WireGuard add extra source files

Signed-off-by: Joseph Mattello <mail@joemattiello.com>

WireguardNetworkExtension/NotificationToken.swift

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2018-2021 WireGuard LLC. All Rights Reserved.
+
+import Foundation
+
+/// This source file contains bits of code from:
+/// https://oleb.net/blog/2018/01/notificationcenter-removeobserver/
+
+/// Wraps the observer token received from
+/// `NotificationCenter.addObserver(forName:object:queue:using:)`
+/// and unregisters it in deinit.
+final class NotificationToken {
+    let notificationCenter: NotificationCenter
+    let token: Any
+
+    init(notificationCenter: NotificationCenter = .default, token: Any) {
+        self.notificationCenter = notificationCenter
+        self.token = token
+    }
+
+    deinit {
+        notificationCenter.removeObserver(token)
+    }
+}
+
+extension NotificationCenter {
+    /// Convenience wrapper for addObserver(forName:object:queue:using:)
+    /// that returns our custom `NotificationToken`.
+    func observe(name: NSNotification.Name?, object obj: Any?, queue: OperationQueue?, using block: @escaping (Notification) -> Void) -> NotificationToken {
+        let token = addObserver(forName: name, object: obj, queue: queue, using: block)
+        return NotificationToken(notificationCenter: self, token: token)
+    }
+}