php-doc-en/functions/session.xml

<?xml encoding="iso-8859-1"?>
<!-- $Revision: 1.54 $ -->
 <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">
&lt;?php
session_register("count");
$HTTP_SESSION_VARS["count"]++;
?&gt;
     </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">
&lt;?php
session_register("count");
$count++;
?&gt;
     </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
    <link linkend="install.configure.enable-trans-sid">
    <literal>--enable-trans-sid</literal></link>. 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">
&lt;?php
session_register ("count");
$count++;
?&gt;

Hello visitor, you have seen this page &lt;?php echo $count; ?&gt; times.&lt;p&gt;

&lt;php?
# the &lt;?=SID?&gt; is necessary to preserve the session id
# in the case that the user has disabled cookies
?&gt;

To continue, &lt;A HREF="nextpage.php?&lt;?=SID?&gt;"&gt;click here&lt;/A&gt;
     </programlisting>
    </example>
   </para>
   <para>
    The <literal>&lt;?=SID?&gt;</literal> is not necessary, if
    <link linkend="install.configure.enable-trans-sid">
    <literal>--enable-trans-sid</literal></link> was used to compile PHP.
   </para>
   <note>
    <para>
     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.
    </para>
   </note>
   <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>
      <warning>
       <para>
        If you leave this set to a world-readable directory, such as
        <filename>/tmp</filename> (the default), other users on the
        server may be able to hijack sessions by getting the list of
        files in that directory.
       </para>
      </warning>
     </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/private_no_expire/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>
     <listitem>
      <simpara>
       <literal>session.use_trans_sid</literal> whether transient sid support
       is enabled or not if enabled by compiling with 
       <link linkend="install.configure.enable-trans-sid">
       <literal>--enable-trans-sid</literal></link>.
       Defaults to <literal>1</literal> (enabled).
      </simpara>
     </listitem>
     <listitem>
      <simpara>
       <literal>url_rewriter.tags</literal> spefifies which html tags are
       rewritten to include session id if transient sid support is enabled. 
       Defaults to <literal>a=href,area=href,frame=src,input=src,form=fakeentry</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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>bool <function>session_start</function></funcdef>
      <void/>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>bool <function>session_destroy</function></funcdef>
      <void/>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>string <function>session_name</function></funcdef>
      <paramdef>string 
       <parameter><optional>name</optional></parameter>
      </paramdef>
     </funcprototype>
    </funcsynopsis>
    <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">
&lt;?php

# set the session name to WebsiteID

$previous_name = session_name ("WebsiteID");

echo "The previous session name was $previous_name&lt;p&gt;";
?&gt;
     </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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>string <function>session_module_name</function></funcdef>
      <paramdef>string 
       <parameter><optional>module</optional></parameter>
      </paramdef>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>string <function>session_save_path</function></funcdef>
      <paramdef>string 
       <parameter><optional>path</optional></parameter>
      </paramdef>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>string <function>session_id</function></funcdef>
      <paramdef>string <parameter><optional>id</optional></parameter></paramdef>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>bool <function>session_register</function></funcdef>
      <paramdef>mixed <parameter>name</parameter></paramdef>
      <paramdef>mixed
       <parameter><optional>...</optional></parameter></paramdef>
     </funcprototype>
    </funcsynopsis>
    <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.
    </para>
    <note>
     <para>
      It is not currently possible to register resource variables in a
      session.  For example, you can not create a connection to a
      database and store the connection id as a session variable and
      expect the connection to still be valid the next time the
      session is restored.  PHP functions that return a resource are
      identified by having a return type of
      <literal>resource</literal> in their function definitions.  A
      list of functions that return resources are available in the
      <link linkend="resource">resource types</link> appendix.
     </para>
    </note>
    <note>
     <para>
      This function was added in PHP 4.0.
     </para>
    </note>
   </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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>bool <function>session_unregister</function></funcdef>
      <paramdef>string <parameter>name</parameter></paramdef>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>void <function>session_unset</function></funcdef>
      <void/>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>bool <function>session_is_registered</function></funcdef>
      <paramdef>string <parameter>name</parameter></paramdef>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>
       array <function>session_get_cookie_params</function>
      </funcdef>
      <void/>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>void <function>session_set_cookie_params</function></funcdef>
      <paramdef>
       int <parameter>lifetime</parameter>
      </paramdef>
      <paramdef>
       string <parameter><optional>path</optional></parameter>
      </paramdef>
      <paramdef>
       string <parameter><optional>domain</optional></parameter>
      </paramdef>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>bool <function>session_decode</function></funcdef>
      <paramdef>string <parameter>data</parameter></paramdef>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>string <function>session_encode</function></funcdef>
      <void/>
     </funcprototype>
    </funcsynopsis>
    <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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>void
       <function>session_set_save_handler</function>
      </funcdef>
      <paramdef>string
      <parameter>open</parameter></paramdef><paramdef>string
      <parameter>close</parameter></paramdef><paramdef>string
      <parameter>read</parameter></paramdef><paramdef>string
      <parameter>write</parameter></paramdef><paramdef>string
      <parameter>destroy</parameter></paramdef><paramdef>string
      <parameter>gc</parameter></paramdef>
     </funcprototype>
    </funcsynopsis>
    <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>
    <note>
     <para>
      The "write" handler is not executed until after the output
      stream is closed.  Thus, output from debugging statements in the
      "write" handler will never be seen in the browser.  If debugging
      output is necessary, it is suggested that the debug output be
      written to a file instead.
     </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">
&lt;?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

?&gt;
      </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>
    <funcsynopsis>
     <funcprototype>
      <funcdef>string <function>session_cache_limiter</function></funcdef>
      <paramdef>string 
       <parameter><optional>cache_limiter</optional></parameter>
      </paramdef>
     </funcprototype>
    </funcsynopsis>
    <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>
     In <literal>private</literal> mode, Expire header sent to the
     client, may cause confusion for some browser including Mozilla.
     You can avoid this problem with
     <literal>private_no_expire</literal> mode. Expire header is never
     sent to the client in this mode.
    </para>
    <note>
     <para>
      <literal>private_no_expire</literal> was added in PHP 4.2.0dev.
     </para>
    </note>
    <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">
&lt;?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&lt;p&gt;";
?&gt;
     </programlisting>
    </example>
    <note>
     <para>
      This function was added in PHP 4.0.3.
     </para>
    </note>
   </refsect1>
  </refentry>

  <refentry id="function.session-write-close">
   <refnamediv>
    <refname>session_write_close</refname>
    <refpurpose>Write session data and end session</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcprototype>
      <funcdef>void <function>session_write_close</function></funcdef>
      <void/>
     </funcprototype>
    </funcsynopsis>
    <para>
     End the current session and store session data.
    </para>
    <para>
     Session data is usually stored after your script terminated
     without the need to call <function>session_write_close</function>, but as
     session data is locked to prevent concurrent writes only one
     script may operate on a session at any time. When using framesets
     together with sessions you will experience the frames loading one
     by one due to this locking. You can reduce the time needed to
     load all the frames by ending the session as soon as all changes
     to session variables are done.
    </para>
<!-- commented out until final decision on implementation
    <para>
     See also: <function>session_readonly</function>.
    </para>
-->
   </refsect1>
  </refentry>

<!-- commented out until final decision on implementation
  <refentry id="function.session-readonly">
   <refnamediv>
    <refname>session_readonly</refname>
    <refpurpose>Begin session - reinitializes freezed variables, but no writeback on request end</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcprototype>
      <funcdef>void <function>session_readonly</function></funcdef>
      <void/>
     </funcprototype>
    </funcsynopsis>
    <para>
     Read in session data without locking the session data. Changing
     session data is not possible, but frameset performance will be improved.
    </para>
   </refsect1>
  </refentry>
-->
 </reference>

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