Notify user of unexpected device link requests

Signal/src/Loki/View Controllers/BaseVC.swift

@@ -5,5 +5,19 @@ class BaseVC : UIViewController {
 
     override func viewDidLoad() {
         setNeedsStatusBarAppearanceUpdate()
+        NotificationCenter.default.addObserver(self, selector: #selector(handleUnexpectedDeviceLinkRequestReceivedNotification), name: .unexpectedDeviceLinkRequestReceived, object: nil)
+    }
+
+    deinit {
+        NotificationCenter.default.removeObserver(self)
+    }
+
+    @objc private func handleUnexpectedDeviceLinkRequestReceivedNotification() {
+        guard DeviceLinkingUtilities.shouldShowUnexpectedDeviceLinkRequestReceivedAlert else { return }
+        DispatchQueue.main.async {
+            let alert = UIAlertController(title: "Device Link Request Received", message: "Open the device link screen by going to \"Settings\"> \"Devices\" > \"Link a Device\" to link your devices.", preferredStyle: .alert)
+            alert.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
+            self.present(alert, animated: true, completion: nil)
+        }
     }
 }

Signal/src/ViewControllers/ConversationView/ConversationViewController.m

@@ -444,6 +444,11 @@ typedef enum : NSUInteger {
                                              selector:@selector(handleMessageFailedNotification:)
                                                  name:NSNotification.messageFailed
                                                object:nil];
+    // Device linking
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(handleUnexpectedDeviceLinkRequestReceivedNotification)
+                                                 name:NSNotification.unexpectedDeviceLinkRequestReceived
+                                               object:nil];
 }
 
 - (BOOL)isGroupConversation
@@ -5479,6 +5484,16 @@ typedef enum : NSUInteger {
     });
 }
 
+- (void)handleUnexpectedDeviceLinkRequestReceivedNotification
+{
+    if (!LKDeviceLinkingUtilities.shouldShowUnexpectedDeviceLinkRequestReceivedAlert) { return; }
+    dispatch_async(dispatch_get_main_queue(), ^{
+        UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Device Link Request Received" message:@"Open the device link screen by going to \"Settings\"> \"Devices\" > \"Link a Device\" to link your devices." preferredStyle:UIAlertControllerStyleAlert];
+        [alert addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:nil]];
+        [self presentViewController:alert animated:YES completion:nil];
+    });
+}
+
 @end
 
 NS_ASSUME_NONNULL_END

SignalServiceKit/src/Loki/API/Multi Device/DeviceLinkingUtilities.swift

@@ -1,6 +1,19 @@
 
-public enum DeviceLinkingUtilities {
-    
+@objc(LKDeviceLinkingUtilities)
+public final class DeviceLinkingUtilities : NSObject {
+    private static var lastUnexpectedDeviceLinkRequestDate: Date? = nil
+
+    private override init() { }
+
+    @objc public static var shouldShowUnexpectedDeviceLinkRequestReceivedAlert: Bool {
+        let now = Date()
+        if let lastUnexpectedDeviceLinkRequestDate = lastUnexpectedDeviceLinkRequestDate {
+            if now.timeIntervalSince(lastUnexpectedDeviceLinkRequestDate) < 30 { return false }
+        }
+        lastUnexpectedDeviceLinkRequestDate = now
+        return true
+    }
+
     // When requesting a device link, the slave device signs the master device's public key. When authorizing
     // a device link, the master device signs the slave device's public key.
     

SignalServiceKit/src/Loki/Utilities/Notification+Loki.swift

@@ -17,6 +17,8 @@ public extension Notification.Name {
     public static let seedViewed = Notification.Name("seedViewed")
     // Interaction
     public static let dataNukeRequested = Notification.Name("dataNukeRequested")
+    // Device linking
+    public static let unexpectedDeviceLinkRequestReceived = Notification.Name("unexpectedDeviceLinkRequestReceived")
 }
 
 @objc public extension NSNotification {
@@ -37,4 +39,6 @@ public extension Notification.Name {
     @objc public static let seedViewed = Notification.Name.seedViewed.rawValue as NSString
     // Interaction
     @objc public static let dataNukeRequested = Notification.Name.dataNukeRequested.rawValue as NSString
+    // Device linking
+    @objc public static let unexpectedDeviceLinkRequestReceived = Notification.Name.unexpectedDeviceLinkRequestReceived.rawValue as NSString
 }

SignalServiceKit/src/Messages/OWSMessageManager.m

@@ -494,6 +494,9 @@ NS_ASSUME_NONNULL_BEGIN
                 }
             } else if (slaveSignature != nil) { // Request
                 OWSLogInfo(@"[Loki] Received a device linking request from: %@", envelope.source); // Not slaveHexEncodedPublicKey
+                if (LKDeviceLinkingSession.current == nil) {
+                    [NSNotificationCenter.defaultCenter postNotificationName:NSNotification.unexpectedDeviceLinkRequestReceived object:nil];
+                }
                 [LKDeviceLinkingSession.current processLinkingRequestFrom:slaveHexEncodedPublicKey to:masterHexEncodedPublicKey with:slaveSignature];
             }
         } else if (contentProto.syncMessage) {