LWRES_BUFFER(3)               BIND9               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 

       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 subregions. 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() respectively increase and decrease
       the used space in buffer *b by n bytes.
       lwres_buffer_add() checks for buffer overflow and
       lwres_buffer_subtract() 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 underflow.

       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)