em_micro_httpd.rb

require 'eventmachine'

class HTTP < EM::Connection
  include EM::P::LineText2

  RESPONSE = <<-PLAIN
HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 12
Connection: keep-alive
Server: test 1.0.0 codename mgabyt

hello world
  PLAIN

  def self.start
    EM.start_server '0.0.0.0', 3001, self
  end

  def initialize
    @buffer = []
  end

  def receive_line(line)
    @buffer << line
    if @buffer.last.strip.empty?
      @buffer.replace []
      send_data RESPONSE
    end
  end
end

EM.run do
  p $$
  HTTP.start
end