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1 | <?php |
2 | /** |
3 | * Service discovery using DNS SRV records |
4 | * |
5 | * This program is free software; you can redistribute it and/or modify |
6 | * it under the terms of the GNU General Public License as published by |
7 | * the Free Software Foundation; either version 2 of the License, or |
8 | * (at your option) any later version. |
9 | * |
10 | * This program is distributed in the hope that it will be useful, |
11 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
12 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
13 | * GNU General Public License for more details. |
14 | * |
15 | * You should have received a copy of the GNU General Public License along |
16 | * with this program; if not, write to the Free Software Foundation, Inc., |
17 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. |
18 | * http://www.gnu.org/copyleft/gpl.html |
19 | * |
20 | * @file |
21 | */ |
22 | |
23 | /** |
24 | * @since 1.29 |
25 | */ |
26 | class DnsSrvDiscoverer { |
27 | /** |
28 | * @var string |
29 | */ |
30 | private $service; |
31 | |
32 | /** |
33 | * @var string |
34 | */ |
35 | private $protocol; |
36 | |
37 | /** |
38 | * @var string|null |
39 | */ |
40 | private $domain; |
41 | |
42 | /** |
43 | * @var callable |
44 | */ |
45 | private $resolver; |
46 | |
47 | /** |
48 | * Construct a new discoverer for the given domain, service, and protocol. |
49 | * |
50 | * @param string $service Name of the service to discover. |
51 | * @param string $protocol Service protocol. Defaults to 'tcp' |
52 | * @param ?string $domain The hostname/domain on which to perform discovery |
53 | * of the given service and protocol. Defaults to null which effectively |
54 | * performs a query relative to the host's configured search domain. |
55 | * @param ?callable $resolver Resolver function. Defaults to using |
56 | * dns_get_record. Primarily useful in testing. |
57 | */ |
58 | public function __construct( |
59 | string $service, |
60 | string $protocol = 'tcp', |
61 | ?string $domain = null, |
62 | ?callable $resolver = null |
63 | ) { |
64 | $this->service = $service; |
65 | $this->protocol = $protocol; |
66 | $this->domain = $domain; |
67 | |
68 | $this->resolver = $resolver ?? static function ( $srv ) { |
69 | return dns_get_record( $srv, DNS_SRV ); |
70 | }; |
71 | } |
72 | |
73 | /** |
74 | * Queries the resolver for an SRV resource record matching the service, |
75 | * protocol, and domain and returns all target/port/priority/weight |
76 | * records. |
77 | * |
78 | * @return array |
79 | */ |
80 | public function getRecords() { |
81 | $result = []; |
82 | |
83 | $records = ( $this->resolver )( $this->getSrvName() ); |
84 | |
85 | // Respect RFC 2782 with regard to a single '.' entry denoting a valid |
86 | // empty response |
87 | if ( |
88 | !$records |
89 | || ( count( $records ) === 1 && $records[0]['target'] === '.' ) |
90 | ) { |
91 | return $result; |
92 | } |
93 | |
94 | foreach ( $records as $record ) { |
95 | $result[] = [ |
96 | 'target' => $record['target'], |
97 | 'port' => (int)$record['port'], |
98 | 'pri' => (int)$record['pri'], |
99 | 'weight' => (int)$record['weight'], |
100 | ]; |
101 | } |
102 | |
103 | return $result; |
104 | } |
105 | |
106 | /** |
107 | * Performs discovery for the domain, service, and protocol, and returns a |
108 | * list of resolved server name/ip and port number pairs sorted by each |
109 | * record's priority, with servers of the same priority randomly shuffled. |
110 | * |
111 | * @return array |
112 | */ |
113 | public function getServers() { |
114 | $records = $this->getRecords(); |
115 | |
116 | usort( $records, static function ( $a, $b ) { |
117 | if ( $a['pri'] === $b['pri'] ) { |
118 | return mt_rand( 0, 1 ) ? 1 : -1; |
119 | } |
120 | |
121 | return $a['pri'] - $b['pri']; |
122 | } ); |
123 | |
124 | $serversAndPorts = []; |
125 | |
126 | foreach ( $records as $record ) { |
127 | $serversAndPorts[] = [ $record['target'], $record['port'] ]; |
128 | } |
129 | |
130 | return $serversAndPorts; |
131 | } |
132 | |
133 | /** |
134 | * Returns the SRV resource record name. |
135 | * |
136 | * @return string |
137 | */ |
138 | public function getSrvName(): string { |
139 | $srv = "_{$this->service}._{$this->protocol}"; |
140 | |
141 | if ( $this->domain === null || $this->domain === '' ) { |
142 | return $srv; |
143 | } |
144 | |
145 | return "$srv.{$this->domain}"; |
146 | } |
147 | } |