Tutorial :ASPX That Returns An Image - Output Cache-able?



I've created an APSX web form that returns a remote image based on some supplied parameters. It can be used like this:

<img src="/ImageGetter.aspx?param1=abc&param2=123" />  

ImageGetter.aspx's markup and code look similar to this:

<%@ OutputCache Duration="100000" VaryByParam="*" Location="ServerAndClient" %>  <%@ Page Language="C#" AutoEventWireup="false" EnableSessionState="False" CodeBehind="ImageGetter.aspx.cs" Inherits="ACME.Helpers.ImageGetter" %>  

This code is called in ImageGetter.aspx's Page_Load method:

byte[] data = null;  Dictionary<string, string> file_locations = GetImageLocations(param1, param2);  try  {      data = new WebClient().DownloadData(file_locations["main"]);  }  catch (WebException wex)  {      try      {          data = new WebClient().DownloadData(file_locations["backup"]);      }      catch (Exception e)      {          throw;      }  }  Response.ContentType = "image/jpeg";  Response.OutputStream.Write(data, 0, data.Length);  Response.End();  

From my testing, it doesn't appear to be caching. Is this possible to do with Output Caching or should I resort to writing my own cache to store the byte arrays depending on query string paramters?


Try dropping the Response.End() as this will terminate the thread prematurely and prevent output caching from taking place.

See: http://bytes.com/groups/net-asp/323363-cache-varybyparam-doesnt-work

You may wish to consider using an ASHX handler and using your own caching method.


Use an ASHX generic handler and use the HttpRuntimeCache (Cache object) to do the job as Codebrain said. It will be faster and WAY more flexible.


Your problem could be a bug in IE - it can't cache if the Vary:* HTTP response header is used, but IIS returns it by default because it's in the HTTP 1.1 spec.

Try adding the following to your web.config:

<system.web>       <caching>          <outputCache omitVaryStar="true" />      </caching>  </system.web>   

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