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
81typedef struct fmemopen_cookie_struct fmemopen_cookie_t;
82struct 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
92static ssize_t
93fmemopen_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
116static ssize_t
117fmemopen_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
150static int
151fmemopen_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
185static int
186fmemopen_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
200FILE *
201fmemopen (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