From c1867947225e709ed1a5d40a55b65b47a32cd553 Mon Sep 17 00:00:00 2001
From: Kunal Mehta <legoktm@member.fsf.org>
Date: Wed, 29 Mar 2017 11:06:32 -0700
Subject: [PATCH] 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
---
 autoload.php                                  |  1 +
 includes/libs/DnsSrvDiscoverer.php            | 92 +++++++++++++++++++
 .../includes/libs/DnsSrvDiscovererTest.php    | 88 ++++++++++++++++++
 3 files changed, 181 insertions(+)
 create mode 100644 includes/libs/DnsSrvDiscoverer.php
 create mode 100644 tests/phpunit/includes/libs/DnsSrvDiscovererTest.php

diff --git a/autoload.php b/autoload.php
index b53c7ae8f0..a11ba8a6ff 100644
--- 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
index 0000000000..c33264db0d
--- /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
index 0000000000..f768d06aa2
--- /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,
+				]
+			],
+		];
+	}
+}
-- 
2.20.1