[dns] Refactor cache to cache many records of the same identity with different values

It now returns a manufactured response object

Author: igorw

Query/CachedExecutor.php

@@ -3,6 +3,7 @@
 namespace React\Dns\Query;
 
 use React\Dns\Model\Message;
+use React\Dns\Model\Record;
 
 class CachedExecutor implements ExecutorInterface
 {
@@ -17,16 +18,43 @@ public function __construct(ExecutorInterface $executor, RecordCache $cache)
 
     public function query($nameserver, Query $query, $callback)
     {
-        $cachedRecord = $this->cache->lookup($query);
-        if (null !== $cachedRecord) {
-            $callback($cachedRecord);
+        $cachedRecords = $this->cache->lookup($query);
+        if (count($cachedRecords)) {
+            $cachedResponse = $this->buildResponse($query, $cachedRecords);
+            $callback($cachedResponse);
             return;
         }
 
         $cache = $this->cache;
         $this->executor->query($nameserver, $query, function ($response) use ($cache, $query, $callback) {
             $callback($response);
-            $cache->storeResponseMessage($response);
+            $cache->storeResponseMessage($query->currentTime, $response);
         });
     }
+
+    private function buildResponse(Query $query, array $cachedRecords)
+    {
+        $response = new Message();
+
+        $response->header->set('id', $this->generateId());
+        $response->header->set('qr', 1);
+        $response->header->set('opcode', Message::OPCODE_QUERY);
+        $response->header->set('rd', 1);
+        $response->header->set('rcode', Message::RCODE_OK);
+
+        $response->questions[] = new Record($query->name, $query->type, $query->class);
+
+        foreach ($cachedRecords as $record) {
+            $response->answers[] = $record;
+        }
+
+        $response->prepare();
+
+        return $response;
+    }
+
+    protected function generateId()
+    {
+        return mt_rand(0, 0xffff);
+    }
 }

Query/Query.php

@@ -7,11 +7,13 @@ class Query
     public $name;
     public $type;
     public $class;
+    public $currentTime;
 
-    public function __construct($name, $type, $class)
+    public function __construct($name, $type, $class, $currentTime)
     {
         $this->name = $name;
         $this->type = $type;
         $this->class = $class;
+        $this->currentTime = $currentTime;
     }
 }

Query/RecordBag.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace React\Dns\Query;
+
+use React\Dns\Model\Message;
+use React\Dns\Model\Record;
+
+class RecordBag
+{
+    private $records = array();
+
+    public function set($currentTime, Record $record)
+    {
+        $this->records[$record->data] = array($currentTime + $record->ttl, $record);
+    }
+
+    public function all()
+    {
+        return array_values(array_map(
+            function ($value) {
+                list($expiresAt, $record) = $value;
+                return $record;
+            },
+            $this->records
+        ));
+    }
+
+    public function expire($currentTime)
+    {
+        foreach ($this->records as $key => $value) {
+            list($expiresAt, $record) = $value;
+            if ($expiresAt <= $currentTime) {
+                unset($this->records[$key]);
+            }
+        }
+    }
+}

Query/RecordCache.php

@@ -11,31 +11,39 @@ class RecordCache
 
     public function lookup(Query $query)
     {
-        $id = $this->serializeQuery($query);
-        $record = isset($this->records[$id]) ? $this->records[$id] : null;
+        $id = $this->serializeQueryToIdentity($query);
+        $records = isset($this->records[$id]) ? $this->records[$id]->all() : array();
 
-        return $record;
+        return $records;
     }
 
-    public function storeResponseMessage(Message $message)
+    public function storeResponseMessage($currentTime, Message $message)
     {
         foreach ($message->answers as $record) {
-            $this->storeRecord($record);
+            $this->storeRecord($currentTime, $record);
         }
     }
 
-    public function storeRecord(Record $record)
+    public function storeRecord($currentTime, Record $record)
     {
-        $id = $this->serializeRecord($record);
-        $this->records[$id] = $record;
+        $id = $this->serializeRecordToIdentity($record);
+        $this->records[$id] = isset($this->records[$id]) ? $this->records[$id] : new RecordBag();
+        $this->records[$id]->set($currentTime, $record);
     }
 
-    public function serializeQuery(Query $query)
+    public function expire($currentTime)
+    {
+        foreach ($records as $recordBag) {
+            $recordBag->expire($currentTime);
+        }
+    }
+
+    public function serializeQueryToIdentity(Query $query)
     {
         return sprintf('%s:%s:%s', $query->name, $query->type, $query->class);
     }
 
-    public function serializeRecord(Record $record)
+    public function serializeRecordToIdentity(Record $record)
     {
         return sprintf('%s:%s:%s', $record->name, $record->type, $record->class);
     }

Resolver/Resolver.php

@@ -27,7 +27,7 @@ public function resolve($domain, $callback, $errback = null)
     {
         $that = $this;
 
-        $query = new Query($domain, Message::TYPE_A, Message::CLASS_IN);
+        $query = new Query($domain, Message::TYPE_A, Message::CLASS_IN, time());
 
         $this->executor->query($this->nameserver, $query, function (Message $response) use ($that, $callback, $errback) {
             try {