Handling “415 Unsupported Media Type” in .NET Core API

The default content type for .NET Core API’s is application/json. So if the content-type is left out, or another content type is used, you will get a “415 Unsupported Media Type”:

This is for example true if you develop an endpoint to capture Content Security Policy Violation Reports. Because the violation report is sent with the application/csp-report content type.

To allow another content-type, you need to specify which type(s) to receive. In ConfigureServices, add the content-type to use to the SupportedMediaTypes:

public void ConfigureServices(IServiceCollection services)
{
  ...
  ...
  // Add MVC API Endpoints
  services.AddControllers(options =>
  {
    var jsonInputFormatter = options.InputFormatters
        .OfType<Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonInputFormatter>()
        .Single();
    jsonInputFormatter.SupportedMediaTypes.Add("application/csp-report");
  }
  );
  ...
  ...
}

Now your endpoint will allow both application/json and application/csp-report content types.

BUT WHAT IF THERE IS NO CONTENT TYPE?

To allow an endpoint to be called without any content-type, you also allow everything to be posted to the endpoint. The endpoint will read the posted content using a streamreader instead of receiving it from a strongly typed parameter.

The endpoint cannot be called using your Swagger documentation.

using Microsoft.AspNetCore.Mvc;
using System.IO;
using System.Text;
using System.Threading.Tasks;

namespace MyCode
{
  [ApiController]
  [Route("/api")]
  public class TestController : ControllerBase
  {
    [HttpPost("test")]
    public async Task<IActionResult> Test()
    {
      using (StreamReader reader = new StreamReader(Request.Body, Encoding.UTF8))
      {
        string message = await reader.ReadToEndAsync();
        // Do something with the received content. For 
        // test pusposes, I will just output the content:
        return base.Ok(message);
      }
    }
  }
}

MORE TO READ:

• Content Security Policy Sample Violation Report from Mozilla
• “415 Unsupported Media Type” for Content-Type “application/csp-report” in ASP.NET Core from StackOverflow
• .NET Core Api – Catch exceptions using a middleware from briancaos
• ASP.Net Core API – “‘s’ is an invalid start of a value. Path: $ | LineNumber: 0 | BytePositionInLine: 0.” from briancaos
• .NET Core MVC Web API – control DateTime format in JSON output using JsonSerializerOptions from briancaos