Node.js dnsPromises.lookupService() Method

The dnsPromises.lookupService() method is an inbuilt application programming interface of the promises object of dns module which is used to resolve the addresses and port number to hostname and service using operating system’s underlying getnameinfo implementation.

Syntax:

dnsPromises.lookupService( address, port )

Parameters: This method has two parameters as mentioned above and described below:

• address: It specifies a string which denotes address to be resolved.
• port: It is a number that specifies the port number of the address whose service to be resolved.

Return Value: This method returns error, hostname and services.

Below examples illustrate the use of dnsPromises.lookupService() method in Node.js:

Example 1:

// Node.js program to demonstrate the
// dnsPromises.lookupService() method

// Accessing promises object from dns module
const dns = require('dns');
const dnsPromises = dns.promises;

// Calling dnsPromises.lookupService() method
// for 127.0.0.1 port  number 22
dnsPromises.lookupService('127.0.0.1', 22).then((res) => {
    console.log(res.hostname, res.service);
});

Output: Here name of my computer is my-lappy

my-lappy ssh

Example 2:

// Node.js program to demonstrate the
// dnsPromises.lookupService() method

// Accessing promises object from dns module
const dns = require('dns');
const dnsPromises = dns.promises;;

// Setting options for dnsPromises.lookup() method
const options = {

    // Setting family as 4 i.e. IPv4
    family: 4,
    hints: dns.ADDRCONFIG | dns.V4MAPPED,
};

dnsPromises.lookup('geeksforgeeks.org', options).then((response) => {
    if(response){
        console.log(response);

        // Calling dnsPromises.lookupService() method
        dnsPromises.lookupService(response.address, 80).then((res) => {
            console.log(res.hostname, res.service);
        });
    }
});

Output:

{ address: '34.218.62.116', family: 4 }
ec2-34-218-62-116.us-west-2.compute.amazonaws.com 334

Note: The above program will compile and run by using the node index.js command.

Reference: https://nodejs.org/api/dns.html#dns_dnspromises_lookupservice_address_port