防止用户恶意或者重复提交数据，进行code验证

anti_spam.php

<?php
$salt = 'qwerty';

if (!empty($_GET['code'])) {
    $code = $_GET['code'];
    list($time, $encode) = explode('_', $code);
    if ($encode != md5($time . $salt)) {
        echo '非法请求';
        exit();
    }
    echo '请求成功';
} else {
    $time = time();
    $code = $time . '_' . md5($time . $salt);
    $link = "http://localhost/test.php?code={$code}";
    echo "<a href={$link}>{$link}</a>";
}
?>