udp multicast example

udpmuticast.c

/*
 *
 * multicast.c
 *
 * The following program sends or receives multicast packets. If invoked
 * with one argument, it sends a packet containing the current time to an
 * arbitrarily chosen multicast group and UDP port. If invoked with no
 * arguments, it receives and prints these packets. Start it as a sender on
 * just one host and as a receiver on all the other hosts
 *
 * */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>

#define EXAMPLE_PORT 61499
#define EXAMPLE_GROUP "226.0.0.1"

main(int argc)
{
        struct sockaddr_in addr;
        int addrlen, sock, cnt;
        struct ip_mreq mreq;
        char message[50];

        /* set up socket */
        sock = socket(AF_INET, SOCK_DGRAM, 0);
        if (sock < 0) {
                perror("socket");
                exit(1);
        }
        bzero((char *)&addr, sizeof(addr));
        addr.sin_family = AF_INET;
        addr.sin_addr.s_addr = htonl(INADDR_ANY);
        addr.sin_port = htons(EXAMPLE_PORT);
        addrlen = sizeof(addr);

        if (argc > 1) {
                /* send */
                addr.sin_addr.s_addr = inet_addr(EXAMPLE_GROUP);
                while (1) {
                        time_t t = time(0);
                        sprintf(message, "time is %-24.24s", ctime(&t));
                        printf("sending: %s\n", message);
                        cnt = sendto(sock, message, sizeof(message), 0,
                                        (struct sockaddr *) &addr, addrlen);
                        if (cnt < 0) {
                                perror("sendto");
                                exit(1);
                        }
                        sleep(5);
                }
        } else {
                int optval = 1;
                if(setsockopt(sock, SOL_SOCKET, SO_REUSEPORT, &optval, sizeof(optval)) < 0){
                        perror("set socket reuse error:");
                }



                /* receive */
                if (bind(sock, (struct sockaddr *)&addr, sizeof(addr)) < 0)
                {
                        perror("bind");
                        exit(1);
                }
                mreq.imr_multiaddr.s_addr = inet_addr(EXAMPLE_GROUP);
                mreq.imr_interface.s_addr = htonl(INADDR_ANY);
                if (setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP,
                                        &mreq, sizeof(mreq)) < 0) {
                        perror("setsockopt mreq");
                        exit(1);
                }
                while (1) {
                        cnt = recvfrom(sock, message, sizeof(message), 0,
                                        (struct sockaddr *) &addr, &addrlen);
                        if (cnt < 0) {
                                perror("recvfrom");
                                exit(1);
                        } else if (cnt == 0) {
                                break;
                        }
                        printf("%s: message = \"%s\"\n", inet_ntoa(addr.sin_addr), message);
                }
        }
}