How to check if a string is a valid URL in Golang?

There are cases where we would want to know if the URL that we got from an http request in the form of a string is even valid or not. In such cases, one can use two functions that the net/url package of Go's standard library provides.

Example 1

The first basic case is to check if the URL is well structured and a valid one, and for that, we can use the ParseRequestURI() function of the URL package.

Consider the code shown below.

package main

import (
   "fmt"
   "net/url"
)

func main() {
   u, err := url.ParseRequestURI("http://golangcode.com")
   if err != nil {
      panic(err)
   }
   fmt.Println(u)
}

Output

If we run the command go run main.go on the above code, then we will get the following output in the terminal.

http://golangcode.com

In the above code, we passed a valid URL with a host and the scheme and if we change it to an invalid one, we will get an error.

Example 2

Consider the code shown below.

package main

import (
   "fmt"
   "net/url"
)

func main() {
   u, err := url.ParseRequestURI("golangcode.com")
   if err != nil {
      panic(err)
   }
   fmt.Println(u)
}

Output

If we run the command go run main.go on the above code, then we will get the following output in the terminal.

panic: parse "golangcode.com": invalid URI for request

There's a catch when using ParseRequestURI() and that is, it considers that the URL was received in an HTTP Request, which can lead to some inconsistencies.

If we pass "Test:Test" string as the argument to the ParseRequestURI() function, then it will not yield any error. So, a better option is to make use of the Parse function along with the ParseRequestURI().

Example 3

Consider the code shown below.

package main

import (
   "fmt"
   "net/url"
)

func main() {
   _, err := url.ParseRequestURI("http://www.google.com")
   if err != nil {
      panic(err)
   }
   u, err := url.Parse("http://www.google.com")
   if err != nil || u.Scheme == "" || u.Host == "" {
      panic(err)
   }

   fmt.Println("All ok")
}

Output

If we run the command go run main.go on the above code, then we will get the following output in the terminal.

All Ok