dbuff.h

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#pragma once
/*
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/** A generic data buffer structure for encoding and decoding
 *
 * Because doing manual length checks is error prone and a waste of everyone's time.
 *
 * @file src/lib/util/dbuff.h
 *
 * @copyright 2020 Arran Cudbard-Bell <a.cudbardb@freeradius.org>
 */
RCSIDH(dbuff_h, "$Id: d3eb3a58c12edd930c35eff1b975bab4567740ce $")
 
#  ifdef __cplusplus
extern "C" {
#  endif
 
#include <errno.h>
#include <freeradius-devel/missing.h>
#include <freeradius-devel/util/debug.h>
#include <freeradius-devel/util/nbo.h>
#include <limits.h>
#include <sys/types.h>
 
DIAG_OFF(cast-align)
 
/** A dbuff
 *
 * dbuffs wrap an underlying buffer, maintaining 'start', 'current', and 'end'
 * position pointers.
 *
 * dbuffs also contain information on if and how the underlying buffer can be
 * extended.
 *
 * For encoding extending means reallocing the underlying buffer so that there's
 * addition space to write data to.
 *
 * For stream decoding extending means shifting out existing data and refilling
 * the underlying buffer from a data source.
 *
 * dbuffs are intended to be organised into hierarchies, with one dbuff per stack
 * frame, initialised from a parent in a higher stack frame.
 *
 * Each time a dbuff is copied (using one of the provided FR_DBUFF_BIND_CURRENT_* macros),
 * the copy's 'start' position is updated to be the 'current' position of its
 * parent.  This ensures length macros report only spaced used/available in the
 * new dbuff and not its parent.
 * Other copy macros may move the 'end' position, to artificially limit the
 * amount of data available.
 */
typedef struct fr_dbuff_s fr_dbuff_t;
 
/** A position marker associated with a dbuff
 *
 * Markers are used whenever the caller needs to access part of the underlying
 * buffer other than the 'start', 'current' or 'end' positions described by
 * a #fr_dbuff_t.
 *
 * Markers are needed because if a #fr_dbuff_t is extended, pointers into the
 * underlying buffer may be invalidated by a realloc or memmove.
 *
 * Markers are intended to be allocated on the stack and associated with a
 * stack-frame-local `fr_dbuff_t`.  Using a stack-frame-local dbuff ensures
 * markers are automatically released when the stack frame is popped so that
 * markers are not leaked.
 */
typedef struct fr_dbuff_marker_s fr_dbuff_marker_t;
 
/** dbuff extension callback
 *
 * This callback is used to extend the underlying buffer.
 *
 * - Where the buffer is being used to aggregate data, this callback will
 * usually call realloc to extend the buffer.
 *
 * - Where the buffer is being used for stream decoding, this callback will
 * usually shift the existing data in the buffer to the left, and read in more
 * data from the stream.
 *
 * After performing an operation on the underlying buffer, this callback should
 * call #fr_dbuff_update to fix position pointers in the current dbuff and its
 * parents and markers.
 *
 * Generally the caller will request the minimum amount the buffer should be
 * extended by.  This callback may choose to ignore the request and extend the
 * buffer by more than the requested amount.
 *
 * @param[in] dbuff             to extend.
 * @param[in] req_extension     How much the caller wants to extend the buffer
 *                              by.
 * @return How much the buffer was extended by.
 * @see fr_dbuff_update
 */
typedef size_t(*fr_dbuff_extend_t)(fr_dbuff_t *dbuff, size_t req_extension);
 
/** A position marker associated with a dbuff
 * @private
 */
struct fr_dbuff_marker_s {
        /** @private
         */
        union {
                uint8_t const *p_i;                     //!< Immutable position pointer.
                uint8_t *p;                             //!< Mutable position pointer.
        };
        fr_dbuff_marker_t       *next;          //!< Next marker in the list.
        fr_dbuff_t              *parent;        //!< Owner of the marker.
};
 
#define FR_DBUFF_ADV_PARENT_CURRENT     0x01            //!< Advance current position of parent.
                                                        //!< Useful for nested encoders/decoders.
#define FR_DBUFF_ADV_PARENT_END         0x02            //!< Advance end pointer of parent.
                                                        ///< Useful for producer/consumer
 
/** A dbuff
 * @private
 */
struct fr_dbuff_s {
        /** @private
         */
        union {
                uint8_t const *buff_i;                  //!< Immutable 'buffer' pointer.
                uint8_t *buff;                          //!< Mutable 'buffer' pointer.
        };
 
        /** @private
         */
        union {
                uint8_t const *start_i;                 //!< Immutable 'start' pointer.
                uint8_t *start;                         //!< Mutable 'start' pointer.
        };
 
        /** @private
         */
        union {
                uint8_t const *end_i;                   //!< Immutable 'end' pointer.
                uint8_t *end;                           //!< Mutable 'end' pointer.
        };
 
        /** @private
         */
        union {
                uint8_t const *p_i;                     //!< Immutable 'current' pointer.
                uint8_t *p;                             //!< Mutable 'current' pointer.
        };
 
        unsigned int            is_const : 1;   //!< The buffer this dbuff wraps is const.
        unsigned int            adv_parent : 2; //!< Whether we advance the parent
                                                ///< of this dbuff.
 
        size_t                  shifted;        //!< How many bytes this sbuff has been
                                                ///< shifted since its creation.
 
        fr_dbuff_extend_t       extend;         //!< Function to re-populate or extend
                                                ///< the buffer.
        void                    *uctx;          //!< Extend uctx data.
 
        fr_dbuff_t              *parent;        //!< The #fr_dbuff_t this #fr_dbuff_t was
                                                ///< created from.
                                                ///< This will usually be the #fr_dbuff_t
                                                ///< passed into a function.
 
        fr_dbuff_marker_t       *m;             //!< Pointers to update if the underlying
                                                ///< buffer changes.
};
 
/** Generic wrapper macro to return if there's insufficient memory to satisfy the request on the dbuff
 *
 */
#define FR_DBUFF_RETURN(_func, ...) \
do { \
        ssize_t _slen = _func(__VA_ARGS__ ); \
        if (_slen < 0) return _slen; \
} while (0)
 
/** Generic wrapper to return an error and an offset from encoding.
 *
 *  Some encoders return PAIR_ENCODE_FATAL_ERROR.  Substracting an
 *  offset from that values means it wraps be be a positive number
 *  near INT64_MAX.  This macro ensures that doesn't happen.
 */
#define FR_DBUFF_ERROR_OFFSET(_slen, _offset) ((_slen < INT32_MAX) ? _slen : _slen - (ssize_t) _offset)
 
/** @name Initialisers
 * @{
 */
 
/** @cond */
 
/** Copy another fr_dbuff_t, modifying it.
 *
 * @private
 */
#define _FR_DBUFF(_dbuff_or_marker, _start, _adv_parent) \
((fr_dbuff_t){ \
        .buff           = fr_dbuff_buff(_dbuff_or_marker), \
        .start          = (_start), \
        .end            = fr_dbuff_end(_dbuff_or_marker), \
        .p              = fr_dbuff_current(_dbuff_or_marker), \
        .is_const       = fr_dbuff_ptr(_dbuff_or_marker)->is_const, \
        .adv_parent     = (_adv_parent), \
        .shifted        = fr_dbuff_ptr(_dbuff_or_marker)->shifted, \
        .extend         = fr_dbuff_ptr(_dbuff_or_marker)->extend, \
        .uctx           = fr_dbuff_ptr(_dbuff_or_marker)->uctx, \
        .parent         = fr_dbuff_ptr(_dbuff_or_marker) \
})
/* @endcond */
 
/** Create a new dbuff pointing to the same underlying buffer
 *
 * - Parent will _NOT_ be advanced by operations on its child.
 * - Child will have its `start` pointer set to the `p` pointer of the parent.
 *
 * @param[in] _dbuff_or_marker  to make an ephemeral copy of.
 */
#define FR_DBUFF(_dbuff_or_marker) _FR_DBUFF(_dbuff_or_marker, fr_dbuff_current(_dbuff_or_marker), 0x00)
 
/** Create a new dbuff pointing to the same underlying buffer
 *
 * - Parent will _NOT_ be advanced by operations on its child.
 * - Child will have its `start` pointer set to the `start` pointer of the parent.
 *
 * @param[in] _dbuff_or_marker  to make an ephemeral copy of.
 */
#define FR_DBUFF_ABS(_dbuff_or_marker) _FR_DBUFF(_dbuff_or_marker, fr_dbuff_start(_dbuff_or_marker), 0x00)
 
/** Create a new dbuff pointing to the same underlying buffer
 *
 * - Parent `p` pointer will be advanced with child's `p` pointer.
 * - Child will have its `start` pointer set to the `p` pointer of the parent.
 *
 * @param[in] _dbuff_or_marker  to make an ephemeral copy of.
 */
#define FR_DBUFF_BIND_CURRENT(_dbuff_or_marker) _FR_DBUFF(_dbuff_or_marker, fr_dbuff_current(_dbuff_or_marker), FR_DBUFF_ADV_PARENT_CURRENT)
 
/** Create a new dbuff pointing to the same underlying buffer
 *
 * - Parent `p` pointer will be advanced with child's `p` pointer.
 * - Child will have its `start` pointer set to the `start` pointer of the parent.
 *
 * @param[in] _dbuff_or_marker  to make an ephemeral copy of.
 */
#define FR_DBUFF_BIND_CURRENT_ABS(_dbuff_or_marker) FR_DBUFF_ABS(_dbuff_or_marker, fr_dbuff_start(_dbuff_or_marker), FR_DBUFF_ADV_PARENT_CURRENT)
 
/** Create a new dbuff pointing to the same underlying buffer
 *
 * This is used to create the producer of a producer/consumer pairs of dbuffs.
 *
 * - Parent `end` pointer will be advanced with child's `p` pointer.
 * - Child will have its `start` pointer set to the `start` pointer of the parent.
 *
 * @param[in] _dbuff_or_marker  to make an ephemeral copy of.
 */
#define FR_DBUFF_BIND_END_ABS(_dbuff_or_marker) _FR_DBUFF(_dbuff_or_marker, fr_dbuff_start(_dbuff_or_marker), FR_DBUFF_ADV_PARENT_END)
 
/** @cond */
/** Limit available bytes in the dbuff to _max when passing it to another function
 *
 * @private
 */
#define _FR_DBUFF_MAX(_dbuff_or_marker, _max, _adv_parent) \
((fr_dbuff_t){ \
        .buff           = fr_dbuff_buff(_dbuff_or_marker), \
        .start          = fr_dbuff_current(_dbuff_or_marker), \
        .end            = (((fr_dbuff_end(_dbuff_or_marker) - (_max) < fr_dbuff_current(_dbuff_or_marker))) ? fr_dbuff_end(_dbuff_or_marker) : (fr_dbuff_current(_dbuff_or_marker) + (_max))), \
        .p              = fr_dbuff_current(_dbuff_or_marker), \
        .is_const       = fr_dbuff_ptr(_dbuff_or_marker)->is_const, \
        .adv_parent     = _adv_parent, \
        .shifted        = fr_dbuff_ptr(_dbuff_or_marker)->shifted, \
        .extend         = NULL, \
        .uctx           = NULL, \
        .parent         = fr_dbuff_ptr(_dbuff_or_marker) \
})
/* @endcond */
 
/** Limit the maximum number of bytes available in the dbuff when passing it to another function
 *
 @code{.c}
 fr_dbuff_t tlv = FR_DBUFF_MAX(dbuff, UINT8_MAX);
 
 if (my_child_encoder(&tlv, vp) < 0) return -1;
 
 return fr_dbuff_advance(dbuff, fr_dbuff_used(tlv))
 @endcode
 *
 * @note Do not use to re-initialise the contents of _dbuff, i.e. to
 *      permanently shrink the exiting dbuff. The parent pointer will loop.
 *
 * @note Do not modify the "child" dbuff directly.  Use the functions
 *       supplied as part of this API.
 *
 * @param[in] _dbuff_or_marker  to reserve bytes in.
 * @param[in] _max              The maximum number of bytes the caller is allowed to write to.
 */
#define FR_DBUFF_MAX(_dbuff_or_marker,  _max) _FR_DBUFF_MAX(_dbuff_or_marker, _max, 0x00)
 
/** Limit the maximum number of bytes available in the dbuff when passing it to another function
 *
 @code{.c}
 my_child_encoder(&FR_DBUFF_MAX_BIND_CURRENT(dbuff, 253), vp);
 @endcode
 *
 * @note Do not use to re-initialise the contents of _dbuff, i.e. to
 *      permanently shrink the exiting dbuff. The parent pointer will loop.
 *
 * @note Do not modify the "child" dbuff directly.  Use the functions
 *       supplied as part of this API.
 *
 * @param[in] _dbuff_or_marker  to reserve bytes in.
 * @param[in] _max              The maximum number of bytes the caller is allowed to write to.
 */
#define FR_DBUFF_MAX_BIND_CURRENT(_dbuff_or_marker,  _max) _FR_DBUFF_MAX(_dbuff_or_marker, _max, FR_DBUFF_ADV_PARENT_CURRENT)
 
/*
 *      GCC is stupid and will warn about output variables
 *      being unnitialised, even if they're not dereferenced.
 */
#if defined(__GNUC__) && __GNUC__ >= 11
DIAG_OFF(maybe-uninitialized)
#endif
/** Does the actual work of initialising a dbuff
 * @private
 */
static inline
#ifndef __COVERITY__
CC_HINT(nonnull)
#endif
void _fr_dbuff_init(fr_dbuff_t *out, uint8_t const *start, uint8_t const *end, bool is_const)
{
        if (unlikely(end < start)) end = start; /* Could be an assert? */
 
        *out = (fr_dbuff_t){
                .buff_i = start,
                .start_i = start,
                .p_i = start,
                .end_i = end,
                .is_const = is_const
        };
}
 
/** Initialise an dbuff for encoding or decoding
 *
 * @param[out] _out             Pointer to buffer to parse
 * @param[in] _start            Start of the buffer to parse.
 * @param[in] _len_or_end       Either an end pointer or the length
 *                              of the buffer we're decoding.
 */
#define fr_dbuff_init(_out, _start, _len_or_end) \
_fr_dbuff_init(_out, \
               (uint8_t const *)(_start), \
               _Generic((_len_or_end), \
                        size_t          : (uint8_t const *)(_start) + (size_t)(_len_or_end), \
                        long            : (uint8_t const *)(_start) + (size_t)(_len_or_end), \
                        int             : (uint8_t const *)(_start) + (size_t)(_len_or_end), \
                        unsigned int    : (uint8_t const *)(_start) + (size_t)(_len_or_end), \
                        uint8_t *       : (uint8_t const *)(_len_or_end), \
                        uint8_t const * : (uint8_t const *)(_len_or_end), \
                        char *          : (uint8_t const *)(_len_or_end), \
                        char const *    : (uint8_t const *)(_len_or_end) \
               ), \
               _Generic((_start), \
                        uint8_t *       : false, \
                        uint8_t const * : true, \
                        char *          : false, \
                        char const *    : true \
               ))
#if defined(__GNUC__) && __GNUC__ >= 11
DIAG_ON(maybe-uninitialized)
#endif
 
#define FR_DBUFF_INIT(_out, _start, _len_or_end) do { \
        fr_dbuff_init(_out, _start, _len_or_end); \
        *(unsigned char *) _start = '\0'; \
  } while (0)
 
size_t  _fr_dbuff_extend_talloc(fr_dbuff_t *dbuff, size_t extension);
 
int     fr_dbuff_trim_talloc(fr_dbuff_t *dbuff, size_t len);
 
int     fr_dbuff_reset_talloc(fr_dbuff_t *dbuff);
 
/** Talloc extension structure use by #fr_dbuff_init_talloc
 * @private
 *
 * Holds the data necessary for creating dynamically
 * extensible buffers.
 */
typedef struct {
        TALLOC_CTX              *ctx;                   //!< Context to alloc new buffers in.
        size_t                  init;                   //!< How much to allocate initially.
        size_t                  max;                    //!< Maximum size of the buffer.
} fr_dbuff_uctx_talloc_t;
 
/** Initialise a special dbuff which automatically extends as additional data is written
 *
 * @param[in] ctx       to allocate buffer in.
 * @param[out] dbuff    to initialise.
 * @param[out] tctx     to initialise.  Must have a lifetime >= to the dbuff.
 * @param[in] init      The length of the initial buffer.
 * @param[in] max       The maximum length of the buffer.
 * @return
 *      - The passed dbuff on success.
 *      - NULL on failure.
 */
static inline fr_dbuff_t *fr_dbuff_init_talloc(TALLOC_CTX *ctx,
                                               fr_dbuff_t *dbuff, fr_dbuff_uctx_talloc_t *tctx,
                                               size_t init, size_t max)
{
        uint8_t *buff;
 
        *tctx = (fr_dbuff_uctx_talloc_t){
                .ctx = ctx,
                .init = init,
                .max = max
        };
 
        /*
         *      Allocate the initial buffer
         *
         *      We always allocate a buffer so we don't trigger ubsan
         *      errors by performing arithmetic on NULL pointers.
         *
         *      Note that unlike sbuffs, we don't need space for a trailing '\0'.
         */
        buff = talloc_zero_array(ctx, uint8_t, init);
        if (!buff) {
                fr_strerror_printf("Failed allocating buffer of %zu bytes", init);
                memset(dbuff, 0, sizeof(*dbuff));       /* clang scan */
                return NULL;
        }
 
        *dbuff = (fr_dbuff_t){
                .buff = buff,
                .start = buff,
                .p = buff,
                .end = buff + init,
                .extend = _fr_dbuff_extend_talloc,
                .uctx = tctx
        };
 
        return dbuff;
}
 
/** Free the talloc buffer associated with a dbuff
 *
 */
static inline void fr_dbuff_free_talloc(fr_dbuff_t *dbuff)
{
        TALLOC_FREE(dbuff->buff);
}
 
size_t  _fr_dbuff_extend_fd(fr_dbuff_t *dbuff, size_t extension);
 
/** File sbuff extension structure use by #fr_dbuff_init_fd
 * @private
 *
 * Holds the data necessary for creating dynamically
 * extensible file buffers.
 */
typedef struct {
        int                     fd;                     //!< fd of file we're reading from.
        uint8_t                 *buff_end;              //!< The true end of the buffer.
        size_t                  max;                    //!< Maximum number of bytes to read.
} fr_dbuff_uctx_fd_t;
 
 
/** Initialise a special dbuff which automatically reads in more data as the buffer is exhausted
 *
 * @param[out] dbuff    to initialise.
 * @param[out] fctx     to initialise.  Must have a lifetime >= to the dbuff.
 * @param[in] buff      Temporary buffer to use for storing file contents.
 * @param[in] len       Length of the temporary buffer.
 * @param[in] fd        descriptor of an open file to read from.
 * @param[in] max       The maximum length of data to read from the file.
 * @return
 *      - The passed dbuff on success.
 *      - NULL on failure.
 */
static inline fr_dbuff_t *fr_dbuff_init_fd(fr_dbuff_t *dbuff, fr_dbuff_uctx_fd_t *fctx,
                                             uint8_t *buff, size_t len, int fd, size_t max)
{
        *fctx = (fr_dbuff_uctx_fd_t){
                .fd = fd,
                .max = max,
                .buff_end = buff + len          //!< Store the real end
        };
 
        *dbuff = (fr_dbuff_t){
                .buff = buff,
                .start = buff,
                .p = buff,
                .end = buff,                    //!< Starts with 0 bytes available
                .extend = _fr_dbuff_extend_fd,
                .uctx = fctx
        };
 
        return dbuff;
}
 
/** Creates a compound literal to pass into functions which accept a dbuff
 *
 * @note The return value of the function should be used to determine how much
 *       data was written to the buffer.
 *
 * @param[in] _start            of the buffer.
 * @param[in] _len_or_end       Length of the buffer or the end pointer.
 */
#define FR_DBUFF_TMP(_start, _len_or_end) \
(fr_dbuff_t){ \
        .buff_i         = (uint8_t const *)(_start), \
        .start_i        = (uint8_t const *)(_start), \
        .end_i          = _Generic((_len_or_end), \
                                size_t          : (uint8_t const *)(_start) + (size_t)(_len_or_end), \
                                long            : (uint8_t const *)(_start) + (size_t)(_len_or_end), \
                                int             : (uint8_t const *)(_start) + (size_t)(_len_or_end), \
                                unsigned int    : (uint8_t const *)(_start) + (size_t)(_len_or_end), \
                                uint8_t *       : (uint8_t const *)(_len_or_end), \
                                uint8_t const * : (uint8_t const *)(_len_or_end), \
                                char *          : (uint8_t const *)(_len_or_end), \
                                char const *    : (uint8_t const *)(_len_or_end) \
                        ), \
        .p_i            = _start, \
        .is_const       = _Generic((_start), \
                                uint8_t *       : false, \
                                uint8_t const * : true, \
                                char *          : false, \
                                char const *    : true \
                        ) \
}
 
/** Structure to encapsulate a thread local dbuff information
 *
 */
typedef struct {
        fr_dbuff_t                      dbuff;          //!< Thread local dbuff.
        fr_dbuff_uctx_talloc_t          tctx;           //!< Thread local tctx.
} fr_dbuff_thread_local_t;
 
static inline int _dbuff_thread_local_free(void *dbtl)
{
        return talloc_free(dbtl);
}
 
/** Create a function local and thread local extensible dbuff
 *
 * @param[out] _out             Where to write a pointer to the thread local dbuff
 * @param[in] _init             Initial size for the dbuff buffer.
 * @param[in] _max              Maximum size of the dbuff buffer.
 */
#define FR_DBUFF_TALLOC_THREAD_LOCAL(_out, _init, _max) \
do { \
        static _Thread_local fr_dbuff_thread_local_t *_dbuff_t_local; \
        if (!_dbuff_t_local) { \
                fr_dbuff_thread_local_t *dbtl = talloc_zero(NULL, fr_dbuff_thread_local_t); \
                fr_dbuff_init_talloc(dbtl, &dbtl->dbuff, &dbtl->tctx, _init, _max); \
                fr_atexit_thread_local(_dbuff_t_local, _dbuff_thread_local_free, dbtl); \
                *(_out) = &_dbuff_t_local->dbuff; \
        } else { \
                fr_dbuff_reset_talloc(&_dbuff_t_local->dbuff); \
                *(_out) = &_dbuff_t_local->dbuff; \
        } \
} while (0)
/** @} */
 
/** @name Extension requests
 *
 * These functions/macros may be used to request that the underlying buffer is
 * either extended to accommodate more data, or that data is shifted out of the
 * buffer, and that the buffer is refilled.
 *
 * @{
 */
 
/** Flag indicating a dbuff is extendable
 */
#define FR_DBUFF_FLAG_EXTENDABLE                0x01
 
/** Flag indicating that during the last extend call the dbuff was extended
 */
#define FR_DBUFF_FLAG_EXTENDED                  0x02
 
/** Whether the buffer is currently extendable and whether it was extended
 */
typedef enum {
        /** dbuff cannot be extended
         */
        FR_DBUFF_NOT_EXTENDABLE                 = 0x00,
 
        /** dbuff can be extended
         */
        FR_DBUFF_EXTENDABLE                     = FR_DBUFF_FLAG_EXTENDABLE,
 
        /** dbuff was extended in the last extend call and may be extended again
         */
        FR_DBUFF_EXTENDABLE_EXTENDED            = FR_DBUFF_FLAG_EXTENDABLE | FR_DBUFF_FLAG_EXTENDED,
 
        /** dbuff was extended in the last extend call but cannot be extended again
         */
        FR_DBUFF_EXTENDED                       = FR_DBUFF_FLAG_EXTENDED
} fr_dbuff_extend_status_t;
 
/** Check if a dbuff can be extended again
 */
#define fr_dbuff_is_extendable(_status)         ((_status) & FR_DBUFF_FLAG_EXTENDABLE)
 
/** Check if the dbuff was extended during the last extend call
 */
#define fr_dbuff_was_extended(_status)          ((_status) & FR_DBUFF_FLAG_EXTENDED)
 
/** Internal function - do not call directly
 * @private
 */
static inline size_t _fr_dbuff_extend_lowat(fr_dbuff_extend_status_t *status, fr_dbuff_t *in,
                                            size_t remaining, size_t lowat)
{
        size_t extended = 0;
 
        if (status && !fr_dbuff_is_extendable(*status)) {
        not_extendable:
                if (status) *status = FR_DBUFF_NOT_EXTENDABLE;
                return remaining;
        }
 
        if (remaining >= lowat) {
                if (status) *status = FR_DBUFF_EXTENDABLE;
                return remaining;
        }
 
        if (!in->extend || !(extended = in->extend(in, lowat - remaining))) goto not_extendable;
 
        if (status) *status = FR_DBUFF_EXTENDABLE_EXTENDED;
 
        return remaining + extended;
}
 
/** Extend if we're below _lowat
 *
 * @param[out] _status          May be NULL.  If fr_dbuff_extend_lowat is used
 *                              in a copy loop, the caller should pass a pointer
 *                              to a #fr_dbuff_extend_status_t.  The initial
 *                              value of the #fr_dbuff_extend_status_t variable
 *                              should be #FR_DBUFF_EXTENDABLE, and will be updated
 *                              to indicate whether the dbuff is extensible,
 *                              whether it was extended, and whether it may be
 *                              extended again.  This information
 *                              is used the loop condition to prevent spurious
 *                              extension calls.
 * @param[in] _dbuff_or_marker  to extend.
 * @param[in] _lowat            If bytes remaining are below the amount, extend.
 * @return
 *      - 0 if there are no bytes left in the buffer and we couldn't extend.
 *      - >0 the number of bytes in the buffer after extending.
 */
#define fr_dbuff_extend_lowat(_status, _dbuff_or_marker, _lowat) \
        _fr_dbuff_extend_lowat(_status, \
                               fr_dbuff_ptr(_dbuff_or_marker), \
                               fr_dbuff_remaining(_dbuff_or_marker), _lowat)
 
/** Extend if we're below _lowat and return if we can't extend above _lowat
 *
 * @param[in] _dbuff_or_marker  to extend.
 * @param[in] _lowat            If bytes remaining are below the amount, extend.
 * @return
 *      - 0 if there are no bytes left in the buffer and we couldn't extend.
 *      - >0 the number of bytes in the buffer after extending.
 */
#define FR_DBUFF_EXTEND_LOWAT_OR_RETURN(_dbuff_or_marker, _lowat) \
do { \
        size_t _remaining = fr_dbuff_extend_lowat(NULL, _dbuff_or_marker, _lowat); \
        if (_remaining < _lowat) return -(_lowat - _remaining); \
} while (0)
 
/** @cond */
/** Extend if we're below _lowat and return if we can't extend above _lowat
 *
 * @private
 *
 * @param[in,out] _pos_p        the position pointer to use.
 * @param[in] _dbuff_or_marker  to extend.
 * @param[in] _lowat            The minimum amount the dbuff should be extended by.
 * @return The number of bytes we would need to satisfy _lowat as a negative integer.
 */
#define _FR_DBUFF_EXTEND_LOWAT_POS_OR_RETURN(_pos_p, _dbuff_or_marker, _lowat) \
do { \
        size_t _remaining = _fr_dbuff_extend_lowat(NULL, \
                                                   fr_dbuff_ptr(_dbuff_or_marker), \
                                                   fr_dbuff_end(_dbuff_or_marker) - (*(_pos_p)), _lowat); \
        if (_remaining < _lowat) return -(_lowat - _remaining); \
} while (0)
/** @endcond */
 
/** Extend if no space remains
 *
 * @param[in] _dbuff    to extend.
 * @return
 *      - 0 if there are no bytes left in the buffer and we couldn't extend.
 *      - >0 the number of bytes in the buffer after extending.
 */
#define fr_dbuff_extend(_dbuff) fr_dbuff_extend_lowat(NULL, _dbuff, 1)
/** @} */
 
/** @name Extension callback helpers
 *
 * These public functions are intended to be called by extension callbacks
 * to fixup dbuffs after the underlying buffer or its contents has been altered.
 * @{
 */
void    fr_dbuff_update(fr_dbuff_t *dbuff, uint8_t *new_buff, size_t new_len);
 
size_t  fr_dbuff_shift(fr_dbuff_t *dbuff, size_t shift);
/** @} */
 
/** @name Length checks
 *
 * These macros return the amount of data used/remaining relative to the dbuff
 * or marker's 'start', 'current', and 'end' pointers.
 *
 * In the majority of cases these macros should not be used and the extension
 * request functions should be used instead.  The only exception to this is if
 * the caller is certain the #fr_dbuff_t is not extensible.
 *
 * @{
 */
/** Return the number of bytes remaining between the dbuff or marker and the end of the buffer
 *
 * @note Do not use this in functions that may be used for stream decoding
 *       unless you're sure you know what you're doing.
 *       The value return does not reflect the number of bytes that may
 *       be potentially read from the stream, only the number of bytes
 *       until the end of the current chunk.
 *
 * @param[in] _dbuff_or_marker  to return the number of bytes remaining for.
 * @return
 *      - >0 the number of bytes remaining before we reach the end of the buffer.
 *      - -0 we're at the end of the buffer.
 */
#define fr_dbuff_remaining(_dbuff_or_marker) \
        ((size_t)(fr_dbuff_end(_dbuff_or_marker) < fr_dbuff_current(_dbuff_or_marker) ? \
                0 : (fr_dbuff_end(_dbuff_or_marker) - fr_dbuff_current(_dbuff_or_marker))))
 
/** Check if _len bytes are available in the dbuff and if not return the number of bytes we'd need
 *
 * @note Do not use this in functions that may be used for stream decoding
 *       unless you're sure you know what you're doing.
 *       The value return does not reflect the number of bytes that may
 *       be potentially read from the stream, only the number of bytes
 *       until the end of the current chunk.
 *
 * @param[in] _dbuff_or_marker  to return the number of bytes remaining for.
 * @param[in] _len              Minimum remaining bytes.
 * @return
 *      - >0 the number of bytes remaining before we reach the end of the buffer.
 *      - -0 we're at the end of the buffer.
 */
#define FR_DBUFF_REMAINING_RETURN(_dbuff_or_marker, _len) \
        if ((_len) > fr_dbuff_remaining(_dbuff_or_marker)) return -((_len) - fr_dbuff_remaining(_dbuff_or_marker))
 
/** Return the number of bytes remaining between the start of the dbuff or marker and the current position
 *
 */
#define fr_dbuff_used(_dbuff_or_marker) \
        ((size_t)(fr_dbuff_start(_dbuff_or_marker) > fr_dbuff_current(_dbuff_or_marker) ? \
                0 : (fr_dbuff_current(_dbuff_or_marker) - fr_dbuff_start(_dbuff_or_marker))))
 
/** The length of the underlying buffer
 *
 * @param[in] _dbuff_or_marker  to return the length of.
 * @return The length of the underlying buffer.
 */
#define fr_dbuff_len(_dbuff_or_marker) \
        ((size_t)(fr_dbuff_end(_dbuff_or_marker) - fr_dbuff_start(_dbuff_or_marker)))
 
/** How many bytes the dbuff or marker is behind its parent
 *
 * @param[in] _dbuff_or_marker
 * @return
 *      - 0 the dbuff or marker is ahead of its parent.
 *      - >0 the number of bytes the marker is behind its parent.
 */
#define fr_dbuff_behind(_dbuff_or_marker) \
        (fr_dbuff_current(_dbuff_or_marker) > fr_dbuff_current((_dbuff_or_marker)->parent) ? \
                0 : fr_dbuff_current((_dbuff_or_marker)->parent) - fr_dbuff_current(_dbuff_or_marker))
 
/** How many bytes the dbuff or marker is ahead of its parent
 *
 * @return
 *      - 0 the dbuff or marker is behind its parent.
 *      - >0 the number of bytes the marker is ahead of its parent.
 */
#define fr_dbuff_ahead(_dbuff_or_marker) \
        (fr_dbuff_current((_dbuff_or_marker)->parent) > fr_dbuff_current(_dbuff_or_marker) ? \
                0 : fr_dbuff_current(_dbuff_or_marker) - fr_dbuff_current((_dbuff_or_marker)->parent))
/** @} */
 
/** @name Accessors
 *
 * Caching the pointers returned by the accessors is strongly discouraged.
 * Cached pointers can become invalidated if the #fr_dbuff_t is extended, as
 * the extensions callback may use realloc or memmove on the underlying buffer.
 *
 @code{.c}
 fr_dbuff_t dbuff;
 fr_dbuff_uctx_talloc_t tctx;
 uint8_t *p;
 
 fr_dbuff_init_talloc(NULL, &dbuff, &tctx, 512, SIZE_MAX);
 
 p = fr_dbuff_current(&dbuff);                  // Cache the start pointer
 fr_dbuff_extend_lowat(&dbuff, 1024);           // Extension call triggers realloc
 
 printf("%s", p);                               // Should print an empty string but may
                                                // SEGV as p may now be invalid.
 @endcode
 *
 * If offsets of a #fr_dbuff_t need to be accessed, markers should be used.
 * If a dbuff is extended all markers associated with it will be updated so that the
 * content they point to remains constant.
 *
 @code{.c}
 fr_dbuff_t dbuff;
 fr_dbuff_uctx_talloc_t tctx;
 fr_dbuff_marker_t m;
 
 fr_dbuff_init_talloc(NULL, &dbuff, &tctx, 512, SIZE_MAX);
 fr_dbuff_marker(&m, &dbuff);
 
 fr_dbuff_extend_lowat(&dbuff, 1024);           // Extension call triggers realloc
 
 printf("%s", fr_dbuff_current(&m));            // Marker was updated when the dbuff
                                                // was extended.  All is well.
 @endcode
 *
 * Using offsets of the pointers returned by accessor functions is also strongly
 * discouraged as it invalidates many of the protections dbuffs give.
 *
 @code{.c}
 uint8_t buff[2];
 fr_dbuff_t dbuff;
 
 fr_dbuff_init(&dbuff, buff, sizeof(buff));
 fr_dbuff_current(&dbuff)[2] = 0x00;            // Write to invalid memory
 @endcode
 *
 * @{
 */
 
/** Return a pointer to the dbuff
 *
 * @param[in] _dbuff_or_marker  to return a pointer to.
 * @return A pointer to the dbuff.
 */
#define fr_dbuff_ptr(_dbuff_or_marker) \
        _Generic((_dbuff_or_marker), \
                 fr_dbuff_t *                   : ((fr_dbuff_t *)(_dbuff_or_marker)), \
                 fr_dbuff_marker_t *            : (((fr_dbuff_marker_t *)(_dbuff_or_marker))->parent) \
        )
 
/** Return a const pointer to the dbuff
 *
 * @param[in] _dbuff_or_marker  to return a pointer to.
 * @return A pointer to the dbuff.
 */
#define fr_dbuff_ptr_const(_dbuff_or_marker) \
        _Generic((_dbuff_or_marker), \
                 fr_dbuff_t *                   : ((fr_dbuff_t const *)(_dbuff_or_marker)), \
                 fr_dbuff_t const *             : ((fr_dbuff_t const *)(_dbuff_or_marker)), \
                 fr_dbuff_marker_t *            : (((fr_dbuff_marker_t const *)(_dbuff_or_marker))->parent), \
                 fr_dbuff_marker_t const *      : (((fr_dbuff_marker_t const *)(_dbuff_or_marker))->parent) \
        )
 
/** Return the underlying buffer in a dbuff or one of marker
 *
 * @param[in] _dbuff_or_marker  to return the buffer for.
 * @return A pointer to the start of the buffer.
 */
#define fr_dbuff_buff(_dbuff_or_marker) \
        _Generic((_dbuff_or_marker), \
                 fr_dbuff_t *                   : (((fr_dbuff_t const *)(_dbuff_or_marker))->buff), \
                 fr_dbuff_t const *             : (((fr_dbuff_t const *)(_dbuff_or_marker))->buff), \
                 fr_dbuff_marker_t *            : (((fr_dbuff_marker_t const *)(_dbuff_or_marker))->parent->buff), \
                 fr_dbuff_marker_t const *      : (((fr_dbuff_marker_t const *)(_dbuff_or_marker))->parent->buff) \
        )
 
/** Return the 'start' position of a dbuff or marker
 *
 * The start position is not necessarily the start of the buffer, and is
 * advanced every time a dbuff is copied.
 *
 * @param[in] _dbuff_or_marker  to return the start position of.
 * @return A pointer to the start position of the buffer.
 */
#define fr_dbuff_start(_dbuff_or_marker) \
        (_Generic((_dbuff_or_marker), \
                  fr_dbuff_t *                  : (((fr_dbuff_t const *)(_dbuff_or_marker))->start), \
                  fr_dbuff_t const *            : (((fr_dbuff_t const *)(_dbuff_or_marker))->start), \
                  fr_dbuff_marker_t *           : (((fr_dbuff_marker_t const *)(_dbuff_or_marker))->parent->start), \
                  fr_dbuff_marker_t const *     : (((fr_dbuff_marker_t const *)(_dbuff_or_marker))->parent->start) \
        ))
 
/** Return the 'current' position of a dbuff or marker
 *
 * @param[in] _dbuff_or_marker  to return the current position of.
 * @return A pointer to the current position of the buffer or marker.
 */
#define fr_dbuff_current(_dbuff_or_marker) \
        (_Generic((_dbuff_or_marker), \
                  fr_dbuff_t *                  : (((fr_dbuff_t const *)(_dbuff_or_marker))->p), \
                  fr_dbuff_t const *            : (((fr_dbuff_t const *)(_dbuff_or_marker))->p), \
                  fr_dbuff_marker_t *           : (((fr_dbuff_marker_t const *)(_dbuff_or_marker))->p), \
                  fr_dbuff_marker_t const *     : (((fr_dbuff_marker_t const *)(_dbuff_or_marker))->p) \
        ))
 
/** @cond */
/** Return a pointer to the 'current' position in a dbuff or marker
 * @private
 *
 * @param[in] _dbuff_or_marker  to return a pointer to the position pointer for.
 * @return A pointer to the position pointer in the dbuff or marker.
 */
#define _fr_dbuff_current_ptr(_dbuff_or_marker) \
        (_Generic((_dbuff_or_marker), \
                  fr_dbuff_t *                  : &(((fr_dbuff_t *)(_dbuff_or_marker))->p), \
                  fr_dbuff_marker_t *           : &(((fr_dbuff_marker_t *)(_dbuff_or_marker))->p) \
        ))
/** @endcond */
 
/** Return the current 'end' position of a dbuff or marker
 *
 * @param[in] _dbuff_or_marker  to return the end position of.
 * @return A pointer to the end position of the buffer or marker.
 */
#define fr_dbuff_end(_dbuff_or_marker) \
        (_Generic((_dbuff_or_marker), \
                  fr_dbuff_t *                  : (((fr_dbuff_t const *)(_dbuff_or_marker))->end), \
                  fr_dbuff_t const *            : (((fr_dbuff_t const *)(_dbuff_or_marker))->end), \
                  fr_dbuff_marker_t *           : (((fr_dbuff_marker_t const *)(_dbuff_or_marker))->parent->end), \
                  fr_dbuff_marker_t const *     : (((fr_dbuff_marker_t const *)(_dbuff_or_marker))->parent->end) \
        ))
/** @} */
 
/** @name Position modification (recursive)
 *
 * Modify the 'current' position pointer of a dbuff or marker.
 * @{
 */
 
/** Set a new 'current' position in a dbuff or marker
 * @private
 */
static inline void _fr_dbuff_set_recurse(fr_dbuff_t *dbuff, uint8_t adv_parent_flags, uint8_t const *p)
{
        if (adv_parent_flags & FR_DBUFF_ADV_PARENT_CURRENT) dbuff->p_i = p;
        if (adv_parent_flags & FR_DBUFF_ADV_PARENT_END) dbuff->end_i = p;
 
        if (dbuff->adv_parent && dbuff->parent) _fr_dbuff_set_recurse(dbuff->parent, dbuff->adv_parent, p);
}
 
/** Set a new 'current' position in a dbuff or marker
 * @private
 *
 * @param[in,out] pos_p         position pointer to modify.
 * @param[out] dbuff            dbuff to use for constraints checks.
 * @param[in] p                 Position to set.
 * @return
 *      - 0     not advanced (p before dbuff start) or after dbuff end.
 *      - >0    the number of bytes the dbuff advanced by.
 *      - <0    the number of bytes the dbuff retreated by.
 *
 */
static inline ssize_t _fr_dbuff_set(uint8_t **pos_p, fr_dbuff_t *dbuff, uint8_t const *p)
{
        uint8_t *c;
 
        if (unlikely(p > dbuff->end)) return -(p - dbuff->end);
        if (unlikely(p < dbuff->start)) return 0;
 
        c = *pos_p;
        if (dbuff->adv_parent && dbuff->parent) _fr_dbuff_set_recurse(dbuff->parent, dbuff->adv_parent, p);
        *pos_p = UNCONST(uint8_t *, p);
 
        return p - c;
}
 
/** Set the 'current' position in a dbuff or marker using another dbuff or marker, a char pointer, or a length value
 *
 * @param[in] _dst      dbuff or marker to set the position for.
 * @param[in] _src      Variable to glean new position from.  Behaviour here
 *                      depends on the type of the variable.
 *                      - dbuff, the current position of the dbuff.
 *                      - marker, the current position of the marker.
 *                      - pointer, the position of the pointer.
 *                      - size_t, _dst->start + _src.
 * @return
 *      - 0     not advanced.
 *      - >0    the number of bytes the dbuff was advanced by.
 *      - <0    the number of bytes required to complete the advancement
 */
#define fr_dbuff_set(_dst, _src) \
_fr_dbuff_set(\
        _fr_dbuff_current_ptr(_dst), fr_dbuff_ptr(_dst), \
        _Generic((_src), \
                fr_dbuff_t *                    : fr_dbuff_current((fr_dbuff_t const *)(_src)), \
                fr_dbuff_marker_t *             : fr_dbuff_current((fr_dbuff_marker_t const *)(_src)), \
                uint8_t const *                 : (uint8_t const *)(_src), \
                uint8_t *                       : (uint8_t const *)(_src), \
                size_t                          : (fr_dbuff_start(_dst) + (uintptr_t)(_src)), \
                long                            : (fr_dbuff_start(_dst) + (uintptr_t)(_src)), \
                int                             : (fr_dbuff_start(_dst) + (uintptr_t)(_src)) \
        ) \
)
 
/** Set the 'current' position in a dbuff or marker returning if _src is out of range
 *
 * @copydetails fr_dbuff_set
 */
#define FR_DBUFF_SET_RETURN(_dst, _src) FR_DBUFF_RETURN(fr_dbuff_set, _dst, _src)
 
/** Set a new 'end' position in a dbuff or marker
 * @private
 *
 * @param[out] dbuff            dbuff to use for constraints checks.
 * @param[in] p                 Position to set.
 * @return
 *      - 0     not advanced (p before dbuff start) or after dbuff end.
 *      - >0    the number of bytes the dbuff was trimmed by.
 */
static inline ssize_t _fr_dbuff_set_end(fr_dbuff_t *dbuff, uint8_t const *p)
{
        if (unlikely(p > dbuff->end)) return -(p - dbuff->end);
        if (unlikely(p < dbuff->start)) return 0;
 
        dbuff->end = UNCONST(uint8_t *, p);
 
        return dbuff->end - p;
}
 
/** Set a new 'end' position in a dbuff or marker
 *
 * @param[out] _dst             dbuff to use for constraints checks.
 * @param[in] _end              Position to set.
 * @return
 *      - 0     not advanced (p before dbuff start) or after dbuff end.
 *      - >0    the number of bytes the dbuff was trimmed by.
 */
#define fr_dbuff_set_end(_dst, _end) \
_fr_dbuff_set_end(\
        fr_dbuff_ptr(_dst), \
        _Generic((_end), \
                fr_dbuff_t *                    : fr_dbuff_current((fr_dbuff_t const *)(_end)), \
                fr_dbuff_marker_t *             : fr_dbuff_current((fr_dbuff_marker_t const *)(_end)), \
                uint8_t const *                 : (uint8_t const *)(_end), \
                uint8_t *                       : (uint8_t const *)(_end) \
        ) \
)
 
 
/** Advance 'current' position in dbuff or marker by _len bytes
 *
 * @param[in] _dbuff_or_marker  to advance.
 * @param[in] _len              How much to advance dbuff by.
 *                              Must be a positive integer.
 * @return
 *      - 0     not advanced.
 *      - >0    the number of bytes the dbuff or marker was advanced by.
 *      - <0    the number of bytes required to complete the advancement
 */
#define fr_dbuff_advance(_dbuff_or_marker, _len)  \
        fr_dbuff_set(_dbuff_or_marker, \
                     (fr_dbuff_current(_dbuff_or_marker) + \
                     (_Generic((_len), \
                        unsigned char : (size_t)(_len), \
                        unsigned short : (size_t)(_len), \
                        unsigned int : (size_t)(_len), \
                        unsigned long : (size_t)(_len), \
                        unsigned long long : (size_t)(_len), \
                        int : (size_t)(_len) \
                     ))))
 
/** Advance the 'current' position in dbuff or marker by _len bytes returning if _len is out of range
 *
 * @copydetails fr_dbuff_advance
 */
#define FR_DBUFF_ADVANCE_RETURN(_dbuff_or_marker, _len) FR_DBUFF_RETURN(fr_dbuff_advance, _dbuff_or_marker, _len)
 
/** Advance a dbuff or marker potentially extending it
 * @private
 *
 * @param[in,out] pos_p         position pointer to modify.
 * @param[out] dbuff            dbuff to use for constraints checks.
 * @param[in] len               Number of bytes to advance by.
 * @return
 *      - 0     not advanced, specified length would take us
 *              past the end of the buffer, and we couldn't extend
 *              by enough bytes.
 *      - >0    the number of bytes the dbuff advanced by.
 *      - <0    the number of bytes we'd need to complete the advance.
 *
 */
static inline ssize_t _fr_dbuff_advance_extend(uint8_t **pos_p, fr_dbuff_t *dbuff, size_t len)
{
        uint8_t *p = *pos_p + len;
 
        if (p > dbuff->end) {
                size_t rel = p - dbuff->start;                          /* Get relative position to the start */
 
                if (!dbuff->extend) {
                oos:
                        return -((dbuff->start + rel) - dbuff->end);
                }
 
                dbuff->extend(dbuff, p - dbuff->end);                   /* Try and extend by the number of bytes over */
                if ((dbuff->start + rel) > dbuff->end) goto oos;
 
                *pos_p = dbuff->start + rel;                            /* Update pos_p */
        } else {
                *pos_p += len;
        }
 
        if (dbuff->adv_parent && dbuff->parent) _fr_dbuff_set_recurse(dbuff->parent, dbuff->adv_parent, *pos_p);
 
        return len;
}
 
/** Advance current'position in dbuff or marker by _len bytes (extending if necessary)
 *
 * @param[in] _dbuff_or_marker  to advance.
 * @param[in] _len              How much to advance dbuff by.
 *                              Must be a positive integer.
 * @return
 *      - 0     not advanced.
 *      - >0    the number of bytes the dbuff or marker was advanced by.
 *      - <0    the number of bytes we'd need to complete the advance.
 */
#define fr_dbuff_advance_extend(_dbuff_or_marker, _len)  \
        _fr_dbuff_advance(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), \
                          (_Generic((_len), \
                                unsigned char : (size_t)(_len), \
                                unsigned short : (size_t)(_len), \
                                unsigned int : (size_t)(_len), \
                                unsigned long : (size_t)(_len), \
                                unsigned long long : (size_t)(_len), \
                                int : (size_t)(_len) \
                          )))
 
#define FR_DBUFF_BIND_EXTEND_RETURN(_dbuff_or_marker, _len) FR_DBUFF_RETURN(fr_dbuff_advance_extend, _dbuff_or_marker, _len)
 
/** Reset the 'current' position of the dbuff or marker to the 'start' of the buffer
 *
 */
#define fr_dbuff_set_to_start(_dbuff_or_marker) \
        fr_dbuff_set(_dbuff_or_marker, fr_dbuff_start(_dbuff_or_marker))
 
/** Reset the 'current' position of the dbuff or marker to the 'end' of the buffer
 *
 */
#define fr_dbuff_set_to_end(_dbuff_or_marker) \
        fr_dbuff_set(_dbuff_or_marker, fr_dbuff_end(_dbuff_or_marker))
/** @} */
 
/** @name Marker management
 *
 * Markers serve two purposes:
 *
 * - Markers allow the caller to track content in a dbuff as the dbuff is extended.
 *   If the caller referred to content using a pointer into the underlying buffer,
 *   that pointer may be invalidated if the buffer were extended.
 *
 * - Markers prevent content being shifted out of the buffer during an extension.
 *
 * Most operations that can be performed on an #fr_dbuff_t can also be performed
 * on a #fr_dbuff_marker_t.
 *
 * It is recommended that markers be created against a stack-frame-local dbuff so
 * that they are automatically released when the framed is popped.
 *
 * @see fr_dbuff_marker_t
 *
 * @{
 */
 
/** Initialises a new marker pointing to the 'current' position of the dbuff
 *
 * @param[out] m        to initialise.
 * @param[in] dbuff     to associate marker with.
 * @return The position the marker was set to.
 */
static inline uint8_t *fr_dbuff_marker(fr_dbuff_marker_t *m, fr_dbuff_t *dbuff)
{
        *m = (fr_dbuff_marker_t){
                .next = dbuff->m,       /* Link into the head */
                .p = dbuff->p,          /* Set the current position in the dbuff */
                .parent = dbuff         /* Record which dbuff this marker was associated with */
        };
        dbuff->m = m;
 
        return dbuff->p;
}
 
/** Releases the specified marker and any markers added before it
 *
 * Pointers should be released in the inverse order to allocation.
 *
 * @param[in] m         to release.
 */
static inline void fr_dbuff_marker_release(fr_dbuff_marker_t *m)
{
        m->parent->m = m->next;
 
#ifndef NDEBUG
        memset(m, 0, sizeof(*m));       /* Use after release */
#endif
}
 
/** Trims the linked list back to the specified pointer and return how many bytes marker was behind p
 *
 * Pointers should be released in the inverse order to allocation.
 *
 * Alternatively the oldest pointer can be released, resulting in any newer pointer
 * also being removed from the list.
 *
 * @param[in] m         to release.
 * @return
 *      - 0 marker is ahead of p.
 *      - >0 the number of bytes the marker is behind p.
 */
static inline size_t fr_dbuff_marker_release_behind(fr_dbuff_marker_t *m)
{
        size_t len = fr_dbuff_behind(m);
        fr_dbuff_marker_release(m);
        return len;
}
 
/** Trims the linked list back to the specified pointer and return how many bytes marker was ahead of p
 *
 * Pointers should be released in the inverse order to allocation.
 *
 * Alternatively the oldest pointer can be released, resulting in any newer pointer
 * also being removed from the list.
 *
 * @param[in] m         to release.
 * @return
 *      - 0 marker is ahead of p.
 *      - >0 the number of bytes the marker is behind p.
 */
static inline size_t fr_dbuff_marker_release_ahead(fr_dbuff_marker_t *m)
{
        size_t len = fr_dbuff_ahead(m);
        fr_dbuff_marker_release(m);
        return len;
}
/** @} */
 
/** @name "in" functions (copy data into a dbuff)
 * @{
 */
 
/** Internal copy function to switch between memcpy and memmove - do not call directly
 *
 * @private
 *
 * @param[out] o_start          Where to copy data to.
 * @param[in] o_end             end of the output buffer.
 * @param[in] i_start           Where to copy data from.
 * @param[in] i_end             end of the source buffer.
 * @return
 *      - 0 on sanity check error.
 *      - >0 the number of bytes copied.
 */
static inline CC_HINT(always_inline) size_t _fr_dbuff_safecpy(uint8_t *o_start, uint8_t *o_end,
                                                              uint8_t const *i_start, uint8_t const *i_end)
{
        ssize_t diff;
        size_t  i_len = i_end - i_start;
 
        if (unlikely((o_end < o_start) || (i_end < i_start))) return 0; /* sanity check */
 
        diff = (o_end - o_start) - (i_len);
        if (diff < 0) return 0;
 
        if ((i_start > o_end) || (i_end < o_start)) {                   /* no-overlap */
                memcpy(o_start,  i_start, i_len);
        } else {                                                        /* overlap */
                memmove(o_start, i_start, i_len);
        }
 
        return (i_len);
}
 
/** Internal function - do not call directly
 *
 * @private
 */
static inline ssize_t _fr_dbuff_in_memcpy(uint8_t **pos_p, fr_dbuff_t *out,
                                          uint8_t const *in, size_t inlen)
{
        fr_assert(!out->is_const);
 
        _FR_DBUFF_EXTEND_LOWAT_POS_OR_RETURN(pos_p, out, inlen);
 
        return _fr_dbuff_set(pos_p, out, (*pos_p) + _fr_dbuff_safecpy((*pos_p), (*pos_p) + inlen, in, in + inlen));             /* Advance out */
}
 
/** Internal function - do not call directly
 *
 * @private
 */
static inline ssize_t _fr_dbuff_in_memcpy_dbuff(uint8_t **pos_p, fr_dbuff_t *out,
                                                uint8_t * const *in_p, fr_dbuff_t const *in, size_t inlen)
{
        fr_dbuff_t      *our_in;
        uint8_t         **our_in_p;
        size_t          ext_len;
 
        memcpy(&our_in, &in, sizeof(our_in));           /* Stupid const issues caused by generics */
        memcpy(&our_in_p, &in_p, sizeof(our_in_p));     /* Stupid const issues caused by generics */
 
        if (inlen == SIZE_MAX) {
                ext_len = _fr_dbuff_extend_lowat(NULL, our_in, fr_dbuff_end(our_in) - (*our_in_p), inlen);
                if (ext_len < inlen) inlen = ext_len;
        } else {
                _FR_DBUFF_EXTEND_LOWAT_POS_OR_RETURN(our_in_p, our_in, inlen);          /* Extend in or return */
        }
        return _fr_dbuff_in_memcpy(pos_p, out, *our_in_p, inlen);                       /* Copy _in to _out */
}
 
/** Copy exactly _inlen bytes into a dbuff or marker
 *
 * If _in is a dbuff and _inlen is greater than the number of bytes available
 * in that dbuff, the copy operation will fail.
 *
 * @note _in will not be advanced.  If this is required #fr_dbuff_move should be used.
 *
 * @param[in] _dbuff_or_marker  to copy data to.
 * @param[in] _in               data to copy in to the dbuff or marker.
 * @param[in] _inlen            How much data we need to copy.
 *                              If _in is a `char *` or `dbuff *` and SIZE_MAX
 *                              is passed, then _inlen will be substituted
 *                              for the length of the data in the dbuff.
 * @return
 *      - 0     no data copied.
 *      - >0    the number of bytes copied to the dbuff.
 *      - <0    the number of bytes we would have needed
 *              to complete the copy operation.
 */
#define fr_dbuff_in_memcpy(_dbuff_or_marker, _in, _inlen) \
        _Generic((_in), \
                uint8_t *               : _fr_dbuff_in_memcpy(_fr_dbuff_current_ptr(_dbuff_or_marker), \
                                                              fr_dbuff_ptr(_dbuff_or_marker), \
                                                              (uint8_t const *)(_in), \
                                                              _inlen), \
                uint8_t const *         : _fr_dbuff_in_memcpy(_fr_dbuff_current_ptr(_dbuff_or_marker), \
                                                              fr_dbuff_ptr(_dbuff_or_marker), \
                                                              (uint8_t const *)(_in), \
                                                              _inlen), \
                char *                  : _fr_dbuff_in_memcpy(_fr_dbuff_current_ptr(_dbuff_or_marker), \
                                                              fr_dbuff_ptr(_dbuff_or_marker), \
                                                              (uint8_t const *)(_in), \
                                                              (size_t)(_inlen) == SIZE_MAX ? strlen((char const *)(_in)) : (_inlen)), \
                char const *            : _fr_dbuff_in_memcpy(_fr_dbuff_current_ptr(_dbuff_or_marker), \
                                                              fr_dbuff_ptr(_dbuff_or_marker), \
                                                              (uint8_t const *)(_in), \
                                                              (size_t)(_inlen) == SIZE_MAX ? strlen((char const *)(_in)) : (_inlen)), \
                fr_dbuff_t *            : _fr_dbuff_in_memcpy_dbuff(_fr_dbuff_current_ptr(_dbuff_or_marker), \
                                                                    fr_dbuff_ptr(_dbuff_or_marker), \
                                                                    &((fr_dbuff_t const *)(_in))->p, \
                                                                    ((fr_dbuff_t const *)(_in)), \
                                                                    _inlen), \
                fr_dbuff_marker_t *     : _fr_dbuff_in_memcpy_dbuff(_fr_dbuff_current_ptr(_dbuff_or_marker), \
                                                                    fr_dbuff_ptr(_dbuff_or_marker), \
                                                                    &((fr_dbuff_marker_t const *)(_in))->p, \
                                                                    ((fr_dbuff_marker_t const *)(_in))->parent, _inlen) \
        )
 
/** Copy exactly _inlen bytes into dbuff or marker returning if there's insufficient space
 * @copydetails fr_dbuff_in_memcpy
 */
#define FR_DBUFF_IN_MEMCPY_RETURN(_dbuff_or_marker, _in, _inlen) FR_DBUFF_RETURN(fr_dbuff_in_memcpy, _dbuff_or_marker, _in, _inlen)
 
/** Internal function - do not call directly
 *
 * @private
 */
static inline size_t _fr_dbuff_in_memcpy_partial(uint8_t **pos_p, fr_dbuff_t *out,
                                                 uint8_t const *in, size_t inlen)
{
        size_t ext_len;
 
        fr_assert(!out->is_const);
 
        ext_len = _fr_dbuff_extend_lowat(NULL, out, fr_dbuff_end(out) - (*pos_p), inlen);
        if (ext_len < inlen) inlen = ext_len;
 
        return _fr_dbuff_set(pos_p, out, (*pos_p) + _fr_dbuff_safecpy((*pos_p), (*pos_p) + inlen, in, in + inlen));
}
 
/** Internal function - do not call directly
 *
 * @private
 */
static inline size_t _fr_dbuff_in_memcpy_partial_dbuff(uint8_t **pos_p, fr_dbuff_t *out,
                                                       uint8_t * const *in_p, fr_dbuff_t const *in, size_t inlen)
{
        fr_dbuff_t      *our_in = UNCONST(fr_dbuff_t *, in);    /* Stupid const issues caused by generics */
        uint8_t         **our_in_p = UNCONST(uint8_t **, in_p); /* Stupid const issues caused by generics */
        size_t          ext_len;
 
        ext_len = _fr_dbuff_extend_lowat(NULL, our_in, fr_dbuff_end(our_in) - (*our_in_p), inlen);
        if (ext_len < inlen) inlen = ext_len;
 
        return _fr_dbuff_in_memcpy_partial(pos_p, out, (*our_in_p), inlen);
}
 
/** Copy at most _inlen bytes into the dbuff
 *
 * Use this variant when writing data to a streaming buffer where
 * partial writes will be tracked.
 *
 * If _in is a #fr_dbuff_t and _inlen is greater than the number of bytes
 * available in that dbuff, the copy operation will truncated.
 *
 * @note _in will not be advanced.  If this is required #fr_dbuff_move should be used.
 *
 * @param[in] _out      to copy data to.
 * @param[in] _in       Data to copy to dbuff.
 * @param[in] _inlen    How much data we need to copy.
 *                      If _in is a char * or dbuff * and SIZE_MAX
 *                      is passed, then _inlen will be substituted
 *                      for the length of the buffer.
 * @return
 *      - 0     no data copied.
 *      - >0    the number of bytes copied to the dbuff.
 */
#define fr_dbuff_in_memcpy_partial(_out, _in, _inlen) \
        _Generic((_in), \
                uint8_t *               : _fr_dbuff_in_memcpy_partial(_fr_dbuff_current_ptr(_out), _out, (uint8_t const *)(_in), _inlen), \
                uint8_t const *         : _fr_dbuff_in_memcpy_partial(_fr_dbuff_current_ptr(_out), _out, (uint8_t const *)(_in), _inlen), \
                char *                  : _fr_dbuff_in_memcpy_partial(_fr_dbuff_current_ptr(_out), _out, (uint8_t const *)(_in), _inlen == SIZE_MAX ? strlen((char const *)(_in)) : _inlen), \
                char const *            : _fr_dbuff_in_memcpy_partial(_fr_dbuff_current_ptr(_out), _out, (uint8_t const *)(_in), _inlen == SIZE_MAX ? strlen((char const *)(_in)) : _inlen), \
                fr_dbuff_t *            : _fr_dbuff_in_memcpy_partial_dbuff(_fr_dbuff_current_ptr(_out), fr_dbuff_ptr(_out), &((fr_dbuff_t const *)(_in))->p, ((fr_dbuff_t const *)(_in)), _inlen), \
                fr_dbuff_marker_t *     : _fr_dbuff_in_memcpy_partial_dbuff(_fr_dbuff_current_ptr(_out), fr_dbuff_ptr(_out), &((fr_dbuff_marker_t const *)(_in))->p, ((fr_dbuff_marker_t const *)(_in))->parent, _inlen) \
        )
 
/** Copy a partial byte sequence into a dbuff
 *
 * @copybrief fr_dbuff_in_memcpy_partial
 *
 * @param[in] _dbuff    to copy byte sequence into.
 * @param[in] ...       bytes to copy.
 */
#define fr_dbuff_in_bytes_partial(_dbuff, ...) \
        fr_dbuff_in_memcpy_partial(_dbuff, ((uint8_t []){ __VA_ARGS__ }), sizeof((uint8_t []){ __VA_ARGS__ }))
 
/** Copy a byte sequence into a dbuff or marker
 *
 * @copybrief fr_dbuff_in_memcpy
 *
 * @param[in] _dbuff_or_marker  to copy byte sequence into.
 * @param[in] ...               bytes to copy.
 */
#define fr_dbuff_in_bytes(_dbuff_or_marker, ...) \
        fr_dbuff_in_memcpy(_dbuff_or_marker, ((uint8_t []){ __VA_ARGS__ }), sizeof((uint8_t []){ __VA_ARGS__ }))
 
/** Copy a byte sequence into a dbuff or marker returning if there's insufficient space
 *
 * @copydetails fr_dbuff_in_bytes
 */
#define FR_DBUFF_IN_BYTES_RETURN(_dbuff_or_marker, ...) \
        FR_DBUFF_IN_MEMCPY_RETURN(_dbuff_or_marker, ((uint8_t []){ __VA_ARGS__ }), sizeof((uint8_t []){ __VA_ARGS__ }))
 
/** Internal function - do not call directly
 *
 * @private
 */
static inline ssize_t _fr_dbuff_memset(uint8_t **pos_p, fr_dbuff_t *dbuff, uint8_t c, size_t inlen)
{
        fr_assert(!dbuff->is_const);
 
        _FR_DBUFF_EXTEND_LOWAT_POS_OR_RETURN(pos_p, dbuff, inlen);
 
        memset((*pos_p), c, inlen);
 
        return _fr_dbuff_set(pos_p, dbuff, (*pos_p) + inlen);
}
 
/** Set _inlen bytes of a dbuff or marker to _c
 *
 * @param[in] _dbuff_or_marker  to copy data to.
 *                              Will be advanced by _inlen bytes.
 * @param[in] _c                Value to set.
 * @param[in] _inlen            How much data we need to copy.
 * @return
 *      - 0     no data set.
 *      - >0    the number of bytes set in the dbuff.
 *      - <0    the number of bytes required.
 */
#define fr_dbuff_memset(_dbuff_or_marker, _c, _inlen) \
        _fr_dbuff_memset(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), _c, _inlen)
 
/** Set _inlen bytes of a dbuff or marker to _c returning if there is insufficient space
 *
 * @copydetails fr_dbuff_memset
 */
#define FR_DBUFF_MEMSET_RETURN(_dbuff_or_marker, _c, _inlen) FR_DBUFF_RETURN(fr_dbuff_memset, _dbuff_or_marker, _c, _inlen)
 
/** @cond */
/** Define integer decoding functions
 * @private
 */
#define FR_DBUFF_PARSE_INT_DEF(_type) \
static inline ssize_t _fr_dbuff_in_##_type(uint8_t **pos_p, fr_dbuff_t *out, _type##_t num) \
{ \
        fr_assert(!out->is_const); \
        _FR_DBUFF_EXTEND_LOWAT_POS_OR_RETURN(pos_p, out, sizeof(_type##_t)); \
        fr_nbo_from_##_type((*pos_p), num); \
        return _fr_dbuff_set(pos_p, out, (*pos_p) + sizeof(_type##_t)); \
}
FR_DBUFF_PARSE_INT_DEF(uint16)
FR_DBUFF_PARSE_INT_DEF(uint32)
FR_DBUFF_PARSE_INT_DEF(uint64)
FR_DBUFF_PARSE_INT_DEF(int16)
FR_DBUFF_PARSE_INT_DEF(int32)
FR_DBUFF_PARSE_INT_DEF(int64)
/** @endcond */
 
/*
 
 */
 
/** Internal function - do not call directly
 *
 * The fr_dbuff_in_<type>() functions take rvalues, so to implement float and
 * double in terms of the same-sized integers, we need a layer that gives us an
 * lvalue whose address we can cast.
 *
 * @private
 */
static inline ssize_t _fr_dbuff_in_float(uint8_t **pos_p, fr_dbuff_t *out, float num)
{
        return _fr_dbuff_in_uint32(pos_p, out, *(uint32_t *)(&num));
}
 
/** Internal function - do not call directly
 *
 * @copydetails _fr_dbuff_in_float
 *
 * @private
 */
static inline ssize_t _fr_dbuff_in_double(uint8_t **pos_p, fr_dbuff_t *out, double num)
{
        return _fr_dbuff_in_uint64(pos_p, out, *(uint64_t *)(&num));
}
 
/** Copy data from a fixed sized C type into a dbuff or marker
 *
 * @param[out] _dbuff_or_marker         to write to.  Integer types will be automatically
                                        converted to big endian byte order.
 * @param[in] _in                       Value to copy.
 * @return
 *      - <0 the number of bytes we would have needed to complete the conversion.
 *      - >0 the number of bytes _dbuff_or_marker was advanced by.
 */
#define fr_dbuff_in(_dbuff_or_marker, _in) \
        _Generic((_in), \
                int8_t          : fr_dbuff_in_bytes(_dbuff_or_marker, (int8_t)_in), \
                int16_t         : _fr_dbuff_in_int16(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), (int16_t)_in), \
                int32_t         : _fr_dbuff_in_int32(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), (int32_t)_in), \
                int64_t         : _fr_dbuff_in_int64(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), (int64_t)_in), \
                uint8_t         : fr_dbuff_in_bytes(_dbuff_or_marker, (uint8_t)_in), \
                uint16_t        : _fr_dbuff_in_uint16(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), (uint16_t)_in), \
                uint32_t        : _fr_dbuff_in_uint32(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), (uint32_t)_in), \
                uint64_t        : _fr_dbuff_in_uint64(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), (uint64_t)_in), \
                float           : _fr_dbuff_in_float(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), (float)_in), \
                double          : _fr_dbuff_in_double(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), (double)_in) \
        )
 
/** Copy data from a fixed sized C type into a dbuff returning if there is insufficient space
 *
 * @copydetails fr_dbuff_in
 */
#define FR_DBUFF_IN_RETURN(_dbuff_or_marker, _in) FR_DBUFF_RETURN(fr_dbuff_in, _dbuff_or_marker, _in)
 
/** Internal function - do not call directly
 * @private
 */
static inline ssize_t _fr_dbuff_in_uint64v(uint8_t **pos_p, fr_dbuff_t *dbuff, uint64_t num)
{
        size_t  ret;
        uint8_t swapped[sizeof(uint64_t)];
 
        ret = ROUND_UP_DIV((size_t)fr_high_bit_pos(num | 0x08), 8);
#ifdef __COVERITY__
        if (ret > sizeof(uint64_t)) return -1;
#endif
        fr_nbo_from_uint64(swapped, num);
 
        return _fr_dbuff_in_memcpy(pos_p, dbuff, (swapped + (sizeof(uint64_t) - ret)), ret);
}
 
/** Copy an integer value into a dbuff or marker using our internal variable length encoding
 *
 * @param[out] _dbuff_or_marker         to copy integer value to.
 * @param[in] _num                      to copy.
 * @return
 *      - <0 the number of bytes we would have needed to encode the integer value.
 *      - >0 the number of bytes used to represent the integer value.
 */
#define fr_dbuff_in_uint64v(_dbuff_or_marker, _num) \
        _fr_dbuff_in_uint64v(_fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), _num)
 
/** Copy an integer value into a dbuff or marker using our internal variable length encoding returning if there is insufficient space
 *
 * @copydetails fr_dbuff_in_uint64v
 */
#define FR_DBUFF_IN_UINT64V(_dbuff_or_marker, _num) FR_DBUFF_RETURN(fr_dbuff_in_uint64v, _dbuff_or_marker, _num)
/** @} */
 
/** @name "move" functions (copy data between dbuffs and markers)
 * @{
 */
/** Internal function - do not call directly
 * @private
 */
size_t _fr_dbuff_move_dbuff_to_dbuff(fr_dbuff_t *out, fr_dbuff_t *in, size_t len);
 
/** Internal function - do not call directly
 * @private
 */
size_t _fr_dbuff_move_dbuff_to_dbuff_marker(fr_dbuff_marker_t *out, fr_dbuff_t *in, size_t len);
 
/** Internal function - do not call directly
 * @private
 */
size_t _fr_dbuff_move_dbuff_marker_to_dbuff(fr_dbuff_t *out, fr_dbuff_marker_t *in, size_t len);
 
/** Internal function - do not call directly
 * @private
 */
size_t _fr_dbuff_move_dbuff_marker_to_dbuff_marker(fr_dbuff_marker_t *out, fr_dbuff_marker_t *in, size_t len);
 
/** Copy in as many bytes as possible from one dbuff or marker to another
 *
 * @warning Advances both _in and _out by _len, this may not be what you want.
 *          If you only want _out to be advanced use fr_dbuff_in_memcpy(_out, _in, _len).
 *          If you only want _in to be advanced use fr_dbuff_out_memcpy(_out, _in, _len).
 *
 * @param[in] _out      to copy into.
 * @param[in] _in       to copy from.
 * @param[in] _len      The maximum length to copy.
 * @return Number of bytes to copy.
 */
#define fr_dbuff_move(_out, _in, _len) \
        _Generic((_out), \
                fr_dbuff_t *            : \
                _Generic((_in), \
                        fr_dbuff_t *            : _fr_dbuff_move_dbuff_to_dbuff((fr_dbuff_t *)_out, \
                                                                                (fr_dbuff_t *)_in, \
                                                                                _len), \
                        fr_dbuff_marker_t *     : _fr_dbuff_move_dbuff_marker_to_dbuff((fr_dbuff_t *)_out, \
                                                                                       (fr_dbuff_marker_t *)_in, \
                                                                                       _len) \
                ), \
                fr_dbuff_marker_t *     : \
                _Generic((_in), \
                        fr_dbuff_t *            : _fr_dbuff_move_dbuff_to_dbuff_marker((fr_dbuff_marker_t *)_out, \
                                                                                       (fr_dbuff_t *)_in, \
                                                                                       _len), \
                        fr_dbuff_marker_t *     : _fr_dbuff_move_dbuff_marker_to_dbuff_marker((fr_dbuff_marker_t *)_out, \
                                                                                              (fr_dbuff_marker_t *)_in, \
                                                                                              _len) \
                ) \
        )
/** @} */
 
/** @name "out" functions (copy data out of a dbuff)
 * @{
 */
 
/** Internal function - do not call directly
 *
 * @private
 */
static inline ssize_t _fr_dbuff_out_memcpy(uint8_t *out, uint8_t **pos_p, fr_dbuff_t *in, size_t outlen)
{
        size_t  ext_len, to_copy, remaining;
 
        for (remaining = outlen; remaining > 0; remaining -= to_copy) {
                to_copy = remaining;
                ext_len = _fr_dbuff_extend_lowat(NULL, in, fr_dbuff_end(in) - (*pos_p), 1);
                if (ext_len == 0) return -remaining;
                if (ext_len < to_copy) to_copy = ext_len;
                out += _fr_dbuff_set(pos_p, in,
                                     (*pos_p) + _fr_dbuff_safecpy(out, out + to_copy, (*pos_p), (*pos_p) + to_copy));
        }
 
        return outlen;
}
/** Internal function - do not call directly
 *
 * @private
 */
static inline ssize_t _fr_dbuff_out_memcpy_dbuff(uint8_t **out_p, fr_dbuff_t *out, uint8_t **pos_p, fr_dbuff_t *in, size_t outlen)
{
        if (outlen == SIZE_MAX) outlen = _fr_dbuff_extend_lowat(NULL, out, fr_dbuff_end(out) - (*out_p), outlen);
 
        return _fr_dbuff_out_memcpy((*out_p), pos_p, in, outlen);
}
 
/** Copy exactly _outlen bytes from the dbuff
 *
 * If _out is a dbuff and _outlen is greater than the number of bytes
 * available in that dbuff, the copy operation will fail.
 *
 * @note _out will not be advanced.  If this is required #fr_dbuff_move should be used.
 *
 * @param[in] _out              either a buffer, or another dbuff/marker to copy data to.
 * @param[in] _dbuff_or_marker  to copy data from.
 * @param[in] _outlen           How much data we need to copy.
 *                              If _out is `fr_dbuff_t *` and SIZE_MAX
 *                              is passed, then _inlen will be substituted
 *                              for the length of the buffer.
 * @return
 *      - 0     no data copied.
 *      - >0    the number of bytes copied.
 *      - <0    the number of bytes we would have needed
 *              to complete the copy operation.
 */
#define fr_dbuff_out_memcpy(_out, _dbuff_or_marker, _outlen) \
        _Generic((_out), \
                 uint8_t *              : _fr_dbuff_out_memcpy((uint8_t *)(_out), \
                                                               _fr_dbuff_current_ptr(_dbuff_or_marker), \
                                                               fr_dbuff_ptr(_dbuff_or_marker), \
                                                               _outlen), \
                 fr_dbuff_t *           : _fr_dbuff_out_memcpy_dbuff(_fr_dbuff_current_ptr((fr_dbuff_t *)_out), \
                                                                     fr_dbuff_ptr((fr_dbuff_t *)(_out)), \
                                                                     _fr_dbuff_current_ptr(_dbuff_or_marker), \
                                                                     fr_dbuff_ptr(_dbuff_or_marker), _outlen), \
                 fr_dbuff_marker_t *    : _fr_dbuff_out_memcpy_dbuff(_fr_dbuff_current_ptr((fr_dbuff_marker_t *)_out), \
                                                                     fr_dbuff_ptr((fr_dbuff_marker_t *)(_out)), \
                                                                     _fr_dbuff_current_ptr(_dbuff_or_marker), \
                                                                     fr_dbuff_ptr(_dbuff_or_marker), _outlen) \
        )
 
/** Copy outlen bytes from the dbuff returning if there's insufficient data in the dbuff
 *
 * @copydetails fr_dbuff_out_memcpy
 */
#define FR_DBUFF_OUT_MEMCPY_RETURN(_out, _dbuff_or_marker, _outlen) FR_DBUFF_RETURN(fr_dbuff_out_memcpy, _out, _dbuff_or_marker, _outlen)
 
/** @cond */
/** Define integer encoding functions
 * @private
 */
#define FR_DBUFF_OUT_DEF(_type) \
static inline ssize_t _fr_dbuff_out_##_type(_type##_t *out, uint8_t **pos_p, fr_dbuff_t *in) \
{ \
        fr_assert(out); \
        FR_DBUFF_EXTEND_LOWAT_OR_RETURN(in, sizeof(_type##_t)); \
        *out = fr_nbo_to_##_type((*pos_p)); \
        return _fr_dbuff_set(pos_p, in, (*pos_p) + sizeof(_type##_t)); \
}
 
FR_DBUFF_OUT_DEF(uint16)
FR_DBUFF_OUT_DEF(uint32)
FR_DBUFF_OUT_DEF(uint64)
FR_DBUFF_OUT_DEF(int16)
FR_DBUFF_OUT_DEF(int32)
FR_DBUFF_OUT_DEF(int64)
 
#define FR_DBUFF_OUT_DEF_NO_SWAP(_type) \
static inline ssize_t _fr_dbuff_out_##_type(_type##_t *out, uint8_t **pos_p, fr_dbuff_t *in) \
{ \
        fr_assert(out); \
        FR_DBUFF_EXTEND_LOWAT_OR_RETURN(in, sizeof(_type##_t)); \
        *out = **pos_p; \
        return _fr_dbuff_set(pos_p, in, (*pos_p) + sizeof(_type##_t)); \
}
 
FR_DBUFF_OUT_DEF_NO_SWAP(uint8)
FR_DBUFF_OUT_DEF_NO_SWAP(int8)
/** @endcond */
 
/** Copy data from a dbuff or marker to a fixed sized C type
 *
 * @param[out] _out                     Where to write the data.  If out is an integer type
 *                                      a byteswap will be performed if native endianness
 *                                      is not big endian.
 * @param[in] _dbuff_or_marker          to copy data from. Will be advanced by the number
 *                                      of bytes consumed, i.e. if out is a uin16_t *,
 *                                      _dbuff_or_marker will be advanced by two bytes.
 * @return
 *      - <0 the number of bytes we would have needed to complete the conversion.
 *      - >0 the number of bytes _in was advanced by.
 */
#define fr_dbuff_out(_out, _dbuff_or_marker) \
        _Generic((_out), \
                uint8_t *       : _fr_dbuff_out_uint8((uint8_t *)(_out), _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker)), \
                uint16_t *      : _fr_dbuff_out_uint16((uint16_t *)(_out), _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker)), \
                uint32_t *      : _fr_dbuff_out_uint32((uint32_t *)(_out), _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker)), \
                uint64_t *      : _fr_dbuff_out_uint64((uint64_t *)(_out), _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker)), \
                int8_t *        : _fr_dbuff_out_int8((int8_t *)(_out), _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker)), \
                int16_t *       : _fr_dbuff_out_int16((int16_t *)(_out), _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker)), \
                int32_t *       : _fr_dbuff_out_int32((int32_t *)(_out), _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker)), \
                int64_t *       : _fr_dbuff_out_int64((int64_t *)(_out), _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker)), \
                float *         : _fr_dbuff_out_uint32((uint32_t *)(_out), _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker)), \
                double *        : _fr_dbuff_out_uint64((uint64_t *)(_out), _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker)) \
        )
 
/** Copy data from a dbuff or marker to a fixed sized C type returning if there is insufficient data
 *
 * @copydetails fr_dbuff_out
 */
#ifndef STATIC_ANALYZER
#define FR_DBUFF_OUT_RETURN(_out, _dbuff_or_marker) FR_DBUFF_RETURN(fr_dbuff_out, _out, _dbuff_or_marker)
#else
#define FR_DBUFF_OUT_RETURN(_out, _dbuff_or_marker) do { *_out = 0; FR_DBUFF_RETURN(fr_dbuff_out, _out, _dbuff_or_marker); } while (0)
#endif
 
/** Internal function - do not call directly
 * @private
 */
static inline ssize_t _fr_dbuff_out_uint64v(uint64_t *num, uint8_t **pos_p, fr_dbuff_t *dbuff, size_t length)
{
        ssize_t         slen;
 
        fr_assert(length > 0 && length <= sizeof(uint64_t));
 
        *num = 0;
        slen = _fr_dbuff_out_memcpy(((uint8_t *) num) + (8 - length), pos_p, dbuff, length);
        if (slen <= 0) return slen;
 
        *num = fr_nbo_to_uint64((uint8_t const *)num);
        return length;
}
 
/** Read bytes from a dbuff or marker and interpret them as a network order unsigned integer
 * @param[in] _num              points to a uint64_t to store the integer in
 * @param[in] _dbuff_or_marker  data to copy bytes from
 * @param[in] _len              number of bytes to read (must be positive and less than eight)
 *
 * @return
 *      - 0     no data read.
 *      - >0    the number of bytes read.
 *      - <0    the number of bytes we would have needed
 *              to complete the read operation.
 */
#define fr_dbuff_out_uint64v(_num, _dbuff_or_marker, _len) \
        _fr_dbuff_out_uint64v(_num, _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), _len)
 
/** Read bytes from a dbuff or marker and interpret them as a network order unsigned integer
 *
 * @copydetails fr_dbuff_out_uint64v
 */
#define FR_DBUFF_OUT_UINT64V_RETURN(_num, _dbuff_or_marker, _len) FR_DBUFF_RETURN(fr_dbuff_out_uint64v, _num, _dbuff_or_marker, _len)
 
/** Internal function - do not call directly
 * @private
 */
static inline ssize_t _fr_dbuff_out_int64v(int64_t *num, uint8_t **pos_p, fr_dbuff_t *dbuff, size_t length)
{
        ssize_t         slen;
        uint8_t         msb = **pos_p;
 
        fr_assert(length > 0 && length <= sizeof(uint64_t));
 
        *num = 0;
        slen = _fr_dbuff_out_memcpy(((uint8_t *) num) + (8 - length), pos_p, dbuff, length);
        if (slen <= 0) return slen;
 
        if (msb & 0x80) memset(((uint8_t *)num), 0xff, sizeof(*num) - length);
        *num = fr_nbo_to_int64((uint8_t const *)num);
 
        return length;
}
 
/** Read bytes from a dbuff or marker and interpret them as a network order signed integer
 * @param[in] _num              points to an int64_t to store the integer in
 * @param[in] _dbuff_or_marker  data to copy bytes from
 * @param[in] _len              number of bytes to read (must be positive and less than eight)
 *
 * @return
 *      - 0     no data read.
 *      - >0    the number of bytes read.
 *      - <0    the number of bytes we would have needed
 *              to complete the read operation.
 */
#define fr_dbuff_out_int64v(_num, _dbuff_or_marker, _len) \
        _fr_dbuff_out_int64v(_num, _fr_dbuff_current_ptr(_dbuff_or_marker), fr_dbuff_ptr(_dbuff_or_marker), _len)
 
/** Read bytes from a dbuff or marker and interpret them as a network order unsigned integer
 *
 * @copydetails fr_dbuff_out_int64v
 */
#define FR_DBUFF_OUT_INT64V_RETURN(_num, _dbuff_or_marker, _len) FR_DBUFF_RETURN(fr_dbuff_out_int64v, _num, _dbuff_or_marker, _len)
 
/** @} */
#ifdef __cplusplus
}
#endif