Sinatra::PubSub

PubSub is a little extension to Sinatra that adds basic publish/subscribe streaming using HTML5 Server Sent Events.

For example, clients can subscribe to events like this:

var es = new EventSource('/subscribe');
es.onmessage = function(e) {
  console.log(JSON.parse(e.data));
};

And then you can broadcast events to them like this:

Sinatra::PubSub.publish_all(type: 'tick')

You can subscribe to specific channels:

var es = new EventSource('/subscribe/sites/123');

And publish to them:

Sinatra::PubSub.publish('sites/123', data: 'hi')

You can find a simple demo on Heroku, which streams a 'tick' every second to your browser.

http://sinatra-pubsub-tick.herokuapp.com

• Thin
• Redis
• Sinatra

Add this line to your application's Gemfile:

gem 'sinatra-pubsub'

And then execute:

$ bundle

Or install it yourself as:

$ gem install sinatra-pubsub

Include it in your Sinatra application like so:

require 'sinatra/pubsub'
register Sinatra::PubSub

This creates a /subscribe/* endpoint, which clients can use with EventSource.

You can publish to channels using the Sinatra::PubSub.publish_all(msg) or Sinatra::publish(channel, msg) methods.

Messages will be automatically serialized to JSON - you'll need to parse them on the client. See the ./examples dir for more use-cases.

It's often a good idea to create a separate streaming server on a subdomain, rather than using your main application server for streaming. This gives you a bit more flexibility, like letting you use a Unicorn for your application server, and Thin for your streaming server. This is a quick guide to creating exactly that on Heroku.

First create your streaming server from the 'basic' example.

git clone https://github.com/maccman/sinatra-pubsub.git
cp -r sinatra-pubsub/examples/basic myapp-stream
cd myapp-stream
bundle install
git init
git add .
git commit -m 'first commit'
heroku create myapp-stream
git push heroku master

Now the server is deployed, you need to setup Redis. If you already have Redis running on your main application server, just run:

heroku config -a myapp-stream | grep REDIS
heroku config:set REDIS_URL=YOUR_REDIS_URL -a myapp-stream

Otherwise install the RedisCloud addon:

heroku addons:add rediscloud -a myapp-stream
heroku config -a myapp-stream | grep REDIS
heroku config:set REDIS_URL=YOUR_REDIS_URL -a myapp-stream

And you're finished! You can subscribe to a channel from any browser like this:

var es = new EventSource('http://myapp-stream.herokuapp.com/subscribe');
es.onmessage = function(e) {
  console.log(JSON.parse(e.data));
};

And publish to the stream from any Ruby client connected to the same Redis server:

Sinatra::PubSub.publish_all('Hello World')