1 files changed, 73 insertions, 0 deletions
diff --git a/tunnel/winipcfg/unicast_address_change_handler.go b/tunnel/winipcfg/unicast_address_change_handler.go
new file mode 100644
index 00000000..b0ae7950
--- /dev/null
+++ b/tunnel/winipcfg/unicast_address_change_handler.go
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
+ */
+
+package winipcfg
+
+import (
+	"sync"
+
+	"golang.org/x/sys/windows"
+)
+
+// UnicastAddressChangeCallback structure allows unicast address change callback handling.
+type UnicastAddressChangeCallback struct {
+	cb func(notificationType MibNotificationType, addr *MibUnicastIPAddressRow)
+}
+
+var (
+	unicastAddressChangeMutex     = sync.Mutex{}
+	unicastAddressChangeCallbacks = make(map[*UnicastAddressChangeCallback]bool)
+	unicastAddressChangeHandle    = windows.Handle(0)
+)
+
+// RegisterUnicastAddressChangeCallback registers a new UnicastAddressChangeCallback. If this particular callback is already
+// registered, the function will silently return. Returned UnicastAddressChangeCallback.Unregister method should be used
+// to unregister.
+func RegisterUnicastAddressChangeCallback(callback func(notificationType MibNotificationType, addr *MibUnicastIPAddressRow)) (*UnicastAddressChangeCallback, error) {
+	cb := &UnicastAddressChangeCallback{callback}
+
+	unicastAddressChangeMutex.Lock()
+	defer unicastAddressChangeMutex.Unlock()
+
+	unicastAddressChangeCallbacks[cb] = true
+
+	if unicastAddressChangeHandle == 0 {
+		err := notifyUnicastIPAddressChange(windows.AF_UNSPEC, windows.NewCallback(unicastAddressChanged), 0, false, &unicastAddressChangeHandle)
+		if err != nil {
+			delete(unicastAddressChangeCallbacks, cb)
+			unicastAddressChangeHandle = 0
+			return nil, err
+		}
+	}
+
+	return cb, nil
+}
+
+// Unregister unregisters the callback.
+func (callback *UnicastAddressChangeCallback) Unregister() error {
+	unicastAddressChangeMutex.Lock()
+	defer unicastAddressChangeMutex.Unlock()
+
+	delete(unicastAddressChangeCallbacks, callback)
+
+	if len(unicastAddressChangeCallbacks) < 1 && unicastAddressChangeHandle != 0 {
+		err := cancelMibChangeNotify2(unicastAddressChangeHandle)
+		if err != nil {
+			return err
+		}
+		unicastAddressChangeHandle = 0
+	}
+
+	return nil
+}
+
+func unicastAddressChanged(callerContext uintptr, row *MibUnicastIPAddressRow, notificationType MibNotificationType) uintptr {
+	unicastAddressChangeMutex.Lock()
+	for cb := range unicastAddressChangeCallbacks {
+		cb.cb(notificationType, row)
+	}
+	unicastAddressChangeMutex.Unlock()
+	return 0
+}