What's the best way to delete a QNetworkReply? - c++

Question

I'm writing an embedded RESTful API client using the Qt5 Embedded layer of OpenEmbedded project. I want my client to be able to send a simple async request to notify my server on what's going on and an other scenario is that my client needs to synchronize data from the server.
To do so I wrote two functions, one to send the request and another to get the response. So if I don't care about the response, I only use the first one.
To be able to use the response with the second one, I use a QNetworkReply * as a member of my class. To keep the QNetworkReply alive, I also set the QNetworkAccessManager as a member of my class.
#include <QtNetwork>
class ApiClient : public QObject
{
Q_OBJECT
public:
ApiClient(QObject *parent = 0);
private:
QString host;
QString key;
quint32 replyTimeout;
QNetworkAccessManager manager;
QNetworkReply *reply;
void sendRequest(const QString &method, const QVariantMap &params = QVariantMap());
QVariantMap getResponse() const;
};
The apiclient.cpp file:
#include "apiclient.h"
ApiClient::ApiClient(QObject *parent) : QObject(parent)
{
}
void ApiClient::sendRequest(const QString &method, const QVariantMap &params)
{
QUrl url(QString("%1/%2/").arg(host).arg(method));
QUrlQuery query;
query.addQueryItem("key", key);
if (!params.empty())
{
QMapIterator<QString, QVariant> it(params);
while (it.hasNext())
{
it.next();
query.addQueryItem(it.key(), it.value().toString());
}
}
url.setQuery(query);
qDebug() << "url: " << url.toString();
reply = manager.get(QNetworkRequest(url));
}
QVariantMap ApiClient::getResponse() const
{
if (!reply)
{
qFatal("No request sent!");
}
QTimer timer;
timer.setSingleShot(true);
QEventLoop loop;
connect(&timer, SIGNAL(timeout()), &loop, SLOT(quit()));
connect(reply, SIGNAL(finished()), &loop, SLOT(quit()));
timer.start(replyTimeout);
loop.exec();
if (timer.isActive())
{
timer.stop();
if (reply->error())
{
qFatal("Wrong reply!");
}
int code = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
if (code != 200)
{
qFatal("Invalid server response!");
}
QJsonDocument result = QJsonDocument::fromJson(reply->readAll());
if (result.isNull())
{
qFatal("Invalid JSON!");
}
reply->deleteLater();
return result.object().toVariantMap();
}
disconnect(reply, SIGNAL(finished()), &loop, SLOT(quit()));
reply->abort();
reply->deleteLater();
return QVariantMap();
}
Is that a good way to proceed? How should I manage the QNetworkReply pointer when other signals are emitted (i.e. error(), sslErrors(), ...)?

Answer 1

QNetworkReply will always emit finished(), even when an error occured.
deleteLater() could even be called in a slot connected to that signal, so that part should be fine.
But I would recommend to look into a more asynchronous approach of handling the request, nested event loops like the on in your getResponse() can lead to "interesting" behavior, because you can basically get into re-entrancy situations in a single threaded program.