How to set Response Header before Server.Transfer in Asp.Net?

Question

I have a page where based on certain conditions I am either doing a Response.Redirect or Server.Transfer. Now I want to add a header for both the cases. So I am doing the following

    Response.AddHeader("Vary", "User-Agent");

    if (condition) 
    {
        Server.Transfer(redirectUrl);
    }
    else
    {
        Response.Redirect(redirectUrl);
    }

Now, when the code goes via Server.Transfer code path, the Vary header is set to * whereas when it goes via Response.Redirect the header is correctly set to User-Agent.

Why does this happen and how can I set the Response Header to be same for both the cases?

Answer 1

Andre is right that the Response object is replaced as part of Server.Transfer. If you want to make the page you're transferring to agnostic of the parent you can probably whack the information into HttpContext.Items and then use an IHttpModule to extract the information and configure the header appropriately. Something like this would probably do the job...

Items.Add(VaryHttpModule.Key, "User-Agent");

if (condition) 
{
    Server.Transfer(redirectUrl);
}
else
{
    Response.Redirect(redirectUrl);
}

public class VaryHttpModule : IHttpModule
{
    public const string Key = "Vary";

    public void Init(HttpApplication context)
    {
        context.PostRequestHandlerExecute +=
            (sender, args) =>
                {
                    HttpContext httpContext = ((HttpApplication)sender).Context;
                    IDictionary items = httpContext.Items;
                    if (!items.Contains(Key))
                    {
                        return;
                    }

                    object vary = items[Key];
                    if (vary == null)
                    {
                        return;
                    }

                    httpContext.Response.Headers.Add("Vary", vary.ToString());
                };
    }

    public void Dispose()
    {
    }
}

Cheers!