Planet CakePHP

There’s a lot of code floating around the internet to communicate with NTP servers, unfortunately none of the ones I found actually worked. Here’s a low level implementation:

/**
* Retrieve time from an NTP server
*
* @param string $host The NTP server to retrieve the time from
* @return int The current unix timestamp
* @author Aidan Lister
* @link http://aidanlister.com/2010/02/retrieve-time-from-an-ntp-server/
*/
function ntp_time($host) {

// Create a socket and connect to NTP server
$sock = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
socket_connect($sock, $host, 123);

// Send request
$msg = "\010" . str_repeat("\0", 47);
socket_send($sock, $msg, strlen($msg), 0);

// Receive response and close socket
socket_recv($sock, $recv, 48, MSG_WAITALL);
socket_close($sock);

// Interpret response
$data = unpack('N12', $recv);
$timestamp = sprintf('%u', $data[9]);

// NTP is number of seconds since 0000 UT on 1 January 1900
// Unix time is seconds since 0000 UT on 1 January 1970
$timestamp -= 2208988800;

return $timestamp;
}

You can use any NTP host you want, ideally something local to you. Otherwise, you can use a random server from the NTP Server Pool.