Allow custom options for transferable headers and non-cached headers

lib/rack/cache/context.rb

@@ -237,7 +237,7 @@ def validate(entry)
 
         entry = entry.dup
         entry.headers.delete('date')
-        %w[Date expires cache-control etag last-modified].each do |name|
+        %w[Date expires cache-control etag last-modified].concat(transfer_headers).each do |name|
           next unless value = response.headers[name]
           entry.headers[name] = value
         end
@@ -286,7 +286,7 @@ def fetch
     # Write the response to the cache.
     def store(response)
       strip_ignore_headers(response)
-      metastore.store(@request, response, entitystore)
+      metastore.store(@request, response, entitystore, non_cached_headers)
       response.headers['age'] = response.age.to_s
     rescue => e
       log_error(e)

lib/rack/cache/meta_store.rb

@@ -58,7 +58,7 @@ def lookup(request, entity_store)
     # Write a cache entry to the store under the given key. Existing
     # entries are read and any that match the response are removed.
     # This method calls #write with the new list of cache entries.
-    def store(request, response, entity_store)
+    def store(request, response, entity_store, non_cached_headers = [])
       key = cache_key(request)
       stored_env = persist_request(request)
 
@@ -97,6 +97,7 @@ def store(request, response, entity_store)
 
       headers = persist_response(response)
       headers.delete('age')
+      non_cached_headers.each{ |h| headers.delete(h) }
 
       entries.unshift [stored_env, headers]
       if request.env['rack-cache.use_native_ttl'] && response.fresh?

lib/rack/cache/options.rb

@@ -86,6 +86,19 @@ def option_name(key)
     # Default: ['set-cookie']
     option_accessor :ignore_headers
 
+    # Set of response headers that are transferred from the backend response
+    # onto the cache entry when validating a cached entity (after receiving a
+    # 304 response from the backend) before sending it to the client.
+    #
+    # Default: []
+    option_accessor :transfer_headers
+
+    # Set of response headers that will be passed to the client when present
+    # in any responses but will not be stored in cached entries.
+    #
+    # Default: []
+    option_accessor :non_cached_headers
+
     # Set of request headers that trigger "private" cache-control behavior
     # on responses that don't explicitly state whether the response is
     # public or private via a cache-control directive. Applications that use
@@ -142,18 +155,20 @@ def set(option, value=self, &block)
   private
     def initialize_options(options={})
       @default_options = {
-        'rack-cache.cache_key'        => Key,
-        'rack-cache.verbose'          => true,
-        'rack-cache.storage'          => Rack::Cache::Storage.instance,
-        'rack-cache.metastore'        => 'heap:/',
-        'rack-cache.entitystore'      => 'heap:/',
-        'rack-cache.default_ttl'      => 0,
-        'rack-cache.ignore_headers'   => ['set-cookie'],
-        'rack-cache.private_headers'  => ['Authorization', 'Cookie'],
-        'rack-cache.allow_reload'     => false,
-        'rack-cache.allow_revalidate' => false,
-        'rack-cache.use_native_ttl'   => false,
-        'rack-cache.fault_tolerant'   => false,
+        'rack-cache.cache_key'          => Key,
+        'rack-cache.verbose'            => true,
+        'rack-cache.storage'            => Rack::Cache::Storage.instance,
+        'rack-cache.metastore'          => 'heap:/',
+        'rack-cache.entitystore'        => 'heap:/',
+        'rack-cache.default_ttl'        => 0,
+        'rack-cache.ignore_headers'     => ['set-cookie'],
+        'rack-cache.transfer_headers'   => [],
+        'rack-cache.non_cached_headers' => [],
+        'rack-cache.private_headers'    => ['Authorization', 'Cookie'],
+        'rack-cache.allow_reload'       => false,
+        'rack-cache.allow_revalidate'   => false,
+        'rack-cache.use_native_ttl'     => false,
+        'rack-cache.fault_tolerant'     => false,
       }
       self.options = options
     end

test/context_test.rb

@@ -776,6 +776,58 @@
     cache.trace.wont_include :miss
   end
 
+  it 'includes specified additional headers from the backend in responses to the client' do
+    count = 0
+    respond_with do |req,res|
+      count += 1
+      res['ETAG'] = '"12345"'
+      res['unique-snowflake'] = '"so-special"'
+      res.status = (count == 1) ? 200 : 304
+    end
+
+    get '/', 'rack-cache.transfer_headers' => ['unique-snowflake']
+    assert app.called?
+    assert response.ok?
+    response.headers.must_include 'unique-snowflake'
+    response['unique-snowflake'].must_equal '"so-special"'
+    cache.trace.must_include :miss
+
+    get '/', 'rack-cache.transfer_headers' => ['unique-snowflake']
+    assert app.called?
+    assert response.ok?
+    response.headers.must_include 'unique-snowflake'
+    response['unique-snowflake'].must_equal '"so-special"'
+    cache.trace.must_include :valid
+  end
+
+  it 'excludes specified headers from being cached in responses' do
+    count = 0
+    respond_with do |req,res|
+      count += 1
+      res['ETAG'] = '"12345"'
+      if count == 1
+        res['not-cached'] = '"1"'
+      end
+      res.status = (count == 1) ? 200 : 304
+    end
+
+    get '/', 'rack-cache.non_cached_headers' => ['not-cached']
+    assert app.called?
+    assert response.ok?
+    response.headers.must_include 'not-cached'
+    cache.trace.must_include :miss
+    cache.trace.must_include :store
+    cache.trace.wont_include :ignore
+
+    get '/', 'rack-cache.non_cached_headers' => ['not-cached']
+    assert app.called?
+    assert response.ok?
+    response.headers.wont_include 'not-cached'
+    cache.trace.must_include :stale
+    cache.trace.must_include :valid
+    cache.trace.must_include :store
+  end
+
   it 'replaces cached responses when validation results in non-304 response' do
     timestamp = Time.now.httpdate
     count = 0