Re: trouble receiving multicast

[Wes Chow <wes@woahnelly.net>]

I've attached a self contained program that exhibits the problem.  I'm
hoping I've merely missed some detail...

Wes

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/** \file A tool for subscribing to multicast addresses. */


#include <stdlib.h>
#include <iostream>
#include <unistd.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/un.h>




int main(int argc, char **argv)
{
    if (argc != 4) {
	std::cout << "usage:  mcasttest dev mcastaddr port" << std::endl;
	return 1;
    }

    const char *dev = argv[1];
    const char *mcastaddr = argv[2];
    int port = atoi(argv[3]);


    int fd = socket(AF_INET, SOCK_DGRAM, 0);
    try {
        // reuse socket
        if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, reinterpret_cast<const char*>(&port), sizeof(port)) != 0)
            throw "couldn't set socket to reuse";

        // bind socket
        struct sockaddr_in saddr;
        saddr.sin_family = AF_INET;
        saddr.sin_port = htons(port);
        saddr.sin_addr.s_addr = htonl(INADDR_ANY);
        if (bind(fd, (struct sockaddr *) &saddr, sizeof(saddr)) != 0)
            throw "couldn't bind address";


        // join mcast group
        struct ip_mreq mreq;
        bzero(&mreq, sizeof(mreq));
        if (inet_pton(AF_INET, mcastaddr, &mreq.imr_multiaddr) <= 0)
            throw "couldn't set mcast address";
        struct ifreq ifreq;
        strncpy(ifreq.ifr_name, dev, IFNAMSIZ);

        if (ioctl(fd, SIOCGIFADDR, &ifreq) < 0)
            throw "couldn't get iface address";

        memcpy(&mreq.imr_interface,
               &((struct sockaddr_in *) &ifreq.ifr_addr)->sin_addr,
               sizeof(struct in_addr));

        if (setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP,
                       reinterpret_cast<const char*>(&mreq), sizeof(mreq)) != 0)
            throw "couldn't join mcast group";
    } catch (const char *err) {
        std::cout << "error:  " << err << std::endl;
        return 1;
    }

    const unsigned int bufsize = 1024;
    char buf[bufsize];
    size_t amt = 0;
    while ( (amt = read(fd, buf, bufsize)) > 0)
        std::cout << "got " << amt << " bytes" << std::endl;

    return 0;
}