/*  Copyright (C) 2024 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 Structure for holding DNS packet data and metadata.
 *
 * \addtogroup pkt
 * @{
 */

#pragma once

#include <assert.h>
#include <stdint.h>

#include "libknot/consts.h"
#include "libknot/dname.h"
#include "libknot/mm_ctx.h"
#include "libknot/rrset.h"
#include "libknot/rrtype/opt.h"
#include "libknot/packet/wire.h"
#include "libknot/packet/compr.h"
#include "libknot/wire.h"

/* Number of packet sections (ANSWER, AUTHORITY, ADDITIONAL). */
#define KNOT_PKT_SECTIONS 3

/*!
 * \brief Packet flags.
 */
enum {
	KNOT_PF_NULL      = 0 << 0, /*!< No flags. */
	KNOT_PF_FREE      = 1 << 1, /*!< Free with packet. */
	KNOT_PF_NOTRUNC   = 1 << 2, /*!< Don't truncate. */
	KNOT_PF_CHECKDUP  = 1 << 3, /*!< Check for duplicates. */
	KNOT_PF_KEEPWIRE  = 1 << 4, /*!< Keep wireformat untouched when parsing. */
	KNOT_PF_NOCANON   = 1 << 5, /*!< Don't canonicalize rrsets during parsing. */
	KNOT_PF_ORIGTTL   = 1 << 6, /*!< Write RRSIGs with their original TTL. */
	KNOT_PF_SOAMINTTL = 1 << 7, /*!< Write SOA with its minimum-ttl as TTL. */
	KNOT_PF_NULLBYTE  = 1 << 8, /*!< At lest one \0 byte is present in some qname label. */
};

typedef struct knot_pkt knot_pkt_t;

/*!
 * \brief Packet section.
 * Points to RRSet and RRSet info arrays in the packet.
 * This structure is required for random access to packet sections.
 */
typedef struct {
	knot_pkt_t *pkt; /*!< Owner. */
	uint16_t pos;    /*!< Position in the rr/rrinfo fields in packet. */
	uint16_t count;  /*!< Number of RRSets in this section. */
} knot_pktsection_t;

/*!
 * \brief Structure representing a DNS packet.
 */
struct knot_pkt {
	uint8_t *wire;         /*!< Wire format of the packet. */
	size_t size;           /*!< Current wire size of the packet. */
	size_t max_size;       /*!< Maximum allowed size of the packet. */
	size_t parsed;         /*!< Parsed size. */
	uint16_t reserved;     /*!< Reserved space. */
	uint16_t qname_size;   /*!< QNAME size. */
	uint16_t rrset_count;  /*!< Packet RRSet count. */
	uint16_t flags;        /*!< Packet flags. */

	knot_rrset_t *opt_rr;   /*!< OPT RR included in the packet. */
	knot_rrset_t *tsig_rr;  /*!< TSIG RR stored in the packet. */

	/*! EDNS option positions in the wire (if parsed from wire). */
	knot_edns_options_t *edns_opts;

	/*! TSIG RR position in the wire (if parsed from wire). */
	struct {
		uint8_t *pos;
		size_t len;
	} tsig_wire;

	/* Packet sections. */
	knot_section_t current;
	knot_pktsection_t sections[KNOT_PKT_SECTIONS];

	/* Packet RRSet (meta)data. */
	size_t rrset_allocd;
	knot_rrinfo_t *rr_info;
	knot_rrset_t *rr;

	knot_mm_t mm; /*!< Memory allocation context. */

	knot_compr_t compr; /*!< Compression context. */

	/*! Lowercased QNAME. MUST BE LAST ITEM! */
	knot_dname_storage_t lower_qname;
};

/*!
 * \brief Create new packet over existing memory, or allocate new from memory context.
 *
 * \note Packet is allocated from given memory context.
 *
 * \param wire If NULL, memory of 'len' size shall be allocated.
 *        Otherwise pointer is used for the wire format of the packet.
 * \param len Wire format length.
 * \param mm Memory context (NULL for default).
 * \return New packet or NULL.
 */
knot_pkt_t *knot_pkt_new(void *wire, uint16_t len, knot_mm_t *mm);

/*!
 * \brief Copy packet.
 *
 * \note Current implementation is not very efficient, as it re-parses the wire.
 *
 * \param dst Target packet.
 * \param src Source packet.
 *
 * \return new packet or NULL
 */
int knot_pkt_copy(knot_pkt_t *dst, const knot_pkt_t *src);

/*!
 * \brief Initialized response from query packet.
 *
 * \note Question is not checked, it is expected to be checked already.
 *
 * \param pkt Given packet.
 * \param query Query.
 * \return KNOT_EOK, KNOT_EINVAL, KNOT_ESPACE
 */
int knot_pkt_init_response(knot_pkt_t *pkt, const knot_pkt_t *query);

/*! \brief Reinitialize packet for another use. */
void knot_pkt_clear(knot_pkt_t *pkt);

/*! \brief Begone you foul creature of the underworld. */
void knot_pkt_free(knot_pkt_t *pkt);

/*!
 * \brief Reserve an arbitrary amount of space in the packet.
 *
 * \return KNOT_EOK
 * \return KNOT_ERANGE if size can't be reserved
 */
int knot_pkt_reserve(knot_pkt_t *pkt, uint16_t size);

/*!
 * \brief Reclaim reserved size.
 *
 * \return KNOT_EOK
 * \return KNOT_ERANGE if size can't be reclaimed
 */
int knot_pkt_reclaim(knot_pkt_t *pkt, uint16_t size);

/*
 * Packet QUESTION accessors.
 */
static inline uint16_t knot_pkt_question_size(const knot_pkt_t *pkt)
{
	if (pkt == NULL || pkt->qname_size == 0) {
		return 0;
	}

	return pkt->qname_size + 2 * sizeof(uint16_t);
}

static inline const knot_dname_t *knot_pkt_qname(const knot_pkt_t *pkt)
{
	if (pkt == NULL || pkt->qname_size == 0) {
		return NULL;
	}

	return pkt->lower_qname;
}

static inline const knot_dname_t *knot_pkt_wire_qname(const knot_pkt_t *pkt)
{
	if (pkt == NULL || pkt->qname_size == 0) {
		return NULL;
	}

	return pkt->wire + KNOT_WIRE_HEADER_SIZE;
}

static inline uint16_t knot_pkt_qtype(const knot_pkt_t *pkt)
{
	if (pkt == NULL || pkt->qname_size == 0) {
		return 0;
	}

	unsigned off = KNOT_WIRE_HEADER_SIZE + pkt->qname_size;
	return knot_wire_read_u16(pkt->wire + off);
}

static inline uint16_t knot_pkt_qclass(const knot_pkt_t *pkt)
{
	if (pkt == NULL || pkt->qname_size == 0) {
		return 0;
	}

	unsigned off = KNOT_WIRE_HEADER_SIZE + pkt->qname_size + sizeof(uint16_t);
	return knot_wire_read_u16(pkt->wire + off);
}

/*
 * Packet writing API.
 */

/*!
 * \brief Begin reading/writing packet section.
 *
 * \note You must proceed in the natural order (ANSWER, AUTHORITY, ADDITIONAL).
 *
 * \param pkt
 * \param section_id
 * \return KNOT_EOK or KNOT_EINVAL
 */
int knot_pkt_begin(knot_pkt_t *pkt, knot_section_t section_id);

/*!
 * \brief Put QUESTION in the packet.
 *
 * \note Since we support QD=1 only, QUESTION is a special type of packet section.
 * \note Must not be used after putting RRsets into the packet.
 *
 * \param pkt
 * \param qname
 * \param qclass
 * \param qtype
 * \return KNOT_EOK or various errors
 */
int knot_pkt_put_question(knot_pkt_t *pkt, const knot_dname_t *qname,
                          uint16_t qclass, uint16_t qtype);

/*!
 * \brief Put RRSet into packet.
 *
 * \note See compr.h for description on how compression hints work.
 * \note Available flags: PF_FREE, KNOT_PF_CHECKDUP, KNOT_PF_NOTRUNC
 *
 * \param pkt
 * \param compr_hint  Compression hint, see enum knot_compr_hint or absolute
 *                    position.
 * \param rr          Given RRSet.
 * \param rotate      Rotate the RRSet order by this count.
 * \param flags       RRSet flags (set PF_FREE if you want RRSet to be freed
 *                    with the packet).
 *
 * \return KNOT_EOK, KNOT_ESPACE, various errors
 */
int knot_pkt_put_rotate(knot_pkt_t *pkt, uint16_t compr_hint, const knot_rrset_t *rr,
                        uint16_t rotate, uint16_t flags);

/*! \brief Same as knot_pkt_put_rotate but without rrset rotation. */
static inline int knot_pkt_put(knot_pkt_t *pkt, uint16_t compr_hint,
                               const knot_rrset_t *rr, uint16_t flags)
{
	return knot_pkt_put_rotate(pkt, compr_hint, rr, 0, flags);
}

/*! \brief Get description of the given packet section. */
static inline const knot_pktsection_t *knot_pkt_section(const knot_pkt_t *pkt,
                                                        knot_section_t section_id)
{
	assert(pkt);
	return &pkt->sections[section_id];
}

/*! \brief Get RRSet from the packet section. */
static inline const knot_rrset_t *knot_pkt_rr(const knot_pktsection_t *section,
                                              uint16_t i)
{
	assert(section);
	return section->pkt->rr + section->pos + i;
}

/*! \brief Get RRSet offset in the packet wire. */
static inline uint16_t knot_pkt_rr_offset(const knot_pktsection_t *section,
                                          uint16_t i)
{
	assert(section);
	return section->pkt->rr_info[section->pos + i].pos;
}

/*
 * Packet parsing API.
 */

/*!
 * \brief Parse both packet question and payload.
 *
 * Parses both QUESTION and all packet sections,
 * includes semantic checks over specific RRs (TSIG, OPT).
 *
 * \note If KNOT_PF_KEEPWIRE is set, TSIG RR is not stripped from the wire
 *       and is processed as any other RR.
 *
 * \param  pkt Given packet.
 * \param  flags Parsing flags (allowed KNOT_PF_KEEPWIRE)
 *
 * \retval KNOT_EOK if success.
 * \retval KNOT_ETRAIL if success but with some trailing data.
 * \retval KNOT_EMALF and other errors.
 */
int knot_pkt_parse(knot_pkt_t *pkt, unsigned flags);

/*!
 * \brief Parse packet header and a QUESTION section.
 */
int knot_pkt_parse_question(knot_pkt_t *pkt);

/*!
 * \brief Get packet extended RCODE.
 *
 * Extended RCODE is created by considering TSIG RCODE, EDNS RCODE and
 * DNS Header RCODE. (See RFC 6895, Section 2.3).
 *
 * \param pkt Packet to get the response code from.
 *
 * \return Whole extended RCODE (0 if pkt == NULL).
 */
uint16_t knot_pkt_ext_rcode(const knot_pkt_t *pkt);

/*!
 * \brief Get packet extended RCODE name.
 *
 * The packet parameter is important as the name depends on TSIG.
 *
 * \param pkt Packet to get the response code from.
 *
 * \return RCODE name (or empty string if not known).
 */
const char *knot_pkt_ext_rcode_name(const knot_pkt_t *pkt);

/*!
 * \brief Checks if there is an OPT RR in the packet.
 */
static inline bool knot_pkt_has_edns(const knot_pkt_t *pkt)
{
	assert(pkt);
	return pkt->opt_rr != NULL;
}

/*!
 * \brief Checks if TSIG is present.
 */
static inline bool knot_pkt_has_tsig(const knot_pkt_t *pkt)
{
	assert(pkt);
	return pkt->tsig_rr != NULL;
}

/*!
 * \brief Checks if DO bit is set in the packet's OPT RR.
 */
static inline bool knot_pkt_has_dnssec(const knot_pkt_t *pkt)
{
	assert(pkt);
	return knot_pkt_has_edns(pkt) && knot_edns_do(pkt->opt_rr);
}

/*!
 * \brief Get specific EDNS option from a parsed packet.
 */
static inline uint8_t *knot_pkt_edns_option(const knot_pkt_t *pkt, uint16_t code)
{
	assert(pkt);
	if (pkt->edns_opts != NULL && code <= KNOT_EDNS_MAX_OPTION_CODE) {
		return pkt->edns_opts->ptr[code];
	} else {
		return NULL;
	}
}

/*!
 * \brief Computes a reasonable Padding data length for a given packet and opt RR.
 *
 * \param pkt     DNS Packet prepared and otherwise ready to go, no OPT yet added.
 * \param opt_rr  OPT RR, not yet including padding.
 *
 * \return Required padding length or -1 if padding not required.
 */
static inline int knot_pkt_default_padding_size(const knot_pkt_t *pkt,
                                                const knot_rrset_t *opt_rr)
{
	if (knot_wire_get_qr(pkt->wire)) {
		return knot_edns_alignment_size(pkt->size + pkt->reserved,
		                                knot_rrset_size(opt_rr),
		                                KNOT_EDNS_ALIGNMENT_RESPONSE_DEFAULT);
	} else {
		return knot_edns_alignment_size(pkt->size + pkt->reserved,
		                                knot_rrset_size(opt_rr),
		                                KNOT_EDNS_ALIGNMENT_QUERY_DEFAULT);
	}
}

static inline size_t knot_pkt_size(const knot_pkt_t *pkt)
{
	assert(pkt);
	return pkt->size + (knot_pkt_has_tsig(pkt) ? pkt->tsig_wire.len : 0);
}

/*! @} */
