#!/usr/bin/perl -w
#
# DNS monitor
#

$| = 1;

my $help = grep(/-h/, @ARGV);
my $verbose = grep(/-v/, @ARGV);

my $noemail = grep(/--noemail/, @ARGV);

die "Usage: $0 [-h] [-v] [--noemail]\n" if $help;

my $email_to = $ENV{'USER'};

die "Env.variable USER is not set" if ! $email_to;

my $confLog    = "/home/olchansk/public_html/pingmon/dnsmon.log";

open(LOG,">>$confLog") || die "Cannot write \"$confLog\": $!\n";

my $emailsubject;
my $emailtext;

#my $h = "smtp.triumf.ca";
my $h = "142.90.100.19";

my $now = time();

my $dns_start = time();
my $gethost = `host $h 2>&1`;
my $dns_done = time();
my $dns_time = $dns_done - $dns_start;

#print "host $h dns time $dns_time\n";

# ladd00.triumf.ca has address 142.90.111.60
#
# host linstore
# linstore.triumf.ca is an alias for linstore.dmz.triumf.ca.
# linstore.dmz.triumf.ca has address 142.90.152.208
# linstore.dmz.triumf.ca has address 142.90.152.209

foreach my $h (sort split(/\n/, $gethost)) {
  if ($h =~ /has address (\d+.*)/) {
    $xip .= "," if ($xip);
    $xip .= $1;
    #print "[$h] IP address [$ip]\n";
  }
  if ($h =~ /alias for (\w+.*)\./) {
    $xip .= "," if ($xip);
    $xip .= "$1";
    #print "[$h] IP address [$ip]\n";
  }
  #print "[$h][$xip]\n";
}

if ($gethost =~ /has address (\d+.*)/) {
  $ip = $1;
  #print "[$h] IP address [$ip]\n";
  if ($dns_time > 1) {
    print LOG "".localtime($now).": $h DNS lookup took $dns_time seconds and returned [$ip]\n";
    $emailsubject = "$h DNS lookup took $dns_time seconds and returned [$ip]\n";
  }
} elsif ($gethost =~ /name pointer (\w+.*)/) {
  $ip = $1;
  #print "[$h] IP address [$ip]\n";
  if ($dns_time > 1) {
    print LOG "".localtime($now).": $h DNS lookup took $dns_time seconds and returned [$ip]\n";
    $emailsubject = "$h DNS lookup took $dns_time seconds and returned [$ip]\n";
    $emailtext = "$h DNS lookup took $dns_time seconds and returned: $gethost\n";
  }
} elsif ($gethost =~ /NXDOMAIN/) {
  # no IP address
  print LOG "".localtime($now).": $h DNS lookup took $dns_time seconds and returned NXDOMAIN\n";
  $emailsubject = "$h DNS lookup took $dns_time seconds and returned NXDOMAIN\n";
  $emailtext = "$h DNS lookup took $dns_time seconds and returned NXDOMAIN: $gethost\n";
} else {
  print LOG "".localtime($now).": $h DNS lookup took $dns_time seconds and returned something strange: $gethost\n";
  $emailsubject = "$h DNS lookup took $dns_time seconds and returned something strange\n";
  $emailtext = "$h DNS lookup took $dns_time seconds and returned something strange: $gethost\n";
}

if ((! $noemail) && $emailsubject) {
  my $cmd = "Mail -s \'dnsmon: $emailsubject\' $email_to";
  #print "Email: $cmd\n";
  open(OUT, "|$cmd");
  print OUT $emailtext;
  print OUT "\n--\ndnsmon\n";
  close OUT;
}

close LOG;

exit 0;

# end file