WebAPI BadRequest Dropping Response Data - angularjs

Question

I have an ASP.NET WebAPI (v2) controller action that has the following general structure:
[HttpPost]
public HttpResponseMessage Post(UserDTO model)
{
try {
// do something
}
catch (Exception ex)
{
var error = new {
errorMessage = ex.Message,
userId = 123,
// some other simple data
};
return Request.CreateResponse(HttpStatusCode.BadRequest, error);
}
return Request.CreateResponse(HttpStatusCode.OK, model);
}
When I run this on my local development server (IIS Express) and an error is thrown, I get the expected JSON payload back.
{
config: {...},
data: {
errorMessage: "User invalid",
userId: 123,
...
},
status: 400,
statusText: "Bad Request"
}
When I run the same code/data on the remote/production server (IIS 8.5), all I get back is:
{
config: {...},
data: "Bad Request,
status: 400,
statusText: "Bad Request"
}
The custom data payload is lost/stripped away from the response. This appears to be related to the HttpStatusCode used in the Request.CreateResponse() call as if I change HttpStatusCode.BadRequest to HttpStatusCode.OK then the custom data payload is downloaded.
As I test, I tried changing the return to Request.CreateErrorResponse(HttpStatusCode.BadRequest, ModelState); but the results were the same, i.e. the data was returned as a simple "Bad Request" string.
For reference, the API is being called by an AngularJS $http.post() call.
Why is the change in HttpStatusCode changing the response payload on the production server but not locally? Any help would be much appreciated.

Answer 1

It turns out this was down to the following section in Web.config
<system.webServer>
<httpErrors errorMode="Custom" existingResponse="Replace">
<remove statusCode="403" />
<error statusCode="403" responseMode="ExecuteURL"
path="/Error/AccessDenied" />
<remove statusCode="404" />
<error statusCode="404" responseMode="ExecuteURL"
path="/Error/NotFound" />
<remove statusCode="500" />
<error statusCode="500" responseMode="ExecuteURL"
path="/Error/ApplicationError" />
</httpErrors>
</system.webServer>
It was 'odd' because these pages were not being returned by the API call, but with their removal, the API call returned the correct payload - presumably the HttpStatusCode.BadRequest was being intercepted by an error handler somewhere hence losing the original response data?
With these handlers I removed, I resorted to using the Application_Error handler in Global.asax as described by ubik404 here.
There may well be a better/alternative way to achieve the same result, but this seems to work.

Answer 2

You need to remove existingResponse="Replace", I just had the same issue and that solved it for me. The default value is Auto.
Your answer lead me to find the real problem, so thanks! :)
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