Simple client/server multicast test

mcasttest.c

/*
 * Compile:
 *
 *   gcc mcasttest.c -o server -Wall
 *   ln -s server client
 *
 * Invoke:
 *
 *   ./client
 *   ./server
 */

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

#define HELLO_PORT 12345
#define HELLO_GROUP "225.0.0.37"
#define MSGBUFSIZE 256

static void die(const char *s) {
        perror(s);
        exit(1);
}

static void server(void) {
        char *message = "Hello, World!";
        int fd, r;
        struct sockaddr_in addr = {
                .sin_family = AF_INET,
                .sin_addr.s_addr = inet_addr(HELLO_GROUP),
                .sin_port = htons(HELLO_PORT),
        };

        /* create what looks like an ordinary UDP socket */
        fd = socket(AF_INET, SOCK_DGRAM, 0);
        if (fd < 0)
                die("socket");

        for (;;) {
                r = sendto(fd, message, strlen(message) + 1, 0, (struct sockaddr *) &addr, sizeof(addr));
                if (r < 0)
                        die("sendto");

                sleep(1);
        }
}

static void client(void) {
        int r, fd;
        char msgbuf[MSGBUFSIZE];
        unsigned one = 1;
        struct sockaddr_in addr = {
                .sin_family = AF_INET,
                .sin_addr.s_addr = htonl(INADDR_ANY),
                .sin_port = htons(HELLO_PORT),
        };
        struct ip_mreq mreq = {
                .imr_multiaddr.s_addr = inet_addr(HELLO_GROUP),
                .imr_interface.s_addr = htonl(INADDR_ANY),
        };

        fd = socket(AF_INET, SOCK_DGRAM, 0);
        if (fd < 0)
                die("socket");

        r = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
        if (r < 0)
                die("setsockopt(SO_REUSEADDR)");

        r = bind(fd, (struct sockaddr *) &addr,sizeof(addr));
        if (r < 0)
                die("bind");

        r = setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));
        if (r < 0)
                die("setsockopt(IP_ADD_MEMBERSHIP)");

        for (;;) {
                unsigned addrlen = sizeof(addr);
                int nbytes;

                nbytes = recvfrom(fd, msgbuf, MSGBUFSIZE, 0, (struct sockaddr *) &addr, &addrlen);
                if (nbytes < 0)
                        die("recvfrom");

                printf("received %d bytes: >%s<\n", nbytes, msgbuf);
        }
}

int main(int argc, char **argv) {

        if (strstr(basename(argv[0]), "server"))
                server();
        else
                client();

        return 0;
}