How to use token in PHP to prevent repeated submission of forms_php tips

<&#63;php
/*
* PHP使用token防止表单重复提交
* 此处理方法纯粹是为了给初学者参考
*/
session_start();
function set_token() {
  $_SESSION['token'] = md5(microtime(true));
}
function valid_token() {
  $return = $_REQUEST['token'] === $_SESSION['token'] &#63; true : false;
  set_token();
  return $return;
}
//如果token为空则生成一个token
if(!isset($_SESSION['token']) || $_SESSION['token']=='') {
  set_token();
}
if(isset($_POST['test'])){
  if(!valid_token()){
    echo "token error";
  }else{
    echo '成功提交，Value:'.$_POST['test'];
  }
}
&#63;>
<form method="post" action="">
  <input type="hidden" name="token" value="<&#63;php echo $_SESSION['token']&#63;>">
  <input type="text" name="test" value="Default">
  <input type="submit" value="提交" />
</form>