***** Checkout the rack-zippy gem, I recommend it over this gist, find it at https://github.com/eliotsykes/rack-zippy ***** An asset server for Rails 3.2.x that serves asset pipeline precompiled assets to clients, including those elusive gzipped (.gz) assets. Sadly Rails' own ActionDispatch::Static middleware does not take care of serving gzippe…

asset_server_middleware.rb

# 1. Add rack-rewrite to your Gemfile and run 'bundle install':
#    gem 'rack-rewrite'
#
# 2. Create a file with the contents below in config/initializers/asset_server_middleware.rb
#
# 3. Rename 'YourApp' below
#
# 4. In config/environments/production.rb and config/environments/test.rb, set:
#    config.serve_static_assets = true
#    config.assets.compile = false
#    config.assets.digest = true
#    config.assets.compress = true
#
# 5. Write some tests to be sure your assets are being served as expected. Your test will
#    probably want to clean and precompile the assets for an accurate test, e.g.:
#    system('bundle exec rake assets:clean assets:precompile')
#
# 6. config/application.rb can be altered so the assets bundler group is only used in development:
#    Bundler.require(*Rails.groups(:assets => %w(development))) # test environment removed
#
# 7. .gitignore the public/assets directory:
#    echo "public/assets" >> .gitignore
YourApp::Application.configure do
  
  # You probably only want config.assets.compile = true in development,
  # and set to false in test+production. When config.assets.compile is
  # true the app uses Sprockets for asset serving at runtime instead
  # of the send_file rules below. This is useful in development when
  # assets can change often.
  serve_precompiled_assets_only = !config.assets.compile
  next unless serve_precompiled_assets_only
  
  config.middleware.swap(ActionDispatch::Static, Rack::Rewrite) do
  
    local_file_path = ->(match, rack_env) {
      path = rack_env['PATH_INFO']
      raise 'Illegal request' if path.include?('..')
      "public#{path}"
    }

    local_gz_file_path = ->(match, rack_env) {
      "#{local_file_path.call(nil, rack_env)}.gz"
    }

    is_gzippable_request = ->(rack_env) {
      client_accepts_gzip = !!(rack_env['HTTP_ACCEPT_ENCODING'] =~ /\bgzip\b/)
      return client_accepts_gzip && File.exists?(local_gz_file_path.call(nil, rack_env))
    }

    is_static_request = ->(rack_env) {
      return File.exists?(local_file_path.call(nil, rack_env))
    }
    
    seconds_in_day = 24*60*60
    seconds_in_month = 31*seconds_in_day
    seconds_in_year = 365*seconds_in_day
    
    send_file %r{\A\/favicon\.ico}, 
      local_file_path,
      :headers => {
        'Cache-Control' => "public, max-age=#{seconds_in_month}",
        'Last-Modified' => 'Mon, 10 Jan 2005 10:00:00 GMT'
      },
      :if => is_static_request

    send_file %r{\A\/robots\.txt},
      local_file_path,
      :headers => {
        'Cache-Control' => "public, max-age=#{seconds_in_day}"
      },
      :if => is_static_request

    # Gzipped css
    send_file %r{\A\/assets\/.+\.css},
      local_gz_file_path,
      :headers => {
        'Vary' => 'Accept-Encoding',
        'Content-Encoding' => 'gzip',
        'Content-Type' => 'text/css',
        'Cache-Control' => "public, max-age=#{seconds_in_year}",
        'Last-Modified' => 'Mon, 10 Jan 2005 10:00:00 GMT'
      },
      :if => is_gzippable_request

    # Gzipped js
    send_file %r{\A\/assets\/.+\.js},
      local_gz_file_path,
      :headers => {
        'Vary' => 'Accept-Encoding',
        'Content-Encoding' => 'gzip',
        'Content-Type' => 'application/javascript',
        'Cache-Control' => "public, max-age=#{seconds_in_year}",
        'Last-Modified' => 'Mon, 10 Jan 2005 10:00:00 GMT'
      },
      :if => is_gzippable_request

    # js+css for gzip-unsupported clients
    send_file %r{\A\/assets\/.+\.(?:css|js)},
      local_file_path,
      :headers => {
          'Vary' => 'Accept-Encoding',
          'Cache-Control' => "public, max-age=#{seconds_in_year}",
          'Last-Modified' => 'Mon, 10 Jan 2005 10:00:00 GMT'
      },
      :if => is_static_request

    # Non-css, non-js assets
    send_file %r{\A\/assets\/.+},
      local_file_path,
      :headers => {
        'Cache-Control' => "public, max-age=#{seconds_in_year}",
        'Last-Modified' => 'Mon, 10 Jan 2005 10:00:00 GMT'
      },
      :if => is_static_request
      
  end

end

Looks good! WIll give it a whirl soon.

Thanks, would love to hear how it goes for you

I've written the rack-zippy gem to supersede this gist: https://github.com/eliotsykes/rack-zippy