Junior Junior - 2 months ago 12
C++ Question

QT make app to check if there is an update on sourceforge.net

I want my QT app to check if there is an update on sourceforge.net. For this I use the request: https://sourceforge.net/projects/kidbasic/best_release.json
If you use this link into a browser you will get some json reply.
So, this is the code:

app.pro

QT += core gui
QT += network
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = app
TEMPLATE = app
SOURCES += main.cpp\
mainwindow.cpp
HEADERS += mainwindow.h


main.cpp

#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();

return a.exec();
}


mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QNetworkReply>
#include <QNetworkAccessManager>
#include <QPushButton>


class MainWindow : public QMainWindow
{
Q_OBJECT

public:
MainWindow(QWidget *parent = 0);
~MainWindow();

public slots:
void replyFinished(QNetworkReply* reply);
void checkForUpdate(void);
};

#endif // MAINWINDOW_H


mainwindow.cpp

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
QWidget * wdg = new QWidget(this);
QPushButton *train_button = new QPushButton(wdg);
train_button->setText(tr("check update"));
setCentralWidget(wdg);
QObject::connect(train_button, SIGNAL(released()), this, SLOT(checkForUpdate()));
}

MainWindow::~MainWindow(){ }

void MainWindow::checkForUpdate(void){
QNetworkRequest request;
QNetworkAccessManager *manager = new QNetworkAccessManager(this);
QSslConfiguration config = QSslConfiguration::defaultConfiguration();
config.setProtocol(QSsl::SecureProtocols);
request.setSslConfiguration(config);

request.setUrl(QUrl("https://sourceforge.net/projects/kidbasic/best_release.json"));
//other urls to test
//request.setUrl(QUrl("https://sourceforge.net/projects/openofficeorg.mirror/files/stats/json?start_date=2014-10-29&end_date=2014-11-04"));
//request.setUrl(QUrl("https://ro.gravatar.com/205e460b479e2e5b48aec07710c08d50.json"));
//request.setUrl(QUrl("http://headers.jsontest.com/"));

request.setHeader(QNetworkRequest::ContentTypeHeader, "application/json");
manager->get(request);
connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*)));
}


void MainWindow::replyFinished(QNetworkReply* reply){
qDebug() << reply->error();
if(reply->error() == QNetworkReply::NoError) {
//process json reply
QString strReply = (QString)reply->readAll();
qDebug() << strReply;
} else {
qDebug() << "ERROR";
}
reply->deleteLater();
}


(To make it work without warnings I take
libeay32.dll
and
ssleay32.dll
from https://indy.fulgan.com/SSL/ and put those files in the same folder with my application - because of
https
).

If I try with others urls I got the correct reply. If I use any
surceforge.net
request, I got this error:
QNetworkReply::NetworkError(RemoteHostClosedError)
.

I make the same requests with https://www.hurl.it and everything seems to be ok. The same results I got with https://httpstatus.io/ too.

How I can get a valid reply from
surceforge.net
with QT?

Answer

sourceforge.netseems to be closing the connection when the HTTP request's user agent string is Mozilla/5.0 (this is the default user agent used by QNetworkAccessManager when no QNetworkRequest::UserAgentHeader has been set).

You might have to set a custom user agent before sending the request:

request.setHeader(QNetworkRequest::UserAgentHeader, "App/1.0");
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