Optimize writing single segment sequences (#24929)

src/Servers/Kestrel/Core/src/Internal/Http/Http1ChunkedEncodingMessageBody.cs

@@ -218,21 +218,6 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http
             _requestBodyPipe.Reset();
         }
 
-        private void Copy(in ReadOnlySequence<byte> readableBuffer, PipeWriter writableBuffer)
-        {
-            if (readableBuffer.IsSingleSegment)
-            {
-                writableBuffer.Write(readableBuffer.FirstSpan);
-            }
-            else
-            {
-                foreach (var memory in readableBuffer)
-                {
-                    writableBuffer.Write(memory.Span);
-                }
-            }
-        }
-
         protected override void OnReadStarted()
         {
             _pumpTask = PumpAsync();
@@ -442,7 +427,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http
             consumed = buffer.GetPosition(actual);
             examined = consumed;
 
-            Copy(buffer.Slice(0, actual), writableBuffer);
+            buffer.Slice(0, actual).CopyTo(writableBuffer);
 
             _inputLength -= actual;
             AddAndCheckObservedBytes(actual);

src/Servers/Kestrel/Core/src/Internal/Http2/Http2FrameWriter.cs

@@ -357,10 +357,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2
 
             WriteHeaderUnsynchronized();
 
-            foreach (var buffer in data)
+            data.CopyTo(_outputWriter);
-            {
-                _outputWriter.Write(buffer.Span);
-            }
 
             // Plus padding
             return;

src/Servers/Kestrel/Core/src/Internal/Http2/Http2Stream.cs

@@ -440,10 +440,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2
                     // Ignore data frames for aborted streams, but only after counting them for purposes of connection level flow control.
                     if (!IsAborted)
                     {
-                        foreach (var segment in dataPayload)
+                        dataPayload.CopyTo(RequestBodyPipe.Writer);
-                        {
-                            RequestBodyPipe.Writer.Write(segment.Span);
-                        }
 
                         // If the stream is completed go ahead and call RequestBodyPipe.Writer.Complete().
                         // Data will still be available to the reader.

src/Shared/ServerInfrastructure/BufferExtensions.cs

@@ -26,6 +26,27 @@ namespace System.Buffers
             return buffer.ToArray();
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void CopyTo(in this ReadOnlySequence<byte> buffer, PipeWriter pipeWriter)
+        {
+            if (buffer.IsSingleSegment)
+            {
+                pipeWriter.Write(buffer.FirstSpan);
+            }
+            else
+            {
+                CopyToMultiSegment(buffer, pipeWriter);
+            }
+        }
+
+        private static void CopyToMultiSegment(in ReadOnlySequence<byte> buffer, PipeWriter pipeWriter)
+        {
+            foreach (var item in buffer)
+            {
+                pipeWriter.Write(item.Span);
+            }
+        }
+
         public static ArraySegment<byte> GetArray(this Memory<byte> buffer)
         {
             return ((ReadOnlyMemory<byte>)buffer).GetArray();