DnsSrvDiscoverer.php

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<?php
class DnsSrvDiscoverer {
    private $service;
 
    private $protocol;
 
    private $domain;
 
    private $resolver;
 
    public function __construct(
        string $service,
        string $protocol = 'tcp',
        ?string $domain = null,
        ?callable $resolver = null
    ) {
        $this->service = $service;
        $this->protocol = $protocol;
        $this->domain = $domain;
 
        $this->resolver = $resolver ?? static function ( $srv ) {
            return dns_get_record( $srv, DNS_SRV );
        };
    }
 
    public function getRecords() {
        $result = [];
 
        $records = ( $this->resolver )( $this->getSrvName() );
 
        // Respect RFC 2782 with regard to a single '.' entry denoting a valid
        // empty response
        if (
            !$records
            || ( count( $records ) === 1 && $records[0]['target'] === '.' )
        ) {
            return $result;
        }
 
        foreach ( $records as $record ) {
            $result[] = [
                'target' => $record['target'],
                'port' => (int)$record['port'],
                'pri' => (int)$record['pri'],
                'weight' => (int)$record['weight'],
            ];
        }
 
        return $result;
    }
 
    public function getServers() {
        $records = $this->getRecords();
 
        usort( $records, static function ( $a, $b ) {
            if ( $a['pri'] === $b['pri'] ) {
                return mt_rand( 0, 1 ) ? 1 : -1;
            }
 
            return $a['pri'] - $b['pri'];
        } );
 
        $serversAndPorts = [];
 
        foreach ( $records as $record ) {
            $serversAndPorts[] = [ $record['target'], $record['port'] ];
        }
 
        return $serversAndPorts;
    }
 
    public function getSrvName(): string {
        $srv = "_{$this->service}._{$this->protocol}";
 
        if ( $this->domain === null || $this->domain === '' ) {
            return $srv;
        }
 
        return "$srv.{$this->domain}";
    }
}