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/Monitor/MonitorContext.php

@@ -0,0 +1,165 @@
+<?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\Monitor;
+
+use Predis\ClientInterface;
+use Predis\NotSupportedException;
+use Predis\Connection\AggregatedConnectionInterface;
+
+/**
+ * Client-side abstraction of a Redis MONITOR context.
+ *
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+class MonitorContext implements \Iterator
+{
+    private $client;
+    private $isValid;
+    private $position;
+
+    /**
+     * @param ClientInterface $client Client instance used by the context.
+     */
+    public function __construct(ClientInterface $client)
+    {
+        $this->checkCapabilities($client);
+        $this->client = $client;
+        $this->openContext();
+    }
+
+    /**
+     * Automatically closes the context when PHP's garbage collector kicks in.
+     */
+    public function __destruct()
+    {
+        $this->closeContext();
+    }
+
+    /**
+     * Checks if the passed client instance satisfies the required conditions
+     * needed to initialize a monitor context.
+     *
+     * @param ClientInterface $client Client instance used by the context.
+     */
+    private function checkCapabilities(ClientInterface $client)
+    {
+        if ($client->getConnection() instanceof AggregatedConnectionInterface) {
+            throw new NotSupportedException('Cannot initialize a monitor context when using aggregated connections');
+        }
+        if ($client->getProfile()->supportsCommand('monitor') === false) {
+            throw new NotSupportedException('The current profile does not support the MONITOR command');
+        }
+    }
+
+    /**
+     * Initializes the context and sends the MONITOR command to the server.
+     */
+    protected function openContext()
+    {
+        $this->isValid = true;
+        $monitor = $this->client->createCommand('monitor');
+        $this->client->executeCommand($monitor);
+    }
+
+    /**
+     * Closes the context. Internally this is done by disconnecting from server
+     * since there is no way to terminate the stream initialized by MONITOR.
+     */
+    public function closeContext()
+    {
+        $this->client->disconnect();
+        $this->isValid = false;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function rewind()
+    {
+        // NOOP
+    }
+
+    /**
+     * Returns the last message payload retrieved from the server.
+     *
+     * @return Object
+     */
+    public function current()
+    {
+        return $this->getValue();
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function key()
+    {
+        return $this->position;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function next()
+    {
+        $this->position++;
+    }
+
+    /**
+     * Checks if the the context is still in a valid state to continue.
+     *
+     * @return bool
+     */
+    public function valid()
+    {
+        return $this->isValid;
+    }
+
+    /**
+     * Waits for a new message from the server generated by MONITOR and
+     * returns it when available.
+     *
+     * @return Object
+     */
+    private function getValue()
+    {
+        $database = 0;
+        $client = null;
+        $event = $this->client->getConnection()->read();
+
+        $callback = function ($matches) use (&$database, &$client) {
+            if (2 === $count = count($matches)) {
+                // Redis <= 2.4
+                $database = (int) $matches[1];
+            }
+
+            if (4 === $count) {
+                // Redis >= 2.6
+                $database = (int) $matches[2];
+                $client = $matches[3];
+            }
+
+            return ' ';
+        };
+
+        $event = preg_replace_callback('/ \(db (\d+)\) | \[(\d+) (.*?)\] /', $callback, $event, 1);
+        @list($timestamp, $command, $arguments) = explode(' ', $event, 3);
+
+        return (object) array(
+            'timestamp' => (float) $timestamp,
+            'database'  => $database,
+            'client'    => $client,
+            'command'   => substr($command, 1, -1),
+            'arguments' => $arguments,
+        );
+    }
+}