HttpClientFactory should not hold onto exceptions indefinitely

src/libraries/Microsoft.Extensions.Http/src/DefaultHttpClientFactory.cs

@@ -115,10 +115,13 @@ public HttpMessageHandler CreateHandler(string name)
         {
             ThrowHelper.ThrowIfNull(name);
 
+            // Refactor the StartHandlerEntryTimer to be based on the name instead of the ActiveHandlerTrackingEntry
+            // And start the timer just before the handler is created.
+            // This will ensure that any exception that might be thrown during the initialzation of the Lazy object
+            // will not persist throughout the lifetime of the application
+            StartHandlerEntryTimer(name);
             ActiveHandlerTrackingEntry entry = _activeHandlers.GetOrAdd(name, _entryFactory).Value;
 
-            StartHandlerEntryTimer(entry);
-
             return entry.Handler;
         }
 

src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/HttpClientHandlerDependencyInjectionTests.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Net.Http;
+using System.Threading;
+
+using FluentAssertions;
+
+using Microsoft.Extensions.DependencyInjection;
+
+using Moq;
+
+using Xunit;
+
+namespace HttpClientHandlerDependencyInjection
+{
+    public class HttpClientHandlerFactoryDependencyInjectionTests
+    {
+        string nextFunctionInput = "throw";
+
+        [Fact]
+        public void Demonstrate_That_ExceptionsInHttpFactoriesPersist_Incorrectly()
+        {
+            var myException = new Exception("The one and only exception");
+            var mockHandlerFactory = new Mock<IHandlerFactory>();
+            mockHandlerFactory
+                .Setup(mock => mock.Create("throw"))
+                .Callback(() => nextFunctionInput = "don't throw")
+                .Throws(myException);
+
+            mockHandlerFactory
+                .Setup(mock => mock.Create("don't throw"))
+                .Returns(new HttpClientHandler());
+
+            var services = GetServiceCollection(mockHandlerFactory.Object);
+            var a = services.GetService<IHttpClientFactory>();
+
+            // Should throw on the first call
+            var act = () => a.CreateClient("myClient");
+            var exFromFirstCall = act.Should().Throw<Exception>().Which;
+
+            mockHandlerFactory.Verify(mock => mock.Create("throw"), Times.Once);
+
+            // Wait 1 second -- It's the minimum handler lifetime possible
+            Thread.Sleep(1001);
+
+            // The following code fails, but should not.
+            // The client that is created is a part of a lazy initialization
+            // The ActiveHandlerTrackingEntry is incorrectly caching the exception indefinitely (https://github.com/dotnet/runtime/blob/main/src/libraries/Microsoft.Extensions.Http/src/DefaultHttpClientFactory.cs#L118)
+            // The entry timer is not being started due to the exception (https://github.com/dotnet/runtime/blob/main/src/libraries/Microsoft.Extensions.Http/src/DefaultHttpClientFactory.cs#L120)
+            ////var client = a.CreateClient("myClient");
+            ////mockHandlerFactory.Verify(mock => mock.Create("don't throw"), Times.Once);
+            ////client.Should().BeOfType<HttpClientHandler>();
+
+            // The following code succeeds, but should not
+            var act2 = () => a.CreateClient("myClient");
+            var exception = act2.Should().Throw<Exception>("The one and only exception").Which;
+            exception.Should().Be(exFromFirstCall);
+        }
+
+        private IServiceProvider GetServiceCollection(IHandlerFactory handlerFactory)
+        {
+            var services = new ServiceCollection();
+            services.AddHttpClient("myClient")
+           .ConfigurePrimaryHttpMessageHandler((p) =>
+           {
+               return handlerFactory.Create(nextFunctionInput);
+           })
+           .SetHandlerLifetime(TimeSpan.FromSeconds(1)); // Minimum timespan is 1 second
+
+            return services.BuildServiceProvider();
+        }
+
+        public interface IHandlerFactory
+        {
+            HttpClientHandler Create(string toDo);
+        }
+    }
+}