Node.js – dns.lookupService() Method

The dns.lookupService() method resolves a given address and port into a hostname and service. This method uses the operating system's underlying getnameinfo implementation. A TypeError will be thrown if the address is not a valid IP address.

Syntax

dns.lookupService(address, port, callback)

Parameters

• address - This parameter takes input for the IP address that needs to be resolved.

• port - This parameter takes input for the port number that is attached with the IP address.

• callback - It will catch errors, if any.

Example 1

Create a file with the name "lookupService.js" and copy the following code. After creating the file, use the command "node lookupService.js" to run this code as shown in the example below −

// dns.lookupService() Demo Example

// Importing the dns module
const dns = require('dns');

// Passing the IP address and port
dns.lookupService('127.0.0.1', 22, (err, hostname, service) => {
   console.log(hostname, service);
});

Output

It will produce the following output −

localhost ssh

Example 2

Let's take another example −

// dns.lookupService() Demo Example

// Importing the dns module
const dns = require('dns');

// Passing the below options to lookup
const options = {
   //IPv4
   family: 4,
   hints: dns.ADDRCONFIG | dns.V4MAPPED,
};

dns.lookup('tutorialsPoint.com',
   options, (err, address, family) => {

      console.log('address:', address);
         if(err){
            console.log(err.stack);
         } else{
         // Calling dns.lookupService() method
         // to retrieve details of IP address
         dns.lookupService(address, 80,(err, hostname, service) => {
            if(err){
               console.log(err.stack);
            }
            // Printing hostname and service
            // as callback
            console.log(hostname, service);
      });
   }
});

Output

address: 157.90.94.102
tutorialspoint.com http