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https://github.com/matrix-construct/construct
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ircd::net::dns: Add crucial support for caching errors.
This commit is contained in:
Jason Volk
parent
b166d0744d
commit
d54d6b687c
2 changed files with 94 additions and 18 deletions
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@ -36,6 +36,7 @@ struct ircd::net::dns::resolver
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char reply[64_KiB] alignas(16); // Buffer for recv
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bool handle_error(const error_code &ec) const;
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bool handle_error(const header &, const rfc1035::question &, const dns::opts &);
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void handle_reply(const header &, const const_buffer &body, tag &);
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void handle_reply(const header &, const const_buffer &body);
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void handle(const error_code &ec, const size_t &) noexcept;
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111
ircd/net.cc
111
ircd/net.cc
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@ -2267,12 +2267,20 @@ ircd::net::dns::operator()(const hostport &hostport,
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(*resolver)(hostport, opts, std::move(cb));
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}
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/// This function has an opportunity to respond from the DNS cache. If it
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/// returns true, that indicates it responded by calling back the user and
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/// nothing further should be done for them. If it returns false, that
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/// indicates it did not respond and to proceed normally. The response can
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/// be of a cached successful result, or a cached error. Both will return
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/// true.
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///
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bool
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ircd::net::dns::query_cache(const hostport &hp,
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const opts &opts,
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const callback &cb)
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{
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thread_local const rfc1035::record *record[resolver::MAX_COUNT];
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std::exception_ptr eptr;
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size_t count{0};
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//TODO: Better deduction
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@ -2292,21 +2300,30 @@ ircd::net::dns::query_cache(const hostport &hp,
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const auto &now{ircd::time()};
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for(auto it(pit.first); it != pit.second; )
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{
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const auto &rr{pit.first->second};
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const auto &rr{it->second};
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// Cached entry is too old, ignore and erase
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if(rr.ttl < now)
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{
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it = map.erase(it);
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continue;
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}
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// Cached entry is a cached error, we set the eptr, but also
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// include the record and increment the count like normal.
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assert(!eptr);
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if(!rr.tgt)
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{
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const auto rcode{3}; //NXDomain
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eptr = std::make_exception_ptr(rfc1035::error
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{
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"protocol error #%u (cached) :%s", rcode, rfc1035::rcode.at(rcode)
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});
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}
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record[count++] = &rr;
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++it;
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}
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if(count)
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cb({}, vector_view<const rfc1035::record *>(record, count));
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return count;
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}
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else // Deduced A query (for now)
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{
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@ -2318,22 +2335,39 @@ ircd::net::dns::query_cache(const hostport &hp,
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const auto &now{ircd::time()};
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for(auto it(pit.first); it != pit.second; )
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{
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const auto &rr{pit.first->second};
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const auto &rr{it->second};
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// Cached entry is too old, ignore and erase
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if(rr.ttl < now)
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{
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it = map.erase(it);
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continue;
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}
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// Cached entry is a cached error, we set the eptr, but also
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// include the record and increment the count like normal.
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assert(!eptr);
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if(!rr.ip4)
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{
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const auto rcode{3}; //NXDomain
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eptr = std::make_exception_ptr(rfc1035::error
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{
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"protocol error #%u (cached) :%s", rcode, rfc1035::rcode.at(rcode)
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});
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}
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record[count++] = &rr;
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++it;
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}
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if(count)
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cb({}, vector_view<const rfc1035::record *>(record, count));
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return count;
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}
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assert(count || !eptr); // no error if no cache response
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assert(!eptr || count == 1); // if error, should only be one entry.
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if(count)
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cb(std::move(eptr), vector_view<const rfc1035::record *>(record, count));
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return count;
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}
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ircd::string_view
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@ -2639,12 +2673,6 @@ try
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"Response header is marked as 'Query' and not 'Response'"
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};
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if(header.rcode)
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throw rfc1035::error
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{
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"protocol error: %s", rfc1035::rcode.at(header.rcode)
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};
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if(header.qdcount > MAX_COUNT || header.ancount > MAX_COUNT)
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throw error
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{
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@ -2661,6 +2689,12 @@ try
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for(size_t i(0); i < header.qdcount; ++i)
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consume(buffer, size(qd.at(i).parse(buffer)));
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if(!handle_error(header, qd.at(0), tag.opts))
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throw rfc1035::error
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{
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"protocol error #%u :%s", header.rcode, rfc1035::rcode.at(header.rcode)
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};
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// Answers are parsed into this buffer
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thread_local std::array<rfc1035::answer, MAX_COUNT> an;
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for(size_t i(0); i < header.ancount; ++i)
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@ -2753,6 +2787,47 @@ catch(const std::exception &e)
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tag.cb(std::current_exception(), {});
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}
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bool
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ircd::net::dns::resolver::handle_error(const header &header,
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const rfc1035::question &q,
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const dns::opts &opts)
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{
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switch(header.rcode)
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{
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case 0: // NoError; continue
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return true;
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case 3: // NXDomain; exception
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{
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if(opts.cache_result) switch(q.qtype)
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{
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case 1: // A
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{
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const auto &host{rstrip(q.name, '.')};
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rfc1035::record::A record;
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record.ttl = ircd::time() + hours(24).count(); //TODO: conf
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cache.A.emplace(host, record);
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break;
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}
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case 33:
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{
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const auto &host{rstrip(q.name, '.')};
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rfc1035::record::SRV record;
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record.ttl = ircd::time() + hours(24).count(); //TODO: conf
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cache.SRV.emplace(host, record);
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break;
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}
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}
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return false;
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}
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default: // Unhandled error; exception
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return false;
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}
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}
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bool
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ircd::net::dns::resolver::handle_error(const error_code &ec)
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const
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