3
                                connections = gmap.New()
    connections是一个保存了conn的地图
    --------------------------------------------------
    conn := connections.Get(parkingNo)
if conn == nil {
    ResponseOK(c, "停车场未连接")
    return
}
    bytes := jsonutil.Marshal(request)
resBytes, err := conn.SendRecvWithTimeout(bytes, -1, 5*time.Second)
// 不会收到返回值,为什么
if err != nil {
    ResponseOK(c, err.Error())
    return
}