Thursday, January 16, 2014

A service oriented Web Server

In this post I would like to discuss how a web server should be considered in the context of a Service Oriented Architecture or a distributed system in general. Usually, the web server is used as a tool which enables the possibility to public files and applications  under the HTTP protocol. Indeed, applications are developed by using some specific technology like PHP, Ruby, Java, etc. and then deployed into a web server for making them available on the web. The same approach is adopted also in Service Oriented Architecture where web services and orchestrators are developed in a given technology and then published in a web server together with the WSDL documents.

Here I want to share one of the results we obtained by developing Jolie as service oriented programming language. In Jolie the web server is just a service which provides its operations under an HTTP protocol and it follows the same programming rules we use for simple services and orchestrators. Here you can find the code of Leonardo, which is a web server completely developed in Jolie:

You can download the code here and try to execute it by simply typing the following command in a shell:

      jolie leonardo.ol www/

where  www/ is the root folder where files are retrieved by Leonardo (remember to create it if it is missing). Now try to add a simple index.html file into the www folder like the following one:

Hello World!

Then open your browser and set the url: http://localhost:8000 and you'll see the html page displayed in it. Try also to add images, css, html pages and subfolders into the www/ folder.
You can change the port by setting the Location_Leonardo parameter of the config.iol file. 

          how can I program the server side behavior of a web application?

And here comes the service oriented approach. First of all let me introduce a new operation called test into the HttpInput by modifying its interface as it follows:

interface HTTPInterface {

Then let me add the implementation of the test operation into the main:

main {
[ default( request )( response ) {
/* ... code of the default operation */
} ] { nullProcess }

[ test( request )( response ) {
format = "html";
response = "Test!"
}] { nullProcess }

Operation test executes a very simple piece of code that is:

  • setting the response format to "html" in order to make the browser able to manage the response as an html file
  • set the response message with a simple html page

Now if we relaunch Leonardo and we point the browser to  http://localhost:8000/test we will see the page generated by the test operation. 

This is a pretty standard way for programming a web application: joining a web page to each operation. You can do it but I don't like it, even if in some cases it could be useful. I prefer to completely decouple the server side from the client side. I prefer to public the operation test as a JSON API which can be used by the client using an AJAX call. In this way I can program the server side as a service and the client side as a dynamic application. In order to this I modify the interface for introducing the message types which are very useful for catching message faults:
type TestType: void {
.message: string

interface HTTPInterface {
test( TestType )( TestType )

Then I modify the implementation of the test operation:

[ test( request )( response ) {
response.message = request.message + " RECEIVED!"
}] { nullProcess }

Finally, I just insert a little bit of Javascript on the client side by modifying the index.html:

  <script type="text/javascript" src=""></script>

 function jolieCall( request, callback ) {
          url: '/test',
          dataType: 'json',
          data: JSON.stringify( request ),
          type: 'POST',
          contentType: 'application/json',
          success: function( data ){callback( data )}
 function afterResponse( data ) {
$( "#test" ).html( data.message )
  <div id="test">
<button onclick="jolieCall( {'message':'Ciao'}, afterResponse )">TEST</button>

That's all! Try to open the index.html page on the browser and click on TEST button. It is worth noting that Jolie recognize the JSON format and sends back a JSON message.

Now, try to add other operations and create a more complex web application.
Have fun!

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