Add arbitrary ping URL to avoid bootstrapping Drupal and executing a view at each refresh

Implemented in latest dev. Here's how it works:

The additional theme parameter ping_base_path is used to inform Views Auto-Refresh that this URL should be hit before the secondary view. The script at this ping URL should accept a GET parameter called timestamp and return a JSON response of the following form:

array(
 'pong' => $count,
);

where $count is 0 if there are no new items since timestamp, > 0 otherwise.

For example, here's a complete ping script:

require('../../../default/settings.php');

global $db_url;
$p = parse_url($db_url);
$mysql = mysql_pconnect($p['host'], $p['user'], @$p['pass']);
if (!$mysql) die('Could not connect to database server.');
mysql_set_charset('utf8', $mysql);
if (!mysql_select_db(str_replace('/', '', $p['path']), $mysql)) die('Could not select database.');

$timestamp = mysql_real_escape_string($_REQUEST['timestamp']);
$type = mysql_real_escape_string($_REQUEST['type']);
$sql = "SELECT COUNT(nid) FROM node WHERE type='" . $type .  "' AND created > " . $timestamp;
if (!empty($_REQUEST['uid'])) {
  $uid = mysql_real_escape_string($_REQUEST['uid']);
  $sql .= " AND uid = " . $uid;
}
$count = mysql_result(mysql_query($sql, $mysql), 0);

print json_encode(array(
  'pong' => $count,
));

mysql_close($mysql);

This script illustrates parsing the Drupal MySQL connection string, getting a number of parameters including timestamp, and returning the expected JSON response.

The Views Auto-Refresh theme function should be called with an additional setting ping_base_path as such:

print theme('views_autorefresh', 5000, views_get_current_view(), array(
  'view_base_path' => 'liveblog/autorefresh', // the path of the update view
  'view_display_id' => 'page_2', // the display of the update view
  'view_name' => 'liveblog', // the name of the update view
  'sourceSelector' => '.view-content', // selector for items container in update view
  'targetSelector' => '.view-content', // selector for items container in on-page view
  'firstClass' => 'first', // class name for first element (optional),
  'lastClass' => 'last', // class name for last element (optional),
  'oddClass' => 'odd', // class name for odd elements (optional)
  'evenClass' => 'even', // class name for even elements (optional)
  'ping_base_path' => drupal_get_path('module', 'liveblog') . '/liveblog.php?type=report, // ping URL (optional)
));

I'm currently focusing on D6, no plans to move to D7 unless someone else wants to undertake the port.