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/* Copyright (C) 2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
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 3 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, see <https://www.gnu.org/licenses/>.
*/
/*!
* \file
*
* \brief Name compression API.
*
* \addtogroup pkt
* @{
*/
#pragma once
#include <stdint.h>
#include "libknot/packet/wire.h"
/*! \brief Compression hint type. */
enum knot_compr_hint {
KNOT_COMPR_HINT_NONE = 0, /* No hint. */
KNOT_COMPR_HINT_NOCOMP = 1, /* Don't compress. */
KNOT_COMPR_HINT_QNAME = KNOT_WIRE_HEADER_SIZE /* Name is QNAME. */
};
/*! \brief Compression hint array offsets. */
enum knot_compr_offset {
KNOT_COMPR_HINT_OWNER = 0, /* First element in the array is RR owner. */
KNOT_COMPR_HINT_RDATA = 1, /* First name in RDATA is at offset 1. */
KNOT_COMPR_HINT_COUNT = 16 /* Maximum number of stored hints per-RR. */
};
/*
* \note A little bit about how compression hints work.
*
* We're storing a RRSet say 'abcd. CNAME [0]net. [1]com.' (owner=abcd. 2 RRs).
* The owner 'abcd.' is same for both RRs, we put it at the offset 0 in rrinfo.compress_ptr
* The names 'net.' and 'com.' are in the RDATA, therefore go to offsets 1 and 2.
* Now this is useful when solving additionals for example, because we can scan
* rrinfo for this RRSet and we know that 'net.' name is at the hint 1 and that leads
* to packet position N. With that, we just put the pointer in without any calculation.
* This is also useful for positive answers, where we know the RRSet owner is always QNAME.
* All in all, we just remember the positions of written domain names.
*/
/*! \brief Additional information about RRSet position and compression hints. */
typedef struct {
uint16_t pos; /* RRSet position in the packet. */
uint16_t flags; /* RRSet flags. */
uint16_t compress_ptr[KNOT_COMPR_HINT_COUNT]; /* Array of compr. ptr hints. */
} knot_rrinfo_t;
/*!
* \brief Name compression context.
*/
typedef struct knot_compr {
uint8_t *wire; /* Packet wireformat. */
knot_rrinfo_t *rrinfo; /* Hints for current RRSet. */
struct {
uint16_t pos; /* Position of current suffix. */
uint8_t labels; /* Label count of the suffix. */
} suffix;
} knot_compr_t;
/*!
* \brief Retrieve compression hint from given offset.
*/
static inline uint16_t knot_compr_hint(const knot_rrinfo_t *info, uint16_t hint_id)
{
if (hint_id < KNOT_COMPR_HINT_COUNT) {
return info->compress_ptr[hint_id];
} else {
return KNOT_COMPR_HINT_NONE;
}
}
/*!
* \brief Store compression hint for given offset.
*/
static inline void knot_compr_hint_set(knot_rrinfo_t *info, uint16_t hint_id,
uint16_t val, uint16_t len)
{
if ((hint_id < KNOT_COMPR_HINT_COUNT) && (val + len < KNOT_WIRE_PTR_MAX)) {
info->compress_ptr[hint_id] = val;
}
}
/*! @} */
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