Server-Sent Events with Rails 4

config.cache_classes = true # SSE needs this true

# Do not eager load code on boot.
config.eager_load = true # SSE needs this true

class PushNotificationsController < ApplicationController
  include ActionController::Live
  Mime::Type.register "text/event-stream", :stream

  def index
    respond_to do |format|
      format.html
      format.stream {
        response.headers['Content-Type'] = 'text/event-stream'
        begin
          loop do
            response.stream.write "data: #{System.status}\n\n"
            sleep 2.second
          end
        rescue IOError # Raised when browser interrupts the connection
        ensure
          response.stream.close # Prevents stream from being open forever
        end
      }
    end
  end
end

var connectToSSE = function () {
  var source = new EventSource('/connect_to_sse');
  source.onopen = function (event) {
    console.log("Open connection!");
  }
  source.onerror = function (event) {
    var txt;
    switch( event.target.readyState ){
        // if reconnecting
        case EventSource.CONNECTING:
            txt = 'Reconnecting...';
            break;
        // if error was fatal
        case EventSource.CLOSED:
            txt = 'Connection failed. Will not retry.';
            break;
    }
    console.log(txt);
  }
  source.onmessage = function(event) {
    console.log("Message: " + event.data);
  }
}
$(document).ready(connectToSSE);

# 
# HTTP streaming for push notifications
# 
get '/connect_to_sse' => 'push_notifications#index', as: :connect_to_sse

<%= render 'layouts/system_status' %>

<%= System.check %>

class System < ActiveRecord::Base

  def self.columns() @columns ||= []; end
 
  def self.column(name, sql_type = nil, default = nil, null = true)
    columns << ActiveRecord::ConnectionAdapters::Column.new(name.to_s, default, sql_type.to_s, null)
  end
  
  column :status, :string

  def self.check
    if Rails.env.production?
      "OK"
    else
      # "OK" 
      "505 fake status"
    end
  end
  
  #
  # to stream to clients
  # 
  def self.status
    "data: #{self.check}"
  end
  
end

pool = 20 # = thin server max threads