Can an ASP.NET HttpHandler handle an http 400 - Bad Request?

Question

We have an HttpHandler that deals directly with binary posts over HTTP from custom client software. The client software occasionally sends data which results in IIS 7 responding with a 400 - Bad Request. Since the "400 Bad Request" is special in that HTTP.SYS transparently handles it in kernel mode without notifying user mode of anything, no errors are raised to be handled in ASP.NET. Is it possible to catch this http 400 in ASP.NET, so that I can write specific data to the Response stream in these scenarios? A redirect to another page isn't an option as it needs to be in the current Request/Response.

Answer 1

If you know what is causing the 400, then you may be able to customise the behaviour of http.sys via the registry to deal with it:

http://support.microsoft.com/kb/820129

However, you should be aware that there are potential security and performance ramifications of doing this.

Another option would be to use a filtering proxy before IIS, thereby capturing the request before it goes any further.

Answer 2

I would instead ask them to fix the custom client software. Give them a report showing the failed requests. If you are able to, run a sniffer such as Wireshark and send them the packets if they do not believe the problem is with their software.

Answer 3

If your custom client causes IIS to trigger HTTP 400, it's probably flawed and is not submitting valid HTTP requests according to the standard. If you can alter the client, it would be the right thing to do. Otherwise, what you're working with is not HTTP, and IIS is designed to handle HTTP requests. Therefore, you should run a custom server for your own protocol (which is a non-standard HTTP like thing).

It's not advised to use IIS/ASP.NET to handle such a request as it might cause some weird unexpected things to happen.