mirrors/hello-dns
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

add 'tres', a teaching resolver (167 lines!)

Browse Source
This commit is contained in:
bert hubert
2018-10-15 09:29:54 +02:00
parent 53b6d2cc5a
commit 60804f94d3
2 changed files with 173 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
tdns/Makefile
View File

@ -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 $@

167
tdns/tres.cc Normal file
View File

@ -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;
}