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Diffstat (limited to '')
| -rw-r--r-- | src/libknot/packet/compr.h | 100 |
1 files changed, 100 insertions, 0 deletions
diff --git a/src/libknot/packet/compr.h b/src/libknot/packet/compr.h new file mode 100644 index 0000000..22c4a8e --- /dev/null +++ b/src/libknot/packet/compr.h @@ -0,0 +1,100 @@ +/* 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 <http://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; + } +} + +/*! @} */ |