push metadata updates from liquidsoap to http stream in sinatra

ideas

* redis pub/sub
  * no support for redis in liquidsoap, could call a ruby script?
* osc?
  * supported directly in liquidsoap

* unix socket
  * would require local sinatra app to communicate with the outside world
* write to file, poll filesystem with fs-events gem
  * would require local sinatra app to communicate with the outside world

Redis idea seems good. I'm already a little familiar with the technology from working with Resque.

pub_metadata.rb

# adopted from https://github.com/gorsuch/sinatra-streaming-example/blob/master/worker.rb

require 'redis'

redis_url = ENV["REDISTOGO_URL"] || "redis://localhost:6379"
uri = URI.parse(redis_url)
r = Redis.new(:host => uri.host, :port => uri.port, :password => uri.password)

meta = ARGV[0]

puts "setting metadata..."
r.publish "metadata", meta

radio.liq

source = on_metadata(pub_metadata, source)

def on_metadata(m) =
  log("metadata changed: #{m}")
  result = get_process_lines("./pub_metadata #{m}")
  log("pub_metadata: #{result}")
end

sinatra_app.js

<script>
  var es = new EventSource('/metadata');
  es.onmessage = function(e) { $('#streamtitle').html(e.title) };
</script>

sinatra_app.rb

# https://github.com/gorsuch/sinatra-streaming-example/blob/master/web.rb

require 'redis'
require 'sinatra'

configure do
  redis_url = ENV["REDISTOGO_URL"] || "redis://localhost:6379"
  uri = URI.parse(redis_url)
  set :redis, Redis.new(:host => uri.host, :port => uri.port, :password => uri.password)
end

get '/metadata' do
  puts "connection made"

  stream do |out|
    settings.redis.subscribe 'metadata' do |on|
      on.message do |channel, message|
        out << "#{message}\n"
      end
    end
  end
end

Seems to be working so far. But I can only stream the events to one client at a time, it seems like. It seems to be very flaky, sometimes the connection just hangs and I don't see any data for a long time.