#include <sys/types.h>  /* for type definitions */
#include <sys/socket.h> /* for socket API calls */
#include <netinet/in.h> /* for address structs */
#include <arpa/inet.h>  /* for sockaddr_in */
#include <net/if.h>
#include <stdio.h>      /* for printf() and fprintf() */
#include <stdlib.h>     /* for atoi() */
#include <string.h>     /* for strlen() */
#include <unistd.h>     /* for close() */

#define MAX_LEN  1024   /* maximum receive string size */
#define MIN_PORT 1024   /* minimum port allowed */
#define MAX_PORT 65535  /* maximum port allowed */

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

  int sock;                     /* socket descriptor */
  int flag_on = 1;              /* socket option flag */
  struct sockaddr_in6 mc_addr;   /* socket address structure */
  char recv_str[MAX_LEN+1];     /* buffer to receive string */
  int recv_len;                 /* length of string received */
  struct ipv6_mreq mc_req;        /* multicast request structure */
  char* mc_addr_str;            /* multicast IP address */
  unsigned short mc_port;       /* multicast port */
  struct sockaddr_in6 from_addr; /* packet source */
  unsigned int from_len;        /* source addr length */
  char *if_name;

  /* validate number of arguments */
  if (argc != 4) {
    fprintf(stderr, 
            "Usage: %s <Multicast IP> <Multicast Port> <Interface Name>\n", 
            argv[0]);
    exit(1);
  }

  mc_addr_str = argv[1];      /* arg 1: multicast ip address */
  mc_port = atoi(argv[2]);    /* arg 2: multicast port number */
  if_name = argv[3];          /* arg 3: interface name */

  /* validate the port range */
  if ((mc_port < MIN_PORT) || (mc_port > MAX_PORT)) {
    fprintf(stderr, "Invalid port number argument %d.\n",
            mc_port);
    fprintf(stderr, "Valid range is between %d and %d.\n",
            MIN_PORT, MAX_PORT);
    exit(1);
  }

  /* create socket to join multicast group on */
  if ((sock = socket(PF_INET6, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
    perror("socket() failed");
    exit(1);
  }
  
  /* set reuse port to on to allow multiple binds per host */
  if ((setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &flag_on,
       sizeof(flag_on))) < 0) {
    perror("setsockopt() 1 failed");
    exit(1);
  }

  /* construct a multicast address structure */
  memset(&mc_addr, 0, sizeof(mc_addr));
  mc_addr.sin6_family      = AF_INET6;
  inet_pton(AF_INET6, mc_addr_str, mc_addr.sin6_addr.s6_addr);
  mc_addr.sin6_port        = htons(mc_port);

  /* bind to multicast address to socket */
  if ((bind(sock, (struct sockaddr *) &mc_addr, 
       sizeof(mc_addr))) < 0) {
    perror("bind() failed");
    exit(1);
  }

  /* construct an IGMP join request structure */
  inet_pton(AF_INET6, mc_addr_str, mc_req.ipv6mr_multiaddr.s6_addr);
  mc_req.ipv6mr_interface = if_nametoindex(if_name);

  /* send an ADD MEMBERSHIP message via setsockopt */
  if ((setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, 
       (void*) &mc_req, sizeof(mc_req))) < 0) {
    perror("setsockopt() 2 failed");
    exit(1);
  }

  for (;;) {          /* loop forever */
    char buffer[64];

    /* clear the receive buffers & structs */
    memset(recv_str, 0, sizeof(recv_str));
    from_len = sizeof(from_addr);
    memset(&from_addr, 0, from_len);

    /* block waiting to receive a packet */
    if ((recv_len = recvfrom(sock, recv_str, MAX_LEN, 0, 
         (struct sockaddr*)&from_addr, &from_len)) < 0) {
      perror("recvfrom() failed");
      exit(1);
    }

    /* output received string */
    printf("Received %d bytes from %s: ", recv_len, 
           inet_ntop(AF_INET6, &from_addr.sin6_addr, buffer, 64));
    printf("%s", recv_str);
  }

  /* send a DROP MEMBERSHIP message via setsockopt */
  if ((setsockopt(sock, IPPROTO_IPV6, IPV6_DROP_MEMBERSHIP, 
       (void*) &mc_req, sizeof(mc_req))) < 0) {
    perror("setsockopt() 3 failed");
    exit(1);
  }

  close(sock);  
}