Objective C - HTTP GET Request API

Question

I've been trying to query Tesco's API Service. Although I've managed comfortably on Python with this, I have been having some trouble with making a request using Objective C. Nothing is being logged on the output. Any help would be appreciated. The program code is shown below:

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        NSURLSessionConfiguration *defaultSessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
        NSURLSession *defaultSession = [NSURLSession sessionWithConfiguration:defaultSessionConfiguration];

        NSURL *url = [NSURL URLWithString:@"https://dev.tescolabs.com/product/?gtin=4548736003446"];
        NSMutableURLRequest *urlRequest = [NSMutableURLRequest requestWithURL:url];

        NSString *postParams = @"subscription key=93a6e21eed2e4ca3a858a0f1fc5aaf03";
        NSData *postData = [postParams dataUsingEncoding:NSUTF8StringEncoding];

        [urlRequest setHTTPMethod:@"GET"];
        [urlRequest setHTTPBody:postData];

        NSURLSessionDataTask *dataTask = [defaultSession dataTaskWithRequest:urlRequest completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            NSLog(@"Response: %@",response);
            NSLog(@"Data: %@",data);
            NSLog(@"Error: %@",error);
        }];
        [dataTask resume];
    }
    return 0;
}

Yeah I've just checked the error in the completion handler and nothing is logged. Also updated the URL and here's the source of the API: https://devportal.tescolabs.com/docs/services/ — , May 01 '17 at 12:19
When you say nothing is being logged, do you mean the error is nil, or that the `NSLog`s are never executed? — koen, May 01 '17 at 12:24
NSLog's are not being executed. @ravi.p tried and no errors logged. — , May 01 '17 at 12:27

score 1 · Answer 1 · answered May 01 '17 at 13:33

I had no choice but to present an answer ... Notice the runloop code:

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSURLSessionConfiguration *defaultSessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
        NSURLSession *defaultSession = [NSURLSession sessionWithConfiguration:defaultSessionConfiguration];

        NSURL *url = [NSURL URLWithString:@"https://dev.tescolabs.com/product/?gtin=4548736003446"];
        NSMutableURLRequest *urlRequest = [NSMutableURLRequest requestWithURL:url];

        NSString *postParams = @"subscription key=93a6e21eed2e4ca3a858a0f1fc5aaf03";
        NSData *postData = [postParams dataUsingEncoding:NSUTF8StringEncoding];

        [urlRequest setHTTPMethod:@"GET"];
        [urlRequest setHTTPBody:postData];

        __block BOOL done = NO;
        NSURLSessionDataTask *dataTask = [defaultSession dataTaskWithRequest:urlRequest completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            NSLog(@"Response: %@",response);
            NSLog(@"Data: %@",data);
            NSLog(@"Error: %@",error);
            done = YES;
        }];
        [dataTask resume];

        while (!done) {
            NSDate *date = [[NSDate alloc] initWithTimeIntervalSinceNow:0.1];
            [[NSRunLoop currentRunLoop] runUntilDate:date];
        }
    }
    return 0;
}

Best answer so far. The NSRunLoop works and finally got a response with that. Error is null and has status code of 500. Btw hide the details such as key. Thanks bud. — , May 01 '17 at 13:37
@Benge please read the docs, it says to assign the key as a header field, not in the post body. RTFM ;) https://devportal.tescolabs.com/docs/services/57f247f9e2813e07d8663943/operations/57f2518fe2813e07d8663945 — Mazyod, May 01 '17 at 13:41

vadian · Answer 2 · 2017-05-01T14:23:42.870

1

Basically you need a run loop to perform a background task.

Your request does not work because the body POST data are not considered using a GET request.
All parameters must be passed in the URL.

To implement the run loop just use CFRunLoopRun() and CFRunLoopStop().

Do not use NSRunLoop ... runUntilDate with a while loop

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        NSURLSessionConfiguration *defaultSessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
        NSURLSession *defaultSession = [NSURLSession sessionWithConfiguration:defaultSessionConfiguration];

        NSURL *url = [NSURL URLWithString:@"https://dev.tescolabs.com/product/? ... "];

        NSURLSessionDataTask *dataTask = [defaultSession dataTaskWithURL: url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            NSLog(@"Response: %@",response);
            NSLog(@"Data: %@",data);
            NSLog(@"Error: %@",error);
            CFRunLoopStop(CFRunLoopGetCurrent());
            exit(EXIT_SUCCESS);
        }];
        [dataTask resume];
    }

    CFRunLoopRun();
    return 0;
}

edited May 01 '17 at 14:23

answered May 01 '17 at 14:08

vadian

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+1 Thanks, I really like your approach. But what's the real harm in a while loop with proper use of retain/release objects that won't collect garbage? – Mazyod May 01 '17 at 14:13
Same goes, why shouldn't you use NSRunLoop with a loop? – May 01 '17 at 14:16
It does not harm. It's just an awkward and inefficient way. – vadian May 01 '17 at 14:17
@Benge Whenever you can avoid polling (this kind of loop), do it. *Don't ask, tell* or *Don't wait, notify*. – vadian May 01 '17 at 14:18
@Vadian, Cheers. – May 01 '17 at 14:20

score 0 · Answer 3 · edited May 23 '17 at 12:02

0

-dataTaskWithRequest:completionHandler: is asynchronous. You are queuing up an action which would be completed later then exiting the program before it completes.

You need a mechanism to wait for the data task to complete before exiting the program.

See: https://stackoverflow.com/a/34200617/1298400 for an example waiting mechanism.

edited May 23 '17 at 12:02

Community

1
1

answered May 01 '17 at 12:33

Jeffery Thomas

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8
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I'm not so sure about using semaphores, since perhaps the callback is delivered on the main thread. Prefer to use `[NSRunLoop runUntilDate:]` – Mazyod May 01 '17 at 12:49
Yeah, the semaphores approach would in essence block the main thread. – May 01 '17 at 12:59
@Mazyod Whatever method he uses, he has to block the main thread. – Jeffery Thomas May 01 '17 at 13:25
@JefferyThomas Nope .. Look into `NSRunLoop` – Mazyod May 01 '17 at 13:27
@Mazyod look at his code sample. He exits the main thread. That's it, program over. If he doesn't block the main thread, there will be no program running to execute his callback. – Jeffery Thomas May 01 '17 at 13:29

Ravi Panchal · Answer 4 · 2017-05-01T13:11:51.980

Try this u need to pass subscription key in header in this request

NSDictionary *headers = @{ @"ocp-apim-subscription-key": @"YourKey"};

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"YourURL"]
                                                       cachePolicy:NSURLRequestUseProtocolCachePolicy
                                                   timeoutInterval:10.0];
[request setHTTPMethod:@"GET"];
[request setAllHTTPHeaderFields:headers];

NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request
                                            completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
                                                if (error) {
                                                    NSLog(@"%@", error);
                                                } else {
                                                    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *) response;
                                                    NSLog(@"%@", httpResponse);
                                                }
                                            }];
[dataTask resume];

Very good approach, unfortunately I've still got no response at all within the output. — , May 01 '17 at 13:30
@Benge it is working properly so can u describe me what is the issue u r facing — Ravi Panchal, May 01 '17 at 13:42

score 0 · Answer 5 · answered Jun 08 '17 at 17:59

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        NSURLSessionConfiguration *defaultSessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
        NSURLSession *defaultSession = [NSURLSession sessionWithConfiguration:defaultSessionConfiguration];

        NSURL *url = [NSURL URLWithString:@"https://dev.tescolabs.com/product/? ... "];

        NSURLSessionDataTask *dataTask = [defaultSession dataTaskWithURL: url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            NSLog(@"Response: %@",response);
            NSLog(@"Data: %@",data);
            NSLog(@"Error: %@",error);
            CFRunLoopStop(CFRunLoopGetCurrent());
            exit(EXIT_SUCCESS);
        }];
        [dataTask resume];
    }

    CFRunLoopRun();
    return 0;
}

Objective C - HTTP GET Request API

5 Answers5