CS001432 - Handling an HTTP redirect with QNetworkAccessManager

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ID	CS001432	Creation date	June 16, 2009
Platform	Qt	Tested on devices	5800 XpressMusic
Category	Qt for Symbian	Subcategory	Networking

Keywords (APIs, classes, methods, functions): QNetworkAccessManager, HTTP redirect

Overview

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

Note: In order to use this code, you need to have Qt for S60 installed on your platform.

Preconditions

Install latest Qt for S60 see Qt for S60 - Installation packages
Check this link for installation guide: How to install the package.
Go through this article: Getting started with Qt for S60

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.

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