codefool's Journal: Interesting PHP snippet

few simple lines of PHP (or equiv in any other language) can pull the real IP from a non-anonymising proxy:

    <?php

    if ($_SERVER['HTTP_X_FORWARDED_FOR'] == NULL) $ip = $_SERVER['REMOTE_ADDR'];
    else {
    $source = $_SERVER['HTTP_X_FORWARDED_FOR'];
    $pattern = "/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/";
    preg_match($pattern, $source, $matches);
    $ip = $matches[0];
    echo "Proxy detected (" . $_SERVER['REMOTE_ADDR'] . ")<br />";
    }

    echo $ip;

    ?>