Handling an HTTP redirect with QNetworkAccessManager

Comments

Blankabbs - Doesn't Mutiple Redirection

Great article but this does not handle multiple redirection. For example if page1 will redirect to page2 and page2 to page3, using this will only redirect from page1 to page2 and would not redirect to page3.

blankabbs 13:07, 22 January 2012 (EET)

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Article Metadata

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Code Example

Source file: Media:QNAMRedirect.zip

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Tested with

Devices(s): 5800 XpressMusic

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Compatibility

Platform(s): Qt

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Article

Keywords: QNetworkAccessManager, HTTP redirect

Created: taaidant (16 Jun 2009)

Last edited: hamishwillee (11 Oct 2012)

Overview

This code shows how to handle an HTTP redirect with QNetworkAccessManager.

Header file

/*
 * Copyright (c) 2009 Nokia Corporation
 */
 
#ifndef QNAMREDIRECT_H
#define QNAMREDIRECT_H
 
#include <QtGui/QMainWindow>
#include <QtGui/QFrame>
#include <QtGui/QVBoxLayout>
#include <QtGui/QLabel>
#include <QtGui/QPushButton>
 
#include <QtNetwork/QNetworkAccessManager>
#include <QtNetwork/QNetworkRequest>
#include <QtNetwork/QNetworkReply>
 
#include <QtCore/QPointer>
#include <QtCore/QUrl>
 
class QNAMRedirect : public QMainWindow
{
    Q_OBJECT
 
public:
	QNAMRedirect(QWidget *parent = 0);
	~QNAMRedirect();
 
private slots:
	void doRequest();
	void replyFinished(QNetworkReply* reply);
 
private:
	QPointer<QNetworkAccessManager> _qnam;
	QUrl _originalUrl;
	QUrl _urlRedirectedTo;
 
	QPointer<QLabel> _textContainer;
 
	QNetworkAccessManager* createQNAM();
	QUrl redirectUrl(const QUrl& possibleRedirectUrl,
	                 const QUrl& oldRedirectUrl) const;
};
 
#endif // QNAMREDIRECT_H

Source file

/*
 * Copyright (c) 2009 Nokia Corporation
 */
 
#include "qnamredirect.h"
 
QNAMRedirect::QNAMRedirect(QWidget *parent) : QMainWindow(parent) {
	_qnam = createQNAM();
	_originalUrl = "http://www.wikipedia.org/wiki/URL_redirection";
 
	QVBoxLayout* layout = new QVBoxLayout;
 
#ifdef Q_OS_SYMBIAN
	setStyleSheet("QLabel, QPushButton{ font: 5pt; }");
#endif
 
	_textContainer = new QLabel("Click the button to test URL redirect!");
	_textContainer->setSizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum);
	_textContainer->setAlignment(Qt::AlignCenter);
	_textContainer->setWordWrap(true);
	layout->addWidget(_textContainer);
 
	QPushButton* testButton = new QPushButton("Click here!");
	/* If the button is clicked, we'll do a request. */
	connect(testButton, SIGNAL(clicked()),
	        this, SLOT(doRequest()));
	layout->addWidget(testButton);
 
	QFrame* frame = new QFrame;
	frame->setLayout(layout);
	setCentralWidget(frame);
}
 
QNAMRedirect::~QNAMRedirect() {
	if(_qnam) {
		_qnam->deleteLater();
	}
	if(_textContainer) {
		_textContainer->deleteLater();
	}
}
 
QNetworkAccessManager* QNAMRedirect::createQNAM() {
	QNetworkAccessManager* qnam = new QNetworkAccessManager(this);
	/* We'll handle the finished reply in replyFinished */
	connect(qnam, SIGNAL(finished(QNetworkReply*)),
	        this, SLOT(replyFinished(QNetworkReply*)));
	return qnam;
}
 
void QNAMRedirect::doRequest() {
	QString text = "QNAMRedirect::doRequest doing request to ";
	text.append(this->_originalUrl.toString());
	this->_textContainer->setText(text);
	/* Let's just create network request for this predifned URL... */
	QNetworkRequest request(this->_originalUrl);
	/* ...and ask the manager to do the request. */
	this->_qnam->get(request);
}
 
void QNAMRedirect::replyFinished(QNetworkReply* reply) {
	/*
	 * Reply is finished!
	 * We'll ask for the reply about the Redirection attribute
	 * http://doc.trolltech.com/qnetworkrequest.html#Attribute-enum
	 */
	QVariant possibleRedirectUrl =
	         reply->attribute(QNetworkRequest::RedirectionTargetAttribute);
 
	/* We'll deduct if the redirection is valid in the redirectUrl function */
	_urlRedirectedTo = this->redirectUrl(possibleRedirectUrl.toUrl(),
	                                     _urlRedirectedTo);
 
	/* If the URL is not empty, we're being redirected. */
	if(!_urlRedirectedTo.isEmpty()) {
		QString text = QString("QNAMRedirect::replyFinished: Redirected to ")
		                      .append(_urlRedirectedTo.toString());
		this->_textContainer->setText(text);
 
		/* We'll do another request to the redirection url. */
		this->_qnam->get(QNetworkRequest(_urlRedirectedTo));
	}
	else {
		/*
		 * We weren't redirected anymore
		 * so we arrived to the final destination...
		 */
		QString text = QString("QNAMRedirect::replyFinished: Arrived to ")
		                      .append(reply->url().toString());
		this->_textContainer->setText(text);
		/* ...so this can be cleared. */
		_urlRedirectedTo.clear();
	}
	/* Clean up. */
	reply->deleteLater();
}
 
QUrl QNAMRedirect::redirectUrl(const QUrl& possibleRedirectUrl,
                               const QUrl& oldRedirectUrl) const {
	QUrl redirectUrl;
	/*
	 * Check if the URL is empty and
	 * that we aren't being fooled into a infinite redirect loop.
	 * We could also keep track of how many redirects we have been to
	 * and set a limit to it, but we'll leave that to you.
	 */
	if(!possibleRedirectUrl.isEmpty() &&
	   possibleRedirectUrl != oldRedirectUrl) {
		redirectUrl = possibleRedirectUrl;
	}
	return redirectUrl;
}

Postconditions

You are able to handle HTTP redirects with QNetworkAccessManager.

Supplementary material

• You can test QNAMRedirect with a test application. The application is available for download at Media:QNAMRedirect.zip.

See also

• Creating an HTTP network request in Qt
• QNetworkAccessManager documentation
• QNetworkRequest documentation