检查表单的提交来源

<?php
$path = $_SERVER['PHP_SELF'];//获取当前文件完整路径
if($_SERVER['REQUEST_METHOD']=="POST"){
$a = $_SERVER['HTTP_REFERER'];//保持完整的URL来源。
$b = "http://{$_SERVER['SERVER_NAME']}$path";//当前服务器名称
echo "当前来源为：<br> $a <br>服务器地址为：<br> $b <br><hr>";
if(strcmp($a,$b)==0){//比较字符串的大小
echo "匹配";
}else{
echo "只能从本站进来，不能从外边进来";
}
}else{
echo "请提交表单";
}
?>
<form action = "<?php echo $path; ?>" method = "POST">
<input type = "submit" value = "提交">
</form>