Support reverse lookups from hosts file

Author: clue

src/Config/HostsFile.php

@@ -107,4 +107,29 @@ public function getIpsForHost($name)
 
         return $ips;
     }
+
+    /**
+     * Returns all hostnames for the given IPv4 or IPv6 address
+     *
+     * @param string $ip
+     * @return string[]
+     */
+    public function getHostsForIp($ip)
+    {
+        // check binary representation of IP to avoid string case and short notation
+        $ip = @inet_pton($ip);
+
+        $names = array();
+        foreach (preg_split('/\r?\n/', $this->contents) as $line) {
+            $parts = preg_split('/\s+/', $line);
+
+            if (inet_pton(array_shift($parts)) === $ip) {
+                foreach ($parts as $part) {
+                    $names[] = $part;
+                }
+            }
+        }
+
+        return $names;
+    }
 }

tests/Config/HostsFileTest.php

@@ -84,4 +84,48 @@ public function testMergesIpv4AndIpv6EntriesOverMultipleLines()
 
         $this->assertEquals(array('127.0.0.1', '::1'), $hosts->getIpsForHost('localhost'));
     }
+
+    public function testReverseLookup()
+    {
+        $hosts = new HostsFile('127.0.0.1 localhost');
+
+        $this->assertEquals(array('localhost'), $hosts->getHostsForIp('127.0.0.1'));
+        $this->assertEquals(array(), $hosts->getHostsForIp('192.168.1.1'));
+    }
+
+    public function testReverseNonIpReturnsNothing()
+    {
+        $hosts = new HostsFile('127.0.0.1 localhost');
+
+        $this->assertEquals(array(), $hosts->getHostsForIp('localhost'));
+        $this->assertEquals(array(), $hosts->getHostsForIp('127.0.0.1.1'));
+    }
+
+    public function testReverseLookupReturnsLowerCaseHost()
+    {
+        $hosts = new HostsFile('127.0.0.1 LocalHost');
+
+        $this->assertEquals(array('localhost'), $hosts->getHostsForIp('127.0.0.1'));
+    }
+
+    public function testReverseLookupChecksNormalizedIpv6()
+    {
+        $hosts = new HostsFile('FE80::00a1 localhost');
+
+        $this->assertEquals(array('localhost'), $hosts->getHostsForIp('fe80::A1'));
+    }
+
+    public function testReverseLookupReturnsMultipleHostsOverSingleLine()
+    {
+        $hosts = new HostsFile("::1 ip6-localhost ip6-loopback");
+
+        $this->assertEquals(array('ip6-localhost', 'ip6-loopback'), $hosts->getHostsForIp('::1'));
+    }
+
+    public function testReverseLookupReturnsMultipleHostsOverMultipleLines()
+    {
+        $hosts = new HostsFile("::1 ip6-localhost\n::1 ip6-loopback");
+
+        $this->assertEquals(array('ip6-localhost', 'ip6-loopback'), $hosts->getHostsForIp('::1'));
+    }
 }