systemctl-socket-daemon

#!/usr/bin/perl

# Copyright 2014 Jan Pazdziora
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

use strict;
use warnings FATAL => 'all';

use IO::Socket::UNIX ();
use Socket ();
use POSIX ();

sub daemonize {
	open(STDERR, '>>', '/var/log/systemctl-socket-daemon.log')        || die "can't write log: $!";
	open(STDOUT, '>&STDERR')     || die "can't write stdout to log: $!";
	chdir("/")                      || die "can't chdir to /: $!";
	open(STDIN,  '<', '/dev/null')     || die "can't read /dev/null: $!";
	defined(my $pid = fork())       || die "can't fork: $!";
	exit if $pid;                   # non-zero now means I am the parent
	(POSIX::setsid() != -1)                || die "Can't start a new session: $!";
}

my ($socket_path, $socket_mode, $service) = @ARGV;
if (not defined $socket_path or not defined $service) {
	die "Usage: $0 /path/to/unix/socket service-to-run\n";
}
if (-e $socket_path) {
	warn "Path [$socket_path] already exists, removing\n";
	unlink $socket_path;
}

my $service_data = `/bin/systemctl show $service 2>&1`;
if ($?) {
	die "Failed to find service [$service]:\n$service_data";
}

my $socket = new IO::Socket::UNIX(
	Type => Socket::SOCK_STREAM,
	Local => $socket_path,
	Listen => Socket::SOMAXCONN
) or die "socket: $!\n";
chmod oct($socket_mode), $socket_path;

daemonize();

while (1) {
	next unless my $connection = $socket->accept;
	my $pid = fork();
	if ($pid == 0) {
		*STDIN = $connection;
		*STDOUT = $connection;
		exec '/bin/systemctl', 'start', $service;
		die "exec should have never reached here\n";
	}
}