xref: /bionic/libc/stdio/freopen.c

/*	$OpenBSD: freopen.c,v 1.9 2005/08/08 08:05:36 espie 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/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.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;

	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 = fp->_file) < 0 && 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);
	_UB(fp)._size = 0;
	WCIO_FREE(fp);
	if (HASLB(fp))
		FREELB(fp);
	fp->_lb._size = 0;

	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;
		}
	}

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

	/*
	 * When opening 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, (fpos_t)0, SEEK_END);
	return (fp);
}