iOS Background Transfer - com.apple.nsurlsessiond folder full of tmp files

Question

We've written a media application that allows you to get a list of latest videos as json list using BACKGROUND FETCH

then it uses BACKGROUND TRANSFER to tell iOS to download the video one by one and go back to sleep and to wake the app when its done.

It does all that but we've noticed that Space Usage is growing and growing.

We added code to clear all downloaded videos but space usage stayed hi in settings.

We downloaded the app folders using Xcode > Organizer> Devices and found the BACKGROUND TRANSFER tmp folder was dull of tmp files.

Shouldn't these be getting cleared out

This is in general the code I use. I think the main is I attach multiple DownloadTask(can be up to 30) to one background session. files vary in size from movies to pdfs.

NSURLSession * backgroundSession_ = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:identifier];


backgroundSession_ = [NSURLSession sessionWithConfiguration:urlSessionConfigurationBACKGROUND_
                                                   delegate:self
                                              delegateQueue:[NSOperationQueue mainQueue]];

NSOperationQueue *mainQueue_ = [NSOperationQueue mainQueue];



NSURLSessionDownloadTask * downloadTask_ = [backgroundSession_ downloadTaskWithURL:url_];

downloadStarted_ = TRUE;
[downloadTask_ resume];

Answer 1

Try something like this before returning from didFinishDownloadingToURL:

// App's Documents directory path
NSString *docsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)firstObject];

// Creating the path for the downloaded file
docsPath = [docsPath stringByAppendingPathComponent:downloadTask.response.suggestedFilename];

// Moving the file from temp location to App's Documents directory
[[NSFileManager defaultManager] moveItemAtPath:location.path toPath:docsPath error:NULL];

---

The documentation states that you should "move the file to a permanent location in your app’s sandbox container directory before returning from this delegate method" (perhaps the Documents directory).

The temp files that gets cleared out after you return from didFinishDownloadingToURL (or if the download failed) - at the OS's discretion (usually under memory pressure).