unsigned long read (char *buf,
                    unsigned long len,
                    bool *isEof)

virtual void readAsync (char          *buf,
                        unsigned long  len,
                        ReadCallback   readCallback,
                        void          *data) = 0

virtual void writeAsync (const char    *buf,
                         unsigned long  len,
                         WriteCallback  writeCallback,
                         void          *data) = 0

virtual void setAsync (bool async) = 0