原始套接字

，使用原始套接字需要具有root权限或者特殊的权限（混杂模式要打开），因为它可以绕过操作系统的网络栈。此外，原始套接字通信在不同的操作系统上可能会有一些差异，上述代码在Linux上编译运行正常。
使用原始套接字进行客户端和服务端通信是比较复杂的，因为它需要手动构建和解析网络数据包。以下是一个简单的示例，展示了如何使用原始套接字进行客户端和服务端通信。
服务端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#define PACKET_SIZE 4096

// 计算校验和
unsigned short checksum(unsigned short *buf, int size) {
    unsigned long sum = 0;
    while (size > 1) {
        sum += *buf++;
        size -= 2;
    }
    if (size == 1) {
        sum += *(unsigned char *)buf;
    }
    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    return (unsigned short)(~sum);
}

int main() {
    int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if (sockfd < 0) {
        perror("socket");
        exit(1);
    }

    char packet[PACKET_SIZE];
    struct sockaddr_in client;
    socklen_t client_len = sizeof(client);

    while (1) {
        memset(packet, 0, PACKET_SIZE);
        if (recvfrom(sockfd, packet, PACKET_SIZE, 0, (struct sockaddr *)&client, &client_len) < 0) {
            perror("recvfrom");
            exit(1);
        }

        struct iphdr *ip = (struct iphdr *)packet;
        struct icmphdr *icmp = (struct icmphdr *)(packet + sizeof(struct iphdr));

        if (icmp->type == ICMP_ECHO) {
            printf("Received ICMP Echo Request from %s\n", inet_ntoa(client.sin_addr));

            // 构造ICMP Echo Reply
            icmp->type = ICMP_ECHOREPLY;
            icmp->checksum = 0;
            icmp->checksum = checksum((unsigned short *)icmp, sizeof(struct icmphdr));

            // 修改源和目的IP地址
            ip->saddr = client.sin_addr.s_addr;
            ip->daddr = inet_addr("192.168.1.100");

            // 发送数据包
            if (sendto(sockfd, packet, sizeof(struct iphdr) + sizeof(struct icmphdr), 0, (struct sockaddr *)&client, client_len) < 0) {
                perror("sendto");
                exit(1);
            }

            printf("Sent ICMP Echo Reply to %s\n", inet_ntoa(client.sin_addr));
        }
    }

    close(sockfd);

    return 0;
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>

#define PACKET_SIZE 4096

// 计算校验和
unsigned short checksum(unsigned short *buf, int size) {
    unsigned long sum = 0;
    while (size > 1) {
        sum += *buf++;
        size -= 2;
    }
    if (size == 1) {
        sum += *(unsigned char *)buf;
    }
    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    return (unsigned short)(~sum);
}

int main() {
    int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if (sockfd < 0) {
        perror("socket");
        exit(1);
    }

    char packet[PACKET_SIZE];
    struct sockaddr_in dest;
    dest.sin_family = AF_INET;
    dest.sin_addr.s_addr = inet_addr("192.168.1.100");  // 服务端IP地址

    struct iphdr *ip = (struct iphdr *)packet;
    struct icmphdr *icmp = (struct icmphdr *)(packet + sizeof(struct iphdr));

    // 构造IP头部
    ip->ihl = 5;
    ip->version = 4;
    ip->ttl = 64;
    ip->protocol = IPPROTO_ICMP;
    ip->saddr = inet_addr("192.168.1.200");  // 源IP地址
    ip->daddr = dest.sin_addr.s_addr;

    // 构造ICMP头部
    icmp->type = ICMP_ECHO;
    icmp->code = 0;
    icmp->un.echo.id = getpid();
    icmp->un.echo.sequence = 1;
    icmp->checksum = 0;
    icmp->checksum = checksum((unsigned short *)icmp, sizeof(struct icmphdr));

    // 发送数据包
    if (sendto(sockfd, packet, sizeof(struct iphdr) + sizeof(struct icmphdr), 0, (struct sockaddr *)&dest, sizeof(dest)) < 0) {
        perror("sendto");
        exit(1);
    }

    // 接收数据包
    while (1) {
        char buffer[PACKET_SIZE];
        struct sockaddr_in src;
        socklen_t src_len = sizeof(src);
        if (recvfrom(sockfd, buffer, PACKET_SIZE, 0, (struct sockaddr *)&src, &src_len) < 0) {
            perror("recvfrom");
            exit(1);
        }

        struct iphdr *recv_ip = (struct iphdr *)buffer;
        struct icmphdr *recv_icmp = (struct icmphdr *)(buffer + sizeof(struct iphdr));

        if (recv_icmp->type == ICMP_ECHOREPLY) {
            printf("Received ICMP Echo Reply from %s\n", inet_ntoa(src.sin_addr));
            break;
        }
    }

    close(sockfd);

    return 0;
}