Support reverse DNS lookups for HostsFileExecutor

Author: clue

src/Query/HostsFileExecutor.php

@@ -28,6 +28,7 @@ public function __construct(HostsFile $hosts, ExecutorInterface $fallback)
     public function query($nameserver, Query $query)
     {
         if ($query->class === Message::CLASS_IN && ($query->type === Message::TYPE_A || $query->type === Message::TYPE_AAAA)) {
+            // forward lookup for type A or AAAA
             $records = array();
             $expectsColon = $query->type === Message::TYPE_AAAA;
             foreach ($this->hosts->getIpsForHost($query->name) as $ip) {
@@ -42,8 +43,47 @@ public function query($nameserver, Query $query)
                     Message::createResponseWithAnswersForQuery($query, $records)
                 );
             }
+        } elseif ($query->class === Message::CLASS_IN && $query->type === Message::TYPE_PTR) {
+            // reverse lookup: extract IPv4 or IPv6 from special `.arpa` domain
+            $ip = $this->getIpFromHost($query->name);
+
+            if ($ip !== null) {
+                $records = array();
+                foreach ($this->hosts->getHostsForIp($ip) as $host) {
+                    $records[] = new Record($query->name, $query->type, $query->class, 0, $host);
+                }
+
+                if ($records) {
+                    return Promise\resolve(
+                        Message::createResponseWithAnswersForQuery($query, $records)
+                    );
+                }
+            }
         }
 
         return $this->fallback->query($nameserver, $query);
     }
+
+    private function getIpFromHost($host)
+    {
+        if (substr($host, -13) === '.in-addr.arpa') {
+            // IPv4: read as IP and reverse bytes
+            $ip = @inet_pton(substr($host, 0, -13));
+            if ($ip === false || isset($ip[4])) {
+                return null;
+            }
+
+            return inet_ntop(strrev($ip));
+        } elseif (substr($host, -9) === '.ip6.arpa') {
+            // IPv6: replace dots, reverse nibbles and interpret as hexadecimal string
+            $ip = @inet_ntop(hex2bin(strrev(str_replace('.', '', substr($host, 0, -9)))));
+            if ($ip === false) {
+                return null;
+            }
+
+            return $ip;
+        } else {
+            return null;
+        }
+    }
 }

tests/Query/HostsFileExecutorTest.php

@@ -67,4 +67,52 @@ public function testFallsBackIfNoIpv6Matches()
 
         $ret = $this->executor->query('8.8.8.8', new Query('google.com', Message::TYPE_AAAA, Message::CLASS_IN, 0));
     }
+
+    public function testDoesReturnReverseIpv4Lookup()
+    {
+        $this->hosts->expects($this->once())->method('getHostsForIp')->with('127.0.0.1')->willReturn(array('localhost'));
+        $this->fallback->expects($this->never())->method('query');
+
+        $this->executor->query('8.8.8.8', new Query('1.0.0.127.in-addr.arpa', Message::TYPE_PTR, Message::CLASS_IN, 0));
+    }
+
+    public function testFallsBackIfNoReverseIpv4Matches()
+    {
+        $this->hosts->expects($this->once())->method('getHostsForIp')->with('127.0.0.1')->willReturn(array());
+        $this->fallback->expects($this->once())->method('query');
+
+        $this->executor->query('8.8.8.8', new Query('1.0.0.127.in-addr.arpa', Message::TYPE_PTR, Message::CLASS_IN, 0));
+    }
+
+    public function testDoesReturnReverseIpv6Lookup()
+    {
+        $this->hosts->expects($this->once())->method('getHostsForIp')->with('2a02:2e0:3fe:100::6')->willReturn(array('ip6-localhost'));
+        $this->fallback->expects($this->never())->method('query');
+
+        $this->executor->query('8.8.8.8', new Query('6.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.e.f.3.0.0.e.2.0.2.0.a.2.ip6.arpa', Message::TYPE_PTR, Message::CLASS_IN, 0));
+    }
+
+    public function testFallsBackForInvalidAddress()
+    {
+        $this->hosts->expects($this->never())->method('getHostsForIp');
+        $this->fallback->expects($this->once())->method('query');
+
+        $this->executor->query('8.8.8.8', new Query('example.com', Message::TYPE_PTR, Message::CLASS_IN, 0));
+    }
+
+    public function testReverseFallsBackForInvalidIpv4Address()
+    {
+        $this->hosts->expects($this->never())->method('getHostsForIp');
+        $this->fallback->expects($this->once())->method('query');
+
+        $this->executor->query('8.8.8.8', new Query('::1.in-addr.arpa', Message::TYPE_PTR, Message::CLASS_IN, 0));
+    }
+
+    public function testReverseFallsBackForInvalidIpv6Address()
+    {
+        $this->hosts->expects($this->never())->method('getHostsForIp');
+        $this->fallback->expects($this->once())->method('query');
+
+        $this->executor->query('8.8.8.8', new Query('abcd.ip6.arpa', Message::TYPE_PTR, Message::CLASS_IN, 0));
+    }
 }