1 /* Fmemopen implementation.
2 Copyright (C) 2000, 2002 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, write to the Free
18 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
19 02111-1307 USA. */
20
21 /*
22 * fmemopen() - "my" version of a string stream
23 * Hanno Mueller, kontakt@hanno.de
24 *
25 *
26 * I needed fmemopen() for an application that I currently work on,
27 * but couldn't find it in libio. The following snippet of code is an
28 * attempt to implement what glibc's documentation describes.
29 *
30 * No, it isn't really tested yet. :-)
31 *
32 *
33 *
34 * I already see some potential problems:
35 *
36 * - I never used the "original" fmemopen(). I am sure that "my"
37 * fmemopen() behaves differently than the original version.
38 *
39 * - The documentation doesn't say wether a string stream allows
40 * seeks. I checked the old fmemopen implementation in glibc's stdio
41 * directory, wasn't quite able to see what is going on in that
42 * source, but as far as I understand there was no seek there. For
43 * my application, I needed fseek() and ftell(), so it's here.
44 *
45 * - "append" mode and fseek(p, SEEK_END) have two different ideas
46 * about the "end" of the stream.
47 *
48 * As described in the documentation, when opening the file in
49 * "append" mode, the position pointer will be set to the first null
50 * character of the string buffer (yet the buffer may already
51 * contain more data). For fseek(), the last byte of the buffer is
52 * used as the end of the stream.
53 *
54 * - It is unclear to me what the documentation tries to say when it
55 * explains what happens when you use fmemopen with a NULL
56 * buffer.
57 *
58 * Quote: "fmemopen [then] allocates an array SIZE bytes long. This
59 * is really only useful if you are going to write things to the
60 * buffer and then read them back in again."
61 *
62 * What does that mean if the original fmemopen() did not allow
63 * seeking? How do you read what you just wrote without seeking back
64 * to the beginning of the stream?
65 *
66 * - I think there should be a second version of fmemopen() that does
67 * not add null characters for each write. (At least in my
68 * application, I am not actually using strings but binary data and
69 * so I don't need the stream to add null characters on its own.)
70 */
71
72 #include <errno.h>
73 #include <libio.h>
74 #include <stdio.h>
75 #include <stdlib.h>
76 #include <string.h>
77 #include <sys/types.h>
78 #include "libioP.h"
79
80
81 typedef struct fmemopen_cookie_struct fmemopen_cookie_t;
82 struct fmemopen_cookie_struct
83 {
84 char *buffer;
85 int mybuffer;
86 size_t size;
87 _IO_off64_t pos;
88 size_t maxpos;
89 };
90
91
92 static ssize_t
fmemopen_read(void * cookie,char * b,size_t s)93 fmemopen_read (void *cookie, char *b, size_t s)
94 {
95 fmemopen_cookie_t *c;
96
97 c = (fmemopen_cookie_t *) cookie;
98
99 if (c->pos + s > c->size)
100 {
101 if ((size_t) c->pos == c->size)
102 return 0;
103 s = c->size - c->pos;
104 }
105
106 memcpy (b, &(c->buffer[c->pos]), s);
107
108 c->pos += s;
109 if ((size_t) c->pos > c->maxpos)
110 c->maxpos = c->pos;
111
112 return s;
113 }
114
115
116 static ssize_t
fmemopen_write(void * cookie,const char * b,size_t s)117 fmemopen_write (void *cookie, const char *b, size_t s)
118 {
119 fmemopen_cookie_t *c;
120 int addnullc;
121
122 c = (fmemopen_cookie_t *) cookie;
123
124 addnullc = s == 0 || b[s - 1] != '\0';
125
126 if (c->pos + s + addnullc > c->size)
127 {
128 if ((size_t) (c->pos + addnullc) == c->size)
129 {
130 __set_errno (ENOSPC);
131 return -1;
132 }
133 s = c->size - c->pos - addnullc;
134 }
135
136 memcpy (&(c->buffer[c->pos]), b, s);
137
138 c->pos += s;
139 if ((size_t) c->pos > c->maxpos)
140 {
141 c->maxpos = c->pos;
142 if (addnullc)
143 c->buffer[c->maxpos] = '\0';
144 }
145
146 return s;
147 }
148
149
150 static int
fmemopen_seek(void * cookie,_IO_off64_t * p,int w)151 fmemopen_seek (void *cookie, _IO_off64_t *p, int w)
152 {
153 _IO_off64_t np;
154 fmemopen_cookie_t *c;
155
156 c = (fmemopen_cookie_t *) cookie;
157
158 switch (w)
159 {
160 case SEEK_SET:
161 np = *p;
162 break;
163
164 case SEEK_CUR:
165 np = c->pos + *p;
166 break;
167
168 case SEEK_END:
169 np = c->size - *p;
170 break;
171
172 default:
173 return -1;
174 }
175
176 if (np < 0 || (size_t) np > c->size)
177 return -1;
178
179 c->pos = np;
180
181 return np;
182 }
183
184
185 static int
fmemopen_close(void * cookie)186 fmemopen_close (void *cookie)
187 {
188 fmemopen_cookie_t *c;
189
190 c = (fmemopen_cookie_t *) cookie;
191
192 if (c->mybuffer)
193 free (c->buffer);
194 free (c);
195
196 return 0;
197 }
198
199
200 FILE *
fmemopen(void * buf,size_t len,const char * mode)201 fmemopen (void *buf, size_t len, const char *mode)
202 {
203 cookie_io_functions_t iof;
204 fmemopen_cookie_t *c;
205
206 c = (fmemopen_cookie_t *) malloc (sizeof (fmemopen_cookie_t));
207 if (c == NULL)
208 return NULL;
209
210 c->mybuffer = (buf == NULL);
211
212 if (c->mybuffer)
213 {
214 c->buffer = (char *) malloc (len);
215 if (c->buffer == NULL)
216 {
217 free (c);
218 return NULL;
219 }
220 c->buffer[0] = '\0';
221 }
222 else
223 c->buffer = buf;
224
225 c->size = len;
226
227 if (mode[0] == 'w')
228 c->buffer[0] = '\0';
229
230 c->maxpos = strlen (c->buffer);
231
232 if (mode[0] == 'a')
233 c->pos = c->maxpos;
234 else
235 c->pos = 0;
236
237 iof.read = fmemopen_read;
238 iof.write = fmemopen_write;
239 iof.seek = fmemopen_seek;
240 iof.close = fmemopen_close;
241
242 return _IO_fopencookie (c, mode, iof);
243 }
244