REST request from iOS background URLSession using APNs - ios

Question

Update 2018-05-25:
I replaced datatask with downloadTask after reading Rob's answer here: https://stackoverflow.com/a/44140059/4666760 . It still does not work when the app is backgrounded.
Hello
I need some help with iOS background tasks. I want to use Apple Push Notification service (APNs) to wake up my app in the background so that it can do a simple RESTful API call to my server. I am able to make it work when the app is in the foreground, but not in the background. I think I do something wrong with the configuration of the URLSession, but I don't know. The entire code for the app and the server is at my repo linked below. Please, clone it and do whatever you like - I just want your help :)
https://github.com/knutvalen/ping
In AppDelegate.swift the app listen for remote notifications:
class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate {
// MARK: - Properties
var window: UIWindow?
// MARK: - Private functions
private func registerForPushNotifications() {
UNUserNotificationCenter.current().delegate = self
UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { (granted, error) in
guard granted else { return }
DispatchQueue.main.async {
UIApplication.shared.registerForRemoteNotifications()
}
}
}
// MARK: - Delegate functions
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
Login.shared.username = "foo"
registerForPushNotifications()
return true
}
func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
let tokenParts = deviceToken.map { data -> String in
return String(format: "%02.2hhx", data)
}
let token = tokenParts.joined()
os_log("AppDelegate application(_:didRegisterForRemoteNotificationsWithDeviceToken:) token: %#", token)
}
func application(_ application: UIApplication, didFailToRegisterForRemoteNotificationsWithError error: Error) {
os_log("AppDelegate application(_:didFailToRegisterForRemoteNotificationsWithError:) error: %#", error.localizedDescription)
}
func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any], fetchCompletionHandler completionHandler: #escaping (UIBackgroundFetchResult) -> Void) {
os_log("AppDelegate application(_:didReceiveRemoteNotification:fetchCompletionHandler:)")
if let aps = userInfo["aps"] as? [String: AnyObject] {
if aps["content-available"] as? Int == 1 {
RestController.shared.onPing = { () in
RestController.shared.onPing = nil
completionHandler(.newData)
os_log("AppDelegate onPing")
}
RestController.shared.pingBackground(login: Login.shared)
// RestController.shared.pingForeground(login: Login.shared)
}
}
}
func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: #escaping () -> Void) {
RestController.shared.backgroundSessionCompletionHandler = completionHandler
}
}
The RestController.swift handles URLSessions with background configurations:
class RestController: NSObject, URLSessionDelegate, URLSessionTaskDelegate, URLSessionDownloadDelegate {
// MARK: - Properties
static let shared = RestController()
let identifier = "no.qassql.ping.background"
let ip = "http://123.456.7.89:3000"
var backgroundUrlSession: URLSession?
var backgroundSessionCompletionHandler: (() -> Void)?
var onPing: (() -> ())?
// MARK: - Initialization
override init() {
super.init()
let configuration = URLSessionConfiguration.background(withIdentifier: identifier)
configuration.isDiscretionary = false
configuration.sessionSendsLaunchEvents = true
backgroundUrlSession = URLSession(configuration: configuration, delegate: self, delegateQueue: nil)
}
// MARK: - Delegate functions
func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
DispatchQueue.main.async {
if let completionHandler = self.backgroundSessionCompletionHandler {
self.backgroundSessionCompletionHandler = nil
completionHandler()
}
}
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
if let error = error {
os_log("RestController urlSession(_:task:didCompleteWithError:) error: %#", error.localizedDescription)
}
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
do {
let data = try Data(contentsOf: location)
let respopnse = downloadTask.response
let error = downloadTask.error
self.completionHandler(data: data, response: respopnse, error: error)
} catch {
os_log("RestController urlSession(_:downloadTask:didFinishDownloadingTo:) error: %#", error.localizedDescription)
}
}
// MARK: - Private functions
private func completionHandler(data: Data?, response: URLResponse?, error: Error?) {
guard let data = data else { return }
if let okResponse = OkResponse.deSerialize(data: data) {
if okResponse.message == ("ping_" + Login.shared.username) {
RestController.shared.onPing?()
}
}
}
// MARK: - Public functions
func pingBackground(login: Login) {
guard let url = URL(string: ip + "/ping") else { return }
var request = URLRequest(url: url, cachePolicy: .reloadIgnoringCacheData, timeoutInterval: 20)
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpMethod = "POST"
request.httpBody = login.serialize()
if let backgroundUrlSession = backgroundUrlSession {
backgroundUrlSession.downloadTask(with: request).resume()
}
}
func pingForeground(login: Login) {
guard let url = URL(string: ip + "/ping") else { return }
var request = URLRequest(url: url)
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpMethod = "POST"
request.httpBody = login.serialize()
URLSession.shared.dataTask(with: request) { (data, response, error) in
return self.completionHandler(data: data, response: response, error: error)
}.resume()
}
}

Answer 1

By adding App provides Voice over IP services as Required Background Mode in info.plist and using PushKit to handle the APNs payloads I were able to do what I wanted. A SSCCE (example) is available at my repository:
https://github.com/knutvalen/ping