How to tell if loaded file came from cache or not?

Question

Trying to work out how I can tell if a downloaded file came from the cache or was freshly downloaded over the net. I need this because users will download multiple files and I am trying to give make an accurate downloader for them. I have made them download a sample file which I have made not to cache by doing the following:
private var _loader:URLLoader;
private var _rootPath:String; = "http:/example.com/speedTest/f4v/";
private var _startDownloadTime:int;
private var _targetSpeed:Number //set elsewhere
private function loadTestSpeedFile():void
            var fileRequest:URLRequest = new URLRequest();
            fileRequest.url = _fullFilePath + "speedTest.f4v";
            var variables:URLVariables = new URLVariables(); 
            variables.nocache = new Date().getTime();
            fileRequest.data = variables;
            _startDownloadTime = flash.utils.getTimer();
            _loader.load(fileRequest);
private function speedTestHandler(e:Event):void
            var endDownloadTime:int = flash.utils.getTimer();
            var timeElapsed:Number =   endDownloadTime - _startDownloadTime;
            timeElapsed = timeElapsed/1000;
            var bytesPerSec:Number = (SIZE_OF_TEST_FILE/timeElapsed);
            var currentSpeedFactor:Number = bytesPerSec/_targetSpeed;
            trace("Speed Test file downloaded in " + timeElapsed + " secs at " + bytesPerSec + " bytes a sec : speedFactor " + currentSpeedFactor);
               //remove this handler and download as normal from a list of files
            _loader.removeEventListener(Event.COMPLETE, speedTestHandler);
            _loader.addEventListener(Event.COMPLETE, completeHandler);
          //download the rest of the files
            download();
I could work out if the other files are downloading much more quickly (say 20X quicker) than the speedTest rate worked out here and then discount it from calculating the download speed and estimated time remaining.
However, it would be much better if there was a way to access properties on the URLoader on the Event.COMPLETE handler to see if the file 'downloaded' was taken from the cache or not. Anyone know of way of doing it more elegantly than the hack described in the last sentence?

Answer 1

Kglad,
Thanks for the interest and reply. Yes, you are right the file load preventing the file being cached is stictly a different matter from that which is bugging me.  I am, however,  using the Progress Event (as in flash.events.ProgressEvent ) in the following event handler listening to it:
private function progressHandler(e:ProgressEvent):void
            var percent:Number = (e.bytesLoaded/e.bytesTotal)*100;
              //other code to resize the gui loader ie scaling it to the percentage.
Again this just tells me how much has been loaded each time the event is fired. On the Event.COMPLETE handler I am getting the load timings pretty much as per the
speedTestHandler(e:Event) I posted. The only difference there is that it loads from an array of filenames (most but not all of which can change on later replays - hence some will be cached and some not) What i need to know is where the file is loaded from - either from the server or the local systems cache. The only way round this is to discard very quick downloads (which must be from the cache) from true calculating download speeds but that is a bit hit and miss. I am asking for a better solution. Hope that makes sense...