ASP.NET HttpModule, strange behaviour when using Response.Write to the current context

I'm trying to understand why this very simple HttpModule fails. The code is a precursor to a simple HttpUrlRewriter that I need to develop for a test project.

It appears that whenever I test the Request, and then execute a Response, the output is not written to the stream!

I've attached the debugger (VS 2008) to the module, and all 3 Response.Write statements in the below get executed, but only the two outer ones actually product output on the page. Have I missed a key understanding or caveat?

Thanks for any help.

Exeucting Environment: ASP.NET 3.5/WinXP/IIS 5

using System; using System.Collections.Generic; using System.Web; using System.Text; using System.Web.UI;

public class Interceptor : IHttpModule
{
    #region IHttpModule Members

    public void Dispose() { }

    public void Init(HttpApplication context)
    {
        context.EndRequest += new EventHandler(TestHandler);
    }

    private void TestHandler(object sender, EventArgs e)
    {
        HttpApplication app = (HttpApplication)sender;
        HttpContext ctx = app.Context;

        if (1 == 1)
        {
            ctx.Response.Write("Hello, 2"); // Works, as expected
        }

        string test = ctx.Request.Url.ToString();
        if (test.Contains("/images")) {
            ctx.Response.Write("Hello, never written"); // 开发者_开发知识库This code executes when the test passes, but nothing is ever written...
        }

        ctx.Response.Write("Hello"); // Works

    }

    #endregion
}

If your requesting an image the Response stream will be different too!

are you sure the breakpoint on that line is hit for the request you are monitoring? Be aware that if you have an image in that /images folder and a .aspx page that contains that image your module will be called twice in the development server (for the aspx and the image), and only once in a default IIS (only for the aspx file). When you have simultaneous requests to the module it's sometime hard to see which breakpoint is on which request.

The answer was, sadly, stupidity on my part. One of those classics that get overlooked!

The request, while containing /image, also happened to be for a binary file. Therefore the Response was written to the stream for that rather than the Page.