lwres_buffer.docbook

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<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 memory
where 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 related
subregions.
The <emphasis>used region</emphasis> and the
<emphasis>available</emphasis> 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.
</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 to
the byte before the <emphasis>current</emphasis> offset (if any).
The <emphasis>remaining</emphasis> 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.
</para>
<para>
The <emphasis>active region</emphasis> 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.
</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 in
buffer
<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>'s
consumed 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 lightweight
resolver 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>