QFile to QByteArray save file name

Question

I have a QFile that needs to be sent through a LAN network. In order to do so, I convert the QFile into QByteArray by doing:

//! [Inside a QTcpSocket class]

// Get the file name using a QFileDialog
QFile file(QFileDialog::getOpenFileName(NULL, tr("Upload a file")));

// If the selected file is valid, continue with the upload
if (!file.fileName().isEmpty) {
    // Read the file and transform the output to a QByteArray
    QByteArray ba = file.readAll();

    // Send the QByteArray
    write(ba);
}

When I receive it, I can transform it easily by using:

void saveFile(QByteArray ba) {
    // Ask the user where he/she wants to save the file
    QFile file(QFileDialog::getSaveFileName(NULL, tr("Save file")));

    // Check that the path is valid
    if (!file.fileName().isEmpty()) {
       // Write contents of ba in file
       file.write(ba);
       // Close the file
       file.close();
    }
}

However, I would like to know the file name (such as Document.docx) or at least know its extension to avoid forcing the user to know exactly which file type he has received.

Ideally, when the file is uploaded, the receiver user will be prompted to save the file. For example:

1. Sender sends Document1.docx
2. Receiver gets prompted if he/she wants to save Document1.docx
3. Based on receiver's decision, Document1.docx is saved in receiver's workstation.

So, my question is: Is there any way to know the name and extension of a QFile when its transformed into a QByteArray and then transformed again (in another computer) into a QFile?

Answer 1

You just read the raw bytes of a file using QFile::readAll().

Q: Is there any way to know the name and extension of a QFile when its transformed into a QByteArray?

No. The file name and extension is not necessarily inserted in bytes of a file. It depends on the file format. For example you can make your custom file with a specific extension and put its name and extension at the begging of the bytes.

You can send the name and extension of the file manually before sending the raw bytes of the file. Before that you can send the length of name and extension and the number of bytes in file. This way you know how many bytes are related to name, extension and raw bytes.

Answer 2

The answer on you particular question is NO. Although particular files contain the so called magic numbers (or signatures) in the beginning of the data, this signature should be unique for particular file format.

But the problem you have described seems not be serious, because you can simply send filename string and extension string separately of the file content.