LWRES_BUFFER(3)LWRES_BUFFER(3)NAME
lwres_buffer_init, lwres_buffer_invalidate,
lwres_buffer_add, lwres_buffer_subtract,
lwres_buffer_clear, lwres_buffer_first, lwres_buffer_for-
ward, lwres_buffer_back, lwres_buffer_getuint8,
lwres_buffer_putuint8, lwres_buffer_getuint16,
lwres_buffer_putuint16, lwres_buffer_getuint32,
lwres_buffer_putuint32, lwres_buffer_putmem,
lwres_buffer_getmem - lightweight resolver buffer manage-
ment
SYNOPSIS
#include <lwres/lwbuffer.h>
void lwres_buffer_init(lwres_buffer_t *b, void *base,
unsigned int length);
void lwres_buffer_invalidate(lwres_buffer_t *b);
void lwres_buffer_add(lwres_buffer_t *b, unsigned int n);
void lwres_buffer_subtract(lwres_buffer_t *b, unsigned int
n);
void lwres_buffer_clear(lwres_buffer_t *b);
void lwres_buffer_first(lwres_buffer_t *b);
void lwres_buffer_forward(lwres_buffer_t *b, unsigned int
n);
void lwres_buffer_back(lwres_buffer_t *b, unsigned int n);
lwres_uint8_t lwres_buffer_getuint8(lwres_buffer_t *b);
void lwres_buffer_putuint8(lwres_buffer_t *b,
lwres_uint8_t val);
lwres_uint16_t lwres_buffer_getuint16(lwres_buffer_t *b);
void lwres_buffer_putuint16(lwres_buffer_t *b,
lwres_uint16_t val);
lwres_uint32_t lwres_buffer_getuint32(lwres_buffer_t *b);
void lwres_buffer_putuint32(lwres_buffer_t *b,
lwres_uint32_t val);
void lwres_buffer_putmem(lwres_buffer_t *b, const unsigned
char *base, unsigned int length);
void lwres_buffer_getmem(lwres_buffer_t *b, unsigned char
*base, unsigned int length);
DESCRIPTION
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. Ini-
tially, 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.
/------------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.
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_sub-
tract() 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_putu-
int16() 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.
BIND9 Jun 30, 2000 LWRES_BUFFER(3)
