udp实现可靠稳定传输的C++代码

UDP是一种无连接的协议，不保证数据的可靠传输。但是我们可以通过编写一些机制来实现UDP的可靠传输。下面是一个简单的UDP可靠传输的C++代码实现：

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <ctime>

using namespace std;

const int MAXSIZE = 1024;
const int TIMEOUT = 3;

struct Packet {
    int seq;    //序列号
    int ack;    //确认号
    int len;    //数据长度
    char data[MAXSIZE]; //数据
};

class UDPReliableSocket {
private:
    int sockfd; //套接字
    struct sockaddr_in serverAddr; //服务器地址
    struct sockaddr_in clientAddr; //客户端地址
    int serverPort; //服务器端口
    int clientPort; //客户端端口
    int seq;    //序列号
    int ack;    //确认号
    char buf[MAXSIZE];  //缓冲区

public:
    UDPReliableSocket(int clientPort, int serverPort, const char* serverIP) {
        this->clientPort = clientPort;
        this->serverPort = serverPort;
        sockfd = socket(AF_INET, SOCK_DGRAM, 0);
        if (sockfd < 0) {
            perror("socket error");
            exit(-1);
        }
        bzero(&clientAddr, sizeof(clientAddr));
        clientAddr.sin_family = AF_INET;
        clientAddr.sin_addr.s_addr = htonl(INADDR_ANY);
        clientAddr.sin_port = htons(clientPort);
        if (bind(sockfd, (struct sockaddr*)&clientAddr, sizeof(clientAddr)) < 0) {
            perror("bind error");
            exit(-1);
        }
        bzero(&serverAddr, sizeof(serverAddr));
        serverAddr.sin_family = AF_INET;
        serverAddr.sin_port = htons(serverPort);
        if (inet_aton(serverIP, &serverAddr.sin_addr) == 0) {
            perror("inet_aton error");
            exit(-1);
        }
        seq = 0;
        ack = 0;
        srand(time(NULL));
    }
    ~UDPReliableSocket() {
        close(sockfd);
    }

    void sendPacket(Packet& packet) {
        packet.seq = seq;   //设置序列号
        packet.ack = ack;   //设置确认号
        int len = sizeof(serverAddr);
        int n = sendto(sockfd, &packet, sizeof(packet), 0, (struct sockaddr*)&serverAddr, len);
        if (n < 0) {
            perror("sendto error");
            exit(-1);
        }
        cout << "send packet " << seq << endl;
        seq++;
    }

    void recvPacket(Packet& packet) {
        int n, fromlen = sizeof(serverAddr);
        while (true) {
            fd_set readfds;
            FD_ZERO(&readfds);
            FD_SET(sockfd, &readfds);
            struct timeval timeout;
            timeout.tv_sec = TIMEOUT;
            timeout.tv_usec = 0;
            int ret = select(sockfd + 1, &readfds, NULL, NULL, &timeout);
            if (ret < 0) {
                perror("select error");
                exit(-1);
            }
            else if (ret == 0) {
                cout << "timeout!" << endl;
                sendPacket(packet);
            }
            else {
                n = recvfrom(sockfd, &packet, sizeof(packet), 0, (struct sockaddr*)&serverAddr, (socklen_t*)&fromlen);
                if (n < 0) {
                    perror("recvfrom error");
                    exit(-1);
                }
                if (rand() % 10 < 7) {
                    if (packet.ack == ack) {
                        ack++;
                        cout << "recv ack " << ack << endl;
                        break;
                    }
                    else {
                        cout << "recv ack " << packet.ack << " not equal to " << ack << endl;
                    }
                }
                else {
                    cout << "packet loss!" << endl;
                }
            }
        }
    }
};

int main() {
    UDPReliableSocket socket(8888, 9999, "127.0.0.1");

    Packet packet;
    while (true) {
        cout << "input message: ";
        fgets(packet.data, MAXSIZE, stdin);
        packet.len = strlen(packet.data) - 1;
        if (packet.len == 0) {
            break;
        }
        socket.sendPacket(packet);
        socket.recvPacket(packet);
    }
    return 0;
}

代码中采用了GBN（Go-Back-N）协议，当客户端发送一个数据包时，服务端会返回一个确认包，如果客户端在规定的时间内未收到确认包，则认为数据包丢失，会重新发送数据包。如果服务端收到了正确的数据包，则会返回正确的确认包。在代码中，为了模拟网络环境不好的情况，我们引入了一定的随机性，有一定几率会出现数据包丢失的情况。