/*	$NetBSD: freopen.c,v 1.22 2018/01/17 01:24:30 kamil Exp $	*/

/*-
 * Copyright (c) 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <wchar.h>
#include <limits.h>
#include "reentrant.h"
#include "local.h"

/*
 * Re-direct an existing, open (probably) file to some other file.
 * ANSI is written such that the original file gets closed if at
 * all possible, no matter what.
 */
FILE *freopen(const char *file, const char *mode, FILE *fp) {
  int f;
  int flags, isopen, oflags, sverrno, wantfd;

  _DIAGASSERT(file != NULL);
  _DIAGASSERT(mode != NULL);
  _DIAGASSERT(fp != NULL);

  if ((flags = __sflags(mode, &oflags)) == 0) {
    (void)fclose(fp);
    return NULL;
  }

  if (!__sdidinit)
    __sinit();

  /*
   * There are actually programs that depend on being able to "freopen"
   * descriptors that weren't originally open.  Keep this from breaking.
   * Remember whether the stream was open to begin with, and which file
   * descriptor (if any) was associated with it.  If it was attached to
   * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
   * should work.  This is unnecessary if it was not a Unix file.
   */
  if (fp->_flags == 0) {
    fp->_flags = __SEOF; /* hold on to it */
    isopen = 0;
    wantfd = -1;
  } else {
    /* flush the stream; ANSI doesn't require this. */
    if (fp->_flags & __SWR)
      (void)__sflush(fp);
    /* if close is NULL, closing is a no-op, hence pointless */
    isopen = fp->_close != NULL;
    if ((wantfd = __sfileno(fp)) == -1 && isopen) {
      (void)(*fp->_close)(fp->_cookie);
      isopen = 0;
    }
  }

  /* Get a new descriptor to refer to the new file. */
  f = open(file, oflags, DEFFILEMODE);
  if (f < 0 && isopen) {
    /* If out of fd's close the old one and try again. */
    if (errno == ENFILE || errno == EMFILE) {
      (void)(*fp->_close)(fp->_cookie);
      isopen = 0;
      f = open(file, oflags, DEFFILEMODE);
    }
  }
  sverrno = errno;

  /*
   * Finish closing fp.  Even if the open succeeded above, we cannot
   * keep fp->_base: it may be the wrong size.  This loses the effect
   * of any setbuffer calls, but stdio has always done this before.
   */
  if (isopen && f != wantfd)
    (void)(*fp->_close)(fp->_cookie);
  if (fp->_flags & __SMBF)
    free((char *)fp->_bf._base);
  fp->_w = 0;
  fp->_r = 0;
  fp->_p = NULL;
  fp->_bf._base = NULL;
  fp->_bf._size = 0;
  fp->_lbfsize = 0;
  if (HASUB(fp))
    FREEUB(fp);
  WCIO_FREE(fp);
  _UB(fp)._size = 0;
  FREELB(fp);

  if (f < 0) {       /* did not get it after all */
    fp->_flags = 0;  /* set it free */
    errno = sverrno; /* restore in case _close clobbered */
    return NULL;
  }

  /*
   * If reopening something that was open before on a real file, try
   * to maintain the descriptor.  Various C library routines (perror)
   * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
   */
  if (wantfd >= 0 && f != wantfd) {
    if (dup2(f, wantfd) >= 0) {
      (void)close(f);
      f = wantfd;
    }
  }

  /*
   * File descriptors are a full int, but _file is only a short.
   * If we get a valid file descriptor that is greater or equal to
   * USHRT_MAX, then the fd will get sign-extended into an
   * invalid file descriptor.  Handle this case by failing the
   * open. (We treat the short as unsigned, and special-case -1).
   */
  if (f >= (int)USHRT_MAX) {
    (void)close(f);
    errno = EMFILE;
    return NULL;
  }

  fp->_flags = flags;
  fp->_file = f;
  fp->_cookie = fp;
  fp->_read = __sread;
  fp->_write = __swrite;
  fp->_seek = __sseek;
  fp->_close = __sclose;

  /*
   * When reopening in append mode, even though we use O_APPEND,
   * we need to seek to the end so that ftell() gets the right
   * answer.  If the user then alters the seek pointer, or
   * the file extends, this will fail, but there is not much
   * we can do about this.  (We could set __SAPP and check in
   * fseek and ftell.)
   */
  if (oflags & O_APPEND)
    (void)__sseek((void *)fp, (off_t)0, SEEK_END);
  return fp;
}
