lwbuffer.c revision 0c27b3fe77ac1d5094ba3521e8142d9e7973133f
/*
* Copyright (C) 2000, 2001, 2004, 2005, 2007, 2014, 2016 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/.
*/
/* $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 <string.h>
#include <lwres/lwbuffer.h>
#include "assert_p.h"
void
{
/*
* Make 'b' refer to the 'length'-byte region starting at base.
*/
b->magic = LWRES_BUFFER_MAGIC;
b->used = 0;
b->current = 0;
b->active = 0;
}
/* Make 'b' an invalid buffer. */
void
{
b->magic = 0;
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)
{
b->used += n;
}
/* Decrease the 'used' region of 'b' by 'n' bytes. */
void
lwres_buffer_subtract(lwres_buffer_t *b, unsigned int n)
{
b->used -= n;
}
/* Make the used region empty. */
void
{
b->used = 0;
b->current = 0;
b->active = 0;
}
/* Make the consumed region empty. */
void
{
b->current = 0;
}
/* Increase the 'consumed' region of 'b' by 'n' bytes. */
void
lwres_buffer_forward(lwres_buffer_t *b, unsigned int n)
{
b->current += n;
}
/* Decrease the 'consumed' region of 'b' by 'n' bytes. */
void
lwres_buffer_back(lwres_buffer_t *b, unsigned int n)
{
b->current -= n;
}
/* Read an unsigned 8-bit integer from 'b' and return it. */
{
unsigned char *cp;
b->current += 1;
return (result);
}
/* Put an unsigned 8-bit integer */
void
{
unsigned char *cp;
b->used += 1;
}
/* Read an unsigned 16-bit integer in network byte order from 'b', convert it to host byte order, and return it. */
{
unsigned char *cp;
b->current += 2;
return (result);
}
/* Put an unsigned 16-bit integer. */
void
{
unsigned char *cp;
b->used += 2;
}
/* Read an unsigned 32-bit integer in network byte order from 'b', convert it to host byte order, and return it. */
{
unsigned char *cp;
b->current += 4;
return (result);
}
/* Put an unsigned 32-bit integer. */
void
{
unsigned char *cp;
b->used += 4;
}
/* copies length bytes of memory at base to b */
void
unsigned int length)
{
unsigned char *cp;
}
/* copies length bytes of memory at b to base */
void
unsigned int length)
{
unsigned char *cp;
}