As peppe also pointed out in the comment, you need to seek the QBuffer
to the beginning after the write and before the read as per the documentation:
QBuffer allows you to access a QByteArray using the QIODevice interface. The QByteArray is treated just as a standard random-accessed file. Example:
QBuffer buffer;
char ch;
buffer.open(QBuffer::ReadWrite);
buffer.write("Qt rocks!");
*** buffer.seek(0); ***
buffer.getChar(&ch); // ch == 'Q'
buffer.getChar(&ch); // ch == 't'
buffer.getChar(&ch); // ch == ' '
buffer.getChar(&ch); // ch == 'r'
To be more concrete for your code, you would need to insert the statement like this:
...
device.seek(0);
qDebug() << "DEVICE BYTES" << device->bytesAvailable(); //NOT 0 ANYMORE!!!! :)
...