Make invalidating responses at the metastore a bit cleaner

lib/rack/cache/headers.rb

@@ -83,6 +83,12 @@ def must_revalidate?
       cache_control.must_revalidate || cache_control.proxy_revalidate
     end
 
+    # Mark the response stale by setting the Age header to be equal to the
+    # maximum age of the response.
+    def expire!
+      headers['Age'] = max_age.to_s if fresh?
+    end
+
     # The date, as specified by the Date header. When no Date header is present,
     # set the Date header to Time.now and return.
     def date

lib/rack/cache/metastore.rb

@@ -38,9 +38,7 @@ def lookup(request, entity_store)
 
       req, res = match
       if body = entity_store.open(res['X-Content-Digest'])
-        status = res.delete('X-Status').to_i
-        response = Rack::Cache::Response.new(status, res, body)
-        response
+        restore_response(res, body)
       else
         # TODO the metastore referenced an entity that doesn't exist in
         # the entitystore. we definitely want to return nil but we should
@@ -73,7 +71,7 @@ def store(request, response, entity_store)
             requests_match?(vary, env, stored_env)
         end
 
-      headers = {'X-Status' => response.status.to_s}.update(response.headers)
+      headers = persist_response(response)
       headers.delete 'Age'
 
       entries.unshift [stored_env, headers]
@@ -93,11 +91,11 @@ def invalidate(request, entity_store)
       key = cache_key(request)
       entries =
         read(key).map do |req, res|
-          response = Rack::Cache::Response.new(0, res, nil) # XXX
+          response = restore_response(res)
           if response.fresh?
-            response.headers['Age'] = (response.max_age + 1).to_s
+            response.expire!
             modified = true
-            [req, response.headers.to_hash]
+            [req, persist_response(response)]
           else
             [req, res]
           end
@@ -116,6 +114,19 @@ def persist_request(request)
       env
     end
 
+    # Converts a stored response hash into a Response object. The caller
+    # is responsible for loading and passing the body if needed.
+    def restore_response(hash, body=nil)
+      status = hash.delete('X-Status').to_i
+      Rack::Cache::Response.new(status, hash, body)
+    end
+
+    def persist_response(response)
+      hash = response.headers.to_hash
+      hash['X-Status'] = response.status.to_s
+      hash
+    end
+
     # Determine whether the two environment hashes are non-varying based on
     # the vary response header value provided.
     def requests_match?(vary, env1, env2)

test/headers_test.rb

@@ -107,6 +107,29 @@ def initialize(*args)
     end
   end
 
+  describe '#expire!' do
+    it 'sets the Age to be equal to the max-age' do
+      @res.headers['Cache-Control'] = 'max-age=100'
+      @res.expire!
+      @res.headers['Age'].should.equal '100'
+    end
+    it 'sets the Age to be equal to the s-maxage when both max-age and s-maxage present' do
+      @res.headers['Cache-Control'] = 'max-age=100, s-maxage=500'
+      @res.expire!
+      @res.headers['Age'].should.equal '500'
+    end
+    it 'does nothing when the response is already stale/expired' do
+      @res.headers['Cache-Control'] = 'max-age=5, s-maxage=500'
+      @res.headers['Age'] = '1000'
+      @res.expire!
+      @res.headers['Age'].should.equal '1000'
+    end
+    it 'does nothing when the response does not include freshness information' do
+      @res.expire!
+      @res.headers.should.not.include 'Age'
+    end
+  end
+
   describe '#ttl' do
     it 'is nil when no Expires or Cache-Control headers present' do
       @res.ttl.should.be.nil