Question

I have a simple Sinatra App running on EventMachine, like this example.

The app is working, now I’d like to allow the routes I’m defining in Sinatra to access the websocket using the EventMachine channel that is created. I naively tried the following, but of course within the Sinatra App, the @channel variable isn’t defined, so this doesn’t work.

require 'em-websocket'
require 'sinatra'

EventMachine.run do
  @channel = EM::Channel.new

  class App < Sinatra::Base
    get '/' do
      erb :index
    end

    post '/test' do
      @channel.push "Post request hit endpoint"
      status 200
    end
  end


  EventMachine::WebSocket.start :host => '0.0.0.0', :port => 8080 do |socket|
    socket.onopen do
      sid = @channel.subscribe { |msg| socket.send msg }
      @channel.push "Subscriber ID #{sid} connected!"

      socket.onmessage do |msg|
        @channel.push "Subscriber <#{sid}> sent message: #{msg}"
      end

      socket.onclose do
        @channel.unsubscribe(sid)
      end
    end
  end

  App.run! :port => 3000
end

How could I access the EventMachine channel I’ve got open within my Sinatra app?

Answer 1

In case others don’t know what we’re talking about in the comments, here’s an example of using a class instance variable in the way I suggested. This runs, but I don’t know if it does what’s expected:

require 'em-websocket'
require 'sinatra'
require 'haml'

module Example

  def self.em_channel
    @em_channel ||= EM::Channel.new
  end

  EventMachine.run do

    class App < Sinatra::Base
      configure do
        enable :inline_templates
      end

      get '/' do
        haml :index
      end

      get '/test' do
        Example.em_channel.push "Test request hit endpoint"
        status 200
      end
    end


    EventMachine::WebSocket.start :host => '0.0.0.0', :port => 8080 do |socket|
      socket.onopen do
        sid = Example.em_channel.subscribe { |msg| socket.send msg }
        Example.em_channel.push "Subscriber ID #{sid} connected!"

        socket.onmessage do |msg|
          Example.em_channel.push "Subscriber <#{sid}> sent message: #{msg}"
        end

        socket.onclose do
          Example.em_channel.unsubscribe(sid)
        end
      end
    end

    App.run!
  end
end

__END__

@@ layout
%html
  = yield

@@ index
%div.title Hello world.