Verifies min/max OS version before downloading app + asks user to download older app version if necessary

AltStore/Operations/DownloadAppOperation.swift

@@ -20,7 +20,6 @@ class DownloadAppOperation: ResultOperation<ALTApplication>
     
     private let appName: String
     private let bundleIdentifier: String
-    private var sourceURL: URL?
     private let destinationURL: URL
     
     private let session = URLSession(configuration: .default)
@@ -33,7 +32,6 @@ class DownloadAppOperation: ResultOperation<ALTApplication>
         
         self.appName = app.name
         self.bundleIdentifier = app.bundleIdentifier
-        self.sourceURL = app.url
         self.destinationURL = destinationURL
         
         super.init()
@@ -54,9 +52,88 @@ class DownloadAppOperation: ResultOperation<ALTApplication>
         
         print("Downloading App:", self.bundleIdentifier)
         
-        guard let sourceURL = self.sourceURL else { return self.finish(.failure(OperationError.appNotFound(name: self.appName))) }
+        // Set _after_ checking self.context.error to prevent overwriting localized failure for previous errors.
+        self.localizedFailure = String(format: NSLocalizedString("%@ could not be downloaded.", comment: ""), self.appName)
         
-        self.downloadApp(from: sourceURL) { result in
+        guard let storeApp = self.app as? StoreApp else {
+            return self.download(self.app)
+        }
+        
+        // Verify storeApp
+        storeApp.managedObjectContext?.perform {
+            do
+            {
+                let latestVersion = try self.verify(storeApp)
+                self.download(latestVersion)
+            }
+            catch let error as VerificationError where error.code == .iOSVersionNotSupported
+            {
+                guard let presentingViewController = self.context.presentingViewController,
+                      let latestSupportedVersion = storeApp.latestSupportedVersion, case let version = latestSupportedVersion.version, version != storeApp.installedApp?.version
+                else { return self.finish(.failure(error)) }
+                
+                let title = NSLocalizedString("Unsupported iOS Version", comment: "")
+                let message = error.localizedDescription + "\n\n" + NSLocalizedString("Would you like to download the last version compatible with this device instead?", comment: "")
+                                
+                DispatchQueue.main.async {
+                    let alertController = UIAlertController(title: title, message: message, preferredStyle: .alert)
+                    alertController.addAction(UIAlertAction(title: UIAlertAction.cancel.title, style: UIAlertAction.cancel.style) { _ in
+                        self.finish(.failure(OperationError.cancelled))
+                    })
+                    alertController.addAction(UIAlertAction(title: String(format: NSLocalizedString("Download %@ %@", comment: ""), self.appName, version), style: .default) { _ in
+                        self.download(latestSupportedVersion)
+                    })
+                    presentingViewController.present(alertController, animated: true)
+                }
+            }
+            catch
+            {
+                self.finish(.failure(error))
+            }
+        }
+    }
+    
+    override func finish(_ result: Result<ALTApplication, Error>)
+    {
+        do
+        {
+            try FileManager.default.removeItem(at: self.temporaryDirectory)
+        }
+        catch
+        {
+            print("Failed to remove DownloadAppOperation temporary directory: \(self.temporaryDirectory).", error)
+        }
+        
+        super.finish(result)
+    }
+}
+
+private extension DownloadAppOperation
+{
+    func verify(_ storeApp: StoreApp) throws -> AppVersion
+    {
+        guard let version = storeApp.latestAvailableVersion else {
+            let failureReason = String(format: NSLocalizedString("The latest version of %@ could not be determined.", comment: ""), self.appName)
+            throw OperationError.unknown(failureReason: failureReason)
+        }
+        
+        if let minOSVersion = version.minOSVersion, !ProcessInfo.processInfo.isOperatingSystemAtLeast(minOSVersion)
+        {
+            throw VerificationError.iOSVersionNotSupported(app: storeApp, requiredOSVersion: minOSVersion)
+        }
+        else if let maxOSVersion = version.maxOSVersion, ProcessInfo.processInfo.operatingSystemVersion > maxOSVersion
+        {
+            throw VerificationError.iOSVersionNotSupported(app: storeApp, requiredOSVersion: maxOSVersion)
+        }
+        
+        return version
+    }
+    
+    func download(@Managed _ app: AppProtocol)
+    {
+        guard let sourceURL = $app.url else { return self.finish(.failure(OperationError.appNotFound(name: self.appName))) }
+        
+        self.downloadIPA(from: sourceURL) { result in
             do
             {
                 let application = try result.get()
@@ -97,24 +174,7 @@ class DownloadAppOperation: ResultOperation<ALTApplication>
         }
     }
     
-    override func finish(_ result: Result<ALTApplication, Error>)
+    func downloadIPA(from sourceURL: URL, completionHandler: @escaping (Result<ALTApplication, Error>) -> Void)
-    {
-        do
-        {
-            try FileManager.default.removeItem(at: self.temporaryDirectory)
-        }
-        catch
-        {
-            print("Failed to remove DownloadAppOperation temporary directory: \(self.temporaryDirectory).", error)
-        }
-        
-        super.finish(result)
-    }
-}
-
-private extension DownloadAppOperation
-{
-    func downloadApp(from sourceURL: URL, completionHandler: @escaping (Result<ALTApplication, Error>) -> Void)
     {
         func finishOperation(_ result: Result<URL, Error>)
         {

AltStore/Operations/VerifyAppOperation.swift

@@ -25,7 +25,10 @@ extension VerificationError
     
     static func privateEntitlements(_ entitlements: [String: Any], app: ALTApplication) -> VerificationError { VerificationError(code: .privateEntitlements, app: app, entitlements: entitlements) }
     static func mismatchedBundleIdentifiers(sourceBundleID: String, app: ALTApplication) -> VerificationError  { VerificationError(code: .mismatchedBundleIdentifiers, app: app, sourceBundleID: sourceBundleID) }
-    static func iOSVersionNotSupported(app: ALTApplication) -> VerificationError  { VerificationError(code: .iOSVersionNotSupported, app: app) }
+    
+    static func iOSVersionNotSupported(app: AppProtocol, osVersion: OperatingSystemVersion = ProcessInfo.processInfo.operatingSystemVersion, requiredOSVersion: OperatingSystemVersion?) -> VerificationError {
+        VerificationError(code: .iOSVersionNotSupported, app: app, deviceOSVersion: osVersion, requiredOSVersion: requiredOSVersion)
+    }
 }
 
 struct VerificationError: ALTLocalizedError
@@ -35,22 +38,44 @@ struct VerificationError: ALTLocalizedError
     var errorTitle: String?
     var errorFailure: String?
     
-    var app: ALTApplication?
+    @Managed var app: AppProtocol?
     var entitlements: [String: Any]?
     var sourceBundleID: String?
+    var deviceOSVersion: OperatingSystemVersion?
+    var requiredOSVersion: OperatingSystemVersion?
     
+    var errorDescription: String? {
+        switch self.code
+        {
+        case .iOSVersionNotSupported:
+            guard let deviceOSVersion else { return nil }
+            
+            var failureReason = self.errorFailureReason
+            if self.app == nil
+            {
+                // failureReason does not start with app name, so make first letter lowercase.
+                let firstLetter = failureReason.prefix(1).lowercased()
+                failureReason = firstLetter + failureReason.dropFirst()
+            }
+            
+            let localizedDescription = String(format: NSLocalizedString("This device is running iOS %@, but %@", comment: ""), deviceOSVersion.stringValue, failureReason)
+            return localizedDescription
+            
+        default: return nil
+        }
+    }
     
     var errorFailureReason: String {
         switch self.code
         {
         case .privateEntitlements:
-            let appName = (self.app?.name as String?).map { String(format: NSLocalizedString("“%@”", comment: ""), $0) } ?? NSLocalizedString("The app", comment: "")
+            let appName = self.$app.name ?? NSLocalizedString("The app", comment: "")
             return String(format: NSLocalizedString("%@ requires private permissions.", comment: ""), appName)
             
         case .mismatchedBundleIdentifiers:
-            if let app = self.app, let bundleID = self.sourceBundleID
+            if let appBundleID = self.$app.bundleIdentifier, let bundleID = self.sourceBundleID
             {
-                return String(format: NSLocalizedString("The bundle ID “%@” does not match the one specified by the source (“%@”).", comment: ""), app.bundleIdentifier, bundleID)
+                return String(format: NSLocalizedString("The bundle ID “%@” does not match the one specified by the source (“%@”).", comment: ""), appBundleID, bundleID)
             }
             else
             {
@@ -58,22 +83,25 @@ struct VerificationError: ALTLocalizedError
             }
             
         case .iOSVersionNotSupported:
-            if let app = self.app
+            let appName = self.$app.name ?? NSLocalizedString("The app", comment: "")
+            let deviceOSVersion = self.deviceOSVersion ?? ProcessInfo.processInfo.operatingSystemVersion
+            
+            guard let requiredOSVersion else {
+                return String(format: NSLocalizedString("%@ does not support iOS %@.", comment: ""), appName, deviceOSVersion.stringValue)
+            }
+            
+            if deviceOSVersion > requiredOSVersion
             {
-                var version = "iOS \(app.minimumiOSVersion.majorVersion).\(app.minimumiOSVersion.minorVersion)"
+                // Device OS version is higher than maximum supported OS version.
-                if app.minimumiOSVersion.patchVersion > 0
-                {
-                    version += ".\(app.minimumiOSVersion.patchVersion)"
-                }
                 
-                let failureReason = String(format: NSLocalizedString("%@ requires %@.", comment: ""), app.name, version)
+                let failureReason = String(format: NSLocalizedString("%@ requires iOS %@ or earlier.", comment: ""), appName, requiredOSVersion.stringValue)
                 return failureReason
             }
             else
             {
-                let version = ProcessInfo.processInfo.operatingSystemVersion.stringValue
+                // Device OS version is lower than minimum supported OS version.
                 
-                let failureReason = String(format: NSLocalizedString("This app does not support iOS %@.", comment: ""), version)
+                let failureReason = String(format: NSLocalizedString("%@ requires iOS %@ or later.", comment: ""), appName, requiredOSVersion.stringValue)
                 return failureReason
             }
         }
@@ -114,7 +142,7 @@ class VerifyAppOperation: ResultOperation<Void>
             }
             
             guard ProcessInfo.processInfo.isOperatingSystemAtLeast(app.minimumiOSVersion) else {
-                throw VerificationError.iOSVersionNotSupported(app: app)
+                throw VerificationError.iOSVersionNotSupported(app: app, requiredOSVersion: app.minimumiOSVersion)
             }
             
             if #available(iOS 13.5, *)
@@ -196,8 +224,7 @@ private extension VerifyAppOperation
                 }))
                 presentingViewController.present(alertController, animated: true, completion: nil)
                 
-            case .mismatchedBundleIdentifiers: return completion(.failure(error))
+            case .mismatchedBundleIdentifiers, .iOSVersionNotSupported: return completion(.failure(error))
-            case .iOSVersionNotSupported: return completion(.failure(error))
             }
         }
     }