Part of the Hostess class from RubyGems.org

hostess.rb

class Hostess < Sinatra::Base

... etc ...

  def serve_via_s3
    serve do
      redirect "http://#{$rubygems_config[:s3_domain]}#{request.path_info}"
    end
  end

... etc ...

  %w[/specs.4.8.gz
     /latest_specs.4.8.gz
     /prerelease_specs.4.8.gz
  ].each do |index|
    get index do
      content_type('application/x-gzip')
      serve_via_s3
    end
  end

... etc ...