Throwing HttpResponseException from WebApi controller when using Owin self host

You can put a breakpoint on the exception in OnException() and view the context.Exception.Response, and see the "Reason Phrase" for an explanation.

You can also do this to access it via code:

((System.Web.Http.HttpResponseException)context.Exception).Response.ReasonPhrase

For me it was

Unsupported Media Type

Which other people have already mentioned can happen when you do a text request, because text requests are not handled by default. If you do want to allow text, maybe look at: how to post plain text to ASP.NET Web API endpoint?

I experienced this while I was using postman to test the web api and the request type was set to plain text instead of application/json.

I don't think the problem is in throwing HttpResponseException. If you look at the stack trace you posted, the problem appears to be in the call to MoveNext(). This is an internal C# representation of the yield statements you have.

I could be wrong, but the easiest way to verify this is to put a breakpoint on the first yield statement and see if it hits it. My guess is that it will, i.e. it won't throw a HttpResponseException. Also, just change your code temporarily to always throw an HttpResponseException and see how it handles it.

I'm currently working on a project that's self-hosted using OWIN and I can throw HttpResponseExceptions without any issues.

On a related note, you may want to investigate global exception handling. I found it very useful to concentrate all my exception handling in one place. Note that HttpResponseException is a special case and is not handled by the global exception handler.

For me, I was missing content-type in my api header. After adding the content-type as application/json resolved this issue for me. Might help others with this.