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a7038d1a0513c8e804937ebc95fc9cb3a46c04f5Mark Andrews - Copyright (C) 2004 Internet Systems Consortium, Inc. ("ISC")
816e576f77e2c46df3e3d97d65822aa8aded7c4bDavid Lawrence - Copyright (C) 2001 Internet Software Consortium.
06bc083413649ab702788657babebd80478a39f0Andreas Gustafsson -
1da9dbcf48dcfc5c1589def3e785844935d1882cAutomatic Updater - Permission to use, copy, modify, and distribute this software for any
9c3531d72aeaad6c5f01efe6a1c82023e1379e4dDavid Lawrence - purpose with or without fee is hereby granted, provided that the above
06bc083413649ab702788657babebd80478a39f0Andreas Gustafsson - copyright notice and this permission notice appear in all copies.
06bc083413649ab702788657babebd80478a39f0Andreas Gustafsson -
06bc083413649ab702788657babebd80478a39f0Andreas Gustafsson - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
06bc083413649ab702788657babebd80478a39f0Andreas Gustafsson - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
06bc083413649ab702788657babebd80478a39f0Andreas Gustafsson - AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
06bc083413649ab702788657babebd80478a39f0Andreas Gustafsson - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
06bc083413649ab702788657babebd80478a39f0Andreas Gustafsson - LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
06bc083413649ab702788657babebd80478a39f0Andreas Gustafsson - OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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4ca54c8f3bafe5a78e0c7c6b3891c426337bddaeBrian Wellington-->
06bc083413649ab702788657babebd80478a39f0Andreas Gustafsson
79bf7c874bb5a01b5b5db44af10b4ae24c89b93eEvan Hunt<!-- $Id: lwres_buffer.html,v 1.5 2004/03/05 08:32:19 marka Exp $ -->
79bf7c874bb5a01b5b5db44af10b4ae24c89b93eEvan Hunt
79bf7c874bb5a01b5b5db44af10b4ae24c89b93eEvan Hunt<HTML
79bf7c874bb5a01b5b5db44af10b4ae24c89b93eEvan Hunt><HEAD
><TITLE
>lwres_buffer</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.73
"></HEAD
><BODY
CLASS="REFENTRY"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><H1
><A
NAME="AEN1"
>lwres_buffer</A
></H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN8"
></A
><H2
>Name</H2
>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&nbsp;--&nbsp;lightweight resolver buffer management</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN26"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN27"
></A
><P
></P
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include &lt;lwres/lwbuffer.h&gt;</PRE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_init</CODE
>(lwres_buffer_t *b, void *base, unsigned int length);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_invalidate</CODE
>(lwres_buffer_t *b);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_add</CODE
>(lwres_buffer_t *b, unsigned int n);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_subtract</CODE
>(lwres_buffer_t *b, unsigned int n);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_clear</CODE
>(lwres_buffer_t *b);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_first</CODE
>(lwres_buffer_t *b);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_forward</CODE
>(lwres_buffer_t *b, unsigned int n);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_back</CODE
>(lwres_buffer_t *b, unsigned int n);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_uint8_t
lwres_buffer_getuint8</CODE
>(lwres_buffer_t *b);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_putuint8</CODE
>(lwres_buffer_t *b, lwres_uint8_t val);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_uint16_t
lwres_buffer_getuint16</CODE
>(lwres_buffer_t *b);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_putuint16</CODE
>(lwres_buffer_t *b, lwres_uint16_t val);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_uint32_t
lwres_buffer_getuint32</CODE
>(lwres_buffer_t *b);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_putuint32</CODE
>(lwres_buffer_t *b, lwres_uint32_t val);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_putmem</CODE
>(lwres_buffer_t *b, const unsigned char *base, unsigned int length);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_buffer_getmem</CODE
>(lwres_buffer_t *b, unsigned char *base, unsigned int length);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN106"
></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
<TT
CLASS="LITERAL"
>isc_buffer_</TT
>
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"
><I
CLASS="EMPHASIS"
>used region</I
></SPAN
> and the
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>available</I
></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"
><I
CLASS="EMPHASIS"
>consumed region</I
></SPAN
> and the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>remaining region</I
></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"
><I
CLASS="EMPHASIS"
>current</I
></SPAN
> offset (if any).
The <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>remaining</I
></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"
><I
CLASS="EMPHASIS"
>active region</I
></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
><P
><PRE
CLASS="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.</PRE
></P
><P
><TT
CLASS="FUNCTION"
>lwres_buffer_init()</TT
>
initializes the
<SPAN
CLASS="TYPE"
>lwres_buffer_t</SPAN
>
<TT
CLASS="PARAMETER"
><I
>*b</I
></TT
>
and assocates it with the memory region of size
<TT
CLASS="PARAMETER"
><I
>length</I
></TT
>
bytes starting at location
<TT
CLASS="PARAMETER"
><I
>base.</I
></TT
></P
><P
><TT
CLASS="FUNCTION"
>lwres_buffer_invalidate()</TT
>
marks the buffer
<TT
CLASS="PARAMETER"
><I
>*b</I
></TT
>
as invalid. Invalidating a buffer after use is not required,
but makes it possible to catch its possible accidental use.</P
><P
>The functions
<TT
CLASS="FUNCTION"
>lwres_buffer_add()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_buffer_subtract()</TT
>
respectively increase and decrease the used space in
buffer
<TT
CLASS="PARAMETER"
><I
>*b</I
></TT
>
by
<TT
CLASS="PARAMETER"
><I
>n</I
></TT
>
bytes.
<TT
CLASS="FUNCTION"
>lwres_buffer_add()</TT
>
checks for buffer overflow and
<TT
CLASS="FUNCTION"
>lwres_buffer_subtract()</TT
>
checks for underflow.
These functions do not allocate or deallocate memory.
They just change the value of
<TT
CLASS="STRUCTFIELD"
><I
>used</I
></TT
>.</P
><P
>A buffer is re-initialised by
<TT
CLASS="FUNCTION"
>lwres_buffer_clear()</TT
>.
The function sets
<TT
CLASS="STRUCTFIELD"
><I
>used</I
></TT
> ,
<TT
CLASS="STRUCTFIELD"
><I
>current</I
></TT
>
and
<TT
CLASS="STRUCTFIELD"
><I
>active</I
></TT
>
to zero.</P
><P
><TT
CLASS="FUNCTION"
>lwres_buffer_first</TT
>
makes the consumed region of buffer
<TT
CLASS="PARAMETER"
><I
>*p</I
></TT
>
empty by setting
<TT
CLASS="STRUCTFIELD"
><I
>current</I
></TT
>
to zero (the start of the buffer).</P
><P
><TT
CLASS="FUNCTION"
>lwres_buffer_forward()</TT
>
increases the consumed region of buffer
<TT
CLASS="PARAMETER"
><I
>*b</I
></TT
>
by
<TT
CLASS="PARAMETER"
><I
>n</I
></TT
>
bytes, checking for overflow.
Similarly,
<TT
CLASS="FUNCTION"
>lwres_buffer_back()</TT
>
decreases buffer
<TT
CLASS="PARAMETER"
><I
>b</I
></TT
>'s
consumed region by
<TT
CLASS="PARAMETER"
><I
>n</I
></TT
>
bytes and checks for underflow.</P
><P
><TT
CLASS="FUNCTION"
>lwres_buffer_getuint8()</TT
>
reads an unsigned 8-bit integer from
<TT
CLASS="PARAMETER"
><I
>*b</I
></TT
>
and returns it.
<TT
CLASS="FUNCTION"
>lwres_buffer_putuint8()</TT
>
writes the unsigned 8-bit integer
<TT
CLASS="PARAMETER"
><I
>val</I
></TT
>
to buffer
<TT
CLASS="PARAMETER"
><I
>*b</I
></TT
>.</P
><P
><TT
CLASS="FUNCTION"
>lwres_buffer_getuint16()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_buffer_getuint32()</TT
>
are identical to
<TT
CLASS="FUNCTION"
>lwres_buffer_putuint8()</TT
>
except that they respectively read an unsigned 16-bit or 32-bit integer
in network byte order from
<TT
CLASS="PARAMETER"
><I
>b</I
></TT
>.
Similarly,
<TT
CLASS="FUNCTION"
>lwres_buffer_putuint16()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_buffer_putuint32()</TT
>
writes the unsigned 16-bit or 32-bit integer
<TT
CLASS="PARAMETER"
><I
>val</I
></TT
>
to buffer
<TT
CLASS="PARAMETER"
><I
>b</I
></TT
>,
in network byte order.</P
><P
>Arbitrary amounts of data are read or written from a lightweight
resolver buffer with
<TT
CLASS="FUNCTION"
>lwres_buffer_getmem()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_buffer_putmem()</TT
>
respectively.
<TT
CLASS="FUNCTION"
>lwres_buffer_putmem()</TT
>
copies
<TT
CLASS="PARAMETER"
><I
>length</I
></TT
>
bytes of memory at
<TT
CLASS="PARAMETER"
><I
>base</I
></TT
>
to
<TT
CLASS="PARAMETER"
><I
>b</I
></TT
>.
Conversely,
<TT
CLASS="FUNCTION"
>lwres_buffer_getmem()</TT
>
copies
<TT
CLASS="PARAMETER"
><I
>length</I
></TT
>
bytes of memory from
<TT
CLASS="PARAMETER"
><I
>b</I
></TT
>
to
<TT
CLASS="PARAMETER"
><I
>base</I
></TT
>.</P
></DIV
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>