96 TCP服务器功能实现

第二步，实现TcpServer的通信功能。

96.1 实现功能

C:\Users\Minwei\Projects\Qt\TcpServer\tcpserverwindow.h：

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#ifndef TCPSERVERWINDOW_H
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#define TCPSERVERWINDOW_H
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#include <QMainWindow>
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#include <QLabel>
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#include <QTcpServer>
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#include <QTcpSocket>
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QT_BEGIN_NAMESPACE
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namespace Ui { class TcpServerWindow; }
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QT_END_NAMESPACE
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class TcpServerWindow : public QMainWindow
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{
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    Q_OBJECT
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public:
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    TcpServerWindow(QWidget *parent = nullptr);
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    ~TcpServerWindow();
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private slots:
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    void on_m_actListen_triggered();
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    void on_m_actClose_triggered();
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    void on_m_actClear_triggered();
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    void on_m_btnSend_clicked();
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    void on_m_server_newConnection();
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    void on_m_socket_readyRead();
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    void on_m_socket_disconnected();
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    void on_m_socket_stateChanged(
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        QAbstractSocket::SocketState socketState);
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    void on_m_socket_error(
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        QAbstractSocket::SocketError socketError);
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private:
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    Ui::TcpServerWindow *ui;
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    QLabel* m_labListenState;
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    QLabel* m_labSocketState;
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    QLabel* m_labSocketError;
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    QTcpServer* m_server;
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    QTcpSocket* m_socket;
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};
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#endif // TCPSERVERWINDOW_H

C:\Users\Minwei\Projects\Qt\TcpServer\tcpserverwindow.cpp：

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#include <QHostInfo>
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#include <QMetaEnum>
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#include "tcpserverwindow.h"
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#include "ui_tcpserverwindow.h"
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TcpServerWindow::TcpServerWindow(QWidget *parent)
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    : QMainWindow(parent)
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    , ui(new Ui::TcpServerWindow)
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    , m_labListenState(new QLabel("监听状态：关闭"))
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    , m_labSocketState(new QLabel(" 套接字状态："))
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    , m_labSocketError(new QLabel(" 套接字错误："))
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    , m_server(new QTcpServer(this))
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    , m_socket(Q_NULLPTR)
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{
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    ui->setupUi(this);
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    for (QHostAddress address : QHostInfo::fromName(
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        QHostInfo::localHostName()).addresses())
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        if(address.protocol() == QAbstractSocket::IPv4Protocol)
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            ui->m_comboLocalAddr->addItem(address.toString());
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    m_labListenState->setMinimumWidth(196);
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    ui->m_statusBar->addWidget(m_labListenState);
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    m_labSocketState->setMinimumWidth(197);
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    ui->m_statusBar->addWidget(m_labSocketState);
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    m_labSocketError->setMinimumWidth(197);
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    ui->m_statusBar->addWidget(m_labSocketError);
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    connect(m_server, SIGNAL(newConnection()),
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        this, SLOT(on_m_server_newConnection()));
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}
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TcpServerWindow::~TcpServerWindow()
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{
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    delete ui;
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}
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void TcpServerWindow::on_m_actListen_triggered()
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{
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    QHostAddress address(ui->m_comboLocalAddr->currentText());
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    quint16 port = ui->m_editLocalPort->text().toUShort();
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    if (m_server->listen(address, port))
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    {
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        ui->m_editOutput->appendPlainText(QString("监听%1:%2成功").
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            arg(address.toString()).arg(port));
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        m_labListenState->setText(QString("监听状态：%1:%2").
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            arg(address.toString()).arg(port));
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    }
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    else
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        ui->m_editOutput->appendPlainText(QString("监听%1:%2失败").
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            arg(address.toString()).arg(port));
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}
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void TcpServerWindow::on_m_actClose_triggered()
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{
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    m_server->close();
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    ui->m_editOutput->appendPlainText("关闭监听");
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    m_labListenState->setText("监听状态：关闭");
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}
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void TcpServerWindow::on_m_actClear_triggered()
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{
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    ui->m_editOutput->clear();
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}
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void TcpServerWindow::on_m_btnSend_clicked()
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{
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    QByteArray data((ui->m_editSend->text() + "\n").toUtf8());
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    qint64 nbytes = m_socket->write(data);
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    if (nbytes == -1)
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        ui->m_editOutput->appendPlainText("发送失败");
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    else
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        ui->m_editOutput->appendPlainText(QString("向%1:%2发送%3字节：%4").
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            arg(m_socket->peerAddress().toString()).arg(m_socket->peerPort()).
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            arg(nbytes).arg(QString(data).trimmed()));
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}
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void TcpServerWindow::on_m_server_newConnection()
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{
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    if (m_socket != Q_NULLPTR &&
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        m_socket->state() == QAbstractSocket::ConnectedState)
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        m_socket->disconnectFromHost();
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    m_socket = m_server->nextPendingConnection();
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    connect(m_socket, SIGNAL(readyRead()),
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        this, SLOT(on_m_socket_readyRead()));
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    connect(m_socket, SIGNAL(disconnected()),
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        this, SLOT(on_m_socket_disconnected()));
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    connect(m_socket, SIGNAL(stateChanged(QAbstractSocket::SocketState)),
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        this, SLOT(on_m_socket_stateChanged(QAbstractSocket::SocketState)));
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    connect(m_socket, SIGNAL(error(QAbstractSocket::SocketError)),
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        this, SLOT(on_m_socket_error(QAbstractSocket::SocketError)));
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    ui->m_editOutput->appendPlainText(QString("接受%1:%2连接").
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        arg(m_socket->peerAddress().toString()).arg(m_socket->peerPort()));
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    ui->m_btnSend->setEnabled(true);
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}
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void TcpServerWindow::on_m_socket_readyRead()
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{
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    while (m_socket->canReadLine())
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    {
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        QByteArray data = m_socket->readLine();
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        ui->m_editOutput->appendPlainText(QString("从%1:%2接收%3字节：%4").
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            arg(m_socket->peerAddress().toString()).arg(m_socket->peerPort()).
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            arg(data.size()).arg(QString(data).trimmed()));
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    }
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}
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void TcpServerWindow::on_m_socket_disconnected()
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{
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    ui->m_btnSend->setEnabled(false);
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    ui->m_editOutput->appendPlainText(QString("断开%1:%2连接").
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        arg(m_socket->peerAddress().toString()).arg(m_socket->peerPort()));
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    m_socket->deleteLater();
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    m_socket = Q_NULLPTR;
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}
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void TcpServerWindow::on_m_socket_stateChanged(
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    QAbstractSocket::SocketState socketState)
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{
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    m_labSocketState->setText(QString(" 套接字状态：%1").arg(
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        QMetaEnum::fromType<QAbstractSocket::SocketState>().
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        valueToKey(socketState)));
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}
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void TcpServerWindow::on_m_socket_error(
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    QAbstractSocket::SocketError socketError)
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{
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    m_labSocketError->setText(QString(" 套接字错误：%1").arg(
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        QMetaEnum::fromType<QAbstractSocket::SocketError>().
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        valueToKey(socketError)));
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}

96.2 测试验证

运行效果如图所示：

96.3 功能局限

这个版本的TCP服务器只能和一个TCP客户机保持连接并通信。当有新客户机向服务器发起连接时，服务器会断开与之前客户机的连接。这主要体现在服务器程序处理QTcpServer对象发射的newConnection信号的槽函数上：

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...
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TcpServerWindow::TcpServerWindow(QWidget *parent)
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    ...
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{
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    ...
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    connect(m_server, SIGNAL(newConnection()),
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        this, SLOT(on_m_server_newConnection()));
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    ...
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}
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...
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void TcpServerWindow::on_m_server_newConnection()
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{
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    ...
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    if (m_socket != Q_NULLPTR &&
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        m_socket->state() == QAbstractSocket::ConnectedState)
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        m_socket->disconnectFromHost();
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    ...
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    m_socket = m_server->nextPendingConnection();
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    ...
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}
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...