Wonder if you'd like to merge in this new middleware I've been using recently? It serves static error pages if one exists with the same name as your status code, e.g. public/500.html
Works a little like Rack::NotFound but encompasses any status code, therefore can be used for 400's, 500's etc.
Added spec tests, not using this in production yet but it goes fine on my dev environment.
Add Rack::ErrorPages with tests, update readme and authors too
Doesn't use Rack::File, needs rebase, please open new pull request if you are still interested