TestHost.WebSocketClient should set Request.Host (#9973)

src/Hosting/TestHost/src/WebSocketClient.cs

@@ -59,6 +59,12 @@ namespace Microsoft.AspNetCore.TestHost
                 scheme = (scheme == "ws") ? "http" : scheme;
                 scheme = (scheme == "wss") ? "https" : scheme;
                 request.Scheme = scheme;
+                if (!request.Host.HasValue)
+                {
+                    request.Host = uri.IsDefaultPort
+                        ? new HostString(HostString.FromUriComponent(uri).Host)
+                        : HostString.FromUriComponent(uri);
+                }
                 request.Path = PathString.FromUriComponent(uri);
                 request.PathBase = PathString.Empty;
                 if (request.Path.StartsWithSegments(_pathBase, out var remainder))

src/Hosting/TestHost/test/WebSocketClientTests.cs

@@ -0,0 +1,56 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Http;
+using Xunit;
+
+namespace Microsoft.AspNetCore.TestHost.Tests
+{
+    public class WebSocketClientTests
+    {
+        [Theory]
+        [InlineData("http://localhost/connect", "localhost")]
+        [InlineData("http://localhost:80/connect", "localhost")]
+        [InlineData("http://localhost:81/connect", "localhost:81")]
+        public async Task ConnectAsync_ShouldSetRequestProperties(string requestUri, string expectedHost)
+        {
+            HttpRequest capturedRequest = null;
+
+            using (var testServer = new TestServer(new WebHostBuilder()
+                .Configure(app =>
+                {
+                    app.Run(ctx =>
+                    {
+                        if (ctx.Request.Path.StartsWithSegments("/connect"))
+                        {
+                            capturedRequest = ctx.Request;
+                        }
+                        return Task.FromResult(0);
+                    });
+                })))
+            {
+                var client = testServer.CreateWebSocketClient();
+
+                try
+                {
+                    await client.ConnectAsync(
+                        uri: new Uri(requestUri),
+                        cancellationToken: default(CancellationToken));
+                }
+                catch
+                {
+                    // An exception will be thrown because our dummy endpoint does not implement a full Web socket server
+                }
+            }
+
+            Assert.Equal("http", capturedRequest.Scheme);
+            Assert.Equal(expectedHost, capturedRequest.Host.Value);
+            Assert.Equal("/connect", capturedRequest.Path);
+        }
+    }
+}