net/quic/quic_packet_creator.cc - platform/external/chromium_org - Git at Google

 // 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/quic_packet_creator.h"

 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "net/quic/crypto/quic_random.h"
 #include "net/quic/quic_ack_notifier.h"
 #include "net/quic/quic_fec_group.h"
 #include "net/quic/quic_utils.h"

 using base::StringPiece;
 using std::make_pair;
 using std::max;
 using std::min;
 using std::pair;
 using std::vector;

 namespace net {

 // A QuicRandom wrapper that gets a bucket of entropy and distributes it
 // bit-by-bit. Replenishes the bucket as needed. Not thread-safe. Expose this
 // class if single bit randomness is needed elsewhere.
 class QuicRandomBoolSource {
  public:
   // random: Source of entropy. Not owned.
   explicit QuicRandomBoolSource(QuicRandom* random)
       : random_(random),
         bit_bucket_(0),
         bit_mask_(0) {}

   ~QuicRandomBoolSource() {}

   // Returns the next random bit from the bucket.
   bool RandBool() {
     if (bit_mask_ == 0) {
       bit_bucket_ = random_->RandUint64();
       bit_mask_ = 1;
     }
     bool result = ((bit_bucket_ & bit_mask_) != 0);
     bit_mask_ <<= 1;
     return result;
   }

  private:
   // Source of entropy.
   QuicRandom* random_;
   // Stored random bits.
   uint64 bit_bucket_;
   // The next available bit has "1" in the mask. Zero means empty bucket.
   uint64 bit_mask_;

   DISALLOW_COPY_AND_ASSIGN(QuicRandomBoolSource);
 };

 QuicPacketCreator::QuicPacketCreator(QuicConnectionId connection_id,
                                      QuicFramer* framer,
                                      QuicRandom* random_generator)
     : connection_id_(connection_id),
       encryption_level_(ENCRYPTION_NONE),
       framer_(framer),
       random_bool_source_(new QuicRandomBoolSource(random_generator)),
       sequence_number_(0),
       should_fec_protect_(false),
       fec_group_number_(0),
       send_version_in_packet_(!framer->is_server()),
       max_packet_length_(kDefaultMaxPacketSize),
       max_packets_per_fec_group_(0),
       connection_id_length_(PACKET_8BYTE_CONNECTION_ID),
       next_sequence_number_length_(PACKET_1BYTE_SEQUENCE_NUMBER),
       sequence_number_length_(next_sequence_number_length_),
       packet_size_(0) {
   framer_->set_fec_builder(this);
 }

 QuicPacketCreator::~QuicPacketCreator() {
 }

 void QuicPacketCreator::OnBuiltFecProtectedPayload(
     const QuicPacketHeader& header, StringPiece payload) {
   if (fec_group_.get()) {
     DCHECK_NE(0u, header.fec_group);
     fec_group_->Update(encryption_level_, header, payload);
   }
 }

 bool QuicPacketCreator::ShouldSendFec(bool force_close) const {
   DCHECK(!HasPendingFrames());
   return fec_group_.get() != NULL && fec_group_->NumReceivedPackets() > 0 &&
       (force_close || fec_group_->NumReceivedPackets() >=
                       max_packets_per_fec_group_);
 }

 bool QuicPacketCreator::IsFecGroupOpen() const {
   return ShouldSendFec(true);
 }

 void QuicPacketCreator::StartFecProtectingPackets() {
   if (!IsFecEnabled()) {
     LOG(DFATAL) << "Cannot start FEC protection when FEC is not enabled.";
     return;
   }
   // TODO(jri): This currently requires that the generator flush out any
   // pending frames when FEC protection is turned on. If current packet can be
   // converted to an FEC protected packet, do it. This will require the
   // generator to check if the resulting expansion still allows the incoming
   // frame to be added to the packet.
   if (HasPendingFrames()) {
     LOG(DFATAL) << "Cannot start FEC protection with pending frames.";
     return;
   }
   DCHECK(!should_fec_protect_);
   should_fec_protect_ = true;
 }

 void QuicPacketCreator::StopFecProtectingPackets() {
   if (fec_group_.get() != NULL) {
     LOG(DFATAL) << "Cannot stop FEC protection with open FEC group.";
     return;
   }
   DCHECK(should_fec_protect_);
   should_fec_protect_ = false;
   fec_group_number_ = 0;
 }

 bool QuicPacketCreator::IsFecProtected() const {
   return should_fec_protect_;
 }

 bool QuicPacketCreator::IsFecEnabled() const {
   return max_packets_per_fec_group_ > 0;
 }

 InFecGroup QuicPacketCreator::MaybeUpdateLengthsAndStartFec() {
   if (fec_group_.get() != NULL) {
     // Don't update any lengths when an FEC group is open, to ensure same
     // packet header size in all packets within a group.
     return IN_FEC_GROUP;
   }
   if (!queued_frames_.empty()) {
     // Don't change creator state if there are frames queued.
     return fec_group_.get() == NULL ? NOT_IN_FEC_GROUP : IN_FEC_GROUP;
   }

   // Update sequence number length only on packet and FEC group boundaries.
   sequence_number_length_ = next_sequence_number_length_;

   if (!should_fec_protect_) {
     return NOT_IN_FEC_GROUP;
   }
   // Start a new FEC group since protection is on. Set the fec group number to
   // the sequence number of the next packet.
   fec_group_number_ = sequence_number() + 1;
   fec_group_.reset(new QuicFecGroup());
   return IN_FEC_GROUP;
 }

 // Stops serializing version of the protocol in packets sent after this call.
 // A packet that is already open might send kQuicVersionSize bytes less than the
 // maximum packet size if we stop sending version before it is serialized.
 void QuicPacketCreator::StopSendingVersion() {
   DCHECK(send_version_in_packet_);
   send_version_in_packet_ = false;
   if (packet_size_ > 0) {
     DCHECK_LT(kQuicVersionSize, packet_size_);
     packet_size_ -= kQuicVersionSize;
   }
 }

 void QuicPacketCreator::UpdateSequenceNumberLength(
       QuicPacketSequenceNumber least_packet_awaited_by_peer,
       QuicByteCount congestion_window) {
   DCHECK_LE(least_packet_awaited_by_peer, sequence_number_ + 1);
   // Since the packet creator will not change sequence number length mid FEC
   // group, include the size of an FEC group to be safe.
   const QuicPacketSequenceNumber current_delta =
       max_packets_per_fec_group_ + sequence_number_ + 1
       - least_packet_awaited_by_peer;
   const uint64 congestion_window_packets =
       congestion_window / max_packet_length_;
   const uint64 delta = max(current_delta, congestion_window_packets);
   next_sequence_number_length_ =
       QuicFramer::GetMinSequenceNumberLength(delta * 4);
 }

 bool QuicPacketCreator::HasRoomForStreamFrame(QuicStreamId id,
                                               QuicStreamOffset offset) const {
   // TODO(jri): This is a simple safe decision for now, but make
   // is_in_fec_group a parameter. Same as with all public methods in
   // QuicPacketCreator.
   return BytesFree() >
       QuicFramer::GetMinStreamFrameSize(framer_->version(), id, offset, true,
                                         should_fec_protect_ ? IN_FEC_GROUP :
                                                               NOT_IN_FEC_GROUP);
 }

 // static
 size_t QuicPacketCreator::StreamFramePacketOverhead(
     QuicVersion version,
     QuicConnectionIdLength connection_id_length,
     bool include_version,
     QuicSequenceNumberLength sequence_number_length,
     QuicStreamOffset offset,
     InFecGroup is_in_fec_group) {
   return GetPacketHeaderSize(connection_id_length, include_version,
                              sequence_number_length, is_in_fec_group) +
       // Assumes this is a stream with a single lone packet.
       QuicFramer::GetMinStreamFrameSize(version, 1u, offset, true,
                                         is_in_fec_group);
 }

 size_t QuicPacketCreator::CreateStreamFrame(QuicStreamId id,
                                             const IOVector& data,
                                             QuicStreamOffset offset,
                                             bool fin,
                                             QuicFrame* frame) {
   DCHECK_GT(max_packet_length_, StreamFramePacketOverhead(
                 framer_->version(), PACKET_8BYTE_CONNECTION_ID, kIncludeVersion,
                 PACKET_6BYTE_SEQUENCE_NUMBER, offset, IN_FEC_GROUP));

   InFecGroup is_in_fec_group = MaybeUpdateLengthsAndStartFec();

   LOG_IF(DFATAL, !HasRoomForStreamFrame(id, offset))
       << "No room for Stream frame, BytesFree: " << BytesFree()
       << " MinStreamFrameSize: "
       << QuicFramer::GetMinStreamFrameSize(
           framer_->version(), id, offset, true, is_in_fec_group);

   if (data.Empty()) {
     LOG_IF(DFATAL, !fin)
         << "Creating a stream frame with no data or fin.";
     // Create a new packet for the fin, if necessary.
     *frame = QuicFrame(new QuicStreamFrame(id, true, offset, data));
     return 0;
   }

   const size_t data_size = data.TotalBufferSize();
   size_t min_frame_size = QuicFramer::GetMinStreamFrameSize(
       framer_->version(), id, offset, /*last_frame_in_packet=*/ true,
       is_in_fec_group);
   size_t bytes_consumed = min<size_t>(BytesFree() - min_frame_size, data_size);

   bool set_fin = fin && bytes_consumed == data_size;  // Last frame.
   IOVector frame_data;
   frame_data.AppendIovecAtMostBytes(data.iovec(), data.Size(),
                                     bytes_consumed);
   DCHECK_EQ(frame_data.TotalBufferSize(), bytes_consumed);
   *frame = QuicFrame(new QuicStreamFrame(id, set_fin, offset, frame_data));
   return bytes_consumed;
 }

 size_t QuicPacketCreator::CreateStreamFrameWithNotifier(
     QuicStreamId id,
     const IOVector& data,
     QuicStreamOffset offset,
     bool fin,
     QuicAckNotifier* notifier,
     QuicFrame* frame) {
   size_t bytes_consumed = CreateStreamFrame(id, data, offset, fin, frame);

   // The frame keeps track of the QuicAckNotifier until it is serialized into
   // a packet. At that point the notifier is informed of the sequence number
   // of the packet that this frame was eventually sent in.
   frame->stream_frame->notifier = notifier;

   return bytes_consumed;
 }

 SerializedPacket QuicPacketCreator::ReserializeAllFrames(
     const QuicFrames& frames,
     QuicSequenceNumberLength original_length) {
   DCHECK(fec_group_.get() == NULL);
   const QuicSequenceNumberLength saved_length = sequence_number_length_;
   const QuicSequenceNumberLength saved_next_length =
       next_sequence_number_length_;
   const bool saved_should_fec_protect = should_fec_protect_;

   // Temporarily set the sequence number length and stop FEC protection.
   sequence_number_length_ = original_length;
   next_sequence_number_length_ = original_length;
   should_fec_protect_ = false;

   // Serialize the packet and restore the FEC and sequence number length state.
   SerializedPacket serialized_packet = SerializeAllFrames(frames);
   sequence_number_length_ = saved_length;
   next_sequence_number_length_ = saved_next_length;
   should_fec_protect_ = saved_should_fec_protect;

   return serialized_packet;
 }

 SerializedPacket QuicPacketCreator::SerializeAllFrames(
     const QuicFrames& frames) {
   // TODO(satyamshekhar): Verify that this DCHECK won't fail. What about queued
   // frames from SendStreamData()[send_stream_should_flush_ == false &&
   // data.empty() == true] and retransmit due to RTO.
   DCHECK_EQ(0u, queued_frames_.size());
   LOG_IF(DFATAL, frames.empty())
       << "Attempt to serialize empty packet";
   for (size_t i = 0; i < frames.size(); ++i) {
     bool success = AddFrame(frames[i], false);
     DCHECK(success);
   }
   SerializedPacket packet = SerializePacket();
   DCHECK(packet.retransmittable_frames == NULL);
   return packet;
 }

 bool QuicPacketCreator::HasPendingFrames() const {
   return !queued_frames_.empty();
 }

 bool QuicPacketCreator::HasPendingRetransmittableFrames() const {
   return queued_retransmittable_frames_.get() != NULL &&
       !queued_retransmittable_frames_->frames().empty();
 }

 size_t QuicPacketCreator::ExpansionOnNewFrame() const {
   // If packet is FEC protected, there's no expansion.
   if (should_fec_protect_) {
       return 0;
   }
   // If the last frame in the packet is a stream frame, then it will expand to
   // include the stream_length field when a new frame is added.
   bool has_trailing_stream_frame =
       !queued_frames_.empty() && queued_frames_.back().type == STREAM_FRAME;
   return has_trailing_stream_frame ? kQuicStreamPayloadLengthSize : 0;
 }

 size_t QuicPacketCreator::BytesFree() const {
   const size_t max_plaintext_size =
       framer_->GetMaxPlaintextSize(max_packet_length_);
   DCHECK_GE(max_plaintext_size, PacketSize());
   return max_plaintext_size - min(max_plaintext_size, PacketSize()
                                   + ExpansionOnNewFrame());
 }

 size_t QuicPacketCreator::PacketSize() const {
   if (!queued_frames_.empty()) {
     return packet_size_;
   }
   if (fec_group_.get() == NULL) {
     // Update sequence number length on packet and FEC boundary.
     sequence_number_length_ = next_sequence_number_length_;
   }
   packet_size_ = GetPacketHeaderSize(
       connection_id_length_, send_version_in_packet_, sequence_number_length_,
       should_fec_protect_ ? IN_FEC_GROUP : NOT_IN_FEC_GROUP);
   return packet_size_;
 }

 bool QuicPacketCreator::AddSavedFrame(const QuicFrame& frame) {
   return AddFrame(frame, true);
 }

 SerializedPacket QuicPacketCreator::SerializePacket() {
   LOG_IF(DFATAL, queued_frames_.empty())
       << "Attempt to serialize empty packet";
   DCHECK_GE(sequence_number_ + 1, fec_group_number_);
   QuicPacketHeader header;
   FillPacketHeader(should_fec_protect_ ? fec_group_number_ : 0, false, &header);

   MaybeAddPadding();

   size_t max_plaintext_size =
       framer_->GetMaxPlaintextSize(max_packet_length_);
   DCHECK_GE(max_plaintext_size, packet_size_);
   // ACK Frames will be truncated only if they're the only frame in the packet,
   // and if packet_size_ was set to max_plaintext_size. If truncation occurred,
   // then GetSerializedFrameLength will have returned all bytes free.
   bool possibly_truncated = packet_size_ == max_plaintext_size &&
                             queued_frames_.size() == 1 &&
                             queued_frames_.back().type == ACK_FRAME;
   SerializedPacket serialized =
       framer_->BuildDataPacket(header, queued_frames_, packet_size_);
   LOG_IF(DFATAL, !serialized.packet)
       << "Failed to serialize " << queued_frames_.size() << " frames.";
   // Because of possible truncation, we can't be confident that our
   // packet size calculation worked correctly.
   if (!possibly_truncated) {
     DCHECK_EQ(packet_size_, serialized.packet->length());
   }
   packet_size_ = 0;
   queued_frames_.clear();
   serialized.retransmittable_frames = queued_retransmittable_frames_.release();
   return serialized;
 }

 SerializedPacket QuicPacketCreator::SerializeFec() {
   if (fec_group_.get() == NULL || fec_group_->NumReceivedPackets() <= 0) {
     LOG(DFATAL) << "SerializeFEC called but no group or zero packets in group.";
     // TODO(jri): Make this a public method of framer?
     SerializedPacket kNoPacket(0, PACKET_1BYTE_SEQUENCE_NUMBER, NULL, 0, NULL);
     return kNoPacket;
   }
   DCHECK_EQ(0u, queued_frames_.size());
   QuicPacketHeader header;
   FillPacketHeader(fec_group_number_, true, &header);
   QuicFecData fec_data;
   fec_data.fec_group = fec_group_->min_protected_packet();
   fec_data.redundancy = fec_group_->payload_parity();
   SerializedPacket serialized = framer_->BuildFecPacket(header, fec_data);
   fec_group_.reset(NULL);
   packet_size_ = 0;
   LOG_IF(DFATAL, !serialized.packet)
       << "Failed to serialize fec packet for group:" << fec_data.fec_group;
   DCHECK_GE(max_packet_length_, serialized.packet->length());
   return serialized;
 }

 SerializedPacket QuicPacketCreator::SerializeConnectionClose(
     QuicConnectionCloseFrame* close_frame) {
   QuicFrames frames;
   frames.push_back(QuicFrame(close_frame));
   return SerializeAllFrames(frames);
 }

 QuicEncryptedPacket* QuicPacketCreator::SerializeVersionNegotiationPacket(
     const QuicVersionVector& supported_versions) {
   DCHECK(framer_->is_server());
   QuicPacketPublicHeader header;
   header.connection_id = connection_id_;
   header.reset_flag = false;
   header.version_flag = true;
   header.versions = supported_versions;
   QuicEncryptedPacket* encrypted =
       framer_->BuildVersionNegotiationPacket(header, supported_versions);
   DCHECK(encrypted);
   DCHECK_GE(max_packet_length_, encrypted->length());
   return encrypted;
 }

 void QuicPacketCreator::FillPacketHeader(QuicFecGroupNumber fec_group,
                                          bool fec_flag,
                                          QuicPacketHeader* header) {
   header->public_header.connection_id = connection_id_;
   header->public_header.reset_flag = false;
   header->public_header.version_flag = send_version_in_packet_;
   header->fec_flag = fec_flag;
   header->packet_sequence_number = ++sequence_number_;
   header->public_header.sequence_number_length = sequence_number_length_;
   header->entropy_flag = random_bool_source_->RandBool();
   header->is_in_fec_group = fec_group == 0 ? NOT_IN_FEC_GROUP : IN_FEC_GROUP;
   header->fec_group = fec_group;
 }

 bool QuicPacketCreator::ShouldRetransmit(const QuicFrame& frame) {
   switch (frame.type) {
     case ACK_FRAME:
     case CONGESTION_FEEDBACK_FRAME:
     case PADDING_FRAME:
     case STOP_WAITING_FRAME:
       return false;
     default:
       return true;
   }
 }

 bool QuicPacketCreator::AddFrame(const QuicFrame& frame,
                                  bool save_retransmittable_frames) {
   DVLOG(1) << "Adding frame: " << frame;
   InFecGroup is_in_fec_group = MaybeUpdateLengthsAndStartFec();

   size_t frame_len = framer_->GetSerializedFrameLength(
       frame, BytesFree(), queued_frames_.empty(), true, is_in_fec_group,
       sequence_number_length_);
   if (frame_len == 0) {
     return false;
   }
   DCHECK_LT(0u, packet_size_);
   packet_size_ += ExpansionOnNewFrame() + frame_len;

   if (save_retransmittable_frames && ShouldRetransmit(frame)) {
     if (queued_retransmittable_frames_.get() == NULL) {
       queued_retransmittable_frames_.reset(new RetransmittableFrames());
     }
     if (frame.type == STREAM_FRAME) {
       queued_frames_.push_back(
           queued_retransmittable_frames_->AddStreamFrame(frame.stream_frame));
     } else {
       queued_frames_.push_back(
           queued_retransmittable_frames_->AddNonStreamFrame(frame));
     }
   } else {
     queued_frames_.push_back(frame);
   }
   return true;
 }

 void QuicPacketCreator::MaybeAddPadding() {
   if (BytesFree() == 0) {
     // Don't pad full packets.
     return;
   }

   // If any of the frames in the current packet are on the crypto stream
   // then they contain handshake messagses, and we should pad them.
   bool is_handshake = false;
   for (size_t i = 0; i < queued_frames_.size(); ++i) {
     if (queued_frames_[i].type == STREAM_FRAME &&
         queued_frames_[i].stream_frame->stream_id == kCryptoStreamId) {
       is_handshake = true;
       break;
     }
   }
   if (!is_handshake) {
     return;
   }

   QuicPaddingFrame padding;
   bool success = AddFrame(QuicFrame(&padding), false);
   DCHECK(success);
 }

 }  // namespace net
	// 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/quic_packet_creator.h"

	#include "base/basictypes.h"
	#include "base/logging.h"
	#include "net/quic/crypto/quic_random.h"
	#include "net/quic/quic_ack_notifier.h"
	#include "net/quic/quic_fec_group.h"
	#include "net/quic/quic_utils.h"

	using base::StringPiece;
	using std::make_pair;
	using std::max;
	using std::min;
	using std::pair;
	using std::vector;

	namespace net {

	// A QuicRandom wrapper that gets a bucket of entropy and distributes it
	// bit-by-bit. Replenishes the bucket as needed. Not thread-safe. Expose this
	// class if single bit randomness is needed elsewhere.
	class QuicRandomBoolSource {
	public:
	// random: Source of entropy. Not owned.
	explicit QuicRandomBoolSource(QuicRandom* random)
	: random_(random),
	bit_bucket_(0),
	bit_mask_(0) {}

	~QuicRandomBoolSource() {}

	// Returns the next random bit from the bucket.
	bool RandBool() {
	if (bit_mask_ == 0) {
	bit_bucket_ = random_->RandUint64();
	bit_mask_ = 1;
	}
	bool result = ((bit_bucket_ & bit_mask_) != 0);
	bit_mask_ <<= 1;
	return result;
	}

	private:
	// Source of entropy.
	QuicRandom* random_;
	// Stored random bits.
	uint64 bit_bucket_;
	// The next available bit has "1" in the mask. Zero means empty bucket.
	uint64 bit_mask_;

	DISALLOW_COPY_AND_ASSIGN(QuicRandomBoolSource);
	};

	QuicPacketCreator::QuicPacketCreator(QuicConnectionId connection_id,
	QuicFramer* framer,
	QuicRandom* random_generator)
	: connection_id_(connection_id),
	encryption_level_(ENCRYPTION_NONE),
	framer_(framer),
	random_bool_source_(new QuicRandomBoolSource(random_generator)),
	sequence_number_(0),
	should_fec_protect_(false),
	fec_group_number_(0),
	send_version_in_packet_(!framer->is_server()),
	max_packet_length_(kDefaultMaxPacketSize),
	max_packets_per_fec_group_(0),
	connection_id_length_(PACKET_8BYTE_CONNECTION_ID),
	next_sequence_number_length_(PACKET_1BYTE_SEQUENCE_NUMBER),
	sequence_number_length_(next_sequence_number_length_),
	packet_size_(0) {
	framer_->set_fec_builder(this);
	}

	QuicPacketCreator::~QuicPacketCreator() {
	}

	void QuicPacketCreator::OnBuiltFecProtectedPayload(
	const QuicPacketHeader& header, StringPiece payload) {
	if (fec_group_.get()) {
	DCHECK_NE(0u, header.fec_group);
	fec_group_->Update(encryption_level_, header, payload);
	}
	}

	bool QuicPacketCreator::ShouldSendFec(bool force_close) const {
	DCHECK(!HasPendingFrames());
	return fec_group_.get() != NULL && fec_group_->NumReceivedPackets() > 0 &&
	(force_close \|\| fec_group_->NumReceivedPackets() >=
	max_packets_per_fec_group_);
	}

	bool QuicPacketCreator::IsFecGroupOpen() const {
	return ShouldSendFec(true);
	}

	void QuicPacketCreator::StartFecProtectingPackets() {
	if (!IsFecEnabled()) {
	LOG(DFATAL) << "Cannot start FEC protection when FEC is not enabled.";
	return;
	}
	// TODO(jri): This currently requires that the generator flush out any
	// pending frames when FEC protection is turned on. If current packet can be
	// converted to an FEC protected packet, do it. This will require the
	// generator to check if the resulting expansion still allows the incoming
	// frame to be added to the packet.
	if (HasPendingFrames()) {
	LOG(DFATAL) << "Cannot start FEC protection with pending frames.";
	return;
	}
	DCHECK(!should_fec_protect_);
	should_fec_protect_ = true;
	}

	void QuicPacketCreator::StopFecProtectingPackets() {
	if (fec_group_.get() != NULL) {
	LOG(DFATAL) << "Cannot stop FEC protection with open FEC group.";
	return;
	}
	DCHECK(should_fec_protect_);
	should_fec_protect_ = false;
	fec_group_number_ = 0;
	}

	bool QuicPacketCreator::IsFecProtected() const {
	return should_fec_protect_;
	}

	bool QuicPacketCreator::IsFecEnabled() const {
	return max_packets_per_fec_group_ > 0;
	}

	InFecGroup QuicPacketCreator::MaybeUpdateLengthsAndStartFec() {
	if (fec_group_.get() != NULL) {
	// Don't update any lengths when an FEC group is open, to ensure same
	// packet header size in all packets within a group.
	return IN_FEC_GROUP;
	}
	if (!queued_frames_.empty()) {
	// Don't change creator state if there are frames queued.
	return fec_group_.get() == NULL ? NOT_IN_FEC_GROUP : IN_FEC_GROUP;
	}

	// Update sequence number length only on packet and FEC group boundaries.
	sequence_number_length_ = next_sequence_number_length_;

	if (!should_fec_protect_) {
	return NOT_IN_FEC_GROUP;
	}
	// Start a new FEC group since protection is on. Set the fec group number to
	// the sequence number of the next packet.
	fec_group_number_ = sequence_number() + 1;
	fec_group_.reset(new QuicFecGroup());
	return IN_FEC_GROUP;
	}

	// Stops serializing version of the protocol in packets sent after this call.
	// A packet that is already open might send kQuicVersionSize bytes less than the
	// maximum packet size if we stop sending version before it is serialized.
	void QuicPacketCreator::StopSendingVersion() {
	DCHECK(send_version_in_packet_);
	send_version_in_packet_ = false;
	if (packet_size_ > 0) {
	DCHECK_LT(kQuicVersionSize, packet_size_);
	packet_size_ -= kQuicVersionSize;
	}
	}

	void QuicPacketCreator::UpdateSequenceNumberLength(
	QuicPacketSequenceNumber least_packet_awaited_by_peer,
	QuicByteCount congestion_window) {
	DCHECK_LE(least_packet_awaited_by_peer, sequence_number_ + 1);
	// Since the packet creator will not change sequence number length mid FEC
	// group, include the size of an FEC group to be safe.
	const QuicPacketSequenceNumber current_delta =
	max_packets_per_fec_group_ + sequence_number_ + 1
	- least_packet_awaited_by_peer;
	const uint64 congestion_window_packets =
	congestion_window / max_packet_length_;
	const uint64 delta = max(current_delta, congestion_window_packets);
	next_sequence_number_length_ =
	QuicFramer::GetMinSequenceNumberLength(delta * 4);
	}

	bool QuicPacketCreator::HasRoomForStreamFrame(QuicStreamId id,
	QuicStreamOffset offset) const {
	// TODO(jri): This is a simple safe decision for now, but make
	// is_in_fec_group a parameter. Same as with all public methods in
	// QuicPacketCreator.
	return BytesFree() >
	QuicFramer::GetMinStreamFrameSize(framer_->version(), id, offset, true,
	should_fec_protect_ ? IN_FEC_GROUP :
	NOT_IN_FEC_GROUP);
	}

	// static
	size_t QuicPacketCreator::StreamFramePacketOverhead(
	QuicVersion version,
	QuicConnectionIdLength connection_id_length,
	bool include_version,
	QuicSequenceNumberLength sequence_number_length,
	QuicStreamOffset offset,
	InFecGroup is_in_fec_group) {
	return GetPacketHeaderSize(connection_id_length, include_version,
	sequence_number_length, is_in_fec_group) +
	// Assumes this is a stream with a single lone packet.
	QuicFramer::GetMinStreamFrameSize(version, 1u, offset, true,
	is_in_fec_group);
	}

	size_t QuicPacketCreator::CreateStreamFrame(QuicStreamId id,
	const IOVector& data,
	QuicStreamOffset offset,
	bool fin,
	QuicFrame* frame) {
	DCHECK_GT(max_packet_length_, StreamFramePacketOverhead(
	framer_->version(), PACKET_8BYTE_CONNECTION_ID, kIncludeVersion,
	PACKET_6BYTE_SEQUENCE_NUMBER, offset, IN_FEC_GROUP));

	InFecGroup is_in_fec_group = MaybeUpdateLengthsAndStartFec();

	LOG_IF(DFATAL, !HasRoomForStreamFrame(id, offset))
	<< "No room for Stream frame, BytesFree: " << BytesFree()
	<< " MinStreamFrameSize: "
	<< QuicFramer::GetMinStreamFrameSize(
	framer_->version(), id, offset, true, is_in_fec_group);

	if (data.Empty()) {
	LOG_IF(DFATAL, !fin)
	<< "Creating a stream frame with no data or fin.";
	// Create a new packet for the fin, if necessary.
	*frame = QuicFrame(new QuicStreamFrame(id, true, offset, data));
	return 0;
	}

	const size_t data_size = data.TotalBufferSize();
	size_t min_frame_size = QuicFramer::GetMinStreamFrameSize(
	framer_->version(), id, offset, /last_frame_in_packet=/ true,
	is_in_fec_group);
	size_t bytes_consumed = min<size_t>(BytesFree() - min_frame_size, data_size);

	bool set_fin = fin && bytes_consumed == data_size; // Last frame.
	IOVector frame_data;
	frame_data.AppendIovecAtMostBytes(data.iovec(), data.Size(),
	bytes_consumed);
	DCHECK_EQ(frame_data.TotalBufferSize(), bytes_consumed);
	*frame = QuicFrame(new QuicStreamFrame(id, set_fin, offset, frame_data));
	return bytes_consumed;
	}

	size_t QuicPacketCreator::CreateStreamFrameWithNotifier(
	QuicStreamId id,
	const IOVector& data,
	QuicStreamOffset offset,
	bool fin,
	QuicAckNotifier* notifier,
	QuicFrame* frame) {
	size_t bytes_consumed = CreateStreamFrame(id, data, offset, fin, frame);

	// The frame keeps track of the QuicAckNotifier until it is serialized into
	// a packet. At that point the notifier is informed of the sequence number
	// of the packet that this frame was eventually sent in.
	frame->stream_frame->notifier = notifier;

	return bytes_consumed;
	}

	SerializedPacket QuicPacketCreator::ReserializeAllFrames(
	const QuicFrames& frames,
	QuicSequenceNumberLength original_length) {
	DCHECK(fec_group_.get() == NULL);
	const QuicSequenceNumberLength saved_length = sequence_number_length_;
	const QuicSequenceNumberLength saved_next_length =
	next_sequence_number_length_;
	const bool saved_should_fec_protect = should_fec_protect_;

	// Temporarily set the sequence number length and stop FEC protection.
	sequence_number_length_ = original_length;
	next_sequence_number_length_ = original_length;
	should_fec_protect_ = false;

	// Serialize the packet and restore the FEC and sequence number length state.
	SerializedPacket serialized_packet = SerializeAllFrames(frames);
	sequence_number_length_ = saved_length;
	next_sequence_number_length_ = saved_next_length;
	should_fec_protect_ = saved_should_fec_protect;

	return serialized_packet;
	}

	SerializedPacket QuicPacketCreator::SerializeAllFrames(
	const QuicFrames& frames) {
	// TODO(satyamshekhar): Verify that this DCHECK won't fail. What about queued
	// frames from SendStreamData()[send_stream_should_flush_ == false &&
	// data.empty() == true] and retransmit due to RTO.
	DCHECK_EQ(0u, queued_frames_.size());
	LOG_IF(DFATAL, frames.empty())
	<< "Attempt to serialize empty packet";
	for (size_t i = 0; i < frames.size(); ++i) {
	bool success = AddFrame(frames[i], false);
	DCHECK(success);
	}
	SerializedPacket packet = SerializePacket();
	DCHECK(packet.retransmittable_frames == NULL);
	return packet;
	}

	bool QuicPacketCreator::HasPendingFrames() const {
	return !queued_frames_.empty();
	}

	bool QuicPacketCreator::HasPendingRetransmittableFrames() const {
	return queued_retransmittable_frames_.get() != NULL &&
	!queued_retransmittable_frames_->frames().empty();
	}

	size_t QuicPacketCreator::ExpansionOnNewFrame() const {
	// If packet is FEC protected, there's no expansion.
	if (should_fec_protect_) {
	return 0;
	}
	// If the last frame in the packet is a stream frame, then it will expand to
	// include the stream_length field when a new frame is added.
	bool has_trailing_stream_frame =
	!queued_frames_.empty() && queued_frames_.back().type == STREAM_FRAME;
	return has_trailing_stream_frame ? kQuicStreamPayloadLengthSize : 0;
	}

	size_t QuicPacketCreator::BytesFree() const {
	const size_t max_plaintext_size =
	framer_->GetMaxPlaintextSize(max_packet_length_);
	DCHECK_GE(max_plaintext_size, PacketSize());
	return max_plaintext_size - min(max_plaintext_size, PacketSize()
	+ ExpansionOnNewFrame());
	}

	size_t QuicPacketCreator::PacketSize() const {
	if (!queued_frames_.empty()) {
	return packet_size_;
	}
	if (fec_group_.get() == NULL) {
	// Update sequence number length on packet and FEC boundary.
	sequence_number_length_ = next_sequence_number_length_;
	}
	packet_size_ = GetPacketHeaderSize(
	connection_id_length_, send_version_in_packet_, sequence_number_length_,
	should_fec_protect_ ? IN_FEC_GROUP : NOT_IN_FEC_GROUP);
	return packet_size_;
	}

	bool QuicPacketCreator::AddSavedFrame(const QuicFrame& frame) {
	return AddFrame(frame, true);
	}

	SerializedPacket QuicPacketCreator::SerializePacket() {
	LOG_IF(DFATAL, queued_frames_.empty())
	<< "Attempt to serialize empty packet";
	DCHECK_GE(sequence_number_ + 1, fec_group_number_);
	QuicPacketHeader header;
	FillPacketHeader(should_fec_protect_ ? fec_group_number_ : 0, false, &header);

	MaybeAddPadding();

	size_t max_plaintext_size =
	framer_->GetMaxPlaintextSize(max_packet_length_);
	DCHECK_GE(max_plaintext_size, packet_size_);
	// ACK Frames will be truncated only if they're the only frame in the packet,
	// and if packet_size_ was set to max_plaintext_size. If truncation occurred,
	// then GetSerializedFrameLength will have returned all bytes free.
	bool possibly_truncated = packet_size_ == max_plaintext_size &&
	queued_frames_.size() == 1 &&
	queued_frames_.back().type == ACK_FRAME;
	SerializedPacket serialized =
	framer_->BuildDataPacket(header, queued_frames_, packet_size_);
	LOG_IF(DFATAL, !serialized.packet)
	<< "Failed to serialize " << queued_frames_.size() << " frames.";
	// Because of possible truncation, we can't be confident that our
	// packet size calculation worked correctly.
	if (!possibly_truncated) {
	DCHECK_EQ(packet_size_, serialized.packet->length());
	}
	packet_size_ = 0;
	queued_frames_.clear();
	serialized.retransmittable_frames = queued_retransmittable_frames_.release();
	return serialized;
	}

	SerializedPacket QuicPacketCreator::SerializeFec() {
	if (fec_group_.get() == NULL \|\| fec_group_->NumReceivedPackets() <= 0) {
	LOG(DFATAL) << "SerializeFEC called but no group or zero packets in group.";
	// TODO(jri): Make this a public method of framer?
	SerializedPacket kNoPacket(0, PACKET_1BYTE_SEQUENCE_NUMBER, NULL, 0, NULL);
	return kNoPacket;
	}
	DCHECK_EQ(0u, queued_frames_.size());
	QuicPacketHeader header;
	FillPacketHeader(fec_group_number_, true, &header);
	QuicFecData fec_data;
	fec_data.fec_group = fec_group_->min_protected_packet();
	fec_data.redundancy = fec_group_->payload_parity();
	SerializedPacket serialized = framer_->BuildFecPacket(header, fec_data);
	fec_group_.reset(NULL);
	packet_size_ = 0;
	LOG_IF(DFATAL, !serialized.packet)
	<< "Failed to serialize fec packet for group:" << fec_data.fec_group;
	DCHECK_GE(max_packet_length_, serialized.packet->length());
	return serialized;
	}

	SerializedPacket QuicPacketCreator::SerializeConnectionClose(
	QuicConnectionCloseFrame* close_frame) {
	QuicFrames frames;
	frames.push_back(QuicFrame(close_frame));
	return SerializeAllFrames(frames);
	}

	QuicEncryptedPacket* QuicPacketCreator::SerializeVersionNegotiationPacket(
	const QuicVersionVector& supported_versions) {
	DCHECK(framer_->is_server());
	QuicPacketPublicHeader header;
	header.connection_id = connection_id_;
	header.reset_flag = false;
	header.version_flag = true;
	header.versions = supported_versions;
	QuicEncryptedPacket* encrypted =
	framer_->BuildVersionNegotiationPacket(header, supported_versions);
	DCHECK(encrypted);
	DCHECK_GE(max_packet_length_, encrypted->length());
	return encrypted;
	}

	void QuicPacketCreator::FillPacketHeader(QuicFecGroupNumber fec_group,
	bool fec_flag,
	QuicPacketHeader* header) {
	header->public_header.connection_id = connection_id_;
	header->public_header.reset_flag = false;
	header->public_header.version_flag = send_version_in_packet_;
	header->fec_flag = fec_flag;
	header->packet_sequence_number = ++sequence_number_;
	header->public_header.sequence_number_length = sequence_number_length_;
	header->entropy_flag = random_bool_source_->RandBool();
	header->is_in_fec_group = fec_group == 0 ? NOT_IN_FEC_GROUP : IN_FEC_GROUP;
	header->fec_group = fec_group;
	}

	bool QuicPacketCreator::ShouldRetransmit(const QuicFrame& frame) {
	switch (frame.type) {
	case ACK_FRAME:
	case CONGESTION_FEEDBACK_FRAME:
	case PADDING_FRAME:
	case STOP_WAITING_FRAME:
	return false;
	default:
	return true;
	}
	}

	bool QuicPacketCreator::AddFrame(const QuicFrame& frame,
	bool save_retransmittable_frames) {
	DVLOG(1) << "Adding frame: " << frame;
	InFecGroup is_in_fec_group = MaybeUpdateLengthsAndStartFec();

	size_t frame_len = framer_->GetSerializedFrameLength(
	frame, BytesFree(), queued_frames_.empty(), true, is_in_fec_group,
	sequence_number_length_);
	if (frame_len == 0) {
	return false;
	}
	DCHECK_LT(0u, packet_size_);
	packet_size_ += ExpansionOnNewFrame() + frame_len;

	if (save_retransmittable_frames && ShouldRetransmit(frame)) {
	if (queued_retransmittable_frames_.get() == NULL) {
	queued_retransmittable_frames_.reset(new RetransmittableFrames());
	}
	if (frame.type == STREAM_FRAME) {
	queued_frames_.push_back(
	queued_retransmittable_frames_->AddStreamFrame(frame.stream_frame));
	} else {
	queued_frames_.push_back(
	queued_retransmittable_frames_->AddNonStreamFrame(frame));
	}
	} else {
	queued_frames_.push_back(frame);
	}
	return true;
	}

	void QuicPacketCreator::MaybeAddPadding() {
	if (BytesFree() == 0) {
	// Don't pad full packets.
	return;
	}

	// If any of the frames in the current packet are on the crypto stream
	// then they contain handshake messagses, and we should pad them.
	bool is_handshake = false;
	for (size_t i = 0; i < queued_frames_.size(); ++i) {
	if (queued_frames_[i].type == STREAM_FRAME &&
	queued_frames_[i].stream_frame->stream_id == kCryptoStreamId) {
	is_handshake = true;
	break;
	}
	}
	if (!is_handshake) {
	return;
	}

	QuicPaddingFrame padding;
	bool success = AddFrame(QuicFrame(&padding), false);
	DCHECK(success);
	}

	} // namespace net