/* * listener.c -- joins a multicast group and echoes all data it receives from * the group to its stdout... * * Antony Courtney, 25/11/94 */ #include #include #include #include #include #include #include #include #include #include #include #include #define HELLO_PORT 50010 #define HELLO_GROUP "225.0.0.37" #define MSGBUFSIZE 256 int main(int argc, char *argv[]) { struct sockaddr_in addr; int fd, nbytes,addrlen; struct ip_mreq mreq; char msgbuf[MSGBUFSIZE]; /* create what looks like an ordinary UDP socket */ if ((fd=socket(AF_INET,SOCK_DGRAM,0)) < 0) { perror("socket"); exit(1); } /* set up destination address */ memset(&addr,0,sizeof(addr)); addr.sin_family=AF_INET; addr.sin_addr.s_addr=htonl(INADDR_ANY); /* N.B.: differs from sender */ addr.sin_port=htons(HELLO_PORT); /* bind to receive address */ if (bind(fd,(struct sockaddr *) &addr,sizeof(addr)) < 0) { perror("bind"); exit(1); } /* use setsockopt() to request that the kernel join a multicast group */ mreq.imr_multiaddr.s_addr=inet_addr(HELLO_GROUP); mreq.imr_interface.s_addr=htonl(INADDR_ANY); if (setsockopt(fd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq)) < 0) { perror("setsockopt"); exit(1); } /* now just enter a read-print loop */ while (1) { addrlen=sizeof(addr); if ((nbytes=recvfrom(fd,msgbuf,MSGBUFSIZE,0, (struct sockaddr *) &addr, (socklen_t *)&addrlen)) < 0) { perror("recvfrom"); exit(1); } printf("from %s %d bytes: %s\n", inet_ntoa(addr.sin_addr), nbytes, msgbuf); } return(EXIT_SUCCESS); }