Create a UI Server Plugin

While using an external web server provides the maximum flexibility to generate dynamic content, the UI Server comes with a simple plugin system that allows applications to hook to the UI Server and generate dynamic content using the Ruby language. It's a good alternative for those developers who know Ruby and do not want to load another web server.

In this example we will go through a simple plugin that hooks to the UI Server and outputs the current date and time.

1. Create an empty application following these steps.
2. Create a “uiserver” folder inside the application's assets folder.
3. Create a “servlet.rb” file inside the “uiserver” folder.

At this point your directory tree should look like:

/server/WebRoot/apps
-- Hello World
---- index.html
---- assets
------ icon.png
------ uiserver
-------- servlet.rb

During startup, the UI Server will scan each application's folder for a assets/uiserver/servlet.rb file. If one is present, it will execute its content and link to it. Be careful that all plugins run within the same process, so a crash has the potential of bringing down the whole server (thus making Glassomium unresponsive).

Inside servlet.rb place the following code:

require './Servlets/ServletPlugin'
 
require 'webrick'
include WEBrick
 
class ServletPlugin
	def get_servlet_handlers
	   {"getDate" => DateServlet }
	end
 
	def initialize
		# Nothing to initialize here
	end
end
 
class DateServlet < WEBrick::HTTPServlet::AbstractServlet
    def initialize(server)
	super(server)
    end
 
    def do_GET(request, response)
      response.status = 200
      response['Content-Type'] = "text/html"
      response.body = Time.new.inspect
    end
end

The code is quite straightforward; every plugin must specify a ServletPlugin class, with a get_servlet_handlers method. This method must return a hash-map in the format:

{ mountPoint1 => ServletClass1,
  mountPoint2 => ServletClass2, 
  ... }

Where the mountPoints are strings specifying the addresses where the servlets will be mounted. A servlet is just a class that takes care of handling a web request. In our example we are telling the UI Server to mount the DateServlet servlet at http://localhost:5555/apps/<APPNAME>/getDate.

It's time for a quick test. Save all changes and (re)start the UI Server (and make sure to pass the –v verbose option).

~/glassomium/server# ruby main.rb --v

If you look at the initialization output you should see a line similar to:

...
Found servlet plugin for <APPNAME>
Mounted plugin at /apps/<APPNAME>/getDate
...

And if you open your web browser to http://localhost:5555/apps/<APPNAME>/getDate you should see:

2012-08-28 20:43:29 -0500

Of course the date and time will reflect the actual time. If you refresh the page the content will change. Congratulations! You just generated some dynamic content!