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Kevin A. McGrail
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Mail::SpamAssassin::DnsResolver - DNS resolution engine


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.



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.


Get a list of nameservers as configured by dns_server directives or as provided by Net::DNS, typically from /etc/resolv.conf


Get or set a list of currently available nameservers, which is typically a known-to-be-good subset of configured nameservers


Re-connect to the first nameserver listed in /etc/resolv.conf or similar platform-dependent source, as provided by Net::DNS.


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);


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

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.

$nfound = $res->poll_responses()

See if there are any bgsend reply packets ready, and return the number of such packets delivered to their callbacks.


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.


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.


Reset socket when done with it.


Clean up for destruction.