/*
    PowerDNS Versatile Database Driven Nameserver
    Copyright (C) 2002-2012  PowerDNS.COM BV

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License version 2
    as published by the Free Software Foundation

    Additionally, the license of this program contains a special
    exception which allows to distribute the program in binary form when
    it is linked against OpenSSL.

    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 St, Fifth Floor, Boston, MA  02110-1301  USA
*/
#include "pdns/auth-zonecache.hh"
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <boost/algorithm/string.hpp>
#include <boost/scoped_array.hpp>
#include "auth-packetcache.hh"
#include "utility.hh"
#include "threadname.hh"
#include "dnssecinfra.hh"
#include "dnsseckeeper.hh"
#include <cstdio>
#include "base32.hh"
#include <cstring>
#include <cstdlib>
#include <sys/types.h>
#include <netinet/tcp.h>
#include <iostream>
#include <string>
#include "tcpreceiver.hh"
#include "sstuff.hh"

#include <cerrno>
#include <csignal>
#include "base64.hh"
#include "ueberbackend.hh"
#include "dnspacket.hh"
#include "nameserver.hh"
#include "distributor.hh"
#include "lock.hh"
#include "logger.hh"
#include "arguments.hh"

#include "auth-main.hh"
#include "packethandler.hh"
#include "statbag.hh"
#include "communicator.hh"
#include "namespaces.hh"
#include "signingpipe.hh"
#include "stubresolver.hh"
#include "proxy-protocol.hh"
#include "noinitvector.hh"
#include "gss_context.hh"
#include "pdnsexception.hh"
extern AuthPacketCache PC;
extern StatBag S;

/**
\file tcpreceiver.cc
\brief This file implements the tcpreceiver that receives and answers questions over TCP/IP
*/

std::unique_ptr<Semaphore> TCPNameserver::d_connectionroom_sem{nullptr};
LockGuarded<std::unique_ptr<PacketHandler>> TCPNameserver::s_P{nullptr};
unsigned int TCPNameserver::d_maxTCPConnections = 0;
NetmaskGroup TCPNameserver::d_ng;
size_t TCPNameserver::d_maxTransactionsPerConn;
size_t TCPNameserver::d_maxConnectionsPerClient;
unsigned int TCPNameserver::d_idleTimeout;
unsigned int TCPNameserver::d_maxConnectionDuration;
LockGuarded<std::map<ComboAddress,size_t,ComboAddress::addressOnlyLessThan>> TCPNameserver::s_clientsCount;

void TCPNameserver::go()
{
  g_log<<Logger::Error<<"Creating backend connection for TCP"<<endl;
  s_P.lock()->reset();
  try {
    *(s_P.lock()) = make_unique<PacketHandler>();
  }
  catch(PDNSException &ae) {
    g_log<<Logger::Error<<"TCP server is unable to launch backends - will try again when questions come in: "<<ae.reason<<endl;
  }

  std::thread th([this](){thread();});
  th.detach();
}

// throws PDNSException if things didn't go according to plan, returns 0 if really 0 bytes were read
static int readnWithTimeout(int fd, void* buffer, unsigned int n, unsigned int idleTimeout, bool throwOnEOF=true, unsigned int totalTimeout=0)
{
  unsigned int bytes=n;
  char *ptr = (char*)buffer;
  int ret;
  time_t start = 0;
  unsigned int remainingTotal = totalTimeout;
  if (totalTimeout) {
    start = time(nullptr);
  }
  while(bytes) {
    ret=read(fd, ptr, bytes);
    if(ret < 0) {
      if(errno==EAGAIN) {
        ret=waitForData(fd, (totalTimeout == 0 || idleTimeout <= remainingTotal) ? idleTimeout : remainingTotal);
        if(ret < 0)
          throw NetworkError("Waiting for data read");
        if(!ret)
          throw NetworkError("Timeout reading data");
        continue;
      }
      else
        throw NetworkError("Reading data: "+stringerror());
    }
    if(!ret) {
      if(!throwOnEOF && n == bytes)
        return 0;
      else
        throw NetworkError("Did not fulfill read from TCP due to EOF");
    }

    ptr += ret;
    bytes -= ret;
    if (totalTimeout) {
      time_t now = time(nullptr);
      const auto elapsed = now - start;
      if (elapsed >= static_cast<time_t>(remainingTotal)) {
        throw NetworkError("Timeout while reading data");
      }
      start = now;
      if (elapsed > 0) {
        remainingTotal -= elapsed;
      }
    }
  }
  return n;
}

// ditto
static void writenWithTimeout(int fd, const void *buffer, unsigned int n, unsigned int idleTimeout)
{
  unsigned int bytes=n;
  const char *ptr = (char*)buffer;
  int ret;
  while(bytes) {
    ret=write(fd, ptr, bytes);
    if(ret < 0) {
      if(errno==EAGAIN) {
        ret=waitForRWData(fd, false, idleTimeout, 0);
        if(ret < 0)
          throw NetworkError("Waiting for data write");
        if(!ret)
          throw NetworkError("Timeout writing data");
        continue;
      }
      else
        throw NetworkError("Writing data: "+stringerror());
    }
    if(!ret) {
      throw NetworkError("Did not fulfill TCP write due to EOF");
    }

    ptr += ret;
    bytes -= ret;
  }
}

void TCPNameserver::sendPacket(std::unique_ptr<DNSPacket>& p, int outsock, bool last)
{
  uint16_t len=htons(p->getString(true).length());

  // this also calls p->getString; call it after our explicit call so throwsOnTruncation=true is honoured
  g_rs.submitResponse(*p, false, last);

  string buffer((const char*)&len, 2);
  buffer.append(p->getString());
  writenWithTimeout(outsock, buffer.c_str(), buffer.length(), d_idleTimeout);
}


void TCPNameserver::getQuestion(int fd, char *mesg, int pktlen, const ComboAddress &remote, unsigned int totalTime)
try
{
  readnWithTimeout(fd, mesg, pktlen, d_idleTimeout, true, totalTime);
}
catch(NetworkError& ae) {
  throw NetworkError("Error reading DNS data from TCP client "+remote.toString()+": "+ae.what());
}

static bool maxConnectionDurationReached(unsigned int maxConnectionDuration, time_t start, unsigned int& remainingTime)
{
  if (maxConnectionDuration) {
    time_t elapsed = time(nullptr) - start;
    if (elapsed >= maxConnectionDuration) {
      return true;
    }
    if (elapsed > 0) {
      remainingTime = static_cast<unsigned int>(maxConnectionDuration - elapsed);
    }
  }
  return false;
}

void TCPNameserver::decrementClientCount(const ComboAddress& remote)
{
  if (d_maxConnectionsPerClient) {
    auto count = s_clientsCount.lock();
    auto it = count->find(remote);
    if (it == count->end()) {
      // this is worrying, but nothing we can do at this point
      return;
    }
    --it->second;
    if (it->second == 0) {
      count->erase(it);
    }
  }
}

// NOLINTNEXTLINE(readability-function-cognitive-complexity)
void TCPNameserver::doConnection(int fd)
{
  setThreadName("pdns/tcpConnect");
  std::unique_ptr<DNSPacket> packet;
  ComboAddress remote, accountremote;
  socklen_t remotelen=sizeof(remote);
  size_t transactions = 0;
  time_t start = 0;
  if (d_maxConnectionDuration) {
    start = time(nullptr);
  }

  if(getpeername(fd, (struct sockaddr *)&remote, &remotelen) < 0) {
    g_log<<Logger::Warning<<"Received question from socket which had no remote address, dropping ("<<stringerror()<<")"<<endl;
    d_connectionroom_sem->post();
    try {
      closesocket(fd);
    }
    catch(const PDNSException& e) {
      g_log<<Logger::Error<<"Error closing TCP socket: "<<e.reason<<endl;
    }
    return;
  }

  setNonBlocking(fd);
  try {
    int mesgsize=65535;
    boost::scoped_array<char> mesg(new char[mesgsize]);
    std::optional<ComboAddress> inner_remote;
    bool inner_tcp = false;

    DLOG(g_log<<"TCP Connection accepted on fd "<<fd<<endl);
    bool logDNSQueries= ::arg().mustDo("log-dns-queries");
    if (g_proxyProtocolACL.match(remote)) {
      unsigned int remainingTime = 0;
      PacketBuffer proxyData;
      proxyData.reserve(g_proxyProtocolMaximumSize);
      ssize_t used;

      // this for-loop ends by throwing, or by having gathered a complete proxy header
      for (;;) {
        used = isProxyHeaderComplete(proxyData);
        if (used < 0) {
          ssize_t origsize = proxyData.size();
          proxyData.resize(origsize + -used);
          if (maxConnectionDurationReached(d_maxConnectionDuration, start, remainingTime)) {
            throw NetworkError("Error reading PROXYv2 header from TCP client "+remote.toString()+": maximum TCP connection duration exceeded");
          }

          try {
            readnWithTimeout(fd, &proxyData[origsize], -used, d_idleTimeout, true, remainingTime);
          }
          catch(NetworkError& ae) {
            throw NetworkError("Error reading PROXYv2 header from TCP client "+remote.toString()+": "+ae.what());
          }
        }
        else if (used == 0) {
          throw NetworkError("Error reading PROXYv2 header from TCP client "+remote.toString()+": PROXYv2 header was invalid");
        }
        else if (static_cast<size_t>(used) > g_proxyProtocolMaximumSize) {
          throw NetworkError("Error reading PROXYv2 header from TCP client "+remote.toString()+": PROXYv2 header too big");
        }
        else { // used > 0 && used <= g_proxyProtocolMaximumSize
          break;
        }
      }
      ComboAddress psource, pdestination;
      bool proxyProto, tcp;
      std::vector<ProxyProtocolValue> ppvalues;

      used = parseProxyHeader(proxyData, proxyProto, psource, pdestination, tcp, ppvalues);
      if (used <= 0) {
        throw NetworkError("Error reading PROXYv2 header from TCP client "+remote.toString()+": PROXYv2 header was invalid");
      }
      if (static_cast<size_t>(used) > g_proxyProtocolMaximumSize) {
        throw NetworkError("Error reading PROXYv2 header from TCP client "+remote.toString()+": PROXYv2 header was oversized");
      }
      inner_remote = psource;
      inner_tcp = tcp;
      accountremote = psource;
    }
    else {
      accountremote = remote;
    }

    for(;;) {
      unsigned int remainingTime = 0;
      transactions++;
      if (d_maxTransactionsPerConn && transactions > d_maxTransactionsPerConn) {
        g_log << Logger::Notice<<"TCP Remote "<< remote <<" exceeded the number of transactions per connection, dropping.";
        break;
      }
      if (maxConnectionDurationReached(d_maxConnectionDuration, start, remainingTime)) {
        g_log << Logger::Notice<<"TCP Remote "<< remote <<" exceeded the maximum TCP connection duration, dropping.";
        break;
      }

      uint16_t pktlen;
      if(!readnWithTimeout(fd, &pktlen, 2, d_idleTimeout, false, remainingTime))
        break;
      else
        pktlen=ntohs(pktlen);

      // this check will always be false *if* no one touches
      // the mesg array. pktlen can be maximum of 65535 as
      // it is 2 byte unsigned variable. In getQuestion, we
      // write to 0 up to pktlen-1 so 65535 is just right.

      // do not remove this check as it will catch if someone
      // decreases the mesg buffer size for some reason.
      if(pktlen > mesgsize) {
        g_log<<Logger::Warning<<"Received an overly large question from "<<remote.toString()<<", dropping"<<endl;
        break;
      }

      if (maxConnectionDurationReached(d_maxConnectionDuration, start, remainingTime)) {
        g_log << Logger::Notice<<"TCP Remote "<< remote <<" exceeded the maximum TCP connection duration, dropping.";
        break;
      }

      getQuestion(fd, mesg.get(), pktlen, remote, remainingTime);
      S.inc("tcp-queries");
      if (accountremote.sin4.sin_family == AF_INET6)
        S.inc("tcp6-queries");
      else
        S.inc("tcp4-queries");

      packet=make_unique<DNSPacket>(true);
      packet->setRemote(&remote);
      packet->d_tcp=true;
      if (inner_remote) {
        packet->d_inner_remote = inner_remote;
        packet->d_tcp = inner_tcp;
      }
      packet->setSocket(fd);
      if(packet->parse(mesg.get(), pktlen)<0)
        break;

      if (packet->hasEDNSCookie())
        S.inc("tcp-cookie-queries");

      if(packet->qtype.getCode()==QType::AXFR) {
        packet->d_xfr=true;
        g_zoneCache.setZoneVariant(*packet);
        doAXFR(packet->qdomainzone, packet, fd);
        continue;
      }

      if(packet->qtype.getCode()==QType::IXFR) {
        packet->d_xfr=true;
        g_zoneCache.setZoneVariant(*packet);
        doIXFR(packet, fd);
        continue;
      }

      std::unique_ptr<DNSPacket> reply;
      auto cached = make_unique<DNSPacket>(false);
      if(logDNSQueries)  {
        g_log << Logger::Notice<<"TCP Remote "<< packet->getRemoteString() <<" wants '" << packet->qdomain<<"|"<<packet->qtype.toString() <<
        "', do = " <<packet->d_dnssecOk <<", bufsize = "<< packet->getMaxReplyLen();
      }

      if (PC.enabled()) {
        if (packet->couldBeCached()) {
          std::string view{};
          if (g_views) {
            Netmask netmask(packet->getInnerRemote());
            view = g_zoneCache.getViewFromNetwork(&netmask);
          }
          if (PC.get(*packet, *cached, view)) { // short circuit - does the PacketCache recognize this question?
            if(logDNSQueries) {
              g_log<<": packetcache HIT"<<endl;
	    }
            cached->setRemote(&packet->d_remote);
            cached->d_inner_remote = packet->d_inner_remote;
            cached->d.id=packet->d.id;
            cached->d.rd=packet->d.rd; // copy in recursion desired bit
            cached->commitD(); // commit d to the packet                        inlined

            sendPacket(cached, fd); // presigned, don't do it again
            continue;
          }
        }
        if(logDNSQueries)
            g_log<<": packetcache MISS"<<endl;
      } else {
        if (logDNSQueries) {
          g_log<<endl;
        }
      }
      {
        auto packetHandler = s_P.lock();
        if (!*packetHandler) {
          g_log<<Logger::Warning<<"TCP server is without backend connections, launching"<<endl;
          *packetHandler = make_unique<PacketHandler>();
        }

        reply = (*packetHandler)->doQuestion(*packet); // we really need to ask the backend :-)
      }

      if(!reply)  // unable to write an answer?
        break;

      sendPacket(reply, fd);
#ifdef ENABLE_GSS_TSIG
      if (g_doGssTSIG) {
        packet->cleanupGSS(reply->d.rcode);
      }
#endif
    }
  }
  catch(PDNSException &ae) {
    s_P.lock()->reset(); // on next call, backend will be recycled
    g_log << Logger::Error << "TCP Connection Thread for client " << remote << " failed, cycling backend: " << ae.reason << endl;
  }
  catch(NetworkError &e) {
    g_log << Logger::Info << "TCP Connection Thread for client " << remote << " died because of network error: " << e.what() << endl;
  }

  catch(std::exception &e) {
    s_P.lock()->reset(); // on next call, backend will be recycled
    g_log << Logger::Error << "TCP Connection Thread for client " << remote << " died because of STL error, cycling backend: " << e.what() << endl;
  }
  catch( ... )
  {
    s_P.lock()->reset(); // on next call, backend will be recycled
    g_log << Logger::Error << "TCP Connection Thread for client " << remote << " caught unknown exception, cycling backend." << endl;
  }
  d_connectionroom_sem->post();

  try {
    closesocket(fd);
  }
  catch(const PDNSException& e) {
    g_log << Logger::Error << "Error closing TCP socket for client " << remote << ": " << e.reason << endl;
  }
  decrementClientCount(remote);
}


bool TCPNameserver::canDoAXFR(std::unique_ptr<DNSPacket>& q, bool isAXFR, std::unique_ptr<PacketHandler>& packetHandler)
{
  if(::arg().mustDo("disable-axfr"))
    return false;

  string logPrefix=string(isAXFR ? "A" : "I")+"XFR-out zone '"+q->qdomainzone.toLogString()+"', client '"+q->getInnerRemote().toStringWithPort()+"', ";

  if(q->d_havetsig) { // if you have one, it must be good
    TSIGRecordContent tsigContent;
    DNSName tsigkeyname;
    string secret;
    if (!packetHandler->checkForCorrectTSIG(*q, &tsigkeyname, &secret, &tsigContent)) {
      return false;
    } else {
      getTSIGHashEnum(tsigContent.d_algoName, q->d_tsig_algo);
#ifdef ENABLE_GSS_TSIG
      if (g_doGssTSIG && q->d_tsig_algo == TSIG_GSS) {
        GssContext gssctx(tsigkeyname);
        if (!gssctx.getPeerPrincipal(q->d_peer_principal)) {
          g_log<<Logger::Warning<<"Failed to extract peer principal from GSS context with keyname '"<<tsigkeyname<<"'"<<endl;
        }
      }
#endif
    }

    DNSSECKeeper dk(packetHandler->getBackend());
#ifdef ENABLE_GSS_TSIG
    if (g_doGssTSIG && q->d_tsig_algo == TSIG_GSS) {
      vector<string> princs;
      packetHandler->getBackend()->getDomainMetadata(q->qdomainzone, "GSS-ALLOW-AXFR-PRINCIPAL", princs);
      for(const std::string& princ :  princs) {
        if (q->d_peer_principal == princ) {
          g_log<<Logger::Warning<<"AXFR of domain '"<<q->qdomainzone<<"' allowed: TSIG signed request with authorized principal '"<<q->d_peer_principal<<"' and algorithm 'gss-tsig'"<<endl;
          return true;
        }
      }
      g_log<<Logger::Warning<<"AXFR of domain '"<<q->qdomainzone<<"' denied: TSIG signed request with principal '"<<q->d_peer_principal<<"' and algorithm 'gss-tsig' is not permitted"<<endl;
      return false;
    }
#endif
    if(!dk.TSIGGrantsAccess(q->qdomainzone, tsigkeyname)) {
      g_log<<Logger::Warning<<logPrefix<<"denied: key with name '"<<tsigkeyname<<"' and algorithm '"<<getTSIGAlgoName(q->d_tsig_algo)<<"' does not grant access"<<endl;
      return false;
    }
    else {
      g_log<<Logger::Notice<<logPrefix<<"allowed: TSIG signed request with authorized key '"<<tsigkeyname<<"' and algorithm '"<<getTSIGAlgoName(q->d_tsig_algo)<<"'"<<endl;
      return true;
    }
  }

  // cerr<<"checking allow-axfr-ips"<<endl;
  if(!(::arg()["allow-axfr-ips"].empty()) && d_ng.match( q->getInnerRemote() )) {
    g_log<<Logger::Notice<<logPrefix<<"allowed: client IP is in allow-axfr-ips"<<endl;
    return true;
  }

  FindNS fns;

  // cerr<<"doing per-zone-axfr-acls"<<endl;
  SOAData sd;
  if(packetHandler->getBackend()->getSOAUncached(q->qdomainzone,sd)) {
    // cerr<<"got backend and SOA"<<endl;
    vector<string> acl;
    packetHandler->getBackend()->getDomainMetadata(q->qdomainzone, "ALLOW-AXFR-FROM", acl);
    for (const auto & i : acl) {
      // cerr<<"matching against "<<*i<<endl;
      if(pdns_iequals(i, "AUTO-NS")) {
        // cerr<<"AUTO-NS magic please!"<<endl;

        DNSResourceRecord rr;
        set<DNSName> nsset;

        sd.db->lookup(QType(QType::NS), q->qdomain, sd.domain_id);
        while (sd.db->get(rr)) {
          nsset.insert(DNSName(rr.content));
        }
        for(const auto & j: nsset) {
          vector<string> nsips=fns.lookup(j, packetHandler->getBackend());
          for(const auto & nsip : nsips) {
            // cerr<<"got "<<*k<<" from AUTO-NS"<<endl;
            if(nsip == q->getInnerRemote().toString())
            {
              // cerr<<"got AUTO-NS hit"<<endl;
              g_log<<Logger::Notice<<logPrefix<<"allowed: client IP is in NSset"<<endl;
              return true;
            }
          }
        }
      }
      else
      {
        Netmask nm = Netmask(i);
        if(nm.match( q->getInnerRemote() ))
        {
          g_log<<Logger::Notice<<logPrefix<<"allowed: client IP is in per-zone ACL"<<endl;
          // cerr<<"hit!"<<endl;
          return true;
        }
      }
    }
  }

  extern CommunicatorClass Communicator;

  if(Communicator.justNotified(q->qdomainzone, q->getInnerRemote().toString())) { // we just notified this ip
    g_log<<Logger::Notice<<logPrefix<<"allowed: client IP is from recently notified secondary"<<endl;
    return true;
  }

  g_log<<Logger::Warning<<logPrefix<<"denied: client IP has no permission"<<endl;
  return false;
}

namespace {
  struct NSECXEntry
  {
    NSECBitmap d_set;
    unsigned int d_ttl;
    bool d_auth;
  };

  static std::unique_ptr<DNSPacket> getFreshAXFRPacket(std::unique_ptr<DNSPacket>& q)
  {
    std::unique_ptr<DNSPacket> ret = std::unique_ptr<DNSPacket>(q->replyPacket());
    ret->setCompress(false);
    ret->d_dnssecOk=false; // RFC 5936, 2.2.5
    ret->d_tcp = true;
    return ret;
  }
}


/** do the actual zone transfer. Return 0 in case of error, 1 in case of success */
// NOLINTNEXTLINE(readability-identifier-length)
int TCPNameserver::doAXFR(const ZoneName &targetZone, std::unique_ptr<DNSPacket>& q, int outsock)  // NOLINT(readability-function-cognitive-complexity)
{
  const DNSName& target = targetZone.operator const DNSName&();
  string logPrefix="AXFR-out zone '"+targetZone.toLogString()+"', client '"+q->getRemoteStringWithPort()+"', ";

  std::unique_ptr<DNSPacket> outpacket= getFreshAXFRPacket(q);
  if(q->d_dnssecOk) {
    outpacket->d_dnssecOk=true; // RFC 5936, 2.2.5 'SHOULD'
  }

  g_log<<Logger::Warning<<logPrefix<<"transfer initiated"<<endl;

  // determine if zone exists and AXFR is allowed using existing backend before spawning a new backend.
  SOAData sd;
  {
    auto packetHandler = s_P.lock();
    DLOG(g_log<<logPrefix<<"looking for SOA"<<endl);    // find domain_id via SOA and list complete domain. No SOA, no AXFR
    if(!*packetHandler) {
      g_log<<Logger::Warning<<"TCP server is without backend connections in doAXFR, launching"<<endl;
      *packetHandler = make_unique<PacketHandler>();
    }

    // canDoAXFR does all the ACL checks, and has the if(disable-axfr) shortcut, call it first.
    if (!canDoAXFR(q, true, *packetHandler)) {
      g_log<<Logger::Warning<<logPrefix<<"failed: client may not request AXFR"<<endl;
      outpacket->setRcode(RCode::NotAuth);
      sendPacket(outpacket,outsock);
      return 0;
    }

    if (!(*packetHandler)->getBackend()->getSOAUncached(targetZone, sd)) {
      g_log<<Logger::Warning<<logPrefix<<"failed: not authoritative"<<endl;
      outpacket->setRcode(RCode::NotAuth);
      sendPacket(outpacket,outsock);
      return 0;
    }
  }

  UeberBackend db;
  if(!db.getSOAUncached(targetZone, sd)) {
    g_log<<Logger::Warning<<logPrefix<<"failed: not authoritative in second instance"<<endl;
    outpacket->setRcode(RCode::NotAuth);
    sendPacket(outpacket,outsock);
    return 0;
  }

  bool securedZone = false;
  bool presignedZone = false;
  bool NSEC3Zone = false;
  bool narrow = false;

  DomainInfo di;
  bool isCatalogZone = sd.db->getDomainInfo(targetZone, di, false) && di.isCatalogType();

  NSEC3PARAMRecordContent ns3pr;

  DNSSECKeeper dk(&db);
  DNSSECKeeper::clearCaches(targetZone);
  if (!isCatalogZone) {
    securedZone = dk.isSecuredZone(targetZone);
    presignedZone = dk.isPresigned(targetZone);
  }

  if(securedZone && dk.getNSEC3PARAM(targetZone, &ns3pr, &narrow)) {
    NSEC3Zone=true;
    if(narrow) {
      g_log<<Logger::Warning<<logPrefix<<"failed: not doing AXFR of an NSEC3 narrow zone"<<endl;
      outpacket->setRcode(RCode::Refused);
      sendPacket(outpacket,outsock);
      return 0;
    }
  }

  TSIGRecordContent trc;
  DNSName tsigkeyname;
  string tsigsecret;

  bool haveTSIGDetails = q->getTSIGDetails(&trc, &tsigkeyname);

  if(haveTSIGDetails && !tsigkeyname.empty()) {
    string tsig64;
    DNSName algorithm=trc.d_algoName;
    if (algorithm == DNSName("hmac-md5.sig-alg.reg.int"))
      algorithm = DNSName("hmac-md5");
    if (algorithm != DNSName("gss-tsig")) {
      if(!db.getTSIGKey(tsigkeyname, algorithm, tsig64)) {
        g_log<<Logger::Warning<<logPrefix<<"TSIG key not found"<<endl;
        return 0;
      }
      if (B64Decode(tsig64, tsigsecret) == -1) {
        g_log<<Logger::Error<<logPrefix<<"unable to Base-64 decode TSIG key '"<<tsigkeyname<<"'"<<endl;
        return 0;
      }
    }
  }


  // SOA *must* go out first, our signing pipe might reorder
  DLOG(g_log<<logPrefix<<"sending out SOA"<<endl);
  DNSZoneRecord soa = makeEditedDNSZRFromSOAData(dk, sd);
  outpacket->addRecord(DNSZoneRecord(soa));
  if(securedZone && !presignedZone) {
    set<ZoneName> authSet;
    authSet.insert(targetZone);
    addRRSigs(dk, db, authSet, outpacket->getRRS());
  }

  if(haveTSIGDetails && !tsigkeyname.empty())
    outpacket->setTSIGDetails(trc, tsigkeyname, tsigsecret, trc.d_mac); // first answer is 'normal'

  sendPacket(outpacket, outsock, false);

  trc.d_mac = outpacket->d_trc.d_mac;
  outpacket = getFreshAXFRPacket(q);


  DNSZoneRecord zrr;
  vector<DNSZoneRecord> zrrs;

  zrr.dr.d_name = target;
  zrr.dr.d_ttl = sd.minimum;

  if(securedZone && !presignedZone) { // this is where the DNSKEYs, CDNSKEYs and CDSs go in
    bool doCDNSKEY = true, doCDS = true;
    string publishCDNSKEY, publishCDS;
    dk.getPublishCDNSKEY(q->qdomainzone, publishCDNSKEY);
    dk.getPublishCDS(q->qdomainzone, publishCDS);

    set<uint32_t> entryPointIds;
    DNSSECKeeper::keyset_t entryPoints = dk.getEntryPoints(targetZone);
    for (auto const& value : entryPoints) {
      entryPointIds.insert(value.second.id);
    }

    DNSSECKeeper::keyset_t keys = dk.getKeys(targetZone);
    for(const DNSSECKeeper::keyset_t::value_type& value :  keys) {
      if (!value.second.published) {
        continue;
      }
      zrr.dr.d_type = QType::DNSKEY;
      zrr.dr.setContent(std::make_shared<DNSKEYRecordContent>(value.first.getDNSKEY()));
      DNSName keyname = NSEC3Zone ? DNSName(toBase32Hex(hashQNameWithSalt(ns3pr, zrr.dr.d_name))) : zrr.dr.d_name;
      zrrs.push_back(zrr);

      // generate CDS and CDNSKEY records
      if(doCDNSKEY && entryPointIds.count(value.second.id) > 0){
        if(!publishCDNSKEY.empty()) {
          zrr.dr.d_type=QType::CDNSKEY;
          if (publishCDNSKEY == "0") {
            doCDNSKEY = false;
            zrr.dr.setContent(PacketHandler::s_deleteCDNSKEYContent);
            zrrs.push_back(zrr);
          } else {
            zrr.dr.setContent(std::make_shared<DNSKEYRecordContent>(value.first.getDNSKEY()));
            zrrs.push_back(zrr);
          }
        }

        if(doCDS && !publishCDS.empty()){
          zrr.dr.d_type=QType::CDS;
          vector<string> digestAlgos;
          stringtok(digestAlgos, publishCDS, ", ");
          if(std::find(digestAlgos.begin(), digestAlgos.end(), "0") != digestAlgos.end()) {
            doCDS = false;
            zrr.dr.setContent(PacketHandler::s_deleteCDSContent);
            zrrs.push_back(zrr);
          } else {
            for(auto const &digestAlgo : digestAlgos) {
              zrr.dr.setContent(std::make_shared<DSRecordContent>(makeDSFromDNSKey(target, value.first.getDNSKEY(), pdns::checked_stoi<uint8_t>(digestAlgo))));
              zrrs.push_back(zrr);
            }
          }
        }
      }
    }

  }

  if(NSEC3Zone) { // now stuff in the NSEC3PARAM
    uint8_t flags = ns3pr.d_flags;
    zrr.dr.d_type = QType::NSEC3PARAM;
    ns3pr.d_flags = 0;
    zrr.dr.setContent(std::make_shared<NSEC3PARAMRecordContent>(ns3pr));
    ns3pr.d_flags = flags;
    DNSName keyname = DNSName(toBase32Hex(hashQNameWithSalt(ns3pr, zrr.dr.d_name)));
    zrrs.push_back(zrr);
  }

  const bool rectify = !(presignedZone || ::arg().mustDo("disable-axfr-rectify"));
  set<DNSName> qnames, nsset, terms;

  // Catalog zone start
  if (di.kind == DomainInfo::Producer) {
    // Ignore all records except NS at apex
    sd.db->lookup(QType::NS, target, di.id);
    while (sd.db->get(zrr)) {
      zrrs.emplace_back(zrr);
    }
    if (zrrs.empty()) {
      zrr.dr.d_name = target;
      zrr.dr.d_ttl = 0;
      zrr.dr.d_type = QType::NS;
      zrr.dr.setContent(std::make_shared<NSRecordContent>("invalid."));
      zrrs.emplace_back(zrr);
    }

    zrrs.emplace_back(CatalogInfo::getCatalogVersionRecord(targetZone));

    vector<CatalogInfo> members;
    if (!sd.db->getCatalogMembers(targetZone, members, CatalogInfo::CatalogType::Producer)) {
      g_log << Logger::Error << logPrefix << "getting catalog members failed, aborting AXFR" << endl;
      outpacket->setRcode(RCode::ServFail);
      sendPacket(outpacket, outsock);
      return 0;
    }
    for (const auto& ci : members) {
      ci.toDNSZoneRecords(targetZone, zrrs);
    }
    if (members.empty()) {
      g_log << Logger::Warning << logPrefix << "catalog zone '" << targetZone << "' has no members" << endl;
    }
    goto send;
  }
  // Catalog zone end

  // now start list zone
  if (!sd.db->list(targetZone, sd.domain_id, isCatalogZone)) {
    g_log<<Logger::Error<<logPrefix<<"backend signals error condition, aborting AXFR"<<endl;
    outpacket->setRcode(RCode::ServFail);
    sendPacket(outpacket,outsock);
    return 0;
  }

  while(sd.db->get(zrr)) {
    if (!presignedZone) {
      if (zrr.dr.d_type == QType::RRSIG) {
        continue;
      }
      if (zrr.dr.d_type == QType::DNSKEY || zrr.dr.d_type == QType::CDNSKEY || zrr.dr.d_type == QType::CDS) {
        if(!::arg().mustDo("direct-dnskey")) {
          continue;
        } else {
          zrr.dr.d_ttl = sd.minimum;
        }
      }
    }
    zrr.dr.d_name.makeUsLowerCase();
    if(zrr.dr.d_name.isPartOf(target)) {
      if (zrr.dr.d_type == QType::ALIAS && (::arg().mustDo("outgoing-axfr-expand-alias") || ::arg()["outgoing-axfr-expand-alias"] == "ignore-errors")) {
        vector<DNSZoneRecord> ips;
        int ret1 = stubDoResolve(getRR<ALIASRecordContent>(zrr.dr)->getContent(), QType::A, ips);
        int ret2 = stubDoResolve(getRR<ALIASRecordContent>(zrr.dr)->getContent(), QType::AAAA, ips);
        if (ret1 != RCode::NoError || ret2 != RCode::NoError) {
          if (::arg()["outgoing-axfr-expand-alias"] == "ignore-errors") {
            if (ret1 != RCode::NoError) {
              g_log << Logger::Error << logPrefix << zrr.dr.d_name.toLogString() << ": error resolving A record for ALIAS target " << zrr.dr.getContent()->getZoneRepresentation() << ", continuing AXFR" << endl;
            }
            if (ret2 != RCode::NoError) {
              g_log << Logger::Error << logPrefix << zrr.dr.d_name.toLogString() << ": error resolving AAAA record for ALIAS target " << zrr.dr.getContent()->getZoneRepresentation() << ", continuing AXFR" << endl;
            }
          }
          else {
            g_log << Logger::Warning << logPrefix << zrr.dr.d_name.toLogString() << ": error resolving for ALIAS " << zrr.dr.getContent()->getZoneRepresentation() << ", aborting AXFR" << endl;
            outpacket->setRcode(RCode::ServFail);
            sendPacket(outpacket, outsock);
            return 0;
          }
        }
        for (auto& ip: ips) {
          zrr.dr.d_type = ip.dr.d_type;
          zrr.dr.setContent(ip.dr.getContent());
          zrrs.push_back(zrr);
        }
        continue;
      }

      if (rectify) {
        if (zrr.dr.d_type) {
          qnames.insert(zrr.dr.d_name);
          if(zrr.dr.d_type == QType::NS && zrr.dr.d_name!=target)
            nsset.insert(zrr.dr.d_name);
        } else {
          // remove existing ents
          continue;
        }
      }
      zrrs.push_back(zrr);
    } else {
      if (zrr.dr.d_type)
        g_log<<Logger::Warning<<logPrefix<<"zone contains out-of-zone data '"<<zrr.dr.d_name<<"|"<<DNSRecordContent::NumberToType(zrr.dr.d_type)<<"', ignoring"<<endl;
    }
  }

  for (auto& loopRR : zrrs) {
    if ((loopRR.dr.d_type == QType::SVCB || loopRR.dr.d_type == QType::HTTPS)) {
      // Process auto hints
      // TODO this is an almost copy of the code in the packethandler
      auto rrc = getRR<SVCBBaseRecordContent>(loopRR.dr);
      if (rrc == nullptr) {
        continue;
      }
      auto newRRC = rrc->clone();
      if (!newRRC) {
        continue;
      }
      DNSName svcTarget = newRRC->getTarget().isRoot() ? loopRR.dr.d_name : newRRC->getTarget();
      if (newRRC->autoHint(SvcParam::ipv4hint)) {
        sd.db->lookup(QType::A, svcTarget, sd.domain_id);
        vector<ComboAddress> hints;
        DNSZoneRecord rr;
        while (sd.db->get(rr)) {
          auto arrc = getRR<ARecordContent>(rr.dr);
          hints.push_back(arrc->getCA());
        }
        if (hints.size() == 0) {
          newRRC->removeParam(SvcParam::ipv4hint);
        } else {
          newRRC->setHints(SvcParam::ipv4hint, hints);
        }
      }

      if (newRRC->autoHint(SvcParam::ipv6hint)) {
        sd.db->lookup(QType::AAAA, svcTarget, sd.domain_id);
        vector<ComboAddress> hints;
        DNSZoneRecord rr;
        while (sd.db->get(rr)) {
          auto arrc = getRR<AAAARecordContent>(rr.dr);
          hints.push_back(arrc->getCA());
        }
        if (hints.size() == 0) {
          newRRC->removeParam(SvcParam::ipv6hint);
        } else {
          newRRC->setHints(SvcParam::ipv6hint, hints);
        }
      }

      loopRR.dr.setContent(std::move(newRRC));
    }
  }

  // Group records by name and type, signpipe stumbles over interrupted rrsets
  if(securedZone && !presignedZone) {
    sort(zrrs.begin(), zrrs.end(), [](const DNSZoneRecord& a, const DNSZoneRecord& b) {
      return std::tie(a.dr.d_name, a.dr.d_type) < std::tie(b.dr.d_name, b.dr.d_type);
    });
  }

  if(rectify) {
    // set auth
    for(DNSZoneRecord &loopZRR :  zrrs) {
      loopZRR.auth=true;
      if (loopZRR.dr.d_type != QType::NS || loopZRR.dr.d_name!=target) {
        DNSName shorter(loopZRR.dr.d_name);
        do {
          if (shorter==target) // apex is always auth
            break;
          if(nsset.count(shorter) && !(loopZRR.dr.d_name==shorter && loopZRR.dr.d_type == QType::DS)) {
            loopZRR.auth=false;
            break;
          }
        } while(shorter.chopOff());
      }
    }

    if(NSEC3Zone) {
      // ents are only required for NSEC3 zones
      uint32_t maxent = ::arg().asNum("max-ent-entries");
      set<DNSName> nsec3set, nonterm;
      for (auto &loopZRR: zrrs) {
        bool skip=false;
        DNSName shorter = loopZRR.dr.d_name;
        if (shorter != target && shorter.chopOff() && shorter != target) {
          do {
            if(nsset.count(shorter)) {
              skip=true;
              break;
            }
          } while(shorter.chopOff() && shorter != target);
        }
        shorter = loopZRR.dr.d_name;
        if(!skip && (loopZRR.dr.d_type != QType::NS || !ns3pr.d_flags)) {
          do {
            if(!nsec3set.count(shorter)) {
              nsec3set.insert(shorter);
            }
          } while(shorter != target && shorter.chopOff());
        }
      }

      for(DNSZoneRecord &loopZRR :  zrrs) {
        DNSName shorter(loopZRR.dr.d_name);
        while(shorter != target && shorter.chopOff()) {
          if(!qnames.count(shorter) && !nonterm.count(shorter) && nsec3set.count(shorter)) {
            if(!(maxent)) {
              g_log<<Logger::Warning<<logPrefix<<"zone has too many empty non terminals, aborting AXFR"<<endl;
              outpacket->setRcode(RCode::ServFail);
              sendPacket(outpacket,outsock);
              return 0;
            }
            nonterm.insert(shorter);
            --maxent;
          }
        }
      }

      for(const auto& nt :  nonterm) {
        DNSZoneRecord tempRR;
        tempRR.dr.d_name=nt;
        tempRR.dr.d_type=QType::ENT;
        tempRR.auth=true;
        zrrs.push_back(tempRR);
      }
    }
  }

send:

  /* now write all other records */

  typedef map<DNSName, NSECXEntry, CanonDNSNameCompare> nsecxrepo_t;
  nsecxrepo_t nsecxrepo;

  ChunkedSigningPipe csp(targetZone, (securedZone && !presignedZone), ::arg().asNum("signing-threads", 1), ::arg().mustDo("workaround-11804") ? 1 : 100);

  DNSName keyname;
  unsigned int udiff;
  DTime dt;
  dt.set();
  for(DNSZoneRecord &loopZRR :  zrrs) {
    if(securedZone && (loopZRR.auth || loopZRR.dr.d_type == QType::NS)) {
      if (NSEC3Zone || loopZRR.dr.d_type) {
        if (presignedZone && NSEC3Zone && loopZRR.dr.d_type == QType::RRSIG && getRR<RRSIGRecordContent>(loopZRR.dr)->d_type == QType::NSEC3) {
          keyname = loopZRR.dr.d_name.makeRelative(sd.qname());
        } else {
          keyname = NSEC3Zone ? DNSName(toBase32Hex(hashQNameWithSalt(ns3pr, loopZRR.dr.d_name))) : loopZRR.dr.d_name;
        }
        NSECXEntry& ne = nsecxrepo[keyname];
        ne.d_ttl = sd.getNegativeTTL();
        ne.d_auth = (ne.d_auth || loopZRR.auth || (NSEC3Zone && (!ns3pr.d_flags)));
        if (loopZRR.dr.d_type && loopZRR.dr.d_type != QType::RRSIG) {
          ne.d_set.set(loopZRR.dr.d_type);
        }
      }
    }

    if (!loopZRR.dr.d_type)
      continue; // skip empty non-terminals

    if(loopZRR.dr.d_type == QType::SOA)
      continue; // skip SOA - would indicate end of AXFR

    if(csp.submit(loopZRR)) {
      for(;;) {
        outpacket->getRRS() = csp.getChunk();
        if(!outpacket->getRRS().empty()) {
          if(haveTSIGDetails && !tsigkeyname.empty())
            outpacket->setTSIGDetails(trc, tsigkeyname, tsigsecret, trc.d_mac, true);
          sendPacket(outpacket, outsock, false);
          trc.d_mac=outpacket->d_trc.d_mac;
          outpacket=getFreshAXFRPacket(q);
        }
        else
          break;
      }
    }
  }
  /*
  udiff=dt.udiffNoReset();
  cerr<<"Starting NSEC: "<<csp.d_signed/(udiff/1000000.0)<<" sigs/s, "<<csp.d_signed<<" / "<<udiff/1000000.0<<endl;
  cerr<<"Outstanding: "<<csp.d_outstanding<<", "<<csp.d_queued - csp.d_signed << endl;
  cerr<<"Ready for consumption: "<<csp.getReady()<<endl;
  */
  if(securedZone) {
    if(NSEC3Zone) {
      for(nsecxrepo_t::const_iterator iter = nsecxrepo.begin(); iter != nsecxrepo.end(); ++iter) {
        if(iter->second.d_auth) {
          NSEC3RecordContent n3rc;
          n3rc.set(iter->second.d_set);
          const auto numberOfTypesSet = n3rc.numberOfTypesSet();
          if (numberOfTypesSet != 0 && (numberOfTypesSet != 1 || !n3rc.isSet(QType::NS))) {
            n3rc.set(QType::RRSIG);
          }
          n3rc.d_salt = ns3pr.d_salt;
          n3rc.d_flags = ns3pr.d_flags;
          n3rc.d_iterations = ns3pr.d_iterations;
          n3rc.d_algorithm = DNSSECKeeper::DIGEST_SHA1; // SHA1, fixed in PowerDNS for now
          nsecxrepo_t::const_iterator inext = iter;
          ++inext;
          if(inext == nsecxrepo.end())
            inext = nsecxrepo.begin();
          while(!inext->second.d_auth && inext != iter)
          {
            ++inext;
            if(inext == nsecxrepo.end())
              inext = nsecxrepo.begin();
          }
          n3rc.d_nexthash = fromBase32Hex(inext->first.toStringNoDot());
          zrr.dr.d_name = iter->first+sd.qname();

          zrr.dr.d_ttl = sd.getNegativeTTL();
          zrr.dr.setContent(std::make_shared<NSEC3RecordContent>(std::move(n3rc)));
          zrr.dr.d_type = QType::NSEC3;
          zrr.dr.d_place = DNSResourceRecord::ANSWER;
          zrr.auth=true;
          if(csp.submit(zrr)) {
            for(;;) {
              outpacket->getRRS() = csp.getChunk();
              if(!outpacket->getRRS().empty()) {
                if(haveTSIGDetails && !tsigkeyname.empty())
                  outpacket->setTSIGDetails(trc, tsigkeyname, tsigsecret, trc.d_mac, true);
                sendPacket(outpacket, outsock, false);
                trc.d_mac=outpacket->d_trc.d_mac;
                outpacket=getFreshAXFRPacket(q);
              }
              else
                break;
            }
          }
        }
      }
    }
    else for(nsecxrepo_t::const_iterator iter = nsecxrepo.begin(); iter != nsecxrepo.end(); ++iter) {
      NSECRecordContent nrc;
      nrc.set(iter->second.d_set);
      nrc.set(QType::RRSIG);
      nrc.set(QType::NSEC);

      if(boost::next(iter) != nsecxrepo.end())
        nrc.d_next = boost::next(iter)->first;
      else
        nrc.d_next=nsecxrepo.begin()->first;
      zrr.dr.d_name = iter->first;

      zrr.dr.d_ttl = sd.getNegativeTTL();
      zrr.dr.setContent(std::make_shared<NSECRecordContent>(std::move(nrc)));
      zrr.dr.d_type = QType::NSEC;
      zrr.dr.d_place = DNSResourceRecord::ANSWER;
      zrr.auth=true;
      if(csp.submit(zrr)) {
        for(;;) {
          outpacket->getRRS() = csp.getChunk();
          if(!outpacket->getRRS().empty()) {
            if(haveTSIGDetails && !tsigkeyname.empty())
              outpacket->setTSIGDetails(trc, tsigkeyname, tsigsecret, trc.d_mac, true);
            sendPacket(outpacket, outsock, false);
            trc.d_mac=outpacket->d_trc.d_mac;
            outpacket=getFreshAXFRPacket(q);
          }
          else
            break;
        }
      }
    }
  }
  /*
  udiff=dt.udiffNoReset();
  cerr<<"Flushing pipe: "<<csp.d_signed/(udiff/1000000.0)<<" sigs/s, "<<csp.d_signed<<" / "<<udiff/1000000.0<<endl;
  cerr<<"Outstanding: "<<csp.d_outstanding<<", "<<csp.d_queued - csp.d_signed << endl;
  cerr<<"Ready for consumption: "<<csp.getReady()<<endl;
  * */
  for(;;) {
    outpacket->getRRS() = csp.getChunk(true); // flush the pipe
    if(!outpacket->getRRS().empty()) {
      if(haveTSIGDetails && !tsigkeyname.empty())
        outpacket->setTSIGDetails(trc, tsigkeyname, tsigsecret, trc.d_mac, true); // first answer is 'normal'
      try {
        sendPacket(outpacket, outsock, false);
      }
      catch (PDNSException& pe) {
        throw PDNSException("during axfr-out of "+target.toString()+", this happened: "+pe.reason);
      }
      trc.d_mac=outpacket->d_trc.d_mac;
      outpacket=getFreshAXFRPacket(q);
    }
    else
      break;
  }

  udiff=dt.udiffNoReset();
  if(securedZone)
    g_log<<Logger::Debug<<logPrefix<<"done signing: "<<csp.d_signed/(udiff/1000000.0)<<" sigs/s, "<<endl;

  DLOG(g_log<<logPrefix<<"done writing out records"<<endl);
  /* and terminate with yet again the SOA record */
  outpacket=getFreshAXFRPacket(q);
  outpacket->addRecord(std::move(soa));
  if(haveTSIGDetails && !tsigkeyname.empty())
    outpacket->setTSIGDetails(trc, tsigkeyname, tsigsecret, trc.d_mac, true);

  sendPacket(outpacket, outsock);

  DLOG(g_log<<logPrefix<<"last packet - close"<<endl);
  g_log<<Logger::Notice<<logPrefix<<"AXFR finished"<<endl;

  return 1;
}

int TCPNameserver::doIXFR(std::unique_ptr<DNSPacket>& q, int outsock)
{
  string logPrefix="IXFR-out zone '"+q->qdomainzone.toLogString()+"', client '"+q->getRemoteStringWithPort()+"', ";

  std::unique_ptr<DNSPacket> outpacket=getFreshAXFRPacket(q);
  if(q->d_dnssecOk)
    outpacket->d_dnssecOk=true; // RFC 5936, 2.2.5 'SHOULD'

  uint32_t serial = 0;
  MOADNSParser mdp(false, q->getString());
  for(const auto & answer : mdp.d_answers) {
    const DNSRecord *dnsRecord = &answer;
    if (dnsRecord->d_type == QType::SOA && dnsRecord->d_place == DNSResourceRecord::AUTHORITY) {
      vector<string>parts;
      stringtok(parts, dnsRecord->getContent()->getZoneRepresentation());
      if (parts.size() >= 3) {
        try {
          pdns::checked_stoi_into(serial, parts[2]);
        }
        catch(const std::out_of_range& oor) {
          g_log<<Logger::Warning<<logPrefix<<"invalid serial in IXFR query"<<endl;
          outpacket->setRcode(RCode::FormErr);
          sendPacket(outpacket,outsock);
          return 0;
        }
      } else {
        g_log<<Logger::Warning<<logPrefix<<"no serial in IXFR query"<<endl;
        outpacket->setRcode(RCode::FormErr);
        sendPacket(outpacket,outsock);
        return 0;
      }
    } else if (dnsRecord->d_type != QType::TSIG && dnsRecord->d_type != QType::OPT) {
      g_log<<Logger::Warning<<logPrefix<<"additional records in IXFR query, type: "<<QType(dnsRecord->d_type).toString()<<endl;
      outpacket->setRcode(RCode::FormErr);
      sendPacket(outpacket,outsock);
      return 0;
    }
  }

  g_log<<Logger::Warning<<logPrefix<<"transfer initiated with serial "<<serial<<endl;

  // determine if zone exists, XFR is allowed, and if IXFR can proceed using existing backend before spawning a new backend.
  SOAData sd;
  bool securedZone;
  bool serialPermitsIXFR;
  {
    auto packetHandler = s_P.lock();
    DLOG(g_log<<logPrefix<<"Looking for SOA"<<endl); // find domain_id via SOA and list complete domain. No SOA, no IXFR
    if(!*packetHandler) {
      g_log<<Logger::Warning<<"TCP server is without backend connections in doIXFR, launching"<<endl;
      *packetHandler = make_unique<PacketHandler>();
    }

    // canDoAXFR does all the ACL checks, and has the if(disable-axfr) shortcut, call it first.
    if(!canDoAXFR(q, false, *packetHandler) || !(*packetHandler)->getBackend()->getSOAUncached(q->qdomainzone, sd)) {
      g_log<<Logger::Warning<<logPrefix<<"failed: not authoritative"<<endl;
      outpacket->setRcode(RCode::NotAuth);
      sendPacket(outpacket,outsock);
      return 0;
    }

    DNSSECKeeper dk((*packetHandler)->getBackend());
    DNSSECKeeper::clearCaches(q->qdomainzone);
    bool narrow = false;
    securedZone = dk.isSecuredZone(q->qdomainzone);
    if(dk.getNSEC3PARAM(q->qdomainzone, nullptr, &narrow)) {
      if(narrow) {
        g_log<<Logger::Warning<<logPrefix<<"not doing IXFR of an NSEC3 narrow zone"<<endl;
        outpacket->setRcode(RCode::Refused);
        sendPacket(outpacket,outsock);
        return 0;
      }
    }

    serialPermitsIXFR = !rfc1982LessThan(serial, calculateEditSOA(sd.serial, dk, sd.zonename));
  }

  if (serialPermitsIXFR) {
    const ZoneName& target = q->qdomainzone;
    TSIGRecordContent trc;
    DNSName tsigkeyname;
    string tsigsecret;

    UeberBackend db;
    DNSSECKeeper dk(&db);

    bool haveTSIGDetails = q->getTSIGDetails(&trc, &tsigkeyname);

    if(haveTSIGDetails && !tsigkeyname.empty()) {
      string tsig64;
      DNSName algorithm=trc.d_algoName; // FIXME400: was toLowerCanonic, compare output
      if (algorithm == DNSName("hmac-md5.sig-alg.reg.int"))
        algorithm = DNSName("hmac-md5");
      if (!db.getTSIGKey(tsigkeyname, algorithm, tsig64)) {
        g_log << Logger::Error << "TSIG key '" << tsigkeyname << "' for domain '" << target << "' not found" << endl;
        return 0;
      }
      if (B64Decode(tsig64, tsigsecret) == -1) {
        g_log<<Logger::Error<<logPrefix<<"unable to Base-64 decode TSIG key '"<<tsigkeyname<<"'"<<endl;
        return 0;
      }
    }

    // SOA *must* go out first, our signing pipe might reorder
    DLOG(g_log<<logPrefix<<"sending out SOA"<<endl);
    DNSZoneRecord soa = makeEditedDNSZRFromSOAData(dk, sd);
    outpacket->addRecord(std::move(soa));
    if(securedZone && outpacket->d_dnssecOk) {
      set<ZoneName> authSet;
      authSet.insert(target);
      addRRSigs(dk, db, authSet, outpacket->getRRS());
    }

    if(haveTSIGDetails && !tsigkeyname.empty())
      outpacket->setTSIGDetails(trc, tsigkeyname, tsigsecret, trc.d_mac); // first answer is 'normal'

    sendPacket(outpacket, outsock);

    g_log<<Logger::Notice<<logPrefix<<"IXFR finished"<<endl;

    return 1;
  }

  g_log<<Logger::Notice<<logPrefix<<"IXFR fallback to AXFR"<<endl;
  return doAXFR(q->qdomainzone, q, outsock);
}

TCPNameserver::~TCPNameserver() = default;
TCPNameserver::TCPNameserver()
{
  d_maxTransactionsPerConn = ::arg().asNum("max-tcp-transactions-per-conn");
  d_idleTimeout = ::arg().asNum("tcp-idle-timeout");
  d_maxConnectionDuration = ::arg().asNum("max-tcp-connection-duration");
  d_maxConnectionsPerClient = ::arg().asNum("max-tcp-connections-per-client");

//  sem_init(&d_connectionroom_sem,0,::arg().asNum("max-tcp-connections"));
  d_connectionroom_sem = make_unique<Semaphore>( ::arg().asNum( "max-tcp-connections" ));
  d_maxTCPConnections = ::arg().asNum( "max-tcp-connections" );

  vector<string>locals;
  stringtok(locals,::arg()["local-address"]," ,");
  if(locals.empty())
    throw PDNSException("No local addresses specified");

  d_ng.toMasks(::arg()["allow-axfr-ips"] );

  signal(SIGPIPE,SIG_IGN);

  for(auto const &laddr : locals) {
    ComboAddress local(laddr, ::arg().asNum("local-port"));

    int s=socket(local.sin4.sin_family, SOCK_STREAM, 0);
    if(s<0)
      throw PDNSException("Unable to acquire TCP socket: "+stringerror());
    setCloseOnExec(s);

    int tmp=1;
    if(setsockopt(s, SOL_SOCKET,SO_REUSEADDR, (char*)&tmp, sizeof tmp) < 0) {
      g_log<<Logger::Error<<"Setsockopt failed"<<endl;
      _exit(1);
    }

    if (::arg().asNum("tcp-fast-open") > 0) {
#ifdef TCP_FASTOPEN
      int fastOpenQueueSize = ::arg().asNum("tcp-fast-open");
      if (setsockopt(s, IPPROTO_TCP, TCP_FASTOPEN, &fastOpenQueueSize, sizeof fastOpenQueueSize) < 0) {
        g_log<<Logger::Error<<"Failed to enable TCP Fast Open for listening socket "<<local.toStringWithPort()<<": "<<stringerror()<<endl;
      }
#else
      g_log<<Logger::Warning<<"TCP Fast Open configured but not supported for listening socket"<<endl;
#endif
    }

    if(::arg().mustDo("non-local-bind"))
      Utility::setBindAny(local.sin4.sin_family, s);

    if(local.isIPv6() && setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY, &tmp, sizeof(tmp)) < 0) {
      g_log<<Logger::Error<<"Failed to set IPv6 socket to IPv6 only, continuing anyhow: "<<stringerror()<<endl;
    }

    if(::bind(s, (sockaddr*)&local, local.getSocklen())<0) {
      int err = errno;
      close(s);
      if( err == EADDRNOTAVAIL && ! ::arg().mustDo("local-address-nonexist-fail") ) {
        g_log<<Logger::Error<<"Address " << local.toString() << " does not exist on this server - skipping TCP bind" << endl;
        continue;
      } else {
        g_log<<Logger::Error<<"Unable to bind to TCP socket " << local.toStringWithPort() << ": "<<stringerror(err)<<endl;
        throw PDNSException("Unable to bind to TCP socket");
      }
    }

    listen(s, 128);
    g_log<<Logger::Error<<"TCP server bound to "<<local.toStringWithPort()<<endl;
    d_sockets.push_back(s);
    struct pollfd pfd;
    memset(&pfd, 0, sizeof(pfd));
    pfd.fd = s;
    pfd.events = POLLIN;
    d_prfds.push_back(pfd);
  }
}


//! Start of TCP operations thread, we launch a new thread for each incoming TCP question
void TCPNameserver::thread()
{
  setThreadName("pdns/tcpnameser");
  try {
    for(;;) {
      int fd;
      ComboAddress remote;
      Utility::socklen_t addrlen=remote.getSocklen();

      int ret=poll(&d_prfds[0], d_prfds.size(), -1); // blocks, forever if need be
      if(ret <= 0)
        continue;

      int sock=-1;
      for(const pollfd& pfd :  d_prfds) {
        if(pfd.revents & POLLIN) {
          sock = pfd.fd;
          remote.sin4.sin_family = AF_INET6;
          addrlen=remote.getSocklen();

          if((fd=accept(sock, (sockaddr*)&remote, &addrlen))<0) {
            int err = errno;
            g_log<<Logger::Error<<"TCP question accept error: "<<stringerror(err)<<endl;

            if(err==EMFILE) {
              g_log<<Logger::Error<<"TCP handler out of filedescriptors, exiting, won't recover from this"<<endl;
              _exit(1);
            }
          }
          else {
            if (d_maxConnectionsPerClient) {
              auto clientsCount = s_clientsCount.lock();
              if ((*clientsCount)[remote] >= d_maxConnectionsPerClient) {
                g_log<<Logger::Notice<<"Limit of simultaneous TCP connections per client reached for "<< remote<<", dropping"<<endl;
                close(fd);
                continue;
              }
              (*clientsCount)[remote]++;
            }

            d_connectionroom_sem->wait(); // blocks if no connections are available

            int room;
            d_connectionroom_sem->getValue( &room);
            if(room<1)
              g_log<<Logger::Warning<<"Limit of simultaneous TCP connections reached - raise max-tcp-connections"<<endl;

            try {
              std::thread connThread(doConnection, fd);
              connThread.detach();
            }
            catch (std::exception& e) {
              g_log<<Logger::Error<<"Error creating thread: "<<e.what()<<endl;
              d_connectionroom_sem->post();
              close(fd);
              decrementClientCount(remote);
            }
          }
        }
      }
    }
  }
  catch(PDNSException &AE) {
    g_log<<Logger::Error<<"TCP Nameserver thread dying because of fatal error: "<<AE.reason<<endl;
  }
  catch(...) {
    g_log<<Logger::Error<<"TCPNameserver dying because of an unexpected fatal error"<<endl;
  }
  _exit(1); // take rest of server with us
}


unsigned int TCPNameserver::numTCPConnections()
{
  int room;
  d_connectionroom_sem->getValue( &room);
  return d_maxTCPConnections - room;
}
