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1 | /* Fmemopen implementation. |
2 | Copyright (C) 2000-2015 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 | ||
82 | typedef struct fmemopen_cookie_struct fmemopen_cookie_t; | |
83 | struct 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 | ||
94 | static ssize_t | |
95 | fmemopen_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 | ||
118 | static ssize_t | |
119 | fmemopen_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 | ||
152 | static int | |
153 | fmemopen_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 | ||
187 | static int | |
188 | fmemopen_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 | ||
202 | FILE * | |
203 | __old_fmemopen (void *buf, size_t len, const char *mode) | |
204 | { | |
205 | cookie_io_functions_t iof; | |
206 | fmemopen_cookie_t *c; | |
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 | return _IO_fopencookie (c, mode, iof); | |
263 | } | |
264 | compat_symbol (libc, __old_fmemopen, fmemopen, GLIBC_2_2); | |
265 | #endif |