pdns/packetcache.hh

   1 /*
   2  * This file is part of PowerDNS or dnsdist.
   3  * Copyright -- PowerDNS.COM B.V. and its contributors
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of version 2 of the GNU General Public License as
   7  * published by the Free Software Foundation.
   8  *
   9  * In addition, for the avoidance of any doubt, permission is granted to
  10  * link this program with OpenSSL and to (re)distribute the binaries
  11  * produced as the result of such linking.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  21  */
  22 #ifndef PACKETCACHE_HH
  23 #define PACKETCACHE_HH
  24
  25 #include "ednsoptions.hh"
  26 #include "misc.hh"
  27 #include "iputils.hh"
  28
  29 class PacketCache : public boost::noncopyable
  30 {
  31 protected:
  32   static uint32_t canHashPacket(const std::string& packet, bool skipECS=true)
  33   {
  34     uint32_t ret = 0;
  35     ret=burtle((const unsigned char*)packet.c_str() + 2, 10, ret); // rest of dnsheader, skip id
  36     size_t packetSize = packet.size();
  37     size_t pos = 12;
  38     const char* end = packet.c_str() + packetSize;
  39     const char* p = packet.c_str() + pos;
  40
  41     for(; p < end && *p; ++p) { // XXX if you embed a 0 in your qname we'll stop lowercasing there
  42       const unsigned char l = dns_tolower(*p); // label lengths can safely be lower cased
  43       ret=burtle(&l, 1, ret);
  44     }                           // XXX the embedded 0 in the qname will break the subnet stripping
  45
  46     struct dnsheader* dh = (struct dnsheader*)packet.c_str();
  47     const char* skipBegin = p;
  48     const char* skipEnd = p;
  49     /* we need at least 1 (final empty label) + 2 (QTYPE) + 2 (QCLASS)
  50        + OPT root label (1), type (2), class (2) and ttl (4)
  51        + the OPT RR rdlen (2)
  52        = 16
  53     */
  54     if(skipECS && ntohs(dh->arcount)==1 && (pos+16) < packetSize) {
  55       char* optionBegin = nullptr;
  56       size_t optionLen = 0;
  57       /* skip the final empty label (1), the qtype (2), qclass (2) */
  58       /* root label (1), type (2), class (2) and ttl (4) */
  59       int res = getEDNSOption((char*) p + 14, end - (p + 14), EDNSOptionCode::ECS, &optionBegin, &optionLen);
  60       if (res == 0) {
  61         skipBegin = optionBegin;
  62         skipEnd = optionBegin + optionLen;
  63       }
  64     }
  65     if (skipBegin > p) {
  66       // cerr << "Hashing from " << (p-packet.c_str()) << " for " << skipBegin-p << "bytes, end is at "<< end-packet.c_str() << endl;
  67       ret = burtle((const unsigned char*)p, skipBegin-p, ret);
  68     }
  69     if (skipEnd < end) {
  70       // cerr << "Hashing from " << (skipEnd-packet.c_str()) << " for " << end-skipEnd << "bytes, end is at " << end-packet.c_str() << endl;
  71       ret = burtle((const unsigned char*) skipEnd, end-skipEnd, ret);
  72     }
  73
  74     return ret;
  75   }
  76 };
  77
  78 #endif /* PACKETCACHE_HH */