This is an update of Using an API to obtain JSON data and get the date string and determine if data is stale

This is a Nagios check that will use an API URL, get JSON data, flatten the data into a usable Perl hash, and ultimately obtain a date string. Once the date is obtained, it should recognize the strftime format based on user input and determine the delta hours or minutes. Once the delta time is calculated, it should return critical, warning, or OK, based on the -c or -w user inputs. I just started Perl a week ago and need some code review to become better at it.

Gitlab Repo


use warnings;
use strict;
use Data::Dumper;
use Monitoring::Plugin;
use LWP::UserAgent;
use JSON::Parse 'parse_json';
use JSON::Parse 'assert_valid_json';
use Hash::Flatten qw(:all);
use DateTime;
use DateTime::Format::Strptime;
use File::Basename;

use vars qw($verbose $warning $critical $timeout $result $url $key $format $zone $units);
my $VERSION = '1.1.0';
my $PROGNAME = basename($0);
my $dateNowUTC = DateTime->now;
my $license = qq{    Copyright (C) 2016 Nathan Snow

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License

my $np = Monitoring::Plugin->new(
    shortname   => "DataFreshness",
    usage       => "Usage: %s [-U|url=<URL>] [-K|key=<key>] [-f|format=<date_format>] [-u|units=<hours/minutes>] [-z|zone=<timezone>] [-c|--critical=<threshold>] [-w|--warning=<threshold>] [-t|timeout=<timeout>] [-v|verbose]",
    version     => $VERSION,
    blurb       => "Retrieve JSON data from an http/s url and check an object's date attribute to determine if the data is stale.",
    url     => "https://gitlab.com/Jedimaster0/check_http_freshness",
    license     => $license,
    plugin      => "check_http_freshness",
    timeout     => 60,

$np->add_arg('url|U=s',     "-U, --url=STRING   \n   URL used to retrieve JSON data. (REQUIRED)", undef, 1);
$np->add_arg('key|K=s',     "-K, --key=STRING   \n   JSON key. Used to find time attribute. (REQUIRED)", undef, 1);
$np->add_arg('format|f=s',  "-f, --format=STRING    \n   Strftime time format (default: %Y%m%dT%H%M%S). \n   For format details see: man strftime", '%Y%m%dT%H%M%S', 0);
$np->add_arg('units|u=s',   "-u, --units=STRING \n   Time units. Can be 'hours', or 'minutes'. (default hours)", 'hours', 0);
$np->add_arg('zone|z=s',    "-z, --zone=STRING  \n   Timezone for JSON date. Can be 'UTC', UTC offset '-0730', or 'America/Boston' (default is UTC)\n   See: http://search.cpan.org/dist/DateTime-TimeZone/lib/DateTime/TimeZone/Catalog.pm" , 'UTC', 0);
$np->add_arg('warning|w=s', "-w, --warning=INTEGER  \n   Warning if data exceeds this time. (default 12 hours)", 12, 0);
$np->add_arg('critical|c=s',    "-c, --critical=INTEGER \n   Critical if data exceeds this time. (default 24 hours)", 24, 0);

my $verbose = $np->opts->verbose;
if ($np->opts->warning >= $np->opts->critical){
    $np->plugin_die( "[ERROR] Warning value must be less than critical value." );
if (($np->opts->units ne "hours") and ($np->opts->units ne "minutes")){
    $np->plugin_die( "[ERROR] Time unites must be either hours or minutes." );

# Configure the user agent and settings for the http/s request.
my $ua = LWP::UserAgent->new;
$ua->protocols_allowed( [ 'http', 'https'] );
my $response = $ua->get($np->opts->url);
if (!$response->is_success) {
    $np->plugin_die( "[ERROR] HTTP/S request unsuccessful: " . $response->status_line );

# Verify the content-type of the response is JSON
my $ok = eval {
    assert_valid_json ($response->content);
    return 1;
if ( !$ok ){
    $np->plugin_die( "[ERROR] Response JSON is invalid. Please verify source data.\n" );
} else {
    # Convert the JSON data into a perl hashrefs
    my $jsonDecoded = parse_json($response->content);
    my $flatHash = flatten($jsonDecoded);

    if ($verbose){print "[SUCCESS] JSON FOUND -> ", Dumper($flatHash), "\n";}

    if (defined $flatHash->{$np->opts->key}){
        if ($verbose){print "[SUCCESS] JSON KEY FOUND -> " . $np->opts->key . ": ", $flatHash>{$np->opts->key}, "\n";}
        my $result = DATETIME_DIFFERENCE(DATETIME_LOOKUP($np->opts->format, $flatHash->{$np->opts->key}));
            return_code => $np->check_threshold( check => $result, warning => $np->opts->warning, critical => $np->opts->critical),
            message => "delta time is $result " . $np->opts->units . "  -w: " . $np->opts->warning . " -c: " . $np->opts->critical,

    } else {
        $np->plugin_die( "[ERROR] Retreived JSON does not contain any data for the specified key: " . $np->opts->key . "\nUse the -v switch to verify the JSON output and use the proper key(s)." );

    my ($dateFormat, $dateFromJSON) = @_;

    my $strp = DateTime::Format::Strptime->new(
        pattern   => $dateFormat,
        time_zone => $np->opts->zone,
        on_error  => sub { $np->plugin_die( "[ERROR] INVALID TIME FORMAT: $dateFormat OR TIME ZONE: " . $np->opts->zone ); },

    my $dt = $strp->parse_datetime($dateFromJSON);
    if (defined $dt){
        if ($verbose){print "[SUCCESS] Time formatted using -> $dateFormat\n", "[SUCCESS] JSON date converted -> $dt " . $np->opts->zone . "\n";}
        return $dt;
    } else {
        $np->plugin_die( "[ERROR] DATE VARIABLE IS NOT DEFINED. Pattern or timezone incorrect." );

# Subtract JSON date/time from now and return delta
    my ($dateInitial) = @_;
    my $deltaDate;
    # Convert to UTC for standardization of computations and it's just easier to read when everything matches.
    $deltaDate = $dateNowUTC->delta_ms($dateInitial);
    if ($verbose){print "[SUCCESS] (NOW) $dateNowUTC UTC - (JSON DATE) $dateInitial " . $dateInitial->time_zone->short_name_for_datetime($dateInitial) . " = " . $deltaDate->in_units($np->opts->units) . " " .  $np->opts->units . "\n";}

    return $deltaDate->in_units($np->opts->units);

1 Answer 1


The code looks pretty good, but here are some suggestions.

There is some unused code which can be deleted, specifically:

use vars qw($verbose $warning $critical $timeout $result $url $key $format $zone $units);

Also, the vars documentation states:

use of this pragma is discouraged

These are also unused:

use File::Basename;
my $PROGNAME = basename($0);

It is best to import only what is needed to avoid namespace pollution. Change the use lines as follows:

use Data::Dumper               qw(Dumper); 
use Monitoring::Plugin         qw();       
use LWP::UserAgent             qw();       
use Hash::Flatten              qw(flatten);       
use DateTime                   qw();       
use DateTime::Format::Strptime qw();

The empty lists (qw()) are not strictly needed in this case, but are there for consistency. They also indicate that no functions will be imported, but the OOP interface will be used.

It is a little strange to see multiple use lines for the same module:

use JSON::Parse 'parse_json';
use JSON::Parse 'assert_valid_json';

This is more customary:

use JSON::Parse qw(parse_json assert_valid_json);

Double quotes interpolate variables, whereas single quotes do not. There is no need to interpolate here:

my $license = qq{    Copyright (C) 2016 Nathan Snow

Using q more clearly shows the intent:

my $license = q{    Copyright (C) 2016 Nathan Snow

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