From 24bdb8ac937e8414b37ef00c817589ae2e80af30 Mon Sep 17 00:00:00 2001
From: Kunal Mehta <legoktm@member.fsf.org>
Date: Mon, 6 Mar 2017 02:01:03 -0800
Subject: [PATCH] Add a class implementing DNS Discovery

etcd supports using SRV records to help clients discover the etcd
cluster:
<https://coreos.com/etcd/docs/latest/v2/clustering.html#dns-discovery>.

This implements a basic class to get a list of servers in the cluster,
and a helper function to pick one in accordance with RFC 2782.
---
 src/SrvDiscoverer.php | 71 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 src/SrvDiscoverer.php

diff --git a/src/SrvDiscoverer.php b/src/SrvDiscoverer.php
new file mode 100644
index 0000000..098ce9e
--- /dev/null
+++ b/src/SrvDiscoverer.php
@@ -0,0 +1,71 @@
+<?php
+
+namespace ActiveCollab\Etcd;
+
+/**
+ * @package ActiveCollab\Etcd
+ */
+class SrvDiscoverer
+{
+
+    /**
+     * @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()
+    {
+        $records = dns_get_record($this->domain, DNS_SRV);
+        $result = [];
+        foreach ($records 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;
+        }
+        $by_prio = [];
+        foreach ($servers as $server) {
+            $by_prio[$server['pri']][] = $server;
+        }
+
+        $min = min(array_keys($by_prio));
+        if (count($by_prio[$min]) == 1) {
+            return $by_prio[$min][0];
+        } else {
+            // Choose randomly
+            $rand = mt_rand(0, count($by_prio[$min])-1);
+            return $by_prio[$min][$rand];
+        }
+    }
+}