UDP - dgram example in Nodejs

Here’s an example of how to use the dgram module in Node.js to create a simple UDP server and client. UDP (User Datagram Protocol) is a communication protocol that allows sending messages (datagrams) without establishing a connection, making it faster but less reliable than TCP.

UDP Server

First, create a UDP server that listens for messages and sends a response back to the client.

udp_server.js:

const dgram = require('dgram');
const server = dgram.createSocket('udp4');

// Event handler for receiving messages
server.on('message', (msg, rinfo) => {
  console.log(`Server received: ${msg} from ${rinfo.address}:${rinfo.port}`);
  
  // Sending a response back to the client
  const response = Buffer.from('Hello from the server!');
  server.send(response, rinfo.port, rinfo.address, (err) => {
    if (err) {
      console.error('Error sending response:', err);
    }
  });
});

// Event handler for server listening
server.on('listening', () => {
  const address = server.address();
  console.log(`Server listening on ${address.address}:${address.port}`);
});

// Bind the server to a specific port and address
server.bind(41234, 'localhost');

UDP Client

Next, create a UDP client that sends a message to the server and handles the response.

udp_client.js:

const dgram = require('dgram');
const client = dgram.createSocket('udp4');

// Message to be sent to the server
const message = Buffer.from('Hello from the client!');

// Event handler for receiving messages from the server
client.on('message', (msg, rinfo) => {
  console.log(`Client received: ${msg} from ${rinfo.address}:${rinfo.port}`);
  
  // Closing the client after receiving the response
  client.close();
});

// Sending the message to the server
client.send(message, 41234, 'localhost', (err) => {
  if (err) {
    console.error('Error sending message:', err);
    client.close();
  } else {
    console.log('Message sent to server');
  }
});

How to Run the Example

1. Start the UDP Server: Open a terminal and run the server script:

   node udp_server.js
   

2. Run the UDP Client: Open another terminal and run the client script:

   node udp_client.js
   

Expected Output

Server Output:

Server listening on 127.0.0.1:41234
Server received: Hello from the client! from 127.0.0.1:some_random_port

Client Output:

Message sent to server
Client received: Hello from the server! from 127.0.0.1:41234

Explanation

1. Server (udp_server.js):

   • The server is created using dgram.createSocket('udp4') for IPv4.
   • It listens for incoming messages on port 41234.
   • When a message is received, it logs the message and the sender's address and port.
   • It then sends a response back to the client.

2. Client (udp_client.js):

   • The client is also created using dgram.createSocket('udp4').
   • It sends a message to the server at port 41234.
   • When it receives a response from the server, it logs the response and then closes the client.

This example demonstrates the basic usage of the dgram module for UDP communication in Node.js, showcasing how to set up a simple server and client to send and receive messages.