Adding new MediaType to NewtonsoftJsonInputFormatter doesn't work

Question

I'd like to add a new MediaType to the MvcOptions input formatter in .Net 5

When I do the following

services.AddControllers();

services.Configure<Microsoft.AspNetCore.Mvc.MvcOptions>(options =>
{
    options.InputFormatters
 .OfType<Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonInputFormatter>()
 .First()
 .SupportedMediaTypes
 .Add(new Microsoft.Net.Http.Headers.MediaTypeHeaderValue("application/csp-report"));
});

everything works fine. But I want to use Newtonsoft.Json instead of the default Json-Serializer so I changed my code to

services.AddControllers()
          .AddNewtonsoftJson();

services.Configure<Microsoft.AspNetCore.Mvc.MvcOptions>(options =>
{
    options.InputFormatters
 .OfType<Microsoft.AspNetCore.Mvc.Formatters.NewtonsoftJsonInputFormatter>()
 .First()
 .SupportedMediaTypes
 .Add(new Microsoft.Net.Http.Headers.MediaTypeHeaderValue("application/csp-report"));
});

But now every time a application/csp-report is send to the controller I get a 415 Status code.

Answer 1

The AddNewtonsoftJson method will add two input formatters (NewtonsoftJsonInputFormatter and NewtonsoftJsonPatchInputFormatter) and when you are calling the OfType both are returning, but because you are selecting the first one, that will be always NewtonsoftJsonPatchInputFormatter that ended up being configured with your new media type not the NewtonsoftJsonInputFormatter that you expected.

So as a possible fix the code could be like:

          .AddNewtonsoftJson();

services.Configure<Microsoft.AspNetCore.Mvc.MvcOptions>(options =>
{
    options.InputFormatters
 .OfType<Microsoft.AspNetCore.Mvc.Formatters.NewtonsoftJsonInputFormatter>()
 .First(f => !(f is Microsoft.AspNetCore.Mvc.Formatters.NewtonsoftJsonPatchInputFormatter))
 .SupportedMediaTypes
 .Add(new Microsoft.Net.Http.Headers.MediaTypeHeaderValue("application/csp-report"));
});

All information here: Adding new MediaType to NewtonsoftJsonInputFormatter doesn't work