$id,
‘opened_at_utc’ => gmdate(‘c’),
], JSON_UNESCAPED_SLASHES) . PHP_EOL;
// Keep this directory inaccessible from the web if your host allows it.
file_put_contents(__DIR__ . ‘/opens.log’, $entry, FILE_APPEND | LOCK_EX);
}
// Prevent ordinary browser/proxy caching as much as possible.
header(‘Content-Type: image/gif’);
header(‘Content-Length: 43’);
header(‘Cache-Control: no-store, no-cache, must-revalidate, max-age=0’);
header(‘Pragma: no-cache’);
header(‘Expires: 0’);
// Transparent 1 x 1 GIF.
echo base64_decode(‘R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==’);