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

// receiver listening port
#define RCVR_PORT 4950

int main(int argc, char *argv[])
{
    int sockfd;
    struct sockaddr_in rcvr_addr;
    struct hostent *he;
    int numbytes;

    if (argc != 3)
    {
        fprintf(stderr,"usage: talker hostname message\n");
        exit(1);
    }

    // translates receiver name to address
    he = gethostbyname(argv[1]) ;
    if (he == NULL)
    {
        perror("gethostbyname");
        exit(1);
    }

    // fills the receiver struct info
    rcvr_addr.sin_family = AF_INET;
    rcvr_addr.sin_port   = htons(RCVR_PORT);
    rcvr_addr.sin_addr   = *((struct in_addr *)he->h_addr);

    // zeroes the rest of the struct
    memset(&(rcvr_addr.sin_zero), '\0', 8);

    // creates the UDP socket
    sockfd = socket (AF_INET, SOCK_DGRAM, 0) ;
    if (sockfd == -1)
    {
        perror("socket");
        exit(1);
    }

    // sends the message to the receiver using the socket
    numbytes = sendto (sockfd, argv[2], strlen(argv[2]), 0,
                       (struct sockaddr *) &rcvr_addr,
                       sizeof(struct sockaddr)) ;
    if (numbytes == -1)
    {
        perror("sendto");
        exit(1);
    }

    printf ("sent %d bytes to host %s port %d\n", numbytes,
            inet_ntoa (rcvr_addr.sin_addr), RCVR_PORT);

    // closes the socket
    close (sockfd);

    return 0;
}