ntp - SNTP network-time client

Import with import "ntp.j" as ntp;. Query a time server over UDP and get back its time plus the local clock offset and round-trip delay. This is the one-shot query half of NTP - a simple SNTP client (RFC 4330 / 5905): it speaks the standard NTP wire protocol (the 48-byte packet on port 123) but does not discipline the clock or run as a daemon. It reports the measurement; acting on it is the caller’s job. Needs the default jennifer binary (net).

import "ntp.j" as ntp;
use io; use time;

def r as ntp.Result init ntp.query("pool.ntp.org");
io.printf("server time: %s  offset: %d ms\n", time.iso($r.serverTime), time.milliseconds($r.offset));

Runnable: examples/modules/ntp_demo.j.

Result

def struct ntp.Result {
    serverTime as time.Time,     # the server's transmit time
    offset as time.Duration,     # local clock offset (server minus local)
    delay as time.Duration       # measured round-trip delay
};

offset is computed from the four SNTP timestamps as ((T2 - T1) + (T3 - T4)) / 2 and delay as (T4 - T1) - (T3 - T2), where T1/T4 are the local send/receive instants and T2/T3 are the server’s receive/transmit timestamps. A positive offset means the local clock is behind the server.

Query

query is the common form (ntp.query("time.example.com")); queryWith takes a full host:port address and an explicit receive timeout in milliseconds. A query that gets no reply within the timeout, or a short / malformed packet, throws Error{kind: "ntp"} - catch it with try / catch. The receive timeout is a real deadline on the UDP socket, so a lost reply fails fast instead of hanging.

Scope

• Query, not discipline. This measures the offset and hands it back; it does not step or slew the system clock (that is the OS / a daemon’s job), and it does no server selection, filtering, or Kiss-o’-Death handling.
• One server per call. Poll several servers and combine the results yourself if you want robustness against a single bad source.
• No authentication. Plain SNTP; no symmetric-key or NTS-secured exchange.

See also

• net.md - the UDP surface (listenUDP / sendTo / recvFrom / setDeadline) the client is built on.
• time.md - the time.Time / time.Duration the result is expressed in.
• modules/index.md - the module catalog and import rules.