Caching Proxy Design Advice

Question

Hi, I'm relatively new to proxies.
I am currently required to design a caching proxy for work.
We have a webservice which serves up data based on calls to it, naturally.
I am required to create a proxy for a rich client application that caches the results of these calls.
The results are basically string names of products identified by a composition of ids.

I could just create a class that acts as my proxy client that caches the results in a cache, I was thinking of using the System.Web.Caching.Cache object.

However I thought I'd ask to see if there are any design aspects and considerations that I have missed. Is there a design that is commonly known that I have not found?

[UPDATE - 12 Oct 2009]
Seems like System.Web.Caching.Cache is not advisable for client side caching.

http://msdn.microsoft.com/en-us/library/system.web.caching.cache.aspx:

The Cache class is not intended for use outside of ASP.NET applications. It was designed and tested for use in ASP.NET to provide caching for Web applications. In other types of applications, such as console applications or Windows Forms applications, ASP.NET caching might not work correctly.

Answer 1

First, I've used System.Web.Caching.Cache in Winforms and Service solutions and never had a problem with it. I recommend mitigating against the disclaimer by testing to ensure the cache works and doesn't leak resources, but none of my testing ever showed this happening.

Alternatively there is a caching solution in Enterprise Library, and probably a bunch of other open source ones you could consider. And there are probably some commercially supported ones too if you prefer.

However, are you hosting your web service in ASP.Net (.asmx extension is usually a good indicator). In that case your still in ASP.Net and so the disclaimer shouldn't apply.

Also note that ASP.Net has caching options you can drive directly from the web.config without having to do any coding.

But all of the above is server side caching.

Assuming your web service is using HTTP (or HTTPS) as the transport layer, then proxy and client caching require use of the HTTP response headers, I think Cache-Control, Expires and possibly Last-Modified are involved. Then it is up to the client and proxies to decide whether they will support caching or not.

Alternatively if your actually trying to write a proxy solution that supports caching (and that would be rewriting a wheel so you should have a good reason to do this) then you probably want a HTTP Handler, with the System.Web.HttpRequest and System.Web.HttpResponse representing the client side of things, and passing the request through to the server using System.Net.HttpWebRequest and System.Net.HttpResponse. The System.Web.Caching.Cache could then support your cached responses on your proxy. That said there would be lots of rules to have to implement here, including HTTP Request headers (also has Cache-Control options).