Using QNetworkAccessManager to download a big file.

mrdebug

I need to download and write a big file. In order to to this I'm Using QNetworkAccessManager. The problem is that I need to write the file directly but the write procedure is very slow because the special drive is not fast as an hard disk.

                QNetworkAccessManager NetworkAccessManager;
                QNetworkReply *pQNetworkReply= NetworkAccessManager.get(QNetworkRequest(QUrl::fromEncoded(Path.toLocal8Bit())));
                QByteArray QBABuffer;
                if (pQNetworkReply) {
                    connect(pQNetworkReply, &QNetworkReply::readyRead, [&]() {
                    ...

The problem is that the readyread implementation must be fast. If I write in it a slow function the software firtly increase the ram usage and then goes to crash.
Is there a way to pause the object QNetworkReply or to reduce the speed of the dowloader?

hskoglund

Hi, you could try doing partial downloads by specifying "Range" and "bytes" in the headers (this requires that the server supports partial downloads but most do nowadays.) More here

SGaist

Hi,

If I remember correctly one thing you could do is to set a small read buffer size so it should slow the transmission.

piervalli

In the opposite aproce i have down 3 phase

initialize to file for upload and chunk size
2 .parallel upload
finalize

You should do

initialize to file for download and chunk size
2 .parallel download
finalize

mrdebug

After a long brainstorming till the brain explosion I have decided to use the QTcpSocket object implementing the http request by hand like this

                    QTcpSocket TcpSocket;
                    TcpSocket.connectToHost(Url.host(), Url.port());
                    if (TcpSocket.waitForConnected()) {
                        TcpSocket.write(QString("GET "+ Url.path()+ " HTTP/1.1\r\n").toLatin1());
                        TcpSocket.write(QString("Host "+ Url.host()+ " \r\n").toLatin1());
                        TcpSocket.write(QString("Connection: close\r\n\r\n").toLatin1());
                        if (TcpSocket.waitForBytesWritten()) {
                            while (TcpSocket.waitForReadyRead()) {
                            ...

Seems to work