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construct/include/ircd/net/dns.h

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// 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.
#pragma once
#define HAVE_IRCD_NET_DNS_H
namespace ircd::net
{
struct dns extern dns;
}
/// DNS resolution suite.
///
/// This is a singleton class; public usage is to make calls on the singleton
/// object like `ircd::net::dns()` etc.
///
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/// Note that in returned rfc1035::records that TTL values are modified from their
/// original value to an absolute epoch time in seconds which we use for caching.
/// This modification only occurs if the dns query allows result caching (default).
///
struct ircd::net::dns
{
struct opts;
struct resolver;
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struct cache;
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struct cache static cache;
struct resolver static *resolver;
struct opts static const opts_default;
using callback = std::function<void (std::exception_ptr, const hostport &, const vector_view<const rfc1035::record *> &)>;
using callback_A_one = std::function<void (std::exception_ptr, const hostport &, const rfc1035::record::A &)>;
using callback_SRV_one = std::function<void (std::exception_ptr, const hostport &, const rfc1035::record::SRV &)>;
using callback_ipport_one = std::function<void (std::exception_ptr, const hostport &, const ipport &)>;
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// (internal) generate strings for rfc1035 questions or dns::cache keys.
static string_view make_SRV_key(const mutable_buffer &out, const hostport &, const opts &);
static string_view unmake_SRV_key(const string_view &);
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public:
// Cache warming
static const callback_A_one prefetch_A;
static const callback_SRV_one prefetch_SRV;
static const callback_ipport_one prefetch_ipport;
// Callback-based interface
void operator()(const hostport &, const opts &, callback);
void operator()(const hostport &, const opts &, callback_A_one);
void operator()(const hostport &, const opts &, callback_SRV_one);
void operator()(const hostport &, const opts &, callback_ipport_one);
// Callback-based interface (default options)
template<class Callback> void operator()(const hostport &, Callback&&);
};
/// DNS resolution options
struct ircd::net::dns::opts
{
/// Overrides the SRV query to make for this resolution. If empty an
/// SRV query may still be made from other deductions. This string is
/// copied at the start of the resolution. It must be a fully qualified
/// SRV query string: Example: "_matrix._tcp."
string_view srv;
/// Specifies the SRV protocol part when deducing the SRV query to be
/// made. This is used when the net::hostport.service string is just
/// the name of the service like "matrix" so we then use this value
/// to build the protocol part of the SRV query string. It is ignored
/// if `srv` is set or if no service is specified (thus no SRV query is
/// made in the first place).
string_view proto{"tcp"};
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/// Whether the dns::cache is checked and may respond to the query.
bool cache_check {true};
/// Whether the result of this lookup from the nameserver should be
/// added to the cache. If true, the TTL value in result records will be
/// modified to an absolute expiration time. If false, no modification
/// occurs from the original value.
bool cache_result {true};
/// When false, nxdomain errors are not treated as exceptions and the
/// eptr of a callback will not be set. Instead, the returned record
/// will contain some nulled / empty data and the user is obliged to
/// know that this is not a real DNS answer but the error's result.
/// Note: Requires that cache_result is set to true. If not, this value
/// is ignored and always considered to be set to true; this is because
/// the returned record is a reference to the cached error.
bool nxdomain_exceptions {true};
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};
/// (internal) DNS cache
struct ircd::net::dns::cache
{
static conf::item<seconds> min_ttl;
static conf::item<seconds> clear_nxdomain;
std::multimap<std::string, rfc1035::record::A, std::less<>> A;
std::multimap<std::string, rfc1035::record::SRV, std::less<>> SRV;
public:
bool get(const hostport &, const opts &, const callback &);
rfc1035::record *put(const rfc1035::question &, const rfc1035::answer &);
rfc1035::record *put_error(const rfc1035::question &, const uint &code);
};
template<class Callback>
void
ircd::net::dns::operator()(const hostport &hostport,
Callback&& callback)
{
operator()(hostport, opts_default, std::forward<Callback>(callback));
}