【数据链路层】封装成帧和透明传输和差错控制

//Ethernet.h
//这里只为上次的Ethernet.h做一补充


int is_accept_ethernet_packet(u_int8_t *packet_content, int len);

void ethernet_protocol_packet_callback(u_char *argument, const struct pcap_pkthdr *packet_header, const u_char *packet_content);

//Ethernet.cpp

#include "Network_IPV4_recv.h"
#include "Network_ARP_recv.h "
//这里需要调用上层提供的接收函数接口交付数据包

int is_accept_ethernet_packet(u_int8_t *packet_content, int len)
{
    struct ethernet_header *ethernet_hdr = (struct ethernet_header *)packet_content;
    int i;
    int flag = 0;

    //检查目的MAC地址是否是广播MAC地址
    for (i = 0; i < 6; i++)
    {
        if (ethernet_hdr->destination_mac[i] != 0xff)break;
    }
    if (i == 6)
    {
        flag = 1;
        printf("It's broadcast packet.\n");
    }

    //检查目的MAC地址是否是本地MAC地址
    for (i = 0; i < 6; i++)
    {
        if (ethernet_hdr->destination_mac[i] != local_mac[i])break;
    }
    if (i == 6)
    {
        flag = 1;
        printf("It's sended to my pc.\n");
    }

    //若上边检查均未通过，返回0表示本数据包不需要接收
    if (!flag)
        return 0;

    //否则检查CRC校验码
    u_int32_t crc = calculate_crc((u_int8_t *)packet_content , len - 4 );
    if (crc != *((u_int32_t *)(packet_content + len - 4)))
    {
        printf("The data has changed.\n");
        return 0;
    }

    //CRC无误则本数据包可以接收，返回1
    return 1;
}

//接收数据帧的回环函数
void ethernet_protocol_packet_callback(u_char *argument, const struct pcap_pkthdr *packet_header, const u_char *packet_content)
{
    int len = packet_header->len;
    if (!is_accept_ethernet_packet((u_int8_t *)packet_content, len))
    {
        return;
    }

    struct ethernet_header *ethernet_hdr = (struct ethernet_header *)packet_content;
    u_int16_t ethernet_type = ntohs(ethernet_hdr->ethernet_type);

    //去掉MAC帧首部，将数据部分根据上层协议交付给相应的上层接收函数
    u_int8_t *upper_buffer = (u_int8_t *)(packet_content + sizeof(ethernet_header));
    switch (ethernet_type)
    {
    case 0x0800:
        printf("Upper layer protocol: IPV4\n");
        network_ipv4_recv(upper_buffer);
        break;
    case 0x0806:
        printf("Upper layer protocol: ARP\n");
        dest_mac=network_arp_recv(upper_buffer);
        break;
    case 0x8035:
        printf("Upper layer protocol: RARP\n");
        //network_rarp_recv();
        break;
    case 0x814c:
        printf("Upper layer protocol: SNMP\n");
        //network_snmp_recv();
        break;
    case 0x8137:
        printf("Upper layer protocol: IPX(Internet Packet Exchange)\n");
        //network_ipx_recv();
        break;
    case 0x86DD:
        printf("Upper layer protocol: IPV6\n");
        //network_ipv6_recv();
        break;
    case 0x880B:
        printf("Upper layer protocol: PPP\n");
        //network_ppp_recv();
        break;
    default:break;
    }
    //以上注释掉的协议均未实现，有兴趣的伙伴可以在看完我的协议栈设计的基础上在进行追加
}

 int ethernet_send_packet(u_int8_t *upper_buffer,u_int8_t
 *destination_mac,u_int16_t ethernet_type) 

network_arp_recv(upper_buffer);
 network_ipv4_recv(upper_buffer); //这两个我们后边会慢慢给大家展示出来