yes yes, don't misunderstand me, i get your suggestion and i did something similar for other purposes. But still i am confused now.
Let clarify my thought: for example, when i send the file, i could send a message with the tag [FILE] and in readyRead() when QString line = QString::fromUtf8(socket->readLine()); get that line i could use "find("[FILE]"); and if positive the server/client knows that the next date will be a file. So with a if who compares the return of find() i can choose what to do?

and sorry for my grammar -.-'