[HttpClientFactory] Revert workaround for empty name HttpClient fallback

src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientBuilderExtensions.cs

@@ -645,16 +645,51 @@ public static IHttpClientBuilder ConfigureAdditionalHttpMessageHandlers(this IHt
             return builder;
         }
 
-#pragma warning disable 1591 // TODO: Document this API. https://github.com/dotnet/runtime/issues/105974
+        /// <summary>
+        /// Registers named <see cref="HttpClient"/> and the related handler pipeline <see cref="HttpMessageHandler"/> as keyed
+        /// services with the client's name as the key, and a lifetime provided in the <paramref name="lifetime" /> parameter.
+        /// By default, the lifetime is <see cref="ServiceLifetime.Scoped"/>.
+        /// </summary>
+        /// <param name="builder">The <see cref="IHttpClientBuilder"/>.</param>
+        /// <param name="lifetime">Lifetime of the keyed services registered.</param>
+        /// <returns>An <see cref="IHttpClientBuilder"/> that can be used to configure the client.</returns>
+        /// <remarks>
+        /// <para>
+        /// A named client resolved from DI as a keyed service will behave similarly to a client you would create with <see cref="IHttpClientFactory.CreateClient(string)"/>. This
+        /// means that the client will continue reusing the same <see cref="HttpMessageHandler"/> instance for the duration of <see cref="HttpClientFactoryOptions.HandlerLifetime"/>,
+        /// and it will continue to use the separate, handler's DI scope instead of the scope it was resolved from.
+        /// </para>
+        /// <para>
+        /// WARNING: Registering the client as a keyed <see cref="ServiceLifetime.Transient"/> service will lead to the <see cref="HttpClient"/> and <see cref="HttpMessageHandler"/>
+        /// instances being captured by DI as both implement <see cref="IDisposable"/>. This might lead to memory leaks if the client is resolved multiple times within a
+        /// <see cref="ServiceLifetime.Singleton"/> service.
+        /// </para>
+        /// <para>
+        /// WARNING: In case of (1) a keyed <see cref="ServiceLifetime.Singleton"/> <see cref="HttpClient"/> registration, or (2) a keyed <see cref="ServiceLifetime.Transient"/>
+        /// <see cref="HttpClient"/> injected into a <see cref="ServiceLifetime.Singleton"/> service, or (3) long-running application scopes,
+        /// the <see cref="HttpClient"/> instances will get captured by a singleton or a long-running scope, so they will NOT be able to participate in the handler rotation,
+        /// which can result in the loss of DNS changes. (This is a similar issue to the one with Typed Clients, that are registered as <see cref="ServiceLifetime.Transient"/> services.)
+        /// </para>
+        /// <para>
+        /// If called twice with for a builder with the same name, the lifetime of the keyed service will be updated to the latest used <see cref="ServiceLifetime"/> value.
+        /// </para>
+        /// <para>
+        /// If called for a typed client, only the related named client and handler will be registered as keyed. The typed client itself will continue to be registered as
+        /// a transient service.
+        /// </para>
+        /// <para>
+        /// If used in conjuction with <see cref="HttpClientFactoryServiceCollectionExtensions.ConfigureHttpClientDefaults(IServiceCollection, Action{IHttpClientBuilder})"/>,
+        /// the key <see cref="KeyedService.AnyKey"/> is used, so any named <see cref="HttpClient"/> instance will be resolvable as a keyed service (unless explicitly opted-out
+        /// from the keyed registration via <see cref="RemoveAsKeyed"/>).
+        /// </para>
+        /// </remarks>
         public static IHttpClientBuilder AddAsKeyed(this IHttpClientBuilder builder, ServiceLifetime lifetime = ServiceLifetime.Scoped)
         {
             ThrowHelper.ThrowIfNull(builder);
 
             string? name = builder.Name;
             IServiceCollection services = builder.Services;
-            HttpClientMappingRegistry registry = GetMappingRegistry(services);
-
-            UpdateEmptyNameHttpClient(services, registry);
+            HttpClientMappingRegistry registry = services.GetMappingRegistry();
 
             if (name == null)
             {
@@ -678,15 +713,25 @@ public static IHttpClientBuilder AddAsKeyed(this IHttpClientBuilder builder, Ser
             return builder;
         }
 
+        /// <summary>
+        /// Removes the keyed registrations for the named <see cref="HttpClient"/> and <see cref="HttpMessageHandler"/>.
+        /// </summary>
+        /// <param name="builder">The <see cref="IHttpClientBuilder"/>.</param>
+        /// <returns>An <see cref="IHttpClientBuilder"/> that can be used to configure the client.</returns>
+        /// <remarks>
+        /// <para>
+        /// If used in conjuction with <see cref="HttpClientFactoryServiceCollectionExtensions.ConfigureHttpClientDefaults(IServiceCollection, Action{IHttpClientBuilder})"/>,
+        /// it will only affect the previous "global" <see cref="KeyedService.AnyKey"/> registration, and won't affect the clients registered for a specific name
+        /// with <see cref="AddAsKeyed"/>.
+        /// </para>
+        /// </remarks>
         public static IHttpClientBuilder RemoveAsKeyed(this IHttpClientBuilder builder)
         {
             ThrowHelper.ThrowIfNull(builder);
 
             string? name = builder.Name;
             IServiceCollection services = builder.Services;
-            HttpClientMappingRegistry registry = GetMappingRegistry(services);
-
-            UpdateEmptyNameHttpClient(services, registry);
+            HttpClientMappingRegistry registry = services.GetMappingRegistry();
 
             if (name == null)
             {
@@ -704,32 +749,6 @@ public static IHttpClientBuilder RemoveAsKeyed(this IHttpClientBuilder builder)
 
             return builder;
         }
-#pragma warning restore 1591
-
-        // workaround for https://github.com/dotnet/runtime/issues/102654
-        private static void UpdateEmptyNameHttpClient(IServiceCollection services, HttpClientMappingRegistry registry)
-        {
-            if (registry.EmptyNameHttpClientDescriptor is not null)
-            {
-                bool removed = services.Remove(registry.EmptyNameHttpClientDescriptor);
-
-                if (removed)
-                {
-                    // trying to add it as keyed instead
-                    if (!registry.KeyedLifetimeMap.ContainsKey(string.Empty))
-                    {
-                        var clientLifetime = new HttpClientKeyedLifetime(string.Empty, ServiceLifetime.Transient);
-                        registry.KeyedLifetimeMap[string.Empty] = clientLifetime;
-                        clientLifetime.AddRegistration(services);
-                    }
-                }
-            }
-
-            if (services.Any(sd => sd.ServiceType == typeof(HttpClient) && sd.ServiceKey is null))
-            {
-                throw new InvalidOperationException($"{nameof(AddAsKeyed)} isn't supported when {nameof(HttpClient)} is registered as a service.");
-            }
-        }
 
         // See comments on HttpClientMappingRegistry.
         private static void ReserveClient(IHttpClientBuilder builder, Type type, string name, bool validateSingleType)
@@ -763,7 +782,11 @@ private static void ReserveClient(IHttpClientBuilder builder, Type type, string
             }
         }
 
-        private static HttpClientMappingRegistry GetMappingRegistry(IServiceCollection services)
-            => HttpClientFactoryServiceCollectionExtensions.GetMappingRegistry(services);
+        internal static HttpClientMappingRegistry GetMappingRegistry(this IServiceCollection services)
+        {
+            var registry = (HttpClientMappingRegistry?)services.Single(sd => sd.ServiceType == typeof(HttpClientMappingRegistry)).ImplementationInstance;
+            Debug.Assert(registry != null);
+            return registry;
+        }
     }
 }

src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientFactoryServiceCollectionExtensions.cs

@@ -63,7 +63,10 @@ public static IServiceCollection AddHttpClient(this IServiceCollection services)
             services.TryAddSingleton(new DefaultHttpClientConfigurationTracker());
 
             // Register default client as HttpClient
-            TryAddEmptyNameHttpClient(services);
+            services.TryAddTransient(s =>
+            {
+                return s.GetRequiredService<IHttpClientFactory>().CreateClient(string.Empty);
+            });
 
             return services;
         }
@@ -831,34 +834,5 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
             builder.AddTypedClient<TClient>(factory);
             return builder;
         }
-
-        internal static HttpClientMappingRegistry GetMappingRegistry(IServiceCollection services)
-        {
-            var registry = (HttpClientMappingRegistry?)services.Single(sd => sd.ServiceType == typeof(HttpClientMappingRegistry)).ImplementationInstance;
-            Debug.Assert(registry != null);
-            return registry;
-        }
-
-        private static void TryAddEmptyNameHttpClient(IServiceCollection services)
-        {
-            HttpClientMappingRegistry mappingRegistry = GetMappingRegistry(services);
-
-            if (mappingRegistry.EmptyNameHttpClientDescriptor is not null)
-            {
-                return;
-            }
-
-            if (services.Any(sd => sd.ServiceType == typeof(HttpClient) && sd.ServiceKey is null))
-            {
-                return;
-            }
-
-            mappingRegistry.EmptyNameHttpClientDescriptor = ServiceDescriptor.Transient(s =>
-            {
-                return s.GetRequiredService<IHttpClientFactory>().CreateClient(string.Empty);
-            });
-
-            services.Add(mappingRegistry.EmptyNameHttpClientDescriptor);
-        }
     }
 }

src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientMappingRegistry.cs

@@ -18,7 +18,5 @@ internal sealed class HttpClientMappingRegistry
         public Dictionary<string, HttpClientKeyedLifetime> KeyedLifetimeMap { get; } = new();
 
         public HttpClientKeyedLifetime? DefaultKeyedLifetime { get; set; }
-
-        public ServiceDescriptor? EmptyNameHttpClientDescriptor { get; set; }
     }
 }

src/libraries/Microsoft.Extensions.Http/tests/Microsoft.Extensions.Http.Tests/DependencyInjection/HttpClientKeyedRegistrationTest.Descriptors.cs

@@ -1,51 +1,13 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System;
 using System.Net.Http;
 using Xunit;
 
 namespace Microsoft.Extensions.DependencyInjection
 {
     public partial class HttpClientKeyedRegistrationTest
     {
-        [Fact]
-        public void AddAsKeyed_EmptyNameHttpClientUpdated() // test for workaround for https://github.com/dotnet/runtime/issues/102654
-        {
-            var serviceCollection = new ServiceCollection();
-
-            serviceCollection.AddHttpClient();
-
-            var emptyNameDescriptor = Assert.Single(serviceCollection, d => d.ServiceType == typeof(HttpClient));
-            Assert.False(emptyNameDescriptor.IsKeyedService);
-
-            serviceCollection.AddHttpClient(Test).AddAsKeyed();
-
-            emptyNameDescriptor = Assert.Single(serviceCollection, d => d.ServiceType == typeof(HttpClient) && !(d.ServiceKey is string s && s == Test));
-            Assert.True(emptyNameDescriptor.IsKeyedService);
-            Assert.Equal(string.Empty, emptyNameDescriptor.ServiceKey);
-        }
-
-        [Fact]
-        public void AddAsKeyed_NonFactoryHttpClientAdded_Throws() // test for workaround for https://github.com/dotnet/runtime/issues/102654
-        {
-            var serviceCollection = new ServiceCollection();
-
-            serviceCollection.AddSingleton(new HttpClient());
-
-            var emptyNameDescriptor = Assert.Single(serviceCollection, d => d.ServiceType == typeof(HttpClient));
-            Assert.False(emptyNameDescriptor.IsKeyedService);
-            Assert.Equal(ServiceLifetime.Singleton, emptyNameDescriptor.Lifetime);
-
-            var builder = serviceCollection.AddHttpClient(Test);
-
-            emptyNameDescriptor = Assert.Single(serviceCollection, d => d.ServiceType == typeof(HttpClient));
-            Assert.False(emptyNameDescriptor.IsKeyedService);
-            Assert.Equal(ServiceLifetime.Singleton, emptyNameDescriptor.Lifetime);
-
-            Assert.Throws<InvalidOperationException>(() => builder.AddAsKeyed());
-        }
-
         [Fact]
         public void AddAsKeyed_ScopedLifetime()
         {
@@ -150,10 +112,10 @@ public void RemoveAsKeyed_PerName_AnyKeyDescriptorRemains()
         }
 
         private static bool IsKeyedClientDescriptor(ServiceDescriptor descriptor)
-            => descriptor.ServiceType == typeof(HttpClient) && descriptor.IsKeyedService && (descriptor.ServiceKey is not string name || name.Length > 0);
+            => descriptor.IsKeyedService && descriptor.ServiceType == typeof(HttpClient);
 
         private static bool IsKeyedHandlerDescriptor(ServiceDescriptor descriptor)
-            => descriptor.ServiceType == typeof(HttpMessageHandler) && descriptor.IsKeyedService && (descriptor.ServiceKey is not string name || name.Length > 0);
+            => descriptor.IsKeyedService && descriptor.ServiceType == typeof(HttpMessageHandler);
 
         private static void AssertSingleKeyedClientDescriptor(IServiceCollection services, ServiceLifetime lifetime, object key)
         {