lwres_buffer_getmem

LWRES_BUFFER(3)						      LWRES_BUFFER(3)



NAME
       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

SYNOPSIS
       #include <lwres/lwbuffer.h>

       void lwres_buffer_init(lwres_buffer_t *b, void *base, unsigned int
       length);

       void lwres_buffer_invalidate(lwres_buffer_t *b);

       void lwres_buffer_add(lwres_buffer_t *b, unsigned int n);

       void lwres_buffer_subtract(lwres_buffer_t *b, unsigned int n);

       void lwres_buffer_clear(lwres_buffer_t *b);

       void lwres_buffer_first(lwres_buffer_t *b);

       void lwres_buffer_forward(lwres_buffer_t *b, unsigned int n);

       void lwres_buffer_back(lwres_buffer_t *b, unsigned int n);

       lwres_uint8_t lwres_buffer_getuint8(lwres_buffer_t *b);

       void lwres_buffer_putuint8(lwres_buffer_t *b, lwres_uint8_t val);

       lwres_uint16_t lwres_buffer_getuint16(lwres_buffer_t *b);

       void lwres_buffer_putuint16(lwres_buffer_t *b, lwres_uint16_t val);

       lwres_uint32_t lwres_buffer_getuint32(lwres_buffer_t *b);

       void lwres_buffer_putuint32(lwres_buffer_t *b, lwres_uint32_t val);

       void lwres_buffer_putmem(lwres_buffer_t *b, const unsigned char *base,
       unsigned int length);

       void lwres_buffer_getmem(lwres_buffer_t *b, unsigned char *base,
       unsigned int length);


DESCRIPTION
       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 isc_buffer_ functions in the ISC library.

       A  buffer is a region of memory, together with a set of related subre-
       gions.  The used region and the available  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.

       The used region is further subdivided into two disjoint	regions:  the
       consumed	 region	 and  the  remaining  region.  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 current offset (if
       any).  The remaining 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.

       The active region 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.



	  /------------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.


       lwres_buffer_init() initializes the lwres_buffer_t *b and assocates it
       with the memory region of size length bytes starting at location base.

       lwres_buffer_invalidate() marks the buffer *b as invalid. Invalidating
       a buffer after use is not required, but makes it possible to catch its
       possible accidental use.

       The functions lwres_buffer_add() and  lwres_buffer_subtract()  respec-
       tively  increase	 and decrease the used space in buffer *b by n bytes.
       lwres_buffer_add() checks for buffer  overflow  and  lwres_buffer_sub-
       tract()	checks	for  underflow.	  These	 functions do not allocate or
       deallocate memory.  They just change the value of used.

       A buffer is re-initialised by lwres_buffer_clear().  The function sets
       used , current and active to zero.

       lwres_buffer_first  makes  the  consumed	 region of buffer *p empty by
       setting current to zero (the start of the buffer).

       lwres_buffer_forward() increases the consumed region of buffer *b by n
       bytes,	checking   for	 overflow.    Similarly,  lwres_buffer_back()
       decreases buffer b’s consumed region by n bytes and checks for  under-
       flow.

       lwres_buffer_getuint8()	reads  an  unsigned 8-bit integer from *b and
       returns it.  lwres_buffer_putuint8() writes the unsigned 8-bit integer
       val to buffer *b.

       lwres_buffer_getuint16() and lwres_buffer_getuint32() are identical to
       lwres_buffer_putuint8() except that they respectively read an unsigned
       16-bit  or  32-bit  integer  in network byte order from b.  Similarly,
       lwres_buffer_putuint16()	 and  lwres_buffer_putuint32()	 writes	  the
       unsigned	 16-bit	 or  32-bit  integer val to buffer b, in network byte
       order.

       Arbitrary amounts of data are  read  or	written	 from  a  lightweight
       resolver	 buffer	 with lwres_buffer_getmem() and lwres_buffer_putmem()
       respectively.  lwres_buffer_putmem() copies length bytes of memory  at
       base  to	 b.  Conversely, lwres_buffer_getmem() copies length bytes of
       memory from b to base.



BIND9				 Jun 30, 2000		      LWRES_BUFFER(3)