Sunday, 22 July 2012

Introducing CacheCow: An HTTP caching framework for server and client


[Level T2] This is a short post to introduce CacheCow, an Open Source framework for HTTP caching on the client and server in ASP.NET Web API.

As some of you probably know, I have been working on caching for a while. If you go back to my post on CachingHandler, you will see that I contributed server-side HTTP caching implementation to the WebApiContrib project and included samples and tests.

However, I realised that even more important part of the caching needs to be implemented on the client. Also implementations of the IEntityTagStore on various databases (in-memory and persisted) and client-side's cache storage all need their own project so this is bigger than just a feature on WebApiContrib. As such, I have decided to start a new project and port the server-side from WebApiContrib. [Please bear in mind, the code in the WebApiContrib will be maintained and supported so if you are using it and have problems or experience bugs, please ping me in twitter or GitHub.]

So CacheCow framework has been born. The name itself is a word game with Cash Cow, meaning it does the heavy lifting for caching with minimal set up hence promises good return on investment :). Project is open source and hosted on GitHub. And yes, I do accept pull requests; Tugberk has done a great job (also with some help from Sayed Ibrahim Hashimi which I am so grateful for) and automated the whole build and NuGet package generation and his PR was merged pretty much immediately. But please contact me before-hand on the work you would like to do - there is ton of interesting work to do.

How to use CacheCow.Server

At the moment, only server-side CacheCow is ready for use. All you need to do is to use NuGet to get the package:

PM> Install-Package CacheCow.Server

This will add the CacheCow.Server and CacheCow.Common DLLs and the rest is all the same as the CachingHandler post and samples. Just add CachingHandler to the config:

GlobalConfiguration.Configuration.MessageHandlers.Add(new CachingHandler());

This will add this handler with all the default settings and will store the cache state in the memory. There are many dials that you can turn and configure the handler according to your resource organisation - just see the sample in WebApiContrib. This sample connects to the CarManager sample and tests various scenarios for a fairly complex resource organisation.

How to use CacheCow.Server.EntityTagStore.SqlServer

As I pointed out above, by default cache state is stored in memory. This is OK for single server or test scenarios but in case of a server farm you would like the cache state to be maintained for whole farm and when a resource cache invalidated, it is done for all servers. In this case you need a central EntityTagStore (cache state store).

Building a cache state store is pretty easy and all you have to do is to implement IEntityTagStore interface which has 5 methods. Since cache might be invalidated not just for a CacheKey (previously called EntityTagKey) but also for a RoutePattern (see CachingHandler post), key-value stores are not rich enough to provide this but conventional databases can be used.

So I have implemented this for SQL Server. In order to get this EntityTagStore, just use NuGet:

PM> Install-Package CacheCow.Server.EntityTagStore.SqlServer

This will download the DLL and also a script file named script.sql located in <project root>\packages\CacheCow.Server.EntityTagStore.SqlServer.0.1.0\scripts

So create a database and run this script against it, and you will get one table and several stored procedures. Then in order to use SqlServerEntityTagStore, create an instance pass it to the CachingHandler constructor. Default constructor relies on a connection string named "EntityTagStore" to be there in your web.config and pointing to your database.

 new CachingHandler(new SqlServerEntityTagStore()));

Alternatively, pass the connection string to the constructor. That is all you have to do use SQL Server EntityTagStore.


I am working on the client CachingHandler to be used with HttpClient. This will initially come with an InMemoryCacheStore but then various persistent cache store implementations can be done (for example file-based, SQL CE, etc)

Also CarManager sample needs to be ported for CacheCow which I am hoping to do very soon - although the old sample does work well.

Any question or comment please ping me on twitter (@aliostad) or GitHub.

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