A little Goliath proof-of-concept for a dynamic custom origin for images in Amazon CloudFront

chomper.rb

# This is a hack. Just playing around.
#
# Original image:
#   http://media.photobattle.me.s3.amazonaws.com/images/5417/original.jpg
#
# To resize, use ImageMagick geometry strings (http://www.imagemagick.org/script/command-line-processing.php#geometry) in place of `original` in the URL.
#
# -- Examples --
#
# Proxies an existing image:
#   http://localhost:9000/images/5417/original.jpg
#
# Resize to fit within 300x300 (no cropping, no upsizing):
#   http://localhost:9000/images/5417/300x300>.jpg
#
# 50% of the original:
#   http://localhost:9000/images/5417/50%.jpg

require 'goliath'
require 'cgi'
require 'em-synchrony/em-http'
require 'mini_magick'

class Chomper < Goliath::API
  use Goliath::Rack::Validation::RequestMethod, %w(GET)
  
  HOST = 'http://media.photobattle.me.s3.amazonaws.com'
  
  def response(env)
    
    key = env['PATH_INFO']
    
    url = "#{HOST}#{key}"
    
    resized_image = EM::HttpRequest.new(url).head

    if resized_image.response_header.status == 200
      # Resized photo already exists. Pass it along.
      resized_image = EM::HttpRequest.new(url).get
      logger.debug "File exists: #{url}"
      return [200, {'X-Chomper' => 'Cache hit'}, resized_image.response]
    else
      _, __, id, format = CGI.unescape(key).split('/')
      logger.debug "id: #{id}, format: #{format}"
      source_url = "#{HOST}/images/#{id}/original.jpg"
      logger.debug "Checking if source exists: #{source_url}"
      source_image = EM::HttpRequest.new(source_url).get
        
      image = MiniMagick::Image.read(source_image.response)
      resize_cmd = format.gsub('.jpg', '')
      logger.debug "Resize: #{resize_cmd}"
      image.resize resize_cmd
        
      stream = StringIO.new
      image.write(stream)
        
      return [200, {'X-Goliath' => 'Cache miss'}, stream.string]
    end
    
    [404, {'X-Goliath' => 'Proxy'}, "Not Found"]
  end
end

# > ruby chomper.rb -sv

Thanks for your sharing.