lwres_buffer_subtract(3)

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 <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

ISC                  Last change: 2007-06-18                    1

LWRES_BUFFER(3)               BIND9               LWRES_BUFFER(3)

     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.

ISC                  Last change: 2007-06-18                    2

LWRES_BUFFER(3)               BIND9               LWRES_BUFFER(3)

           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.

AUTHOR

     Internet Systems Consortium, Inc.

COPYRIGHT

     Copyright 8c9 2004, 2005, 2007, 2014-2016 Internet Systems

ISC                  Last change: 2007-06-18                    3

LWRES_BUFFER(3)               BIND9               LWRES_BUFFER(3)

     Consortium, Inc. ("ISC")
     Copyright 8c9 2000, 2001 Internet Software Consortium.

ISC                  Last change: 2007-06-18                    4