config.ru

require 'rack'
require 'puma'
require 'thread'

class Middleware
  def initialize(app)
    @app = app
    @queue = Queue.new    
    @thread = Thread.new { run_loop }
  end

  def call(env)
    if delay_response?(env)
      response = @app.(env)

      io = env["rack.hijack"].()
      @queue.push([io, response, Time.now + 5])
      [-1, {}, []]
    else
      @app.(env)
    end
  end

  def delay_response?(env)
    true
  end

  def run_loop
    loop do
      io, response, at = @queue.pop

      delay = at - Time.now
      sleep(delay) if delay > 0

      code, headers, body = response
      io.puts "HTTP/1.1 #{ code }\r\n\r\n#{ body.join }"
      io.close
    end
  end
end

run Middleware.new(->(env) { [200, {}, ["hi"]] })