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ircd::net::dns: Allow an exception to calling back with nxdomain as an exception.

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This commit is contained in:
Jason Volk 2018-04-28 16:42:18 -07:00
parent 1d408173dc
commit 4e796c896a
3 changed files with 37 additions and 7 deletions
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9
include/ircd/net/dns.h
View file

@ -84,6 +84,15 @@ struct ircd::net::dns::opts
/// 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};
};
/// (internal) DNS cache

2
include/ircd/net/resolver.h
View file

@ -41,7 +41,7 @@ struct ircd::net::dns::resolver
char reply[64_KiB] alignas(16); // Buffer for recv
bool handle_error(const error_code &ec) const;
bool handle_error(const header &, const rfc1035::question &, const dns::opts &);
bool handle_error(const header &, const rfc1035::question &, tag &);
void handle_reply(const header &, const const_buffer &body, tag &);
void handle_reply(const header &, const const_buffer &body);
void handle(const error_code &ec, const size_t &) noexcept;

33
ircd/net.cc
View file

@ -2384,7 +2384,7 @@ ircd::net::dns::prefetch_A{[]
/// an automatic chain of queries such as SRV and A/AAAA based on the input and
/// intermediate results.
void
ircd::net::dns::operator()(const hostport &hostport,
ircd::net::dns::operator()(const hostport &hp,
const opts &opts,
callback_ipport_one callback)
{
@ -2706,7 +2706,7 @@ ircd::net::dns::cache::get(const hostport &hp,
// Cached entry is a cached error, we set the eptr, but also
// include the record and increment the count like normal.
assert(!eptr);
if(!rr.tgt || !rr.port)
if((!rr.tgt || !rr.port) && opts.nxdomain_exceptions)
{
//TODO: we don't cache what the error was, assuming it's
//TODO: NXDomain can be incorrect and in bad ways downstream...
@ -3176,7 +3176,7 @@ try
for(size_t i(0); i < header.qdcount; ++i)
consume(buffer, size(qd.at(i).parse(buffer)));
if(!handle_error(header, qd.at(0), tag.opts))
if(!handle_error(header, qd.at(0), tag))
throw rfc1035::error
{
"protocol error #%u :%s", header.rcode, rfc1035::rcode.at(header.rcode)
@ -3268,13 +3268,16 @@ catch(const std::exception &e)
e.what());
if(tag.cb)
{
assert(tag.opts.nxdomain_exceptions);
tag.cb(std::current_exception(), {});
}
}
bool
ircd::net::dns::resolver::handle_error(const header &header,
const rfc1035::question &question,
const dns::opts &opts)
tag &tag)
{
switch(header.rcode)
{
@ -3282,10 +3285,28 @@ ircd::net::dns::resolver::handle_error(const header &header,
return true;
case 3: // NXDomain; exception
if(opts.cache_result)
cache.put_error(question, header.rcode);
{
if(!tag.opts.cache_result)
return false;
const auto *record
{
cache.put_error(question, header.rcode)
};
// When the user doesn't want an eptr for nxdomain we just make
// their callback here and then null the cb pointer so it's not
// called again. It is done here because we have a reference to
// the cached error record readily accessible.
if(!tag.opts.nxdomain_exceptions && tag.cb)
{
assert(record);
tag.cb({}, vector_view<const rfc1035::record *>(&record, 1));
tag.cb = {};
}
return false;
}
default: // Unhandled error; exception
return false;