NSURLSession hangs on iOS 7.0.x

Question

We have configured NSULRSession

- (NSURLSession *)downloadSession
{
    static NSURLSession *session = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{

        NSOperationQueue *delegateQueue = [[NSOperationQueue alloc] init];

        NSString *identifier = ORDERS_DOWNLOADER_SESSION_IDENTIFIER;
        NSURLSessionConfiguration* sessionConfig = [NSURLSessionConfiguration backgroundSessionConfiguration:identifier];
        session = [NSURLSession sessionWithConfiguration:sessionConfig
                                                                delegate:self
                                                           delegateQueue:delegateQueue];
    });

    return session;
}

On iOS 7.0.x built no SDK 7.0 and 7.1. Problem doesn't appears on iOS 7.1.

We often can see the following:

• start performing background downloading

  [AppDelegate application:performFetchWithCompletionHandler:]

• But after 30 seconds we don't have any callbacks to our delegate.

We have implemented

 - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error

 - (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session

 - (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location

 - (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes

 - (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
willPerformHTTPRedirection:(NSHTTPURLResponse *)response
        newRequest:(NSURLRequest *)request
 completionHandler:(void (^)(NSURLRequest *))completionHandler

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
 needNewBodyStream:(void (^)(NSInputStream *bodyStream))completionHandler

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
   didSendBodyData:(int64_t)bytesSent
    totalBytesSent:(int64_t)totalBytesSent
totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend

• We don't have any callbacks on it.

What may be wrong? It looks like iOS 7.0.x problem. Is there any good workarounds?

Answer 1

That is an issue of iOS

more info here: https://devforums.apple.com/message/926113#926113

Any solutions / workarounds? I'm seeing the same problem.

Tested using a basic [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"..."]] and -downloadTaskWithRequest:

A couple of observations:

1. The very first time the app calls -downloadTaskWithRequest: it works perfectly.

2. Subsequent calls to -downloadTaskWithRequest: return nil, until the app is killed.

Now we have only one workaround: Multiple calls of task creation method. And it works for us! Usually it has effect on second-third time.

_task = [[self downloadSession] downloadTaskWithRequest:request completionHandler:nil];

// Workaround to solve issue https://devforums.apple.com/message/926113
// Occurs consistently on iOS 7.0.5 and lower
// Sometimes _task may not be initialized, so we try again:
if (!_task)
{
    for (int i = 0; i < 5; i++)
    {
        NSLog(@"%s, attempt #%d to recreate download task", __func__, i + 1);

        _task = [[self downloadSession] downloadTaskWithRequest:request completionHandler:nil];
        if (_task)
        {
            break;
        }
    }
}