prxoy http://10-1-3-20.example.com/ to http://10.1.3.20/

proxy.rb

require 'rubygems'
require 'em-proxy'
require 'http/parser' # gem install http_parser.rb
require 'UUID'

# > ruby em-proxy-http.rb
# > curl --proxy localhost:9889 www.google.com

host = "0.0.0.0"
port = 9889
puts "listening on #{host}:#{port}..."

Proxy.start(:host => host, :port => port) do |conn|

  @p = Http::Parser.new
  @p.on_headers_complete = proc do |h|
    session = UUID.generate
    puts "New session: #{session} (#{h.inspect})"

    host, port = h['Host'].split(':')
    dest = host.split('.').first.gsub('-', '.')
    begin
      conn.server session, :host => dest, :port => 80
      conn.relay_to_servers @buffer
    rescue
      conn.close_connection
    end

    @buffer.clear
  end

  @buffer = ''

  conn.on_connect do |data,b|
    #puts [:on_connect, data, b].inspect
  end

  conn.on_data do |data|
    @buffer << data
    @p << data
    data
  end

  conn.on_response do |backend, resp|
    #puts [:on_response, backend, resp].inspect
    resp
  end

  conn.on_finish do |backend, name|
    #puts [:on_finish, name].inspect
  end
end