Use multicast loopbacking.

[mctap.git] / src / mctap.c

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

#include "utils.h"

static void usage(FILE *out)
{
    fprintf(out, "usage: mctap [-h] MCASTGROUP PORT\n");
}

static char *formataddress(struct sockaddr *arg, socklen_t arglen)
{
    struct sockaddr_in *ipv4;
    struct sockaddr_in6 *ipv6;
    static char *ret = NULL;
    char buf[1024];
    
    if(ret != NULL)
	free(ret);
    ret = NULL;
    switch(arg->sa_family)
    {
    case AF_UNIX:
	ret = strdup("Unix socket");
	break;
    case AF_INET:
	ipv4 = (struct sockaddr_in *)arg;
	if(inet_ntop(AF_INET, &ipv4->sin_addr, buf, sizeof(buf)) == NULL)
	    return(NULL);
	ret = sprintf2("%s:%i", buf, (int)ntohs(ipv4->sin_port));
	break;
    case AF_INET6:
	ipv6 = (struct sockaddr_in6 *)arg;
	if(inet_ntop(AF_INET6, &ipv6->sin6_addr, buf, sizeof(buf)) == NULL)
	    return(NULL);
	ret = sprintf2("[%s]:%i", buf, (int)ntohs(ipv6->sin6_port));
	break;
    default:
	errno = EPFNOSUPPORT;
	break;
    }
    return(ret);
}

static int mkmcastsk4(struct in_addr group, int port)
{
    int fd;
    int soval;
    struct sockaddr_in nm;
    struct ip_mreqn mreq;
    
    fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
    soval = 1;
    if(setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &soval, sizeof(soval)))
	return(-1);
    memset(&nm, 0, sizeof(nm));
    nm.sin_family = AF_INET;
    nm.sin_port = htons(port);
    if(bind(fd, (struct sockaddr *)&nm, sizeof(nm)))
	return(-1);
    memset(&mreq, 0, sizeof(mreq));
    mreq.imr_multiaddr = group;
    if(setsockopt(fd, SOL_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq)))
	return(-1);
    soval = 1;
    if(setsockopt(fd, SOL_IP, IP_MULTICAST_LOOP, &soval, sizeof(soval)))
	return(-1);
    return(fd);
}

static void test(int fd)
{
    char buf[65536];
    int ret;
    struct sockaddr_storage nm;
    socklen_t nmlen;
    
    while(1) {
	nmlen = sizeof(nm);
	ret = recvfrom(fd, buf, sizeof(buf), 0, (struct sockaddr *)&nm, &nmlen);
	if(ret < 0) {
	    fprintf(stderr, "mctap: recvfrom: %s\n", strerror(ret));
	    exit(1);
	}
	printf("%s %i:\n", formataddress((struct sockaddr *)&nm, nmlen), ret);
    }
}

int main(int argc, char **argv)
{
    int c;
    int sock;
    struct in_addr group;
    int port;
    
    while((c = getopt(argc, argv, "h")) >= 0) {
	switch(c) {
	case 'h':
	    usage(stdout);
	    return(0);
	default:
	    usage(stderr);
	    exit(1);
	}
    }
    if(argc - optind < 2) {
	usage(stderr);
	exit(1);
    }
    if(!inet_aton(argv[optind], &group)) {
	fprintf(stderr, "mctap: invalid group address: %s\n", argv[optind]);
	exit(1);
    }
    port = atoi(argv[optind + 1]);
    if((sock = mkmcastsk4(group, port)) < 0) {
	fprintf(stderr, "mctap: could not create multicast socket: %s\n", strerror(errno));
	exit(1);
    }
    
    test(sock);
    return(0);
}