Rack Middleware to tell you dimensions of an image

ImageSizer

# JRuby version of ImageScience (other image toolkits are available)
require 'image_voodoo'

class ImageSizer
  def initialize(app, mime_types=%w[image/jpeg image/png image/gif])
    @app = app
    @mime_types = mime_types
  end

  def call(env)
    status, headers, response = @app.call(env)
    if @mime_types.include? headers['Content-Type']
      headers['X-Content-Dimensions'] = getXY(response)
    end
    [status,headers,response]
  end

  def getXY(response)
    s = ''
    response.each { |l| s << l }
    return 'n/a' if s.empty? # don't break HEADs
    im = ImageVoodoo.with_bytes(StringIO.new(s).read)
    return "#{im.width}x#{im.height}"
  end
end