1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1990, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Chris Torek.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#if defined(LIBC_SCCS) && !defined(lint)
36static char sccsid[] = "@(#)ungetc.c	8.2 (Berkeley) 11/3/93";
37#endif /* LIBC_SCCS and not lint */
38#include <sys/cdefs.h>
39__FBSDID("$FreeBSD$");
40
41#include "namespace.h"
42#include <stdio.h>
43#include <stdlib.h>
44#include <string.h>
45#include "un-namespace.h"
46#include "local.h"
47#include "libc_private.h"
48
49static int __submore(FILE *);
50
51/*
52 * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
53 * the buffer moves, so that it points the same distance from the end,
54 * and move the bytes in the buffer around as necessary so that they
55 * are all at the end (stack-style).
56 */
57static int
58__submore(FILE *fp)
59{
60	int i;
61	unsigned char *p;
62
63	if (fp->_ub._base == fp->_ubuf) {
64		/*
65		 * Get a new buffer (rather than expanding the old one).
66		 */
67		if ((p = malloc((size_t)BUFSIZ)) == NULL)
68			return (EOF);
69		fp->_ub._base = p;
70		fp->_ub._size = BUFSIZ;
71		p += BUFSIZ - sizeof(fp->_ubuf);
72		for (i = sizeof(fp->_ubuf); --i >= 0;)
73			p[i] = fp->_ubuf[i];
74		fp->_p = p;
75		return (0);
76	}
77	i = fp->_ub._size;
78	p = reallocarray(fp->_ub._base, i, 2);
79	if (p == NULL)
80		return (EOF);
81	/* no overlap (hence can use memcpy) because we doubled the size */
82	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
83	fp->_p = p + i;
84	fp->_ub._base = p;
85	fp->_ub._size = i * 2;
86	return (0);
87}
88
89/*
90 * MT-safe version
91 */
92int
93ungetc(int c, FILE *fp)
94{
95	int ret;
96
97	if (!__sdidinit)
98		__sinit();
99	FLOCKFILE_CANCELSAFE(fp);
100	ORIENT(fp, -1);
101	ret = __ungetc(c, fp);
102	FUNLOCKFILE_CANCELSAFE();
103	return (ret);
104}
105
106/*
107 * Non-MT-safe version
108 */
109int
110__ungetc(int c, FILE *fp)
111{
112
113	if (c == EOF)
114		return (EOF);
115	if ((fp->_flags & __SRD) == 0) {
116		/*
117		 * Not already reading: no good unless reading-and-writing.
118		 * Otherwise, flush any current write stuff.
119		 */
120		if ((fp->_flags & __SRW) == 0)
121			return (EOF);
122		if (fp->_flags & __SWR) {
123			if (__sflush(fp))
124				return (EOF);
125			fp->_flags &= ~__SWR;
126			fp->_w = 0;
127			fp->_lbfsize = 0;
128		}
129		fp->_flags |= __SRD;
130	}
131	c = (unsigned char)c;
132
133	/*
134	 * If we are in the middle of ungetc'ing, just continue.
135	 * This may require expanding the current ungetc buffer.
136	 */
137	if (HASUB(fp)) {
138		if (fp->_r >= fp->_ub._size && __submore(fp))
139			return (EOF);
140		*--fp->_p = c;
141		fp->_r++;
142		return (c);
143	}
144	fp->_flags &= ~__SEOF;
145
146	/*
147	 * If we can handle this by simply backing up, do so,
148	 * but never replace the original character.
149	 * (This makes sscanf() work when scanning `const' data.)
150	 */
151	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
152	    fp->_p[-1] == c) {
153		fp->_p--;
154		fp->_r++;
155		return (c);
156	}
157
158	/*
159	 * Create an ungetc buffer.
160	 * Initially, we will use the `reserve' buffer.
161	 */
162	fp->_ur = fp->_r;
163	fp->_up = fp->_p;
164	fp->_ub._base = fp->_ubuf;
165	fp->_ub._size = sizeof(fp->_ubuf);
166	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
167	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
168	fp->_r = 1;
169	return (c);
170}
171