AdxOpenRtbResponseAttribute.cs

using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;

namespace Inasync {

    /// <summary>
    /// AdX OpenRTB に適したレスポンスにする属性。
    /// </summary>
    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
    public sealed class AdxOpenRtbResponseAttribute : Attribute, IAsyncResultFilter {

        /// <summary>
        /// 強制的に No Bid にするか否か。
        /// </summary>
        public bool ForceNoBid { get; set; } = false;

        public Task OnResultExecutionAsync(ResultExecutingContext context, ResultExecutionDelegate next) {
            // Http Response Header
            // https://developers.google.com/authorized-buyers/rtb/openrtb-guide#checking-the-openrtb-version
            context.HttpContext.Response.Headers.Add("x-openrtb-version", "2.5");

            if (ForceNoBid || context.Result is ObjectResult result && result.Value == null) {
                // No Bid Response
                // https://developers.google.com/authorized-buyers/rtb/openrtb-guide#no-bid
                context.Result = new StatusCodeResult(204);
            }

            return next();
        }
    }
}