It’s been a few weeks now since Google announced Java support on their App Engine infrastructure. Since Java support also adds support for JRuby, it is now possible to deploy Rails or Sinatra or any other Rack based applications to Google. In my case, I am playing with Sinatra đ This is an excelent step-by-step tutorial on how to get started with Sinatra App. If you running your applications on App Engine, you might be interested (at least I was) in reducing your application load by using some sort of page cache. Since Google won’t allow you to write out files, I figured using their MemCachedService might be pretty nice way to work around this issue. Ryan Tomayko has written a very nice Rack middle-ware, Rack::Cache, which provides support for cache control and validation and looked to me like a very nice solution. Following is my extension to Ryan’s work, which will allow to use Rack::Cache with Google Memcache as a meta-data and entity storage.
I have the following code in ./lib/cache.rb file:
require 'java'
require 'rack/cache'
require 'yaml'
module Cache
module MC
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
module ClassMethods
def clear
MC::Service.clearAll
end
def exists?(key)
MC::Service.contains(key)
end
alias_method :contains?, :exists?
def get(key)
value = MC::Service.get(key)
YAML.load(value) if value
end
def put(key, value, ttl = nil)
expiration = ttl ? MC::Expiration.byDeltaSeconds(ttl) : nil
MC::Service.put(key, value.to_yaml, 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
module Service
extend Cache::ClassMethods
end
end
module Rack::Cache
class MetaStore
public
class GAEStore < MetaStore
attr_reader :cache
def initialize(options = {})
@cache = Cache::Service
@cache.namespace = options[:namespace] if options[:namespace]
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)
end
def self.resolve(uri)
self.new(:namespace => uri.host)
end
end
GAECACHE = GAEStore
GAE = GAEStore
end
class EntityStore
public
class GAEStore < EntityStore
attr_reader :cache
def initialize(options = {})
@cache = Cache::Service
@cache.namespace = options[:namespace] if options[:namespace]
end
def exist?(key)
@cache.exists?(key)
end
def read(key)
result = @cache.get(key)
result
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 self.resolve(uri)
self.new(:namespace => uri.host)
end
end
GAECACHE = GAEStore
GAE = GAEStore
end
end
Add the following into config.ru:
……..
require ‘application’
use Rack::Cache, {:metastore => ‘gae://namespace‘, :entitystore => ‘gae://namespace‘}
run Sinatra::Application
In order to make it work properly, read Ryan’s documentation on all supported options.
I am hoping this is helpful đ
