php-doc-en/functions/session.xml

 <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>
    <literal>track_vars</literal> and <literal>register_globals</literal>
    configuration settings influence how the session variables get stored
    and restored.
   </para> 
   <para>
    If <literal>track_vars</literal> is enabled and 
    <literal>register_globals</literal> 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 <literal>track_vars</literal> enabled
     </title>
     <programlisting role="php">
&lt;?php
session_register("count");
$HTTP_SESSION_VARS["count"]++;
?&gt;
     </programlisting>
    </example>
   </para>
   <para>
    If <literal>register_globals</literal> 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 <literal>register_globals</literal> enabled
     </title>
     <programlisting role="php">
&lt;?php
session_register("count");
$count++;
?&gt;
     </programlisting>
    </example>
   </para>
   <para>
    If both <literal>track_vars</literal> and 
    <literal>register_globals</literal> 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 appropiate 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;? 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>
    To implement database storage you need PHP code and a user level
    function <function>session_set_save_handler</function>. You would
    have to extend the following functions to cover MySQL or another
    database.
   </para>
   <para>
    <example>
     <title>
      Usage of <function>session_set_save_handler</function>
     </title>
     <programlisting role="php">
&lt;?php

function open ($save_path, $session_name) {
    echo "open ($save_path, $session_name)\n";
    return true;
}

function close() {
    echo "close\n";
    return true;
}

function read ($key) {
    echo "write ($key, $val)\n";
    return "foo|i:1;";
}

function write ($key, $val) {
    echo "write ($key, $val)\n";
    return true;
}

function destroy ($key) {
    return true;
}

function gc ($maxlifetime) {
    return true;
}

session_set_save_handler ("open", "close", "read", "write", "destroy", "gc");

session_start();

$foo++;

?>
     </programlisting>
    </example>
   </para> 
   <para>
    Will produce this results:
   </para>
   <para>
    <programlisting>
$ ./php save_handler.php
Content-Type: text/html
Set-cookie: PHPSESSID=f08b925af0ecb52bdd2de97d95cdbe6b

open (/tmp, PHPSESSID)
read (f08b925af0ecb52bdd2de97d95cdbe6b)
write (f08b925af0ecb52bdd2de97d95cdbe6b, foo|i:2;)
close
    </programlisting>
   </para>
   <para>
    The <literal>&lt;?=SID?&gt;</literal> is not necessary, if
    <literal>--enable-trans-sid</literal> was used to compile PHP.
   </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 start 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> determines whether
       session ids referred to by external sites will be
       eliminated. If session ids are propagated using the URL method,
       users not knowing about the impact might publish session
       ids. This can lead to security problems which this check tries
       to defeat. Defaults to <literal>0</literal>.
      </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>
    <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>void <function>session_destroy</function></funcdef>
      <void/>
     </funcprototype>
    </funcsynopsis>
    <simpara>
     <function>session_destroy</function> destroys all of the data
     associated with the current session.
    </simpara>
    <note>
     <para>
      This function was added in PHP 4.0.
     </para>
    </note>
   </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 resetted 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.
     <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>
    <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>bool <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>

 </reference>

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