gistfile1.swift

public func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, willCacheResponse proposedResponse: NSCachedURLResponse, completionHandler: (NSCachedURLResponse!) -> Void) {
    let response = proposedResponse.response
    let httpResponse = response as NSHTTPURLResponse
    let headers: [NSObject: AnyObject] = httpResponse.allHeaderFields
    
    var cachedResponse: NSCachedURLResponse!
    if !contains(headers.keys, "Cache-Control") {
        var modifiedHeaders: [NSObject: AnyObject] = headers
        modifiedHeaders["Cache-Control"] = "max-age=60"
        let modifiedResponse = NSHTTPURLResponse(URL: httpResponse.URL!, statusCode: httpResponse.statusCode, HTTPVersion: "HTTP/1.1", headerFields: modifiedHeaders)
        cachedResponse = NSCachedURLResponse(response: modifiedResponse!, data: proposedResponse.data, userInfo: proposedResponse.userInfo, storagePolicy: proposedResponse.storagePolicy)
    } else {
        cachedResponse = proposedResponse
    }
    
    completionHandler(cachedResponse)
}