synchronous NSURLSessionDataTask using objective-c - objective-c

Question

I'm try to do synchronous NSURLSessionDataTask with the below code but unable to proceed.
__block NSData *rData = nil;
__block BOOL taskDone = NO;
__block NSData *rError = nil;
NSURL *url = [NSURL URLWithString:dataURL];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url cachePolicy:1 timeoutInterval:30];
NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration ephemeralSessionConfiguration] delegate:nil delegateQueue:nil];
NSURLSessionDataTask *taskData = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
rData = [NSData dataWithData:data];
rError = [error copy];
taskDone = YES;
}];
[taskData resume];
while (taskDone == NO) {
if (_close == YES) {
[taskData cancel];
return nil;
}
usleep(20000);
}
I need to synchronous call so that I can remove the while loop which is not needed.
Below is my code with synchronous call using semaphore
dispatch_semaphore_t sem;
__block NSData *rData = nil;
__block BOOL taskDone = NO;
__block NSData *rError = nil;
NSURL *url = [NSURL URLWithString:dataURL];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url cachePolicy:1 timeoutInterval:30];
// creating semaphore
    sem = dispatch_semaphore_create(0);
NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration ephemeralSessionConfiguration] delegate:nil delegateQueue:nil];
NSURLSessionDataTask *taskData = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
rData = [NSData dataWithData:data];
rError = [error copy];
taskDone = YES;
//call semaphore
        dispatch_semaphore_signal(sem);
}];
[taskData resume];
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
dispatch_release(sema);
// THIS part not sure... how can we accommodate this below code
while (taskDone == NO) {
if (_close == YES) {
[taskData cancel];
return nil;
}
usleep(20000);
}
above code could be correct ?

Answer 1

I understand that what you want to do is wait for the DataTask to be completed before continue with you code, the best way is to put your request in a function with a completionHandler.
First create a function that will return a NSURLSessionDataTask with a completion handler:
-(NSURLSessionDataTask*)startSessionDataTaskWithCompletionHandler:(void (^)(NSData *myData))completionBlock {
//Set your request
NSString *dataURL = #"www.yoururl.com";
NSURL *url = [NSURL URLWithString:dataURL];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url cachePolicy:1 timeoutInterval:30];
// I recommend to use sharedSession because is a simple request, so its not needed a specific session configuration.
NSURLSessionDataTask *dataTask = [[NSURLSession sharedSession] dataTaskWithRequest: request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if (!error) {
if (completionBlock){
completionBlock(data);
return;
//When you call this function, the completionBlock will use this data
}
} else {
//Error handle
return;
}
}];
[dataTask resume];
return dataTask;
}
Then you can call this function from anywhere:
NSURLSessionTask *task = [self startSessionDataTaskWithCompletionHandler:^(NSData *myData) {
// put whatever code you want to perform when the asynchronous data task finish, for example:
rData = [NSData dataWithData:myData];
}];
if (!task) {
// handle failure to create task any way you want
}

Answer 2

You can make NSURLSessionDataTask synchronous with PromiseKit. Install it manually or add the following line to the Podfile if you use CocoaPods (tested with CocoaPods 1.7.3):
pod "PromiseKit", "6.10.0"
Add the following line to the top of the code file:
#import PromiseKit;
Then create a wrapper for your task:
- (AnyPromise*)promiseToLoadData:(NSString*)dataURL {
return [AnyPromise promiseWithResolverBlock:^(PMKResolver _Nonnull resolver) {
NSURL *url = [NSURL URLWithString:dataURL];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url cachePolicy:1 timeoutInterval:30];
NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration ephemeralSessionConfiguration] delegate:nil delegateQueue:nil];
NSURLSessionDataTask *taskData = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
if (error != nil) {
resolver([error copy]);
} else {
resolver([NSData dataWithData:data]);
}
}];
[taskData resume];
}];
}
Use wait to resolve the promise synchronously:
id value = [self promiseToLoadData:#"http://your.url"].wait;
if ([value isKindOfClass:[NSData class]]) {
NSLog(#"%#", [[NSString alloc] initWithData:value encoding:NSUTF8StringEncoding]);
}