iOS9 sendSynchronousRequest deprecated

I wrote the following solution for the cases when you actually need for synchronous request which blocks the current thread execution. I use this code for migration from NSURLConnection to NSURLSession in the complex solution where it was quite a hassle to just change to async approach. With this solution the migration is just method name replacement.

NOTE: If you have a simple case, please use the accepted answer instead.

- (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse **)response error:(NSError **)error
{

    NSError __block *err = NULL;
    NSData __block *data;
    BOOL __block reqProcessed = false;
    NSURLResponse __block *resp;

    [[[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData * _Nullable _data, NSURLResponse * _Nullable _response, NSError * _Nullable _error) {
        resp = _response;
        err = _error;
        data = _data;
        reqProcessed = true;
    }] resume];

    while (!reqProcessed) {
        [NSThread sleepForTimeInterval:0.02];
    }
    if (response != nil)
        *response = resp;
    if (error != nil)
        *error = err;
    return data;
}

Usage (simple replace NSURLConnection to this method):

//NSData *data = [NSURLConnection sendSynchronousRequest:theRequest returningResponse:&resp error:&err];
NSData *data = [self sendSynchronousRequest:theRequest returningResponse:&resp error:&err];

If you need to block the current thread (like Mike Keskinov's answer), best to use gdc semaphore instead of doing a [NSThread sleepForTimeInterval:0]. e.g.

dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
NSURLSession *session = [NSURLSession sharedSession];
[[session dataTaskWithURL:[NSURL URLWithString:londonWeatherUrl]
          completionHandler:^(NSData *data,
                              NSURLResponse *response,
                              NSError *error) {
            // handle response
            dispatch_semaphore_signal(semaphore);

  }] resume];

dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

and Swift (tested on 5.0):

let semaphore = DispatchSemaphore(value:0)

URLSession.shared.dataTask(with: serverUrl) { (httpData, response, error) in
    // handle response
    semaphore.signal()
}.resume()

semaphore.wait()

Use NSURLSession instead like below,

For Objective-C

NSURLSession *session = [NSURLSession sharedSession];
[[session dataTaskWithURL:[NSURL URLWithString:londonWeatherUrl]
          completionHandler:^(NSData *data,
                              NSURLResponse *response,
                              NSError *error) {
            // handle response

  }] resume];

For Swift,

var request = NSMutableURLRequest(URL: NSURL(string: "YOUR URL"))
var session = NSURLSession.sharedSession()
request.HTTPMethod = "POST"

var params = ["username":"username", "password":"password"] as Dictionary<String, String>

var err: NSError?
request.HTTPBody = NSJSONSerialization.dataWithJSONObject(params, options: nil, error: &err)
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.addValue("application/json", forHTTPHeaderField: "Accept")

var task = session.dataTaskWithRequest(request, completionHandler: {data, response, error -> Void in
    println("Response: \(response)")})

task.resume()

I have modified the code of Nilesh Patel a little bit, so you can use the old call, just by changing class name.

+ (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse **)response error:(NSError **)error {
__block NSData *blockData = nil;
@try {

        __block NSURLResponse *blockResponse = nil;
        __block NSError *blockError = nil;

        dispatch_group_t group = dispatch_group_create();
        dispatch_group_enter(group);

        NSURLSession *session = [NSURLSession sharedSession];
        [[session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable subData, NSURLResponse * _Nullable subResponse, NSError * _Nullable subError) {

            blockData = subData;
            blockError = subError;
            blockResponse = subResponse;

            dispatch_group_leave(group);
        }] resume];

        dispatch_group_wait(group,  DISPATCH_TIME_FOREVER);

        *error = blockError;
        *response = blockResponse;

    } @catch (NSException *exception) {

        NSLog(@"%@", exception.description);
    } @finally {
        return blockData;
    }
}