Qt Creator is used as the ide for this small app that is being developed
I am attempting to use QNetworkAccessManager to retrieve some information from a website. After the request is 'posted' to the web, the finished() signal is triggered, however the pointer that is passed to the finishedSlot() function does not appear to be pointing to an instantiated object, it is just address of the ponter. The code for the button click that starts the request and the code for the finishedSlot() method is shown below.
In the watch window, I would have expected to see a triangle next to 'reply' that when expaned would show all the data member of QNetworkReply object. Instead it has a single value of #0x80c770 which looks like the pointer address.
I'd appreciate input from anyone who can help me to understand why my pointer doesn't appeart to be pointing the the QNetworkReply object.
void MainWindow::on_btnGetOAuthToken_clicked()
{
QUrl serviceUrl("https://api.ProPhotoWebsite.com/services/oauth/authorize.mg");
QUrl postData;
postData.addQueryItem("method", "ProPhotoWebsite.auth.getRequestToken");
postData.addQueryItem("oauth_consumer_key", "AAAAAAAAAAAAAAAAAAAAAAAA"); //example key
postData.addQueryItem("oauth_nonce",QUuid::createUuid().toString());
postData.addQueryItem("oauth_signature_method","PLAINTEXT");
postData.addQueryItem("oauth_signature","999999999999999999999999999"); //example
postData.addQueryItem("oauth_timestamp", QString::number(QDateTime::currentMSecsSinceEpoch()/1000));
postData.addQueryItem("oauth_version","1.0");
//...
QNetworkRequest request(serviceUrl);
request.setHeader(QNetworkRequest::ContentTypeHeader,
"application/x-www-form-urlencoded");
// Call the webservice
QNetworkAccessManager *nam = new QNetworkAccessManager(this);
connect(nam, SIGNAL(finished(QNetworkReply*)),
SLOT(finishedSlot(QNetworkReply*)));
nam->post(request,postData.encodedQuery());
}
void MainWindow::finishedSlot(QNetworkReply *reply)
{
// Reading attributes of the reply
// e.g. the HTTP status code
QVariant statusCodeV =
reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
// Or the target URL if it was a redirect:
QVariant redirectionTargetUrl =
reply->attribute(QNetworkRequest::RedirectionTargetAttribute);
// see CS001432 on how to handle this
// no error received?
if (reply->error() == QNetworkReply::NoError)
{
QByteArray bytes = reply->readAll(); // bytes
QString string(bytes); // string
ui->lblWarning->setText(string);
}
else
{
// handle errors here
}
// need to dispose reply
delete reply;
}
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 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.
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".
In my App, I have a method to upload files to the server, this works fine.
But when I call this method multiple times at once (like iterating over the result of a chooseFilesDialog) the first 7 (more or less) files are uploaded correctly, the others never get uploaded.
I think this has to be linked with the fact the server doesn't allow more than X connections from the same source maybe?
How can I make sure the upload waits for a free, established connection?
this is my method:
QString Api::FTPUpload(QString origin, QString destination)
{
qint64 timestamp = QDateTime::currentMSecsSinceEpoch();
QUrl url("ftp://ftp."+getLSPro("domain")+destination);
url.setUserName(getLSPro("user"));
url.setPassword(getLSPro("pwd"));
QFile *data = new QFile(origin, this);
if (data->open(QIODevice::ReadOnly))
{
QNetworkAccessManager *nam = new QNetworkAccessManager();
QNetworkReply *reply = nam->put(QNetworkRequest(url), data);
reply->setObjectName(QString::number(timestamp));
connect(reply, SIGNAL(uploadProgress(qint64, qint64)), SLOT(uploadProgress(qint64, qint64)));
return QString::number(timestamp);
}
else
{
qDebug() << "Could not open file to FTP";
return 0;
}
}
void Api::uploadProgress(qint64 done, qint64 total) {
QNetworkReply *reply = (QNetworkReply*)sender();
emit broadCast("uploadProgress","{\"ref\":\""+reply->objectName()+"\" , \"done\":\""+QString::number(done)+"\", \"total\":\""+QString::number(total)+"\"}");
}
First, don't create a QNetworkManager every time you start an upload.
Second, you definitely have to delete everything you new(), otherwise you are left with memory leaks. This includes the QFile, the QNetworkManager AND the QNetworkReply (!).
Third, you have to wait for the finished() signal.
Api::Api() { //in the constructor create the network access manager
nam = new QNetworkAccessManager()
QObject::connect(nam, SIGNAL(finished(QNetworkReply*)), this, SLOT(finished(QNetworkReply*)));
}
Api::~Api() { //in the destructor delete the allocated object
delete nam;
}
bool Api::ftpUpload(QString origin, QString destination) {
qint64 timestamp = QDateTime::currentMSecsSinceEpoch();
QUrl url("ftp://ftp."+getLSPro("domain")+destination);
url.setUserName(getLSPro("user"));
url.setPassword(getLSPro("pwd"));
//no allocation of the file object;
//will automatically be destroyed when going out of scope
//I use readAll() (see further) to fetch the data
//this is OK, as long as the files are not too big
//If they are, you should allocate the QFile object
//and destroy it when the request is finished
//So, you would need to implement some bookkeeping,
//which I left out here for simplicity
QFile file(origin);
if (file.open(QIODevice::ReadOnly)) {
QByteArray data = file.readAll(); //Okay, if your files are not too big
nam->put(QNetworkRequest(url), data);
return true;
//the finished() signal will be emitted when this request is finished
//now you can go on, and start another request
}
else {
return false;
}
}
void Api::finished(QNetworkReply *reply) {
reply->deleteLater(); //important!!!!
}