Objective C Block within Block generates Leak. How can I solve it? - objective-c

Question

Why does this code generates a leak? How could it be solved?
This is the original call:
NSString * url = #"https://theserverurl/user/login" ;
NSDictionary *parameters = #{#"login":#"the-email#mail.com", #"password":#"encrypted-password"} ;
[[BackEndAPI sharedManager] NSURLSessionOperation: #"POST" url: url parameters: parameters success:^(NSURLRequest *request, NSHTTPURLResponse * response, id responseObject) {
// Success
} failure:^(IDLEngineError *engineError) {
// Failure
}] ;
This is the singleton which handles the NSURL request:
- (NSMutableURLRequest *) NSURLSessionOperation:(NSString *) restOperation
url:(NSString *)url
parameters:(id)parameters
success:(void (^)(NSMutableURLRequest *request, NSHTTPURLResponse * response, id responseObject))success
failure:(void (^)(IDLEngineError *))failure {
NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
__weak id weakSelf = self ;
// POST
if ([restOperation isEqualToString:#"POST"]) {
NSError *error;
NSURLSession *session = [NSURLSession sessionWithConfiguration: sessionConfig ];
// Create the request
__block NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL: [NSURL URLWithString: url ] ];
[request setValue:#"application/json" forHTTPHeaderField:#"Content-Type"] ;
request.HTTPMethod = #"POST";
NSData *postData = [NSJSONSerialization dataWithJSONObject: parameters options: 0 error:&error];
[request setHTTPBody:postData];
// Perform operation
NSURLSessionDataTask * task = [session dataTaskWithRequest: request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
// This generates a leak!!!!
success(request, nil, nil) ;
}] ;
[task resume] ;
}
return nil ;
}
Please take a look to the leaked app on GitHub:
https://github.com/arkyxperience/myleakedapp
Find also here the report (screenshot) coming from Instruments:

Answer 1

It turns out the leak is with NSURLSessionDataTask. If you isolate the following piece of code, the leak will remain:
NSString * url = #"https://theserverurl/user/login" ;
NSDictionary *parameters = #{#"login":#"the-email#mail.com", #"password":#"encrypted-password"} ;
NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
NSError *error;
NSURLSession *session = [NSURLSession sessionWithConfiguration: sessionConfig ];
// Create the request
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL: [NSURL URLWithString: url ] ];
[request setValue:#"application/json" forHTTPHeaderField:#"Content-Type"] ;
request.HTTPMethod = #"POST";
NSData *postData = [NSJSONSerialization dataWithJSONObject: parameters options: 0 error:&error];
[request setHTTPBody:postData];
// Perform operation
NSURLSessionDataTask * task = [session dataTaskWithRequest: request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
}] ;
[task resume] ;
Am I doing anything wrong?

Answer 2

OK, i tried your github code, looks like there is no leak. What object is leaking after all? To test this code please add restoration id to your controller. In this code dealloc is being triggered even tho i don't use weak to call controller. So controller is not leaking, complete block does not have a retain loop. Don't see anything that can leak in NSURLSessionOperation:. So what exactly is leaking?
- (void)viewDidLoad {
[super viewDidLoad];
NSString * url = #"https://google.com" ;
NSDictionary *parameters = #{#"login":#"the-email#mail.com", #"password":#"encrypted-password"} ;
[[BackEndAPI sharedManager] NSURLSessionOperation: #"POST" url: url parameters: parameters success:^(NSURLRequest *request, NSHTTPURLResponse * response, id responseObject) {
NSLog(#"finish");
dispatch_async(dispatch_get_main_queue(), ^{
self.view.window.rootViewController = [self.storyboard instantiateViewControllerWithIdentifier:#"ViewController"];
});
} failure:^(NSError * error) {
NSLog(#"fail");
}];
}
- (void)dealloc {
NSLog(#"Did dealloc");
}