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@KatelynHaworth
Created June 22, 2017 05:03
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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 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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