Question

For three days now I try to come up with a workable code to simply download a file from an Url, but I had my fair share of problems so far and now I am at a point where I can’t see the error.

First of all, my code:

main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    w.downloadArchive(QString("https://bitbucket.org/BattleClinic/evemon/downloads/EVEMon-binaries-1.8.1.4016.zip"), QCoreApplication::applicationDirPath(), QString("evemon.zip"));

    return a.exec();
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QFile>
#include <QFileInfo>
#include <QNetworkAccessManager>
#include <QNetworkReply>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
    bool downloadArchive(QString archiveUrl, QString saveToPath, QString archiveName);

private slots:
    void downloadReadyRead();
    void downloadProgress(qint64 bytesReceived, qint64 bytesTotal);
    void downloadFinished();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QMessageBox>

QNetworkAccessManager manager;
QFile *file;
QNetworkReply *reply;

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->downloadLabel->hide();
    ui->downloadProgressBar->hide();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::downloadReadyRead()
{
    if(file)
    {
        file->write(reply->readAll());
    }
}

void MainWindow::downloadProgress(qint64 bytesReceived, qint64 bytesTotal)
{
    ui->downloadProgressBar->setMaximum(bytesTotal);
    ui->downloadProgressBar->setValue(bytesReceived);
}

void MainWindow::downloadFinished()
{
    downloadReadyRead();
    file->flush();
    file->close();

    if(reply->error())
    {
        QMessageBox::information(this, "Download failed", tr("Failed: %1").arg(reply->errorString()));
    }

    reply->deleteLater();
    reply = NULL;
    delete file;
    file = NULL;

    ui->downloadLabel->hide();
    ui->downloadProgressBar->hide();
}

bool MainWindow::downloadArchive(QString archiveUrl, QString saveToPath, QString archiveName)
{
    QUrl url(archiveUrl);

    if(archiveName.count() <= 0)
    {
        return false;
    }

    if(QFile::exists(saveToPath + "/" + archiveName))
    {
        QFile::remove(saveToPath + "/" + archiveName);
    }

    file = new QFile(saveToPath + "/" + archiveName);

    if(!file->open(QIODevice::WriteOnly))
    {
        delete file;
        file = NULL;
        return false;
    }

    reply = manager.get(QNetworkRequest(url));

    connect(reply, SIGNAL(finished()), this, SLOT(downloadFinished()));
    connect(reply, SIGNAL(readyRead()), this, SLOT(downloadReadyRead()));
    connect(reply, SIGNAL(downloadProgress(qint64,qint64)), this, SLOT(downloadProgress(qint64,qint64)));

    ui->downloadLabel->setText(QString("Downloading %1...").arg(archiveName));
    ui->downloadLabel->show();
    ui->downloadProgressBar->show();

    return true;
}

Downloader.pro

QT       += core gui network

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = Downloader
TEMPLATE = app


SOURCES += main.cpp\
        mainwindow.cpp

HEADERS  += mainwindow.h

FORMS    += mainwindow.ui

In mainwindow.cpp I’m checking for an error and print it to a MessageBox, in case there is one. The first error I had with the current code in the reply was “Unable to init SSL Context”, because I’m requesting data from a https-site. I googled a while and found the solution to be two files called “libeay32.dll” and “ssleay32.dll” I had to copy to the executable’s directory.

There are now no more errors within the reply (at least the MessageBox doesn’t show up)….however, after the downloadFinished Function was executed, the downloaded file has a size of 0 kb, which makes me think, their wasn’t at all a download happening.

I skipped the “if(reply->error())” statement and showed the MessageBox no matter what….I got an: “Unknown Error”. Should an “Unknown Error” not set the “if(reply->error())” statement to true?

There is no problem with permissions either….I tried it as Admin….so no problem at creating the file itself.
Can anyone help me to get that code working?
Do I miss any dlls or an #include?

Thanks

Answer 1

Make sure that it works for a non-ssl file. Then to add ssl support, try following the directions in the answers to this question:

Qt SSL support missing

Also try using qDebug in your code instead of the QMessageBox most of the time. It makes adding debugging lines easier, and it won’t interrupt your code or fill your screen with QMessageBoxes.