In this article, we are going to discuss building the Node.js DNS module. A DNS module is used to do the DNS lookup and underlying operating system name resolution functionalities through an asynchronous network wrapper. We use the following syntax to import an asynchronous network wrapper.
// Command to import DNS Module in Node.js.
var dns = require("dns");
Methods present in the DNS Module of Node.Js
The following are the basic methods and their descriptions which are present in the DNS Module of Node.js.
|
S No |
Method |
Description |
|
1. |
dns.lookup(hostname[, options], callback) |
This method is used to resolve a hostname (e.g. ‘www.eduonix.com’) into A (IPv4) default or AAAA (IPv6) address record. Options can be an object or integer. If options is an integer, then it must be 4 or 6 for IPv4 or IPv6 respectively. |
|
2. |
dns.lookupService(address, port, callback) |
This method is used to resolve the given address and port into a hostname and service using the getnameinfo. |
|
3. |
dns.resolve(hostname[, rrtype], callback) |
This method is used to resolve a hostname (e.g. ‘www.eduonix.com’) into an array of the record types specified by rrtype. |
|
4. |
dns.resolve4(hostname, callback) |
This method is same as dns.resolve () method but only for IPv4 queries (A records). Addresses is an array of IPv4 addresses (e.g. [‘ 67.227.229.33’, etc.]). |
|
5. |
dns.resolve6(hostname, callback) |
This method is same as dns.resolve4 () except for IPv6 queries (an AAAA query). |
|
6. |
dns.resolveMx (hostname, callback) |
This method is same as dns.resolve (), but only for mail exchange queries (MX records). |
|
7. |
dns.resolveTxt (hostname, callback) |
This method is same as dns.resolve (), but only for text queries (TXT records). |
|
8. |
dns.resolveSrv (hostname, callback) |
This method is same as dns.resolve (), but only for service records (SRV records). |
|
9. |
dns.resolveSoa(hostname, callback) |
This method is same as dns.resolve (), but only for start of authority record queries (SOA record). |
|
10. |
dns.resolveNs (hostname, callback) |
This method is same as dns.resolve (), but only for name server records (NS records). |
|
11 |
dns.resolveCname (hostname, callback) |
This method is same as dns.resolve (), but only for canonical name records (CNAME records). |
|
12 |
dns.reverse (ip, callback) |
This method is used to resolve an ip address to an array of hostnames. |
|
13 |
dns.getServers () |
This method is used to return an array of IP addresses as strings that are currently being used for resolution. |
|
14 |
dns.setServers (servers) |
For the given array of IP addresses as strings, this method is used to set them as the servers in order to use for resolving. |
‘dns.resolve ()’ method rrtypes:
The following are the rrtypes used by ‘dns.resolve ()’ method:
|
S No. |
rrtypes |
Description |
|
1. |
A |
This rrtype is used for the IPV4 addresses, which are default. |
|
2. |
AAAA |
This rrtype is used for the IPV6 addresses. |
|
3. |
CNAME |
This rrtype is used for the canonical name records. |
|
4. |
MX |
This rrtype is used for the mail exchange records. |
|
5. |
NS |
This rrtype is used for the name server records. |
|
6. |
PTR |
This rrtype is used for the reverse IP lookups. |
|
7. |
SOA |
This rrtype is used for the start of authority record. |
|
8. |
SRV |
This rrtype is used for the SRV records. |
|
9. |
TXT |
This rrtype is used for the text records. |
Error Codes returned by DNS query
The following are the error codes returned by the DNS Query.
|
S No. |
Error Codes |
Description |
|
1. |
dns.NODATA |
This error code is returned by the DNS server when there is no data. |
|
2. |
dns.FORMERR |
This error code is returned by the DNS server when query was badly formatted. |
|
3. |
dns.SERVFAIL |
This error code is returned by the DNS server when there is general failure. |
|
4. |
dns.NOTFOUND |
This error code is returned by the DNS server when domain name not found. |
|
5. |
dns.NOTIMP |
This error code is returned by the DNS server when it does not implement requested operation. |
|
6. |
dns.REFUSED |
This error code is returned by the DNS server when DNS server refused the query. |
|
7. |
dns.BADQUERY |
This error code is returned by the DNS server when there is a badly formatted DNS query. |
|
8. |
dns.BADNAME |
This error code is returned by the DNS server when there is a badly formatted hostname. |
|
9. |
dns.BADFAMILY |
This error code is returned by the DNS server when unsupported address family. |
|
10. |
dns.BADRESP |
This error code is returned by the DNS server when there is a badly formatted DNS reply. |
|
11. |
dns.CONNREFUSED |
This error code is returned by the DNS server when it could not contact the DNS servers. |
|
12. |
dns.TIMEOUT |
Timeout while contacting DNS servers. |
|
13. |
dns.EOF |
This error code is returned by the DNS server at the end of a file. |
|
14. |
dns.FILE |
This error code is returned by the DNS server when there is an error reading the file. |
|
15. |
dns.NOMEM |
This error code is returned by the DNS server when it is out of memory. |
|
16. |
dns.DESTRUCTION |
This error code is returned by the DNS server when the channel is being destroyed. |
|
17. |
dns.BADSTR |
This error code is returned by the DNS server when there is a badly formatted string. |
|
18. |
dns.BADFLAGS |
This error code is returned by the DNS server when the Illegal flags are specified. |
|
19. |
dns.NONAME |
This error code is returned by the DNS server when the given hostname is not numeric. |
|
20. |
dns.BADHINTS |
This error code is returned by the DNS server when Illegal hints flags are specified. |
|
21. |
dns.NOTINITIALIZED |
This error code is returned by the DNS server when c-ares library initialization has not yet been performed. |
|
22. |
dns.LOADIPHLPAPI |
This error code is returned by the DNS server when there is an error in loading iphlpapi.dll. |
|
23. |
dns.ADDRGETNETWORKPARAMS |
This error code is returned by the DNS server when it could not find the GetNetworkParams function. |
|
24. |
dns.CANCELLED |
This error code is returned by the DNS server when the DNS query is cancelled. |
Example on use of DNS Module in Node.js Application
In the following example, we are going to demonstrate the use of the above DNS module methods. Here, we are going to create one js file named DNSModuleServer.js, which has the following code.
DNSModuleServer.js
var dns = require('dns');
dns.lookup('www.eduonix.com', function onLookup(err, address, family) {
console.log('IP Address for www.eduonix.com:', address);
dns.reverse(address, function (err, hostnames) {
if (err) {
console.log(err.stack);
}
console.log('reverse for IP Address ' + address + ': ' + JSON.stringify(hostnames));
});
});
Explanation of the code
In the above code, we are looking up ‘www.eduonix.com’ domain and retrieving IP address which are printed on the console. Next, we are using the ‘reverse’ method to print the reverse of the host name by using the method ‘JSON.stringify (hostnames))’.
Output
When we execute the above Node.js programs, then we will observe the following output on the console.
IP Address for www.eduonix.com: 67.227.229.33 reverse for IP Address 67.227.229.33: ["host.eduonix.com"]
Source code for this DNS module of Node.js blog
Conclusion: –
In this article, we discussed the various methods present in the DNS module of Node.js. We have imported the DNS module and use the associated methods to build a DNS Module utility.
