In QUIC, send data is copied to streams rather than frames. Protected by FLAGS_quic_reloadable_flag…

net/quic/core/quic_stream_send_buffer.h

Index: net/quic/core/quic_stream_send_buffer.h
diff --git a/net/quic/core/quic_stream_send_buffer.h b/net/quic/core/quic_stream_send_buffer.h
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+// Copyright (c) 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_QUIC_CORE_QUIC_STREAM_SEND_BUFFER_H_
+#define NET_QUIC_CORE_QUIC_STREAM_SEND_BUFFER_H_
+
+#include <deque>
+
+#include "net/quic/core/frames/quic_stream_frame.h"
+#include "net/quic/core/quic_iovector.h"
+
+namespace net {
+
+class QuicDataWriter;
+
+// QuicStreamDataSlice comprises information of a piece of stream data.
+struct QuicStreamDataSlice {
+  QuicStreamDataSlice(UniqueStreamBuffer data,
+                      QuicStreamOffset offset,
+                      QuicByteCount data_length);
+  QuicStreamDataSlice(const QuicStreamDataSlice& other) = delete;
+  QuicStreamDataSlice(QuicStreamDataSlice&& other) = delete;
+  ~QuicStreamDataSlice();
+
+  // Stream data of this data slice.
+  UniqueStreamBuffer data;
+  // Location of this data slice in the stream.
+  QuicStreamOffset offset;
+  // Length of this data slice in bytes.
+  QuicByteCount data_length;
+  // Length of payload which is waiting for acks.
+  QuicByteCount data_length_waiting_for_acks;
+};
+
+// QuicStreamSendBuffer contains a list of QuicStreamDataSlices. New data slices
+// are added to the tail of the list. Data slices are removed from the head of
+// the list when they get fully acked. Stream data can be retrieved and acked
+// across slice boundaries.
+class QUIC_EXPORT_PRIVATE QuicStreamSendBuffer {
+ public:
+  explicit QuicStreamSendBuffer(QuicBufferAllocator* allocator);
+  QuicStreamSendBuffer(const QuicStreamSendBuffer& other) = delete;
+  QuicStreamSendBuffer(QuicStreamSendBuffer&& other) = delete;
+  ~QuicStreamSendBuffer();
+
+  // Save |data_length| of data starts at |iov_offset| in |iov| to send buffer.
+  void SaveStreamData(QuicIOVector iov,
+                      size_t iov_offset,
+                      QuicStreamOffset offset,
+                      QuicByteCount data_length);
+
+  // Write |data_length| of data starts at |offset|.
+  bool WriteStreamData(QuicStreamOffset offset,
+                       QuicByteCount data_length,
+                       QuicDataWriter* writer);
+
+  // Called when data [offset, offset + data_length) is acked or removed as
+  // stream is canceled. Removes fully acked data slice from send buffer.
+  void RemoveStreamFrame(QuicStreamOffset offset, QuicByteCount data_length);
+
+  // Number of data slices in send buffer.
+  size_t size() const;
+
+ private:
+  std::deque<QuicStreamDataSlice> send_buffer_;
+
+  QuicBufferAllocator* allocator_;
+};
+
+}  // namespace net
+
+#endif  // NET_QUIC_CORE_QUIC_STREAM_SEND_BUFFER_H_