How to use output caching on .ashx handler

Question

How can I use output caching with a .ashx handler? In this case I'm doing some heavy image processing and would like the handler to be cached for a minute or so.

Also, does anyone have any recommendations on how to prevent dogpiling?

Answer 1

There are some good sources but you want to cache you processing server side and client-side.

Adding HTTP headers should help in the client side caching

here are some Response headers to get started on..

You can spend hours tweaking them until you get the desired performance

//Adds document content type
context.Response.ContentType = currentDocument.MimeType;
context.Response.Cache.SetCacheability(HttpCacheability.Public);
context.Response.Cache.SetExpires(DateTime.Now.AddMinutes(10));
context.Response.Cache.SetMaxAge(new TimeSpan(0,10,0)); 
context.Response.AddHeader("Last-Modified", currentDocument.LastUpdated.ToLongDateString());

// Send back the file content
context.Response.BinaryWrite(currentDocument.Document);

As for server side caching that is a different monster... and there are plenty of caching resources out there...

Answer 2

I used the following with success and thought it worthwhile to post here .

Manually controlling the ASP.NET page output cache

From http://dotnetperls.com/cache-examples-aspnet

Setting cache options in Handler.ashx files

First, you can use HTTP handlers in ASP.NET for a faster way to server dynamic content than Web Form pages. Handler.ashx is the default name for an ASP.NET generic handler. You need to use the HttpContext parameter and access the Response that way.

Sample code excerpted:

<%@ WebHandler Language="C#" Class="Handler" %>

C# to cache response for 1 hour

using System;
using System.Web;

public class Handler : IHttpHandler {

    public void ProcessRequest (HttpContext context) {
        // Cache this handler response for 1 hour.
        HttpCachePolicy c = context.Response.Cache;
        c.SetCacheability(HttpCacheability.Public);
        c.SetMaxAge(new TimeSpan(1, 0, 0));
    }

    public bool IsReusable {
        get {
            return false;
        }
    }
}