Behind the curtain

I am loving this module! I've made a small change to provide additional granularity in the access control:

/**
 * This function added to provide granularity for access
 * to files only if the user's role matches the node's
 * primary taxonomy term -- mrtoner 12/27/2007
 */
function filefield_myperms($node='') {
   global $user;
    
   $tids = '';
   $vid = 1;
   if ($node) {
      $terms = taxonomy_node_get_terms_by_vocabulary($node, $vid);
   } else {
      $terms = taxonomy_node_get_terms_by_vocabulary(arg(1), $vid);
   }
   foreach ($terms as $term) {
      $tids[] = $term->name;
   }
   if (in_array($tids[0],$user->roles)) {
      return TRUE;
   } else {
      return FALSE;
   }
}

...

function theme_filefield($file) {
  if ((user_access('view filefield uploads') || filefield_myperms()) && is_file($file['filepath']) && $file['list']) {

...

function filefield_file_download($file) {
    $file = file_create_path($file);
    $result = db_query("SELECT * FROM {files} WHERE filepath = '%s'", $file);
    if ($file = db_fetch_object($result)) {
      if (user_access('view filefield uploads') || filefield_myperms($file->nid)) {

...

My reason for doing this is that -- normally -- all users with 'view filefield uploads' permission can download any file if they have access to its associated node. For my project, all users have access to all nodes, but each user has access to only specific files.

So, I assign a taxonomy term to each node and a corresponding role to the user. Now, any user -- even anonymous -- can view the node, but only those with a role matching the taxonomy term can see the download link or download the file. And I don't need a full-blown access control module, which -- as far as I can tell -- would limit access to the entire node instead of just the associated file.

(If this can be done more elegantly, I'm open to suggestions.)

My reason for posting this: although this works, I need to further my Drupal Continuing Education. How does it work? Specifically, I mean what magic does Drupal use to know to pass the file request through the FileField module so that this access control works?

Don