Qt UDP 网络编程详解
一、UDP 协议核心特性
无连接协议：通信前无需建立连接
面向数据报：每次发送/接收独立的数据包
轻量高效：头部开销小（仅8字节）
不可靠传输：
不保证数据包顺序
不保证数据包到达
无自动重传机制
适用场景：
实时音视频传输
DNS 查询
网络状态广播
游戏状态同步
二、Qt UDP 核心类
类名 | 功能说明 |
|---|---|
QUdpSocket | UDP 数据报套接字 |
QHostAddress | IP 地址封装 |
QNetworkDatagram | 数据报容器（Qt 5.8+） |
三、UDP 发送端实现
#include <QUdpSocket>
#include <QDebug>class UdpSender : public QObject {Q_OBJECT
public:explicit UdpSender(QObject *parent = nullptr) : QObject(parent), udpSocket(new QUdpSocket(this)) {// 设置广播选项udpSocket->setSocketOption(QAbstractSocket::MulticastTtlOption, 1);}// 发送广播消息void broadcastMessage(const QString &message) {QByteArray datagram = message.toUtf8();// 发送到广播地址qint64 bytesSent = udpSocket->writeDatagram(datagram,QHostAddress::Broadcast, // 255.255.255.25545454);if (bytesSent == -1) {qWarning() << "Failed to send datagram:" << udpSocket->errorString();} else {qInfo() << "Broadcasted message:" << message << "to" << QHostAddress::Broadcast.toString();}}// 发送到指定地址void sendTo(const QString &message, const QHostAddress &address, quint16 port) {QByteArray datagram = message.toUtf8();udpSocket->writeDatagram(datagram, address, port);}private:QUdpSocket *udpSocket;
};
四、UDP 接收端实现
#include <QUdpSocket>
#include <QNetworkDatagram>class UdpReceiver : public QObject {Q_OBJECT
public:explicit UdpReceiver(QObject *parent = nullptr) : QObject(parent), udpSocket(new QUdpSocket(this)) {// 绑定到端口接收数据if (!udpSocket->bind(45454, QUdpSocket::ShareAddress)) {qCritical() << "Bind failed:" << udpSocket->errorString();return;}qInfo() << "Listening on UDP port 45454...";// 连接数据到达信号connect(udpSocket, &QUdpSocket::readyRead, this, &UdpReceiver::processPendingDatagrams);}private slots:void processPendingDatagrams() {while (udpSocket->hasPendingDatagrams()) {// 使用QNetworkDatagram获取元数据（Qt 5.8+）QNetworkDatagram datagram = udpSocket->receiveDatagram();if (!datagram.isValid()) continue;QByteArray data = datagram.data();QHostAddress senderAddress = datagram.senderAddress();quint16 senderPort = datagram.senderPort();qInfo() << "Received from" << senderAddress.toString() << ":" << senderPort << "=>" << data;// 示例：处理特定命令if (data.startsWith("PING")) {sendResponse(senderAddress, senderPort);}}}void sendResponse(const QHostAddress &addr, quint16 port) {udpSocket->writeDatagram("PONG", addr, port);}private:QUdpSocket *udpSocket;
};
五、关键技术解析
绑定模式选项
// 常用绑定选项
udpSocket->bind(port, QUdpSocket::ShareAddress); // 允许多个套接字绑定同一端口
udpSocket->bind(port, QUdpSocket::ReuseAddressHint); // 地址重用
udpSocket->bind(QHostAddress::AnyIPv4); // 监听所有IPv4接口
数据报读写方法对比
// 传统方法（Qt 4/5）
char buffer[1024];
qint64 size = udpSocket->pendingDatagramSize();
udpSocket->readDatagram(buffer, size, &senderAddr, &senderPort);// 现代方法（Qt 5.8+）
QNetworkDatagram datagram = udpSocket->receiveDatagram();
if (datagram.isValid()) {QByteArray data = datagram.data();// 使用datagram.senderAddress()等获取元数据
}
广播与组播
// IPv4 广播
udpSocket->writeDatagram(data, QHostAddress::Broadcast, port);// IPv6 组播
QHostAddress groupAddress("FF02::1"); // 所有节点组播地址
udpSocket->joinMulticastGroup(groupAddress);
udpSocket->writeDatagram(data, groupAddress, port);
六、高级应用场景
实现服务发现协议
// 服务端广播服务信息
void ServiceDiscoverer::broadcastService() {QJsonObject serviceInfo{{"name", "File Server"},{"type", "_fileserver._tcp"},{"port", 8080},{"ip", getLocalIP()}};QByteArray datagram = QJsonDocument(serviceInfo).toJson();udpSocket->writeDatagram(datagram, QHostAddress::Broadcast, 5353);
}// 客户端监听服务
void ServiceBrowser::startDiscovery() {udpSocket->bind(5353, QUdpSocket::ShareAddress);connect(udpSocket, &QUdpSocket::readyRead, [this]() {while (udpSocket->hasPendingDatagrams()) {QNetworkDatagram datagram = udpSocket->receiveDatagram();QJsonObject service = QJsonDocument::fromJson(datagram.data()).object();emit serviceDiscovered(service);}});
}
实现简单可靠传输
// 带序列号的数据报
struct ReliableDatagram {quint32 sequence;QByteArray payload;
};// 发送端
void sendReliable(const QByteArray &data) {static quint32 seq = 0;ReliableDatagram dg{++seq, data};QByteArray datagram;QDataStream out(&datagram, QIODevice::WriteOnly);out << dg.sequence << dg.payload;udpSocket->writeDatagram(datagram, receiverAddr, port);// 启动重传定时器QTimer::singleShot(200, [this, seq, datagram]() {if (!acknowledged.contains(seq)) {udpSocket->writeDatagram(datagram, receiverAddr, port); // 重传}});
}// 接收端
void processDatagram() {QNetworkDatagram dg = udpSocket->receiveDatagram();ReliableDatagram packet;QDataStream in(dg.data());in >> packet.sequence >> packet.payload;// 发送ACKQByteArray ack;QDataStream ackOut(&ack, QIODevice::WriteOnly);ackOut << packet.sequence;udpSocket->writeDatagram(ack, dg.senderAddress(), dg.senderPort());// 处理数据if (packet.sequence > lastSequence) {processPayload(packet.payload);lastSequence = packet.sequence;}
}
七、调试与优化技巧
网络诊断命令
# 查看UDP端口监听
netstat -anu# 测试UDP连通性
nc -u <host> <port>
性能优化
// 增大发送缓冲区
udpSocket->setSocketOption(QAbstractSocket::SendBufferSizeSocketOption, 1024 * 1024);// 禁用拥塞控制 (实时应用)
udpSocket->setSocketOption(QAbstractSocket::LowDelayOption, 1);// 使用原始套接字 (需要权限)
if (udpSocket->bind(QHostAddress::Any, port, QUdpSocket::DontShareAddress)) {udpSocket->setSocketOption(QAbstractSocket::SendBufferSizeSocketOption, 0);
}
错误处理
connect(udpSocket, &QAbstractSocket::errorOccurred, [](QAbstractSocket::SocketError error) {switch(error) {case QAbstractSocket::AddressInUseError:qCritical() << "Port already in use";break;case QAbstractSocket::DatagramTooLargeError:qWarning() << "Datagram exceeds MTU size";break;case QAbstractSocket::NetworkError:qWarning() << "Network error occurred";break;default:qWarning() << "UDP error:" << error;}
});
八、完整示例：局域网设备发现
// 设备发现广播器
class DeviceBroadcaster : public QObject {
public:DeviceBroadcaster() {connect(&timer, &QTimer::timeout, this, &DeviceBroadcaster::broadcast);timer.start(5000); // 每5秒广播一次}private:void broadcast() {QJsonObject deviceInfo{{"name", QSysInfo::machineHostName()},{"os", QSysInfo::prettyProductName()},{"ip", getLocalIP()},{"timestamp", QDateTime::currentSecsSinceEpoch()}};QByteArray datagram = QJsonDocument(deviceInfo).toJson();QUdpSocket socket;socket.writeDatagram(datagram, QHostAddress::Broadcast, 37020);}QString getLocalIP() {foreach (const QHostAddress &address, QNetworkInterface::allAddresses()) {if (address.protocol() == QAbstractSocket::IPv4Protocol && address != QHostAddress::LocalHost) {return address.toString();}}return "127.0.0.1";}QTimer timer;
};// 设备发现监听器
class DeviceListener : public QObject {
public:DeviceListener() {udpSocket.bind(37020, QUdpSocket::ShareAddress);connect(&udpSocket, &QUdpSocket::readyRead, this, &DeviceListener::processDatagrams);}signals:void deviceFound(const QJsonObject &deviceInfo);private:void processDatagrams() {while (udpSocket.hasPendingDatagrams()) {QNetworkDatagram datagram = udpSocket.receiveDatagram();QJsonObject device = QJsonDocument::fromJson(datagram.data()).object();// 过滤过期的广播qint64 now = QDateTime::currentSecsSinceEpoch();if (now - device["timestamp"].toInt() < 10) {emit deviceFound(device);}}}QUdpSocket udpSocket;
};
最佳实践：对于需要可靠传输的场景，可在应用层实现ACK机制和序列号；对于实时流媒体，可结合RTP协议；在公网环境中使用时，需注意NAT穿透问题（可借助STUN/TURN服务器）。