Function queryOnce

ntp/ntp.ts:68–148

(host: string, timeoutMs = 2500)

    const packet = Buffer.alloc(48);
    // LI = 0 (no warning), VN = 4, Mode = 3 (client) -> 0b00 100 011 = 0x23
    packet[0] = 0x23;
    // Transmit timestamp: set to client time (optional but good practice)
    const t1ms = Date.now();
    const t1 = toNtpSecondsAndFrac(t1ms);
    packet.writeUInt32BE(t1.sec, 40);
    packet.writeUInt32BE(t1.frac, 44);

    function cleanup() {
      try {
        socket.close();
      } catch {}
      if (timeoutTimer) clearTimeout(timeoutTimer);
    }

    socket.once("error", (err) => {
      cleanup();
      reject(err);
    });

    socket.once("message", (msg, rinfo) => {
      const t4ms = Date.now();
      try {
        // Parse stratum and timestamps
        const stratum = msg[1];
        const t2ms = readNtpTimestamp(msg, 32);
        const t3ms = readNtpTimestamp(msg, 40);

        let delayMs: number | undefined;
        let offsetMs: number | undefined;
        let serverTimeMs: number | undefined;

        if (typeof t2ms === "number" && typeof t3ms === "number") {
          // Full NTP offset/delay calculation
          delayMs = (t4ms - t1ms) - (t3ms - t2ms);
          offsetMs = ((t2ms - t1ms) + (t3ms - t4ms)) / 2;
          // Best estimate of server time when received = t4 + offset
          serverTimeMs = Math.round(t4ms + (offsetMs || 0));
        } else if (typeof t3ms === "number") {
          // Fallback: assume symmetric path, use half the RTT
          const rtt = t4ms - t1ms;
          delayMs = rtt;
          offsetMs = t3ms - (t1ms + rtt / 2);
          serverTimeMs = Math.round(t4ms + (offsetMs || 0));
        }

        cleanup();
        resolve({
          server: host,
          ip: rinfo?.address,
          stratum,
          delayMs,
          offsetMs,
          serverTimeMs,
          raw: msg,
        });
      } catch (e) {
        cleanup();
        reject(e);