how to properly send async request using NSURLSession?

Question

since NSURLConnection has been deprecated in iOS 9, I've attempting covering my code into NSURLSession but no success. Here is my old code:

class Book: NSObject {

    var pfBook : PFObject
    var coverImage : UIImage!

    init(pfBook: PFObject) {
        self.pfBook = pfBook
    }

    func fetchCoverImage(completion: (image: UIImage?, error: NSError?) -> Void) {
        let urlString = self.pfBook["s3thumbnailUrl"] as! String
        let url = NSURL(string: urlString)
        let request = NSURLRequest(URL: url!)
        let queue = dispatch_get_main_queue()

        NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) { (response: NSURLResponse?, data: NSData?, error: NSError?) in
            if error == nil {
                dispatch_async(dispatch_get_main_queue()){
                self.coverImage = UIImage(data: data!)
                completion(image: self.coverImage, error: nil)
                }
            } else {
                completion(image: nil, error: error)
            }
        }
    }
}

here's the new NSURLSession I attempted:

class Book: NSObject {

    var pfBook : PFObject
    var coverImage : UIImage!

    init(pfBook: PFObject) {
        self.pfBook = pfBook
    }

    func fetchCoverImage(completion: (image: UIImage?, error: NSError?) -> Void) {
        let urlString = self.pfBook["s3thumbnailUrl"] as! String
        let url = NSURL(string: urlString)
        let request = NSURLRequest(URL: url!)
        let session = NSURLSession.sharedSession()

        let task = session.dataTaskWithRequest(request, completionHandler: {data, response, error -> Void in
            if error == nil {
                dispatch_async(dispatch_get_main_queue()){
                    self.coverImage = UIImage(data: data!)
                    completion(image: self.coverImage, error: nil)
                }
            }else {
                completion(image: nil, error: error)
            }

        })

        task.resume()
    }
}

When I run the app, my debugger is just spewing out errors, like so:

`2015-09-17 03:05:15.270 MyApp[562:59901] NSURLSession/NSURLConnection HTTP load failed (kCFStreamErrorDomainSSL, -9802)
2015-09-17 03:05:15.331 My App[562:59936] This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.
 Stack:(
    0   CoreFoundation                      0x0000000183da4f74 <redacted> + 148
    1   libobjc.A.dylib                     0x0000000198997f80 objc_exception_throw + 56
    2   CoreFoundation                      0x0000000183da4ea4 <redacted> + 0
    3   Foundation                          0x0000000184dbe5d8 <redacted> + 88
    4   Foundation                          0x0000000184c40a1c <redacted> + 36
    5   UIKit                               0x00000001893ff958 <redacted> + 64
    6   UIKit                               0x00000001893ffb9c <redacted> + 548
    7   UIKit                               0x00000001893ff968 <redacted> + 80
    8   UIKit                               0x00000001892f62d8 <redacted> + 240
    9   UIKit                               0x000000018943f35c <redacted> + 640
    10  UIKit                               0x00000001893fc79c <redacted> + 144
    11  UIKit                               0x00000001893fc79c <redacted> + 144
    12  UIKit                               0x00000001893fc6d4 <redacted> + 68
    13  UIKit                               0x00000001893fc228 <redacted> + 120
    14  UIKit                               0x00000001893fc194 <redacted> + 280
    15  UIKit                               0x0000000189400d68 <redacted> + 1048
    16  UIKit                               0x00000001893fcc3c <redacted> + 244
    17  UIKit                               0x0000000189b25e8c <redacted> + 460
    18  UIKit                               0x0000000189b260f4 <redacted> + 200
    19  UIKit                               0x0000000189b25dbc <redacted> + 252
    20  UIKit                               0x0000000189b260f4 <redacted> + 200
    21  UIKit                               0x0000000189b25dbc <redacted> + 252
    22  UIKit                               0x00000001893ff968 <redacted> + 80
    23  UIKit                               0x0000000189b260c8 <redacted> + 156
    24  UIKit                               0x000000018940083c <redacted> + 100
    25  UIKit                               0x00000001893ff968 <redacted> + 80
    26  UIKit                               0x0000000189400470 <redacted> + 244
    27  UIKit                               0x0000000189b2397c <redacted> + 352
    28  UIKit                               0x0000000189af0f24 <redacted> + 200
    29  UIKit                               0x0000000189aefdec <redacted> + 72
    30  UIKit                               0x0000000189aefd88 <redacted> + 48
    31  UIKit                               0x0000000189ad6cf4 <redacted> + 104
    32  UIKit                               0x0000000189ad7264 <redacted> + 1108
    33  UIKit                               0x0000000189ae26f4 <redacted> + 436
    34  UIKit                               0x00000001894dd6f8 <redacted> + 4108
    35  UIKit                               0x0000000189ae4128 <redacted> + 132
    36  UIKit                               0x0000000189309dc0 <redacted> + 80
    37  UIKit                               0x0000000189ae3830 <redacted> + 2656
    38  UIKit                               0x0000000189ae1af8 <redacted> + 12448
    39  UIKit                               0x00000001894d87d8 <redacted> + 364
    40  MyApp                   0x0000000100101934 _TFFC17MyApp29ThirdCollectionViewController14collectionViewFS0_FTCSo16UICollectionView22cellForItemAtIndexPathCSo11NSIndexPath_CSo20UICollectionViewCellU_FTGSqCSo7UIImage_GSqCSo7NSError__T_ + 316
    41  MyApp                   0x00000001000b25fc`
`_TFFC17MyApp4Book15fetchCoverImageFS0_FFT5imageGSqCSo7UIImage_5errorGSqCSo7NSError__T_T_U_FTGSqCSo6NSData_GSqCSo13NSURLResponse_GSqS2___T_ + 580

    2015-09-17 03:05:15.353 MyApp[562:59936] This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.

what should I adjust?

What is your question? What's wrong with your `NSURLSession`? — Desdenova, Sep 17 '15 at 06:43
What you are getting is a security error. `errSSLFatalAlert = -9802` as defined in `` header. [Check This](http://stackoverflow.com/a/30779212/771231) — Desdenova, Sep 17 '15 at 07:52
that answer says NSURLSession is suggested, which i am implementing @Desdenova — John Durand, Sep 17 '15 at 08:14

score 4 · Answer 1 · edited Sep 17 '15 at 06:46

First of all i would like to mention few things that,

NSURLConnection is deprecated in OS X 10.11 and iOS 9.0 but:

Not going away, apps using it will still work
New features will be added to NSURLSession
Not supported on watchOS

Secondly,

Using NSURLSession and sending async call with it is as easy as with NSURLConnection.

This is a sample code to send an async request. Hope it helps.

NSURLSession *session = [NSURLSession sharedSession];
[[session dataTaskWithURL:[NSURL URLWithString:londonWeatherUrl]
          completionHandler:^(NSData *data,
                              NSURLResponse *response,
                              NSError *error) {
            // handle response

  }] resume];

dataTaskWithURL is intended to replace sendAsynchronousRequest in NSURLConnection.

is there anyway you can create an answer tying my code provided in my question ? — John Durand, Sep 17 '15 at 06:50

score 1 · Answer 2 · answered May 16 '17 at 08:09

with swift3,

let liveInfoUrl = URL(string: "http://192.168.1.66/api/cloud/app/liveInfo/7777")
let task = URLSession.shared.dataTask(with: liveInfoUrl! as URL) {data, response, error in
    guard let data = data, error == nil else { return }
    print(String(data: data, encoding: String.Encoding(rawValue: String.Encoding.utf8.rawValue)) ?? "aaaa")
}
task.resume()

score 0 · Answer 3 · answered Sep 17 '15 at 07:28

function below is working fine for me.

func fetchCoverImage(completion: (image: UIImage?, error: NSError?) -> Void) {

    //        let url = NSURL(string: urlString)
    var request = NSMutableURLRequest(URL: NSURL(string: "http://www.fnordware.com/superpng/pnggrad16rgb.png")!)
    let session = NSURLSession.sharedSession()

    let task = session.dataTaskWithRequest(request, completionHandler: {data, response, error -> Void in
        if error == nil {
            dispatch_async(dispatch_get_main_queue()){
                self.coverImage?.image = UIImage(data: data!)
                completion(image: self.coverImage?.image, error: nil)
            }
        }else {
            completion(image: nil, error: error)
        }

    })

    task.resume()
}

}

Let me know if you face any issue using this. I just changed the url to some png image.

would you mind entering [this chat](http://chat.stackoverflow.com/rooms/89883/ios-9-conversion) for a very brief moment? — John Durand, Sep 17 '15 at 07:38

score 0 · Answer 4 · answered Sep 21 '15 at 23:34

There's probably nothing wrong with your code. NSURLConnection will do the same thing if you compile against the iOS 9 SDK. You're running into App Transport Security restrictions. Read about it here:

https://developer.apple.com/library/prerelease/ios/technotes/App-Transport-Security-Technote/

Basically, if you want to access URLs without strong encryption, you have to modify your Info.plist file to tell iOS to let you do do.

how to properly send async request using NSURLSession?

4 Answers4