Create a new data structure StreamSequencerBuffer for QuicStreamSequencer. Currently QuicStreamSequ…

net/quic/stream_sequencer_buffer.h

+// Copyright (c) 2015 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_STREAM_SEQUENCER_BUFFER_H_
+#define NET_QUIC_STREAM_SEQUENCER_BUFFER_H_
+
+// StreamSequencerBuffer implements QuicStreamSequencerBufferInterface.
+// It is a circular stream buffer with random write and
+// in-sequence read. It consists of an std::vector of pointers pointing
+// to memory blocks created as needed and a std::list of Gaps to indicate
+// the missing data between the data already written into the buffer.
+// - Data are written in with offset indicating where it should be in the
+// stream, and the buffer grown as needed (up to the maximum buffer capacity),
+// without expensive copying (extra blocks are allocated).
+// - Data can be read from the buffer if there is no gap before it,
+// and the buffer shrinks as the data are consumed.
+// - An upper limit on the number of blocks in the buffer provides an upper
+//   bound on memory use.
+//
+// This class is thread-unsafe.
+//
+// StreamSequencerBuffer maintains a concept of the readable region, which
+// contains all written data that has not been read.
+// It promises stability of the underlying memory addresses in the readable
+// region, so pointers into it can be maintained, and the offset of a pointer
+// from the start of the read region can be calculated.
+//
+// Expected Use:
+//  StreamSequencerBuffer buffer(2.5 * 8 * 1024);
+//  std::string source(1024, 'a');
+//  base::StringPiece std::string_piece(source.data(), source.size());
+//  size_t written = 0;
+//  buffer.OnStreamData(800, std::string_piece, GetEpollClockNow(), &written);
+//  source = std::string{800, 'b'};
+//  base::StringPiece std::string_piece1(source.data(), 800);
+//  // Try to write to [1, 801), but should fail due to overlapping,
+//  // res should be QUIC_INVALID_STREAM_DATA
+//  auto res = buffer.OnStreamData(1, std::string_piece1, &written));
+//  // write to [0, 800), res should be QUIC_NO_ERROR
+//  auto res = buffer.OnStreamData(0, std::string_piece1, GetEpollClockNow(),
+//                                  &written);
+//
+//  // Read into a iovec array with total capacity of 120 bytes.
+//  char dest[120];
+//  iovec iovecs[3]{iovec{dest, 40}, iovec{dest + 40, 40},
+//                  iovec{dest + 80, 40}};
+//  size_t read = buffer.Readv(iovecs, 3);
+//
+//  // Get single readable region with timestamp.
+//  QuicTime t;
+//  iovec iov;
+//  buffer.GetReadableRegion(iov, &t);
+//
+//  // Get readable regions from [256, 1024) and consume some of it.
+//  iovec iovs[2];
+//  int iov_count = buffer.GetReadableRegions(iovs, 2);
+//  // Consume some bytes in iovs, returning number of bytes having been
+//  consumed.
+//  size_t consumed = consume_iovs(iovs, iov_count);
+//  buffer.MarkConsumed(consumed);
+
+#include <functional>
+#include <list>
+#include <memory>
+
+#include "base/macros.h"
+#include "net/quic/quic_protocol.h"
+#include "net/quic/quic_stream_sequencer_buffer_interface.h"
+
+namespace net {
+
+namespace test {
+class StreamSequencerBufferPeer;
+}  // namespace test
+
+class NET_EXPORT_PRIVATE StreamSequencerBuffer : public QuicStreamSequencerBufferInterface {
+ public:
+  // A Gap indicates a missing chunk of bytes between
+  // [begin_offset, end_offset) in the stream
+  struct Gap {
+    Gap(QuicStreamOffset begin_offset, QuicStreamOffset end_offset);
+    QuicStreamOffset begin_offset;
+    QuicStreamOffset end_offset;
+  };
+
+  // A FrameInfo stores the length of a frame and the time it arrived.
+  struct FrameInfo {
+    FrameInfo();
+    FrameInfo(size_t length, QuicTime timestamp);
+
+    size_t length;
+    QuicTime timestamp;
+  };
+
+  // Size of blocks used by this buffer.
+  // Choose 8K to make block large enough to hold multiple frames, each of
+  // which could be up to 1.5 KB.
+  static const size_t kBlockSizeBytes = 8 * 1024;  // 8KB
+
+  // The basic storage block used by this buffer.
+  struct BufferBlock {
+    char buffer[kBlockSizeBytes];
+  };
+
+  explicit StreamSequencerBuffer(size_t max_capacity_bytes);
+
+  ~StreamSequencerBuffer() override;
+
+  // QuicStreamSequencerBufferInterface implementation.
+  void Clear() override;
+  bool Empty() const override;
+  QuicErrorCode OnStreamData(QuicStreamOffset offset,
+                             base::StringPiece data,
+                             QuicTime timestamp,
+                             size_t* bytes_buffered) override;
+  size_t Readv(const struct iovec* dest_iov, size_t dest_count) override;
+  int GetReadableRegions(struct iovec* iov, int iov_len) const override;
+  bool GetReadableRegion(iovec* iov, QuicTime* timestamp) const override;
+  bool MarkConsumed(size_t bytes_buffered) override;
+  size_t FlushBufferedFrames() override;
+  bool HasBytesToRead() const override;
+  QuicStreamOffset BytesConsumed() const override;
+  size_t BytesBuffered() const override;
+
+ private:
+  friend class test::StreamSequencerBufferPeer;
+
+  // Dispose the given buffer block.
+  // After calling this method, blocks_[index] is set to nullptr
+  // in order to indicate that no memory set is allocated for that block.
+  void RetireBlock(size_t index);
+
+  // Should only be called after the indexed block is read till the end of the
+  // block or a gap has been reached.
+  // If the block at |block_index| contains no buffered data, then the block is
+  // retired.
+  void RetireBlockIfEmpty(size_t block_index);
+
+  // Called within OnStreamData() to update the gap OnStreamData() writes into
+  // (remove, split or change begin/end offset).
+  void UpdateGapList(std::list<Gap>::iterator gap_with_new_data_written,
+                     QuicStreamOffset start_offset,
+                     size_t bytes_written);
+
+  // Calculate the capacity of block at specified index.
+  // Return value should be either kBlockSizeBytes for non-trailing blocks and
+  // max_buffer_capacity % kBlockSizeBytes for trailing block.
+  size_t GetBlockCapacity(size_t index) const;
+
+  // Does not check if offset is within reasonable range.
+  size_t GetBlockIndex(QuicStreamOffset offset) const;
+
+  // Given an offset in the stream, return the offset from the beginning of the
+  // block which contains this data.
+  size_t GetInBlockOffset(QuicStreamOffset offset) const;
+
+  // Get offset relative to index 0 in logical 1st block to start next read.
+  size_t ReadOffset() const;
+
+  // Get the index of the logical 1st block to start next read.
+  size_t NextBlockToRead() const;
+
+  // Returns number of bytes available to be read out.
+  size_t ReadableBytes() const;
+
+  // Called after Readv() and MarkConsumed() to keep frame_arrival_time_map_
+  // up to date.
+  // |offset| is the byte next read should start from. All frames before it
+  // should be removed from the map.
+  void UpdateFrameArrivalMap(QuicStreamOffset offset);
+
+  // The maximum total capacity of this buffer in byte, as constructed.
+  const size_t max_buffer_capacity_bytes_;
+
+  // How many blocks this buffer would need when it reaches full capacity.
+  const size_t blocks_count_;
+
+  // Number of bytes read out of buffer.
+  QuicStreamOffset total_bytes_read_;
+
+  // Contains Gaps which represents currently missing data.
+  std::list<Gap> gaps_;
+
+  // An ordered, variable-length std::list of blocks, with the length limited
+  // such that the number of blocks never exceeds blocks_count_.
+  // Each std::list entry can hold up to kBlockSizeBytes bytes.
+  std::vector<BufferBlock*> blocks_;
+
+  // Number of bytes in buffer.
+  size_t num_bytes_buffered_;
+
+  // Stores all the buffered frames' start offset, length and arrival time.
+  std::map<QuicStreamOffset, FrameInfo> frame_arrival_time_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(StreamSequencerBuffer);
+};
+}  // namespace net
+
+#endif  // NET_QUIC_STREAM_SEQUENCER_BUFFER_H_