Extjs 4 downloading a file through ajax call

Question

The problem is very simple: i have to download a file when i submit a form, it's an ajax call when the form is submitted which lets me build a file with the data taken from the form, server side, and then send it as a link to an alert. The fact is that my boss want the file to be downloaded directly and not through a link in an alert. So i had to make sure that the file is available server side through tornado(web):

        self.set_header('Content-Type', 'application/octet-stream')
        self.set_header('Content-Disposition', 'attachment; filename=clients_counter.zip')
        with open("static/clients_counter.zip", 'r') as f:
            while True:
                data = f.read()
                if not data:
                    break
        self.write(data)
        self.finish()

The server side code seems to work fine, but the client side (extjs4.1) is really a nightmare. This is how my ajax call looks like now, and it doesn't work:

Ext.Ajax.request({
method : "GET",
url : 'http://whatever.com/count?client='+client+'&start='+start+'&end='+end,
timeout : 30000,
success :
         function (response) {
    //Ext.Msg.alert(response.responseText);
            desktop.getWindow('count-win').doClose();
            return response;
       }//handler,
     failure : 
     function(response) {
    alert("Wrong request");
    }});

Answer 1

I think you can take a much easier solution. Forget about the ajax, and just get plain old js to open the file for you:

window.open('http://whatever.com/count?client='+client+'&start='+start+'&end='+end)

This will open a new tab and start the download from there.