Question

If a request is made to my Web API service that has a Content-Type header containing a type not supported by that service, it returns a 500 Internal Server Error status code with a message similar to the following:

{"Message":"An error has occurred.","ExceptionMessage":"No MediaTypeFormatter is available to read an object of type 'MyDto' from content with media type 'application/UnsupportedContentType'.","ExceptionType":"System.InvalidOperationException","StackTrace":" at System.Net.Http.HttpContentExtensions.ReadAsAsync[T](HttpContent content, Type type, IEnumerable`1 formatters, IFormatterLogger formatterLogger)
   at System.Net.Http.HttpContentExtensions.ReadAsAsync(HttpContent content, Type type, IEnumerable`1 formatters, IFormatterLogger formatterLogger)
   at System.Web.Http.ModelBinding.FormatterParameterBinding.ReadContentAsync(HttpRequestMessage request, Type type, IEnumerable`1 formatters, IFormatterLogger formatterLogger)
   at System.Web.Http.ModelBinding.FormatterParameterBinding.ExecuteBindingAsync(ModelMetadataProvider metadataProvider, HttpActionContext actionContext, CancellationToken cancellationToken)
   at System.Web.Http.Controllers.HttpActionBinding.<>c__DisplayClass1.<ExecuteBindingAsync>b__0(HttpParameterBinding parameterBinder)
   at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
   at System.Threading.Tasks.TaskHelpers.IterateImpl(IEnumerator`1 enumerator, CancellationToken cancellationToken)"}

I would instead prefer to return a 415 Unsupported Media Type status code as recommended, e.g, here.

How do I configure my service to do this?

Answer 1

Here is the solution I came up with to this problem.

It’s broadly based on the one described here for sending a 406 Not Acceptable status code when there’s no acceptable response content type.

public class UnsupportedMediaTypeConnegHandler : DelegatingHandler {
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
                                                           CancellationToken cancellationToken) {
        var contentType = request.Content.Headers.ContentType;
        var formatters = request.GetConfiguration().Formatters;
        var hasFormetterForContentType = formatters //
            .Any(formatter => formatter.SupportedMediaTypes.Contains(contentType));

        if (!hasFormetterForContentType) {
            return Task<HttpResponseMessage>.Factory //
                .StartNew(() => new HttpResponseMessage(HttpStatusCode.UnsupportedMediaType));
        }

        return base.SendAsync(request, cancellationToken);
    }
}

And when setting up your service config:

config.MessageHandlers.Add(new UnsupportedMediaTypeConnegHandler());

Note that this requires that that the char sets match as well. You could loosen this restriction by checking only the MediaType property of the header.