#include <errno.h>       /* for perror                            */
#include <netinet/in.h>  /* for sockaddr_in, INADDR_ANY           */
#include <stdlib.h>      /* for atoi, exit                        */
#include <stdio.h>       /* for fprintf, perror                   */
#include <sys/socket.h>  /* for socket, bind, socklen_t, recvfrom */
                         /*     AF_INET, SOCK_DGRAM               */
#include <sys/types.h>   /* for socket, bind, uint16_t, ssize_t   */
#include <unistd.h>      /* for read, write                       */

#define BLKSIZE  1024

void main(int argc, char *argv[])
/*
 *  This is a server test of UDP. 
 *  It receives datagrams from a well-known port 
 *  and outputs them to standard output. 
 */
{
    uint16_t port;
    int sock;
    struct sockaddr_in server;
    struct sockaddr_in client;
    ssize_t bytesread;
    ssize_t byteswritten;
    socklen_t clientlen;
    char buf[BLKSIZE];
       
    if (argc != 2) {
        fprintf(stderr, "Usage: %s port\n", argv[0]);
        exit(1);
    }
                       /* set up the address of the server */
    server.sin_family = AF_INET;
    port = (uint16_t)atoi(argv[1]); 
    server.sin_port = htons(port);
    server.sin_addr.s_addr = htonl(INADDR_ANY);

                       /* create the socket */
   if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
      perror("Unable to create socket");
      exit(1);
   } 
                      /* bind the socket to a well-known port */
   if ( bind(sock, (struct sockaddr *)&server, sizeof(server)) < 0) {
      perror("Unable to bind well-known port to socket");
      exit(1);
   }

                      /* receive from clients */
   while( (bytesread = recvfrom(sock, buf, (size_t)BLKSIZE, 0, (struct sockaddr *)&client, 
                                &clientlen) ) > 0) {
      byteswritten = write(STDOUT_FILENO, buf, (size_t)bytesread);
      if (bytesread != byteswritten) {
          fprintf(stderr, "Error writing %ld bytes, %ld bytes written\n",
             (long)bytesread, (long)byteswritten);
      }
   }
   close(sock);
   exit(0);
}