<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.1//EN"><!-- - Copyright (C) 2004  Internet Systems Consortium, Inc. ("ISC") - Copyright (C) 2001  Internet Software Consortium. - - Permission to use, copy, modify, and distribute this software for any - purpose with or without fee is hereby granted, provided that the above - copyright notice and this permission notice appear in all copies. - - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY - AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM - LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE - OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR - PERFORMANCE OF THIS SOFTWARE.--><!-- $Id: lwres_buffer.docbook,v 1.2 2004/09/20 18:00:50 mcr Exp $ --><refentry><refentryinfo><date>Jun 30, 2000</date></refentryinfo><refmeta><refentrytitle>lwres_buffer</refentrytitle><manvolnum>3</manvolnum><refmiscinfo>BIND9</refmiscinfo></refmeta><refnamediv><refname>lwres_buffer_init</refname><refname>lwres_buffer_invalidate</refname><refname>lwres_buffer_add</refname><refname>lwres_buffer_subtract</refname><refname>lwres_buffer_clear</refname><refname>lwres_buffer_first</refname><refname>lwres_buffer_forward</refname><refname>lwres_buffer_back</refname><refname>lwres_buffer_getuint8</refname><refname>lwres_buffer_putuint8</refname><refname>lwres_buffer_getuint16</refname><refname>lwres_buffer_putuint16</refname><refname>lwres_buffer_getuint32</refname><refname>lwres_buffer_putuint32</refname><refname>lwres_buffer_putmem</refname><refname>lwres_buffer_getmem</refname><refpurpose>lightweight resolver buffer management</refpurpose></refnamediv><refsynopsisdiv><funcsynopsis><funcsynopsisinfo>#include &lt;lwres/lwbuffer.h&gt;</funcsynopsisinfo><funcprototype><funcdef>void<function>lwres_buffer_init</function></funcdef><paramdef>lwres_buffer_t *b</paramdef><paramdef>void *base</paramdef><paramdef>unsigned int length</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_invalidate</function></funcdef><paramdef>lwres_buffer_t *b</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_add</function></funcdef><paramdef>lwres_buffer_t *b</paramdef><paramdef>unsigned int n</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_subtract</function></funcdef><paramdef>lwres_buffer_t *b</paramdef><paramdef>unsigned int n</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_clear</function></funcdef><paramdef>lwres_buffer_t *b</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_first</function></funcdef><paramdef>lwres_buffer_t *b</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_forward</function></funcdef><paramdef>lwres_buffer_t *b</paramdef><paramdef>unsigned int n</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_back</function></funcdef><paramdef>lwres_buffer_t *b</paramdef><paramdef>unsigned int n</paramdef></funcprototype><funcprototype><funcdef>lwres_uint8_t<function>lwres_buffer_getuint8</function></funcdef><paramdef>lwres_buffer_t *b</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_putuint8</function></funcdef><paramdef>lwres_buffer_t *b</paramdef><paramdef>lwres_uint8_t val</paramdef></funcprototype><funcprototype><funcdef>lwres_uint16_t<function>lwres_buffer_getuint16</function></funcdef><paramdef>lwres_buffer_t *b</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_putuint16</function></funcdef><paramdef>lwres_buffer_t *b</paramdef><paramdef>lwres_uint16_t val</paramdef></funcprototype><funcprototype><funcdef>lwres_uint32_t<function>lwres_buffer_getuint32</function></funcdef><paramdef>lwres_buffer_t *b</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_putuint32</function></funcdef><paramdef>lwres_buffer_t *b</paramdef><paramdef>lwres_uint32_t val</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_putmem</function></funcdef><paramdef>lwres_buffer_t *b</paramdef><paramdef>const unsigned char *base</paramdef><paramdef>unsigned int length</paramdef></funcprototype><funcprototype><funcdef>void<function>lwres_buffer_getmem</function></funcdef><paramdef>lwres_buffer_t *b</paramdef><paramdef>unsigned char *base</paramdef><paramdef>unsigned int length</paramdef></funcprototype></funcsynopsis></refsynopsisdiv><refsect1><title>DESCRIPTION</title><para>These functions provide bounds checked access to a region of memorywhere data is being read or written.They are based on, and similar to, the<literal>isc_buffer_</literal>functions in the ISC library.</para><para>A buffer is a region of memory, together with a set of relatedsubregions.The <emphasis>used region</emphasis> and the<emphasis>available</emphasis> region are disjoint, andtheir union is the buffer's region.The used region extends from the beginning of the buffer region to thelast used byte.The available region extends from one byte greater than the last usedbyte to the end of the  buffer's region.The size of the used region can be changed using variousbuffer commands.Initially, the used region is empty.</para><para>The used region is further subdivided into two disjoint regions: the<emphasis>consumed region</emphasis> and the <emphasis>remaining region</emphasis>.The union of these two regions is the used region.The consumed region extends from the beginning of the used region tothe byte before the <emphasis>current</emphasis> offset (if any).The <emphasis>remaining</emphasis> region the current pointer to the end of the usedregion.The size of the consumed region can be changed using variousbuffer commands.Initially, the consumed region is empty.</para><para>The <emphasis>active region</emphasis> is an (optional) subregion of the remainingregion.It extends from the current offset to an offset in theremaining region.Initially, the active region is empty.If the current offset advances beyond the chosen offset,the active region will also be empty.</para><para><programlisting>    /------------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.</programlisting></para><para><function>lwres_buffer_init()</function>initializes the<type>lwres_buffer_t</type><parameter>*b</parameter>and assocates it with the memory region of size<parameter>length</parameter>bytes starting at location<parameter>base.</parameter></para><para><function>lwres_buffer_invalidate()</function>marks the buffer<parameter>*b</parameter>as invalid.  Invalidating a buffer after use is not required,but makes it possible to catch its possible accidental use.</para><para>The functions<function>lwres_buffer_add()</function>and<function>lwres_buffer_subtract()</function>respectively increase and decrease the used space inbuffer<parameter>*b</parameter>by<parameter>n</parameter>bytes.<function>lwres_buffer_add()</function>checks for buffer overflow and<function>lwres_buffer_subtract()</function>checks for underflow.These functions do not allocate or deallocate memory.They just change the value of<structfield>used</structfield>.</para><para>A buffer is re-initialised by<function>lwres_buffer_clear()</function>.The function sets<structfield>used</structfield> ,<structfield>current</structfield>and<structfield>active</structfield>to zero.</para><para><function>lwres_buffer_first</function>makes the consumed region of buffer<parameter>*p</parameter>empty by setting<structfield>current</structfield>to zero (the start of the buffer).</para><para><function>lwres_buffer_forward()</function>increases the consumed region of buffer<parameter>*b</parameter>by<parameter>n</parameter>bytes, checking for overflow.Similarly,<function>lwres_buffer_back()</function>decreases buffer<parameter>b</parameter>'sconsumed region by<parameter>n</parameter>bytes and checks for underflow.</para><para><function>lwres_buffer_getuint8()</function>reads an unsigned 8-bit integer from<parameter>*b</parameter>and returns it.<function>lwres_buffer_putuint8()</function>writes the unsigned 8-bit integer<parameter>val</parameter>to buffer<parameter>*b</parameter>.</para><para><function>lwres_buffer_getuint16()</function>and<function>lwres_buffer_getuint32()</function>are identical to<function>lwres_buffer_putuint8()</function>except that they respectively read an unsigned 16-bit or 32-bit integer in network byte order from<parameter>b</parameter>.Similarly,<function>lwres_buffer_putuint16()</function>and<function>lwres_buffer_putuint32()</function>writes the unsigned 16-bit or 32-bit integer<parameter>val</parameter>to buffer<parameter>b</parameter>,in network byte order.</para><para>Arbitrary amounts of data are read or written from a lightweightresolver buffer with<function>lwres_buffer_getmem()</function>and<function>lwres_buffer_putmem()</function>respectively.<function>lwres_buffer_putmem()</function>copies<parameter>length</parameter>bytes of memory at<parameter>base</parameter>to<parameter>b</parameter>.Conversely,<function>lwres_buffer_getmem()</function>copies<parameter>length</parameter>bytes of memory from<parameter>b</parameter>to<parameter>base</parameter>.</para></refsect1></refentry>