gistfile1.m

- (void)uploadImage:(UIImage *)image 
  completionHandler:(void (^)(NSDictionary *uploadResponse, NSError *error))completionHandler {
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
    [self get:[self uploadURL] completionHandler:^(id responseData, NSError *error) {
        if (error) {
            completionHandler(nil, error);
        } else if (!responseData) {
            completionHandler(nil, [NSError errorWithDomain:@"Upload Failed" code:500 userInfo:nil]);
        } else {
            NSDictionary *response = (NSDictionary *)responseData;
            NSLog(@"response:%@",response);
            
            NSURL *url = [NSURL URLWithString:[response objectForKey:@"data"]];
            NSString *imageFileName = [[NSUUID UUID] UUIDString];
            [self uploadImageToGoogleCloud:image uploadUrl:url fileName:imageFileName completionHandler:completionHandler];
        }
    }];
}

- (void)uploadImageToGoogleCloud:(UIImage *)image
                       uploadUrl:(NSURL *)uploadURL
                        fileName:(NSString *)fileName
               completionHandler:(void (^)(NSDictionary *uploadResponse, NSError *error))completionHandler {

    NSData *imageData = UIImagePNGRepresentation(image);
    
    NSString *boundary = @"0xKhTmLbOuNdArY";
    NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; boundary=%@",boundary];
    
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:uploadURL];
    [request setHTTPMethod:@"POST"];
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *upLoadSession = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:nil];
    
    NSMutableData *body = [NSMutableData data];
    [request addValue:contentType forHTTPHeaderField:@"Content-Type"];
    [body appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n",boundary] dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:[[NSString stringWithString:[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"userfile\"; filename=\"%@\"\r\n",fileName]] dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:[@"Content-Type: image/png\r\n\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
    
    [body appendData:[NSData dataWithData:imageData]];
    [body appendData:[[NSString stringWithFormat:@"\r\n--%@--\r\n",boundary] dataUsingEncoding:NSUTF8StringEncoding]];

    NSURLSessionUploadTask *uploadTask = [upLoadSession uploadTaskWithRequest:request
                                                                     fromData:body
                                                            completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
        [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
        NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*) response;
        int statusCode = httpResponse.statusCode;
        if (statusCode == 200) {
            NSDictionary *responseJSON = [self responseJSON:data];
            NSLog(@"RESPONSE:%@", responseJSON);
            completionHandler (responseJSON, nil);
        } else {
            NSString *responseString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
            completionHandler (nil, [NSError errorWithDomain:responseString code:500 userInfo:nil]);
        }
    }];
    [uploadTask resume];
}