nxvipin / eventcore

The core notification application.

Eventcore

Eventcore is the core notification application of the Simple Real Time Notification System. It is a simple implementation of publish/subscribe pattern over the WebSocket protocol.

Getting Started

You need to have a redis server running on the default port for this to work.

If you do not have redis on your system:

git clone https://github.com/antirez/redis
cd redis
make
make test
./src/redis-server

You should have a redis server running by now. Now we will fetch the application and all its dependencies:

git clone https://github.com/swvist/eventcore
cd eventcore/
wget http://cloud.github.com/downloads/basho/rebar/rebar && chmod u+x rebar
./rebar get-deps

Now we are ready to compile and execute the eventcore application:

./rebar compile
erl -s crypto -pa ebin/ deps/*/ebin/

I got the application running. Now what? (Client Quickstart)

If you do not see any weird error messages, you have the server running. Congrats! But where is the client? All the communication happens over the WebSocket protocol so all you need is a WebSocket client. Fire up the latest version of Chrome and start the console (ctrl+shift+i). In the console:

var ws = new WebSocket("ws://127.0.0.1:8080/websocket");
ws.onmessage  = function(d){console.log(d.data);};
ws.send("register:testclient");
ws.send("subscribe:testchannel");

Congrats, you have got the client running as well. Now to see some pub/sub action, go to the terminal where the eventcore application is running and hit enter till you receive the prompt. Once you have that, you can publish messages to the testchannel and the chrome client, subscribed to that channel, should receive the message:

channel:publish("testchannel", <<"Test Message for the Chrome cleint">>).

Now go check the Chrome console. Voila! You get the message and everything is working fine. If not, ping me.

How it works?

The clients connect to the WebSocket server and registers online with a username. There is no authorization and no client can reserve a username (This works more or less like IRC). Any client is free to register with any available username which is a string of characters. Once registered the client can subscribe to different channels.

Whenever the publisher publishes a message to a channel, all online clients subscribed to that channel will receive the message. Currently the clients cannot publish to a channel. There is an Erlang API which can be used to publish to the channel. In the near future publishing support will be added to the communication protocol and a RESTful API is also in the pipeline. See Roadmap for more details. All the data like presence information and channel subscription information is stored in the Redis data store.

(Client) Communication Protocol

The (websocket) client talks to the server with a simple text protocol that is described below:

Register a client on the server register:

Subscribe to a channel (Only a registered client can do this) subscribe:<CHANNEL_NAME>

Erlang API

The Erlang API allows publishers to publish messages to different channels.

Publish API channel:publish(<CHANNEL_NAME>, ).

Note: CHANNEL_NAME is a string and the MESSAGE is a binary term.

Future Roadmap

• Extending the comm protocol to allow the client to publish and unsubscribe.
• Adding a HTTP API to publish messages.
• Tests, tests & more tests!
• Get a new name. This one was a code name and is not very intutive.
• Release! (That should make this 0.1)
• Allow different backends. Probably one simple ets/mensia to begin with.
• Think about what can be added to this list!

Contribute

Fork & send a pull request. Be descriptive :)

Authors

Vipin Nair (swvist) [email protected]

License

Eventcore is available under MIT License. Eventcore uses Poolboy which is in public domain and Eredis which is under the MIT License.