#ifndef DOWNLOADER_H
#define DOWNLOADER_H

#include <QObject>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QUrl>
#include <QDateTime>
#include <QFile>
#include <QDebug>

class Downloader : public QObject
{
    Q_OBJECT
public:
    explicit Downloader(QObject *parent = 0);
    void doDownload();

signals:
	 void finished() const;

public slots:
    void replyOk(QNetworkReply *reply);

private:
   QNetworkAccessManager *manager;

};

#endif // DOWNLOADER_H

--------------------------

#include "Downloader.h"

Downloader::Downloader(QObject *parent) :
    QObject(parent)
{
}

void Downloader::doDownload()
{
    manager = new QNetworkAccessManager(this);

    connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyOk(QNetworkReply*)));

    manager->get(QNetworkRequest(QUrl("https://www.google.com/killer-robots.txt")));
}

void Downloader::replyOk (QNetworkReply *reply)
{

    if(reply->error())
    {
        qDebug() << "ERROR!";
        qDebug() << reply->errorString();
    }
    else
    {
        qDebug() << reply->header(QNetworkRequest::ContentTypeHeader).toString();
        qDebug() << reply->header(QNetworkRequest::LastModifiedHeader).toDateTime().toString();
        qDebug() << reply->header(QNetworkRequest::ContentLengthHeader).toULongLong();
        qDebug() << reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
        qDebug() << reply->attribute(QNetworkRequest::HttpReasonPhraseAttribute).toString();

        QFile *file = new QFile("C:\\downloaded.txt");
        if(file->open(QFile::Append))
        {
            file->write(reply->readAll());
            file->flush();
            file->close();
        }
        delete file;
    }
    reply->deleteLater();

	emit finished();
}

--------------------------------------

-MainDownload.cpp-

#include Downloader.h

MainDownload::MainDownload()
{
}

void MainDownload::ExecuteDownload()
{
	Downloader *D = new Downloader();
	D->doDownload();
	connect(D, &Downloader::finished, D, &Downloader::deleteLater);
}