Add HostsFileExecutor to explicitly take hosts file into account

Author: clue

README.md

@@ -14,6 +14,7 @@ easily be used to create a DNS server.
 * [Caching](#caching)
   * [Custom cache adapter](#custom-cache-adapter)
 * [Advanced usage](#advanced-usage)
+  * [HostsFileExecutor](#hostsfileexecutor)
 * [Install](#install)
 * [Tests](#tests)
 * [License](#license)
@@ -118,6 +119,24 @@ $loop->run();
 
 See also the [fourth example](examples).
 
+### HostsFileExecutor
+
+Note that the above `Executor` class always performs an actual DNS query.
+If you also want to take entries from your hosts file into account, you may
+use this code:
+
+```php
+$hosts = \React\Dns\Config\HostsFile::loadFromPathBlocking();
+
+$executor = new Executor($loop, new Parser(), new BinaryDumper(), null);
+$executor = new HostsFileExecutor($hosts, $executor);
+
+$executor->query(
+    '8.8.8.8:53', 
+    new Query('localhost', Message::TYPE_A, Message::CLASS_IN, time())
+);
+```
+
 ## Install
 
 The recommended way to install this library is [through Composer](http://getcomposer.org).

src/Query/HostsFileExecutor.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace React\Dns\Query;
+
+use React\Dns\Config\HostsFile;
+use React\Dns\Model\Message;
+use React\Dns\Model\Record;
+use React\Promise;
+
+/**
+ * Resolves hosts from the givne HostsFile or falls back to another executor
+ *
+ * If the host is found in the hosts file, it will not be passed to the actual
+ * DNS executor. If the host is not found in the hosts file, it will be passed
+ * to the DNS executor as a fallback.
+ */
+class HostsFileExecutor implements ExecutorInterface
+{
+    private $hosts;
+    private $fallback;
+
+    public function __construct(HostsFile $hosts, ExecutorInterface $fallback)
+    {
+        $this->hosts = $hosts;
+        $this->fallback = $fallback;
+    }
+
+    public function query($nameserver, Query $query)
+    {
+        if ($query->class === Message::CLASS_IN && $query->type === Message::TYPE_A) {
+            $ips = $this->hosts->getIpsForHost($query->name);
+            if ($ips) {
+                $records = array();
+                foreach ($ips as $ip) {
+                    $records[] = new Record($query->name, $query->type, $query->class, 0, $ip);
+                }
+
+                return Promise\resolve(
+                    Message::createResponseWithAnswersForQuery($query, $records)
+                );
+            }
+        }
+
+        return $this->fallback->query($nameserver, $query);
+    }
+}

tests/Query/HostsFileExecutorTest.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace React\Tests\Dns\Query;
+
+use React\Tests\Dns\TestCase;
+use React\Dns\Query\HostsFileExecutor;
+use React\Dns\Query\Query;
+use React\Dns\Model\Message;
+
+class HostsFileExecutorTest extends TestCase
+{
+    private $hosts;
+    private $fallback;
+    private $executor;
+
+    public function setUp()
+    {
+        $this->hosts = $this->getMockBuilder('React\Dns\Config\HostsFile')->disableOriginalConstructor()->getMock();
+        $this->fallback = $this->getMockBuilder('React\Dns\Query\ExecutorInterface')->getMock();
+        $this->executor = new HostsFileExecutor($this->hosts, $this->fallback);
+    }
+
+    public function testDoesNotTryToGetIpsForMxQuery()
+    {
+        $this->hosts->expects($this->never())->method('getIpsForHost');
+        $this->fallback->expects($this->once())->method('query');
+
+        $this->executor->query('8.8.8.8', new Query('google.com', Message::TYPE_MX, Message::CLASS_IN, 0));
+    }
+
+    public function testFallsBackIfNoIpsWereFound()
+    {
+        $this->hosts->expects($this->once())->method('getIpsForHost')->willReturn(array());
+        $this->fallback->expects($this->once())->method('query');
+
+        $this->executor->query('8.8.8.8', new Query('google.com', Message::TYPE_A, Message::CLASS_IN, 0));
+    }
+
+    public function testReturnsResponseMessageIfIpsWereFound()
+    {
+        $this->hosts->expects($this->once())->method('getIpsForHost')->willReturn(array('127.0.0.1'));
+        $this->fallback->expects($this->never())->method('query');
+
+        $ret = $this->executor->query('8.8.8.8', new Query('google.com', Message::TYPE_A, Message::CLASS_IN, 0));
+    }
+}