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.

#include "s_dns.h"

ircd::mapi::header
IRCD_MODULE
{
	"Domain Name System Client, Cache & Components",
	[] // init
	{
		ircd::net::dns::resolver_init();
	},
	[] // fini
	{
		ircd::net::dns::resolver_fini();
	}
};

/// 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,
                                opts opts,
                                callback_ipport_one callback)
{
	auto handler
	{
		std::bind(&handle_ipport__A, std::move(callback), ph::_1, ph::_2, ph::_3)
	};

	if(!hp.service)
		return _resolve__A(hp, opts, std::move(handler));

	opts.nxdomain_exceptions = false;
	_resolve__SRV(hp, opts, [opts(opts), handler(std::move(handler))]
	(std::exception_ptr eptr, hostport hp, const rfc1035::record::SRV &record)
	mutable
	{
		if(eptr)
		{
			static const rfc1035::record::A empty;
			return handler(std::move(eptr), hp, empty);
		}

		opts.qtype = 0;
		opts.nxdomain_exceptions = true;
		hp.host = record.tgt?: unmake_SRV_key(hp.host);
		hp.port = record.port? record.port : hp.port;
		_resolve__A(hp, opts, std::move(handler));
	});
}

void
ircd::net::dns::handle_ipport__A(callback_ipport_one callback,
                                 std::exception_ptr eptr,
                                 const hostport &hp,
                                 const rfc1035::record::A &record)
{
	static const ircd::net::not_found no_record
	{
		"Host has no A record"
	};

	if(!eptr && !record.ip4)
		eptr = std::make_exception_ptr(no_record);

	const ipport ipport
	{
		record.ip4, port(hp)
	};

	callback(std::move(eptr), hp, ipport);
}

/// 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,
                              opts opts,
                              callback_SRV_one callback)
{
	static const auto &qtype
	{
		rfc1035::qtype.at("SRV")
	};

	if(unlikely(opts.qtype && opts.qtype != qtype))
		throw error
		{
			"Specified query type '%s' (%u) but user's callback is for SRV records only.",
			rfc1035::rqtype.at(opts.qtype),
			opts.qtype
		};

	if(!opts.qtype)
		opts.qtype = qtype;

	auto handler
	{
		std::bind(&handle__SRV, std::move(callback), ph::_1, ph::_2, ph::_3)
	};

	_resolve__(hp, opts, std::move(handler));
}

void
ircd::net::dns::handle__SRV(callback_SRV_one callback,
                            std::exception_ptr eptr,
                            const hostport &hp,
                            const records &rrs)
{
	static const rfc1035::record::SRV empty;
	static const auto &qtype
	{
		rfc1035::qtype.at("SRV")
	};

	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 != qtype)
			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,
                            opts opts,
                            callback_A_one callback)
{
	static const auto &qtype
	{
		rfc1035::qtype.at("A")
	};

	if(unlikely(opts.qtype && opts.qtype != qtype))
		throw error
		{
			"Specified query type '%s' (%u) but user's callback is for A records only.",
			rfc1035::rqtype.at(opts.qtype),
			opts.qtype
		};

	if(!opts.qtype)
		opts.qtype = qtype;

	auto handler
	{
		std::bind(&handle__A, std::move(callback), ph::_1, ph::_2, ph::_3)
	};

	_resolve__(hp, opts, std::move(handler));
}

void
ircd::net::dns::handle__A(callback_A_one callback,
                          std::exception_ptr eptr,
                          const hostport &hp,
                          const records &rrs)
{
	static const rfc1035::record::A empty;
	static const auto &qtype
	{
		rfc1035::qtype.at("A")
	};

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

	// Get the actual number of A records in these results
	size_t rec_count(0);
	for(size_t i(0); i < rrs.size(); ++i)
		rec_count += rrs.at(i)->type == qtype;

	// Make a random selection for round-robin; rand::integer's range
	// is inclusive so it's shifted down by one.
	uint64_t selection
	{
		rec_count > 1?
			rand::integer(1, rec_count) - 1:
			0
	};

	assert(!rec_count || selection < rec_count);
	assert(rec_count || selection == 0);
	for(size_t i(0); i < rrs.size(); ++i)
	{
		const auto &rr(*rrs.at(i));
		if(rr.type != qtype)
			continue;

		if(selection-- != 0)
			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 &opts,
                           callback cb)
{
	if(unlikely(!opts.qtype))
		throw error
		{
			"A query type is required; not specified; cannot be deduced here."
		};

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

	resolver_call(hp, opts, std::move(cb));
}