how to fetch /socket.io/socket.io.js ? about socket.io HOT 3 CLOSED

package main

import (
	"os"
	"os/signal"
	"syscall"

	"github.com/zishang520/engine.io/v2/log"
	"github.com/zishang520/engine.io/v2/types"
	"github.com/zishang520/socket.io/v2/socket"
)

func main() {
	log.DEBUG = true
	c := socket.DefaultServerOptions()
	// c.SetConnectionStateRecovery(&socket.ConnectionStateRecovery{})
	// c.SetAllowEIO3(true)
	c.SetServeClient(true)
	// c.SetCors(&types.Cors{
	// 	Origin:      "http://127.0.0.1:8000",
	// 	Credentials: true,
	// })
	httpServer := types.CreateServer(nil)
	io := socket.NewServer(httpServer, c)
	io.On("connection", func(clients ...interface{}) {
		client := clients[0].(*socket.Socket)
		client.On("disconnect", func(...interface{}) {
			// utils.Log().Success("/ test disconnect")
		})
	})
	httpServer.Listen("127.0.0.1:3000", nil)

	exit := make(chan struct{})
	SignalC := make(chan os.Signal)

	signal.Notify(SignalC, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)
	go func() {
		for s := range SignalC {
			switch s {
			case syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT:
				close(exit)
				return
			}
		}
	}()

	<-exit
	io.Close(nil)
	os.Exit(0)
}