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A simple go program leveraging the Window API to listen for IPv4 network address change events
package main
import (
"log"
"syscall"
"unsafe"
"golang.org/x/sys/windows"
)
var (
modws2_32 = windows.NewLazySystemDLL("ws2_32.dll")
modiphlpapi = windows.NewLazySystemDLL("iphlpapi.dll")
procWSACreateEvent = modws2_32.NewProc("WSACreateEvent")
procNotifyAddrChange = modiphlpapi.NewProc("NotifyAddrChange")
)
func main() {
log.Printf("Library [ws2_32.dll] loaded at %#v", modws2_32.Handle())
log.Printf("Library [iphlpapi.dll] loaded at %#v", modiphlpapi.Handle())
log.Printf("Symbol [WSACreateEvent] loaded at %#v", procWSACreateEvent.Addr())
log.Printf("Symbol [NotifyAddrChange] loaded at %#v", procNotifyAddrChange.Addr())
var (
err error
overlap *windows.Overlapped = &windows.Overlapped{}
)
log.Println("Invoking WSACreateEvent()")
overlap.HEvent, err = WSACreateEvent()
if err != nil {
log.Fatalf("failed to create internal windows event: %s", err)
} else {
log.Printf("Got handle at: %#v\n", overlap.HEvent)
}
event_loop:
for {
log.Println("Invoking NotifyAddrChange()")
notifyHandle := windows.Handle(0)
syscall.Syscall(uintptr(procNotifyAddrChange.Addr()), 2, uintptr(notifyHandle), uintptr(unsafe.Pointer(overlap)), 0)
log.Println("Waiting for network changes")
event, err := windows.WaitForSingleObject(overlap.HEvent, windows.INFINITE)
switch event {
case windows.WAIT_OBJECT_0:
log.Println("Windows kernel notified of a network address change")
// TODO(lh): Act upon interface changes
default:
log.Println(err)
break event_loop
}
}
windows.Close(overlap.HEvent)
}
func WSACreateEvent() (windows.Handle, error) {
handlePtr, _, errNum := syscall.Syscall(procWSACreateEvent.Addr(), 0, 0, 0, 0)
if handlePtr == 0 {
return 0, errNum
} else {
return windows.Handle(handlePtr), nil
}
}
@tmm1

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@tmm1 tmm1 commented Mar 23, 2018

Thanks for sharing! FYI, it's also possible to call NotifyAddrChange in synchronous mode, where you just pass nil for both arguments and it blocks until a change occurs.

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