*nativeBind).ipv6.SyscallConn()
+	if err != nil {
+		return err
+	}
+	err2 := sysconn.Control(func(fd uintptr) {
+		err = windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IPV6, sockoptIPV6_UNICAST_IF, int(interfaceIndex))
+	})
+	if err2 != nil {
+		return err2
+	}
+	if err != nil {
+		return err
+	}
+	return nil
+}