Add class for service discovery using DNS SRV records

The SrvDiscoverer class can be used to find services (e.g. etcd) using
DNS SRV records.

Change-Id: Ia636d02535a3bb592eb896137cfb787a9ce6442a

diff --git a/autoload.php b/autoload.php
index b53c7ae..a11ba8a 100644 (file)
--- a/autoload.php
+++ b/autoload.php
@@ -383,6 +383,7 @@ $wgAutoloadLocalClasses = [
        'Digit2Html' => __DIR__ . '/maintenance/language/digit2html.php',
        'DjVuHandler' => __DIR__ . '/includes/media/DjVu.php',
        'DjVuImage' => __DIR__ . '/includes/media/DjVuImage.php',
+       'DnsSrvDiscoverer' => __DIR__ . '/includes/libs/DnsSrvDiscoverer.php',
        'DoubleRedirectJob' => __DIR__ . '/includes/jobqueue/jobs/DoubleRedirectJob.php',
        'DoubleRedirectsPage' => __DIR__ . '/includes/specials/SpecialDoubleRedirects.php',
        'DoubleReplacer' => __DIR__ . '/includes/libs/replacers/DoubleReplacer.php',

diff --git a/includes/libs/DnsSrvDiscoverer.php b/includes/libs/DnsSrvDiscoverer.php
new file mode 100644 (file)
index 0000000..c33264d
--- /dev/null
+++ b/includes/libs/DnsSrvDiscoverer.php
@@ -0,0 +1,92 @@
+<?php
+/**
+ * Service discovery using DNS SRV records
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ */
+
+/**
+ * @since 1.29
+ */
+class DnsSrvDiscoverer {
+       /**
+        * @var string
+        */
+       private $domain;
+
+       /**
+        * @param string $domain
+        */
+       public function __construct( $domain ) {
+               $this->domain = $domain;
+       }
+
+       /**
+        * Fetch the servers with a DNS SRV request
+        *
+        * @return array
+        */
+       public function getServers() {
+               $result = [];
+               foreach ( $this->getDnsRecords() as $record ) {
+                       $result[] = [
+                               'target' => $record['target'],
+                               'port' => $record['port'],
+                               'pri' => $record['pri'],
+                               'weight' => $record['weight'],
+                       ];
+               }
+
+               return $result;
+       }
+
+       /**
+        * Pick a server according to the priority fields.
+        * Note that weight is currently ignored.
+        *
+        * @param array $servers from getServers
+        * @return array|bool
+        */
+       public function pickServer( array $servers ) {
+               if ( !$servers ) {
+                       return false;
+               }
+
+               $srvsByPrio = [];
+               foreach ( $servers as $server ) {
+                       $srvsByPrio[$server['pri']][] = $server;
+               }
+
+               $min = min( array_keys( $srvsByPrio ) );
+               if ( count( $srvsByPrio[$min] ) == 1 ) {
+                       return $srvsByPrio[$min][0];
+               } else {
+                       // Choose randomly
+                       $rand = mt_rand( 0, count( $srvsByPrio[$min] ) - 1 );
+
+                       return $srvsByPrio[$min][$rand];
+               }
+       }
+
+       /**
+        * @return array[]
+        */
+       protected function getDnsRecords() {
+               return dns_get_record( $this->domain, DNS_SRV );
+       }
+}

diff --git a/tests/phpunit/includes/libs/DnsSrvDiscovererTest.php b/tests/phpunit/includes/libs/DnsSrvDiscovererTest.php
new file mode 100644 (file)
index 0000000..f768d06
--- /dev/null
+++ b/tests/phpunit/includes/libs/DnsSrvDiscovererTest.php
@@ -0,0 +1,88 @@
+<?php
+
+class DnsSrvDiscovererTest extends PHPUnit_Framework_TestCase {
+       /**
+        * @covers DnsSrvDiscoverer
+        * @dataProvider provideRecords
+        */
+       public function testPickServer( $params, $expected ) {
+               $discoverer = new DnsSrvDiscoverer( '_etcd._tcp.eqiad.wmnet' );
+               $record = $discoverer->pickServer( $params );
+
+               $this->assertEquals( $expected, $record );
+
+       }
+
+       public static function provideRecords() {
+               return [
+                       [
+                               [ // record list
+                                       [
+                                               'target' => 'conf1003.eqiad.wmnet',
+                                               'port' => 'SRV',
+                                               'pri' => 0,
+                                               'weight' => 1,
+                                       ],
+                                       [
+                                               'target' => 'conf1002.eqiad.wmnet',
+                                               'port' => 'SRV',
+                                               'pri' => 1,
+                                               'weight' => 1,
+                                       ],
+                                       [
+                                               'target' => 'conf1001.eqiad.wmnet',
+                                               'port' => 'SRV',
+                                               'pri' => 2,
+                                               'weight' => 1,
+                                       ],
+                               ], // selected record
+                               [
+                                       'target' => 'conf1003.eqiad.wmnet',
+                                       'port' => 'SRV',
+                                       'pri' => 0,
+                                       'weight' => 1,
+                               ]
+                       ],
+                       [
+                               [ // record list
+                                       [
+                                               'target' => 'conf1003or2.eqiad.wmnet',
+                                               'port' => 'SRV',
+                                               'pri' => 0,
+                                               'weight' => 1,
+                                       ],
+                                       [
+                                               'target' => 'conf1003or2.eqiad.wmnet',
+                                               'port' => 'SRV',
+                                               'pri' => 0,
+                                               'weight' => 1,
+                                       ],
+                                       [
+                                               'target' => 'conf1001.eqiad.wmnet',
+                                               'port' => 'SRV',
+                                               'pri' => 2,
+                                               'weight' => 1,
+                                       ],
+                                       [
+                                               'target' => 'conf1004.eqiad.wmnet',
+                                               'port' => 'SRV',
+                                               'pri' => 2,
+                                               'weight' => 1,
+                                       ],
+                                       [
+                                               'target' => 'conf1005.eqiad.wmnet',
+                                               'port' => 'SRV',
+                                               'pri' => 3,
+                                               'weight' => 1,
+                                       ],
+                               ], // selected record
+                               [
+                                       'target' => 'conf1003or2.eqiad.wmnet',
+                                       'port' => 'SRV',
+                                       'pri' => 0,
+                                       'weight' => 1,
+                               ]
+                       ],
+               ];
+       }
+}