用c语言写一段ipv6数据包分片代码

以下是一段基于C语言实现IPv6数据包分片的代码。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>

// 定义IPv6头部结构体
typedef struct ipv6_header {
    uint32_t version_traffic_flow;  // 版本号、流量标记
    uint16_t payload_length;        // 负载长度
    uint8_t next_header;            // 下一个头部类型
    uint8_t hop_limit;              // 跳数限制
    uint8_t source_addr[16];        // 源地址
    uint8_t dest_addr[16];          // 目标地址
} ipv6_header_t;

// 定义IPv6分片头部结构体
typedef struct ipv6_fragment_header {
    uint8_t next_header;            // 下一个头部类型
    uint8_t reserved;               // 保留字段
    uint16_t fragment_offset;       // 分片偏移
    uint32_t identification;        // 标识符
} ipv6_fragment_header_t;

// 分片函数
int ipv6_fragment(ipv6_header_t *ipv6_hdr, uint8_t *payload, uint16_t payload_len, uint16_t mtu) {
    uint16_t offset = 0;    // 记录偏移量
    uint16_t last_frag_size = 0;    // 记录最后一个分片的大小
    uint32_t identification = rand();    // 随机生成标识符

    while (payload_len > 0) {
        ipv6_fragment_header_t fragment_hdr = {
            .next_header = ipv6_hdr->next_header,
            .reserved = 0,
            .fragment_offset = (offset >> 3),    // 偏移量以8字节为单位
            .identification = identification
        };
        uint16_t frag_size = (mtu - sizeof(ipv6_header_t) - sizeof(ipv6_fragment_header_t));    // 计算分片大小
        if (frag_size > payload_len) {
            frag_size = payload_len;
            last_frag_size = frag_size;
        }
        ipv6_hdr->payload_length = htons(frag_size + sizeof(ipv6_fragment_header_t));    // 更新负载长度

        // 构造分片数据包
        uint8_t *fragment_pkt = (uint8_t *)malloc(mtu * sizeof(uint8_t));
        memcpy(fragment_pkt, ipv6_hdr, sizeof(ipv6_header_t));
        memcpy(fragment_pkt + sizeof(ipv6_header_t), &fragment_hdr, sizeof(ipv6_fragment_header_t));
        memcpy(fragment_pkt + sizeof(ipv6_header_t) + sizeof(ipv6_fragment_header_t), payload + offset, frag_size);

        // TODO: 发送分片数据包

        offset += frag_size;
        payload_len -= frag_size;
        free(fragment_pkt);
    }

    return last_frag_size;
}

int main() {
    // 构造IPv6数据包
    ipv6_header_t ipv6_hdr = {
        .version_traffic_flow = 0x60000000,    // 版本号: 6，流量标记: 0
        .payload_length = 0,
        .next_header = 17,    // 下一个头部类型: UDP
        .hop_limit = 64,    // 跳数限制: 64
        .source_addr = {0x20, 0x01, 0x0d, 0xb8, 0x00, 0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef, 0x01, 0x23, 0x45},    // 源地址
        .dest_addr = {0x20, 0x01, 0x0d, 0xb8, 0x00, 0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef, 0x01, 0x23, 0x46}    // 目标地址
    };
    uint8_t payload[] = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10};    // 负载数据
    uint16_t payload_len = sizeof(payload);

    // 分片并发送数据包
    uint16_t mtu = 1280;    // 最大传输单元
    uint16_t last_frag_size = ipv6_fragment(&ipv6_hdr, payload, payload_len, mtu);

    return 0;
}