How to upload to ASP.NET in Objective-C using NSURLSession

Question

I need to upload an image to my ASP.Net website, i have got it to work with NSURLConnection but when i needed to upload extremely big files, it crashes due to the lack of ram to transfer the file to NSData then upload it. So I found out about the new API NSURLSession and the method uploadTaskWithRequest:withFile to allow bigger files to be transferred. I have changed the max file limit on the ASP.NET server to allow huge files, and tested it and it works with large files (100MB+), but at some point the phone does not have enough ram to allocate the NSData of the file, when I use NSURLConnection. I have tried NSURLSession numerous times with no success.

Heres an example of what i've tried:

    NSString *urlString = [NSString stringWithFormat:@"https://examplesecuresite.com/Index.aspx?username=%@", username];
    NSMutableURLRequest *request =
    [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:urlString]];
    [request setHTTPMethod:@"PUT"];

    // 3
    NSData *noteContents = UIImageJPEGRepresentation(image, 1);

    // 4
    NSURLSession *session = [[NSURLSession alloc] init];
    NSURLSessionUploadTask *uploadTask = [session
                                          uploadTaskWithRequest:request
                                          fromData:noteContents];
    [uploadTask resume];

Answer 1

A couple of reactions:

1. This is not how you create a NSURLSession. You should either use the shared session:

   NSURLSession *session = [NSURLSession sharedSession];
   

   Or create a configuration with a delegate (obviously, implementing the NSURLSessionTaskDelegate and NSURLSessionDelegate protocols) and use that:

   NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
   NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
   NSURLSessionUploadTask *uploadTask = [session uploadTaskWithRequest:request
                                                              fromData:noteContents];
   

   Or create a configuration without a delegate (but create upload task with completion block) and use that:

   NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
   NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];
   NSURLSessionUploadTask *uploadTask = [session uploadTaskWithRequest:request fromData:noteContents completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
       if (error) {
           NSLog(@"%@", error);
           return;
       }
   
       // do whatever other checking you want of the response here
   }];
   

2. I don't know why you're retrieving the NSData from the UIImage. If this is a UIImage that you created dynamically (e.g. a screen snapshot), then fine, that's what you have to do. But if you can go back to the original asset (e.g. the original asset from ALAssetLibrary, the file we used in imageWithContentsOfFile or imageWithContentsOfURL, etc.), often that will be more efficient (both smaller asset as well as you can upload directly from persistent storage).

   Unfortunately, using UIImageJPEGRepresentation with a quality setting of 1.0 often retrieves a much larger NSData than the original asset. (Plus we preserve any meta data, if any, its far more memory efficient, etc.) You can use a factor of 0.9 or 0.8, which is lossy, but will result in a much smaller file. If you really want something lossless, often UIImagePNGRepresentation will generate a smaller file than UIImageJPEGRepresentation with a quality setting of 1.0.

3. If you're worried about a memory efficient approach, this seems no more efficient. You're uploading a NSData in RAM. Any approach that consists of loading the data into a NSData will be no more memory efficient than your other approach, most likely.

   If you want to be more memory efficient, avoid loading the image into an NSData at all (if you can), and just use the uploadTaskWithRequest:fromFile: with the original asset.

4. By the way, if you had the image in a file in persistent storage, it doesn't strike me that you have to make the shift to NSURLSession solely to address the memory issues. Strikes me that you could have use the delegate-based NSURLConnection, returning a NSInputStream from connection:needNewBodyStream: rather than loading the image into a NSData.