Asynchronous NSURLConnection leaking

Question

I know that issue has been reported tons of times but almost all the answers concerned non ARC projects and I have been stuck for days now. I have looked in many forums and articles. I hope I could find some help here.

I use an asynchronous NSURLConnection request in order to download pictures, with IOS 5, using ARC, as follow (code inspired from the book "Learning IPAd programming") :

-(void) dowloadImageAtURL:(NSURL *)URL
{
    if (URL)
    {        
        self.image = nil;
        self.receivedData = [[NSMutableData alloc] init];
        NSURLRequest *request = [NSURLRequest requestWithURL:URL cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
        [[NSURLCache sharedURLCache] setMemoryCapacity:0];
        [[NSURLCache sharedURLCache] setDiskCapacity:0];
        NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request              // Building asynchronous connection
                                                               delegate:self
                                                              startImmediately:NO];                 // This is the key to not run the connection synchronous
        [connection scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];     // We use the current loop but it will still be asynchronous
                                                                                                    // because of the mode added to the current loop
        [connection start];
        request = nil;
    }
}

#pragma marks - NSURLConnection delegate Methods

/*
 Called when the web server responds to the request.
 When the method is called, the receivedData property is reset with a length of zero, clearing any previously stored data.
 This ensures that only the data received from the final request is captured (see NSURLConnectionDelegate reference).
 */
- (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    [self.receivedData setLength:0];
    NSURLCache *sharedCache = [[NSURLCache alloc] initWithMemoryCapacity:0 diskCapacity:0 diskPath:nil];
    [NSURLCache setSharedURLCache:sharedCache];
    sharedCache = nil;
    connection = nil;
}


/*
 Called when data is received from the network. The method can be called a multiple times during a single request.
 The data is appended to the data already stored in the receivedData property.
 */
- (void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [self.receivedData appendData:data];

}


/*
 Called after the request has completed all data and all data has been received. This method converts
 the data stored to a UIImage object. 
 */
- (void) connectionDidFinishLoading:(NSURLConnection *)connection
{
    self.image = [UIImage imageWithData:self.receivedData];
    self.receivedData = nil;
    connection = nil;
    NSURLCache *sharedCache = [[NSURLCache alloc] initWithMemoryCapacity:0 diskCapacity:0 diskPath:nil];
    [NSURLCache setSharedURLCache:sharedCache];
    sharedCache = nil;

    // Here we post a notification to the observer
    [[NSNotificationCenter defaultCenter] postNotificationName:@"com.perfectmemory.famille.imageupdated" object:self];
}


/*
 Called if an error is detected at any time during the download process.
 */
- (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    self.receivedData = nil;
    connection = nil;
    NSURLCache *sharedCache = [[NSURLCache alloc] initWithMemoryCapacity:0 diskCapacity:0 diskPath:nil];
    [NSURLCache setSharedURLCache:sharedCache];
    sharedCache = nil;

    // Here we post a notification to the observer
    [[NSNotificationCenter defaultCenter] postNotificationName:@"com.perfectmemory.famille.imageupdated" object:self];

}

When running this code, the download works well but I can see leaks in the XCode instruments

• URLConnectionLoader::LoaderConnectionEventQueue
• URLConnection::scheduleWithRunLoop
• CFURLResponse

• URLConnectionInstanceData

  I have used the following helps to try to fix the issue, such as clearing the cache, but no success :

• NSURLConnection Leaks -- Why?
• http://www.friendlydeveloper.com/2010/04/successfully-working-around-the-infamous-nsurlconnection-leak/
• NSURLConnection leak?

I also tried to release the connection in each concerned delegate methods with :

connection = nil

But still no success. I really don't understand what is going on. I can't find unreleased objects. Could you please help me ? It's very frustrating since I guess this asynchronous download request is very common.

Thanks a lot in advance.