lwres_buffer_subtract(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
       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.

AUTHOR

       Internet Systems Consortium, Inc.

COPYRIGHT

       Copyright (C) 2004, 2005, 2007, 2014-2016 Internet Systems Consortium,
       Inc. ("ISC")
       Copyright (C) 2000, 2001 Internet Software Consortium.

ISC                               2007-06-18                   LWRES_BUFFER(3)