Fix TestServer hang with duplex streaming requests (#17158)

src/Hosting/TestHost/src/HttpContextBuilder.cs

@@ -110,8 +110,10 @@ namespace Microsoft.AspNetCore.TestHost
                 try
                 {
                     await _application.ProcessRequestAsync(_testContext);
-                    await CompleteRequestAsync();
+
+                    // Matches Kestrel server: response is completed before request is drained
                     await CompleteResponseAsync();
+                    await CompleteRequestAsync();
                     _application.DisposeContext(_testContext, exception: null);
                 }
                 catch (Exception ex)
@@ -171,18 +173,9 @@ namespace Microsoft.AspNetCore.TestHost
                 await _requestPipe.Reader.CompleteAsync();
             }
 
-            if (_sendRequestStreamTask != null)
-            {
-                try
-                {
-                    // Ensure duplex request is either completely read or has been aborted.
-                    await _sendRequestStreamTask;
-                }
-                catch (OperationCanceledException)
-                {
-                    // Request was canceled, likely because it wasn't read before the request ended.
-                }
-            }
+            // Don't wait for request to drain. It could block indefinitely. In a real server
+            // we would wait for a timeout and then kill the socket.
+            // Potential future improvement: add logging that the request timed out
         }
 
         internal async Task CompleteResponseAsync()

src/Hosting/TestHost/test/TestClientTests.cs

@@ -384,6 +384,53 @@ namespace Microsoft.AspNetCore.TestHost
             await writeTask;
         }
 
+        [Fact]
+        public async Task ClientStreaming_ResponseCompletesWithoutResponseBodyWrite()
+        {
+            // Arrange
+            var requestStreamTcs = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
+
+            RequestDelegate appDelegate = ctx =>
+            {
+                ctx.Response.Headers["test-header"] = "true";
+                return Task.CompletedTask;
+            };
+
+            Stream requestStream = null;
+
+            var builder = new WebHostBuilder().Configure(app => app.Run(appDelegate));
+            var server = new TestServer(builder);
+            var client = server.CreateClient();
+
+            var httpRequest = new HttpRequestMessage(HttpMethod.Post, "http://localhost:12345");
+            httpRequest.Version = new Version(2, 0);
+            httpRequest.Content = new PushContent(async stream =>
+            {
+                requestStream = stream;
+                await requestStreamTcs.Task;
+            });
+
+            // Act
+            var response = await client.SendAsync(httpRequest, HttpCompletionOption.ResponseHeadersRead).WithTimeout();
+
+            var responseContent = await response.Content.ReadAsStreamAsync().WithTimeout();
+
+            // Assert
+            response.EnsureSuccessStatusCode();
+            Assert.Equal("true", response.Headers.GetValues("test-header").Single());
+
+            // Read response
+            byte[] buffer = new byte[1024];
+            var length = await responseContent.ReadAsync(buffer).AsTask().WithTimeout();
+            Assert.Equal(0, length);
+
+            // Writing to request stream will fail because server is complete
+            await Assert.ThrowsAnyAsync<Exception>(() => requestStream.WriteAsync(buffer).AsTask());
+
+            // Unblock request
+            requestStreamTcs.TrySetResult(null);
+        }
+
         [Fact]
         public async Task ClientStreaming_ServerAbort()
         {