linux 接收udp组播数据包后反馈链路层数据

这个是借鉴了网上代码，然后自己总结了一下

#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>


#include <linux/if_packet.h>
#include <linux/if_ether.h>
#include <arpa/inet.h>

#include <netdb.h>            // struct addrinfo
#include <sys/types.h>        // needed for socket(), uint8_t, uint16_t, uint32_t
#include <sys/socket.h>       // needed for socket()
#include <netinet/in.h>       // IPPROTO_ICMP, INET_ADDRSTRLEN
#include <netinet/ip.h>       // struct ip and IP_MAXPACKET (which is 65535)
#include <netinet/ip_icmp.h>  // struct icmp, ICMP_ECHO
#include <arpa/inet.h>        // inet_pton() and inet_ntop()
#include <sys/ioctl.h>        // macro ioctl is defined
#include <bits/ioctls.h>      // defines values for argument "request" of ioctl.
#include <net/if.h>           // struct ifreq
#include <linux/if_ether.h>   // ETH_P_IP = 0x0800, ETH_P_IPV6 = 0x86DD
#include <linux/if_packet.h>  // struct sockaddr_ll (see man 7 packet)
#include <net/ethernet.h>
#include <errno.h>            // errno, perror()

#define BUFFER_MAX 2048

#define ETH_P_DEAN 2088
uint8_t dst_mac[6];
char interface[16];

int sendData()
{
    int i, datalen,frame_length, sd, bytes;
    //char *interface="eth0";
    uint8_t data[IP_MAXPACKET];
    uint8_t src_mac[6];
    //uint8_t src_ip[];
    in_addr_t src_ipaddr;

    uint8_t ether_frame[IP_MAXPACKET];
    struct sockaddr_ll device;
    struct ifreq ifr;
    struct sockaddr_in  sin;

    // Submit request for a socket descriptor to look up interface.
    //第一次创建socket是为了获取本地网卡信息
    if ((sd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0) {
        perror ("socket() failed to get socket descriptor for using ioctl() ");
        exit (EXIT_FAILURE);
    }

    // Use ioctl() to look up interface name and get its MAC address.
    memset (&ifr, 0, sizeof (ifr));
    snprintf (ifr.ifr_name, sizeof (ifr.ifr_name), "%s", interface);

    //SIOCGIFADDR 获取interface address
    if (ioctl(sd, SIOCGIFADDR, &ifr) >= 0) {    
        memcpy(&sin, &ifr.ifr_addr, sizeof(ifr.ifr_addr));
        src_ipaddr = sin.sin_addr.s_addr;
        printf("\n\nip:%x  %s\n", sin.sin_addr.s_addr,inet_ntoa(sin.sin_addr));
    }
    if (ioctl (sd, SIOCGIFHWADDR, &ifr) < 0) {
        perror ("ioctl() failed to get source MAC address ");
        return (EXIT_FAILURE);
    }

    close (sd);

    // Copy source MAC address.
    memcpy (src_mac, ifr.ifr_hwaddr.sa_data, 6);

    // Report source MAC address to stdout.
    printf ("\n\nMAC address for interface %s is ", interface);
    for (i=0; i<5; i++) {
        printf ("%02x:", src_mac[i]);
    }
    printf ("%02x\n", src_mac[5]);



    // Find interface index from interface name and store index in
    // struct sockaddr_ll device, which will be used as an argument of sendto().
    memset (&device, 0, sizeof (device));
    if ((device.sll_ifindex = if_nametoindex (interface)) == 0) {
        perror ("if_nametoindex() failed to obtain interface index ");
        exit (EXIT_FAILURE);
    }
    printf ("Index for interface %s is %i\n", interface, device.sll_ifindex);

    // Fill out sockaddr_ll.
    device.sll_family = AF_PACKET;
    memcpy (device.sll_addr, src_mac, 6);
    device.sll_halen = htons (6);

    // 发送的data，长度可以任意，但是抓包时看到最小数据长度为46，这是以太网协议规定
    //以太网帧数据域部分最小为46字节，不足的自动补零处理
    datalen = 12;
    data[0] = src_ipaddr & 0x000000ff;
    src_ipaddr>>=8;
    data[1] = src_ipaddr & 0x000000ff;
    src_ipaddr>>=8;
    data[2] = src_ipaddr & 0x000000ff;
    src_ipaddr>>=8;
    data[3] = src_ipaddr & 0x000000ff;
    data[4] = ' ';
    data[5] = ' ';
    data[6] = ' ';
    data[7] = ' ';
    data[8] = ' ';
    data[9] = ' ';
    data[10] = ' ';
    data[11] = ' ';
char * ip_addr = inet_ntoa(sin.sin_addr);
    // Fill out ethernet frame header.
    frame_length = 6 + 6 + 2   + datalen;

    // Destination and Source MAC addresses
    memcpy (ether_frame, dst_mac, 6);
    memcpy (ether_frame + 6, src_mac, 6);
    ether_frame[12] = ETH_P_DEAN / 256;
    ether_frame[13] = ETH_P_DEAN % 256;

    // data
    memcpy (ether_frame + 14 , data, datalen);

    for(int i = 0; i < 16; i++){
        printf("%.2x ", data[i]);
    }
    printf("\n");
    // Submit request for a raw socket descriptor.
    if ((sd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0) {//创建正真发送的socket
        perror ("socket() failed ");
        exit (EXIT_FAILURE);
    }

    // Send ethernet frame to socket.
    if ((bytes = sendto (sd, ether_frame, frame_length, 0, (struct sockaddr *) &device, sizeof (device))) <= 0) {
        perror ("sendto() failed");
        exit (EXIT_FAILURE);
    }
    printf ("send num=%d,read num=%d\n",frame_length,bytes);

    // Close socket descriptor.
    close (sd);
    return (EXIT_SUCCESS);
}

int main(int argc, char *argv[])
{
    if(argc ==1){
        memcpy (interface, "eth0", 4);
    }else{
        strcpy(interface, argv[1]);
        //interface = argv[1];
    }
    int sock, n_read;
    char buffer[BUFFER_MAX];
    char  *eth_head;

    if((sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) < 0)
    {
        fprintf(stdout, "create socket error\n");
        exit(0);
    }

    while(1)
    {
        struct sockaddr_in clientAddr;
        int n;
        socklen_t len = sizeof(clientAddr);
        n_read = recvfrom(sock, buffer, 2048, 0, (struct sockaddr*)&clientAddr, &len);
        if(n_read < 42)
        {
            fprintf(stdout, "Incomplete header, packet corrupt\n");
            continue;
        }
        if(n_read > 100){
            continue;
        }
        eth_head = buffer;

        if(eth_head[23] == 0x11 && eth_head[34] == 0x06 &&eth_head[35] == 0x22){
            printf("\n----------------1570 port---------------------\n");
            int i=0;
            for(i=0;i<n_read;i++){
                printf("%.2X ",(unsigned char)eth_head[i]);
                if(((i+1)%16)==0) printf("\n");
            }

            for(int index = 6; index < 12; index++){
                dst_mac[index-6] = eth_head[index];//设置目的网卡地址

            }

            sendData();

            printf("\n-----------------------------------------------\n");
        }
    }
}