_node_access_rebuild_batch_operation does not handle a corner case

API page: https://api.drupal.org/api/drupal/modules%21node%21node.module/function/...

First, although it may seem to be, this is not a duplicate of previous issue threads about rebuilding content access permissions. (I have scanned them all, and none of them surface this issue, which is present in the 7.28 version of node.module.)

The expected behavior of this function is that it terminates once all its processing of the batch in question has been completed.

However, this is not always the case. At times, due to matters outside this function's scope of concerns, the assignment statement:

$nids = db_query_range( ... )

returns an empty array. But the code assumes this can never happen, and thus does not check for it. In failing to do so, the function opens itself up to triggering an infinite loop, because it repeatedly performs the assignment:

$context['finished'] = $context['sandbox']['progress'] / $context['sandbox']['max'];

which will always yield a fraction (less than 1).

The following coding of the function resolves this issue, plus it cleans up two pieces of coding sloppiness (as noted in the added comments):

function _node_access_rebuild_batch_operation(&$context) {

  if (empty($context['sandbox'])) {
    // Initiate multistep processing.
    $context['sandbox']['progress'] = 0;
    $context['sandbox']['current_node'] = 0;
    // carry max as a proper integer in the array, not as the string '1'
    $context['sandbox']['max'] = intval( db_query('SELECT COUNT(DISTINCT nid) FROM {node}')->fetchField() );
  }

  // Process the next 20 nodes.
  $limit = 20;
  $nids = db_query_range("SELECT nid FROM {node} WHERE nid > :nid ORDER BY nid ASC", 0, $limit, array(':nid' => $context['sandbox']['current_node']))->fetchCol();

  // look for the corner case
  if( ! empty( $nids ) ) {
	$nodes = node_load_multiple($nids, array(), TRUE);
	foreach ($nodes as $nid => $node) {
	  // To preserve database integrity, only acquire grants if the node
	  // loads successfully.
	  if (!empty($node)) {
		node_access_acquire_grants($node);
	  }
	  $context['sandbox']['progress']++;
	  $context['sandbox']['current_node'] = $nid;
	}
  }
  // handle the corner case
  else {
  	$context['sandbox']['progress'] = $context['sandbox']['max'];
  }

  // Multistep processing : report progress.
  if ($context['sandbox']['progress'] < $context['sandbox']['max']) {
    $context['finished'] = $context['sandbox']['progress'] / $context['sandbox']['max'];
  }
  // do not assume that the passed-in value was 1
  else {
    $context['finished'] = 1;
  }
  
}