Google AppEngine memcache entity store and metastore implementations

To use GAE's memcache with rack-cache, set the :metastore and
:entitystore options as follows:

    use Rack::Cache,
      :metastore   => 'gae://cache-meta',
      :entitystore => 'gae://cache-body'

The 'cache-meta' and 'cache-body' parts are memcache namespace
prefixes and should be set to different values.

lib/rack/cache/appengine.rb

@@ -0,0 +1,52 @@
+require 'base64'
+
+module Rack::Cache::AppEngine
+
+  module MC
+    require 'java'
+
+    import com.google.appengine.api.memcache.Expiration;
+    import com.google.appengine.api.memcache.MemcacheService;
+    import com.google.appengine.api.memcache.MemcacheServiceFactory;
+    import com.google.appengine.api.memcache.Stats;
+
+    Service = MemcacheServiceFactory.getMemcacheService
+  end unless defined?(Rack::Cache::AppEngine::MC)
+
+  class MemCache
+
+      def initialize(options = {})
+        @cache = MC::Service
+        @cache.namespace = options[:namespace] if options[:namespace]
+      end
+
+      def contains?(key)
+        MC::Service.contains(key)
+      end
+
+      def get(key)
+        value = MC::Service.get(key)
+        Marshal.load(Base64.decode64(value)) if value
+      end
+
+      def put(key, value, ttl = nil)
+        expiration = ttl ? MC::Expiration.byDeltaSeconds(ttl) : nil
+        value = Base64.encode64(Marshal.dump(value)).gsub(/\n/, '')
+        MC::Service.put(key, value, expiration)
+      end
+
+      def namespace
+        MC::Service.getNamespace
+      end
+
+      def namespace=(value)
+        MC::Service.setNamespace(value.to_s)
+      end
+
+      def delete(key)
+        MC::Service.delete(key)
+      end
+
+  end
+
+end

lib/rack/cache/entitystore.rb

@@ -282,6 +282,52 @@ def purge(key)
       end
 
     MEMCACHED = MEMCACHE
+
+    class GAEStore < EntityStore
+      attr_reader :cache
+
+      def initialize(options = {})
+        require 'rack/cache/appengine'
+        @cache = Rack::Cache::AppEngine::MemCache.new(options)
+      end
+
+      def exist?(key)
+        cache.contains?(key)
+      end
+
+      def read(key)
+        cache.get(key)
+      end
+
+      def open(key)
+        if data = read(key)
+          [data]
+        else
+          nil
+        end
+      end
+
+      def write(body)
+        buf = StringIO.new
+        key, size = slurp(body){|part| buf.write(part) }
+        cache.put(key, buf.string)
+        [key, size]
+      end
+
+      def purge(key)
+        cache.delete(key)
+        nil
+      end
+
+      def self.resolve(uri)
+        self.new(:namespace => uri.host)
+      end
+
+    end
+
+    GAECACHE = GAEStore
+    GAE = GAEStore
+
   end
 
 end

lib/rack/cache/metastore.rb

@@ -360,6 +360,40 @@ def purge(key)
         MemCache
       end
     MEMCACHED = MemCache
+
+    class GAEStore < MetaStore
+      attr_reader :cache
+
+      def initialize(options = {})
+        require 'rack/cache/appengine'
+        @cache = Rack::Cache::AppEngine::MemCache.new(options)
+      end
+
+      def read(key)
+        key = hexdigest(key)
+        cache.get(key) || []
+      end
+
+      def write(key, entries)
+        key = hexdigest(key)
+        cache.put(key, entries)
+      end
+
+      def purge(key)
+        key = hexdigest(key)
+        cache.delete(key)
+        nil
+      end
+
+      def self.resolve(uri)
+        self.new(:namespace => uri.host)
+      end
+
+    end
+
+    GAECACHE = GAEStore
+    GAE = GAEStore
+
   end
 
 end

rack-cache.gemspec

@@ -4,7 +4,7 @@ Gem::Specification.new do |s|
 
   s.name = 'rack-cache'
   s.version = '0.4'
-  s.date = '2009-03-16'
+  s.date = '2009-04-28'
 
   s.description = "HTTP Caching for Rack"
   s.summary     = "HTTP Caching for Rack"
@@ -30,6 +30,7 @@ Gem::Specification.new do |s|
     example/sinatra/app.rb
     example/sinatra/views/index.erb
     lib/rack/cache.rb
+    lib/rack/cache/appengine.rb
     lib/rack/cache/cachecontrol.rb
     lib/rack/cache/context.rb
     lib/rack/cache/entitystore.rb

test/entitystore_test.rb

@@ -200,4 +200,31 @@ def sha_like?
       end
     end
   end
+
+  need_java 'entity store testing' do
+    module Rack::Cache::AppEngine
+      module MC
+        class << (Service = {})
+
+          def contains(key); include?(key); end
+          def get(key); self[key]; end;
+          def put(key, value, ttl = nil)
+            self[key] = value
+          end  
+        end
+
+      end
+    end
+
+    describe 'GAEStore' do
+      it_should_behave_like 'A Rack::Cache::EntityStore Implementation'
+      before do
+        puts Rack::Cache::AppEngine::MC::Service.inspect
+        @store = Rack::Cache::EntityStore::GAEStore.new
+      end
+      after do
+        @store = nil
+      end
+    end
+  end
 end

test/metastore_test.rb

@@ -272,4 +272,31 @@ def self.call(request); request.path_info.reverse end
       end
     end
   end
+
+  need_java 'entity store testing' do
+    module Rack::Cache::AppEngine
+      module MC
+        class << (Service = {})
+
+          def contains(key); include?(key); end
+          def get(key); self[key]; end;
+          def put(key, value, ttl = nil)
+            self[key] = value
+          end  
+
+        end
+      end
+    end
+
+    describe 'GAEStore' do
+      it_should_behave_like 'A Rack::Cache::MetaStore Implementation'
+      before :each do
+        Rack::Cache::AppEngine::MC::Service.clear
+        @store = Rack::Cache::MetaStore::GAEStore.new
+        @entity_store = Rack::Cache::EntityStore::Heap.new
+      end
+    end
+
+  end
+
 end

test/spec_setup.rb

@@ -69,6 +69,16 @@ def need_memcache(forwhat)
   end
 end
 
+def need_java(forwhat)
+
+  if RUBY_PLATFORM =~ /java/
+    yield
+  else
+    STDERR.puts "skipping app engine #{forwhat}"
+  end
+end
+
+
 # Setup the load path ..
 $LOAD_PATH.unshift File.dirname(File.dirname(__FILE__)) + '/lib'
 $LOAD_PATH.unshift File.dirname(__FILE__)