Storing a file in Swift 2+ from URLSession

Question

I'm downloading a large file and when it finishes the

URLSession(session: NSURLSession, 
           downloadTask: NSURLSessionDownloadTask,
           didFinishDownloadingToURL location: NSURL)

method gets called.

I want to save the resulting file locally, NSSearchPathDirectory.DocumentDirectory for instance. But I'm having some issues with this, mainly because the files are quite large 500MB+

I have tried:

NSFileManager.defaultManager().createFileAtPath(savePath, 
                                                contents: fileData, 
                                                attributes: nil)

Which works fine for smaller files < 100MB but larger files die with

Code=12 "Cannot allocate memory"

When trying to convert the downloaded file to NSData like this:

let data: NSData = try NSData(contentsOfURL: location,
                              options: NSDataReadingOptions.DataReadingMappedIfSafe)

The question is, is there another way to convert the location: NSURL to NSData just so there are no memory issues with large files?

Or is there a better way to save the large file other than NSFileManager.defaultManager().createFileAtPath() just so it doesn't require NSData?

Answer 1

Try using NSFileManager's copyItemAtURL:toURL:error: to copy the file from location to wherever you want