Add background app refresh support

ElementX/Sources/Application/AppCoordinator.swift

@@ -14,6 +14,7 @@
 // limitations under the License.
 //
 
+import BackgroundTasks
 import Combine
 import MatrixRustSDK
 import SwiftUI
@@ -49,6 +50,7 @@ class AppCoordinator: AppCoordinatorProtocol {
     private var userSessionObserver: AnyCancellable?
     private var networkMonitorObserver: AnyCancellable?
     private var initialSyncObserver: AnyCancellable?
+    private var backgroundRefreshSyncObserver: AnyCancellable?
 
     let notificationManager: NotificationManagerProtocol
 
@@ -93,6 +95,8 @@ class AppCoordinator: AppCoordinatorProtocol {
 
         observeApplicationState()
         observeNetworkState()
+
+        registerBackgroundAppRefresh()
     }
 
     func start() {
@@ -143,6 +147,7 @@ class AppCoordinator: AppCoordinatorProtocol {
         userSessionStore.reset()
     }
 
+    // swiftlint:disable:next cyclomatic_complexity
     private func setupStateMachine() {
         stateMachine.addTransitionHandler { [weak self] context in
             guard let self else { return }
@@ -342,7 +347,7 @@ class AppCoordinator: AppCoordinatorProtocol {
                 case .didReceiveAuthError(let isSoftLogout):
                     stateMachine.processEvent(.signOut(isSoft: isSoftLogout))
                 case .updateRestorationToken:
-                    userSessionStore.refreshRestorationToken(for: userSession)
+                    _ = userSessionStore.refreshRestorationToken(for: userSession)
                 default:
                     break
                 }
@@ -384,11 +389,10 @@ class AppCoordinator: AppCoordinatorProtocol {
         initialSyncObserver = userSession.clientProxy
             .callbacks
             .receive(on: DispatchQueue.main)
-            .sink { [weak self] callback in
-                if case .receivedSyncUpdate = callback {
-                    ServiceLocator.shared.userIndicatorController.retractIndicatorWithId(identifier)
-                    self?.initialSyncObserver?.cancel()
-                }
+            .filter(\.isSyncUpdate)
+            .sink { [weak self] _ in
+                ServiceLocator.shared.userIndicatorController.retractIndicatorWithId(identifier)
+                self?.initialSyncObserver?.cancel()
             }
     }
 
@@ -412,11 +416,17 @@ class AppCoordinator: AppCoordinatorProtocol {
         }
 
         backgroundTask = backgroundTaskService.startBackgroundTask(withName: "SuspendApp: \(UUID().uuidString)") { [weak self] in
-            self?.stopSync()
+            guard let self else { return }
 
-            self?.backgroundTask = nil
-            self?.isSuspended = true
+            stopSync()
+
+            backgroundTask = nil
+            isSuspended = true
         }
+
+        // This does seem to work if scheduled from the background task above
+        // Schedule it here instead but with an earliest being date of 30 seconds
+        scheduleBackgroundAppRefresh()
     }
 
     @objc
@@ -432,6 +442,8 @@ class AppCoordinator: AppCoordinatorProtocol {
         }
     }
 
+    // MARK: Other
+
     private func observeNetworkState() {
         let reachabilityNotificationIdentifier = "io.element.elementx.reachability.notification"
         networkMonitorObserver = ServiceLocator.shared.networkMonitor.reachabilityPublisher.sink { reachable in
@@ -474,6 +486,63 @@ class AppCoordinator: AppCoordinatorProtocol {
             hideLoadingIndicator()
         }
     }
+
+    // MARK: Background app refresh
+
+    private func registerBackgroundAppRefresh() {
+        let result = BGTaskScheduler.shared.register(forTaskWithIdentifier: ServiceLocator.shared.settings.backgroundAppRefreshTaskIdentifier, using: .main) { [weak self] task in
+            guard let task = task as? BGAppRefreshTask else {
+                MXLog.error("Invalid background app refresh configuration")
+                return
+            }
+
+            self?.handleBackgroundAppRefresh(task)
+        }
+
+        MXLog.info("Register background app refresh with result: \(result)")
+    }
+
+    private func scheduleBackgroundAppRefresh() {
+        let request = BGAppRefreshTaskRequest(identifier: ServiceLocator.shared.settings.backgroundAppRefreshTaskIdentifier)
+
+        // We have other background tasks that keep the app alive
+        request.earliestBeginDate = Date(timeIntervalSinceNow: 30)
+
+        do {
+            try BGTaskScheduler.shared.submit(request)
+            MXLog.info("Successfully scheduled background app refresh task")
+        } catch {
+            MXLog.error("Failed scheduling background app refresh with error :\(error)")
+        }
+    }
+
+    private func handleBackgroundAppRefresh(_ task: BGAppRefreshTask) {
+        MXLog.info("Started background app refresh")
+
+        // This is important for the app to keep refreshing in the background
+        scheduleBackgroundAppRefresh()
+
+        task.expirationHandler = { [weak self] in
+            MXLog.info("Background app refresh task expired")
+            self?.stopSync()
+            task.setTaskCompleted(success: true)
+        }
+
+        startSync()
+
+        // Be a good citizen, run for a max of 10 SS responses or 10 seconds
+        // An SS request will time out after 30 seconds if no new data is available
+        backgroundRefreshSyncObserver = userSession?.clientProxy
+            .callbacks
+            .filter(\.isSyncUpdate)
+            .collect(.byTimeOrCount(DispatchQueue.main, .seconds(10), 10))
+            .sink(receiveValue: { [weak self] _ in
+                MXLog.info("Background app refresh finished")
+                self?.backgroundRefreshSyncObserver?.cancel()
+                self?.stopSync()
+                task.setTaskCompleted(success: true)
+            })
+    }
 }
 
 // MARK: - AuthenticationCoordinatorDelegate

ElementX/Sources/Application/AppSettings.swift

@@ -84,6 +84,9 @@ final class AppSettings {
     /// that don't yet have an officially trusted proxy configured in their well-known.
     let slidingSyncProxyURL: URL? = nil
 
+    /// The task identifier used for background app refresh. Also used in main target's the Info.plist
+    let backgroundAppRefreshTaskIdentifier = "io.element.elementx.background.refresh"
+
     // MARK: - Authentication
 
     /// The URL that is opened when tapping the Learn more button on the sliding sync alert during authentication.

ElementX/Sources/Services/Client/ClientProxyProtocol.swift

@@ -23,6 +23,14 @@ enum ClientProxyCallback {
     case receivedAuthError(isSoftLogout: Bool)
     case receivedNotification(NotificationItemProxyProtocol)
     case updateRestorationToken
+
+    var isSyncUpdate: Bool {
+        if case .receivedSyncUpdate = self {
+            return true
+        } else {
+            return false
+        }
+    }
 }
 
 enum ClientProxyError: Error {

ElementX/SupportingFiles/Info.plist

@@ -2,6 +2,10 @@
 <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <plist version="1.0">
 <dict>
+	<key>BGTaskSchedulerPermittedIdentifiers</key>
+	<array>
+		<string>io.element.elementx.background.refresh</string>
+	</array>
 	<key>CFBundleDevelopmentRegion</key>
 	<string>$(DEVELOPMENT_LANGUAGE)</string>
 	<key>CFBundleDisplayName</key>
@@ -30,6 +34,10 @@
 	<array>
 		<string>INSendMessageIntent</string>
 	</array>
+	<key>UIBackgroundModes</key>
+	<array>
+		<string>fetch</string>
+	</array>
 	<key>UILaunchStoryboardName</key>
 	<string>LaunchScreen</string>
 	<key>UISupportedInterfaceOrientations</key>

ElementX/SupportingFiles/target.yml

@@ -64,6 +64,12 @@ targets:
         ]
         NSCameraUsageDescription: The camera is used to take and upload photos and videos.
         NSMicrophoneUsageDescription: The microphone is used to take videos.
+        UIBackgroundModes: [
+          fetch
+        ]
+        BGTaskSchedulerPermittedIdentifiers: [
+          io.element.elementx.background.refresh
+        ]
 
 
     settings: