got error message "control frame is not final" when using websocketUtil.ReadServerText

[Jekinnnnnn]

client side:

func startTest(c *gin.Context) {
	type Request struct {
		Cnt int
		Url string
	}
	req := new(Request)
	if err := c.ShouldBind(req); err != nil {
		c.JSON(http.StatusOK, gin.H{
			"Errcode": errno.ErrWrongParam.Code(),
			"Errmsg":  errno.ErrWrongParam.Error(),
		})
		return
	}
	statistics := make([]chan int, req.Cnt)
	for i := 0; i < req.Cnt; i++ {
		statistics[i] = make(chan int)
		go func(index int, url string, res chan int) {
			conn, _, _, err := websocket.DefaultDialer.Dial(context.Background(), url)
			if err != nil {
				log.Println("dial fail index = ", index)
				res <- 1
				return
			}
			defer conn.Close()
			text := "hello world"
			err = websocketUtil.WriteClientMessage(conn, websocket.OpText, []byte(text))
			if err != nil {
				log.Println("WriteMessage failed 111:", err)
				res <- 2
				return
			}

			message, err := websocketUtil.ReadServerText(conn)
			if err != nil {
				log.Println("ReadMessage failed 222:", err)
				res <- 3
				return
			}
			log.Println("ReadMessage :", string(message))
			sleepSec := rand.Int31n(40)
			log.Println("start sleep =", sleepSec, " s")
			time.Sleep(time.Duration(sleepSec) * time.Second)
			res <- 4
		}(i, req.Url, statistics[i])
	}
	dialFailCnt := float64(0)
	writeFailCnt := float64(0)
	readFailCnt := float64(0)
	finishCnt := float64(0)
	for _, ch := range statistics {
		res := <-ch
		switch res {
		case 1:
			dialFailCnt++
		case 2:
			writeFailCnt++
		case 3:
			readFailCnt++
		case 4:
			finishCnt++
		}
	}
	floatTotal := float64(req.Cnt)
	log.Println(fmt.Sprintf("total=%d,dialFailRate=%f,writeFailRate=%f,readFailRate=%f,successRate=%f", req.Cnt, dialFailCnt/floatTotal, writeFailCnt/floatTotal, readFailCnt/floatTotal, finishCnt/floatTotal))
}

server side:

func readClientData(Conn *net.Conn) {
	for {
		message, msgType, err := websocketUtil.ReadClientData(Conn)
		if err != nil {
			break
		}
        if msgType == websocket.OpText {
			_ = websocketUtil.WriteServerMessage(Conn, msgType, []byte("send echo"))
        }
	}
}

i start a benchmark test in my 4c8g machine with code above,(obviously i removed some project-related code) when i test 5000 connection got result total=5000,dialFailRate=0.000000,writeFailRate=0.000000,readFailRate=0.004600,successRate=0.995400 all realFail errors are control frame is not final. it's a bug or my wrong usage? besides, after upgrading websocket, i bind a unique id with each connection which has lock competition that raising high cpu load, but according to the statistical results, it seems irrelevant to the question.

[Jekinnnnnn]

now server detect closed websocket by matching message "^ws closed:" which return from websocketUtil.ReadClientData is there has a better way to do this?