IIS logs show HTTP 404, but browser gets HTTP 500

Discrepancy between error codes

[aakk9999]

I am trying to find out why there is a discrepancy between error codes shown in IIS server logs and the actual error returned to browser. Here is some background info:

- IIS 7
- Rewrite module in use, set up to rewrite all requests to custom rewrite/redirect module
- Custom rewrite module handles fine URLs that are set up in custom rewrite or redirect tables (performing either redirect or transferring the request to a correct script)
- However, if the URL is NOT set up in rewrite/redirect tables, then it executes Server.TransferRequest to the originally requested URL
- If originally requested URL is for existing scripts, then the page renders fine.

However, if the request comes for non-existing script/non-existing URL (which is neither redirected nor rewritten), then I can see that Server.TransferRequest results in 404 in IIS logs, but browser receives HTTP 500

So the question is why does Server.TrasnferRequest(requestURL,true); correctly logs 404 in IIS server logs, but returns HTTP 500 to browser?

For example, if we have the following in custom rewrite/redirect script:

requestURL = "/non-existant-url"
Server.TransferRequest(requestURL,true);

Is there some error response that will be returned that needs to be checked after that call and then send programatically 404 based on the response? Or anything else?

Many thanks

[Ocean10000]

I am guessing you have a 404 error page setup which it being transfered to. And it is this page which is generating the 500 error for what ever reason.

[aakk9999]

Many thanks, I will investigate. (I am not developer, just trying to help dev. agency to debug).

I am almost certain that there is no custom 404 page setup. Do you have any idea what would happen in this case for Server.TransferRequest that cannot work?

I have the following code that I think is the culprit and if I add few lines shown in bold below, would this fix the issue?

private void RenderPage(mNewRequestURL)
{
try
{
// transfer the URL
Server.TransferRequest(mNewRequestURL, true);
}
catch (Exception myEx)
{
throw myEx;

// unfortunately I have no idea what myEx above does but this is
// where the current (original) code finishes. If we add
// the code shown below, would this result in returning 404
// to the client if server transfer attempts to transfer
// to non-existing page? Or does this piece of code
// needs to be above "throw myEx" ?

log.Error("A: Server.TransferRequest attempt for non-existing URL - return 404");
Response.Clear();
Response.StatusCode = 404;
Response.Status = "404 Page Not Found";
Response.End();
}
}

[Ocean10000]

I see the bug.

Comment out the "throw myEx;" line and it will reach the 404 handling code which you want.

[aakk9999]

Thank you :)