File downloads and REST

If you're talking about resources, it makes more sense to make that
file it's own resource.

map.resources :foos do |foo|
  foo.resource :download # assuming there's one 'dynamic' file per Foo record

GET /foos/1/download # downloads/index action.

Part of the rails restful routing style was to stick to the core 7
actions (index, show, new, edit, update, create, destroy) by bringing
out the "inner resource". This makes more sense if folks can also
update or destroy the extra resource. Then you wouldn't need several
actions like show_download, create_download, etc.