Retwis ported to modern Redis data types.

The example (and related documentation at redis.io) was not updated for
5 years. Redis had no sorted sets and hashes when the original code was
written (!). An update was really needed.

We also use a modern PHP client now: Predis. A copy is shipped within
this repository to make life easier to newcomers trying Redis for the
first time via this example.

Predis/Session/SessionHandler.php

@@ -0,0 +1,138 @@
+<?php
+
+/*
+ * This file is part of the Predis package.
+ *
+ * (c) Daniele Alessandri <suppakilla@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Predis\Session;
+
+use SessionHandlerInterface;
+use Predis\ClientInterface;
+
+/**
+ * Session handler class that relies on Predis\Client to store PHP's sessions
+ * data into one or multiple Redis servers.
+ *
+ * This class is mostly intended for PHP 5.4 but it can be used under PHP 5.3 provided
+ * that a polyfill for `SessionHandlerInterface` is defined by either you or an external
+ * package such as `symfony/http-foundation`.
+ *
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+class SessionHandler implements SessionHandlerInterface
+{
+    protected $client;
+    protected $ttl;
+
+    /**
+     * @param ClientInterface $client  Fully initialized client instance.
+     * @param array           $options Session handler options.
+     */
+    public function __construct(ClientInterface $client, Array $options = array())
+    {
+        $this->client = $client;
+        $this->ttl = (int) (isset($options['gc_maxlifetime']) ? $options['gc_maxlifetime'] : ini_get('session.gc_maxlifetime'));
+    }
+
+    /**
+     * Registers the handler instance as the current session handler.
+     */
+    public function register()
+    {
+        if (version_compare(PHP_VERSION, '5.4.0') >= 0) {
+            session_set_save_handler($this, true);
+        } else {
+            session_set_save_handler(
+                array($this, 'open'),
+                array($this, 'close'),
+                array($this, 'read'),
+                array($this, 'write'),
+                array($this, 'destroy'),
+                array($this, 'gc')
+            );
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function open($save_path, $session_id)
+    {
+        // NOOP
+        return true;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function close()
+    {
+        // NOOP
+        return true;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function gc($maxlifetime)
+    {
+        // NOOP
+        return true;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function read($session_id)
+    {
+        if ($data = $this->client->get($session_id)) {
+            return $data;
+        }
+
+        return '';
+    }
+    /**
+     * {@inheritdoc}
+     */
+    public function write($session_id, $session_data)
+    {
+        $this->client->setex($session_id, $this->ttl, $session_data);
+
+        return true;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function destroy($session_id)
+    {
+        $this->client->del($session_id);
+
+        return true;
+    }
+
+    /**
+     * Returns the underlying client instance.
+     *
+     * @return ClientInterface
+     */
+    public function getClient()
+    {
+        return $this->client;
+    }
+
+    /**
+     * Returns the session max lifetime value.
+     *
+     * @return int
+     */
+    public function getMaxLifeTime()
+    {
+        return $this->ttl;
+    }
+}