- Qt 5.5
- Qt Network
- Loopback Example
- dialog.cpp Example File
- Qt 5.5.1 Reference Documentation

# dialog.cpp Example File

loopback/dialog.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2015 The Qt Company Ltd.
    ** Contact: http://www.qt.io/licensing/
    **
    ** This file is part of the examples of the Qt Toolkit.
    **
    ** $QT_BEGIN_LICENSE:BSD$
    ** You may use this file under the terms of the BSD license as follows:
    **
    ** "Redistribution and use in source and binary forms, with or without
    ** modification, are permitted provided that the following conditions are
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    **   * Redistributions of source code must retain the above copyright
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    **     from this software without specific prior written permission.
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    #include <QtWidgets>
    #include <QtNetwork>

    #include "dialog.h"

    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, SIGNAL(clicked()), this, SLOT(start()));
        connect(quitButton, SIGNAL(clicked()), this, SLOT(close()));
        connect(&tcpServer, SIGNAL(newConnection()),
                this, SLOT(acceptConnection()));
        connect(&tcpClient, SIGNAL(connected()), this, SLOT(startTransfer()));
        connect(&tcpClient, SIGNAL(bytesWritten(qint64)),
                this, SLOT(updateClientProgress(qint64)));
        connect(&tcpClient, SIGNAL(error(QAbstractSocket::SocketError)),
                this, SLOT(displayError(QAbstractSocket::SocketError)));

        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();
        connect(tcpServerConnection, SIGNAL(readyRead()),
                this, SLOT(updateServerProgress()));
        connect(tcpServerConnection, SIGNAL(error(QAbstractSocket::SocketError)),
                this, SLOT(displayError(QAbstractSocket::SocketError)));

        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)
    {
        // callen 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 -= (int)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
    }