(PHP 8 >= 8.3.0, PHP 8)
socket_atmark — Determines whether socket is at out-of-band mark
Example #1 Using socket_atmark() to set the source address
<?php
// Create a new socket
$sock = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
var_dump(socket_atmark($sock));
// Close
socket_close($sock);
?>