QNetworkAccessManager GET request emits finished signal without start downloading the file

[pratapp123]

We are developing a Qt5 webkit application which loads html5\javascript\css3 pages. Trying to download a file of size 3MB. So created HTTP GET request using QNetworkAccessManager::get() method. But finished signal is emitted immediately with empty data on QNetworkReply::readAll() and there is no network error reported.

This is reported on Windows 7 and Mac 10.9 with Qt 5.2.0 source code build.
Here is sample code:

startDownload:

@ NetworkRequest request(url);
QNetworkReply reply = mNetworkManager->get(request);
QObject::connect(mNetworkManager,SIGNAL(finished(QNetworkReply)),this, SLOT(downloadFinished(QNetworkReply*)));@

In downloadFinished slot:
@if (reply->error() != QNetwrkReply::NoError){
qDebug()<<"download is failed"<< reply->errorString()
}
else {
QFile file(location);
if(file.open(QIODevice::WriteOnly)) {
file.write(reply->readAll());
}
}
reply->deleteLater();@

So I would like to know the possibilities of this failure and potential fixes. I don't have much information on this as i couldn't reproduce the issue. Only few of our customers reported the issue.

Please let me know if any further information needed on the same.

Thanks in advance.

Best Regards,
Pratap

[ChrisW67]

HTTPS URL and no OpenSSL libraries installed?
Proxy required?

[ckakman]

Hi,

I don't have much experience with QNAM but looking at the "NetworkError enum values":http://doc.qt.io/qt-5/qnetworkreply.html#NetworkError-enum that can be returned by QNetworkReply::error(), there is a note saying that NoError is reported when a redirect is necessary. Maybe you shold look into that.

[pratapp123]

Thank you very much for the response.. I believe this could be one of the possibilities since QNAM emits the replyFinished signal with out even start downloading. Please let me know if any other possibilities.

[andre]

If a redirect is needed, you should be able to get that information from the network reply itself. We do something like this:

@
void FileDownloader::requestFinished()
{
QVariant redirectionTarget = m_reply->attribute(QNetworkRequest::RedirectionTargetAttribute);
// Check for redirection.
if (!redirectionTarget.isNull()) {
m_reply->disconnect(this);
m_reply->abort();
m_reply->deleteLater();

    // ...

    m_requestUrl = redirectionTarget.toUrl();

    start();
    return;
}

// handle other cases
}
@

Another possiblity is that you are getting an SSL error. Did you also check that? Connect to the sslErrors signal to find out.

[pratapp123]

Thank you very much for the fix. But It was found that the URL which is used to download is a direct URL. So there won't be any chance of redirects.

I guess QNetworkAccessManager will throw an error QNetworkReply::SslHandshakeFailedError if it is failed with openSSL . We are also building openSSL library and supplying it the application bundle. So I don't think any issue with OpenSSL.

Thank you.

[quote author="Andre" date="1421135968"]If a redirect is needed, you should be able to get that information from the network reply itself. We do something like this:

@
void FileDownloader::requestFinished()
{
QVariant redirectionTarget = m_reply->attribute(QNetworkRequest::RedirectionTargetAttribute);
// Check for redirection.
if (!redirectionTarget.isNull()) {
m_reply->disconnect(this);
m_reply->abort();
m_reply->deleteLater();

    // ...

    m_requestUrl = redirectionTarget.toUrl();

    start();
    return;
}

// handle other cases
}
@

Another possiblity is that you are getting an SSL error. Did you also check that? Connect to the sslErrors signal to find out.[/quote]

[Almer_Cz]

Hi, i have same issue reporeted here:"QNetworkReply readAll() gets empty data on finished()":http://qt-project.org/forums/viewthread/52434/

[quote author="pratapp123" date="1420805703"]
This is reported on Windows 7 and Mac 10.9 with Qt 5.2.0 source code build.
[/quote]

Where did you read this? It seems to be even in Qt 5.4.0 still unresolved. I have suspected, that on both systems GET is read by some internal service (like RPC server or similar).

Or did you manage to fix it?