DNS-fcrdns.cpp

   1 #include "DNS-fcrdns.hpp"
   2
   3 #include "IP4.hpp"
   4 #include "IP6.hpp"
   5
   6 #include <algorithm>
   7
   8 #include <glog/logging.h>
   9
  10 // <https://en.wikipedia.org/wiki/Forward-confirmed_reverse_DNS>
  11
  12 namespace DNS {
  13
  14 std::vector<std::string> fcrdns4(Resolver& res, std::string_view addr)
  15 {
  16   auto const reversed{IP4::reverse(addr)};
  17
  18   // The reverse part, check PTR records.
  19   auto const ptrs = res.get_records(RR_type::PTR, reversed + "in-addr.arpa");
  20
  21   std::vector<std::string> fcrdns;
  22
  23   for (auto const& ptr : ptrs) {
  24     if (std::holds_alternative<DNS::RR_PTR>(ptr)) {
  25       // The forward part, check each PTR for matching A record.
  26       auto const addrs =
  27           res.get_strings(RR_type::A, std::get<DNS::RR_PTR>(ptr).str());
  28       if (std::find(begin(addrs), end(addrs), addr) != end(addrs)) {
  29         fcrdns.push_back(std::get<DNS::RR_PTR>(ptr).str());
  30       }
  31     }
  32   }
  33
  34   // Sort 1st by name length: short to long.
  35   std::sort(begin(fcrdns), end(fcrdns),
  36             [](std::string_view a, std::string_view b) {
  37               if (a.length() != b.length())
  38                 return a.length() < b.length();
  39               return a < b;
  40             });
  41
  42   auto const last = std::unique(fcrdns.begin(), fcrdns.end());
  43   fcrdns.erase(last, fcrdns.end());
  44
  45   return fcrdns;
  46 }
  47
  48 std::vector<std::string> fcrdns6(Resolver& res, std::string_view addr)
  49 {
  50   auto const reversed{IP6::reverse(addr)};
  51
  52   // The reverse part, check PTR records.
  53   auto const ptrs = res.get_records(RR_type::PTR, reversed + "ip6.arpa");
  54
  55   std::vector<std::string> fcrdns;
  56
  57   for (auto const& ptr : ptrs) {
  58     if (std::holds_alternative<DNS::RR_PTR>(ptr)) {
  59       // The forward part, check each PTR for matching AAAA record.
  60       auto const addrs =
  61           res.get_strings(RR_type::AAAA, std::get<DNS::RR_PTR>(ptr).str());
  62       if (std::find(begin(addrs), end(addrs), addr) != end(addrs)) {
  63         fcrdns.push_back(std::get<DNS::RR_PTR>(ptr).str());
  64       }
  65     }
  66   }
  67
  68   // Sort 1st by name length: short to long.
  69   std::sort(begin(fcrdns), end(fcrdns), [](auto a, auto b) {
  70     if (size(a) != size(b))
  71       return size(a) < size(b);
  72     return a < b;
  73   });
  74
  75   return fcrdns;
  76 }
  77
  78 std::vector<std::string> fcrdns(Resolver& res, std::string_view addr)
  79 {
  80   // <https://en.wikipedia.org/wiki/Forward-confirmed_reverse_DNS>
  81
  82   if (IP4::is_address(addr))
  83     return fcrdns4(res, addr);
  84   if (IP6::is_address(addr))
  85     return fcrdns6(res, addr);
  86   LOG(FATAL) << "not a valid IP address " << addr;
  87 }
  88 } // namespace DNS