QNetworkReply sometimes emits spurious downloadProgress signal with invalid bytesTotal value for cached content

If we're trying to access some HTTP content which has been cached, we usually get a single QNetworkReply::downloadProgress(), with both the params (bytesReceived and bytesTotal) as 0.

However, sometimes we get an extra QNetworkReply::downloadProgress() signal with bytesReceived as 0 and bytesTotal) as -1!

I think this is incorrect behaviour.

Ideally, both the parameters should reflect the actual content size. Even if this behaviour has been historically present, the -ve bytesTotal value seems clearly wrong.

I'm attaching a small application for testing this behaviour.

This was tested using Nginx. I used the following config section for sending back cache headers (put this in your /etc/nginx/sites-available/default):

location /cached {
    root   /var/www/nginx-default;
    expires max;
    add_header Cache-Control public;
}

Create a cached folder under your webserver's root dir (/var/www/nginx-default in this case) and place the file you want cached there. The pragma above works for requests coming to the cached dir only.