How to return a specific status code and no contents from Controller?

The best way to do it is:

return this.StatusCode(StatusCodes.Status418ImATeapot, "Error message");

StatusCodes has every kind of return status and you can see all of them here.

Once you choose your StatusCode, return it with a message.

Look at how the current Object Results are created. Here is the BadRequestObjectResult. Just an extension of the ObjectResult with a value and StatusCode.

https://github.com/aspnet/Mvc/blob/master/src/Microsoft.AspNetCore.Mvc.Core/BadRequestObjectResult.cs

I created a TimeoutExceptionObjectResult just the same way for 408.

/// <summary>
/// An <see cref="ObjectResult"/> that when executed will produce a Request Timeout (408) response.
/// </summary>
[DefaultStatusCode(DefaultStatusCode)]
public class TimeoutExceptionObjectResult : ObjectResult
{
    private const int DefaultStatusCode = StatusCodes.Status408RequestTimeout;

    /// <summary>
    /// Creates a new <see cref="TimeoutExceptionObjectResult"/> instance.
    /// </summary>
    /// <param name="error">Contains the errors to be returned to the client.</param>
    public TimeoutExceptionObjectResult(object error)
        : base(error)
    {
        StatusCode = DefaultStatusCode;
    }
}

Client:

if (ex is TimeoutException)
{
    return new TimeoutExceptionObjectResult("The request timed out.");
}

this.HttpContext.Response.StatusCode = 418; // I'm a teapot

How to end the request?

Try other solution, just:

return StatusCode(418);

You could use StatusCode(???) to return any HTTP status code.

Also, you can use dedicated results:

Success:

• return Ok() ← Http status code 200
• return Created() ← Http status code 201
• return NoContent(); ← Http status code 204

Client Error:

• return BadRequest(); ← Http status code 400
• return Unauthorized(); ← Http status code 401
• return NotFound(); ← Http status code 404

More details:

• ControllerBase Class (Thanks @Technetium)
• StatusCodes.cs (consts aviable in ASP.NET Core)
• HTTP Status Codes on Wiki
• HTTP Status Codes IANA

This code might work for non-.NET Core MVC controllers:

this.HttpContext.Response.StatusCode = 418; // I'm a teapot
return Json(new { status = "mer" }, JsonRequestBehavior.AllowGet);