README.md

ntp-time-sync

Node.JS module to fetch the current time from NTP servers and returns offset information.

ℹ️ NTP requires UDP which is not available in a browser context!

Installation

# using Yarn
$ yarn add ntp-time-sync

# using NPM
$ npm install ntp-time-sync

Usage

Consider using the library as a singleton, so that not every call to getTime fires new NTP packages. The library itself will manage minimum/maximum poll times.

Several requests to multiple NTP time servers are fired and the responses will be aggregated.

// ES6:
import { NtpTimeSync } from "ntp-time-sync";
// pre-ES6:
// const NtpTimeSync = require("ntp-time-sync").NtpTimeSync;

const timeSync = NtpTimeSync.getInstance();

// request 1
timeSync.getTime().then(function (result) {
  console.log("current system time", new Date());
  console.log("real time", result.now);
  console.log("offset in milliseconds", result.offset);
})

// request 2, will use cached offset from previous request
timeSync.getTime().then(function (result) {
  console.log("current system time", new Date());
  console.log("real time", result.now);
  console.log("offset in milliseconds", result.offset);
})

// ES2017 style
const result = await timeSync.getTime();
console.log("real time", result.now);

<ntpTimeSyncInstance>.getTime() returns a Promise object which will eventually be resolved with a object containing the following information:

Property	Description
now	Current NTP time ("real time")
offset	Calculated offset between local system time and NTP time

<ntpTimeSyncInstance>.now() returns a Date object containing the correct time for the moment when the function was called. In contrast to getTime(), which will return the correct time for the moment the Promise gets resolved.

Options

You can pass custom options to the constructor of NtpTimeSync or NtpTimeSync.getInstance(options). These will be merged with the following defaults:

const defaultOptions = {
  // list of NTP time servers, optionally including a port (defaults to 123)
  servers: [
    "0.pool.ntp.org",
    "1.pool.ntp.org",
    "2.pool.ntp.org",
    "3.pool.ntp.org"
  ],

  // required amount of valid samples in order to calculate the time
  sampleCount: 8,

  // amount of time in milliseconds to wait for a single NTP response
  replyTimeout: 3000,

  // defaults as of RFC5905
  ntpDefaults: {
    port: 123,
    version: 4,
    tolerance: 15e-6,
    minPoll: 4,
    maxPoll: 17,
    maxDispersion: 16,
    minDispersion: 0.005,
    maxDistance: 1,
    maxStratum: 16,
    precision: -18,
    referenceDate: new Date("Jan 01 1900 GMT")
  }
};