From 60804f94d37dab07ee6dd0b378c618619fda4bf0 Mon Sep 17 00:00:00 2001
From: bert hubert <bert.hubert@netherlabs.nl>
Date: Mon, 15 Oct 2018 09:29:54 +0200
Subject: [PATCH] add 'tres', a teaching resolver (167 lines!)

---
 tdns/Makefile |   8 ++-
 tdns/tres.cc  | 167 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 173 insertions(+), 2 deletions(-)
 create mode 100644 tdns/tres.cc

diff --git a/tdns/Makefile b/tdns/Makefile
index b2e0640..efcefd4 100644
--- a/tdns/Makefile
+++ b/tdns/Makefile
@@ -1,14 +1,14 @@
 CXXFLAGS:=-std=gnu++14 -Wall -O2 -MMD -MP -ggdb -Iext/simplesocket -Iext/catch -pthread
 CFLAGS:= -Wall -O2 -MMD -MP -ggdb 
 
-PROGRAMS = tdns tdig tdns-c-test
+PROGRAMS = tdns tdig tres tdns-c-test
 
 all: $(PROGRAMS)
 
 clean:
 	rm -f *~ *.o *.d test $(PROGRAMS)
 
-check: testrunner tdns tdig
+check: testrunner tdns tdig 
 	./testrunner
 	cd tests ; ./basic
 
@@ -20,6 +20,10 @@ tdns: tdns.o record-types.o dns-storage.o dnsmessages.o contents.o ext/simplesoc
 tdig: tdig.o record-types.o dns-storage.o dnsmessages.o ext/simplesocket/comboaddress.o ext/simplesocket/sclasses.o ext/simplesocket/swrappers.o
 	g++ -std=gnu++14 $^ -o $@ -pthread
 
+tres: tres.o record-types.o dns-storage.o dnsmessages.o ext/simplesocket/comboaddress.o ext/simplesocket/sclasses.o ext/simplesocket/swrappers.o
+	g++ -std=gnu++14 $^ -o $@ -pthread
+
+
 tdns-c-test: tdns-c-test.o tdns-c.o record-types.o dns-storage.o dnsmessages.o ext/simplesocket/comboaddress.o ext/simplesocket/sclasses.o ext/simplesocket/swrappers.o
 	g++ -std=gnu++14 $^ -o $@ 
 
diff --git a/tdns/tres.cc b/tdns/tres.cc
new file mode 100644
index 0000000..6f1724c
--- /dev/null
+++ b/tdns/tres.cc
@@ -0,0 +1,167 @@
+#include <cstdint>
+#include <vector>
+#include <map>
+#include <stdexcept>
+#include "sclasses.hh"
+#include <thread>
+#include <signal.h>
+#include "record-types.hh"
+
+/*! 
+   @file
+   @brief Tiny resolver
+*/
+
+using namespace std;
+
+multimap<DNSName, ComboAddress> g_root;
+
+ComboAddress getIP(const std::unique_ptr<RRGen>& rr)
+{
+  ComboAddress ret;
+  if(auto ptr = dynamic_cast<AGen*>(rr.get()))
+    ret=ptr->getIP();
+  else if(auto ptr = dynamic_cast<AAAAGen*>(rr.get()))
+    ret=ptr->getIP();
+
+  ret.sin4.sin_port = htons(53);
+  return ret;
+}
+
+vector<std::unique_ptr<RRGen>> resolveAt(const DNSName& dn, const DNSType& dt, int depth=0, const multimap<DNSName, ComboAddress>& servers=g_root)
+{
+  std::string prefix(depth, ' ');
+  prefix += dn.toString() + " ";
+  DNSMessageWriter dmw(dn, dt);
+          
+  dmw.dh.rd = false;
+  dmw.randomizeID();
+  dmw.setEDNS(4000, false);
+
+  vector<std::unique_ptr<RRGen>> ret;
+  for(auto& sp : servers) {
+    ret.clear();
+    ComboAddress server=sp.second;
+    server.sin4.sin_port = htons(53);
+
+    try {
+      cout << prefix<<"Sending to server "<<server.toString()<<endl;
+      Socket sock(server.sin4.sin_family, SOCK_DGRAM);
+      SConnect(sock, server);
+      SWrite(sock, dmw.serialize());
+      
+      string resp =SRecvfrom(sock, 65535, server); 
+      
+      DNSMessageReader dmr(resp);
+      
+      DNSSection rrsection;
+      uint32_t ttl;
+      
+      DNSName rrdn;
+      DNSType rrdt;
+      
+      dmr.getQuestion(rrdn, rrdt);
+      
+      cout << prefix<<"Received "<<resp.size()<<" byte response with RCode "<<(RCode)dmr.dh.rcode<<", qname " <<dn<<", qtype "<<dt<<", aa: "<<dmr.dh.aa << endl;
+      
+      // check rrdn == dn, rrdt == dt, transaction id
+
+      if((RCode)dmr.dh.rcode == RCode::Nxdomain) {
+        cout << prefix<<"Got an Nxdomain, it does not exist"<<endl;
+        return ret;
+      }
+      if((RCode)dmr.dh.rcode != RCode::Noerror) {
+        throw std::runtime_error(string("Answer from authoritative server had an error: ") + toString((RCode)dmr.dh.rcode));
+      }
+      if(dmr.dh.aa) {
+        cout << prefix<<"Answer says it is authoritative!"<<endl;
+      }
+      
+      std::unique_ptr<RRGen> rr;
+      set<DNSName> nsses;
+      multimap<DNSName, ComboAddress> addresses;
+      while(dmr.getRR(rrsection, rrdn, rrdt, ttl, rr)) {
+        cout << prefix << rrsection<<" "<<rrdn<< " IN " << rrdt << " " << ttl << " " <<rr->toString()<<endl;
+        if(dmr.dh.aa==1) {
+          if(dn == rrdn && dt == rrdt) {
+            cout << prefix<<"We got an answer to our question!"<<endl;
+            ret.push_back(std::move(rr));
+          }
+          if(dn == rrdn && rrdt == DNSType::CNAME) {
+            DNSName target = dynamic_cast<CNAMEGen*>(rr.get())->d_name;
+            cout << prefix<<"We got a CNAME to " << target <<", chasing"<<endl;
+            return resolveAt(target, dt, depth + 1);
+          }
+        }
+        else {
+          if(rrsection == DNSSection::Authority && rrdt == DNSType::NS)
+            nsses.insert(dynamic_cast<NSGen*>(rr.get())->d_name);
+          else if(rrsection == DNSSection::Additional && nsses.count(rrdn) && (rrdt == DNSType::A || rrdt == DNSType::AAAA)) {
+            addresses.insert({rrdn, getIP(rr)});
+          }
+        }
+      }
+      if(!ret.empty()) {
+        cout << prefix<<"Done, returning "<<ret.size()<<" results\n";
+        return ret;
+      }
+      if(!addresses.empty()) {
+        cout << prefix<<"Have "<<addresses.size()<<" IP addresses to iterate to: ";
+        for(const auto& p : addresses)
+          cout << p.first <<"="<<p.second.toString()<<" ";
+        cout <<endl;
+        return resolveAt(dn, dt, depth+1, addresses);
+      }
+      else {
+        cout << prefix<<"Don't have a resolved nameserver to ask, trying to resolve "<<nsses.size()<<" names"<<endl;
+        multimap<DNSName, ComboAddress> newns;
+        for(const auto& name: nsses) {
+          cout << prefix<<"Attempting to resolve NS "<<name<<endl;
+          auto result = resolveAt(name, DNSType::A, depth+1);
+          cout << prefix<<"Got "<<result.size()<<" nameserver IPv4 addresses, adding to list"<<endl;
+          for(const auto& res : result)
+            newns.insert({name, getIP(res)});
+          result = resolveAt(name, DNSType::AAAA, depth+1);
+          cout << prefix<<"Got "<<result.size()<<" nameserver IPv6 addresses, adding to list"<<endl;
+          for(const auto& res : result)
+            newns.insert({name, getIP(res)});
+        }
+        cout << prefix<<"We now have "<<newns.size()<<" resolved names to try"<<endl;
+        auto res2 = resolveAt(dn, dt, depth+1, newns);
+        if(!res2.empty())
+          return res2;
+      }
+      break;
+    }
+    catch(std::exception& e) {
+      cout << prefix <<"Error resolving: " << e.what() << endl;
+    }
+  }
+  return ret;
+}
+
+int main(int argc, char** argv)
+try
+{
+  if(argc != 3) {
+    cerr<<"Syntax: tres name type\n";
+    return(EXIT_FAILURE);
+  }
+  signal(SIGPIPE, SIG_IGN);
+
+  DNSName dn = makeDNSName(argv[1]);
+  DNSType dt = makeDNSType(argv[2]);
+  g_root = {{makeDNSName("k.root-servers.net"), ComboAddress("193.0.14.129", 53)}};;
+
+  auto res = resolveAt(dn, dt);
+  cout<<"Result: "<<endl;
+  for(const auto& r : res) {
+    cout<<r->toString()<<endl;
+  }
+  
+}
+catch(std::exception& e)
+{
+  cerr<<"Fatal error: "<<e.what()<<endl;
+  return EXIT_FAILURE;
+}