download a file from a server

Hi i need download a apk file from a server, I guess being the dispositvo downloaded this file ask me (if you want to install the app). Somehow I think if you can do, but I can not find the result.

This is the following code

var xhr = Titanium.Network.createHTTPClient({
                    onload: function() {
                        // first, grab a "handle" to the file where you'll store the downloaded data
                        var f = Ti.Filesystem.getFile(Ti.Filesystem.applicationDataDirectory,'app.apk');
                        f.write(this.responseData); // write to the file
                        Ti.App.fireEvent('graphic_downloaded', {filepath:f.nativePath});
                    },
 
                });
                xhr.open('GET','http://file');
                xhr.send();

Can you help me solve this problem please

thanks