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How can I change ASP.NET Web API to never return a text/html 404 response? I'd rather it send back XML/JSON with an ExceptionMessage or Message. It doesn't make sense to return HTML from an API, IMO.

Just to clarify, this is for cases when the URL truly is invalid.

Another problem is that I am hosting MVC and Web API in the same project, so I need to respond differently. I am guessing it will depend on whether the URL starts with "api".

Travis Parks
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  • What does the returned HTML contain? Are you sure that this error is returned by the Web API? Are those custom 404 messages returned by your Web API endpoints? Or 404 related to endpoints not found? – Darin Dimitrov Jan 22 '14 at 20:52
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    This is someone trying to request something from my API and they just totally type in the wrong URL. – Travis Parks Jan 22 '14 at 20:55
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    But this has nothing to do with Web API. Why is your question tagged with it in this case? This is the standard ASP.NET error page. I wrote some example of how you could handle errors using the Application_Error event in Global.asax: http://stackoverflow.com/a/5229581/29407 – Darin Dimitrov Jan 22 '14 at 20:55
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    Could you please explain why it doesn't have anything to do with Web API? I understand that normally you use `customErrors` to change the response. Is this as simple as setting the URL to a desired API end-point? Is there a way to discern whether it is an API call vs. an MVC call? – Travis Parks Jan 22 '14 at 20:59
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    It doesn't have anything to do with the Web API because the Web API handles only routes it can match in your route definitions. Everything else propagates as a 404 Exception. Its handling then is a matter of the hosting environment, which I suppose in your case is ASP.NET (since you mentioned something about ASP.NET MVC) – Darin Dimitrov Jan 22 '14 at 21:01
  • I see, so before Web API even gets involved it is seeing that the URL is invalid. I will tweak your answer to the question you posted above to look for "api" in the URL. – Travis Parks Jan 22 '14 at 21:03

2 Answers2

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You do not get those HTML data if you simply call throw new HttpResponseException(HttpStatusCode.NotFound); somewhere in your ApiController's methods.

You get this page only when routing mechanism can't fit your request to any of your ApiController's methods. So the HTML message is attached on the application level not in ApiControllers. Here is very good example how you can handle errors in your ASP.NET application Custom error pages on ASP>NET MVC3.

I would even go further and check if the request comes to WebAPI (not to MVC), and if so redirect to IHttpActionResult in ErrorsContoller. How to prepare IHttpActionResult for response you can read here Action Results in Web API 2

Community
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Sebastian Xawery Wiśniowiecki
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Have you tried using an Exception Filter? This may allow you to capture exceptions and then set the response type "applications/json", message, etc.

Paul Fryer
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