This engine is designed to allow Server-Sent Events to be broadcast to all listeners from anywhere in your Rails app. At the moment it only works with Thread based Rack servers like Puma.

Plans are to hook it up to Redis if you need to use process-based servers like Unicorn.

This has been mostly tested with Ruby v2.2.1 and Rails v4.2.1 + Puma.

This uses the Rack socket hijacking functionality to avoid having to occupy a thread per connection. Now only 1 extra thread in your app is required.

gem 'sse-rails-engine'

Mount the engine in your config/routes.rb:

Rails.application.routes.draw do
  mount SseRailsEngine::Engine, at: '/sse'
end

To use, initialize the connection on the client side, so add the following javascript:

$(document).ready(function () {
  var source = new EventSource('/sse');

  source.addEventListener('test', function(e) {
    // Do something
  }, true);
});

Then you can send an event from anywhere in your app:

SseRailsEngine.send_event('test', { foo: 'bar' })

It supports the idea of channels so that if pages don't need to receive certain events, then you won't waste the bandwidth or processing on the server:

Clientside:

$(document).ready(function () {
  var source = new EventSource('/sse?channels=foo,bar,baz');

  source.addEventListener('other', function(e) {
    // Will never be called
  }, true);

  source.addEventListener('foo', function(e) {
    // Do stuff
  }, true);
});

Serverside:

SseRailsEngine.send_event('foo', '') # Sent to the client
SseRailsEngine.send_event('other', '') # Won't be sent to the client

You can now enable the 'Access-Control-Allow-Origin' header in connection replies as well by setting: SseRailsEngine.access_control_allow_origin = 'https://example.org'

You may need to configure nginx to not buffer or cache SSE connections: http://stackoverflow.com/questions/13672743/eventsource-server-sent-events-through-nginx

MIT - Have at it! :)