Replace WebClient with HttpClient

OpenRA.Game/Support/HttpClientFactory.cs

@@ -0,0 +1,48 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2020 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using System;
+using System.Net.Http;
+
+namespace OpenRA.Support
+{
+	public class HttpClientFactory
+	{
+#if !MONO
+		const int MaxConnectionPerServer = 20;
+		static readonly TimeSpan ConnectionLifeTime = TimeSpan.FromMinutes(1);
+#endif
+
+		static readonly Lazy<HttpMessageHandler> Handler = new Lazy<HttpMessageHandler>(GetHandler);
+
+		public static HttpClient Create()
+		{
+			return new HttpClient(Handler.Value, false);
+		}
+
+		static HttpMessageHandler GetHandler()
+		{
+#if !MONO
+			return new SocketsHttpHandler
+			{
+				// https://github.com/dotnet/corefx/issues/26895
+				// https://github.com/dotnet/corefx/issues/26331
+				// https://github.com/dotnet/corefx/pull/26839
+				PooledConnectionLifetime = ConnectionLifeTime,
+				PooledConnectionIdleTimeout = ConnectionLifeTime,
+				MaxConnectionsPerServer = MaxConnectionPerServer
+			};
+#else
+			return new HttpClientHandler();
+#endif
+		}
+	}
+}