From: molnarl AT cdata DOT tvnet DOT hu
Date: Fri, 21 Nov 1997 14:04:08 +0100 (MET)
To: djgpp-workers AT delorie DOT com
Subject: popen/pclose update
Message-ID: <Pine.SOL.3.95.971121135940.1111A-100000@dumballah.tvnet.hu>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Precedence: bulk

Hi Workers!

It's time to update popen()/pclose() again :-) I've found a bug in
pclose: if you write something like this: pclose (stdin), you will
get a SIGSEGV. After looking at the code, I decided to reimplement
the whole stuff, because the original code seems too unsafe for me.

I added a new feature too, popen-ed but not pclose-d files are
removed when the program exits.

However I have a question: if you look at the line with '!!!' in
pclose, could you tell me why I have to include that line? I don't
understand why fflush is not enough. Any idea?

Laszlo

ps: I don't use diff because I changed every line :) but the
copyright message.

[Here is the original copyright stuff]

#include <libc/stubs.h>
#include <io.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <libc/file.h>

/* hold file pointer, command, mode, and the status of the command */
struct pipe_list {
  FILE *fp;
  int exit_status;
  struct pipe_list *next;
  char *command, mode;
};

/* static, global list pointer */
static struct pipe_list *pl = NULL;

FILE *
popen (const char *cm, const char *md) /* program name, pipe mode */
{
  struct pipe_list *l1;
  int fd;
  char *temp_name=NULL;

  /* make new node */
  if ((l1 = (struct pipe_list *) malloc (sizeof (*l1)))
     && (temp_name = strdup (tmpnam (0))))
  {
    l1->fp = NULL;
    l1->command = NULL;
    l1->next = pl;
    l1->exit_status = -1;
    l1->mode = md[0];

    /* if caller wants to read */
    if (md[0] == 'r' && (fd = dup (fileno (stdout))) >= 0)
    {
      if ((l1->fp = freopen (temp_name, "wb", stdout)))
      {
        l1->exit_status = system (cm);
        if (dup2 (fd, fileno (stdout)) >= 0)
          l1->fp = fopen (temp_name, md);
      }
      close (fd);
    }
    /* if caller wants to write */
    else if (md[0] == 'w' && (l1->command = strdup (cm)))
      l1->fp = fopen (temp_name, md);

    if (l1->fp)
    {
      l1->fp->_flag |= _IORMONCL; /* remove on close */
      l1->fp->_name_to_remove = temp_name;
      return (pl = l1)->fp;
    }
    free (l1->command);
  }
  free (temp_name);
  free (l1);
  return NULL;
}

int
pclose (FILE *pp)
{
  struct pipe_list *l1, **l2;   /* list pointers */
  int retval=-1;                /* function return value */

  for (l2 = &pl; *l2 && (*l2)->fp != pp; l2 = &((*l2)->next))
    ;
  if (!(l1 = *l2))
    return retval;
  *l2 = l1->next;

  /* if pipe was opened to write */
  if (l1->mode == 'w')
  {
    int fd;
    fflush (l1->fp);
    close (fileno (l1->fp));     /* !!! Ugly, but needed !!! */

    if ((fd = dup (fileno (stdin))) >= 0
       && (freopen (l1->fp->_name_to_remove, "rb", stdin)))
    {
      retval = system (l1->command);
      dup2 (fd, fileno (stdin));
    }
    close (fd);
    free (l1->command);
  }
  else
    /* if pipe was opened to read, return the exit status we saved */
    retval = l1->exit_status;

  fclose (l1->fp);              /* this removes the temp file */
  free (l1);
  return retval;                /* retval==0 ? OK : ERROR */
}