[Qt-interest] QNetworkAccessManager and FTP woes

[Markus Goetz]

ext Robert Caldecott wrote:
> I am trying to upload files to an FTP server using
> QNetworkAccessManager (instead of using QFtp as recommended by the Qt
> documentation.)  I am using Qt 4.5 on Windows XP and am attempting to
> upload files to an IIS FTP server.
>
> The problem I am having is that sometimes the upload just stops - no
> 'error' or 'finished' signal is sent - the process just doesn't
> complete.  This seems to happen 90% of the time if the file size I am
> uploaded exceeds 16Kb.
>   This is driving me nuts and I wonder if using
> QNetworkAccessManager for FTP uploads was the right decision.  Note
> also that I am trying to upload binary files.
>
> Here is some sample code:
>
>   QNetworkAccessManager* manager = new QNetworkAccessManager(this);
>   QFile* file = new QFile("c:/tmp/somefile.exe");
>   file->open(QIODevice::ReadOnly);
>
>   QNetworkReply* reply =
> manager->put(QNetworkRequest(QUrl("ftp://server/folder/somefile.exe")),
> file);
>   connect(reply, SIGNAL(uploadProgress(qint64,qint64)), this,
> SLOT(uploadProgress(qint64,qint64)));
>   connect(reply, SIGNAL(error(QNetworkReply::NetworkError)), this,
> SLOT(error(QNetworkReply::NetworkError)));
>   connect(reply, SIGNAL(finished()), this, SLOT(finished()));
>   
Can you send a complete minimal example? Maybe you are accidently 
delete()ing the upload file object somewhere?
> I have added some debug output to my slots and I usually see something
> like this:
>
>   uploadProgress  16384   2490368
>   uploadProgress  32768   2490368
>
> i.e. In this case am trying to PUT a 2490368 byte file.  The above is
> all I see - no finished or error slots are called - the process just
> seems to stall.
>
> Does anyone know what I am doing wrong before I try QFtp instead?  Is
> IIS going to be a problem (I hope not!!!).  Does the Qt 4.6 RC fix
> anything in this area?
>
> I traced into the core Qt code and the problem seems to be in QFtp.cpp
> - the QFtpDTP::writeData() function contains the following code:
>
>   qint64 read = data.dev->read(buf, blockSize);
>
> And sometimes this returns 0 - for no reason that I can see.  This
> scuppers the upload process.
>   
Strange.
> I have also tried reading the entire file into a QByteArray and using
> the alternative QNetworkAccessManager::put function but I get the same
> problem. 
For a QByteArray it should write the whole array to the socket at once, 
e.g. the stalling read() calls should be no problem:
socket->write(data.ba->data(), data.ba->size());
Or were you using a QBuffer (which is a QIODevice) to wrap the 
QByteArray and sent that?

Markus