QNetworkReply readAll() gets empty data on finished()

[p3c0]

Hi,

You need to connect to QNAM's "finished()":http://doc.qt.io/qt-5/qnetworkaccessmanager.html#finished signal and not to the QNetworkReply's signal.

[Almer_Cz]

Ok, fine.

But - use either QNetworkReply that is return value from get() function or the one from QNAM's finish slot?

[p3c0]

QNAM’s finish slot.

[Almer_Cz]

Ok, must say i did tried it before, but ok. (as documentation says it is emitted in tandem so it doesn't matter if i use finish() on saved QNetworkReplay or QNetworkAccessManager).

Same result - code now looks like this.

Header:

@class MainWindow : public QMainWindow, public Ui::mainWindow
{
Q_OBJECT

private:
QNetworkAccessManager m_netAccessManager;

public:
MainWindow( QWidget * parent = 0 );
~MainWindow();

private slots:
void httpFinished( QNetworkReply * httpReply );

// menu slots
void updateFonds();

};@

Source:

@MainWindow::MainWindow( QWidget * parent )
: QMainWindow( parent )
{
setupUi(this);
connect( &m_netAccessManager, SIGNAL(finished(QNetworkReply *)), this, SLOT(httpFinished( QNetworkReply *) ) );
};

MainWindow::~MainWindow()
{};

void MainWindow::httpFinished( QNetworkReply * httpReply )
{
// check for error
if ( httpReply->error() )
{
QString form("Download of %1 failed: %2\n");
this->statusbar->showMessage( form.arg(httpReply->url().toEncoded().constData()).arg(qPrintable(httpReply->errorString())) );
} else {
// get http response code
QVariant statusCodeV = httpReply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
QVariant contentLengthV = httpReply->header(QNetworkRequest::ContentLengthHeader);
QVariant redirectionTargetUrl = httpReply->attribute(QNetworkRequest::RedirectionTargetAttribute);

    if ( statusCodeV.toInt() == 302 )
    {
        QNetworkRequest request( redirectionTargetUrl.toUrl() );
        m_netAccessManager.get(request);

        httpReply->deleteLater();
        return;
    }

    qDebug() << statusCodeV.toString();
    qDebug() << contentLengthV.toString();
    qDebug() << httpReply->readAll();
}

httpReply->deleteLater();

};

void MainWindow::updateFonds()
{
QUrl url = QString::fromLocal8Bit("http://www.qt-project.org");
QNetworkRequest request(url);

reply = m_netAccessManager.get( request );

};@

[p3c0]

You might be getting a redirection, to check it, check if redirectionTargetUrl is not null. Remove if ( statusCodeV.toInt() == 302 ).
Try following:
@
qDebug() << httpReply->readAll() //This will provide some useful info.

QVariant redirectionTargetUrl = httpReply->attribute(QNetworkRequest::RedirectionTargetAttribute);

if(!redirectionTargetUrl!=null) {
QUrl newUrl = QUrl(redirectionTargetUrl.toUrl());
QNetworkRequest request(newUrl);
reply = m_netAccessManager..get(request);
}
@

[Almer_Cz]

Hm..ok, so be it (server can send wrong HTTP response code).

@void MainWindow::httpFinished( QNetworkReply * httpReply )
{
// check for error
if ( httpReply->error() )
{
QString form("Download of %1 failed: %2\n");
this->statusbar->showMessage( form.arg(httpReply->url().toEncoded().constData()).arg(qPrintable(httpReply->errorString())) );
} else {
QVariant contentLengthV = httpReply->header(QNetworkRequest::ContentLengthHeader);
QVariant statusCodeV = httpReply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
qDebug() << statusCodeV.toString();
qDebug() << httpReply->readAll();
qDebug() << contentLengthV.toString();

    QVariant redirectionTargetUrl = httpReply->attribute(QNetworkRequest::RedirectionTargetAttribute);

    if ( !redirectionTargetUrl.isNull() )
    {
        QNetworkRequest request( redirectionTargetUrl.toUrl() );
        m_netAccessManager.get(request);

        httpReply->deleteLater();
        return;
    }
}

httpReply->deleteLater();

};@

And i still get (HTTP CODE, and LENGTH)
@"200"
"180900"@

[p3c0]

Well I'm not sure about the problem now. The following code works for me. Try it,
@
ui(new Ui::Dialog), m_qnam()
{
ui->setupUi(this);
connect(&m_qnam,SIGNAL(finished(QNetworkReply*)),
this,SLOT(onFinished(QNetworkReply*)));

QUrl url = QString::fromLocal8Bit("http://www.qt-project.org");
QNetworkRequest request(url);
m_qnam.get(request);

}

void Dialog::onFinished(QNetworkReply* reply)
{
QVariant redirectionTarget =
reply->attribute(QNetworkRequest::RedirectionTargetAttribute);
qDebug() << redirectionTarget;
if (!redirectionTarget.isNull()) {
QUrl newUrl = QUrl(redirectionTarget.toUrl());
QNetworkRequest request(newUrl);
m_qnam.get(request);
} else {
qDebug() << reply->readAll();
}
reply->deleteLater();
}
@

[Almer_Cz]

Can u pls post whole code? (header including)

[p3c0]

Sure its the default template for Qt Widgets Aplication with Dialog as base class. Here's the header
@
#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>
#include <QNetworkAccessManager>
#include <QNetworkReply>

namespace Ui {
class Dialog;
}

class Dialog : public QDialog
{
Q_OBJECT

public:
explicit Dialog(QWidget *parent = 0);
~Dialog();

public slots:
void onFinished(QNetworkReply *reply);

private:
Ui::Dialog *ui;
QNetworkAccessManager m_qnam;
};

#endif // DIALOG_H
@

[p3c0]

And dialog.cpp
@
#include "dialog.h"
#include "ui_dialog.h"

#include <QNetworkRequest>

Dialog::Dialog(QWidget parent) :
QDialog(parent),
ui(new Ui::Dialog), m_qnam()
{
ui->setupUi(this);
connect(&m_qnam,SIGNAL(finished(QNetworkReply)),
this,SLOT(onFinished(QNetworkReply*)));
QUrl url = QString::fromLocal8Bit("http://www.qt-project.org");
QNetworkRequest request(url);
m_qnam.get(request);
}

Dialog::~Dialog()
{
delete ui;
}

void Dialog::onFinished(QNetworkReply* reply)
{
QVariant redirectionTarget = reply->attribute(QNetworkRequest::RedirectionTargetAttribute);
qDebug() << redirectionTarget;
if (!redirectionTarget.isNull()) {
QUrl newUrl = QUrl(redirectionTarget.toUrl());
QNetworkRequest request(newUrl);
m_qnam.get(request);
} else {
qDebug() << reply->readAll();
}
reply->deleteLater();
}
@

[Almer_Cz]

Result:

@'Sample.exe': Loaded 'D:\Dev\qt-prebuild\5.4\msvc2010_opengl\bin\icuin53.dll', Binary was not built with debug information.
'Sample.exe': Loaded 'D:\Dev\qt-prebuild\5.4\msvc2010_opengl\bin\icuuc53.dll', Binary was not built with debug information.
'Sample.exe': Loaded 'D:\Dev\qt-prebuild\5.4\msvc2010_opengl\bin\icudt53.dll', Binary was not built with debug information.
'Sample.exe': Loaded 'D:\Dev\qt-prebuild\5.4\msvc2010_opengl\bin\Qt5Widgetsd.dll', Symbols loaded.
'Sample.exe': Loaded 'D:\Dev\qt-prebuild\5.4\msvc2010_opengl\bin\Qt5Guid.dll', Symbols loaded.
'Sample.exe': Loaded 'D:\Dev\qt-prebuild\5.4\msvc2010_opengl\bin\Qt5Networkd.dll', Symbols loaded.
'Sample.exe': Loaded 'D:\Dev\qt-prebuild\5.4\msvc2010_opengl\plugins\platforms\qwindowsd.dll', Symbols loaded.
'Sample.exe': Loaded 'D:\Dev\qt-prebuild\5.4\msvc2010_opengl\plugins\bearer\qgenericbearerd.dll', Symbols loaded.
'Sample.exe': Loaded 'D:\Dev\qt-prebuild\5.4\msvc2010_opengl\plugins\bearer\qnativewifibearerd.dll', Symbols loaded.
QVariant(QUrl, QUrl("http://qt-project.org/") )
The thread 'Win32 Thread' (0x1148) has exited with code 0 (0x0).
QVariant(Invalid)
@

So, first time it is redirecting - ok, second time is requested url and no output....

[p3c0]

Strange. Which Qt Version?
Anyway, "here's":https://drive.google.com/file/d/0B3rkZH6q1E7oV2MwbkUzTVRrQlE/view?usp=sharing the complete project
Download and check if it works as it is.

[Almer_Cz]

As original post (and tags) says:

Qt 5.1.1 (msvc 2010 version without OGL) and Qt 5.4 (msvc 2010 version with OGL). Downloaded from online installer...

Edit: ur code has same result..

[p3c0]

That's weird. It works perfectly on my system, Ubuntu 14.04. Try removing reply->deleteLater() from onFinished(QNetworkReply* reply) slot.

[Almer_Cz]

Surely. I am not new to Qt even in programming.

I tried even my own compiled versions and same result. I have also tried make it synchronous (after calling get, i entered into event loop and woke up when finished is emit).

The only thing which works is catching readyRead signal and store chunks.

For my perspective, something is reading that buffer before i get it on finish slot. Or closes it or idk...

[p3c0]

But there's nothing in the code that I sent which would cause some abrupt buffer reading. I'm now running out if ideas.
Surely someone other has a better explanation for this behaviour.

[ckakman]

Is it possible, somehow, that the function in which the request is sent is called more than once? If this is the case, than when the slot is called, let's say, for the first QNetworkReply object, you access the second or third instance which has no data yet.

Even if this is not the case, it is not a good idea to keep a member variable to the QNetworkReply object. Connecting the slot to the QNAM::finished(QNetworkReply*) signal is better because you know for sure from which QNetworkReply object to readAll().

[Almer_Cz]

Hi,

didn't see you replied here. I am unable to fix it, even when storing link to QNetworkReply - and check whenever sender() is this reply.

It seems that buffer is somehow read in inner slot, before emitting finish(). and it doesnt matter if it is emitted by QNR or QNAM.

It seems not only me has same problem: "http://qt-project.org/forums/viewthread/51848/":http://qt-project.org/forums/viewthread/51848/

Edit: it seems to have something to do with windows, not code. Maybe some point here?
@'Sample.exe': Loaded 'C:\Windows\SysWOW64\WSHTCPIP.DLL', Cannot find or open the PDB file
QVariant(Invalid)
'Sample.exe': Unloaded 'C:\Windows\SysWOW64\WSHTCPIP.DLL'
@

[tongcb]

@Almer_Cz
i meet the problem to with release version,
but with debug version every this is ok.
Qt 4.8.6
.......

[IanMoone]

@p3c0 said in QNetworkReply readAll() gets empty data on finished():

request

Hello,

I wake up this topic because I had exactly the same issue, because I may found the origin of the problem.

I have those error in the application output (still have them, and I use only http request) :

qt.network.ssl: QSslSocket: cannot resolve SSL_set_alpn_protos
qt.network.ssl: QSslSocket: cannot resolve SSL_CTX_set_alpn_select_cb
qt.network.ssl: QSslSocket: cannot resolve SSL_get0_alpn_selected

This bug report says that those errors are relevant, but I have remove OpenVPN that use OpenSSL and OpenMG but it doesn't seems related.

I am using Qt 5.9.2 on Windows 10 64bits.

I still have few troubles to print the content, some times the print disappear or is cut, but I know that it is good with the debugger or simply because the parsing after is working fine.

QByteArray  content = reply->readAll();

qDebug() << "Status Code: " << statusCode;
qDebug() << "Content length: " << contentLength;
qDebug() << "Content type: " << contentType;
qDebug() << "Redirect target url: " << redirectionTargetUrl;

qDebug() << "Response:\n" << content;                   // No always full ("Response:" text can be cut too???)

PS: Too me it seems to be black magic.

Serie::Serie()
    : mNetworkAccessManager(new QNetworkAccessManager)
{
    QObject::connect(mNetworkAccessManager, &QNetworkAccessManager::finished,
                     this, &Serie::onLoadFinished);
}

Serie::~Serie()
{
    QObject::disconnect(mNetworkAccessManager, &QNetworkAccessManager::finished,
                        this, &Serie::onLoadFinished);
    delete mNetworkAccessManager;
}

void Serie::searchAddictedId()
{
    mNetworkAccessManager->get(QNetworkRequest(QUrl("http://google.fr")));
}

void Serie::onLoadFinished(QNetworkReply* reply)
{
    if (reply->error() != QNetworkReply::NoError)
    {
        qDebug() << reply->errorString();
        reply->deleteLater();
        return;
    }

    int         statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
    int         contentLength = reply->header(QNetworkRequest::ContentLengthHeader).toInt();
    QString     contentType = reply->header(QNetworkRequest::ContentTypeHeader).toString();
    QUrl        redirectionTargetUrl = reply->attribute(QNetworkRequest::RedirectionTargetAttribute).toUrl();
    QByteArray  content = reply->readAll();

    qDebug() << "Status Code: " << statusCode;
    qDebug() << "Content length: " << contentLength;
    qDebug() << "Content type: " << contentType;
    qDebug() << "Redirect target url: " << redirectionTargetUrl;

    qDebug() << "Response:\n" << content.toStdString().c_str();

    if (redirectionTargetUrl.isEmpty() == false)
    {
        qDebug() << "Redirect to: " << redirectionTargetUrl;
        mNetworkAccessManager->get(QNetworkRequest(redirectionTargetUrl));
        reply->deleteLater();
        return;
    }

    QXmlStreamReader    xml;

    xml.addData(content);

    ....

    reply->deleteLater();
}