go实现本地数据库

package main

import (
   "log"
   "net/http"
   "fmt"
   "strconv"
)


func main() {
   db := database{"shoes": 50, "socks": 5}
   http.HandleFunc("/list", db.list)
   http.HandleFunc("/price", db.price)
   http.HandleFunc("/add",db.add)
   log.Fatal(http.ListenAndServe("localhost:8000", nil))
}

type dollars float32

func (d dollars) String() string { return fmt.Sprintf("$%.2f", d) }

type database map[string]dollars

func (db database) add(w http.ResponseWriter, req *http.Request) {
   k := req.URL.Query().Get("key");
   v := req.URL.Query().Get("value");
   if _,ok := db[k]; ok {
      fmt.Printf("the %s is existing\n",k)
      return
   }
   vv,_ := strconv.Atoi(v);
   db[k] = dollars(vv);
}

func (db database) list(w http.ResponseWriter, req *http.Request) {
   for item, price := range db {
      fmt.Fprintf(w, "%s: %s\n", item, price)
   }
}

func (db database) price(w http.