Getting a file size from a server before downloading it

Is there a way to get the file size of say a zip file before it gets downloaded. As detailed in this post https://developer.appcelerator.com/question/26001/copying-a-file-from-a-server-to-your-harddisk, I can download the file. I would like to give my application like a status bar or something but in order to do this I need the file size. I tried using header information but I can't seem to access it until after it is done downloading.

This is not always supported by the webserver, but the HTTP method "HEAD" can be used for this purpose. An example on how to use it (untested, but should work):

var xhr = Titanium.Network.createHTTPClient();
  xhr.onload = function() {
    Ti.API.info( this.getResponseHeader('Content-Length') );
  };
 
  xhr.open('HEAD', url);
  xhr.send();

So send a HEAD request of the download URL, if you get the Content-Length in the response headers you know the size, else you can display a more generic/animated progress indicator.

(You can try Ti.API.info( this.getResponseHeaders() ); instead for more header variables.)