Node.js dns.lookupService() Method
The dns.lookupService() method is an inbuilt application programming interface of the dns module which is used to resolve the addresses and port number to hostname using operating system’s underlying getnameinfo implementation.
Syntax:
dns.lookupService( address, port, callback )
Parameters: This method has three parameters as mentioned above and described below:
- address: It specifies a string which denotes the address to be resolved.
- port: It is a number that specifies the port number of the address whose service is to be resolved.
- callback: It specifies a function to be called after resolution of the address and port.
- error: It specifies error if generated.
- hostname: String representation of the hostname. e.g. w3wiki.net
- service: It’s a string, specifies name of the service. e.g. http
Return Value: This method returns error, hostname and services through callback function. These data are passed as parameters to the callback function.
Below examples illustrate the use of dns.lookupService() method in Node.js:
Example 1: IP for localhost
// Accessing dns module const dns = require('dns'); // Calling dns.lookupService() method for // 127.0.0.1 port number 22 dns.lookupService('127.0.0.1', 22, (err, hostname, service) => { // Printing hostname and service as callback console.log(hostname, service); }); |
Output: Here name of my computer is my-lappy
my-lappy ssh
Example 2:
// Accessing dns module const dns = require('dns'); // Setting options for dns.lookup() method const options = { // Setting family as 4 i.e. IPv4 family: 4, hints: dns.ADDRCONFIG | dns.V4MAPPED, }; dns.lookup('www.w3wiki.net', options, (err, address, family) => { console.log('address:', address); if(err){ console.log(err.stack); } else{ // Calling dns.lookupService() method 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: 42.106.162.241 42-106-162-241.live.vodafone.in http
Note: The above program will compile and run by using the node filename.js command.
Reference: https://nodejs.org/api/dns.html#dns_dns_lookupservice_address_port_callback