NSURLSession NSURLCache is not working as expected

I see strange behavior when using NSURLCache and have exhausted all parameters, but posting here ... so here it is:

I am trying to implement NSURLCache

as a basic caching mechanism in combination with NSURLSession

. And using Charles and Simple println()

, I notice that no matter what I do, my application keeps coming back to the server and re-requests previous requests.

I have verified that my server is sending the following headers sequentially:

 Cache-Control:public, max-age=31449600
 Content-Length:74289
 Content-Type:image/jpeg
 ETag:"abcdf"
 Expires:Sun, 03 Jan 2016 20:58:01 GMT
 Last-Modified:Sat, 09 Nov 2013 08:05:53 GMT

      

        
        
        
      

    

But when I make the following request:

let req = NSURLRequest(URL: NSURL(string: URLString)!, cachePolicy: .ReturnCacheDataElseLoad, timeoutInterval: 15)

      

        
        
        
      

    

NSURLSession

willCacheResponse:

The delegate method is not called at all:

func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, willCacheResponse proposedResponse: NSCachedURLResponse, completionHandler: (NSCachedURLResponse!) -> Void) {

      

        
        
        
      

    

However, by simply requesting NSURLRequest(URL: NSURL(string: URLString)!)

without specifying a specific one cachePolicy

, then the call willCacheResponse:

is invoked. However, the next time the same request is made, the application will return to the server ...

I am not making any modifications to the response objects in any of the NSURLSession delegate methods, and my requests are everything HTTP GET

.

What am I missing?

I read a lot about this on NSURLCache:

• https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/URLLoadingSystem/Concepts/CachePolicies.html
• http://nshipster.com/nsurlcache/
• http://petersteinberger.com/blog/2012/nsurlcache-uses-a-disk-cache-as-of-ios5/
• NSURLCache does not cache
• various other SO threads ...

Customization: Xcode6.1, Swift, iOS8 +

Edit: I pushed the main example on github to show my issue: https://github.com/opfeffer/nsurlcache

Check it out and let me know what I am doing wrong!