relnote: refactoring the buffering logic in QUIC's stream sequencer.

net/quic/quic_frame_list.cc

+// 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.
+
+#include "net/quic/quic_frame_list.h"
+
+#include "base/logging.h"
+
+namespace net {
+
+QuicFrameList::FrameData::FrameData(QuicStreamOffset offset, string segment)
+    : offset(offset), segment(segment) {}
+
+QuicFrameList::QuicFrameList() {}
+
+QuicFrameList::~QuicFrameList() {
+  Clear();
+}
+
+QuicErrorCode QuicFrameList::WriteAtOffset(QuicStreamOffset offset,
+                                           StringPiece data,
+                                           size_t* const bytes_written) {
+  *bytes_written = 0;
+  const size_t data_len = data.size();
+  auto insertion_point = FindInsertionPoint(offset, data_len);
+  if (IsDuplicate(offset, data_len, insertion_point)) {
+    return QUIC_NO_ERROR;
+  }
+
+  if (FrameOverlapsBufferedData(offset, data_len, insertion_point)) {
+    return QUIC_INVALID_STREAM_DATA;
+  }
+
+  DVLOG(1) << "Buffering stream data at offset " << offset;
+  // Inserting an empty string and then copying to avoid the extra copy.
+  insertion_point = frame_list_.insert(insertion_point, FrameData(offset, ""));
+  data.CopyToString(&insertion_point->segment);
+  *bytes_written = data_len;
+  return QUIC_NO_ERROR;
+}
+
+// Finds the place the frame should be inserted.  If an identical frame is
+// present, stops on the identical frame.
+list<QuicFrameList::FrameData>::iterator QuicFrameList::FindInsertionPoint(
+    QuicStreamOffset offset,
+    size_t len) {
+  if (frame_list_.empty()) {
+    return frame_list_.begin();
+  }
+  // If it's after all buffered_frames, return the end.
+  if (offset >=
+      (frame_list_.rbegin()->offset + frame_list_.rbegin()->segment.length())) {
+    return frame_list_.end();
+  }
+  auto iter = frame_list_.begin();
+  // Only advance the iterator if the data begins after the already received
+  // frame.  If the new frame overlaps with an existing frame, the iterator will
+  // still point to the frame it overlaps with.
+  while (iter != frame_list_.end() &&
+         offset >= iter->offset + iter->segment.length()) {
+    ++iter;
+  }
+  return iter;
+}
+
+// Returns true if |frame| contains data which overlaps buffered data
+// (indicating an invalid stream frame has been received).
+bool QuicFrameList::FrameOverlapsBufferedData(
+    QuicStreamOffset offset,
+    size_t data_len,
+    list<FrameData>::const_iterator insertion_point) const {
+  if (frame_list_.empty() || insertion_point == frame_list_.end()) {
+    return false;
+  }
+  // If there is a buffered frame with a higher starting offset, then check to
+  // see if the new frame overlaps the beginning of the higher frame.
+  if (offset < insertion_point->offset &&
+      offset + data_len > insertion_point->offset) {
+    DVLOG(1) << "New frame overlaps next frame: " << offset << " + " << data_len
+             << " > " << insertion_point->offset;
+    return true;
+  }
+  // If there is a buffered frame with a lower starting offset, then check to
+  // see if the buffered frame runs into the new frame.
+  if (offset >= insertion_point->offset &&
+      offset < insertion_point->offset + insertion_point->segment.length()) {
+    DVLOG(1) << "Preceeding frame overlaps new frame: "
+             << insertion_point->offset << " + "
+             << insertion_point->segment.length() << " > " << offset;
+    return true;
+  }
+
+  return false;
+}
+
+// Returns true if the sequencer has received this frame before.
+bool QuicFrameList::IsDuplicate(
+    QuicStreamOffset offset,
+    size_t data_len,
+    list<FrameData>::const_iterator insertion_point) const {
+  // A frame is duplicate if the frame offset is smaller than the bytes consumed
+  // or identical to an already received frame.
+  return offset < total_bytes_read_ || (insertion_point != frame_list_.end() &&
+                                        offset == insertion_point->offset);
+}
+
+int QuicFrameList::GetReadableRegions(struct iovec* iov, int iov_len) const {
+  list<FrameData>::const_iterator it = frame_list_.begin();
+  int index = 0;
+  QuicStreamOffset offset = total_bytes_read_;
+  while (it != frame_list_.end() && index < iov_len) {
+    if (it->offset != offset) {
+      return index;
+    }
+
+    iov[index].iov_base =
+        static_cast<void*>(const_cast<char*>(it->segment.data()));
+    iov[index].iov_len = it->segment.size();
+    offset += it->segment.size();
+
+    ++index;
+    ++it;
+  }
+  return index;
+}
+
+bool QuicFrameList::IncreaseTotalReadAndInvalidate(size_t bytes_used) {
+  size_t end_offset = total_bytes_read_ + bytes_used;
+  while (!frame_list_.empty() && end_offset != total_bytes_read_) {
+    list<FrameData>::iterator it = frame_list_.begin();
+    if (it->offset != total_bytes_read_) {
+      return false;
+    }
+
+    if (it->offset + it->segment.length() <= end_offset) {
+      total_bytes_read_ += it->segment.length();
+      // This chunk is entirely consumed.
+      frame_list_.erase(it);
+      continue;
+    }
+
+    // Partially consume this frame.
+    size_t delta = end_offset - it->offset;
+    total_bytes_read_ += delta;
+    string new_data = it->segment.substr(delta);
+    frame_list_.erase(it);
+    frame_list_.push_front(FrameData(total_bytes_read_, new_data));
+    break;
+  }
+  return true;
+}
+
+size_t QuicFrameList::ReadvAndInvalidate(const struct iovec* iov,
+                                         size_t iov_len) {
+  list<FrameData>::iterator it = frame_list_.begin();
+  size_t iov_index = 0;
+  size_t iov_offset = 0;
+  size_t frame_offset = 0;
+  QuicStreamOffset initial_bytes_consumed = total_bytes_read_;
+
+  while (iov_index < iov_len && it != frame_list_.end() &&
+         it->offset == total_bytes_read_) {
+    int bytes_to_read = std::min(iov[iov_index].iov_len - iov_offset,
+                                 it->segment.size() - frame_offset);
+
+    char* iov_ptr = static_cast<char*>(iov[iov_index].iov_base) + iov_offset;
+    memcpy(iov_ptr, it->segment.data() + frame_offset, bytes_to_read);
+    frame_offset += bytes_to_read;
+    iov_offset += bytes_to_read;
+
+    if (iov[iov_index].iov_len == iov_offset) {
+      // We've filled this buffer.
+      iov_offset = 0;
+      ++iov_index;
+    }
+    if (it->segment.size() == frame_offset) {
+      // We've copied this whole frame
+      total_bytes_read_ += it->segment.size();
+      frame_list_.erase(it);
+      it = frame_list_.begin();
+      frame_offset = 0;
+    }
+  }
+  // Done copying.  If there is a partial frame, update it.
+  if (frame_offset != 0) {
+    frame_list_.push_front(
+        FrameData(it->offset + frame_offset, it->segment.substr(frame_offset)));
+    frame_list_.erase(it);
+    total_bytes_read_ += frame_offset;
+  }
+  return total_bytes_read_ - initial_bytes_consumed;
+}
+
+bool QuicFrameList::HasBytesToRead() const {
+  return !frame_list_.empty() &&
+         frame_list_.begin()->offset == total_bytes_read_;
+}
+}  // namespace net_quic