multicast based on udp

1.概念

单播，是用于两个主机之间传送数据;

广播，是一个主机对局域网内的所有主机发送数据;

多播，又称为组播，它是对一组特定的主机通信。

　　将网络上同一类型业务逻辑上分组，只和组内的成员通信，其它主机没有加入组则不能通信。与单播相同的是，组播允许在Internet上通信，而广播只是同一局域网内的主机通信。组播地址是特定的，D类地址用于组播，即244.0.0.0到239.255.255.255. 并划分为局部连接多播地址，预留多播地址和管理权限多播地址3类。

　　(1)局部多播地址 （224.0.0.-224.0.0.255)为路由协议和其它用途保留的地址，路由器不转发此范围的IP包

　　(2)预留多播地址   (224.0.1.0-238.255.255.255)可用于全球范围内或网络协议

　　(3)管理权限的多播 (239.0.0.0-239.255.255.255) 可供组织内使用，类型于私有IP，不用于Internet,可限制多播范围

2. 多播套接字设置

可用setsockopt或getsockopt设置或得到多播选项. 常用的多播选项如下所示:

IP_MULTICAST_TTL    设置多播的TTL值

　　Sets the Time To Live (TTL) in the IP header for outgoing multicast datagrams.  By default it is set to 1.  TTL of 0 are not transmitted on any sub-network.  Multicast datagrams with a TTL of greater than 1 may be delivered to more than one sub-network, if there are one or more multicast routers attached to the first sub-network.

IP_MULTICAST_IF      获取或设置多播接口

　　Sets the interface over which outgoing multicast datagrams are sent.

IP_MULTICAST_LOOP   禁止多播数据回送到本地loop接口

　　Specifies whether or not a copy of an outgoing multicast datagram is delivered to the sending host as long as it is a member of the multicast group.

IP_ADD_MEMBERSHIP   将指定的接口加入多播

 　　Joins the multicast group specified.

IP_DROP_MEMBERSHIP  退出多播组

　　 Leaves the multicast group specified.

struct ip_mreq{
  struct in_addr imn_multicastaddr;//多播组地址
  struct in_addr imr_interface;//加入的接口的IP地址
}

int ttl=255;
setsockopt(s,IPPROTO_IP,IP_MULTICAST_TTL,&ttl,sizeof(ttl));//设置跳数
s-套接字描述符
PROTO_IP-选项所在的协议层
IP_MULTICAST_TTL-选项名
&ttl-设置的内存缓冲区
sizeof(ttl)-设置的内存缓冲区长度

struct in_addr in;
setsockopt(s,IPPROTO_IP,IP_MUTLICAST_IF,&in,sizeof(in));//设置组播接口

int yes=1;
setsockopt(s,IPPROTO_IP,IP_MULTICAST_LOOP,&yes,sizeof(yes));//设置数据回送到本地回环接口

struct ip_mreq addreq;
setsockopt(s,IPPROTO_IP,IP_ADD_MEMBERSHIP,&req,sizeof(req));//加入组播组

struct ip_mreq dropreq;
setsockopt(s,IPPROTO_IP,IP_DROP_MEMBERSHIP,&dropreq,sizeof(dropreq));//离开组播组

3. 多播程序的设计流程

(1)建立socket

(2)设置TTL值 IP_MULTICAST_TTL

(3)设置是否允许本地回环 IP_MULTICAST_LOOP

(4)加入多播组 IP_ADD_MEMBERSHIP

(5)发送数据 send

(6)接收数据 recv

(7)退出多播组 IP_DROP_MEMBERSHIP

mulcastserver.c

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <errno.h>
#define BUFLEN 255

int main(int argc, char **argv)
{
    struct sockaddr_in peeraddr;
    struct in_addr ia;
    int sockfd;
    char recmsg[BUFLEN + 1];
    unsigned int socklen, n;
    struct hostent *group;
    struct ip_mreq mreq;
/* 创建 socket 用于UDP通讯 */
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) 
    {
        printf("socket creating err in udptalk
");
        exit(1);
    }
/* 设置要加入组播的地址 */
    bzero(&mreq, sizeof(struct ip_mreq));
    if (argv[1]) 
    {
        if ((group = gethostbyname(argv[1])) == (struct hostent *) 0)
        {
            perror("gethostbyname");
            exit(errno);
        }
    } 
    else 
    {
        printf("you should give me a group address, 224.0.0.0-239.255.255.255
");
        exit(errno);
    }
    
    bcopy((void *) group->h_addr, (void *) &ia, group->h_length);
/* 设置组地址 */
    bcopy(&ia, &mreq.imr_multiaddr.s_addr, sizeof(struct in_addr));
/* 设置发送组播消息的源主机的地址信息 */
    mreq.imr_interface.s_addr = htonl(INADDR_ANY);
/* 把本机加入组播地址，即本机网卡作为组播成员，只有加入组才能收到组播消息 */
    if (setsockopt(sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq,sizeof(struct ip_mreq)) == -1) 
    {
        perror("setsockopt");
        exit(-1);
    }
    
    socklen = sizeof(struct sockaddr_in);
    memset(&peeraddr, 0, socklen);
    peeraddr.sin_family = AF_INET;
    
    if (argv[2])
    {
        peeraddr.sin_port = htons(atoi(argv[2]));
    }
    else
    {
        peeraddr.sin_port = htons(7838);
    }
    
    if (argv[1]) 
    {
        if (inet_pton(AF_INET, argv[1], &peeraddr.sin_addr) <= 0) 
        {
            printf("Wrong dest IP address!
");
            exit(0);
        }
    } 
    else 
    {
        printf("no group address given, 224.0.0.0-239.255.255.255
");
        exit(errno);
    }
/* 绑定自己的端口和IP信息到socket上 */
    if (bind(sockfd, (struct sockaddr *) &peeraddr,sizeof(struct sockaddr_in)) == -1) 
    {
        printf("Bind error
");
        exit(0);
    }
/* 循环接收网络上来的组播消息 */
for (;;) 
{
    printf("before recvfrom!
");
    bzero(recmsg, BUFLEN + 1);
    n = recvfrom(sockfd, recmsg, BUFLEN, 0,(struct sockaddr *) &peeraddr, &socklen);
    if (n < 0) 
    {
        printf("recvfrom err in udptalk!
");
        exit(4);
    } 
    else 
    {
        /* 成功接收到数据报 */
        recmsg[n] = 0;
        printf("server peer:%s
", recmsg);
    }
}
}

mulcastclient.c

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFLEN 255

int main(int argc, char **argv)
{
    struct sockaddr_in peeraddr, myaddr;
    int sockfd;
    char recmsg[BUFLEN + 1];
    unsigned int socklen;
/* 创建 socket 用于UDP通讯 */
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) 
    {
        printf("socket creating error
");
        exit(1);    
    }
    socklen = sizeof(struct sockaddr_in);
/* 设置对方的端口和IP信息 */
    memset(&peeraddr, 0, socklen);
    peeraddr.sin_family = AF_INET;
    if (argv[2])
    {
        peeraddr.sin_port = htons(atoi(argv[2]));
    }
    else
    {
        peeraddr.sin_port = htons(7838);
    }
    
    if (argv[1]) 
    {
    /* 注意这里设置的对方地址是指组播地址，而不是对方的实际IP地址 */
        if (inet_pton(AF_INET, argv[1], &peeraddr.sin_addr) <= 0) 
        {
            printf("wrong group address!
");
            exit(0);
        }
    }
     else 
    {
        printf("no group address!
");
        exit(0);
    }
    
/* 设置自己的端口和IP信息 */
    memset(&myaddr, 0, socklen);
    myaddr.sin_family = AF_INET;
    if (argv[4])
    {
        myaddr.sin_port = htons(atoi(argv[4]));
    }
    else
    {
        myaddr.sin_port = htons(23456);
    }
    
    if (argv[3]) 
    {
        if (inet_pton(AF_INET, argv[3], &myaddr.sin_addr) <= 0)
        {
            printf("self ip address error!
");
            exit(0);
        }
    } 
    else
    {
        myaddr.sin_addr.s_addr = INADDR_ANY;
    }
    
/* 绑定自己的端口和IP信息到socket上 */
    if (bind(sockfd, (struct sockaddr *) &myaddr,sizeof(struct sockaddr_in)) == -1)
    {
        printf("Bind error
");
        exit(0);
    }
/* 循环接受用户输入的消息发送组播消息 */
    for (;;) 
    {
        /* 接受用户输入 */
        bzero(recmsg, BUFLEN + 1);
        if (fgets(recmsg, BUFLEN, stdin) == (char *) EOF)
        {
            exit(0);
        }
        /* 发送消息 */
        if (sendto(sockfd, recmsg, strlen(recmsg), 0,(struct sockaddr *) &peeraddr,sizeof(struct sockaddr_in)) < 0)
        {
            printf("sendto error!
");
            exit(3);
        }
    
        printf("client:'%s'send ok
", recmsg);
    }
}