snapshot.rb

require 'snip_snap'
require 'hpricot'

module Rack

  # = Rack::Snapshot
  #
  # Takes the image tags in your page and expands them using some of the popular
  # image sharing services.  Currently supports these services:
  #
  #  * Skitch
  #  * Img.ly
  #  * Twitpic
  #  * Yfrog
  #  * Flickr (requires setting the API key - see below)
  #  * Twitgoo
  #
  # For example, this image tag that links to the public version of a snapshot:
  #
  #   <img src="http://img.ly/3ey" class="expand" />
  # 
  # Might be expanded to:
  #
  #   <img class="expand" src="http://img.ly/uploads/000/012/434/large_ChillPill13.jpg" />
  #
  # This middleware will attempt to expand any image tag with the class of "expand" by default,
  # but this can be overridden:
  #
  #   use Rack::Snapshot, :class_name => 'snapshot'
  #
  # See Rack::Snapsnot#new for recognized options.
  #
  class Snapshot

    # Recognized options:
    #   
    #   +class_name+ 
    #     Override the default class ("expand") with a name of your choosing.  Image
    #     tags that contain this class name will be subject to expansion through the 
    #     appropriate API.
    #
    #   +flickr_api_key+
    #     If provided, will allow you to expand full URLs for the Flickr service.
    #
    def initialize(app, options = {})
      self.options = options
      @app = app
    end

    def call(env)
      status, @headers, @response = @app.call(env)

      if html?
        (document/"img[@class~='#{@image_class_name}']").each do |image|
          image['src'] = full_image_url(image)
        end
        
        @response = document.to_s  
        @headers['Content-Length'] = @response.length.to_s
      end

      [status, @headers, [@response]]
    end
    
    def options=(options)
      @image_class_name = options[:class_name] || 'expand'
      SnipSnap.flickr_api_key = options[:flickr_api_key]
    end

    private
    def response_body
      body = String.new
      @response.each {|line| body << line }
      body
    end
    
    def document
      @document ||= Hpricot(response_body)
    end
    
    def full_image_url(image)
      source = image['src']
      client = SnipSnap.from_url(source)
      if client.image?
        source = client.image_url
      end
      source
    end
    
    def html?
      @headers.fetch('Content-Type', '').include?('text/html')
    end

  end
end