#import <Foundation/Foundation.h>

dispatch_semaphore_t sema = dispatch_semaphore_create(0);

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"server-url.com/archive/start"]
  cachePolicy:NSURLRequestUseProtocolCachePolicy
  timeoutInterval:10.0];
NSDictionary *headers = @{
  @"Content-Type": @"application/json"
};

[request setAllHTTPHeaderFields:headers];
NSData *postData = [[NSData alloc] initWithData:[@"{\"sessionId\": \"value goes here\"}" dataUsingEncoding:NSUTF8StringEncoding]];
[request setHTTPBody:postData];

[request setHTTPMethod:@"POST"];

NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request
completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
  if (error) {
    NSLog(@"%@", error);
    dispatch_semaphore_signal(sema);
  } else {
    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *) response;
    NSError *parseError = nil;
    NSDictionary *responseDictionary = [NSJSONSerialization JSONObjectWithData:data options:0 error:&parseError];
    NSLog(@"%@",responseDictionary);
    dispatch_semaphore_signal(sema);
  }
}];
[dataTask resume];
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);