Query a TIME server

To query a server using the TIME protocol, I wrote this little class which will walk a list of TIME servers until it gets a valid response and return the current UNIX timestamp.

ntp_time.class.php

<?php
 
/**
 * @author Markus Birth <markus@birth-online.de>
 * @link http://www.xenocafe.com/tutorials/php/ntp_time_synchronization/index.php
 * @link http://www.kloth.net/software/timesrv1.php
 */
 
class NTP_TIME {
    protected static $port = 37;
    protected static $servers = array(
        'ptbtime1.ptb.de',
        'ptbtime2.ptb.de',
        'ntp0.fau.de',
        'ntps1-0.cs.tu-berlin.de',
        'ntps1-1.cs.tu-berlin.de',
        'ntps1-0.uni-erlangen.de',
        'ntp-p1.obspm.fr',
        'time.ien.it',
        'time.nrc.ca',
        'time.nist.gov',
        'nist1.datum.com',
        'time-a.timefreq.bldrdoc.gov',
        'utcnist.colorado.edu',
    );
 
    public static function query() {
        $got_time = false;
        foreach ( self::$servers as $ntpserver ) {
            $fp = @fsockopen( $ntpserver, 37, $errno, $errstr, 30 );
            if ( !$fp ) {
                // offline or connection refused, try next
                continue;
            }
            $data = '';
            while ( !feof( $fp ) ) {
                $data .= fgets( $fp, 4 );
            }
            fclose( $fp );
 
            if ( strlen( $data ) == 4 ) {
                $got_time = true;
                break;
            }
        }
 
        if ( !$got_time ) return false;
 
        $time1900 = hexdec( bin2hex( $data ) );
        $timestamp = $time1900 - 2208988800;   // Time server is based on 1900 while Unix is based on 1970
 
        return $timestamp;
    }
}
 
?>