Meeting With Francesco Cesarini and the ECUG

Last week I was invited by the Erlang China User Group to meet Francesco Cesarini from Erlang Solutions who was in Shanghai. Since he's the author of the Erlang Programming book by O'Reilly this was an amazing opportunity to learn more about Erlang from someone with real world experience in the field.

The guys from the ECUG picked up a nice Chinese restaurant where we shared our experience about Erlang from our several points of view.

I had my share of questions about topics such as Riak, Mnesia, RabbitMQ, Ejabberd and what not. It was nice to learn how big the Erlang world is in the enterprise, how is it used for serious matters such as banking, item traceability, and of course all the other features of Erlang, like reliability, performance, etc.

One important topic in which we all agreed was how the language gap between English and Chinese produces two phenomena that can slow down Erlang in becoming popular in China and at the same time keeps the rest of the world unaware of what Chinese companies are doing with Erlang.

Luckly this will start to change since the Erlang Programming book is about to be released in Chinese and the guys from the ECUG are translating some of Erlang documentation to Chinese.

Besides that I plan to give my 2 cents by writting some blog posts in english about the Erlang movement here in China. Also we have talked with the guys from the ECUG to have some Conferences about RabbitMQ and other Erlang products that we use at the company I work for.

To end my post I'd like to share a couple of pictures from our meeting:

Xihe Yu with Francesco Cesarini

The gang with Francesco Cesarini

Sharing Sessions Between PHP and Ejabberd

In my last post I wrote about a pet project I started to share sessions between PHP an Python. In this post I want to show you how we can share the sessions between PHP and Ejabberd.

So here's the problem. In one of the projects where we want to use XMPP we have a users databasase of around 2.5 millions users. We want that those users are able to login to our Ejabberd server using the same database. This means that every time a user logs into our site, we will query the database with PHP to see if he's allowed to login, and then ejabberd will query the
database again for the same purpose. Now, since the user is already authenticated in our PHP app, why don't we just share the session information with Ejabberd? Here's where InspectorD comes into play.

The first piece that we will use to solve this problem are Ejabberd external authentication scripts. In our case instead of authenticating against a database, we will user InspectorD to check whether a user is authenticated in our website. To do this we need to find some means of passing PHP's session_id to our auth script. How to do this?

In PHP there's a function called session_id() that returns the current session_id key. We will use this string as a user password for Ejabberd, so for example, using Strophe we can do something like this:

connection = new Strophe.Connection(BOSH_SERVICE);
connection.connect(+'@someserver', , onConnect);

Then Ejabberd will call our external authenticatinon script passing that nickname and the session_id as password. In our case we store the session information in Memcache, so our script will use the class SessionInspectorMemcache from InspectorD library. This class will connect to the session memcahe and from there will retrieve the session information belonging to that session_id. Finally it will return True or False depending if the user related to that session_id is authenticated or not.

You can see the complete authentication script here

If you are not using memcache to store the session information then you can create a Python class that extends from InspectorD's SessionInspector class and implements the getData method. You can see an example on the SessionInspectorMemcache class.

I hope this may result useful to you and don't hesitate to clone and improve InspectorD source code.

NOTE: I did a similar script using PHP but I found it somehow harder to implement than using InspectorD code. If you want to see that code, just ask in the comments and I will post it on github.