Add HttpRequest.Flush[Async]

src/Microsoft.AspNetCore.SystemWebAdapters/Generated/Ref.Standard.cs

@@ -291,6 +291,8 @@ internal HttpResponse() { }
         public void ClearContent() { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public void ClearHeaders() { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public void End() { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public void Flush() { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
+        public System.Threading.Tasks.Task FlushAsync() { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public void Redirect(string url) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public void Redirect(string url, bool endResponse) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}
         public void RedirectPermanent(string url) { throw new System.PlatformNotSupportedException("Only supported when running on ASP.NET Core or System.Web");}

src/Microsoft.AspNetCore.SystemWebAdapters/HttpResponse.cs

@@ -5,6 +5,7 @@
 using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Text;
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.Diagnostics;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Features;
@@ -252,6 +253,10 @@ private string ResolvePath(string url)
 
         public void SetCookie(HttpCookie cookie) => Cookies.Set(cookie);
 
+        public void Flush() => _response.Body.Flush();
+
+        public Task FlushAsync() => _response.Body.FlushAsync(_response.HttpContext.RequestAborted);
+
         public void End() => AdapterFeature.EndAsync().GetAwaiter().GetResult();
 
         public void Write(char ch) => Output.Write(ch);

test/Microsoft.AspNetCore.SystemWebAdapters.Tests/HttpResponseTests.cs

@@ -5,6 +5,7 @@
 using System.IO;
 using System.Text;
 using System.Threading;
+using System.Threading.Tasks;
 using AutoFixture;
 using Microsoft.AspNetCore.Diagnostics;
 using Microsoft.AspNetCore.Http;
@@ -173,6 +174,45 @@ public void EndNoFeature()
         Assert.Throws<InvalidOperationException>(() => response.End());
     }
 
+    [Fact]
+    public void Flush()
+    {
+        // Arrange
+        var responseCore = new Mock<HttpResponseCore>();
+        var stream = new Mock<Stream>();
+        responseCore.Setup(r => r.Body).Returns(stream.Object);
+
+        var response = new HttpResponse(responseCore.Object);
+
+        // Act
+        response.Flush();
+
+        // Assert
+        stream.Verify(s => s.Flush(), Times.Once);
+    }
+
+    [Fact]
+    public async Task FlushAsync()
+    {
+        // Arrange
+        using var tcs = new CancellationTokenSource();
+        var contextCore = new Mock<HttpContextCore>();
+        contextCore.Setup(s => s.RequestAborted).Returns(tcs.Token);
+
+        var responseCore = new Mock<HttpResponseCore>();
+        var stream = new Mock<Stream>();
+        responseCore.Setup(r => r.Body).Returns(stream.Object);
+        responseCore.Setup(r => r.HttpContext).Returns(contextCore.Object);
+
+        var response = new HttpResponse(responseCore.Object);
+
+        // Act
+        await response.FlushAsync();
+
+        // Assert
+        stream.Verify(s => s.FlushAsync(tcs.Token), Times.Once);
+    }
+
     [Fact]
     public void ContentType()
     {