php-doc-en/reference/session/functions/session-create-id.xml

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<refentry xmlns="http://docbook.org/ns/docbook" xml:id="function.session-create-id">
 <refnamediv>
  <refname>session_create_id</refname>
  <refpurpose>Create new session id</refpurpose>
 </refnamediv>
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>string</type><methodname>session_create_id</methodname>
   <methodparam choice="opt"><type>string</type><parameter>prefix</parameter></methodparam>
  </methodsynopsis>
  <para>
   <function>session_create_id</function> is used to create new
   session id for the current session. It returns collision free
   session id.
  </para>
  <para>
   If session is not active, collision check is omitted.
  </para>
  <para>
   Session ID is created according to php.ini settings.
  </para>
  <para>
   It is important to use the same user ID of your web server for GC
   task script. Otherwise, you may have permission problems especially
   with files save handler.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>prefix</parameter></term>
      <listitem>
       <para>
        If <parameter>prefix</parameter> is specified, new session id
        is prefixed by <parameter>prefix</parameter>. Not all
        characters are allowed within the session id.  Characters in
        the range <literal>a-z A-Z 0-9 , (comma) and -
        (minus)</literal> are allowed.
       </para> 
      </listitem>
     </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   <function>session_create_id</function> returns new collision free
   session id for the current session. If it is used without active
   session, it omits collision check.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>session_create_id</function> example with <function>session_regenerate_id</function></title>
    <programlisting role="php">
<![CDATA[
<?php
// My session start function support timestamp management
function my_session_start() {
    session_start();
    // Do not allow to use too old session ID
    if (!empty($_SESSION['deleted_time']) && $_SESSION['deleted_time'] < time() - 180) {
        session_destroy();
        session_start();
    }
}

// My session regenerate id function
function my_session_regenerate_id() {
    // Call session_create_id() while session is active to 
    // make sure collision free.
    if (session_status() != PHP_SESSION_ACTIVE) {
        session_start();
    }
    // WARNING: Never use confidential strings for prefix!
    $newid = session_create_id('myprefix-');
    // Set deleted timestamp. Session data must not be deleted immediately for reasons.
    $_SESSION['deleted_time'] = time();
    // Finish session
    session_commit();
    // Make sure to accept user defined session ID
    // NOTE: You must enable use_strict_mode for normal operations.
    ini_set('session.use_strict_mode', 0);
    // Set new custom session ID
    session_id($newid);
    // Start with custom session ID
    session_start();
}

// Make sure use_strict_mode is enabled.
// use_strict_mode is mandatory for security reasons.
ini_set('session.use_strict_mode', 1);
my_session_start();

// Session ID must be regenerated when
//  - User logged in
//  - User logged out
//  - Certain period has passed
my_session_regenerate_id();

// Write useful codes
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>session_regenerate_id</function></member>
    <member><function>session_start</function></member>
    <member><link linkend="ini.session.use-strict-mode">session.use_strict_mode</link></member>
    <member><methodname>SessionHandler::create_sid</methodname></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>


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