Returning assetbundle download progress on mobile

Hello all,

I've been trying to show the assetbundle download progress on Android and iOS. I found this post...

http://answers.unity3d.com/questions/594668/wwwprogress-not-working-on-android-ios-1.html

I understand it has to do with the return header, but I'm new to this and my be missing something simple. The post shows the php with just one assetbundle, "myAssetBundle.unity3d". I tried to adjust it to retrieve any assetbundle from the path I post to it...

Here is my c#:

 string location = "http://www.mysite.com/media/" + assetWebLink;
         string url = "http://www.mysite.com/media/assetBundle_retrieve.php";
         WWWForm form = new WWWForm();
         form.AddField("myAction", "download_myAssetBundle");
         form.AddField("bundleLocation", location);
         WWW assetBundle_get = new WWW(url, form);
 
         //set text to download progress
         while(!assetBundle_get.isDone)
         {
             Debug.Log(assetBundle_get.progress);
             int dlProgress = Mathf.FloorToInt(assetBundle_get.progress * 100);
             purchaseButtonLabel.text = dlProgress.ToString() + "%";
             yield return null;
         }
 
         yield return assetBundle_get;
 
         Debug.Log(assetBundle_get.text);

my php:

if($_POST['myAction']=="download_myAssetBundle") {

     $location = $_POST['bundleLocation'];
     
 //    $escaped_loc = pg_escape_literal($location);

 //    $attachment_location = $escaped_loc;
     header($_SERVER["SERVER_PROTOCOL"] . " 200 OK");
     header("Cache-Control: public");
     header("Content-Type: application/zip");
     header("Content-Transfer-Encoding: Binary");
     header("Content-Length:".filesize($location));
     header("Content-Disposition: attachment; filename=".basename($location));
     readfile($location);
     echo "Working properly";
     Die();
 }

I took out the $escape_loc because it was adding '' around the file location.

I get this error from the debug text...

Warning: filesize(): stat failed for http://www.mysite.com/media/asset_bundles/android/bundlename.assetbundle in /mysite/media/assetBundle_retrieve.php on line 50

Warning: Cannot modify header information - headers already sent by (output started at /mysite/media/assetBundle_retrieve.php:50) in /mysite/media/assetBundle_retrieve.php on line 50

Warning: Cannot modify header information - headers already sent by (output started at /mysite/media/assetBundle_retrieve.php:50) in /mysite/media/assetBundle_retrieve.php on line 51

How can I get the progress if I can't modify the header to send it?

Thanks in advance for any direction!

Jeff