如何在dropbox sdk中强制下载文件

I am using dropbox php sdk and i want to download the file through the browser . I have a file preview link But away to understand how can i download the file . I am using the function

function GetLink($dropbox_file, $preview=true, $short=true, &$expires=null)
    {
        if(is_object($dropbox_file) && !empty($dropbox_file->path)) $dropbox_file = $dropbox_file->path;
        $url = $this->apiCall(($preview?"shares":"media")."/$this->rootPath/$dropbox_file", "POST", array('locale' => null, 'short_url'=> $preview ? $short : null));
        $expires = strtotime($url->expires);
        return $url->url;
    }

and this is producing a link to preview the file like https://db.tt/S3znA2kE and if i open this link it becomes https://www.dropbox.com/s/64h549xaofsm67p/readme.txt i know file can download if i will pass ?dl=1 but can't understand HOW

Two possibilities:

1. You could stop passing "true" in the short parameter and thus get a long URL to start with. Then you can just use the dl=1 parameter directly.

2. If, for some reason, you need to get a short URL, you could then expand it by doing an HTTP HEAD and looking at the returned Location header. E.g. (using curl):

   $ curl -I https://db.tt/S3znA2kE
   HTTP/1.1 302 FOUND
   Server: nginx
   Date: Thu, 07 Aug 2014 21:16:19 GMT
   Content-Type: text/html; charset=utf-8
   Connection: keep-alive
   location: https://www.dropbox.com/s/64h549xaofsm67p/readme.txt
   pragma: no-cache
   cache-control: no-cache
   

   After you have the full expanded URL, you can modify it to use the dl=1 parameter.

Then you might need to crawl actual url using this example or I think you can grab content and point within DOM and swing back to url.