asp.net mvc - Is it possible to use custom error pages with MVC site but not Web API?

Question

I have an MVC project with a /api folder which contains my Web API controllers. I want the following things:

• My MVC site to serve a custom error page when an error occurs
• My Web API to serve the default error response (json/xml containing exception and stack trace)

In the web.config for my MVC site, I have an httpErrors node, and have set the errorMode to "Custom" so that I can have nice error pages when 404s/500s/etc. occur during browsing of the MVC site:

<httpErrors errorMode="Custom" existingResponse="Replace">
  <remove statusCode="404" subStatusCode="-1" />
  <remove statusCode="500" subStatusCode="-1" />
  <remove statusCode="403" subStatusCode="-1" />
  <error prefixLanguageFilePath="" statusCode="404" path="Content
otfound.htm" responseMode="File" />
  <error statusCode="500" path="/Errors" responseMode="ExecuteURL" />
  <error statusCode="403" path="/Errors/Http403" responseMode="ExecuteURL" /></httpErrors>

With that configuration however, the API will serve the custom error page when an error occurs, not json/xml with the exception/stack trace (which is the desired behavior).

Is there a way to configure custom errors to only apply to my MVC site and not the Web API? This blog says there is not (http://blog.kristandyson.com/2012/11/iis-httperrors-aspnet-web-api-fully.html), but I'd like to hear if anyone else has found a work around since that blog was published.

I suppose if there is not I could create a separate project/assembly for my Web API project. That would allow me to configure httpErrors for MVC and Web API separately, but I would prefer not to create another project just so I have yet another web.config to configure.

Answer 1

Well, after a nearly a year of letting this question marinade, I gave it another shot. Here's the web.config magic that got me what I wanted:

<!-- inside of <configuration> to allow error
    responses from requests to /api through -->
<location path="api">
    <system.webServer>
      <validation validateIntegratedModeConfiguration="false" />
      <httpErrors errorMode="DetailedLocalOnly" existingResponse="PassThrough" >
        <clear/>
      </httpErrors>
    </system.webServer>
</location>

<!-- original httpErrors, inside of <location path="." inheritInChildApplications="false">
 to serve custom error pages when the MVC site returns an error code -->
<httpErrors errorMode="Custom" existingResponse="Replace">
      <remove statusCode="400" subStatusCode="-1" />
      <remove statusCode="404" subStatusCode="-1" />
      <remove statusCode="500" subStatusCode="-1" />
      <remove statusCode="403" subStatusCode="-1" />
      <error statusCode="400" prefixLanguageFilePath="" path="Content
otfound.htm" responseMode="File"/>
      <error prefixLanguageFilePath="" statusCode="404" path="Content
otfound.htm" responseMode="File" />
      <error statusCode="500" path="/errors" responseMode="ExecuteURL" />
      <error statusCode="403" path="/errors/http403" responseMode="ExecuteURL" />
    </httpErrors>

The crux of what's going on here is that the <location> node allows you to override settings made at a less specific path. So while we have errorMode="Custom" for path=".", we override that for the our Web API's path with the <location path="api"> node, and the httpErrors configuration within it.

I had seen nodes before, but it didn't dawn on me that this was their purpose until now. This article goes into more detail on the configuration inheritance model of IIS/.NET, which I found very informative: http://weblogs.asp.net/jongalloway/10-things-asp-net-developers-should-know-about-web-config-inheritance-and-overrides