qtcpSocket详解

LYOBOYI1232026-02-09 10:42

Qt QTcpSocket 详解

1. QTcpSocket 概述

QTcpSocket 是 Qt 中用于 TCP 网络通信的类，它提供了面向连接的可靠数据传输。

2. 基本使用流程

2.1 创建和连接

cpp

复制代码 
// 创建 TCP Socket
QTcpSocket *socket = new QTcpSocket(this);

// 连接到服务器
socket->connectToHost("example.com", 1234);

// 检查连接状态
if (socket->waitForConnected(3000)) {
    qDebug() << "Connected!";
} else {
    qDebug() << "Connection failed:" << socket->errorString();
}

2.2 信号槽连接

cpp

复制代码 
// 连接相关信号
connect(socket, &QTcpSocket::connected, this, &MyClass::onConnected);
connect(socket, &QTcpSocket::disconnected, this, &MyClass::onDisconnected);
connect(socket, &QTcpSocket::readyRead, this, &MyClass::onReadyRead);
connect(socket, &QTcpSocket::bytesWritten, this, &MyClass::onBytesWritten);
connect(socket, QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::errorOccurred),
        this, &MyClass::onSocketError);

// 或者使用旧式信号槽语法（兼容性更好）
connect(socket, SIGNAL(error(QAbstractSocket::SocketError)),
        this, SLOT(onSocketError(QAbstractSocket::SocketError)));

3. 数据传输

3.1 发送数据

cpp

复制代码 
// 发送文本数据
QString message = "Hello Server!";
QByteArray data = message.toUtf8();  // 转换为 UTF-8 字节数组
socket->write(data);
socket->flush();  // 强制发送缓冲区数据

// 发送二进制数据
QByteArray binaryData;
QDataStream stream(&binaryData, QIODevice::WriteOnly);
stream << qint32(100) << QString("Test") << QByteArray("Data");
socket->write(binaryData);

// 发送带长度前缀的数据（推荐）
void sendData(const QByteArray &data)
{
    QByteArray block;
    QDataStream out(&block, QIODevice::WriteOnly);
    out.setVersion(QDataStream::Qt_5_15);
    
    // 先写入数据长度（4字节）
    out << quint32(0) << data;
    
    // 回到开头，写入实际长度
    out.device()->seek(0);
    out << quint32(block.size() - sizeof(quint32));
    
    socket->write(block);
}

3.2 接收数据

cpp

复制代码 
// 读取所有可用数据
void onReadyRead()
{
    QByteArray data = socket->readAll();
    qDebug() << "Received:" << data;
}

// 按行读取（如果使用换行符分隔）
void onReadyRead()
{
    while (socket->canReadLine()) {
        QByteArray line = socket->readLine();
        qDebug() << "Line:" << line.trimmed();
    }
}

// 读取带长度前缀的数据
void onReadyRead()
{
    static qint32 blockSize = 0;
    
    while (socket->bytesAvailable() > 0) {
        if (blockSize == 0) {
            // 检查是否有足够的数据读取长度前缀
            if (socket->bytesAvailable() < sizeof(quint32))
                return;
            
            QDataStream in(socket);
            in.setVersion(QDataStream::Qt_5_15);
            in >> blockSize;
        }
        
        // 检查完整数据包是否到达
        if (socket->bytesAvailable() < blockSize)
            return;
        
        // 读取完整数据
        QByteArray data = socket->read(blockSize);
        processData(data);
        
        blockSize = 0;  // 重置，准备读取下一个数据包
    }
}

4. 错误处理

cpp

复制代码 
void onSocketError(QAbstractSocket::SocketError socketError)
{
    switch (socketError) {
    case QAbstractSocket::ConnectionRefusedError:
        qDebug() << "Connection refused";
        break;
    case QAbstractSocket::RemoteHostClosedError:
        qDebug() << "Remote host closed connection";
        break;
    case QAbstractSocket::HostNotFoundError:
        qDebug() << "Host not found";
        break;
    case QAbstractSocket::SocketTimeoutError:
        qDebug() << "Connection timeout";
        break;
    case QAbstractSocket::NetworkError:
        qDebug() << "Network error";
        break;
    default:
        qDebug() << "Error:" << socket->errorString();
    }
}

5. 状态管理

cpp

复制代码 
// 检查当前状态
QAbstractSocket::SocketState state = socket->state();
switch (state) {
    case QAbstractSocket::UnconnectedState:
        qDebug() << "Not connected";
        break;
    case QAbstractSocket::HostLookupState:
        qDebug() << "Looking up host...";
        break;
    case QAbstractSocket::ConnectingState:
        qDebug() << "Connecting...";
        break;
    case QAbstractSocket::ConnectedState:
        qDebug() << "Connected";
        break;
    case QAbstractSocket::ClosingState:
        qDebug() << "Closing...";
        break;
}

// 检查是否可读/可写
if (socket->isReadable()) {
    // 可以读取数据
}

if (socket->isWritable()) {
    // 可以写入数据
}

// 获取本地和远程地址信息
QString localAddress = socket->localAddress().toString();
quint16 localPort = socket->localPort();
QString peerAddress = socket->peerAddress().toString();
quint16 peerPort = socket->peerPort();
QString peerName = socket->peerName();

6. 高级功能

6.1 设置 Socket 选项

cpp

复制代码 
// 设置缓冲区大小
socket->setReadBufferSize(1024 * 1024);  // 1MB
socket->setSocketOption(QAbstractSocket::SendBufferSizeSocketOption, 1024 * 1024);

// 设置超时
socket->setSocketOption(QAbstractSocket::LowDelayOption, 1);  // 启用 Nagle 算法

// 设置保持连接
socket->setSocketOption(QAbstractSocket::KeepAliveOption, 1);

// 获取选项值
int bufferSize = socket->socketOption(QAbstractSocket::SendBufferSizeSocketOption).toInt();

6.2 使用代理

cpp

复制代码 
// 设置代理
QNetworkProxy proxy;
proxy.setType(QNetworkProxy::Socks5Proxy);
proxy.setHostName("proxy.example.com");
proxy.setPort(1080);
proxy.setUser("username");
proxy.setPassword("password");
socket->setProxy(proxy);

6.3 SSL/TLS 支持（使用 QSslSocket）

cpp

复制代码 
#include <QSslSocket>
#include <QSslConfiguration>

QSslSocket *sslSocket = new QSslSocket(this);

// 设置 SSL 配置
QSslConfiguration sslConfig = sslSocket->sslConfiguration();
sslConfig.setProtocol(QSsl::TlsV1_2OrLater);
sslSocket->setSslConfiguration(sslConfig);

// 验证证书
connect(sslSocket, QOverload<const QList<QSslError> &>::of(&QSslSocket::sslErrors),
        this, &MyClass::onSslErrors);

// 建立安全连接
sslSocket->connectToHostEncrypted("secure.example.com", 443);

7. 完整客户端示例

cpp

复制代码 
class TcpClient : public QObject
{
    Q_OBJECT
public:
    explicit TcpClient(QObject *parent = nullptr)
        : QObject(parent)
    {
        socket = new QTcpSocket(this);
        
        // 连接信号槽
        connect(socket, &QTcpSocket::connected, this, &TcpClient::onConnected);
        connect(socket, &QTcpSocket::disconnected, this, &TcpClient::onDisconnected);
        connect(socket, &QTcpSocket::readyRead, this, &TcpClient::onReadyRead);
        connect(socket, &QTcpSocket::bytesWritten, this, &TcpClient::onBytesWritten);
        connect(socket, SIGNAL(error(QAbstractSocket::SocketError)),
                this, SLOT(onSocketError(QAbstractSocket::SocketError)));
    }
    
    void connectToServer(const QString &host, quint16 port)
    {
        qDebug() << "Connecting to" << host << ":" << port;
        socket->connectToHost(host, port);
        
        if (!socket->waitForConnected(5000)) {
            qDebug() << "Connection failed:" << socket->errorString();
        }
    }
    
    void sendMessage(const QString &message)
    {
        if (socket->state() == QAbstractSocket::ConnectedState) {
            QByteArray data = message.toUtf8();
            socket->write(data);
            qDebug() << "Sent:" << message;
        }
    }
    
    void disconnectFromServer()
    {
        socket->disconnectFromHost();
        if (socket->state() != QAbstractSocket::UnconnectedState) {
            socket->waitForDisconnected(3000);
        }
    }
    
private slots:
    void onConnected()
    {
        qDebug() << "Connected to server";
        emit connected();
    }
    
    void onDisconnected()
    {
        qDebug() << "Disconnected from server";
        emit disconnected();
    }
    
    void onReadyRead()
    {
        QByteArray data = socket->readAll();
        QString message = QString::fromUtf8(data);
        qDebug() << "Received:" << message;
        emit messageReceived(message);
    }
    
    void onBytesWritten(qint64 bytes)
    {
        qDebug() << "Bytes written:" << bytes;
    }
    
    void onSocketError(QAbstractSocket::SocketError error)
    {
        qDebug() << "Socket error:" << socket->errorString();
        emit errorOccurred(socket->errorString());
    }
    
signals:
    void connected();
    void disconnected();
    void messageReceived(const QString &message);
    void errorOccurred(const QString &errorString);
    
private:
    QTcpSocket *socket;
};

8. 与 QTcpServer 配合使用

cpp

复制代码 
// 服务器端示例
class TcpServer : public QObject
{
    Q_OBJECT
public:
    explicit TcpServer(QObject *parent = nullptr)
        : QObject(parent)
    {
        server = new QTcpServer(this);
        connect(server, &QTcpServer::newConnection, this, &TcpServer::onNewConnection);
    }
    
    bool start(quint16 port)
    {
        if (!server->listen(QHostAddress::Any, port)) {
            qDebug() << "Server could not start:" << server->errorString();
            return false;
        }
        qDebug() << "Server started on port" << port;
        return true;
    }
    
    void stop()
    {
        server->close();
        qDeleteAll(clients);
        clients.clear();
    }
    
private slots:
    void onNewConnection()
    {
        QTcpSocket *clientSocket = server->nextPendingConnection();
        Client *client = new Client(clientSocket, this);
        clients.append(client);
        
        connect(client, &Client::disconnected, this, [this, client]() {
            clients.removeOne(client);
            client->deleteLater();
        });
        
        qDebug() << "New client connected from" 
                 << clientSocket->peerAddress().toString()
                 << ":" << clientSocket->peerPort();
    }
    
private:
    QTcpServer *server;
    QList<Client*> clients;
};

// 客户端处理器
class Client : public QObject
{
    Q_OBJECT
public:
    Client(QTcpSocket *socket, QObject *parent = nullptr)
        : QObject(parent), socket(socket)
    {
        connect(socket, &QTcpSocket::readyRead, this, &Client::onReadyRead);
        connect(socket, &QTcpSocket::disconnected, this, &Client::disconnected);
    }
    
private slots:
    void onReadyRead()
    {
        QByteArray data = socket->readAll();
        // 处理客户端数据
        processData(data);
        
        // 回复客户端
        QString response = "OK";
        socket->write(response.toUtf8());
    }
    
signals:
    void disconnected();
    
private:
    QTcpSocket *socket;
};

9. 最佳实践和注意事项

9.1 数据编码

cpp

复制代码 
// 始终指定编码
QString text = QString::fromUtf8(data);  // 从 UTF-8 解码
QByteArray data = text.toUtf8();         // 编码为 UTF-8

// 或者在 QDataStream 中指定版本
QDataStream stream(&data, QIODevice::ReadOnly);
stream.setVersion(QDataStream::Qt_5_15);  // 指定 Qt 版本以确保兼容性

9.2 超时处理

cpp

复制代码 
// 设置操作超时
if (!socket->waitForConnected(5000)) {
    // 连接超时
}

if (!socket->waitForReadyRead(3000)) {
    // 读取超时
}

if (!socket->waitForBytesWritten(3000)) {
    // 写入超时
}

9.3 线程安全

cpp

复制代码 
// 在多线程环境中使用
class NetworkThread : public QThread
{
    Q_OBJECT
public:
    void run() override {
        QTcpSocket socket;
        socket.connectToHost("example.com", 80);
        // ... 其他操作
    }
};

// 或者使用 moveToThread
QTcpSocket *socket = new QTcpSocket();
socket->moveToThread(workerThread);

9.4 资源清理

cpp

复制代码 
// 正确关闭连接
void closeConnection()
{
    socket->disconnectFromHost();
    if (socket->state() != QAbstractSocket::UnconnectedState) {
        socket->waitForDisconnected(3000);
    }
    socket->close();
    socket->deleteLater();
}

// 在析构函数中清理
~MyClass() {
    if (socket && socket->state() == QAbstractSocket::ConnectedState) {
        socket->disconnectFromHost();
        socket->waitForDisconnected(1000);
    }
    delete socket;
}

10. 常见问题解决

10.1 粘包/拆包问题

cpp

复制代码 
// 解决方案：使用固定长度、分隔符或长度前缀
// 示例：长度前缀法
void sendPacket(const QByteArray &data)
{
    quint32 length = data.size();
    QByteArray packet;
    QDataStream out(&packet, QIODevice::WriteOnly);
    out << length;
    packet.append(data);
    socket->write(packet);
}

QByteArray readPacket()
{
    if (expectedSize == 0) {
        if (socket->bytesAvailable() < sizeof(quint32))
            return QByteArray();
        
        QDataStream in(socket);
        in >> expectedSize;
    }
    
    if (socket->bytesAvailable() < expectedSize)
        return QByteArray();
    
    QByteArray data = socket->read(expectedSize);
    expectedSize = 0;
    return data;
}

10.2 大文件传输

cpp

复制代码 
// 分块传输大文件
void sendFile(const QString &filePath)
{
    QFile file(filePath);
    if (!file.open(QIODevice::ReadOnly))
        return;
    
    // 发送文件信息（大小、文件名等）
    QByteArray header;
    QDataStream out(&header, QIODevice::WriteOnly);
    out << quint64(file.size()) << QFileInfo(file).fileName();
    socket->write(header);
    
    // 分块发送文件内容
    const qint64 chunkSize = 64 * 1024;  // 64KB
    while (!file.atEnd()) {
        QByteArray chunk = file.read(chunkSize);
        socket->write(chunk);
        socket->waitForBytesWritten();
    }
    
    file.close();
}

总结

  1. QTcpSocket 提供完整的 TCP 客户端功能

  2. 使用信号槽机制处理异步事件

  3. 注意数据编码和格式，特别是跨平台时

  4. 正确处理粘包/拆包问题

  5. 实现适当的错误处理和超时机制

  6. 在多线程环境中小心使用，确保线程安全

  7. 及时释放资源，避免内存泄漏

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