QNetworkReply - how to set bandwidth limit properly ?

[#Dragon]

Hi, I'm trying to set speed limit in my application using QNetworkReply but my code doesn't work properly.

QNetworkReply* reply;
    if(postData.isEmpty()) {
        reply = m_manager->get(*this->generateRequest(url));
    } else {
        reply = m_manager->post(*this->generateRequest(url),postData);
    }
    if(Values().DOWNLOAD_SPEED_LIMIT && (this->m_name != "Updater")){
        reply->setReadBufferSize(Values().DOWNLOAD_SPEED_LIMIT_VALUE);
    }

QNetworkReply* reply;
    if(postData.isEmpty()) {
        reply = m_manager->get(*this->generateRequest(url));
    } else {
        reply = m_manager->post(*this->generateRequest(url),postData);
    }
    if(Values().DOWNLOAD_SPEED_LIMIT && (this->m_name != "Updater")){
        reply->setReadBufferSize(Values().DOWNLOAD_SPEED_LIMIT_VALUE);
    }

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I don't know why but for some reasons setReadBufferSize doesn't work, I need really simple solution...

Thanks for any help
Cheers