I would like to make a class for accessing data via REST API, for example:
class MeteoStation{
int getLatestTemperature();
int getLatestPessure();
private:
QNetworkManager nmng;
}
How could I implement this methods? Usually I was using something like:
int MeteoStation::getLatestTemperature(){
...
QEventLoop eventLoop;
connect(&m_nam,SIGNAL(finished(QNetworkReply*)),&eventLoop,SLOT(quit()));
QNetworkReply *reply = m_nam.get( req );
eventLoop.exec();
reply->readAll()
...
}
But since using inner QEventLoop is not recommended, how should I see to whom the response belong to?
MeteoStation::MeteoStation(){
connect(&nmam, SIGNAL(finished(QNetworkReply*)),
this, SLOT(parseNetworkResponse(QNetworkReply*)));
}
void MeteoStation::parseNetworkResponse( QNetworkReply *finished )
{
QByteArray data = finished->readAll();
...
Yes and it would be nice to have the class thread save. How are you solving that in your code?
How bad is making the call synchronous with:
QNetworkRequest req(url);
QScopedPointer<QNetworkReply> reply(nam.get(req));
QTime timeout= QTime::currentTime().addSecs(10);
while( QTime::currentTime() < timeout && !reply->isFinished()){
QCoreApplication::processEvents(QEventLoop::AllEvents, 100);
}
if (reply->error() != QNetworkReply::NoError) {
qDebug() << "Failure" <<reply->errorString();
}
QByteArray data = reply->readAll();
I've resolved my problem using QCoreApplication::processEvents(). The response is there within ms and I'm able to implement functionality close to libcurl.
QNetworkRequest req(url);
QScopedPointer<QNetworkReply> reply(nam.get(req));
QTime timeout= QTime::currentTime().addSecs(10);
while( QTime::currentTime() < timeout && !reply->isFinished()){
QCoreApplication::processEvents(QEventLoop::AllEvents, 100);
}
if (reply->error() != QNetworkReply::NoError) {
qDebug() << "Failure" <<reply->errorString();
}
QByteArray data = reply->readAll();
The Qt docs should provide all info you need.
You creat a nam, connect the finished signal, send the request.
QNetworkAccessManager *manager = new QNetworkAccessManager(this);
connect(manager, SIGNAL(finished(QNetworkReply*)),
this, SLOT(parseNetworkResponse(QNetworkReply*)));
manager->get(QNetworkRequest(QUrl("http://qt-project.org")));
Detecting to which request a reply belongs should not be too hard. The reply contains the url. It might be different, but not that different:
...but for a variety of reasons it can be different (for example, a
file path being made absolute or canonical).
QUrl QNetworkReply::url() const
Returns the URL of the content downloaded or uploaded. Note that the
URL may be different from that of the original request.
Related
I have started started working with Qt framework and after reading the documentation for Qt5 and some examples across some blogs, I wrote the following program but I does not seem to do the correct job.
I am writing a class for which I need to write a method Login and logout.
For login method, I am writing following code:
void User::login()
{
const QUrl loginUrl = (this->m_url).append("/api/auth/login");
QNetworkRequest loginRequest;
loginRequest.setUrl(loginUrl);
loginRequest.setHeader(QNetworkRequest::ContentTypeHeader, "application/json");
QJsonObject body;
QJsonObject data;
data.insert("userName", this->m_userName);
data.insert("password", this->m_password);
body.insert("data", data);
body.insert("provider", "LDAP");
//loginRequest.setBody(QJsonDocument(body).toJson());
const QByteArray json = QJsonDocument(body).toJson();
QNetworkReply* reply = m_manager.post(loginRequest, QJsonDocument(body).toJson());
while (!reply->isFinished())
{
// wait for the request to complete
}
QByteArray response_data = reply->readAll();
QJsonDocument responseJson = QJsonDocument::fromJson(response_data);
reply->deleteLater();
std::cout << response_data.toStdString() << std::endl;
}
After I call this method in my main function, If I check in fiddler, I cannot see any request made also, the program goes into infinite loop. Can you tell me what is wrong?
Cause
As you say, the program goes into infinite loop. The very one you have created:
while (!reply->isFinished())
{
// wait for the request to complete
}
Simply put, with QNetworkReply* reply = m_manager.post(loginRequest, QJsonDocument(body).toJson()); you do not send a request, but merely declare your wish to do so. Right after that you block the event loop, leaving Qt no chance to fulfill your wish.
Solution
Use signals and slots as intended. Think about team as events and callbacks. A good starting point is the description of QNetworkAccessManager:
QNetworkAccessManager *manager = new QNetworkAccessManager(this);
connect(manager, &QNetworkAccessManager::finished,
this, &MyClass::replyFinished);
How do I read the data from a QNetworkReply response from a specific URL before QWebPage does? but when the finished() signal is emited the reply is read already by QWebPage, so connect readyRead() or call reply->readAll() return nothing. I tried overload acceptNavigationRequest() method in my own QWebPage class, something like this:
bool webPage::acceptNavigationRequest(QWebFrame *frame, const QNetworkRequest &request, QWebPage::NavigationType type)
{
//qDebug() << "filename = " << request.rawHeader("content-disposition");
if(request.url().path() == QStringLiteral("download.php"))
{
QNetworkReply *reply = networkAccessManager()->get(request);
QFile file;
file.setFileName(filename);
if(!file.open(QIODevice::ReadWrite))
{
/* handle error */
}
file.write(reply->readAll());
file.close();
return false;
}
But I couldn't manage to reply work... the returned reply is invalid (don't even return a http status code, I know it means the http request sent is invalid but i don't know why).
Different approachs to solve this are welcome!
Using the finished slot with a lambda expression, you can do this: -
QNetworkReply* reply = networkAccessManager()->get(request);
connect(reply, &QNetworkReply::finished, [=]() {
if(reply->error() == QNetworkReply::NoError)
{
QByteArray response = reply->readAll();
// do something with the data...
}
else // handle error
{
qDebug(pReply->errorString());
}
});
I’m trying to implement a simple version checker below.
I’m getting a zero error code reading the file, but the file
contents show up blank. You can access the file via browser,
permissions are ok.
void check_version()
{
QNetworkAccessManager *nam = new QNetworkAccessManager();
QUrl data_url("http://www.example.com/version.txt");
QNetworkRequest req(data_url);
QNetworkReply *reply = nam->get(req);
QByteArray data = reply->readAll() ;
QString s1(data);
int err = reply->error();
QString s2 = QString::number(err);
delete reply;
delete nam;
QMessageBox::critical(0, "",s1+" "+s2,QMessageBox::Cancel);
}
I gather the problem is that I need to wait to read until the get is finished, so I need a signal and a slot: the signal tells the slot to read the data.
pseudocode:
QObject::connect(&rep, SIGNAL( rep is finished ),
QByteArray newver , SLOT( reply->readAll() ));
How do I set up a signal/slot for my task?
You're right, you have to wait until the get() is "finished" in order to obtain the whole response with a call to readAll().
Following a working example to start with:
// ...
QNetworkAccessManager *nam = new QNetworkAccessManager();
QUrl data_url("http://www.example.com/version.txt");
QNetworkReply* reply = nam->get(QNetworkRequest(data_url));
QEventLoop eventLoop;
QObject::connect(reply, SIGNAL(finished()), &eventLoop, SLOT(quit()));
eventLoop.exec();
if (reply->error() != QNetworkReply::NoError)
{
// Something went wrong. Error can be retrieved with: reply->error()
}
else
{
// Call reply->readAll() and do what you need with the data
}
// ...
This example will block until the reply is ready. If you need an asynchronous behavior you can just connect the signal finished() to a custom slot and check for error and/or read there. I do not recommend to connect the signal finished() directly to readAll() because "sometimes errors happen".
I'm trying to have my application download a file from a URL, typically an EXE or a Jar, not that this should change much though. I have this all running in a thread, but I don't think that will make a difference (if it does let me know).
So Do_Download is my function that creates the manager, sets the URL and request, and performs get. I then try to connect the finished signal to the slot the will write the file.
void DownloadManager::Do_Download() {
QNetworkAccessManager *netManager = new QNetworkAccessManager(this);
QUrl url(install_mirror); //istall_mirror is the URL provided by user
QNetworkRequest req(url);
QNetworkReply *reply = netManager->get(req);
connect(reply, SIGNAL(finished()), this, SLOT(writeData()));
}
My writeData function checks for errors, and if there are no errors it writes the data to file.
void DownloadManager::writeData() {
QNetworkReply *reply = qobject_cast<QNetworkReply*>(sender());
if (reply) {
if (reply->error() == QNetworkReply::NoError) {
QFile file(location);
if(file.open(QIODevice::WriteOnly)) {
file.write(reply->readAll());
} else {
errorMessage = "Error writing downloaded file for mirror installation";
}
} else {
//get http status code
int httpStatus = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
errorMessage = "HTTP Error code while downloading from mirror: " + httpStatus;
}
reply->deleteLater();
} else {
errorMessage = "Error downloading file from installation mirror";
}
}
The problem being there is no data being written. It just creates a 0Kb file.
I tried adding a download progress slot so I could see what was going on recieving the data. So I added this to my Do_Download method.
connect(reply, SIGNAL(downloadProgress(qint64,qint64)), this, SLOT(DL_Progress(qint64,qint64)));
void DownloadManager::DL_Progress(qint64 recieved, qint64 total) {
std::cout << recieved << " / " << total << endl;
}
The output displays one time as 0 / 01
What am I doing wrong?
The only problem I see in your code is you are not waiting for the download to be finished. The NetworkRequest object would be destructed at the end of function call.
So, I would rewrite Do_Download like this (QEventLoop syncronizes the network request):
void DownloadManager::Do_Download() {
QEventLoop eventLoop;
QNetworkAccessManager *netManager = new QNetworkAccessManager(this);
QUrl url(install_mirror); //istall_mirror is the URL provided by user
QNetworkRequest req(url);
QNetworkReply *reply = netManager->get(req);
connect(reply, SIGNAL(finished()), &eventLoop, SLOT(quit()));
eventLoop.exec();
writeData(reply);
}
I know that in version 4.8 each http request gets its own thread to run.
I'm doing a links checker app that does a lot of http requests in a while loop and I notice in the windows task manager that my app is using more than 1600 threads over time and the number never goes down, only up until it crashes the app. (I'm guessing that is the cause.)
My question is, does QNetworkAccessManager have an option to use thread pool?
Or does it have an option to clean its threads after it finishes its http request?
This is the main loop:
while(!rpm_urlStack->isEmpty())
{
QString url = rpm_urlStack->top();
//define the reply
QNetworkReply *reply;
rpm_urlStack->pop();
QString urlForReq(url);
bool returnVal = true;
QNetworkRequest request;
request.setUrl(QUrl(urlForReq));
request.setRawHeader("User-Agent", USER_AGENT.toUtf8());
request.setRawHeader("Accept-Charset", "ISO-8859-1,utf-8;q=0.7,*;q=0.7");
request.setRawHeader("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");
request.setRawHeader("Accept-Language", "en-us,en;q=0.5");
request.setRawHeader("Connection", "Keep-Alive");
QEventLoop loop;
reply = m_networkManager->get(request);
connect(reply, SIGNAL(finished()), &loop, SLOT(quit()));
loop.exit();
if(!loop.isRunning()) {
loop.exec();
}
RequestFinishedHandler(reply);
// this is how I delete the reply object
delete reply;
}
RequestFinishedHandler(QNetworkReply *reply)
{
if (reply->error() > 0) {
QNetworkReply::NetworkError networkError = reply->error();
QString err = reply->errorString();
} else {
QVariant vStatusCodeV = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
QMutexLocker lock(_pMutex); // _pMutex defined as class member
char *buffer;
buffer = getCurrentDateTime();
QTextStream out(m_file);
out << buffer << " " << _sCurrentUrl << "\n";
lock.unlock();
if(vStatusCodeV.toInt() == 200) {
QString ApiResponse;
QByteArray data;
data=reply->readAll();
ApiResponse.append(QString::fromUtf8(data));
}
}
}
It appears that to be effective, the deleteLater method must be called from within an event loop, which must regain control of execution to handle garbage collection.
Maybe you should refactor your code to have the event loop replace your while loop. Alternatively, since you're not using the finished slot to process the reply, perhaps you can delete the reply directly at the end of the RequestFinishedHandler function.