xref: /bionic/libc/upstream-openbsd/lib/libc/stdio/fgetln.c

/*	$OpenBSD: fgetln.c,v 1.13 2015/01/05 21:58:52 millert 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 <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "local.h"

/*
 * Expand the line buffer.  Return -1 on error.
 */
static int
__slbexpand(FILE *fp, size_t newsize)
{
	void *p;

	if (fp->_lb._size >= newsize)
		return (0);
	if ((p = realloc(fp->_lb._base, newsize)) == NULL)
		return (-1);
	fp->_lb._base = p;
	fp->_lb._size = newsize;
	return (0);
}

/*
 * Get an input line.  The returned pointer often (but not always)
 * points into a stdio buffer.  Fgetline does not alter the text of
 * the returned line (which is thus not a C string because it will
 * not necessarily end with '\0'), but does allow callers to modify
 * it if they wish.  Thus, we set __SMOD in case the caller does.
 */
char *
fgetln(FILE *fp, size_t *lenp)
{
	unsigned char *p;
	char *ret;
	size_t len;
	size_t off;

	FLOCKFILE(fp);
	_SET_ORIENTATION(fp, -1);

	/* make sure there is input */
	if (fp->_r <= 0 && __srefill(fp))
		goto error;

	/* look for a newline in the input */
	if ((p = memchr((void *)fp->_p, '\n', fp->_r)) != NULL) {
		/*
		 * Found one.  Flag buffer as modified to keep fseek from
		 * `optimising' a backward seek, in case the user stomps on
		 * the text.
		 */
		p++;		/* advance over it */
		ret = (char *)fp->_p;
		*lenp = len = p - fp->_p;
		fp->_flags |= __SMOD;
		fp->_r -= len;
		fp->_p = p;
		FUNLOCKFILE(fp);
		return (ret);
	}

	/*
	 * We have to copy the current buffered data to the line buffer.
	 * As a bonus, though, we can leave off the __SMOD.
	 *
	 * OPTIMISTIC is length that we (optimistically) expect will
	 * accommodate the `rest' of the string, on each trip through the
	 * loop below.
	 */
#define OPTIMISTIC 80

	for (len = fp->_r, off = 0;; len += fp->_r) {
		size_t diff;

		/*
		 * Make sure there is room for more bytes.  Copy data from
		 * file buffer to line buffer, refill file and look for
		 * newline.  The loop stops only when we find a newline.
		 */
		if (__slbexpand(fp, len + OPTIMISTIC))
			goto error;
		(void)memcpy((void *)(fp->_lb._base + off), (void *)fp->_p,
		    len - off);
		off = len;
		if (__srefill(fp))
			break;	/* EOF or error: return partial line */
		if ((p = memchr((void *)fp->_p, '\n', fp->_r)) == NULL)
			continue;

		/* got it: finish up the line (like code above) */
		p++;
		diff = p - fp->_p;
		len += diff;
		if (__slbexpand(fp, len))
			goto error;
		(void)memcpy((void *)(fp->_lb._base + off), (void *)fp->_p,
		    diff);
		fp->_r -= diff;
		fp->_p = p;
		break;
	}
	*lenp = len;
	ret = (char *)fp->_lb._base;
	FUNLOCKFILE(fp);
	return (ret);

error:
	FUNLOCKFILE(fp);
	*lenp = 0;
	return (NULL);
}