1 files changed, 73 insertions, 0 deletions
diff --git a/tunnel/winipcfg/interface_change_handler.go b/tunnel/winipcfg/interface_change_handler.go
new file mode 100644
index 00000000..6bb8cf2b
--- /dev/null
+++ b/tunnel/winipcfg/interface_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"
+)
+
+// InterfaceChangeCallback structure allows interface change callback handling.
+type InterfaceChangeCallback struct {
+	cb func(notificationType MibNotificationType, iface *MibIPInterfaceRow)
+}
+
+var (
+	interfaceChangeMutex     = sync.Mutex{}
+	interfaceChangeCallbacks = make(map[*InterfaceChangeCallback]bool)
+	interfaceChangeHandle    = windows.Handle(0)
+)
+
+// RegisterInterfaceChangeCallback registers a new InterfaceChangeCallback. If this particular callback is already
+// registered, the function will silently return. Returned InterfaceChangeCallback.Unregister method should be used
+// to unregister.
+func RegisterInterfaceChangeCallback(callback func(notificationType MibNotificationType, iface *MibIPInterfaceRow)) (*InterfaceChangeCallback, error) {
+	cb := &InterfaceChangeCallback{callback}
+
+	interfaceChangeMutex.Lock()
+	defer interfaceChangeMutex.Unlock()
+
+	interfaceChangeCallbacks[cb] = true
+
+	if interfaceChangeHandle == 0 {
+		err := notifyIPInterfaceChange(windows.AF_UNSPEC, windows.NewCallback(interfaceChanged), 0, false, &interfaceChangeHandle)
+		if err != nil {
+			delete(interfaceChangeCallbacks, cb)
+			interfaceChangeHandle = 0
+			return nil, err
+		}
+	}
+
+	return cb, nil
+}
+
+// Unregister unregisters the callback.
+func (callback *InterfaceChangeCallback) Unregister() error {
+	interfaceChangeMutex.Lock()
+	defer interfaceChangeMutex.Unlock()
+
+	delete(interfaceChangeCallbacks, callback)
+
+	if len(interfaceChangeCallbacks) < 1 && interfaceChangeHandle != 0 {
+		err := cancelMibChangeNotify2(interfaceChangeHandle)
+		if err != nil {
+			return err
+		}
+		interfaceChangeHandle = 0
+	}
+
+	return nil
+}
+
+func interfaceChanged(callerContext uintptr, row *MibIPInterfaceRow, notificationType MibNotificationType) uintptr {
+	interfaceChangeMutex.Lock()
+	for cb := range interfaceChangeCallbacks {
+		cb.cb(notificationType, row)
+	}
+	interfaceChangeMutex.Unlock()
+	return 0
+}