Good pattern for Internet requests with Grand Central Dispatch?

Question

I'm currently using synchronous ASIHTTPRequest with GCD queues to download data from the Internet, then parse the response data with JSONKit. What do you think about this pattern. Thank you in advance.

Here is my code:

    dispatch_async(queue, ^(void) {

        // Request is ASIHTTPRequest.
        [request startSynchronous];

        // Parse JSON.
        NSArray *array = [[request responseData] objectFromJSONDataWithParseOptions:JKParseOptionLooseUnicode];

        // Callback on the main queue to update UI.
        dispatch_async(dispatch_get_main_queue(), ^(void) {
            callbackBlock(array);
        });
    });

EDIT: The reason I use ASIHTTPRequest is that I need to modify the request header for OAuth and use POST method to upload images.

Answer 1

So you replaced this

- (void)doDownload {
    NSURL *url = [NSURL URLWithString:@"http://foobar.com"];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    connection = [[NSURLConnection alloc] initWithRequest:aURLRequest delegate:self];
    receivedData = [[NSMutableData data] retain];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [_receivedData appendData:data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSArray *array = [_receivedData objectFromJSONDataWithParseOptions:JKParseOptionLooseUnicode];
    callbackBlock(array);       
}

with this -

- (void)doDownload {
    NSURL *url = [NSURL URLWithString:@"http://foobar.com"];
    ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    dispatch_async(queue, ^(void) {
        [request startSynchronous];
        NSArray *array = [[request responseData] objectFromJSONDataWithParseOptions:JKParseOptionLooseUnicode];

        // Callback on the main queue to update UI.
        dispatch_async(dispatch_get_main_queue(), ^(void) {
            callbackBlock(array);
        });
    });
}

and 10,000+ lines of code from ASIHTTPRequest.

What has it got you?

NSURLConnection is fully asynchronous, uses GCD, caches, automatic zip/unzip, etc, etc..

For that reason, and going solely on the (possibly incomplete) information you provided, i'd say that it was a really awful piece of code.

Of course, context is everything - and you may have a really, really, really good reason for reimplementing the already existing functionality of Library code provided by Apple.