Undo use of pipewriter in FileBufferingWriteStream

src/Http/WebUtilities/ref/Microsoft.AspNetCore.WebUtilities.netcoreapp.cs

@@ -77,8 +77,6 @@ protected override void Dispose(bool disposing) { }
         [System.Diagnostics.DebuggerStepThroughAttribute]
         public override System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }
         [System.Diagnostics.DebuggerStepThroughAttribute]
-        public System.Threading.Tasks.Task DrainBufferAsync(System.IO.Pipelines.PipeWriter destination, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
-        [System.Diagnostics.DebuggerStepThroughAttribute]
         public System.Threading.Tasks.Task DrainBufferAsync(System.IO.Stream destination, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public override void Flush() { }
         public override System.Threading.Tasks.Task FlushAsync(System.Threading.CancellationToken cancellationToken) { throw null; }

src/Http/WebUtilities/src/FileBufferingWriteStream.cs

@@ -186,25 +186,8 @@ public async Task DrainBufferAsync(Stream destination, CancellationToken cancell
             // unspooled content. Copy the FileStream content first when available.
             if (FileStream != null)
             {
-                // We make a new stream for async reads from disk and async writes to the destination
-                await using var readStream = new FileStream(FileStream.Name, FileMode.Open, FileAccess.Read, FileShare.Delete | FileShare.ReadWrite, bufferSize: 1, useAsync: true);
-
-                await readStream.CopyToAsync(destination, cancellationToken);
-
-                // This is created with delete on close
-                await FileStream.DisposeAsync();
-                FileStream = null;
-            }
+                await FileStream.FlushAsync(cancellationToken);
 
-            await PagedByteBuffer.MoveToAsync(destination, cancellationToken);
-        }
-
-        public async Task DrainBufferAsync(PipeWriter destination, CancellationToken cancellationToken = default)
-        {
-            // When not null, FileStream always has "older" spooled content. The PagedByteBuffer always has "newer"
-            // unspooled content. Copy the FileStream content first when available.
-            if (FileStream != null)
-            {
                 // We make a new stream for async reads from disk and async writes to the destination
                 await using var readStream = new FileStream(FileStream.Name, FileMode.Open, FileAccess.Read, FileShare.Delete | FileShare.ReadWrite, bufferSize: 1, useAsync: true);
 

src/Http/WebUtilities/test/FileBufferingWriteStreamTests.cs

@@ -371,6 +371,24 @@ public async Task DrainBufferAsync_WithContentInDisk_CopiesContentFromMemoryStre
             Assert.Equal(0, bufferingStream.Length);
         }
 
+        [Fact]
+        public async Task DrainBufferAsync_IncludesContentPossiblyBufferedByFileStream()
+        {
+            // We want to ensure that the FileStream (which has a 1-byte buffer) flushes prior to the other read stream reading input.
+            // Arrange
+            var input = new byte[] { 3, };
+            using var bufferingStream = new FileBufferingWriteStream(0, tempFileDirectoryAccessor: () => TempDirectory);
+            bufferingStream.Write(input, 0, input.Length);
+            var memoryStream = new MemoryStream();
+
+            // Act
+            await bufferingStream.DrainBufferAsync(memoryStream, default);
+
+            // Assert
+            Assert.Equal(input, memoryStream.ToArray());
+            Assert.Equal(0, bufferingStream.Length);
+        }
+
         public void Dispose()
         {
             try

src/Mvc/Mvc.Formatters.Xml/src/XmlSerializerOutputFormatter.cs

@@ -261,7 +261,7 @@ public override async Task WriteResponseBodyAsync(OutputFormatterWriteContext co
                 if (fileBufferingWriteStream != null)
                 {
                     response.ContentLength = fileBufferingWriteStream.Length;
-                    await fileBufferingWriteStream.DrainBufferAsync(response.BodyWriter);
+                    await fileBufferingWriteStream.DrainBufferAsync(response.Body);
                 }
             }
             finally

src/Mvc/Mvc.NewtonsoftJson/src/NewtonsoftJsonOutputFormatter.cs

@@ -155,7 +155,7 @@ public override async Task WriteResponseBodyAsync(OutputFormatterWriteContext co
                 if (fileBufferingWriteStream != null)
                 {
                     response.ContentLength = fileBufferingWriteStream.Length;
-                    await fileBufferingWriteStream.DrainBufferAsync(response.BodyWriter);
+                    await fileBufferingWriteStream.DrainBufferAsync(response.Body);
                 }
             }
             finally

src/Mvc/test/Mvc.FunctionalTests/JsonOutputFormatterTestBase.cs

@@ -154,15 +154,17 @@ public virtual async Task Formatting_DictionaryType()
             Assert.Equal(expected, await response.Content.ReadAsStringAsync());
         }
 
-        [Fact]
-        public virtual async Task Formatting_LargeObject()
+        [Theory]
+        [InlineData(65 * 1024)]
+        [InlineData(2 * 1024 * 1024)]
+        public virtual async Task Formatting_LargeObject(int size)
         {
             // Arrange
-            var expectedName = "This is long so we can test large objects " + new string('a', 1024 * 65);
+            var expectedName = "This is long so we can test large objects " + new string('a', size);
             var expected = $"{{\"id\":10,\"name\":\"{expectedName}\",\"streetName\":null}}";
 
             // Act
-            var response = await Client.GetAsync($"/JsonOutputFormatter/{nameof(JsonOutputFormatterController.LargeObjectResult)}");
+            var response = await Client.GetAsync($"/JsonOutputFormatter/{nameof(JsonOutputFormatterController.LargeObjectResult)}/{size}");
 
             // Assert
             await response.AssertStatusCodeAsync(HttpStatusCode.OK);

src/Mvc/test/WebSites/FormatterWebSite/Controllers/JsonOutputFormatterController.cs

@@ -44,12 +44,12 @@ public ActionResult<Dictionary<string, string>> DictionaryResult() =>
                 ["Key3"] = null,
             };
 
-        [HttpGet]
-        public ActionResult<SimpleModel> LargeObjectResult() =>
+        [HttpGet("{size:int}")]
+        public ActionResult<SimpleModel> LargeObjectResult(int size) =>
             new SimpleModel
             {
                 Id = 10,
-                Name = "This is long so we can test large objects " + new string('a', 1024 * 65),
+                Name = "This is long so we can test large objects " + new string('a', size),
             };
 
         [HttpGet]