#!/usr/bin/perl -w
# Copyright (c) 2007, Rhodes University, All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
#  * Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
#  * Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
#  * Neither the name of Rhodes University nor the names of its contributors
#    may be used to endorse or promote products derived from this software
#    without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
# IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
# LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
# NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#
use strict;
use Net::Ping;
use IPC::Shareable;
use vars qw/%mxs/;
tie %mxs, 'IPC::Shareable', 'tsmx', { 'create' => 1 };

sub test_mx ($) {
  my $mx = lc(shift);

  # shortcut - immediately return if we've checked in the last five minutes
  return uc ($mxs{$mx}[0]) if (exists ($mxs{$mx}) and $mxs{$mx}[1] > time () - 300);

  # do a TCP ping
  my $p = Net::Ping->new ('tcp', 3);
  $p->{'port_num'} = getservbyname ('smtp', 'tcp');
  my $alive = $p->ping ($mx);
  
  # work out what state we're in and cache it
  $mxs{$mx}[1] = time ();
  if (defined ($alive) and $alive) {
    $mxs{$mx}[0] = 'true';
  } else {
    $mxs{$mx}[0] = 'false';
  }

  # let the program know whether or not the MX is alive
  return $mxs{$mx}[0];  

}