How to upload task in background using afnetworking

I'm trying to upload large files using AFNetworking and have the upload continue when the application is in the background.

I can upload files just fine, but when I attempt to use a background configuration -- the application crashes with the following stacktrace: Exception: EXC_BAD_ACCESS (code=1, address=0x8000001f))

_CFStreamSetDispatchQueue
-[__NSCFBackgroundDataTask captureStream:]
__70-[__NSCFBackgroundDataTask _onqueue_needNewBodyStream:withCompletion:]_block_invoke_2
_dispatch_call_block_and_release
_dispatch_queue_drain
_dispatch_queue_invoke
_dispatch_root_queue_drain
_dispatch_worker_thread3
_pthread_wqthread

Here is some example code:

Note: When I use [NSURLSessionConfiguration defaultSessionConfiguration] the upload succeeds but will not continue when the application is in the background. [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:@"com.company.appname.uploadservice"] causes the application to crash.

NSMutableURLRequest *request = [[AFHTTPRequestSerializer serializer] multipartFormRequestWithMethod:@"POST" URLString:[uploadBundle.uploadUrl absoluteString] parameters:[uploadBundle getParameters] constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
    [formData appendPartWithFileURL:uploadBundle.fileDataUrl name:uploadBundle.fileName fileName:uploadBundle.fileName mimeType:uploadBundle.mimeType error:nil];
} error:nil];

Authentication *authentication = [Authentication getInstance];
[request addValue:authentication.token forHTTPHeaderField:@"token"];
[request addValue:authentication.authorization forHTTPHeaderField:@"Authorization"];

//NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:@"com.company.appname.uploadservice"];
AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:configuration];

NSProgress *progress = nil;
_currentUploadTask = [manager uploadTaskWithStreamedRequest:request progress:&progress completionHandler:^(NSURLResponse *response, id responseObject, NSError *error) {
    if (error) {
        NSLog(@"Error: %@", error);
    } else {
        NSLog(@"%@ %@", response, responseObject);
    }
}];

I'm answering my own question in hopes that it will help a few people.

I can't find this documented anywhere, but it looks like you have to use uploadTaskWithRequest:fromFile:progress:completionHandler: when using a background session configuration.

Here is a simple example:

AppDelegate *appDelegate = (AppDelegate *) [[UIApplication sharedApplication] delegate];

id config = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:@"com.opentext.core.uploadservice"];
id session = [NSURLSession sessionWithConfiguration:config delegate:appDelegate delegateQueue:[NSOperationQueue new]];

OMGMultipartFormData *multipartFormData = [OMGMultipartFormData new];
//[multipartFormData addFile:data parameterName:@"file" filename:nil contentType:nil];
[multipartFormData addParameters:[uploadBundle getParameters]];

NSURLRequest *rq = [OMGHTTPURLRQ POST:[uploadBundle.uploadUrl absoluteString] :multipartFormData];

id path = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"upload.NSData"];
[rq.HTTPBody writeToFile:path atomically:YES];

[[session uploadTaskWithRequest:rq fromFile:[NSURL fileURLWithPath:path]] resume];