Hide "sensitive" views from the App Switcher

Signal/AppLaunch/AppDelegate.swift

@@ -369,13 +369,14 @@ final class AppDelegate: UIResponder, UIApplicationDelegate {
         }
     }
 
-    private lazy var screenLockUI = ScreenLockUI(appReadiness: appReadiness)
-
     private func configureGlobalUI(in window: UIWindow) {
+        let screenLockUI = AppEnvironment.shared.screenLockUI
+        let windowManager = AppEnvironment.shared.windowManagerRef
+
         Theme.setupSignalAppearance()
 
         screenLockUI.setupWithRootWindow(window)
-        AppEnvironment.shared.windowManagerRef.setupWithRootWindow(window, screenBlockingWindow: screenLockUI.screenBlockingWindow)
+        windowManager.setupWithRootWindow(window, screenBlockingWindow: screenLockUI.screenBlockingWindow)
         screenLockUI.startObserving()
     }
 
@@ -1770,15 +1771,23 @@ final class AppDelegate: UIResponder, UIApplicationDelegate {
         }
         let isVideo = isVideoCall(intent)
 
-        Task { @MainActor [appReadiness, screenLockUI] in
+        Task { @MainActor [appReadiness] in
             do {
                 try await appReadiness.waitForAppReady()
+            } catch {
+                return
+            }
+
+            let callService = AppEnvironment.shared.callService!
+            let screenLockUI = AppEnvironment.shared.screenLockUI
+            let tsAccountManager = DependenciesBridge.shared.tsAccountManager
+
+            do {
                 try await screenLockUI.waitForScreenUnlockThrowingPrevious()
             } catch {
                 return
             }
 
-            let tsAccountManager = DependenciesBridge.shared.tsAccountManager
             guard tsAccountManager.registrationStateWithMaybeSneakyTransaction.isRegistered else {
                 Logger.warn("Ignoring user activity; not registered.")
                 return
@@ -1796,7 +1805,6 @@ final class AppDelegate: UIResponder, UIApplicationDelegate {
             // * It can be received if the user taps the "video" button for a contact
             // in the contacts app. If so, the correct response is to try to initiate a
             // new call to that user - unless there is another call in progress.
-            let callService = AppEnvironment.shared.callService!
             if let currentCall = callService.callServiceState.currentCall {
                 if isVideo, case .individual = currentCall.mode, currentCall.mode.matches(callTarget) {
                     Logger.info("Upgrading existing call to video")
@@ -1933,12 +1941,18 @@ extension AppDelegate: UNUserNotificationCenterDelegate {
         withCompletionHandler completionHandler: @escaping () -> Void,
     ) {
         let startDate = MonotonicDate()
-        Task { @MainActor [appReadiness, screenLockUI] () -> Void in
+        Task { @MainActor [appReadiness] () -> Void in
             defer { completionHandler() }
 
-            try await self.appReadiness.waitForAppReady()
+            do {
+                try await self.appReadiness.waitForAppReady()
+            } catch {
+                return
+            }
 
+            let screenLockUI = AppEnvironment.shared.screenLockUI
             let backgroundMessageFetcherFactory = DependenciesBridge.shared.backgroundMessageFetcherFactory
+
             let backgroundMessageFetcher = backgroundMessageFetcherFactory.buildFetcher()
             // So that we open up a connection for replies.
             await backgroundMessageFetcher.start()

Signal/AppLaunch/AppEnvironment.swift

@@ -22,12 +22,12 @@ public class AppEnvironment: NSObject {
     @MainActor
     var ownedObjects = [AnyObject]()
 
+    let cvAudioPlayerRef: CVAudioPlayer
     let deviceTransferServiceRef: DeviceTransferService
     let pushRegistrationManagerRef: PushRegistrationManager
-
-    let cvAudioPlayerRef = CVAudioPlayer()
-    let speechManagerRef = SpeechManager()
-    let windowManagerRef = WindowManager()
+    let screenLockUI: ScreenLockUI
+    let speechManagerRef: SpeechManager
+    let windowManagerRef: WindowManager
 
     private(set) var appIconBadgeUpdater: AppIconBadgeUpdater!
     private(set) var avatarHistoryManager: AvatarHistoryManager!
@@ -44,8 +44,12 @@ public class AppEnvironment: NSObject {
     private var registrationIdMismatchManager: RegistrationIdMismatchManager!
 
     init(appReadiness: AppReadiness, deviceTransferService: DeviceTransferService) {
+        self.cvAudioPlayerRef = CVAudioPlayer()
         self.deviceTransferServiceRef = deviceTransferService
+        self.screenLockUI = ScreenLockUI(appReadiness: appReadiness)
         self.pushRegistrationManagerRef = PushRegistrationManager(appReadiness: appReadiness)
+        self.speechManagerRef = SpeechManager()
+        self.windowManagerRef = WindowManager()
 
         super.init()
 

Signal/Backups/BackupRecordKeyViewController.swift

@@ -77,6 +77,9 @@ class BackupRecordKeyViewController: OWSViewController, OWSNavigationChildContro
     override func viewDidLoad() {
         super.viewDidLoad()
 
+        let screenLockUI = AppEnvironment.shared.screenLockUI
+        screenLockUI.sensitiveContentDidLoad(inViewController: self)
+
         view.backgroundColor = .Signal.groupedBackground
 
         if let onBackPressedBlock {

Signal/Backups/EnterAccountEntropyPoolViewController.swift

@@ -51,6 +51,9 @@ class EnterAccountEntropyPoolViewController: OWSViewController {
     override func viewDidLoad() {
         super.viewDidLoad()
 
+        let screenLockUI = AppEnvironment.shared.screenLockUI
+        screenLockUI.sensitiveContentDidLoad(inViewController: self)
+
         view.backgroundColor = colorConfig.background
         navigationItem.rightBarButtonItem = UIBarButtonItem(
             title: CommonStrings.nextButton,

Signal/src/ViewControllers/AppSettings/Payments/PaymentsViewPassphraseGridViewController.swift

@@ -25,6 +25,9 @@ class PaymentsViewPassphraseGridViewController: OWSViewController {
     override func viewDidLoad() {
         super.viewDidLoad()
 
+        let screenLockUI = AppEnvironment.shared.screenLockUI
+        screenLockUI.sensitiveContentDidLoad(inViewController: self)
+
         title = OWSLocalizedString(
             "SETTINGS_PAYMENTS_VIEW_PASSPHRASE_TITLE",
             comment: "Title for the 'view payments passphrase' view of the app settings.",

Signal/util/ScreenLockUI.swift

@@ -124,7 +124,7 @@ class ScreenLockUI {
         self.appReadiness = appReadiness
     }
 
-    // MARK: - Public
+    // MARK: -
 
     func setupWithRootWindow(_ rootWindow: UIWindow) {
         AssertIsOnMainThread()
@@ -180,6 +180,21 @@ class ScreenLockUI {
         }
     }
 
+    // MARK: - Sensitive Content
+
+    /// Tracks view controllers displaying "sensitive content" that should be
+    /// hidden from the App Switcher.
+    private var sensitiveContentViewControllers: WeakArray<UIViewController> = []
+
+    @MainActor
+    func sensitiveContentDidLoad(inViewController viewController: UIViewController) {
+        if sensitiveContentViewControllers.contains(where: { $0 === viewController }) {
+            return
+        }
+
+        sensitiveContentViewControllers.append(viewController)
+    }
+
     // MARK: - UI
 
     private func updateScreenBlockingWindowWithUIState(_ uiState: ScreenLockViewController.UIState) {
@@ -251,7 +266,16 @@ class ScreenLockUI {
             return .none
         }
 
-        guard SSKEnvironment.shared.preferencesRef.isScreenSecurityEnabled else {
+        // Cull any "sensitive content" view controllers that aren't actually
+        // presenting content. (Their presence here may suggest a retain cycle.)
+        sensitiveContentViewControllers.removeAll(where: { viewController in
+            !viewController.isViewLoaded || viewController.view.window == nil
+        })
+
+        guard
+            SSKEnvironment.shared.preferencesRef.isScreenSecurityEnabled
+            || sensitiveContentViewControllers.elements.count > 0
+        else {
             return .none
         }
 

SignalServiceKit/Util/Weak.swift

@@ -50,6 +50,16 @@ public struct WeakArray<Element> {
         }
     }
 
+    public func contains(where predictate: (Element) -> Bool) -> Bool {
+        return array.contains { weakElement in
+            if let element = weakElement.value, predictate(element) {
+                return true
+            }
+
+            return false
+        }
+    }
+
     public mutating func cullExpired() {
         array.removeAll { weakBox in
             weakBox.value == nil