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Merged
wibosco merged 1 commit into from
Mar 19, 2025
Merged

Handling server errors #3

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53 changes: 33 additions & 20 deletions BackgroundTransfer-Example/Network/BackgroundDownloadService.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -12,8 +12,9 @@ import os
enum BackgroundDownloadServiceError: Error {
case missingInstructionsError
case fileSystemError(_ underlyingError: Error)
case networkError(_ underlyingError: Error)
case unknownError
case networkError(_ underlyingError: Error?)
case unexpectedResponseError
case unexpectedStatusCode
}

class BackgroundDownloadService: NSObject {
Expand All @@ -22,9 +23,7 @@ class BackgroundDownloadService: NSObject {
private var session: URLSession!

private var foregroundCompletionHandlers = [String: ((result: Result<URL, BackgroundDownloadServiceError>) -> ())]()

private var userDefaults = UserDefaults.standard


private let queue = DispatchQueue(label: "com.williamboles.background.download.service")

// MARK: - Singleton
Expand Down Expand Up @@ -53,7 +52,7 @@ class BackgroundDownloadService: NSObject {
os_log(.info, "Scheduling to download: %{public}@", remoteURL.absoluteString)

self?.foregroundCompletionHandlers[remoteURL.absoluteString] = completionHandler
self?.userDefaults.set(localURL, forKey: remoteURL.absoluteString)
UserDefaults.standard.set(localURL, forKey: remoteURL.absoluteString)

let task = self?.session.downloadTask(with: remoteURL)
task?.earliestBeginDate = Date().addingTimeInterval(2) // Remove this in production, the delay was added for demonstration purposes only
Expand All @@ -65,7 +64,9 @@ class BackgroundDownloadService: NSObject {
// MARK: - URLSessionDownloadDelegate

extension BackgroundDownloadService: URLSessionDownloadDelegate {
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
func urlSession(_ session: URLSession,
downloadTask: URLSessionDownloadTask,
didFinishDownloadingTo location: URL) {
queue.sync {
guard let originalRequestURL = downloadTask.originalRequest?.url?.absoluteString else {
os_log(.error, "Unexpected nil URL")
Expand All @@ -76,14 +77,28 @@ extension BackgroundDownloadService: URLSessionDownloadDelegate {

defer {
self.foregroundCompletionHandlers[originalRequestURL] = nil
self.userDefaults.removeObject(forKey: originalRequestURL)
UserDefaults.standard.removeObject(forKey: originalRequestURL)
}

os_log(.info, "Downloaded: %{public}@", originalRequestURL)
os_log(.info, "Download request completed for: %{public}@", originalRequestURL)

let foregroundCompletionHandler = self.foregroundCompletionHandlers[originalRequestURL]

guard let saveDownloadToURL = self.userDefaults.url(forKey: originalRequestURL) else {
guard let response = downloadTask.response as? HTTPURLResponse else {
os_log(.error, "Unexpected response for: %{public}@", originalRequestURL)
foregroundCompletionHandler?(.failure(.unexpectedResponseError))
return
}

guard response.statusCode == 200 else {
os_log(.error, "Unexpected status code of: %{public}d, for: %{public}@", response.statusCode, originalRequestURL)
foregroundCompletionHandler?(.failure(.unexpectedStatusCode))
return
}

os_log(.info, "Download successful for: %{public}@", originalRequestURL)

guard let saveDownloadToURL = UserDefaults.standard.url(forKey: originalRequestURL) else {
os_log(.error, "Unable to find existing download item for: %{public}@", originalRequestURL)
foregroundCompletionHandler?(.failure(.missingInstructionsError))

Expand All @@ -101,8 +116,14 @@ extension BackgroundDownloadService: URLSessionDownloadDelegate {
}
}

func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
func urlSession(_ session: URLSession,
task: URLSessionTask,
didCompleteWithError error: Error?) {
queue.async { [weak self] in
guard let error = error else {
return
}

guard let originalRequestURL = task.originalRequest?.url?.absoluteString else {
os_log(.error, "Unexpected nil URL")

Expand All @@ -111,20 +132,12 @@ extension BackgroundDownloadService: URLSessionDownloadDelegate {

defer {
self?.foregroundCompletionHandlers[originalRequestURL] = nil
self?.userDefaults.removeObject(forKey: originalRequestURL)
UserDefaults.standard.removeObject(forKey: originalRequestURL)
}

os_log(.info, "Download failed for: %{public}@", originalRequestURL)

let foregroundCompletionHandler = self?.foregroundCompletionHandlers[originalRequestURL]

guard let error = error else {
os_log(.error, "Unknown error caused download to fail for: %{public}@", originalRequestURL)
foregroundCompletionHandler?(.failure(.unknownError))

return
}

foregroundCompletionHandler?(.failure(.networkError(error)))
}
}
Expand Down