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/*
* 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.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <string>
#include "shuffle.hh"
#include "dns_random.hh"
#include "dnsparser.hh"
// shuffle, maintaining some semblance of order
void pdns::shuffle(std::vector<DNSZoneRecord>& rrs)
{
std::vector<DNSZoneRecord>::iterator first;
std::vector<DNSZoneRecord>::iterator second;
// We assume the CNAMES are listed first in the ANSWER section and the the other records
// and we want to shuffle the other records only
// First we scan for the first non-CNAME ANSWER record
for (first = rrs.begin(); first != rrs.end(); ++first) {
if (first->dr.d_place == DNSResourceRecord::ANSWER && first->dr.d_type != QType::CNAME) {
break;
}
}
// And then for one past the last ANSWER record
for (second = first; second != rrs.end(); ++second) {
if (second->dr.d_place != DNSResourceRecord::ANSWER) {
break;
}
}
// Now shuffle the non-CNAME ANSWER records
dns_random_engine randomEngine;
if (second - first > 1) {
shuffle(first, second, randomEngine);
}
// now shuffle the ADDITIONAL records in the same manner as the ANSWER records
for (first = second; first != rrs.end(); ++first) {
if (first->dr.d_place == DNSResourceRecord::ADDITIONAL && first->dr.d_type != QType::CNAME) {
break;
}
}
for (second = first; second != rrs.end(); ++second) {
if (second->dr.d_place != DNSResourceRecord::ADDITIONAL) {
break;
}
}
if (second - first > 1) {
shuffle(first, second, randomEngine);
}
// we don't shuffle the rest
}
// shuffle, maintaining some semblance of order
static void shuffle(std::vector<DNSRecord>& rrs, bool includingAdditionals)
{
// This shuffles in the same style as the above method, keeping CNAME in the front and RRSIGs at the end
std::vector<DNSRecord>::iterator first;
std::vector<DNSRecord>::iterator second;
for (first = rrs.begin(); first != rrs.end(); ++first) {
if (first->d_place == DNSResourceRecord::ANSWER && first->d_type != QType::CNAME) {
break;
}
}
for (second = first; second != rrs.end(); ++second) {
if (second->d_place != DNSResourceRecord::ANSWER || second->d_type == QType::RRSIG) {
break;
}
}
pdns::dns_random_engine randomEngine;
if (second - first > 1) {
shuffle(first, second, randomEngine);
}
if (!includingAdditionals) {
return;
}
// now shuffle the additional records
for (first = second; first != rrs.end(); ++first) {
if (first->d_place == DNSResourceRecord::ADDITIONAL && first->d_type != QType::CNAME) {
break;
}
}
for (second = first; second != rrs.end(); ++second) {
if (second->d_place != DNSResourceRecord::ADDITIONAL) {
break;
}
}
if (second - first > 1) {
shuffle(first, second, randomEngine);
}
// we don't shuffle the rest
}
static uint16_t mapTypesToOrder(uint16_t type)
{
if (type == QType::CNAME) {
return 0;
}
if (type == QType::RRSIG) {
return 65535;
}
return 1;
}
// make sure rrs is sorted in d_place order to avoid surprises later
// then shuffle the parts that desire shuffling
void pdns::orderAndShuffle(vector<DNSRecord>& rrs, bool includingAdditionals)
{
std::stable_sort(rrs.begin(), rrs.end(), [](const DNSRecord& lhs, const DNSRecord& rhs) {
return std::tuple(lhs.d_place, mapTypesToOrder(lhs.d_type)) < std::tuple(rhs.d_place, mapTypesToOrder(rhs.d_type));
});
shuffle(rrs, includingAdditionals);
}
unsigned int pdns::dedupRecords(vector<DNSRecord>& rrs)
{
// This function tries to avoid unnecessary work
// First a vector with zero or one element does not need dedupping
if (rrs.size() <= 1) {
return 0;
}
// If we have a larger vector, first check if we actually have duplicates.
// We assume the most common case is: no
std::unordered_set<std::string> seen;
std::vector<bool> dups(rrs.size(), false);
unsigned int counter = 0;
unsigned int numDups = 0;
seen.reserve(rrs.size());
for (const auto& rec : rrs) {
auto key = rec.getContent()->serialize(rec.d_name, true, true, true);
// This ignores class, ttl and place by using constants for those
if (!seen.emplace(std::move(key)).second) {
dups[counter] = true;
numDups++;
}
++counter;
}
if (numDups == 0) {
// Original is fine as-is.
return 0;
}
// We avoid calling erase, as it calls a lot of move constructors. This can hurt, especially if
// you call it on a large vector multiple times.
// So we just take the elements that are unique
std::vector<DNSRecord> ret;
ret.reserve(rrs.size() - numDups);
for (counter = 0; counter < rrs.size(); ++counter) {
if (!dups[counter]) {
ret.emplace_back(std::move(rrs[counter]));
}
}
rrs = std::move(ret);
return numDups;
}
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