C++ Qt QFileSystemWatcher file upload double

Sk1F0x · wrote on 23 Aug 2013, 04:19

I am having issues where the file is being uploaded twice to the server.

I am using the QFileSystemWatcher class from C++ Qt on Windows XP to send a file when the folder changes The files are small (1-12kb).

The application sends the files by scanning the folder whenever it changes (on directoryChanged signal), loop through the files and send the one that I need. The server responds with an xml file that is returned into the same folder for another application to processes it.

Apparently what’s happening is that on some systems there are 2 very fast directoryChanged signals at nearly the same time and there are two very fast file uploads happening.

The server is running Apache and PHP, and there’s a simple MUTEX in place on the PHP side, but I just wanted to get to the root of the problem which seems to be on the Qt side. I'm open to using another class, another library or straight C++.

Here is some code, I stripped all the irrelevant content:
@this->w = new QFileSystemWatcher();
this->w->addPath("C:/POSERA/MaitreD/DATA/INT");

QStringList directoryList = w->directories();
Q_FOREACH(QString directory, directoryList)
qDebug() << "Watching Main Directory name: " << directory << endl;

DirectoryWatcher* dw = new DirectoryWatcher;

QObject::connect(
this->w, SIGNAL(directoryChanged(const QString&)),
dw, SLOT(directoryChanged(const QString&))
);@

Sk1F0x · wrote on 23 Aug 2013, 04:20

and the DirectoryWatcher.cpp:
@DirectoryWatcher::DirectoryWatcher(QWidget* parent) : QWidget(parent)
{
lockSend = false;
}

void DirectoryWatcher::directoryChanged(const QString& str) {

directoryLastChanged = str;

QByteArray byteArray = str.toUtf8();
const char* cString = byteArray.constData();

sendChangedFiles(cString);

}

void DirectoryWatcher::sendChangedFiles(const char* path) {

DIR *dir;
struct dirent *ent;
if ((dir = opendir (path)) != NULL) {

    QString str;

    while ((ent = readdir (dir)) != NULL) {
        str = QString("%1/%2").arg(path, ent->d_name);

        QFileInfo info(str);



        if (lockSend == false && (info.completeSuffix() == "xml" || info.completeSuffix() == "XML") && info.baseName() != "" && !info.baseName().startsWith("REDM") && !info.baseName().startsWith("REFT")) {

            // reset the counter.
            this->resendCounter = 0;

            sendFileAndAccept(str.toUtf8().constData());

        }

    }

    closedir (dir);
} else {
    qDebug() << "Could not open directory" << endl;
}

}

class QNetworkRequest;
class QNetworkReply;
void DirectoryWatcher::sendFileAndAccept(const char* path) {

// increment the resend counter
this->resendCounter++;

QFileInfo fileInfo(path);

QNetworkAccessManager * mgr = new QNetworkAccessManager(this);
connect(mgr,SIGNAL(finished(QNetworkReply*)),this,SLOT(saveResponse(QNetworkReply*)));
connect(mgr,SIGNAL(finished(QNetworkReply*)),mgr,SLOT(deleteLater())); // @todo delete later

QHttpMultiPart *multiPart = new QHttpMultiPart(QHttpMultiPart::FormDataType);

QHttpPart filePart;
filePart.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("text/xml")); // @todo test
filePart.setHeader(QNetworkRequest::ContentDispositionHeader, QVariant("form-data; name=\"someFile\"; filename=\"" + fileInfo.baseName() + ".xml\""));

currentFileSent = fileInfo.baseName();

QFile *file = new QFile&#40;path&#41;;
file->open(QIODevice::ReadOnly);
filePart.setBodyDevice(file);
file->setParent(multiPart); // we cannot delete the file now, so delete it with the multiPart

multiPart->append(filePart);

// POST request
QNetworkReply *reply = mgr->post(QNetworkRequest(QUrl(XXXXXX)), multiPart);

multiPart->setParent(reply); // delete the multiPart with the reply

// lock
lockSend = true;

}

void DirectoryWatcher::saveResponse(QNetworkReply *rep) {

// get the response
QByteArray bts = rep->readAll();
QString str(bts);

// compute new path
QString partName = currentFileSent.mid(1, currentFileSent.length());
QString newPath = QString("%1/A%2.xml").arg(directoryLastChanged, partName);

qDebug() << "new path: " << newPath << endl;

switch (rep->error()) {
    case QNetworkReply::NoError: {
        qDebug() << "NO ERROR" << endl;

        // save response to a file.

        QFile file&#40;newPath&#41;;
        file.open(QIODevice::WriteOnly | QIODevice::Text);
        QTextStream out(&file);
        out << str;

        file.close();

        break;
    }
    default:

// case QNetworkReply::TimeoutError :
// case QNetworkReply::HostNotFoundError :
qDebug() << "NETWORK REPLY ERROR" << endl;
// resend the file if the counter is < 10
if (this->resendCounter < 5) {

            // delay by n sec
            QTime dieTime = QTime::currentTime().addSecs(1);
            while( QTime::currentTime() < dieTime )
                QCoreApplication::processEvents(QEventLoop::AllEvents, 100);

            sendFileAndAccept(this->lastPathSent.toStdString().c_str());
        } else {

            // after 10 attempts, we're probably sure that the network is down
            // save the file somewhere and generate a default one to prevent timeouts.

            qDebug() << "Saving file for later..." << endl;
            if (!saveFileForLater(lastPathSent.toStdString().c_str())) {
                qDebug() << "ERROR SAVING FILE, CHECK IF FOLDER EXISTS AND THE PERMISSIONS." << endl;
            }

            // generate a default one to prevent timeouts.
            qDebug() << "Generate a default file..." << endl;
            // ...
        }

        break;
}

// unlock
lockSend = false;

rep->deleteLater(); // prevent memory leak

}

bool DirectoryWatcher::saveFileForLater(const char* pathToRequestFile) {

QFile file&#40;pathToRequestFile&#41;;
if (!file.open(QIODevice::ReadOnly | QIODevice::Text)) {
    qDebug() << "readonly and text" << endl;
    return false;
}

QString path(pathToRequestFile);
QFileInfo fileinfo(path);

QString newPath = "C:\\data\\offline\\" + fileinfo.fileName();

return file.copy(newPath);

}@