/*
 * 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.
 */
#ifndef PACKETCACHE_HH
#define PACKETCACHE_HH

#include "ednsoptions.hh"
#include "misc.hh"
#include "iputils.hh"

class PacketCache : public boost::noncopyable
{
public:
  static uint32_t canHashPacket(const std::string& packet, uint16_t* ecsBegin, uint16_t* ecsEnd)
  {
    uint32_t ret = 0;
    ret = burtle(reinterpret_cast<const unsigned char*>(packet.c_str()) + 2, sizeof(dnsheader) - 2, ret); // rest of dnsheader, skip id
    size_t packetSize = packet.size();
    size_t pos = sizeof(dnsheader);
    const char* end = packet.c_str() + packetSize;
    const char* p = packet.c_str() + pos;

    for(; p < end && *p; ++p, ++pos) { // XXX if you embed a 0 in your qname we'll stop lowercasing there
      const unsigned char l = dns_tolower(*p); // label lengths can safely be lower cased
      ret=burtle(&l, 1, ret);
    }                           // XXX the embedded 0 in the qname will break the subnet stripping

    const struct dnsheader* dh = reinterpret_cast<const struct dnsheader*>(packet.c_str());
    const char* skipBegin = p;
    const char* skipEnd = p;
    if (ecsBegin != nullptr && ecsEnd != nullptr) {
      *ecsBegin = 0;
      *ecsEnd = 0;
    }
    /* we need at least 1 (final empty label) + 2 (QTYPE) + 2 (QCLASS)
       + OPT root label (1), type (2), class (2) and ttl (4)
       + the OPT RR rdlen (2)
       = 16
    */
    if(ntohs(dh->arcount)==1 && (pos+16) < packetSize) {
      char* optionBegin = nullptr;
      size_t optionLen = 0;
      /* skip the final empty label (1), the qtype (2), qclass (2) */
      /* root label (1), type (2), class (2) and ttl (4) */
      int res = getEDNSOption(const_cast<char*>(reinterpret_cast<const char*>(p)) + 14, end - (p + 14), EDNSOptionCode::ECS, &optionBegin, &optionLen);
      if (res == 0) {
        skipBegin = optionBegin;
        skipEnd = optionBegin + optionLen;
        if (ecsBegin != nullptr && ecsEnd != nullptr) {
          *ecsBegin = optionBegin - packet.c_str();
          *ecsEnd = *ecsBegin + optionLen;
        }
      }
    }
    if (skipBegin > p) {
      ret = burtle(reinterpret_cast<const unsigned char*>(p), skipBegin-p, ret);
    }
    if (skipEnd < end) {
      ret = burtle(reinterpret_cast<const unsigned char*>(skipEnd), end-skipEnd, ret);
    }

    return ret;
  }

  static uint32_t canHashPacket(const std::string& packet)
  {
    uint32_t ret = 0;
    ret = burtle(reinterpret_cast<const unsigned char*>(packet.c_str()) + 2, sizeof(dnsheader) - 2, ret); // rest of dnsheader, skip id
    size_t packetSize = packet.size();
    size_t pos = sizeof(dnsheader);
    const char* end = packet.c_str() + packetSize;
    const char* p = packet.c_str() + pos;

    for(; p < end && *p; ++p) { // XXX if you embed a 0 in your qname we'll stop lowercasing there
      const unsigned char l = dns_tolower(*p); // label lengths can safely be lower cased
      ret=burtle(&l, 1, ret);
    }                           // XXX the embedded 0 in the qname will break the subnet stripping

    if (p < end) {
      ret = burtle(reinterpret_cast<const unsigned char*>(p), end-p, ret);
    }

    return ret;
  }

  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)
  {
    if (!queryHeaderMatches(cachedQuery, query)) {
      return false;
    }

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

    return (cachedQuery.compare(pos, cachedQuery.size() - pos, query, pos, query.size() - pos) == 0);
  }

  static bool queryMatches(const std::string& cachedQuery, const std::string& query, const DNSName& qname, uint16_t ecsBegin, uint16_t ecsEnd)
  {
    if (!queryHeaderMatches(cachedQuery, query)) {
      return false;
    }

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

    if (ecsBegin != 0 && ecsBegin >= pos && ecsEnd > ecsBegin) {
      if (cachedQuery.compare(pos, ecsBegin - pos, query, pos, ecsBegin - pos) != 0) {
        return false;
      }

      if (cachedQuery.compare(ecsEnd, cachedQuery.size() - ecsEnd, query, ecsEnd, query.size() - ecsEnd) != 0) {
        return false;
      }
    }
    else {
      if (cachedQuery.compare(pos, cachedQuery.size() - pos, query, pos, query.size() - pos) != 0) {
        return false;
      }
    }

    return true;
  }

};

#endif /* PACKETCACHE_HH */
