dns features (#1404)

* add some dns txt records for stuff we want to expose

* fix txt records

* txt records for snode info

* dont send cname as it mangles the response

* check for 3 parts not 3 characters

llarp/dns/message.cpp

@@ -322,6 +322,32 @@ namespace llarp
       }
     }
 
+    void
+    Message::AddTXTReply(std::string str, RR_TTL_t ttl)
+    {
+      auto& rec = answers.emplace_back();
+      rec.rr_name = questions[0].qname;
+      rec.rr_class = qClassIN;
+      rec.rr_type = qTypeTXT;
+      rec.ttl = ttl;
+      std::array<byte_t, 1024> tmp{};
+      llarp_buffer_t buf(tmp);
+      while (not str.empty())
+      {
+        const auto left = std::min(str.size(), size_t{256});
+        const auto sub = str.substr(0, left);
+        uint8_t byte = left;
+        *buf.cur = byte;
+        buf.cur++;
+        if (not buf.write(sub.begin(), sub.end()))
+          throw std::length_error("text record too big");
+        str = str.substr(left);
+      }
+      buf.sz = buf.cur - buf.base;
+      rec.rData.resize(buf.sz);
+      std::copy_n(buf.base, buf.sz, rec.rData.data());
+    }
+
     void Message::AddNXReply(RR_TTL_t)
     {
       if (questions.size())

llarp/dns/message.hpp

@@ -74,6 +74,9 @@ namespace llarp
       void
       AddNSReply(std::string name, RR_TTL_t ttl = 1);
 
+      void
+      AddTXTReply(std::string value, RR_TTL_t ttl = 1);
+
       bool
       Encode(llarp_buffer_t* buf) const override;
 

llarp/dns/question.cpp

@@ -64,6 +64,13 @@ namespace llarp
       return (qname == "localhost.loki." or llarp::ends_with(qname, ".localhost.loki."));
     }
 
+    bool
+    Question::HasSubdomains() const
+    {
+      const auto parts = split(qname, ".", true);
+      return parts.size() >= 3;
+    }
+
     std::string
     Question::Subdomains() const
     {

llarp/dns/question.hpp

@@ -44,6 +44,10 @@ namespace llarp
       bool
       IsLocalhost() const;
 
+      /// return true if we have subdomains in ths question
+      bool
+      HasSubdomains() const;
+
       /// get subdomain(s), if any, from qname
       std::string
       Subdomains() const;

llarp/handlers/tun.cpp

@@ -387,8 +387,64 @@ namespace llarp
         lnsName = nameparts[nameparts.size() - 2];
         lnsName += ".loki"sv;
       }
+      if (msg.questions[0].qtype == dns::qTypeTXT)
+      {
+        RouterID snode;
+        if (snode.FromString(qname))
+        {
+          m_router->LookupRouter(snode, [reply, msg = std::move(msg)](const auto& found) mutable {
+            if (found.empty())
+            {
+              msg.AddNXReply();
+            }
+            else
+            {
+              std::stringstream ss;
+              for (const auto& rc : found)
+                rc.ToTXTRecord(ss);
+              msg.AddTXTReply(ss.str());
+            }
+            reply(msg);
+          });
+          return true;
+        }
+        else if (msg.questions[0].IsLocalhost() and msg.questions[0].HasSubdomains())
+        {
+          const auto subdomain = msg.questions[0].Subdomains();
+          if (subdomain == "exit")
+          {
+            if (HasExit())
+            {
+              std::stringstream ss;
+              m_ExitMap.ForEachEntry([&ss](const auto& range, const auto& exit) {
+                ss << range.ToString() << "=" << exit.ToString() << "; ";
+              });
+              msg.AddTXTReply(ss.str());
+            }
+            else
+            {
+              msg.AddNXReply();
+            }
+          }
+          else if (subdomain == "netid")
+          {
+            std::stringstream ss;
+            ss << "netid=" << m_router->rc().netID.ToString() << ";";
+            msg.AddTXTReply(ss.str());
+          }
+          else
+          {
+            msg.AddNXReply();
+          }
+        }
+        else
+        {
+          msg.AddNXReply();
+        }
 
-      if (msg.questions[0].qtype == dns::qTypeMX)
+        reply(msg);
+      }
+      else if (msg.questions[0].qtype == dns::qTypeMX)
       {
         // mx record
         service::Address addr;
@@ -508,7 +564,6 @@ namespace llarp
                   return;
                 }
                 LogInfo(name, " ", lnsName, " resolved to ", maybe->ToString());
-                msg->AddCNAMEReply(maybe->ToString());
                 ReplyToLokiDNSWhenReady(*maybe, msg, isV6);
               });
         }

llarp/router_contact.cpp

@@ -105,6 +105,21 @@ namespace llarp
     return false;
   }
 
+  std::ostream&
+  RouterContact::ToTXTRecord(std::ostream& out) const
+  {
+    for (const auto& addr : addrs)
+    {
+      out << "ai_addr=" << addr.toIpAddress() << "; ";
+      out << "ai_pk=" << addr.pubkey.ToHex() << "; ";
+    }
+    out << "updated=" << last_updated.count() << "; ";
+    out << "onion_pk=" << enckey.ToHex() << "; ";
+    if (routerVersion.has_value())
+      out << "router_version=" << routerVersion->ToString() << "; ";
+    return out;
+  }
+
   bool
   RouterContact::BEncodeSignedSection(llarp_buffer_t* buf) const
   {

llarp/router_contact.hpp

@@ -135,6 +135,9 @@ namespace llarp
     bool
     BEncodeSignedSection(llarp_buffer_t* buf) const;
 
+    std::ostream&
+    ToTXTRecord(std::ostream& out) const;
+
     bool
     operator==(const RouterContact& other) const
     {