Golang with letsencrypt https and http-->https redirect

server.go

package main

import (
	"crypto/tls"
	"net/http"

	"golang.org/x/crypto/acme/autocert"
)

func main() {
	certManager := autocert.Manager{
		Prompt:     autocert.AcceptTOS,
		HostPolicy: autocert.HostWhitelist("example.com"), //your domain here
		Cache:      autocert.DirCache("certs"),            //folder for storing certificates
	}

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Hello world"))
	})

	server := &http.Server{
		Addr: ":443",
		TLSConfig: &tls.Config{
			GetCertificate: certManager.GetCertificate,
		},
	}

	go http.ListenAndServe(":80", http.HandlerFunc(redirectToHTTPS))

	server.ListenAndServeTLS("", "") //key and cert are comming from Let's Encrypt
}

func redirectToHTTPS(w http.ResponseWriter, req *http.Request) {
	http.Redirect(w, req, "https://"+req.Host+req.URL.String(), http.StatusMovedPermanently)
}