IIS responses with HTML instead of JSON on ASP .NET MVC3 - json

Question

The subject is selfexplanatory. I've developer and production environments. Developer env. is my localhost machine. I've action methods in contolers that sets response status code to 500 when something wents wrong (error occured, or logical inconsistance) and returns Json-answer. My common method looks like that:
[HttpPost]
public ActionResult DoSomething(int id)
{
try
{
// some useful code
}
catch(Exception ex)
{
Response.StatusCode = 500;
Json(new { message = "error" }, JsonBehaviour.AllowGet)
}
}
On the client side in production env. when such an error occured ajax.response looks like an HTML-code, instead of expected JSON.
Consider this:
<div class="content-container">
<fieldset>
<h2>500 - Internal server error.</h2>
<h3>There is a problem with the resource you are looking for, and it cannot be displayed.</h3>
</fieldset>
</div>
Filter context is not an option. I think it is some sort of IIS or web.config issue.
SOLUTION:
We decided to add TrySkipIisCustomErrors in BeginRequest in Global.asax and it is solved problems in each method in our application.

Answer 1

I guess that IIS is serving some friendly error page. You could try skipping this page by setting the TrySkipIisCustomErrors property on the response:
catch(Exception ex)
{
Response.StatusCode = 500;
Response.TrySkipIisCustomErrors = true;
return Json(new { message = "error" }, JsonBehaviour.AllowGet)
}

Answer 2

Is your IIS configured to treat application/json as a valid mime-type? You may check that in properties for the server in IIS Manager and click MIME Types. If json is not there then click "New", enter "JSON" for the extension, and "application/json" for the MIME type.

Answer 3

I solved this by writing a custom json result, which uses json.net as the serializer. This is overkill for just the IIS fix but it means it's reusable.
public class JsonNetResult : JsonResult
{
//public Encoding ContentEncoding { get; set; }
//public string ContentType { get; set; }
public object Response { get; set; }
public HttpStatusCode HttpStatusCode { get; set; }
public JsonSerializerSettings SerializerSettings { get; set; }
public Formatting Formatting { get; set; }
public JsonNetResult(HttpStatusCode httpStatusCode = HttpStatusCode.OK)
{
Formatting = Formatting.Indented;
SerializerSettings = new JsonSerializerSettings { };
SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
HttpStatusCode = httpStatusCode;
}
public override void ExecuteResult(ControllerContext context)
{
if (context == null)
throw new ArgumentNullException("context");
HttpResponseBase response = context.HttpContext.Response;
response.TrySkipIisCustomErrors = true;
response.ContentType = !string.IsNullOrEmpty(ContentType) ? ContentType : "application/json";
if (ContentEncoding != null)
response.ContentEncoding = ContentEncoding;
response.StatusCode = (int) HttpStatusCode;
if (Response != null)
{
JsonTextWriter writer = new JsonTextWriter(response.Output) { Formatting = Formatting };
JsonSerializer serializer = JsonSerializer.Create(SerializerSettings);
serializer.Serialize(writer, Response);
writer.Flush();
}
}
}
Use:
try
{
return new JsonNetResult()
{
Response = "response data here"
};
}
catch (Exception ex)
{
return new JsonNetResult(HttpStatusCode.InternalServerError)
{
Response = new JsonResponseModel
{
Messages = new List<string> { ex.Message },
Success = false,
}
};
}