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 + ];
     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, );
     if (sockfd < )
     {
         printf("socket creating err in udptalk\n");
         exit();
     }
 /* 设置要加入组播的地址 */
     bzero(&mreq, sizeof(struct ip_mreq));
     if (argv[])
     {
         if ((group = gethostbyname(argv[])) == (struct hostent *) )
         {
             perror("gethostbyname");
             exit(errno);
         }
     }
     else
     {
         printf("you should give me a group address, 224.0.0.0-239.255.255.255\n");
         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)) == -)
     {
         perror("setsockopt");
         exit(-);
     }

     socklen = sizeof(struct sockaddr_in);
     memset(&peeraddr, , socklen);
     peeraddr.sin_family = AF_INET;

     if (argv[])
     {
         peeraddr.sin_port = htons(atoi(argv[]));
     }
     else
     {
         peeraddr.sin_port = htons();
     }

     if (argv[])
     {
         if (inet_pton(AF_INET, argv[], &peeraddr.sin_addr) <= )
         {
             printf("Wrong dest IP address!\n");
             exit();
         }
     }
     else
     {
         printf("no group address given, 224.0.0.0-239.255.255.255\n");
         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)) == -)
     {
         printf("Bind error\n");
         exit();
     }
 /* 循环接收网络上来的组播消息 */
 for (;;)
 {
     printf("before recvfrom!\n");
     bzero(recmsg, BUFLEN + );
     n = recvfrom(sockfd, recmsg, BUFLEN, ,(struct sockaddr *) &peeraddr, &socklen);
     if (n < )
     {
         printf("recvfrom err in udptalk!\n");
         exit();
     }
     else
     {
         /* 成功接收到数据报 */
         recmsg[n] = ;
         printf("server peer:%s\n", 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 + ];
     unsigned int socklen;
 /* 创建 socket 用于UDP通讯 */
     sockfd = socket(AF_INET, SOCK_DGRAM, );
     if (sockfd < )
     {
         printf("socket creating error\n");
         exit();
     }
     socklen = sizeof(struct sockaddr_in);
 /* 设置对方的端口和IP信息 */
     memset(&peeraddr, , socklen);
     peeraddr.sin_family = AF_INET;
     if (argv[])
     {
         peeraddr.sin_port = htons(atoi(argv[]));
     }
     else
     {
         peeraddr.sin_port = htons();
     }

     if (argv[])
     {
     /* 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[], &peeraddr.sin_addr) <= )
         {
             printf("wrong group address!\n");
             exit();
         }
     }
      else
     {
         printf("no group address!\n");
         exit();
     }

 /* 设置自己的端口和IP信息 */
     memset(&myaddr, , socklen);
     myaddr.sin_family = AF_INET;
     if (argv[])
     {
         myaddr.sin_port = htons(atoi(argv[]));
     }
     else
     {
         myaddr.sin_port = htons();
     }

     if (argv[])
     {
         if (inet_pton(AF_INET, argv[], &myaddr.sin_addr) <= )
         {
             printf("self ip address error!\n");
             exit();
         }
     }
     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)) == -)
     {
         printf("Bind error\n");
         exit();
     }
 /* 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 + );
         if (fgets(recmsg, BUFLEN, stdin) == (char *) EOF)
         {
             exit();
         }
         /* 发送消息 */
         if (sendto(sockfd, recmsg, strlen(recmsg), ,(struct sockaddr *) &peeraddr,sizeof(struct sockaddr_in)) < )
         {
             printf("sendto error!\n");
             exit();
         }

         printf("client:'%s'send ok\n", recmsg);
     }
 }