dh: Add Procrastinating after N requests handler

src/rm.DelegatingHandlers/ProcrastinatingAfterNRequestsHandler.cs

@@ -0,0 +1,57 @@
+using System;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace rm.DelegatingHandlers;
+
+/// <summary>
+/// Causes delay after N requests to induce http timeouts.
+/// </summary>
+public class ProcrastinatingAfterNRequestsHandler : DelegatingHandler
+{
+	private readonly IProcrastinatingAfterNRequestsHandlerSettings procrastinatingAfterNRequestsHandlerSettings;
+
+	private long n;
+
+	/// <inheritdoc cref="ProcrastinatingAfterNRequestsHandler" />
+	public ProcrastinatingAfterNRequestsHandler(
+		IProcrastinatingAfterNRequestsHandlerSettings procrastinatingAfterNRequestsHandlerSettings)
+	{
+		this.procrastinatingAfterNRequestsHandlerSettings = procrastinatingAfterNRequestsHandlerSettings
+			?? throw new ArgumentNullException(nameof(procrastinatingAfterNRequestsHandlerSettings));
+	}
+
+	protected override async Task<HttpResponseMessage> SendAsync(
+		HttpRequestMessage request,
+		CancellationToken cancellationToken)
+	{
+		if (Interlocked.Read(ref n) >= procrastinatingAfterNRequestsHandlerSettings.N)
+		{
+			await Task.Delay(procrastinatingAfterNRequestsHandlerSettings.DelayInMilliseconds, cancellationToken)
+				.ConfigureAwait(false);
+		}
+
+		var response = await base.SendAsync(request, cancellationToken)
+			.ConfigureAwait(false);
+
+		if (Interlocked.Read(ref n) < procrastinatingAfterNRequestsHandlerSettings.N)
+		{
+			Interlocked.Increment(ref n);
+		}
+
+		return response;
+	}
+}
+
+public interface IProcrastinatingAfterNRequestsHandlerSettings
+{
+	long N { get; }
+	int DelayInMilliseconds { get; }
+}
+
+public record class ProcrastinatingAfterNRequestsHandlerSettings : IProcrastinatingAfterNRequestsHandlerSettings
+{
+	public long N { get; init; }
+	public int DelayInMilliseconds { get; init; }
+}

tests/rm.DelegatingHandlersTest/ProcrastinatingAfterNRequestsHandlerTests.cs

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+using System.Diagnostics;
+using System.Net.Http;
+using AutoFixture;
+using AutoFixture.AutoMoq;
+using NUnit.Framework;
+using rm.DelegatingHandlers;
+
+namespace rm.DelegatingHandlersTest;
+
+[TestFixture]
+public class ProcrastinatingAfterNRequestsHandlerTests
+{
+	[Retry(5)]
+	[Test]
+	public async Task Procrastinates()
+	{
+		var fixture = new Fixture().Customize(new AutoMoqCustomization());
+
+		var n = 5;
+		var delayInMilliseconds = 25;
+		var procrastinatingAfterNRequestsHandler = new ProcrastinatingAfterNRequestsHandler(
+			new ProcrastinatingAfterNRequestsHandlerSettings
+			{
+				N = n,
+				DelayInMilliseconds = delayInMilliseconds,
+			});
+
+		using var invoker = HttpMessageInvokerFactory.Create(
+			fixture.Create<HttpMessageHandler>(), procrastinatingAfterNRequestsHandler);
+
+		for (int i = 0; i < n; i++)
+		{
+			using var _ = await invoker.SendAsync(fixture.Create<HttpRequestMessage>(), CancellationToken.None);
+		}
+		using var requestMessage = fixture.Create<HttpRequestMessage>();
+		var stopwatch = Stopwatch.StartNew();
+		using var response = await invoker.SendAsync(requestMessage, CancellationToken.None);
+		stopwatch.Stop();
+		Console.WriteLine(stopwatch.ElapsedMilliseconds);
+
+		Assert.GreaterOrEqual(stopwatch.ElapsedMilliseconds, delayInMilliseconds);
+	}
+
+	[Test]
+	public async Task Does_Not_Procrastinate()
+	{
+		var fixture = new Fixture().Customize(new AutoMoqCustomization());
+
+		var n = 5;
+		var delayInMilliseconds = 1000;
+		var procrastinatingAfterNRequestsHandler = new ProcrastinatingAfterNRequestsHandler(
+			new ProcrastinatingAfterNRequestsHandlerSettings
+			{
+				N = n,
+				DelayInMilliseconds = delayInMilliseconds,
+			});
+
+		using var invoker = HttpMessageInvokerFactory.Create(
+			fixture.Create<HttpMessageHandler>(), procrastinatingAfterNRequestsHandler);
+
+		using var requestMessage = fixture.Create<HttpRequestMessage>();
+		var stopwatch = Stopwatch.StartNew();
+		using var response = await invoker.SendAsync(requestMessage, CancellationToken.None);
+		stopwatch.Stop();
+		Console.WriteLine(stopwatch.ElapsedMilliseconds);
+
+		Assert.Less(stopwatch.ElapsedMilliseconds, delayInMilliseconds);
+	}
+}