endpoint.php

<?php

define('RELAY_HOST', '127.0.0.1');
define('RELAY_PORT', 4545);
define('APP_TOKEN', 'REMOVED');

header('Content-type: application/json');

if (!isset($_REQUEST['token']) || $_REQUEST['token'] !== APP_TOKEN) {
	echo json_encode(array(
		'status' => 'error',
		'message' => 'Application token is invalid.'
	));
	exit;
}

if (isset($_REQUEST['title']) && isset($_REQUEST['message'])) {
	$title = $_REQUEST['title'];
	$message = $_REQUEST['message'];
} else {
	echo json_encode(array(
		'status' => 'error',
		'message' => 'Malformed request.'
	));
	exit;
}

$client = stream_socket_client('tcp://' . RELAY_HOST . ':' . RELAY_PORT, $errno, $error);

if ($client === false) {
	echo json_encode(array(
		'status' => 'error',
		'message' => 'Could not connect to relay server.'
	));
	exit;
}

fwrite($client, json_encode(array(
	'title' => $title,
	'message' => $message
)) . PHP_EOL);

fclose($client);

echo json_encode(array('status' => 'success'));
exit;

extnotifd-linux.rb

#!/usr/bin/env ruby

require 'socket'
require 'dbus'
require 'yajl'

Process.detach(fork do
  server = TCPServer.new('127.0.0.1', 4545)

  loop do
    Thread.start(server.accept) do |client|
      d = DBus::SessionBus.instance
      o = d.service('org.freedesktop.Notifications').object('/org/freedesktop/Notifications')
      o.introspect
      i = o['org.freedesktop.Notifications']
      
      request = Yajl::Parser.parse(client.gets.strip)
      i.Notify('extnotifd', 0, 'info', request['title'], request['message'], [], {}, 2000)
      
      client.close
    end
  end
end)

extnotifd-osx.rb

#!/usr/bin/env ruby

require 'socket'
require 'yajl'
require 'terminal-notifier'

Process.detach(fork do
	server = TCPServer.new('127.0.0.1', 4545)

	loop do
		Thread.start(server.accept) do |client|
			request = Yajl::Parser.parse(client.gets.strip)
			TerminalNotifier.notify(request['message'], title: request['title'])

			client.close
		end
	end
end)