Added hosts executor that resolves address based on a hosts file.

src/Query/HostsExecutor.php

@@ -0,0 +1,55 @@
+<?php
+
+
+namespace React\Dns\Query;
+
+
+use React\Dns\Model\Message;
+use React\Dns\Model\Record;
+use React\Promise\Deferred;
+
+class HostsExecutor implements ExecutorInterface
+{
+    private $ipv4 = [];
+    private $ivp6 = [];
+
+    public function __construct($file = '/etc/hosts')
+    {
+        if (file_exists($file)) {
+            foreach(file($file) as $line) {
+                // IPV4
+                if (preg_match('/^(?<ip>(?:\d+\.){3}\d+)\s*(?<name>.*?)\s*$/', $line, $matches)) {
+                    $this->add4($matches['ip'], $matches['name']);
+                } elseif (preg_match('/^(?<ip>(?:[:a-f0-9]+))\s*(?<name>.*?)\s*$/', $line, $matches)) {
+                    $this->add6($matches['ip'], $matches['name']);
+                }
+            }
+        }
+    }
+
+
+    public function query($nameserver, Query $query)
+    {
+        $result = new Deferred();
+        if ($query->type === Message::TYPE_A
+            && isset($this->ipv4[$query->name])) {
+            $response = new Message();
+            $response->answers[] = new Record($query->name, $query->type, $query->class, 0, $this->ipv4[$query->name]);
+            $result->resolve($response);
+        } else {
+            $result->reject('Name not found in hosts file.');
+        }
+        return $result->promise();
+    }
+
+    public function add4($address, $name)
+    {
+        $this->ipv4[$name] = $address;
+    }
+
+    public function add6($address, $name)
+    {
+        $this->ipv6[$name] = $address;
+
+    }
+}

tests/Fixtures/etc/hosts

@@ -0,0 +1,9 @@
+127.0.0.1	localhost
+127.0.1.1	host-pc
+
+# The following lines are desirable for IPv6 capable hosts
+::1     ip6-localhost ip6-loopback
+fe00::0 ip6-localnet
+ff00::0 ip6-mcastprefix
+ff02::1 ip6-allnodes
+ff02::2 ip6-allrouters

tests/Query/HostsExecutorTest.php

@@ -0,0 +1,70 @@
+<?php
+
+namespace React\Tests\Dns\Query;
+
+use React\Dns\Query\ExecutorInterface;
+use React\Dns\Query\HostsExecutor;
+use React\Dns\Query\Query;
+use React\Dns\Model\Message;
+use React\Dns\Model\Record;
+
+class HostsExecutorTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @var ExecutorInterface
+     */
+    public $executor;
+
+    public function setUp()
+    {
+        $this->loop = $this->getMock('React\EventLoop\LoopInterface');
+        $this->executor = new HostsExecutor(__DIR__.'/../Fixtures/etc/hosts');
+
+    }
+
+    public function testRegisteredName()
+    {
+        $query = new Query('host-pc', Message::TYPE_A, Message::CLASS_IN, 1345656451);
+        /** @var \React\Promise\Promise$response */
+        $response = $this->executor->query(null, $query);
+
+        $success = $this->createCallableMock();
+        $success
+            ->expects($this->once())
+            ->method('__invoke')
+            ->with($this->isInstanceOf('React\Dns\Model\Message'))
+            ;
+        $response->then($success, $this->expectCallableNever());
+
+    }
+
+    public function testUnRegisteredName()
+    {
+        $query = new Query('some-host', Message::TYPE_A, Message::CLASS_IN, 1345656451);
+        /** @var \React\Promise\Promise$response */
+        $response = $this->executor->query(null, $query);
+
+        $err = $this->createCallableMock();
+        $err
+            ->expects($this->once())
+            ->method('__invoke')
+            ;
+        $response->then($this->expectCallableNever(), $err);
+
+    }
+
+    protected function expectCallableNever()
+    {
+        $mock = $this->createCallableMock();
+        $mock
+            ->expects($this->never())
+            ->method('__invoke');
+
+        return $mock;
+    }
+
+    protected function createCallableMock()
+    {
+        return $this->getMock('React\Tests\Dns\CallableStub');
+    }
+}