#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <sys/time.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>

int readn(int socket_fd, unsigned char *ptr, int len);

int main(int argc, char *argv[])
{
  struct sockaddr_in serv_sock_addr, client_sock_addr;
  int cli_addrlen, socket_fd, socket_fd2;
  unsigned char data;
  int port_number;

  if (argc != 2)
    {
      printf("Usage: tcp_server <port number> \n");
      exit(1);
    }

  port_number = atoi(argv[1]);
  if (port_number < 1024) 
    {
      printf("Invalid port number. Port < 1024. Aborting ...\n");
      exit(1);
    }

  if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) exit(1);
  bzero((char *) &serv_sock_addr, sizeof(serv_sock_addr));
  serv_sock_addr.sin_family = AF_INET;
  serv_sock_addr.sin_addr.s_addr = htonl(INADDR_ANY);
  serv_sock_addr.sin_port = htons((short)port_number);
  
  if (bind(socket_fd, (struct sockaddr *) &serv_sock_addr,
	   sizeof(serv_sock_addr)) < 0) exit(1);
  listen(socket_fd, 5);
  cli_addrlen = sizeof(client_sock_addr);
  
  socket_fd2 = accept(socket_fd, (struct sockaddr *)
		      &client_sock_addr, &cli_addrlen);
  if (socket_fd2 < 0) exit(1);
  while (1)
    {
      read(socket_fd2, &data, 1);
      if (data == 0) 
	{
	 close(socket_fd2);
	 break;
	}
      else
	write(socket_fd2, &data, 1);
    }
  close(socket_fd);
}

int readn(int socket_fd, unsigned char *ptr, int len)
{
  int remaining, read_size;
  
  remaining = len;
  while (remaining > 0)
    {
      read_size = read(socket_fd, ptr, remaining);
      if (read_size < 0) return(read_size);
      else if (read_size == 0) break;
      
      remaining -= read_size;
      ptr += read_size;
    }
  return(len - remaining);
}