qt - Download big files with QNetworkreply::readAll freeze for a few seconds -


i used example doc http://doc.qt.io/qt-4.8/qnetworkaccessmanager.html

i create startdownload:

connect(pushbutton, signal(clicked(bool)), this, slot(startdownload(bool)));

in startdownload(bool) put this:

file = new qfile("c:/foo/bar/bigfile.7z"); file->open(qiodevice::writeonly);  qnetworkrequest request; request.seturl(qurl("http://localhost/bigfile.7z")); request.setrawheader("user-agent", "myownbrowser 1.0");  qnetworkreply *reply = manager->get(request);  connect(reply, signal(readyread()), this, slot(slotreadyread())); connect(reply, signal(error(qnetworkreply::networkerror)),         this, slot(sloterror(qnetworkreply::networkerror))); connect(reply, signal(sslerrors(qlist<qsslerror>)),         this, slot(slotsslerrors(qlist<qsslerror>)));

in slotreadyread put this:

file->write(reply->readall());

but when download arrives @ end there small freezing 2 seconds , returns normal , download complete. problem occurs if file i'm trying transfer large.

this expected behavior. qiodevice::readall() block thread until download completes. it's possible qfile::write() may block depending on disk speed , caching policy. readall() method may consume quite bit of ram if file large enough.

the simplest solution download file in smaller chunks using read() instead of readall().

now said, there's no easy way find perfect buffer size read network , write disk; it's going depend on how network connection responds vs. disk write speed.


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