#!/usr/bin/perl -Tw

# These prevent taint checking failures
$ENV{PATH} = '/bin:/usr/bin';
delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};

use strict;
use diagnostics;

use vars qw($VERSION $ua);
$VERSION = '0.01';

require LWP::UserAgent;

###### Config ########
my $test_script_url = 'http://www.example.com:81/perl/test.pl';
my $monitor_email   = 'root@localhost';
my $restart_command = '/home/httpd/httpd_perl/bin/apachectl restart';
my $mail_program    = '/usr/lib/sendmail -t -n';
######################

$ua  = LWP::UserAgent->new;
$ua->agent("$0/watchdog " . $ua->agent);
# Uncomment the following two lines if running behind a firewall
# my $proxy = "http://www-proxy";
# $ua->proxy('http', $proxy) if $proxy;

# If it returns '1' it means that the service is alive, no need to
# continue
exit if checkurl($test_script_url);

# Houston, we have a problem.
# The server seems to be down, try to restart it.
my $status = system $restart_command;

my $message = ($status == 0)
            ? "Server was down and successfully restarted!"
            : "Server is down. Can't restart.";
  
my $subject = ($status == 0)
            ? "Attention! Webserver restarted"
            : "Attention! Webserver is down. can't restart";

# email the monitoring person
my $to = $monitor_email;
my $from = $monitor_email;
send_mail($from, $to, $subject, $message);

# input:  URL to check 
# output: 1 for success, 0 for failure
#######################
sub checkurl {
    my($url) = @_;

    # Fetch document 
    my $res = $ua->request(HTTP::Request->new(GET => $url));

    # Check the result status
    return 1 if $res->is_success;

    # failed
    return 0;
}

# send email about the problem 
#######################  
sub send_mail {
    my($from, $to, $subject, $messagebody) = @_;

    open MAIL, "|$mail_program"
        or die "Can't open a pipe to a $mail_program :$!\n";
 
    print MAIL <<__END_OF_MAIL__;
To: $to
From: $from
Subject: $subject

$messagebody

Your faithful watchdog

__END_OF_MAIL__

    close MAIL or die "failed to close |$mail_program: $!";
}