Rack::Digestif

A rack middleware that ensures Sprockets assets are served regardless of whether the asset digest matches.

All asset URLs such as:

/assets/application-a1d0c6e83f027327d8461063f4ac58a6.css

are rewritten to remove the digest:

/assets/application.css

This works thanks to Sprockets compiling both digest and non-digest filenames in the assets directory.

Sprockets (and the Rails asset pipeline) uses MD5 hashes on the asset filenames to create cache-busting URLs. Although these new URLs are awesome they introduce a problem that the old query-string method did not have: requests to assets with an out-of-date digest will receive a 404. Why is this a problem? During a deployment there's a gap in between when the browser receives the HTML and when it requests an asset, and during that time the server may and probably will be updated and that poor customer will end up with an unstyled or javascript-less page.

Luckily the fix is easy; Sprockets generates every compiled file with and without a digest, so all that's needed is to rewrite incoming requests to remove the digest from the path. You can do this in nginx or HTTP proxy, rack-rewrite, or using Rack::Digestif.

$ gem install rack-digestif

Add it to your Rackup config.ru file like so:

require 'rack/digestif'
use Rack::Digestif

By default Rack::Digestif will rewrite all incoming URLs that have a digest. If you want to limit it to a given path, such as /assets, you simply pass the path as the first argument:

use Rack::Digestif, "/assets/"

Firstly add it to your Gemfile, and then add the middleware in application.rb like so:

config.middleware.insert_before ActionDispatch::Static, Rack::Digestif

As James A Rosen pointed out this isn't the ideal solution because you're serving up a new assets to old pages.

Rack::Digestif just brings things back on par with the old query-string method. If this isn't robust enough for you then ditch it and consider another approach, such as pushing compiled assets up to S3 and making sure old versions of assets exist across deployments.

See MIT-LICENSE for details.