Fix #1947 - Check expected files are still present before restoring a session.

Author: stefanceriu

ElementX/Sources/Services/UserSession/SessionDirectories.swift

@@ -51,6 +51,14 @@ struct SessionDirectories: Hashable, Codable {
         }
     }
 
+    /// Check that mission critical files (the crypto db) are still in the right place when restoring a session
+    /// iOS might decide to move the app with its user defaults and keychain but without
+    /// some of the files stored in the shared container e.g. after a device transfer, offloading etc.
+    /// If that happens we should fail the session restoration.
+    func isNonTransientUserDataValid() -> Bool {
+        FileManager.default.fileExists(atPath: dataPath.appending("/matrix-sdk-crypto.sqlite3"))
+    }
+    
     private func deleteFiles(at url: URL, with prefix: String) throws {
         let sessionDirectoryContents = try FileManager.default.contentsOfDirectory(at: url, includingPropertiesForKeys: nil)
         for url in sessionDirectoryContents where url.lastPathComponent.hasPrefix(prefix) {

ElementX/Sources/Services/UserSession/UserSessionStore.swift

@@ -118,6 +118,11 @@ class UserSessionStore: UserSessionStoreProtocol {
             MXLog.info("Restoring client with encrypted store.")
         }
 
+        guard credentials.restorationToken.sessionDirectories.isNonTransientUserDataValid() else {
+            MXLog.error("Failed restoring login, missing non-transient user data")
+            return .failure(.failedRestoringLogin)
+        }
+        
         let homeserverURL = credentials.restorationToken.session.homeserverUrl
 
         let builder = ClientBuilder