Add support for caching both body and headers in Garner::Mixins::Rack

[dblock]

We have monkey patched the Rack mixin to allow caching both headers and body, like this:

module Garner
  module Cache
    class Identity
      TRACKED_HEADERS = %w{ X-Total-Count }

      alias_method :_fetch, :fetch
      def fetch(&block)
        if @key_hash[:tracked_grape_headers]
          result, headers = _fetch do
            result = yield
            headers = @ruby_context.header.slice(*TRACKED_HEADERS) if @ruby_context.respond_to?(:header)
            [result, headers]
          end

          (headers || {}).each do |key, value|
            @ruby_context.header(key, value) if @ruby_context.respond_to?(:header)
          end

          result
        else
          _fetch(&block)
        end
      end

    end
  end
end

require "garner/mixins/rack"

module Garner
  module Mixins
    module Rack

      alias_method :_garner, :garner
      def garner(&block)
        response, headers = _garner.key({ tracked_grape_headers: true }, &block)
      end

    end
  end
end

It should be possible to roll this functionality into Garner. The Identity part should probably become more generic to store data and metadata, while the Rack mixin would just reuse that functionality.

[fancyremarker]

What would the API for a feature like this look like, in your opinion? I want to be careful not to complicate the API too much to support this feature.

[monfresh]

+1 for this feature. Without it, I can't use Garner because we send Pagination info via the Link header and other custom headers which clients that consume our API rely on. I'll try @dblock's patch in the meantime.

[onomated]

+1 Same here. Issues with pagination info in the header

[rdurgarao]

+1 Same issue with header cache

[scottraio]

+1

[ShallmentMo]

+1 with https://github.com/monterail/grape-kaminari