text: ////////////////////////////////////////////////////////////////////////////////
  /// DISCLAIMER
  ///
  /// Copyright 2014-2021 ArangoDB GmbH, Cologne, Germany
  /// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
  ///
  /// Licensed under the Apache License, Version 2.0 (the "License");
  /// you may not use this file except in compliance with the License.
  /// You may obtain a copy of the License at
  ///
  ///     http://www.apache.org/licenses/LICENSE-2.0
  ///
  /// Unless required by applicable law or agreed to in writing, software
  /// distributed under the License is distributed on an "AS IS" BASIS,
  /// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  /// See the License for the specific language governing permissions and
  /// limitations under the License.
  ///
  /// Copyright holder is ArangoDB GmbH, Cologne, Germany
  ///
  /// @author Dr. Frank Celler
  /// @author Copyright 2016, ArangoDB GmbH, Cologne, Germany
  ////////////////////////////////////////////////////////////////////////////////
  
  #include "EndpointSrv.h"
  
  #include <algorithm>
  #include <vector>
  
  #ifndef _WIN32
  
  #define BIND_4_COMPAT 1  // LINUX
  #define BIND_8_COMPAT 1  // MACOSX
  
  #include <arpa/nameser.h>
  #include <netinet/in.h>
  #include <resolv.h>
  
  #include "Basics/StringUtils.h"
  #include "Logger/LogMacros.h"
  #include "Logger/Logger.h"
  #include "Logger/LoggerStream.h"
  
  using namespace arangodb;
  using namespace arangodb::basics;
  
  #if PACKETSZ > 1024
  #define MAXPACKET PACKETSZ
  #else
  #define MAXPACKET 1024
  #endif
  
  union QueryBuffer {
    ::HEADER header;
    unsigned char buffer[MAXPACKET];
  };
  
  struct SrvRecord {
    int priority;
    int weight;
    int port;
    std::string name;
  };
  
  static std::vector<SrvRecord> srvRecords(std::string const& specification) {
    res_init();
  
    char const* dname = specification.c_str();
    int nclass = ns_c_in;
    int type = ns_t_srv;
  
    QueryBuffer answer;
    int anslen = sizeof(answer);
  
    int n = res_search(dname, nclass, type, answer.buffer, anslen);
  
    std::vector<SrvRecord> services;
  
    if (n != -1) {
      HEADER* hp = &answer.header;
  
      int qdcount = ntohs(hp->qdcount);
      int ancount = ntohs(hp->ancount);
  
      unsigned char* msg = answer.buffer;
      unsigned char* eom = msg + n;
      unsigned char* cp = msg + sizeof(HEADER);
  
      unsigned char hostbuf[256];
  
      while (0 < qdcount-- && cp < eom) {
        n = dn_expand(msg, eom, cp, (char*)hostbuf, 256);
  
        if (n < 0) {
          LOG_TOPIC("c39cc", WARN, arangodb::Logger::FIXME)
              << "DNS record for '" << specification << "' is corrupt";
          return {};
        }
  
        cp += n + QFIXEDSZ;
      }
  
      // loop through the answer buffer and extract SRV records
      while (0 < ancount-- && cp < eom) {
        n = dn_expand(msg, eom, cp, (char*)hostbuf, 256);
  
        if (n < 0) {
          LOG_TOPIC("352d9", WARN, arangodb::Logger::FIXME)
              << "DNS record for '" << specification << "' is corrupt";
          return {};
        }
  
        cp += n;
  
        int type;
        GETSHORT(type, cp);
  
        int nclass;
        GETSHORT(nclass, cp);
  
        int ttl;
        GETLONG(ttl, cp);
  
        int dlen;
        GETSHORT(dlen, cp);
  
        int priority;
        GETSHORT(priority, cp);
  
        int weight;
        GETSHORT(weight, cp);
  
        int port;
        GETSHORT(port, cp);
  
        n = dn_expand(msg, eom, cp, (char*)hostbuf, 256);
  
        if (n < 0) {
          LOG_TOPIC("4c4db", WARN, arangodb::Logger::FIXME)
              << "DNS record for '" << specification << "' is corrupt";
          break;
        }
  
        cp += n;
  
        LOG_TOPIC("b1488", TRACE, arangodb::Logger::FIXME)
            << "DNS record for '" << specification << "': type " << type
            << ", class " << nclass << ", ttl " << ttl << ", len " << dlen
            << ", prio " << priority << ", weight " << weight << ", port " << port
            << ", host '" << hostbuf << "'";
  
        if (type != T_SRV) {
          continue;
        }
  
        SrvRecord srv;
  
        srv.weight = weight;
        srv.priority = priority;
        srv.port = port;
        srv.name = (char*)hostbuf;
  
        services.push_back(srv);
      }
    } else {
      LOG_TOPIC("b804a", WARN, arangodb::Logger::FIXME)
          << "DNS record for '" << specification << "' not found";
    }
  
    std::sort(services.begin(), services.end(), [](SrvRecord const& lhs, SrvRecord const& rhs) {
      if (lhs.priority != rhs.priority) {
        return lhs.priority < rhs.priority;
      }
  
      return lhs.weight > rhs.weight;
    });
  
    return services;
  }
  
  #else
  
  static std::vector<SrvRecord> srvRecords(std::string const& specification) {
    return {};
  }
  
  #endif
  
  EndpointSrv::EndpointSrv(std::string const& specification)
      : Endpoint(DomainType::SRV, EndpointType::CLIENT, TransportType::HTTP,
                 EncryptionType::NONE, specification, 0) {}
  
  EndpointSrv::~EndpointSrv() = default;
  
  bool EndpointSrv::isConnected() const {
    if (_endpoint != nullptr) {
      return _endpoint->isConnected();
    }
  
    return false;
  }
  
  TRI_socket_t EndpointSrv::connect(double connectTimeout, double requestTimeout) {
    auto services = srvRecords(_specification);
  
    TRI_socket_t res;
  
    for (auto service : services) {
      std::string spec = "tcp://" + service.name + ":" + StringUtils::itoa(service.port);
  
      _endpoint.reset(Endpoint::clientFactory(spec));
  
      res = _endpoint->connect(connectTimeout, requestTimeout);
  
      if (_endpoint->isConnected()) {
        return res;
      }
    }
  
    TRI_invalidatesocket(&res);
    return res;
  }
  
  void EndpointSrv::disconnect() {
    if (_endpoint != nullptr) {
      _endpoint->disconnect();
    }
  }
  
  int EndpointSrv::domain() const {
    if (_endpoint != nullptr) {
      return _endpoint->domain();
    }
  
    return -1;
  }
  
  int EndpointSrv::port() const {
    if (_endpoint != nullptr) {
      return _endpoint->port();
    }
  
    return -1;
  }
  
  std::string EndpointSrv::host() const {
    if (_endpoint != nullptr) {
      return _endpoint->host();
    }
  
    return "";
  }
  
  std::string EndpointSrv::hostAndPort() const {
    if (_endpoint != nullptr) {
      return _endpoint->hostAndPort();
    }
  
    return "";
  }
  