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

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

static void show_socket_settings(int sock)
{
  int loop, ttl;
  size_t size;

  size = sizeof(loop);
  getsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &loop, &size);
  printf("IPV6_MULTICAST_LOOP(%d) = %d\n", size, loop);

  size = sizeof(ttl);
  getsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, &size);
  printf("IPV6_MULTICAST_HOPS(%d) = %d\n", size, ttl);
}

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

  int sock;                   /* socket descriptor */
  char send_str[MAX_LEN];     /* string to send */
  struct sockaddr_in6 mc_addr; /* socket address structure */
  unsigned int send_len;      /* length of string to send */
  char* mc_addr_str;          /* multicast IP address */
  unsigned short mc_port;     /* multicast port */
  int mc_ttl=1;     /* time to live (hop count) */

  /* validate number of arguments */
  if (argc != 3) {
    fprintf(stderr, 
            "Usage: %s <Multicast IP> <Multicast Port>\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 */

  /* 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 a socket for sending to the multicast address */
  if ((sock = socket(PF_INET6, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
    perror("socket() failed");
    exit(1);
  }

  show_socket_settings(sock);
  
  /* set the TTL (time to live/hop count) for the send */
  if ((setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, 
       (void*) &mc_ttl, sizeof(mc_ttl))) < 0) {
    perror("setsockopt() 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);

  printf("Begin typing (return to send, ctrl-C to quit):\n");

  /* clear send buffer */
  memset(send_str, 0, sizeof(send_str));

  while (fgets(send_str, MAX_LEN, stdin)) {
    send_len = strlen(send_str);

    /* send string to multicast address */
    if ((sendto(sock, send_str, send_len, 0, 
         (struct sockaddr *) &mc_addr, 
         sizeof(mc_addr))) != send_len) {
      perror("sendto() sent incorrect number of bytes");
      exit(1);
    }

    /* clear send buffer */
    memset(send_str, 0, sizeof(send_str));
  }

  show_socket_settings(sock);

  close(sock);  

  exit(0);
}