text: /**
   *    Copyright (C) 2017 MongoDB Inc.
   *
   *    This program is free software: you can redistribute it and/or modify
   *    it under the terms of the GNU Affero General Public License, version 3,
   *    as published by the Free Software Foundation.
   *
   *    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 Affero General Public License for more details.
   *
   *    You should have received a copy of the GNU Affero General Public License
   *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
   *
   *    As a special exception, the copyright holders give permission to link the
   *    code of portions of this program with the OpenSSL library under certain
   *    conditions as described in each individual source file and distribute
   *    linked combinations including the program with the OpenSSL library. You
   *    must comply with the GNU Affero General Public License in all respects for
   *    all of the code used other than as permitted herein. If you modify file(s)
   *    with this exception, you may extend this exception to your version of the
   *    file(s), but you are not obligated to do so. If you do not wish to do so,
   *    delete this exception statement from your version. If you delete this
   *    exception statement from all source files in the program, then also delete
   *    it in the license file.
   */
  
  #include "mongo/platform/basic.h"
  
  #include "mongo/util/dns_query.h"
  
  #include <array>
  #include <cassert>
  #include <cstdint>
  #include <exception>
  #include <iostream>
  #include <memory>
  #include <sstream>
  #include <stdexcept>
  #include <string>
  #include <vector>
  
  #include <boost/noncopyable.hpp>
  
  #include "mongo/bson/util/builder.h"
  
  // It is safe to include the implementation "headers" in an anonymous namespace, as the code is
  // meant to live in a single TU -- this one.  Include one of these headers last.
  #define MONGO_UTIL_DNS_QUERY_PLATFORM_INCLUDE_WHITELIST
  #ifdef WIN32
  #include "mongo/util/dns_query_windows-impl.h"
  #else
  #include "mongo/util/dns_query_posix-impl.h"
  #endif
  #undef MONGO_UTIL_DNS_QUERY_PLATFORM_INCLUDE_WHITELIST
  
  using std::begin;
  using std::end;
  using namespace std::literals::string_literals;
  
  namespace mongo {
  
  /**
   * Returns a string with the IP address or domain name listed...
   */
  std::vector<std::string> dns::lookupARecords(const std::string& service) {
      DNSQueryState dnsQuery;
      auto response = dnsQuery.lookup(service, DNSQueryClass::kInternet, DNSQueryType::kAddress);
  
      std::vector<std::string> rv;
  
      for (const auto& entry : response) {
          try {
              rv.push_back(entry.addressEntry());
          } catch (const ExceptionFor<ErrorCodes::DNSRecordTypeMismatch>&) {
          }
      }
  
      if (rv.empty()) {
          StringBuilder oss;
          oss << "Looking up " << service << " A record yielded ";
          if (response.size() == 0) {
              oss << "no results.";
          } else {
              oss << "no A records but " << response.size() << " other records";
          }
          uasserted(ErrorCodes::DNSProtocolError, oss.str());
      }
  
      return rv;
  }
  
  std::vector<dns::SRVHostEntry> dns::lookupSRVRecords(const std::string& service) {
      DNSQueryState dnsQuery;
  
      auto response = dnsQuery.lookup(service, DNSQueryClass::kInternet, DNSQueryType::kSRV);
  
      std::vector<SRVHostEntry> rv;
  
      for (const auto& entry : response) {
          try {
              rv.push_back(entry.srvHostEntry());
          } catch (const ExceptionFor<ErrorCodes::DNSRecordTypeMismatch>&) {
          }
      }
  
      if (rv.empty()) {
          StringBuilder oss;
          oss << "Looking up " << service << " SRV record yielded ";
          if (response.size() == 0) {
              oss << "no results.";
          } else {
              oss << "no SRV records but " << response.size() << " other records";
          }
          uasserted(ErrorCodes::DNSProtocolError, oss.str());
      }
  
      return rv;
  }
  
  std::vector<std::string> dns::lookupTXTRecords(const std::string& service) {
      DNSQueryState dnsQuery;
  
      auto response = dnsQuery.lookup(service, DNSQueryClass::kInternet, DNSQueryType::kTXT);
  
      std::vector<std::string> rv;
  
      for (auto& entry : response) {
          try {
              auto txtEntry = entry.txtEntry();
              rv.insert(end(rv),
                        std::make_move_iterator(begin(txtEntry)),
                        std::make_move_iterator(end(txtEntry)));
          } catch (const ExceptionFor<ErrorCodes::DNSRecordTypeMismatch>&) {
          }
      }
  
      return rv;
  }
  
  std::vector<std::string> dns::getTXTRecords(const std::string& service) try {
      return lookupTXTRecords(service);
  } catch (const ExceptionFor<ErrorCodes::DNSHostNotFound>&) {
      return {};
  }
  }  // namespace mongo
  