Node.js socket.setMulticastLoopback() Method

The socket.setMulticastLoopback() method is an inbuilt application programming interface of class Socket within dgram module which is used to set or clear the IP_MULTICAST_LOOP socket option which helps the server in receiving the multicast packet at the local interface.

Syntax:

const socket.setMulticastLoopback( flag )

Parameters: This method takes the Boolean value as a parameter true for enabling the IP_MULTICAST_LOOP socket option and false for disabling it.

Return Value: This method does not return any value.

Example 1: In this example, we will see the use of the socket.setMulticastLoopback() method

Filename: index.js

Javascript

// Node.js program to demonstrate the
// socket.setMulticastLoopback() method

// Importing dgram module
const dgram = require('dgram');

// Creating and initializing client
// and server socket
let server = dgram.createSocket("udp4");
let client = dgram.createSocket("udp4");
let broadcast_address = 12345;

// Catching the message event
server.on("message", function (msg) {

    // Displaying the client message
    process.stdout.write("UDP String: " + msg + "\n");

    // Exiting process
    process.exit();
})
    .bind(broadcast_address, () => {

        // Enable the IP_MULTICAST_LOOP socket option
        // by using the setMulticastLoopback() method
        server.setMulticastLoopback(true);
    });

// Client sending message to server
client.send("Hello", 0, 7,
    broadcast_address, "localhost");

Output:

UDP String: Hello

Example 2: In this example, we will see the use of the socket.setMulticastLoopback() method

Filename: index.js

Javascript

// Node.js program to demonstrate the
// socket.setMulticastLoopback() method

// Importing dgram module
const dgram = require('dgram');

// Creating and initializing client
// and server socket
let client = dgram.createSocket("udp4");
let server = dgram.createSocket("udp4");

// Catching the message event
server.on("message", function (msg) {

    // Displaying the client message
    process.stdout.write("UDP String: " + msg + "\n");

    // Exiting process
    process.exit();
});

// Catching the listening event
server.on('listening', () => {
    const address = server.address();
    console.log(`server listening
        ${address.address}:${address.port}`);
});

// Binding server with port address
server.bind(1234, () => {

    // Enable the IP_MULTICAST_LOOP socket option
    // by using the setMulticastLoopback() method
    server.setMulticastLoopback(true);
});

// Client sending message to server
client.send("Hello", 0, 7, 1234, "localhost");

Output:

server listening 0.0.0.0:1234
UDP String: Hello

Run the index.js file using the following command:

node index.js

Reference: https://nodejs.org/dist/latest-v12.x/docs/api/dgram.html#dgram_socket_setmulticastloopback_flag