#define _GNU_SOURCE 1
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/tcp.h>
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>

#define PORT 5000

int
main (void)
{
  struct sockaddr_in sockaddr;
  socklen_t tmp;
  int listen_fd, send_fd, recv_fd;
  char charbuf;
  ssize_t ssize;
  int i;

  setbuf (stdout, NULL);

  /* bind/listen.  */
  errno = 0;
  listen_fd = socket (PF_INET, SOCK_STREAM, IPPROTO_TCP);
  assert (listen_fd != -1);

  sockaddr.sin_family = PF_INET;
  sockaddr.sin_port = htons (PORT);
  sockaddr.sin_addr.s_addr = INADDR_ANY;

  if (bind (listen_fd, (struct sockaddr *) &sockaddr, sizeof (sockaddr))
      || listen (listen_fd, 1))
    perror ("Can't bind address");

  /* Connect.  */
  send_fd = socket (PF_INET,SOCK_STREAM, 0);
  assert (send_fd != -1);

  memset (&sockaddr, 0, sizeof sockaddr);
  sockaddr.sin_family = AF_INET;
  sockaddr.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
  sockaddr.sin_port = htons (PORT);

  i = connect (send_fd, (struct sockaddr *) &sockaddr, sizeof (sockaddr));
  assert (i == 0);

  /* Accept.  */
  tmp = sizeof (sockaddr);
  recv_fd = accept (listen_fd, (struct sockaddr *) &sockaddr, &tmp);
  assert (recv_fd != -1);

  /* Send.  */
  charbuf = 'a';
  ssize = send (send_fd, &charbuf, 1, 0);
  assert (ssize == 1);

  /* Now that data has been queued, close the receiving end.  */
  fputs ("sleeping ...", stdout);
  sleep (1);
  fputs (" closing ...", stdout);
  close (recv_fd);
  sleep (1);
  puts (" done");

  /* Try sending again.  */
  charbuf = 'b';
  errno = 0;
  ssize = send (send_fd, &charbuf, 1, 0);
  assert_perror (errno);
  assert (ssize == 1);
  puts ("send ok");

  return 0;
}