Asynchronous NSURLConnection in concurrent NSOperation

DownloadOperation.h

@interface DownloadOperation : NSOperation
{
    NSURLRequest *request;
    NSURLConnection *connection;
    NSMutableData *receivedData;
}

@property(readonly) BOOL isExecuting;
@property(readonly) BOOL isFinished;

@property(readonly) NSData *receivedData;

- (id) initWithRequest: (NSURLRequest*) rq;

@end

DownloadOperation.m

#import "DownloadOperation.h"

@interface DownloadOperation ()
@property(assign) BOOL isExecuting;
@property(assign) BOOL isFinished;
@end

@implementation DownloadOperation
@synthesize isExecuting, isFinished, receivedData;

#pragma mark Initialization

- (id) initWithRequest: (NSURLRequest*) rq
{
    [super init];
    request = [rq retain];
    return self;
}

- (void) dealloc
{
    [request release];
    [super dealloc];
}

#pragma mark NSOperation Stuff

- (void) start
{
    NSParameterAssert(request);

    // Bail out early if cancelled.
    if ([self isCancelled]) {
        [self setIsFinished:YES];
        [self setIsExecuting:NO];
        return;
    }
    
    [self setIsExecuting:YES];
    [self setIsFinished:NO];
    receivedData = [[NSMutableData alloc] init];
    
    // Make sure the connection runs in the main run loop.
    connection = [[NSURLConnection alloc] initWithRequest:request
        delegate:self startImmediately:NO];
    [connection scheduleInRunLoop:[NSRunLoop mainRunLoop]
        forMode:NSDefaultRunLoopMode];
    [connection start];
}

- (BOOL) isConcurrent
{
    return YES;
}

#pragma mark NSURLConnection Callbacks

- (void) connection: (NSURLConnection*) cn didReceiveData: (NSData*) data
{
    // Not cancelled, receive data.
    if (![self isCancelled]) {
        [receivedData appendData:data];
        return;
    }
    
    // Cancelled, tear down connection.
    [self setIsExecuting:NO];
    [self setIsFinished:YES];
    [connection cancel];
    [connection release];
    [receivedData release];
}

- (void) connectionDidFinishLoading: (NSURLConnection*) cn
{
    [self setIsExecuting:NO];
    [self setIsFinished:YES];
    [receivedData release];
    [connection release];
}

- (void) connection: (NSURLConnection*) cn didFailWithError: (NSError*) error
{
    [self setIsExecuting:NO];
    [self setIsFinished:YES];
    [connection release];
    [receivedData release];
}

// http://stackoverflow.com/questions/3573236
+ (BOOL) automaticallyNotifiesObserversForKey: (NSString*) key
{
    return YES;
}

@end