Adobe XMP parser for JPEG files, in Ruby

xmp.rb

def xmp(filename)
  xap = "http://ns.adobe.com/xap/1.0/\0".freeze
  f = File.open(filename, 'r')
  xml = nil

  begin
    return nil unless f.readbyte == 0xFF
    return nil unless f.readbyte == 0xD8
    while !f.eof
      case f.readbyte
      when 0xFF
        case f.readbyte
        when 0xE1
          size = f.read(2).unpack('H*').first.hex
          next unless size > xap.length
          
          ns = f.read(xap.length)
          if ns == xap
            xml = f.read(size - xap.length - 2)
            break
          end
        end
      end
    end
  ensure
    f.close
  end

  xml
end


require 'nokogiri'
puts Nokogiri::XML.parse xmp('yeah.jpg')