1/* Fmemopen implementation.
2 Copyright (C) 2000-2016 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 <http://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 <libio.h>
75#include <stdio.h>
76#include <stdlib.h>
77#include <stdint.h>
78#include <string.h>
79#include <sys/types.h>
80
81
82typedef struct fmemopen_cookie_struct fmemopen_cookie_t;
83struct fmemopen_cookie_struct
84{
85 char *buffer;
86 int mybuffer;
87 int binmode;
88 size_t size;
89 _IO_off64_t pos;
90 size_t maxpos;
91};
92
93
94static ssize_t
95fmemopen_read (void *cookie, char *b, size_t s)
96{
97 fmemopen_cookie_t *c;
98
99 c = (fmemopen_cookie_t *) cookie;
100
101 if (c->pos + s > c->size)
102 {
103 if ((size_t) c->pos == c->size)
104 return 0;
105 s = c->size - c->pos;
106 }
107
108 memcpy (b, &(c->buffer[c->pos]), s);
109
110 c->pos += s;
111 if ((size_t) c->pos > c->maxpos)
112 c->maxpos = c->pos;
113
114 return s;
115}
116
117
118static ssize_t
119fmemopen_write (void *cookie, const char *b, size_t s)
120{
121 fmemopen_cookie_t *c;
122 int addnullc;
123
124 c = (fmemopen_cookie_t *) cookie;
125
126 addnullc = c->binmode == 0 && (s == 0 || b[s - 1] != '\0');
127
128 if (c->pos + s + addnullc > c->size)
129 {
130 if ((size_t) (c->pos + addnullc) >= c->size)
131 {
132 __set_errno (ENOSPC);
133 return 0;
134 }
135 s = c->size - c->pos - addnullc;
136 }
137
138 memcpy (&(c->buffer[c->pos]), b, s);
139
140 c->pos += s;
141 if ((size_t) c->pos > c->maxpos)
142 {
143 c->maxpos = c->pos;
144 if (addnullc)
145 c->buffer[c->maxpos] = '\0';
146 }
147
148 return s;
149}
150
151
152static int
153fmemopen_seek (void *cookie, _IO_off64_t *p, int w)
154{
155 _IO_off64_t np;
156 fmemopen_cookie_t *c;
157
158 c = (fmemopen_cookie_t *) cookie;
159
160 switch (w)
161 {
162 case SEEK_SET:
163 np = *p;
164 break;
165
166 case SEEK_CUR:
167 np = c->pos + *p;
168 break;
169
170 case SEEK_END:
171 np = (c->binmode ? c->size : c->maxpos) - *p;
172 break;
173
174 default:
175 return -1;
176 }
177
178 if (np < 0 || (size_t) np > c->size)
179 return -1;
180
181 *p = c->pos = np;
182
183 return 0;
184}
185
186
187static int
188fmemopen_close (void *cookie)
189{
190 fmemopen_cookie_t *c;
191
192 c = (fmemopen_cookie_t *) cookie;
193
194 if (c->mybuffer)
195 free (c->buffer);
196 free (c);
197
198 return 0;
199}
200
201
202FILE *
203__old_fmemopen (void *buf, size_t len, const char *mode)
204{
205 cookie_io_functions_t iof;
206 fmemopen_cookie_t *c;
207 FILE *result;
208
209 if (__glibc_unlikely (len == 0))
210 {
211 einval:
212 __set_errno (EINVAL);
213 return NULL;
214 }
215
216 c = (fmemopen_cookie_t *) malloc (sizeof (fmemopen_cookie_t));
217 if (c == NULL)
218 return NULL;
219
220 c->mybuffer = (buf == NULL);
221
222 if (c->mybuffer)
223 {
224 c->buffer = (char *) malloc (len);
225 if (c->buffer == NULL)
226 {
227 free (c);
228 return NULL;
229 }
230 c->buffer[0] = '\0';
231 c->maxpos = 0;
232 }
233 else
234 {
235 if (__glibc_unlikely ((uintptr_t) len > -(uintptr_t) buf))
236 {
237 free (c);
238 goto einval;
239 }
240
241 c->buffer = buf;
242
243 if (mode[0] == 'w')
244 c->buffer[0] = '\0';
245
246 c->maxpos = strnlen (c->buffer, len);
247 }
248
249 c->size = len;
250
251 if (mode[0] == 'a')
252 c->pos = c->maxpos;
253 else
254 c->pos = 0;
255
256 c->binmode = mode[0] != '\0' && mode[1] == 'b';
257
258 iof.read = fmemopen_read;
259 iof.write = fmemopen_write;
260 iof.seek = fmemopen_seek;
261 iof.close = fmemopen_close;
262
263 result = _IO_fopencookie (c, mode, iof);
264 if (__glibc_unlikely (result == NULL))
265 {
266 if (c->mybuffer)
267 free (c->buffer);
268
269 free (c);
270 }
271
272 return result;
273}
274compat_symbol (libc, __old_fmemopen, fmemopen, GLIBC_2_2);
275#endif
276