eShopOnContainers/src/Services/Ordering/Ordering.API/Infrastructure/Middlewares/FailingMiddleware.cs

using Microsoft.AspNetCore.Http;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Ordering.API.Infrastructure.Middlewares
{
    public class FailingMiddleware
    {
        private readonly RequestDelegate _next;
        private bool _mustFail;
        private readonly FailingOptions _options;
        public FailingMiddleware(RequestDelegate next, FailingOptions options)
        {
            _next = next;
            _options = options;
            _mustFail = false;
        }
        public async Task Invoke(HttpContext context)
        {
            var path = context.Request.Path;
            if (path.Equals(_options.ConfigPath, StringComparison.OrdinalIgnoreCase))
            {
                await ProcessConfigRequest(context);
                return;
            }


            if (_mustFail)
            {
                context.Response.StatusCode = (int)System.Net.HttpStatusCode.InternalServerError;
                context.Response.ContentType = "text/plain";
                await context.Response.WriteAsync("Failed due to FailingMiddleware enabled.");
            }
            else
            {
                await _next.Invoke(context);
            }
        }

        private async Task ProcessConfigRequest(HttpContext context)
        {
            var enable = context.Request.Query.Keys.Any(k => k == "enable");
            var disable = context.Request.Query.Keys.Any(k => k == "disable");

            if (enable && disable)
            {
                throw new ArgumentException("Must use enable or disable querystring values, but not both");
            }

            if (disable)
            {
                _mustFail = false;
                await SendOkResponse(context, "FailingMiddleware disabled. Further requests will be processed.");
                return;
            }
            if (enable)
            {
                _mustFail = true;
                await SendOkResponse(context, "FailingMiddleware enabled. Further requests will return HTTP 500");
                return;
            }

            // If reach here, that means that no valid parameter has been passed. Just output status
            await SendOkResponse(context, string.Format("FailingMiddleware is {0}", _mustFail ? "enabled" : "disabled"));
            return;
        }

        private async Task SendOkResponse(HttpContext context, string message)
        {
            context.Response.StatusCode = (int)System.Net.HttpStatusCode.OK;
            context.Response.ContentType = "text/plain";
            await context.Response.WriteAsync(message);
        }

    }
}