summaryrefslogtreecommitdiffstats
path: root/lib/lwres/lwbuffer.c
blob: 9cdf5edad304355286a0a1dbd0d16a2120ae4048 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
/*
 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * See the COPYRIGHT file distributed with this work for additional
 * information regarding copyright ownership.
 */

/* $Id: lwbuffer.c,v 1.15 2007/06/19 23:47:22 tbox Exp $ */

/*! \file */

/**
 *    These functions provide bounds checked access to a region of memory
 *    where data is being read or written. They are based on, and similar
 *    to, the isc_buffer_ functions in the ISC library.
 *
 *    A buffer is a region of memory, together with a set of related
 *    subregions. The used region and the available region are disjoint, and
 *    their union is the buffer's region. The used region extends from the
 *    beginning of the buffer region to the last used byte. The available
 *    region extends from one byte greater than the last used byte to the
 *    end of the buffer's region. The size of the used region can be changed
 *    using various buffer commands. Initially, the used region is empty.
 *
 *    The used region is further subdivided into two disjoint regions: the
 *    consumed region and the remaining region. The union of these two
 *    regions is the used region. The consumed region extends from the
 *    beginning of the used region to the byte before the current offset (if
 *    any). The remaining region the current pointer to the end of the used
 *    region. The size of the consumed region can be changed using various
 *    buffer commands. Initially, the consumed region is empty.
 *
 *    The active region is an (optional) subregion of the remaining region.
 *    It extends from the current offset to an offset in the remaining
 *    region. Initially, the active region is empty. If the current offset
 *    advances beyond the chosen offset, the active region will also be
 *    empty.
 *
 *
 * \verbatim
 *    /------------entire length---------------\\
 *    /----- used region -----\\/-- available --\\
 *    +----------------------------------------+
 *    | consumed  | remaining |                |
 *    +----------------------------------------+
 *    a           b     c     d                e
 *
 *   a == base of buffer.
 *   b == current pointer.  Can be anywhere between a and d.
 *   c == active pointer.  Meaningful between b and d.
 *   d == used pointer.
 *   e == length of buffer.
 *
 *   a-e == entire length of buffer.
 *   a-d == used region.
 *   a-b == consumed region.
 *   b-d == remaining region.
 *   b-c == optional active region.
 * \endverbatim
 *
 *    lwres_buffer_init() initializes the lwres_buffer_t *b and assocates it
 *    with the memory region of size length bytes starting at location base.
 *
 *    lwres_buffer_invalidate() marks the buffer *b as invalid. Invalidating
 *    a buffer after use is not required, but makes it possible to catch its
 *    possible accidental use.
 *
 *    The functions lwres_buffer_add() and lwres_buffer_subtract()
 *    respectively increase and decrease the used space in buffer *b by n
 *    bytes. lwres_buffer_add() checks for buffer overflow and
 *    lwres_buffer_subtract() checks for underflow. These functions do not
 *    allocate or deallocate memory. They just change the value of used.
 *
 *    A buffer is re-initialised by lwres_buffer_clear(). The function sets
 *    used , current and active to zero.
 *
 *    lwres_buffer_first() makes the consumed region of buffer *p empty by
 *    setting current to zero (the start of the buffer).
 *
 *    lwres_buffer_forward() increases the consumed region of buffer *b by n
 *    bytes, checking for overflow. Similarly, lwres_buffer_back() decreases
 *    buffer b's consumed region by n bytes and checks for underflow.
 *
 *    lwres_buffer_getuint8() reads an unsigned 8-bit integer from *b and
 *    returns it. lwres_buffer_putuint8() writes the unsigned 8-bit integer
 *    val to buffer *b.
 *
 *    lwres_buffer_getuint16() and lwres_buffer_getuint32() are identical to
 *    lwres_buffer_putuint8() except that they respectively read an unsigned
 *    16-bit or 32-bit integer in network byte order from b. Similarly,
 *    lwres_buffer_putuint16() and lwres_buffer_putuint32() writes the
 *    unsigned 16-bit or 32-bit integer val to buffer b, in network byte
 *    order.
 *
 *    Arbitrary amounts of data are read or written from a lightweight
 *    resolver buffer with lwres_buffer_getmem() and lwres_buffer_putmem()
 *    respectively. lwres_buffer_putmem() copies length bytes of memory at
 *    base to b. Conversely, lwres_buffer_getmem() copies length bytes of
 *    memory from b to base.
 */

#include <config.h>

#include <inttypes.h>
#include <string.h>

#include <lwres/lwbuffer.h>

#include "assert_p.h"

void
lwres_buffer_init(lwres_buffer_t *b, void *base, unsigned int length)
{
	/*
	 * Make 'b' refer to the 'length'-byte region starting at base.
	 */

	REQUIRE(b != NULL);

	b->magic = LWRES_BUFFER_MAGIC;
	b->base = base;
	b->length = length;
	b->used = 0;
	b->current = 0;
	b->active = 0;
}

/*  Make 'b' an invalid buffer. */
void
lwres_buffer_invalidate(lwres_buffer_t *b)
{

	REQUIRE(LWRES_BUFFER_VALID(b));

	b->magic = 0;
	b->base = NULL;
	b->length = 0;
	b->used = 0;
	b->current = 0;
	b->active = 0;
}

/* Increase the 'used' region of 'b' by 'n' bytes. */
void
lwres_buffer_add(lwres_buffer_t *b, unsigned int n)
{

	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->used + n <= b->length);

	b->used += n;
}

/* Decrease the 'used' region of 'b' by 'n' bytes. */
void
lwres_buffer_subtract(lwres_buffer_t *b, unsigned int n)
{

	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->used >= n);

	b->used -= n;
	if (b->current > b->used)
		b->current = b->used;
	if (b->active > b->used)
		b->active = b->used;
}

/* Make the used region empty. */
void
lwres_buffer_clear(lwres_buffer_t *b)
{

	REQUIRE(LWRES_BUFFER_VALID(b));

	b->used = 0;
	b->current = 0;
	b->active = 0;
}

/* Make the consumed region empty. */
void
lwres_buffer_first(lwres_buffer_t *b)
{

	REQUIRE(LWRES_BUFFER_VALID(b));

	b->current = 0;
}

/* Increase the 'consumed' region of 'b' by 'n' bytes. */
void
lwres_buffer_forward(lwres_buffer_t *b, unsigned int n)
{

	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->current + n <= b->used);

	b->current += n;
}

/* Decrease the 'consumed' region of 'b' by 'n' bytes. */
void
lwres_buffer_back(lwres_buffer_t *b, unsigned int n)
{

	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(n <= b->current);

	b->current -= n;
}

/* Read an unsigned 8-bit integer from 'b' and return it. */
uint8_t
lwres_buffer_getuint8(lwres_buffer_t *b)
{
	unsigned char *cp;
	uint8_t result;


	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->used - b->current >= 1);

	cp = b->base;
	cp += b->current;
	b->current += 1;
	result = ((unsigned int)(cp[0]));

	return (result);
}

/* Put an unsigned 8-bit integer */
void
lwres_buffer_putuint8(lwres_buffer_t *b, uint8_t val)
{
	unsigned char *cp;

	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->used + 1 <= b->length);

	cp = b->base;
	cp += b->used;
	b->used += 1;
	cp[0] = (val & 0x00ff);
}

/*  Read an unsigned 16-bit integer in network byte order from 'b', convert it to host byte order, and return it. */
uint16_t
lwres_buffer_getuint16(lwres_buffer_t *b)
{
	unsigned char *cp;
	uint16_t result;


	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->used - b->current >= 2);

	cp = b->base;
	cp += b->current;
	b->current += 2;
	result = ((unsigned int)(cp[0])) << 8;
	result |= ((unsigned int)(cp[1]));

	return (result);
}

/* Put an unsigned 16-bit integer. */
void
lwres_buffer_putuint16(lwres_buffer_t *b, uint16_t val)
{
	unsigned char *cp;

	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->used + 2 <= b->length);

	cp = b->base;
	cp += b->used;
	b->used += 2;
	cp[0] = (val & 0xff00) >> 8;
	cp[1] = (val & 0x00ff);
}

/*  Read an unsigned 32-bit integer in network byte order from 'b', convert it to host byte order, and return it. */
uint32_t
lwres_buffer_getuint32(lwres_buffer_t *b)
{
	unsigned char *cp;
	uint32_t result;

	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->used - b->current >= 4);

	cp = b->base;
	cp += b->current;
	b->current += 4;
	result = ((unsigned int)(cp[0])) << 24;
	result |= ((unsigned int)(cp[1])) << 16;
	result |= ((unsigned int)(cp[2])) << 8;
	result |= ((unsigned int)(cp[3]));

	return (result);
}

/* Put an unsigned 32-bit integer. */
void
lwres_buffer_putuint32(lwres_buffer_t *b, uint32_t val)
{
	unsigned char *cp;

	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->used + 4 <= b->length);

	cp = b->base;
	cp += b->used;
	b->used += 4;
	cp[0] = (unsigned char)((val & 0xff000000) >> 24);
	cp[1] = (unsigned char)((val & 0x00ff0000) >> 16);
	cp[2] = (unsigned char)((val & 0x0000ff00) >> 8);
	cp[3] = (unsigned char)(val & 0x000000ff);
}

/* copies length bytes of memory at base to b */
void
lwres_buffer_putmem(lwres_buffer_t *b, const unsigned char *base,
		    unsigned int length)
{
	unsigned char *cp;

	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->used + length <= b->length);

	cp = (unsigned char *)b->base + b->used;
	memmove(cp, base, length);
	b->used += length;
}

/* copies length bytes of memory at b to base */
void
lwres_buffer_getmem(lwres_buffer_t *b, unsigned char *base,
		    unsigned int length)
{
	unsigned char *cp;

	REQUIRE(LWRES_BUFFER_VALID(b));
	REQUIRE(b->used - b->current >= length);

	cp = b->base;
	cp += b->current;
	b->current += length;

	memmove(base, cp, length);
}