simple udp server

udp_server.c

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

#define BUFSIZE 1024

void error(char *msg) {
  perror(msg);
  exit(1);
}

int main(int argc, char **argv) {
  int sockfd, clientlen, optval, n;
  struct sockaddr_in clientaddr;
  struct hostent *hostp;
  char buf[BUFSIZE], *hostaddrp;

  sockfd = socket(AF_INET, SOCK_DGRAM, 0);
  if (sockfd < 0) error("ERROR opening socket");

  optval = 1;
  setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (const void *)&optval , sizeof(int));
  clientlen = sizeof(clientaddr);

  while (1) {

    bzero(buf, BUFSIZE);

    /* uncomment from here */
    clientaddr.sin_family = AF_INET;
    clientaddr.sin_port = htons(6655);
    n = sendto(sockfd, buf, strlen(buf), 0, (struct sockaddr *) &clientaddr, clientlen);
    if (n < 0) error("ERROR in sendto");
    /* to here */

    n = recvfrom(sockfd, buf, BUFSIZE, 0, (struct sockaddr *) &clientaddr, &clientlen);
    if (n < 0) error("ERROR in recvfrom");

    hostp = gethostbyaddr((const char *)&clientaddr.sin_addr.s_addr, sizeof(clientaddr.sin_addr.s_addr), AF_INET);
    if (hostp == NULL) error("ERROR on gethostbyaddr");
    hostaddrp = inet_ntoa(clientaddr.sin_addr);
    if (hostaddrp == NULL) error("ERROR on inet_ntoa\n");
    printf("server received datagram from %s (%s)\n", hostp->h_name, hostaddrp);
    printf("server received %d/%d bytes: %s\n", strlen(buf), n, buf);
    
    n = sendto(sockfd, buf, strlen(buf), 0, (struct sockaddr *) &clientaddr, clientlen);
    if (n < 0) error("ERROR in sendto");
  }