[dns] Introduce CachedExecutor, does not expire records yet

Author: igorw

Query/CachedExecutor.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace React\Dns\Query;
+
+use React\Dns\Model\Message;
+
+class CachedExecutor implements ExecutorInterface
+{
+    private $executor;
+    private $cache;
+
+    public function __construct(ExecutorInterface $executor, RecordCache $cache)
+    {
+        $this->executor = $executor;
+        $this->cache = $cache;
+    }
+
+    public function query($nameserver, Query $query, $callback)
+    {
+        $cachedRecord = $this->cache->lookup($query);
+        if (null !== $cachedRecord) {
+            $callback($cachedRecord);
+            return;
+        }
+
+        $cache = $this->cache;
+        $this->executor->query($nameserver, $query, function ($response) use ($cache, $query, $callback) {
+            $callback($response);
+            $cache->storeResponseMessage($response);
+        });
+    }
+}

Query/RecordCache.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace React\Dns\Query;
+
+use React\Dns\Model\Message;
+use React\Dns\Model\Record;
+
+class RecordCache
+{
+    private $records = array();
+
+    public function lookup(Query $query)
+    {
+        $id = $this->serializeQuery($query);
+        $record = isset($this->records[$id]) ? $this->records[$id] : null;
+
+        return $record;
+    }
+
+    public function storeResponseMessage(Message $message)
+    {
+        foreach ($message->answers as $record) {
+            $this->storeRecord($record);
+        }
+    }
+
+    public function storeRecord(Record $record)
+    {
+        $id = $this->serializeRecord($record);
+        $this->records[$id] = $record;
+    }
+
+    public function serializeQuery(Query $query)
+    {
+        return sprintf('%s:%s:%s', $query->name, $query->type, $query->class);
+    }
+
+    public function serializeRecord(Record $record)
+    {
+        return sprintf('%s:%s:%s', $record->name, $record->type, $record->class);
+    }
+}