gistfile1.rb

require 'rubygems'
require 'sinatra'
require 'tempfile'

class Jaxer
  class << self
    def json_to_png(json)
      
      # producing tempfile
      file = Tempfile.new('jaxer')
      
      
      file.open do |f|
        yield(f)
      end
    end
  end
end

get '/' do
  Jaxer.json_to_png(params[:data]) do |img|
    @str = 'hello'
  end
  
  @str
end

not_found do
  'resource missing'
end