Linux---指定网卡发送UDP组播

该场景是用于终端Linux设备，入网后定时发送UDP组播，从而服务端可以发现同一个局域网内所有按照此协议下的设备。

大佬：Talk is cheap.Show me the code！

捞仔：好的，大佬！

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define UDP_ADDR "239.255.255.250"
#define UDP_PORT 3702
#define SEND_PORT 3702
#define MAC_SIZE    18
#define IP_SIZE     16
#define ETHX     "eth0"

// function declare
int get_local_mac(const char *eth_inf, char *mac); // 获取本机mac
int get_local_ip(const char *eth_inf, char *ip); // 获取本机ip

// 获取本机mac
int get_local_mac(const char *eth_inf, char *mac)
{
    struct ifreq ifr;
    int sd;

    bzero(&ifr, sizeof(struct ifreq));
    if( (sd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("get %s mac address socket creat error\n", eth_inf);
        return -1;
    }

    strncpy(ifr.ifr_name, eth_inf, sizeof(ifr.ifr_name) - 1);

    if(ioctl(sd, SIOCGIFHWADDR, &ifr) < 0)
    {
        printf("get %s mac address error\n", eth_inf);
        close(sd);
        return -1;
    }

    snprintf(mac, MAC_SIZE, "%02x:%02x:%02x:%02x:%02x:%02x",
             (unsigned char)ifr.ifr_hwaddr.sa_data[0],
            (unsigned char)ifr.ifr_hwaddr.sa_data[1],
            (unsigned char)ifr.ifr_hwaddr.sa_data[2],
            (unsigned char)ifr.ifr_hwaddr.sa_data[3],
            (unsigned char)ifr.ifr_hwaddr.sa_data[4],
            (unsigned char)ifr.ifr_hwaddr.sa_data[5]);

    close(sd);

    return 0;
}

//获取网卡对应IP地址[其中eth是网卡名字 如“eth0” “eth1”等,ipaddr是输出参数]
// 获取本机ip
int get_local_ip(const char *eth_inf, char *ip)
{
    int sd;
    struct sockaddr_in sin;
    struct ifreq ifr;

    sd = socket(AF_INET, SOCK_DGRAM, 0);
    if (-1 == sd)
    {
        printf("socket error: %s\n", strerror(errno));
        return -1;
    }

    strncpy(ifr.ifr_name, eth_inf, IFNAMSIZ);
    ifr.ifr_name[IFNAMSIZ - 1] = 0;

    // if error: No such device
    if (ioctl(sd, SIOCGIFADDR, &ifr) < 0)
    {
        printf("ioctl error: %s\n", strerror(errno));
        close(sd);
        return -1;
    }

    memcpy(&sin, &ifr.ifr_addr, sizeof(sin));
    snprintf(ip, IP_SIZE, "%s", inet_ntoa(sin.sin_addr));

    close(sd);
    return 0;
}

int main(int argc, char **argv)
{

    struct sockaddr_in addr, mcast_addr;
    int fd;
    struct ip_mreq ipmr;
    char ip[IP_SIZE];
    char mac_addr[MAC_SIZE];
    //char *mac_addr = {0};
    int ret = -1;
    //char msg[8];

    unsigned char chrUDP[124] = { '\x56','\x5a','\x00','\x00','\x02','\x01',
                                  '\x09' ,'\x05','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x03' ,'\x7e',
                                  '\xc9' ,'\x77','\xfc','\xf6','\xeb','\x14','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00' ,'\x00',
                                  '\x00' ,'\x00','\x00','\x00','\x00','\x00','\x7c','\x00','\x00','\x00','\xc0','\xa8','\x0a','\x64','\x50' ,'\x00',
                                  '\x00' ,'\x00','\x53','\x56','\x5a','\x54','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00' ,'\x00',
                                  '\x00' ,'\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00','\x00' ,'\x00',
                                  '\x00' ,'\x00','\x00','\x00','\x00','\x00','\x0b','\x00','\x00','\x00','\x2e','\x00','\x00','\x00','\x00' ,'\x00',
                                  '\x00' ,'\x00','\x01','\x00','\x00','\x0d','\x0d','\x00','\x00','\x00','\xc0','\xa8','\x0a','\x01','\xff' ,'\xff',
                                  '\xff' ,'\x00','\x72','\x00','\x00','\x00'};
    if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
    {
        perror("create socket failed!");
        return -1;
    }

    get_local_mac(ETHX, mac_addr);
    printf("local %s mac: %s\n", ETHX, mac_addr);
    //get_mac(ETHX, mac_addr);
    //printf("local %s mac: %s\n", ETHX, mac_addr);


    unsigned char mac[6] = {0};
    char *pchStr = strtok(mac_addr, ":");
    int  nTotal = 0;

    while (NULL != pchStr)
    {
        mac[nTotal++] = (SwitchChar(*pchStr) << 4) | SwitchChar(*(pchStr+1));
        pchStr = strtok(NULL, ":");
    }

    printf("mac is %02x%02x%02x%02x%02x%02x\n",mac[0],mac[1],mac[2],mac[3],mac[4],mac[5]);

    memcpy(chrUDP+20, mac, 6);
    //printf("mac is %02x\n",mac[5]);


    get_local_ip(ETHX, ip);
    printf("local %s ip: %s\n", ETHX, ip);
    inet_pton(AF_INET, ip, &addr.sin_addr.s_addr);


    memset(&addr,0,sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(SEND_PORT);
    //addr.sin_addr.s_addr = htonl(INADDR_ANY);
    addr.sin_addr.s_addr = inet_addr(ip);

    ret = bind(fd, (struct sockaddr*)&addr, sizeof(addr));
    if(ret < 0)
    {
        printf("bind error!!!");
        perror("bind:");
        close(fd);
        return -1;
    }

/**********************************************************************************************
**将本地socket添加到多播组中，注意，此处针对struct ip_mreq结构体需要填充两个成员，
**成员ipmr.imr_interface.s_addr的值指定的是将要发送的网卡的ip地址，
**成员impr.imr_multiaddr指定的是组播地址；
**如果指定为INADDR_ANY则系统会绑定一个默认网卡的具体ip（根据默认网关选择），则会出现特定网卡可以发送和接收组播信息，
**另一网卡不可以。即指定INADDR_ANY并不能把所有网卡都添加多播组中，必须明确指定对应网卡ip才可以。
***********************************************************************************************/

    struct in_addr inaddr = {0};
    inaddr.s_addr = inet_addr(ip);
    ipmr.imr_interface.s_addr = inaddr.s_addr;
    ipmr.imr_multiaddr.s_addr = inet_addr(UDP_ADDR);
    ret=setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (const char*)&ipmr, sizeof(ipmr));


    /*此处指定组播数据的出口网卡，如果不设置则会根据路由表指定默认路由出口*/

    if(-1 == setsockopt(fd, IPPROTO_IP, IP_MULTICAST_IF, (char *)&inaddr, sizeof(inaddr)))
    {
        printf("set error IP_MULTICAST_IF %s\n", ip);
        perror("Setting IP_MULTICAST_IF error:");
        close(fd);
        fd = -1;
    }


    memset(&mcast_addr, 0, sizeof(mcast_addr));
    mcast_addr.sin_family = AF_INET;
    mcast_addr.sin_addr.s_addr = inet_addr(UDP_ADDR);
    mcast_addr.sin_port = htons(UDP_PORT);

    while(1){
        if (sendto(fd, (const char *)chrUDP, sizeof(chrUDP), 0, (struct sockaddr *)&mcast_addr, sizeof(mcast_addr)) < 0)
        {
            perror("sendto");
            return -1;
        }
        printf("send ok!\n");

        sleep(8);
    }

    setsockopt(fd, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mcast_addr, sizeof(mcast_addr));
    close(fd);

    return 0;
}

说明：

1. 可以指定某一个网卡ETHX，来发送组播；

2. 可以绑定不一样的组播UDP_IP和端口UDP_PORT，并且可以指定发送端口SEND_PORT;

3. 发送的数据中某一段用MAC地址替换，以发送含有本设备独有的信息，防止发现设备是不能同时发现多个；

4. 测试时，用抓包工具Wireshark，抓取UDP数据，用于验证结果。