Introduction
One of the advantages of using Go is Standard Library, Go has built in library that is already included when installing Go on your machine. There are many libraries you can use to build such as web application, rest API, command line interface (CLI), and many more just using Standard Library.
Today, I'm going to show you how to Lookup the IP, Nameservers, and CNAME for a particular host.
I assume you know a basic understanding of Go and setup GOPATH on your machine. Check this link about GOPATH https://github.com/golang/go/wiki/SettingGOPATH
Build
We are gonna using Go modules to create the app.
- Create directory
go-lookup
. - Move to the
go-lookup
directory and rungo mod init go-lookup
to initialize the modules.
Then create a new file main.go
inside the root directory. We're gonna use main.go
to create the function and act as the main application also.
Here is the initial code inside main.go
package main
import "fmt"
func main() {
fmt.Println("Hello from APP")
}
Build and run the program with go run main.go
, make sure you are already in the directory.
$ go run main.go
Hello from APP
As you can see, the program will print Hello from APP using Println
from the fmt
package.
Lookup the DNS Records from the given domain name
Open main.go
and remove the Println
line as before, and now we're going to use the net package to lookup the DNS name. First, create a variable to store the domain name inside the main function.
- import "fmt"
+ import (
+ "fmt"
+ "net"
+ )
- fmt.Println("Hello from APP")
+ // Define domain name
+ host := "maful.web.id"
+ fmt.Printf("Domain: %s\n\n", host)
Then, use LookupNS
function from the net
package
// Lookup the DNS Records from the domain name
ns, err := net.LookupNS(host)
if err != nil {
panic(err)
}
LookupNS
will return the pointer of the NS array, so we have to loop the ns
variable to print the Nameserver. If an error occurs, stop the program immediately by using panic.
// Looping the Nameserver and ignore the index
for _, v := range ns {
fmt.Println(v.Host)
}
fmt.Println()
Finally, build and run again. You should see the list of Nameserver for the given domain name, in this case, is my domain.
$ go run main.go
ns1.vercel-dns.com.
ns2.vercel-dns.com.
Lookup the IP addresses
Secondly, we still use the same package to lookup the IP addresses with the LookupIP function.
fmt.Println("Looks up the IP Addresses")
ips, err := net.LookupIP(host)
if err != nil {
panic(err)
}
for i := range ips {
fmt.Println(ips[i])
}
fmt.Println()
LookupIP
will return a slice of bytes, so we just need to use index to get the IP. Here is the result so far when you build and run the program.
$ go run main.go
76.76.21.21
76.76.21.21
is the IP of the domain.
Lookup the CNAME
Lastly, we will use the LookupCNAME
function from the net
library to get CNAME (wikipedia).
fmt.Println("Looks up the CNAME")
cname, err := net.LookupCNAME(host)
if err != nil {
panic(err)
}
fmt.Println(cname)
We don't need looping like the previous one, we just print the cname
directly because LookupCNAME
returns string. Here is the result:
$ go run main.go
maful.web.id.
Conclusion
Finally, we have created a simple application using Go. Based on what we code before, we can refactor the code into several functions, but we're not doing in this tutorial.
package main
import (
"fmt"
"net"
)
func main() {
// Define domain name
host := "maful.web.id"
fmt.Printf("Domain: %s\n\n", host)
// Lookup the DNS Records from the domain name
fmt.Println("Looks up the Nameservers")
ns, err := net.LookupNS(host)
if err != nil {
panic(err)
}
// Looping the Nameserver and ignore the index
for _, v := range ns {
fmt.Println(v.Host)
}
fmt.Println()
fmt.Println("Looks up the IP Addresses")
ips, err := net.LookupIP(host)
if err != nil {
panic(err)
}
for i := range ips {
fmt.Println(ips[i])
}
fmt.Println()
fmt.Println("Looks up the CNAME")
cname, err := net.LookupCNAME(host)
if err != nil {
panic(err)
}
fmt.Println(cname)
}
Full result
$ go run main.go
Domain: maful.web.id
Looks up the Nameservers
ns2.vercel-dns.com.
ns1.vercel-dns.com.
Looks up the IP Addresses
76.76.21.21
Looks up the CNAME
maful.web.id.
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