pdns/recursordist/rec-system-resolve.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
  23 #pragma once
  24
  25 #include "config.h"
  26
  27 #include <condition_variable>
  28 #include <functional>
  29 #include <thread>
  30
  31 #include "namespaces.hh"
  32 #include "iputils.hh"
  33 #include "lock.hh"
  34
  35 /************************************************************************************************
  36 The pdns::RecResolve class implements a facility to use the system configured resolver. At the moment
  37 of writing, this can only be used to configure forwarding by name instead of IP.
  38  ************************************************************************************************/
  39
  40 /************************************************************************************************
  41 DESIGN CONSIDERATIONS
  42
  43 - all names looked up with lookupAndRegister() will be entered into a table.
  44
  45 - the names in the table will ber periodically checked by a refresh thread. Set the period (before
  46   starting to use the system resolver) by calling pdns::RecResolve::setInstanceParameters().
  47
  48 - if *a* name resolves to a different result than stored, we will call the callback. Currently this is
  49    used to call the equivalent of rec_control reload-zones
  50
  51 - A manual rec_control reload-zones will *also* flush the existing table before doing the reload, so
  52   we force a re-resolve all names. See
  53   rec_channel_rec.cc:reloadZoneConfigurationWithSysResolveReset()
  54
  55 **************************************************************************************************/
  56
  57 /************************************************************************************************
  58 PRACTICAL CONSIDERATIONS/IMPLEMENTATION LIMITS
  59
  60 - Currently the facility is *only* used by the forwarding code
  61
  62 - We resolve with AI_ADDRCONFIG, the address families enabled will depend on the network config
  63   of the machine
  64
  65 - We pick the first address that getaddrinfo() produced. Currently no handling of multiple addresses
  66   and/or multiple address families.
  67
  68 - There is a check to detect *some* cases of self-resolve. This is done by resolving
  69   id.server/CH/TXT and comparing the result to the system-id set. Both false positives and false
  70   negatives can occur.
  71
  72 **************************************************************************************************/
  73 namespace pdns
  74 {
  75 class RecResolve
  76 {
  77 public:
  78   // Should be called before any getInstance() call is done
  79   static void setInstanceParameters(std::string serverID, time_t ttl, time_t interval, bool selfResolveCheck, const std::function<void()>& callback);
  80   // Get "the" instance of the system resolver.
  81   static RecResolve& getInstance();
  82
  83   RecResolve(time_t ttl, time_t interval, bool selfResolveCheck, const std::function<void()>& callback = nullptr);
  84   ~RecResolve();
  85   // Lookup a name and register it in the names to be checked if not already there
  86   ComboAddress lookupAndRegister(const std::string& name, time_t now);
  87   // Lookup a name which must be already registered
  88   ComboAddress lookup(const std::string& name);
  89
  90   // When an instance is created, it will run a refresh thread, stop it with this method
  91   void stopRefresher();
  92   // And restart it again
  93   void startRefresher();
  94   // Wipe one or all names
  95   void wipe(const std::string& name = "");
  96
  97 private:
  98   bool refresh(time_t now);
  99   struct AddressData
 100   {
 101     ComboAddress d_address;
 102     time_t d_ttd{0};
 103   };
 104   struct ResolveData
 105   {
 106     std::map<std::string, AddressData> d_map;
 107   };
 108   LockGuarded<ResolveData> d_data;
 109   const time_t d_ttl;
 110
 111   // This private class implements the refresher thread
 112   class Refresher
 113   {
 114   public:
 115     Refresher(time_t interval, const std::function<void()>& callback, bool selfResolveCheck, pdns::RecResolve& res);
 116     Refresher(const Refresher&) = delete;
 117     Refresher(Refresher&&) = delete;
 118     Refresher& operator=(const Refresher&) = delete;
 119     Refresher& operator=(Refresher&&) = delete;
 120     ~Refresher();
 121
 122     void start();
 123     void finish();
 124     void trigger();
 125
 126   private:
 127     void refreshLoop();
 128
 129     pdns::RecResolve& d_resolver;
 130     std::function<void()> d_callback;
 131     const time_t d_interval;
 132     std::thread d_thread;
 133     std::mutex mutex;
 134     std::condition_variable condVar;
 135     std::atomic<bool> wakeup{false};
 136     std::atomic<bool> stop{false};
 137     const bool d_selfResolveCheck;
 138   };
 139
 140   Refresher d_refresher;
 141
 142   static std::string s_serverID;
 143   static std::function<void()> s_callback;
 144   static time_t s_ttl;
 145   static time_t s_interval;
 146   static bool s_selfResolveCheck;
 147 };
 148
 149 }