Mail::SpamAssassin::DnsResolver(3) User Contributed Perl Documentation Mail::SpamAssassin::DnsResolver(3)

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)
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.
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.

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.
2023-07-26 perl v5.38.0