Faraday Http Cache

a Faraday middleware that respects HTTP cache, by checking expiration and validation of the stored responses.

Installation

Add it to your Gemfile:

gem 'faraday-http-cache'

Usage and configuration

You have to use the middleware in the Faraday instance that you want to, along with a suitable store to cache the responses. You can use the new shortcut using a symbol or passing the middleware class

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache
  # or
  builder.use Faraday::HttpCache, store: Rails.cache

  builder.adapter Faraday.default_adapter
end

The middleware accepts a store option for the cache backend responsible for recording the API responses that should be stored. Stores should respond to write and read, just like an object from the ActiveSupport::Cache API.

# Connect the middleware to a Memcache instance.
store = ActiveSupport::Cache.lookup_store(:mem_cache_store, ['localhost:11211'])

client = Faraday.new do |builder|
  builder.use :http_cache, store: store
  builder.adapter Faraday.default_adapter
end

# Or use the Rails.cache instance inside your Rails app.
client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache
  builder.adapter Faraday.default_adapter
end

The default store provided is a simple in memory cache that lives on the client instance, so it's important to configure a proper one for your production environment.

the stdlib JSON module is used for serialization by default. If you expect to be dealing with images, you can use Marshal instead, or if you want to use another json library like oj or yajl-ruby.

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache, serializer: Marshal
  builder.adapter Faraday.default_adapter
end

Logging

You can provide a :logger option that will be receive debug informations based on the middleware operations:

client = Faraday.new do |builder|
  builder.use :http_cache, store: Rails.cache, logger: Rails.logger
  builder.adapter Faraday.default_adapter
end

client.get('http://site/api/users')
# logs "HTTP Cache: [GET users] miss, store"

See it live

You can clone this repository, install it's dependencies with Bundler (run bundle install) and execute the files under the examples directory to see a sample of the middleware usage.

What get's cached?

The middleware will use the following headers to make caching decisions:

Cache-Control
Age
Last-Modified
ETag
Expires

Cache-Control

The max-age, must-revalidate, proxy-revalidate and s-maxage directives are checked.

Shared vs. non-shared caches

By default, the middleware acts as a "shared cache" per RFC 2616. This means it does not cache responses with Cache-Control: private. This behavior can be changed by passing in the :shared_cache configuration option:

client = Faraday.new do |builder|
  builder.use :http_cache, shared_cache: false
  builder.adapter Faraday.default_adapter
end

client.get('http://site/api/some-private-resource') # => will be cached

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