#769 use SocketsHttpHandler on supported platforms

src/Flurl.Http/Configuration/FlurlClientBuilder.cs

@@ -23,7 +23,11 @@ public interface IFlurlClientBuilder
 		/// <summary>
 		/// Configure the inner-most HttpMessageHandler associated with this IFlurlClient.
 		/// </summary>
+#if NETCOREAPP2_1_OR_GREATER
+		IFlurlClientBuilder ConfigureInnerHandler(Action<SocketsHttpHandler> configAction);
+#else
 		IFlurlClientBuilder ConfigureInnerHandler(Action<HttpClientHandler> configAction);
+#endif
 
 		/// <summary>
 		/// Add a provided DelegatingHandler to the IFlurlClient.
@@ -44,9 +48,13 @@ public class FlurlClientBuilder : IFlurlClientBuilder
 		private readonly IFlurlClientFactory _factory;
 		private readonly string _baseUrl;
 		private readonly List<Func<DelegatingHandler>> _addMiddleware = new();
-		private readonly List<Action<HttpClient>> _configClient = new();
-		private readonly List<Action<HttpClientHandler>> _configHandler = new();
 		private readonly List<Action<FlurlHttpSettings>> _configSettings = new();
+		private readonly List<Action<HttpClient>> _configClient = new();
+#if NETCOREAPP2_1_OR_GREATER
+		private readonly HandlerBuilder<SocketsHttpHandler> _handlerBuilder = new();
+#else
+		private readonly HandlerBuilder<HttpClientHandler> _handlerBuilder = new();
+#endif
 
 		/// <summary>
 		/// Creates a new FlurlClientBuilder.
@@ -80,24 +88,20 @@ public IFlurlClientBuilder ConfigureHttpClient(Action<HttpClient> configAction)
 		}
 
 		/// <inheritdoc />
+#if NETCOREAPP2_1_OR_GREATER
+		public IFlurlClientBuilder ConfigureInnerHandler(Action<SocketsHttpHandler> configAction) {
+#else
 		public IFlurlClientBuilder ConfigureInnerHandler(Action<HttpClientHandler> configAction) {
-			_configHandler.Add(configAction);
+#endif
+			_handlerBuilder.Configs.Add(configAction);
 			return this;
 		}
 
 		/// <inheritdoc />
 		public IFlurlClient Build() {
-			var innerHandler = _factory.CreateInnerHandler();
-			foreach (var config in _configHandler) {
-				if (innerHandler is HttpClientHandler hch)
-					config(hch);
-				else
-					throw new Exception("ConfigureInnerHandler can only be used when IFlurlClientFactory.CreateInnerHandler returns an instance of HttpClientFactory.");
-			}
+			var outerHandler = _handlerBuilder.Build(_factory);
 
-			HttpMessageHandler outerHandler = innerHandler;
-			foreach (var createMW in Enumerable.Reverse(_addMiddleware)) {
-				var middleware = createMW();
+			foreach (var middleware in Enumerable.Reverse(_addMiddleware).Select(create => create())) {
 				middleware.InnerHandler = outerHandler;
 				outerHandler = middleware;
 			}
@@ -107,11 +111,27 @@ public IFlurlClient Build() {
 				config(httpCli);
 
 			var flurlCli = new FlurlClient(httpCli, _baseUrl);
-			foreach (var config in _configSettings) {
+			foreach (var config in _configSettings)
 				config(flurlCli.Settings);
-			}
 
 			return flurlCli;
 		}
+
+		// helper class to keep those compiler switches from getting too messy
+		private class HandlerBuilder<T> where T : HttpMessageHandler
+		{
+			public List<Action<T>> Configs { get; } = new();
+
+			public HttpMessageHandler Build(IFlurlClientFactory fac) {
+				var handler = fac.CreateInnerHandler();
+				foreach (var config in Configs) {
+					if (handler is T h)
+						config(h);
+					else
+						throw new Exception($"ConfigureInnerHandler expected an instance of {typeof(T).Name} but received an instance of {handler.GetType().Name}.");
+				}
+				return handler;
+			}
+		}
 	}
 }

src/Flurl.Http/Configuration/FlurlClientFactory.cs

@@ -5,24 +5,23 @@
 namespace Flurl.Http.Configuration
 {
 	/// <summary>
-	/// Interface for methods used to build and cache IFlurlClient instances.
+	/// Interface for helper methods used to construct IFlurlClient instances.
 	/// </summary>
 	public interface IFlurlClientFactory
 	{
 		/// <summary>
-		/// Defines how HttpClient should be instantiated and configured by default. Do NOT attempt
-		/// to cache/reuse HttpClient instances here - that should be done at the FlurlClient level
-		/// via a custom FlurlClientFactory that gets registered globally.
+		/// Creates and configures a new HttpClient as needed when a new IFlurlClient instance is created.
+		/// Implementors should NOT attempt to cache or reuse HttpClient instances here - their lifetime is
+		/// bound one-to-one with an IFlurlClient, whose caching and reuse is managed by IFlurlClientCache.
 		/// </summary>
-		/// <param name="handler">The HttpMessageHandler used to construct the HttpClient.</param>
-		/// <returns></returns>
+		/// <param name="handler">The HttpMessageHandler passed to the constructor of the HttpClient.</param>
 		HttpClient CreateHttpClient(HttpMessageHandler handler);
 
 		/// <summary>
-		/// Defines how the HttpMessageHandler used by HttpClients that are created by
-		/// this factory should be instantiated and configured. 
+		/// Creates and configures a new HttpMessageHandler as needed when a new IFlurlClient instance is created.
+		/// The default implementation creates an instance of SocketsHttpHandler for platforms that support it,
+		/// otherwise HttpClientHandler.
 		/// </summary>
-		/// <returns></returns>
 		HttpMessageHandler CreateInnerHandler();
 	}
 
@@ -42,38 +41,37 @@ public static class FlurlClientFactoryExtensions
 	/// </summary>
 	public class DefaultFlurlClientFactory : IFlurlClientFactory
 	{
-		/// <summary>
-		/// Override in custom factory to customize the creation of HttpClient used in all Flurl HTTP calls
-		/// (except when one is passed explicitly to the FlurlClient constructor). In order not to lose
-		/// Flurl.Http functionality, it is recommended to call base.CreateClient and customize the result.
-		/// </summary>
+		/// <inheritdoc />
 		public virtual HttpClient CreateHttpClient(HttpMessageHandler handler) {
 			return new HttpClient(handler);
 		}
 
 		/// <summary>
-		/// Override in custom factory to customize the creation of the top-level HttpMessageHandler used in all
-		/// Flurl HTTP calls (except when an HttpClient is passed explicitly to the FlurlClient constructor).
-		/// In order not to lose Flurl.Http functionality, it is recommended to call base.CreateMessageHandler, and
-		/// either customize the returned HttpClientHandler, or set it as the InnerHandler of a DelegatingHandler.
+		/// Creates and configures a new HttpMessageHandler as needed when a new IFlurlClient instance is created.
 		/// </summary>
 		public virtual HttpMessageHandler CreateInnerHandler() {
-			var httpClientHandler = new HttpClientHandler();
+			// Flurl has its own mechanisms for managing cookies and redirects, so we need to disable them in the inner handler.
+#if NETCOREAPP2_1_OR_GREATER
+			var handler = new SocketsHttpHandler {
+				UseCookies = false,
+				AllowAutoRedirect = false,
+				AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate
+			};
+#else
+			var handler = new HttpClientHandler();
 
-			// flurl has its own mechanisms for managing cookies and redirects
+			if (handler.SupportsRedirectConfiguration)
+				handler.AllowAutoRedirect = false;
 
-			try { httpClientHandler.UseCookies = false; }
-			catch (PlatformNotSupportedException) { } // look out for WASM platforms (#543)
+			// #266
+			// deflate not working? see #474
+			if (handler.SupportsAutomaticDecompression)
+				handler.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
 
-			if (httpClientHandler.SupportsRedirectConfiguration)
-				httpClientHandler.AllowAutoRedirect = false;
-
-			if (httpClientHandler.SupportsAutomaticDecompression) {
-				// #266
-				// deflate not working? see #474
-				httpClientHandler.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
-			}
-			return httpClientHandler;
+			try { handler.UseCookies = false; }
+			catch (PlatformNotSupportedException) { } // look out for WASM platforms (#543)
+#endif
+			return handler;
 		}
 	}
 }

test/Flurl.Test/Http/FlurlClientBuilderTests.cs

@@ -1,8 +1,6 @@
 using System;
-using System.Collections.Generic;
 using System.Linq;
 using System.Net.Http;
-using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using Flurl.Http;
@@ -52,6 +50,21 @@ public async Task can_add_middleware() {
 			Assert.AreEqual("blocked by flurl!", resp);
 		}
 
+		[Test]
+		public void inner_hanlder_is_SocketsHttpHandler_when_supported() {
+			var supported = typeof(HttpClientHandler).Assembly.DefinedTypes.Any(t => t.Name == "SocketsHttpHandler");
+#if NET
+			Assert.IsTrue(supported, "SocketsHttpHandler should be defined"); // sanity check (tests the test, basically)
+#endif
+			HttpMessageHandler handler = null;
+			new FlurlClientBuilder()
+				.ConfigureInnerHandler(h => handler = h)
+				.Build();
+
+			var expected = supported ? "SocketsHttpHandler" : "HttpClientHandler";
+			Assert.AreEqual(expected, handler?.GetType().Name);
+		}
+
 		class BlockingHandler : DelegatingHandler
 		{
 			private readonly string _msg;