1. module ntp-client
   1. function ntp-client.demo (argv)
   2. function ntp-client.getNetworkTime (server, port, callback)
   3. number ntp-client.defaultNtpPort
   4. number ntp-client.ntpReplyTimeout
   5. string ntp-client.defaultNtpServer

module ntp-client

function ntp-client.demo (argv)

• description and source-code

  demo = function (argv) {
      exports.getNetworkTime(
          exports.defaultNtpServer,
          exports.defaultNtpPort,
          function (err, date) {
              if (err) {
                  console.error(err);
                  return;
              }
  
              console.log(date);
          });
  }

• example usage

  n/a

function ntp-client.getNetworkTime (server, port, callback)

• description and source-code

  getNetworkTime = function (server, port, callback) {
      if (callback === null || typeof callback !== "function") {
          return;
      }
  
      server = server || exports.defaultNtpServer;
      port = port || exports.defaultNtpPort;
  
      var client = dgram.createSocket("udp4"),
          ntpData = new Buffer(48);
  
      // RFC 2030 -> LI = 0 (no warning, 2 bits), VN = 3 (IPv4 only, 3 bits), Mode = 3 (Client Mode, 3 bits) -> 1 byte
      // -> rtol(LI, 6) ^ rotl(VN, 3) ^ rotl(Mode, 0)
      // -> = 0x00 ^ 0x18 ^ 0x03
      ntpData[0] = 0x1B;
  
      for (var i = 1; i < 48; i++) {
          ntpData[i] = 0;
      }
  
      var timeout = setTimeout(function () {
          client.close();
          callback("Timeout waiting for NTP response.", null);
      }, exports.ntpReplyTimeout);
  
      // Some errors can happen before/after send() or cause send() to was impossible.
      // Some errors will also be given to the send() callback.
      // We keep a flag, therefore, to prevent multiple callbacks.
      // NOTE : the error callback is not generalised, as the client has to lose the connection also, apparently.
      var errorFired = false;
  
      client.on('error', function (err) {
          if (errorFired) {
              return;
          }
  
          callback(err, null);
          errorFired = true;
  
          clearTimeout(timeout);
      });
  
      client.send(ntpData, 0, ntpData.length, port, server, function (err) {
          if (err) {
              if (errorFired) {
                  return;
              }
              clearTimeout(timeout);
              callback(err, null);
              errorFired = true;
              client.close();
              return;
          }
  
          client.once('message', function (msg) {
              clearTimeout(timeout);
              client.close();
  
              // Offset to get to the "Transmit Timestamp" field (time at which the reply
              // departed the server for the client, in 64-bit timestamp format."
              var offsetTransmitTime = 40,
                  intpart = 0,
                  fractpart = 0;
  
              // Get the seconds part
              for (var i = 0; i <= 3; i++) {
                  intpart = 256 * intpart + msg[offsetTransmitTime + i];
              }
  
              // Get the seconds fraction
              for (i = 4; i <= 7; i++) {
                  fractpart = 256 * fractpart + msg[offsetTransmitTime + i];
              }
  
              var milliseconds = (intpart * 1000 + (fractpart * 1000) / 0x100000000);
  
              // **UTC** time
              var date = new Date("Jan 01 1900 GMT");
              date.setUTCMilliseconds(date.getUTCMilliseconds() + milliseconds);
  
              callback(null, date);
          });
      });
  }

• example usage

  ...
  
  ## Getting Started
  Install the module with: `npm install ntp-client`
  
  ```javascript
  var ntpClient = require('ntp-client');
  
  ntpClient.getNetworkTime("pool.ntp.org", 123, function(err, date) {
  if(err) {
      console.error(err);
      return;
  }
  
  console.log("Current time : ");
  console.log(date); // Mon Jul 08 2013 21:31:31 GMT+0200 (Paris, Madrid (heure d’été))
  ...