LWRES_BUFFER
NAME
lwres_buffer_init, lwres_buffer_invalidate, lwres_buffer_add, lwres_buffer_subtract, lwres_buffer_clear, lwres_buffer_first, lwres_buffer_forward, 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 management
SYNOPSIS
#include <lwres/lwbuffer.h>
I void lwres_buffer_init(lwres_buffer_t * b , void * base , unsigned int length );
I void lwres_buffer_invalidate(lwres_buffer_t * b );
I void lwres_buffer_add(lwres_buffer_t * b , unsigned int n );
I void lwres_buffer_subtract(lwres_buffer_t * b , unsigned int n );
I void lwres_buffer_clear(lwres_buffer_t * b );
I void lwres_buffer_first(lwres_buffer_t * b );
I void lwres_buffer_forward(lwres_buffer_t * b , unsigned int n );
I void lwres_buffer_back(lwres_buffer_t * b , unsigned int n );
I lwres_uint8_t lwres_buffer_getuint8(lwres_buffer_t * b );
I void lwres_buffer_putuint8(lwres_buffer_t * b , lwres_uint8_t val );
I lwres_uint16_t lwres_buffer_getuint16(lwres_buffer_t * b );
I void lwres_buffer_putuint16(lwres_buffer_t * b , lwres_uint16_t val );
I lwres_uint32_t lwres_buffer_getuint32(lwres_buffer_t * b );
I void lwres_buffer_putuint32(lwres_buffer_t * b , lwres_uint32_t val );
I void lwres_buffer_putmem(lwres_buffer_t * b , const unsigned char * base , unsigned int length );
I 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. 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.
/------------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_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.
COPYRIGHT
Copyright 2004, 2005, 2007 Internet Systems Consortium, Inc. ("ISC")
Copyright 2000, 2001 Internet Software Consortium.
