PHP. Руководство по PHP. 2005

Session Handling Functions

Пред.

След.

CXXIII. Session Handling Functions

Введение

Session support in PHP consists of a way to preserve certain data

across subsequent accesses. This enables you to build more

customized applications and increase the appeal of your web site.

A visitor accessing your web site is assigned an unique id, the

so-called session id. This is either stored in a cookie on the

user side or is propagated in the URL.

The session support allows you to register arbitrary numbers of

variables to be preserved across requests. When a visitor accesses

your site, PHP will check automatically (if session.auto_start

is set to 1) or on your request (explicitly through

session_start() or implicitly through

session_register()) whether a specific session

id has been sent with the request. If this is the case, the prior

saved environment is recreated.

Предостережение

- If you do turn on - session.auto_start then you cannot put objects into

your sessions since the class definition has to be

loaded before starting the session in order to recreate the

objects in your session.

All registered variables are serialized after the request

finishes. Registered variables which are undefined are marked as

being not defined. On subsequent accesses, these are not defined

by the session module unless the user defines them later.

Внимание

- Some types of data can not be serialized thus stored in sessions. It

includes resource variables or objects with circular

references (i.e. objects which passes a reference to itself to another

object).

Замечание:

Session handling was added in PHP4.0.

Замечание:

Please note when working with sessions that a record of a session

is not created until a variable has been registered using the

session_register() function or by adding a new

key to the $_SESSION superglobal array. This

holds true regardless of if a session has been started using the

session_start() function.

Sessions and security

External links: Session fixation

The session module cannot guarantee that the information you store

in a session is only viewed by the user who created the session. You need

to take additional measures to actively protect the integrity of the

session, depending on the value associated with it.

Assess the importance of the data carried by your sessions and deploy

additional protections -- this usually comes at a price, reduced

convenience for the user. For example, if you want to protect users from

simple social engineering tactics, you need to enable

session.use_only_cookies. In that case,

cookies must be enabled unconditionally on the user side, or

sessions will not work.

There are several ways to leak an existing session id to third parties.

A leaked session id enables the third party to access all resources which

are associated with a specific id. First, URLs carrying session ids. If

you link to an external site, the URL including the session id might be

stored in the external site's referrer logs. Second, a more active

attacker might listen to your network traffic. If it is not encrypted,

session ids will flow in plain text over the network. The solution here

is to implement SSL on your server and make it mandatory for users.

Требования

Эти функции всегда доступны.

Замечание:

Optionally you can use shared memory allocation (mm), developed by

Ralf S. Engelschall, for session storage. You have to download

mm and install it. This option is not

available for Windows platforms. Note that the session storage module

for mm does not guarantee that concurrent accesses to the same session

are properly locked. It might be more appropriate to use a shared memory

based filesystem (such as tmpfs on Solaris/Linux, or /dev/md on BSD) to

store sessions in files, because they are properly locked.

Установка

Session support is enabled in PHP by default. If you would

not like to build your PHP with session support, you should

specify the --disable-session

option to configure. To use shared memory allocation (mm) for session

storage configure PHP --with-mm[=DIR] .

Версия PHP для

Windows имеет встроенную поддержку данного расширения. Это означает, что

для использования данных функций не требуется загрузка никаких

дополнительных расширений.

Замечание:

By default, all data related to a particular session will be stored in

a file in the directory specified by the session.save_path INI option.

A file for each session (regardless of if any data is associated with

that session) will be created. This is due to the fact that a session

is opened (a file is created) but no data is even written to that file.

Note that this behavior is a side-effect of the limitations of working

with the file system and it is possible that a custom session handler

(such as one which uses a database) does not keep track of sessions

which store no data.

Настройка во время выполнения

-Поведение этих функций зависит от установок в php.ini.

Таблица 1. Session configuration options

Name	Default	Changeable	Changelog
session.save_path	""	PHP_INI_ALL
session.name	"PHPSESSID"	PHP_INI_ALL
session.save_handler	"files"	PHP_INI_ALL
session.auto_start	"0"	PHP_INI_ALL
session.gc_probability	"1"	PHP_INI_ALL
session.gc_divisor	"100"	PHP_INI_ALL	Available since PHP4.3.2.
session.gc_maxlifetime	"1440"	PHP_INI_ALL
session.serialize_handler	"php"	PHP_INI_ALL
session.cookie_lifetime	"0"	PHP_INI_ALL
session.cookie_path	"/"	PHP_INI_ALL
session.cookie_domain	""	PHP_INI_ALL
session.cookie_secure	""	PHP_INI_ALL	Available since PHP4.0.4.
session.use_cookies	"1"	PHP_INI_ALL
session.use_only_cookies	"0"	PHP_INI_ALL	Available since PHP4.3.0.
session.referer_check	""	PHP_INI_ALL
session.entropy_file	""	PHP_INI_ALL
session.entropy_length	"0"	PHP_INI_ALL
session.cache_limiter	"nocache"	PHP_INI_ALL
session.cache_expire	"180"	PHP_INI_ALL
session.use_trans_sid	"0"	PHP_INI_ALL	PHP_INI_ALL in PHP <= 4.2.3. PHP_INI_PERDIR in PHP < 5. Available since PHP4.0.3.
session.bug_compat_42	"1"	PHP_INI_ALL	Available since PHP4.3.0.
session.bug_compat_warn	"1"	PHP_INI_ALL	Available since PHP4.3.0.
session.hash_function	"0"	PHP_INI_ALL	Available since PHP5.0.0.
session.hash_bits_per_character	"4"	PHP_INI_ALL	Available since PHP5.0.0.
url_rewriter.tags	"a=href,area=href,frame=src,form=,fieldset="	PHP_INI_ALL	Available since PHP4.0.4.

Для подробного описания констант

PHP_INI_*, обратитесь к документации функции ini_set().

The session management system supports a number of configuration

options which you can place in your php.ini file. We will give a

short overview.

session.save_handler

string

session.save_handler defines the name of the

handler which is used for storing and retrieving data

associated with a session. Defaults to

files. See also

session_set_save_handler().

session.save_path

string

session.save_path defines the argument which

is passed to the save handler. If you choose the default files

handler, this is the path where the files are created. Defaults to

/tmp. See also

session_save_path().

There is an optional N argument to this directive that determines

the number of directory levels your session files will be spread

around in. For example, setting to '5;/tmp'

may end up creating a session file and location like

/tmp/4/b/1/e/3/sess_4b1e384ad74619bd212e236e52a5a174If

. In order to use N you must create all of these

directories before use. A small shell script exists in

ext/session to do this, it's called

mod_files.sh. Also note that if N is

used and greater than 0 then automatic garbage collection will

not be performed, see a copy of php.ini for further

information. Also, if you use N, be sure to surround

session.save_path in

"quotes" because the separator (;) is

also used for comments in php.ini.

Внимание

- If you leave this set to a world-readable directory, such as

/tmp (the default), other users on the

server may be able to hijack sessions by getting the list of

files in that directory.

Замечание:

Prior to PHP4.3.6, Windows users had to change this variable in order

to use PHP's session functions. A valid path must be specified, e.g.:

c:/temp.

session.name

string

session.name specifies the name of the

session which is used as cookie name. It should only contain

alphanumeric characters. Defaults to PHPSESSID.

Типы ресурсов

Данное расширение не определяет никакие типы ресурсов.

Предопределенные константы

-Перечисленные ниже константы определены данным расширением и могут быть

доступны только в том случае, если PHP был собран с

поддержкой этого расширения или же в том случае, если

данное расширение подгружается во время выполнения.

SID

(string)

Constant containing either the session name and session ID in

the form of "name=ID" or empty string

if session ID was set in an appropriate session cookie.

Примеры

Замечание:

As of PHP4.1.0, $_SESSION is available as a

global variable just like $_POST,

$_GET, $_REQUEST and so on.

Unlike $HTTP_SESSION_VARS,

$_SESSION is always global. Therefore, you do not

need to use the global

keyword for $_SESSION. Please note that this

documentation has been changed to use

$_SESSION everywhere. You can substitute

$HTTP_SESSION_VARS for

$_SESSION, if you prefer the former. Also note

that you must start your session using session_start()

before use of $_SESSION becomes available.

The keys in the $_SESSION associative

array are subject to the

same limitations as regular variable names in PHP, i.e. they cannot

start with a number and must start with a letter or underscore.

For more details see the section on

variables in this manual.

If register_globals

is disabled, only members of the global associative array

$_SESSION can be registered as session

variables. The restored session variables will only be available

in the array $_SESSION.

Use of $_SESSION (or

$HTTP_SESSION_VARS with PHP4.0.6 or less) is

recommended for improved security and code readability. With

$_SESSION, there is no need to use the

session_register(),

session_unregister(),

session_is_registered() functions. Session variables

are accessible like any other variables.

Пример 1.

Registering a variable with $_SESSION.


<?
session_start();
//Use $HTTP_SESSION_VARS with PHP4.0.6 or less
if (!isset($_SESSION['count'])){
$_SESSION['count'] = 0;
}else{
$_SESSION['count']++;
}

?>

Пример 2.

Unregistering a variable with $_SESSION and

register_globals disabled.


<?
session_start();
//Use $HTTP_SESSION_VARS with PHP4.0.6 or less
unset($_SESSION['count']);

?>

Предостережение

- Do NOT unset the whole $_SESSION with

unset($_SESSION) as this will disable the

registering of session variables through the

$_SESSION superglobal.

Внимание

- You can't use references in session variables as there is no feasible way

to restore a reference to another variable.

Пример 3.

Unregistering a variable with register_globals

enabled, after registering it using

$_SESSION.


<?
session_start();
//With PHP4.3 and later, you can also simply use the prior example.
session_unregister('count');

?>

If register_globals

is enabled, then each global variable can be registered as session

variable. Upon a restart of a session, these variables will be restored

to corresponding global variables. Since PHP must know which global

variables are registered as session variables, users need to register

variables with session_register() function.

You can avoid this by simply setting entries in

$_SESSION.

Предостережение

- Before PHP4.3, if you are using $_SESSION and you

have disabled register_globals,

don't use session_register(),

session_is_registered() or

session_unregister().

If you enable register_globals,

session_unregister() should be used since

session variables are registered as global variables when

session data is deserialized. Disabling register_globals

is recommended for both security and performance reasons.

Пример 4.

Registering a variable with register_globals

enabled


<?
if (! isset($_SESSION['count'])){
$_SESSION['count'] = 1;
}else{
$_SESSION['count']++;
}

?>

If register_globals

is enabled, then the global variables and the

$_SESSION entries will automatically reference the

same values which were registered in the prior session instance.

There is a defect in PHP4.2.3 and earlier. If you register a new

session variable by using session_register(), the

entry in the global scope and the $_SESSION entry will

not reference the same value until the next

session_start(). I.e. a modification to the newly

registered global variable will not be reflected by the

$_SESSION entry. This has been corrected in PHP4.3.

Passing the Session ID

There are two methods to propagate a session id:

URL parameter

The session module supports both methods. Cookies are optimal, but

because they are not always available, we also provide an alternative

way. The second method embeds the session id directly into URLs.

PHP is capable of transforming links transparently. Unless you are using

PHP4.2 or later, you need to enable it manually when building PHP.

Under Unix, pass - --enable-trans-sid to configure. If this build

option and the run-time option

session.use_trans_sid are enabled, relative

URIs will be changed to contain the session id automatically.

Замечание:

The arg_separator.output

php.ini directive allows to customize the argument seperator. For full

XHTML conformance, specify & there.

Alternatively, you can use the constant SID which is

always defined. If the client did not send an appropriate session

cookie, it has the form session_name=session_id.

Otherwise, it expands to an empty string. Thus, you can embed it

unconditionally into URLs.

The following example demonstrates how to register a variable, and

how to link correctly to another page using SID.

Пример 5. Counting the number of hits of a single user


<?
if (!session_is_registered('count')){
session_register('count');
$count = 1;
}else{
$count++;
}
?>
<p>
Hello visitor, you have seen this page <?php echo $count; ?> times.
</p>
<p>
To continue, <a href="nextpage.php?<?php echo strip_tags(SID); ?>">click
here</a>.

</p>

The strip_tags() is used when printing the SID

in order to prevent XSS related attacks.

Printing the SID, like shown above, is not necessary if

- --enable-trans-sid was used to compile PHP.

Замечание:

Non-relative URLs are assumed to point to external sites and

hence don't append the SID, as it would be a security risk to

leak the SID to a different server.