Posts Tagged ‘Erlang based chat engine’


Changes in Chatterl

July 23, 2009

I haven’t worked on Chatterl for a few months but there are some fundemental changes that had been made back in March, apologies for the slow update but honestly I haven’t had much time with learning Rails & freelance work.


Well the main changes in chatterl are the following:

  • Message storage
  • Registration
  • Introduction of unit tests
  • API calls

I’ll go over each section, highlighting the main changes & who it affects Chatterl as a whole.


After implementing Chatterl‘s basic functionality (see chatterl post). The next step was to create to implement CWIGA, Chatterl Web Interface Gateway API. With this new module Chatterl is able to be interacted with purely via HTTP. The first implementation was rough, the original source can be found here, though it allowed me to get a decent understanding of mochiweb at the time helped me produce this article. After implementing unit tests to cover the project as a whole I felt comfortable to make a few fundamental changes to CWIGA’s API and requests to Chatterl.


I’ve added very basic registration functionality to Chatterl, allowing users to register to the system, giving them the ability to retrieve archived messages & later creation of their own chat groups. In hindsight I’d like to move this functionality to the front-end (which I’ll more than likely be in Rails).

Message Storage

Again this was more experimental on my part and something I would like to move over to couchDB when I get the chance, for the moment, Chatterluses mnesia to store users messages when they are not logged into the system.

Added test cases

One of the main issues I’ve been having with Sinan more than anything else, was seperating my tests from the source code. I really hated the idea of having test & implementation code mixed in, so I stayed away from any kind of real testing until I got my head around it. Thanks to Kev Smith‘s own code, I finally got my head around EUnit, which I posted a short post on here.

Before I was comfortable with implementing any more functionality I had set out to cover as much of Chatterl‘s code as possible. In doing so I uncovered a number of silly little bugs (oversights) in the coding logics & made the necessary changes.

General cleanup

The way chatterl is called has also been improved, instead of having to go into erl you can simple run ./ within the cd _build/development/apps/chatterl- directory. This will start up all the processes need to use chatterl.

CWIGA is setup to listen on port 9000, so you can call it using curl or via a browser of your choice. It accepts XML & JSON requests & has been made more RESTful.

Hopefully in the near future I’ll have time to rewrite the code base and improve on the basic functionality but for the meantime I hope this helps others as much as its been an experience for me.


Lighting up the tunnErl part 7 – Chatterl meets Nitrogen

March 13, 2009

Well it’s been a has been a while since I have posted a blog, mainly down to the amount of time I’ve been spending playing around with Chatterl & Nitrogen. I have come a way since first playing around with Erlang I decided a few months ago to make Chatterl my main personal project. I played around with BeepBeep around the same time as Nitrogen, for one reason or another I picked up Nitrogen quite quickly and decided to run with that as Chatterl‘s prototype frontend.

I have to admit though I have never really been a fan of event driven frameworks, especially those that mask mark up language but after a day or two of messing around with Nitrogen I found it quite a pleasant experience.

The learning curve can be somewhat steep as the documentation is not as good as it could be, I also have issues with having the root directory starting with /web/, so the admin directory would be, hopefully this will be changed in the near future. Besides those minor gripes Nitrogen is starting off as a nice framework.

Well I wish I had some time to run through a little tutorial, for the moment the best I can do is show you how I implemented some of the functionality need for Chatterl‘s front-end. Below is a list of features I’ll be concentration on:

  • Main body
  • Validate Message
  • Client Panel
  • Message Panel
  • Groups Body
  • Users Panel

We’re working with Chatterl‘s Web Interface API (CWIGA) which works on, I prefer JSON so I’ve only implemented functionality to handle this. The implementation code is very similar to that I’ve written about previous so I wont waste bytes (see Twitterl), I’ll just say that we need to connect to CWIGA via HTTP.

For the curious, the code can be found the functionality needed to interact with Chatterl can be found in the file chatterl_cwiga_handler.erl. The actual calls are defined within Chatterl interface.

Now we have the basics for interacting with Chatterl over HTTP, lets have a look at how this all ties in with working with Nitrogen. I won’t go over how Nitrogen works as that part is pretty well documented in a few placed (Nitrogen, Jón Grétar) but I will explain the functionality I’ve implemented for chatterl_nitrogen.

Main body
body() ->
ChatBody = [ #panel { id=messageBodyPanel} ],
Left = [ #panel
{ id=leftPanel,body=[client_panel(),message_panel(),
[#panel { id=groupsPanel, body=[groups_body()]}],users_panel()] } ],
Right = [ #panel { id=rightPanel, body=[ChatBody] } ],
Container = #panel { id=containerPanel, body=[Left,Right] },

Ok now what the hell is all that??? Well it doesn’t look like it but this is how Nitrogen renders HTML, we structure our HTML using Nitrogen‘s elements & actions which in turns renders our pages for us.

Firstly we define the containers needed to organise the chat window, Allowing me to have the chat box on the right, whilst having all the other features (message box, groups list, etc) on the left. As you may of already guessed the element #panel represents a div with XHTML, id’s act as you would expect & can be manipulated with CSS as usual.

Validate Message
validate_message() ->
wf:wire(messageTextBox, messageTextBox, #validate
{ validators=[
#is_required { text="You forgot to submit a message." },
#min_length { length=2, text="Title must be at least 2 characters long." }]}).

Here we use the method wf:wire which basically connects an element to another, so a input box could be ‘wired’ to a submit button. In this case we want to make sure that we validation only when the messageTextBox has data, validate it. The next two lines do exactly that, firstly #is_required makes sure that we actually have a value, whilst #min_length gives a validation error if it has not been adhered to. The response are triggered by AJAX using JQuery, so as soon as an event is caught it is handled asynchronously.

Client Panel
client_panel() ->
[#panel { id=clientPanel, body=[get_client_panel()]}].

This panel is pretty straight forward, it simply defines a DIV elements which calls get_client_panel/0 which in turn determine what actions are needed. This method will be explained better shortly.

Message Panel
message_panel() ->
[#panel { id=messagePanel, body=[
#label { id=messageLabel, text="Message:" },
#textbox { id=messageTextBox, text="", style="width: 100px;", postback=group_message}

This is the the DIV element that is used by the user to send messages to chatterl. We have a couple of things we have encountered yet, our postback, which will be explained shortly & two elements (#label & #textbox). Pretty straight forward right. What about this postback thingie? Well postbacks are in fact our AJAX calls, allowing the user to interact with the systems backend seemlessly. We’ll see how these are handled in the Events section.

Groups Body
groups_body() ->
SelectedGroup = wf:q(groupsDropDown),
#panel { class=groupsPanel, body=[
#h1 { text="Groups" },
#label { text="Select a group to join:" },
#dropdown { id=groupsDropDown, value=SelectedGroup,
options = [ #option { value=Group, text=Group }
|| Group <- chatterl_interface:get_groups()],
postback=join_group} ] }.

Here we have an panel which allows users to select a group to join, we again use a postback to handle our AJAX call & use the chatterl_interface module to retrieve a list of groups from Chatterl.

Users Panel
users_panel() ->
SelectedUser = wf:q(usersDropDown),
[#panel { id=usersPanel, body=[
#label { id=usersLabel, text="Select a user:" },
#dropdown { id=usersDropDown, value=SelectedUser,
options = [ #option { value=User, text=User }
|| User <- chatterl_interface:get_users()] } ]}].

This should be pretty self explanatory as it is more aless the same functionality as groups_body/0.

Get client Panel
get_client_panel() ->
case wf:session(client) of
undefined ->
wf:wire(groupsPanel, #hide {}),
wf:wire(messagePanel, #hide {}),
Client ->
wf:comet(fun() -> update_status("messages",1000) end),
wf:wire(groupsPanel, #show {}),
wf:wire(messagePanel, #show {}),

Well this method basically checks to see if a user is connected if they are then we display the messagePanel, groupsPanel along with groupsJoinedPanel. We allow the messages panel to update, giving the user the most up to date messages from Chatterl. We lastly set the client_panel to client_logout_panel/1, which we’ll have a look at shortly, this method basically allows the user to disconnect once they have connected successfully to Chatterl.

Client login Panel
client_login_panel() ->
#panel { id=loginPanel,
#label { text="Client name:" },
#textbox { id=userNameTextBox, text="", style="width: 100px;", html_encode=true, postback=connect }]}.

Client logout panel
client_logout_panel(Client) ->
#panel { id=logoutPanel,
#inplace_textbox { id=userNameTextBox, text=Client, html_encode=true, start_mode=view },
#button { id=theButton, text="Disconnect", postback=disconnect }]}.

This method is pretty much the same the the client_login_panel/0, with 1 small change, instead of connecting to Chatterl we want to disconnect. The principle is still the same, create an event, passing the postback (disconnect).
which in turn disconnects the user from Chatterl.

Update status
update_status(Type,Timeout) ->
process_flag(trap_exit, true),
case Type of
undefined -> ok;
"messages" -> loop_messages(Timeout);
{"general",StatusType} -> loop_status(Timeout,StatusType);
_ -> io:format("Unknown loop type: ~s",[Type])


Connect Event
event(connect) ->
[Client] = wf:q(userNameTextBox),
case chatterl_interface:connect(Client) of
{ok,Message} ->
wf:update(clientPanel, #panel { body=[get_client_panel()] });
{error,Error} -> wf:wire(#alert { text=Error })

Above is the actually postback method call event(connect) which utilises chatterl_interface:connect/1 allowing us to make a connection to Chatterl directly. If the request is successful we create a new session wf:session(client,Client) & update our clientPanel so that they user can logout as you would expect.We do this by using the wf:update/2 method that dynamically changes XHTML elements on the fly.

Disconnect Event
event(disconnect) ->
case chatterl_interface:disconnect(wf:session(client)) of
{ok,Message} ->
wf:update(messageBodyPanel, #panel { body=[] }),
wf:update(clientPanel, #panel { body=[get_client_panel()] }); % Should redirect here.
{error,Error} ->
wf:wire(#alert { text=Error })

Well there’s the disconnect event, nothing to dramatic here, simply unregister the client & selectedGroup cookies& update the page so that the client_panel is set back to its default.


Chatterl – Erlang based chat engine

January 1, 2009

Well I’ve been hacking around for the past few months trying to get my head around Erlang. After playing around with Twitterl I decided I should start a new project (OTP based) which I have a decent understanding of & have wanted to work on for some time. A chat system was the first thing that came to mind, I’ve worked on and built a few in my time and thought Erlang would be a good language to build a chat engine from scratch.

For those not interested in the long description and prefer to dive in source, you can find a copy of the project at github.


A chat system that can be housed over a number of nodes and track clients over varying devices, at the time of the writing the system works over multiple nodes and is able to do the basics (connect to a group, send message to other clients and connected groups).

The main focus of this project is to create a chat system that is highly reliable as well as scaleable. Other developers will be able to create add-on modules that are able to interact with chatterl and further enhance the functionality of chatterl and the chatterl clients experience.

As mentioned the system is OTP based, of which it uses Sinan to maintain its builds.

Installing Chatterl

At the moment of this writing Chatterl is still in alpha so their is no real release at the moment, to get it running you will need to do the following:

git-clone git:// &&
cd chatterl &&
sinan doc && 
sinan dist &&
cd _/build/development/tar &&
sudo faxien install-release chatterl-

The above presumes that you have Sinan configured & installed, if you haven’t refer to erlware.
You will need to change to cookie & name values to something else, doing so should drop you into the erlang shell & ready to run the Chatterl application. To run a client on a different machine you will need to do the above if (making sure that the -sname is not the same as any other connected nodes & that the cookie is the same) if connecting on the same box simply cd to the ebin directory and run the following command:

erl -name bar -setcookie abc

From here you will need to make sure that they nodes can connect via:


Where foo is the node name & is the tld of the node box (indicated within yout hosts file or dns server).
Once you receive the infamous pong response you are ready to roll.


  • Client login/logout to Chatterl.
  • List Chatterl groups.
  • List Chatterl users.
  • Login/logout of a chatterl group.
  • Send message to a group and other clients.

Future Features

  • Centralised Error logging and data storage.
  • Client customisable routines (able to poll RSS feeds, twitter, FB and the such like).
  • Better handling of errors.
  • User registration.
  • FB Connect.
  • Chat bots (AIML based).
  • Web interface/API.
  • Chat modules handler(banning, censorship, chatbots).


Starting the server
Chatterl server runs as an OTP application and uses a supervisor to manage it (in later versions there will be options to spawn multiple servers, allowing for a more fault tolerant chat system). To start up the server you simply need to run the following command:


Which will initialise the server allowing clients to connect and groups to be created. Groups can be created on differing nodes as long as the node can communicate with the chatterl_serv.

Starting a group
Chatterl groups can be started on any node that can communicate with the server, this allows the user to create a number of groups on varying nodes, helping with general organisation as well a performance and reliablity.

A group can be initialised by calling the command:


which will spawn a group process which users can connect to.

Connection to chatterl
At the time of this writing chatterl_clients can only spawn a client per node, this will later be changed once the web interface has been fully implemented, possibly to a refactoring the client to a parameterised module.
For the moment node users must follow the basic OTP configurations (same cookie, valid DNS name, etc). Creating a connection to the server is done by using the following command.


This will initialise a user and connect them to chatterl_serv (must be done before users can join a group or communicate with other chatterl users).

Disconnecting from chatterl
Chatterl clients can simply disconnect from chatterl by issuing the following command:


This will disconnect the user from all the groups they are currently connected to as well as the actual Chatterl server.

Joining a group
This can be done by using the following command:


If the group exists the user is able to join the group allowing them to send message to the room.

Dropping from a group
This is as simple as connection, simply supply the following command:


This will send a message to the group, which will handle the termination.

Sending group message


GroupName being the name of the group the client is connected to, Message being the message that you want to send to the receiving client. If the message is sent successfully all users connected to the group will receive the message.

Sending a private message
This allows a Chatterl client to send a private message to another client, by executing the following:


If the message is sent successfully then the sender will receive follow message:


in turn sending the message to the receipients node.