php-doc-en/reference/session/sessionhandler.xml

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<phpdoc:classref xml:id="class.sessionhandler" xmlns:phpdoc="http://php.net/ns/phpdoc" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude">

 <title>The SessionHandler class</title>
 <titleabbrev>SessionHandler</titleabbrev>

 <partintro>

<!-- {{{ SessionHandler intro -->
  <section xml:id="sessionhandler.intro">
   &reftitle.intro;
   <para>
    <classname>SessionHandler</classname> a special class that can be used to expose
    the current internal PHP session save handler by inheritance.  There are six methods which
    wrap the six internal session save handler callbacks (<parameter>open</parameter>, <parameter>close</parameter>,
    <parameter>read</parameter>, <parameter>write</parameter>, <parameter>destroy</parameter> and <parameter>gc</parameter>).
    By default, this class will wrap whatever internal save handler is set as as defined by the
    <link linkend="ini.session.save-handler">session.save_handler</link> configuration directive which is usually
    <parameter>files</parameter> by default.
    Other internal session save handlers are provided by PHP extensions such as SQLite (as <parameter>sqlite</parameter>),
    Memcache (as <parameter>memcache</parameter>), and Memcached (as <parameter>memcached</parameter>).
   </para>
   <para>
    When a plain instance of <classname>SessionHandler</classname> is set as the save handler using
    <function>session_set_save_handler</function> it will wrap the current save handlers.
    A class extending from <classname>SessionHandler</classname> allows you to override
    the methods or intercept or filter them by calls the parent class methods which ultimately wrap
    the interal PHP session handlers.
   </para>
   <para>
    This allows you, for example, to intercept the <parameter>read</parameter> and <parameter>write</parameter>
    methods to encrypt/decrypt the session data and then pass the result to and from the parent class.
    Alternatively one might chose to entirely override a method like the garbage collection callback
    <parameter>gc</parameter>.
   </para>
   <para>
    Because the <classname>SessionHandler</classname> wraps the current internal save handler
    methods, the above example of encryption can be applied to any internal save handler without
    having to know the internals of the handlers.
   </para>
   <para>
    To use this class, first set the save handler you wish to expose using
    <link linkend="ini.session.save-handler">session.save_handler</link> and then pass an instance of
    <classname>SessionHandler</classname> or one extending it to <function>session_set_save_handler</function>.
   </para>
   <para>
    Please note the callback methods of this class are designed to be called internally by
    PHP and are not meant to be called from user-space code.  The return values are equally processed internally
    by PHP.  For more information on the session workflow, please refer <function>session_set_save_handler</function>.
   </para>
  </section>
<!-- }}} -->

  <section xml:id="sessionhandler.synopsis">
   &reftitle.classsynopsis;

<!-- {{{ Synopsis -->
   <classsynopsis>
    <ooclass><classname>SessionHandler</classname></ooclass>

<!-- {{{ Class synopsis -->
    <classsynopsisinfo>
     <ooclass>
      <classname>SessionHandler</classname>
     </ooclass>

     <oointerface>
      <interfacename>SessionHandlerInterface</interfacename>
     </oointerface>
    </classsynopsisinfo>
<!-- }}} -->

    <classsynopsisinfo role="comment">&Methods;</classsynopsisinfo>
    <xi:include xpointer="xmlns(db=http://docbook.org/ns/docbook) xpointer(id('class.sessionhandler')/db:refentry/db:refsect1[@role='description']/descendant::db:methodsynopsis[1])" />
   </classsynopsis>
<!-- }}} -->

  </section>

  <section xml:id="session.notes">
   <warning>
    <para>
     This class is designed to expose the current internal PHP session save handler, if you you want to
     write your own custom save handlers, please implement the <classname>SessionHandlerInterface</classname>
     interface instead of extending from <classname>SessionHandler</classname>.
    </para>
   </warning>
  </section>

  <section xml:id="sessionhandler.examples">
   <example>
    <title>
     Using <classname>SessionHandler</classname> to add encryption to internal PHP save handlers.
    </title>
    <programlisting role="php">
<![CDATA[
<?php
class EncryptedSessionHandler extends SessionHandler
{
    private $key;

    public function __construct($key)
    {
        $this->key = $key;
    }

    public function read($id)
    {
        $data = parent::read($id);

        return mycrypt_decrypt(MCRYPT_3DES, $this->key, $data, MCRYPT_MODE_ECB);
    }

    public function write($id, $data)
    {
        $data = mcrypt_encrypt(MCRYPT_3DES, $this->key, $data, MCRYPT_MODE_ECB);

        return parent::write($id, $data);
    }
}

// we'll intercept the native 'files' handler, but will equally work
// with other internal native handlers like 'sqlite', 'memcache' or 'memcached'
// which are provided by PHP extensions.
ini_set('session.save_handler', 'files');
$handler = new EncryptedSessionHandler('mykey');
session_set_save_handler($handler, true);
session_start();

// proceed to set and retrieve values by key from $_SESSION
]]>
    </programlisting>
   </example>
   <note>
    <para>
     Since this class' methods are designed to be called internally by PHP as part of the normal session workflow,
     child class calls to parent methods (i.e. the actual internal native handlers) will return &false; unless
     the session has actually been started (either automatically, or by explicit <function>session_start</function>.
     This is important to consider when writing unit tests where the class methods might be invoked manually.
    </para>
   </note>
  </section>

 </partintro>

 &reference.session.entities.sessionhandler;

</phpdoc:classref>

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