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PHP Session的一个警告

Published on 13 July 2009 by laruence

警告全文如下:

PHP Warning:  Unknown: Your script possibly relies on a session side-effect
which existed until PHP 4.2.3. Please be advised that the session extension does
not consider global variables as a source of data, unless register_globals is enabled.
You can disable this functionality and this warning by setting session.bug_compat_42
or session.bug_compat_warn to off, respectively. in Unknown on

关于这个问题, 网上有多种解决办法, 但都是不知所以然的答案, 那么真正的原因是什么呢, 怎么解决呢?
请首先记住这一点. 在PHP4.2开始, register_globals默认设置为了OFF.
在4.2.3以后, 为了兼容以前的模式, PHP引入了bug_compat_42, 当启用这个选项以后(默认启用), PHP将容许自动将SESSION中的变量做为全局变量使用. 只不过如果bug_compat_warn选项开启的情况下, 会报告这个特性的被使用.
来看一段代码,

<?php
session_start();
var_dump($_SESSION);
$name = 'laruence';
$_SESSION['name'] = null;
?>

上面的代码, 在bug_compat_42开启, register_globals关闭的情况下, 俩次刷新页面的输出, 分别为:

//第一次:
	array(0) {}
//第二次
	array(1) { ["a"]=> string(8) "laruence" }

为什么第二次不是NULL呢, 因为在bug_compat_42开启的情况下, PHP会认为变量a是$_SESSION['a']的一个引用, 在session_close的时候, 会把变量a的值回写.
而在这个过程中, 如果bug_compat_warn开启, 则会抛出文章开头的警告.
So, that it is~

那么, 它具体给出警告的条件是什么呢? 知道了这些条件, 我们就可以避免这个警告了,
在PHPSRC/ext/session/session.c中, 有我们想要的一切答案:

static void php_session_save_current_state(TSRMLS_D) /* {{{ */
{
	int ret = FAILURE;
	IF_SESSION_VARS() {
		//如果存在Session数组
		if (PS(bug_compat) && !PG(register_globals)) {
			HashTable *ht = Z_ARRVAL_P(PS(http_session_vars));
			HashPosition pos;
			zval **val;
			int do_warn = 0;
			zend_hash_internal_pointer_reset_ex(ht, &pos);
			while (zend_hash_get_current_data_ex(ht
						, (void **) &val, &pos) != FAILURE) {
				if (Z_TYPE_PP(val) == IS_NULL) { //变量为null
					if (migrate_global(ht, &pos TSRMLS_CC)) {//变量回写
						do_warn = 1;
					}
				}
				zend_hash_move_forward_ex(ht, &pos);
			}
			if (do_warn && PS(bug_compat_warn)) {
				php_error_docref(NULL TSRMLS_CC, E_WARNING, "Your script possibly
 relies on a session side-effect which existed until PHP 4.2.3 ..........");
				//后面省略

可见, 如果不开启bug_compat_42(现在很少用到这个特性, 开启的话有的时候反而会造成迷惑), 或者不开始bug_compat_warn, 或者在register_globals开启的情况下, 都不会看到这个警告.
另外, 如果开启bug_compat_42, 还可能遇到如下的NOTICE..

PHP Notice:  Unknown: The session bug compatibility code will not try to
locate the global variable $324324 due to its numeric nature in Unknown on line 0

这是当你在$_SESSION中使用数字索引的时候, 可能会引发的警告.

Filed in PHP应用, PHP源码分析

14 Comments

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  6. TottyAndBaty
    TottyAndBaty August 19, 2009

    感谢站长的回答,这是我的那个源文件，代码在php5下测试没有问题，在 php4 下报错，第二个问题也是出在这里
    <?php
    session_start();
    class cart
    {
    function cart()
    {
    if(!isset($_SESSION[“cart”]))
    {
    $_SESSION[“cart”]=array();
    }
    }
    //测试用
    function printcart()
    {
    echo “”;
    print_r($_SESSION[“cart”]);
    echo “”;
    }
    //清空购物车
    function clearcart()
    {
    unset($_SESSION[“cart”]);
    }
    //检查指定ID的商品是否存在
    function iscart($cartid)
    {
    $iscart[“action”]=false;
    foreach($_SESSION[“cart”] as $key=>$value)
    {
    if($value[“id”]==$cartid)
    {
    $iscart[“action”]=true;
    $iscart[“key”]=$key;
    }
    }
    return $iscart;
    }
    //购买，依次传入ID,数量，价格，单位，名称
    function addcart($cartid,$count,$price,$danwei,$name)
    {
    $iscart=$this->iscart($cartid);
    if($iscart[“action”])
    {
    $_SESSION[“cart”][$iscart[“key”]][“count”]+=$count;
    $c= $_SESSION[“cart”][$iscart[“key”]][“count”];
    $price= $_SESSION[“cart”][$iscart[“key”]][“price”];
    $_SESSION[“cart”][$iscart[“key”]][“total”]=$c*$price;
    }
    else
    {
    $total=$count*$price;
    $_SESSION[“cart”][]=array(“id”=>$cartid,
    “count”=>$count,
    “price”=>$price,
    “total”=>$total,
    “danwei”=>$danwei,
    “name”=>$name
    );
    }
    }
    //重复购买，默认一次为1个
    function addMore($cartid,$count=1)
    {
    $iscart=$this->iscart($cartid);
    if($iscart[“action”])
    {
    $_SESSION[“cart”][$iscart[“key”]][“count”]+=$count;
    $c= $_SESSION[“cart”][$iscart[“key”]][“count”];
    $price= $_SESSION[“cart”][$iscart[“key”]][“price”];
    $_SESSION[“cart”][$iscart[“key”]][“total”]=$c*$price;
    }
    }
    //减少数量，默认为1
    function moveout($cartid)
    {
    //删除某件商品
    $iscart=$this->iscart($cartid);
    unset($_SESSION[“cart”][$iscart[“key”]]);
    }
    //删除某件商品
    function delcart($cartid,$count)
    {
    //修改件数
    $iscart=$this->iscart($cartid);
    if($iscart[“action”])
    {
    $_SESSION[“cart”][$iscart[“key”]][“count”]-=$count;
    $c= $_SESSION[“cart”][$iscart[“key”]][“count”];
    $price= $_SESSION[“cart”][$iscart[“key”]][“price”];
    $_SESSION[“cart”][$iscart[“key”]][“total”]=$c*$price;
    if($_SESSION[“cart”][$iscart[“key”]][“count”]

  7. 雪候鸟
    雪候鸟 August 14, 2009

    @TottyAndBaty 第一个问题, 你是否在PHP5中使用了auto_load机制?
    Session在反序列化你的对象的时候, 如果找不到对象的类定义, 那么这个对象的类型就会是_PHP_Incomplete_Class Object,
    解决方法是在,session_start之前, 载入你的类定义.
    至于,第二个问题, 我没遇到过, 你能给个重现代码么?

  8. TottyAndBaty
    TottyAndBaty August 14, 2009

    文章很精彩！看到你写的这篇文章，我想起了我之前使用session做的一个购物车，
    服务器的register_globals=off,我的购物车本身的类名叫cart,而我的购物车保存在$_SESSION[“cart”]中，在php5 下运行可以，但是php4下却报错了，系统提示：__PHP_Incomplete_Class Object，当然我把类名改一下或者改一下$_SESSION问题就可以解决，不知道为什么。
    这个问题解决了，但是后来又出现问题，我使用了一个 $_SESSION[“count”],这个也报错了，好像把这里的count理解为函数了，博主是否帮忙解释一下？谢谢

  9. panjinww
    panjinww July 14, 2009

    学习了，貌似咱少的就是这种钻研的精神！

  10. sky
    sky July 14, 2009

    这种多见于兼容php4脚本的情况

  11. keyvalue
    keyvalue July 14, 2009

    好文，知其所以然的路很艰难，你却如履平地。。。

    • 雪候鸟
      雪候鸟 July 14, 2009

      你的文采真好, 夸的我开心的~ 嘿嘿

  12. xi2008wang
    xi2008wang July 13, 2009

    在源代码面前没有密码.

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