Redis Pub/Sub and Rails 4 Live Streaming

So today I got to play a bit with the newly minded Rails 4 RC 1. A new feature is Live Streaming so I decided to see how it would work with redis publish / subscribe channels.

So lets create an infinite loop which is publishing on the redis queue “namespaced:stream”

require 'redis'
require 'json'

$i = 1
redis = Redis.new
begin
    data = {"time" => "#{ Time.now }" }
    redis.publish("namespaced:stream", data.to_json)
    sleep 1
    $i +=1
end while $i > 0

Lets have that running indefinitely, it is now publishing on the channel namespaced:stream.

Lets install the latest Ruby on Rails 4 and get a streaming controller up and running

class StreamsController < ActionController::Base
    include ActionController::Live
  
    def the_stream
        response.headers['Content-Type'] = 'text/event-stream'
        redis = Redis.new
        redis.subscribe('namespaced:stream') do |on|
            on.message do |event, data|
                response.stream.write("data:#{ data }\n\n")
            end
        end
        ensure
            response.stream.close
        end
    end
end

Make sure you install the puma server and start it.

Now head to /streams/the_stream

Viola, pub/sub with live streaming through Rails 4 + Redis. You could hook up some javascript to access this data.

Stick this in item.js $(document).ready(initialize);

function initialize() {
    var source = new EventSource('/products/latest-product-events');
    source.addEventListener('message', function(e) {
        console.log("Received "+e.data);
        updateItemsPage(e.data);
    }, false);

    source.addEventListener('open', function(e) {
        console.log("Connection was opened.");
    }, false);

    source.addEventListener('error', function(e) {
        if (e.readyState == EventSource.CLOSED) {
            console.log("Connection was closed.");
        }else{
            console.log("Something else");
        }
    }, false);
};

function updateItemsPage(event) {
    var item = $('<li>').text(event);
    $('#items').prepend(item);
}

So, why is this cool? Well, firstly it leverages an advanced key-value store, Redis. Next, Rails 4 Live streaming is is a huge advantage. It allows Rails apps to be competitive with Node.js. Unfortunately most Rails application servers are not able to stream, so throw thin + unicorn out. Puma is the way forward it would seem.

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