/**********************************************
 *
 Pierre A. Humblet. Jan 24, 2002

 This demo program exposes a bug where there
 are two listen on the same tcp port.
 New connections may or may not be accepted 

**********************************************/
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <signal.h>
#include <netinet/in.h>
#include <unistd.h>

enum {FALSE, TRUE};
static int sighup_seen;
static int call_seen;

/*************************************************
*             SIGHUP Handler                     *
*************************************************/
static void
sighup_handler(int sig)
{
sig = sig;    /* Keep picky compilers happy */
sighup_seen = TRUE;
signal(SIGHUP, sighup_handler);
}

/*************************************************
*             main                               *
*************************************************/
main(int argc, char * argv[])
{
  int on = 1, sockfd, newsockfd, lcount, peer_size, pid;
  struct sockaddr_in addr, peer;
  fd_set select_listen;
  FILE *outfd;

  /************************************************
   *
   Open a socket and listen on port 999

  ************************************************/

  sockfd = socket(AF_INET, SOCK_STREAM, 0);
  if (sockfd < 0) 
    printf("socket: %s\n", strerror(errno));

  if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
    printf("setsockopt: %s\n", strerror(errno));
  
  memset(&addr, 0, sizeof(addr));
  addr.sin_family = AF_INET;
  addr.sin_port = htons(999);
  addr.sin_addr.s_addr = INADDR_ANY;
  if (bind(sockfd, (struct sockaddr *) &addr, sizeof(addr)) < 0)
    printf("bind: %s\n", strerror(errno));
  
  if (listen(sockfd, 2) < 0) 
    printf("listen: %d %s\n", errno, strerror(errno));
 
  sighup_seen = FALSE;
  signal(SIGHUP, sighup_handler);

  call_seen = FALSE;
  pid = getpid();

  /************************************************
   *
   Now wait for a call or sighup, causing a re-exec
   After a re-exec following a call, there are two
   listen on port 999 (netstat -a)
   Incoming calls may or may not work.
   
  ************************************************/

  while(1) {
    FD_ZERO(&select_listen);
    FD_SET(sockfd, &select_listen);
    if (getenv("EXEC") != NULL) {
        printf("netstat -a will show two listen on port 999\n");
    }
    else if (call_seen == FALSE) { 
        printf("telnet localhost 999\n");
    }
    else 
        printf("kill -HUP %d\n", pid);
    lcount = select(sockfd + 1, &select_listen, NULL, NULL, NULL);
    if (lcount == 1) {
      peer_size = sizeof(peer);
      newsockfd = accept(sockfd, (struct sockaddr *) &peer, &peer_size);
      if (newsockfd < 0) {
        printf("accept: %s\n", strerror(errno));
      }
      else {
        printf("Got a call\n");
        call_seen = TRUE;
        outfd = fdopen(newsockfd, "wb");
        if (outfd == NULL)
            printf("fdopen: %s\n", strerror(errno));
        if (fork() == 0) {
          signal(SIGHUP, SIG_IGN);
          close(sockfd);     /* Close the listening socket */
          fprintf(outfd, "quit with ESC  CTRL-] and quit then\n");
          fprintf(outfd, "kill -HUP %d\n", pid);
          fprintf(outfd, "netstat -a will show two listen on port 999\n");
          fflush(outfd);
          /* In this demo we sleep. In reality the child is working */
          sleep(60);
          printf("Child exiting\n");
          fclose(outfd);    /* Close the accepted socket */
          exit(0);
        }
        else {
          fclose(outfd);    /* Close the accepted socket */
        }
      }
    }
    else if (sighup_seen == TRUE) {
      if (call_seen == TRUE) putenv("EXEC=1");
      close(sockfd);        /* Close the listening socket */
      signal(SIGHUP, SIG_IGN);
      printf("Signal seen. Execing\n");
      execv(argv[0], argv);
    }
    else printf("Error %s\n", strerror(errno));
  }
}