Wolfram CAPTCHA Sinatra App

captcha.rb

require 'rubygems'
require 'sinatra'
require 'nokogiri'
require 'digest'
require 'net/http'
require 'cgi'

configure do
  set :config, YAML.load_file(File.join(File.dirname(__FILE__), 'config.yml'))
  set :api_key, settings.config['api_key']
  set :api_base, "http://api.wolframalpha.com/v2/query"
  set :captcha_length, 6
end

get '/' do
  "hello world"
end

get '/captcha/:secret' do
  # Calculate our CAPTCHA and request it from Wolfram's API. Then parse the response.
  captcha = CGI::escape(Digest::MD5.hexdigest(params[:secret])[0, settings.captcha_length])
  key     = CGI::escape(settings.api_key)
  url     = URI.parse(settings.api_base + "?input=captcha+#{captcha}&appid=#{key}")
  resp    = Net::HTTP.get_response(url)
  xml     = Nokogiri::XML(resp.body)

  # need to remove the other attributes, because it contains the plaintext as an alt attribute
  @img     = xml.search('pod#Result > subpod[primary="true"] > img').first.attr('src') 

  content_type 'text/html'
  "<img src='#{@img}' />"
end

# vim: set ft=ruby sw=2 ts=2 :