Handle download errors

BookPlayer/Coordinators/LibraryListCoordinator.swift

@@ -85,6 +85,7 @@ class LibraryListCoordinator: ItemListCoordinator, UINavigationControllerDelegat
     loadLastBookIfNeeded()
     syncList()
     bindImportObserverIfNeeded()
+    bindDownloadErrorObserver()
 
     if let appDelegate = AppDelegate.shared {
       for action in appDelegate.pendingURLActions {
@@ -136,6 +137,13 @@ class LibraryListCoordinator: ItemListCoordinator, UINavigationControllerDelegat
     notifyPendingFiles()
   }
 
+  func bindDownloadErrorObserver() {
+    syncService.downloadErrorPublisher.sink { (relativePath, error) in
+      self.showAlert("network_error_title".localized, message: "\(relativePath)\n\(error.localizedDescription)")
+    }
+    .store(in: &disposeBag)
+  }
+
   @MainActor
   func notifyPendingFiles() {
     // Get reference of all the files located inside the Documents, Shared and Inbox folders

BookPlayer/Library/ItemList Screen/ItemListViewModel.swift

@@ -211,12 +211,12 @@ class ItemListViewModel: ViewModelProtocol {
       ))
     }
 
-    singleDownloadProgressDelegateInterface.didFinishDownloadingTask = { [weak self] (task, fileURL) in
-      self?.handleSingleDownloadTaskFinished(task, fileURL: fileURL)
-    }
-
-    singleDownloadProgressDelegateInterface.didFinishTaskWithError = { [weak self] (task, error) in
-      self?.handleSingleDownloadTaskFinishedWithError(task, error: error)
+    singleDownloadProgressDelegateInterface.didFinishDownloadingTask = { [weak self] (task, fileURL, error) in
+      if let error {
+        self?.handleSingleDownloadTaskFinishedWithError(task, error: error)
+      } else if let fileURL {
+        self?.handleSingleDownloadTaskFinished(task, fileURL: fileURL)
+      }
     }
   }
 

Shared/Network/BPDownloadURLSession.swift

@@ -19,7 +19,7 @@ public class BPDownloadURLSession {
   ///   - didFinishDownloadingTask: Callback triggered when the download task is finished
   public init(
     downloadProgressUpdated: @escaping ((URLSessionDownloadTask, Double) -> Void),
-    didFinishDownloadingTask: @escaping ((URLSessionDownloadTask, URL) -> Void)
+    didFinishDownloadingTask: @escaping ((URLSessionTask, URL?, Error?) -> Void)
   ) {
     let bundleIdentifier: String = Bundle.main.configurationValue(for: .bundleIdentifier)
 

Shared/Network/BPTaskDownloadDelegate.swift

@@ -10,10 +10,7 @@ import Foundation
 
 public class BPTaskDownloadDelegate: NSObject, URLSessionDownloadDelegate {
   /// Callback triggered when the download task is finished
-  public var didFinishDownloadingTask: ((URLSessionDownloadTask, URL) -> Void)?
-  /// Callback triggered when the download task fails
-  /// - Note: the Error parameter represents client side errors
-  public var didFinishTaskWithError: ((URLSessionTask, Error?) -> Void)?
+  public var didFinishDownloadingTask: ((URLSessionTask, URL?, Error?) -> Void)?
   /// Callback triggered when there's an update on the download progress
   public var downloadProgressUpdated: ((URLSessionDownloadTask, Double) -> Void)?
   /// Delegate callback when download finishes
@@ -22,12 +19,21 @@ public class BPTaskDownloadDelegate: NSObject, URLSessionDownloadDelegate {
     downloadTask: URLSessionDownloadTask,
     didFinishDownloadingTo location: URL
   ) {
-    didFinishDownloadingTask?(downloadTask, location)
+    didFinishDownloadingTask?(
+      downloadTask,
+      location,
+      parseErrorFromTask(downloadTask)
+    )
   }
 
   /// Note: this gets called even if there's no error
-  public func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
-    didFinishTaskWithError?(task, error)
+  public func urlSession(
+    _ session: URLSession,
+    task: URLSessionTask,
+    didCompleteWithError error: Error?
+  ) {
+    let error = error ?? parseErrorFromTask(task)
+    didFinishDownloadingTask?(task, nil, error)
   }
 
   /// Delegate callback when there's a progress update for the ongoing download
@@ -42,4 +48,16 @@ public class BPTaskDownloadDelegate: NSObject, URLSessionDownloadDelegate {
 
     downloadProgressUpdated?(downloadTask, Double(calculatedProgress))
   }
+
+  private func parseErrorFromTask(_ task: URLSessionTask) -> Error? {
+    guard
+      let response = task.response as? HTTPURLResponse,
+      response.statusCode >= 400
+    else {
+      return nil
+    }
+
+    let errorCode = URLError.Code(rawValue: response.statusCode)
+    return URLError(errorCode)
+  }
 }

Shared/Services/Sync/SyncService.swift

@@ -27,6 +27,8 @@ public protocol SyncServiceProtocol {
   var downloadCompletedPublisher: PassthroughSubject<(String, String, String?), Never> { get }
   /// Progress publisher for ongoing-download tasks
   var downloadProgressPublisher: PassthroughSubject<(String, String, String?, Double), Never> { get }
+  /// Error publisher for ongoing-download tasks
+  var downloadErrorPublisher: PassthroughSubject<(String, Error), Never> { get }
 
   /// Count of the currently queued sync jobs
   func queuedJobsCount() async -> Int
@@ -105,17 +107,20 @@ public final class SyncService: SyncServiceProtocol, BPLogger {
   public var downloadCompletedPublisher = PassthroughSubject<(String, String, String?), Never>()
   /// Progress publisher for ongoing-download tasks
   public var downloadProgressPublisher = PassthroughSubject<(String, String, String?, Double), Never>()
+  /// Error publisher for ongoing-download tasks
+  public var downloadErrorPublisher = PassthroughSubject<(String, Error), Never>()
   /// Background URL session to handle downloading synced items
   private lazy var downloadURLSession: BPDownloadURLSession = {
     BPDownloadURLSession { task, progress in
       self.handleDownloadProgressUpdated(
         task: task,
         individualProgress: progress
       )
-    } didFinishDownloadingTask: { task, location in
+    } didFinishDownloadingTask: { task, location, error in
       self.handleFinishedDownload(
         task: task,
-        location: location
+        location: location,
+        error: error
       )
     }
   }()
@@ -547,26 +552,39 @@ extension SyncService {
 }
 
 extension SyncService {
-  private func handleFinishedDownload(task: URLSessionTask, location: URL) {
+  private func handleFinishedDownload(
+    task: URLSessionTask,
+    location: URL?,
+    error: Error?
+  ) {
     guard let relativePath = task.taskDescription else { return }
 
     do {
-      let fileURL = DataManager.getProcessedFolderURL().appendingPathComponent(relativePath)
+      if error == nil,
+         let location {
+        let fileURL = DataManager.getProcessedFolderURL().appendingPathComponent(relativePath)
 
-      /// If there's already something there, replace with new finished download
-      if FileManager.default.fileExists(atPath: fileURL.path) {
-        try FileManager.default.removeItem(at: fileURL)
-      }
-      try DataManager.createContainingFolderIfNeeded(for: fileURL)
-      try FileManager.default.moveItem(at: location, to: fileURL)
+        /// If there's already something there, replace with new finished download
+        if FileManager.default.fileExists(atPath: fileURL.path) {
+          try FileManager.default.removeItem(at: fileURL)
+        }
+        try DataManager.createContainingFolderIfNeeded(for: fileURL)
+        try FileManager.default.moveItem(at: location, to: fileURL)
 
-      Task {
-        await self.libraryService.loadChaptersIfNeeded(relativePath: relativePath)
+        Task {
+          await self.libraryService.loadChaptersIfNeeded(relativePath: relativePath)
+        }
       }
     } catch {
       Self.logger.trace("Error moving downloaded file to the destination: \(error.localizedDescription)")
     }
 
+    if let error {
+      DispatchQueue.main.async {
+        self.downloadErrorPublisher.send((relativePath, error))
+      }
+    }
+
     guard let startingItemPath = ongoingTasksParentReference[relativePath] else {
       initiatingFolderReference[relativePath] = nil
       return