dh: Add ServicePointOnExceptionLogging handler

src/rm.DelegatingHandlers/ServicePointOnExceptionLoggingHandler.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Net;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+using Serilog;
+
+namespace rm.DelegatingHandlers;
+
+/// <summary>
+/// Logs <see cref="ServicePoint"/> stats for <see cref="HttpRequestMessage.RequestUri"/> with exception.
+/// </summary>
+public class ServicePointOnExceptionLoggingHandler : DelegatingHandler
+{
+	private readonly ILogger logger;
+
+	/// <inheritdoc cref="ServicePointOnExceptionLoggingHandler" />
+	public ServicePointOnExceptionLoggingHandler(
+		ILogger logger)
+	{
+		this.logger = logger?.ForContext(GetType())
+			?? throw new ArgumentNullException(nameof(logger));
+	}
+
+	protected override async Task<HttpResponseMessage> SendAsync(
+		HttpRequestMessage request,
+		CancellationToken cancellationToken)
+	{
+		try
+		{
+			return await base.SendAsync(request, cancellationToken)
+				.ConfigureAwait(false);
+		}
+		catch (Exception ex)
+		{
+			var servicePoint = ServicePointManager.FindServicePoint(request.RequestUri);
+			var props = ServicePointHelpers.GetServicePointEnrichers(servicePoint);
+
+			logger.ForContext(props)
+				.Error(ex, "ServicePoint stats");
+
+			throw;
+		}
+	}
+}

tests/rm.DelegatingHandlersTest/ServicePointOnExceptionLoggingHandlerTests.cs

@@ -0,0 +1,60 @@
+using System.Net.Http;
+using AutoFixture;
+using AutoFixture.AutoMoq;
+using Moq;
+using NUnit.Framework;
+using rm.DelegatingHandlers;
+using Serilog;
+using Serilog.Core;
+
+namespace rm.DelegatingHandlersTest;
+
+[TestFixture]
+public class ServicePointOnExceptionLoggingHandlerTests
+{
+	[Test]
+	public async Task Does_Not_Log_ServicePoint_Stats()
+	{
+		var fixture = new Fixture().Customize(new AutoMoqCustomization());
+
+		var loggerMock = fixture.Freeze<Mock<ILogger>>();
+		loggerMock.Setup(x => x.ForContext(It.IsAny<Type>())).Returns(loggerMock.Object);
+		loggerMock.Setup(x => x.ForContext(It.IsAny<IEnumerable<ILogEventEnricher>>())).Returns(loggerMock.Object);
+		var servicePointOnExceptionLoggingHandler = new ServicePointOnExceptionLoggingHandler(loggerMock.Object);
+
+		using var invoker = HttpMessageInvokerFactory.Create(
+			fixture.Create<HttpMessageHandler>(), servicePointOnExceptionLoggingHandler);
+
+		using var requestMessage = fixture.Create<HttpRequestMessage>();
+		using var _ = await invoker.SendAsync(requestMessage, CancellationToken.None);
+
+		loggerMock.Verify((x) =>
+			x.Error(It.IsAny<string>()),
+			Times.Never);
+	}
+
+	[Test]
+	public void Logs_ServicePoint_Stats_During_Exception()
+	{
+		var fixture = new Fixture().Customize(new AutoMoqCustomization());
+
+		var loggerMock = fixture.Freeze<Mock<ILogger>>();
+		loggerMock.Setup(x => x.ForContext(It.IsAny<Type>())).Returns(loggerMock.Object);
+		loggerMock.Setup(x => x.ForContext(It.IsAny<IEnumerable<ILogEventEnricher>>())).Returns(loggerMock.Object);
+		var servicePointOnExceptionLoggingHandler = new ServicePointOnExceptionLoggingHandler(loggerMock.Object);
+		var throwingHandler = new ThrowingHandler(new TurnDownForWhatException());
+
+		using var invoker = HttpMessageInvokerFactory.Create(
+			fixture.Create<HttpMessageHandler>(), servicePointOnExceptionLoggingHandler, throwingHandler);
+
+		using var requestMessage = fixture.Create<HttpRequestMessage>();
+		var ex = Assert.ThrowsAsync<TurnDownForWhatException>(async () =>
+		{
+			using var _ = await invoker.SendAsync(requestMessage, CancellationToken.None);
+		});
+
+		loggerMock.Verify((x) =>
+			x.Error(ex, "ServicePoint stats"),
+			Times.Once);
+	}
+}