runtime.rb

require 'rack'
require 'async/websocket/adapters/rack'

GUID = '3f35e4f2-3920-4797-9044-c4046ea4fb53'

def create_websocket_accept (nonce)
  Digest::SHA1.base64digest "#{nonce}#{GUID}"
end

def get_response_headers (env)
  request = Rack::Request.new env

  return [
    ['Sec-Websocket-Protocol', (request.get_header 'HTTP_SEC_WEBSOCKET_PROTOCOL')],
    ['Sec-Websocket-Version', (request.get_header 'HTTP_SEC_WEBSOCKET_VERSION')],
    ['Sec-Websocket-Accept', (create_websocket_accept request.get_header 'HTTP_SEC_WEBSOCKET_KEY')],
  ]
end

def get_response_protocols (env)
  return ['ws']
end

App = lambda do |env|
  Async::WebSocket::Adapters::Rack.open(env, headers: (get_response_headers env), protocols: (get_response_protocols env)) do |connection|
    while message = connection.read
      pp message
    end
  end or [200, {}, ["Hello World"]]
end