Linux网络套接字：获取网络参数

这篇文章主要讲怎么通过编程获取Linux的网络参数：
    1、获取mac地址
    2、获取网络接口号
    3、获取ipv4地址
    4、获取ipv6地址
    5、获取子网掩码
    6、获取接口标志
    其中后面4个参数都可以通过getifaddrs()函数获取
代码中用到的一些宏定义

#define Print(fmt, args...) printf("[%s, %d] "fmt"\n", __func__, __LINE__, ##args)
#define MAC_ADDR_SIZE   6
#define IPV6_ADDR_LEN 16

1、获取本地mac地址

void get_mac_addr(int sockfd, char *devName, unsigned char *mac)
{
        struct ifreq ifr;

        strncpy(ifr.ifr_name, devName, sizeof(ifr.ifr_name));
        if (ioctl(sockfd, SIOCGIFHWADDR, &ifr) < 0)
        {
                Print("ioctl: %s", strerror(errno));
                return;
        }

        memcpy(mac, ifr.ifr_hwaddr.sa_data, MAC_ADDR_SIZE);

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

2、获取网络接口号
    方法一：使用ioctl函数来实现，是我所见使用比较广泛的一种 方法

int get_ifindex1(int sockfd, char *devName)
{
        struct ifreq ifr;

        strncpy(ifr.ifr_name, devName, sizeof(ifr.ifr_name));
        if (ioctl(sockfd, SIOCGIFINDEX, &ifr) < 0)
        {
                Print("ioctl: %s", strerror(errno));
                return -1;
        }

        printf("get ifindex1: %d\n", ifr.ifr_ifindex);
        return ifr.ifr_ifindex;
}

    方法二：是用if_nametoindex函数来实现，与之相反的函数是if_indextoname。个人感觉使用这种方式更为简洁，但很少看到有人用这种方式来实现。不知道为什么。

int get_ifindex2(char *devName)
{
        unsigned int ifindex;

        if (0 == (ifindex = if_nametoindex(devName)))
        {
                Print("if_nametoindex failed: %s", strerror(errno));
                return -1;
        }

        printf("get ifindex2: %d\n", ifindex);
        return ifindex;
}

3、获取ip地址

void get_ipaddr(int sockfd, char *devName)
{
        struct sockaddr_in *sin;
        struct ifreq ifr;

        memset(&ifr, 0, sizeof(ifr));
        strncpy(ifr.ifr_name, devName, sizeof(ifr.ifr_name));

        if (ioctl(sockfd, SIOCGIFADDR, &ifr) < 0)
        {
                Print("ioctl SIOCGIFADDR: %s", strerror(errno));
                return;
        }

        sin = (struct sockaddr_in *)&ifr.ifr_addr;
        printf("get ip address of %s: %s\n", devName, inet_ntoa(sin->sin_addr));
        return;
}

4、获取ipv6地址
    方法一：使用函数getifaddrs，实例参考man手册来的。显然这个函数也可以用来获取ipv4地址。但一定要记得释放内存。
    PS:第一次看到这么用“？：”运算符的，感觉很新颖。

void get_ip6addr1()
{
        struct ifaddrs *ifaddr, *ifa;
        int family, s;
        char host[NI_MAXHOST];

        if (getifaddrs(&ifaddr) == -1)
        {
                Print("getifaddr failed: %s", strerror(errno));
                return;
        }

        /*walk through linked list, maintaining head pointer
         so we can free list later*/
        for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next)
        {
                if (NULL == ifa->ifa_addr)
                {
                        continue;
                }

                family = ifa->ifa_addr->sa_family;
                printf("%s address family: %d%s\n",
                        ifa->ifa_name, family,
                        (AF_PACKET == family) ? "(AF_PACKET)" :
                        (AF_INET == family) ? "(AF_INET)" :
                        (AF_INET6 == family) ? "(AF_INET6)" : "");

                if ((AF_INET == family) || (AF_INET6 == family))
                {
                        s = getnameinfo(ifa->ifa_addr,
                                (AF_INET == family) ? sizeof(struct sockaddr_in) :
                                                      sizeof(struct sockaddr_in6),
                                host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
                        if (0 != s)
                        {
                                Print("getnameinfo failed: %s\n", gai_strerror(s));
                                return;
                        }
                        printf("\taddress: <%s>\n", host);
                }
        }
        freeifaddrs(ifaddr);//释放内存，不要忘了

        return;
}

    下面是这个函数在我的虚拟机上运行的结果：

lo address family: 17(AF_PACKET)
eth0 address family: 17(AF_PACKET)
lo address family: 2(AF_INET)
    address: <127.0.0.1>
eth0 address family: 2(AF_INET)
    address: <192.168.1.104>
lo address family: 10(AF_INET6)
    address: <::1>
eth0 address family: 10(AF_INET6)
    address: <fe80::20c:29ff:fedc:a8f6%eth0>

    方法二：这种方法是从以前某个版本的busybox中的ifconfig源码中看到的，直接分析/proc/net/if_inet6文件

void get_ip6addr2(char *ifname)
{
        unsigned char addr[IPV6_ADDR_LEN];
        char devname[20];
        int if_idx, dad_status, scope, plen, prelen;
        char addr6p[8][5];
        char addrStr[40];
        FILE *f;

        if (NULL == (f = fopen("/proc/net/if_inet6", "r")))
        {
                Print("open if_inet6 err failed");
                return;
        }

        while (EOF != fscanf(f, "%4s%4s%4s%4s%4s%4s%4s%4s %02x %02x %02x %02x %20s\n",
                addr6p[0], addr6p[1], addr6p[2], addr6p[3],
                addr6p[4], addr6p[5], addr6p[6], addr6p[7],
                &if_idx, &plen, &scope, &dad_status, devname))
        {
                if (strcmp(devname, ifname))
                {
                        continue;
                }

                sprintf(addrStr, "%s:%s:%s:%s:%s:%s:%s:%s",
                        addr6p[0], addr6p[1], addr6p[2], addr6p[3],
                        addr6p[4], addr6p[5], addr6p[6], addr6p[7]);

                printf("get ipv6 address of %s: %s\n", ifname, addrStr);
                inet_pton(AF_INET6, addrStr, addr);
        }
}

5、获取子网掩码
    方法一：使用ioctl函数

void get_netMask1(int sockfd, char *devName)
{
        struct ifreq ifr;
        struct sockaddr_in *mask = NULL;

        memset(&ifr, 0, sizeof(ifr));
        strncpy(ifr.ifr_name, devName, sizeof(ifr.ifr_name));

        if(ioctl(sockfd, SIOCGIFNETMASK, &ifr) < 0)
        {
                Print("ioctl SIOCGIFNETMASK: %s", strerror(errno));
                return;
        }

        mask = (struct sockaddr_in *)&(ifr.ifr_netmask);
        printf("get net mask of %s: %s\n", devName, inet_ntoa(mask->sin_addr));
}

    方法二：使用getifaddrs函数

void get_netMask2(char *devName)
{
        struct ifaddrs *ifaddr = NULL, *ifa = NULL;
        struct sockaddr_in *addr = NULL, *mask = NULL;
        char addrStr[16], maskStr[16];

        if (getifaddrs(&ifaddr) < 0)
        {
                Print("getifaddrs failed: %s", strerror(errno));
                return;
        }

        for (ifa = ifaddr; NULL != ifa; ifa = ifa->ifa_next)
        {
                if (strcmp(ifa->ifa_name, devName))
                {
                        continue;
                }

                if (ifa->ifa_addr->sa_family != AF_INET)
                {
                        continue;
                }

                if ((NULL == ifa->ifa_addr) || (NULL == ifa->ifa_netmask))
                {
                        continue;
                }

                addr = (struct sockaddr_in *)ifa->ifa_addr;
                mask = (struct sockaddr_in *)ifa->ifa_netmask;
                strncpy(addrStr, inet_ntoa(addr->sin_addr), sizeof(addrStr));
                strncpy(maskStr, inet_ntoa(mask->sin_addr), sizeof(maskStr));

                printf("dev-%s  addr-%s  mask-%s\n", devName, addrStr, maskStr);
        }

        freeifaddrs(ifaddr);
}

6、获取接口标志
    方法一：使用ioctl，通过man netdevice可以获得更多关于ioctl以及标志的说明

void get_flags1(int sockfd, char *devName)
{
        struct ifreq ifr;
        unsigned int flags;

        memset(&ifr, 0, sizeof(ifr));
        strncpy(ifr.ifr_name, devName, sizeof(ifr.ifr_name));
        if (ioctl(sockfd, SIOCGIFFLAGS, &ifr) < 0)
        {
                Print("ioctl SIOCGIFFLAGS: %s", strerror(errno));
                return;
        }

        flags = ifr.ifr_flags;

        printf("get flags of %s: %08x\n", devName, flags);
        if (flags & IFF_UP) printf("UP ");
        if (flags & IFF_BROADCAST) printf("BROADCAST ");
        if (flags & IFF_DEBUG) printf("DEBUG ");
        if (flags & IFF_LOOPBACK) printf("LOOPBACK ");
        /*更多标志可通过man netdevice获取*/
        printf("\n");
}

    方法二：使用getifaddrs函数

void get_flags2(char *devName)
{
        struct ifaddrs *ifaddr = NULL, *ifa = NULL;
        unsigned int flags;

        if (getifaddrs(&ifaddr) < 0)
        {
                Print("getifaddrs failed: %s", strerror(errno));
                return;
        }

        for (ifa = ifaddr; NULL != ifa; ifa = ifa->ifa_next)
        {
                if (!strcmp(ifa->ifa_name, devName))
                {
                        break;
                }
        }
        if (NULL != ifa)
        {
                flags = ifa->ifa_flags;
                printf("get flags of %s: %08x\n", devName, flags);
        }

        freeifaddrs(ifaddr);
}

    从上面不难看出，如果只需要获取一个网络参数，使用ioctl比较简单。如果需要同时获取多个参数，推荐使用getifaddrs方法。