Setting public_file_server.headers except for some files - ruby-on-rails

Question

I use this in production.rb :
config.public_file_server.headers = {
'Cache-Control' => 'public, s-maxage=31536000, maxage=31536000',
'Expires' => "#{1.year.from_now.to_formatted_s(:rfc822)}"
}
I use public files through a cdn.mydomain.com, which is reading from www.mydomain.com and it copies the cache-control from www.mydomain.com, that I set with public_file_server.headers.
The issue is that I want some files from /public to not have those cache-control, for example for my service-worker.js
Is there a way to set those cache control only for one folder in /public for example?
The other solution would be to remove this public_file_server.headers configuration, and setting the cache control on the cdn level (I use cdn.mydomain.com/publicfile), and keeping www.mydomain.com/serviceworker without cache control, for the service worker.
But maybe there is a chance to config this at the Rails level?

Answer 1

I had exactly the same problem: PWA built with Rails using CDN (Cloudfront). For the assets I want to use cache headers with far future expires, but the ServiceWorker needs Cache-control: No-cache.
Because CloudFront doesn't allow to add or change headers by itself, I need a solution on the app level. After some research I found a solution in a blogpost. The idea is to set headers via public_file_server.headers and add a middleware to change this for the ServiceWorker file.
Also, you wrote maxage=, it should be max-age=.
Here is the code I use:
production.rb:
config.public_file_server.enabled = ENV['RAILS_SERVE_STATIC_FILES'].present?
config.public_file_server.headers = {
'Cache-Control' => 'public, s-maxage=31536000, max-age=15552000',
'Expires' => 1.year.from_now.to_formatted_s(:rfc822)
}
if ENV['RAILS_SERVE_STATIC_FILES'].present?
config.middleware.insert_before ActionDispatch::Static, ServiceWorkerManager, ['sw.js']
end
app/middleware/service_worker_manager.rb:
# Taken from https://codeburst.io/service-workers-rails-middleware-841d0194144d
#
class ServiceWorkerManager
# We’ll pass 'service_workers' when we register this middleware.
def initialize(app, service_workers)
#app = app
#service_workers = service_workers
end
def call(env)
# Let the next middleware classes & app do their thing first…
status, headers, response = #app.call(env)
dont_cache = #service_workers.any? { |worker_name| env['REQUEST_PATH'].include?(worker_name) }
# …and modify the response if a service worker was fetched.
if dont_cache
headers['Cache-Control'] = 'no-cache'
headers.except!('Expires')
end
[status, headers, response]
end
end