Quine Eval Server - An experiment

server.rb

# Quine Eval Server - An experiment
# =================================
# 
# This server, when run, will accept POST requests on the root ('/') where the post body is ruby code to eval.
# This server also makes a copy of its source code, and includes the eval'd statements in the new source.
# Because this is a sinatra server, you can use this to create new routes and build up a web service incrementally while running.
#
# Example post to server using curl:
# curl -vv -XPOST -d 'get "/hi" do ; "hi!" ; end' 'http://localhost:4567'
#
# * This is an experiment. This is probably irresponsible to use in production, but is interesting nonetheless :)

require 'sinatra/base'
# This will be the output server source code which is created from this server and code passed to the server by posting to '/'
$_output = File.new "new_server.rb", "w"
$_server_file = File.readlines(File.expand_path(__FILE__, Dir.pwd))
$_output_line_start = __LINE__ + 1 ; $_output.print $_server_file[0...$_output_line_start].join
class DynamicEvalServer < Sinatra::Base
  def self._binding
    binding
  end
  # Posting to the root will let users pass executable code to this server. This code will be saved along with the server in the output.
  post '/' do
    a = request.body.read
    begin
      eval a, self.class._binding
      $_output.puts a
      halt 200
    rescue
      halt 400
    end
  end
  run!
end
$_output.print $_server_file[$_output_line_start...$_server_file.length].join
$_output.close