convenience script for starting openvpn and update resolv.conf based on what was PUSHed by the server; handy on the *BSDs

ovpn.pl

#!/usr/bin/env perl

unless ($> == 0) {
    die "Must run ovpn.pl as root!\n";
}

unless ($ARGV[0]) {
    die "Usage: ovpn.pl <conf-file-in-cwd>\n";
}

my $conf_file = $ARGV[0];

if ($conf_file =~ /\//) {
    die "[fatal] must run ovpn.pl from the config directory\n";
}

if ($conf_file =~ "random(?:-([A-Z]{2}))*") {
    my (@confs, $country);
    if ($country = $1) {
        @confs = glob("ipvanish-$country*.ovpn");
    } else {
        @confs = glob("*.ovpn");
    }
    if (scalar(@confs) == 0) {
        if ($country) {
            die "[fatal] couldn't find any configs in country '$country' to choose from\n";
        } else {
            die "[fatal] couldn't find any configs to choose from\n";
        }
    }

    my $chosen_idx;
    my $rolls = int(rand(int($#confs / 8)));
    for (my $i = 0; $i < $rolls; $i++) {
        $chosen_idx = int(rand($#confs));
    }

    # the last roll is the config
    $conf_file = $confs[$chosen_idx];

    print "[random] randomly chose $conf_file\n";
}

my $perl_pid = $$;
my $dns_servers = [];

$SIG{ALRM} = sub {
    return unless $$ == $perl_pid;
    if (scalar(@$dns_servers)) {
        print "@{[scalar localtime]} automatically generating resolv.conf from vpn PUSHed values\n";
        system("mv -f /etc/resolv.conf /tmp/resolv.conf.$$.ovpnorig");
        open my $rc, '>', '/etc/resolv.conf' or die "Can't open /etc/resolv.conf for writing: $!\n";
        print $rc "# resolv.conf autogenerated by ovpn.pl at @{[scalar localtime ]}\n";
        while (my $ns = shift @$dns_servers) {
            print $rc "nameserver $ns\n";
        }
    } else {
        warn "@{[scalar localtime]} - warning - dns_servers array was empty\n";
    }
};

# clean up.
$SIG{INT} = $SIG{KILL} = $SIG{TERM} = \&cleanup;

# open VPN after signal handlers are installed.
open my $fh, '-|', "openvpn --config $conf_file";
while (my $line = <$fh>) {
    if ($line =~ /PUSH:/) {
        @dns_servers = ();
        while ($line =~ /dhcp-option DNS ([\d\.]+)/g) {
            push(@$dns_servers, $1);
        }
        alarm 3;
    }
    print "$line";
}

# openvpn died, clean up.
cleanup();

sub cleanup {
    return unless $$ == $perl_pid;
    if (-e "/tmp/resolv.conf.$$.ovpnorig") {
        print STDOUT "@{[scalar localtime]} - exiting - restoring original resolv.conf\n";
        system("mv -f /tmp/resolv.conf.$$.ovpnorig /etc/resolv.conf");
        exit;
    }
}