Check if ASP.NET WebForms page exists based upon relative URL provided in Query String

Question

Given a query string url of the form "~/folder/page.aspx", is there a way to check if that page exists within the scope of the application?

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I'm in a situation where I'm fixing a minor bug where, if a user attempts to log in to the application from a set of publicly accessible application error pages, then they're redirected back to that public error page. I've been asked to have the user be redirected to the main home page if they're logging in to the application from this state.

So far I've fixed the issue by hard coding the paths to the affected pages in a switch statement, checking the querystring against the hardcoded paths. I feel this is hacky and bad, and would love a more dynamic solution, but I can't seem to find one.

Any help would be greatly appreciated.

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Edit - Specifically, my preferred solution would simply be to check that the path defined by the query string url (without a priori knowledge of the exact format) leads to a specified folder within the scope of the application.

Answer 1

So, after looking some more, I discovered Server.MapPath. I can use this in conjunction with System.IO.Directory to see if the file is contained within the directory.

string targetUrl = Request.QueryString["redirect"];
string serverUrlPath = Server.MapPath(targetUrl);
string serverDirPath = Server.MapPath("~/ErrorPages");

foreach (string file in Directory.EnumerateFiles(serverDirPath))
{
  if (file.Equals(serverUrlPath, StringComparison.OrdinalIgnoreCase))
  {
    Response.Redirect(Master.ProjectSearchRedirect());
  }
}

Response.Redirect(targetUrl);

I was hoping for something a little more refined (even just a Directory.Contains kind of encapsulation).