[release/6.0] Don't reuse Pipe buffer when body is read (#39376)

* Don't reuse Pipe buffer when body is read

Fixes #38771

* Fix spacing after merge

* Fix spacing

* Update Http1ContentLengthMessageBody.cs

Co-authored-by: Sebastien Ros <[email protected]>

Author: github-actions[bot]

src/Servers/Kestrel/Core/src/Internal/Http/Http1ContentLengthMessageBody.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Buffers;
 using System.Diagnostics;
 using System.Globalization;
 using System.IO.Pipelines;
@@ -213,17 +214,25 @@ public override void AdvanceTo(SequencePosition consumed, SequencePosition exami
 
             _isReading = false;
 
+            // The current body is read, though there might be more bytes to read on the stream with pipelining
             if (_readCompleted)
             {
-                // If the old stored _readResult was canceled, it's already been observed. Do not store a canceled read result permanently.
-                _readResult = new ReadResult(_readResult.Buffer.Slice(consumed, _readResult.Buffer.End), isCanceled: false, isCompleted: true);
+                var buffer = _readResult.Buffer.Slice(consumed, _readResult.Buffer.End);
 
-                if (!_finalAdvanceCalled && _readResult.Buffer.Length == 0)
+                if (!_finalAdvanceCalled && buffer.IsEmpty)
                 {
+                    // Don't reference the old buffer as it will be released by the pipe after calling AdvanceTo
+                    _readResult = new ReadResult(new ReadOnlySequence<byte>(), isCanceled: false, isCompleted: true);
+
                     _context.Input.AdvanceTo(consumed);
                     _finalAdvanceCalled = true;
                     _context.OnTrailersComplete();
                 }
+                else
+                {
+                    // If the old stored _readResult was canceled, it's already been observed. Do not store a canceled read result permanently.
+                    _readResult = new ReadResult(buffer, isCanceled: false, isCompleted: true);
+                }
 
                 return;
             }

src/Servers/Kestrel/test/InMemory.FunctionalTests/RequestTests.cs

@@ -1083,6 +1083,43 @@ await connection.ReceiveEnd(
             }
         }
 
+        [Fact]
+        public async Task ContentLengthReadAsyncPipeReaderReadsCompletedBody()
+        {
+            var testContext = new TestServiceContext(LoggerFactory);
+
+            await using (var server = new TestServer(async httpContext =>
+            {
+                using var ms1 = new MemoryStream();
+                using var ms2 = new MemoryStream();
+
+                // Read the body completely, and ensure the second read doesn't fail
+                await httpContext.Request.BodyReader.CopyToAsync(ms1);
+                await httpContext.Request.BodyReader.CopyToAsync(ms2);
+
+                Assert.Equal(22, ms1.ToArray().Length);
+                Assert.Empty(ms2.ToArray());
+            }, testContext))
+            {
+                using (var connection = server.CreateConnection())
+                {
+                    await connection.Send(
+                        "POST / HTTP/1.0",
+                        "Host:",
+                        "Content-Length: 22",
+                        "",
+                        "MyVariableOne=ValueOne");
+                    await connection.Receive(
+                        "HTTP/1.1 200 OK",
+                        "Content-Length: 0",
+                        "Connection: close",
+                        $"Date: {testContext.DateHeaderValue}",
+                        "",
+                        "");
+                }
+            }
+        }
+
         [Fact]
         public async Task ContentLengthReadAsyncSingleBytesAtATime()
         {