yourip/main.go

package main

import (
  "log"
  "net/http"
  "encoding/json"
)

type output struct{}

func (o output) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	jsonOutput, err :=  json.MarshalIndent (r.RemoteAddr, "", " ")
	if err != nil {
		w.Write([]byte(err.Error()))
	}
	w.Write(jsonOutput)
}

func main() {
	log.Fatal(http.ListenAndServe(":8080", output{}))
}