How to resume an old download in an file QtNetwork



  • how to resume an old download in an file QtNetwork i know how to pause an resume but i have started a download and then paused it and then quit my application and then i have to open my application again and then resume so here is the problem how do i write the new data at the end of file i have opened the file in append mode and then write but the problem in append mode it will add data at the last
    so whenever the downloadprogress ic alled i read the whole downloaded to file but in append mode it will add and so file is corrupt i have seen everythin every example and even arora arora has a very ordinary download manager which does not have this feature



  • You need to signal to the server that you don't want to get the file starting from the beginning but at some byte offset. This can be done via the HTTP request header, see the RFC specifications about this. The appropriate header information can then be written to a QNetworkRequest with setRawHeader.

    //EDIT: Here are the necessary specifications: https://tools.ietf.org/html/rfc2616 section 14.35



  • i know this man and i have already done it and i am getting the file after the pos but the problem is with saving with QFile please give me a small example



  • I don't understand this:

    bq. i have opened the file in append mode and then write but the problem in append mode it will add data at the last
    so whenever the downloadprogress ic alled i read the whole downloaded to file but in append mode it will add and so file is corrupt

    What are you saying is your problem?
    Opening in append mode and continue writing is the correct way.



  • see my problem
    i have opened the file in append mode now every time download progress is called i write the data to file everything seems ok but not now see
    i am reading the whole reply (this is he only way i have) into file so
    olddata = olddata + all the datat downloaded till now
    file = olddata
    now you see the file is appending the whole downloaded till that time agagin so it will append the download every times this function is called ih ope this understands



  • show the code of the slot connected to QNetworkReply::downloadProgress. I still don't see why a normal QFile::write would add all the old data and the new chunk to the file. Considering that a QIODevice::read (on the QNetworkReply) advances its internal position.



  • @void downloadfile::savedownloaded(qint64 downloaded, qint64 total)
    {
    file->write(reply->readAll());
    int percentage = 0;
    if(total > 0)
    {
    qDebug() << "yooo";
    percentage = ((downloaded+downloadsizeatpause) * 100) / (downloadsizeatpause+total);
    }
    qDebug() << "foo" << downloadsizeatpause;
    emit downloadprogress(downloaded+downloadsizeatpause , total+downloadsizeatpause , percentage);
    }@



  • Have you tried connecting that slot to readyRead? What does bytesAvailable() return in each iteration before and after readAll?

    This doc paragraph might also be interesting for you:
    The downloadProgress() signal is also emitted when data is received, but the number of bytes contained in it may not represent the actual bytes received, if any transformation is done to the contents (for example, decompressing and removing the protocol overhead).

    It's not clear what this is supposed to mean:

    bq. now you see the file is appending the whole downloaded till that time agagin so it will append the download every times this function is called ih ope this understands

    This sounds as if QNetworkReply isn't a sequential device and you somehow reset the position to 0 at every read. But it's sequential so that shouldn't happen. Are you sure you open your file properly and the error isn't in some other part of the code that handles the file?

    (Further you might want to look up an indian C++/Qt forum, it's really hard figuring out what you're actually trying to say.)



  • how you know i am an indian i am trying opening the file in readwrite mode and seeking the file to last i hope this works posting the code soon sfetr developing



  • developer I'm also write download program but Im amater in QT programming, Can you show your code for me reference
    thanks


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