Prevent system from deleting caches while app is running

Mixin/Service/DeviceTransfer/DeviceTransferClient.swift

@@ -21,10 +21,10 @@ final class DeviceTransferClient {
     private let key: DeviceTransferKey
     private let remotePlatform: DeviceTransferPlatform
     private let connection: NWConnection
+    private let cacheContainerURL: URL
+    private let messageProcessor: DeviceTransferMessageProcessor
     private let queue = Queue(label: "one.mixin.messenger.DeviceTransferClient")
-    private let cacheContainerURL = FileManager.default.temporaryDirectory.appendingPathComponent("DeviceTransfer", isDirectory: true)
     private let speedInspector = NetworkSpeedInspector()
-    private let messageProcessor: DeviceTransferMessageProcessor
 
     private weak var statisticsTimer: Timer?
 
@@ -40,7 +40,18 @@ final class DeviceTransferClient {
         Unmanaged<DeviceTransferClient>.passUnretained(self).toOpaque()
     }
 
-    init(hostname: String, port: UInt16, code: UInt16, key: DeviceTransferKey, remotePlatform: DeviceTransferPlatform) {
+    init(hostname: String, port: UInt16, code: UInt16, key: DeviceTransferKey, remotePlatform: DeviceTransferPlatform) throws {
+        // https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/FileSystemOverview/FileSystemOverview.html#//apple_ref/doc/uid/TP40010672-CH2-SW2
+        // In iOS 5.0 and later, the system may delete the Caches directory on rare occasions when the system is very low on disk space.
+        // This will never occur while an app is running.
+        let manager = FileManager.default
+        let cacheContainerURL = try manager.url(for: .cachesDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
+            .appendingPathComponent("DeviceTransfer")
+        if manager.fileExists(atPath: cacheContainerURL.path) {
+            try? manager.removeItem(at: cacheContainerURL)
+        }
+        try manager.createDirectory(at: cacheContainerURL, withIntermediateDirectories: true)
+
         self.hostname = hostname
         self.port = port
         self.code = code
@@ -52,6 +63,7 @@ final class DeviceTransferClient {
             let endpoint = NWEndpoint.hostPort(host: host, port: port)
             return NWConnection(to: endpoint, using: .deviceTransfer)
         }()
+        self.cacheContainerURL = cacheContainerURL
         self.messageProcessor = .init(key: key.aes,
                                       remotePlatform: remotePlatform,
                                       cacheContainerURL: cacheContainerURL,
@@ -65,17 +77,6 @@ final class DeviceTransferClient {
 
     func start() {
         Logger.general.info(category: "DeviceTransferClient", message: "Will start connecting to [\(hostname)]:\(port)")
-        do {
-            let manager = FileManager.default
-            if manager.fileExists(atPath: cacheContainerURL.path) {
-                try? manager.removeItem(at: cacheContainerURL)
-            }
-            try manager.createDirectory(at: cacheContainerURL, withIntermediateDirectories: true)
-        } catch {
-            Logger.general.error(category: "DeviceTransferClient", message: "Failed to create cache container: \(error)")
-            fail(error: .createCacheContainer(error))
-            return
-        }
         messageProcessor.$processingError
             .receive(on: queue.dispatchQueue)
             .sink { error in

Mixin/Service/DeviceTransfer/DeviceTransferError.swift

@@ -7,6 +7,5 @@ enum DeviceTransferError: Error {
     case mismatchedHMAC(local: Data, remote: Data)
     case connectionFailed(Error)
     case receiveFile(Error)
-    case createCacheContainer(Error)
     case importing(DeviceTransferMessageProcessor.ProcessingError)
 }

Mixin/UserInterface/Controllers/DeviceTransfer/RestoreFromDesktopViewController.swift

@@ -119,17 +119,24 @@ extension RestoreFromDesktopViewController {
             dataSource.replaceSection(at: 0, with: section, animation: .automatic)
             tableView.isUserInteractionEnabled = true
         case let .push(context):
-            let client = DeviceTransferClient(hostname: context.hostname,
-                                              port: context.port,
-                                              code: context.code,
-                                              key: context.key,
-                                              remotePlatform: command.platform)
-            stateObserver = client.$state
-                .receive(on: DispatchQueue.main)
-                .sink { [weak self] state in
-                    self?.stateDidChange(client: client, state: state)
+            do {
+                let client = try DeviceTransferClient(hostname: context.hostname,
+                                                      port: context.port,
+                                                      code: context.code,
+                                                      key: context.key,
+                                                      remotePlatform: command.platform)
+                stateObserver = client.$state
+                    .receive(on: DispatchQueue.main)
+                    .sink { [weak self] state in
+                        self?.stateDidChange(client: client, state: state)
+                    }
+                client.start()
+            } catch {
+                Logger.general.error(category: "RestoreFromDesktop", message: "Unable to init client: \(error)")
+                alert(R.string.localizable.connection_establishment_failed(), message: nil) { _ in
+                    self.navigationController?.popViewController(animated: true)
                 }
-            client.start()
+            }
         default:
             Logger.general.info(category: "RestoreFromDesktop", message: "Invalid command")
             alert(R.string.localizable.connection_establishment_failed(), message: nil) { _ in

Mixin/UserInterface/Windows/UrlWindow.swift

@@ -888,17 +888,22 @@ class UrlWindow {
             UIApplication.currentActivity()?.alert(R.string.localizable.unable_synced_between_different_account())
             return true
         }
-        let client = DeviceTransferClient(hostname: context.hostname,
-                                          port: context.port,
-                                          code: context.code,
-                                          key: context.key,
-                                          remotePlatform: command.platform)
-        client.start()
-        let progress = DeviceTransferProgressViewController(connection: .client(client, .phone))
-        if let navigationController = AppDelegate.current.mainWindow.rootViewController as? UINavigationController {
-            navigationController.pushViewController(progress, animated: true)
-        } else {
-            AppDelegate.current.mainWindow.rootViewController?.present(progress, animated: true)
+        do {
+            let client = try DeviceTransferClient(hostname: context.hostname,
+                                                  port: context.port,
+                                                  code: context.code,
+                                                  key: context.key,
+                                                  remotePlatform: command.platform)
+            client.start()
+            let progress = DeviceTransferProgressViewController(connection: .client(client, .phone))
+            if let navigationController = AppDelegate.current.mainWindow.rootViewController as? UINavigationController {
+                navigationController.pushViewController(progress, animated: true)
+            } else {
+                AppDelegate.current.mainWindow.rootViewController?.present(progress, animated: true)
+            }
+        } catch {
+            Logger.general.error(category: "UrlWindow", message: "Unable to init client: \(error)")
+            UIApplication.currentActivity()?.alert(R.string.localizable.connection_establishment_failed())
         }
         return true
     }