How do I make an ASP.NET Core void/Task action method return 204 No Content

Question

How do I configure the response type of a void/Task action method to be 204 No Content rather than 200 OK?

For example, consider a simple controller:

public class MyController : Controller
{
    [HttpPost("foo")]
    public async Task Foo() {
        await Task.CompletedTask;
    }

    [HttpPost("bar")]
    public async Task<IActionResult> Bar() {
        await Task.CompletedTask;
        return NoContent();
    }
}

I'd like both methods to return 204 No Content, but the default (and thus what /foo returns) seems to be 200 OK. I tried various things, such as adding a [ProducesResponseType(204)] attribute to /foo, but I haven't found anything that seems to have any effect.

Answer 1

Here is a solution that returns 204 instead of 200 for all controller methods that return void or Task. First, create a result filter:

using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc.Controllers;
using Microsoft.AspNetCore.Mvc.Filters;
using static Microsoft.AspNetCore.Http.StatusCodes;

namespace StackOverflow.SampleCode
{
    /// <summary>
    /// A filter that transforms http status code 200 OK to 204 No Content for controller actions that return nothing,
    /// i.e. <see cref="System.Void"/> or <see cref="Task"/>.
    /// </summary>
    internal class VoidAndTaskTo204NoContentFilter : IResultFilter
    {
        /// <inheritdoc/>
        public void OnResultExecuting(ResultExecutingContext context)
        {
            if (context.ActionDescriptor is ControllerActionDescriptor actionDescriptor)
            {
                var returnType = actionDescriptor.MethodInfo.ReturnType;
                if (returnType == typeof(void) || returnType == typeof(Task))
                {
                    context.HttpContext.Response.StatusCode = Status204NoContent;
                }
            }
        }

        /// <inheritdoc/>
        public void OnResultExecuted(ResultExecutedContext context)
        {
        }
    }
}

Then register the filter globally:

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers(options => options.Filters.Add<VoidAndTaskTo204NoContentFilter>());
}

This will affect all your controller methods.