如何判断会话是否有效？

Per request, there are a few different ways that you can tell whether or not a session has been started, such as:

根据请求，您可以通过几种不同的方式判断会话是否已启动，例如：

$isSessionActive = (session_id() != "");

Or:

要么：

$isSessionActive = defined('SID');

However, these both fail if you start a session, then close it; session_id() will return the prior session's ID, while SID will be defined. Likewise, calling session_start() at this point will generate an E_NOTICE if you already have a session active. Is there a sane way to check if a session is currently active, without having to resort to output buffering, the shut-up operator (@session_start()), or something else equally as hacky?

但是，如果你开始一个会话，然后关闭它们，这些都会失败; session_id（）将返回先前会话的ID，同时将定义SID。同样，如果您已经激活会话，此时调用session_start（）将生成E_NOTICE。是否有一种理智的方法来检查会话当前是否处于活动状态，而不必求助于输出缓冲，关闭运算符（@session_start（））或其他类似hacky的东西？

EDIT: I wrote a patch to try to get this functionality included in PHP: http://bugs.php.net/bug.php?id=52982

编辑：我写了一个补丁试图让这个功能包含在PHP中：http：//bugs.php.net/bug.php？id = 52982

EDIT 8/29/2011: New function added to PHP 5.4 to fix this: "Expose session status via new function, session_status"

编辑8/29/2011：添加到PHP 5.4的新功能修复此问题：“通过新函数，session_status公开会话状态”

// as of 8/29/2011
$isSessionActive = (session_status() == PHP_SESSION_ACTIVE);

EDIT 12/5/11: session_status() on the PHP manual.

编辑12/5/11：PHP手册上的session_status（）。

7 个解决方案

#1

See edits to the original question; basically, PHP 5.4 and above now has a function called session_status() to solve this problem!

查看原始问题的编辑;基本上，PHP 5.4及以上版本现在有一个名为session_status（）的函数来解决这个问题！

"Expose session status via new function, session_status" (SVN Revision 315745)

“通过新函数session_status公开会话状态”（SVN修订版315745）

If you need this functionality in a pre-PHP 5.4 version, see hakre's answer.

如果您在PHP 5.4之前的版本中需要此功能，请参阅hakre的答案。

#2

I worked around this by adding a couple wrapper functions around the various session creation/closing/destroying functions. Basically:

我通过在各种会话创建/关闭/销毁功能周围添加几个包装函数来解决这个问题。基本上：

function open_session() {
     session_start();
     $_SESSION['is_open'] = TRUE;
}

function close_session() {
   session_write_close();
   $_SESSION['is_open'] = FALSE;
}

function destroy_session() {
   session_destroy();
   $_SESSION['is_open'] = FALSE;
}

function session_is_open() {
   return($_SESSION['is_open']);
}

Hackish, but accomplished what I needed.

哈金，但完成了我需要的。

#3

I'm running into this as well, and a setting in $_SESSION is not an option for me. For PHP 5.3.8:

我也遇到了这个问题，$ _SESSION中的设置对我来说不是一个选项。对于PHP 5.3.8：

1. If any session has been started with the request, define('SID') will return FALSE, as well as $_SESSION is unset.
2. 如果已经使用请求启动了任何会话，则define（'SID'）将返回FALSE，并且未设置$ _SESSION。
3. This is independent whether or not session_id() has been used to set a session id or not.
4. 无论是否已使用session_id（）来设置会话ID，这都是独立的。
5. After the first session_start(), SID is defined and $_SESSION is set to an empty array.
6. 在第一个session_start（）之后，定义了SID并将$ _SESSION设置为空数组。
7. session_destroy() does unset the session_id(), it's an empty string then. SID will remain defined (and set to it's previous value which might be an empty string). $_SESSION is left unchanged. It will get reset/populated next time session_start is called.
8. session_destroy（）取消设置session_id（），然后它是一个空字符串。 SID将保持定义（并设置为之前的值，可能是空字符串）。 $ _SESSION保持不变。它将在下次调用session_start时重置/填充。

With these states, especially as session_id() can be called in between to set the id for the next session, it's not possible to safely determine the session status with SID, $_SESSION and session_id().

使用这些状态，特别是可以在两者之间调用session_id（）来设置下一个会话的id，因此无法使用SID，$ _SESSION和session_id（）安全地确定会话状态。

"Trying" with session_start() (e.g. with @) might not be really helpful, as this will change the session status and changing the contents of $_SESSION (and adding a set-cookie header if the cookie was not part of the request). It was not fitting in my case.

“尝试”用在session_start（）（例如，用@）可能不是真正有用的，因为这将改变会话状态和改变$ _SESSION内容（并添加一个Set-Cookie头如果cookie没有请求的一部分） 。这不适合我的情况。

While I was running tests, I came across the behaviour, that you can not try to change the ini setting of session.serialize_handler when the session is active, not even when you set it to the same value. Same is true for session.use_trans_sid^Docs which is more lightweight. This lead me to the following function:

当我运行测试时，我遇到了这样的行为，即当会话处于活动状态时，您无法尝试更改session.serialize_handler的ini设置，即使您将其设置为相同的值也是如此。 session.use_trans_sidDocs也是如此，它更轻量级。这引出了以下功能：

/**
 * @return bool
 */
function session_is_active()
{
    $setting = 'session.use_trans_sid';
    $current = ini_get($setting);
    if (FALSE === $current)
    {
        throw new UnexpectedValueException(sprintf('Setting %s does not exists.', $setting));
    }
    $result = @ini_set($setting, $current); 
    return $result !== $current;
}

As far as I can see, the error is checking for active session status only (not disabled), so this should not return a false positive when sessions are disabled.

据我所知，错误是仅检查活动会话状态（未禁用），因此在禁用会话时不应返回误报。

To get this function compatible with PHP 5.2, it needs a little modification:

要使此功能与PHP 5.2兼容，需要稍加修改：

/**
 * @return bool
 */
function session_is_active()
{
    $setting = 'session.use_trans_sid';
    $current = ini_get($setting);
    if (FALSE === $current)
    {
        throw new UnexpectedValueException(sprintf('Setting %s does not exists.', $setting));
    }
    $testate = "mix$current$current";
    $old = @ini_set($setting, $testate);
    $peek = @ini_set($setting, $current);
    $result = $peek === $current || $peek === FALSE;
    return $result;
}

Some sandbox.

一些沙盒。

#4

The following code only dumps one session_id() for me, not two

以下代码仅为我转储一个session_id（），而不是两个

session_start();
echo session_id();
session_destroy();
echo session_id();

If you're having difficulties with this still you can try creating a variable to check, that you destroy when you destroy the session.

如果你仍然遇到困难，你可以尝试创建一个变量来检查，当你销毁会话时你会破坏它。

session_start();
$_SESSION['intialized'] = 'This will not print';
$_SESSION = array(); // Unset all variables
session_destroy();
echo $_SESSION['initialized']; // No output

#5

Here's a good drop in replacement that won't break stuff when you move to 5.4:

这是一个很好的替代品，当你转到5.4时不会破坏东西：

if(!function_exists('session_status')){
    function session_active(){
        return defined('SID');   
    }
}else{
    function session_active(){
        return (session_status() == PHP_SESSION_ACTIVE);   
    }        
}

#6

Ken, if the session is destroyed, the $_SESSION array should not be available...or at the very least, your values should be unset. So, in theory (untested) you should be able to check the array for a value to know if anything is currently set.

Ken，如果会话被破坏，$ _SESSION数组应该不可用......或者至少，你的值应该是未设置的。因此，理论上（未经测试）您应该能够检查数组中的值以了解当前是否设置了任何内容。

#7

There are multiple places you need to check to verify the session is active:

您需要检查多个位置以验证会话是否处于活动状态：

1- cookie exists and is not expired 2- underlying session storage mechanism (file system or database) has a record matching the cookie.

1- cookie存在且未过期2-基础会话存储机制（文件系统或数据库）具有与cookie匹配的记录。