sendudp C file, modified from Paul Kryzanowski

sendudp.c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <netdb.h>

/* somewhat modified version of Paul Kryzanowski's example
 * https://www.cs.rutgers.edu/~pxk/417/notes/sockets/udp.html 
 */

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

  if (argc != 4 && argc != 5) {
    printf("usage:\n  sendudp <host> <port> <message> [recv]\n");
    return -1;
  }

  int sock;
  struct hostent* hp;
  struct sockaddr_in servaddr;
  char * my_message = argv[3];
  
  servaddr.sin_family = AF_INET;
  servaddr.sin_port = htons(atoi(argv[2]));
  hp = gethostbyname(argv[1]);

  if (!hp) {
    printf("problems\n");
    return 0;
  }

  sock = socket (AF_INET, SOCK_DGRAM, 0);

  if (sock < 0) {
    printf("problem opening socket");
  }

  memcpy((void*)&servaddr.sin_addr, 
    hp->h_addr_list[0], 
    hp->h_length);

  int sendto_ret;
  sendto_ret = sendto(sock, my_message, strlen(my_message), 0, 
    (struct sockaddr*)&servaddr, sizeof(servaddr));

  if (argc == 5 && !strcmp(argv[4],"recv")) {
    int buffsize = 18000;
    char buffer[buffsize]; /* Will not surpass this */
    int ret;
    struct sockaddr_in remote;
    socklen_t addlen = sizeof(remote);

    memset(buffer, 0, buffsize);

    printf("Waiting for response...\n");
    ret = recvfrom(sock, buffer, buffsize, 0, 
            (struct sockaddr*)&remote, &addlen);

    printf("[%s]\n", buffer);
  }

  if (sendto_ret < 0) {
    perror("problem sending ");
  }
  
  close(sock);
 
  return 0;
}