#!/bin/bash
# -*- bash -*-

: << =cut

=head1 NAME

dnsperftest - Monitor response times of multiple DNS servers

=head1 DESCRIPTION

Query all name servers in /etc/resolv.conf for a list of domains
and report the average response time.

=head1 CONFIGURATION

DNS servers in /etc/resolv.conf are used automatically

"env.resolvconf" can be used to pass a custom resolv.conf path

A list of default domains is checked

Example configuration:

    [dnsperftest]
        env.resolvconf /etc/resolv.conf.cweiske
        env.domains fsf.org fsfe.org munin-monitoring.org
        env.warning 0.2
        env.critical 0.9

=head1 AUTHORS

L<Christian Weiske|https://cweiske.de/>

based on https://github.com/cleanbrowsing/dnsperftest

=back

=head1 LICENSE

GPLv3

=head1 MAGIC MARKERS

 #%# family=auto
 #%# capatilities=autoconf

=cut

DIG=${dig:-dig}

DOMAINS=${domains:-www.google.com amazon.com facebook.com www.youtube.com www.reddit.com  wikipedia.org twitter.com gmail.com www.google.com whatsapp.com}

RESOLVCONF=${resolvconf:-/etc/resolv.conf}

if [ "$1" == "autoconf" ]; then
    if ! which "$DIG" >/dev/null; then
        echo "no (missing 'dig' executable)"
        exit 0
    elif ! which "bc" >/dev/null; then
        echo "no (missing 'bc' executable)"
        exit 0
    elif ! test -f "$RESOLVCONF"; then
        echo "no (resolvconf does not exist at $RESOLVCONF)"
        exit 0
    fi
    echo "yes"
    exit 0
fi

if [ -f "$RESOLVCONF" ]; then
    NAMESERVERS=$(grep ^nameserver "$RESOLVCONF" | cut -d " " -f 2)
fi

if [ -z "$NAMESERVERS" ]; then
    echo "No nameservers found"
    exit 1
fi

if [ "$1" == "config" ]; then
    echo "graph_title DNS server resonse times"
    echo "graph_vlabel seconds"
    echo "graph_category dns"
    echo "graph_args --base 1000 -l 0"
    for nameserverIp in $NAMESERVERS; do
        fieldname=$(echo "$nameserverIp" | sed 's/[.:]/_/g')
        echo "ns$fieldname.label $nameserverIp"

        if [ ! -z "$warning" ]; then
            echo "ns$fieldname.warning $warning"
        fi
        if [ ! -z "$critical" ]; then
            echo "ns$fieldname.critical $critical"
        fi
    done
    exit 0
fi

for nameserverIp in $NAMESERVERS; do
    ftime=0

    totaldomains=0
    for domain in $DOMAINS; do
        totaldomains=$((totaldomains + 1))
        ttime=$(
            "$DIG" +tries=1 +time=2 +stats @"$nameserverIp" "$domain"\
                | grep "Query time:"\
                | cut -d : -f 2-\
                | cut -d " " -f 2
        )
        if [ -z "$ttime" ]; then
            #"time out" is 1s = 1000ms
            ttime=1000
        elif [ "$ttime" = "0" ]; then
            ttime=1
        fi
        ftime=$((ftime + ttime))
    done
    avg=$(bc -l <<< "scale=5; $ftime/$totaldomains / 1000")

    fieldname=$(echo "$nameserverIp" | sed 's/[.:]/_/g')
    echo "ns$fieldname.value $avg"
done