CORS enabled HTTP server that tells users their IP

ipecho.go

package main

import (
	"net"
	"net/http"
)

func main() {
	http.HandleFunc("/", func(resp http.ResponseWriter, req *http.Request) {
		resp.Header().Set("Access-Control-Allow-Origin", "*")
		ip, _, err := net.SplitHostPort(req.RemoteAddr)
		if err != nil {
			http.Error(resp, err.Error(), http.StatusInternalServerError)
			return
		}
		resp.Write([]byte(ip))
	})
	panic(http.ListenAndServe(":80", nil))
}