lwres/man/lwres_buffer.html

<!--
 - Copyright (C) 2004, 2005, 2007 Internet Systems Consortium, Inc. ("ISC")
 - Copyright (C) 2000, 2001 Internet Software Consortium.
 -
 - Permission to use, copy, modify, and/or 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.
-->
<!-- $Id$ -->
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>lwres_buffer</title>
<meta name="generator" content="DocBook XSL Stylesheets V1.71.1">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
<a name="id2476275"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2>Name</h2>
<p>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 &#8212; lightweight resolver buffer management</p>
</div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<div class="funcsynopsis">
<pre class="funcsynopsisinfo">
#include &lt;lwres/lwbuffer.h&gt;
</pre>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_init</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>void *�</td>
<td>
<var class="pdparam">base</var>, </td>
</tr>
<tr>
<td>�</td>
<td>unsigned int �</td>
<td>
<var class="pdparam">length</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em"><tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_invalidate</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var><code>)</code>;</td>
</tr></table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_add</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>unsigned int �</td>
<td>
<var class="pdparam">n</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_subtract</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>unsigned int �</td>
<td>
<var class="pdparam">n</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em"><tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_clear</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var><code>)</code>;</td>
</tr></table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em"><tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_first</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var><code>)</code>;</td>
</tr></table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_forward</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>unsigned int �</td>
<td>
<var class="pdparam">n</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_back</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>unsigned int �</td>
<td>
<var class="pdparam">n</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em"><tr>
<td><code class="funcdef">
lwres_uint8_t
<b class="fsfunc">lwres_buffer_getuint8</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var><code>)</code>;</td>
</tr></table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_putuint8</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_uint8_t �</td>
<td>
<var class="pdparam">val</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em"><tr>
<td><code class="funcdef">
lwres_uint16_t
<b class="fsfunc">lwres_buffer_getuint16</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var><code>)</code>;</td>
</tr></table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_putuint16</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_uint16_t �</td>
<td>
<var class="pdparam">val</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em"><tr>
<td><code class="funcdef">
lwres_uint32_t
<b class="fsfunc">lwres_buffer_getuint32</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var><code>)</code>;</td>
</tr></table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_putuint32</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>lwres_uint32_t �</td>
<td>
<var class="pdparam">val</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_putmem</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>const unsigned char *�</td>
<td>
<var class="pdparam">base</var>, </td>
</tr>
<tr>
<td>�</td>
<td>unsigned int �</td>
<td>
<var class="pdparam">length</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
<tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_buffer_getmem</b>(</code></td>
<td>lwres_buffer_t *�</td>
<td>
<var class="pdparam">b</var>, </td>
</tr>
<tr>
<td>�</td>
<td>unsigned char *�</td>
<td>
<var class="pdparam">base</var>, </td>
</tr>
<tr>
<td>�</td>
<td>unsigned int �</td>
<td>
<var class="pdparam">length</var><code>)</code>;</td>
</tr>
</table>
</div>
</div>
<div class="refsect1" lang="en">
<a name="id2543892"></a><h2>DESCRIPTION</h2>
<p>
      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
      <code class="literal">isc_buffer_</code>
      functions in the ISC library.
    </p>
<p>
      A buffer is a region of memory, together with a set of related
      subregions.
      The <span class="emphasis"><em>used region</em></span> and the
      <span class="emphasis"><em>available</em></span> 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.
    </p>
<p>
      The used region is further subdivided into two disjoint regions: the
      <span class="emphasis"><em>consumed region</em></span> and the <span class="emphasis"><em>remaining region</em></span>.
      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 <span class="emphasis"><em>current</em></span> offset (if any).
      The <span class="emphasis"><em>remaining</em></span> 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.
    </p>
<p>
      The <span class="emphasis"><em>active region</em></span> 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.
    </p>
<pre class="programlisting">
   /------------entire length---------------\\
   /----- used region -----\\/-- available --\\
   +----------------------------------------+
   | consumed  | remaining |                |
   +----------------------------------------+
   a           b     c     d                e
      </pre>
<p>
    </p>
<pre class="programlisting">
  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.
      </pre>
<p>
    </p>
<pre class="programlisting">
  a-e == entire length of buffer.
  a-d == used region.
  a-b == consumed region.
  b-d == remaining region.
  b-c == optional active region.
</pre>
<p>
    </p>
<p><code class="function">lwres_buffer_init()</code>
      initializes the
      <span class="type">lwres_buffer_t</span>
      <em class="parameter"><code>*b</code></em>
      and assocates it with the memory region of size
      <em class="parameter"><code>length</code></em>
      bytes starting at location
      <em class="parameter"><code>base.</code></em>
    </p>
<p><code class="function">lwres_buffer_invalidate()</code>
      marks the buffer <em class="parameter"><code>*b</code></em>
      as invalid.  Invalidating a buffer after use is not required,
      but makes it possible to catch its possible accidental use.
    </p>
<p>
      The functions
      <code class="function">lwres_buffer_add()</code>
      and
      <code class="function">lwres_buffer_subtract()</code>
      respectively increase and decrease the used space in
      buffer
      <em class="parameter"><code>*b</code></em>
      by
      <em class="parameter"><code>n</code></em>
      bytes.
      <code class="function">lwres_buffer_add()</code>
      checks for buffer overflow and
      <code class="function">lwres_buffer_subtract()</code>
      checks for underflow.
      These functions do not allocate or deallocate memory.
      They just change the value of
      <em class="structfield"><code>used</code></em>.
    </p>
<p>
      A buffer is re-initialised by
      <code class="function">lwres_buffer_clear()</code>.
      The function sets
      <em class="structfield"><code>used</code></em>,
      <em class="structfield"><code>current</code></em>
      and
      <em class="structfield"><code>active</code></em>
      to zero.
    </p>
<p><code class="function">lwres_buffer_first</code>
      makes the consumed region of buffer
      <em class="parameter"><code>*p</code></em>
      empty by setting
      <em class="structfield"><code>current</code></em>
      to zero (the start of the buffer).
    </p>
<p><code class="function">lwres_buffer_forward()</code>
      increases the consumed region of buffer
      <em class="parameter"><code>*b</code></em>
      by
      <em class="parameter"><code>n</code></em>
      bytes, checking for overflow.
      Similarly,
      <code class="function">lwres_buffer_back()</code>
      decreases buffer
      <em class="parameter"><code>b</code></em>'s
      consumed region by
      <em class="parameter"><code>n</code></em>
      bytes and checks for underflow.
    </p>
<p><code class="function">lwres_buffer_getuint8()</code>
      reads an unsigned 8-bit integer from
      <em class="parameter"><code>*b</code></em>
      and returns it.
      <code class="function">lwres_buffer_putuint8()</code>
      writes the unsigned 8-bit integer
      <em class="parameter"><code>val</code></em>
      to buffer
      <em class="parameter"><code>*b</code></em>.
    </p>
<p><code class="function">lwres_buffer_getuint16()</code>
      and
      <code class="function">lwres_buffer_getuint32()</code>
      are identical to
      <code class="function">lwres_buffer_putuint8()</code>
      except that they respectively read an unsigned 16-bit or 32-bit integer
      in network byte order from
      <em class="parameter"><code>b</code></em>.
      Similarly,
      <code class="function">lwres_buffer_putuint16()</code>
      and
      <code class="function">lwres_buffer_putuint32()</code>
      writes the unsigned 16-bit or 32-bit integer
      <em class="parameter"><code>val</code></em>
      to buffer
      <em class="parameter"><code>b</code></em>,
      in network byte order.
    </p>
<p>
      Arbitrary amounts of data are read or written from a lightweight
      resolver buffer with
      <code class="function">lwres_buffer_getmem()</code>
      and
      <code class="function">lwres_buffer_putmem()</code>
      respectively.
      <code class="function">lwres_buffer_putmem()</code>
      copies
      <em class="parameter"><code>length</code></em>
      bytes of memory at
      <em class="parameter"><code>base</code></em>
      to
      <em class="parameter"><code>b</code></em>.
      Conversely,
      <code class="function">lwres_buffer_getmem()</code>
      copies
      <em class="parameter"><code>length</code></em>
      bytes of memory from
      <em class="parameter"><code>b</code></em>
      to
      <em class="parameter"><code>base</code></em>.
    </p>
</div>
</div></body>
</html>