NAME

       Mail::SpamAssassin::DnsResolver - DNS resolution engine

DESCRIPTION

       This is a DNS resolution engine for SpamAssassin, implemented in order to reduce file
       descriptor usage by Net::DNS and avoid a response collision bug in that module.

METHODS

       $res->load_resolver()
           Load the "Net::DNS::Resolver" object.  Returns 0 if Net::DNS cannot be used, 1 if it
           is available.

       $resolver = $res->get_resolver()
           Return the "Net::DNS::Resolver" object.

       $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

       $res->available_nameservers()
           Get or set a list of currently available nameservers, which is typically a known-to-
           be-good subset of configured nameservers

       $res->connect_sock()
           Re-connect to the first nameserver listed in "/etc/resolv.conf" or similar platform-
           dependent source, as provided by "Net::DNS".

       $res->get_sock()
           Return the "IO::Socket::INET" object used to communicate with the nameserver.

       $packet = new_dns_packet ($domain, $type, $class)
           A wrapper for Net::DNS::Packet::new() which traps a die thrown by it.

           To use this, change calls to "Net::DNS::Resolver::bgsend" from:

               $res->bgsend($domain, $type);

           to:

               $res->bgsend(Mail::SpamAssassin::DnsResolver::new_dns_packet($domain, $type, $class));

       $id = $res->bgsend($domain, $type, $class, $cb)
           DIRECT USE DISCOURAGED, please use bgsend_and_start_lookup in plugins.

           Quite similar to "Net::DNS::Resolver::bgsend", except that when a reply packet
           eventually arrives, and "poll_responses" is called, the callback sub reference $cb
           will be called.

           Note that $type and $class may be "undef", in which case they will default to "A" and
           "IN", respectively.

           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:

             my $id = $self->{resolver}->bgsend($domain, $type, undef, sub {
                   my ($reply, $reply_id, $timestamp) = @_;
                   $self->got_a_reply($reply, $reply_id);
                 });

           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.

       $id = $res->bgread()
           Similar to "Net::DNS::Resolver::bgread".  Reads a DNS packet from a supplied socket,
           decodes it, and returns a Net::DNS::Packet object if successful.  Dies on error.

       $nfound = $res->poll_responses()
           See if there are any "bgsend" reply packets ready, and return the number of such
           packets delivered to their callbacks.

       $res->bgabort()
           Call this to release pending requests from memory, when aborting backgrounded
           requests, or when the scan is complete.  "Mail::SpamAssassin::PerMsgStatus::check"
           calls this before returning.

       $packet = $res->send($name, $type, $class)
           Emulates Net::DNS::Resolver::send().

           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
           AsyncLoop::bgsend_and_start_lookup().  As such it should be avoided for mainstream
           usage.  Currently used through Mail::SPF::Server by the SPF plugin.

       $res->errorstring()
           Little more than a stub for callers expecting this from "Net::DNS::Resolver".

           If called immediately after a call to $res->send this will return "query timed out" if
           the $res->send DNS query timed out.  Otherwise "unknown error or no error" will be
           returned.

           No other errors are reported.

       $res->finish_socket()
           Reset socket when done with it.

       $res->finish()
           Clean up for destruction.