NSURLErrorDomain error code -999 in iOS

I've been trying to use Corona SDK's Facebook API to post the score on the game I'm developing on facebook. However, I'm having a problem with it. During the first time I try to post to facebook, I get this error after login and user authentication:

NSURLErrorDomain error code -999

Then, it won't post on facebook. What are possible causes of this error and how can I address it? I tried searching the web but couldn't find information about it. Thanks in advance.

By the way, I am not using webview on my app. Just the widget api and a show_dialog listener in my Facebook class.

The error has been documented on the Mac Developer Library(iOS docs)

The concerned segment from the documentation will be:

URL Loading System Error Codes

These values are returned as the error code property of an NSError object with the domain “NSURLErrorDomain”.
enum
{
   NSURLErrorUnknown = -1,
   NSURLErrorCancelled = -999,
   NSURLErrorBadURL = -1000,
   NSURLErrorTimedOut = -1001,

As you can see; -999 is caused by ErrorCancelled. This means: another request is made before the previous request is completed.

hjpotter92 is absolutely right, I just want to provide solution for my case. Hopefully it is useful for you as well. Here is my situation:

On log in page > press log in > pop up loading dialog > call log in service > dismiss dialog > push another screen > call another service --> cause error -999

To fix it, I put a delay between dismissing dialog and pushing new screen:

    [indicatorAlert dismissWithClickedButtonIndex:0 animated:YES];
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 0.01 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
                [self performSegueWithIdentifier:@"HomeSegue" sender:nil];
            });

It is strange that this issue happens on iOS 7 only.

Just wanted to add here, when receiving a -999 "cancelled" the problem usually is one of two things:

You're executing the exact same request again.
You're maintaining a weak reference to your manager object that gets deallocated prematurely. (Create strong reference)

I didn't use Corona SDK's Facebook API but I encountered this problem when using Alamofire, the secondRequest always cancel in execution with the error -999, according to the posts I found on internet, the reason is that session property is deinit before completion of async work since it is out of the scope, I finally solved this problem by deinit the session property manually so the compiler won't deinit it at wrong position:

class SessionManager {
    var session:SessionManager?

    init() {
        self.session = SessionManager(configuration:URLSessionConfiguration.ephemeral)
    }
    private func firstRequest() {
        guard let session = self.session else {return}
        session.request(request_url).responseData {response in
            if let data=response.data {
                self.secondRequest()
            }
    }
    private func secondRequest() {
        guard let session = self.session else {return}
        session.request(request_url).responseData {response in
            if let data=response.data {
                self.secondRequest()
            }
            //session will no longer be needed, deinit it
            self.session = nil
    }

    }

I have faced the same error with Alamofire and it was because the certificate pinning. The certificate wasn't valid anymore, so I had to remove it and add the new one. Hope it helps.

Our company's app has many -999 error in iOS. I have searched around, find the reason has two, like the network task has been dealloc or the certificate isn't valid. But I have checked our code, these two aren't possible. I am using Alamofire which is using URLSession. Luckily, our company's android app's network is normal. So we check the difference. We found the http request from iOS is Http2.0, while android is Http1.1. So we force the backend http support version down to http1.1, then -999 error count descends!!!

I think there maybe some bug in Apple's URLSession. Check the link New NSURLSession for every DataTask overkill? for some detail thoughts

来源：https://stackoverflow.com/questions/16073519/nsurlerrordomain-error-code-999-in-ios

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