Rails streaming

application.js

//= require jquery
//= require jquery_ujs

$(function() {
  var source = new EventSource('/stream');
  source.addEventListener('counter', function(e) {
    $('body').after(e.data + '<br />');
  });
});

posts_controller.rb

class PostsController < ApplicationController
  # ...

  def stream
    response.headers.delete('Content-Length')
    response.headers['Cache-Control'] = 'no-cache'
    response.headers['Content-Type'] = 'text/event-stream'

    self.response_body = Enumerator.new do |y|
      loop do
        if (Time.current.sec % 5).zero?
          y << "event: counter\n"
          y << "data: 5 seconds passed\n\n"
        end
        sleep 1
      end
    end
  end

  # The new approach
  # include ActionController::Live
  def stream
    response.headers['Content-Type'] = 'text/event-stream'

    begin
      loop do
        if (Time.current.sec % 5).zero?
          response.stream.write("event: counter\n")
          response.stream.write("data: 5 seconds passed\n\n")
        end
        sleep 1
      end
    rescue IOError
      # Catch when the client disconnects
    ensure
      response.stream.close
    end
  end

  # ...
end

z.caveats

- close stream
- IE has not server-sent events
- preload_frameworks & allow_concurrency options in development
- Puma, Thin, Rainbow! servers