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<?xml version="1.0" encoding="utf-8"?>
<reference id="ref.session">
<title>Session handling functions</title>
<titleabbrev>Sessions</titleabbrev>
<partintro>
<para>
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.
</para>
<para>
If you are familiar with the session management of PHPLIB, you
will notice that some concepts are similar to PHP's session
support.
</para>
<para>
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.
</para>
<para>
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
<function>session_start</function> or implicitly through
<function>session_register</function>) whether a specific session
id has been sent with the request. If this is the case, the prior
saved environment is recreated.
</para>
<para>
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.
</para>
<para>
The <link
linkend="ini.track-vars"><literal>track_vars</literal></link> and
<link
linkend="ini.register-globals"><literal>register_globals</literal></link>
configuration settings influence how the session variables get
stored and restored.
</para>
<note>
<para>
As of PHP 4.0.3, <link
linkend="ini.track-vars"><literal>track_vars</literal></link> is
always turned on.
</para>
</note>
<para>
If <link
linkend="ini.track-vars"><literal>track_vars</literal></link> is
enabled and <link
linkend="ini.register-globals"><literal>register_globals</literal></link>
is disabled, only members of the global associative array
$HTTP_SESSION_VARS can be registered as session variables. The
restored session variables will only be available in the array
$HTTP_SESSION_VARS.
<example>
<title>
Registering a variable with <link
linkend="ini.track-vars"><literal>track_vars</literal></link>
enabled
</title>
<programlisting role="php">
<?php
session_register("count");
$HTTP_SESSION_VARS["count"]++;
?>
</programlisting>
</example>
</para>
<para>
If <link
linkend="ini.register-globals"><literal>register_globals</literal></link>
is enabled, then all global variables can be registered as session
variables and the session variables will be restored to
corresponding global variables.
<example>
<title>
Registering a variable with <link
linkend="ini.register-globals"><literal>register_globals</literal></link>
enabled
</title>
<programlisting role="php">
<?php
session_register("count");
$count++;
?>
</programlisting>
</example>
</para>
<para>
If both <link
linkend="ini.track-vars"><literal>track_vars</literal></link> and
<link
linkend="ini.register-globals"><literal>register_globals</literal></link>
are enabled, then the globals variables and the $HTTP_SESSION_VARS
entries will reference the same value.
</para>
<para>
There are two methods to propagate a session id:
<itemizedlist>
<listitem>
<simpara>
Cookies
</simpara>
</listitem>
<listitem>
<simpara>
URL parameter
</simpara>
</listitem>
</itemizedlist>
</para>
<para>
The session module supports both methods. Cookies are optimal, but
since they are not reliable (clients are not bound to accept
them), we cannot rely on them. The second method embeds the
session id directly into URLs.
</para>
<para>
PHP is capable of doing this transparently when compiled with
<literal>--enable-trans-sid</literal>. If you enable this option,
relative URIs will be changed to contain the session id
automatically. Alternatively, you can use the constant
<literal>SID</literal> which is defined, if the client did not
send the appropriate cookie. <literal>SID</literal> is either of
the form <literal>session_name=session_id</literal> or is an empty
string.
</para>
<para>
The following example demonstrates how to register a variable, and
how to link correctly to another page using SID.
<example>
<title>Counting the number of hits of a single user</title>
<programlisting role="php">
<?php
session_register ("count");
$count++;
?>
Hello visitor, you have seen this page <?php echo $count; ?> times.<p>
<php?
# the <?=SID?> is necessary to preserve the session id
# in the case that the user has disabled cookies
?>
To continue, <A HREF="nextpage.php?<?=SID?>">click here</A>
</programlisting>
</example>
</para>
<para>
The <literal><?=SID?></literal> is not necessary, if
<literal>--enable-trans-sid</literal> was used to compile PHP.
</para>
<para>
To implement database storage, or any other storage method, you
will need to use <function>session_set_save_handler</function> to
create a set of user-level storage functions.
</para>
<para>
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.
<itemizedlist>
<listitem>
<simpara>
<literal>session.save_handler</literal> defines the name of the
handler which is used for storing and retrieving data
associated with a session. Defaults to
<literal>files</literal>.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.save_path</literal> 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 <literal>/tmp</literal>.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.name</literal> specifies the name of the
session which is used as cookie name. It should only contain
alphanumeric characters. Defaults to
<literal>PHPSESSID</literal>.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.auto_start</literal> specifies whether the
session module starts a session automatically on request
startup. Defaults to <literal>0</literal> (disabled).
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.cookie_lifetime</literal> specifies the lifetime of
the cookie in seconds which is sent to the browser. The value 0
means "until the browser is closed." Defaults to
<literal>0</literal>.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.serialize_handler</literal> defines the name
of the handler which is used to serialize/deserialize
data. Currently, a PHP internal format (name
<literal>php</literal>) and WDDX is supported (name
<literal>wddx</literal>). WDDX is only available, if PHP is
compiled with <link linkend="ref.wddx">WDDX
support</link>. Defaults to <literal>php</literal>.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.gc_probability</literal> specifies the
probability that the gc (garbage collection) routine is started
on each request in percent. Defaults to <literal>1</literal>.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.gc_maxlifetime</literal> specifies the number
of seconds after which data will be seen as 'garbage' and
cleaned up.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.referer_check</literal> contains the substring you
want to check each HTTP Referer for. If the Referer was sent by the
client and the substring was not found, the embedded session id will
be marked as invalid. Defaults to the empty string.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.entropy_file</literal> gives a path to an
external resource (file) which will be used as an additional
entropy source in the session id creation process. Examples are
<literal>/dev/random</literal> or
<literal>/dev/urandom</literal> which are available on many
Unix systems.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.entropy_length</literal> specifies the number
of bytes which will be read from the file specified
above. Defaults to <literal>0</literal> (disabled).
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.use_cookies</literal> specifies whether the
module will use cookies to store the session id on the client
side. Defaults to <literal>1</literal> (enabled).
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.cookie_path</literal> specifies path to set
in session_cookie. Defaults to <literal>/</literal>.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.cookie_domain</literal> specifies domain to
set in session_cookie. Default is none at all.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.cache_limiter</literal> specifies cache control
method to use for session pages (nocache/private/public).
Defaults to <literal>nocache</literal>.
</simpara>
</listitem>
<listitem>
<simpara>
<literal>session.cache_expire</literal> specifies time-to-live
for cached session pages in minutes, this has no effect for
nocache limiter. Defaults to <literal>180</literal>.
</simpara>
</listitem>
</itemizedlist>
<note>
<para>
Session handling was added in PHP 4.0.
</para>
</note>
</para>
</partintro>
<refentry id="function.session-start">
<refnamediv>
<refname>session_start</refname>
<refpurpose>Initialize session data</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>bool</type><methodname>session_start</methodname>
<void/>
</methodsynopsis>
<simpara>
<function>session_start</function> creates a session (or resumes
the current one based on the session id being passed via a GET
variable or a cookie).</simpara>
<simpara>
This function always returns &true;.
</simpara>
<note>
<para>
This function was added in PHP 4.0.
</para>
</note>
</refsect1>
</refentry>
<refentry id="function.session-destroy">
<refnamediv>
<refname>session_destroy</refname>
<refpurpose>Destroys all data registered to a session</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>bool</type><methodname>session_destroy</methodname>
<void/>
</methodsynopsis>
<simpara>
<function>session_destroy</function> destroys all of the data
associated with the current session.
</simpara>
<simpara>
This function returns &true; on success and &false; on failure to destroy
the session data.
</simpara>
</refsect1>
</refentry>
<refentry id="function.session-name">
<refnamediv>
<refname>session_name</refname>
<refpurpose>Get and/or set the current session name</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>string</type><methodname>session_name</methodname>
<methodparam choice="opt"><type>string</type><parameter>name</parameter></methodparam>
</methodsynopsis>
<para>
<function>session_name</function> returns the name of the current
session. If <parameter>name</parameter> is specified, the name of
the current session is changed to its value.
</para>
<para>
The session name references the session id in cookies and
URLs. It should contain only alphanumeric characters; it should
be short and descriptive (i.e. for users with enabled cookie
warnings). The session name is reset to the default value
stored in <literal>session.name</literal> at request startup
time. Thus, you need to call <function>session_name</function>
for every request (and before <function>session_start</function>
or <function>session_register</function> are called).
</para>
<example>
<title><function>session_name</function> examples</title>
<programlisting role="php">
<?php
# set the session name to WebsiteID
$previous_name = session_name ("WebsiteID");
echo "The previous session name was $previous_name<p>";
?>
</programlisting>
</example>
<note>
<para>
This function was added in PHP 4.0.
</para>
</note>
</refsect1>
</refentry>
<refentry id="function.session-module-name">
<refnamediv>
<refname>session_module_name</refname>
<refpurpose>Get and/or set the current session module</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>string</type><methodname>session_module_name</methodname>
<methodparam choice="opt"><type>string</type><parameter>module</parameter></methodparam>
</methodsynopsis>
<para>
<function>session_module_name</function> returns the name of the
current session module. If <parameter>module</parameter> is
specified, that module will be used instead.
<note>
<para>
This function was added in PHP 4.0.
</para>
</note>
</para>
</refsect1>
</refentry>
<refentry id="function.session-save-path">
<refnamediv>
<refname>session_save_path</refname>
<refpurpose>Get and/or set the current session save path</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>string</type><methodname>session_save_path</methodname>
<methodparam choice="opt"><type>string</type><parameter>path</parameter></methodparam>
</methodsynopsis>
<para>
<function>session_save_path</function> returns the path of the current
directory used to save session data. If <parameter>path</parameter>
is specified, the path to which data is saved will be changed.
<note>
<para>
On some operating systems, you may want to specify a path on a
filesystem that handles lots of small files efficiently. For
example, on Linux, reiserfs may provide better performance than
ext2fs.
</para>
</note>
<note>
<para>
This function was added in PHP 4.0.
</para>
</note>
</para>
</refsect1>
</refentry>
<refentry id="function.session-id">
<refnamediv>
<refname>session_id</refname>
<refpurpose>Get and/or set the current session id</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>string</type><methodname>session_id</methodname>
<methodparam choice="opt"><type>string</type><parameter>id</parameter></methodparam>
</methodsynopsis>
<para>
<function>session_id</function> returns the session id for the
current session. If <parameter>id</parameter> is specified, it
will replace the current session id.
</para>
<para>
The constant <systemitem>SID</systemitem> can also be used to
retrieve the current name and session id as a string suitable for
adding to URLs.
</para>
</refsect1>
</refentry>
<refentry id="function.session-register">
<refnamediv>
<refname>session_register</refname>
<refpurpose>
Register one or more variables with the current session
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>bool</type><methodname>session_register</methodname>
<methodparam><type>mixed</type><parameter>name</parameter></methodparam>
<methodparam choice="opt"><type>mixed</type><parameter>...</parameter></methodparam>
</methodsynopsis>
<para>
<function>session_register</function> variable number of
arguments, any of which can be either a string holding the
variable name or an array consisting of such variable names or
other arrays. For each encountered variable name,
<function>session_register</function> registers the global
variable named by it with the current session.
</para>
<para>
This function returns &true; when the variable is successfully
registered with the session.
<note>
<para>
This function was added in PHP 4.0.
</para>
</note>
</para>
</refsect1>
</refentry>
<refentry id="function.session-unregister">
<refnamediv>
<refname>session_unregister</refname>
<refpurpose>
Unregister a variable from the current session
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>bool</type><methodname>session_unregister</methodname>
<methodparam><type>string</type><parameter>name</parameter></methodparam>
</methodsynopsis>
<para>
<function>session_unregister</function> unregisters (forgets)
the global variable named <parameter>name</parameter> from the
current session.
</para>
<para>
This function returns &true; when the variable is successfully
unregistered from the session.
<note>
<para>
This function was added in PHP 4.0.
</para>
</note>
</para>
</refsect1>
</refentry>
<refentry id="function.session-unset">
<refnamediv>
<refname>session_unset</refname>
<refpurpose>
Free all session variables
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>void</type><methodname>session_unset</methodname>
<void/>
</methodsynopsis>
<para>
The <function>session_unset</function> function free's all session variables
currently registered.
</para>
</refsect1>
</refentry>
<refentry id="function.session-is-registered">
<refnamediv>
<refname>session_is_registered</refname>
<refpurpose>
Find out if a variable is registered in a session
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>bool</type><methodname>session_is_registered</methodname>
<methodparam><type>string</type><parameter>name</parameter></methodparam>
</methodsynopsis>
<para>
<function>session_is_registered</function> returns &true; if there
is a variable with the name <parameter>name</parameter>
registered in the current session.
<note>
<para>
This function was added in PHP 4.0.
</para>
</note>
</para>
</refsect1>
</refentry>
<refentry id="function.session-get-cookie-params">
<refnamediv>
<refname>session_get_cookie_params</refname>
<refpurpose>
Get the session cookie parameters
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>array</type><methodname>session_get_cookie_params</methodname>
<void/>
</methodsynopsis>
<para>
The <function>session_get_cookie_params</function> function returns an
array with the current session cookie information, the array contains
the following items:
<itemizedlist>
<listitem>
<simpara>
"lifetime" - The lifetime of the cookie.
</simpara>
</listitem>
<listitem>
<simpara>
"path" - The path where information is stored.
</simpara>
</listitem>
<listitem>
<simpara>
"domain" - The domain of the cookie.
</simpara>
</listitem>
</itemizedlist>
</para>
</refsect1>
</refentry>
<refentry id="function.session-set-cookie-params">
<refnamediv>
<refname>session_set_cookie_params</refname>
<refpurpose>
Set the session cookie parameters
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>void</type><methodname>session_set_cookie_params</methodname>
<methodparam><type>int</type><parameter>lifetime</parameter></methodparam>
<methodparam choice="opt"><type>string</type><parameter>path</parameter></methodparam>
<methodparam choice="opt"><type>string</type><parameter>domain</parameter></methodparam>
</methodsynopsis>
<para>
Set cookie parameters defined in the php.ini file. The effect of this
function only lasts for the duration of the script.
</para>
</refsect1>
</refentry>
<refentry id="function.session-decode">
<refnamediv>
<refname>session_decode</refname>
<refpurpose>Decodes session data from a string</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>bool</type><methodname>session_decode</methodname>
<methodparam><type>string</type><parameter>data</parameter></methodparam>
</methodsynopsis>
<para>
<function>session_decode</function> decodes the session data in
<parameter>data</parameter>, setting variables stored in the
session.
<note>
<para>
This function was added in PHP 4.0.
</para>
</note>
</para>
</refsect1>
</refentry>
<refentry id="function.session-encode">
<refnamediv>
<refname>session_encode</refname>
<refpurpose>
Encodes the current session data as a string
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>string</type><methodname>session_encode</methodname>
<void/>
</methodsynopsis>
<para>
<function>session_encode</function> returns a string with the
contents of the current session encoded within.
<note>
<para>
This function was added in PHP 4.0.
</para>
</note>
</para>
</refsect1>
</refentry>
<refentry id="function.session-set-save-handler">
<refnamediv>
<refname>session_set_save_handler</refname>
<refpurpose>
Sets user-level session storage functions
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>void</type><methodname>session_set_save_handler</methodname>
<methodparam><type>string</type><parameter>open</parameter></methodparam><methodparam><type>string</type><parameter>close</parameter></methodparam><methodparam><type>string</type><parameter>read</parameter></methodparam><methodparam><type>string</type><parameter>write</parameter></methodparam><methodparam><type>string</type><parameter>destroy</parameter></methodparam><methodparam><type>string</type><parameter>gc</parameter></methodparam>
</methodsynopsis>
<para>
<function>session_set_save_handler</function> sets the user-level
session storage functions which are used for storing and
retrieving data associated with a session. This is most useful
when a storage method other than those supplied by PHP sessions
is preferred. i.e. Storing the session data in a local database.
</para>
<note>
<para>
You must set the configuration option
<parameter>session.save_handler</parameter> to
<parameter>user</parameter> in your php.ini file for
<function>session_set_save_handler</function> to take effect.
</para>
</note>
<para>
The following example provides file based session
storage similar to the PHP sessions default save handler
<parameter>files</parameter>. This example could easily be
extended to cover database storage using your favorite PHP
supported database engine.
</para>
<para>
<example>
<title>
<function>session_set_save_handler</function> example
</title>
<programlisting role="php">
<?php
function open ($save_path, $session_name) {
global $sess_save_path, $sess_session_name;
$sess_save_path = $save_path;
$sess_session_name = $session_name;
return(true);
}
function close() {
return(true);
}
function read ($id) {
global $sess_save_path, $sess_session_name;
$sess_file = "$sess_save_path/sess_$id";
if ($fp = @fopen($sess_file, "r")) {
$sess_data = fread($fp, filesize($sess_file));
return($sess_data);
} else {
return("");
}
}
function write ($id, $sess_data) {
global $sess_save_path, $sess_session_name;
$sess_file = "$sess_save_path/sess_$id";
if ($fp = @fopen($sess_file, "w")) {
return(fwrite($fp, $sess_data));
} else {
return(false);
}
}
function destroy ($id) {
global $sess_save_path, $sess_session_name;
$sess_file = "$sess_save_path/sess_$id";
return(@unlink($sess_file));
}
/*********************************************
* WARNING - You will need to implement some *
* sort of garbage collection routine here. *
*********************************************/
function gc ($maxlifetime) {
return true;
}
session_set_save_handler ("open", "close", "read", "write", "destroy", "gc");
session_start();
// proceed to use sessions normally
?>
</programlisting>
</example>
</para>
</refsect1>
</refentry>
<refentry id="function.session-cache-limiter">
<refnamediv>
<refname>session_cache_limiter</refname>
<refpurpose>Get and/or set the current cache limiter</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>string</type><methodname>session_cache_limiter</methodname>
<methodparam choice="opt"><type>string</type><parameter>cache_limiter</parameter></methodparam>
</methodsynopsis>
<para>
<function>session_cache_limiter</function> returns the name of the
current cache limiter. If <parameter>cache_limiter</parameter> is
specified, the name of the current cache limiter is changed to the
new value.
</para>
<para>
The cache limiter controls the cache control HTTP headers sent to the
client. These headers determine the rules by which the page content
may be cached. Setting the cache limiter to <literal>nocache</literal>,
for example, would disallow any client-side caching. A value of
<literal>public</literal>, however, would permit caching. It can also
be set to <literal>private</literal>, which is slightly more restrictive
than <literal>public</literal>.
</para>
<para>
The cache limiter is reset to the default value stored in
<literal>session.cache_limiter</literal> at request startup time. Thus,
you need to call <function>session_cache_limiter</function> for every
request (and before <function>session_start</function> is called).
</para>
<example>
<title><function>session_cache_limiter</function> examples</title>
<programlisting role="php">
<?php
# set the cache limiter to 'private'
session_cache_limiter('private');
$cache_limiter = session_cache_limiter();
echo "The cache limiter is now set to $cache_limiter<p>";
?>
</programlisting>
</example>
<note>
<para>
This function was added in PHP 4.0.3.
</para>
</note>
</refsect1>
</refentry>
</reference>
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