PHP简单利用token防止表单重复提交

/*
* PHP简单利用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'] ? 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($_POST['test'])){
if(!valid_token()){
echo "token error";
}else{
echo time();
}
}
?>
<form method=post action="">
<input type="hidden" name="token" value="<?=$_SESSION['token']?>">
<input type="text" name="test" value="value">
<input type="submit">
</form>