How to support websocket?

[Leadrive]

Hi, I test this project. And I want to support the ws.

package main

import (
	"flag"
	"io"
	"log"
	"net"
	"net/http"
	"time"

	websocket "github.com/gorilla/websocket"
	gows "golang.org/x/net/websocket"
)

var (
	flagBind    = flag.String("bind", ":8883", "bind to")
	flagBackend = flag.String("be", "127.0.0.1:1883", "nats server")
	flagToken   = flag.String("token", "test", "secret token for http connection")
	flagPath    = flag.String("http-path", "mq", "http path to websockets")
)
var upgrader = websocket.Upgrader{
	ReadBufferSize:  1024,
	WriteBufferSize: 1024,
}

func copyWorker(dst io.Writer, src io.Reader, doneCh chan bool) {
	io.Copy(dst, src)
	doneCh <- true
}

func relayHandler(ws *gows.Conn) {
	log.Println("relayHandler")
	conn, err := net.Dial("tcp", *flagBackend)
	if err != nil {
		log.Printf("[ERROR] %v \n", err)
		return
	}

	//if binaryMode {
	//	// ws.PayloadType = websocket.BinaryFrame
	//}

	doneCh := make(chan bool)

	go copyWorker(conn, ws, doneCh)
	go copyWorker(ws, conn, doneCh)

	<-doneCh
	conn.Close()
	ws.Close()
	<-doneCh
}

func main() {
	flag.Parse()
	log.Printf("bind:%s, backend:%s\n", *flagBind, *flagBackend)
	upgrader.CheckOrigin = func(r *http.Request) bool { return true }
	// nginx config
	/*
		location /  {
			proxy_redirect off;
			proxy_pass http://127.0.0.1:8883/;
			proxy_http_version 1.1;
			proxy_set_header Host $host;
			proxy_set_header Upgrade $http_upgrade;
			proxy_set_header Connection Upgrade;
			proxy_set_header X-real-ip $remote_addr;
			proxy_set_header X-Forwarded-For $remote_addr;
		}
	*/
	http.Handle("/js", gows.Handler(relayHandler))
	http.HandleFunc("/js/health", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("OK"))
	})
	http.HandleFunc("/mqtt/health", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("OK"))
	})
	http.HandleFunc("/mqtt", func(w http.ResponseWriter, r *http.Request) { // go
		log.Printf("request mqtt\n")
		//if r.URL.Query().Get("token") != *flagToken {
		//	http.NotFound(w, r)
		//	return
		//}
		conn, err := upgrader.Upgrade(w, r, nil)
		if err != nil {
			log.Printf("%v\n", err)
			return
		}

		ncon, err := net.Dial("tcp", *flagBackend)
		if err != nil {
			log.Printf("%v", err)
			conn.Close()
			return
		}
		doneCh := make(chan bool)

		conn.UnderlyingConn().(*net.TCPConn).SetKeepAlivePeriod(1 * time.Second)

		go copyWorker(ncon, conn.UnderlyingConn(), doneCh)
		go copyWorker(conn.UnderlyingConn(), ncon, doneCh)

		<-doneCh

		ncon.Close()
		conn.Close()

		<-doneCh
	})

	http.ListenAndServe(*flagBind, nil)
}

After I test it on MQTTX with ws://xxx.xxx.xxx.xxx:8883/mqtt
It take a panic
ERROR 2022/09/06 01:06:39 %!v(PANIC=String method: runtime error: invalid memory address or nil pointer dereference) unexpected EOF
DEBUG 2022/09/06 01:06:39 %!v(PANIC=String method: runtime error: invalid memory address or nil pointer dereference) client connection could not be established