package main

import (
	"crypto/subtle"
	"net/http"
	"sync"
)

var (
	mu  sync.RWMutex
	ip  string
	key string
)

func main() {
	http.HandleFunc("/get", func(w http.ResponseWriter, r *http.Request) {
		if r.Method == "GET" {
			mu.RLock()
			defer mu.RUnlock()
			w.Write([]byte(ip))
			return
		}
		http.Error(w, "bad request", http.StatusBadRequest)
	})
	http.HandleFunc("/set", func(w http.ResponseWriter, r *http.Request) {
		if r.Method == "GET" {
			r.ParseForm()
			if subtle.ConstantTimeCompare([]byte(key), []byte(r.FormValue("token"))) == 1 {
				mu.Lock()
				defer mu.Unlock()
				ip = r.FormValue("ip")
				w.Write([]byte("ok"))
				return
			}
		}
		http.Error(w, "bad request", http.StatusBadRequest)
	})
	panic(http.ListenAndServe("127.0.0.1:9090", nil))
}