1/* Fmemopen implementation.
2 Copyright (C) 2000-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Hanno Mueller, kontakt@hanno.de, 2000.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20/*
21 * fmemopen() - "my" version of a string stream
22 * Hanno Mueller, kontakt@hanno.de
23 *
24 *
25 * I needed fmemopen() for an application that I currently work on,
26 * but couldn't find it in libio. The following snippet of code is an
27 * attempt to implement what glibc's documentation describes.
28 *
29 *
30 *
31 * I already see some potential problems:
32 *
33 * - I never used the "original" fmemopen(). I am sure that "my"
34 * fmemopen() behaves differently than the original version.
35 *
36 * - The documentation doesn't say wether a string stream allows
37 * seeks. I checked the old fmemopen implementation in glibc's stdio
38 * directory, wasn't quite able to see what is going on in that
39 * source, but as far as I understand there was no seek there. For
40 * my application, I needed fseek() and ftell(), so it's here.
41 *
42 * - "append" mode and fseek(p, SEEK_END) have two different ideas
43 * about the "end" of the stream.
44 *
45 * As described in the documentation, when opening the file in
46 * "append" mode, the position pointer will be set to the first null
47 * character of the string buffer (yet the buffer may already
48 * contain more data). For fseek(), the last byte of the buffer is
49 * used as the end of the stream.
50 *
51 * - It is unclear to me what the documentation tries to say when it
52 * explains what happens when you use fmemopen with a NULL
53 * buffer.
54 *
55 * Quote: "fmemopen [then] allocates an array SIZE bytes long. This
56 * is really only useful if you are going to write things to the
57 * buffer and then read them back in again."
58 *
59 * What does that mean if the original fmemopen() did not allow
60 * seeking? How do you read what you just wrote without seeking back
61 * to the beginning of the stream?
62 *
63 * - I think there should be a second version of fmemopen() that does
64 * not add null characters for each write. (At least in my
65 * application, I am not actually using strings but binary data and
66 * so I don't need the stream to add null characters on its own.)
67 */
68
69#include "libioP.h"
70
71#if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_22)
72
73#include <errno.h>
74#include <stdio.h>
75#include <stdlib.h>
76#include <stdint.h>
77#include <string.h>
78#include <sys/types.h>
79
80
81typedef struct fmemopen_cookie_struct fmemopen_cookie_t;
82struct fmemopen_cookie_struct
83{
84 char *buffer;
85 int mybuffer;
86 int binmode;
87 size_t size;
88 off64_t pos;
89 size_t maxpos;
90};
91
92
93static ssize_t
94fmemopen_read (void *cookie, char *b, size_t s)
95{
96 fmemopen_cookie_t *c;
97
98 c = (fmemopen_cookie_t *) cookie;
99
100 if (c->pos + s > c->size)
101 {
102 if ((size_t) c->pos == c->size)
103 return 0;
104 s = c->size - c->pos;
105 }
106
107 memcpy (b, &(c->buffer[c->pos]), s);
108
109 c->pos += s;
110 if ((size_t) c->pos > c->maxpos)
111 c->maxpos = c->pos;
112
113 return s;
114}
115
116
117static ssize_t
118fmemopen_write (void *cookie, const char *b, size_t s)
119{
120 fmemopen_cookie_t *c;
121 int addnullc;
122
123 c = (fmemopen_cookie_t *) cookie;
124
125 addnullc = c->binmode == 0 && (s == 0 || b[s - 1] != '\0');
126
127 if (c->pos + s + addnullc > c->size)
128 {
129 if ((size_t) (c->pos + addnullc) >= c->size)
130 {
131 __set_errno (ENOSPC);
132 return 0;
133 }
134 s = c->size - c->pos - addnullc;
135 }
136
137 memcpy (&(c->buffer[c->pos]), b, s);
138
139 c->pos += s;
140 if ((size_t) c->pos > c->maxpos)
141 {
142 c->maxpos = c->pos;
143 if (addnullc)
144 c->buffer[c->maxpos] = '\0';
145 }
146
147 return s;
148}
149
150
151static int
152fmemopen_seek (void *cookie, off64_t *p, int w)
153{
154 off64_t np;
155 fmemopen_cookie_t *c;
156
157 c = (fmemopen_cookie_t *) cookie;
158
159 switch (w)
160 {
161 case SEEK_SET:
162 np = *p;
163 break;
164
165 case SEEK_CUR:
166 np = c->pos + *p;
167 break;
168
169 case SEEK_END:
170 np = (c->binmode ? c->size : c->maxpos) - *p;
171 break;
172
173 default:
174 return -1;
175 }
176
177 if (np < 0 || (size_t) np > c->size)
178 return -1;
179
180 *p = c->pos = np;
181
182 return 0;
183}
184
185
186static int
187fmemopen_close (void *cookie)
188{
189 fmemopen_cookie_t *c;
190
191 c = (fmemopen_cookie_t *) cookie;
192
193 if (c->mybuffer)
194 free (c->buffer);
195 free (c);
196
197 return 0;
198}
199
200
201FILE *
202__old_fmemopen (void *buf, size_t len, const char *mode)
203{
204 cookie_io_functions_t iof;
205 fmemopen_cookie_t *c;
206 FILE *result;
207
208 if (__glibc_unlikely (len == 0))
209 {
210 einval:
211 __set_errno (EINVAL);
212 return NULL;
213 }
214
215 c = (fmemopen_cookie_t *) malloc (sizeof (fmemopen_cookie_t));
216 if (c == NULL)
217 return NULL;
218
219 c->mybuffer = (buf == NULL);
220
221 if (c->mybuffer)
222 {
223 c->buffer = (char *) malloc (len);
224 if (c->buffer == NULL)
225 {
226 free (c);
227 return NULL;
228 }
229 c->buffer[0] = '\0';
230 c->maxpos = 0;
231 }
232 else
233 {
234 if (__glibc_unlikely ((uintptr_t) len > -(uintptr_t) buf))
235 {
236 free (c);
237 goto einval;
238 }
239
240 c->buffer = buf;
241
242 if (mode[0] == 'w')
243 c->buffer[0] = '\0';
244
245 c->maxpos = strnlen (c->buffer, len);
246 }
247
248 c->size = len;
249
250 if (mode[0] == 'a')
251 c->pos = c->maxpos;
252 else
253 c->pos = 0;
254
255 c->binmode = mode[0] != '\0' && mode[1] == 'b';
256
257 iof.read = fmemopen_read;
258 iof.write = fmemopen_write;
259 iof.seek = fmemopen_seek;
260 iof.close = fmemopen_close;
261
262 result = _IO_fopencookie (c, mode, iof);
263 if (__glibc_unlikely (result == NULL))
264 {
265 if (c->mybuffer)
266 free (c->buffer);
267
268 free (c);
269 }
270
271 return result;
272}
273compat_symbol (libc, __old_fmemopen, fmemopen, GLIBC_2_2);
274#endif
275