Udp编程 - 客户端和服务端的注意事项

网上有很多教程，他们说发送使用sendto,接收使用recvfrom就可以，确实如此。但是你会用吗?

我们以QT(C++)为例,来使用这个udp实现自发自收的功能(途中我们会用到QThread来开启我们的线程)

服务端(线程)

#include "udpserverthread.h"
#include <QDebug>
#include <string>

UdpServerThread::UdpServerThread(QObject *parent)
    :QThread(parent)
{
    
    
    if(WSAStartup(MAKEWORD(2,2),&wsaData) != 0){
    
    
        qDebug("server init faild");
    }
    isStop = true;
}
//SOCKET serverSocket
//sockaddr_in serverAddr
//int serverLen = sizeof(serverAddr)
void UdpServerThread::run(){
    
    
    qDebug() << "server thread is run";
    uint8_t recv[896];	//接收字符
    isStop = false;	//控制循环标志位
    while(!isStop){
    
    
        int size = recvfrom(serverSocket,(char *)recv,sizeof(recv),
                            0,(SOCKADDR *)&serverAddr,&serverLen); //接收
        if(size > 0){
    
    
            qDebug() << "size:" << size; //打印接收到数据的大小
        }
    }
}

void UdpServerThread::stop(){
    
    
    isStop = true;
}

UdpServerThread::~UdpServerThread(){
    
    

}

我们这里只是一个接收到数据就打印的案例

客户端(线程)

#include "udpclientthread.h"
#include <QDebug>

UdpClientThread::UdpClientThread(QObject *parent)
    :QThread(parent)
{
    
    
    if(WSAStartup(MAKEWORD(2,2),&wsaData) != 0){
    
    
        qDebug("client init faild");
    }
    isStop = true;
}

void UdpClientThread::run(){
    
    
    qDebug() << "client thread is run";
    while (!isStop) {
    
    
    //发送，没什么效果，不用去管
        /*int dataSize = sendto(clientSocket,buffer_char,sizeof(buffer),0,
                              (SOCKADDR *)&clientAddr,clientLen);
        if(dataSize <= 0){
            closesocket(clientSocket);
        }*/
    }
}

void UdpClientThread::stop(){
    
    
    isStop = true;
}

UdpClientThread::~UdpClientThread(){
    
    

}

这里也没什么，就一个线程

主函数

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    
    
    ui->setupUi(this);
	//实例化客户端和服务端(线程)
    clientThread = new UdpClientThread;
    serverThread = new UdpServerThread;
    //信号和槽
    connect(ui->pushButton,&QPushButton::clicked,this,&MainWindow::on_pushButton_network);
    connect(ui->pushButton_testSend,&QPushButton::clicked,this,&MainWindow::on_pushButton_TestSend);
}

void MainWindow::on_pushButton_network(){
    
    
    //client
    clientThread->clientSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    //udpThread->sockWIN: SOCKET sockWIN;
    if(clientThread->clientSocket != INVALID_SOCKET){
    
    //INVALID_SOCKET:检查错误以确保套接字是有效的套接字
        closesocket(clientThread->clientSocket);//关闭套接字
    }
    clientThread->clientSocket = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);
    if(clientThread->clientSocket == INVALID_SOCKET){
    
    //INVALID_SOCKET:检查错误以确保套接字是有效的套接字
        QMessageBox::critical(this, tr("错误"), tr("无法创建 Socket！"));//显示提示
        return;
    }

    clientThread->clientAddr.sin_family = AF_INET;
    clientThread->clientAddr.sin_addr.S_un.S_addr = inet_addr("192.168.1.191");
    clientThread->clientAddr.sin_port = htons(8080);

    clientThread->serverAddr.sin_family = AF_INET;
    clientThread->serverAddr.sin_addr.S_un.S_addr = inet_addr("192.168.1.191");
    clientThread->serverAddr.sin_port = htons(5505);

    if (bind(clientThread->clientSocket, (sockaddr *)&clientThread->clientAddr,
             sizeof(clientThread->clientAddr)) == SOCKET_ERROR)
    {
    
    //绑定出错
        closesocket(clientThread->clientSocket);
        clientThread->clientSocket = INVALID_SOCKET;
        QMessageBox::critical(this, tr("错误"), tr("端口无法打开或被占用！"));
        return;
    }
    //server
    serverThread->serverSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    //udpThread->sockWIN: SOCKET sockWIN;
    if(serverThread->serverSocket != INVALID_SOCKET){
    
    //INVALID_SOCKET:检查错误以确保套接字是有效的套接字
        closesocket(serverThread->serverSocket);//关闭套接字
    }
    serverThread->serverSocket = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);
    if(serverThread->serverSocket == INVALID_SOCKET){
    
    //INVALID_SOCKET:检查错误以确保套接字是有效的套接字
        QMessageBox::critical(this, tr("错误"), tr("无法创建 Socket！"));//显示提示
        return;
    }

    serverThread->clientAddr.sin_family = AF_INET;
    serverThread->clientAddr.sin_addr.S_un.S_addr = inet_addr("192.168.1.191");
    serverThread->clientAddr.sin_port = htons(5505);

    serverThread->serverAddr.sin_family = AF_INET;
    serverThread->serverAddr.sin_addr.S_un.S_addr = inet_addr("192.168.1.191");
    serverThread->serverAddr.sin_port = htons(8080);

    if (bind(serverThread->serverSocket, (sockaddr *)&serverThread->clientAddr,
             sizeof(serverThread->clientAddr)) == SOCKET_ERROR)
    {
    
    //绑定出错
        closesocket(serverThread->serverSocket);
        serverThread->serverSocket = INVALID_SOCKET;
        QMessageBox::critical(this, tr("错误"), tr("端口无法打开或被占用！"));
        return;
    }

    clientThread->start();
    serverThread->start();
}

void MainWindow::on_pushButton_TestSend(){
    
    
//发送
    uint8_t buffer[896];
    uint8_t recv[896];
    buffer[0] = 0x66;
    buffer[1] = 0xff;
    buffer[2] = 0xec;
    char *buff_char = reinterpret_cast<char *>(buffer);
    char *recv_char = reinterpret_cast<char *>(recv);
    int dataSize = sendto(clientThread->clientSocket,buff_char,sizeof(buff_char),0,
                                        (SOCKADDR *)&clientThread->serverAddr,clientThread->serverLen);
    qDebug() << "main test send size:" << dataSize;
//    int size = recvfrom(serverThread->serverSocket,(char *)recv,sizeof(recv),0,
//                        (SOCKADDR *)&serverThread->clientAddr,&serverThread->clientLen);
//    qDebug() << "main test recv size" << size;
}

MainWindow::~MainWindow()
{
    
    
    delete ui;
}

关于信号和槽这里你只需要知道，我们通过一个ui界面的按键，按下按键触发on_pushButton_network(打开线程和网路)和on_pushButton_TestSend(客户端发送固定数据)俩个函数
关于Qt线程 | 关于C++线程

注意点

我们这个接收recvfrom和发送sendto的俩个函数中的内容

1. 参数一: 发送的绑定的是发送的socket套接字; 接收的是接收的socket套接字
2. 参数二: 发送的是发送的数组(缓存);接收的是接收的数组(缓存)
3. 参数三:发送的是发送的数组(缓存)大小;接收的是接收的数组(缓存)大小
4. 参数四:先不用管，默认给它0
5. 参数五: 是一个SOCKADDR。注意发送端是发送端绑定的对方地址和发送端绑定的对方地址的大小;服务端是服务端绑定的对方(可以是发送端)地址和服务端绑定的对方(可以是发送端)地址的大小

在客户端和服务端进行自我绑定的时候，俩个端口要想Tx->Rx,Rx->Tx那样要反正来，不能Tx->Tx,Rx->Rx

即便是有客户端和线程的加护，也不能直接在run()中一直发送数据