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/Protocol/Text/ResponseMultiBulkHandler.php

@@ -0,0 +1,72 @@
+<?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\Protocol\Text;
+
+use Predis\CommunicationException;
+use Predis\Connection\ComposableConnectionInterface;
+use Predis\Protocol\ProtocolException;
+use Predis\Protocol\ResponseHandlerInterface;
+
+/**
+ * Implements a response handler for multi-bulk replies using the standard
+ * wire protocol defined by Redis.
+ *
+ * @link http://redis.io/topics/protocol
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+class ResponseMultiBulkHandler implements ResponseHandlerInterface
+{
+    /**
+     * Handles a multi-bulk reply returned by Redis.
+     *
+     * @param  ComposableConnectionInterface $connection   Connection to Redis.
+     * @param  string                        $lengthString Number of items in the multi-bulk reply.
+     * @return array
+     */
+    public function handle(ComposableConnectionInterface $connection, $lengthString)
+    {
+        $length = (int) $lengthString;
+
+        if ("$length" !== $lengthString) {
+            CommunicationException::handle(new ProtocolException(
+                $connection, "Cannot parse '$lengthString' as multi-bulk length"
+            ));
+        }
+
+        if ($length === -1) {
+            return null;
+        }
+
+        $list = array();
+
+        if ($length > 0) {
+            $handlersCache = array();
+            $reader = $connection->getProtocol()->getReader();
+
+            for ($i = 0; $i < $length; $i++) {
+                $header = $connection->readLine();
+                $prefix = $header[0];
+
+                if (isset($handlersCache[$prefix])) {
+                    $handler = $handlersCache[$prefix];
+                } else {
+                    $handler = $reader->getHandler($prefix);
+                    $handlersCache[$prefix] = $handler;
+                }
+
+                $list[$i] = $handler->handle($connection, substr($header, 1));
+            }
+        }
+
+        return $list;
+    }
+}