Simple UDP Client and Server in Node.js ==> ( Echo Server )

udp.js

var udp = require('dgram');

// --------------------creating a udp server --------------------

// creating a udp server
var server = udp.createSocket('udp4');

// emits when any error occurs
server.on('error',function(error){
  console.log('Error: ' + error);
  server.close();
});

// emits on new datagram msg
server.on('message',function(msg,info){
  console.log('Data received from client : ' + msg.toString());
  console.log('Received %d bytes from %s:%d\n',msg.length, info.address, info.port);

//sending msg
server.send(msg,info.port,'localhost',function(error){
  if(error){
    client.close();
  }else{
    console.log('Data sent !!!');
  }

});

});

//emits when socket is ready and listening for datagram msgs
server.on('listening',function(){
  var address = server.address();
  var port = address.port;
  var family = address.family;
  var ipaddr = address.address;
  console.log('Server is listening at port' + port);
  console.log('Server ip :' + ipaddr);
  console.log('Server is IP4/IP6 : ' + family);
});

//emits after the socket is closed using socket.close();
server.on('close',function(){
  console.log('Socket is closed !');
});

server.bind(2222);

setTimeout(function(){
server.close();
},8000);

// -------------------- udp client ----------------

var buffer = require('buffer');

// creating a client socket
var client = udp.createSocket('udp4');

//buffer msg
var data = Buffer.from('siddheshrane');

client.on('message',function(msg,info){
  console.log('Data received from server : ' + msg.toString());
  console.log('Received %d bytes from %s:%d\n',msg.length, info.address, info.port);
});

//sending msg
client.send(data,2222,'localhost',function(error){
  if(error){
    client.close();
  }else{
    console.log('Data sent !!!');
  }
});

var data1 = Buffer.from('hello');
var data2 = Buffer.from('world');

//sending multiple msg
client.send([data1,data2],2222,'localhost',function(error){
  if(error){
    client.close();
  }else{
    console.log('Data sent !!!');
  }
});

Very helpful!

Thank you!!

Declaring the buffer variable, which is not used or it really should be in Pascal case?
var buffer = require('buffer');

While the Buffer class is available within the global scope, it is still recommended to explicitly reference it via an import or require statement.

I want to get my home PC's public IP(behind NAT) by modified these codes a little:
On the server side, print client's IP in the "onMessage()", and on the client side, send UDP datagram by nc command (echo -n 'x' | nc -4uw0 $server $port).
It works fine from my notebook, but not work from the home PC.
I run tcpdump on the server, it can captured all datagrams, but the datagrams from home PC can't reach "onMessage()", why?

To simplify the case, I run nc on the server side, found out that the first message from home PC alway lost in server's stdout.

However, nc works fine from the notebook.

The server and home PC' OS is ubuntu 22.04. The notebook is Mac OS.
Thanks.