/*

 * This file is part of PowerDNS or dnsdist.

 * Copyright -- PowerDNS.COM B.V. and its contributors

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of version 2 of the GNU General Public License as

 * published by the Free Software Foundation.

 *

 * In addition, for the avoidance of any doubt, permission is granted to

 * link this program with OpenSSL and to (re)distribute the binaries

 * produced as the result of such linking.

 *

 * 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 Street, Fifth Floor, Boston, MA 02110-1301 USA.

 */

#pragma once

#include "ednsoptions.hh"

#include "misc.hh"

#include "iputils.hh"

class PacketCache : public boost::noncopyable

{

public:

  /* hash the packet from the provided position, which should point right after tje qname. This skips:

     - the query ID ;

     - EDNS Cookie options, if any ;

     - Any given option code present in optionsToSkip

  */

  static uint32_t hashAfterQname(const std::string_view& packet, uint32_t currentHash, size_t pos, const std::unordered_set<uint16_t>& optionsToSkip = {EDNSOptionCode::COOKIE})

  {

    const size_t packetSize = packet.size();

    assert(packetSize >= sizeof(dnsheader));

    /* we need at least 2 (QTYPE) + 2 (QCLASS)

       + OPT root label (1), type (2), class (2) and ttl (4)

       + the OPT RR rdlen (2)

       = 15

    */

    const dnsheader_aligned dnsheaderdata(packet.data());

    const struct dnsheader *dh = dnsheaderdata.get();

    if (ntohs(dh->qdcount) != 1 || ntohs(dh->ancount) != 0 || ntohs(dh->nscount) != 0 || ntohs(dh->arcount) != 1 || (pos + 15) >= packetSize) {

      if (packetSize > pos) {

        currentHash = burtle(reinterpret_cast<const unsigned char*>(&packet.at(pos)), packetSize - pos, currentHash);

      }

      return currentHash;

    }

    currentHash = burtle(reinterpret_cast<const unsigned char*>(&packet.at(pos)), 15, currentHash);

    /* skip the qtype (2), qclass (2) */

    /* root label (1), type (2), class (2) and ttl (4) */

    /* already hashed above */

    pos += 13;

    const uint16_t rdLen = ((static_cast<uint16_t>(packet.at(pos)) * 256) + static_cast<uint16_t>(packet.at(pos + 1)));

    /* skip the rd length */

    /* already hashed above */

    pos += 2;

    if (rdLen > (packetSize - pos)) {

      if (pos < packetSize) {

        currentHash = burtle(reinterpret_cast<const unsigned char*>(&packet.at(pos)), packetSize - pos, currentHash);

      }

      return currentHash;

    }

    uint16_t rdataRead = 0;

    uint16_t optionCode;

    uint16_t optionLen;

    while (pos < packetSize && rdataRead < rdLen && getNextEDNSOption(&packet.at(pos), rdLen - rdataRead, optionCode, optionLen)) {

      if (optionLen > (rdLen - rdataRead - 4)) {

        if (packetSize > pos) {

          currentHash = burtle(reinterpret_cast<const unsigned char*>(&packet.at(pos)), packetSize - pos, currentHash);

        }

        return currentHash;

      }

      if (optionsToSkip.count(optionCode) == 0) {

        /* hash the option code, length and content */

        currentHash = burtle(reinterpret_cast<const unsigned char*>(&packet.at(pos)), 4 + optionLen, currentHash);

      }

      else {

        /* skip option: hash only its code and length */

        currentHash = burtle(reinterpret_cast<const unsigned char*>(&packet.at(pos)), 4, currentHash);

      }

      pos += 4 + optionLen;

      rdataRead += 4 + optionLen;

    }

    if (pos < packetSize) {

      currentHash = burtle(reinterpret_cast<const unsigned char*>(&packet.at(pos)), packetSize - pos, currentHash);

    }

    return currentHash;

  }

  static uint32_t hashHeaderAndQName(const std::string& packet, size_t& pos)

  {

    const size_t packetSize = packet.size();

    assert(packetSize >= sizeof(dnsheader));

    // Quite some bits in the header are actually irrelevant for

    // incoming queries.  If we ever change that and ignore them for

    // hashing, don't forget to also adapt the `queryHeaderMatches`

    // code, as it should be consistent with the hash function.

    uint32_t currentHash = burtle(reinterpret_cast<const unsigned char*>(&packet.at(2)), sizeof(dnsheader) - 2, 0); // rest of dnsheader, skip id

    for (pos = sizeof(dnsheader); pos < packetSize; ) {

      const unsigned char labelLen = static_cast<unsigned char>(packet.at(pos));

      ++pos;

      if (labelLen == 0) {

        break;

      }

      pos = std::min(pos + labelLen, packetSize);

    }

    return burtleCI(reinterpret_cast<const unsigned char*>(&packet.at(sizeof(dnsheader))), pos - sizeof(dnsheader), currentHash);

  }

  /* hash the packet from the beginning, including the qname. This skips:

     - the query ID ;

     - EDNS Cookie options, if any ;

     - Any given option code present in optionsToSkip

  */

  static uint32_t canHashPacket(const std::string& packet, const std::unordered_set<uint16_t>& optionsToSkip = {EDNSOptionCode::COOKIE})

  {

    size_t pos = 0;

    uint32_t currentHash = hashHeaderAndQName(packet, pos);

    if (pos >= packet.size()) {

      return currentHash;

    }

    return hashAfterQname(packet, currentHash, pos, optionsToSkip);

  }

  static bool queryHeaderMatches(const std::string& cachedQuery, const std::string& query)

  {

    if (cachedQuery.size() != query.size()) {

      return false;

    }

    return (cachedQuery.compare(/* skip the ID */ 2, sizeof(dnsheader) - 2, query, 2, sizeof(dnsheader) - 2) == 0);

  }

  static bool queryMatches(const std::string& cachedQuery, const std::string& query, const DNSName& qname, const std::unordered_set<uint16_t>& optionsToIgnore)

  {

    const size_t querySize = query.size();

    const size_t cachedQuerySize = cachedQuery.size();

    if (querySize != cachedQuerySize) {

      return false;

    }

    if (!queryHeaderMatches(cachedQuery, query)) {

      return false;

    }

    size_t pos = sizeof(dnsheader) + qname.wirelength();

    /* we need at least 2 (QTYPE) + 2 (QCLASS)

       + OPT root label (1), type (2), class (2) and ttl (4)

       + the OPT RR rdlen (2)

       = 15

    */

    const dnsheader_aligned dnsheaderdata(query.data());

    const struct dnsheader* dh = dnsheaderdata.get();

    if (ntohs(dh->qdcount) != 1 || ntohs(dh->ancount) != 0 || ntohs(dh->nscount) != 0 || ntohs(dh->arcount) != 1 || (pos + 15) >= querySize || optionsToIgnore.empty()) {

      return cachedQuery.compare(pos, cachedQuerySize - pos, query, pos, querySize - pos) == 0;

    }

    /* compare up to the first option, if any */

    if (cachedQuery.compare(pos, 15, query, pos, 15) != 0) {

      return false;

    }

    /* skip the qtype (2), qclass (2) */

    /* root label (1), type (2), class (2) and ttl (4) */

    /* already compared above */

    pos += 13;

    const uint16_t rdLen = ((static_cast<unsigned char>(query.at(pos)) * 256) + static_cast<unsigned char>(query.at(pos + 1)));

    /* skip the rd length */

    /* already compared above */

    pos += sizeof(uint16_t);

    if (rdLen > (querySize - pos)) {

      /* something is wrong, let's just compare everything */

      return cachedQuery.compare(pos, cachedQuerySize - pos, query, pos, querySize - pos) == 0;

    }

    uint16_t rdataRead = 0;

    uint16_t optionCode;

    uint16_t optionLen;

    while (pos < querySize && rdataRead < rdLen && getNextEDNSOption(&query.at(pos), rdLen - rdataRead, optionCode, optionLen)) {

      if (optionLen > (rdLen - rdataRead)) {

        return cachedQuery.compare(pos, cachedQuerySize - pos, query, pos, querySize - pos) == 0;

      }

      /* compare the option code and length */

      if (cachedQuery.compare(pos, 4, query, pos, 4) != 0) {

        return false;

      }

      pos += 4;

      rdataRead += 4;

      if (optionLen > 0 && optionsToIgnore.count(optionCode) == 0) {

        if (cachedQuery.compare(pos, optionLen, query, pos, optionLen) != 0) {

          return false;

        }

      }

      pos += optionLen;

      rdataRead += optionLen;

    }

    if (pos >= querySize) {

        return true;

    }

    return cachedQuery.compare(pos, cachedQuerySize - pos, query, pos, querySize - pos) == 0;

  }

};