dialog.cpp Example File

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 #include "dialog.h"

 #include <QtNetwork>
 #include <QtWidgets>

 static const int TotalBytes = 50 * 1024 * 1024;
 static const int PayloadSize = 64 * 1024; // 64 KB

 Dialog::Dialog(QWidget *parent)
     : QDialog(parent)
 {
     clientProgressBar = new QProgressBar;
     clientStatusLabel = new QLabel(tr("Client ready"));
     serverProgressBar = new QProgressBar;
     serverStatusLabel = new QLabel(tr("Server ready"));

     startButton = new QPushButton(tr("&Start"));
     quitButton = new QPushButton(tr("&Quit"));

     buttonBox = new QDialogButtonBox;
     buttonBox->addButton(startButton, QDialogButtonBox::ActionRole);
     buttonBox->addButton(quitButton, QDialogButtonBox::RejectRole);

     connect(startButton, &QAbstractButton::clicked, this, &Dialog::start);
     connect(quitButton, &QAbstractButton::clicked, this, &QWidget::close);
     connect(&tcpServer, &QTcpServer::newConnection,
             this, &Dialog::acceptConnection);
     connect(&tcpClient, &QAbstractSocket::connected, this, &Dialog::startTransfer);
     connect(&tcpClient, &QIODevice::bytesWritten,
             this, &Dialog::updateClientProgress);
     connect(&tcpClient, QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::error),
             this, &Dialog::displayError);

     QVBoxLayout *mainLayout = new QVBoxLayout;
     mainLayout->addWidget(clientProgressBar);
     mainLayout->addWidget(clientStatusLabel);
     mainLayout->addWidget(serverProgressBar);
     mainLayout->addWidget(serverStatusLabel);
     mainLayout->addStretch(1);
     mainLayout->addSpacing(10);
     mainLayout->addWidget(buttonBox);
     setLayout(mainLayout);

     setWindowTitle(tr("Loopback"));
 }

 void Dialog::start()
 {
     startButton->setEnabled(false);

 #ifndef QT_NO_CURSOR
     QApplication::setOverrideCursor(Qt::WaitCursor);
 #endif

     bytesWritten = 0;
     bytesReceived = 0;

     while (!tcpServer.isListening() && !tcpServer.listen()) {
         QMessageBox::StandardButton ret = QMessageBox::critical(this,
                                         tr("Loopback"),
                                         tr("Unable to start the test: %1.")
                                         .arg(tcpServer.errorString()),
                                         QMessageBox::Retry
                                         | QMessageBox::Cancel);
         if (ret == QMessageBox::Cancel)
             return;
     }

     serverStatusLabel->setText(tr("Listening"));
     clientStatusLabel->setText(tr("Connecting"));
     tcpClient.connectToHost(QHostAddress::LocalHost, tcpServer.serverPort());
 }

 void Dialog::acceptConnection()
 {
     tcpServerConnection = tcpServer.nextPendingConnection();
     if (!tcpServerConnection) {
         serverStatusLabel->setText(tr("Error: got invalid pending connection!"));
         return;
     }

     connect(tcpServerConnection, &QIODevice::readyRead,
             this, &Dialog::updateServerProgress);
     connect(tcpServerConnection,
             QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::error),
             this, &Dialog::displayError);
     connect(tcpServerConnection, &QTcpSocket::disconnected,
             tcpServerConnection, &QTcpSocket::deleteLater);

     serverStatusLabel->setText(tr("Accepted connection"));
     tcpServer.close();
 }

 void Dialog::startTransfer()
 {
     // called when the TCP client connected to the loopback server
     bytesToWrite = TotalBytes - int(tcpClient.write(QByteArray(PayloadSize, '@')));
     clientStatusLabel->setText(tr("Connected"));
 }

 void Dialog::updateServerProgress()
 {
     bytesReceived += int(tcpServerConnection->bytesAvailable());
     tcpServerConnection->readAll();

     serverProgressBar->setMaximum(TotalBytes);
     serverProgressBar->setValue(bytesReceived);
     serverStatusLabel->setText(tr("Received %1MB")
                                .arg(bytesReceived / (1024 * 1024)));

     if (bytesReceived == TotalBytes) {
         tcpServerConnection->close();
         startButton->setEnabled(true);
 #ifndef QT_NO_CURSOR
         QApplication::restoreOverrideCursor();
 #endif
     }
 }

 void Dialog::updateClientProgress(qint64 numBytes)
 {
     // called when the TCP client has written some bytes
     bytesWritten += int(numBytes);

     // only write more if not finished and when the Qt write buffer is below a certain size.
     if (bytesToWrite > 0 && tcpClient.bytesToWrite() <= 4 * PayloadSize)
         bytesToWrite -= tcpClient.write(QByteArray(qMin(bytesToWrite, PayloadSize), '@'));

     clientProgressBar->setMaximum(TotalBytes);
     clientProgressBar->setValue(bytesWritten);
     clientStatusLabel->setText(tr("Sent %1MB").arg(bytesWritten / (1024 * 1024)));
 }

 void Dialog::displayError(QAbstractSocket::SocketError socketError)
 {
     if (socketError == QTcpSocket::RemoteHostClosedError)
         return;

     QMessageBox::information(this, tr("Network error"),
                              tr("The following error occurred: %1.")
                              .arg(tcpClient.errorString()));

     tcpClient.close();
     tcpServer.close();
     clientProgressBar->reset();
     serverProgressBar->reset();
     clientStatusLabel->setText(tr("Client ready"));
     serverStatusLabel->setText(tr("Server ready"));
     startButton->setEnabled(true);
 #ifndef QT_NO_CURSOR
     QApplication::restoreOverrideCursor();
 #endif
 }