Check if a redirect then change the query string

I would like to remove the query parameter 'mobile' from all requests that are redirects. The page Redirect.aspx redirects a visitor to Default.aspx?mobile=1. And when a visitor browses to Redirect,aspx, then eventually he should be led to the Default.aspx without a parameter in the address bar. Steps I took: So, I have to remove the query parameter "mobile" from a query string if the current request is a redirect. And here is the problem: I'm checking if status code is 3xx and query has 'mobile' parameter, but this condition never equals true.

Redirect.aspx:

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);
    Context.Response.Redirect("Default.aspx?mobile=1");
}

RemoveParamModule:

public class RemoveParamModule : IHttpModule
{
    public void Init(HttpApplication context)
    {
        context.EndRequest += RewriteHandler;
    }

    private void RewriteHandler(object sender, EventArgs eventArgs)
    {
        var context = (HttpApplication)sender;
        var statusCode = context.Response.StatusCode;
        if (statusCode.IsInRange(300, 399) && context.Request.QueryString["mobile"] != null)
        {
            DeleteMobileParameter(context.Request.QueryString);
            context.Response.Redirect(context.Request.Path, true);
        }
    }

    private static void DeleteMobileParameter(NameValueCollection collection)
    {
        var readOnlyProperty = collection.GetType().GetProperty("IsReadOnly", BindingFlags.Instance | BindingFlags.NonPublic);
        readOnlyProperty.SetValue(collection, false, null);
        collection.Remove("mobile");
        readOnlyProperty.SetValue(collection, true, null);
    }

    public void Dispose()
    {
    }
}

Why do the requests in the module either have statusCode=302 or the parameter 'mobile' but never both at the same time? And how can I remove the parameter 'mobile' for the redirects?

Solution

Response.Redirect creates response from server for previously requested URL. Then, client browser receives this response and just GETs new URL, which server will process with usual 200 result.

So basically:

Request:  GET Response.aspx
Response: 302 Default.aspx?mobile=1

Request:  GET Default.aspx?mobile=1
Response: 200 <body>

So if I correctly understood your needs - you shouldn't parse mobile from Request URL, but analyze you Response instead.

Also Response.Redirect might throw ThreadAbortException so be careful with several Redirects in the same pipeline.