lwres_buffer.html revision 2cd182921e1b04ccda0a56995c4cc491c882af04
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<HTML
><HEAD
><TITLE
>lwres_buffer</TITLE
><META
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"></HEAD
><BODY
CLASS="REFENTRY"
BGCOLOR="#FFFFFF"
TEXT="#000000"
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VLINK="#840084"
ALINK="#0000FF"
><H1
><A
NAME="AEN1"
></A
>lwres_buffer</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 -- lightweight resolver buffer management</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN26"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><P
></P
><A
NAME="AEN27"
></A
><PRE
CLASS="FUNCSYNOPSISINFO"
><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
<VAR
CLASS="LITERAL"
>isc_buffer_</VAR
>
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
><CODE
CLASS="FUNCTION"
>lwres_buffer_init()</CODE
>
initializes the
<SPAN
CLASS="TYPE"
>lwres_buffer_t</SPAN
>
<VAR
CLASS="PARAMETER"
>*b</VAR
>
and assocates it with the memory region of size
<VAR
CLASS="PARAMETER"
>length</VAR
>
bytes starting at location
<VAR
CLASS="PARAMETER"
>base.</VAR
></P
><P
><CODE
CLASS="FUNCTION"
>lwres_buffer_invalidate()</CODE
>
marks the buffer
<VAR
CLASS="PARAMETER"
>*b</VAR
>
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
<VAR
CLASS="PARAMETER"
>*b</VAR
>
by
<VAR
CLASS="PARAMETER"
>n</VAR
>
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
<CODE
CLASS="STRUCTFIELD"
>used</CODE
>.</P
><P
>A buffer is re-initialised by
<CODE
CLASS="FUNCTION"
>lwres_buffer_clear()</CODE
>.
The function sets
<CODE
CLASS="STRUCTFIELD"
>used</CODE
> ,
<CODE
CLASS="STRUCTFIELD"
>current</CODE
>
and
<CODE
CLASS="STRUCTFIELD"
>active</CODE
>
to zero.</P
><P
><CODE
CLASS="FUNCTION"
>lwres_buffer_first</CODE
>
makes the consumed region of buffer
<VAR
CLASS="PARAMETER"
>*p</VAR
>
empty by setting
<CODE
CLASS="STRUCTFIELD"
>current</CODE
>
to zero (the start of the buffer).</P
><P
><CODE
CLASS="FUNCTION"
>lwres_buffer_forward()</CODE
>
increases the consumed region of buffer
<VAR
CLASS="PARAMETER"
>*b</VAR
>
by
<VAR
CLASS="PARAMETER"
>n</VAR
>
bytes, checking for overflow.
Similarly,
<CODE
CLASS="FUNCTION"
>lwres_buffer_back()</CODE
>
decreases buffer
<VAR
CLASS="PARAMETER"
>b</VAR
>'s
consumed region by
<VAR
CLASS="PARAMETER"
>n</VAR
>
bytes and checks for underflow.</P
><P
><CODE
CLASS="FUNCTION"
>lwres_buffer_getuint8()</CODE
>
reads an unsigned 8-bit integer from
<VAR
CLASS="PARAMETER"
>*b</VAR
>
and returns it.
<CODE
CLASS="FUNCTION"
>lwres_buffer_putuint8()</CODE
>
writes the unsigned 8-bit integer
<VAR
CLASS="PARAMETER"
>val</VAR
>
to buffer
<VAR
CLASS="PARAMETER"
>*b</VAR
>.</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
<VAR
CLASS="PARAMETER"
>b</VAR
>.
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
<VAR
CLASS="PARAMETER"
>val</VAR
>
to buffer
<VAR
CLASS="PARAMETER"
>b</VAR
>,
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
<VAR
CLASS="PARAMETER"
>length</VAR
>
bytes of memory at
<VAR
CLASS="PARAMETER"
>base</VAR
>
to
<VAR
CLASS="PARAMETER"
>b</VAR
>.
Conversely,
<CODE
CLASS="FUNCTION"
>lwres_buffer_getmem()</CODE
>
copies
<VAR
CLASS="PARAMETER"
>length</VAR
>
bytes of memory from
<VAR
CLASS="PARAMETER"
>b</VAR
>
to
<VAR
CLASS="PARAMETER"
>base</VAR
>.</P
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