Request znc.in/self-message capability in irssi

cap_znc_self_message.pl

use strict;
use Irssi;
use vars qw($VERSION %IRSSI);
# Derived from: cap_sasl.pl and server_time.pl
# See also: https://irssi.org/NEWS/#v0-8-18

$VERSION = '0.1';
%IRSSI = (
    authors     => 'poppyschmo',
    contact     => 'poppyschmo@users.noreply.github.com',
    name        => 'cap_znc_self_message',
    description => 'Requests znc.in/self-message, implemented since 0.8.18',
    license     => 'MIT',
    url         => 'http://defs.ircdocs.horse/info/selfmessages.html',
);

sub event_cap {
    my ($server, $args, $nick, $address) = @_;
    if ($args !~ /^\S+ (\S+) :(.*)$/) {
        return;
    } elsif ($1 eq 'LS'
             && !$server->{connected}
             && grep($_ eq 'znc.in/self-message', split(/\s+/, $2))) {
        $server->send_raw_now('CAP REQ :znc.in/self-message');
    }
    # According to <https://ircv3.github.io/specs/core/
    #               capability-negotiation-3.1.html#the-cap-nak-subcommand>,
    # separate NAK rejections are issued per offending REQ
    elsif ($1 eq 'NAK' && $2 eq 'znc.in/self-message') {
        my $msg ="\x02warning\x02 server rejected 'znc.in/self-message'";
        $server->print('', $msg);
    }
}
Irssi::signal_add('event cap', \&event_cap);