Change cache control headers

ViewController.swift

//
//  ViewController.swift
//  CacheDelegate
//
//  Created by Heng, William (Mobile Developer) on 23/03/2016.
//  Copyright © 2016 Heng, William (Mobile Developer). All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let urlString = "ANY URL THAT RETURNS JSON"
        
        let myDelegate = MySessionDataDelegate(shouldChangeCache: true)
        let session = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration() , delegate: myDelegate, delegateQueue: nil)
        let url = NSURL(string: urlString)!
        let request = NSURLRequest(URL: url, cachePolicy: NSURLRequestCachePolicy.UseProtocolCachePolicy, timeoutInterval: 60)
        
        for _ in 0...3 {
            let dataTask = session.dataTaskWithRequest(request)
            dataTask.resume()
            
            sleep(1)
        }
    }
    
    class MySessionDataDelegate : NSObject, NSURLSessionDataDelegate {
        var shouldChangeCache = false
        
        init(shouldChangeCache : Bool) {
            self.shouldChangeCache = shouldChangeCache
        }
        
        func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, willCacheResponse proposedResponse: NSCachedURLResponse, completionHandler: (NSCachedURLResponse?) -> Void) {
            var headerFields : [String : String] = (proposedResponse.response as! NSHTTPURLResponse).allHeaderFields as! [String : String]
            var responseToCache : NSCachedURLResponse = proposedResponse
            
            if (shouldChangeCache) {
                let url = proposedResponse.response.URL!
                let oldHTTPResponse = (proposedResponse.response as! NSHTTPURLResponse)
                let statusCode = oldHTTPResponse.statusCode
                headerFields["Cache-Control"] = "no-cache, max-age=0"
                
                let HTTPVersion = "HTTP/1.1"
                let newResponse = NSHTTPURLResponse(URL: url, statusCode: statusCode, HTTPVersion: HTTPVersion, headerFields: headerFields)
                responseToCache = NSCachedURLResponse(response: newResponse!, data: proposedResponse.data)
            }
            
            print("header cache: \(headerFields["Cache-Control"])")
            completionHandler(responseToCache)
        }
        
        func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
            do {
                let myData = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.AllowFragments)
                print("received \(myData)")
            } catch {
                print("Cannot deserialise")
            }
        }
        
        func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
            if error != nil {
                print("Error \(error)")
            }
        }
    }
}