gistfile1.rb

# Given a controller that looks like this
class ModelsController < ApplicationController
  load_and_authorize_resource  #CanCan

  def show
    if stale? @model
      respond_to do |format|
        format.json do
          @model
        end
      end
    end
  end

end

# The spec looks like this
context "http caching" do
  context "given a model" do
    before do
      @model = Factory :model, :user => @brett
    end
    context "on the first request" do
      it "returns a 200" do
        get :show, :id => @model.id, :format => :json
        response.code.should == "200"
      end
    end
    context "on a subsequent request" do
      before do
        get :show, :id => @model.id, :format => :json
        response.code.should == "200"
        response.headers['ETag'].should be_present
        response.headers['Last-Modified'].should be_present
        @etag = response.headers['ETag']
        @last_modified = response.headers['Last-Modified']
      end
      context "if it is not stale" do
        before do
          request.env['HTTP_IF_NONE_MATCH'] = @etag
          request.env['HTTP_IF_MODIFIED_SINCE'] = @last_modified
        end
        it "returns a 304" do
          get :show, :id => @model.id, :format => :json
          response.code.should == "304"
        end
      end
      context "if it has been updated" do
        before do
          sleep 1 # To ensure the model.updated_at has a delta of at least 1 sec
          @model.touch
          request.env['HTTP_IF_NONE_MATCH'] = @etag
          request.env['HTTP_IF_MODIFIED_SINCE'] = @last_modified
        end
        it "returns a 200" do
          # Initialize account_item instance in the controller so CanCan
          # will load up the resource from the db again
          controller.instance_variable_set(:@model, nil)

          get :show, :id => @model.id, :format => :json
          response.code.should == "200"
        end
      end
    end
  end
end