Create thumbnails from images stored in S3

thumber.rb

require 'rack/thumb'
require 'rack/s3'

class Thumber

  def initialize(app)
    @app = stack_app app
  end

  def stack_app(app)
    Rack::Builder.new do
      map '/thumb' do
        use Rack::Thumb

        run(lambda do |env|
          Rails.logger.info "Thumber /thumb: #{ CloudApp.s3.bucket }#{ env['PATH_INFO'] }"

          status, headers, body = Rack::S3.new(:bucket => CloudApp.s3.bucket).
                                           call(env)

          [ status, Thumber.mangle_headers(env['PATH_INFO'], headers), body ]
        end)
      end

      # Ignore all other requests
      map '/' do
        run lambda { |env| app.call env }
      end
    end
  end

  def call(env)
    @app.call env
  end

  def self.mangle_headers(path_info, headers)
    headers.merge('Cache-Control' => "public; max-age=#{ 1.month }").
            tap do |new_headers|
              if new_headers['Content-Type'] == 'binary/octet-stream'
                new_content_type = MIME::Types.type_for(path_info).first.
                                     try(:content_type)

                if new_content_type
                  new_headers['Content-Type'] = new_content_type
                end
              end
            end
  end

end