ubercart file download feature working with cck file field

working on the same issue, i think i will need to code a custom hook on the node save to fill out that value from the filefield

basically what i did was to go with filefield all the way and code everything i needed in views, so filefield handles the upload, i am protecting the upload folder with .htaccess redirecting every request from that folder through a custom hook_menu callback in my custom module
the function checks if the user has access (has bought the product or is owner/admin) and if it does, it calls the same functions that handle the private downloads in drupal, or returns an access denied page
the custom code i mentioned done in views, is just an user panel listing all available downloads via products bought
i think this was more flexible than ubercart private downloads (because of views integration

Something like this (ive replaced certain tokens in ALL CAPS):

#
# .htaccess custom settings:
#

<IfModule mod_rewrite.c>
  RewriteEngine on
  RewriteRule ^sites/default/files/MY-FILE-STORAGE-PATH/(.+)$ index.php?q=MY-FILE-STORAGE-PATH-download/$1 [L,QSA]
</IfModule>

/**
 * Implementation of hook_menu().
 *  http://api.drupal.org/api/function/hook_menu
 */
//* function MYMODULE_menu
function MYMODULE_menu() {
        $items = array() ;

        $items['MY-FILE-STORAGE-PATH-download/%node/%'] = array(
                'title' => 'File download'
                , 'description' => 'File download.'
                , 'page callback' => '_MYMODULE_MY-FILE-STORAGE-PATH_download'
                , 'page arguments' => array(1, 2)
                , 'access arguments' => array('access content')
                , 'file' => 'MYMODULE.MY-FILE-STORAGE-PATH-download.inc'
                , 'type' => MENU_CALLBACK
        ) ;

        return $items ;
} // function MYMODULE_menu */

//* function _MYMODULE_MY-FILE-STORAGE-PATH_download
function _MYMODULE_MY-FILE-STORAGE-PATH_download($node, $filename) {
        global $user ;
        if ( $node->type != 'PRODUCT-TYPE' || ! strlen($filename) ) {
                return drupal_not_found() ;
        }
        if ( $node->uid != $user->uid && ! user_access('download all PRODUCT-TYPE') ) {
                $order_count = db_result(db_query('SELECT COUNT(o.order_id) FROM {uc_orders} o, {uc_order_products} p WHERE o.order_status = \'completed\' AND o.order_id = p.order_id AND p.nid = %d AND o.uid = %d', $node->nid, $user->uid)) ;
                if ( $order_count < 1 ) {
                        drupal_set_message(t('Download access denied.'), 'error') ;
                        return drupal_goto('node/' . $node->nid) ;
                }
        }
        $filefields = array('field_TYPE_file_pdf', 'field_TYPE_file_zip' /* etc.. my product nodes can contain multiple cck filefields so im checking all */) ;
        foreach ( $filefields as $filefield ) {
                if ( ! property_exists($node, $filefield) ) continue ;
                if ( strcmp($filename, $node->{$filefield}[0]['filename']) ) continue ;
                $filepath = $node->{$filefield}[0]['filepath'] ;
                $filemime = $node->{$filefield}[0]['filemime'] ;
                $origname = $node->{$filefield}[0]['origname'] ;
                $headers = array(
                        'Content-Type: ' . $filemime
                        , 'Content-Disposition: attachment; filename="' . $origname . '"'
                        , 'Content-Length: ' . filesize($filepath)
                ) ;
                return file_transfer($filepath, $headers) ;
        }
        return drupal_not_found() ;
} // function _MYMODULE_MY-FILE-STORAGE-PATH_download */

with .htaccess control over file directories, you also need to be careful about blocking the drupal core private files serving mechanism, something like this:

/**
 * Implementation of hook_file_download().
 *  http://api.drupal.org/api/function/hook_file_download
 */
//* function MYMODULE_file_download
function MYMODULE_file_download($filepath) {
        if ( strpos($filepath, 'MY-FILE-STORAGE-PATH/') === 0 ) return -1 ;
} // function MYMODULE_file_download */

and i forgot to mention that filefield saved the files to a path like this in my files directory: "files/CONTENT-TYPE/NID/filename.ext".. this allowed me to get the nid from the path above.. im using the http://drupal.org/project/filefield_paths module for this

hope this helps..

P.S. please excuse the input filter messing up my api.drupal.org links.. ive left those on as pointers