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/ResponseBulkHandler.php

@@ -0,0 +1,53 @@
+<?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 bulk replies using the standard wire
+ * protocol defined by Redis.
+ *
+ * @link http://redis.io/topics/protocol
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+class ResponseBulkHandler implements ResponseHandlerInterface
+{
+    /**
+     * Handles a bulk reply returned by Redis.
+     *
+     * @param  ComposableConnectionInterface $connection   Connection to Redis.
+     * @param  string                        $lengthString Bytes size of the bulk reply.
+     * @return string
+     */
+    public function handle(ComposableConnectionInterface $connection, $lengthString)
+    {
+        $length = (int) $lengthString;
+
+        if ("$length" !== $lengthString) {
+            CommunicationException::handle(new ProtocolException(
+                $connection, "Cannot parse '$lengthString' as bulk length"
+            ));
+        }
+
+        if ($length >= 0) {
+            return substr($connection->readBytes($length + 2), 0, -2);
+        }
+
+        if ($length == -1) {
+            return null;
+        }
+    }
+}