How do I retrieve the domain from a URL?

In Go, how can I extract only the domain name from a URL string?

Before:

https://www.example.com/some-random-url
www.example.com/some-random-url
example.com/some-random-url
www.example.com
subdomain.example.com

After:

example.com

Also, I'm limited to using the Golang standard library.

I've finally figured it out.

package main

import (
	"fmt"
	"log"
	"net/url"
	"strings"
)

func main() {
	url, err := url.Parse("https://www.example.com")
	if err != nil {
		log.Fatal(err)
	}
	parts := strings.Split(url.Hostname(), ".")
	domain := parts[len(parts)-2] + "." + parts[len(parts)-1]
	fmt.Println(domain)
}

example.com

If the domain is something like subdomain.example.com than it will give you a panic.

https://play.golang.org/p/Li0PviAr2jU

I think since your examples has incorrect URLs as well, you need to use Regular Expresssion to extract the domain in the URL. Please find the sample code below to get the domain for the examples you shared:

package main

import (
	"fmt"
	"regexp"
)

// Main function
func main() {

	// Finding regexp from the given string
	// Using FindString() method
	m := regexp.MustCompile(`\.?([^.]*.com)`)

	fmt.Println(m.FindStringSubmatch("https://www.example.com/some-random-url")[1])
	fmt.Println(m.FindStringSubmatch("www.example.com/some-random-url")[1])
	fmt.Println(m.FindStringSubmatch("example.com/some-random-url")[1])
	fmt.Println(m.FindStringSubmatch("www.example.com")[1])
	fmt.Println(m.FindStringSubmatch("subdomain.example.com")[1])

}

Ideally, this covers all the cases (including incorrectly formed URLs). You can easily update RegEx if there is any URL that doesn't get parsed correctly.

Go Playground link for the above: here.

This solution

func extractDomain(urlLikeString string) string {

	urlLikeString = strings.TrimSpace(urlLikeString)

	if regexp.MustCompile(`^https?`).MatchString(urlLikeString) {
		read, _ := url.Parse(urlLikeString)
		urlLikeString = read.Host
	}

	if regexp.MustCompile(`^www\.`).MatchString(urlLikeString) {
		urlLikeString = regexp.MustCompile(`^www\.`).ReplaceAllString(urlLikeString, "")
	}

	return regexp.MustCompile(`([a-z0-9\-]+\.)+[a-z0-9\-]+`).FindString(urlLikeString)
}

will turn this

"   ",
"aaa",
"not domain",
"ca.mail.google.com",
"google.com",
" google.com ",
" www.google.com/a/example.com",
"www.google.com/f/example.com",
"google.com/f/example.com",
"http://google.com/f/abc.com",
"http://google.com/f/?wow=xyz.com",
"http://google.com/f/?wow=www.xyz.com",
"http://www.google.com/f/abc.com",
"https://www.google.com/f/abc.com",
"https://mail.google.com/f/abc.com",
"https://123.google.com/f/abc.com",
"https://xn-ddf3.google.com/f/abc.com",

into this

[empty string]
[empty string]
[empty string]
ca.mail.google.com
google.com
google.com
google.com
google.com
google.com
google.com
google.com
google.com
google.com
google.com
mail.google.com
123.google.com
xn-ddf3.google.com

"net/url" method url.Parse won't handle domain-like string, like: bla bla google.com.

I think this can be helpful

package main
import (
"fmt"
"log"
"net/url"
"strings"
)
func main() {
strArray := []string{
"www.google.co.in",
"https://google.in",
"instagram.com",
"nymag.com",
"http://www.example.com/?airport=approval&box=brother",
"https://www.example.com/babies.php#birds",
"http://example.org/bear",
"www.google.co.in",
"google.com",
"https://www.bbb.org/search/business-review-form/",
"https://www.localvisibilitysystem.com/2015/08/19/how-to-use-meetup-sponsorships-for-local-marketing-and-seo-dave-oremlands-tips/",
"http://www.example.com/boat/advertisement?actor=bat#boundary",
"https://www.example.com/",
"https://www.google.com",
"https://www.example.com/army/approval.htm?basket=bottle",
"http://example.com/board.aspx?afternoon=appliance&angle=ball",
"http://www.example.com/",
"http://example.com/",
"http://www.example.com/",
"livejournal.com",
"delicious.com",
"illinois.edu",
"instagram.com",
"nymag.com",
"altervista.org",
"t.co",
"reddit.com",
"tinyurl.com",
}
var hostname string
var temp []string
for i := 0; i < len(strArray); i++ {
url, err := url.Parse(strArray[i])
if err != nil {
log.Fatal(err)
}
var urlstr string = url.String()

here prefix and host name will be filtered

	if strings.HasPrefix(urlstr, "https") {
hostname = strings.TrimPrefix(urlstr, "https://")
} else if strings.HasPrefix(urlstr, "http") {
hostname = strings.TrimPrefix(urlstr, "http://")
} else {
hostname = urlstr
}
if strings.HasPrefix(hostname, "www") {
hostname = strings.TrimPrefix(hostname, "www.")
}
if strings.Contains(hostname, "/") {
temp = strings.Split(hostname, "/")
fmt.Println(temp[0])
} else {
fmt.Println(hostname)
}
}
}

output:

 google.co.in
google.in
instagram.com
nymag.com
example.com
example.com
example.org
google.co.in
google.com
bbb.org
localvisibilitysystem.com
example.com
example.com
google.com
example.com
example.com
example.com
example.com
example.com
livejournal.com
delicious.com
illinois.edu
instagram.com
nymag.com
altervista.org
t.co
reddit.com
tinyurl.com

this will give you required Domain from any url
Go Playground link for the above:
https://go.dev/play/p/vfCOAnTNqh8