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+/*
+ * 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);
+}