A small web server built with Ractor that runs Rack apps

config.ru

require 'etc'
require 'socket'
require 'webrick'

Ractor.make_shareable(WEBrick::Config::HTTP)
Ractor.make_shareable(WEBrick::HTTPUtils::HEADER_CLASSES)
Ractor.make_shareable(WEBrick::HTTPStatus::StatusMessage)

class App
  def call(env)
    if env["PATH_INFO"] == "/"
      [200, {}, ["It works!"]]
    else
      [404, {}, ["Not Found"]]
    end
  end
end

class RactorServer
  CPU_COUNT = Etc.nprocessors

  def self.run(app, **options)
    new(app, options).start
  end

  def initialize(app, options)
    @app = app
    @options = options
  end

  def start
    port = Ractor::Port.new
    dispatcher = Ractor.new(port) do |port|
      controller = Ractor::Port.new
      todo = Ractor::Port.new
      port.send([controller, todo])
      loop do
        worker = controller.receive
        worker.send(todo.receive, move: true)
      end
    end
    controller, todo = port.receive
    port.close

    workers = CPU_COUNT.times.map do
      Ractor.new(@app, @options, controller) do |app, options, controller|
        loop do
          controller.send(Ractor.current)
          s = Ractor.receive

          request = WEBrick::HTTPRequest.new(WEBrick::Config::HTTP.merge(RequestTimeout: nil))
          request.parse(s)

          env = request.meta_vars
          status, headers, body = app.call(env)

          response = WEBrick::HTTPResponse.new(WEBrick::Config::HTTP)
          response.status = status
          body.each { |part| response.body << part }
          response.send_response(s)
        end
      end
    end

    listener = Ractor.new(todo) do |todo|
      server = TCPServer.new(8080)
      loop do
        conn, _ = server.accept
        todo.send(conn, move: true)
      end
    end

    loop do
      Ractor.select(dispatcher, *workers, listener)
      # if the line above returned, one of the dispatcher, the workers or the listener has crashed
    end
  end
end

Rackup::Handler.register :ractor_server, RactorServer

run App.new