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.\" ========================================================================
.\"
.IX Title "Mail::SpamAssassin::DnsResolver 3pm"
.TH Mail::SpamAssassin::DnsResolver 3pm "2021-03-26" "perl v5.28.1" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Mail::SpamAssassin::DnsResolver \- DNS resolution engine
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This is a \s-1DNS\s0 resolution engine for SpamAssassin, implemented in order to
reduce file descriptor usage by Net::DNS and avoid a response collision bug in
that module.
.SH "METHODS"
.IX Header "METHODS"
.ie n .IP "$res\->\fBload_resolver()\fR" 4
.el .IP "\f(CW$res\fR\->\fBload_resolver()\fR" 4
.IX Item "$res->load_resolver()"
Load the \f(CW\*(C`Net::DNS::Resolver\*(C'\fR object.  Returns 0 if Net::DNS cannot be used,
1 if it is available.
.ie n .IP "$resolver = $res\->\fBget_resolver()\fR" 4
.el .IP "\f(CW$resolver\fR = \f(CW$res\fR\->\fBget_resolver()\fR" 4
.IX Item "$resolver = $res->get_resolver()"
Return the \f(CW\*(C`Net::DNS::Resolver\*(C'\fR object.
.ie n .IP "$res\->\fBconfigured_nameservers()\fR" 4
.el .IP "\f(CW$res\fR\->\fBconfigured_nameservers()\fR" 4
.IX Item "$res->configured_nameservers()"
Get a list of nameservers as configured by dns_server directives
or as provided by Net::DNS, typically from /etc/resolv.conf
.ie n .IP "$res\->\fBavailable_nameservers()\fR" 4
.el .IP "\f(CW$res\fR\->\fBavailable_nameservers()\fR" 4
.IX Item "$res->available_nameservers()"
Get or set a list of currently available nameservers,
which is typically a known-to-be-good subset of configured nameservers
.ie n .IP "$res\->\fBconnect_sock()\fR" 4
.el .IP "\f(CW$res\fR\->\fBconnect_sock()\fR" 4
.IX Item "$res->connect_sock()"
Re-connect to the first nameserver listed in \f(CW\*(C`/etc/resolv.conf\*(C'\fR or similar
platform-dependent source, as provided by \f(CW\*(C`Net::DNS\*(C'\fR.
.ie n .IP "$res\->\fBget_sock()\fR" 4
.el .IP "\f(CW$res\fR\->\fBget_sock()\fR" 4
.IX Item "$res->get_sock()"
Return the \f(CW\*(C`IO::Socket::INET\*(C'\fR object used to communicate with
the nameserver.
.ie n .IP "$packet = new_dns_packet ($domain, $type, $class)" 4
.el .IP "\f(CW$packet\fR = new_dns_packet ($domain, \f(CW$type\fR, \f(CW$class\fR)" 4
.IX Item "$packet = new_dns_packet ($domain, $type, $class)"
A wrapper for \f(CW\*(C`Net::DNS::Packet::new()\*(C'\fR which traps a die thrown by it.
.Sp
To use this, change calls to \f(CW\*(C`Net::DNS::Resolver::bgsend\*(C'\fR from:
.Sp
.Vb 1
\&    $res\->bgsend($domain, $type);
.Ve
.Sp
to:
.Sp
.Vb 1
\&    $res\->bgsend(Mail::SpamAssassin::DnsResolver::new_dns_packet($domain, $type, $class));
.Ve
.ie n .IP "$id = $res\->bgsend($domain, $type, $class, $cb)" 4
.el .IP "\f(CW$id\fR = \f(CW$res\fR\->bgsend($domain, \f(CW$type\fR, \f(CW$class\fR, \f(CW$cb\fR)" 4
.IX Item "$id = $res->bgsend($domain, $type, $class, $cb)"
Quite similar to \f(CW\*(C`Net::DNS::Resolver::bgsend\*(C'\fR, except that when a reply
packet eventually arrives, and \f(CW\*(C`poll_responses\*(C'\fR is called, the callback
sub reference \f(CW$cb\fR will be called.
.Sp
Note that \f(CW$type\fR and \f(CW$class\fR may be \f(CW\*(C`undef\*(C'\fR, in which case they
will default to \f(CW\*(C`A\*(C'\fR and \f(CW\*(C`IN\*(C'\fR, respectively.
.Sp
The callback sub will be called with three arguments \*(-- the packet that was
delivered, and an id string that fingerprints the query packet and the expected
reply. The third argument is a timestamp (Unix time, floating point), captured
at the time the packet was collected. It is expected that a closure callback
be used, like so:
.Sp
.Vb 4
\&  my $id = $self\->{resolver}\->bgsend($domain, $type, undef, sub {
\&        my ($reply, $reply_id, $timestamp) = @_;
\&        $self\->got_a_reply ($reply, $reply_id);
\&      });
.Ve
.Sp
The callback can ignore the reply as an invalid packet sent to the listening
port if the reply id does not match the return value from bgsend.
.ie n .IP "$id = $res\->\fBbgread()\fR" 4
.el .IP "\f(CW$id\fR = \f(CW$res\fR\->\fBbgread()\fR" 4
.IX Item "$id = $res->bgread()"
Similar to \f(CW\*(C`Net::DNS::Resolver::bgread\*(C'\fR.  Reads a \s-1DNS\s0 packet from
a supplied socket, decodes it, and returns a Net::DNS::Packet object
if successful.  Dies on error.
.ie n .IP "$nfound = $res\->\fBpoll_responses()\fR" 4
.el .IP "\f(CW$nfound\fR = \f(CW$res\fR\->\fBpoll_responses()\fR" 4
.IX Item "$nfound = $res->poll_responses()"
See if there are any \f(CW\*(C`bgsend\*(C'\fR reply packets ready, and return
the number of such packets delivered to their callbacks.
.ie n .IP "$res\->\fBbgabort()\fR" 4
.el .IP "\f(CW$res\fR\->\fBbgabort()\fR" 4
.IX Item "$res->bgabort()"
Call this to release pending requests from memory, when aborting backgrounded
requests, or when the scan is complete.
\&\f(CW\*(C`Mail::SpamAssassin::PerMsgStatus::check\*(C'\fR calls this before returning.
.ie n .IP "$packet = $res\->send($name, $type, $class)" 4
.el .IP "\f(CW$packet\fR = \f(CW$res\fR\->send($name, \f(CW$type\fR, \f(CW$class\fR)" 4
.IX Item "$packet = $res->send($name, $type, $class)"
Emulates \f(CW\*(C`Net::DNS::Resolver::send()\*(C'\fR.
.Sp
This subroutine is a simple synchronous leftover from SpamAssassin version
3.3 and does not participate in packet query caching and callback grouping
as implemented by \fBAsyncLoop::bgsend_and_start_lookup()\fR.  As such it should
be avoided for mainstream usage.  Currently used through Mail::SPF::Server
by the \s-1SPF\s0 plugin.
.ie n .IP "$res\->\fBerrorstring()\fR" 4
.el .IP "\f(CW$res\fR\->\fBerrorstring()\fR" 4
.IX Item "$res->errorstring()"
Little more than a stub for callers expecting this from \f(CW\*(C`Net::DNS::Resolver\*(C'\fR.
.Sp
If called immediately after a call to \f(CW$res\fR\->send this will return
\&\f(CW\*(C`query timed out\*(C'\fR if the \f(CW$res\fR\->send \s-1DNS\s0 query timed out.  Otherwise 
\&\f(CW\*(C`unknown error or no error\*(C'\fR will be returned.
.Sp
No other errors are reported.
.ie n .IP "$res\->\fBfinish_socket()\fR" 4
.el .IP "\f(CW$res\fR\->\fBfinish_socket()\fR" 4
.IX Item "$res->finish_socket()"
Reset socket when done with it.
.ie n .IP "$res\->\fBfinish()\fR" 4
.el .IP "\f(CW$res\fR\->\fBfinish()\fR" 4
.IX Item "$res->finish()"
Clean up for destruction.