URLSessionTaskDelegate never called in Command Line tool [duplicate] - swift

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How to prevent a Command Line Tool from exiting before asynchronous operation completes
(7 answers)
Closed 2 years ago.
I'm trying to write my first Swift command line tool. The tool creates a network request and I want to print the progress of the request using URLSessionTaskDelegate.
The basic URL request code is here:
EDIT: updating more complete example
class ApiSession: NSObject, URLSessionTaskDelegate {
func makeRequest(request: URLRequest,
callback: #escaping (Data?, URLResponse?, Error?) -> Void) {
let urlSession = URLSession(configuration: .default, delegate: self, delegateQueue: .main)
let task = urlSession.dataTask(with: request, completionHandler: callback)
task.resume()
urlSession.finishTasksAndInvalidate()
}
func urlSession(_ session: URLSession, taskIsWaitingForConnectivity task: URLSessionTask) {
print("WAITING")
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
print("TEST TEST")
}
func urlSession(_ session: URLSession, didBecomeInvalidWithError error: Error?) {
print("BECAME INVALID")
}
}
func main() throws {
let apiSession = ApiSession()
let request = URLRequest(url: URLComponents(string: "http://example.com/")!.url!)
let sem = DispatchSemaphore(value: 0)
apiSession.makeRequest(request: request) { (data, response, err) in
if (err != nil) {
print(err.debugDescription)
}
print(data)
sem.signal()
}
// Code hangs here waiting for completion block to get called, but it never does when OperationQueue is main
let _ = sem.wait(timeout: .distantFuture)
}
do {
try main()
} catch (let error) {
print("ERROR: \(error)")
}
When I use a basic URLSession object the request completes fine. However, if I attempt to pass in my own URLSessionTaskDelegate to print the bytesSent, the call never happens. Furthermore, if I set my delegateQueue to OperationQueue.main, the request itself never completes.
I'm sure there's some kind of concurrency issue here, but I have no idea where to start debugging this. Any help is appreciated!

Does your CLI app have a RunLoop defined? Without a RunLoop, it will exit and any pending tasks are deallocated when your main exits. Try adding something like:
while RunLoop.main.run(mode: .default, before: .distantFuture) {}
At the end of your main file.

Related

Am unable to receive HTTP responses with UIViewController set as URLSessionDelegate

Wed 5/18 Additional Info added at Step 5
I am able to create a URLSesion, build a request with a file to upload and successfully call it from my app. On my server side, the proper script is called, uploaded file is saved, etc,. However, I am not receiving the HTTP responses, data, etc.
Actually had this working without the delegate, when the HTTP response functions were within the task itself. But am now trying to expand functionality and am missing something while trying implement the delegate.
The trimmed code is below, and it all works, with the exception of setting up UIViewController as the URLSession delegate. Just trying to figure out why my UIViewController is not receiving the HTTP responses.
Below is the code for:
UIViewController
Class which creates the upload session (UploadService)
Extension for
UIViewController which I want to use to process the responses
How the previous task looked, when it worked. Before I tried to implement the delegate.
Used print to confirm that my UIViewConroller is the delegate, yet it still receives no HTTP response, data, or error messages
UIViewController
class UploadInv : UIViewController {
var xFile : XFile?
...create UI....
let uploadService = UploadService()
lazy var uploadSession: URLSession = {
let configuration = URLSessionConfiguration.default
return URLSession(configuration: configuration, delegate: self, delegateQueue: .main)
}()
override func viewWillAppear(_ animated: Bool) {
...
}
override func viewDidLoad() {
super.viewDidLoad()
uploadService.uploadSession = uploadSession
... code the lays out all buttons, labels, etc...
}
#objc func buttonAction(sender: UIButton!) {
guard let theButton = sender else { return}
let myTag = theButton.tag
switch myTag {
//button to start upload
case ButtType.up.rawValue:
uploadService.start(upFile: xFile!, script: "uploadOrig.pl", upLoadInvClass: self)
uploadService.task?.resume()
//button to select file to upload
case ButtType.file.rawValue:
... file xFile with file info
}
}
UploadService
class UploadService {
var uploadSession : URLSession!
var task: URLSessionUploadTask?
func start(upFile: XFile, script: String, upLoadInvClass: UploadInv) {
var request = upFile.makeUrlReq(upFile: upFile, script: script)
task = uploadSession.uploadTask(with: request, from: request.httpBody! )
print("\(uploadSession.delegate)")
task?.resume()
}
}
extension
extension UploadInv: UIDocumentPickerDelegate, URLSessionDelegate {
func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
... file xFile info for upload ....
... http request created ....
}
// Below are the three simple functions which I would handle
// responses the server, but these never seem to get called.
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
if let err = error {
print("Error: \(err.localizedDescription)")
}
}
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: (URLSession.ResponseDisposition) -> Void) {
print("didReceive response")
completionHandler(URLSession.ResponseDisposition.allow)
}
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
print("didReceive data")
if let responseText = String(data: data, encoding: .utf8) {
print(responseText)
}
}
}
Pre-Delegate model which worked
class UploadService {
var uploadSession = URLSession.shared
func start(upFile: XFile, script: String, upLoadInvClass: UploadInv) {
var request = upFile.makeUrlReq(upFile: upFile, script: script)
uploadSession.uploadTask(with: request, from: request.httpBody )
{ (data, response, error) in
if let response = response {
upLoadInvClass.upResp(resp: response)
}
if let error = error {
upLoadInvClass.upErr(error: error)
}
if let data = data {
upLoadInvClass.upData(data: data)
}
}.resume()
}
}
Step 5:
task = uploadSession.uploadTask(with: request, from: request.httpBody! )
print("\(uploadSession.delegate)")
task?.resume()
For other newbies also stuck on this, it turns out there's more than one delegate to look at. There are:
URLSessionTaskDelegate, URLSessionDataDelegate, URLSessionDownloadDelegate, and more. So obviously I was using the wrong one, might have been fell trap to "autocomplete." Nevertheless, I have to make sure I read more documentation on the subject.
Thanks to Scott who "passively/aggressively" gave me the answer, here, while still allowing me to "think." I mean that as a compliment. He told me to add the line:
assert(uploadSession.delegate! is URLSessionDataDelegate)

Background URLSession + Combine?

When attempting to send a background request with URLSession's dataTaskPublisher method:
URLSession(configuration: URLSessionConfiguration.background(withIdentifier: "example"))
.dataTaskPublisher(for: URL(string: "https://google.com")!)
.map(\.data)
.sink(receiveCompletion: { print($0) }) { print($0) }
I receive the error
Completion handler blocks are not supported in background sessions. Use a delegate instead.
This makes sense to me, sink is a bunch of completion handlers. So, I tried to build a Subscriber:
class ExampleSubscriber: Subscriber {
typealias Input = Data
typealias Failure = URLError
func receive(subscription: Subscription) {
subscription.request(.max(1))
}
func receive(_ input: Data) -> Subscribers.Demand {
print(input)
return Subscribers.Demand.none
}
func receive(completion: Subscribers.Completion<URLError>) {}
}
and subscribe with the Subscriber:
URLSession(configuration: URLSessionConfiguration.background(withIdentifier: "example"))
.dataTaskPublisher(for: URL(string: "https://google.com")!)
.map(\.data)
.subscribe(ExampleSubscriber())
and I receive the same error:
Completion handler blocks are not supported in background sessions. Use a delegate instead.
Is it possible to perform a background request using dataTaskPublisher or do I have to use a delegate to URLSession?
URLSession.DataTaskPublisher is built on top of URLSessionDataTask and sets a completion handler on the task. So you cannot use DataTaskPublisher with a background session.
You can find the source code of DataTaskPublisher in the Swift project repo. Here are the relevant lines:
let task = p.session.dataTask(
with: p.request,
completionHandler: handleResponse(data:response:error:)
)

URLSession downloadTask behavior when running in the background?

I have an app that needs to download a file which may be rather large (perhaps as large as 20 MB). I've been reading up on URLSession downloadTasks and how they work when the app goes to the background or is terminated by iOS. I'd like for the download to continue and from what I've read, that's possible. I found a blog post here that discusses this topic in some detail.
Based on what I've read, I first created a download manager class that looks like this:
class DownloadManager : NSObject, URLSessionDownloadDelegate, URLSessionTaskDelegate {
static var shared = DownloadManager()
var backgroundSessionCompletionHandler: (() -> Void)?
var session : URLSession {
get {
let config = URLSessionConfiguration.background(withIdentifier: "\(Bundle.main.bundleIdentifier!).background")
return URLSession(configuration: config, delegate: self, delegateQueue: OperationQueue())
}
}
private override init() {
}
func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
DispatchQueue.main.async {
if let completionHandler = self.backgroundSessionCompletionHandler {
self.backgroundSessionCompletionHandler = nil
completionHandler()
}
}
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
if let sessionId = session.configuration.identifier {
log.info("Download task finished for session ID: \(sessionId), task ID: \(downloadTask.taskIdentifier); file was downloaded to \(location)")
do {
// just for testing purposes
try FileManager.default.removeItem(at: location)
print("Deleted downloaded file from \(location)")
} catch {
print(error)
}
}
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
if totalBytesExpectedToWrite > 0 {
let progress = Float(totalBytesWritten) / Float(totalBytesExpectedToWrite)
let progressPercentage = progress * 100
print("Download with task identifier: \(downloadTask.taskIdentifier) is \(progressPercentage)% complete...")
}
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
if let error = error {
print("Task failed with error: \(error)")
} else {
print("Task completed successfully.")
}
}
}
I also add this method in my AppDelegate:
func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: #escaping () -> Void) {
DownloadManager.shared.backgroundSessionCompletionHandler = completionHandler
// if the app gets terminated, I need to reconstruct the URLSessionConfiguration and the URLSession in order to "re-connect" to the previous URLSession instance and process the completed download tasks
// for now, I'm just putting the app in the background (not terminating it) so I've commented out the lines below
//let config = URLSessionConfiguration.background(withIdentifier: identifier)
//let session = URLSession(configuration: config, delegate: DownloadManager.shared, delegateQueue: OperationQueue.main)
// since my app hasn't been terminated, my existing URLSession should still be around and doesn't need to be re-created
let session = DownloadManager.shared.session
session.getTasksWithCompletionHandler { (dataTasks, uploadTasks, downloadTasks) -> Void in
// downloadTasks = [URLSessionDownloadTask]
print("There are \(downloadTasks.count) download tasks associated with this session.")
for downloadTask in downloadTasks {
print("downloadTask.taskIdentifier = \(downloadTask.taskIdentifier)")
}
}
}
Finally, I start my test download like this:
let session = DownloadManager.shared.session
// this is a 100MB PDF file that I'm using for testing
let testUrl = URL(string: "https://scholar.princeton.edu/sites/default/files/oversize_pdf_test_0.pdf")!
let task = session.downloadTask(with: testUrl)
// I think I'll ultimately need to persist the session ID, task ID and a file path for use in the delegate methods once the download has completed
task.resume()
When I run this code and start my download, I see the delegate methods being called but I also see a message that says:
A background URLSession with identifier com.example.testapp.background already exists!
I think this is happening because of the following call in application:handleEventsForBackgroundURLSession:completionHandler:
let session = DownloadManager.shared.session
The getter for the session property in my DownloadManager class (which I took directly from the blog post cited previously) is always trying to create a new URLSession using the background configuration. As I understand it, if my app had been terminated, then this would be the appropriate behavior to "reconnect" to the original URLSession. But since may app is not being terminated but rather just going to the background, when the call to application:handleEventsForBackgroundURLSession:completionHandler: happens, I should be referencing the existing instance of URLSession. At least I think that's what the problem is. Can anyone clarify this behavior for me? Thanks!
Your problem is that you are creating a new session every time you reference the session variable:
var session : URLSession {
get {
let config = URLSessionConfiguration.background(withIdentifier: "\(Bundle.main.bundleIdentifier!).background")
return URLSession(configuration: config, delegate: self, delegateQueue: OperationQueue())
}
}
Instead, keep the session as an instance variable, and just get it:
class DownloadManager:NSObject {
static var shared = DownloadManager()
var delegate = DownloadManagerSessionDelegate()
var session:URLSession
let config = URLSessionConfiguration.background(withIdentifier: "\(Bundle.main.bundleIdentifier!).background")
override init() {
session = URLSession(configuration: config, delegate: delegate, delegateQueue: OperationQueue())
super.init()
}
}
class DownloadManagerSessionDelegate: NSObject, URLSessionDelegate {
// implement here
}
When I do this in a playground, it shows that repeated calls give the same session, and no error:
The session doesn't live in-process, it's part of the OS. You're incrementing reference count every time you access your session variable as written, which causes the error.

Renamed issues in Swift

I'm working on programming with Swift for the first time, and in doing so I'm following along with this tutorial. Unfortunately it looks like the tutorial is a little outdated and most of the code is throwing Buildtime errors. The most reoccurring error is the NSURLSession has been renamed to URLSession. I've tried letting Swift fix it, but in many cases it just starts throwing warnings.I'm also getting a Value type HomeModel has no member'parseJSON' error as well as a NSDat is not implicitly convertible to data error. From what I can tell, it looks like the NSURL is no longer used, but I'm not sure about the other two. Seeing how this is the first Swift project I've worked on, I'm not sure how to fix these. Can someone provide some insight on how to fix these mistakes?
here is the code:
import Foundation
protocol HomeModelProtocal: class {
func itemsDownloaded(items: NSArray)
}
class HomeModel: NSObject, NSURLSessionDataDelegate {
//properties
weak var delegate: HomeModelProtocal!
var data : NSMutableData = NSMutableData()
let urlPath: String = "http://testurl.com/service.php" //this will be changed to the path where service.php lives
func downloadItems() {
let url: NSURL = NSURL(string: urlPath)!
var session: NSURLSession!
let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
session = NSURLSession(configuration: configuration, delegate: self, delegateQueue: nil)
let task = session.dataTaskWithURL(url)
task.resume()
}
func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
self.data.appendData(data);
}
func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
if error != nil {
print("Failed to download data")
}else {
print("Data downloaded")
self.parseJSON()
}
}
}
Several basic types have dropped the "NS" prefix in Swift 3.0. Earlier in swift 2.2, we used to have NSUserDefaults, NSURLSession, NSFileManager etc. Now, most of them dropped their prefix "NS" and changed to UserDefaults, URLSession, FileManager etc.
Your code contains a lot of types with 'NS' prefix. By simply removing it, your code can be converted to Swift 3. Your converted code looks like as shown below:
protocol HomeModelProtocal: class {
func itemsDownloaded(items: NSArray)
}
class HomeModel: NSObject, URLSessionDataDelegate {
//properties
weak var delegate: HomeModelProtocal!
var data : Data = Data()
let urlPath: String = "http://testurl.com/service.php" //this will be changed to the path where service.php lives
func downloadItems() {
let url: URL = URL(string: urlPath)!
var session: URLSession!
let configuration = URLSessionConfiguration.default
session = URLSession(configuration: configuration, delegate: self, delegateQueue: nil)
let task = session.dataTask(with: url)
task.resume()
}
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
self.data.append(data);
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
if error != nil {
print("Failed to download data")
}else {
print("Data downloaded")
self.parseJSON() // This class doesn't have a function parseJSON(). So, it's giving you an error like this
}
}
}
Also, I don't see any function called parseJSON() in your class. I believe you have to add it.

NSURLSession didReceiveData not being triggered

I'm having a problem detecting when data is being received using NSURLSession. The equivalent code with NSURLConnection does work, but that's not included here.
In this example, I'm doing a request to google.com. The completionHandler works and "complete" is printed (also the data, etc if you change the code).
However didReceiveData isn't triggered and "received data" is never printed.
I've been through the docs and done a ton of searching and I think this looks right, but I can't seem to get it to work. Definitely would appreciate any help with this.
(I need to use didReceiveData because I'm going to parsing a streaming json api.)
Thanks!
import UIKit
class ViewController: UIViewController, NSURLSessionDelegate, NSURLSessionDataDelegate, NSURLSessionTaskDelegate {
override func viewDidAppear(animated: Bool) {
let session = NSURLSession.sharedSession()
var task = session.dataTaskWithURL(NSURL(string: "https://google.com")!, completionHandler: { (data, response, error) -> Void in
print("complete")
})
task.resume()
}
func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
print("received data")
}
}
There were two issues.
When the session is created, you must define a delegate. That was the main reason didReceiveData wasn't being called.
The second issue is that if you use a completionHandler block, then all the delegates functions are bypassed. In the code for NSURlSession, it says
extension NSURLSession {
/*
* data task convenience methods. These methods create tasks that
* bypass the normal delegate calls for response and data delivery,
* and provide a simple cancelable asynchronous interface to receiving
* data. Errors will be returned in the NSURLErrorDomain,
* see <Foundation/NSURLError.h>. The delegate, if any, will still be
* called for authentication challenges.
*/
You must implement each delegate function you need to check for completion, errors, etc.
The updated code is below:
import UIKit
class ViewController: UIViewController, NSURLSessionDelegate {
override func viewDidAppear(animated: Bool) {
let config = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: config, delegate: self, delegateQueue: nil)
var task = session.dataTaskWithURL(NSURL(string: "https://google.com")!)
task.resume()
}
func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
print("received data")
}
}
You can get data in completionHandler only. Why do you want to use didReceiveData?
Below code will show you how you can get the received data
override func viewDidAppear(animated: Bool) {
let session = NSURLSession.sharedSession()
var task = session.dataTaskWithURL(NSURL(string: "https://google.com")!, completionHandler: { (data, response, error) -> Void in
if NSJSONSerialization.isValidJSONObject(data){
if let jsonParam = try? NSJSONSerialization.dataWithJSONObject(dictData, options: []){
print("Result Data : \(jsonParam)")
}
}
})
task.resume()
}