组播

组播

单播只能发给一个接收方，广播发给所有主机，但过多的广播会大量占用网络带宽，造成网络风暴，影响通信。

组播（多播）为折中方式，只有加入某个多播组的主机才能收到数据。

组播的IP地址：224.0.0.1 ~ 239.255.255.254（中间除去广播地址）

---

组播的发送

1）创建UDP套接字

2）指定目标地址与端口

3）发送数据包

/*udp demo */

/* usage:
 * ./client serv_ip serv_port 
*/
#include "net.h"
void usage (char *s)
{
    printf ("\nThis is multicast demo!\n");
    printf ("\nUsage:\n\t %s serv_ip serv_port", s);
    printf ("\n\t serv_ip: udp server ip address(between 224~239 segment)");
    printf ("\n\t serv_port: udp server port(serv_port > 5000)\n\n");
}

int main (int argc, char *argv[])
{
    int fd = -1;
    int port = SERV_PORT;

    port = atoi (argv[2]);
    if (port < 0 || (port > 0 && port <= 5000)) {
        usage (argv[0]);
        exit (1);
    }
    struct sockaddr_in sin;
    if (argc != 3) {
        usage (argv[0]);
        exit (1);
    }

    /* 1. 创建socket fd */
    if ((fd = socket (AF_INET, SOCK_DGRAM, 0)) < 0) {    //UDP缂栫▼
        perror ("socket");
        exit (1);
    }

    /*2.1 填充struct sockaddr_in */
    bzero (&sin, sizeof (sin));

    sin.sin_family = AF_INET;
    sin.sin_port = htons (SERV_PORT);    //HBD转为NBD
#if 0
    sin.sin_addr.s_addr = inet_addr (argv[1]);
#else
    if (inet_pton (AF_INET, argv[1], (void *) &sin.sin_addr) != 1) {
        perror ("inet_pton");
        exit (1);
    }
#endif
    printf ("multicast started!\n");
    char buf[BUFSIZ];
    while (1) {
        fprintf (stderr, "pls input string:");
        bzero (buf, BUFSIZ);
        if (fgets (buf, BUFSIZ - 1, stdin) == NULL) {
            perror ("fgets");
            continue;
        }

        sendto (fd, buf, strlen (buf), 0, (struct sockaddr *) &sin, sizeof (sin));

        if (!strncasecmp (buf, QUIT_STR, strlen (QUIT_STR))) {    
            printf ("Client is exited!\n");
            break;
        }

    }
    close (fd);
    return 0;
}

组播的接收

1）创建UDP套接字

2）加入多播组

3）绑定地址与端口

4）接收数据包

#include "net.h"

int main (void)
{

    int fd = -1;
    struct sockaddr_in sin;

    /* 1. 创建socket fd */
    if ((fd = socket (AF_INET, SOCK_DGRAM, 0)) < 0) {    //udp
        perror ("socket");
        exit (1);
    }

    /* 2. 允许地址快速重用 */
    int b_reuse = 1;
    setsockopt (fd, SOL_SOCKET, SO_REUSEADDR, &b_reuse, sizeof (int));

    /*加入多播组*/
    struct ip_mreq mreq;
    bzero(&mreq, sizeof(mreq)); //清零
    mreq.imr_multiaddr.s_addr = inet_addr(MULTICAST_IP);
    mreq.imr_interface.s_addr = htonl(INADDR_ANY);
    
    setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP,&mreq, sizeof(mreq));

    /*2. 绑定*/
    /*2.1 填充struct sockaddr_in */
    bzero (&sin, sizeof (sin));
    sin.sin_family = AF_INET;
    sin.sin_port = htons (SERV_PORT);    
    /* 使服务器可绑定在任意IP */
#if 1
    sin.sin_addr.s_addr = htonl (INADDR_ANY);
#else
    if (inet_pton (AF_INET, SERV_IP_ADDR, (void *) &sin.sin_addr) != 1) {
        perror ("inet_pton");
        exit (1);
    }
#endif
    /*2.2 绑定 */
    if (bind (fd, (struct sockaddr *) &sin, sizeof (sin)) < 0) {
        perror ("bind");
        exit (1);
    }

    char buf[BUFSIZ];
    struct sockaddr_in cin;
    socklen_t addrlen = sizeof (cin);
    printf ("\nmulticast demo started!\n");
    while (1) {
        bzero (buf, BUFSIZ);
        if (recvfrom (fd, buf, BUFSIZ - 1, 0, (struct sockaddr *) &cin, &addrlen) < 0) {
            perror ("recvfrom");
            continue;
        }

        char ipv4_addr[16];
        if (!inet_ntop (AF_INET, (void *) &cin.sin_addr, ipv4_addr, sizeof (cin))) {
            perror ("inet_ntop");
            exit (1);
        }

        printf ("Recived from(%s:%d), data:%s", ipv4_addr, ntohs (cin.sin_port), buf);

        if (!strncasecmp (buf, QUIT_STR, strlen (QUIT_STR))) {    /
            printf ("Client(%s:%d) is exiting!\n", ipv4_addr, ntohs (cin.sin_port));
        }

    }

    close (fd);

    return 0;
}