Call onDataAvailable when there are incoming data available on socket opened via connect() or in another way (QLocalSocket, etc.).
bytes - number of bytes available to read from socket, -1 if the number of bytes is unknown
errno error code:
* EINVAL if EveusbEventHandler was not set via setEventHandler or in case of some other errors
* E2BIG if message from daemon exceeds MSG_LEN_MAX bytes
* EIO if underlying call to readFromDaemon() returned -1
* ENODATA if readFromDaemon() returned zero (connection was closed by remote side)
See poll/select, QLocalSocket::onDataAvailable, etc.
To perform read on socket, it calls EveusbEventHandler::readFromDaemon().
If a complete message is received from daemon, it calls onMessage() and corresponding member of EveusbEventHandler.
You should close the socket if an error is returned.