Problematic caching with rack cache

Question

I am trying to cache a response from a server locally per example shown here.

#!/usr/bin/env ruby

require 'restclient/components'
require 'rack/cache'
RestClient.enable Rack::Cache,
                  :metastore => 'file:/tmp/cache/meta',
                  :entitystore => 'file:/tmp/cache/body',
                  :verbose => true
RestClient.get 'http://www.google.com/intl/en/policies/privacy/?fg=1'

Somehow I always get miss as a response and the folder is empty. I guess caching doesn't work for me. What am I doing wrong?

cache: [GET /intl/en/policies/privacy/?fg=1] miss

Update

The repsponse header contains:

Cache-Control: must-revalidate, private, max-age=0

So I guess my question is how to intercept a response before it is processed and modify response header fields?

Have you looked at the response headers? Perhaps they don't allow caching — Frederick Cheung, Apr 24 '15 at 06:24
They don't allow caching, but I am looking to override this behavior. I need to be able to force caching at will on the client. — bioffe, Apr 24 '15 at 11:13

score 2 · Answer 1 · answered Apr 24 '15 at 16:28

Rack::Cache is "standards-compliant", which in this case means it pays attention to the cache headers. It has an option for allow_reload, but that won't help with the specific header you're seeing.

So to use Rack::Cache, you'd need to either intercept the request first, probably by monkeypatching Rack::Cache, or you'd need to fork Rack::Cache to allow the behavior you want. I wouldn't do either of those here.

In this case, I'd recommend not using Rack::Cache, and instead directly writing a very simple cache based on raw RestClient. Check the cache freshness yourself and only send the request if you need to.

This is exactly what I ended up doing. – bioffe Apr 24 '15 at 16:38 — bioffe, Apr 24 '15 at 16:38

Problematic caching with rack cache

1 Answers1