Invalidate instead of purge on non-GET/POST requests

Sets the Age header to the max_age + 1 before storing the
entry, causing it to be invalid the next time its retrieved from
cache. The Age header is no longer written when storing fresh/valid
entries.

CHANGES

@@ -2,7 +2,8 @@
 
   * Invalidate cache entries that match the request URL on non-GET/HEAD
     requests. i.e., POST, PUT, DELETE cause matching cache entries to
-    be purged.
+    be invalidated. The cache entry is validated with the backend using
+    a conditional GET the next time it's requested.
 
   * Implement "Cache-Control: max-age=N" request directive by forcing
     validation when the max-age provided exceeds the age of the cache

lib/rack/cache/context.rb

@@ -135,7 +135,6 @@ def dispatch
       # tidy up response a bit
       response.not_modified! if not_modified?(response)
       response.body = [] if @original_request.head?
-      response.headers.delete 'X-Status'
       response.to_a
     end
 
@@ -195,7 +194,6 @@ def validate(entry)
         if backend_response.status == 304
           record :valid
           entry = entry.dup
-          entry.headers.delete('Age')
           entry.headers.delete('Date')
           %w[Date Expires Cache-Control Etag Last-Modified].each do |name|
             next unless value = backend_response.headers[name]

lib/rack/cache/headers.rb

@@ -200,7 +200,7 @@ def date
 
     # The age of the response.
     def age
-      [(now - date).to_i, 0].max
+      (headers['Age'] ||  [(now - date).to_i, 0].max).to_i
     end
 
     # The number of seconds after the time specified in the response's Date

lib/rack/cache/metastore.rb

@@ -38,7 +38,8 @@ def lookup(request, entity_store)
 
       req, res = match
       if body = entity_store.open(res['X-Content-Digest'])
-        response = Rack::Cache::Response.new(res['X-Status'].to_i, res, body)
+        status = res.delete('X-Status').to_i
+        response = Rack::Cache::Response.new(status, res, body)
         response.activate!
         response
       else
@@ -57,7 +58,6 @@ def store(request, response, entity_store)
 
       # write the response body to the entity store if this is the
       # original response.
-      response['X-Status'] = response.status.to_s
       if response['X-Content-Digest'].nil?
         digest, size = entity_store.write(response.body)
         response['X-Content-Digest'] = digest
@@ -74,7 +74,11 @@ def store(request, response, entity_store)
           (vary == res['Vary']) &&
             requests_match?(vary, env, stored_env)
         end
-      entries.unshift [stored_env, {}.update(response.headers)]
+
+      headers = {'X-Status' => response.status.to_s}.update(response.headers)
+      headers.delete 'Age'
+
+      entries.unshift [stored_env, headers]
       write key, entries
       key
     end
@@ -86,14 +90,15 @@ def cache_key(request)
     end
 
     # Invalidate all cache entries that match the request.
-    #
-    # TODO: This should not purge the entries but rather mark them as
-    # stale so that they're revalidated on the next request.
     def invalidate(request, entity_store)
       key = cache_key(request)
       entries = read(key)
-      entries.each { |req,res| entity_store.purge(res['X-Content-Digest']) }
-      purge(key)
+      entries = entries.map do |req, res|
+        res = Rack::Cache::Response.new(0, res, nil)
+        res.headers['Age'] = res.max_age + 1
+        [req, res.headers]
+      end
+      write key, entries
     end
 
   private

lib/rack/cache/response.rb

@@ -36,7 +36,6 @@ def initialize(status, headers, body)
       @status = status
       @headers = Rack::Utils::HeaderHash.new(headers)
       @body = body
-      @now = Time.now
       @headers['Date'] ||= now.httpdate
     end
 
@@ -57,7 +56,7 @@ def []=(header_name, header_value)
 
     # Called immediately after an object is loaded from the cache.
     def activate!
-      headers['Age'] = age.to_i.to_s
+      headers['Age'] = age.to_s
     end
 
     # Return the status, headers, and body in a three-tuple.

test/context_test.rb

@@ -23,6 +23,7 @@
       app.should.be.called
       response.should.be.ok
       cache.trace.should.include :invalidate
+      cache.trace.should.include :pass
     end
   end
 
@@ -555,7 +556,7 @@
     response['Content-Length'].should.equal 'Hello World'.length.to_s
   end
 
-  it 'purges cached responses on POST' do
+  it 'invalidates cached responses on POST' do
     respond_with do |req,res|
       if req.request_method == 'GET'
         res.status = 200
@@ -577,20 +578,29 @@
     cache.trace.should.include :miss
     cache.trace.should.include :store
 
+    # make sure it is valid
+    get '/'
+    app.should.not.called
+    response.should.be.ok
+    response.body.should.equal 'Hello World'
+    cache.trace.should.include :fresh
+
     # now POST to same URL
     post '/'
     app.should.be.called
     response.should.be.redirect
     response['Location'].should.equal '/'
     cache.trace.should.include :invalidate
+    cache.trace.should.include :pass
     response.body.should.equal ''
 
     # now make sure it was actually invalidated
     get '/'
     app.should.be.called
     response.should.be.ok
     response.body.should.equal 'Hello World'
-    cache.trace.should.include :miss
+    cache.trace.should.include :stale
+    cache.trace.should.include :invalid
     cache.trace.should.include :store
   end
 

test/metastore_test.rb

@@ -143,10 +143,12 @@ def self.call(request); request.path_info.reverse end
     body.should.equal 'test'
   end
 
-  it 'purges meta and entity store entries with #invalidate' do
+  it 'invalidates meta and entity store entries with #invalidate' do
     store_simple_entry
     @store.invalidate(@request, @entity_store)
-    response = @store.lookup(@request, @entity_store).should.be.nil
+    response = @store.lookup(@request, @entity_store)
+    response.should.be.kind_of Rack::Cache::Response
+    response.should.be.stale
   end
 
   it 'succeeds quietly when #invalidate called with no matching entries' do