construct/modules/s_dns.cc

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

using namespace ircd;

mapi::header
IRCD_MODULE
{
	"Server Domain Names Cache & Modular Components"
};

namespace ircd::net::dns
{
	extern "C" void _resolve__(const hostport &, const opts &, callback);
	extern "C" void _resolve__A(const hostport &, const opts &, callback_A_one);
	extern "C" void _resolve__SRV(const hostport &, const opts &, callback_SRV_one);
	extern "C" void _resolve_ipport(const hostport &, const opts &, callback_ipport_one);
}

/// Convenience composition with a single ipport callback. This is the result of
/// an automatic chain of queries such as SRV and A/AAAA based on the input and
/// intermediate results.
void
ircd::net::dns::_resolve_ipport(const hostport &hp,
                                const opts &opts,
                                callback_ipport_one callback)
{
	//TODO: ip6
	auto calluser{[callback(std::move(callback))]
	(std::exception_ptr eptr, const hostport &hp, const uint32_t &ip)
	{
		if(eptr)
			return callback(std::move(eptr), hp, {});

		if(!ip)
		{
			static const net::not_found no_record
			{
				"Host has no A record"
			};

			return callback(std::make_exception_ptr(no_record), hp, {});
		}

		const ipport ipport{ip, port(hp)};
		callback(std::move(eptr), hp, ipport);
	}};

	if(!hp.service)
		return _resolve__A(hp, opts, [calluser(std::move(calluser))]
		(std::exception_ptr eptr, const hostport &hp, const rfc1035::record::A &record)
		{
			calluser(std::move(eptr), hp, record.ip4);
		});

	auto srv_opts{opts};
	srv_opts.nxdomain_exceptions = false;
	_resolve__SRV(hp, srv_opts, [opts(opts), calluser(std::move(calluser))]
	(std::exception_ptr eptr, hostport hp, const rfc1035::record::SRV &record)
	mutable
	{
		if(eptr)
			return calluser(std::move(eptr), hp, 0);

		if(record.port != 0)
			hp.port = record.port;

		hp.host = record.tgt?: unmake_SRV_key(hp.host);

		// Have to kill the service name to not run another SRV query now.
		hp.service = {};
		opts.srv = {};
		opts.proto = {};

		_resolve__A(hp, opts, [calluser(std::move(calluser))]
		(std::exception_ptr eptr, const hostport &hp, const rfc1035::record::A &record)
		{
			calluser(std::move(eptr), hp, record.ip4);
		});
	});
}

/// Convenience callback with a single SRV record which was selected from
/// the vector with stochastic respect for weighting and priority.
void
ircd::net::dns::_resolve__SRV(const hostport &hp,
                              const opts &opts,
                              callback_SRV_one callback)
{
	_resolve__(hp, opts, [callback(std::move(callback))]
	(std::exception_ptr eptr, const hostport &hp, const vector_view<const rfc1035::record *> rrs)
	{
		static const rfc1035::record::SRV empty;

		if(eptr)
			return callback(std::move(eptr), hp, empty);

		//TODO: prng on weight / prio plz
		for(size_t i(0); i < rrs.size(); ++i)
		{
			const auto &rr{*rrs.at(i)};
			if(rr.type != 33)
				continue;

			const auto &record(rr.as<const rfc1035::record::SRV>());
			return callback(std::move(eptr), hp, record);
		}

		return callback(std::move(eptr), hp, empty);
	});
}

/// Convenience callback with a single A record which was selected from
/// the vector randomly.
void
ircd::net::dns::_resolve__A(const hostport &hp,
                            const opts &opts,
                            callback_A_one callback)
{
	_resolve__(hp, opts, [callback(std::move(callback))]
	(std::exception_ptr eptr, const hostport &hp, const vector_view<const rfc1035::record *> &rrs)
	{
		static const rfc1035::record::A empty;

		if(eptr)
			return callback(std::move(eptr), hp, empty);

		//TODO: prng plz
		for(size_t i(0); i < rrs.size(); ++i)
		{
			const auto &rr{*rrs.at(i)};
			if(rr.type != 1)
				continue;

			const auto &record(rr.as<const rfc1035::record::A>());
			return callback(std::move(eptr), hp, record);
		}

		return callback(std::move(eptr), hp, empty);
	});
}

/// Fundamental callback with a vector of abstract resource records.
void
ircd::net::dns::_resolve__(const hostport &hp,
                           const opts &op,
                           callback cb)
try
{
	using prototype = void (const hostport &, const opts &, callback &&);

	static mods::import<prototype> resolver_resolve
	{
		"s_resolver", "_resolve_"
	};

	if(op.cache_check)
		if(cache::get(hp, op, cb))
			return;

	resolver_resolve(hp, op, std::move(cb));
}
catch(const mods::unavailable &e)
{
	thread_local char buf[128];
	log::error
	{
		log, "Unable to resolve '%s' :%s",
		string(buf, hp),
		e.what()
	};

	throw;
}

namespace ircd::net::dns::cache
{
	std::multimap<std::string, rfc1035::record::A, std::less<>>
	cache_A;

	std::multimap<std::string, rfc1035::record::SRV, std::less<>>
	cache_SRV;

	extern "C" rfc1035::record *_put(const rfc1035::question &, const rfc1035::answer &);
	extern "C" rfc1035::record *_put_error(const rfc1035::question &, const uint &code);
	extern "C" bool _get(const hostport &, const opts &, const callback &);
	extern "C" bool _for_each(const uint16_t &type, const closure &);
}

ircd::rfc1035::record *
ircd::net::dns::cache::_put_error(const rfc1035::question &question,
                                  const uint &code)
{
	const auto &host
	{
		rstrip(question.name, '.')
	};

	assert(!empty(host));
	switch(question.qtype)
	{
		case 1: // A
		{
			auto &map{cache_A};
			auto pit
			{
				map.equal_range(host)
			};

			auto it
			{
				pit.first != pit.second?
					map.erase(pit.first, pit.second):
					pit.first
			};

			rfc1035::record::A record;
			record.ttl = ircd::time() + seconds(dns::cache::clear_nxdomain).count(); //TODO: code
			it = map.emplace_hint(it, host, record);
			return &it->second;
		}

		case 33: // SRV
		{
			auto &map{cache_SRV};
			auto pit
			{
				map.equal_range(host)
			};

			auto it
			{
				pit.first != pit.second?
					map.erase(pit.first, pit.second):
					pit.first
			};

			rfc1035::record::SRV record;
			record.ttl = ircd::time() + seconds(dns::cache::clear_nxdomain).count(); //TODO: code
			it = map.emplace_hint(it, host, record);
			return &it->second;
		}
	}

	return nullptr;
}

ircd::rfc1035::record *
ircd::net::dns::cache::_put(const rfc1035::question &question,
                            const rfc1035::answer &answer)
{
	const auto &host
	{
		rstrip(question.name, '.')
	};

	assert(!empty(host));
	switch(answer.qtype)
	{
		case 1: // A
		{
			auto &map{cache_A};
			auto pit
			{
				map.equal_range(host)
			};

			auto it(pit.first);
			while(it != pit.second)
			{
				const auto &rr{it->second};
				if(rr == answer)
					it = map.erase(it);
				else
					++it;
			}

			const auto &iit
			{
				map.emplace_hint(it, host, answer)
			};

			return &iit->second;
		}

		case 33: // SRV
		{
			auto &map{cache_SRV};
			auto pit
			{
				map.equal_range(host)
			};

			auto it(pit.first);
			while(it != pit.second)
			{
				const auto &rr{it->second};
				if(rr == answer)
					it = map.erase(it);
				else
					++it;
			}

			const auto &iit
			{
				map.emplace_hint(it, host, answer)
			};

			return &iit->second;
		}

		default:
			return nullptr;
	}
}

/// This function has an opportunity to respond from the DNS cache. If it
/// returns true, that indicates it responded by calling back the user and
/// nothing further should be done for them. If it returns false, that
/// indicates it did not respond and to proceed normally. The response can
/// be of a cached successful result, or a cached error. Both will return
/// true.
bool
ircd::net::dns::cache::_get(const hostport &hp,
                            const opts &opts,
                            const callback &cb)
{
	// It's no use putting the result record array on the stack in case this
	// function is either called from an ircd::ctx or calls back an ircd::ctx.
	// If the ctx yields the records can still be evicted from the cache.
	// It's better to just force the user to conform here rather than adding
	// ref counting and other pornographic complications to this cache.
	const ctx::critical_assertion ca;
	thread_local std::array<const rfc1035::record *, MAX_COUNT> record;
	std::exception_ptr eptr;
	size_t count{0};

	//TODO: Better deduction
	if(hp.service || opts.srv) // deduced SRV query
	{
		assert(!empty(host(hp)));
		thread_local char srvbuf[512];
		const string_view srvhost
		{
			make_SRV_key(srvbuf, hp, opts)
		};

		auto &map{cache_SRV};
		const auto pit{map.equal_range(srvhost)};
		if(pit.first == pit.second)
			return false;

		const auto &now{ircd::time()};
		for(auto it(pit.first); it != pit.second; )
		{
			const auto &rr{it->second};

			// Cached entry is too old, ignore and erase
			if(rr.ttl < now)
			{
				it = map.erase(it);
				continue;
			}

			// Cached entry is a cached error, we set the eptr, but also
			// include the record and increment the count like normal.
			if((!rr.tgt || !rr.port) && opts.nxdomain_exceptions && !eptr)
			{
				//TODO: we don't cache what the error was, assuming it's
				//TODO: NXDomain can be incorrect and in bad ways downstream...
				static const auto rcode{3}; //NXDomain
				eptr = std::make_exception_ptr(rfc1035::error
				{
					"protocol error #%u (cached) :%s", rcode, rfc1035::rcode.at(rcode)
				});
			}

			if(count < record.size())
				record.at(count++) = &rr;

			++it;
		}
	}
	else // Deduced A query (for now)
	{
		auto &map{cache_A};
		const auto &key{rstrip(host(hp), '.')};
		if(unlikely(empty(key)))
			return false;

		const auto pit{map.equal_range(key)};
		if(pit.first == pit.second)
			return false;

		const auto &now{ircd::time()};
		for(auto it(pit.first); it != pit.second; )
		{
			const auto &rr{it->second};

			// Cached entry is too old, ignore and erase
			if(rr.ttl < now)
			{
				it = map.erase(it);
				continue;
			}

			// Cached entry is a cached error, we set the eptr, but also
			// include the record and increment the count like normal.
			if(!rr.ip4 && !eptr)
			{
				//TODO: we don't cache what the error was, assuming it's
				//TODO: NXDomain can be incorrect and in bad ways downstream...
				static const auto rcode{3}; //NXDomain
				eptr = std::make_exception_ptr(rfc1035::error
				{
					"protocol error #%u (cached) :%s", rcode, rfc1035::rcode.at(rcode)
				});
			}

			if(count < record.size())
				record.at(count++) = &rr;

			++it;
		}
	}

	assert(count || !eptr);        // no error if no cache response
	assert(!eptr || count == 1);   // if error, should only be one entry.

	if(count)
		cb(std::move(eptr), hp, vector_view<const rfc1035::record *>(record.data(), count));

	return count;
}

bool
ircd::net::dns::cache::_for_each(const uint16_t &type,
                                 const closure &closure)
{
	switch(type)
	{
		case 1: // A
		{
			for(const auto &pair : cache_A)
			{
				const auto &host(pair.first);
				const auto &record(pair.second);
				if(!closure(host, record))
					return false;
			}

			return true;
		}

		case 33: // SRV
		{
			for(const auto &pair : cache_SRV)
			{
				const auto &host(pair.first);
				const auto &record(pair.second);
				if(!closure(host, record))
					return false;
			}

			return true;
		}

		default:
			return true;
	}
}