#include <stdio.h>      /* for fprintf() */
#include <sys/socket.h> /* for socket(), connect(), send(), and recv() */
#include <arpa/inet.h>  /* for sockaddr_in and inet_addr() */
#include <stdlib.h>     /* for atoi() and exit() */
#include <string.h>     /* for memset() */
#include <unistd.h>     /* for sleep() */

void DieWithError(char *errorMessage);  /* External error handling function */

int main(int argc, char *argv[])
{
    int sock;                         /* Socket */
    struct sockaddr_in multicastAddr; /* Multicast address */
    char *multicastIP;                /* IP Multicast address */
    unsigned short multicastPort;     /* Server port */
    char *sendString;                 /* String to multicast */
    unsigned char multicastTTL;       /* TTL of multicast packets */
    unsigned int sendStringLen;       /* Length of string to multicast */

    if ((argc < 4) || (argc > 5))         /* Test for correct number of parameters */
    {
        fprintf(stderr,"Usage:  %s <Multicast Address> <Port> <Send String> [<TTL>]\n",
                 argv[0]);
        exit(1);
    }

    multicastIP = argv[1];            /* First arg:  multicast IP address */ 
    multicastPort = atoi(argv[2]);    /* Second arg:  multicast port */
    sendString = argv[3];             /* Third arg:  String to multicast */

    if (argc == 5)                     /* Is TTL specified on command-line? */
        multicastTTL = atoi(argv[4]);  /* Command-line specified TTL */
    else
        multicastTTL = 1;              /* Default TTL = 1 */

    /* Create socket for sending/receiving datagrams */
    if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
        DieWithError("socket() failed");

    /* Set TTL of multicast packet */
    if (setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL, (void *) &multicastTTL, 
          sizeof(multicastTTL)) < 0)
        DieWithError("setsockopt() failed");

    /* Construct local address structure */
    memset(&multicastAddr, 0, sizeof(multicastAddr));   /* Zero out structure */
    multicastAddr.sin_family = AF_INET;                 /* Internet address family */
    multicastAddr.sin_addr.s_addr = inet_addr(multicastIP);/* Multicast IP address */
    multicastAddr.sin_port = htons(multicastPort);         /* Multicast port */

    sendStringLen = strlen(sendString);  /* Find length of sendString */
    for (;;) /* Run forever */
    {
        /* Multicast sendString in datagram to clients every 3 seconds */
        if (sendto(sock, sendString, sendStringLen, 0, (struct sockaddr *) 
              &multicastAddr, sizeof(multicastAddr)) != sendStringLen)
            DieWithError("sendto() sent a different number of bytes than expected");
        sleep(3);
    }
    /* NOT REACHED */
}