var upgrader = websocket.Upgrader{
    ReadBufferSize:  1024,
    WriteBufferSize: 1024,
    CheckOrigin: func(r *http.Request) bool {
        // в проде — whitelist Origin, не return true всегда
        return r.Host == "localhost:8080"
    },
}

func wsHandler(w http.ResponseWriter, r *http.Request) {
    conn, err := upgrader.Upgrade(w, r, nil)
    if err != nil {
        log.Print("upgrade:", err)
        return
    }
    defer conn.Close()

    for {
        mt, msg, err := conn.ReadMessage()
        if err != nil {
            break
        }
        log.Printf("recv type=%d len=%d", mt, len(msg))
        if err := conn.WriteMessage(mt, msg); err != nil {
            break
        }
    }
}

func main() {
    http.HandleFunc("/ws", wsHandler)
    log.Fatal(http.ListenAndServe(":8080", nil))
}