Let QUIC be able to add random padding of [1,256] bytes after fin is consumed for a stream. Random …

net/quic/core/quic_packet_creator.cc

 // Copyright (c) 2012 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/core/quic_packet_creator.h"
 
 #include <algorithm>
 #include <cstdint>
 
 #include "base/macros.h"
@@ skipping 26 matching lines @@
       buffer_allocator_(buffer_allocator),
       send_version_in_packet_(framer->perspective() == Perspective::IS_CLIENT),
       next_packet_number_length_(PACKET_1BYTE_PACKET_NUMBER),
       have_diversification_nonce_(false),
       max_packet_length_(0),
       connection_id_length_(PACKET_8BYTE_CONNECTION_ID),
       packet_size_(0),
       connection_id_(connection_id),
       packet_(0, PACKET_1BYTE_PACKET_NUMBER, nullptr, 0, false, false),
       latched_flag_no_stop_waiting_frames_(
-          FLAGS_quic_reloadable_flag_quic_no_stop_waiting_frames) {
+          FLAGS_quic_reloadable_flag_quic_no_stop_waiting_frames),
+      pending_padding_bytes_(0),
+      needs_full_padding_(false) {
   SetMaxPacketLength(kDefaultMaxPacketSize);
 }
 
 QuicPacketCreator::~QuicPacketCreator() {
   DeleteFrames(&packet_.retransmittable_frames);
 }
 
 void QuicPacketCreator::SetEncrypter(EncryptionLevel level,
                                      QuicEncrypter* encrypter) {
   framer_->SetEncrypter(level, encrypter);
@@ skipping 85 matching lines @@
       delete frame->stream_frame;
       return false;
     }
   }
   if (!AddFrame(*frame, /*save_retransmittable_frames=*/true)) {
     // Fails if we try to write unencrypted stream data.
     delete frame->stream_frame;
     return false;
   }
   if (needs_full_padding) {
-    packet_.num_padding_bytes = -1;
+    needs_full_padding_ = true;
   }
+
   return true;
 }
 
 bool QuicPacketCreator::HasRoomForStreamFrame(QuicStreamId id,
                                               QuicStreamOffset offset) {
   return BytesFree() > QuicFramer::GetMinStreamFrameSize(id, offset, true);
 }
 
 // static
 size_t QuicPacketCreator::StreamFramePacketOverhead(
@@ skipping 107 matching lines @@
     char* buffer,
     size_t buffer_len) {
   DCHECK(queued_frames_.empty());
   DCHECK_EQ(0, packet_.num_padding_bytes);
   QUIC_BUG_IF(retransmission.retransmittable_frames.empty())
       << "Attempt to serialize empty packet";
   const EncryptionLevel default_encryption_level = packet_.encryption_level;
 
   // Temporarily set the packet number length and change the encryption level.
   packet_.packet_number_length = retransmission.packet_number_length;
-  packet_.num_padding_bytes = retransmission.num_padding_bytes;
+  if (retransmission.num_padding_bytes == -1) {
+    // Only retransmit padding when original packet needs full padding. Padding
+    // from pending_padding_bytes_ are not retransmitted.
+    needs_full_padding_ = true;
+  }
   // Only preserve the original encryption level if it's a handshake packet or
   // if we haven't gone forward secure.
   if (retransmission.has_crypto_handshake ||
       packet_.encryption_level != ENCRYPTION_FORWARD_SECURE) {
     packet_.encryption_level = retransmission.encryption_level;
   }
 
   // Serialize the packet and restore packet number length state.
   for (const QuicFrame& frame : retransmission.retransmittable_frames) {
     bool success = AddFrame(frame, false);
     QUIC_BUG_IF(!success) << " Failed to add frame of type:" << frame.type
                           << " num_frames:"
                           << retransmission.retransmittable_frames.size()
                           << " retransmission.packet_number_length:"
                           << retransmission.packet_number_length
                           << " packet_.packet_number_length:"
                           << packet_.packet_number_length;
   }
   SerializePacket(buffer, buffer_len);
   packet_.original_packet_number = retransmission.packet_number;
   packet_.transmission_type = retransmission.transmission_type;
   OnSerializedPacket();
   // Restore old values.
   packet_.encryption_level = default_encryption_level;
 }
 
 void QuicPacketCreator::Flush() {
-  if (!HasPendingFrames()) {
+  if (!HasPendingFrames() && pending_padding_bytes_ == 0) {
     return;
   }
 
   QUIC_CACHELINE_ALIGNED char seralized_packet_buffer[kMaxPacketSize];
   SerializePacket(seralized_packet_buffer, kMaxPacketSize);
   OnSerializedPacket();
 }
 
 void QuicPacketCreator::OnSerializedPacket() {
   if (packet_.encrypted_buffer == nullptr) {
@@ skipping 14 matching lines @@
   packet_.has_stop_waiting = false;
   packet_.has_crypto_handshake = NOT_HANDSHAKE;
   packet_.num_padding_bytes = 0;
   packet_.original_packet_number = 0;
   packet_.transmission_type = NOT_RETRANSMISSION;
   packet_.encrypted_buffer = nullptr;
   packet_.encrypted_length = 0;
   DCHECK(packet_.retransmittable_frames.empty());
   packet_.listeners.clear();
   packet_.largest_acked = 0;
+  needs_full_padding_ = false;
 }
 
 void QuicPacketCreator::CreateAndSerializeStreamFrame(
     QuicStreamId id,
     const QuicIOVector& iov,
     QuicStreamOffset iov_offset,
     QuicStreamOffset stream_offset,
     bool fin,
     QuicReferenceCountedPointer<QuicAckListenerInterface> ack_listener,
     size_t* num_bytes_consumed) {
@@ skipping 93 matching lines @@
       IncludeNonceInPublicHeader(), packet_.packet_number_length);
   return packet_size_;
 }
 
 bool QuicPacketCreator::AddSavedFrame(const QuicFrame& frame) {
   return AddFrame(frame, /*save_retransmittable_frames=*/true);
 }
 
 bool QuicPacketCreator::AddPaddedSavedFrame(const QuicFrame& frame) {
   if (AddFrame(frame, /*save_retransmittable_frames=*/true)) {
-    packet_.num_padding_bytes = -1;
+    needs_full_padding_ = true;
     return true;
   }
   return false;
 }
 
 void QuicPacketCreator::AddAckListener(
     QuicReferenceCountedPointer<QuicAckListenerInterface> ack_listener,
     QuicPacketLength length) {
   DCHECK(!queued_frames_.empty());
   packet_.listeners.emplace_back(std::move(ack_listener), length);
 }
 
 void QuicPacketCreator::SerializePacket(char* encrypted_buffer,
                                         size_t encrypted_buffer_len) {
   DCHECK_LT(0u, encrypted_buffer_len);
-  QUIC_BUG_IF(queued_frames_.empty()) << "Attempt to serialize empty packet";
+  QUIC_BUG_IF(queued_frames_.empty() && pending_padding_bytes_ == 0)
+      << "Attempt to serialize empty packet";
   QuicPacketHeader header;
   // FillPacketHeader increments packet_number_.
   FillPacketHeader(&header);
 
   MaybeAddPadding();
 
   DCHECK_GE(max_plaintext_size_, packet_size_);
   // Use the packet_size_ instead of the buffer size to ensure smaller
   // packet sizes are properly used.
   size_t length = framer_->BuildDataPacket(header, queued_frames_,
@@ skipping 124 matching lines @@
     packet_.has_stop_waiting = true;
   }
   if (debug_delegate_ != nullptr) {
     debug_delegate_->OnFrameAddedToPacket(frame);
   }
 
   return true;
 }
 
 void QuicPacketCreator::MaybeAddPadding() {
-  if (packet_.num_padding_bytes == 0) {
-    return;
-  }
-
+  // The current packet should have no padding bytes because padding is only
+  // added when this method is called just before the packet is serialized.
+  DCHECK_EQ(0, packet_.num_padding_bytes);
   if (BytesFree() == 0) {
     // Don't pad full packets.
     return;
   }
 
+  if (!needs_full_padding_ && pending_padding_bytes_ == 0) {
+    // Do not need padding.
+    return;
+  }
+
+  if (needs_full_padding_) {
+    // Full padding does not consume pending padding bytes.
+    packet_.num_padding_bytes = -1;
+  } else {
+    packet_.num_padding_bytes =
+        std::min<int16_t>(pending_padding_bytes_, BytesFree());
+    pending_padding_bytes_ -= packet_.num_padding_bytes;
+  }
+
   bool success =
       AddFrame(QuicFrame(QuicPaddingFrame(packet_.num_padding_bytes)), false);
   DCHECK(success);
 }
 
 bool QuicPacketCreator::IncludeNonceInPublicHeader() {
   return have_diversification_nonce_ &&
          packet_.encryption_level == ENCRYPTION_INITIAL;
 }
 
+void QuicPacketCreator::AddPendingPadding(QuicByteCount size) {
+  pending_padding_bytes_ += size;
+}
+
 }  // namespace net