Thread: Problem on Multicast UDP receiver

Hello,

I am in the process of setting up a multicast UDP receiver (group 224.2.2.2) under IPv4.

However, when I send a UDP message on the 224.2.2.2, I don't receive anything at the receiver. Whereas when I send a UDP message on the localhost, it works very well. I think that adding the receiver to the multicast group is not done correctly but I can't guess why. Could someone please help me?

I put the code for my multicast receiver:

Code:

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

#define BUFSIZE 100000

int main(int argc, char **argv) {
  int sfd, s, rsz, r;
  struct addrinfo hints;
  struct addrinfo *result, *rp;
  ssize_t nrecv;
  char buf[BUFSIZE];
  struct sockaddr_storage from;
  socklen_t fromlen;
  char host[NI_MAXHOST], service[NI_MAXSERV];

  if (argc != 2) {
    printf("Usage: %s port \n", argv[0]);
    exit(EXIT_FAILURE);
  }

 /* Construction of the local address (for bind) */
  memset(&hints, 0, sizeof(struct addrinfo));
  hints.ai_family = AF_INET;
  hints.ai_socktype = SOCK_DGRAM;       /* Datagram socket */
  hints.ai_protocol = 0; 

  s = getaddrinfo(NULL, argv[1], &hints, &result);
  if (s != 0) {
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
    exit(EXIT_FAILURE);
  }

  /* getaddrinfo () returns a list of address structures.
     We try each address until bind (2) succeeds.
     If socket (2) (or bind (2)) fails, we close the socket and we
     try the following address. */
  for (rp = result; rp != NULL; rp = rp->ai_next) {

    /* Creation of the socket */
    sfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
    if (sfd == -1)
      continue;

    /* Association of a port to the socket */
    r = bind(sfd, rp->ai_addr, rp->ai_addrlen);
    if (r == 0)
      break;            /* Success */
    close(sfd);
  }

  if (rp == NULL) {     /* no valid address */
    perror("bind");
    exit(EXIT_FAILURE);
  }
  freeaddrinfo(result); /* no need anymore */

  /* allow multiple sockets to use the same port number */
  int reuse = 1;
  if (setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(reuse)) < 0)
  {
     perror("setsockopt SO_REUSEADDR");
  }


  /* ask the kernel to join a multicast group which is 224.2.2.2*/
  struct ip_mreq mreq;
  mreq.imr_multiaddr.s_addr = inet_addr("224.2.2.2");
  mreq.imr_interface.s_addr = htonl(INADDR_ANY);
  if (setsockopt(sfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&mreq, sizeof(mreq)) < 0)
  {
    perror("setsockopt IP_ADD_MEMBERSHIP");
  }

  /* communication loop */
  for (;;) {
    /* data reception */
    fromlen = sizeof(from);
    nrecv = recvfrom(sfd, &buf, BUFSIZE, 0, (struct sockaddr *)&from, &fromlen);
    if (nrecv == -1) {
      perror("Socket read error\n");
      exit(EXIT_FAILURE);
    }
    printf("received %zd bytes\n", nrecv);

    /* Recognition of the client machine*/
    s = getnameinfo((struct sockaddr *)&from, fromlen,
			host, NI_MAXHOST, service, NI_MAXSERV,
			NI_NUMERICHOST | NI_NUMERICSERV);
    if (s == 0)
      printf("Transmitter '%s'  Port '%s'\n", host, service);
    else
      printf("Error: %s\n", gai_strerror(s));
  }
}