C++中ICMP协议如何实现

在C++中，要实现ICMP协议，通常需要使用原始套接字（raw sockets）来发送和接收ICMP数据包

#include<iostream>
#include <cstring>
#include <unistd.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/types.h>

const int ICMP_PACKET_SIZE = 64;

// 构建ICMP请求数据包
void build_icmp_packet(char *buffer, int &length) {
    icmphdr *icmp = (icmphdr *) buffer;
    
    // 设置ICMP类型为回显请求
    icmp->type = ICMP_ECHO;
    icmp->code = 0;
    icmp->checksum = 0;
    icmp->un.echo.id = htons(getpid());
    icmp->un.echo.sequence = htons(1);

    // 计算校验和
    int checksum = 0;
    for (int i = 0; i< length / 2; ++i) {
        checksum += ((unsigned short *) buffer)[i];
    }
    while (checksum >> 16) {
        checksum = (checksum & 0xffff) + (checksum >> 16);
    }
    icmp->checksum = ~checksum;
}

int main() {
    int sockfd;
    struct sockaddr_in dest_addr;
    char buffer[ICMP_PACKET_SIZE];
    int length = ICMP_PACKET_SIZE;

    // 创建原始套接字
    if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) < 0) {
        std::cerr << "Failed to create raw socket"<< std::endl;
        return -1;
    }

    // 设置目标地址
    dest_addr.sin_family = AF_INET;
    dest_addr.sin_addr.s_addr = inet_addr("8.8.8.8");

    // 构建ICMP请求数据包
    build_icmp_packet(buffer, length);

    // 发送ICMP请求数据包
    if (sendto(sockfd, buffer, length, 0, (struct sockaddr *) &dest_addr, sizeof(dest_addr)) < 0) {
        std::cerr << "Failed to send ICMP packet"<< std::endl;
        close(sockfd);
        return -1;
    }

    // 接收ICMP响应数据包
    socklen_t addr_len = sizeof(dest_addr);
    if (recvfrom(sockfd, buffer, length, 0, (struct sockaddr *) &dest_addr, &addr_len) < 0) {
        std::cerr << "Failed to receive ICMP packet"<< std::endl;
        close(sockfd);
        return -1;
    }

    // 处理ICMP响应数据包
    icmphdr *icmp = (icmphdr *) buffer;
    if (icmp->type == ICMP_ECHOREPLY) {
        std::cout << "Received ICMP echo reply from " << inet_ntoa(dest_addr.sin_addr)<< std::endl;
    } else {
        std::cerr << "Received unexpected ICMP packet type: " << icmp->type<< std::endl;
    }

    // 关闭套接字
    close(sockfd);

    return 0;
}

这个示例程序首先创建一个原始套接字，然后构建一个ICMP回显请求数据包，并将其发送到指定的目标地址。接着，程序等待接收ICMP响应数据包，并检查其类型是否为回显响应。如果是，则输出相应的信息；否则，输出错误信息。最后，关闭套接字。

注意：运行此程序可能需要root权限，因为原始套接字需要特殊权限。在Linux系统上，可以使用sudo命令运行程序。