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<refentry xmlns="http://docbook.org/ns/docbook" xml:id="function.session-set-save-handler">
 <refnamediv>
  <refname>session_set_save_handler</refname>
  <refpurpose>Sets user-level session storage functions</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>bool</type><methodname>session_set_save_handler</methodname>
   <methodparam><type>callable</type><parameter>open</parameter></methodparam>
   <methodparam><type>callable</type><parameter>close</parameter></methodparam>
   <methodparam><type>callable</type><parameter>read</parameter></methodparam>
   <methodparam><type>callable</type><parameter>write</parameter></methodparam>
   <methodparam><type>callable</type><parameter>destroy</parameter></methodparam>
   <methodparam><type>callable</type><parameter>gc</parameter></methodparam>
  </methodsynopsis>
  <para>
   Since PHP 5.4 it is possible to register the following prototype:
  </para>
  <methodsynopsis>
   <type>bool</type><methodname>session_set_save_handler</methodname>
   <methodparam><type>SessionHandlerInterface</type><parameter>sessionhandler</parameter></methodparam>
   <methodparam choice="opt"><type>bool</type><parameter>register_shutdown</parameter><initializer>true</initializer></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>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   This function has two prototypes.
   <variablelist>
    <varlistentry>
     <term><parameter>sessionhandler</parameter></term>
     <listitem>
      <para>
       An instance of a class implementing
       <interfacename>SessionHandlerInterface</interfacename>, such as
       <classname>SessionHandler</classname>, to register as the session
       handler. Since PHP 5.4 only.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>register_shutdown</parameter></term>
     <listitem>
      <para>
       Register <function>session_write_close</function> as a
       <function>register_shutdown_function</function> function.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>

   or

   <variablelist>
    <varlistentry>
     <term><parameter>open(string $savePath, string $sessionName)</parameter></term>
     <listitem>
      <para>
       The open callback works like a constructor in classes and is
       executed when the session is being opened.  It is the first callback
       function executed when the session is started automatically or
       manually with <function>session_start</function>.
       Return value is &true; for success, &false; for failure.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>close()</parameter></term>
     <listitem>
      <para>
       The close callback works like a destructor in classes and is
       executed after the session write callback has been called. It is also invoked when
       <function>session_write_close</function> is called.
       Return value should be &true; for success, &false; for failure.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>read(string $sessionId)</parameter></term>
     <listitem>
      <para>
       The <parameter>read</parameter> callback must always return a session encoded (serialized)
       string, or an empty string if there is no data to read.
      </para>
      <para>
       This callback is called internally by PHP when the session starts or
       when <function>session_start</function> is called.  Before this callback is invoked
       PHP will invoke the <parameter>open</parameter> callback.
      </para>
      <para>
       The value this callback returns must be in exactly the same serialized format that was originally
       passed for storage to the <parameter>write</parameter> callback.  The value returned will be
       unserialized automatically by PHP and used to populate the <varname>$_SESSION</varname> superglobal.
       While the data looks similar to <function>serialize</function> please note it is a different format
       which is speficied in the <link linkend="ini.session.serialize-handler">session.serialize_handler</link> ini setting.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>write(string $sessionId, string $data)</parameter></term>
     <listitem>
      <para>
       The <parameter>write</parameter> callback is called when the session needs to be saved and closed. This
       callback receives the current session ID a serialized version the <varname>$_SESSION</varname> superglobal.  The serialization
       method used internally by PHP is specified in the <link linkend="ini.session.serialize-handler">session.serialize_handler</link> ini setting.
      </para>
      <para>
       The serialized session data passed to this callback should be stored against the passed session ID. When retrieving
       this data, the <parameter>read</parameter> callback must return the exact value that was originally passed to
       the <parameter>write</parameter> callback.
      </para>
      <para>
       This callback is invoked when PHP shuts down or explicitly when <function>session_write_close</function>
       is called.  Note that after executing this function PHP will internally execute the <parameter>close</parameter> callback.
       <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>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>destroy($sessionId)</parameter></term>
     <listitem>
      <para>
       This callback is executed when a session is destroyed with <function>session_destroy</function> or with
       <function>session_regenerate_id</function> with the destroy parameter set to &true;.
       Return value should be &true; for success, &false; for failure.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>gc($lifetime)</parameter></term>
     <listitem>
      <para>
       The garbage collector callback is invoked internally by PHP periodically in order to
       purge old session data.  The frequency is controlled by
       <link linkend="ini.session.gc-probability">session.gc_probability</link> and <link linkend="ini.session.gc-divisor">session.gc_divisor</link>.
       The value of lifetime which is passed to this callback can be set in <link linkend="ini.session.gc-maxlifetime">session.gc_maxlifetime</link>.
       Return value should be &true; for success, &false; for failure.
      </para>
     </listitem>
    </varlistentry>   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   &return.success;
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>
     Custom session handler: see full code in <classname>SessionHandlerInterface</classname> synposis.
    </title>
    <para>
     The following code is for PHP version 5.4.0 and above.  We just show the invokation here, the full example can be
     seen in the <classname>SessionHandlerInterface</classname> synposis linked above.
    </para>
    <para>
     Note we use the OOP prototype with <function>session_set_save_handler</function> and
     register the shutdown function using the function's parameter flag.  This is generally
     advised when registering objects as session save handlers.
    </para>
    <programlisting role="php">
<![CDATA[
<?php
class MySessionHandler implements SessionHandlerInterface
{
    // implement interfaces here
}

$handler = new MySessionHandler();
session_set_save_handler($handler, true);
session_start();

// proceed to set and retrieve values by key from $_SESSION
]]>
    </programlisting>
   </example>
   <example>
    <title>Custom session save handler using objects</title>
    <para>
     The following code is for PHP versions less than 5.4.0.
    </para>
    <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>
     Note we additionally register the shutdown function <function>session_write_close</function>
     using <function>register_shutdown_function</function> under PHP less than 5.4.0.
     This is generally advised when registering objects as session save handlers under PHP less
     than 5.4.0.
    </para>
    <programlisting role="php">
<![CDATA[
<?php
class FileSessionHandler
{
    private $savePath;

    function open($savePath, $sessionName)
    {
        $this->savePath = $savePath;
        if (!is_dir($this->savePath)) {
            mkdir($this->savePath, 0777);
        }

        return true;
    }

    function close()
    {
        return true;
    }

    function read($id)
    {
        return (string)@file_get_contents("$this->savePath/sess_$id");
    }

    function write($id, $data)
    {
        return file_put_contents("$this->savePath/sess_$id", $data) === false ? false : true;
    }

    function destroy($id)
    {
        $file = "$this->savePath/sess_$id";
        if (file_exists($file)) {
            unlink($file);
        }

        return true;
    }

    function gc($maxlifetime)
    {
        foreach (glob("$this->savePath/sess_*") as $file) {
            if (filemtime($file) + $maxlifetime < time() && file_exists($file)) {
                unlink($file);
            }
        }

        return true;
    }
}

$handler = new FileSessionHandler();
session_set_save_handler(
    array($handler, 'open'),
    array($handler, 'close'),
    array($handler, 'read'),
    array($handler, 'write'),
    array($handler, 'destroy'),
    array($handler, 'gc')
    );

// the following prevents unexpected effects when using objects as save handlers
register_shutdown_function('session_write_close');

session_start();
// proceed to set and retrieve values by key from $_SESSION
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <warning>
   <para>
    When using objects as session save handlers, it is important to register the
    shutdown function with PHP to avoid unexpected side-effects from the way
    PHP internally destroys objects on shutdown and may prevent the
    <parameter>write</parameter> and <parameter>close</parameter> from being called.
    Typically you should register <parameter>'session_write_close'</parameter> using the
    <function>register_shutdown_function</function> function.
   </para>
   <para>
    As of PHP 5.4.0 you can use <function>session_register_shutdown</function> or
    simply use the 'register shutdown' flag when invoking
    <function>session_set_save_handler</function> using the OOP method and passing an
    instance that implements <classname>SessionHandlerInterface</classname>.
   </para>
  </warning>
  <warning>
   <para>
    As of PHP 5.0.5 the <parameter>write</parameter> and
    <parameter>close</parameter> handlers are called after object
    destruction and therefore cannot use objects or throw exceptions.
    Exceptions are not able to be caught since will not be caught nor will
    any exception trace be displayed and the execution will just cease unexpectedly.
    The object destructors can however use sessions.
   </para>
   <para>
    It is possible to call <function>session_write_close</function> from the
    destructor to solve this chicken and egg problem but the most reliable way is
    to register the shutdown function as described above.
   </para>
  </warning>
  <warning>
   <para>
    Current working directory is changed with some SAPIs if session is
    closed in the script termination. It is possible to close the session
    earlier with <function>session_write_close</function>.
   </para>
  </warning>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <informaltable>
   <tgroup cols="2">
    <thead>
     <row>
      <entry>&Version;</entry>
      <entry>&Description;</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry>5.4.0</entry>
      <entry>
       Added <interfacename>SessionHandlerInterface</interfacename> for implementing session handlers and
       <classname>SessionHandler</classname> to expose internal PHP session handlers.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </informaltable>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member>
     The <link linkend="ini.session.save-handler">session.save_handler</link>
     configuration directive
    </member>
    <member>
     The <link linkend="ini.session.serialize-handler">session.serialize_handler</link>
     configuration directive.
    </member>
    <member>The <function>register_shutdown_function</function></member>
    <member>The <function>session_register_shutdown</function> for PHP 5.4.0+</member>
   </simplelist>
  </para>
 </refsect1>

</refentry>

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