icmp校验和计算代码

以下是一个简单的 ICMP 校验和计算代码示例：

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

unsigned short checksum(unsigned short *buf, int nwords)
{
    unsigned long sum;
    for (sum = 0; nwords > 0; nwords--)
        sum += *buf++;
    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    return (unsigned short)(~sum);
}

int main(int argc, char *argv[])
{
    struct icmphdr icmp_hdr;
    struct iphdr ip_hdr;
    char packet[IP_MAXPACKET];
    memset(packet, 0, IP_MAXPACKET);

    // 构造 ICMP 报文头
    icmp_hdr.type = ICMP_ECHO;
    icmp_hdr.code = 0;
    icmp_hdr.checksum = 0;
    icmp_hdr.un.echo.id = 1234;
    icmp_hdr.un.echo.sequence = 1;

    // 计算 ICMP 校验和
    icmp_hdr.checksum = checksum((unsigned short *)&icmp_hdr, sizeof(icmp_hdr) / 2);

    // 构造 IP 报文头
    ip_hdr.version = 4;
    ip_hdr.ihl = 5;
    ip_hdr.tos = 0;
    ip_hdr.tot_len = sizeof(struct iphdr) + sizeof(struct icmphdr);
    ip_hdr.id = htons(54321);
    ip_hdr.frag_off = 0;
    ip_hdr.ttl = 255;
    ip_hdr.protocol = IPPROTO_ICMP;
    ip_hdr.check = 0;
    ip_hdr.saddr = inet_addr("192.168.1.1");
    ip_hdr.daddr = inet_addr("192.168.1.2");

    // 将 ICMP 报文头和 IP 报文头拼接起来
    memcpy(packet, &ip_hdr, sizeof(ip_hdr));
    memcpy(packet + sizeof(ip_hdr), &icmp_hdr, sizeof(icmp_hdr));

    // 发送 ICMP 报文
    // ...

    return 0;
}

注意：这只是一个简单的示例代码，实际应用中需要根据具体情况进行修改和完善。